RU2323276C2 - Silver-plating electrolyte - Google Patents

Abstract

FIELD: electroplating, possibly application of gloss silver coating out of cyan free electrolytes.

SUBSTANCE: electrolyte contains soluble compound of silver, comlexing agent 5,5 - dimethylhydantoin, electrically conducting salt of alkali metal, alkali reagent, glossing additive 3 -pyridinesulphonic acid, depassivating additive N - alkylpyrrolidon having 2 - 5 C atoms in alkyl radical. Coating is applied from aqueous solution of electrolyte with pH 9.5 - 11.5.

EFFECT: possibility for applying stable high quality mirror coating during long period of electrolyte operation while using soluble silver anode.

3 cl, 3 ex

Description

The invention relates to chemistry and technology of precious metals and can be used when applying shiny decorative coatings on jewelry, on current-carrying parts of the electronic and electrical industries, in the production of mirrors for special industrial purposes and, in particular, relates to compositions of cyanide-free silver electrolytes.

Known cyanide-free pyrophosphate electrolyte containing silver pyrophosphate complex, potassium pyrophosphate, potassium carbonate and wetting additives. The well-known electrolyte provides thin shiny coatings of silver (Andryushchenko F.K., Orekhova V.V. Metal protection. 1969. No. 3, S.287-292).

However, these coatings have a blue tint and become dull with an increase in coating thickness; in addition, pyrophosphate electrolytes are prone to passivation of silver anodes and the deposition of a dense precipitate of carbonates on the surface of the anode.

Cyanide-free electrolytes are known, which include organic compounds forming complex compounds with silver (US 5601696, 02/11/1997, US 5911866, 06/15/1999, US 6210556, 04/03/2001).

Closest to the proposed electrolyte is a brilliant silvering electrolyte containing a complex compound of silver with 5.5-dimethyl hydantoin, 5.5-dimethyl hydantoin, an electrically conductive alkali metal or ammonium salt, sulfamic acid, alkali metal hydroxide for pH adjustment, a bright-forming additive - 2.2 Β-dipyridyl and, possibly, a passivating additive from pyridine derivatives (nicotinamide, isonicotinamide, 2-aminopyridine, etc.) (US 2005/0183961 A1, 25.08.2005).

The disadvantages of this electrolyte are the low silver deposition rate, low stability of the bright-forming additive (in particular, 2,2′-dipyridyl) and its decomposition during the operation of the electrolyte, which affects the quality of the resulting coatings. In addition, during prolonged use of the electrodes, passivation of silver soluble anodes occurs.

The objective of the invention is to provide a cyanide-free electrolyte that stably provides mirror-gloss silvering, stable in the process of obtaining coatings, providing a high deposition rate of silver, i.e. reducing the duration of the coating process.

The problem is solved by the described silvering electrolyte, which includes: a soluble silver compound, 5,5-dimethylhydantoin as a complexing agent, an alkali metal electrically conductive salt, an alkaline reagent, a bright-forming additive - 3-pyridinesulfonic acid, a passivation additive selected from N-alkylpyrrolidones with the number of carbon atoms in the alkyl radical from 2 to 5.

Preferably, as a soluble silver compound, the electrolyte contains silver nitrate or methanesulfonate, sodium nitrate as an electrically conductive salt, and potassium hydroxide as an alkaline reagent.

In working condition, the electrolyte contains the aforementioned components in an aqueous solution having a pH of from 9.5 to 11.5, with the content of the components in the solution:

silver nitrate or methanesulfonate 10-40 g / l (Ag) sodium nitrate 20-50 g / l potassium hydroxide 9-10 g / l 5,5-dimethylhydantoin 100-160 g / l 3-pyridinesulfonic acid 0.05-0.5 g / l N-alkylpyrrolidone 0.5-5.0 g / l water the rest is up to 1 liter

The most preferred contents of the electrolyte components in its working condition are selected empirically and are due to the following.

An increase in silver concentration above 40 g / l leads to an ineffectively high consumption of silver, while the main indicators do not improve. A decrease in silver concentration below 10 g / l can lead to instability of the electrolysis process and, as a consequence, to a deterioration in the quality of the coating.

The concentration of 5,5-dimethylhydantoin 100-160 g / l provides binding to the complex of all silver in solution, as well as binding to the complex of silver, dissolved on the anode.

At concentrations of compounds of N-alkylpyrrolidone (usually N-methylpyrrolidone, N-ethylpyrrolidone, N-isopropylpyrrolidone, etc.) are used less than 0.5 g / l, anodic passivation of silver is possible; at concentrations of more than 5 g / l, coatings may become somewhat dull.

When the concentration of 3-pyridinesulfonic acid is less than 0.05 g / l, silver coatings grow dull with an increase in coating thickness of more than 3 μm, and at a concentration of more than 0.5 g / l, the coating may darken at the ends of the products, where usually a higher current density.

The pH range from 9.5 to 11.5 is selected based on the maximum stability of silver complex compounds with 5.5-dimethylhydantoin.

The proposed electrolyte is tested on an enlarged laboratory scale.

Example 1

An aqueous electrolyte solution was prepared containing: silver nitrate at a rate of 10 g / l for metal, complexing agent - 5.5-dimethylhydantoin - 100 g / l, sodium nitrate 40 g / l, depassivator - N-methylpyrrolidone - 0.5 g / l , brightening additive - 3-pyridine sulfonic acid with a concentration of 0.5 g / l and potassium hydroxide - 9.4 g / l. At a solution pH of 10.8, the process of obtaining coated in a Hull cell is carried out at room temperature, with stirring of the electrolyte, at a current strength of 0.5 amperes for 4 minutes, with a soluble silver anode. Mirror-gloss coating obtained in the range from 0.1 to 0.3 A / DM ² . The deposition rate at a current density of 0.3 A / cm ² is equal to 0.25 μm / min. The amount of silver released at the cathode is equal to the amount of silver dissolved at the anode; the current efficiency is close to 100%. Coating experiments were carried out for a month. Passivation of the anode was not observed, the solution remained transparent, and the quality of the coatings remained stable.

Example 2

An aqueous electrolyte solution was prepared containing: silver nitrate at a rate of 40 g / l for metal, a complexing agent - 5.5 dimethylhydantoin - 160 g / l, sodium nitrate - 20 g / l, a depassivator - N-ethylpyrrolidone - 3.5 g / l , the bright-forming additive is 3-pyridine sulfonic acid — 0.05 g / l, and the pH regulator — potassium hydroxide — 9.6 g / l, the pH of the solution was 10.8. In the Hull cell, a coating was prepared at room temperature, with stirring of the electrolyte, at a current strength of 0.5 amperes for 4 minutes, with a soluble silver anode. Mirror-gloss coating is obtained in the range from 0.2 to 0.5 A / DM ² . The silver deposition rate at a current density of 0.5 A / cm ² is 0.34 μm / min. The amount of silver released at the cathode is equal to the amount of silver dissolved at the anode; the current efficiency is close to 100%. Coating experiments were carried out for a month. No passivation of the anode was observed, the solution remained transparent, and the coating quality remained stable.

Example 3

From an aqueous electrolyte solution containing: silver nitrate at a rate of 25 g / l for metal, a complexing agent - 5.5 dimethylhydantoin - 140 g / l, potassium nitrate - 50 g / l, a depassivator - N-isopropylpyrrolidone - 5.0 g / l , a bright-forming additive - 3-pyridine sulfonic acid - 0.35 g / l and potassium hydroxide - 9.7 g / l, at pH-11.5, a silver coating process was carried out in the Hull cell. Precipitation conditions: room temperature, electrolyte mixing, current strength of 0.5 amperes, time - 4 minutes, soluble silver anode. Received a mirror-shiny coating in the range from 0.2 to 0.4 A / DM ² . The silver deposition rate at a current density of 0.4 A / cm ² is 0.29 μm / min. The amount of silver released at the cathode is equal to the amount of silver dissolved at the anode; the current efficiency is close to 100%. Coating experiments were carried out for a month. No passivation of the anode was observed, the solution remained transparent, and the quality of the coatings remained stable.

An example of a prototype (US 2005/0183961).

The composition of the aqueous electrolyte solution: complex silver with 5.5-dimethyl hydantoin - 25 g / l silver, sulfamic acid - 52.5 g / l, potassium hydroxide - 60 g / l, 5.5-dimethyl hydantoin - 80 g / l and brightening and depassivating additives: 2.2′-dipyridyl - 5.0 g / l and pyridine derivative (nicotinamide) - 50 g / l. At pH = 11, a process was carried out in a Hull cell at room temperature with stirring of the electrolyte at a current strength of 0.5 amperes for 4 minutes using a soluble silver anode. Mirror-gloss coating obtained in the range from 0.10 to 0.25 A / DM ² . The silver deposition rate at a current density of 0.25 A / cm ² is 0.12 μm / min. The amount of silver released at the cathode is greater than the amount of silver dissolved at the anode, the current efficiency at the cathode is close to 100%, the current efficiency at the anode is 67%. Coating experiments were carried out for a month. After using the electrolyte for 1 week, the anode is passivated, while the anode current efficiency decreased to 12%, and a colloidal precipitate appeared in the solution, the quality of the coatings deteriorated, and the coatings became dull and uneven.

From the above examples it is seen that the proposed invention ensures the achievement of the task, because The claimed composition of the electrolyte provides an improvement in the specular gloss of coatings, an increase in the silver deposition rate, and stability of the electrolyte over a long period of work.

Claims (3)

1. Silvering electrolyte containing a soluble silver compound, 5,5-dimethylhydantoin as a complexing agent, an electrically conductive alkali metal salt, an alkaline reagent, a brightening additive, a passivating additive and water, characterized in that it contains 3-pyridinesulfonic acid as a brightening additive, as a depassivating additive, a compound selected from N-alkylpyrrolidones with the number of carbon atoms in the alkyl radical is from 2 to 5. 2. The electrolyte according to claim 1, characterized in that it contains silver nitrate or methanesulfonate as a soluble silver compound, sodium nitrate as an electrically conductive salt, and potassium hydroxide as an alkaline reagent. 3. The electrolyte according to claim 1 or 2, characterized in that it contains the aforementioned components in an aqueous solution having a pH of from 9.5 to 11.5 with the following content in the solution, g / l: silver nitrate or methanesulfonate 10-40 (silver) sodium nitrate 20-50 potassium hydroxide 9-10 5,5-dimethylhydantoin 100-160 3-pyridinesulfonic acid 0.05-0.5 N-alkylpyrrolidone 0.5-5.0