RU2569876C1 - Method for decorative electrochemical finishing of silver surface - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes treating with aqueous sodium thiosulphate solution with Na₂S₂O₃·5H₂O content of 790 g/l at temperature of 20±2°C using pulsed unipolar and bipolar rectangular currents with the following amplitude-time parameters: t_puls=100-500 mcs, t_{"отр."puls}=100-500 mcs, t_"з"=100-500 mcs, t_pause=100-500 mcs, amplitude current density in a positive polarity pulse i_puls=0.25-0.8 A/cm², amplitude current density in a reverse polarity pulse i_{"отр."puls}=0-0.6 A/cm², and treatment duration of 2-4 minutes, wherein the current is unipolar at I_{"отр."puls}=0.

EFFECT: forming fine, medium and large patterns on irregularly shaped surfaces, including thin-wall and thin-sheet articles.

7 dwg, 1 tbl, 6 ex

Description

The invention relates to the field of electrochemical methods of decorative surface treatment, and in particular to methods of electrochemical etching of a surface in order to impart a decorative texture.

A known method of decorative surface finish of silver 925 sample [McGras Jinx. Jewelry decoration. - M .: Art-Rodnik, 2007, p. 42-47], in which the surface texture is created by chemical etching of the surface areas that are not protected by a specially applied mask in a 25-30% aqueous solution of nitric acid (analogue).

The proposed method is implemented using an aggressive environment (25-30% aqueous solution of nitric acid). The texture pattern is rather large and regular, as it is formed by holes in a specially applied protective layer, which significantly limits the scope of the method and does not allow the texture to be formed on the complex surfaces of thin parts.

A known method of electrochemical invoicing of the surface of silver 925 with a master alloy of copper [Galanin S.I., Galamy Yu.V. Investigation of the process of electrochemical invoicing of the surface of silver alloys 925 samples // ENI Design. Theory and Practice, vol. 5. M .: MGUPI, 2010 .-- S.1-15. Access mode: http: //www.enidtp.rn], in which the treatment is carried out in a 10% aqueous solution of nitric acid HNO ₃ . Medium surface is formed at an electrolyte temperature of t = 70 ° C, anodic current density i = 2.5 A / cm ² , processing time τ = 0.5 min. The large-surface silver surface is formed at an electrolyte temperature of t = 75 ° C, anodic current density i = 2.5 A / cm ² , and processing time τ = 1 min. The formed texture is visible to the naked eye and is suitable for decorating the surface (prototype).

The known method is implemented in an aggressive electrolyte (10% aqueous solution of nitric acid HNO ₃ ) at a high electrolyte temperature (70-75 ° C), which leads to a significant environmental impact and is dangerous for maintenance personnel. In addition, the dimensions of the irregularities of the texture are not clear, which complicates the practical implementation of the method.

The technical task of the invention is the formation of small, medium and large textures on complex surfaces, including thin-walled and thin-sheet products made of an alloy of silver 925 sample with copper.

The stated technical problem is achieved by the fact that electrochemical invoicing is carried out in an aqueous solution of sodium thiosulfate with a content of Na ₂ R ₂ O ₃ × 5H ₂ O - 790 g / l at a temperature of 20 ± 2 ° C using rectangular unipolar and bipolar currents of the following amplitude -temporal parameters (Fig. 1) (the current is unipolar when the current in the return pulse is zero I _neg.imp = 0): t _imp = 100-500 μs; t _neg.imp = 100-500 μs; t _s = 100-500 μs; t _pauses = 100-500 μs; the amplitude current density in a pulse of positive polarity i _imp = 0.25-0.8 A / cm ² , the amplitude current density in a pulse of reverse polarity i _neg.imp = 0-0.6 A / cm ² and the processing time is 2-4 minutes .

Fig. 1. Type of bipolar pulse output current:

t _imp - the duration of the current pulse of positive polarity (ITPP);

t _neg.imp is the pulse duration of the current reverse polarity (ITOP);

t _s - the delay between the end of the ITPP and the beginning of ITOP;

t _pauses - a pause between the end of the ITOP and the beginning of the subsequent ITPP;

I _imp - the amplitude of the ITPP;

I _neg.imp - amplitude of ITOP;

I _imp - the amplitude current density in a pulse of positive polarity;

i _neg.imp is the amplitude current density in a pulse of reverse polarity.

The essence of the method can be explained as follows.

Electrochemical invoicing of the surface of metals and alloys is effectively carried out in the field of passive dissolution, when the processes of surface passivation and destruction of the passive film compete with each other with the prevalence of the second process and the start of activation of the metal surface. In this case, in a fairly narrow range of potentials and current densities, it is possible to create conditions for uneven dissolution rates of various sections of the anode surface and the formation of an irregular structure and micro-roughness of the surface with a pronounced visual decorative effect. Moreover, the formation of pronounced decorative structures is possible on complex surfaces without applying any mechanical forces to them and without using a tool. This allows you to process with high speed the surface of thin-walled and thin-sheet jewelry of any area and complex shape.

EXAMPLES OF SPECIFIC EXECUTION

Table 1 shows examples of the formation of various textures on the surface of silver 925 samples (92.5% - silver, 7.5% - copper) at various amplitude-time parameters of current pulses.

The electrolyte is an aqueous solution of sodium thiosulfate Na ₂ S ₂ O ₃ × 5H ₂ O - 790 g / l at a temperature of 20 ± 2 ° C.

Claims (1)

The method of decorative electrochemical invoicing of the surface of silver 925 with a master alloy of copper, characterized in that the treatment is carried out in an aqueous solution of sodium thiosulfate Na ₂ S ₂ O ₃ × 5H ₂ O - 790 g / l at a temperature of 20 ± 2 ° C using pulsed unipolar and rectangular-shaped bipolar currents of the following amplitude-time parameters: t _imp = 100-500 μs, t _neg.imp = 100-500 μs, t _s = 100-500 μs, t _pauses = 100-500 μs, amplitude current density in a direct pulse polarity i _imp = 0.25-0.8 A / cm ² , the amplitude current density in a pulse of reverse polarity i _{from p.imp} = 0-0.6 A / cm ² and the processing time of 2-4 minutes, and the current is unipolar when i _neg.imp = 0.

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