Surface finishing of complex geometryes by solid-particle based CSE for turboflow

Abstract

The present invention relates to a surface finishing method and a specialized electrolyte designed for optimal performance under turbulent conditions. This innovative approach utilizes Conductive Suspension Electrolytes (CSE), a solid particle-based electrolyte system in which free electrically conductive solid bodies are suspended in a conductive fluid medium. Unlike previous technologies, this system enhances ion transport and surface treatment efficiency, particularly under high-motion or turbulent environments, ensuring uniform and precise finishing even on complex geometries. The conductive medium prevents short-circuiting the electrochemical cell, ensuring at least part of the ion transport to be carried out by the solid bodies. The method is adaptable to different electrical currents and processing conditions, offering a flexible and scalable solution. By combining controlled turbulence with a tailored electrolyte composition, the invention significantly improves processing speed, surface quality, and overall efficiency, addressing key limitations of traditional electropolishing techniques while maintaining environmental and economic advantages.

Description

[0001] SURFACE FINISHING OF COMPLEX GEOMETRYES BY SOLIDPARTICLE BASED CSE FOR TURBOFLOW

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of surface finishing. More particularly, the disclosure relates to homogeneous surface finishing of parts by ion transport with different sizes and shapes.

[0004] BACKGROUND

[0005] In the field of surface finishing, achieving a uniform and high-quality finish on parts of varying shapes and sizes remains a significant challenge. Various surface finishing techniques, including liquid electropolishing and abrasive surface finishing, have been developed to enhance the aesthetic and functional properties of materials by reducing surface roughness and eliminating defects. However, these conventional methods present several drawbacks that limit their efficiency, precision, and environmental sustainability.

[0006] Liquid electropolishing techniques, while effective in surface rounding, suffer from inefficient roughness reduction and excessive material removal. This high mass extraction not only compromises the dimensional integrity of the part but also results in significant material wastage. Additionally, the use of liquid electrolytes in traditional electropolishing processes raises concerns regarding toxicity and environmental impact, necessitating stringent waste management protocols and increasing operational costs.

[0007] Passive layer technology has been introduced as an improvement to traditional electrochemical polishing by employing an electrolytic solution containing compounds from the alkylbenzenesulfonic family, as described in International Application No. PCT / EP2007 / 003628 (published as WO 2007 / 121999 A2). This approach facilitates the formation of a resistive layer over the treated surface, ensuring that surface protrusions are preferentially electropolished when exposed by chemically inert particles. However, despite its ability to selectively remove peaks, this technique still exhibits inefficiencies in roughness reduction, high mass extraction rates, and slow processing speeds. The resulting surface finish often lacks precision and definition, making it less suitable for applications requiring high-quality finishing with minimal material loss.

[0008] To address these limitations, DryLyte technology has been developed as a solid particle-based electrolyte system, where solid bodies retain a liquid electrolyte, making them conductive within a preferably gaseous environment, as described in InternationalApplication No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1). This approach improves selectivity by favoring the removal of peaks over valleys due to solid-solid interactions. While said DryLyte technology presents environmental benefits and reduced fluid rheology, achieving homogeneous results on large and complex geometries remains challenging. Furthermore, the treating speed is relatively low, limiting its scalability for industrial applications.

[0009] Dry Suspension technology builds upon DryLyte by introducing a non-conductive fluid or emulsion within the interstitial space between the solid bodies. This fluid, which is preferably immiscible with the conductive solution retained by the solid particles, enhances the uniformity of results when applied to complex geometries and large parts, as described in International Application No. PCT / ES2021 / 070864 (published as WO 2022 / 123096 A1). Although this advancement mitigates some of the homogeneity issues associated with DryLyte technology, the system continues to suffer from low electrolyte conductivity, which restricts the overall surface treatment speed.

[0010] Projection technologies represent another alternative, employing a projection polishing system based on solid particle-based electrolytes. This approach allows for a more targeted and customizable surface finishing process, making it suitable for parts with varying sizes and geometries, as described in International Application No. PCT / ES2020 / 070499 (published as WO 2021 / 019121 A1). However, due to the localized nature of the projection system, surface treatment is performed sequentially rather than simultaneously, leading to lower processing speeds. Additionally, the electrical connectivity between particles is intermittently lost upon being propelled, reducing overall current transmission efficiency.

[0011] Turboflow technology introduces an immersion finishing system that utilizes turbulence to enhance surface treatment capabilities, particularly for large and complex geometries. This system relies on a solid particle-based electrolyte that enables more efficient treatment speeds compared to other dry electrolytic methods, as described in European Patent Application No. EP24383077.5. Despite these advantages, turbulence-driven processes experience reduced charge transmission due to inefficient electrolytes, leading to low current density and loss of electrical connectivity between the particles, which makes it difficult for being implemented for treating big parts for industrial applications.

[0012] There remains a pressing need for the development of advanced solid particlebased electrolytes that ensure consistent and efficient ion transport through solid-solid interactions. Such a system should exhibit higher conductivity and improved charge transmission capabilities, particularly in conditions involving high particle mobility or turbulence. By overcoming the existing limitations of charge transfer efficiency andprocessing speed, a next-generation surface finishing system could provide a commercially viable, high-performance solution adaptable to a broad range of industrial applications.

[0013] SUMMARY

[0014] A first aspect of the invention relates to a surface treatment method using a solid particle-based electrolyte as described in the following introduced by reference International Applications No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1) and No. PCT / ES2021 / 070864 (published as WO 2022 / 123096 A1), but in a conductive environment. Wherein the previous specified technologies uses electrically conductive solid bodies retaining an liquid electrolyte to make them electrically conductive allocated in a non-conductive environment while performing a surface finishing by ion transport to a metal part; this new family of electrolytes, referred to in the present disclosure as Conductive Suspension Electrolytes (CSE), differs from previous solid particle-based electrolytes, on the medium being significantly conductive with respect to the solid particles. Significantly conductive is understood herein as the medium having a conductivity that is not negligible with respect to the conductivity of the electrically conductive solid bodies. For instance, the conductivity of the medium being at least 10% of the conductivity of the electrically conductive solid bodies, in particular being at least 25 % or at least 30%. In some embodiments the conductivity of the medium is higher than, equal to or lower than the conductivity of the electrically conductive solid bodies.

[0015] Thus, in a CES and a method as the described herein the medium presents a conductivity of at least 10% of the conductivity of the set of free electrically conductive solid bodies, in particular being at least 25 % and more in particular at least 30%.

[0016] The above-mentioned conductivity % refers to the conductivity ratios measured under stationary conditions, described more in detail below.

[0017] In particular embodiments, an CSE according to the present invention includes a first plurality of electrically conductive particles and at least one abrasive particle, such as, e.g., a second plurality of abrasive particles, may be suitably used for surface finishing an object, one or more of the electrically conductive particles of the first plurality of electrically conductive particles comprising an electrolyte, as described in International Application No. PCT / EP2024 / 080378 (published as WO 2025 / 088203 A1) introduced here by reference.

[0018] The present invention utilizes at least a first plurality of electrically conductive solid bodies within a particular electrolytic environment, wherein the solid bodies facilitate ion transport, thereby preserving the benefits of prior solutions while enhancing processing speed and overcoming the limitations described in the background. In prior techniques, it was believed that the conductivity of the medium should be negligible compared to that ofthe particles to prevent liquid short-circuiting of the electrochemical system and to ensure that ion transport remained guided through the solid bodies. Surprisingly, it has now been discovered that by using a specific structural arrangement of solid bodies and conductive mediums, ion exchange activity is maintained predominantly within the solid bodies under particular configurations of the medium in which they are dispersed. The use of polarizable particles, such as dielectric polymers, enhances this effect, while incorporating chemically active particles, such as ion-exchange resins containing a polar solvent, enables ion migration under electrophoretic effects.

[0019] In some embodiments, a method according to the present invention involves applying an electric potential difference between at least two electrodes, an anode and a cathode, wherein at least one surface to be treated is coupled, namely electrically coupled, to one of the electrodes. The two electrodes are electrically connected via the Conductive Suspension Electrolyte (CSE), which includes a set of free electrically conductive solid bodies suspended in a medium comprising a conductive fluid. The medium exhibits a significant level of conductivity relative to the set of free solid bodies, allowing an ion exchange reaction to take place between the surface to be treated and the solid bodies, thereby achieving the desired surface finish.

[0020] In some embodiments, to enhance surface finishing uniformity, the method as described herein further comprises inducing motion or turbulence in the medium. Inducing motion or turbulence to the medium is preferably characterized by Reynolds numbers from 102to 107in the medium or ultimately in the CSE.

[0021] Without being bound to any theory inducing motion or turbulence to the medium may prevent the formation of continuous chains of direct contact between the solid bodies, thereby ensuring that no direct physical bridge electrically connects the two electrodes. Instead, the medium is characterized by sufficient ion connectivity between the set of solid bodies, ensuring effective ion transport. As a result, the two electrodes are electrically coupled via a non-direct, physically non-contacting bridge of solid bodies, maintaining efficient ohmic contact throughout the process.

[0022] In some embodiments, the method particularly includes steps of:

[0023] inducing motion or turbulence to the medium so that no continuous and stable chain of direct contact between particles electrically connects the two electrodes;

[0024] comprising a medium characterized to provide sufficient ion connectivity between a set of solid bodies to ensure ion transport; and

[0025] electrically coupling the two electrodes trough said non-direct physically contacting bridge of solid bodies and thereby ensuring the omics contact between the solid bodies comprised within the bridge.A second aspect of the present invention is a CSE including at least the following elements:

[0026] - A first plurality of free solid bodies, in particular selected from polarizable and / or dielectric particles, capable of retaining, e.g., with porosity and affinity or capacity to retain, an electrolyte liquid to make them electrically conductive, also referred to as electrically conductive free solid bodies

[0027] The electrolyte liquid retained by the first plurality

[0028] - A conductive medium in the environment or in the interstitial space between the first plurality.

[0029] The conductive medium is the medium comprising a conductive fluid. In some embodiment the medium is in the form of a liquid phase or comprises a liquid phase.

[0030] In some embodiments, the CSE comprises, e.g.,

[0031] a set of solid bodies comprising between 10 - 80 % wt, of a first polar solution retained within the resin, the % wt. based on the total weight of solid bodies and the first polar solution

[0032] a medium

[0033] o comprising from 10 to 50 % wt. of the conductive fluid, preferably the conductive fluid being a second polar solution, based on the total weight of the medium; and optionally

[0034] o further comprising from 0 to 80 % wt. surfactants and / or an apolar solution between, based on the total weight of the medium.

[0035] In particular embodiments, the conductivity of the medium is equal to or lower than the conductivity of the solid bodies, ensuring controlled ion transport dynamics within the CSE, also referred to as CSE system. Specifically, the conductivity of the medium, when measured in the absence of free solid bodies, ranges from 10% to 100% of the conductivity of the CSE as measured at rest and at room temperature, in particular, between 20% and 90%, more in particular, between 30% and 60%.

[0036] The above-mentioned conductivity % refers to the conductivity ratios measured under stationary conditions, described more in detail below.

[0037] Furthermore, the stability of the system is demonstrated by ensuring that the conductivity readings of both the CSE and the medium, when measured at rest and at room temperature, remain consistent over a period of five minutes, with fluctuations not exceeding ±10% of the original value, in particular not exceeding ±5%. Furthermore, the stationary properties of a CSE refers to that the conductivity readings of both the first plurality of free solid bodies and the medium when measured at rest and at room temperature, remain consistent over a period of five minutes, with fluctuations not exceeding ±10% of the original value, in particular not exceeding ±5%. Without being boundto any theory, this ensures that the electrolyte system maintains its conductive properties throughout the surface treatment process, thereby enabling predictable and repeatable results across various applications.

[0038] In some embodiments, the electrical conductivity of the medium is less than, equal to, or greater than the electrical conductivity of the first plurality of electrically conductive free solid bodies. In particular embodiments, during an initial time interval of the measurement, for example within about 5 to about 60 seconds, the electrical conductivity of the medium is equal to or greater than the electrical conductivity of a first plurality of dielectric particles. Under dynamic surface-treatment conditions, however, the surface treatment of the dielectric particles becomes dominant relative to that of the medium.

[0039] In some embodiments, a CSE further comprises a non-conductive fluid. In particular embodiments, the non-conductive fluid is part of the conductive medium, for example, introduced in the form of an emulsion. Without being bound to any theory, the emulsion may prevent the conductive medium from short-circuiting the ion exchange between at least to electrodes within a galvanic surface treatment.

[0040] In some embodiments, a conductivity measurement is performed using conventional electrical conductivity measurement techniques known in the art. Such techniques may include, without limitation, the use of two-electrode or four-electrode conductivity probes, contact or non-contact conductivity sensors, impedance-based measurement methods, or alternating-current (AC) conductivity measurements. In certain embodiments, the conductivity is determined by applying a known electrical potential across spaced electrodes in contact with the medium and measuring the resulting electrical current, from which conductivity is calculated. In other embodiments, the conductivity measurement is obtained using impedance spectroscopy, conductivity cells, or inline or offline conductivity meters configured to operate under static or dynamic conditions.

[0041] In some embodiments, the conductivity measurement is performed using a conductivity cell having a predetermined or calibrated cell constant, which depends on the geometry, spacing, and effective surface area of the electrodes. The cell constant may be selected or adjusted based on the expected conductivity range of the medium, for example to accommodate low-, medium-, or high-conductivity systems. In certain embodiments, the cell constant is determined by calibration using reference solutions of known conductivity prior to measurement.

[0042] Suitable laboratory equipment for performing the conductivity measurement may include, without limitation, benchtop or portable conductivity meters, impedance analyzers, LCR meters, electrochemical workstations, or multifunction meters configured to measure conductivity, resistance, or impedance. In some embodiments, the conductivity cell comprises metallic electrodes, such as stainless steel, platinum, graphite, or othercorrosion-resistant conductive materials, arranged in a parallel-plate, concentric, or coaxial configuration. In other embodiments, flow-through cells or immersion probes are employed, enabling conductivity measurements under static or dynamic conditions, including in suspensions, slurries, or particle-containing systems.

[0043] It is preferred for the conductivity measurement to be performed using conductivity meters, such as METTLER TOLEDO SevenCompact TM Duo S213, and a conductivity prove such as lnLab®731-ISM.

[0044] In a third aspect, the present invention provides a part with a surface treated using the disclosed ion transport method. The treated surface achieves a homogeneously polished finish with a roughness (Ra) below 1 micrometer and a roughness dispersion of less than 10% across all treated areas. In some embodiments, the surface roughness decreases from above 3 micrometers to below 1 micrometer in less than one hour while maintaining uniformity, ensuring high precision and improved surface quality.

[0045] In a fourth aspect, the invention provides an apparatus for finishing surfaces by ion transport. The apparatus includes at least two electrodes, the two electrodes being an anode and a cathode, with the surface to be treated coupled to one of them. A Conductive Suspension Electrolyte (CSE) electrically connects the electrodes, consisting of free electrically conductive solid bodies in a medium, e.g., suspended in a medium comprising a conductive fluid. The medium exhibits significant conductivity relative to the solid bodies, enabling ion exchange during processing. In some embodiments, the apparatus incorporates a motion-inducing mechanism to induce motion and / or turbulence to the medium which may contribute to preventing the formation of continuous conductive chains between solid bodies while ensuring sufficient ion connectivity for controlled ion transport. Additionally, in some embodiments, an electrical coupling mechanism may ensure the electrodes remain connected through a non-direct physically contacting bridge of solid bodies, optimizing the surface finishing process.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] 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:

[0048] Figure 1-A shows an assembly in accordance with some embodiments.

[0049] Figure 1-B shows an assembly in accordance with some embodiments.Figure 2 shows a detail of a step within the method according with some embodiments.

[0050] Figure 3 shows an assembly in accordance with some embodiments under turbulent conditions.

[0051] Figure 4 represents the formation mechanism of a resistive layer over a metal surface being treated according to some embodiments, in particular, illustrates formation of a resistive and / or viscous layer (402) at a surface of the part being treated (403), wherein the viscous layer (402) is formed, e.g., dodecylbenzene sulfonic acid, octanoic acid, hexanoic acid, components (401) present in the medium being accumulated on the surface being treated (403) by the influence of the electric field (E).

[0052] Figure 5 shows a graph of the conductivity (o) of a liquid medium (501) and a particle (502), overtime, after applying an electric potential difference, where the conductivity of the liquid medium of the interstitial space is higher than the free solid bodies, the liquid medium presents a time-dependent conductivity behavior that decays trough the time, and the time at which the conductivity of the liquid medium becomes equal to that of the particle is referred to as thm (503), in particular shows a conductivity decay of the conductivity of a liquid medium over time below the conductivity of the solid bodies under dynamic conditions according to some embodiments.

[0053] DETAILED DESCRIPTION

[0054] The present invention relates to a surface finishing method, through ion transport, and a specialized electrolyte, assembly and a polishing result designed in certain embodiments for an optimal performance under high motion and / or turbulent conditions by the help of the use of Conductive Suspension Electrolytes (CSE).

[0055] In certain embodiments, the motion or turbulence introduced in the method comprises steps of shooting or projecting the charged or polarized particles towards an objective through a nuzzle.

[0056] This innovative approach utilizes CSE, a solid particle-based electrolyte system in which free electrically conductive solid bodies are in a medium comprising a conductive fluid, in particular suspended in a conductive fluid medium. Unlike previous technologies, this system enhances ion transport and surface treatment efficiency, particularly through the electrically conductive solid bodies selected from polarizable and / or dielectric particles and / or under high-motion and / or turbulent environments, ensuring uniform and precise finishing even on complex geometries. Without being bound to any theory, the conductive medium may prevent short-circuiting the electrochemical cell, ensuring at least part of the ion transport to be carried out by the solid bodies, offering the benefits attributed to solid-particle based electrolytes. The method is adaptable to different electrical currents and processing conditions, offering a flexible and scalable solution. In particular embodiments, by combining controlled motion and / or turbulence with a tailored electrolyte composition, the invention significantly improves processing speed, surface quality, and overall efficiency, addressing key limitations of traditional electropolishing techniques while maintaining environmental and economic advantages.

[0057] In particular embodiments, the invention operates under varied electrical currents and processing conditions, including alternating electrode polarities using different waveform shapes (such as rectangular, triangular, or sinusoidal waves) as well as varying pulse frequencies ranging from 0.1 Hz to 9 MHz and / or turbulent flow regimes characterized by Reynolds numbers from 102to 107. These conditions may particularly benefit a specific dielectric behaviors of the solid bodies in the medium, in particular the suspended particles and the conductivity of the surrounding medium.

[0058] The dielectric constant of the solid bodies directly influences their polarization and depolarization dynamics. An increase in dielectric constant increases capacitance and, consequently, the electrical relaxation time (T = RC). In the context of the invention, the relaxation time is considered equivalent to the time required for a particle to polarize or depolarize under an external electric field (E).

[0059] In some embodiments, under high-turbulence (e.g. Reynolds numbers of more than 2300) conditions and a medium having a low-conductivity (e.g., having a conductivity from 1 pS / cm to 10 mS / cm, representing at least a value below 10% with respect to the particles and / or the CSE, also referred to as a low-conductivity interstitial media), particles with higher dielectric constants (e.g., of at least 8) are preferred. Without being bound to any theory, longer relaxation times may allow the particles to remain polarized for longer and to transmit a higher electrical potential toward the opposing electrode.

[0060] Conversely, in other embodiments, when the conductivity of the medium increases (e.g., the medium has a conductivity of at least 10 mS / cm), particles with lower dielectric constants (e.g., of at most 8) may be preferred to further contribute to the performance of the surface finishing method.

[0061] Similarly, changes in waveform shape and frequency of the electrical currents may produce effects analogous to variations in turbulence. For instance, abrupt voltage transitions, such as those associated with rectangular waveforms or high-frequency signals, may be preferred when using particles with sufficiently low dielectric constants (e.g., of at most 8) to favour the current to dynamically follow rapid voltage changes. On the other hand, increasing the conductivity of the medium may further enhance current adaptability, improving efficiency across a broad range of electrical excitation conditions.In some embodiments, the conductivity of the medium is equal to or lower than the conductivity of the solid bodies. Without being bound to any theory in such conditions electrical transport within the CSE system may be preferentially performed and / or dominated by the solid bodies rather than by the liquid medium alone. For instance, the conductivity of the medium, measured in the absence of free solid bodies, may be within the range of 10% to 100% of the conductivity of the CSE at rest and at room temperature, more particularly between 20% and 90%, and even more particularly between 30% and 60%. For such medium conductivities, the electrical field distribution within the system may be stabilized and mainly guided through the particle network. This controlled balance may contribute to prevent uncontrolled current flow through the medium, e.g., in the form of a liquid phase, and promotes uniform, localized electrochemical activity at the surface of the workpiece. Furthermore, within these conductivity ranges, the interaction between the applied electrical excitation and the suspended solid bodies may enable dynamic modulation of current pathways, particularly under alternating or pulsed electrical conditions. Surprisingly, the medium does not behave as a direct electrical short-circuit between electrodes but instead acts as a supporting phase that enables the polarization and depolarization of the solid bodies. As a result, in particular embodiments, ion transport and electrochemical reactions appear to be predominantly governed by the collective behavior of the particles, leading to improved surface uniformity, reduced pitting, and enhanced process stability compared to conventional liquid-only electrolytes of similar conductivity. Without being bound to any theory, a system as described herein introduces, provides, a CSE including a conductive fluid medium in which free electrically conductive solid bodies are suspended and in ohmic contact, thereby improving ion transport efficiency and enhancing processing speed.

[0062] As represented in Figure 1 , a first aspect of the present invention relates to surface finishing method through ion transport comprising the steps of:

[0063] applying an electric potential difference between at least two electrodes (101), an anode (102) and a cathode (103), wherein at least one surface to be treated is coupled to one of the electrodes;

[0064] connecting the at least two electrodes with a Conductive Suspension Electrolyte (CSE);

[0065] wherein the CSE includes a set of free electrically conductive solid bodies (105) in a medium comprising a conductive fluid, characterized in that the medium presents a significant conductivity with respect to the set of free solid bodies; and

[0066] producing upon contact an ion exchange between the surface to be treated and the set of free electrically conductive solid bodies, and thereby finishing the at least one surface.

[0067] Particular embodiments of the invention include a method including steps of:inducing motion or turbulence to the medium so that no stable chain of direct contact between particles electrically connects the two electrodes;

[0068] comprising a medium characterized to provide sufficient ion connectivity between a set of solid bodies to ensure ion transport; and

[0069] electrically coupling the two electrodes trough said non-direct physically contacting bridge of solid bodies and thereby ensuring the ohmic contact between the solid bodies comprised within the bridge (110).

[0070] The solid bodies within a CSE facilitate ion exchange between the treated surface and the electrolyte, ensuring a uniform surface finish. Unlike previous solid particle-based electrolytes, the medium used in the CSE presents a significant conductivity relative to the polarizable solid bodies, allowing for optimized voltage transmission through the solid particles.

[0071] In some embodiments, using polarizable or dielectric particles, as electrically conductive solid bodies, allows for the solid bodies (105), such as ion-exchange resins, to transmit the current from the anode to the cathode without the need for direct contact between particles (110). Without being limited or bonded to any theory, polarizable particles are capable for presenting a positive (112) and a negative (113) pole of a solid body. If the electrical potential difference from two solid bodies is strong enough, the charged spices can migrate through the solvent from one particle to another because of electrophoresis, ensuring the passage of current. In some embodiments, the electrophoretic ion flow is carried out through a meniscus (111) connecting two particles.

[0072] Furthermore, in some embodiments, increasing the motion of the solid bodies or the turbulence applied to a CSE the distance separating the solid bodies can increase, decreasing the potential difference between two polarized particles and decreasing the current, and though the processing speed, until a point where there is no current. By increasing the voltage or introducing more charged spices on the medium, and thereby increasing its conductivity, more ions migrate and higher currents are obtained.

[0073] In other particular embodiments, and without being bound to any theory, a galvanic effect associated with the solid bodies predominates not because the particles exhibit higher intrinsic electrical conductivity than the liquid medium, but rather due to their dielectric properties in combination with electrode spacing, applied voltage levels, electrical excitation conditions and / or dynamic chemical behavior. In this embodiment, the liquid continuous phase connecting the electrodes may be more conductive than the solid bodies themselves. Despite this, the solid bodies become preferentially involved in the electrochemical process through polarization effects, field concentration, and interfacial charge accumulation, resulting in a dominant contribution of the particles to the overall electrical and electrochemical behavior of the system.Surprisingly, in some embodiments, even when the continuous liquid phase comprises a highly conductive or chemically aggressive medium, such as a strong acid, the predominance of the particle-driven galvanic effect appears to prevent the occurrence of surface defects typically associated with direct exposure to such liquids. The electric field and electrochemical activity are likely effectively redistributed through the suspended particles, thereby shielding the treated surface from appreciable uncontrolled attack by the liquid phase. This enables, in some embodiments, the use of highly conductive or reactive liquids while maintaining high surface quality, further contributing to reduced corrosion damage, and improved process control, representing a further significant and unexpected advantage over conventional electrochemical treatment systems.

[0074] In certain embodiments of the present invention, the free electrically conductive solid bodies in the media, are suspended dielectric particles comprising, e.g., ion-exchange materials capable of retaining a conductive solution within their structure or at their surface. Although such particles may exhibit an intrinsic electrical conductivity equal to or lower than that of the surrounding media (e.g. forming a liquid continuous phase), their ability to locally store ions and participate in interfacial charge exchange enables them to act as preferential electrochemical intermediaries. For instance, under applied electrical excitation, the electrochemical activity may therefore be redistributed toward the particle-electrolyte and particle-workpiece interfaces, rather than being governed solely by bulk conduction through the liquid medium.

[0075] In some embodiments, the electric potential difference may be applied using alternating or pulsed electrical signals. In some particular embodiments, the type of signal may be selected such that the response of the liquid phase remains predominantly resistive, while the particle-associated interfaces exhibit a delayed or persistent polarization behavior. It has been found that this temporal mismatch does not block current through the liquid phase, but instead appears to advantageously limit uncontrolled faradaic reactions occurring directly within the bulk liquid or at exposed regions of the workpiece. As a result, the effective electrochemical reaction rate at the treated surface may be governed primarily by the ion-exchanging particles, leading to improved surface uniformity and reduced defect formation. Alternating electrical excitation according to some embodiments comprise frequencies ranging from 10 kHz to 1MHz, preferably from 50 kHz to 300 kHz.

[0076] In some embodiments, the conductivity of the medium comprising the conductive fluid which forms, e.g., a liquid continuous phase connecting the electrodes may exceed that of the free solid bodies in the medium, e.g., particles suspended therein, including cases where the conductive fluid of the medium comprises a highly conductive or chemically aggressive electrolyte such as a strong acid. Surprisingly, despite the higher bulk conductivity of the liquid, surface damage typically associated with direct liquid-drivenelectrochemical attack is mitigated. This effect arises because the free electrically conductive solid bodies, and in particular ion-retaining dielectric particles, locally modulate the electric field and charge transfer dynamics, thereby predominating in the electrochemical interaction with the workpiece and shielding the surface from uncontrolled liquid-phase reactions.

[0077] The viscosity of the medium, e.g., as a liquid continuous phase, may further contribute to the advantages of methods described herei. Without being bound to any theory, Increased viscosity may reduce convective ion transport and limits rapid charge redistribution within the bulk liquid, thereby extending the effective influence of particle-mediated polarization and ion exchange. By appropriately selecting the viscosity of the medium in combination with particle properties and electrical excitation conditions, the direct liquid-dominated electrochemical pathways may be further supressed while maintaining sufficient ionic mobility for controlled surface treatment. In some embodiments conductive liquid mediums are selected with dynamic viscosity between 0.01 Pa s and 5 Pa s, In particular embodiments of high turbulence, preferably at most 1 Pa s.

[0078] Accordingly, the combined selection of particle dielectric behavior, ion-exchange capacity, liquid conductivity, viscosity, electrode spacing, and applied voltage waveform enables the establishment of a further controlled electrochemical regime in which effective surface processing is dominated by the suspended particles rather than by the liquid phase alone. This controlled regime may be maintained without requiring the liquid medium to behave as an electrical insulator, and without imposing a hard upper frequency cutoff, thereby providing a robust and flexible operating window for advanced electropolishing and surface finishing applications.

[0079] In some embodiments, where the conductivity of the medium, e.g., the liquid of the interstitial space, is higher than the conductivity of the free solid bodies. In such donditions, the liquid medium may present a time-dependent conductivity behavior, whereby the conductivity of the medium may decay through the time as the method proceeds, as illustrated in, e.g., Figure 5. This liquid conductivity decay (501) trough time may be at least faster than that of the solid particles conductivity decay (502) and thereby, in some embodiments a limit time thm (503) of galvanic pulse and / or a galvanic treatment, wherein the conductivity of the medium equals de conductivity of the free solid bodies, is at least higher than the limit time thm (503), resulting on a predominant galvanic effect of the electrically conductive particles compared to that of the liquid medium.

[0080] In some particular embodiments, a decay of the liquid medium conductivity and / or the liquid medium galvanic effect is due to a formation of a resistive and / or viscous layer (402) at a surface of the part being treated (403) as exemplified in, e.g., Figure 4. In some embodiments after the formation of the resistive layer there is a growth over time thatincreases its resistivity over time, at some point decreasing the conductivity of the liquidpart interfaces below that of the solid bodies-part interfaces.

[0081] In particular embodiments, a resistive layer, of ions present in the medium, is formed as a viscous layer due to a gradient of the ionic concentration toward a surface of a part being treated. In other particular embodiments, a viscous layer is formed as a result of the polarization and / or migration of, e.g., surfactants (402) over the surface being treated (403). In other embodiments where the liquid medium comprises an emulsion (e.g., a polar-in-apolar (P / A) emulsion, such as water-in-oil (w / o) type, or apolar-in-polar (A / P) emulsion, such as an oil-in-water (o / w) type polar-apolar-type, or intermediate states between them) a resistive is layer is formed by an emulsion inversion during the polarity change (401) of the galvanic cell as a consequence of the different chemical compounds’ migration at the metal surface-liquid medium interface.

[0082] In some embodiments the conductive fluid comprises a polar solvent, in particular selected from: protic solvents, aprotic solvents, deep eutectic solvents, or combinations thereof; and ionic species selected from: metal cations, inorganic anions, organic anions, supporting electrolyte cations, or complexed ions.

[0083] In some embodiments, a medium (e.g. a liquid medium) suitable for generating resistive layer in a CSE as described herein comprises a polar solvent, either protic (i.e. , water, ethylene glycol, glycerol) or aprotic (dimethyl sulfoxide, dimethylformamide, propylene carbonate) and ionic species, such as metal cation families (e.g., Fe2+, Fe3+, Cr®+, Al3+, Cu2+), inorganic anion families (e.g., phosphates, sulphates, nitrates), organic anion families (e.g., methoanosulfonates, carboxilates), supporting electrolyte cations (e.g., H+, NH4+) and complexed ion species, deep eutectic solvents (DES), or a combination thereof.

[0084] In some embodiments the liquid retained by the solid particles (also referred to herein as the electrolyte liquid, is a polar liquid different from the polar solvent of the medium, and may comprise more favorable solvents and ion species to carry out a predominant ion exchange between the surface being treated, such as a strong acid in water solution. In some other embodiments the liquid retained by the solid bodies is the same as the conductive fluid contained in the medium, e.g., a polar solution retained by the solid bodies presents the same composition as a polar solution present in the medium.

[0085] In some embodiments, a medium suitable for generating resistive layer may further comprise a moderator liquid which may be selected from an organic solvent such as Hydrocarbons (e.g., alkane oils, mineral oil, isoparafines, toluene), silicon fluids (e.g., Polydimethylsiloxane, Silicone oil), Fluorinated solvents (e.g., Perfluorohexane, Perfluorodecalin), Aromatic oils, ester oils, and bio-based oils.

[0086] In some embodiments, a medium suitable for generating resistive layer further comprise a surfactant. In some embodiments a surfactant may be selected from anionic,cationic, non-ionic or zwitterionic surfactants. In some embodiments the head group is selected from carboxylates sulfates, phosphates, ethoxylates or sugar-based. In some embodiments the molecular architecture may include linear, ramphoid or cyclic c-H chains.

[0087] In particular embodiments, an organic sulfonic acid (e.g., dodecilbenzenesulfonic acid may be present in the medium optionally in combination with a fatty acid.

[0088] The previous mechanisms of resistive layer formations are only examples and do not limit or exclude other mechanisms known in the art to form resistive layers in conductive liquid-surface interfaces.

[0089] An aspect of the present invention relates to a surface finishing method through ion transport comprising the steps of: applying an electric potential difference between at least two electrodes (101), an anode (102) and a cathode (103), wherein at least one surface to be treated is coupled to one of the electrodes; connecting the at least two electrodes with a Conductive Suspension Electrolyte (CSE); wherein the CSE includes a set of free solid bodies (105) suspended in a medium comprising a conductive fluid; characterized in that the medium presents a conductivity which is equal to, higher than the conductivity of the set of free solid bodies, and wherein the set of free solid bodies comprises ion-exchange and / or dielectric materials capable of retaining a conductive solution, enabling their becoming polarized under the applied electric potential difference; and producing, upon contact, an ion exchange between the at least one surface to be treated and the set of free solid bodies, wherein the ion transport and electrochemical surface finishing may be predominantly governed by particle-mediated interfacial charge transfer and polarization effects rather than by bulk conductive transport through the medium alone, thereby finishing the at least one surface.

[0090] Another aspect of the present invention relates to a method for surface finishing through ion transport using a Conductive Suspension Electrolyte (CSE), comprising the steps of: applying an electric potential difference between at least two electrodes (101), comprising an anode (102) and a cathode (103), wherein at least one surface to be treated is electrically coupled to one of the electrodes; connecting the at least two electrodes with the CSE, wherein the CSE comprises the medium in the form of a liquid phase and a plurality of free solid bodies (105) suspended therein; wherein the liquid phase in the CSE has a dynamic viscosity between 0.01 Pa s and 5 Pa s, which is thought to limit bulk convective ion transport while maintaining controlled mobility of the free solid bodies. Preferably, the liquid phase has an electrical conductivity equal to or greater than that of the plurality of free solid bodies, preferably the liquid phase having a conductivity from 5 mS / cm to 500 mS / cm, more preferably from 20 mS / cm to 200 mS / cm; and the free solid bodies preferably have an electrical conductivity from 1 mS / cm to 100 mS / cm, more preferably from 10 to 50 mS / cm. The free solid bodies may also preferably comprise ion-exchange particles retaining a conductive solution (also referred to herein as electrolyte liquid). In some embodiments, the free solid bodies exhibit a dielectric constant from 3 to 20 and / or an Ion Exchange Capacity from 1.8 to 5 eq / L, preferably a dielectric constant from 8 to 15 and / or an Ion Exchange Capacity from 2.2 to 4 eq / L.

[0091] The electric potential difference may be applied as a DC current or an AC current. Preferably an AC current may be applied with a frequency equal or higher than 1 KHz.

[0092] In some embodiments, the electric potential difference is applied in the form of pulsed or alternating electrical excitation having a frequency from 10 kHz to 1MHz, preferably from 50 kHz to 300 kHz; and producing a relative motion between the particles and the at least one surface being treated, favoring an ion exchange upon contact.

[0093] In some embodiments, the dielectric constant of the medium, of the electrically conductive solid bodies, or of the CSE (that combines the medium and solid bodies), is measured using conventional dielectric measurement techniques known in the art. Such techniques may include capacitance-based measurements, impedance or admittance measurements, or frequency-dependent dielectric spectroscopy methods. In some embodiments, the dielectric constant is determined by positioning the material to be measured between or in proximity to spaced electrodes forming a capacitor of known geometry, applying an alternating electrical signal, and measuring the resulting capacitance, from which the dielectric constant is calculated.

[0094] In some embodiments, the measurement is performed using a dielectric measurement cell having a predetermined or calibrated cell constant, which depends on electrode geometry, spacing, and effective area. The cell constant may be selected or adjusted according to the expected dielectric constant range of the material under investigation. Calibration may be performed using reference materials or standard substances having known dielectric constants.

[0095] Suitable laboratory equipment for measuring the dielectric constant may include, without limitation, LCR meters, impedance analyzers, dielectric spectrometers, electrochemical workstations, or capacitance meters capable of operating over a selected frequency range. In certain embodiments, the electrodes comprise metallic or conductive materials such as stainless steel, platinum, gold, or graphite and may be arranged in parallel-plate, coaxial, or concentric configurations. In other embodiments, the dielectric constant is measured under static or dynamic conditions, including in liquids, gels, suspensions, slurries, or particle-containing systems.

[0096] The dielectric constant of the solid bodies may also be, and is typically, derived from the properties provided by the supplier.

[0097] In some embodiments, the dynamic viscosity of a fluid or a fluid-particle system is measured using conventional viscosity measurement techniques known in the art. Suchtechniques may include rotational, oscillatory, capillary-based, or vibrational viscosity measurements. In certain embodiments, the dynamic viscosity is determined by subjecting the fluid or fluid-particle system to a controlled shear or deformation and measuring the resulting resistance to flow, from which viscosity is calculated.

[0098] In some embodiments, the measurement is performed using a viscosity measurement cell or fixture having a predetermined geometry and calibration constant, which depends on the measurement configuration, such as cone-and-plate, parallel-plate, coaxial cylinder (Couette), or concentric cylinder geometries. The measurement system may be calibrated using reference fluids having known viscosities prior to measurement. In certain embodiments, the viscosity measurement is conducted over a selected shear rate or shear stress range, thereby enabling characterization of Newtonian or non-Newtonian behavior.

[0099] Suitable laboratory equipment for measuring dynamic viscosity may include, without limitation, rotational viscometers, rheometers, capillary viscometers, oscillatory rheometers, vibrational viscometers, or inline viscosity sensors. In some embodiments, the viscosity is measured under controlled temperature conditions and, optionally, under static or dynamic flow conditions. In other embodiments, the measurement is performed on particlecontaining systems, suspensions, slurries, or dispersions, including systems comprising abrasive or polarizable particles, wherein the measurement geometry and operating conditions are selected to accommodate particle size, particle concentration, and sedimentation behavior.

[0100] Figure 2 represents the distance under which two different poles, positive (211 and 221) and negative (212 and 222), of two polarized particles, are capable of exchanging ions (213 and 223) through a meniscus of a conductive solution (213 and 223) at a certain critical distance (216 and 226) after which the meniscus is broken. In several particular embodiments, including a conductive medium based on an emulsion, surfactants (214 and 224) are included to modify the surface tension of the conductive meniscus (213 and 223), enabling the control of the critical distance (216 and 226).

[0101] In some embodiments, the system, e.g., a CSE combination as described herein, is configured in terms of the surface tension between the meniscus and the environment in a way that ensures connectivity between two solid bodies separated by a larger distance. By reducing the surface tension from (214) to a lower one (224) of the conductive meniscus relative to its surroundings, the stability of the liquid bridge is enhanced changing the critical distance d1 (216) to a higher one d2 (266), allowing ion exchange to persist over a greater separation. This effect can be achieved through the addition of surfactants from (214) to (224), which lower the interfacial energy, or by tuning the composition of the conductive medium to optimize its wetting properties. In some embodiments surfactants with a lowHydrophilic-Lipophilic Balance (HLB) are selected, such as between 0 and 8 HLB, in particular, between 6 and 3. These surfactants are preferably used for embodiments where an emulsion is a w / o-type emulsion present in the environment. In some other embodiments surfactants with a high Hydrophilic-Lipophilic Balance (HLB) are selected, such as between 8 and 20 HLB, in particular, between 8 and 18. These surfactants are preferably used for embodiments where an emulsion is a w / o-type emulsions present in the environment.

[0102] Moreover, when the surface tension at the interface between a conductive meniscus and a surrounding oil phase is carefully adjusted, the meniscus can exhibit increased elongation before reaching the critical distance at which it breaks. This enables a controlled extension of the conductive bridge, facilitating sustained electrical connectivity and ion transport between polarized particles. In cases where the medium is an emulsion, the dispersed phase can further contribute to modifying the mechanical properties of the meniscus, thereby influencing its stability and response to external perturbations.

[0103] By strategically selecting surfactant types and concentrations, it is possible to finetune the critical distance at which the meniscus remains intact. A lower surface tension promotes greater flexibility and extension of the meniscus, while higher surface tension leads to premature rupture. These adjustments provide a means to optimize the system for specific applications requiring controlled ion exchange over varying distances.

[0104] All the possible combinations between the cases represented in Figure 1-A and 1-B fall within the scope of the present invention.

[0105] In the present invention, surfactants including non-linear aliphatic chains with some asymmetries are of high interest, such as oleic acid, ricinoleic acid, linoleic acid, and isostearic acid. Additionally, surfactants incorporating aromatic groups, such as benzyl dodecyl sulfate and alkylphenol ethoxylates, are also considered for their ability to modify interfacial properties. The effect of these surfactants is to create a metastable meniscus capable of high elongation and adapting geometries that ensure efficient ion communication between particles, even under highly turbulent conditions.

[0106] By introducing asymmetry in the molecular structure, these surfactants contribute to the formation of a meniscus that can withstand dynamic deformations while maintaining connectivity between polarized particles. This adaptability is particularly advantageous in environments where fluctuating forces or sudden changes in separation distance could otherwise lead to premature rupture of the conductive bridge. The resulting stabilization mechanism allows for more robust ion exchange, improving the efficiency and reliability of the system across a broader range of operational conditions.

[0107] A conductivity reading according to the present disclosure is to be understood as any measurement representative of the current sensibility of the system over a voltage inputwithout changing its value through a period of 5 minutes in a percentage of 10% higher or lower to the original one, measured at rest and at room temperature.

[0108] A conductivity measurement or value according to the present disclosure and any comparative conductivity value of the constituents of a CSE is to be understood as measured at rest and at room temperature, and remaining consistent over a period of five minutes, with fluctuations not exceeding ±10% of the original value, in particular not exceeding ±5%. In Figure 5, the recording is of a dynamic process, the conductivity does not remain consistent over time, and therefore this does not apply.

[0109] The method as described herein may utilize, e.g., in applying the electric potential difference between the at least two electrodes, either direct current (DC) or alternating current (AC). In particular embodiments, an AC is used with a frequency equal to or higher than 0.1 kHz, allowing for greater flexibility in different applications. In some particular embodiments, high frequency can help on the solid bodies ohmic commutation.

[0110] In some embodiments, a method according to the present invention includes steps of shooting or projecting the charged or polarized electrically conductive solid particles (105) towards a surface to be treated (102 or 103) by ion transport.

[0111] In particular embodiments a method according to the present invention includes steps of generating a relative motion between the charged or polarized electrically conductive solid particles (105) with respect to a surface, e.g., an immersed surface, to be treated (102 or 103) inside of a receptacle containing the CSE, so that ion transport is carried out upon contact.

[0112] In particular embodiments, the method as described herein incorporates turbulence or motion within the medium, preventing direct contact chains from forming between the solid bodies, electrically connecting the electrodes through a controlled network of free-moving conductive particles. This approach enhances ion transport and provides a stable, consistent finishing effect on the treated surface.

[0113] By utilizing this advanced electrolyte system, such as the use of a CSE in methods as described herein, the invention offers a commercially viable solution for improving surface finishing processes, addressing the limitations of prior technologies while maintaining environmental sustainability and cost-effectiveness.

[0114] In galvanic surface finishing based on immersion methods that utilizes turbulence to enhance surface treatment capabilities, particularly for large and complex geometries, relying on a solid particle-based electrolyte, introduced by reference from European Patent Application No. EP24383077.5, CSEs as described herein offer an optimized performance.

[0115] A second aspect of the present invention relates to the CSE to perform the previously described method.

[0116] A CSE includes at least the following elements:- A first plurality of free solid bodies, in particular polarizable or dielectric particles, capable to retain, e.g., with porosity and affinity or capacity to retain, an electrolyte liquid to make them electrically conductive

[0117] The electrolyte liquid retained by the first plurality

[0118] - A conductive medium, e.g., in the environment or in the interstitial space between the first plurality

[0119] Optionally a second plurality of abrasive particles for obtaining a mechanochemical hybrid surface finishing

[0120] A first plurality of free solid bodies, e.g., polarizable or dielectric particles, with porosity and affinity or capacity to retain an electrolyte liquid to make them electrically conductive, of a CSE according to the present invention comprise suitable polymeric materials may be, e.g., ion exchange resins.

[0121] In some embodiments the first plurality of polarizable or dielectric particles retains the liquid electrolyte trough any or any combination of the following properties: porosity, affinity, capillarity, absorption, ion-exchange capability, surface functionalization, electrostatic interaction, chemical bonding, physical entrapment, swelling behavior, and hygroscopicity.

[0122] In some embodiments, the electrically conductive free solid bodies or particles are of a material selected from: strong and weakly acidic cationic resins, strong and weakly basic anion exchange resins and chelating resins, and more preferably are cationic exchange resins, as such resins contribute to capturing metal ions extracted in the electropolishing processes.

[0123] In ion exchange technology, resins are categorized as strong or weak based on the ionization characteristics of their functional groups, influenced by their pKa values, which determines 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.

[0124] In some embodiments, electrically conductive free solid bodies or particles are of orcomprise 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 examples 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.

[0125] In some embodiments, electrically conductive free solid bodies or 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.

[0126] In some embodiments, electrically conductive free solid bodies or 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.

[0127] In some embodiments, electrically conductive free solid bodies or 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 alkalineenvironments, 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(styrene-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.

[0128] In some embodiments, electrically conductive free solid bodies or 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.

[0129] In some embodiments, the free solid bodies comprise particles of a polymeric material preferably of a sulfonated divinylbenzene 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.

[0130] Alternatively, the free solid bodies comprise particles of a polymeric material preferably 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.

[0131] In some embodiments, electrically conductive free solid bodies or 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 functionalgroups that are of the chelating type such as, for example, iminodiacetic, aminophosphonic, polyamine, 2-picolylamine, thiourea, amidoxime, isothiouronium, 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.

[0132] Depending on the specific type of polymer and functional groups included, the exact composition of the electrically conductive free solid bodies or 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.

[0133] 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.

[0134] The electrically conductive free solid bodies or 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 ionexchange 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.

[0135] In some embodiments, electrically conductive free solid bodies or particles have a porous 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 particlesurface contact is more defined, resulting in a lower final roughness.

[0136] In particular embodiments, when performing an electropolishing method under turbulent conditions, the current may decrease. A possible method to overcome the decrease of current during an increase of turbulent conditions, according to the present invention, comprises or consists of increasing the time under which an isolated free solid body keeps a previously established charge. A first plurality of free solid bodies, according to some embodiments, is made from porous materials, such as ion-exchange resins. These resins may feature functional groups like sulfonic or carboxylic groups for metal ion retention, or chelating groups for selective interaction with transition metals. The functional groups, together with the degree of crosslinking, determine the resin’s ion exchange capacity (IEC), which is an adjustable parameter for controlling its performance.

[0137] In particular, strong acid cation (SAC) resins with an IEC ranging from 1.8 to 2.5 eq / L typically offer robust ion exchange ability and maintain performance across a broadpH range, ideal for acidic conditions. These resins generally exhibit dielectric constants between 5 and 20, owing to their high ionic content and strong water affinity. For weak acid cation (WAC) resins, the IEC typically ranges from 1.0 to 1.8 eq / L, and their effectiveness is pH-dependent, performing best in moderately acidic to neutral environments. These resins typically have dielectric constants between 3 and 15, reflecting their lower ionic content and reduced water absorption.

[0138] Similarly, strong base anion (SBA) resins with an IEC of 0.9 to 1.5 eq / L and weak base anion (WBA) resins with an IEC of 1.0 to 1.4 eq / L offer effective ion exchange in neutral to alkaline environments. SBA resins generally exhibit dielectric constants between 4 and 16, while WBA resins typically range from 3 to 12. The dielectric constants of these resins are influenced by their ionic content and hydration levels, with higher values typically correlating with higher IEC.

[0139] Increasing the ion exchange capacity of a resin results in a higher dielectric constant, as higher ionic content and water retention improve the resin's polarizability. This enhancement increases the resin's ability to withstand higher turbulent conditions, making it more viable in such environments. Ion exchange resins comprised in a first plurality of the present invention may have an IEC ranging from 0.1 to 5 eq / L, particularly between 1.5 and 3 eq / L, and more specifically between 1.7 and 2.5 eq / L. These resins would exhibit dielectric constants in the range of 4 to 20, depending on the specific resin type. These properties contribute to the resin's resilience under variable turbulent conditions, improving the performance and efficiency of the method described in the invention.

[0140] In some embodiments, the ion-exchange capacity of an ion-exchange resin is measured using conventional ion-exchange capacity determination methods known in the art and is expressed as equivalents per unit volume, for example equivalents per liter (eq / L). In certain embodiments, the ion-exchange capacity is determined by contacting a known volume of the resin with a solution containing a known concentration of exchangeable ions under controlled conditions, allowing ion exchange to occur, and subsequently quantifying the number of ions exchanged.

[0141] In some embodiments, the measurement is performed using batch, column, or flow-through test configurations. In a batch method, the resin is equilibrated with an excess of a standard ionic solution, and the concentration of ions in the solution before and after contact with the resin is measured. In a column method, the resin is packed into a column of known volume and subjected to a standard regenerant or exchange solution, and the effluent is analyzed to determine the total exchanged ionic equivalents.

[0142] The ion-exchange capacity may be calculated based on the measured quantity of exchanged ions and the known volume of the resin, and reported as eq / L. Suitable analytical techniques for quantifying exchanged ions may include, without limitation, acid-base titration, conductometric titration, potentiometric titration, ion chromatography, atomic absorption spectroscopy, inductively coupled plasma spectroscopy, or other analytical methods suitable for determining ionic concentration.

[0143] Suitable laboratory equipment for measuring ion-exchange capacity may include, without limitation, titration systems, burettes, pH meters, conductivity meters, analytical balances, chromatography systems, spectroscopic analyzers, and column test apparatus. In certain embodiments, the measurement is performed under controlled temperature, pH, and ionic strength conditions, and the resin may be conditioned, regenerated, or pretreated prior to measurement in accordance with standard testing protocols.

[0144] The ion exchange capacity is typically known from the supplier of the ion exchange resin and does not need to be measured.

[0145] In particular embodiments the liquid electrolyte retained by a first plurality of free solid bodies in a CSE according to the present invention includes an acidic aqueous solution, e.g., an aqueous solution of hydrofluoric acid (HF), sulfuric acid, sulfonic acids (e.g., methanesulfonic acid, MSA), phosphoric acid (such as orthophosphoric acid), carboxylic acids, citric acid, and hydrochloric acid. Preferably, the electrolyte may be an aqueous solution of sulfuric acid or MSA.

[0146] In some embodiments, electrically conductive free solid bodies or particles comprise a combination of particles having different types of electrolytes (e.g., aqueous solutions of different acids). For instance, the electrically conductive particles may comprise particles comprising an aqueous solution of MSA and particles comprising an aqueous solution of sulfuric acid.

[0147] The electrically conductive free solid bodies used in this method, and other methods as described herein, may feature porosity or affinity properties that enable them to retain electrolyte liquid, making them more effective conductors. In particular embodiments, the free solid bodies may comprise or consist of a cationic ion-exchange resin that retains an electrolyte liquid comprising methanesulfonic acid (MSA) in a concentration ranging from 0.1% to 70% by weight.

[0148] In some embodiments, the total concentration of the acids in the electrolyte, e.g. the liquid retained by the free solid bodies, may vary from 0.1 to 70 wt.% with respect to the total mass of the water plus the acid, in particular from 1 to 40 wt.%. In some embodiments, an acid concentration from 5 % and 30 wt.% relative to the mass of the water plus the acid is used.

[0149] In particular, a HF solution such as, e.g., a 90 to 99% water, H2O, and 10 to 1% HF, by weight of acid to the total weight of water and acid may be used. As another example, an aqueous solution of sulfuric acid may be used having, e.g., a 90 to 99% water, H2O, and 10 to 1% of sulfuric acid, in particular 5 to 1% of sulfuric acid, by weight of acid to the totalweight of water and acid. Similarly, an aqueous solution of methanesulfonic acid (MSA) may be used having, e.g., a 90 to 99.5% water, H2O, and 10 to 0.5 % of MSA, in particular from 5 to 1 % of MSA, by weight of acid to the total weight of water and acid. Similarly, an aqueous solution of orthophosphoric acid may be used having 90 to 99.5% water, H2O, and 10 to 0.5 % of orthophosphoric acid, in particular from 5 to 1 % of orthophosphoric acid, by weight of acid to the total weight of water and acid.

[0150] In some embodiments, the electrolyte, e.g. the liquid retained by the free solid bodies, is an ionic liquid or a conductive liquid polymer.

[0151] In some embodiments a liquid electrolyte, e.g., retained by the free solid bodies and in particular embodiments retained by an ion exchange resin, is water, distilled water or deionized water.

[0152] In some embodiments a liquid electrolyte, e.g., retained by the free solid bodies and in particular embodiments retained by an ion exchange resin, comprise a Deep Eutectic Solvent (DES), e.g., based on Choline chloride (ChCI) and Ethylene glycol (EG) in different ratios such as 1:2, 1:3, 1:4 (ChCI : EG).

[0153] A conductive medium, e.g., in the environment or in the interstitial space between the first plurality of free solid bodies, of a CSE according to some embodiments of the present invention presents the following described features.

[0154] In several particular embodiments, preferably, the conductivity of the medium is lower than the conductivity of the particles, in particular between 10 % and 99% with respect to that of the particles, more in particular between 30 and 70 %.

[0155] As represented in Figure 1-A, a method including a CSE and or a CSE to perform the method, includes a conductive medium, e.g., a medium comprising a conductive fluid, presenting a conductivity equal to or lower than the conductivity of the solid bodies, the conductive medium of a CSE includes a single conductive phase (106), where the medium can be a solvent comprising or with the potential for gather ion transported by electrophoresis between two solid particles, such as aqueous solutions. In some cases, a single conductive phase (106) comprises a solvent miscible in the electrolyte solution retained by the solid bodies, such as aqueous solutions containing ions in the case where the solid bodies retaining aqueous electrolytes such as acids. In other particular embodiments a single conductive phase (106) comprises a solvent immiscible in the electrolyte solution retained by the solid bodies, such as apolar solutions containing ions and a cosolvent to stabilize the ions in said apolar solution in the case where the solid bodies retaining aqueous electrolytes such as acids.

[0156] In other embodiments, the conductive medium of a CSE includes at least two different phases (106 or 109 and 104 or 108) or more.In some embodiments, the medium comprises an emulsion that enhances the stability and efficiency of the electrochemical process. The emulsion is composed of a conductive fluid and a less-conductive fluid, where the latter is immiscible in the former. Depending on the desired properties, the emulsion can be either a polar-in-apolar (P / A) emulsion, such as water-in-oil type, or apolar-in-polar (A / P) emulsion, such as an oil-in-water type. Without being bound to any theory, the presence of a non-conductive fluid may advantageously prevent the conductive liquid from short-circuiting the system, maintaining the integrity of ion transport through the solid bodies.

[0157] As represented in Figure 1-A, a method including a CSE and or a CSE to perform the method, includes a conductive medium, e.g., a medium comprising a conductive fluid, presenting conductivity equal to or lower than the conductivity of the solid bodies, a CSE according to some embodiments comprises a conductive medium comprising at least two phases. A first phase (104) is more conductive than a second phase (106) immiscible in the first phase at rest and at a room temperature between 15 °C and 30 °C. In some embodiments of the invention, a conductive medium comprises a polar-in-apolar (P / A) emulsion where the polar solution (104) is dispersed on an apolar solution.

[0158] As represented on Figure 1-B, a method including a CSE wherein the conductivity of the medium measured without the free solid bodies is from 10 % to 100 % of the conductivity measured CSE, at rest and at room temperature; the corresponding CSE comprises a conductive medium including at least two phases. A first phase (108) is more conductive than a second phase (109) immiscible in the first phase at rest and at a room temperature between 15 °C and 30 °C. In some embodiments of the invention, a conductive medium comprises an apolar-in-polar (A / P) emulsion. In some configurations of the present embodiments, the polar solution (108) can present higher conductivity than the solid bodies or particles (105) but the turbulence induced to the CSE is high enough to disperse the polar phase (108) in the apolar phase (109) preventing the conductive medium to short-circuit the galvanic action of the solid particles (105) which would not offer the advantages of solidparticle based electrolytes, thereby advantageously spanning the suitability of a method and a CSE as described herein. In the present embodiment the conductivity of the medium is higher than that of the solid bodies, and the emulsion comprises a non-conductive fluid which also contributes in preventing the conductive liquid to short-circuit the set of free electrically conductive solid bodies under said working conditions.

[0159] When a liquid conductive medium is used, the proportion of liquid medium to electrically conductive free solid bodies or particles may be from 2 to 10 L of liquid medium, in particular from 4 to 7 L, per 5 to 15 kg of electrically conductive particles, in particular from 6 to 11 kg. Such proportion has been found to work particularly well for combinations further comprising abrasive particles as described herein.As mentioned, in particular embodiments, a conductive liquid medium may comprise a first conductive phase which may be selected from conductive solutions or conductive emulsions.

[0160] Conductive solutions present in a first conductive phase, according to some embodiments, may comprise aqueous solutions presenting a certain presence of ions in the medium, such as NaCI or hydronium. In order to enhance conductivity, additional ionic species may be introduced, including both inorganic and organic electrolytes, within concentration ranges typical of electrolyte solutions or below their standard values to maintain stability and compatibility with other components. Suitable inorganic electrolytes may include sodium chloride (NaCI), potassium chloride (KCI), lithium chloride (LiCI), sodium sulfate (Na2SO4), potassium sulfate (K2SO4), and ammonium sulfate ((NH4)2SO4), which can contribute to ionic strength and improve charge transport properties within the solution.

[0161] In addition to neutral salts, acids may be incorporated to further modulate conductivity. These may include strong acids such as sulfuric acid (H2SO4), hydrochloric acid (HCI), nitric acid (HNO3), and phosphoric acid (H3PO4), which can increase the presence of hydronium ions (H3O+) in the medium, significantly boosting conductivity. Organic acids, including acetic acid, citric acid, and oxalic acid, may also be employed at controlled concentrations to fine-tune pH and ionic characteristics without causing excessive reactivity with other system components.

[0162] Furthermore, sulfonic acids with hydrocarbon chains may be introduced to further enhance conductivity while maintaining compatibility with other surfactants and ionexchange resins. These may include alkylbenzene sulfonic acids such as dodecylbenzene sulfonic acid, toluene sulfonic acid, and methane sulfonic acid, which contribute to ionic conductivity while preserving the stability of the medium. The concentrations of these acids and electrolytes may typically range from values below 0.01 M up to concentrations found in standard electrolyte solutions, depending on the desired balance between conductivity, chemical stability, and interaction with other active components in the system.

[0163] In some embodiments, the combination of these ionic species with ethoxylated carboxylic acids, non-ethoxylated carboxylic acids, fatty alcohols, and ethoxylated fatty alcohols, such as isotridecanol ethoxylated with three moles of ethylene oxide (isotridecanol 3EO), can contribute to an optimized conductive medium. The overall formulation may be adjusted to achieve specific conductivity targets while ensuring compatibility with the resins of choice ,e.g., sulfonic ion-exchange resins, preventing undesired neutralization or precipitation reactions.

[0164] Conductive solutions present in a first conductive phase, according to some embodiments may comprise a solution of ethoxylated carboxylic acids, non-ethoxylatedcarboxylic acids, fatty alcohols, and water in proportions ranging from 7:3 to 3:7 in wt. Among the ethoxylated carboxylic acids, ethoxylated oleic acid may be included along with other ethoxylated fatty acids such as ethoxylated stearic acid, ethoxylated lauric acid, and ethoxylated myristic acid. Non-ethoxylated carboxylic acids may include oleic acid, stearic acid, lauric acid, and myristic acid, while fatty alcohols such as cetyl alcohol, stearyl alcohol, and lauryl alcohol may also be present within the specified proportion range. Additionally, ethoxylated fatty alcohols, such as isotridecanol ethoxylated with three moles of ethylene oxide (isotridecanol 3EO), may be included to modify the physicochemical properties of the solution, contributing to improved solubility, emulsification, and surface activity.

[0165] Since a 1 :1 wt. solution of ethoxylated oleic acid and water alone is not significantly conductive, in some embodiments, an ionic surfactant may be introduced to enhance conductivity without interfering with other system components. To ensure compatibility with systems utilizing, e.g., a sulfonic acid-based ion-exchange resin, preferably the selected ionic surfactant should not chemically neutralize or strongly interact with the resin’s functional groups. In this context, anionic surfactants such as sodium dodecyl sulfate, ammonium lauryl sulfate, and sodium laureth sulfate may be employed to enhance conductivity while maintaining chemical stability with the sulfonic acid groups of the ionexchange resin. In cases where only surface tension reduction is required without increasing conductivity, nonionic surfactants such as ethoxylated alcohols, polysorbates, or ethoxylated fatty acids may be utilized.

[0166] In some embodiments, the conductivity of the liquid medium may be further enhanced by incorporating sulfonic acids with hydrocarbon chains. These sulfonic acids, which may include alkylbenzene sulfonic acids, dodecylbenzene sulfonic acid, or linear alkyl sulfonic acids, can contribute to the ionic charge density of the solution, increasing overall conductivity while maintaining compatibility with the ion-exchange resin. The concentration and selection of sulfonic acids may be adjusted to optimize conductivity without causing undesirable interactions with other system components.

[0167] In some embodiments, the conductive liquid medium may further include additional electrolytes or conductive additives to optimize performance based on application-specific requirements. The precise formulation may be adjusted depending on the desired balance between conductivity, stability, and interaction with the ion-exchange resin, ensuring that the solution remains effective within the defined range of component proportions.

[0168] As mentioned, in particular embodiments, a conductive liquid medium may comprise a second non-conductive phase which may be selected from hydrocarbons, organic solvents, water immiscible solvents, organic compounds, essential oils, silicone and silicone oils, and fluorinated solvents, and emulsions, among others. They can be used alone or in combination with each other.Hydrocarbons may be particularly selected from C5-C30 hydrocarbons, more in particular from C6-C16 hydrocarbons.

[0169] Water immiscible solvents and organic compounds may be selected from, for example, aliphatic alcohols like 1 -octanol, organic carbonates like propylene carbonate, ethylene carbonate, among others.

[0170] Silicones and silicone oils as described herein, are understood to be those oligomers, polymers, cycles or other structures that include O- Si bonds in their main chain. Silicone oils may include dimethylsiloxane units -OSi(Me2)- as well as cyclic ones such as hexamethylcyclotrisiloxane, in particular polydimethylsiloxanes may be used.

[0171] Fluorinated solvents are understood as solvents that incorporate at least one fluorine atom in their chemical structure and may include fluorinated and perfluorinated fluids.

[0172] The conductive medium can be composed of various elements or combinations thereof, including gases, such as air, aliphatic chains, surfactants, polar solutions, acids, fatty acids, fatty alcohols, ethoxylated alcohols, and organic molecules containing phosphonic, nitric, or amino groups, along with electrolytes.

[0173] In specific embodiments, the medium comprises between 50% to 20% by weight of a fatty acid ranging from C8 to C40, such as oleic acid; between 0% to 80% by weight of a non-conductive aliphatic chain solution, such as C8 to C16 hydrocarbons; between 5% to 60% by weight of a polar solution, such as water; between 1% to 20% of an electrolyte, such as 70% methanesulfonic acid; and between 0.1% and 10% of an ionic surfactant, such as dodecyl benzenesulfonic acid (DBS).

[0174] In accordance with a third aspect of the present invention, a part having a surface treated by the disclosed method is provided. In certain embodiments, the invention comprises a part with a surface that has been finished using the ion transport process described herein, resulting in a homogeneously polished surface with a roughness (Ra) below 1 micrometer. The treated surface exhibits a dispersion of roughness values lower than 10% across all treated areas, ensuring a uniform finish.

[0175] In some embodiments, the surface roughness (Ra) of the part decreases from an initial value above 3 micrometers to below 1 micrometer in less than one hour of treatment, while maintaining the homogeneity criteria across all treated surfaces. This rapid and uniform reduction in roughness enhances the surface quality and functional properties of the part, making it suitable for applications requiring high precision and smooth finishes.

[0176] A fourth aspect of the present invention comprises an apparatus for finishing a surface by ion transport is provided. The apparatus comprises at least two electrodes, including an anode and a cathode, wherein at least one surface to be treated is coupled to one of the electrodes. The apparatus further includes a Conductive Suspension Electrolyte (CSE) that electrically connects the at least two electrodes. The CSE consists of a set offree electrically conductive solid bodies suspended within a medium that comprises a conductive fluid. The medium is characterized by a conductivity that is significant relative to the set of free solid bodies. During operation, the electrically conductive solid bodies facilitate an ion exchange process upon contact with the surface to be treated, thereby enabling the finishing of the surface.

[0177] In some embodiments, the apparatus may further comprise a motion-inducing mechanism to generate turbulence within the medium. This turbulence prevents the formation of a continuous and stable chain of direct contact between the solid bodies. Instead, the medium is configured to provide sufficient ion connectivity between the set of solid bodies, ensuring the effective transport of ions between the electrodes. Additionally, the apparatus includes an electrical coupling mechanism that allows the electrodes to be electrically connected through a non-direct physically contacting bridge of solid bodies. This configuration ensures the omic contact between the solid bodies forming the bridge, thereby maintaining controlled ion transport and optimizing the surface finishing process.

[0178] In some embodiments a motion-inducing mechanism to generate turbulence within the medium includes means to generate agitation, stirring, pumping, and vibration. Thereby, and without being bound to any theory, a non-continuous and stable chain of direct contact between particles electrically connecting the two electrodes is favoured.

[0179] EXAMPLES

[0180] Several objects made out of different materials were subjected to a surface treatment by the following general method, according to an embodiment according to Figure 3:

[0181] - holding the object with a moving arm and connecting the object to a pole of an electric source (303),

[0182] - connecting a meshed platinated titanium cathode (307), inside a container (307) comprising particles (305) in a medium (306), to the opposite pole of the electric source;

[0183] - immerging the object (303) into a container contained in a medium, whereby the object was completely covered by a CSE;

[0184] - providing turbulence to the medium by the help of an apparatus (308).

[0185] - optionally 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; and

[0186] - the object was removed from the particles, to provide a surface treated object.

[0187] Example 1 :

[0188] The CSE used on the example represented on Figure 3 comprises:o 74 % in volume (700 L) of electrically conductive particles made of:

[0189] • 98 % wt. of spherical particles with a heterogeneous particle size distribution ranging between 0.3 - 1.1 mm in diameter of sulfonated gel styrene divinylbenzene particles in an acid format after being dried up to get a constant moisture of 35 - 45 wt. % with respect to the total weight of the solid bodies.

[0190] • 2 % of methanesulfonic acid at a concentration of 70% wt.

[0191] o 26 % in volume (243 L) of a conductive medium made of:

[0192] • 73,8 % wt. of hydroseal: a mixture of aliphatic hydrocarbons with a carbon chain between 12-15 C containing less than 2% of aromatic groups, and 2.7% by weight of octanoic acid 90 - 99 % purity.

[0193] • 1 ,48 % wt. of ethoxylated alcohol with an ethoxylation of 2,5 mol and 10 carbons.

[0194] • 25.75% wt. of water

[0195] • 2.08 of methanesulfonic acid at a concentration of 70% wt.

[0196] • 0,74 % wt. of sodium natural sulfonate.

[0197] • 0.27 % wt. of oleic acid

[0198] • 0.08 % wt. of dodecylbenzene sulfonic acid

[0199] In this particular embodiment the container (307) is a cube of a size of 1m. In other possible configurations of the inventions, the container adopts other shapes and sizes.

[0200] The deepness under which the apparatus for providing turbulent relative motion (308) between free electrically conductive solid bodies within a medium (306) is allocated is 1 m. The deepness can be adjusted in order to control the turbulence. In a particular embodiment it is located at the bottom of the receptacle, in others between a profundity of 50 % and 90 % with respect to the height of the surface, more in particular between 70 % and 80%

[0201] The apparatus for providing turbulent relative motion (308) between free electrically conductive solid bodies within a fluid, in some particular embodiments is a turbine, but it can be any other possible system. A turbine can be configured between 10 - 200 RMP, particularly between 30 - 100 RMP, and more in particular between 50 - 70 RPM.

[0202] The polished par on the example is a cube of 11 cm of diameter, made out of tool steel. The used parameters are a DC at 30 V, with a current of 5 A. After a polishing process of 90 min, the roughness has been decreased homogeneously from Ra = 1 ,5 pm to a Ra = 0,7 pm.In different realizations of the invention, other electrical parameters or polarities can be used to achieve de desired result.

[0203] Example 2:

[0204] A CSE used on the present example comprises:

[0205] o 74 % in volume (700 L) of electrically conductive particles made of:

[0206] • spherical particles with a heterogeneous particle size distribution ranging between 0.3 - 1.1 mm in diameter of sulfonated gel styrene divinylbenzene particles in an acid format after being dried up to get a constant moisture of 51 wt. % with respect to the total weight of the solid bodies.

[0207] o 26 % in volume (243 L) of a conductive medium made of:

[0208] • 40 % in volume of oleic acid ethoxylate with an average of 4 ethylene oxide (EO) units per mole of oleic acid.

[0209] • 40% in volume of deionized water

[0210] • 20% in volume of methanesulfonic acid at a concentration of 70% wt. The conductivity of the obtained liquid is 129.5 mS / cm and the conductivity of the overall mixture is 158.6 mS / cm.

[0211] In particular embodiments the concentration of the used sulfonic acid ranges from 5% to 70% in wt., preferably from 10% to 30% wt., in particular from 15% to 25% wt.

[0212] In this particular embodiment the container (307) is a cube of a size of 1m. In other possible configurations of the inventions, the container adopts other shapes and sizes.

[0213] The deepness under which the apparatus for providing turbulent relative motion (308) between free electrically conductive solid bodies within a medium (306) is allocated is 1 m. The deepness can be adjusted in order to control the turbulence. In a particular embodiment it is located at the bottom of the receptacle, in others between a profundity of 50 % and 90 % with respect to the height of the surface, more in particular between 70 % and 80%

[0214] The apparatus for providing turbulent relative motion (308) between free electrically conductive solid bodies within a fluid, in some particular embodiments is a turbine, but it can be any other possible system. A turbine can be configured between 10 - 200 RMP, particularly between 30 - 100 RMP, and more in particular between 50 - 70 RPM.

[0215] The polished par on the example is a cube of 11 cm of diameter, made out of tool steel. The used parameters are a DC at 5 V, with a current of 10 A. After a polishing processof 30 min, the roughness has been decreased homogeneously from Ra = 2,5 pm to a Ra = 1,2 pm.

[0216] In different realizations of the invention, other electrical parameters or polarities can be used to achieve the desired result.

[0217] Example 3

[0218] Several objects made of different materials were subjected to a surface treatment according to an embodiment of the present invention, as represented in Figure 3, 4 and 5, using the following general method:

[0219] • holding the object (303) with a moving arm and connecting the object to a pole of an electric source (301);

[0220] • connecting a cathode (302) comprising a mesh of platinated titanium, positioned inside a container (307) containing electrically conductive particles (305) suspended in a medium (306), to the opposite pole of the electric source;

[0221] • immersing the object (303) into the container, whereby the object was completely covered by the Conductive Suspension Electrolyte (CSE);

[0222] • providing turbulence to the medium by the help of an apparatus (308) for generating relative motion between the free electrically conductive solid bodies and the fluid of the medium;

[0223] • optionally moving the object inside the particles, thereby allowing repeated contact of the particles with the surface of the object for a predetermined time; and

[0224] • removing the object from the particles to obtain a surface-treated object.

[0225] In this embodiment, the CSE comprised:

[0226] o 67.35% in weight (500 g) of electrically conductive particles, consisting of:

[0227] spherical particles with a heterogeneous particle size distribution ranging from 0.3 - 1.1 mm in diameter, formed of sulfonated gel styrene- divinylbenzene in an acid format, dried to a constant moisture content of 51 wt% relative to the total weight of the solid bodies;

[0228] o 32.65% in weight (242.4 g) of a liquid medium, consisting of:

[0229] 82.51% in weight of hydroseal, a mixture of aliphatic hydrocarbons with a carbon chain of 12-15 C and less than 2% aromatic groups;

[0230] 12.21% in weight of methanesulfonic acid at a concentration of 70% wt.;4.62% in weight of hexanoic acid (>98% purity);

[0231] 0.66% in weight of dodecylbenzene sulfonic acid.

[0232] In this particular embodiment, the container (307) was configured as a prism measuring 0.28 m in length, 0.18 m in width, and 0.15 m in height. In other embodiments, the container may assume different shapes and sizes according to processing requirements.

[0233] The apparatus providing turbulent relative motion (308) between the free electrically conductive solid bodies and the fluid was a rotating paddle positioned at the bottom of the container. The paddle moved from side to side to ensure uniform turbulence and equitable flow across all surfaces of the workpiece, promoting consistent particle-surface contact.

[0234] The treated object in this example was a cube of 11 cm edge length made of tool steel. A direct current of 30 V and 5 A was applied for 90 minutes. Following the treatment, the surface roughness of the workpiece decreased homogeneously from Ra = 1.5 pm to Ra = 0.7 pm.

[0235] In alternative realizations of the invention, different electrical parameters, polarities, container geometries, or particle-to-medium ratios may be employed to achieve desired surface finishing characteristics.

Claims

CLAIMS1. A method to finish a surface by ion transport, comprising the steps of:applying an electric potential difference between at least two electrodes, an anode and a cathode, wherein at least one surface to be treated is coupled to one of the electrodes;connecting the at least two electrodes with a Conductive Suspension Electrolyte (CSE);wherein the CSE includes a set of free electrically conductive solid bodies in a medium comprising a conductive fluid, characterized in that the medium presents a significant conductivity with respect to the set of free solid bodies; and contacting the surface to be treated with the set of free electrically conductive solid bodies producing upon contact an ion exchange between the surface to be treated and the set of free electrically conductive solid bodies, and thereby finishing the at least one surface.

2. The method of claim 1 wherein the medium presents a conductivity of at least 10% of the conductivity of the set of free electrically conductive solid bodies, preferably at least 25 %, and more preferably at least 30%.

3. The method according to claim 1 or 2, wherein the conductivity of the medium is higher than that of the solid bodies, and the medium and / or CSE further comprises a non-conductive fluid.

4. The method according to any one of the preceding claims further comprising inducing motion or turbulence to the medium, in particular by agitation, stirring, pumping, and vibration.

5. The method according to claim 4 comprising inducing motion or turbulence to the medium characterized by Reynolds numbers from 102to 107in the CSE.

6. The method according to any one of the preceding claims wherein the CSE comprises- a set of solid bodies comprising between 10 - 80 % wt, of a first polar solution retained within the resin, the % wt. based on the total weight of solid bodies and the first polar solution - a mediumcomprising from 10 to 50 % wt. of the conductive fluid, preferably the conductive fluid being a second polar solution, based on the total weight of the medium; and optionally further comprising from 0 to 80 % wt. surfactants and / or an apolar solution between, based on the total weight of the medium.

7. The method according to any one of the preceding claims, wherein the conductivity of the medium is equal to or lower than the conductivity of the solid bodies.

8. The method according to any one of the preceding claims, wherein the conductivity of the medium measured without the free solid bodies is from 10 % to 100 %, in particular from 25% to 75 %, more in particular from 30% to 60% of the conductivity measured CSE, at rest and at room temperature.

9. The method according to any one of the preceding claims, wherein the conductivity reading of the CSE and the medium, at rest and at room temperature, does not change its value through a period of 5 minutes in a percentage of 10% higher or lower to the original one.

10. The method according to any one of the preceding claims, wherein the medium comprises an emulsion.

11. The method according to claim 10, wherein the emulsion comprises a conductive fluid and a non-conductive fluid.

12. The method according to claim 11, wherein the non-conductive fluid is immiscible with the conductive fluid.

13. The method according to any one of claims 10 to 12, wherein the emulsion is an apolar-in-polar (A / P) type emulsion.

14. The method to any one of claims 10 to 13, wherein the emulsion is polar-in-apolar (P / A) type emulsion.

15. The method according to claim any one of the preceding claims, wherein the electric potential difference is applied as a DC current.

16. The method according to any one of the preceding claims, wherein the electric potential difference applied as an AC current, preferably with a frequency equal or higher than 1 KHz.

17. The method according to any one of the preceding claims, wherein the electrically conductive solid bodies retain an electrolyte liquid.

18. The method according to any of the preceding claims, wherein the electrically conductive solid bodies comprise porosity and / or affinity to retain an electrolyte liquid to make them electrically conductive.

19. The method according to any one of the preceding claims, wherein the electrically conductive solid bodies comprise a cationic ion exchange resin retaining an electrolyte liquid, preferably comprising MSA from 0.1 % to 70 % Wt, in particular between 1 % to 70 % Wt.

20. The method according to any one of the preceding claims, wherein the medium comprises or is composed by an element or a combination of elements selected from: air, aliphatic chains, surfactants, polar solution, acids, fatty acids, fatty alcohols, ethoxylated alcohols, organic molecules comprising phosphonic groups, organic molecules comprising nitric groups, organic molecules comprising aminos groups and electrolytes.

21. The method according to any one of the preceding claims, wherein the medium comprises or is composed by:between 80 % to 20 % Wt. of a fatty acid between or ethoxylated fatty acid C8 to C40, such as oleic acid or oleic acid EO4;between 0 % to 80 % Wt. of a non-conductive aliphatic chains’ solution, such as C8 to C16;between 5 % to 60% wt. of a polar solution, such as water;between a 1 % to 20 % of an electrolyte, such as MSA at 70% wt; and between 0.1 and 10 % of an ionic surfactant, such as DBS.

22. The method according to any one of the preceding claims, wherein the electric potential difference is applied as a galvanic pulse or a sequence of galvanic pulses having a duration lower than the time thm (503).

23. The method according to any one of the preceding claims, wherein the conductive fluid comprises a polar solvent, preferably selected from: protic solvents, aprotic solvents, deep eutectic solvents, or combinations thereof; and ionic species, preferably selected from: metal cations, inorganic anions, organic anions, supporting electrolyte cations, or complexed ions.

24. The method according to claim 23, wherein the free solid bodies retain a polar liquid having a chemical composition different from the polar solvent of the conductive fluid.

25. The method according to any one of the preceding claims, wherein the medium further comprises an organic moderative phase selected from hydrocarbons, silicone fluids, fluorinated solvents, aromatic oils, ester oils, or bio-based oils.

26. The method according to any one of the preceding claims, wherein the medium further comprises at least one surfactant selected from anionic, cationic, non-ionic, or zwitterionic surfactants.

27. A method for surface finishing through ion transport using a Conductive Suspension Electrolyte (CSE), comprising:applying an electric potential difference between at least two electrodes (101), comprising an anode (102) and a cathode (103), wherein at least one surface to be treated is electrically coupled to one of the electrodes;connecting the at least two electrodes with the CSE, wherein the CSE comprises a medium which is a liquid phase and a plurality of free solid bodies (105) suspended therein;applying the electric potential difference as a pulsed or alternating electrical excitation; andproducing a relative motion between the free solid bodies and the surface to be treated such that ion exchange occurs upon contact;wherein the medium has a dynamic viscosity from 0.01 Pa s to 5 Pa s; wherein the liquid phase has an electrical conductivity equal to or greater than that of the plurality of free solid bodies; wherein the plurality of free solid bodies comprises ionexchange and / or dielectric particles retaining a conductive solution.

28. The method according to any one of the previous claims, wherein the electrical conductivity of the medium is from 5 mS / cm to 500 mS / cm, preferably from 20 mS / cm to 200 mS / cm.

29. The method according to any one of the previous claims, wherein the electrically conductive free solid bodies have an electrical conductivity from 1 mS / cm to 100 mS / cm, preferably from 10 mS / cm to 50 mS / cm.

30. The method according to any one of the previous claims, wherein the electrically conductive free solid bodies exhibit a dielectric constant from 3 to 20.

31. The method according to any one of the previous claims, wherein the electrically conductive free solid bodies exhibit an ion-exchange capacity from 1 eq / L to 5 eq / L, preferably from 2.2 eq / L to 4 eq / L.

32. The method according to any one of the preceding claims, wherein the electric potential difference is applied as a pulsed or alternating electrical excitation, preferably having a frequency from 10 kHz to 1 MHz, preferably from 50 kHz to 300 kHz.

33. The method according to claim 32, wherein the electric potential difference is applied as a pulsed electrical excitation and the pulsed electrical excitation comprises pulse durations from 100 ns to 10 ms, preferably between 1 ps and 1 ms.

34. The method according to claim 32 or 33, wherein the electric potential difference is applied as a pulsed electrical excitation and the duty cycle of the pulsed electrical excitation is between 5 % and 95 %, preferably between 20 % and 80 % relative to the pulsed electrical excitation.

35. The method according to any one of claims 27 to 34, wherein the relative motion between the free solid bodies and the surface to be treated is produced by agitation, stirring, pumping, vibration, or induced turbulence.

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