Organic compounds comprising hydrophilic groups, such as fatty acids and alcohols for the surface finishing of objects

Abstract

The present disclosure relates to the field of object surface finishing. More particularly, the disclosure relates to methods for surface finishing of objects and objects with surfaces finished with such methods. More in particular, the present disclosure relates to the use of organic compounds comprising hydrophilic groups for the surface finishing of objects, in particular using electrically conductive particles. Organic compounds comprising hydrophilic groups may be selected from organic compounds comprising carboxyl groups (e.g., fatty acids); hydroxyl groups (e.g., alcohols); sulfonic, sulfate, sulfone or thiol groups; nitro or nitrate groups; phosphate groups; and / or amine groups.

Description

[0001] ORGANIC COMPOUNDS COMPRISING HYDROPHILIC GROUPS, SUCH AS FATTY ACIDS AND ALCOHOLS FOR THE SURFACE FINISHING OF OBJECTS

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to the field of object surface finishing. More particularly, the disclosure relates to methods for surface finishing of objects and objects with surfaces finished with such methods. More in particular, the present disclosure relates to the use of organic compounds comprising hydrophilic groups, such as fatty acids, alcohols, and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, for the surface finishing of objects, in particular using electrically conductive particles.

[0004] BACKGROUND

[0005] Different systems for surface finishing, smoothing, polishing and other finishing of surfaces of objects are known.

[0006] For example, electropolishing methods (also known as electrochemical polishing, anodic polishing, or electrolytic polishing) have been long used for removing material from a workpiece, typically a metallic workpiece, by applying a certain voltage to the workpiece which can be made particularly high at the edges or tips thereof, so that at those edges or tips the unwanted projections are burned off by small arcs. Other electropolishing methods may comprise immersing a metal part in an electrolyte bath and polishing upon application of an electric potential difference. Some electropolishing methods have been described using electrically conductive particles. Reference is made to, for instance, the International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1), which describes a method for smoothing and polishing metals via ion transport by means of free solid bodies, and the solid bodies that are electrically conductive for carrying out said method. Reference is also made to the International Application No. PCT / ES2021 / 070065 (published as WO 2022 / 123096 A1) which describes the treatment of metallic surfaces and refers to an electrolytic medium comprising solid particles and a non-conductive fluid, the process that uses said medium, and the device for carrying out the process.

[0007] There is a need for new methods for surface finishing that assist in modulating the surface finishing and / or adapting them to the needs of specific finishes and / or objects and materials to be surface finished. For instance, there is a need for a more homogeneous surface finishing for heterogeneous surfaces containing different materials, e.g., different metals, that may react differently to surface finishing processes resulting in uneven finishes. SUMMARY

[0008] It has now been found that organic compounds comprising hydrophilic groups, such as carboxyl groups (e.g., fatty acids); hydroxyl groups (e.g., alcohols); sulfonic, sulfate, sulfone or thiol groups; nitro or nitrate groups; phosphate groups; and / or amine groups, may be useful additives in surface finishing processes and, in particular, electropolishing methods using electrically conductive particles. For instance, as described in more detail below, the use of an organic compound comprising hydrophilic groups, such as a fatty acid and / or an alcohol (in particular glycols such as ethylene glycol) may contribute to modulating the surface finishes to achieve specific desired finishes and to work on specific objects and / or materials to be surface finished.

[0009] Accordingly, the present disclosure relates to the use of organic compounds comprising hydrophilic groups, such as fatty acids, alcohols and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, preferably fatty acids and alcohols, and more preferably fatty acids, for surface finishing at least one surface of an object. In particular it relates to a method for surface finishing at least one surface of an object, using a medium comprising a plurality of electrically conductive particles the medium further comprising a fluid, wherein the fluid comprises an organic compound comprising hydrophilic groups, such as a fatty acid and an alcohol, or other organic compounds comprising hydrophilic groups as described above and, in more detail, below. The present disclosure also relates to an object comprising one or more surfaces that are surface finished with such a method; an object comprising one or more surfaces that are surface finished, wherein at least one surface of the one or more surfaces has, in the entire at least one surface, an average roughness value Ra less than or equal to 80 nm, preferably less than or equal to 60 nm, more preferably less than or equal to 50 nm.

[0010] A fluid for use in a method as described above, also referred to as an electrolyte, including an organic compound comprising hydrophilic groups may contribute to the formation of a resistive protective layer on the surface of the object (e.g. a metal surface) being treated and thereby contributing to achieve better control over the surface finished product, obtained as a result of the surface finishing treatment. In some embodiments the organic compound comprising hydrophilic groups comprises carboxyl groups and / or hydroxyl groups, and may be particularly selected from a fatty acid and an alcohol. In other embodiments, the organic compound comprising hydrophilic groups is selected from organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups. In some preferred embodiments the organic compound comprising hydrophilic groups comprises carboxyl groups, and more preferably is a fatty acid. The present disclosure also relates to a fluid comprising said organic compound comprising hydrophilic groups as defined above and in more detail below.

[0011] The present disclosure also relates to a medium comprising said fluid and a plurality of electrically conductive particles, as also defined above and in more detail below.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] T o 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:

[0014] Figure 1 : Example of an electropolishing method, including methods described in WO 2017 / 186992 A1.

[0015] Figures 2A and 2B: Illustrations of the application of an alternate voltage and / or current on the object to be surface finished in the presence of a fatty acid.

[0016] Figure 3: Surface of an aluminum sheet before (A) and after (B) the surface finishing treatment of Example 2.

[0017] Figure 4: External surface of a carbonated steel gear before (A) and after (B) the surface finishing treatment of Example 3.

[0018] Figure 5: Possible configurations of the ethylene glycol molecule (configurations n = 1 , 2, 3 and 4) in an electric field (E), each configuration n with its dipole moment (p) and frequency (fn).

[0019] Figure 6: Migration of ethylene glycol molecules in an electric filed (E), and formation of an ethylene glycol layer on a surface to be surface finished.

[0020] DETAILED DESCRIPTION

[0021] As indicated above the instant disclosure relates to a method for surface finishing at least one surface of an object, using a medium comprising a plurality of electrically conductive particles the medium further comprising a fluid, wherein the fluid comprises an organic compound comprising hydrophilic groups, such as organic compounds comprising carboxyl groups (e.g. a fatty acid) and hydroxyl groups (e.g., an alcohol such as ethylene glycol), and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups.

[0022] Methods for surface finishing using a plurality of electrically conductive particles have been described in the art. Reference is made to, for instance, the International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1), which describes a method for smoothing and polishing metals via ion transport by means of free solid bodies, and the solid bodies that are electrically conductive for carrying out said method. Such an example of an electropolishing method is illustrated in Figure 1. In such an example the method may comprise, e.g., the connection of the parts 1 , e.g., a metal part, to the positive pole of a current generator, by means of a securing element 2 associated with a device, and the subjecting thereof to friction with particles 4 of free solid bodies which are electrically conductive and included in a receptacle 3 with a gaseous environment occupying the interstitial space 5, and which contact electrically with the negative pole (cathode) of the current generator, via the receptacle 3 directly or via a ring acting as a cathode. The solid bodies may be particles 4 with the porosity and affinity to retain electrolyte liquid, e.g., below the saturation level, and have an electrical conductivity. Reference is also made to the International Application No. PCT / ES2021 / 070065 (published as WO 2022 / 123096 A1) which describes the treatment of metallic surfaces and refers to an electrolytic medium comprising solid particles and a non-conductive fluid, the process that uses said medium, and the device for carrying out the process.

[0023] In a method as described herein known methods have been modified by using an organic compound comprising hydrophilic groups, such as organic compounds comprising carboxyl groups (e.g., a fatty acid) and / or hydroxyl groups (e.g., an alcohol) and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, in particular a fatty acid and / or an alcohol, in the medium comprising electrically conductive particles. In a method as described herein the plurality of electrically conductive particles in the medium bear the weight of interacting with the surface of the object to achieve the surface finishing as previously described. However, the presence of the organic compound comprising hydrophilic groups such as a fatty acid, an alcohol and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, has been found to modulate the interaction of the electrically conductive particles with the surface of the object to be surface finished.

[0024] In particular, a method for surface finishing at least one surface of an object as described herein, may comprise: submerging the object in a medium comprising a plurality of electrically conductive particles such that the at least one surface is in contact with the medium; and at least while the object is submerged applying a voltage and / or a current to the object; and producing relative movement between the at least one surface and the plurality of electrically conductive particles in the medium; the object being electrically connected with a first pole of at least one electric source; the electrically conductive particles and / or the medium containing the electrically conductive particles and / or a container containing the medium being electrically connected with a second pole of the at least one electric source; the medium further comprising a fluid, wherein the fluid comprises an organic compound comprising hydrophilic groups such as a fatty acid, an alcohol and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, in particular a fatty acid and / or an alcohol.

[0025] An organic compound comprising hydrophilic groups may be an organic compound comprising a carboxyl group (such as a fatty acid) and / or a hydroxyl group (such as an alcohol). The fatty acid may be selected from C3 to C50 fatty acids, e.g., C4 to C50 fatty acids in particular from C6 to C30 fatty acids, more in particular from C8 to C28 fatty acids. The alcohol may be selected from a C2 to C50 alcohol, in particular a C2 to C10 alcohol, comprising one or more hydroxyl groups. In particular, the alcohol may be a glycol, comprising two hydroxyl groups and may preferably be ethylene glycol. The alcohol may also be a fatty alcohol such as from C4 to C50 fatty alcohols, in particular from C6 to C30 fatty alcohols and more in particular from C8 to C28 fatty alcohols.

[0026] Organic compounds comprising sulfonic, sulfate, sulfone or thiol groups may be selected from sulfonic acids, such as alkylbenzene sulfonic acids and their salts, including sodium dodecylbenzenesulfonate (SDBS) and sodium toluenesulfonate; and sulfate esters and their salts, such as sodium lauryl sulfate (SLS) and ammonium SLS.

[0027] Organic compounds comprising nitro or nitrate groups may be selected from alkyl nitrates, and nitroalkanes, including nitromethane or nitroethane.

[0028] Organic compounds comprising phosphate groups may be selected from aryl phosphates such as triphenyl phosphate (TPP), tricresyl phosphate (TCP); alkyl phosphates such as diethyl phosphate or tributyl phosphate; and phosphate esters such as monoalkyl or dialkyl phosphate esters.

[0029] Organic compounds comprising amine groups may be selected from primary amines such as ethylamine and propylamine; secondary amines such as diethylamine and dipropylamine), and tertiary amines (e.g., triethylamine and tributylamine). In some embodiments the organic compound comprising hydrophilic groups is a fatty acid and / or an alcohol.

[0030] In some other embodiments the organic compound comprising hydrophilic groups is an organic compound comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups.

[0031] Submerging the object in a medium comprising a plurality of electrically conductive particles such that the at least one surface is in contact with the medium, may comprise, e.g. introducing the object into a container, such as a receptacle, a tray and a keg, comprising the medium comprising the plurality of electrically conductive particles. The container may be provided with mixing means, e.g., selected from a stirrer, a rotator, a displacer, a shaker, a vibrator, a propeller.

[0032] Alternatively, submerging the object in a medium comprising a plurality of electrically conductive particles such that the at least one surface is in contact with the medium, may comprise, projecting a medium comprising the plurality of electrically conductive particles onto the object. Projecting the medium may be performed by, e.g., spraying the medium comprising the plurality of electrically conductive particles. Spraying may be performed using a sprayer.

[0033] Applying a voltage and / or a current to the object, may comprise, e.g., connecting the object to be surface treated to a first electrical pole of a current generator and connecting a second pole opposite the first pole to the medium comprising the electrically conductive particles. For instance, the object to be surface treated may be connected to the first pole (e.g., the positive pole) of a current generator, by means of a securing element, and the electrically conductive particles may be included in a container which is in contact electrically with the second pole (e.g., negative pole) of the current generator, via the container directly or via a ring acting as a second pole. As a mode of example, reference may be made to the International Application No. PCT / ES2017 / 070247 (published as WO 2017 / 186992 A1). Alternatively, when submerging is performed by, e.g., projection, applying a voltage and / or a current to the object, may comprise connecting the second pole of the current generator opposite the first pole to a device that transmit the current to the electrically conductive particles, e.g. a beam of electrically conductive particles, supplied from a reservoir in combination with the medium comprising the same and the device projects the electrically conductive particles to the object, thereby closing the electrical circuit. As a mode of example reference may be made to the International Application No. PCT / ES2020 / 070499 (published as WO 2021 / 019121 A1) and Spanish Patent Application No. 202230989 (published as ES 2942541 A1).

[0034] Producing relative movement between the at least one surface and the plurality of electrically conductive particles in the medium may be achieved by moving one or both of the plurality of electrically conductive particles and the at least one surface. The relative movement may be attained by way of any motion, such as displacing, rotating, mixing, stirring, vibrating, shaking, spraying, propelling, sucking, etc.; a plurality of motion types may be combined simultaneously or sequentially to provide linear motion and / or rotational motion.

[0035] A fluid in a medium of a method as described herein may be electrically non- conductive or conductive. In several embodiments the fluid may preferably be non- conductive. The use of non-conductive fluids may advantageously result in the electrical conductivity of the surface polishing system being due to, mostly or totally, the electrically conductive particles. For instance, an electrically non-conductive fluid may have a conductivity of at most 1 pS / cm, in particular at most 0.5 pS / cm, and more in particular at most 0.1 pS / cm.

[0036] It has been found that the presence of an organic compound comprising hydrophilic groups such as a fatty acid and / or an alcohol as described herein may contribute to the fluid to being non-conductive or conductive depending on the form of the organic compound comprising hydrophilic groups, for instance, whether is a fatty acid or an alcohol or the form of the fatty acid, e.g., if used in neutral form or as a salt, and / or the presence of other components in the fluid that may contribute to the conductivity or the non-conductivity of the fluid.

[0037] An organic compound comprising hydrophilic groups as used herein has the meaning commonly used in the art. In particular, it is an organic compound, such as a hydrocarbon, that has one or more hydrophilic groups, also referred to as polar groups, such as a carboxyl, a hydroxyl group, sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, in particular a carboxyl or a hydroxyl group. The organic compound may also have both a hydrophilic and a hydrophobic (lipophilic) group or region. For instance, fatty acids have a polar head (the carboxyl group) that is hydrophilic and an apolar tail that defines a hydrophobic region, including, e.g., aliphatic and aromatic regions. Similarly, glycols such as ethylene glycol and other alcohols such as fatty alcohols, have polar groups (e.g., hydroxyl groups) and apolar groups or regions (e.g., the hydrocarbon parts) each defining hydrophilic and hydrophobic regions. Similarly organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups, in addition to these hydrophilic groups may also have hydrophobic groups or regions (e.g., hydrocarbon parts).

[0038] Fatty acids as used herein has the meaning commonly used in the art. In particular, a fatty acid is understood by a person skilled in the art a carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group. Fatty acids may be naturally occurring or derived from naturally occurring products such as fatty acids derived from esters in fats and oils. Fatty acids may also be synthetic.

[0039] Organic compounds comprising carboxyl groups are compounds known in the art having one or more -COOH groups, in their neutral form or ionic form (e.g., used as a salt), preferably comprising one carboxyl group, such as fatty acids. Fatty acids for surface finishing an object may be used, e.g., in a method as described herein in their neutral form or a salt, e.g. of an alkali or an alkaline earth metal ion. For instance, a fatty acid salt may be selected from a sodium, potassium, calcium and magnesium fatty acid salt. Organic compounds comprising hydroxyl groups are compounds known in the art having one or more -OH groups, preferably comprising one or two carboxyl groups, such as alcohols and mono- or di-alcohols. Alcohols as used herein has the meaning commonly used in the art. In particular, alcohols are hydrocarbons comprising one or more hydroxyl groups as described above, and may be particularly be selected from glycols (such as ethylene glycol) and fatty alcohols (which are similar to fatty acids in that they have a hydrocarbon chain and a terminal hydroxyl group, instead of a carboxyl group of the fatty acids).

[0040] Organic compounds comprising sulfonic, sulfate, sulfone or thiol groups are compounds known in the art, having one or more -S(=O)2-OH groups (also represented as -SO3H) or -OS(=O)2-OH, -S(=O)2-, or -SH, respectively, in their neutral form or ionic form used as, e.g., a salt, preferably comprising one sulfonic, sulfate, sulfone or thiol group. Sulfonic or sulfate groups may be particularly preferred.

[0041] Organic compounds comprising nitro or nitrate groups are compounds known in the art, having one or more -NO2 or -ONO2 groups respectively, preferably comprising one nitro or nitrate group.

[0042] Organic compounds comprising phosphate groups are compounds known in the art, having one or more -OP(=O)O2H2 groups, in their neutral form or ionic form, e.g., used as a salt, preferably comprising one phosphate group

[0043] Organic compounds comprising amine groups are compounds known in the art, and may typically be primary, secondary or tertiary amines, having one or more -NH2, -NH-R or -NR2 groups respectively, in their neutral form or ionic form, e.g., used as a salt.

[0044] Said particular organic compounds comprising hydrophilic groups have been found to work particularly well to modulate surface finishing processes, ensuring better control over the resulting surface quality, compared to other compounds that may also be used in a method as described herein but may not work so well such as ketones, amide groups, or carboxylic acids other than fatty acids (e.g., nitrobenzoic acid).

[0045] Organic compounds comprising hydrophilic groups as described herein can exhibit a wide range of structural diversity, which may influence their functionality within the system and ultimately their effects in the surface finishing method. While linear aliphatic compounds comprising said hydrophilic groups may be typically used, cyclic structures also hold significant potential as effective agents in this context. Cyclic organic compounds comprising hydrophilic groups may offer unique advantages, such as improved stability or specific interaction patterns with the surface being treated. Examples of such compounds include sugars like fructose, glucose, and sucrose, which contain hydroxyl groups and can form protective layers through their unique chemical interactions with the surface of the object to be surface treated (e.g. a metal surface). In a method as described herein, it is notable that organic compounds comprising hydrophilic groups (acting as control, modulating and / or protective agents) may be used as such and have an effect as such or may also derive from a precursor or may have a different effect upon transformation within the system during the execution of the method. For instance, certain compounds, such as sugars (e.g., fructose) may as such have an effect as a compound comprising hydroxyl groups but may also undergo transformations during the process, yielding derivatives like levulinic acid that continue to contribute to the system’s protective functionality. Similarly, esters can undergo hydrolysis, releasing carboxylic acids and alcohols (e.g., glycols) that play a role in maintaining surface integrity and uniformity during electropolishing.

[0046] Combinations of organic compounds comprising hydrophilic groups have also been found to work particularly well. In some embodiments, a combination of a fatty acid and an alcohol may be used. Fatty acids and / or alcohols (e.g., glycols such as ethylene glycol) may also be used in combination with organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups; and / or amine groups. In some embodiments, alcohols (e.g., glycols such as ethylene glycol) may be used in particular combination with organic compounds comprising sulfonic, sulfate, sulfone or thiol groups (e.g. dodecyl benzene sulfonic acid and / or petroleum sulfonic acids or salts thereof). In other embodiments, fatty acids (e.g., oleic acid) may be used in particular combination with organic compounds comprising sulfonic, sulfate, sulfone or thiol groups (e.g. dodecyl benzene sulfonic acid and / or petroleum sulfonic acids or salts thereof). In some embodiments, alcohols (e.g., glycols) may be used in combination with organic compounds comprising nitro or nitrate groups. In some embodiments, fatty acids and / or alcohols (e.g., glycols such as ethylene glycol) may be used in combination with organic compounds comprising phosphate groups. In some embodiments, organic compounds comprising amine groups may be used in combination with fatty acids, alcohols and / or organic compounds comprising phosphate groups.

[0047] It has been surprisingly found that the use of organic compounds comprising hydrophilic groups such as fatty acids and alcohols and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, and amine groups as described herein, provide a method which allows for a better surface finishing control. For instance, by using an organic compound comprising hydrophilic groups such as a fatty acid and an alcohol and other organic compounds as described herein good results are achieved surface finishing (e.g., polishing) materials which may be susceptible to corrosive evolution during electropolishing. Good results have been observed by reducing the number of defects in the objects to be polished caused by the electropolishing method, providing objects with higher uniformity of the surface finishing. In particular, higher uniformity has been observed in terms of final roughness of the surface finished object, independently of the initial conditions of the surface of the object. Without being bound to any theory this may be attributed to the resistive equalizing resistance of the formed resistive layer as described in more detail below. Furthermore, the use of an organic compound comprising hydrophilic groups such as a fatty acid and / or an alcohol has been found to reach values of roughness which are not possible with other methods, particularly for some materials that have been proven to be difficult. The use of an organic compound comprising hydrophilic groups such as a fatty acid and / or an alcohol has also been found to result in higher efficiency of the polishing process, when compared to, e.g., an equivalent process in the absence of a fatty acid, owing to a reduction of water molecule evolution, resulting in similar mass extraction ratios with lower density currents than those achieved in the absence of fatty acid and / or an alcohol.

[0048] The efficiency (in the units between brackets) may be expressed by the following formula:

[0049] (1) Efficiency [g / C] = m / Q, wherein Am is the mass difference (of the surface treated object prior to and after the surface treatment) in grams (g), and Q is the charge corresponding to the anodic pulse of the current in Coulombs (C), defined by the following integral: wherein l(+) is the current corresponding to the anodic pulse in Amperes (A).

[0050] The higher the g / C the higher the efficiency of the method. In several embodiments, the efficiency of a method as described herein, as determined by formula (1) may be from 10-7to 5 1 O'4g / C, in particular from 10'6to 10'5g / C.

[0051] Furthermore, the presence of an organic compound comprising hydrophilic groups such as a fatty acid and / or an alcohol and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups as described herein may also allow to work with higher voltages when compared to working without the fatty acid. For instance, in a method as described herein the voltage may be from 1 to 120 volts (V), in particular from 10 to 80 V. It has been found that such voltages can be used, without imparting damage to the object to be surface treated, owing to the presence of a fatty acid and / or alcohols as described herein. Being able to work to such voltages may also contribute to the efficiency of a method as described herein and to modulate the surface finishing results achieved with such methods.

[0052] Without being bound to any theory, the advantageous effects of organic compounds comprising hydrophilic groups such as fatty acids and / or alcohols and other organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups in uses and processes as described herein may be linked to their dual polar-nonpolar nature. In particular, as a person skilled in the art would understand, fatty acids have a polar carboxylic acid head and a nonpolar hydrocarbon tail. Similarly, alcohols as described herein such as glycols and fatty alcohols have hydrophilic groups and may also have apolar parts. This confers the organic compounds comprising hydrophilic groups such as fatty acids and / or alcohols with the ability to engage in polar and nonpolar interactions. It is believed that in surface modifying processes, such as methods as described herein, the polar carboxylic acid head of the fatty acid and the hydrophilic hydroxyl group of the alcohols is able to interact with the object to be polished forming coordination bonds on the surface of the object to be polished. Such interactions may be particularly favored for metallic objects.

[0053] Without being bound to any theory, it is believed that the polarity of the carboxylic acid heads of fatty acids as described herein may be sufficiently strong to form said coordinating interactions on the surface of the object to be surface-treated and at the same time sufficiently low to prevent repulsion of the carboxylic acid heads. This would result in the formation of a homogeneous and ordered layer of fatty acids on the surface of the object to be treated that would modulate the surface-treatment to which the object is being subjected to. The layer of fatty acids formed on the object to be surface finished, it is believed to contribute to the modulation of the surface finishing. Such layers may be regarded as protective layers that may contribute to preventing damage caused by the surface finishing process. At the same time such layers may contribute to achieving levels of rugosity that are inferior to those achieved in the absence of the fatty acid, owing to a modulated surface finishing that is able to selectively remove material on the areas of the surface that is most required, e.g., on the peaks rather than the valleys of the surface being treated.

[0054] Similarly, alcohols as described herein such as glycols and in particular ethylene glycol or fatty alcohols, are also believed to interact with the surface of the object to be surface-treated through their hydrophilic groups and forming similar protecting layers described above for the fatty acids, and also having a modulating capacity of the surfacetreatment. For instance, Figure 5 shows possible configurations of the ethylene glycol molecule (configurations n = 1 , 2, 3 and 4) in an electric field (E, 101), each configuration (n) with its dipole moment (p) and frequency (fn). Ethylene glycol has the following structure: HO-CH2-CH2-OH and contains two hydroxyl groups (-OH), which are highly electronegative. These oxygen atoms attract electrons towards themselves, creating an electron density in the regions where the hydroxyl groups are present, forming dipoles in each -OH group. Regarding geometry, the ethylene glycol molecule is not linear and may adopt different configurations as depicted in Figure 5, e.g., configuration 1 (107), configuration 2 (108), configuration 3 (109), and configuration 4 (110) due to the rotation around the carbon-carbon (C-C) and carbon-oxygen (C-O) bonds, including the two depicted gauche conformations (109 and 110), where the two hydroxyl groups (-OH) are in a relatively close position, and may form hydrogen bonds with each other, and the two depicted anti-conformations (107 and 108), in which the two -OH groups are as far apart as possible. This can minimize steric repulsion between the hydroxyls but does not allow the formation of intramolecular hydrogen bonds.

[0055] The oxygen atoms are situated in positions where they can create a net dipole moment. This means that the charge distribution is not symmetrical, and the molecule has regions with partial negative charges near the oxygen atoms and regions with partial positive charges near the hydrogen atoms, generating different dipole moments (p) for each configuration (102, 103, 104, and 105 in figure 5).

[0056] Apart from these two extreme conformations, there are many other possible orientations due to the rotation of the bonds. Each configuration may have its respective frequency of occurrence (fn), f1 for configuration 1 (111), f2 for configuration 2 (112), f3 for configuration 3 (113), and f4 for configuration 4 (114). Additionally, each configuration can vary in energy depending on the interactions between the hydrogen atoms and the functional groups. In absence of an electric field the population of the different configurations will be determined by the energy of each configuration, but may be regarded to be equivalent for all configurations depicted in figure 5 (f1 ~ f2 = f3 ~ f4).

[0057] When an electric field (E, 101) is applied to a collection of molecules, they tend to reorient in response to the field due to the interaction between the dipole moment of the molecules and the electric field. Conformations that present a stronger dipole moment in the direction of the field, such as in figure 5 the dipolar moment of, e.g., configuration 3 (104), maximizes the alignment of the dipoles of the -OH groups (109) with the field and will be favored, and thereby their frequence of occurrence may increase respect to other configurations (e.g., f3 » f 1 , f2, f4), whereas other configurations will be less favored (such as configuration 4) and their frequence of occurrence will be lower (e.g. f4 < f1 , f2, f3).

[0058] This can lead to a predominance of certain conformations over others.

[0059] Such arrangement of the molecules may ultimately lead to migration and formation of an ethylene glycol layer, as illustrated in figure 6, wherein an electrochemical process is represented with a cathode (120), which acts as the negative electrode of the system, and an anode (121), that is the positive electrode and represents the surface of the object to be surface finished (e.g., a metal object to be polished). Between these two electrodes the medium comprising the electrically conducive particles is placed inside of a receptable (122), which medium comprises a fluid which in figure 6 particularly comprises ethylene glycol (123). The ethylene glycol molecules are depicted in various geometric configurations, reflecting their ability to adopt different conformations due to the rotation of their bonds as explained above. When an electric field is applied, the ethylene glycol particles begin to migrate towards the positively charged anode. This migration occurs due to the electrostatic forces acting on the polar molecules in the presence of the electric field. On the surface of the anode, the ethylene glycol molecules form a protective layer (124) created by the electrostatic interactions between the ethylene glycol particles and the anode, serving to protect the surface of the object to be surface treated from excessive chemical attacks during the surface finishing process. Similar to what is described above for the fatty acid, the formation of this layer with ethylene glycol, but also other alcohols as described herein, contributes to maintaining the integrity of the surface of the object and to obtaining a uniform and controlled surface finishing (e.g., polish).

[0060] Furthermore, and still without being bound to any theory, the interaction of such alcohols with the surface to be surface-treated, may be somewhat more subtle than that of fatty acids, as the hydroxyl groups may rely on physical absorption, through electrostatic forces, onto the surface of the object to be surface-treated, whereas the interaction of fatty acids may also have a chemical component. Such weaker interaction of alcohols may be advantageous in some applications, as the alcohols may be removed from the surface more easily than fatty acids. The use of alcohols may also be advantageous, in contrast with fatty acids, in that they do not have an acidic pH, and may be less corrosive which may be of interest for some applications. Furthermore, glycols such as ethylene glycols have good electrical and heat conductivity and miscibility with polar solvents. Also, glycols being smaller than fatty acids and fatty alcohols, may also advantageously be faster in forming said protective layers. Also due to their smaller size have a lower tendency in forming structures such as micelles. Finally, glycols may typically be more viscous and less volatile than fatty acids and fatty alcohols, which may contribute to the effective life-time of the medium, as will have a lower tendency to volatilize upon use. Another advantage of alcohols, and in particular glycols such as ethylene glycol, is that they may be cheaper and may be used in lower amounts than fatty acids.

[0061] In contrast with alcohols, fatty acids may form more robust protective layers which may be advantageous for some applications. Fatty acids may also contribute to the conductivity of the medium favoring the surface-treating process. In view of the differences between fatty acids and alcohols, it may be advantageous to choose one type or another, or any combination thereof, of organic compound comprising hydrophilic groups depending on the final application or desired results.

[0062] Similar effects have been observed for other organic compounds having hydrophilic groups such as organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, or amine groups as described herein. Such other organic compounds have been found to modulate the surface finishing of objects in methods as described herein. Different compounds may offer different particular effects as described above in detail for the fatty acids and alcohols.

[0063] Specific organic compounds comprising hydrophilic groups may be selected for a specific system with a particular type of electrically conductive particles for a specific application or specific material of object to be surface finished, thereby offering further tailoring of the system to achieve enhanced results.

[0064] For instance, organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, which are highly polar, are also capable of forming a protective resistive layer over a surface of the object (e.g., a metal surface) to be surface treated with electrochemical processes such as a method as described herein. In particular, sulfonic acids, such as alkylbenzene sulfonic acids, and their salts, including sodium dodecylbenzenesulfonate (SDBS) and sodium toluenesulfonate, can be effective in surface finishing applications and possess strong acidity, which may contribute to facilitates their interaction with the surface of the object to be surface treated (e.g. metal surface) to create a stable dielectric layer. Additionally, sulfate esters such as sodium lauryl sulfate (SLS) and ammonium sulfate offer similar benefits by forming a resistive protective layer that enhances uniformity in surface treatment. Sulfonic and sulfate-based compounds may be used in combination with alcohols (e.g., glycols, such as ethylene glycol), to buffer their acidic properties, thus preventing excessive etching or corrosion while maintaining their surface protective capabilities. As a particular example, sulfonic, sulfate, sulfone or thiol molecules such as dodecylbenzene sulfonic acid have been used for providing high homogeneous results while achieving Ra roughness values below 100 micrometers, when employed as a primary protective element in methods as described herein.

[0065] Organic compounds including nitro or nitrate groups, also contribute to forming a resistive polarization layer over the surface of the object (e.g. a metal surface) to be surface treated during the electropolishing process such as in a method as described herein. In particular, organic nitrates, such as alkyl nitrates, and nitroalkanes, including nitromethane or nitroethane, are highly reactive and capable of forming thin dielectric layers that protect against localized corrosion. Nitro- or nitrate-based compounds are generally unstable under certain conditions, they can be used in combination with alcohols, glycols, or fatty acids to moderate their reactivity and enhance their ability to form a protective layer without causing undesired reactions with the surface of the object to be surface treated (e.g., a metal surface).

[0066] Organic compounds containing phosphate groups also form a resistive protective layer over the surface of the object (e.g. a metal surface) to be surface treated with an electrochemical process such as a method as described herein. In particular, organophosphates such as triphenyl phosphate (TPP), tricresyl phosphate (TCP), and alkyl phosphates like diethyl phosphate or tributyl phosphate, have highly polar phosphate groups that interact effectively with conductive surfaces (e.g., metal surfaces) to create stable, dielectric layers. These compounds not only enhance surface resistivity but also prevent localized corrosion by providing a uniform protective barrier. Additionally, phosphate esters such as monoalkyl or dialkyl phosphate esters are particularly useful in forming a durable and hydrophilic protective layer. Organic compounds comprising phosphate groups may also be employed in conjunction with glycols, such as ethylene glycol, or fatty acids to balance their reactivity and maintain the electrolyte's stability. Their versatility and effectiveness make phosphates a valuable class of compounds for electropolishing applications and other surface finishing processes.

[0067] Organic compounds containing amine groups can also employed as protective agents capable of forming a resistive layer over surfaces of the object (e.g. a metal surface) to be surface treated with electrochemical processes such as a method as described herein. Amines, such as primary amines (e.g., ethylamine and propylamine), secondary amines (e.g., diethylamine and dipropylamine), and tertiary amines (e.g., triethylamine and tributylamine), exhibit polar characteristics that enable their interaction with, e.g., the metal surface. These interactions contribute to the formation of a stable protective barrier, preventing localized corrosion and enhancing surface uniformity. It has been found that the use of organic compounds with hydrophilic groups such as amines as described herein, may contribute to neutralizing or capturing acidic compounds generated during electrochemical reactions. Their presence may contribute to ensure a balanced chemical environment, enabling the generation of homogeneous results and surfaces free of defects, thereby enhancing the overall quality of the surface finishing process.

[0068] Additionally, organic molecules containing both hydroxyl and amine groups, such as alkanolamines, e.g., monoethanolamine, diethanolamine, and triethanolamine, combine the properties of alcohols and amines, making them particularly effective in buffering the electrolyte while providing protection. These compounds are versatile and can also be used in combination with fatty acids, glycols, or phosphates to further improve the consistency and effectiveness of the resistive layer during electropolishing and surface finishing processes.

[0069] Such protective layer, formed by organic compounds comprising carboxyl groups (e.g., fatty acids) and / or hydroxyl groups (alcohols) and organic compounds comprising sulfonic, sulfate, sulfone or thiol groups, nitro or nitrate groups, phosphate groups, and / or amine groups as described herein as described above, may also be regarded to act as a resistive barrier between the surface of the object to be surface finished and the electrically conductive layer. It may thereby contribute to preventing undesired high current density localizations and reducing defects resulting from the electropolishing surface finishing processes itself.

[0070] Such protective layer may also contribute to making the surface finishing more efficient, in particular with respect to the electrochemical processes as the protective layer may reduce the surface of the object to be surface finished that is connected to a pole that is available for, e.g., water evolution, resulting in non-aeration of the electropolishing process as a consequence of the protective layer requiring less density current to achieve the same mass extraction when compared those obtained in the absence of the fatty acid.

[0071] Furthermore, depending on the material that is surface treated (e.g., aluminum or carbides to name some examples) the presence of a fatty acid as described herein may allow to use surface finishing conditions which would be damaging to the material in absence of the fatty acid.

[0072] In several embodiments the fluid may comprise from 0.1 to 100 wt.% of organic compound comprising polar groups (e.g., hydrophilic groups) such as fatty acid and / or alcohol based and other organic compounds as described herein on the total weight of the fluid component of the medium, in particular from 0.5 to 90 wt.%, more in particular from 1 to 75 wt.%, yet more in particular from 5 to 60 wt.%, and even more in particular from 7 to 50 wt.% of fatty acid and / or alcohol. Such amounts of fatty acid and / or alcohol have been found to provide a good result, presumably owing to a good mobility of the fatty acid and / or alcohol upon application of the current / voltage and as described below good surface coverage of the surface of the object to be surface finished as described above.

[0073] In some embodiments, alcohols (such as ethylene glycol) may be used in particularly low amounts such as from 0.01 to 10 wt.%, in particular from 0.15 to 5 wt.% and more in particular from 0.2 to 1 wt.%, and yet more in particular from 0.25 to 0.5 wt.%. In other particular embodiments alcohols (such as ethylene glycol) may be used in particularly high amounts such as from 20 % to 100%, in particular from 25 to 50 wt.% and more in particular from 30 to 40 wt.%, and yet more in particular from 32 to 35 wt.%. Such high amounts may be particularly adequate, e.g., when working at a high current densities (> 1A / cm2) and / or high working voltages (>100 V), C4 to C50 fatty acids, in particular from C6 to C30 fatty acids, more in particular from C8 to C28 fatty acids, have been found suited in modulating surface finishing processes as described herein. Long chain fatty acids e.g. from C28 to C50, may have nonpolar chains with a tendency to interact with each other and form on the surface of the object to be surface finished that are less uniform. C4 to C7 fatty acids may have increased volatility which may be less suited to work under conditions where they could be inhaled. C8 fatty acids may be particularly preferred as they have been found to result in the advantageous properties whilst having a reduced volatility, thereby reducing the risk of it being inhaled. Nonetheless, other lengths may contribute to further modulating the surface finishing to achieve particularly desired results or for surface finishing specific type of surfaces or materials.

[0074] Alcohols, and ethylene glycol in particular, have been found to achieve good results as described above for fatty acids and particularly good results for carbide surfaces, as they are typically volatile molecules and miscible in water they may present a higher capacity for achieving a uniform protective film along the surface to be surface finished, triggering a bigger uniformity potential than, e.g., that presented by the fatty acid in terms of leveling between the different constituents of the material. Furthermore, as a consequence of the potential higher mobility of alcohols (e.g., ethylene glycol) and the facility, compared to that of the fatty acids, for being removed from the surface to be surface finished, facilitating the surface finishing and the cleaning of the surface finished object. Additionally, in a ceramic- metallic composite material comprising, e.g., tungsten carbide as the ceramic phase and a cobalt alloy as a binder, using of alcohol such as ethylene glycol may reduce the probability to observe regrowing of the cobalt metallic binder caused by, e.g., a remanent ionization on the environment after an electric pulse. In a method as described herein for surface finishing tungsten carbide objects, controlling the acidity of the medium is critical to prevent corrosion defects such as etching. It has been found that the use of organic compounds with hydrophilic groups such as hydroxyls, including alcohols such as fatty alcohols and glycols, may contribute to neutralizing or capturing acidic compounds generated during electrochemical reactions. Their presence may contribute to ensure a balanced chemical environment, enabling the generation of homogeneous results and surfaces free of defects, thereby enhancing the overall quality of the surface finishing process.

[0075] In a method as described herein a combination of organic compounds comprising a carboxyl group and a hydroxyl group (such as a fatty acid and / or an alcohols) may also be used. Under the acidic conditions of an electrochemical surface finishing process as described herein, fatty acids and alcohols may react to form an ester. The esterification reaction is a reversible chemical process where a carboxylic acid, such as a fatty acid, reacts with an alcohol to form an ester and water. This reaction is typically catalyzed by an acid, such as sulfuric acid, sulfonic acids (such as methane sulfonic), nitric acids, HF, HCI, phosphoric acids, etc. that may also be present in the medium. The equilibrium between ester formation and hydrolysis may contribute to providing a dynamic balance, allowing esters to form away from the object to be surface treated and dissociate back into fatty acids and alcohols near the surface of the object (e.g., a metal surface) being electropolished. This dynamic process facilitates the continuous deposition of protective layers, enhancing surface resistivity and preventing localized corrosion. Several parameters may influence the esterification reaction and allow for its precise control. A temperature from 40°C to 60°C, may typically favor a balance between ester formation and dissociation. Agitation or stirring ensures uniform mixing of reactants, promoting consistent reactions throughout the electrolyte. The concentration or molar ratio of the acid to alcohol also shifts the equilibrium; an excess of one reactant can drive the reaction toward esterification or hydrolysis as needed, e.g., to favour certain finishes in a particular object to be treated. Additionally, catalysts such as phosphoric acid can be used to adjust the reaction speed, while the presence or removal of water affects the equilibrium, either favoring ester formation or facilitating hydrolysis. In some embodiments a combination of levulinic acid with ethanol or a combination of octanoic acid with isopropanol may be used. Levulinic acid may esterify with ethanol to produce ethyl levulinate and water, and octanoic acid may esterify with isopropanol to produce isopropyl octanoate and water. Similarly, octanoic acid can react with ethylene glycol, resulting in the formation of mono- or di-esters, such as mono- or di- octanoic acid ethylene glycol ester, and water. These reversible reactions ensure that esters formed in the bulk of the electrolyte can dissociate near the surface being polished, maintaining a steady release of fatty acids and alcohols.

[0076] In some embodiments, organic compounds comprising hydroxyl groups may be polyols which may be cyclic sugars such as sucrose and / or fructose. In a method as described herein, such sugars may undergo hydrolysis. For instance, the hydrolysis of fructose and / or sucrose may take place in the presence of water and an acidic catalyst in an electrochemical surface treating method as described herein. Under such acidic conditions, fructose or sucrose breaks down into hydroxymethylfurfural (HMF), which subsequently undergoes hydration and fragmentation to produce levulinic acid and formic acid. These acids can then participate in esterification reactions with alcohols present in the electrolyte. As described above, levulinic acid can react with ethanol to form ethyl levulinate and water, while formic acid can react with methanol to produce methyl formate and water. Similar to what is discussed above such a chain of reactions provide a dynamic equilibrium where the acids and their esters continuously form and dissociate within the electrolyte. The products and intermediates, such as levulinic acid and formic acid esters, contribute to maintaining a steady release of protective agents near the surface of the object being surface treated (e.g. a metal surface), enhancing the uniformity and quality of the surface finishing process.

[0077] In a method as described herein, comprising organic compounds comprising carboxyl groups and hydroxyl groups that may undergo esterification and hydrolysis as described above, esterification reactions may typically proceed in the bulk of the electrolyte, while hydrolysis may typically occur near the surface being treated (e.g., a metal surface), ensuring a continuous supply of fatty acids and alcohols for surface coverage. This balance enables the formation of a uniform, resistive protective layer that remains consistent throughout the polishing process, significantly improving the quality and efficiency of the electropolishing treatment.

[0078] In a method as described herein the fluid of the medium may further comprise a solvent, in several embodiments one or more solvents may be present. The solvent may be referred to as a first solvent and as a second solvent, independently of whether only one solvent is present, or two solvents are present.

[0079] In several embodiments, in a method as described herein the fluid of the medium may further comprise a first solvent. The first solvent may be polar or nonpolar. The first solvent may preferably be a polar solvent, and more preferably the polar solvent may be water. In several embodiments the water may be deionized water. It has been found that deionized water may advantageously contribute to providing an electrically non-conductive fluid.

[0080] In the presence of a first solvent as described herein and in particular a polar solvent such as water, where the organic molecule comprising hydrophilic groups are fatty acids and / or fatty alcohols, the fatty acids and / or fatty alcohols also may form micelles, upon the interaction of the polar carboxylic acid heads with the of the first solvent, e.g., molecules of water. Depending on the nature and amount of the first solvent, the micelles formed may be different. For instance, where the first solvent is a polar solvent and the amount of a polar solvent such as water is low with respect to the amount of fatty acid and / or fatty alcohol, fatty acids and / or fatty alcohols may encapsulate the polar solvent such as water in the interior of the micelles, the polar heads of the fatty acids also oriented towards the interior in order to interact with the polar solvent and the nonpolar tails pointing outwards to the surface of the micelles. On the other hand, if the first solvent is a polar solvent such as water but the amount of the first solvent is high with respect to the amount of fatty acid and / or fatty alcohol, then the non-polar tails of the fatty acids and / or fatty alcohols may occupy the interior of the micelles and the polar carboxylic heads may interact with the polar solvent such as water on the surface of the micelles. It may be preferred for the micelles to form to encapsulate the first solvent, and in particular a polar first solvent such as water, in the interior.

[0081] The formation of such micelles may contribute to physically separating the first (polar) and second (nonpolar) solvents. Such separation it is believed to contribute to reducing the freedom of movement of the solvents and reduces the entropy of the system, which also advantageously contributes to the efficiency of the surface finishing.

[0082] The formation of such micelles may also contribute to the modulating of the surfacetreatment. For instance, encapsulation of water in the micelles may contribute to make the fluid of the medium less conductive or even non-conductive. Encapsulation of water in the micelles may also contribute to reducing the water evolution in an electrolytic process and increasing the efficiency of the surface finishing.

[0083] In several embodiments, and preferably where the organic compound comprising hydrophilic groups is an alcohol the first solvent may preferably be a polar solvent, e.g., water. In several particular, embodiments the first solvent, e.g., water, may be the only solvent. Where the organic compound comprising, hydrophilic groups is an alcohol, and in particular a glycol such as ethylene glycol, and the fluid comprising a polar solvent such as water as the first solvent (and preferably only solvent), micelles may not be formed.

[0084] In several embodiments the fluid may comprise from 0 to 99.9 wt.% of the first solvent based on the total weight of the fluid component of the medium, in particular from 10 to 99.5 wt.%, more in particular from 25 to 99 wt.%, more in particular 40 to 98 wt.%, yet more in particular from 40 to 95 wt.%, even more in particular from 50 to 93 wt.%, yet even more in particular from 75 to 93 w.t% of the first solvent.

[0085] In several embodiments the fluid may comprise a weight maximum amount of first solvent, e.g., water, with respect to the weight amount of electrically conductive particles. For instance, the weight ratio of the first solvent with respect to the electrically conductive particles may be of at most 0.8:1 , in particular of at most 0.6:1 and more in particular of at most 0.4:1 , wherein the weight of the electrically conductive particles includes the weight of any water or electrolyte contained therein (as discussed in more detail below).

[0086] In several embodiments, in a method as described herein the fluid of the medium may further comprise a second solvent, e.g., instead of the first solvent or in addition to the first solvent. The second solvent may be different from the first solvent, particularly if both the first and second solvent are present.

[0087] The second solvent may be a polar or a nonpolar solvent. In several particular embodiments, the second solvent may be a nonpolar solvent, more preferably may be a nonpolar organic solvent, in particular the second solvent is nonpolar organic solvent selected from selected from polyethylene glycol (PEG) and hydrocarbons, in particular from C4 to C52 hydrocarbons, more in particular from C4 to 050 hydrocarbons, yet more in particular from 05 to 030 hydrocarbons, even more in particular 05 to 020 and even yet more in particular from 06 to 016 hydrocarbons. Hydrocarbons may be aliphatic hydrocarbons and / or aromatic hydrocarbons and may preferably be aliphatic hydrocarbons. Aliphatic hydrocarbons may typically comprise less than 2% of aromatic groups. Preferably hydrocarbons may be selected from a mixture of aliphatic hydrocarbons, in particular a mixture of 012-015 aliphatic hydrocarbons.

[0088] The presence of a second solvent and in particular a nonpolar solvent, such as a hydrocarbon as described herein, may also contribute to the formation of micelles of fatty acid in a similar manner as described above for the first solvent, depending on the nature and amount of the second solvent. For a nonpolar second solvent such as a hydrocarbon present in an amount lower than the amount of a polar first solvent such as water, the fatty acid may encapsulate the nonpolar second solvent with the nonpolar tails of the fatty acid in the interior of the micelle, and water may be present outside the micelles interacting with the polar carboxylic acid heads of the fatty acid, and vice versa, when the amount of the nonpolar second solvent is higher than the amount of water may be trapped with the polar carboxylic acid heads of the fatty acids inside the micelles and the nonpolar tails of the fatty acids on the surface of the micelles facing the second non polar solvent.

[0089] In several embodiments, the second solvent may replace part of all of the first solvent in the fluid. However, in other embodiments, the fluid may comprise 0 wt.% of the second solvent. If present, the second solvent may replace from 5 to 100 wt.% of the first solvent, in particular from 10 to 80 wt.%, yet more in particular from 25 to 75 wt.% of the first solvent. In several embodiments the only solvent of the fluid may be the second solvent, e.g., a hydrocarbon.

[0090] In several embodiments, the weight ratio of the first solvent (e.g., water) to the second solvent (e.g., hydrocarbon) of the fluid may be from 20:1 to 1 :20, in particular from 10: 1 to 1 :10 and yet more in particular from 5:1 to 1 :5. In several particular embodiments, the weight ratio of the first solvent to the second solvent may be from 3: 1 to 20: 1 , in particular from 4:1 to 15:1 and yet more in particular from 5:1 to 10: 1.

[0091] In several embodiments only one solvent may be present. When only one solvent is present the solvent may be a non-polar or a polar solvent as defined above for the first and second solvent.

[0092] In several particular embodiments the fluid may comprise a first solvent and may not comprise a second solvent. In several more particular embodiments the fluid may comprise from 30 to 100 wt.% of fatty acid, from 0 to 60 wt.% of the first solvent and 0 wt.% of the second solvent. In several alternative particular embodiments, the fluid may comprise from 0.1 to 50 wt.% of fatty acid, from 50 to 99.9 wt.% of the first solvent and 0 wt.% of the second solvent. The

[0093] In several particular embodiments the fluid may comprise a first solvent and may also comprise a second solvent. In several more particular embodiments of the fluid may comprise from 10 to 70 wt.% of fatty acid, from 5 to 20 wt.% of the first solvent and 0.1 to 10 wt.% of the second solvent. The wt.% with respect to the total weight of the fluid. If the fluid comprises components other than fatty acid and the first and second solvent, e.g., surfactants, they may replace part of the first or second solvent in the wt.% amount that they are added, as also defined below.

[0094] In several particular embodiments the fluid may only comprise a second solvent, e.g., a hydrocarbon. In several more particular embodiments, the fluid may comprise, e.g., from 5 to 15 wt.% of fatty acid and from 85 to 95 wt.% of the second solvent, based on the total weight of the fluid. If the fluid comprises components other than fatty acid and the second solvent, e.g., surfactants, they may replace part of the second solvent in the wt.% amount that they are added, as also defined below.

[0095] It may be preferred for the first solvent to be water and for the second solvent to be a hydrocarbon as defined above. The hydrocarbon may be preferably selected from from hydrocarbons as defined above and in particular from a mixture of aliphatic hydrocarbons, and more in particular a mixture of C12-C15 aliphatic hydrocarbons.

[0096] It has been found that the presence of the second solvent, and a hydrocarbon in particular, in combination with the first solvent it may contribute to improve the movement of the electrically conductive particles in the medium, adding freedom of movement to the particles. It may also contribute to a better cohesion of the electrically conductive particles. Without being bound to any theory this may contribute to the electrically conductive particles better reaching the surface of the object subjected to the surface finishing method and to the conductivity of the electrically conductive particles, ultimately improving the surface finishing method and the surface treated objects obtained thereby. The surfactant may also act as can act as a lubricant, fluidizer, or both.

[0097] The lubricating effect may contribute to decreasing the frictional force between two bodies. On the one hand, the friction between electrically conductive particles and on the other, the friction between the electrically conductive particles and the object to be surface finished. Without being bound to any theory, the presence of a surfactant may also contribute to reducing the amount of conductive liquid expelled from the electrically conductive particles due to the reduction of normal stresses. It has been found that this may translates into a less aggressive and more controlled surface finishing process, which results in a reduction in surface finishing intensity.

[0098] The fluidizing effect may contribute to decreasing the viscosity of the system. Without being bound to any theory, the presence of the surfactant may modify the rheology of the medium and the fluid dynamics of the particles as they circulate on the surface of the object to be surface finished. This can be achieved, e.g., without having to increasing the fluid / electrically conductive particle ratio, which would also decrease the viscosity of the medium but to the detriment of conductivity, as the greater the amount of fluid, the lower the density of particles in the medium that transmit the electric field from cathode to anode, resulting in a lower surface finishing rate. Therefore, the presence of the surfactant may decrease the viscosity without adversely affecting the conductivity of the system.

[0099] In some embodiments, the fluid of the medium comprising the electrically conductive particles may comprise a third, a fourth or more solvents presenting different properties between them and allowing for a custom combination of polar and apolar solvents. As an illustrative example, a combination of two polar solvents, such as water and polyethylene glycol may be mixed with a combination of two apolar solvents, such as aliphatic carbon chains or oils together with silicones is also under the scope of the present disclosure, as well as the corresponding selection of proportion between the solvent and the types and proportions of surfactant to adjust the surface tensions of the interfaces between each phase.

[0100] In a method as described herein a fatty acid may be selected from saturated and unsaturated fatty acids. It may be preferred for the fatty acid to be selected from saturated fatty acids.

[0101] In a method as described herein a fatty acid may be selected from linear and branched fatty acids. It may be preferred for the fatty acid to be selected from linear fatty acids.

[0102] In several embodiments, the fatty acid may be selected from a C8 fatty acid such as caprylic acid (also referred to in the art as octanoic acid); a C18 fatty acid such as stearic acid and oleic acid, preferably stearic acid; a C7 fatty acid such as enanthic acid; a C6 fatty acid such as caproic acid and leucic acid; a C5 fatty acid such as levulinic acid; and a C3 fatty acid such as lactic acid; preferably the fatty acid is selected from a C18 and a C8 fatty acid, preferably from caprylic acid, stearic acid and oleic acid. In some embodiments the fatty acid may be selected from stearic acid and caprylic acid or from oleic acid and caprylic acid. In some embodiments the fatty acid may be oleic acid. It may be preferred for the fatty acid to be a C8 fatty acid and in particular caprylic as it is the shortest fatty acid chain with low volatility, and may contribute to the mobility of the fatty acid and at the same time facilitate the handling of the medium without risk of volatilization of the fatty acid. Furthermore, caprylic acid is a saturated and linear fatty acid that has been found to work particularly well in surface finishing methods as described herein.

[0103] The nature of the nonpolar tail of the fatty acid may also influence the surface finishing. Without being bound to any theory it is believed that linear and nonpolar tails of saturated fatty acids may offer a more compact packing and form more compact protective layers on the surface of the object to be surface finished, branching or kinking of the nonpolar tail of the fatty acid may hinder the packing and reduce the effect of the fatty acid. Thus, it may be useful to modulate the effect of the fatty acid by using nonpolar tails of different natures, it may be preferred for a fatty acid to be selected from linear and saturated fatty acids, as it is believed to favor a tight packing of the fatty acid onto the surface of the object to be surface finished.

[0104] Similarly packing of the fatty acids may also be more compact and favorable when all the fatty acids in the fluid of the medium are of the same nature, e.g., they have same length and have the same nonpolar tail. Accordingly, even though in a method as described herein a fatty acid may be selected from plurality of fatty acids and the fluid may comprise a mixture of fatty acids, it may be preferred for the fatty acid consist of one type of fatty acid.

[0105] Nonetheless, the length of the hydrocarbon chains of the fatty acids and the structure of the fatty acids may be varied to achieve a particularly desired final result or for a particular surface or material, in particular may be varied to modulate the surface finishing depending on the microstructural defects and microconstituents phases of the surface or material to be surface finished.

[0106] In several embodiments the alcohol may be selected from monohydric alcohols or polyhydric alcohols.

[0107] In several particular embodiments the alcohol may be a glycol. Glycols are dihydric alcohols, also known as diols, in which the two hydroxy groups are on different carbon atoms of a hydrocarbon chain. Preferred glycols may be from 02 to 05 glycols, in particular from 02 to 04 glycols. Examples of glycols include, e.g., ethylene glycol (ethane-1 ,2-diol), propylene glycol (propane-1 , 2-diol and / or propane 1 ,3-diol) and butylene glycol (butane- 1 ,4-diol, butane-1 , 2-diol and / or butane-1 ,3-diol). A glycol may preferably be ethylene glycol.

[0108] In several particular embodiments the alcohol may be a fatty alcohol, such as from 03 to 050 fatty alcohols, in particular from 04 to 050 fatty alcohols, in particular from 06 to 030 fatty alcohols and more in particular from 08 to 028 fatty alcohols such as, 1 -octanol, 2-octanol, 2-ethylehexanol, 1-decanol among others. Fatty alcohols may also be particularly selected from 010 alcohols such as decanol; 013 alcohols such as isotridecanol, 016 alcohols such as hexodecanol; 04 alcohols such as 1 and 2 butanol; 03 alcohols such as isopropanol or propanol preferably isopropanol. For instance, it has been found that isopropanol presents particular interesting final results in several embodiments of a method as described herein where uniform surface finishing is required over a metal matrix composite (MMC) material.

[0109] In some embodiments the alcohol may be a polyol such as a sugar, including, e.g., fructose, glucose and sucrose. As detailed elsewhere in the present specification, such sugars may themselves display an effect but may also derive into fatty acids providing under the method conditions which in its turn can provide an additional effect.

[0110] In several embodiments, organic compounds comprising carboxyl groups and / or hydroxyl groups may be cyclic organic molecules, including cyclic fatty alcohols, cyclic polyols (e.g., sugars as described above) or cyclic fatty acids. Such cyclic compounds may be utilized as polarizable agents capable of forming a protective resistive layer over metal surfaces. For instance, cyclopropanol, cyclohexanol, and their derivatives represent examples of cyclic fatty alcohols that exhibit hydrophilic properties and can enhance the stability and uniformity of the protective layer during surface finishing. Similarly, cyclic fatty acids such as cyclopropane carboxylic acid or cyclohexane carboxylic acid are highly effective due to their ability to form stable interactions with the surface of the object to be surface treated (e.g., a metal surface). These cyclic molecules offer distinct advantages, including low volatility and enhanced chemical stability compared to their linear counterparts, making them particularly suitable for applications requiring consistent surface finishing and long-term corrosion resistance.

[0111] In several embodiments, in a method as described herein the fluid of the medium comprising the electrically conductive particles, may comprise a surfactant in addition to the fatty acid, first solvent and second solvent. For instance, a surfactant may favor the mobility of the fatty acid and / or the formation of the fatty acid micelles or protective layers on the surface of the object to be surface finished.

[0112] Suitable surfactants may include, e.g., ethoxylates (such as C5-C15 ethoxylated alcohols), sulfonic acids and their salts (e.g., a sodium salt of petroleum sulfonic acids with, e.g., CAS No. 68608-26-4, and dodecyl benzenesulfonic acid) and / or glycols. Surfactants may themselves be organic compounds comprising a hydroxyl or sulfonic group as a hydrophilic group. However, they may be referred to as surfactants when used in combination with other organic compounds comprising hydrophilic groups.

[0113] In particular embodiments, the fluid of the medium comprising the electrically conductive particles may comprise water as the first solvent, a hydrocarbon as the second solvent and a surfactant in addition to the fatty acid. What is described above for the water, the hydrocarbon, the surfactant and the fatty acid also applies herein. It may be preferred for the hydrocarbon to be selected from hydrocarbons as defined above and in particular from a mixture of aliphatic hydrocarbons, in particular a mixture of C12-C15 aliphatic hydrocarbons and for the surfactant to be selected from, e.g., a sodium salt of petroleum sulfonic acids (such as CAS No. 68608-26-4), dodecyl benzenesulfonic acid, and C5-C15 ethoxylated alcohols.

[0114] The presence of a hydrocarbon may further contribute to the conductivity or the electrically conductive particles. Without being bound to any theory the presence of the surfactant may influence the interaction of the first and second solvent with the particles modifying the electrical conductivity. The presence of a surfactant may contribute to maintain a good electrical conductivity.

[0115] If present a surfactant may be present in an amount from 0.01 to 2 wt.% with respect to the total weight of the fluid, in particular from 0.05 to 1 wt.%, in particular from 0.1 to 0.5 wt.%. In several embodiments, a method as described herein the fluid of the medium comprising the electrically conductive particles, may comprise additional components other than the surfactant, the fatty acid, the first solvent and the second solvent.

[0116] Even though such additional components may be useful to contribute in modulating the surface finishing of methods as described herein they are not necessary and it may be preferred for the fluid of the medium not to include such additional components. Examples of additional components may include acids such as methanesulfonic acid (MSA), nitric acid, nitrate salts, such as sodium nitrate or potassium nitrate, and / or dodecylbenzenesulfonic acid. Nitrate salts may serve as additives that stabilize the electrolyte and contribute to a uniform finishing of the object surface treated in a method as described herein. If such additional components are present the fluid may comprise from 0.01 to 5 wt.% of additional components, based on the total weight amount of the fluid, in particular from in particular from 0.05 to 1 wt.%.

[0117] In a method as described herein the application a voltage and / or a current to the object may induce the movement of the fatty acid and contribute to the interaction of the fatty acid with the surface of the object to be surface finished and the formation of the protective layer of fatty acid on said surface. Where the fatty acid is forming micelles in the fluid the application of the voltage and / or current may also break such micelles and induce the movement of the fatty acid towards the surface of the object to be surface finishing.

[0118] In several embodiments, the voltage and / or a current may be applied in an alternate. In such embodiments the alternation of the voltage / current may contribute to the formation and a breakage of the protective layer of fatty acid on the surface of the object to be surface finished. Alternating the formation and breakage of the protective layer of fatty acid may contribute to the modulation of the surface finishing by allowing the electrically conductive particles to interact directly with the surface of the object to be surface finished for finite periods of time, where the surface of the object is free from the fatty acid protective layer, but allow for a faster surface finishing when compared to the fatty acid protective layer being permanently formed on the surface of the object.

[0119] An illustrative example of the action of such alternate voltage and / or current on the fatty acid may be found in Figures 2A and 2B. Figure 2A shows the behavior of the fatty acid molecules when the electric field E is in one direction, and 2B shows the behavior of the same when the electric field E is in the opposite direction. The formation and breakage of the micelles of fatty acids (12) and of the protective layer of fatty acid (11) on the surface (10) of the object that is surface treated is illustrated. The shape of the micelles of fatty acids (12) will depend on the other components of the medium such as the fluid composition and in particular on the presence, the nature, and the amount of the first and second solvent. In other embodiments the fatty acids may not be arranged in micelles but may take other arrangements within the fluid or medium.

[0120] The electrically conductive particles may be of any material capable of retaining liquid, such as, for example, polymeric materials, mineral, ceramic, organic compounds, inorganic compounds, of plant origin, and are preferably of polymeric material. Electrically conductive particles of a polymeric material may simply be referred to herein as polymeric particles.

[0121] Suitable polymeric materials may be, e.g., ion exchange resins.

[0122] In some embodiments, in a method as described herein some or all electrically conductive particles of the plurality of electrically conductive particles may comprise a resin. The resin may be of a polymeric material.

[0123] In several embodiments the electrically conductive particles may be 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.

[0124] In several particular embodiments, the polymeric material of the resin may be of a sulfonated divinylbenzene (S-DVB) and styrene copolymer, since it is a material resistant to acid and the oxidative action of the process. It 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.

[0125] Alternatively, the polymeric material of the resin may be 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.

[0126] In several particular embodiments, electrically conductive particles are of polymeric materials including functional groups that are capable of capturing or retaining the metal ions generated during the process, such as acid, amino, or chelating groups. These functional groups can be of the acidic type, such as sulfonic acid or carboxylic acid 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. It is also possible to use functional groups 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. It may be preferred for the functional groups to be acidic groups and more preferably sulfonic acid groups.

[0127] Depending on the specific type of polymer and functional groups included, the exact composition of the electrically conductive, particles may vary and may be adjusted. As a mode of example, in several particular embodiments electrically conductive particles may be of a cationic resin of a gel copolymer styrene-divinylbenzene (DVB), which may preferably be sulfonated (i.e., comprise sulfonic groups).

[0128] 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.

[0129] In a method as described herein some or all electrically conductive particles of the plurality of electrically conductive particles may comprise water or an electrolyte.

[0130] The electrically conductive particles may be regarded to encapsulate the water or the electrolyte. Such electrically conductive particles 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 electrically conductive particles 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.

[0131] In several embodiments, electrically conductive particles may have a porous structure, which facilitates the exchange of fluids resulting in a faster process. Alternatively, the particles may have a gel-like structure. In this case the fluid exchange is more restricted, which results in a slower process, however, the particle-surface contact is more defined, resulting in a lower final roughness.

[0132] The electrically conductive particle may be of a porous material, whereby the electrolyte may be contained inside the porous of the material.

[0133] Preferably the particles are porous, this porosity is selected from: microporosity, mesoporosity, macroporosity and fractal porosity.

[0134] The shape of electrically conductive particles as described herein may preferably be spheric and / or spheroid.

[0135] Typically, the porous material is not saturated with the water or the electrolyte. Thereby, the water or the electrolyte may be released when in contact with, e.g., the surface of the object to be surface finished.

[0136] In several embodiments electrically conductive particles may comprise water. For instance, electrically conductive particles (such as ion exchange resins as defined above) may be hydrated with water. Hydration of the electrically conductive particles may have a hydration from 5 to 100 wt.%, in particular from 10 to 75 wt.% hydration and more in particular from 15 to 55 wt.% hydration, the % of hydration being defined as the weight amount of water over the total weight of the particle. A desired degree of hydration may be achieved by means known in the art, e.g. subjecting the dry particles (e.g., of ion exchange resins) to swelling in water until a desired degree of hydration is achieved, and / or subjecting hydrated particles to drying to achieve a desired degree of hydration.

[0137] In several embodiments electrically conductive particles may comprise an electrolyte. The function of the electrolyte is twofold: on the one hand, it conducts electricity, and on the other, it dissolves the oxides that are formed on the surface to be treated.

[0138] Preferably an electrolyte may be selected from an acidic aqueous solution.

[0139] In some embodiments, the electrolyte is an acidic aqueous solution, e.g., an aqueous solution selected from an aqueous solution of sulfuric acid, sulfonic acids (e.g., MSA), phosphoric acid, nitric acid, carboxylic acids, citric acid, and hydrochloric acid. Preferably the electrolyte may be an aqueous solution of sulfuric acid and / or MSA.

[0140] In several embodiments electrically conductive particles may 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.

[0141] The total concentration the acids in the electrolyte may be 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 several embodiments an acid concentration from 1 to 10 wt. % relative to the mass of the water plus the acid may be used.

[0142] In particular, 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 total weight 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.

[0143] In some embodiments, the electrolyte, may be an ionic liquid or a conductive liquid polymer.

[0144] A method described herein may be used to obtain any desired Ra and / or Rt and / or Rz value, which may depend on the type of material, roughness of the initial object and final application. For instance, a method as described herein may be suitably used for reducing the roughness to very low values, suitable for very demanding applications. As a mode of example for, e.g., most demanding applications, without being limited thereto, methods as described herein may provide surface treated objects with Ra of less than or equal to 80 nm, preferably less than or equal to 60 nm and more preferably less than or equal to 50 nm. For instance, Ra values may vary from 5 to 80 nm, in particular from 10 to 60 nm, and more in particular from 20 to 50 nm. In several embodiments, a method described herein and / or the surface finishing step is carried out at a temperature from room temperature (from 15 to 30 °C, e.g., 25°C) to 80°C, in particular from 30°C to 60°C and more in particular from 40°C to 50°C; all the endpoints being included in the ranges. These temperatures may advantageously contribute to reducing the time of the surface treatment to obtain a desired final roughness.

[0145] A higher temperature can be advantageous to enhance the surface finishing as the resistance of the surface to be surface finished typically becomes lower, thereby easing the effect of the abrasive particles, but also of the electrically conductive particles as the kinetics of the electrochemical reactions are altered by the higher temperature.

[0146] A temperature above 60°C may be used for short periods of time or less frequently because it damages the electrolyte within electrically conductive particles of the first plurality of electrically conductive particles.

[0147] In some embodiments, a method described herein and / or the surface finishing step is carried out at around atmospheric pressure, e.g., from 0.080 to 0.500 MPa, in particular from 0.090 to 0.250 MPa, more in particular from 0.095 to 0.150 MPa, and yet more in particular about 0.101 MPa. In some particular embodiments a method described herein and / or the surface finishing step is carried out at higher pressures, e.g., above 0.500 MPa.

[0148] In some embodiments higher pressures, e.g., above 0.500 MPa may be combined with lower temperatures, e.g., below 15 °C, in particular below 10 °C. In several embodiments, the relative movement between the object and the combination has a speed between 0.01 m / s and 5 m / s, in particular between 0.1 m / s and 1 m / s, and more in particular less than or equal to 0.5 m / s. In several embodiments, the relative movement between the object and the combination has a speed between 0.6 rpm (i.e. , revolutions per minute) and 600 rpm (namely, between 3.768 rad / s and 3,768 rad / s), in particular between 6 rpm and 300 rpm (namely, between 37.68 rad / s and 1 ,884 rad / s), and more in particular less than or equal to 60 rpm (namely, 376.8 rad / s). All the aforesaid endpoints being included in the respective ranges.

[0149] The time of the surface finishing step may depend on the initial roughness properties of the object, and / or the desired final roughness, and / or the speed of the relative movement between the combination and the at least one surface.

[0150] As a mode of example, the time of the surface finishing step may vary from, e.g., 0.25 h to 5.0 h, in particular from 0.5 h to 3.0 h, and more in particular from 0.75 h to 2.0 h.

[0151] At the end of a surface finishing step the fluid and / or the electrically conductive particles of the medium may be reused. If necessary, fresh fluid and / or electrically conductive may be added or may replace the used fluid and / or particles for a subsequent treatment. In several embodiments a basic resin may be added, such as Dupont Amberlite IRA67 resin. The amount of basic resin may vary. As a mode of example, the amount of basic resin may be, e.g., about 1% by weight of the electrically conductive particles. Addition of a basic resin may advantageously contribute to absorbing cationic contaminants. By freeing the counter anions, anionic contaminants may also be absorbed by the acidic resin, creating a mutual compensation.

[0152] In a method as described herein the at least one surface of the object may comprise any conductive surface. As a mode of example, the at least on surface may be, e.g., a metallic surface, a ceramic surface or a conductive polymeric surface.

[0153] In several particular embodiments, the object may be, e.g., a metallic object, a ceramic object or an object of a conductive polymer, including manufactured objects and, in particular, 3D printed objects. The object may preferably be a metallic object. A metallic object may be, e.g., a pure metal or a metal alloy. In particular the metallic or ceramic object may comprise a transition metal selected from, e.g., iron (Fe), copper (Cu), cobalt (Co), chromium (Cr), aluminum (Al), titanium (Ti), nickel (Ni), silver (Ag), gold (Au), and tungsten (W), and ions thereof.

[0154] For instance, the at least one surface of the object may comprise a metallic surface, and preferably the metallic surface comprises aluminum alloy, such as aluminum silicon alloy; an iron carbon alloy such as iron carbide, cast iron and carbon steel alloy; carbides other than iron carbide such as titanium carbide, tungsten carbide, zirconium carbide, and chromium carbide; and / or a copper and zinc alloy (e.g., brass).

[0155] Such materials are known to be particularly difficult to be surface finished by, e.g., electropolishing methods. It has been surprisingly found that a method as described herein wherein a fatty acid is used in the fluid of the media is particularly suited for such difficult materials and it allows reaching rugosity values that cannot be achieved by other methods.

[0156] For instance, biphasic materials, with one or more phases in their microstructure, where there may be a difference in the conductivity or electrochemical potential between phases, may particularly benefit from methods as described herein, including metallic surfaces as defined above.

[0157] Ceramic objects that may be used in a method as described herein may, e.g., have at least 0.1 wt.% metallic component and up to 99.9 wt.% of ceramic content. Metals present in the ceramic objects may be the same as detailed above for the metallic objects. Suitable examples of ceramic objects may include, for instance, a ceramic filled in a metallic binder.

[0158] The instant disclosure further relates to an object comprising one or more surfaces that are surface finished, the one or more surfaces being surface finished with a method as described herein.

[0159] It has been found that the use of a fatty acid in method as described herein not only provides a process with improved advantages but also results in surface finished objects that have properties that cannot be achieved by other methods. For instance, the rugosity levels achieved for surfaces finished by a method as described herein are particularly low.

[0160] Accordingly, the present disclosure also relates to an object comprising one or more surfaces that are surface finished, wherein at least one surface of the one or more surfaces has, in the entire at least one surface, an average roughness value Ra less than or equal to 80 nm, preferably less than or equal to 60 nm and more preferably less than or equal to 50 nm. For instance, Ra values may vary from 5 to 80 nm, in particular from 10 to 60 nm, and more in particular from 20 to 50 nm.

[0161] Furthermore, as also described above surface finished objects obtained by methods as described herein also have a particularly homogeneous surfaces and low number of defects. For instance, it has been particularly and surprisingly found that where the object being surface treated is a machined object, e.g. a carbide object machined by electrical discharge machining (EDM) a surface finishing with a method as described herein results in a surface-finished object that has a uniform surface free of irregularities or visible marks.

[0162] Such properties conferred to surface finished objects obtainable or obtained by methods as described herein (e.g., with such low roughness and defect levels), allow for methods as described herein to be suitable for most demanding applications, and may be useful to obtain objects with finishes suitable for such demanding applications.

[0163] For instance, some particularly demanding applications are objects therefor include, e.g., optical applications and optical devices such as mirrors and lenses for telescopes, microscopes, refractive lenses; low friction applications and devices therefor such as bearings and gears; applications that require low surface tension, anti-adhesion properties and anti-biofouling; and applications that require biocompatibility. Accordingly, the instant disclosure also relates to the use of fatty acid and surface finishing methods for such applications and objects.

[0164] Methods as described herein have also been found to provide objects comprising one or more surfaces that are surface finished, wherein there is no significant hardness loss on the surface compared to those surfaces which have been finished using other techniques. This is particularly relevant for objects comprising surfaces that are sensitive to such hardness loss such as metallic surfaces.

[0165] Methods as described herein have also been found to be particularly useful for use in homogeneous automated polishing. Such methods tend to result in scratches in the surface of the objects being polished. It has been found that the use of a fatty acids in methods as described herein may be applied to such homogeneous automated polishing to provide surface finished objects devoid of surface scratches.

[0166] In several embodiments the objects of methods as described herein and surface finished objects obtained by or obtainable by such methods may be one of the following: optical objects such as mirrors and lenses, in particular mirrors and lenses for telescopes, microscopes, refractive lenses; low friction objects such as bearings and gears; low surface tension objects, anti-adhesion properties and anti-biofouling; biocompatible objects; a blade of a jet engine; a blade of a wind turbine; a clock or a watch part; a dental prosthesis; a casted part or object: a machined part or object, a shaped part or object; and an additively manufactured part or object, such as a 3D printed object. Other specific objects that may be surface treated by methods as described herein, include for instance: polishing of parts made of carbides such as carbide punches; carbide cutting tools; carbide inserts in machining tools; carbide molds.

[0167] The instant disclosure further relates to the use of a fatty acid and / or an alcohol as described herein for surface finishing at least one surface of an object, wherein the fatty acid may be selected from C4 to C50 fatty acids, in particular from C6 to C30 fatty acids, more in particular from C8 to C28 fatty acids and the alcohol may be selected from glycols and fatty alcohols.

[0168] In particular, it may be preferred that for such uses surface finishing is performed by electropolishing.

[0169] The fatty acid and / or alcohol for such uses may be as defined above for methods as described herein.

[0170] Such uses may particularly be according to a method as described herein. Accordingly, all that is described above for the methods and surface finished objects of the present disclosure also apply to such uses. Such uses may include, e.g., the preparation of surfaces for subsequent coatings and also improve the precision and lifespan of tools and dies subjected to a surface treatment method as described herein.

[0171] In this text, the term “includes”, “comprises” and derivations thereof (such as “including”, “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0172] On the other hand, the disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

[0173] The instant disclosure is further illustrated by the following examples without being limited thereto or thereby. EXAMPLES

[0174] Several objects were subjected to a surface treatment by the following general method: holding the object with a moving arm and connecting the object to a pole of an electric source, connecting a container comprising electrically conductive particles and a fluid comprising a fatty acid, water as a first solvent and a C5-C30 as a second solvent. immerging the object into a container contained in a medium, whereby the object was completely covered by the particles, and moving the object inside of the particles thereby moving the particles relative to the object and allowing the contact of the particles with the surface of the object, for a specific amount of time;

[0175] - the object was removed from the particles, to provide a surface treated object.

[0176] The objects and the electrically conductive particles and fluids in medium used for each surface treatment are defined for each example below.

[0177] The electrically conductive particles used are defined for each of the examples below.

[0178] The objects were moved inside the particles achieving a relative movement between the particles and the object as detailed for each example below.

[0179] Example 1 : Surface treatment of Carbides

[0180] A drill made of tungsten carbide containing cobalt was processed using an electrolytic surface treatment medium comprising:

[0181] 500 g of electrically conductive particles comprising a combination of: o a 33.33 wt% of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.% o a 33.33 wt% of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.% and further grinded o a 33.33 wt% of sulfonated gel styrene divinylbenzene particles with size 0.21 - 0.24 mm, with a hydration of 31 wt.%.

[0182] 100 g of deionized H2O and

[0183] 130 g of octanoic acid.

[0184] The drill of tungsten carbide was connected to a pole to be used as a cathode and submerged in a pot containing the electrolyte and an iridium titanium mesh that served as an anode.

[0185] The piece was submerged in the particles and moved combining an orbital motion and a helical movement for 10 minutes. An alternating current was applied of +35 V during 40 ns and -60 V during 320 ns.

[0186] This process was able to polish the entire surface of the piece, even the interior parts of the drill, something that had not been achieved yet.

[0187] Example 2: Surface treatment of Aluminum

[0188] An aluminum plate was processed using an electrolytic surface treatment medium comprising:

[0189] 500 g of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.%, and then dried 27% of their weight, to a hydration of about 15 wt.%.

[0190] 25 g of methanosulfonic acid.

[0191] 50 g of deionized H2O.

[0192] 280 g of octanoic acid.

[0193] The piece was connected to a pole to be used as a cathode and submerged in a pot containing the electrolyte and an iridium titanium circular mesh that served as an anode.

[0194] The piece was submerged into the particles while a current of 90 V was applied. It was moved with an orbital motion for 10 minutes.

[0195] The piece presented a flat surface and high reflectivity.

[0196] Figure 3 shows the surface of the aluminum sheet before (A) and after (B) the surface finishing treatment. The image was recorded using Scanning Electron Microscopy (SEM) with secondary electrons detector.

[0197] Example 3: Surface treatment of carbonated steel

[0198] A piece of a carbon steel gear was processed with the next electrolyte:

[0199] 500 g of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.%, and then dried 35% of their weight, to a final hydration of about 19 wt.%.

[0200] 25 g of methanosulfonic acid.

[0201] 70 g of propylene glycol.

[0202] 240 g of octanoic acid.

[0203] The piece was connected to a pole to be used as a cathode and submerged in a pot containing the electrolyte and an iridium titanium circular mesh that served as an anode. The piece was submerged into the particles while a current of 80 V was applied. It was moved with an orbital motion for 10 minutes.

[0204] This procedure was able to polish the exterior of the piece with the best results ever seen. Figure 4 shows the external surface of the carbonated steel gear before (A) and after (B) the surface finishing treatment. The image was recorded with a SEM with secondary electrons detector.

[0205] Example 4: Surface treatment of Aluminum 6082 alloy

[0206] A cylindric bottle stopper made of Aluminum 6082 alloy was processed using an electrolytic surface treatment medium comprising:

[0207] 5728.9 g of electrically conductive particles obtained by adding o 214.7 g of methane sulphonic acid with 70% wt. purity and o 756.9 g of deionized H2O. to 4757.2 g of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter having a water hydration of 35.16 wt.%.

[0208] 3686 g of a non-conductive fluid comprising a combination of: o 3370 g of a mixture of aliphatic hydrocarbons with a carbon chain between 12-15 C containing less than 2% of aromatic groups. o 310.9 g of oleic acid. o 3.85 g of sodium salt of petroleum sulfonic acids (CAS 68608-26-4) o 1.6 g of dodecyl benzenesulfonic acid.

[0209] The bottle stopper was connected to a pole to be used as a cathode and submerged in a pot containing the electrolytic surface treatment medium and an iridium titanium mesh that served as an anode.

[0210] The piece was submerged in the medium and moved combining an orbital motion and a helical movement for 30 minutes.

[0211] An alternating current was applied of +30 V during 100 ps and -30 V during 20 ps and with time lapses between the different polarizations of 30 ps.

[0212] The temperature of the electrolyte was between 25 - 35 °C. The current density of the process was between 0,05 - 0,3 A / cm3.

[0213] This process was able to polish the entire surface of the piece, obtaining a mirror surface with final roughness values Ra < 80 nm.

[0214] Example 5: Surface treatment of carbide punches

[0215] A carbide punch was processed using an electrolytic surface treatment medium comprising a mixture of:

[0216] 500 g of electrically conductive particles comprising a combination of: o 99 wt.% Sulfonated gel styrene divinylbenzene particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.% as obtained after a washing process comprising rinsing the particles with distilled water (at a temperature below 100 °C ) until the washes obtained had a pH falling between 4.5 and 7 and partially drying the particles to obtain said hydration of 55% o 1 wt. % weak base anion exchange resin composed of an acrylic crosslinked with divinylbenzene backbone and functionalized with a tertiary amine (Resin Dupont Amberlite IRA67) with a hydration of 55 wt.%. Acting as a chemical moderating particle.

[0217] 1000 g of a fluid comprising a combination of: o 200 g of ethylene glycol (of a 99% purity) o 800 g of deionized H2O

[0218] The carbide punch was connected to a pole to be used as a cathode and submerged in a pot containing the electrolytic surface treatment medium and an iridium titanium mesh that served as an anode.

[0219] The piece was submerged in the medium and moved combining an orbital motion and a helical movement for 30 minutes.

[0220] An alternating current was applied of +15 V during 5 or 10 ps and -60 V during 25 or 50 ps and with time lapses between the different polarizations being as low as possible.

[0221] The temperature of the electrolyte was between 25 - 35 °C. The current density of the process was between 0,05 - 0,3 A / cm3.

[0222] This process was able to polish the entire surface of the piece, obtaining a mirror surface with final roughness values Ra < 30 nm.

[0223] Example 6: Surface treatment of a tungsten carbide with an electrolyte comprising fructose

[0224] A drill (with an approximate cylindrical geometry of 80x10 mm) made of tungsten carbide containing cobalt was processed using an electrolytic surface treatment medium comprising:

[0225] • 500 g of electrically conductive particles comprising a combination of: o 33.33 wt.% of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.% o 33.33 wt.% of sulfonated gel styrene divinylbenzene particles of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.% and further grinded, obtaining as a result a dispersion of crushed particles with different sizes and geometries. o 33.33 wt.% of sulfonated gel styrene divinylbenzene particles with size 0.21 - 0.24 mm, with a hydration of 31 wt.%. a fluid comprising a combination of: o 110 g of deionized H2O and o 55 g of commercial fructose.

[0226] The drill of tungsten carbide was connected to a pole to be used as a cathode and submerged in a pot containing the electrolyte and an iridium titanium mesh that served as an anode.

[0227] The piece was submerged in the particles and moved combining an orbital motion and a helical movement for 10 minutes.

[0228] The temperature during the surface finishing process was kept between 20 and 60 °C, preferably between 25 and 35°C.

[0229] An alternating current was applied of +20 V during 20 ns and -50 V during 100 ns.

[0230] This process was able to polish the entire surface of the piece, even the interior parts of the drill. After extracting it form the electrolyte, the piece was covered in a high viscosity liquid layer, which was easily cleaned with water.

[0231] Example 7: Surface treatment of a tungsten carbide with an electrolyte comprising dodecylbenzene sulfonic acid (DBS)

[0232] A tungsten carbide punch (with an approximate cylindrical geometry of 55x25 mm) was processed using an electrolytic surface treatment medium comprising a mixture of:

[0233] • 250 g of electrically conductive particles comprising of grinded sulfonated gel styrene divinylbenzene particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm of diameter with a hydration of 55 wt.% as obtained after a washing process comprising rinsing the particles with distilled water (at a temperature below 100 °C) until the washes obtained had a pH falling between 4,5 and 7 and partially drying the particles to obtain said hydration of 55%

[0234] • 1801 .8 g of a fluid comprising a combination of: o 500 g of ethylene glycol (of a 99% purity) o 1750 g of deionized H2O o 1.8 g of DBS acid.

[0235] The carbide punch was connected to a pole to be used as a cathode and submerged in a pot containing the electrolytic surface treatment medium and an iridium titanium mesh that served as an anode.

[0236] The piece was submerged in the medium and moved combining an orbital motion with an in-and-out of the electrolyte movement for 30 minutes.

[0237] An alternating current was applied of +50 V during 20 ps and -60 V during 100 ps and with time lapses between the positive and negative polarization of 100 ps.

[0238] This process was able to polish the tight corners of a piece with complex geometry, something that it had not been achieved before in other conventional polishing techniques

Claims

CLAIMS1. A method for surface finishing at least one surface of an object, comprising: submerging the object in a medium comprising a plurality of electrically conductive particles such that the at least one surface is in contact with the medium; and at least while the object is submerged: applying a voltage and / or a current to the object; and producing relative movement between the at least one surface and the plurality of electrically conductive particles in the medium; the object being electrically connected with a first pole of at least one electric source; the electrically conductive particles and / or the medium containing the electrically conductive particles and / or a container containing the medium being electrically connected with a second pole of the at least one electric source; the medium further comprising a fluid, wherein the fluid comprises an organic compound comprising hydrophilic groups selected from a fatty acid selected from C3 to C50 fatty acids, in particular from C4 to C50 fatty acids, more in particular from C6 to C30 fatty acids, yet more in particular from C8 to C28 fatty acids; an alcohol selected from C2 to C50 alcohols, in particular from C2 to C10 alcohols, comprising one or more hydroxyl groups; an organic compound comprising sulfonic, sulfate, sulfone or thiol groups, in particular selected from sulfonic acids, such as alkylbenzene sulfonic acids and their salts, such as sodium dodecylbenzenesulfonate (SDBS) and sodium toluenesulfonate; and sulfate esters and their salts, such as sodium lauryl sulfate (SLS) and ammonium SLS; an organic compound comprising nitro or nitrate groups, in particular selected from alkyl nitrates, and nitroalkanes, more in particular selected from nitromethane and nitroethane; an organic compound comprising phosphate groups, in particular selected from aryl phosphates, such as triphenyl phosphate (TPP), tricresyl phosphate (TCP); alkyl phosphates such as diethyl phosphate or tributyl phosphate; and phosphate esters such as monoalkyl or dialkyl phosphate esters; and / or an organic compound comprising amine groups, in particular selected from primary amines such as ethylamine and propylamine; secondary amines such as diethylamine and dipropylamine); and tertiary amines (e.g., triethylamine and tributylamine).

2. The method of claim 1 , wherein the fluid of the medium further comprises a first solvent, preferably the first solvent is a polar solvent and more preferably the polar solvent is water, and, optionally, the fluid of the medium further comprises a second solvent different from the first solvent, preferably the second solvent is a nonpolar solvent, more preferably is nonpolar organic solvent, in particular the second solvent is a nonpolar organic solvent selected from polyethylene glycol (PEG) and hydrocarbons, in particular from 04 to C52 hydrocarbons, in particular from 04 to 050 hydrocarbons, more in particular from 05 to 030 hydrocarbons, yet more in particular from 05 to 020 hydrocarbons, even more in particular 05 to 018 hydrocarbons and yet even more in particular from 06 to 016.

3. The method of claim 1 , wherein the fluid of the medium further comprises a second solvent, preferably the second solvent is a nonpolar solvent, more preferably is nonpolar organic solvent, in particular the second solvent is a nonpolar organic solvent selected from polyethylene glycol (PEG) and hydrocarbons, in particular from 04 to 052 hydrocarbons, in particular from 04 to 050 hydrocarbons, more in particular from 05 to 030 hydrocarbons, yet more in particular from 05 to 020, even more in particular 05 to 018 hydrocarbons and yet even more in particular from 06 to 016.

4. The method of any one of claims 1 to 3, wherein the fatty acid is selected from saturated and unsaturated fatty acids, preferably saturated fatty acids.

5. The method of any one of claims 1 to 4, wherein the fatty acid is selected from linear and branched fatty acids, preferably linear fatty acids.

6. The method of any one of claims 1 to 5, wherein the fatty acid is selected from a 08 fatty acid such as caprylic acid; 018 fatty acid such as stearic acid and oleic acid, preferably oleic acid; a 07 fatty acid such as enanthic acid; and a 06 fatty acid such as caproic acid and leucic acid; a 05 fatty acid such as levulinic acid; and a 03 fatty acid such as lactic acid; preferably the fatty acid is selected from a 08 and a 018 fatty acid, more preferably from caprylic acid, oleic acid and stearic acid and, and yet more preferably the fatty acid is caprylic acid.

7. The method of any one of claims 1 to 6, wherein the alcohol is selected from glycols, in particular is selected from 02 to 05 glycols, more in particular is selected from ethylene glycol, propylene glycol and butylene glycol, and preferably the alcohol is ethylene glycol.

8. The method of any one of claims 1 to 6 wherein the alcohol is selected from fatty alcohols, in particular is selected from C3 to C50 fatty alcohols, in particular from C4 to C50 fatty alcohols, more in particular from C6 to C30 fatty alcohols and yet more in particular from C8 to C28 fatty alcohols.

9. The method of any one of claims 1 to 8, wherein some or all electrically conductive particles of the plurality of electrically conductive particles comprise a resin.

10. The method of any one of claims 1 to 9, wherein some or all electrically conductive particles of the plurality of electrically conductive particles comprise water or an electrolyte, preferably an electrolyte selected from an acidic aqueous solution, more preferably may be selected from an aqueous solution of sulfuric acid, methanesulfonic acid (MSA), phosphoric acid, nitric acid, carboxylic acids, citric acid, and hydrochloric acid, and yet more preferably the electrolyte may be an aqueous solution of sulfuric acid and / or MSA.

11. The method of any one of claims 1 to 10, wherein the fluid comprises from 0.1 to 100 wt.% of fatty acid based on the total weight of the fluid component of the medium, in particular from 0.5 to 90 wt.%, more in particular from 1 to 75 wt.%, yet more in particular from 5 to 60 wt.%, and even more in particular from 7 to 50 wt.% of fatty acid.

12. The method of any one of claims 1 to 11 , wherein the fluid comprises from 0 to 99.9 wt.% of the first solvent, in particular from 10 to 99.5 wt.% of the first solvent, more in particular from 25 to 99 wt.% of the first solvent, yet more in particular from 40 to 95 wt.% of the first solvent and even more in particular from 50 to 93% of the first solvent.

13. The method of claim 12, wherein the first solvent partially or totally replaced by the second solvent, from 5 to 100 wt.% of the first solvent, in particular from 10 to 80 wt.%, yet more in particular from 25 to 75 wt.% of the first solvent is replaced by the second solvent.

14. The method of any one of claims 1 to 13, wherein the at least one surface of the object comprises a metallic surface, a ceramic surface or conductive polymeric surface.

15. The method of any one of claims 1 to 14, wherein the at least one surface of the object comprises a metallic surface, and preferably the metallic surface comprises aluminum alloy, such as aluminum silicon alloy; an iron carbon alloy such as iron carbide, cast iron and carbon steel alloy; carbides other than iron carbide, such as titanium carbide,tungsten carbide, zirconium carbide, and chromium carbide; and / or a copper and zinc alloy such as brass.

16. An object comprising one or more surfaces that are surface finished, the one or more surfaces being surface finished with a method according to any one of claims 1 to 15.

17. An object comprising one or more surfaces that are surface finished, wherein at least one surface of the one or more surfaces has, in the entire at least one surface, an average roughness value Ra less than or equal to 80 nm, preferably less than or equal to 60 nm, and more preferably less than or equal to 50 nm.

18. The method of any one of claims 1 to 15 or the object of any one of claims 16 to 17, wherein the object is one of the following: optical objects such as mirrors and lenses, in particular mirrors and lenses for telescopes, microscopes, refractive lenses; low friction objects such as bearings and gears; low surface tension objects, anti-adhesion properties and anti-biofouling; biocompatible objects; a blade of a jet engine; a blade of a wind turbine; a clock or a watch part; a dental prosthesis; a casted part or object: a machined part or object, a shaped part or object; and an additively manufactured part or object, such as a 3D printed object.

19. Use of a compound comprising hydrophilic groups, for surface finishing at least one surface of an object, wherein the organic compound comprising hydrophilic groups is selected from a fatty acid selected from C3 to C50 fatty acids, in particular from C4 to C50 fatty acids, more in particular from C6 to C30 fatty acids, yet more in particular from C8 to C28 fatty acids; an alcohol selected from C2 to C50 alcohols, in particular from C2 to C10 alcohols, comprising one or more hydroxyl groups; an organic compound comprising sulfonic, sulfate, sulfone or thiol groups, in particular selected from sulfonic acids, such as alkylbenzene sulfonic acids and their salts, such as sodium dodecylbenzenesulfonate (SDBS) and sodium toluenesulfonate; and sulfate esters and their salts, such as sodium lauryl sulfate (SLS) and ammonium SLS; an organic compound comprising nitro or nitrate groups, in particular selected from alkyl nitrates, and nitroalkanes, more in particular selected from nitromethane and nitroethane;an organic compound comprising phosphate groups, in particular selected from aryl phosphates, such as triphenyl phosphate (TPP), tricresyl phosphate (TCP); alkyl phosphates such as diethyl phosphate or tributyl phosphate; and phosphate esters such as monoalkyl or dialkyl phosphate esters; and / or an organic compound comprising amine groups, in particular selected from primary amines such as ethylamine and propylamine; secondary amines such as diethylamine and dipropylamine); and tertiary amines (e.g., triethylamine and tributylamine).

20. The use of claim 19, wherein surface finishing is performed by electropolishing.

21. The use of claim 19 or 20, wherein the fatty acid is as defined for the method of any one of claims 4 to 6 and / or the alcohol is as defined for the method of any one of claims 7 to 8.

22. The use of claim any one of claims 19 to 21 , wherein the use is according to the method of any one of claims 1 to 15 or 18.

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