Compositions, methods and equipments to surface finish metals by magnetic dry electrolytes

Abstract

The present disclosure relates to compositions, assemblies, systems and methods for surface finishing, e.g., smoothing and polishing electrically conductive parts (e.g., metals or metal parts), e.g., via ion transport by means of said compositions, also referred herein as Magnetic Dry Electrolytes (MDEs), comprising free solid bodies retaining a liquid electrolyte used in combination with magnetic particles and / or magnetic fields. Thereby, the free solid bodies retaining the liquid electrolyte may be made magnetically active. The presence of the magnetic particles and / or magnetic fields presents a wide range of possible application, e.g., regarding the control and synchronization of the electrically conductive free solid bodies motion, packing factor and the electrochemical pulses and properties of the particles and the surface treatment, e.g., surface finishing, on which they are used, including the smoothing and polishing of electrically conductive parts, e.g., metal parts, for example punches, gears or inner channels (e.g., metal parts with inner channels).

Description

[0001] COMPOSITIONS, METHODS AND EQUIPMENTS TO SURFACE FINISH METALS BY MAGNETIC DRY ELECTROLYTES

[0002] FIELD OF APPLICATION OF THE INVENTION

[0003] The present disclosure relates to the field of surface finishing. More particularly, the disclosure relates to assemblies, systems, methods and compositions (electrolytes) for surface finishing of objects and relates to objects with surfaces finished with such methods. Said compositions used in said assemblies’ methods and systems comprising electrically conductive free solid bodies used in combination with magnetic particles and / or magnetic fields. More in particular, they represent a relevant improvement regarding the homogeneity and results control of electrochemical processes relying on, e.g., consisting on, electrically conductive free solid bodies, an improvement on the anticorrosive properties obtained, e.g., in the parts surface finished with the same, and an increase of the life span of the electropolishing medium, e.g., used in said assemblies, systems and methods. More in particular, the present disclosure relates to the magneto electropolishing field, representing a significant advance, among others, on the motion control of electrically conductive free solid bodies with respect to the surfaces to be treated.

[0004] BACKGROUND OF THE INVENTION

[0005] The present invention relates to surface finishing systems, specifically, methods for smoothing, polishing, and other treatments of object surfaces. Various technologies for surface finishing, including electropolishing (also known as electrochemical polishing, anodic polishing, or electrolytic polishing), have been widely used to remove material from workpieces, e.g., electrically conductive parts, typically metallic, by applying a specific voltage that is particularly high at the edges or tips. This process burns off unwanted projections by small arcs. These small arcs refer to localized electrical discharges occurring at micro-protuberances on the workpiece surface when the distance between the electrodes falls below a critical threshold, leading to the vaporization of such projections. While effective for surface smoothing, such discharges can adversely affect surface integrity and dimensional tolerances if not properly controlled, due to localized thermal and material removal effects. Other electropolishing methods involve immersing a metal part in an electrolyte bath and applying an electric potential difference to polish the surface. Some methods utilize electrically conductive particles, as described in, e.g., International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1), which outlines a method for smoothing and polishing metals via ion transport using electrically conductive free solid bodies, and International Application No. PCT / ES2021 / 070065 (published as WO2022 / 123096 A1), which discusses treating metallic surfaces using an electrolytic medium comprising solid particles and a non-conductive fluid. Such processes are also referred to as dry electropolishing processes. Despite these advancements, several limitations persist. A significant challenge is controlling the relative movement between free solid bodies and the objects or parts, e.g., the metal surface, being treated. Complex geometries can prevent free solid bodies from effectively reaching all surfaces, particularly concave surfaces and inner channels, of said objects or parts being treated, resulting in an uneven finish. Known mechanical methods for providing relative motion between particles and the treated surface lack the precision required for complex geometries or for fine control of surface roughness.

[0006] Additionally, defects can arise when electrically conductive free solid bodies remain stationary in contact with the metal surface, leaving projection marks. This issue is more pronounced in areas with limited access for relative particle movement. The chaotic nature of fluid dynamics during polishing can lead to unpredictable particle movements, causing undesirable results such as oxidation due to insufficient particle pressure in turbulent zones. Ensuring adequate pressure between electrically conductive free solid bodies and the surface is critical for effective electrical field connection, preventing electrical isolation between the anode and cathode.

[0007] Electrically conductive free solid bodies incorporating ion exchange resins also face material removal capacity limits due to resin saturation. The lifespan of these solid bodies is determined by the metal ion absorption kinetics of the resin, with reaction kinetics becoming in-suffi- cient below a certain saturation level, leading to poor surface results. Enhancing the anticorrosive properties of surfaces is also challenging in dry electropolishing processes compared to conventional electrochemical methods, where magnetic fields have been already used to improve corrosion resistance. To date magnetic components (e.g., magnetic particles and / or magnetic fields) have not been used in dry methods with electrically conductive free solid bodies, a.k.a. dry electropolishing processes.

[0008] There are several projection systems using electrically conductive free solid bodies as the ion transport element removing the material during a surface treatment, e.g., whereby the electrically conductive free solid bodies are projected onto the object or part to be surface, for instance, making use of gravity or devices such as hoses or cannons propelling the electrically conductive free solid bodies through a nozzle. As described in International Application No. PCT / ES2020 / 070499 (published as WO 2021 / 019121 A1), which outlines a method for smoothing and polishing metals via ion transport using electrically conductive free solid bodies in a projection system; or as described in International Application No. PCT / ES2023 / 070675 (published as WO 2024 / 105293 A1), which outlines a method for smoothing and polishing metals via ion transport by means of projecting electrically conductive free solid bodies. These projection methods, assemblies and systems present limitations on the electrical conductivity through the projected electrically conductive free solid bodies between the cathode and the anode. Having strong limitations on the projection flow, speed and the distance from the nozzle to the metal surface to be treated in order to ensure electrical contact. It is known that a presence of magnetic fields during electropolishing, the so-called magneto electropolishing “T. Hryniewicz, R. Rokicki, K. Rokosz, Corrosion and surface characterization of titanium biomaterial after magneto-electropolishing, Surf Coat Technol 203 (2009) ISOSISIS" is used to improve the corrosion resistance on auto-passivating materials. However, induced magnetic fields due to current flow through electrically connected particles introduce further complications, e.g., when used in dry electropolishing processes. Strong magnetic fields can induce currents opposing the galvanic cell polarity, obstructing surface treatment.

[0009] Integrating magnetic particles into electrically conductive free solid bodies without affecting electrolyte conductivity, e.g., between electrically conductive free solid bodies, presents additional challenges. Conductive magnetic particles risk causing short circuits, while nonconductive particles may block current flow, hindering surface treatment. Specific configurations are required to prevent magnetic particle degradation in acidic environments typical of electropolishing processes, e.g., to further enhance the functional life of such systems.

[0010] The fabrication of nanomagnetic particles has been studied. It has also been of an investigation interest the fabrication of magnetic resins beds “E. Sikora, . Hajdu, G. Muranszky, K.K. Katona, I. Kocserha, T. Kanazawa, B. Riser, B. Viskolcz, L. Vanyorek, Application of ion-exchange resin beads to produce magnetic adsorbents, Chemical Papers 75 (2021) 1187-1195". There are publications describing methods to obtain a magnetic resin beds like exposed in “M. Park, K.D. Daniels, S. Wu, A.D. Ziska, S.A. Snyder, Magnetic ion-exchange (MIEX) resin for perfluorinated alkylsubstance (PFAS) removal in groundwater: Roles of atomic charges for adsorption, Water Res 181 (2020)’’ or in “ Ren, Y. Han, X. Lei, C. Lu, J. Liu, G. Zhang, B. Zhang, Q. Zhang, A magnetic ion exchange resin with high efficiency of removing Cr (VI), Colloids Surf A Physico- chem Eng Asp 604 (2020)”, where they were investigating residual water heavy metal treatments and how to boost metallic ion absorption by the mentioned ion exchange resins. However, it has never been configured to be used as a part of an electropolishing or magnetic electropolishing process by means of, e.g., consisting on, electrically conductive free solid bodies retaining an electrolyte liquid to make them conductive, said electrolyte liquid having a dissolving potential of the mentioned magnetic particles. In other words, so far electrically conductive free solid bodies, e.g., including ionic exchange resins, have not been used in combination with magnetic elements, such as magnetic particles and / or magnetic fields, for electropolishing or magnetic electropolishing processes, specially wherein electropolishing processes require electrolytes which have the potential of dissolving magnetic particles, e.g., due to the high acidity of the electrolytes typically used and the metallic nature of magnetic particles.

[0011] In view of such problems, there is a need for improving existing methods for preparing magnetic ion exchange resin beds may be particularly improved for application in electropolishing processes, e.g., galvanic polishing processes, using, e.g., activation steps for making them particularly suitable for said a galvanic polishing process. Finding configurations that maintain galvanic ability without compromising magnetic properties over time, such as avoiding dissolution by electrolyte liquids, such as strong acids used in, e.g., electropolishing processes, is not straightforward. Furthermore, for optimal application of such methods it has been found that it is advantageous to ensure optimal relative movement between particles and the treated surface while maintaining effective magnetic behavior and avoiding particle conglomeration or reactions thereby particularly consistent and replicable surface treatments may be advantageously obtained.

[0012] Thus, there is a need for improved methods and systems for surface finishing. Preferably methods that address one or more of particle movement control, particles pressure control, particle connectivity, anticorrosive properties and the electrolyte life-span, advantageously providing homogeneous results while maintaining effective properties through time and through different surface treatments, and preferably also consistent, high-quality surface treatment results.

[0013] SUMMARY OF THE INVENTION

[0014] This invention refers to a method for smoothing and polishing metals via ion transport by means of free solid bodies, a Dry Electrolyte, including magnetic particles and / or magnetic fields, in some particular cases, to make them magnetically polarizable. The first Dry Magnetic Electrolyte (DME).

[0015] It has now been found that compositions comprising a plurality of electrically conductive free solid bodies (also referred to herein as Dry Magnetic Electrolytes, DMEs) may be used in combination with magnetic elements, such as magnetic particles and / or magnetic fields, resolving at least some of the issues described above of electropolishing processes in general and dry electropolishing processes in particular.

[0016] In particular, an aspect of the present disclosure relates to a composition comprising: a plurality of electrically conductive free solid bodies retaining a liquid electrolyte; a medium comprising a fluid; a plurality of magnetic particles; the medium containing the plurality of electrically conductive free solid bodies and the plurality of magnetic particles.

[0017] Such compositions have been found to be particularly useful as particulate (dry) electrolytes for surface finishing an electrically conductive part, e.g., metal part, by ion transport.

[0018] The present disclosure further relates to assemblies comprising such compositions, optionally in combination with means for creating a magnetic field and to assemblies comprising electrically conductive free solid bodies retaining a liquid electrolyte contained in a medium comprising a fluid and further comprising means for creating a magnetic field.

[0019] The present disclosure further relates to the use of such compositions and assemblies for surface finishing an electrically conductive part, in particular a metal part. The present disclosure further relates to methods method for surface finishing an electrically conductive part, in particular a metal part, using said composition and assemblies, and to a surface finished electrically conductive part, in particular a metal part, obtainable by the said surface finishing methods.

[0020] Using the above indicated compositions, assemblies and methods - e.g., those above- mentioned ion exchange resins in a dry electropolishing process relying on, consisting on, electrically conductive free solid bodies in combination with magnetic elements, such as magnetic particles and / or magnetic fields - gives an enhanced and new method for solving the limitations of the electropolishing process described above.

[0021] As indicated above, an object of this invention concretely refers to a Magnetic Dry Electrolyte, method and assembly, system and components to surface finish a product, e.g., an electrically conducting part such as a metal part, including, e.g., the smoothing and polishing metal parts, for example dental prostheses, gears and inner channels, based on the ion transport by means of free solid bodies, that means particles, that is distinguished to the prior art, essentially, in that said electrically conductive free solid bodies and / or its environment include at some extend a magnetic particle and / or magnetic field, capable of interacting with the electrically conductive free solid bodies and / or its environment by magnetic elements. Said interaction being an electrochemical interaction by the influence of the induced electromagnetic field; a controlled motion of the electrically conductive free solid bodies (MDE) by the help of an external magnetic field; or any other possible interaction between the solid bodies, e.g., electrically conductive free solid bodies, its environment and magnetic elements.

[0022] The presence of the magnetic particles and / or magnetic fields presents a wide range of possible applications regarding the control and synchronization of the electrically conductive free solid bodies motion, packing factor and the electrochemical pulses and properties of the particles, e.g., electrically conductive free solid bodies and / or magnetic particles that may be present, during the treatment, surface finishing method or process. In some embodiments, the present invention enables the synchronization between parking factors and / or pressures of the conductive particles in different stages of the electrochemical pulses applied.

[0023] Without being bound to any theory, different embodiments have been invented in which a magneto galvanic surface treatment consisting of electrically conductive free solid bodies including magnetic particles, a DME, having an optimal electrical and magnetic behavior, sustained through time and through different processes. Such methods providing a high potential on precisely controlling, by applying magnetic fields, the relative movement of the particles fractioning each other and the surface being treated in an unpracticable manner by the known methods up to date. Some particular embodiments allow the user to have a high precision on the pressure control under which the charged particles interact to adjust the current flow and the power of the galvanic surface treatment, boosting or limiting it by applying a particularly configured magnetic field.

[0024] Compositions, assemblies and methods as described herein unlock a number of possibilities to fine tune dry electropolishing processes and adapt them to specific parts to be treated or to attain specific results.

[0025] For instance, some of the previously mentioned unlocked possibilities may be in regard to the motion control of the Magnetic Dry Electrolyte enables obtaining high control on the surface treatment all over parts with complex geometries, such as a homogeneous treatment. The complex geometries are to be understood as, for example, concave surfaces, inner channels, leeward areas, among others. It is possible to adjust the packing factor and the relative movement of the Magnetic Dry Electrolyte with respect to every surface to be treated by the help of magnetic fields, and by said mechanism, to have a precise control of the polishing result all over the part regardless of the complexity of the geometry, in some particular cases, achieving a homogeneous surface treatment on all surfaces of complex geometries, unachievable by the previous state of art.

[0026] The properties of compositions as described herein, electrically conductive free solid bodies in combination with magnetic elements such as magnetic particles and / or magnetic fields (also referred to as Magnetic Dry Electrolytes, MDE) make them suitable for, e.g., polishing the inner surfaces of tubes of any kind, such as gun canons; also gears, turbines, turbine blades, acetabulum, bearing gears or any other part considered under a complex shape.

[0027] In some embodiments high precision may be obtained of the motion paths of the components of Magnetic Dry Electrolytes, e.g., the electroconductive free solid bodies and if present magnetic particles. The high precision of the motion paths of the components of Magnetic Dry Electrolytes as described herein gives unique properties for generating high precision patterns on metallic surfaces, which is of special interest on the field of bearing gears and semiconductors, or even, for creating patterns in inner channels such as for gun canons and positioning spindles.

[0028] The materials treatable by Magnetic Dry Electrolytes are, e.g., cast iron, steel, tool steel, stainless-steel, titanium alloys, aluminum alloys, Nikel alloys, CoCr alloys, Hard metals alloys, Cupper alloys, brass, Zamak, semiconductors, gold, silver and platinum among others.

[0029] Introducing magnetic properties to electrically conductive free solid bodies may have a significant effect on the dielectric capacity of said free solid bodies. In particular, it may be possible to change the dielectric capacity of ion exchange resins, more in particular, to increase the dielectric constant of sulfonated polystyrene-divinylbenzene cationic ion exchange resins. Such an increase on the dielectric constant may advantageously increase the period of time under which an electrically isolated particle can retain charge by a previous electrical charging step. The previous mentioned feature combined by the attraction between magnetically polarized electrically conductive free solid bodies make the Magnetic Dry Electrolyte, in particular compositions comprising both electrically conductive free solid bodies and magnetic particles, the perfect candidate for working under the projection mechanisms described on the background. In some embodiments, combining the keeping time of charge by a most likely electrical connection between projected electrically conductive free solid bodies because of magnetic attraction, the Magnetic Dry electrolytes in particular compositions comprising both electrically conductive free solid bodies and magnetic particles, make it possible to increase the distance between the projecting nozzle and the surface to be treated without losing the electrical connection, thereby solving some of the previously mentioned limitations on the prior art projection systems.

[0030] In addition to the motion and dielectric control, compositions, assemblies, uses thereof and methods as described herein, may provide better life span of the electrolyte, e.g., the composition comprising the electrically conductive fee solid bodies, while having the potential of being configured for enhancing the anticorrosive properties of auto passivating metals.

[0031] A set, a plurality, of electrically conductive free solid bodies, e.g., including an ion exchange resin in its structure, presents, has, a limit on the material removal capacity, an upper limit represents the saturation point in which the metal ions fully occupy all free reactive radicals present on the chemical structure of the resin. However, the life span of the electrically conductive free solid bodies is not only given by the mentioned upper limit, but it is defined by the absorption kinetics of the metal ions by the resin. At a certain saturation level below the upper limit, the reaction kinetics between the resin and the metal ions is not sufficient to ensure the required electropolishing conditions, resulting in a deficient surface result, deficient surface finishing or deficient conditions, such as time and / or energy consumption, to attain certain desired surface finishing effects. That threshold, e.g., of saturation level wherein efficiency is reduced, represents the cost of treating a sample for a user. The closer that level, threshold, to the upper limit the more benefits obtained during the working conditions. Compositions, assemblies, uses thereof and methods as described herein, including a DME, e.g., as the plurality of electrically conductive free solid bodies, that may include ion exchange resins, is under magnetic fields and / or combined with magnetic particles, the exchange kinetics between the metal ions and the composition, e.g., including the resin, is increased, triggering a closer polishing threshold to the mentioned upper limit.

[0032] The use of magnetic elements in combination with electrically conductive free solid bodies in dry electropolishing systems and processes as described herein may favor the decrease on the presence or even elimination of certain metallic species formed during the redox reaction of the polishing process (e.g., Cr (VI)) that are disruptive in the formation of oxide layers responsible for passivating metal parts being surface treated. By the decrease or the elimination of such specific species passivation of metal parts is directly improved with dry magnetic electropolishing systems and processes as described herein ultimately improving the corrosion resistance (anticorrosive properties) of metal parts (stainless-steel) being surface treated. In many different applications of a surface treatment, anticorrosive properties of the surfaces are required. In dry magnetic electropolishing processes (DME polishing treatments), an enhancement of the formation of an auto passivation oxide layer may be performed, or may be directly obtained as described above, providing corrosion resistance to the surface. In some particular embodiments, by combining dry electropolishing with magnetic elements, e.g., by the addition of magnetic particles and / or fields to electrically conductive free solid bodies, e.g., the ion exchange resin, it is possible to obtain a lower formation of certain metal ions that prevent or difficult the formation of said passivation layers. More in particular, some ion exchange resins can be magnetically configured in such a way that the efficiency of ion extraction of Cr (VI) from the metal and into, e.g., the free solid bodies, is particularly promoted, and by said mechanism, Cr (VI), an ion disturbing the formation of passivating oxides layers, is less available in the medium and the anticorrosive properties of electrically conductive parts, e.g., stainless-steel surface treatments may be enhanced.

[0033] Without being bound to any theory, in some embodiments, e.g., when many different magnetic particles are placed and randomly in the present magnetic electrolyte, as described herein, either on its structure or in its environment, the random orientation of the magnetic dipoles creates a null net magnetic field of the whole mixture. When there is a presence of a magnetic field the magnetic domains are oriented along the field direction, generating a magnetic dipole of at least part of the product. By modulating or oscillating the mentioned magnetic field is possible to turn the product, i.e., the composition, into a magnetic compound, composition, with ability to move and to compact depending on the motion and the application of said magnetic field. More particularly, and without being bound to any theory, in some embodiments, e.g., when magnetic particles are placed randomly in combination with the free electrically conducting free solid bodies , as described herein, either within the free solid bodies (e.g., in their structure) or in the medium comprising the same, the random orientation of the magnetic di-poles of the magnetic particles may create a null net magnetic force of the whole composition, resulting on an static state. When there is a presence of a magnetic field the magnetic domains of the magnetic particles are oriented along the field direction, generating a magnetic dipole of at least part of the product. By modulating or oscillating the mentioned magnetic field it is possible to turn the composition comprising electrically conductive free solid bodies and magnetic particles into a magnetic composition, experimenting static or variable forces with ability to move and to compact depending on the motion and the application of said magnetic field.

[0034] In certain embodiments, the magnetic dry electrolyte may include needle-like ion exchange resins or other anisotropic magnetic particles with elongated geometries. Such non-sym- metrical shapes exhibit a stronger magnetic susceptibility under field oscillation or rotation compared to isotropic bodies such as spheres. This behavior is due to the enhanced torque that acts along the longitudinal axis of the particles, which enables more complex and directional motion when subjected to time-varying magnetic fields. These needle-like particles not only interact more efficiently with oscillating magnetic flux but also demonstrate improved coverage and mixing capabilities when distributed within a bulk matrix or across a workpiece surface.

[0035] Another important consideration lies in the mass of the magnetic particles used in particular embodiments, ranging from 0.0001 g to 10 g, more specifically from 0.0001-1 g or 0.01-0.1 g. Without being bound to any theory, heavier particles may provide greater inertial resistance and kinetic momentum under a magnetic field, e.g., during field-induced tumbling. This may contribute to a more forceful and sustained impact with surrounding components or substrates, enhancing mechanical and electrochemical interaction. Increasing particle mass within this range has been observed to be advantageous in, e.g., magnetic tumbling systems to overcome static friction or weak magnetic retention forces, especially in dry systems where fluid lubrication is absent. This inertial benefit becomes particularly relevant in applications where the magnetic field strength is moderate and must be supplemented by physical properties of the particles to achieve motion. For these reasons it may be of a particular interest including a liquid environment on the interstitial spaces of the solid particles present in a MDE, such as silicones and hydrocarbons, that minimizes the friction forces while enhances the flowability of the system.

[0036] In some embodiments, mechanical agitation is used, e.g., to initiate or enhance the motion of the particles of the magnetic dry electrolyte. In practice, incorporating vibrational platforms, ultrasonic shaking, or low-amplitude mechanical oscillators can assist in overcoming initial resistive forces, particularly static inter-particle or substrate friction. This hybrid approach, combining magnetic oscillation with mechanical energy input, where agitation assists in unlocking particle mobility, may be used for enabling more consistent and controllable dynamics in the presence of a magnetic field.

[0037] Some aspects of the performance of the system may be further improved by, e.g., fine tuning of the magnetic field's oscillation frequency is required based on the specific mass, geometry, and magnetic susceptibility of the particles. For instance, lighter particles may require higher frequency fields to maintain motion, while heavier ones benefit from lower-frequency oscillations to leverage their inertia without damping their movement. Adjusting field intensity in parallel ensures that the torque and translational forces remain sufficient to initiate and sustain the desired type of particle motion; be it rotation, tumbling, or chaotic agitation. These tuning parameters may be configured for tailoring the behavior of the magnetic dry electrolyte to specific functional outcomes, such as targeted compaction, directed mixing, or field-driven assembly. Another further advantage of working both with magnetic particles and a magnetic field may be that, once the field is applied and the magnetic domains of the magnetic particles are oriented, an attraction force, binding the oriented magnetic particles and, e.g., the electrolytic component attached to it (such as electrically conductive free solid bodies incorporating magnetic particles), may appear. Again, without being bound to any theory, such interaction may generate an effect of how compact and to the pressure of the contacting electrically charged solid bodies during the process, having a direct impact on the current applied to the sample and to the speed of the surface treatment. Without being bound to any theory, the higher attraction forces between two contacting and magnetically attracted free solid bodies the bigger and stronger liquid meniscus (e.g., of the liquid electrolyte retained by the free solid bodies)may be formed, this meniscus is thought to be the responsible for vesiculating the ion transport between the solid particles; and thereby the higher the magnetic attraction, the bigger the meniscus and consequently a higher ion transport rate may be achieved.

[0038] The use of a combination of magnetic particles, e.g., incorporated to the electrically conductive free solid bodies and a magnetic field, may further have the advantage, e.g., owing to the electrolyte being polarized into a magnetic and compact plurality of particles, to make it possible to precisely control its trajectory making it possible to easily adjust the polishing required or desired to each area of the surface to be treated. In particular, it can have several advantages on controlling the result all over a part having, consisting on, a complex geometry, particularly suitable for providing a homogeneous result, impossible to obtain by the conventional methods. For instance, significant challenges have been encountered in achieving a uniform surface finish with a final roughness (Ra) below 0.3 pm when employing conventional dry electropolishing (DEP) methods, particularly when starting from initial surface roughness values above Ra = 1 pm. These challenges become especially pronounced in parts, workpieces, featuring concavities with radii smaller than 5 cm, more particularly below 1 cm, and in certain cases, below 0.2 cm. In addition, in applications requiring enhanced corrosion resistance — such as metals comprising iron and at least chromium (such as stainless-steel), more in particular those involving, e.g., stainless-steel alloys like AISI 316L — conventional methods have exhibited limitations in attaining a chromium- to-iron (Cr / Fe) surface ratio greater than 1.2, as determined by X-ray photoelectron spectroscopy (XPS). Such ratios are particularly interesting with respect to improving corrosion resistance.

[0039] These technical limitations have been found to be effectively overcome through the implementation of the novel Magnetic Dry Electropolishing (MDE) technology as described herein. Accordingly, in one aspect, the present invention relates to a surface-treated part, in particular a metal part comprising iron and at least chromium (such as stainless-steel), wherein the surface has been processed using MDE technology to achieve a Cr / Fe surface atomic ratio ranging from 1 .2 to 5.0, more particularly from 1 .5 to 3.5. It has surprisingly found that compositions, systems and methods as described herein may more efficiently remove metallic iron from the surface of metal parts when compared to the removal of, e.g., metallic chromium, thereby increasing the Cr / Fe atomic ratio of the surface treated. Additionally, the invention enables a substantial reduction in surface roughness, from initial values exceeding Ra = 1 pm to final values below Ra = 0.3 pm, preferably below Ra = 0.2 pm. Notably, compositions, systems and methods as described herein have been found to provide particularly good results, and even a synergistic improvement, in both surface topography and corrosion resistance, particularly in components exhibiting complex geometries, such as deep or narrow concavities, wherein conventional electropolishing methods fail to deliver consistent results. The MDE process ensures homogeneous polishing across intricate surface contours while simultaneously forming a Cr-enriched passive layer, thereby enhancing anticorrosive performance in a reliable and repeatable manner.

[0040] All in all, in the surface finishing of an electrically conductive part to be treated with a method as described herein, which has different finishes in different areas of its surface, owing, e.g., to its method of manufacture, the process may be adjusted to the requirements of each different area to obtain the same or very similar surface finish in the different areas, resulting in an homogeneous result overall.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:

[0043] Figure 1 - A: Illustrative example, schematic representation, of an electropolishing method, including methods described in, e.g., WO 2017 / 186992 A1 in combination to a Magnetic Dry Electrolyte, in combination with magnetic particles and a magnetic field, in particular showing an assembly and method using such an assembly comprising an electric connector (108) connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106) providing a current (107) and an electric field (104); a fixing system (not shown) connected to the electric connector (108) and adapted to hold the electrically conductive part to be treated (e.g., a metal part) as the anode (102) or the cathode (103); a container, receptacle, (101) comprising a plurality of electrically conductive free solid bodies (109) in combination with a plurality of magnetic particles (110) in a medium, environment (114), and comprising means (111) for creating a magnetic field (105) as well as a mobility element of the magnetic field source (112) providing a magnetic field change, the illustrative example also showing the velocity of the magnetic field change (113).

[0044] Figure 1 - B: Representation of a particular behavior of the electrically conductive and magnetic free solid bodies, showing a magnetic attraction force FM (114), a magnetic velocity force Fv (115), induced particle magnetic poles (116), induced particle electric poles (117), positive and negative, and a detail (118) of a polarized magnetic particle (110) under the magnetic field (105).

[0045] Figure 1 - C: Illustrative example, schematic representation, of an electropolishing method, including methods described in, e.g., WO 2017 / 186992 A1 in combination with a magnetic field (105) but in absence of magnetic particles (110) , in particular a diagram, showing an assembly and method using such an assembly comprising an electric connector (108) connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106) providing a current (107) and an electric field (104); a fixing system (not shown) connected to the electric connector (108) and adapted to hold the electrically conductive part to be treated (e.g., a metal part) as the anode (102) or the cathode (103); a container, receptacle, (101) comprising a plurality of electrically conductive free solid bodies (109) in a medium, environment (114), and comprising means (111) for creating a magnetic field (105) as well as a mobility element of the magnetic field source (112) providing a magnetic field change, the illustrative example also showing the velocity of the magnetic field change (113).

[0046] Figure 2: Illustration, schematic representation, of the three general and extreme cases in which magnetic particles can be included in a Magnetic Dry Electrolyte, how a plurality of magnetic particles may be combined with a plurality of electrically conductive free solid bodies, in particular showing three receptacles (201) comprising electrically conductive free solid bodies (202) and magnetic particles (203) in a medium, environment, (204), in different configurations. Firstly, on the left, magnetic particles are included on electrically conductive free solid bodies (206), wherein the magnetic particles are, for instance, at the surface of the free solid bodies (211), e.g., on an external moderation liquid, or inside the free solid bodies (212), e.g., at the solid structure of the solid bodies. Secondly, in the middle, (bigger) magnetic particles are included in the medium, environment, outside of the free solid bodies (208); and thirdly, on the right, magnetic particles are in the medium, environment, outside of the free solid bodies but included in a liquid medium, e.g., suspended / dispersed or dissolved in the liquid medium (207).

[0047] Figure 3: Representation of a strategy for protecting magnetic particles in a Magnetic Dry Electrolyte from the electrolyte liquid retained by the electrically conductive free solid bodies. In particular, the schematic representation shows a receptacle (301) comprising a medium, environment, (304), an electrically conductive free solid body (302) retaining an electrolyte, e.g., an acidic electrolyte such as H2SO4 (305), and magnetic particles (303) contained in the free solid body, wherein the magnetic particles comprise a protective magnetic coating (306).

[0048] Figure 4: Illustration of a method, an assembly or system for surface finishing, e.g., engraved punctual polishing comprising a MDE controlled by an external magnetic field. In particular, the schematic representation shows a cathode (401) and an anode (403), with an electrically conductive part to be surface treated, e.g., a metal part, acting as cathode or anode, with magnetic solid bodies (402), e.g., electrically conductive free solid bodies comprising magnetic particles conferring magnetic properties to the free solid bodies, and a magnetic field source (404) generating a Magnetic attraction force, e.g., on an X direction FMX (407) and / or on a Y direction FMY (408), and a velocity v (406), the magnetic field source allowing a directed movement of the magnetic solid bodies through magnetic attraction forces in different directions and at the velocity v, said movement in turn allowing generating a specific engraving on to the electrically conductive part being surface treated (metal part) to provide an engraved (405) part, or a polished engraved part obtained from surface treating a (unpolished) part previously comprising an engraving.

[0049] Figure 5: Axial longitudinal cut of a 3D representation of an assembly, system or a method for punch polishing comprising mechanical adjustment and synchronization with polishing parameters using an electromagnet, with the capability of executing controlled cyclic compaction for the polishing of concave surfaces synchronized to the polishing parameters. In particular, the schematic representation shows a cathode (501) and an anode (503), with an electrically conductive part to be surface treated, e.g., a metal part, acting as cathode or anode, with a MDE (502), e.g., a plurality of electrically conductive free solid bodies in combination with a plurality of magnetic particles, contained in a container, receptacle, (504), and a surface to be treated (509), from the electrically conductive part, such as the metal part, at least partly contained in the receptacle and in contact with the MDE, connected through a fixing system (506) to means of generating motion (505) and to the positive pole of a power source provided with a synchronization element (507) and further provided with an electro magnet (508).

[0050] Figure 6: Axial longitudinal cut of a 3D representation of an assembly, system or method for surface treatments of curved inner channels, e.g., of an electrically conductive part to be surface-finished, involving a controlled distribution of magnetic fields within an interior space or tube to ensure a uniform motion profile of the MDE across various surfaces. In particular, the schematic representation shows two magnetic field sources B1 (604) and B2 (605) about an electrically conductive part to be surface-finished, e.g., metal part, in the shape of a curved tube acting as anode / metal (601 and 603) and having a MDE (602), e.g., a plurality of electrically conductive free solid bodies in combination with a plurality of magnetic particles, in its interior, moving at two different velocities velocity 1 v1 (607) and velocity 2 v2 (608), as well as an inner cathode (606),

[0051] Figure 7: Axial longitudinal cut of a 3D representation of an assembly, system or a method for anti-gravity polishing, to counteract gravitational pressure compacting the solid bodies, thereby controlling heterogeneous or differential polishing along the gravitational axis. In particular, the schematic representation shows a cathode / metal (701) and an electrically conductive part to be surface-finished (e.g., metal part) connected through a fixing system (706) to a positive pole and acting as anode / metal (703) and a MDE (702), e.g., a plurality of electrically conductive free solid bodies in combination with a plurality of magnetic particles, contained in a container, receptacle, (704), and a surface to be treated (707), from the electrically conductive part, such as the metal part, at least partly contained in the receptacle (704) and in contact with the MDE, the receptacle comprising magnetic sources (705).

[0052] Figure 8: Axial longitudinal cut of a 3D representation of an assembly, system or a method for polishing pattern station. In particular, the schematic representation shows a container, receptacle, (804), comprising magnet sources (805) and a cathode / metal (801) supported by a fixing system and an electrically conductive part to be surface-finished (e.g., metal part) connected to a positive pole and acting as anode / metal (803) and a MDE (802), e.g., a plurality of electrically conductive free solid bodies in combination with a plurality of magnetic particles, placed between the anode and the cathode whereby the surface to be treated (807) is exposed to the MDE.

[0053] DETAILED DESCRIPTION

[0054] The instant disclosure relates to composition comprising: a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte (305); a plurality of magnetic particles (203); and a medium (204) comprising a fluid; wherein the medium (204) contains the plurality of electrically conductive free solid bodies (202) and the plurality of magnetic particles (203).

[0055] Such compositions may be referred to herein as magnetic dry electrolyte (MDE).

[0056] In some embodiments, a Magnetic Dry Electrolyte (MDE) comprises: a set of electrically conductive free solid bodies configured to retain a liquid electrolyte (202); an electrolyte liquid retained by the electrically conductive free solid bodies; a set of magnetic particles (203) or means for creating a magnetic field; and a medium where said electrically conductive free solid bodies are located (204), said medium including a liquid, a gas or a combination of both.

[0057] Electrically conductive free solid bodies have a conductivity, when retaining a liquid electrolyte, of at least equal or higher than 10 pS / cm as determined by, e.g., a two-electrode conductometric method using a calibrated conductivity meter in accordance with ISO 7888: 1985 or ASTM D1125-95(2013). An appropriate measurement may be carried out by immersing the material, either liquid granular or porous solid saturated in a non-metallic container under controlled temperature (25 ± 0.5°C). The two electrodes, typically platinum or stainless-steel, may be spaced with a defined cell constant (K, in cm-1) determined by prior calibration. Conductivity can then be recorded once the value stabilizes, typically within 60 seconds. Materials are deemed electrically conductive if the measured value exceeds 10 pS / cm under these standardized conditions.

[0058] It is important to note there is no absolute lower limit that universally defines conductivity I non-conductivity; instead, the relevance of a material’s conductivity / non-conductivity may preferably be considered in context. Typically, a material may be regarded as not-significantly conductive if it exhibits a conductivity lower than 50% of that of the conductive reference material; more particularly, lower than 10%, and most particularly, lower than 1%. For example, if a particular embodiment is directed to electrically conductive free solid bodies with a conductivity of 10000 pS / cm, a non-significantly conductive comparative material would not necessarily need to have a conductivity below 10 pS / cm, but may have a conductivity, e.g., below 5000 pS / cm, more particularly below 1000 pS / cm, and most particularly below 100 pS / cm. This relative approach ensures meaningful comparison and functional distinction between conductive and non- conductive materials in the context of compositions, systems and methods described herein.

[0059] The fluid of the medium in a composition as described herein may be a liquid, a gas or a combination of both. In some embodiments the fluid may be air, in some embodiments the fluid may be solvent (or mixtures of solvents), a solution or combinations thereof. In some embodiments the fluid is a polar solvent, a non-polar solvent or a combination of both. In some embodiments the fluid may comprise water, hydrocarbons (e.g. aliphatic hydrocarbon chains in particular from C5 to C30 hydrocarbons), surfactants, such as fatty acids, toluene sulfonate, trans-cinnamal- dehyde, and dodecylpiridinium bromide, or hydrocarbons with polar head groups other than carboxylic acids, such as ketones, hydroxyl groups (e.g., hexylene glycol, and isopropanol), amide groups, or carboxylic acids other than fatty acids (e.g., nitrobenzoic acid). In some embodiments the fluid is an aqueous solution, in particular the aqueous solution may be water or an aqueous solution including salts, such as NaCI at 0.1 - 2 M. The medium may comprise a moderation fluid, and more in particular a liquid acting as a moderation liquid. A moderation fluid is to be understood in the context of the present disclosure as any fluid that is non-significantly conductive with respect to the conductivity of the electrically conductive solid bodies. Such a fluid may contribute to the composition by providing one or more functionalities in relation to the dry electrolyte, including but not limited to: electrochemical mediation between conductive particles or between conductive particles and the part being treated, modification of flowability, adjustment of system density, surface tension at the interfaces, friction forces and control of viscosity. The moderation fluid may thus play a role not only in the physical behavior of the medium but also in facilitating or modulating interactions within the electrochemical environment, provided it does not itself contribute significant ionic conductivity relative to the electrically conductive free solid bodies. In some embodiments a moderation fluid is a liquid such as water.

[0060] In a composition as described herein, the plurality of magnetic particles (203) may be included within the electrically conductive free solid bodies (202). Such particles may be referred to as magnetic electrically conductive free solid bodies or simply as magnetic solid bodies.

[0061] In some embodiments, the magnetic particles (203) are included to the electrically conductive free solid body’s structure (206). This may be performed as described in more detail below.

[0062] In some embodiments, the magnetic particles (203) are included within the medium (204) outside the plurality of electrically conductive free solid bodies (202). The medium may, thus comprise the plurality of magnetic particles and the plurality electrically conductive free solid bodies as separate entities.

[0063] For instance, the magnetic particles (203) may be included within the medium (204) of a set of electrically conductive free solid bodies (207 and 208), e.g., within the medium comprising the plurality of electrically conductive free solid bodies.

[0064] In some particular embodiments, a medium comprising magnetic particles outside of the plurality of electrically conductive bodies, may be used in combination with magnetic solid bodies as described above (also incorporating magnetic particles within the electrically conductive solid bodies) or may be used with electrically conductive free solid bodies which do not have magnetic particles incorporated therein.

[0065] In some embodiments, where the plurality of magnetic particles is in the medium, outside of the electrically conductive free solid bodies, the electrically conductive bodies may incorporate magnetic particles upon contact with the magnetic particles also present in the medium, e.g., on the surface or within the electrically conductive free solid bodies, and the plurality of magnetic particles may be both outside and within the electrically conductive free solid bodies.

[0066] In some embodiments, in a composition as described herein the magnetic particles (203) are included within the medium (204) in the form of a ferrofluid (207). For instance, the magnetic particles (203) are included on a liquid medium forming a ferrofluid (207). A ferrofluid may also be used in combination with magnetic solid bodies as described above or may be used with electrically conductive free solid bodies which do not have magnetic particles incorporated therein. Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended inside a carrier fluid (usually an organic or polar solvent, such as hydrocarbons or water). In some particular embodiments comprising a ferrofluid medium, it is preferable to use non-conductive magnetic particles to avoid the medium short-circuiting the galvanic action of the electrically conductive free solid bodies. Suitable examples of such non-conductive magnetic particles include BiFeO3(bismuth ferrite), BaFei20i9 (barium hexaferrite), and SrFei20i9(strontium hexaferrite), all of which exhibit low electrical conductivity (typically below 10 pS / cm) while maintaining magnetic responsiveness.

[0067] In some embodiments a composition as described herein further comprises abrasive and / or moderation particles. For instance, the MDE may include, e.g., at least, an abrasive and / or moderation particle.

[0068] The use of abrasive particles has been described in combination with electropolishing processes in, e.g., international application number PCT / EP2024 / 080378.

[0069] In the context of the present disclosure, an abrasive particle may be understood to be any particle exhibiting sufficient surface roughness, hardness, density, or inertial mass such that, when brought into contact with a substrate, object, part under operative conditions, it is capable of causing a scratch, groove, indentation, or plastic deformation on the surface of that sub- strate / object / part being treated. Whether a particle qualifies as abrasive depends not only on its intrinsic properties but also on the mechanical characteristics of the target substrate, such as its hardness, ductility, or coating thickness.

[0070] The hardness of abrasive particles may be from 3 to 10 in the mohs scale, in particular from 5 to 9.75 mohs, more in particular from 6 to 9.5 mohs, and yet more in particular from 7.5 to 9.25 mohs.

[0071] To determine whether a particle may be considered abrasive for a given application, standardized test methods may be employed. These include, for example, the Mohs hardness test for assessing scratch resistance, Vickers or Knoop microhardness tests for precise hardness evaluation, and tribological methods such as ASTM G132 (pin-on-disk wear testing) or scratch tests using calibrated stylus instruments to measure surface damage. Additionally, particle surface texture and roughness may be assessed using contact stylus profilometry, a widely available and cost-effective technique that provides quantitative measurements of surface roughness parameters (such as Ra and Rz) with micron-scale resolution. Such profilometers are conventionally used in industrial and laboratory settings to evaluate whether a particle's surface morphology contributes to its abrasive behavior.

[0072] The geometry of abrasive particles may typically include edges, owing to the nature of their specific surface and / or shape. For instance, abrasive particles may be prismatic, e.g., of triangular base or another geometrical base; cylindric; cubic; rhombic; pyramidal; conic; and / or spheric.

[0073] The material of abrasive particles may be synthetic (i.e. , manufactured) and / or natural (i.e., naturally sourced, e.g., mined minerals). In some embodiments, the abrasive particles are preferably synthetic abrasive particles. Some natural abrasive particles (e.g., zirconia alumina, diamond dust, etc.) may also be manufactured, and synthetic versions of naturally sourced abrasive particles may be preferred due to difficult availability and higher costs of the naturally sourced abrasive particles. Additionally, or alternatively, synthetic particles may be preferred as they may be more effective as abrasives, since they may be free of impurities that natural abrasive particles may comprise.

[0074] In some embodiments, abrasive particles (synthetic and / or natural) of the at least one abrasive particle are selected from alumina (aluminum (III) oxide: AI2O3), e.g., in the form of corundum, emery (impure corundum), and ceramic aluminum oxide, including white AI2O3, brown AhCh and gray AI2O3; zirconia (zirconium dioxide); zirconia alumina (a combination of aluminum (III) oxide and zirconium dioxide); iron(lll) oxide (e.g., ceramic iron oxide); borazon (cubic boron nitride or CBN); boron carbide; glass powder; steel abrasive; silicon carbide (carborundum); calcite (calcium carbonate); diamond dust; novaculite; pumice; sand; garnet; sandstone; rotten stone (Tripoli); powdered feldspar; staurolite; and slag (a by-product of processes for smelting ores and recycling metals, comprising a mixture of metal oxides and silicon dioxide).

[0075] In some embodiments, the at least one abrasive particle comprises a plurality of abrasive particles. In some particular embodiments, a plurality of abrasive particles may comprise more than one type of abrasive particles, e.g., two, three or more different types of abrasive particles.

[0076] Embodiments of the disclosure include at least one abrasive particle or a plurality of abrasive particles wherein the abrasive particles comprise or are of charged polymers combined with abrasive powders, also referred to herein as abrasive composites or abrasive composite particles. Abrasive powders may include powders particularly suited for specific applications such as in polishing, and chemical-mechanical planarization (CMP). For instance, the abrasive composites may include powders such as silica, alumina, cerium oxide, zirconium dioxide, silicon carbide, titanium dioxide, and nanodiamonds, dispersed in a charged polymer matrix. The charged polymer enhances the dispersion, electrostatic stability, and adhesion to substrates of abrasive particles comprising the same. Examples of charged polymers include polyacrylic acid (PAA), polyethyleneimine (PEI), polydiallyldimethylammonium chloride (PDDA), and poly(sodium acrylate).

[0077] As indicated above compositions, systems and methods described herein may additionally or alternatively comprise or use moderation (or moderating) particles. During the electropolishing process, the electrically conductive free solid bodies may be regarded to have two functions: a chemical action of dissolution of oxides and salts that provokes cleaning the surface to be polished; and a function of electric conductivity, to drive the electropolishing method. The use of moderating particles has been found to limit the chemical attack action of the electrically conductive free solid bodies and / or to limit their electric conductivity function. Thereby two types of moderating particles may be distinguished and used; the moderating particles moderating the chemical action and the moderating particles moderating the electric conductivity.

[0078] Moderating particles of the chemical action of the active particles have the capacity to absorb and / or to neutralize the acid exudates of the active particles.

[0079] A preferred embodiment of the moderating particles of the chemical action are particles of acrylic gel polymer with amino functional groups, e.g., containing water or distilled water. These particles, when contacting the surface of the metal part, absorb the possible acid rests left by the active particles, that are neutralized within the particle with the amino group. This way, the uncontrolled acid action of the acid of the acid remains is limited. Due to the gel nature of acrylic gel polymer particles, it may be preferred to renew or add moderating particles, as the surface finishing method progresses. For example, a method may start with the composition comprising, e.g., 0.5% of the volume of moderating particles and more particles may be added after a given time, for example, 0.5% with respect to the initial volume every 2 hours of operation. These moderating particles are of preferred use for carbon steels polish.

[0080] A second preferred embodiment of the moderating particles of the chemical action of the active particle are polymers that are under the saturation point, which have the capacity to absorb liquid, that means, partly dry particles. Preferably, such partly saturated particles are resins of ionic exchange based on, e.g., a sulfonated styrene copolymer and divinylbenzene, of a similar or same nature to the resin of the electrically conductive free solid bodies.

[0081] Without being bound to any theory, during the methods as described herein, these particles may absorb the acid exudates that remain on the surface of the electrically conductive part, e.g., metal part, to be surface treated, e.g., polished. When the moderating particles of the chemical action of the active particles are saturated, that means that they cannot any longer absorb more acid, at which point an additional amount of moderating particles may be added to the com- position / system.to maintain the moderating activity. The already saturated moderating particles may or may not be removed, as they do not pose any problems because, once saturated, they may also act as electrically conductive free solid bodies. The great advantage of these moderating particles of the chemical action of the partly dry active particles is that there is no limit of amount that can be used because virtually, after the use, they become active particles.

[0082] A third preferred embodiment of the moderating particles of the chemical action, are particles retaining a basic solution. During methods as described herein, these particles neutralize, directly on the metal surface, the acid exudates, in addition to generate basic exudates that protect the surface from further acid attacks, so they are especially useful in sensitive metals. Preferably, the basic solution contains bases that do not react with the air, are water-soluble and little volatile such as, for example, monoethanolamine, diethanolamine triethanolamine, triethylamine, buffer solutions with a base of phosphates or acetates, etc. The great advantage of this system is its effectiveness to eliminate the acid wastes from the metal surface. It is specially advised for very sensitive metal surfaces, such as low alloy steels.

[0083] The moderating particles of the electric conductivity of the active particles may be, e.g., non-electrically conductive particles, which are substantially not conductive with respect to the electrically conductive free solid bodies, as defined above.

[0084] Without being bound to any theory, t moderating particles of the electric conductivity may limit the number of electric preferential paths that can reach, from, e.g., the cathode, the surface of the electrically conductive part being treated, e.g., the metal surface of a metal part, e.g., acting as anode. On the other hand, this may increase the homogeneity of the finish of more exposed areas with the more occluded areas of the part being treated, because the possible number of electric paths is equalized. On the other hand, the presence of these moderating particles of the electric conductivity may locally and momentarily break the electric contact of the surface which may consequently breaks the resonances that may be established in the system, that can cause undulations in the final finish, providing, e.g., an orange-peel-type finish. A great advantage of the said moderating particles of the electric conductivity is the final finish they produce, with higher quality with a finish hardly with undulations.

[0085] These moderating particles of the electric conductivity can be polymer, ceramics, etc. with a density, size and shape such that no mass segregation of the electrically conductive solid bodies occurs. As a mode of example, moderating particles may be used with densities, sizes and shapes similar to those of the electrically conductive solid bodies. For instance, moderating particles may be used

[0086] - with densities being, e.g., from 0.8 to 1 g / cm3,

[0087] - with their longer dimension being, e.g., their diameter, from 0.3 to 2 mm;

[0088] - with shapes being, e.g., spherical and / or needle-shaped.

[0089] The moderating particles of the electric conductivity can be of any non-electrically conductive material preferably being is acid resistant or that can resist during a given time the contact with the liquid electrolyte retained by the electrically conductive free solid bodies during the process. The preferred materials are polymers in which the main polymeric chain contains only C-C bonds such as, for example, polymers derived from styrene, divinylbenzene, ethylene, propylene, acrylates, acrylamides, vinyl, vinyl chloride, tetrafluoroethylene, nation, among many others. The moderating particles of the electric conductivity can also be derived from silicium such as silica gel and functionalized silicas.

[0090] In some embodiments, the plurality of magnetic particles (203) includes, e.g., Fe304, BiFeO3, BaFe12019and / or SrFe12O19particles, e.g., nano-particles, preferably at least include Fe304particles, e.g., nano-particles. Preferably, the magnetic particles may be nano-particles. For instance, a set of magnetic particles (203) may include Fe304or BiFeO3or BaFe12019or SrFe12O19nano-particles. Such particles do not present electrical conductivity.

[0091] In several embodiments, e.g., depending on how the magnetic particles are combined with the electrically conductive fee solid bodies and the medium comprising the same, it is possible to select appropriate magnetic particles to improve the magnetic response and at the same time restricting the conductivity to the galvanic action of the electrically conductive free solid bodies. For instance, when using electrically conductive magnetic particles such as Fe3O4(magnetite), which typically present a conductivity in the range of 1 ,000,000 to 10,000,000 pS / cm and a saturation magnetization around 90 to 100 emu / g, methods and system designs may be applied to minimize or prevent the magnetic particles from establishing direct electrical contact with each other or with other conductive parts of the medium thereby minimizing the risk of short-circuiting or uncontrolled current pathways. This can be addressed through strategies applied to the magnetic particles such as spatial separation, insulating layers, or embedding them within a non- conductive matrix, for instance using the embodiments where the magnetic particles are included within the electrically conductive free solid bodies, e.g., by nucleation (206), results in the magnetic particles being surrounded by the matrix of the free solid bodies preventing the magnetic particles themselves .

[0092] Alternatively, to simplify implementation and improve electrochemical control, non-con- ductive magnetic particles can be used. For example, BiFeO3(bismuth ferrite) has a typical conductivity range of 10 to 1 ,000 pS / cm and a relatively low saturation magnetization of approximately 5 to 10 emu / g, making it suitable when minimal magnetic force is sufficient. BaFei20i9 (barium hexaferrite) presents conductivity values between 0.1 and 10 pS / cm with magnetization typically around 50 to 60 emu / g, while SrFei20i9(strontium hexaferrite) exhibits similar conductivity levels of 0.1 to 10 pS / cm and magnetization in the range of 60 to 70 emu / g. These materials are advantageous in that they allow the system to respond magnetically without contributing significant ionic conductivity, thereby maintaining the integrity of the electrochemical system and ensuring that electrical conduction remains confined to the intended galvanic action between the conductive solid bodies. The choice of particle type and positioning strategy within the medium must therefore be aligned with the functional objectives of each embodiment, balancing the need for magnetic actuation with precise electrochemical behavior.

[0093] In some embodiments the plurality of magnetic particles (203) includes, e.g., a polymeric material, such as magnetic particle charged Epoxy resins, Nylon, PPS Polyurethane, PVC, PP. Such particles do not present electrical conductivity.

[0094] The electrical conductivity of magnetic particles that do not present electrical conductivity may be, e.g., of at most 1 pS / cm, as measured using a two-electrode conductivity cell in accordance with ISO 7888:1985 or ASTM D1125, by compacting a powder of the magnetic particles to be measured into a loosely packed bed or pellet, moistening it with deionized water (resistivity >18 MQ cm), and measuring at 25 ± 0.5 °C. The value may vary slightly depending on moisture absorption or surface treatment but remains well below the threshold of electrochemical activity, ensuring the medium remains electrically insulating in the context of the galvanic system.

[0095] Fe304, BiFeO3, BaFe12019and / or SrFe12O19particles or nano-particles are known in the art. Such particles may be added to the composition as such, in the form of preformed particles, e.g., nano-particles. Such particles may also be formed during the preparation of the composition, e.g., as explained in more detail below. Briefly, and as a mode of example, in some embodiments Fe304nanoparticles may be included within the sulfonated styrene divinylbenzene particles are obtainable by Fe304nanoparticle precipitation reaction in the presence of the sulfonated styrene divinylbenzene particles, said precipitation comprising, e.g., incorporating a NaOH dissolution to a previously prepared dispersion of the sulfonated styrene divinylbenzene particles in an aqueous solution comprising FeCl2■ 4H2O and FeCl2■ 6H2O.

[0096] In some embodiments, in a composition as described herein, the magnetic particles (303) include a protective magnetic coating (306), e.g., wherein a set (or plurality) of the magnetic particles (303) include a protective magnetic coating (306).

[0097] A protective magnetic coating as used herein refers to, e.g., a physical, mechanical, and / or chemical barrier applied to the surface of magnetic particles included in a Magnetic Dry Electrolyte (MDE) as described herein with the purpose of stabilizing their magnetic properties during various electropolishing processes. Such coatings may prevent degradation, oxidation, or dissolution of the magnetic core material under electrochemical stress, particularly in aggressive environments. In some embodiments, the protective magnetic coating allows the formulation to tolerate high concentrations of strong acids, such as phosphoric acid, sulfuric acid, or mixtures thereof, without significant loss of magnetic responsiveness or particle integrity. Suitable examples of protective coatings include thin layers of inert polymers (e.g., polytetrafluoroethylene, polyethylene, or polyurethane), silica coatings, or chemically resistant oxides such as alumina or titania. These coatings may be applied by, e.g., sol-gel methods, plasma deposition, or surface grafting techniques. As described elsewhere in the present text, such coatings may contribute in preserving and improving the function and recyclability of the magnetic particles during repeated cycles of use, e.g., repeated electropolishing cycles.

[0098] In some embodiments, in a composition as described herein, the protective magnetic coating (306) of the magnetic particles is hydrophobic. For instance, in some embodiments at least one of a set of the magnetic particles (303) include a hydrophobic protective magnetic coating (306). A hydrophobic magnetic coating includes a molecular hydrophobic coating over the magnetic particles which prevent acids to contact and dissolving them. As a mode of example, a protective hydrophobic shell grown on Fe304particles has been described on “D. Wang, K. Guan, Z. Bai, F. Liu, Facile preparation of acid-resistant magnetite particles for removal of Sb(lll) from strong acidic solution, Sci Tech nol Adv Mater 17 (2016) 80-88)”, where a three-step hydrolysis process was used to form three layers of protective shells around Fe3O4nanoparticles. The middle layer, enriched with hydrophobic methyl groups, effectively prevented the magnetic core from being corroded by strong acids. These coated magnetite particles demonstrated resistance to 1 M HCI and 2.5 M H2SO4, showing a higher acid resistance than previously reported materials. After additional surface modification with amino-methylene-phosphonic groups, the particles also exhibited strong performance in adsorbing Sb(lll) ions in acidic media. This strategy illustrates a generalizable method that can be applied to protect other magnetic or functional particles from degradation under harsh chemical conditions.

[0099] In a representative method for forming the hydrophobic shell, Fe3O4powders are first dispersed in ethanol and subjected to ultrasonic agitation to ensure uniform suspension. Subsequently, water and aqueous ammonia are added under vigorous stirring to adjust the pH, with the entire mixture maintained at, e.g., 30 °C. After initial stabilization, tetraethyl orthosilicate (TEOS) is introduced to initiate silica shell formation around the magnetic cores. Following an initial reaction phase, additional TEOS and dimethyldimethoxysilane (DMDES) are added to build up a secondary layer incorporating hydrophobic methyl groups. The process is repeated through a third treatment stage, involving fresh DMDES addition and extended reaction time to complete the formation of a dense, acid-resistant, hydrophobic silica shell. Throughout the procedure, magnetic separation is used to isolate and purify the coated particles after each stage. The final product, typically denoted as Fe3O4@SiO2@SiO-Me, exhibits enhanced stability under strong acidic conditions due to the presence of hydrophobic methyl groups embedded in the shell structure.

[0100] Magnetic particles may have a wide range of shapes and sizes. In some embodiments magnetic particles have a shape selected from spherical, prismatic, cubic, and needle-shape. In some embodiments magnetic particles have sizes with their longest dimension from nanometers to centimeters, e.g., from 10 nm to 5 cm, in particular 50 nm to 2 cm, more in particular from 100 nm and 2 mm.

[0101] The plurality of electrically conductive free solid bodies are a plurality of particles (free solid bodies) that retain a liquid electrolyte. The liquid electrolyte contributes to making the free solid bodies electrically conductive, as described above.

[0102] The free solid bodies may comprise polymeric materials and may be, e.g., ion exchange resins.

[0103] The free solid bodies may have a spherical shape but may also have a non-symmetrical shape. For instance, ion exchange resins with non-symmetrical shapes may be used. Particularly, needle-like ion exchange resins may be preferably used. Without being bound to any theory such needle-like particles may have a higher susceptibility under magnetic fields oscillations. However, spherical shape particles may also be typically used.

[0104] In some embodiments, the electrically conductive free solid bodies, also referred to as electrically conductive particles, are of a material selected from: strong and weak acidic cationic resins, strong and weak basic anion exchange resins and chelating resins, and more preferably are cationic exchange resins.

[0105] In some embodiments the electrically conductive free solid bodies may be of weak ion exchange resins. Weak ion exchange resins may advantageously have a lower effect on the reduction of magnetic oxides that may be used as material of the magnetic particles, and therefore may contribute to improving the working life of systems comprising magnetic particles of magnetic oxides such as Fe304, BiFeO3, BaFe12019and / or SrFe12O19particles or nano-particles

[0106] Such resins contribute to capturing metal ions extracted in the electropolishing processes. In ion exchange technology, resins may be categorized as strong or weak based on the ionization characteristics of their functional groups, influenced by their pKa values, which may determine their ion-exchange behavior in varying pH environments. Strong ion-exchange resins possess functional groups that remain fully ionized across a wide pH range, making them effective in diverse conditions. In contrast, weak ion-exchange resins have functional groups with higher pKa values, meaning their ionization, and thus their ion-exchange capacity, is more pH-sensitive. Generally, resins having groups with a pKa of up to 3 may be regarded strong acidic cationic resins also referred to as strong acid cation (SAC) resins. Resins having groups with a pKa of above 3 and up to about 6 may be regarded as a week acid cation (WAC) resins. Resins having groups with a pKa from 7 to about 10 may be regarded as weak base anion (WBA) resins, and resins having groups with a pKa higher than 10, e.g., about 12 or 13 may be regarded as strong base anionic (SBA) resins. Chelating resins may have groups with a range of different pKas depending on the nature of the chelating group of the resin, e.g., with a pKa ranging from 1 to 10. In some embodiments, electrically conductive particles are of or comprise a SAC resin, in particular a SAC such as styrene-divinylbenzene with a macroporous or gel structure, having sulfonic acid (-SO3H) groups as functional components. These sulfonic acid groups have a pKa of approximately -2, ensuring they remain fully ionized across a broad pH range, including in highly acidic environments. This enables consistent cation exchange performance. Particular exmples include poly(perfluorosulfonic acid) resins, perfluoro vinyl ether polymers with sulfonic acid groups, and Polytetrafluoroethylene (PTFE) with sulfonic acid side chains, which are highly resistant to pH fluctuations. Other strong acid cation resins include Phenol-formaldehyde sulfonic acid resin, sulfonated phenolic polymers, and crosslinked polyacrylic resins with sulfonic acid functional groups, all of which maintain high efficiency in both acidic and neutral conditions due to their low pKa values.

[0107] In some embodiments, electrically conductive particles are of or comprise a WAC resin, in particular a WAC such as poly(acrylic acid) or crosslinked poly(acrylic acid) resins. These resins feature carboxylic acid (-COOH) groups with a pKa typically in the range of 4.5 to 6.0, making them pH-sensitive and more suitable for environments that are moderately acidic to neutral. They are less effective in strongly acidic solutions due to partial ionization at low pH. Other WAC resins include poly(acrylic acid-co-divinylbenzene), poly(methacrylic acid), and crosslinked iminodiacetic acid-functionalized resins, all of which exhibit ion-exchange properties optimized for pH levels where carboxyl groups are ionized, ensuring effective cation capture and release in more controlled pH conditions.

[0108] In some embodiments, electrically conductive particles are of or comprise chelating resins, which enhance the selectivity for metal ions through functional groups such as iminodiacetic acid and aminophosphonic acid. These groups form stable chelates with specific metal ions. Iminodiacetic acid has a pKa of approximately 2.5 and 9.5, allowing for selective metal ion capture at different pH levels, while aminophosphonic acid has a pKa around 1 .5 and 6.5, making it ideal for selectively recovering metals like calcium and other multivalent ions from complex solutions. Examples of such resins include Poly(styrene-divinylbenzene) resin functionalized with these chelating groups, crosslinked iminodiacetic acid or aminophosphonic acid resins, and thiourea-functionalized styrene-divinylbenzene resins. These resins are particularly useful for selective metal recovery in mixed or harsh chemical environments, providing high specificity even in the presence of competing ions.

[0109] In some embodiments, electrically conductive particles are of or comprise a SBA resin, in particular a SBA which utilizes functional groups like quaternary ammonium (-NR4+) that remain fully ionized across a wide pH range. These resins have a pKa greater than 12, ensuring consistent performance in both neutral and highly alkaline environments, where they can effectively exchange anions such as sulfate, nitrate, and chloride. SBA resins are highly stable and do not lose their ion-exchange capacity even in extreme pH conditions, making them ideal for processes requiring strong anion capture. Particular examples of SBA resins include crosslinked poly(sty- rene-divinylbenzene) resins functionalized with quaternary ammonium groups, and other resins with similar high-pKa ammonium-based functional groups. These resins are particularly suitable for applications involving the removal or recovery of strong acid anions from highly alkaline or near-neutral solutions.

[0110] In some embodiments, electrically conductive particles are of or comprise a WBA resin, in particular a WBA which includes functional groups such as primary, secondary, or tertiary amines (- NH2, -NHR, -NR2) that exhibit a pKa in the range of 7 to 10, meaning they are only partially ionized in moderately acidic to neutral pH environments. WBA resins are effective in absorbing weak acid anions, such as organic acids or carbonates, in environments where strong base anions are not as prevalent. Unlike SBA resins, WBA resins become less effective in strongly alkaline conditions, where their functional groups are not ionized, and they tend to lose their capacity in highly basic environments. Typical examples of WBA resins include crosslinked poly(styrene- divinylbenzene) resins functionalized with amine groups and copolymers of acrylic or methacrylic acids. These resins are commonly used in applications where selective removal of weak acid anions is required, especially in solutions with pH levels that can be easily controlled for optimal ion exchange.

[0111] In some embodiments, the particles of polymeric material are of a sulfonated divinylben- zene S-DVB and styrene copolymer, since it is a material resistant to acid and the oxidative action of the process. The material has the ability to act as an ion exchanger, which favors the extraction of metal from the surface to be surface finished (e.g., polished) by storing the ions.

[0112] Alternatively, the polymeric material particles are of a copolymer containing units derived from acrylic acid or methacrylic acid. This includes derivatives with different functional groups such as acrylic acid, acrylamide, cyanoacrylate, alkyl acrylates, among others, and the corresponding methacrylate analogs.

[0113] In some embodiments, electrically conductive particles are of polymeric materials including functional groups that are capable of capturing or retaining the metal ions generated during the process, such as acid, amino, or chelating groups, including the groups as described above. These functional groups can be of the acidic type, such as sulfonic or carboxylic groups. These acidic functional groups are especially useful in this application as they have good chemical resistance and are capable of retaining a wide variety of metal ions. In some embodiments, the polymeric materials include functional groups that are of the chelating type such as, for example, iminodiacetic, aminophosphonic, polyamine, 2-picolylamine, thiourea, amidoxime, isothiou- ronium, bispicolilamine, among others. These chelating groups have a high selectivity over the transition metals versus alkali or alkaline earth metals, which allows them to be more flexible in the formulation and does not require the use of distilled water.

[0114] Depending on the specific type of polymer and functional groups included, the exact composition of the electrically conductive, particles may vary and may be adjusted. As a mode of example, in some embodiments, electrically conductive particles are of a cationic resin of a gel copolymer styrene-divinylbenzene (DVB), which may preferably be sulfonated.

[0115] Ion exchange resins suitable as electrically conductive particles as described herein may typically be available commercially required characteristics to be used as polymeric material particles.

[0116] The electrically conductive particles may have at least a surface thereof that encapsulates the electrolyte, and such surface may be of a particular material such as, for example but without limitation, an ion-exchange resin, preferably cationic ion-exchange resin that are preferably acid, for example but without limitation, polystyrene divinylbenzene. The encapsulating surface may let the electrolyte escape, at least partially, upon the particle contacting a surface or another particle, and it may also let electrolyte on the surface of, e.g., the object to be surface finished, to be absorbed again into the particle.

[0117] In some embodiments, electrically conductive particles have a porous structure (e.g., macroporous, mesoporous, and microporous, preferably microporous structure), which facilitates the exchange of fluids resulting in a faster process. Alternatively, in some embodiments, the particles have a gel-like structure. In this case the fluid exchange is more restricted, which results in a slower process, however, the particle-surface contact is more defined, which may result in a lower final roughness.

[0118] In some embodiments, in a composition as described herein the electrically conductive free solid bodies (202), in particular the free solid bodies retaining the liquid electrolyte, are ion exchange resins, preferably selected from sulfonated styrene divinylbenzene particles, a type of crosslinker divinylbenzene and 4-vinylbenzyl chloride, and more preferably are or comprise sulfonated styrene divinylbenzene particles. Such types of resins are known in the art and have been described for other surface treating, e.g., electropolishing applications, in, for instance, international applications published as WO2017186992A1 , WO2021156531 A1 , WO2022123096A1 , and W02025088203A1.

[0119] Electrically conductive free solid bodies may have a size typical from ion-exchange resins. In some embodiments, electrically conductive free solid bodies may have their longer dimension to be, e.g., from 0.3 to 2 mm.

[0120] In a composition as described herein, the liquid electrolyte (305), retained by the solid bodies, may be an aqueous solution, e.g., water; a deep eutectic solvent, e.g., 1 :2 (Choline chloride: Ethylene glycol); a strong acid solution including, e.g., as methanesulfonic acid, sulfuric acid and / or phosphoric acid, preferably in concentrations below 10%); or a weak acid solution, e.g., carboxylic acids like acetic acids.

[0121] In some embodiments, the liquid electrolyte (305) (retained by the free solid bodies) is selected from, e.g., a solution (such as an aqueous solution including an aqueous salt solution, e.g., an aqueous sodium chloride salt solution, preferably at a concentration ranging from 0.01 M to 2 M, in particular from 0.05 M to 0.5 M). Other conventional aqueous electrolytes based on salts (rather than acids) used for electropolishing include sodium sulfate (Na2SO4), potassium chloride (KOI), sodium nitrate (NaNO3), and ammonium sulfate ((NH4)2SO4), typically employed in similar concentration ranges of 0.01 M to 1 M, depending on the desired ionic strength, conductivity, and the nature of the substrate material. These salt-based electrolytes provide stable ionic conductivity while avoiding corrosivity associated with strong acids, making them suitable for controlled or buffered electropolishing conditions or for applications requiring milder media. In some embodiments an aqueous comprises an acid solution, e.g., a strong acid solution, including, e.g., as methanesulfonic acid, sulfuric acid and / or phosphoric acid, preferably in concentrations below 10%); or a weak acid solution, e.g., carboxylic acids like acetic acid) a deep eutectic solvent, an ionic liquid and / or ionized water, preferably selected from an aqueous acid solution, an aqueous salt solutions, deep eutectic solvent and an ionic liquid, and more preferably is an acid solution. Aqueous salt solutions may have a concentration of the salt from 0.01 M to 2 M, in particular from 0.1 M to 1 M.

[0122] An acid solution may be an aqueous solution of sulfuric acid, hydrochloric acid, phosphoric acid, and / or sulfonic acid (e.g., methane-sulfonic acid), preferably of an acid selected from sulfuric acid and / or sulfonic acid, more preferably an aqueous solution of both sulfuric acid and sulfonic acid or a combination of an aqueous solution of sulfuric acid and a an aqueous solution of sulfonic acid (e.g., methane sulfonic acid).

[0123] A deep eutectic solvent (DES) may be formed by mixing a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA) in a specific molar ratio to create a eutectic mixture with a melting point lower than either component. In some embodiments, a DES is selected from, e.g., choline chloride:urea (e.g., at a ratio 1 :2), choline chloride:glycerol (e.g., at a ratio 1 :2), or choline chloride:ethylene glycol (e.g., at a ratio 1 :2). In some embodiments a DES is preferably selected from a composition based on choline chloride and ethylene glycol, e.g., a choline chloride:ethylene glycol DES having a ratio of 1 :2.

[0124] In other embodiments, other DES are used, such as solvent NaFSA-KFSA (e.g., a 56:44 mol / mol) binary system, such as super concentrated solutions of 35 mol Kg-1Na0 55K0 A2FSA / H2O and 33 mol Kg-1Na045K0 55FSA / H2O at 25 °C, or either saturated 20 mol kg-1 NaFSA or 31 mol kg-1 KFSA solution, or 33 mol Kg-1Na045K0 55FSA / H2O, or any other of the mentioned families, DES family. As a mode of example, the use of deep eutectic solvents has been described on literature by “Y. Liu, L. Wang, Z. Lv, Z. Bu, X. Hu, Environment friendly dry electrochemical polishing of nickel with ion-exchange resin particles wetted by deep eutectic solvent, n.d.’Ahe use of deep eutectic solvents (DES) for dry electrolytes. The use of DES in binary’s systems for batteries has been discussed on “T. Hosaka, A. Noda, K. Kubota, K. Chiguchi, Y. Matsuda, K. Ida, S. Yasuno, S. Komaba, Superconcentrated NaFSA-KFSA Aqueous Electrolytes for 2 V-Class Dual-Ion Batteries, ACS Appl Mater Interfaces 14 (2022) 23507-23517”.

[0125] An ionic liquid, a salt in the liquid state at or near room temperature typically composed of bulky organic cations and various anions, exhibiting low volatility and high thermal stability, may be selected from, for example, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), or choline-based ionic liquids.

[0126] Ionized water, referring to water that has been subjected to ion exchange or electrolysis to increase the concentration of free ions, thereby enhancing its conductivity, may include, for example, deionized water doped with controlled amounts of Na+, K+, Cl" or OH" ions, or electrolyzed water with pH-adjusted properties (acidic or alkaline) used for enhanced ionic interaction in electrochemical systems.

[0127] In some embodiments, in a composition as described herein, the electrically conductive free solid bodies are sulfonated styrene divinylbenzene particles and the magnetic particles include Fe304nanoparticles, preferably the Fe304nanoparticles are included within the sulfonated styrene divinylbenzene particles. More preferably, the Fe304nanoparticles may be included within the sulfonated styrene divinylbenzene particles are obtainable by Fe304nanoparticle precipitation reaction in the presence of the sulfonated styrene divinylbenzene particles, said precipitation comprising incorporating a NaOH dissolution to a previously prepared dispersion of the sulfonated styrene divinylbenzene particles in an aqueous solution comprising FeCl2■ 4H2O and FeCl2■ 6H2O.

[0128] For instance, in some embodiments in the MDE at least one of a set of the magnetic particles (203) are included to the to the electrically conductive free solid body’s structure (206) trough nanoparticle Fe304(303) precipitation reaction after incorporating a NaOH dissolution to a previously prepared solution including FeCl2■ 4H2O and FeCl2■ 6H2O on H2O with sulfonated styrene divinylbenzene particles (202).

[0129] In some embodiments, in a composition as described herein, e.g., the MDE, the ratio of the plurality of magnetic particles to the plurality of electrically conductive free solid bodies is from 0.1 to 10 wt.%, in particular, from 1 to 8 wt.%, and more in particular from 4 to 7 wt.%. The wt.% being based on the weight of the magnetic particles with respect to the total weight of electrically conductive free solid bodies, taking into account the weight of the free solid bodies and the weight of the liquid electrolyte retained therein.

[0130] The present disclosure also relates to the use of a composition as described herein for surface finishing an electrically conductive part, in particular a metal part. Compositions as described herein are useful for surface finishing, e.g., electropolishing, by ion transport. The combination of the electrically conductive particles with magnetic elements, e.g., magnetic particles and / or a magnetic field as described herein, as explained in detail in the present disclosure, have several advantages when compared to other surface finishing uses and methods, using electrically conductive free solid bodies, in absence of such magnetic elements. Without being bound to any theory, magnetic particles in absence of a magnetic field may be influenced by the electric field in an electrochemical process, e.g., an electropolishing process, and may positively influence the performance of the process through several mechanisms. The presence of magnetic particles, particularly those comprising oxides, can enhance the abrasive action of the solid bodies by contributing additional surface roughness and mechanical hardness. Furthermore, their inclusion may increase the Young's modulus of the composite particles, which helps minimize the meniscus formed between the particle and the treated surface during the electropolishing process. This reduction in the meniscus effect enhances surface-surface contact efficiency, leading to lower final surface roughness by promoting more uniform ion ablation and a high leveling achieved over the treated surface. Additionally, the incorporation of nanomagnetic particles into the matrix of the solid bodies can increase ion exchange rates by facilitating more efficient transport of charged species, thereby extending the effective lifespan of the electrolyte. These particles can also contribute to improved anticorrosive performance and enhanced extraction of hexavalent chromium (Cr(VI)), which is particularly relevant for maintaining surface integrity in martensitic stainless-steels where Cr(VI) can disrupt the protective Cr2O3passivation layer.

[0131] The present disclosure also relates to an assembly for surface finishing an electrically conductive part, in particular a metal part, comprising: an electric connector (108) connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106); a fixing system connected to the electric connector (108) and adapted to hold the electrically conductive part to be treated as the anode (102) or the cathode (103); a container comprising a composition as described herein, e.g., MDE; means for generating a relative movement of a surface of the electrically conductive part to be treated with respect to the composition; and optionally comprising means (111) for creating a magnetic field (105).

[0132] The means for creating a magnetic field is typically configured to apply the magnetic field (105) to at least part of the composition in the container and / or to the electrically conductive part to be surface treated.

[0133] An assembly as described herein comprising a composition including magnetic particles, e.g., MDE, as described above, may preferably have means for creating a magnetic field.

[0134] For instance, the assembly may be configured to surface treat a metal part, comprising: an electric connector (108) connecting the anode (102) to the positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106); a fixing system adapted to the electric connector (108) to hold the metal part as one of the two electrodes (102 or 103) means for generating a relative movement between the surface to be treated (102 or 103) with respect to the MDE (109, 110 and 114); said Magnetic Dry Electrolyte including free electrically conductive solid bodies (109) retaining an electrolyte liquid; and said Magnetic Dry Electrolyte also including, at least, a magnetic particle (110) or means for creating a magnetic field (111 and 105).

[0135] An electrically conductive part may preferably be a metal part. However, parts of other electrically conductive materials may also be used. Electrically conductive parts suitable for electropolishing methods may be known in the art.

[0136] A metal may include pure metals and metal alloys. A metal part may comprise metals selected from, e.g., Fe, Co, Ni, Ti, Al, Cr, Cu, Au, Ag, and Pt. A metal alloy may be selected from, e.g., cast iron, steel, tool steel, stainless-steel, titanium alloys, aluminum alloys, nickel alloys, CoCr alloys, hard metals alloys, cupper alloys, brass, inconel alloys, zamak, semiconductors, gold, silver and platinum among others.

[0137] As a mode of example, electrically conductive parts may also include parts of ceramicmetal composite materials such as carbide parts, e.g., as disclosed in PCT / ES2024 / 070564, in particular, it may include tungsten carbide (WC), W(Ti,Ta)C-Co, Ti(C,N)-FeN), among other carbides with metallic binders based on cobalt, nickel, iron, chromium, or combinations thereof in different proportions.

[0138] As a mode of example, electrically conductive parts may also include parts of a material selected from metals, metal alloys, semiconductors (such as silicon or gallium arsenide), conductive ceramics, conductive polymers, ionizable materials susceptible to surface treatment by redox reactions (e.g., doped oxides or sulfides), and composite materials containing electrically conductive fillers (such as carbon nanotubes or metal nanoparticles). An electrically conductive part for assemblies as described herein, is also suited for uses and methods as described below.

[0139] The present disclosure also relates to an assembly for surface finishing an electrically conductive part, in particular a metal part, comprising: an electric connector (108) connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (107); a fixing means connected to the electric connector (108) and adapted to hold the electrically conductive part to be treated as the anode (102) or the cathode (103); a container comprising a composition comprising a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte and a medium (204) comprising a fluid, wherein the medium contains the plurality of electrically conductive free solid bodies (202); means for generating a relative movement of a surface of the electrically conductive part to be treated with respect to the composition in the container; and means (111) for creating a magnetic field (105).

[0140] The means for creating a magnetic field is configured to apply the magnetic field (105) to at least part of the composition in the container and / or to the electrically conductive part to be surface treated.

[0141] In assemblies as described herein a fixing means or a fixing system are any means known in the art suitable for attaching and connecting the relevant elements of the system. As a mode of examples fixing means or systems may be selected from, e.g., magnets, clamps, hooks, and screws.

[0142] Fixing means may also be further adapted to the specific needs of the elements that they are attaching / connecting. For instance, fixing means attaching the electrically conductive part to the connector in an electrically conductive manner to allow the electrically conductive part to become the anode or cathode. For instance, such fixing means may be electrically conductive or may include electrically conductive elements.

[0143] In such assemblies, where the assembly comprises means for creating a magnetic field, the composition does not necessarily comprise magnetic particles, and may not comprise magnetic particles.

[0144] Without being bound to any theory, a plurality of electrically conductive free solid bodies retaining a liquid electrolyte and a medium in absence of magnetic particles, may be influenced by the magnetic field in an electrochemical process, e.g., an electropolishing process. In particular, e.g., when the electrically conductive part, in particular a metal part, the presence of a magnetic field, in absence of magnetic particles, may favour passivation of the metal part. Furthermore, in absence of magnetic particles, strong acids may be used without needing to protect the magnetic particles from them.

[0145] In the absence of magnetic particles, the application of a magnetic field can still significantly influence the behavior and effectiveness of the solid bodies used in the Magnetic Dry Electrolyte (MDE) even in absence of magnetic particles. When the solid bodies themselves are nonmagnetic, the external magnetic field can be configured to improve the transmission and distribution of the electric field throughout the particle bed. This is achieved by minimizing disruptions caused by induced magnetic fields that may arise from interconnected chains of conductive particles. Proper magnetic field orientation and frequency help to avoid such interference, ensuring more uniform field lines and thus enhancing the overall conductivity of the medium.

[0146] Moreover, in dry or solid-particle-based electrolytes, a challenge remains to achieving sufficient anticorrosive performance without relying on strong oxidizing agents — such as nitric acid or hydrogen peroxide — which are commonly used in liquid electrolytes but detrimental to the chemical integrity of the free solid bodies (particles). The use of external magnetic fields, particularly at optimized frequencies and intensities, has been found to boost anticorrosive effectiveness without requiring such aggressive chemical agents. This field-induced enhancement is critical for protecting sensitive metallic substrates and prolonging the functional life of both the part and the electrolyte system.

[0147] In some embodiments, in magnetoelectropolishing methods as described herein, using dry electrolytes or solid-particle based electrolytes in combination with a magnetic field, the magnetic field strengths used to enhance the anticorrosive properties of metal parts, e.g., such as stainless-steel parts, may range, e.g., from 0.1 to 3 Tesla, in particular from 0.5 to 2 Tesla. Sronger effects may be observed for higher fields up to 3 Tesla. Both static (DC) and alternating (AC) magnetic fields may be employed, where AC fields generally operate within frequencies, e.g., from 10 Hz to several 20 kHz to optimize ion transport and surface reactions.

[0148] In some embodiments, the magnetic field is oriented perpendicular to the direction of the electric current, maximizing the magnetohydrodynamic (MHD) effect which may improve electrolyte agitation and confer a uniform ion diffusion at the surface, but other configurations may also be used.

[0149] In some embodiments, the duration of magnetic field application matches the electropolishing process time, e.g., ranging from 1 to 360 minutes. In some embodiments, pulsed application synchronized with current pulses can also be used to tailor surface characteristics. Without being bound to any theory, these parameters may collectively promote the formation of uniform, protective passive films, reduce surface roughness, and increase resistance to localized corrosion such as pitting, especially in chloride-rich environments.

[0150] In assemblies as described herein, having means for creating a magnetic field (111), is typically configured to apply the magnetic field (105) to at least part of the composition in the container (comprising or not magnetic particles), and / or to the electrically conductive part to be surface treated. Preferably means for creating a magnetic field (111), is configured to apply the magnetic field (105) to at least part of the composition in the container (comprising or not magnetic particles). Thereby the magnetic field may interact with the composition. In some embodiments, in assemblies including means for generating a magnetic field (111), said magnetic field (105) interacts with the magnetic particles (110) of the Magnetic Dry Electrolyte.

[0151] Assemblies as described herein, having means for creating a magnetic field (111), may further include means for applying a change (112 and 113) to the magnetic field (105) created by said means for creating a magnetic field.

[0152] Means for applying a change to the magnetic field (112 and 113) may include, for example, electromagnets controlled by variable current sources, rotating permanent magnets, or electromechanical systems capable of repositioning the magnetic sources during operation. These means can dynamically alter key parameters of the magnetic field such as intensity, direction, gradient, or rotation speed.

[0153] In some embodiments, alternating magnetic fields are generated by modulating the input current to the electromagnets, producing, e.g., sinusoidal or pulsed waveforms from 10 Hz and several kHz (e.g., 1 to 4 kHz).

[0154] In some embodiments, rotational magnetic fields are created by physically rotating the magnet assembly or by sequential activation of multi-axis electromagnets, producing a changing field orientation with defined angular velocities (e.g., from 30 to 300 rpm or more). Such dynamic fields are particularly useful to enhance surface homogeneity and electrolyte flow, and in applications to control particle motion, direction, and uniformity of surface treatment across complex geometries.

[0155] Assemblies as described herein, having means for creating a magnetic field (111), may further comprise a synchronization system (507) configured to synchronize the means for creating a magnetic field with the electrical power supply.

[0156] In some embodiments the magnetic source (508) is configured to control the compaction of the composition, e.g., MDE (502), synchronizing said compaction with the electrical pulses of the current generator with a synchronization system (507).

[0157] Means for synchronization may include the use of, e.g., electronic switching systems, such as MOSFET or relay-based circuits, integrated within the power supply control architecture (507). These systems allow the magnetic source (508), e.g., an electromagnet, to be activated or deactivated selectively based on the polarity of the electrical pulses provided by the power supply. For instance, the electromagnet may be connected in series with the output branch corresponding to the anodic pulse, ensuring that the magnetic field is applied only during anodic polarization, which is typically responsible for material removal in electropolishing. Conversely, it may be selectively activated during cathodic pulses if desired. The other polarity configuration may be used depending on the application. This configuration can be achieved through switching units or polaritysensitive relays, allowing for precise timing of the magnetic compaction force in synchronization with the electrochemical reaction. The result is a dynamic control of the compaction or loosening of the Magnetic Dry Electrolyte (502), which helps regulate particle mobility, contact pressure, and ion exchange rate during electropolishing. This synchronization enhances both surface uniformity and process stability, particularly in pulse-modulated or asymmetric current regimes.

[0158] Assemblies as described herein, having means for creating a magnetic field (111), may further comprise an anti-gravity system, preferably wherein the anti-gravity system comprises magnetic sources (705), arranged along the vertical axis of the container.

[0159] Anti-gravity means may include one or more magnetic sources (705), such as electromagnets or permanent magnets, arranged vertically along the axis of the container to generate an upward-directed magnetic field gradient. Without being bound to any theory, such a setup may create an anti-gravity effect by exerting an upward magnetic force on magnetic particles or composite solid bodies with embedded magnetic components. The packing depth, density, and magnetization level of the particles in the Magnetic Dry Electrolyte may influence the effectiveness of this anti-gravity system. To regulate this effect, the intensity, spacing, and field geometry of the magnetic sources may be dynamically adjusted. For instance, a tighter particle bed or greater vertical depth would require higher magnetic field strength and reduced spacing between magnets to overcome the gravitational and compaction pressure from the accumulated layers. In some embodiments, the spacing between the magnetic sources may progressively decrease along the vertical axis from bottom to top, enabling a gradual lift or suspension of deeper layers. This configuration allows fine control over particle levitation, density distribution, and electrolyte flow, which can enhance polishing uniformity and reduce particle agglomeration or compaction at the bottom of the container.

[0160] In assemblies as described herein, having means for creating a magnetic field (111), the means for creating a magnetic field may be configured to control the motion of the composition in a way that leaves a desired pattern on the surface of the electrically conductive part, in particular a metal part, to be treated.

[0161] In some embodiments, assemblies as described herein comprise magnet sources (805) configured to control the motion of the M DE in a way that leaves a desired pattern over the metal surface (807).

[0162] Assemblies as described herein may further comprise agitating means, e.g. means for mechanical agitation. Agitation, e.g., mechanical agitation, may help generating a movement of the particles (e.g., magnetic particles and / or electrically conductive free solid bodies), and facilitating the interaction of the same with the electrical and / or magnetic fields and / or facilitating a movement lead by magnetic forces of the magnetic fields, generated by magnetic source, e.g., an external magnetic source.

[0163] The present disclosure also relates to the use of an assembly as described herein for surface finishing an electrically conductive part, in particular a metal part. In some embodiments, such assemblies may further incorporate conventional agitation systems, including mechanical impellers or vibration systems operating at various frequencies, such as ultrasonic frequencies, to enhance particle mobility, fluid distribution, and surface interaction efficiency during the finishing process.

[0164] The present disclosure also relates to a method for surface finishing an electrically conductive part, in particular a metal part, comprising: connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106), by means of an electric connector (108), wherein the electrically conductive part, in particular the metal part, to be treated acts as the anode or the cathode (102 or 103) by connecting the electrically conductive part, in particular the metal part, to the positive or negative pole of the electrical power supply by a fixing means connected to the electric connector (108); placing the anode and the cathode in a container comprising the composition as described herein (comprising magnetic particles); generating a relative movement of a surface of the electrically conductive part, in particular the metal part, to be treated with respect to the composition in the container; and optionally generating a magnetic field (111), wherein at least part of the composition is within range of the generated magnetic field (105).

[0165] The expression 'within range of the generated magnetic field' as used herein refers to the operative spatial region in which the magnetic field retains sufficient intensity to influence at least one physical property of the composition, such as particle alignment, mobility, compaction, or magnetic responsiveness, acknowledging that magnetic field strength decreases with distance from the magnetic field source.

[0166] An electrically conductive part for uses and methods as described herein, may be as described above for the assemblies.

[0167] The present disclosure also relates to a method for surface finishing an electrically conductive part, in particular a metal part, comprising: connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106), by means of an electric connector (108), wherein the electrically conductive part, in particular the metal part, to be treated acts as the anode or the cathode (102 or 103) by connecting the electrically conductive part, in particular the metal part, to the positive or negative pole of the electrical power supply by a fixing means connected to the electric connector (108); placing the anode and the cathode in a container comprising a composition comprising a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte and a medium (204) comprising a fluid, wherein the medium contains the plurality of electrically conductive free solid bodies (202); generating a relative movement of a surface of the electrically conductive part, in particular the metal part, to be treated with respect to the composition in the container; and generating a magnetic field (111), wherein at least part of the composition is within range of the generated magnetic field (105).

[0168] In some embodiments, a method for surface treating a metal part, comprises: connecting an anode electrode (102) to the positive pole of an electrical power supply (106) and connecting a cathode electrode (103) to a negative pole of said electrical power supply (106); subjecting and connecting a metal part to be treated (102 or 103), to any of the two electrodes, by fixing means (108); connecting cathode (103) and anode (104) by contacting said electrodes with a Magnetic Dry Electrolyte; said Magnetic Dry Electrolyte including free electrically conductive solid bodies (109) retaining an electrolyte liquid; and said Magnetic Dry Electrolyte also including, at least, a magnetic particle (110) or means for creating a magnetic field (111 and 105).

[0169] In some embodiments, in a method as described herein, the composition (having magnetic particles) has a distribution of solid bodies in the container wherein solid bodies placed in higher regions of the container exercise a gravitational pressure compacting solid bodies placed in lower regions of the container and the method comprises counteracting the gravitational pressure compacting the solid bodies (702) of the lower regions of the container, by means of an anti-gravity system, wherein the anti-gravity system comprises magnetic sources (705), arranged along a vertical axis of the container. In some embodiments such a method, comprises an anti-gravity system, comprising magnetic sources (705), arranged along the vertical axis of a receptacle (704) to counteract gravitational pressure compacting the solid bodies (702), thereby controlling heterogeneous polishing along the gravitational axis.

[0170] In some embodiments, a method as described herein may comprise agitation, e.g., mechanical agitation. Agitation may help generating a movement of the particles (e.g., magnetic particles and / or electrically conductive free solid bodies), and facilitating the interaction of the same with the electrical and / or magnetic fields and / or facilitating a movement lead by magnetic forces of the magnetic fields, generated by magnetic source, e.g., an external magnetic source.

[0171] In some embodiments a method as described herein may be for punctual, linear or extrusion surface finishing. Methods as described herein may be particularly suitable for engraving or engraved polishing.

[0172] In some embodiments a method as described herein is for punctual, linear or extrusion surface finishing. Methods as described herein may be particularly suitable for engraving or engraved polishing.

[0173] Punctual finishing, e.g., punctual surface finishing, refers to a localized treatment of a specific point or small area on the surface of the electrically conductive part. It may be achieved by directing a compact mass of the composition (e.g., Magnetic Dry Electrolyte) to a defined spot using a nozzle or small electrode tip. Examples include micro-polishing specific contact areas on microelectronic components or localized removal of corrosion spots on surgical instruments.

[0174] Linear finishing, e.g., linear surface finishing, refers to treating the surface along a defined path or track in a straight or curved line, typically following the movement of an electrode, applicator, or surface contact unit across the part. Examples include polishing weld seams, surface finishing along cutting edges, or controlled line-etching of decorative patterns on metallic panels.

[0175] Extrusion surface finishing involves feeding the composition through a channel, aperture, or nozzle while the part moves relative to it, or vice versa, to apply a continuous stream or path of material capable of surface finishing. Examples include guiding a rod or wire through a tube filled with the composition for uniform circumferential polishing, or extruding the composition through a slit over flat panels for broad surface treatment. Engraving or engraved polishing refers to the selective removal or controlled modification of the surface topography to form patterns, marks, or textures, while also achieving surface smoothness or luster. Examples include polishing pre-etched logos on stainless-steel, smoothing of decorative cavities on metal plates, or producing mirror-finish engraved microchannels in precision tools.

[0176] In some embodiments, methods for punctual, linear or extrusion surface finishing, comprise steps of: applying MDE (402) onto the surface to be polished (405), connected to a pole of a power supply (403); positioning a counter electrode (401), connected to the other pole of a power supply, at a certain distance from the surface to treated (405) and the MDE (402), avoiding the contact; means for generating a magnetic field (404); configuring the distance from the electrodes (401 and 403), the power of the magnetic source (404), and means for applying changes on the magnetic field (406) generated by the magnetic source (404), to ensure the formation of a bridge by the electrically conductive free solid bodies of the MDE (402) between the first and second poles (403 and 401), thereby connecting the surface to be polished (405) for its surface finishing by ion transport; controlling the motion of the MDE (402) through the surface to be polished (405) by said means (406).

[0177] In some embodiments, in a method as described herein the electrically conductive part, in particular the metal part, to be treated comprises a channel or a tube having an inner surface; the method is for the surface treatment of said inner surfaces; and the electrically conductive part, in particular the metal part, acts as the anode, wherein connecting the electrically conductive part, in particular the metal part, to the positive pole of the electrical power supply comprises connecting the inner surface to be treated to said positive pole; and wherein the cathode is configured to be at least partially introduced to the inner tube or channel (601), and to leave enough space for the composition to circulate through said inner tube or channel (601), and the method comprises at least partially introducing the cathode to the inner tube or channel. In some embodiments such a method may comprise the recirculation of the composition (e.g., MDE) (602) through said inner tube or channel, in particular, recirculation may be forced, e.g., by pumping means. In some embodiments such a method may comprise distributing and configuring magnetic sources (604 and 605) through the inner tube or channel (601) of the electrically conductive part, to control the motion profiles (607 and 608) of the composition (e.g. MDE) (602).

[0178] In some embodiments, a method as described herein includes a system for the surface treatment of inner surfaces comprising steps of: connecting an inner surface of a tube or channel to be treated to a first pole of a current generator (601); connecting an inner cathode to a second pole of a current generator (606) at least partially introduced to the inner tube or channel (601), configured in a way that leaves enough space for the MDE to circulate through said inner tube or channel (601); forcing the recirculation, by pumping means, of the MDE (602) trough said inner surface of a tube or channel to be treated (601); distributing and configuring magnetic sources (604 and 605) through the inner tube or channel (601) to control the motion profiles (607 and 608) of the MDE (602).

[0179] In some embodiments, a method for surface finishing as described herein uses an assembly as described herein. As described above, the composition of the assembly may or not comprise magnetic particles. Where the composition comprises magnetic particles, the assembly may optionally comprise means for generating a magnetic field, and where the composition does not necessarily comprise magnetic particles, the assembly comprises means for generating a magnetic field.

[0180] The present disclosure further relates to a surface finished electrically conductive part, in particular a metal part, obtainable by the surface finishing method as described herein. Preferably, the surface finished electrically conductive part is a metal part. More preferably the surface finished metal part has a passivation layer from 1 nm to 30 nm thickness in particular from 1.5 to 15 nm, which may vary depending on the metal substrate and processing parameters.

[0181] Advantageously, such a passivation layer improves corrosion resistance by forming a stable and dense oxide or oxyhydroxide film, reduces surface roughness, and enhances biocompatibility in medical applications. In particular embodiments, the formation of a thin and uniform passivation layer also leads to increased resistance to pitting and intergranular corrosion in stainless-steels, better electrical insulation in microelectronic applications, and reduced ion leaching in high-purity environments.

[0182] Some aspects of the present disclosure are described in more detail in the following paragraphs.

[0183] 1) A first aspect of the invention refers to a method to work with the previously described magnetic electrolyte in order to overcome the problematics, some issues, exposed in, e.g., the background: PROCESSING METHOD OR SYSTEM

[0184] As indicated above the instant disclosure relates to methods, compositions, assemblies and systems for surface finishing at least one surface of an object, e.g., surface finishing an electrically conductive part such as a metal part, using a medium comprising a plurality of electrically conductive particles including a magnetic element, e.g., magnetic particles and / or magnetic fields, an MDE.

[0185] Methods for surface finishing using a plurality of electrically conductive particles have been described in the art. Reference is made to, for instance, the International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1), which describes a method for smoothing and polishing metals via ion transport by means of free solid bodies, and the solid bodies that are electrically conductive for carrying out said method. Such a method complemented by magnetic elements, e.g., the magnetic fields and / or magnetic components, such as magnetic particles, is illustrated in Figures 1 A, B and C.

[0186] Figure 1 A is a graphical representation of a particular realization of a Magnetic Dry Electrolyte and a method for working with said Magnetic Dry Electrolyte. A method for surface finishing, surface treating, a metal part comprising: connecting the anode (102) to a positive pole of an electrical power supply (106) by the help of an electric connector (108) and connecting a cathode (103) to a negative pole of said electrical power supply (106); subjecting a metal part (102) or (103), connected to one of the electrodes, with a fixing system adapted to said electric connector (108); connecting the cathode (103) to the anode (104) by contacting a magnetic dry electrolyte including free electrically conductive solid bodies (109) inside of a receptacle (101), said electrically conductive solid bodies (109) comprising a structure retaining an electrolyte liquid to make them electrically conductive, resulting on a current (107), e.g., flowing through the electrical power supply (106) and an ion transport trough the solid bodies on the direction of a created electrical field (104), the Magnetic Dry Electrolyte including a magnetic element, e.g., at least a magnetic particle and / or field (110) to provide them magnetic activity, making them magnetically active, as represented in the detail for a polarized magnetic particle (118) (e.g., in Figure 1-B) ; optionally, in several particular embodiments, means for generating a magnetic field (111), e.g., an external magnetic field, said magnetic field (105) interacting with the magnetic particles (110) of the magnetic dry electrolyte and making magnetic free electrically conductive solid bodies (109), also referred to as magnetic dry electrolyte. Such magnetic dry electrolyte, owing to the presence of magnetic particles, may be susceptible to respond for any adapted means for inducing a change on the magnetic field (112), for example by generating a velocity to the magnetically source means (113) or by any other possible means.

[0187] Figure 1 - B illustrates the interaction between two free electrically conductive solid bodies

[0188] (109) in a particular embodiment of the invention in which the magnetic particles (110) are included within the solid structure of the said solid bodies under the electrical (E) and magnetic (B) fields as shown and described in Figure 1 - A.

[0189] As represented in the detail of a polarized magnetic particle (118), the magnetic particles

[0190] (110) are magnetically polarized when submitted under, subjected to, a magnetic field (105), aligning the south and north polarity along the magnetic field vector. Under no electrical and magnetic field, the electrically conductive free solid bodies, with or without magnetic particles, preferably, do not present any electrical or magnetic polarization. As a result of applying a magnetic field, e.g., external magnetic fields (105), the magnetic particles may be oriented along the same magnetic field direction that may result in a net magnetic global polarization of the solid bodies (116). The same effect may occur with a plurality of electrically conductive free solid bodies, with magnetic particles, e.g., different connected free solid bodies, acquiring an oriented magnetic polarization (116) along the magnetic field (105) potentially triggering a magnetic attraction force FM (114), e.g., between the two solid bodies resulting in an increase of the current (107) from Figure 1 - A. Moreover, in some embodiments, as a result of a change on the magnetic field, induced by, e.g., a mobility element (112) of the magnetic field source represented on Figure 1 - A, the motion force, magnetic velocity force Fv, (115) represented in Figure 1 - B may produce the motion of the electrically conductive free solid bodies on, e.g., the same direction of a velocity applied to a magnetically source means (113).

[0191] In addition, as a result of applying an electric field (104), e.g., external electric fields (104), a net electric global polarization of the solid bodies (117) generally appears, which in turn may trigger the ion transport between the particles to happen.

[0192] Figure 1 - C shows a schematic representation of an electropolishing method, including methods described in, e.g., WO 2017 / 186992 A1 in combination with a magnetic field (105) but in absence of magnetic particles (110). The advantages of the use of a magnetic field even in absence of magnetic particles has been described in detail above.

[0193] Figure 4 shows a representation of a system, an assembly, or a method for surface finishing an electrically conductive part, e.g., for punctual, linear or extrusion surface finishing, particularly suitable for engraving or engraved polishing, that may comprise the steps of: applying MDE (402) onto the part to be surface finished, e.g., the surface to be polished (405), connected to a pole of a power supply (403); positioning a counter electrode (401), connected to the other pole of a power supply, at a certain distance from the surface to treated (405), ensuring no electrical connection between the two electrodes (403 and 401) through the MDE (402); means for generating a magnetic field (404) ensuring a controlled magnetic response (408 and 407) by the MDE (402); configuring the distance from the electrodes (401 and 403), the power of the magnetic source (404), and means for applying changes on the magnetic field (406) generated by the magnetic source (404), to ensure the formation of a bridge by the electrically conductive free solid bodies of the MDE (402) between the first and second poles (403 and 401) thereby closing the electrical connection for surface finishing, e.g., punctual, linear, or extrusion surface finishing of the surface to be polished (405); controlling the motion and speed of the MDE (402) through the surface to be polished (405) by said means (406).

[0194] Some particular embodiments comprised on the representation of Figure 4, the surface to be finished (405) includes the polishing of a pre-existing engraved electrically conductive part. In other particular embodiments the surface to be finished (405) includes the engraving of a surface, generating a desired pattern by ion transport and controlling its shape by the means for applying changes on the magnetic field (406) generated by the magnetic source (404).

[0195] An extrusion surface finishing in the present text is to be understood as any surface finishing of a metal surface to be treated where the motion of the electrolyte is controlled over two special dimensions projected through said surface (405).

[0196] In several particular embodiments the environment between the two electrodes of the electrochemical cell, the fluid of the medium, comprising the plurality of electrically conductive free solid bodies (202) and the plurality of magnetic particles (203), is a gas, particularly air; in other embodiments is a liquid, particularly a moderating fluid or water. A moderating liquid may comprise an aqueous solution including, e.g., an aqueous salt solution, e.g., an aqueous sodium chloride salt solution at a concentration which is not limited typically range from 0.01 M to 2 M, in particular from 0.05 M to 0.5 M). Other conventional aqueous electrolytes based on salts (rather than acids) that may be used as moderating liquid include, e.g., sodium sulfate (Na2SO4), potassium chloride (KOI), sodium nitrate (NaNO3), and ammonium sulfate ((NH4)2SO4), typically employed in similar concentration ranges of 0.01 M to 1 M, depending on the desired ionic strength, conductivity, and the nature of the substrate material. By changing said environment, it is possible to modify the rheology, viscosity, density and other parameters modifying, e.g., the magnetic field intensity contributing to inducing a force (407), e.g., FMX, that may contribute to ensuring the motion of the electrically conductive free solid bodies of the MDE (402) and / or a force (408), e.g., FMY that may contribute to ensuring the formation of a bridge electrically connecting the two electrodes (401 and 403) by the MDE (407). In some embodiments, the environment can be connected to a control temperature recirculation system that may contribute to avoid, when desired or required, uncontrolled temperature evolution during the surface treatment.

[0197] In several particular embodiments it is possible to work under an anti-gravity polishing system, as described for and shown in Figure 7. The depicted system comprises, e.g., magnetic sources, such as electromagnets, permanent magnets or coils (705), arranged along the vertical axis of the polishing receptacle, container, (704) to control or counteract gravitational pressure compacting the solid bodies (702), thereby preventing heterogeneous or differential polishing along the gravitational axis. Typically, in immersion dry electropolishing systems comprising, e.g., consisting on, free solid bodies, in large polishing surfaces (707), such as for higher dimensions than 10 cm along the vertical axis, a surface treatment gradient result appears because of gravitational forces. In particular embodiments for an anti-gravity polishing, a toroidal cube is used, distributing magnetic sources all over the permitter of the receptacle, in some cases behind the cathode (701), in other cases also coupled to the anode (703) by fixing means (706). The intensity, separation and the synchronization between the magnetic sources, in particular embodiments, is to be empirically adjusted to control or counteract gravitational pressure, given a particular system configuration.

[0198] A typical limitation of the previous state of art is the control of the polishing result over inner channel surfaces having complex shapes, such as curved tubes. For instance, if a dry electrolyte is pumped through an inner tube a preferential treatment area will appear at the concavity of the curvature or knee rather than at the convexity of the curvature or knee. Without being bound to any theory, such preferential treatment area may be as a result of obtaining higher friction forces applied by the MDE (602) to the anode or the surface to be polished (601) caused by higher velocities (607) at the concavity compared to lower velocities (608) at the convexities.

[0199] Figure 6 represents an assembly, system or method for surface treatments, surface finishing, of curved inner channels, e.g., electrically conductive parts comprising such curved inner channels, involving a controlled distribution of magnetic fields within an interior space or tube to ensure a uniform motion profile of the MDE (602) across various surfaces to be treated (601).

[0200] The system represented in Figure 6 includes:

[0201] Connecting an inner surface of a tube or channel to be treated to a first pole of a current generator (601); connecting an inner cathode to a second pole of a current generator (606) at least partially introduced to the inner tube or channel (601), configured in a way that leaves enough space for the MDE to circulate through said inner tube or channel (601); forcing the recirculation, by pumping means, of the MDE (602) trough said inner surface of a tube or channel to be treated (601); distributing and configuring magnetic sources (604 and 605) through the inner tube or channel (601) to control the motion profiles (607 and 608) of the MDE (602).

[0202] In some particular embodiments a different magnetic source is located on the concavity of the tube (604) from the magnetic source from the convexity (605). Them creating a differential magnetic field capable of precisely controlling the velocity profile of the particles (607 and 608) on the tube. Without a magnetic source, typically from conventional pump means, V1 (607) may typically be higher than V2 (608) leaving an heterogenous treatment. In several embodiments, the magnetic fields interacting to the MDE (602) generate an equal V1 and V2, resulting on a homogeneous result.

[0203] In particular embodiments, an assembly, system, or method as described herein may also be used for generating desired engraved shapes to modify the inner surface, thereby also modifying, e.g., its tribological properties, of said inner channel, like typically required to improve the aerodynamic bullet propulsion within canons. 2) / second aspect of the invention refers to the Magnetic Dry Electrolyte, including electrically conductive free solid bodies and magnetic elements: MAGNETIC DRY ELECTROLYTE

[0204] In particular, as described above, the instant disclosure relates to a composition comprising: a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte (305); a plurality of magnetic particles (203); and a medium (204) comprising a fluid; the medium (204) containing the plurality of electrically conductive free solid bodies (202) and the plurality of magnetic particles (203).

[0205] Such compositions may be referred to herein as magnetic dry electrolyte (MDE).

[0206] Figure 2 illustrates three extreme cases of particular embodiments of a Magnetic Dry Electrolyte. It is to be mentioned the scope of protection covers any intermediate case between the three exposed embodiment as any possible combination between them. The three extreme scenarios are divided on: Magnetic particles included on the electrically conductive free solid bodies (206) on the left; magnetic particles included on the environment where the free solid bodies are located (208) in the middle; and magnetic particles dissolved on the liquid environment where the free solid bodies are located (207) to the right.

[0207] In several particular embodiments, the elements comprising a Magnetic Dry Electrolyte are further described.

[0208] - A set of electrically conductive free solid bodies with ability to retain a liquid electrolyte to increase their electrical conductivity (202). For instance, free solid bodies prior to retaining liquid electrolyte may have an electrical conductivity lower than 10 pS / cm, in particular, lower than 1 or 0.1 pS / cm, and when retaining a liquid electrolyte may have an electrical conductivity higher than 10 pS / cm, particularly higher than 100 pS / cm, more in particular between 1000 and 100000 pS / cm.

[0209] - An electrolyte liquid, liquid electrolyte, retained by the electrically conductive free solid bodies.

[0210] - A magnetic element, e.g., a set (plurality) of magnetic particles (203) and / or magnetic fields. Said set of magnetic particles may be included, as also described elsewhere, in, e.g., either of the following elements: o Attached to the electrically conductive free solid body’s solid structure (206). o Present in the environment, medium, of the set of electrically conductive free solid bodies, regardless if it includes a liquid, a gas or a combination of bough (207 and 208).

[0211] - A medium or environment where at least the electrically conductive free solid bodies are located (204), comprising a fluid, regardless if it includes a moderation liquid, a gas or a combination of both, e.g., as also described elsewhere in the present specification.

[0212] Optionally a set of abrasive and / or moderation particles used to improve the surface treatment performance.

[0213] In some cases, the ratio of the magnetic particles to the electrically conductive free solid is between 0.1 and 10 wt.%, particularly between 1 and 8 wt.%, more in particular between 4 and 7 wt.%. It is an important aspect to consider as such specific ratios may contribute to an optimal magnetic property of the free solid bodies without affecting its ion transport capacity, and its electrical conductivity.

[0214] In some embodiments, in a composition as described herein the plurality of magnetic particles (203) are included within the electrically conductive free solid bodies (202).

[0215] In some embodiments, wherein the plurality of magnetic particles are included within the electrically conductive free solid bodies: the magnetic particles are, for instance, at the surface of the free solid bodies (211), e.g., on an external moderation liquid, or inside the free solid bodies (212), e.g., at the solid structure of the solid bodies.

[0216] In some embodiments, in a composition as described herein the magnetic particles (203) are included within the medium (204) outside the plurality of electrically conductive free solid bodies (202). In some particular embodiments, wherein magnetic particles are included in the medium, environment, outside of the free solid bodies (208 and 207); such particles may be of similar size or even bigger than the free solid bodies (208) or may be smaller than the free solid bodies (207). In some particular embodiments, magnetic particles, e.g., smaller than the free solid bodies are in the medium environment, outside of the free solid bodies but included in a liquid medium, e.g., suspended / dispersed or dissolved in the liquid medium (207). In some embodiments, in a composition as described herein the magnetic particles (203) are included within the medium (204) in the form of, e.g., a ferrofluid (207). A ferrofluid is a fluid that becomes highly magnetized in the presence of a magnetic field. Ferrofluids are colloidal suspensions made of nanoscale ferromagnetic particles suspended in a carrier fluid.

[0217] Such embodiments and some other (particular) embodiments thereof are discussed in more detail in the following.

[0218] As a person skilled in the art understand particles may be generated by dissolution and further precipitation. Dissolution followed by precipitation may be used for introducing the magnetic particles within the electrically conductive free solid bodies, on their surface, or also outside the electrically conductive free solid bodies, in the medium comprising the electrically conductive free solid bodies. As a person skilled in the art also understands, magnetic particles may also be directly suspended / dispersed to be included within the electrically conductive free solid bodies, on their surface, or also outside the electrically conductive free solid bodies, in the medium comprising the electrically conductive free solid bodies. In some embodiments, where the plurality of magnetic particles is in the medium, outside of the electrically conductive free solid bodies, the electrically conductive bodies may incorporate magnetic particles upon contact with the magnetic particles also present in the medium, e.g., on the surface or within the electrically conductive free solid bodies, and the plurality of magnetic particles may be both outside and within the electrically conductive free solid bodies.

[0219] In the present disclosure, occasionally the terms dissolving / suspending / dispersing may be used indistinctively.

[0220] Without being limited to the following description, below are described three different possible configurations in which the magnetic particles can be included to electrically conductive free solid bodies, e.g., a conventional dry electrolyte. Any other configuration, intermediate description or a combination of the three following extreme cases, meeting the essential elements previously described, is within the scope of protection of the present document.

[0221] A) MAGNETIC PARTICLES INCLUDED ON THE ELECTRICALLY CONDUCTIVE FREE SOLID BODIES (206)

[0222] Wherein the plurality of magnetic particles is included within the electrically conductive free solid bodies, a composition as described herein may be a MDE in which the magnetic particles (203) are attached by some method to the electrically conductive free solid bodies (202). Being attached meaning there is no net relative velocity between the magnetic particle with respect to the attached electrically conductive free solid body (202), the electrically conductive free solid body to which the magnetic particle is attached, because of any attracting force between them.

[0223] A particular embodiment in which the magnetic particle (203) is attached a to an electrically conductive free solid body (202) is by, e.g., a method comprising, dissolving a magnetic particle with a size smaller than that of the porosity of the electrically conductive free solid body in the electrolyte liquid to be retained, e.g., absorbed or adsorbed by the free solid bodies to make them electrically conductive (212). It may be preferred, or even in some instances a requirement, e.g., depending on the electrolyte liquid (to be) retained by the free solid bodies, for the present method, for such a method, to find a magnetic particle with no electrochemical interaction with the liquid electrolyte to be absorbed by the particle. Smaller particle sizes than that of the porosity of the electrically conductive free solid bodies is also desirable, and depending on the specific type of interaction and amount of magnetic particles may also be required, so it does not block the expulsion of acid under the working conditions. In a more particular embodiment of the invention, it is possible to use as electrically conductive free solid bodies (202) a cationic gel or microporous ion-exchange resin, e.g., such as or consisting on sulfonated polystyrene polyvinyl benzene or a type of crosslinker divinylbenzene or 4-vinylbenzyl chloride, as the electrically conductive free solid bodies (202); the liquid electrolyte may be ,e.g., an electrolytic solution, particularly an acid solution, a deep eutectic solvent ionized water or an ionic liquid, more particularly an acid solution consisting on sulfuric acid or a sulfonic acid, such us methane-sulfonic acid; a magnetic particle (203) may be suspended or dissolved, preferably dissolved and subsequently precipitated inside of the free solid bodies, in the retained liquid electrolyte, e.g., electrolytic solution, by the free solid bodies to make them electrically conductive. The magnetic particle may be, and preferably is, soluble in said liquid electrolyte, e.g., electrolytic solution, and there is no electrochemical reactivity between them. Particularly, among other substances it is possible to use as magnetic particles (203) Fe304or BiFeO2or BaFe12O19or SrFe12O19. Preferably the plurality of magnetic particles (203) include Fe304or BiFeO2or BaFe12O19or SrFe12O19nano-particles, preferably at least include Fe204nanoparticles. In particular, such nanoparticles, nanomagnetic particles, may be, e.g., 10-800 nm in size. Such particle sizes may advantageously guarantee that they can be incorporated, e.g., absorbed by the solid body without causing an obstruction at the porous present on the structure of the solid bodies (202), so the galvanic process is not blocked; optionally a moderation fluid may be present in or may be used as the environment, medium, (204). In some particular embodiments the medium (204) comprising a fluid may comprise a non-conductive liquid, e.g., deionized water, in others a non- conductive liquid (204) may be selected from substances or combination of substances like aliphatic chains in particular from C5 to C30 hydrocarbons, surfactants, such as fatty acids, toluene sulfonate, trans-cinnamaldehyde, and dodecylpiridinium bromide, or hydrocarbons with polar head groups other than carboxylic acids, such as ketones, hydroxyl groups (e.g., hexylene glycol, and isopropanol), amide groups, or carboxylic acids other than fatty acids as described herein (e.g., nitrobenzoic acid).

[0224] Another particular embodiment comprises attaching at least a magnetic particle (203) onto the surface of the electrically conductive free solid bodies by, e.g., suspending or dispersing or dissolving, said magnetic particles on an external moderation liquid (211), or a liquid coating (205) adsorbed or retained by capillary forces at the external surface of the solid bodies. In the preset embodiment, without being bound to any theory, a liquid is used to moderate the electrochemical or mechanical interaction between the free solid bodies (202) and between the free solid bodies and the surface to be polished, while being used as a carrier of the magnetic particles. The previous preferred size restrictions described above may also be relevant or may not be relevant for the present embodiment, as the particles typically retain the capacity of ion exchange despite having the magnetic particles on their surface. The size or mass of the magnetic particles may be defined by the thickness of the adsorbed liquid on the external layer of the solid bodies.

[0225] In a more particular embodiment of the invention, it is possible to use as electrically conductive free solid bodies (202) a cationic gel or microporous ion-exchange resin, comprising or consisting of sulfonated polystyrene polyvinyl benzene or a type of crosslinker divinylbenzene or 4-vinylbenzyl chloride, as the electrically conductive free solid bodies. In some embodiments, an electrolytic solution may be used which may particularly be an acid solution, a deep eutectic solvent ionized water or an ionic liquid, more particularly it may be an acid solution consisting on sulfuric acid or a sulfonic acid, such us methane-sulfonic acid. In some embodiments, a moderation liquid may be used as the fluid of the medium. A moderation liquid may be, e.g., a non-conductive liquid in a proportion that only covers an adsorbed layer of the electrically conductive free solid bodies (205) leaving empty interstitial space between them, filled by a gas, such as air, as the environment (204), the medium, the fluid of the medium, said moderation liquid (205), in some cases may include a polar solution or water, such as in the form of an emulsion, e.g. a conductive liquid, in others a moderation liquid may include substances or combinations of substances like aliphatic chains - aliphatic hydrocarbon chains - in particular from C5 to C30 hydrocarbons, surfactants, such as fatty acids, toluene sulfonate, trans-cinnamaldehyde, and dodecylpiridinium bromide, or hydrocarbons with polar head groups other than carboxylic acids, such as ketones, hydroxyl groups (e.g., hexylene glycol, and isopropanol), amide groups, or carboxylic acids other than fatty acids as described herein (e.g., nitrobenzoic acid). In some embodiments a magnetic particle (203), may be selected from Fe204or BiFeO2or BaFe12O19or SrFe12O19nanomagnetic particles of 10-800 nm size or bilayer-grafted Fe304nanomagnetic particles by an oleic acid activation may be used, e.g., solved, dispersed, in said moderation liquid (205) in a way that covers the electrically conductive free solid bodies (202) with a liquid layer with magnetic properties. A combination of all or part of the above may also be particularly used.

[0226] Another particular embodiment comprises a method comprising physically attaching at least a magnetic particle (203) to the solid structure (212) of the electrically conductive free solid bodies (202). In the present method the magnetic particles are solidary to the solid bodies, incrusted in its morphological structure or by any other fiscal interaction. In a more particular embodiment, it is possible to use as electrically conductive free solid bodies (202) a cationic gel or microporous ion-exchange resin, consisting on sulfonated polystyrene polyvinyl benzene or a type of crosslinker divinylbenzene or 4-vinylbenzyl chloride, as the electrically conductive free solid bodies; the magnetic particle (203), like Fe204or BiFeO2or BaFe12O19or SrFe12O19nanomagnetic particles of 10-800 nm size or bilayer-grafted Fe304nanomagnetic particles by an oleic acid activation, can be included by a reaction in which the ionized atoms, like Fe2 +and Fe3+first react to the free radicals of the polymer, like the sulfonic groups SO2~ , by dissolution and the magnetic particles are precipitated directly inside the resin structure by an addition of a base, like NaOH or NH3, after which the particle is preferably cleaned, e.g., with methanol and dried, to provide a so called magnetic resin; an electrolytic solution is added to the magnetic resin, particularly an acid solution, more particularly an acid solution consisting on sulfuric acid or a sulfonic acid, such us methane-sulfonic acid or any other possible acid; optionally is possible a to add a non-conductive liquid as an environment (204) moderator, e.g., of the rheology and galvanic interactions, said moderation liquid (204), in some cases including a polar solution or water, in others including substances or combination of substances like aliphatic chains - aliphatic hydrocarbon chains - in particular from C5 to C30 hydrocarbons, surfactants, such as fatty acids, toluene sulfonate, trans-cinnamaldehyde, and dodecylpiridinium bromide, or hydrocarbons with polar head groups other than carboxylic acids, such as ketones, hydroxyl groups (e.g., hexylene glycol, and isopropanol), amide groups, or carboxylic acids other than fatty acids as described herein (e.g., nitrobenzoic acid).

[0227] In some particular embodiments it is possible to include to physically attach at least a magnetic particle (203) to the solid structure (212) of the electrically conductive free solid bodies

[0228] (202) together with abrasive dust previously included on the fabrication of said solid bodies. Obtaining as a result what is referred to herein as a Hybrid Magnetic Dry Electrolyte (HMDE) combining electrochemical, mechanical and magnetic properties.

[0229] In some of the previously described embodiments, there may be a risk of losing the magnetic particles (203), e.g., in the medium, or the magnetic properties (203 and 209) of the Magnetic Dry Electrolyte, e.g., within the electrically conductive free solid bodies, in some cases, because of an acidic dissolution of said particles, e.g., by an acidic electrolyte and / or an acidic fluid, e.g., an acidic liquid, in the medium. In particular, magnetic particles, the magnetic particle

[0230] (203), like Fe204or BiFeO2Fe204or BiFeO2or BaFe12O19or SrFe12O19nanomagnetic particles of 10-800 nm size or bilayer-grafted Fe304nanomagnetic particles by an oleic acid activation, can be dissolve when included in contact with a strong acid, such as sulfuric acid, hydrochloric acid, phosphoric acid, methane sulfonic acid, etc.

[0231] Figure 3 is used to illustrate the strategies for protecting magnetic particles (303) in a Magnetic Dry Electrolyte from the electrolyte liquid (305) retained by the electrically conductive free solid bodies (302), located on a receptacle (301) in some environment (304) regardless of it is a gaseous or a liquid environment.

[0232] In some particular embodiments, the electrolyte liquid (305) includes a strong acid, such as sulfuric acid, hydrochloric acid, phosphoric acid, a sulfonic acid (e.g., methane sulfonic acid, in particular, selected from sulfuric acid and methane sulfonic acid. More in particular, in some cases, the solid bodies (302) include a sulfonated polystyrene polyvinyl benzene. More in particular, in some cases, the magnetic particles (303) include Fe304Fe304or BiFeO2or BaFe12O19or SrFe12O19nanomagnetic particles. Said magnetic particles (303) reacting with said strong acid (305), losing the magnetic properties of the Magnetic Dry Electrolyte through time, with time. In some particular embodiments it is possible to include a protective magnetic coating (306) avoiding, preventing, the reaction between the liquid electrolyte (305) and the magnetic particles. In some particular embodiments, the coating (306) comprises covering the Fe304nanomagnetic particles by an oleic acid layer, e.g., resulting on bilayer-grafted Fe204nanomagnetic particles obtained by an oleic acid activation, or octanoic acid activation, which decreases the reactivity between said magnetic particles (303) and the liquid electrolyte (305). In other particular embodiments, the protecting coating (306) includes a hydrophobic coating, avoiding any possible interaction of polar fluids with the magnetic particles (303). More in particular, the hydrophobic shell (306) can be grown on Fe304nanomagnetic particles (303) by the following procedure: dispersing a mixture of Fe204powders (303), or the magnetized electrically conductive free solid bodies (302) of a MDE including Fe204in its solid structure, in, e.g., 150 ml of ethanol sonicated for 30 min, after which 25 ml of distilled water and 1 ml of aqueous ammonia added into the mixture successively with strong stirring to adjust pH, to adjust the temperature to 30°C and to inject 10 ml of formaldehyde and tetraethyl orthosilicate (TEOS) into the mixture, followed by a reaction time. Injecting again 1 ml of aqueous ammonia, adding 10 ml of TEOS and 6 ml of Dimethyldiethoxysilane (DMDES) into the flask, and maintaining the reaction for 4 h. The previously separated and cleaned magnetic powders, to be dispersed into 150 ml of ethanol and 25 ml of pure water. After, injecting 1 ml of aqueous ammonia and 6 ml of DMDES in sequence, the reaction being maintained under strong stirring for a given time at 30°C. Finally, obtaining Fe204particles coated by a hydrophobic silica layer (306), or magnetized electrically conductive free solid bodies of a MDE including Fe204particles coated by a hydrophobic silica layer in its solid structure (particular embodiment of, e.g., Figure 3), where the magnetic properties are kept trough time in contact with strong acids (305).

[0233] Another particular configuration of the invention illustrated in Figure 3 is by avoiding the step of creating a protective magnetic coating (306) while using a liquid electrolyte (305) incapable of reacting with the magnetic particles (303), such as, in the case of using Fe204nanomagnetic particles included on the solid bodies (302) retaining an amount of electrolyte liquid (305) not based on strong acids. In said configuration different electrolytes (305), liquid electrolytes, can be used or selected. In several particular embodiments the electrolyte (305) can be selected from salt-based electrolytes, in particular NaCI based electrolytes in aqueous solutions or in ethylene glycol or Lithium or potassium-based electrolytes. In other particular embodiments, the electrolyte (305), the liquid electrolyte, can be selected from an ionic liquid family. In other particular embodiments, the electrolyte (305) can be selected from a deep eutectic solvent (DES) family, such as a composition based on choline chloride and ethylene glycol, in other particular embodiments, other DES are used, such as solvent NaFSA-KFSA (56:44 mol / mol) binary system, super concentrated solutions of 35 mol Kg-1Na0 55K042FSA / H2O and 33 mol Kg-1NaQA5KQ 55FSA / H2O at 25 °C, or either saturated 20 mol kg-1 NaFSA or 31 mol kg-1 KFSA solution, or 33 mol Kg-1Na0A5K0 55FSA / H2O, or any other of the mentioned families.

[0234] B) MAGNETIC PARTICLES DISOLVED, DISPERSED, IN A LIQUID ENVIRONMENT WHERE THE ELECTRICALLY CONDUCTIVE FREE SOLID BODIES ARE INCLUDED (207)

[0235] The present MDE relates to the case in which the magnetic particles are dissolved, dispersed, in a liquid medium or environment (204) where the electrically conductive free solid bodies are located. The magnetic particles may also be dispersed / suspended in the fluid, e.g., a liquid, of said medium or environment.

[0236] In several particular embodiments, the solid bodies (202) are dissolved, or, preferably, dispersed, in a liquid moderation medium (204). Said medium may be used either as a galvanic interaction moderator, as a rheological component or a combination of both. The liquid environment used (204), e.g., as a liquid moderation medium, can be made of a polar solvent, a non-polar solvent or a combination of both, depending on the specific application or surface treatment. In particular embodiments a non-conductive liquid (204) including substances or combination of substances like aliphatic chains in particular from C5 to C30 hydrocarbons, surfactants, such as fatty acids, toluene sulfonate, trans-cinnamaldehyde, and dodecylpiridinium bromide, or hydrocarbons with polar head groups other than carboxylic acids, such as ketones, hydroxyl groups (e.g., hexylene glycol, and isopropanol), amide groups, or carboxylic acids other than fatty acids as described herein (e.g., nitrobenzoic acid). In other embodiments the moderation fluid (204), is water, more in particular deionized water.

[0237] In a particular embodiment, the magnetic particles (203) are dissolved, dispersed / suspended, in the medium, e.g., in said moderations liquids (204). The solubility of the magnetic particles on the moderation liquid is an important factor to consider for this particular case. Agitation may be used to achieve dispersion of the magnetic particles in the medium, depending on the viscosity of the solvent, the proportion of the magnetic particles dispersed on the liquid, the size of the magnetic particles, the agitation and working temperature a moderation ferrofluid (204) can be achieved, e.g., a higher amount of particles may be suitably dispersed. Such dispersions / suspensions of magnetic particles in a fluid, e.g., a moderation liquid, may conform a ferrofluid, e.g., a moderation ferrofluid. Without being bound to any theory, the properties of a ferrofluid advantageously make it possible to control the motion and packing factor or pressure of the solid bodies (202) by the help of, e.g., magnetic fields without any need for modifying its structure or composition.

[0238] Preferably, in some embodiments, the magnetic particles (203) used are substantially not- electrically conductive, thereby preventing conductivity flowing through the environment where they are located, in a way that the current flow is canalized or carried out by the electrically conductive free solid bodies, as described in detail above. For instance, magnetic particles may be used that do not present electrical conductivity, such as magnetic particles selected from, e.g., Fe304, BiFeO3, BaFe12019and / or SrFe12O19particles and, e.g., magnetic particle charged Epoxy resins, Nylon, PPS Polyurethane, PVC, and PP.

[0239] In some particular embodiments a moderation ferrofluid (204 and 203) is achieved by combining moderation fluids (204) including water with magnetic particles (203) including Fe204or BiFeO or BaFe12O19or SrFe12O19nano-particles (203).

[0240] In other particular embodiments a moderation ferrofluid (204 and 203) is achieved by combining moderation fluids (204) including aliphatic chains in particular from C5 to C30 hydrocarbons and surfactants, with magnetic particles (203) including Fe304or BiFeO2or BaFe12O19or SrFe12O19nano-particles (203).

[0241] In other particular embodiments a moderation ferrofluid (204 and 203) is achieved by combining moderation fluids (204) including fatty acids, such as oleic acid and octanoic acid, and surfactants, with magnetic particles (203) including Fe204or BiFeO2or BaFe12O19or SrFe12O19nano-particles (203).

[0242] In the previous embodiments, the ratio between the moderation fluid (204) and the magnetic particles (203) is from 1 :10 to 10000:1 in weight, in particular between 1 :1 - 1000:1 in weight, and more in particular between 5:1 - 50:1 in weight.

[0243] In the ferrofluidic embodiment it is possible to control the pressure or the packing factor of the electrically conductive free solid bodies (202) by a magnetic evacuation (e.g., of the magnetic field 209) of the moderation fluid in the adjacent areas. Magnetic evacuation as used herein, refers to the displacement or migration of, e.g., the ferrofluid caused by the application of magnetic fields, resulting in a localized reduction of fluid in a specific area. This creates a pressure imbalance that increases the compaction and contact force of the electrically conductive free solid bodies in the region from which the ferrofluid has been drawn away. The magnetic control (e.g., of the magnetic field 209) of the moderation fluid (204, 203) enables the indirect movement control of the electrically conductive free solid bodies by the generation of liquid pressure gradients by the help of a magnetic force (209).

[0244] C) MAGNETIC PARTICLES INCLUDED ON THE ENVIRONMENT WHERE THE ELECTRICALLY CONDUCTIVE FREE SOLID BODIES ARE INCLUDED (208)

[0245] The present MDE relates to the case in which the magnetic particles are present in the medium or environment (204) where the electrically conductive free solid bodies are located.

[0246] As illustrated in Figure 2, in other particular embodiments the magnetic particles are bigger in size, comparable or bigger than the size of the electrically conductive free solid bodies and present in the environment (204) of the MDE (208) (Figure 2 in the middle). The medium or environment (204) can be a gas, such as air, or a liquid, such as water or an oil-based moderation fluid. Preferably, the magnetic particles (204) selected can be configured with the rest of the magnetic electrolyte article so there is no risk of short-circuit during the galvanic surface treatment. For instance, non-electrically conductive magnetic particles may be used or if electrically conductive magnetic particles are used, these may be coated with non-conductive materials or presenting a sufficiently low conductivity to prevent the current flow from generating short-circuits. In this context, the conductivity threshold to avoid short-circuit conditions may be, e.g., below 10“6S / cm (1 pS / cm), which is considered the practical boundary for insulating behavior in electropolishing or electrochemical environments. Materials with conductivities below this value are unlikely to create parasitic electrical paths between electrodes.

[0247] To ensure this, electrically conductive magnetic particles — such as Fe3O4(magnetite), BaFei20i9 (barium hexaferrite), or SrFei20i9(strontium hexaferrite), can be coated with insulating layers. Examples include silica (SiO2) coatings, polymer coatings (e.g., polyethylene glycol, epoxy resins), or acid-resistant hydrophobic shells such as those made from methyl- functionalized silanes. These coatings electrically isolate the magnetic cores while preserving magnetic responsiveness.

[0248] Alternatively, inherently non-conductive magnetic materials such as ferrite ceramics or coated polymer-based magnetic beads can be selected. For instance, nylon-encapsulated ferrite particles or magnetic epoxy resins are commonly used in industrial systems to eliminate short- circuit risks while enabling magnetic control and modulation.

[0249] In a particular embodiment the magnetic particles (203) include a ceramic material, such as Fe204or BaFe12O19or SrFe12O19’, or a polymeric material, such as magnetic particle charged Epoxy resins, Nylon, PPS Polyurethane, PVC, PP; not presenting electrical conductivity.

[0250] In some other cases the magnetic particles (203) include elements presenting an electrical conductivity, such as Fe, Ni, Co Alloys or Alnico, Samarium-Cobalt (SmCo), Neodymium, Neodymium-lron-Boron (NdFeB), configured in a way that a short-circuit is avoided. For example, coating the magnetic particles (203) with a non-conductive material isolating them from any electrical current, like PTFE, Glass, Epoxy Resins, Parylene, Silicone coatings, while enabling them to respond to the applied magnetic fields. In some particular embodiments the magnetic particles (203) include the magnets used in magnetic stirring lab machines, covered / protected by a polymeric non-conductive layer.

[0251] In some embodiments, e.g., in the present particular embodiment of a MDE, the motion of the electrically conductive free solid bodies is controlled by the wave pressures generated by the movement of the permanent magnets under the presence of magnetic fields.

[0252] In several embodiments, a MDE include a combination of magnetic particles included on the environment (208), e.g., in the medium outside of the electrically conductive bodies, with magnetic particles included on the electrically conductive free solid bodies (206), e.g., within the electrically conductive free solid such as inside or on the surface, also referred to electrically conductive magnetic free solid bodies or simply magnetic solid bodies. Without being bound to any theory, in the mentioned combination, the magnetic solid bodies (202 and 203) may be attracted to the bigger magnetic particles (203) present in the environment (204), generating a compact layer of solid bodies (202) surrounding the bigger magnetic particles (203) present on the environment (204). It may also be possible to control the macroscopic movement of the bigger magnetic particles (203) present on the environment (204), by, a magnetic field source, e.g., an external magnetic field (209), indirectly controlling the motion of the solid bodies (202).

[0253] This advantageously allows for an independent control of particle motion and electrochemical behavior, which is particularly desirable in configurations where high electrical conductivity of the free solid bodies may be advantageously achieved and used sustain efficient current densities and processing speeds, while particle flow or redistribution is guided via the non- electrically conductive but magnetically responsive environmental particles.

[0254] In such embodiments, the electrically conductive particles (202) can retain highly concentrated acids while the macroscopic motion and compaction behavior of the composition is directed via magnetically active particles (203) in the surrounding medium which can present an abrasive function as well. This separation of functions allows for hybrid electrochemicalmechanical setups, including configurations resembling magnetic tumbling systems hybridized with the electrochemical function of the free solid bodies. Such systems provide enhanced processing rates and surface uniformity, which is especially advantageous for finishing roughly machined or additively manufactured (e.g., 3D printed) parts where faster material removal and surface homogenization is critical.

[0255] In several embodiments, a MDE include a combination of magnetic particles included in the environment (208), e.g., outside of the electrically conductive solid bodies, with magnetic particles dissolved, dispersed in the liquid environment, e.g., as a ferrofluid (207). Without being bound to any theory, in the mentioned combination, the magnetic liquid environment (204 and 203) may be attracted to the bigger magnetic particles (203) present on the environment (204), generating lower presence of solid bodies (202) surrounding the bigger magnetic particles (203) present on the environment (204). It may also be possible to control the macroscopic movement of the bigger magnetic particles (203) present on the environment (204), by an external magnetic field (209), indirectly controlling the motion of the solid bodies (202). This configuration may be especially useful in surface treatments involving concave or hard-to-reach areas, where a combined mechanical and electrochemical action is needed. In this case, the movement of the larger magnetic particles helps guide and drag the surrounding magnetized solid particles into those areas. This ensures that even in recessed or complex geometries, the solid particles remain in contact with the surface, allowing consistent electropolishing or surface finishing effects.

[0256] 3) A third aspect of the invention refers to an assembly or an apparatus in which some particular embodiments of the previously described Magnetic Dry Electrolyte and processing methods can be used:

[0257] ASSEMBLY OR APPARATUS

[0258] Figure 1 A and B are a graphical representation of a particular realization of a Magnetic Dry Electrolyte and a system or assembly for working with said MDE.

[0259] An assembly configured to surface treat an electrically conductive part, e.g., a metal part, comprising: an electric connector (108) connecting the anode (102) to the positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106); a fixing system adapted to the electric connector (108) to hold the metal part as one of the two electrodes (102 or 103), represented as one of any of the two electrodes, a fixing system adapted by means for generating a relative movement between the surface to be treated (102 or 103) with respect to the MDE (109 and 110 and 114) located inside of a receptacle 101 ; said MDE including electrically conductive solid bodies (109) comprising a solid structure retaining an electrolyte liquid to make them electrically conductive, resulting on a current (107) flowing through the electrical power supply (106) and an ion transport trough the solid bodies on the direction of a generated electrical field (104), the Magnetic Dry Electrolyte including magnetic at least a magnetic particle and / or field (110 , 105) to provide magnetic activity, as represented in the detail of a polarized magnetic particle (118); optionally, in several particular embodiments, means for generating an external magnetic field (111), said magnetic field (105), in some cases, interacting with the magnetic particles (110) of the magnetic dry electrolyte and making the free electrically conductive solid bodies (109) susceptible to respond under a change on the magnetic field (112), and, optionally, means for applying a velocity to the magnetically source means (113) or a change to the generated magnetic field (205).

[0260] In assemblies as described herein, a fixing system or fixing means adapted by means for generating a relative movement between the surface to be with respect to the MDE located inside of the receptacle may be any suitable fixing means as described above, further provided with a moving element. For instance, means for generating a relative movement may include, e.g., a motor, pump, hydraulic system etc.

[0261] In some realizations of the invention, the magnetic source is a permanent magnet, in some cases, including on a ferromagnetic material. Said ferromagnetic material comprising, for example, any of the further possible options: Fe, Ni, Co Alloys or Alnico, Samarium-Cobalt (SmCo), Neodymium, Neodymium-lron-Boron (NdFeB), Fe204or BaFe12O19or SrFe12O19. The mentioned magnetic source (111), in some particular embodiments, generating magnetic fields (105) interacting with the magnetic particles (110) polarizing them while making the solid bodies (109) susceptible to respond (114 or 115) to any change on the applied magnetic field (113).

[0262] In other realizations of the invention, the magnetic source (111) comprises or consists on a solenoid or an electric coil capable of generating induced magnetic fields by applying a current. In particular, electromagnets are a suitable candidate for being selected as a magnetic source (111). Different electromagnets concatenations can be used, in a way that enables controlling the magnetic field (105) by a synchro modulation of the polarity and power of the electromagnets (113), generating magnetic forces (114, 115) strong enough to overcome the weight of the forces included on a MDE, producing a controlled motion of the electrically conductive free solid bodies (109). In several particular embodiments, it is possible to have a synchronization between the electrical pulses defining the polarity and amplitude under which the electrical power supply (106) works, and the magnetic field produced by the magnetic source. It enables the possibility of controlling the packing factor and pressure generated by the induced magnetic force (114) of the applied magnetic field (105). In said configuration being able do have a precise selection or control of the magnetic polarization (116) and the electric polarization (117) of the free solid bodies (109).

[0263] Figure 5 illustrates an assembly, a system or a method for, e.g., punch polishing an electrically conductive part comprising mechanical adjustment and synchronization with polishing parameters using magnetic means, like an electromagnet, with the capability of executing controlled cyclic compaction for the polishing of concave surfaces synchronized to the polishing parameters.

[0264] An assembly for, e.g., punch polishing with a MDE that comprises:

[0265] A cathode (501) connected to a first pole of a current generator and an anode (503) connected to a second pole; a fixing system adapted to connect the metal part to one of the two electrodes (501 and 503) while holding the surface to be polished (506), such as concave surface like a punch or a gear, inside a receptacle (501), containing a MDE (502); means for generating motion to the metal part with respect to the MDE (502); and a magnetic source, like an electromagnet (508), configured to control the compaction of the MDE (502), synchronizing said compaction, optionally with the motion applied to the surface to be polished (509), and with the electrical pulses of the current generator with a synchronization system (507).

[0266] In the previously described system, it is possible to achieve a highly controlled surface treatment precision over complex surfaces (509), such as concave surfaces. Particularly punches including engraved surfaces, an engraving, or relieves, where the motion applied by conventional methods makes it impossible for the free solid bodies of the MDE (502) to reach all the geometry to be polished. In several particular embodiments, in order to avoid the appearance of treatment defects as a consequence of an inappropriate friction force between the solid bodies and the metal surface to be polished, considering a certain level of current; it is to be preferred to control and to synchronize the polarities under which the current generator (501 and 503) works to the electromagnet activity. By controlling said electromagnet activity it is possible, for example, to apply a higher friction or pressure by the solid bodies (502) to the surface to be treated (509) when the metal part acts as an anode (503) and a lower friction or pressure by the solid bodies (502) to the surface to be treated (509) when the metal part acts as a cathode, at the same time, generating a recirculation of the MDE (502) at the working area (509).

[0267] A particular embodiment illustrated on the axial longitudinal cut of a 3D representation of Figure 8 is an assembly, system or a method for, e.g., a polishing pattern station.

[0268] The assembly of Figure 8 of a polishing pattern station for a MDE comprises:

[0269] A support connected to a first pole of a power supply (803) with means for holding a metal surface to be treated (807); said metal surface (807) in contact to a MDE (802) inside of a receptacle (804); a cathode connected to a second pole of a current generator (801) adapted to a fixing system (806) for contacting said MDE (802) with enough distance from the metal surface (807) to avoid short-circuit; and magnet sources (805) configured to control the motion of the MDE in a way that leaves a desired pattern over the metal surface (807).

[0270] The polishing apparatus, consisting on a pattern station, may feature a uniform magnetic field configuration that allows for the application of uniform and / or controlled pressure and polishing direction on a product facilitating continuous linear polishing with optimal electrolyte utilization.

[0271] A particular application for said polishing pattern station is semiconductor polishing system comprising one or more polishing stations with various movement configurations, enabling the creation of desired polishing patterns improving the efficiency of electronic elements, such as diodes or transistors, in particular, silicon-based semiconductors.

[0272] EXAMPLES

[0273] Several objects (electrically conductive parts) were subjected to a surface treatment, surface finishing, by the following general method: holding the object with a moving arm and connecting the object to a pole of an electric source, connecting a container comprising a Magnetic Dry Electrolyte, to, e.g, the opposite pole of the electric source, the container being cylindrical with a top opening and electrically connected to a platinated titanium mesh serving as the cathode, via a metallic connector attached to a cooper wire, such as an SSL screw in this case, to ensure reliable electrical contact, immerging the object into the container containing the MDE, whereby the object was at least partially covered by the particles, and moving the object inside of the particles thereby moving the particles relative to the object and allowing the contact of the particles with the surface of the object, for a specific amount of time; optionally, applying an external magnetic field affecting at some extent the state of the MDE. the object was removed from the particles, to provide a surface treated, surface finished, object (electrically conductive part). The objects and MDE comprising the electrically conductive particles, magnetic particles and fluids in medium used for each surface treatment are defined for each example below.

[0274] The MDE used are defined for each of the examples below.

[0275] The objects were moved inside the particles achieving a relative movement between the particles and the object as detailed for each example below.

[0276] The electric potential applied to the objects were configured depending on the material to be polished and the MDE used, as detailed for each example below.

[0277] Example 1 : Surface treatment of Inconel square by a DME

[0278] A machined 3D printed electrically conductive part, a squared Inconel sample, was processed using 475 g of a magnetic dry electrolyte comprising a combination of: o Sulfonated microporous styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter, as indicated by the ion exchange resin supplier, with a hydration of 42 wt.% o The hydration liquid electrolyte used to consist in 15 wt.% of methane sulfonic acid diluted in deionized water o The sulfonated gel styrene divinylbenzene particles in a sodic format, whereby protons of the particles were substituted by sodium cations, after being magnetically activated by 10 g of Fe304nanomagnetic particles included on the solid polymeric structure according to the following method:

[0279] ■ Dissolving 14.84 g of FeCl2■ 4H2O and 40.18 g of de FeCl3■ 6H2O on 1050 ml of H2O

[0280] • Adding 350 g of the sulfonated microporous styrene divinylbenzene particles of 0.3 to 1 .18 mm of diameter with a hydration of 30 wt.% of water

[0281] ■ Stirring for at least 5 min

[0282] ■ Adding 70 ml NaOH at 40 wt. %

[0283] ■ Stirring for at least 20 min

[0284] ■ Leave it rest for at least 30 min

[0285] ■ Separate the magnetically active solid bodies by decantation methods

[0286] ■ Wash the product twice with ethanol

[0287] ■ Rins the product twice with water

[0288] ■ To dry the resin at 55°C for 1.5 h.

[0289] The squared Inconel sample was processed connecting it to the positive pole of a current generator, also connecting an iridium titanium mesh to the second pole, used as cathode, and all submerged in a pot containing the MDE.

[0290] Circular motion was applied with an amplitude of 5 cm of radius, at 60 RPM.

[0291] An alternating current was applied of +35 V during 10 ps and -35 V during 100 ps and 10 ps between pulses with a current density of 0.025 A / cm2.

[0292] After 5 min polishing the roughness was decreased from Ra = 0.250 \im to a saturation of Ra = 0.180 \im. Achieving a higher level of brightness.

[0293] Adding a permanent magnet of neodymium of 6 cm3next to the targeted surface a higher packing surrounding the permanent magnet due to the interacting magnetic fields between the magnet and the MDE a higher quality of the surface finish was obtained under the same polishing conditions. The current density increased to 0.026 A / cm2and the final roughness saturation after 1 min polishing decreased to Ra = 0.130 \im. Achieving a higher level of brightness.

[0294] Example 2: Surface treatment Tungsten Carbide Punch by a DME

[0295] A tungsten carbide punch containing cobalt was processed using 705 g of a magnetic dry electrolyte comprising a combination of: o 475 g sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter, known from the supplier, with a hydration of 55 wt.% o The hydration liquid electrolyte used to consist on deionized water. o 100 g of deionized water o 130 g of octanoic acid o The sulfonated gel styrene divinylbenzene particles in a sodic format after being magnetically activated by 10 g of Fe304nanomagnetic particles included on the solid polymeric structure according to the following method:

[0296] ■ Dissolving 14.84 g of FeCl2■ AH20 and 40.18 g of de FeCl3■ 6H2O on 1050 ml of H2O

[0297] • Adding 350 g Sulfonated microporous styrene divinylbenzene particles of 0.3 to 1 .18 mm of diameter with a hydration of 30 wt.% of water

[0298] ■ Stirring for at least 5 min

[0299] ■ Adding 70 ml NaOH at 40 wt. %

[0300] ■ Stirring for at least 20 min

[0301] ■ Leave it rest for at least 30 min

[0302] ■ Separate the magnetically active solid bodies by decantation methods

[0303] ■ Wash the product twice with ethanol

[0304] ■ Rins the product twice with water

[0305] ■ To dry the resin at 55°C for 0.75 - 1 h, until desired humidity of 55 wt. % is achieved.

[0306] The tungsten carbide punch was processed connecting it to the positive pole of a current generator, also connecting an iridium titanium mesh to the second pole, used as cathode, and all submerged in a pot, container, containing the MDE.

[0307] Circular motion was applied with an amplitude of 5 cm of radius, at 60 RPM. An alternating current was applied of +35 V during 40 ns and -60 V during 320 ns and 10 ps between pulses with a current density of 0.04 Al cm .

[0308] After 5 min polishing the roughness was decreased from Ra = 0.350 \im to a saturation of Ra = 0.150 \im. Achieving a higher level of brightness. Adding a permanent magnet of neodymium of 6 cm3located next to the cathode, located at the bottom of the receptacle and adding a vertical movement in that direction, higher packing surrounding the permanent magnet due to the interacting magnetic fields between the magnet and the MDE a higher finish quality of the concave surfaces was obtained under the same polishing conditions. The current density increased to 0.042 Al cm2and the final roughness saturation after 3 min polishing decreased to Ra = 0.120 \im. Achieving a higher level of brightness and more penetration over the punch reliefs.

Claims

CLAIMS1 . A composition for surface finishing an electrically conductive part comprising: a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte (305); a plurality of magnetic particles (203); and a medium (204) comprising a fluid; wherein the medium (204) contains the plurality of electrically conductive free solid bodies(202) and the plurality of magnetic particles (203).

2. The composition of claim 1 , wherein the plurality of magnetic particles (203) is included within the electrically conductive free solid bodies (206).

3. The composition of claim 1 , wherein the plurality of magnetic particles (203) is included within the medium (204) outside the plurality of electrically conductive free solid bodies (207 and 208).

4. The composition of claim 3, wherein the magnetic particles (203) are included within the medium (204) in the form of a ferrofluid (207).

5. The composition of any one of claims 1 to 4, wherein the composition further comprises abrasive and / or moderation particles.

6. The composition of any one of claims 1 to 5, wherein the plurality of magnetic particles(203) include Fe304, BiFe03, BaFe12019and / or SrFe12O19nano-particles, preferably at least include Fe304nanoparticles.

7. The composition of any one of claims 1 to 6, wherein the liquid electrolyte (305) is a deep eutectic solvent or an ionic liquid.

8. The composition of any one of claims 1 to 7, wherein the magnetic particles (303) include a protective magnetic coating (306).

9. The composition of claim 8, wherein the protective magnetic coating (306) is hydrophobic.

10. The composition of any one of claims 1 to 9, wherein the electrically conductive free solid bodies (202) retaining the liquid electrolyte, are particles of an ion-exchange resin, preferablyselected from acid ion-exchange resins, and more preferably are sulfonated styrene divinylben- zene particles, retaining the liquid electrolyte.

11. The composition of any one of claims 1 to 10, wherein the electrically conductive free solid bodies are sulfonated styrene divinylbenzene particles and the magnetic particles include Fe304nanoparticles, preferably the Fe304nanoparticles are included within the sulfonated styrene divinylbenzene particles, and more preferably the Fe304nanoparticles included within the sulfonated styrene divinylbenzene particles are obtainable by Fe304nanoparticle precipitation reaction in the presence of the sulfonated styrene divinylbenzene particles, said precipitation comprising incorporating a NaOH dissolution to a previously prepared dispersion of the sulfonated styrene divinylbenzene particles in an aqueous solution comprising FeCl2■ 4H2O and FeCl2■ 6H2O.

12. The composition of any of claims 1 to 11 , wherein the ratio of the plurality of magnetic particles to the plurality of electrically conductive free solid bodies is from 0.1 to 10 wt.%, in particular from 1 to 8 wt.%, and more in particular from 4 to 7 wt.%.

13. Use of the composition according to any one of claims 1 to 12 for surface finishing a electrically conductive part, in particular a metal part.

14. An assembly for surface finishing an electrically conductive part, in particular a metal part, comprising: an electric connector (108) connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply; a fixing system connected to the electric connector (108) and adapted to hold the electrically conductive part to be treated as the anode (102) or the cathode (103); a container comprising a composition according to any one of claims 1 to 12; means for generating a relative movement of a surface of the electrically conductive part to be treated with respect to the composition.

15. The assembly of claim 14 further comprising means (111) for creating a magnetic field (105).

16. An assembly for surface finishing an electrically conductive part, in particular a metal part, comprising: an electric connector (108) connecting an anode (102) to a positive pole of an electricalpower supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply; a fixing means connected to the electric connector (108) and adapted to hold the electrically conductive part to be treated as the anode (102) or the cathode (103); a container comprising a composition comprising a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte and a medium (204) comprising a fluid, wherein the medium contains the plurality of electrically conductive free solid bodies (202); means for generating a relative movement of a surface of the electrically conductive part to be treated with respect to the composition in the container; and means (111) for creating a magnetic field (105).

17. The assembly of claim 15 or 16, further comprising means for applying a change (112 and 113) to the magnetic field (105) created by said means for creating a magnetic field.

18. The assembly of any one of claims 15 to 17, further comprising a synchronization system (507) configured to synchronize the means for creating a magnetic field with the electrical power supply.

19. The assembly of claims 14 or 15, or the assembly of claims 17 or 18 comprising a composition according to any one of claims 1 to 12, further comprising an anti-gravity system, preferably wherein the anti-gravity system comprises magnetic sources (705) arranged along the vertical axis of the container.

20. The assembly of any one of claims of 15 to 19, wherein the means for creating a magnetic field configured to control the motion of the composition in a way that leaves a desired pattern on the surface of the electrically conductive part, in particular a metal part, to be treated.

21. Use of the assembly of any one of claims 14 to 20 for surface finishing an electrically conductive part, in particular a metal part.

22. A method for surface finishing an electrically conductive part, in particular a metal part, comprising: connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106), by means of an electric connector (108), wherein the electrically conductive part, in particular the metal part, to be treated acts as the anode or the cathode (102 or 103) by connecting the electrically conductive part, in particular the metal part, to the positive or negative pole of the electrical power supply bya fixing means connected to the electric connector (108); placing the anode and the cathode in a container comprising the composition according to any one of claims 1 to 12; generating a relative movement of a surface of the electrically conductive part, in particular the metal part, to be treated with respect to the composition in the container.

23. The method of claim 22 further comprising generating a magnetic field (111), wherein at least part of the composition is within range of the generated magnetic field (105).

24. A method for surface finishing an electrically conductive part, in particular a metal part, comprising: connecting an anode (102) to a positive pole of an electrical power supply (106) and connecting a cathode (103) to a negative pole of said electrical power supply (106), by means of an electric connector (108), wherein the electrically conductive part, in particular the metal part, to be treated acts as the anode or the cathode (102 or 103) by connecting the electrically conductive part, in particular the metal part, to the positive or negative pole of the electrical power supply by a fixing means connected to the electric connector (108); placing the anode and the cathode in a container comprising a composition comprising a plurality of electrically conductive free solid bodies (202) retaining a liquid electrolyte and a medium (204) comprising a fluid, wherein the medium contains the plurality of electrically conductive free solid bodies (202); generating a relative movement of a surface of the electrically conductive part, in particular the metal part, to be treated with respect to the composition in the container; and generating a magnetic field (111), wherein at least part of the composition is within range of the generated magnetic field (105).

25. The method of claim 22 or 23, wherein the composition has a distribution of solid bodies in the container wherein solid bodies placed in higher regions of the container exercise a gravitational pressure compacting solid bodies placed in lower regions of the container and the method comprises counteracting the gravitational pressure compacting the solid bodies (702) of the lower regions of the container, by means of an anti-gravity system, wherein the anti-gravity system comprises magnetic sources (705) arranged along a vertical axis of the container.

26. The method of any one of claims 22 to 25, wherein the electrically conductive part, in particular the metal part, to be treated comprises a channel or a tube having an inner surface; the method is for the surface treatment of said inner surfaces; and the electrically conductive part, in particular the metal part, acts as the anode, wherein connecting the electrically conductive part,in particular the metal part, to the positive pole of the electrical power supply comprises connecting the inner surface to be treated to said positive pole; and wherein the cathode is configured to be at least partially introduced to the inner tube or channel (601), and to leave enough space for the composition to circulate through said inner tube or channel (601), and the method comprises at least partially introducing the cathode to the inner tube or channel.

27. The method of any one of claims 22 to 26 using the assembly of any one of claims 14 to 20.

28. A surface finished electrically conductive part, in particular a metal part, obtainable by the surface finishing method of any one of claims 22 to 27, preferably wherein the surface finished electrically conductive part is a metal part.

29. The surface finished electrically conductive part of claim 28, wherein the metal part fulfils one or more of:- is a stainless-steel part, preferably having a Cr / Fe surface atomic ratio from 1.2 to 5.0, more preferably from 1.5 to 3.5;- is a metal part having a passivation layer from to 1 nm to 30 nm thickness in particular from 1.5 to 15 nm thickness; and- has a surface roughness (Ra) of below 0.3 pm.

Images