WO2012072219A1 - Method for the electrochemical polishing of metallic objects and electrolyte solution suitable therefor - Google Patents

Abstract

The invention relates to a method for the electrochemical polishing of metallic objects, in particular from the group comprising copper (Cu), zinc (Zn), silver (Ag), tin (Sn), gold (Au), platinum (Pt) and alloys containing at least one of said metals, wherein the metallic object is electrically conductively connected to an anode and is dipped into an electrolyte solution having a cathode, and an electric voltage is applied to the electrodes. The invention further relates to an electrolyte solution suitable for this purpose, which contains the following components or consists entirely thereof: (a) between 2 and 50% by mass of at least one ethoxylated alcohol; (b) between 2 and 50% by mass of at least one substance from the group of sulfonic acids and sulfonates; (c) between 0.2 and 10% by mass of at least one inorganic acid; (d) between 6 and 50% by mass of at least one liquid hydrocarbon; and (e) between 5 and 90% by mass of water; wherein the pH of the electrolyte solution is at least 1.

Description

 Process for the electrochemical polishing of metal objects and suitable electrolyte solution for this purpose

The invention relates to a method for the electrochemical polishing of metal objects, in particular from the group copper (Cu), zinc (Zn), silver (Ag), tin (Sn), gold (Au), platinum (Pt) and at least one of these metals containing alloys, wherein the metal object is electrically conductively connected to an anode and immersed in an electrolyte solution having a cathode, wherein the electrodes are subjected to an electrical voltage. It also relates to a suitable electrolyte solution for the electrochemical polishing of metals, in particular from the group copper (Cu), zinc (Zn), silver (Ag), tin (Sn), gold (Au), platinum (Pt) and at least one of these metals containing alloys.

Electropolishing is a known method of abrasive surface treatment in which the articles to be electro-polished are immersed in an electrolyte solution and connected to the positive electrode (anode) of a voltage source. In the electrolyte solution, the negative electrode (cathode) of the voltage source is arranged, so that it comes as a result of the electrical conductivity of the solution to a current flow, which provides for the surface, anodic removal of the metal article. The electrodes can be fed either with DC voltage or with pulsed voltages. Usually, the objects are moved in the electrolyte solution in order to minimize concentration gradients formed there.

1

CONFIRMATION COPY It should also be noted at this point that the term "electrochemical polishing" in the context of the present invention includes an electrochemical smoothing and an electrochemical glazing.

The selection of a suitable electrolyte solution here represents an important parameter, it has been shown that some solutions that lead in one metal to a perfect electropolishing, in another metal achieve virtually no effect or in a rough, jagged or matt surface result. Thus, for example, strong inorganic acids, in particular phosphoric acid and sulfuric acid, are used for electropolishing aluminum and steel, which may be mixed with alcohols. For copper and brass, e.g. a mixture of phosphoric acid and alcohols.

DE 10 2005 055 768 A1 describes an electrolyte composition for the electrolytic cleaning and descaling of metallic workpieces, in particular of steel, wherein the electrolyte composition primarily contains hydrochloric acid and sulfuric acid from main constituents. In one embodiment, the electrolyte composition may include an alcohol polyethylene glycol ether, an n-alkylbenzenesulfonate sodium salt, a secondary alkanesulfonate sodium salt, and minor amounts of a mineral oil based defoamer. For use in the electrolytic cleaning and descaling of a metallic workpiece, 5% by mass of the aforementioned electrolyte composition is mixed with 75% by mass of water and 20% by mass of hydrochloric acid to form the final electrolyte, which has a pH far below 0 having. As far as precious metals or semi-precious metals, such as jewelry, are to be treated by electropolishing, so silver in particular is a problem insofar as a perfectly shiny, visually appealing and smooth surface using known electrolyte solutions can not be practically obtained. For this purpose, on the one hand currently cyanide (CN ^~) are used electrolyte solutions, which are able to provide satisfactory results in addition to their high toxicity and consequent handling problematic in particular in silver. WO 2007/121999 A2 describes an electrolytic solution intended for electropolishing which contains alkylbenzenesulfonic acid or alkylbenzenesulfonates, ie their salts or derivatives. According to the exemplary embodiment specified in the document, the electrolyte solution consists of between 2.4% by mass and 3.2% by mass of decylbenzenesulfonates in the form of sodium salts, between 12% by mass and 15% by mass of dialkylbenzenesulfonic acid Alkyl Radials between 10 and 14 carbon atoms, between 13 Mass .-% and 16.5 Mass .- a petroleum fraction having 17 to 35 carbon atoms, between 0.2 Mass.-I and 0.7 Mass .-% ethanolamine, 1.4 Mass .-% copper sulfate and water. However, this electrolyte solution, in particular for the electropolishing of silver, has proved to be of only very limited suitability.

The invention is therefore based on the object to propose a suitable for the electropolishing of silver and preferably other precious and / or semiprecious metals, simple and cost-effective electrolyte solution of the type mentioned, which has a very low potential health hazard and therefore in a simple manner is manageable. It is also interested in a drive for the electrochemical polishing of metal objects including those made of silver or its alloys of the type mentioned.

According to the invention, this object is achieved with an electrolyte solution of the type mentioned in the introduction which contains the following ingredients:

(a) between 2 and 50 mass% of at least one ethoxylated alcohol;

 (b) between 2 and 50 mass. -I at least one substance from the group of sulfonic acids and sulfonates;

 (c) between 0.2 and 10 mass% of at least one inorganic acid;

 (d) between 6 and 50% by weight of at least one liquid hydrocarbon; and

 (e) between 5 and 90% by weight of water;

wherein the pH of the electrolyte solution is at least 1.

In procedural terms, the invention also provides for solving this problem in an electropolishing method of the type mentioned above, that an electrolyte solution is used with the aforementioned composition.

Surprisingly, it has been found that an electrolyte solution which contains or also entirely consists of the abovementioned components (a) to (e) in the abovementioned proportions has outstanding suitability for the electropolitre of silver and silver-containing alloys, which is also the case of objects with a very complex Surface structure, such as jewelry, a smooth, shiny surface can be awarded. The same applies to other precious and semi-precious metals and their alloys, for example, copper, tin, zinc, brass, bronze, gold or platinum or alloys thereof formed from the aforementioned and / or other alloying ingredients. A further advantage of the electrolytic solution according to the invention is that it does not necessarily have to be used at elevated temperatures for electropolitical use, but in particular also enables electropolishing at room temperature. The health risk potential of the solution according to the invention is very low and consequently permits simple and uncomplicated handling by the operating personnel of a corresponding electropolishing device. In this case, the solution is very low odor to practically odorless, and in particular may also have a certain viscosity, and mostly largely transparent, although in spite of a certain brown color, which may have the solution, any objects that undergo an electropolishing in the solution, visually detected can be.

Component (a): Ethoxylated Alcohol: The ethoxylated alcohol of the electrolytic solution according to the invention may in a preferred embodiment have between 5 and 30 carbon atoms, especially between 7 and 25 carbon atoms, preferably between 9 and 20 carbon atoms, with a chain length of such ethoxylated alcohol with between about 10 and about 16 carbon atoms has been found to be particularly advantageous. It should be noted that the said chain length in each case on the ethoxylated alcohol and not on refers to the ethoxylation obtained by addition of ethylene oxide during the ethoxylation.

In a further preferred embodiment, the ethoxylated alcohol can be an alkanol, in particular an isoalkanol, and it can furthermore be advantageous if the ethoxylated alcohol is a primary alcohol, i. the hydroxyl group (OH group) binds to a terminal carbon atom.

Moreover, it may be advantageous if the ethoxylated alcohol has a relatively low degree of ethoxylation (EO) of in particular between 1 and 50, preferably between 1 and 40, most preferably between 1 and 30. Particularly preferred degrees of ethoxylation are between about 1 and about 20, and more preferably between about 2 and about 20.

The ethoxylated alcohol may, in a further preferred embodiment, be a monoalcohol having only one hydroxyl group.

Component (b): sulfonic acid or sulfonate:

The at least one substance from the group of the sulfonic acids and sulfonates of the electrolytic solution according to the invention can preferably be selected from the group of arenesulfonic acids and arenesulfonates (ie the sulfur atom of the sulfonic acid or sulfonate group binds to an aromatic group), in particular from the group of benzenesulfonic acids, alkylbenzenesulfonates. sulfonic acids, benzenesulfonates and alkylbenzenesulfonates. The at least one substance from the group of sulfonic acids and sulfonates may furthermore preferably be selected from the group of benzenesulfonic acid, their alkyl derivatives, in particular their C 10 -C 16 -alkyl derivatives, preferably their C 10 -C 13 -alkyl derivatives, and salts of benzenesulfonic acid and their alkyl derivatives, especially with alkali metal (eg sodium and potassium salts), alkaline earth metal (eg magnesium and calcium salts), ammonium ions (NH ₄ ⁺ ) and / or organic amines, in particular triethanolamine and / or triethylamine. In particular, alkyl derivatives of benzenesulfonic acids and their sulfonates have proved to be particularly advantageous for the electrochemical polishing.

Component (c): Inorganic acid:

While the inorganic acid used for the electrolytic solution according to the invention are primarily strong acids having a relatively high pKa value, according to an advantageous embodiment it can be provided that the at least one inorganic acid from the group of mineral acids such as nitric acid (HNO3), sulfuric acid ( H ₂ S0 ₄ ), phosphoric acid (H3PO4), hydrochloric acid (HCl) and the like, in particular from the group of oxidizing mineral acids, such as preferably nitric acid and / or nitrous acid (HN0 ₂ ) is selected. In particular, nitric acid has proven to be particularly advantageous for electrochemical polishing.

Component (d): Liquid hydrocarbon or hydrocarbon mixture:

The at least one liquid hydrocarbon of the electrolytic solution according to the invention may preferably comprise a ketone ten length between 5 and 30 carbon atoms, in particular between 5 and 25 carbon atoms, preferably between 5 and 20 carbon atoms, wherein chain lengths between about 5 and about 18 carbon atoms have proven to be particularly advantageous.

According to a preferred embodiment, it may in particular be provided that the at least one liquid hydrocarbon is a hydrocarbon mixture, in particular from the group of petroleum or a petroleum fraction (eg one having a boiling point or boiling range between about 80 ° C and about 350 ° C, preferably between about 90 ° C and about 330 ° C, especially between about 100 ° C and about 310 ° C), preferably in the form of light petroleum (kerosene), gasoline or a gasoline fraction, such as example mineral spirits (eg with a boiling point or Siedebe rich between about 25 ° C and about 100 ° C), white spirit or the like. In this case, in particular those hydrocarbon mixtures come into consideration, as obtained in the fractional distillation of petroleum, wherein - as already mentioned - in particular the resulting petroleum fraction or sub-fractions thereof and vorzugswei se light petroleum fraction, i. the kerosene fraction as well as the gasoline fraction including the light benzene fraction have proved suitable.

The at least one liquid hydrocarbon or the hydrocarbon mixture may in a preferred embodiment ei nen boiling point or a boiling range between 25 ° C and 350 ° C, in particular between 50 ° C and 330 ° C, preferably between 75 ° C and 310 ° C. wherein a particularly preferred boiling range may be between about 80 ° C and 300 ° C. Component (s): Water:

In order to prevent an uncontrolled entry of salts and, where appropriate, further ingredients in the inventive Elek trolytlösung and locally different Lei tungswasserqualitäten account, it may be useful if the water is present in the form of demineralized or distilled water or in the form of pure water.

Other parameters:

With regard to the proportions by mass of the above components (a) to (e), which contains or also consists entirely of the electrolyte solution according to the invention, the following proportions can be provided in a preferred embodiment:

(a) between 3.5 and 40 mass%, in particular between 5 and 30 mass%, preferably between about 10 and about 20 mass%, of the at least one ethoxylated alcohol;

 (b) between 3.5 and 40 mass%, in particular between 5 and 30 mass%, preferably between about 7.5 and about 25 mass%, of the at least one substance from the group of sulfonic acids and sulfonates;

 (c) between 0.2 and 7.5 mass%, in particular between 0.2 and 5 mass%, preferably between about 0.2 and about

4% by mass, containing at least one inorganic acid;

 (d) between 8 and 40 mass%, in particular between 10 and 30 mass%, preferably between about 10 and about

20% by mass, of the at least one liquid hydrocarbon; and (e) between 10 and 80 mass%, in particular between 15 and 70 mass%, preferably between about 25 and about 65 mass%, of water. A pH of the electrolytic solution according to the invention which is advantageous for electropolishing is expediently between 1 and 5, in particular between 1.5 and 4.5, preferably between 2 and 3.5, in particular a pH in the range from about 2 to about 3 has proved to be particularly advantageous.

With regard to a preferred redox potential, redox potentials of the electrolyte solution of between 350 mV and 700 mV, in particular between

400 mV and 650 mV, preferably between 450 mV and 600 proved to be advantageous.

In addition, it can be provided that the electrolyte solution also contains a proportion of granule particles, in particular in the form of plastic particles. Such granule particles, which should be suitably chemically inert to the components of the solution, may serve to be whirled up on the occasion of the electrochemical polishing of metal objects and to come into contact with the objects in order to minimize the formation of a concentration gradient on the surface of the objects to keep low.

An inventive method for electrochemical polishing of metal objects, in particular from the group copper (Cu), zinc (Zn), silver (Ag), tin (Sn), gold (Au), platinum (Pt), wherein the metal article with a Anode electrically conductively connected and in an electric lytlösung is immersed with a cathode and the electrodes are subjected to an electrical voltage is characterized in that an electrolyte solution of the aforementioned type is used, wherein the method otherwise in a conventional manner known to the expert can be performed.

In particular, between 0.5 V and 20 V, in particular between 0.75 V and 15 V, preferably between about 1 V and about 10 V, has proved favorable as electrode voltage in connection with the electrolyte solution according to the invention. In this case, the object to be treated can be connected in a customary manner to the positive electrode (anode), while the negative electrode (cathode) is immersed in the electrolyte solution or, in particular, substantially completely inside a container accommodating the solution, around the objects to be treated, to ensure as homogeneous a current density as possible. The electrode voltage may also be changed during an electropolishing process, e.g. depending on the state and type of metal surface of the workpiece different voltages over different periods of time can be adjusted. In addition, the voltage may be, for example, a DC voltage or a pulsed voltage.

With regard to the advantageous current density set on the occasion of the electropolishing, this may preferably be between 0.1 and 5 A / dm ² , in particular between 0.2 and 4 A / dm ² , preferably between 0.3 and 3 A / dm ² . For example, a voltage density of between about 0.5 A / dm ^{2 and} about 2.5 A / dm ^{2 has} proved particularly suitable for silver and its alloys. With regard to an above-mentioned opposition to the formation of a concentration gradient on the surface of the metal objects to be treated, these should preferably be moved in the electrolyte solution, wherein in the case of an electrolyte solution containing granules particles can be moved at least at periodic intervals in the fluidized granules, as already indicated above.

In the following, exemplary embodiments are given for each electrolytic solution composed of the same constituents, which have proven to be outstandingly suitable for electrochemical polishing, including the electrochemical smoothing and shining of metal objects and in particular of silver and its alloys.

Component (a): isotridecanol (C13H27OH), ethoxylated with a degree of ethoxylation (EO) of 2-5

 CAS-No. [69011-36-5]

 MARLIPAL 0 13/50 ™, Sasol Germany GmbH (EN)

(10 to 20 mass%, e.g., about 15 mass%);

Component (b): benzenesulfonic acid, C10-13-alkyl derivatives,

 Compounds with triethanolamine

 CAS-No. [68411-31-4]

 MARLOPON AT 50 ™, Sasol Germany GmbH (DE)

(containing benzenesulfonic acid, C10-13-alkyl derivatives, tri- ethanolamine between 50 and 60%)

 (15 to 30 mass%, e.g., about 25 mass%);

Component (c) nitric acid (HN0 ₃ ), concentrated

 CAS-No. [7697-37-2]

 (1 to 5 mass%, e.g., 2.5 mass%);

Component (d) Mixture of kerosene components, hydrocarbon mixture, range C9 to C16, boiling range 130 ° C to 290 ° C

 CAS Nos. [8008-20-6], [64742-81-0],

 [64742-47-8]

 No. 139 - Petroleum kerosene, No. 140 - Petro leum, Agip Deutschland GmbH (DE)

 (10 to 20 mass%, e.g., about 15 mass%);

Component (e): Distilled water

 (25 to 65 mass%, e.g., about 42.5 mass%

Other parameters: pH: about 2;

 Redox potential: about 520 mV.

Embodiment 2:

Component (a): isotridecanol (C ₃ H ₂ OH), ethoxylated with an ethoxylation degree (EO) 2-5

 CAS-No. [69011-36-5]

 MARLIPAL 0 13/50 ™, Sasol Germany GmbH (DE) (10 to 20 mass I, e.g., about 10 mass%);

Component (b): benzenesulfonic acid, C10-13-alkyl derivatives,

 Compounds with triethanolamine

 CAS-No. [68411-31-4]

 MARLOPON AT 50 ™, Sasol Germany GmbH (DE) (containing benzenesulfonic acid,

C10-13 alkyl derivatives, compounds with tri- ethanolamine between 50 and 60%)

 (15 to 30 mass%, e.g., about 23 mass%);

Component (c): nitric acid (HN0 ₃ ), concentrated

 CAS-No. [7697-37-2]

 (1 to 5 mass%, e.g., 1.6 mass%);

Component (d): mixture of kerosene components, hydrocarbon mixture, range C9 to C16, boiling range 130 ° C to 290 ° C

 CAS Nos. [8008-20-6], [64742-81-0],

 [64742-47-8]

 No. 139 - Petroleum kerosene, No. 140 - Petroleum, Agip Deutschland GmbH (DE)

 (10 to 20 mass%, e.g., about 13 mass%);

Component (e): Distilled water

 (25 to 65 mass%, e.g., about 52.4 mass%)

Other parameters: pH: about 2.3;

 Redox potential: about 510 mV.

Claims

claims Electrolytic solution for the electrochemical polishing of metals, in particular from the group consisting of copper (Cu), zinc (Zn), silver (Ag), tin (Sn), gold (Au), platinum (PT) and at least one of these metals-containing alloys, comprising:  (a) between 2 and 50% by weight of at least one ethoxylated alcohol;  (b) between 2 and 50% by weight of at least one substance selected from the group consisting of sulfonic acids and sulfonates;  (c) between 0.2 and 10 mass% of at least one inorganic acid;  (d) between 6 and 50 mass% of at least one liquid hydrocarbon; and  (e) between 5 and 90% by weight of water; wherein the pH of the electrolyte solution is at least 1. Electrolyte solution according to claim 1, characterized in that the ethoxylated alcohol according to (a) has between 5 and 30 carbon atoms, in particular between 7 and 25 carbon atoms, preferably between 9 and 20 carbon atoms. Electrolyte solution according to claim 1 or 2, characterized in that the ethoxylated alcohol according to (a) is an alkanol, in particular an isoalkanol. Electrolyte solution according to one of Claims 1 to 3, characterized in that the ethoxylated alcohol is measure (a) is a primary alcohol. Electrolyte solution according to one of claims 1 to 4, characterized in that the ethoxylated alcohol according to (a) has a degree of ethoxylation (EO) between 1 and 50, in particular between 1 and 40, preferably between 1 and 30. Electrolytic solution according to one of claims 1 to 5, characterized in that the at least one substance from the group of sulfonic acids and sulfonates according to (b) from the group of arenesulfonic acids and arenesulfonates, in particular from the group of benzenesulfonic acids, alkylbenzenesulfonic acids, benzenesulfonates and alkylbenzene - sulfonate, is selected. Electrolyte solution according to one of claims 1 to 6, characterized in that the at least one substance from the group of sulfonic acids and sulfonates according to (b) from the group benzenesulfonic acid, their alkyl derivatives, in particular their C10-C16-alkyl derivatives, preferably their C10-C13- Alkyl derivatives, as well as salts of benzenesulfonic acid and their alkyl derivatives, in particular with alkali metal, alkaline earth metal, ammonium ions and / or organic amines, in particular triethanolamine and / or triethylamine. Electrolyte solution according to one of claims 1 to 7, characterized in that the at least one inorganic acid from the group of mineral acids, in particular from the group of oxidizing mineral acids, is selected. Electrolyte solution according to one of claims 1 to 8, characterized in that the at least one inorganic acid from the group nitric acid (HN0 ₃ ), nitrous acid (HN0 ₂ ) and mixtures thereof is selected. Electrolyte solution according to one of claims 1 to 9, characterized in that the at least one liquid hydrocarbon according to (d) has a chain length of between 30 and 30 carbon atoms, in particular between 5 and 25 carbon atoms, preferably between 5 and 20 carbon atoms. Electrolyte solution according to one of claims 1 to 10, characterized in that the at least one liquid hydrocarbon according to (d) is a hydrocarbon mixture, in particular from the group of petroleum or a petroleum fraction, preferably in the form of light petroleum (kerosene), gasoline or a Benzine fraction. Electrolyte solution according to one of claims 1 to 11, characterized in that the at least one liquid hydrocarbon according to (d) or the hydrocarbon mixture has a boiling point or a boiling range between 25 ° C and 350 ° C, in particular between 50 ° C and 330 ° C, preferably between 75 ° C and 310 ° C, having. 13. Electrolyte solution according to one of claims 1 to 12, characterized in that the water according to (e) is demineralized or distilled water. Electrolyte solution according to one of claims 1 to 13, characterized in that it (a) between 3.5 and 40% by weight, in particular between 5 and 30% by weight, of the at least one ethoxylated alcohol;  (b) between 3.5 and 40 mass%, in particular between 5 and 30 mass%, of the at least one substance from the group of sulfonic acids and sulfonates;  (c) between 0.2 and 7.5 mass%, in particular between 0.2 and 5 mass%, of the at least one inorganic acid;  (d) between 8 and 40 mass%, in particular between 10 and 30 mass%, of the at least one liquid hydrocarbon; and  (e) contains between 10 and 80 mass%, in particular between 15 and 70 mass%, of water. Electrolyte solution according to one of claims 1 to 14, characterized in that it has a pH between 1 and 5, in particular between 1.5 and 4.5, preferably between 2 and 3.5. Electrolyte solution according to one of claims 1 to 15, characterized in that it has a redox potential between 350 mV and 700 mV, in particular between 400 mV and 650 mV, preferably between 450 mV and 600 mV. Electrolyte solution according to one of claims 1 to 16, characterized in that it further contains a proportion of granules particles, in particular in the form of Plastic particles. 18. A method for the electrochemical polishing of metal objects, in particular from the group copper (Cu), zinc (Zn), silver (Ag), tin (Sn), gold (Au), platinum (Pt) and at least one of these metals containing alloys, wherein the metal object is electrically conductively connected to an anode and immersed in an electrolyte solution having a cathode, wherein the electrodes are subjected to an electrical voltage, characterized in that an electrolyte solution according to one of Claims 1 to 17 is used. A method according to claim 18, characterized in that an electrode voltage between 0.5 V and 20 V, in particular between 0.75 V and 15 V is set. A method according to claim 18 or 19, characterized in that a current density between 0.1 and 5 A / dm ² , in particular between 0.2 and 4 A / dm ² , preferably between 0.3 and 3 A / dm ² , is set Method according to one of claims 18 to 20, characterized in that the objects are moved in the electrolyte solution, wherein in the case of a Granulatpar particles containing electrolyte solution, the objects are moved to at least at periodic intervals in the fluidized granules.