Electrolyte for silver plating of copper wire and bronze wire

Abstract

FIELD: electroplating.SUBSTANCE: invention relates to the field of electroplating, in particular to the electrochemical deposition of silver coating on copper wire and its alloys, and can be used for the production of cable and conductor products. The silvering electrolyte contains components in the following ratio, g / l: dicyanoargentate 30-50 (in terms of metallic silver), potassium thiocyanate 100-250, potassium carbonate 40-70, potassium sodium tartrate tetrahydrate 10-80, potassium antimony tartrate no more than 0.7, alizarin oil no more than 45, tetrahydrofuryl alcohol no more than 75.EFFECT: providing a fine-crystalline homogeneous structure of the coating and the possibility of obtaining a coating with a thickness of up to 50 μm with sufficient plasticity and resistance to peeling during further deformation processing, as well as the possibility of carrying out silvering at high current densities of 5-8 A / dm2.1 cl, 1 ex

Description

[0001] Field of technology to which the invention relates

[0002] The invention relates to the field of electroplating, to the electrochemical deposition of a silver coating on copper wire and its alloys from cyanide-free electrolytes.

[0003] Technology Level

[0004] Currently, the issue of choosing an electrolyte for silver plating on copper and its alloy wire is a pressing one. Commonly used electrolytes for silver plating copper and its alloys include cyanide, pyrophosphate, ferricyanide, sulfite, iodide, thiocyanate, and others. However, not all known electrolytes are suitable for silver plating on copper wire.The production of silver-plated copper wire is technologically complex due to its long length and small cross-section. High demands are placed on the uniformity of the coating (the coating thickness must be stable along the entire circumference of the wire), the durability and plasticity of the coating during deformation processing of the wire after silver plating (today, the coating of the wire after galvanic deposition does not meet the specified requirements for cable and wire products; compaction of the coating by drawing is necessary), the stability of the structure along the length and thickness of the wire and the speed of coating deposition, which must ensure production on an industrial scale.

[0005] The most studied and highest-quality silver coating is cyanide electrolyte. However, cyanide electrolyte is highly toxic due to the free potassium cyanide. Its use requires compliance with environmental safety regulations and the creation of specially equipped work areas, which entails significant risks and financial costs.

[0006] The disadvantage of iodine silver plating electrolytes, in addition to the yellowish tint, is the fragility and roughness of the coatings.

[0007] Pyrophosphate electrolytes have a high cost of solution and are practically not used in industry.

[0008] Cyanide-free electrolytes that provide high-quality coatings comparable to cyanide-based electrolytes include ferricyanide and dicyanoargentate-rhodanite electrolytes. These electrolytes are similar to cyanide, with cathodic and anodic current efficiencies approaching 100%, stable in operation, and produce matte coatings with a fine-crystalline structure [1].

[0009] The main problem with the use of iron cyanide and dicyanoargentate-rhodanite electrolytes in the production of copper silver-plated wire is the relatively low operating current density, which makes the technology economically impractical on an industrial scale.

[0010] Current density is one of the key process characteristics for electrolytic silver plating of copper wire and its alloys. Increasing current density increases bath productivity, reduces shop and general plant costs, and reduces labor costs. However, due to increased voltage, current leakage, and anode passivation, specific energy consumption increases, and coating quality deteriorates due to the increased risk of discharge of harmful impurities. Electrolyte purification costs and precious metal losses also increase.

[0011] Ferricyanide electrolytes have so far demonstrated superior current density characteristics compared to dicyanoargentate-rhodanite electrolytes. A silvering electrolyte known from the prior art is described in Russian Federation Patent No. 2652681, IPC C25D 3 / 46, publication date 04 / 28 / 2018, based on 30-40 g / l silver chloride, 100-110 g / l potassium ferricyanide, 40-60 g / l potassium carbonate, 100-110 g / l potassium thiocyanate and 10-20 g / l Rochelle salt [2]. According to the description in Patent No. 2652681, this electrolyte is competitive with cyanide electrolyte in terms of productivity while being environmentally safe to use. Current efficiency close to 100% is guaranteed at high current density up to 8.6 A / dm 2 , which ensures a silver deposition rate of up to 5.49 µm / min. These high figures make this process economically feasible.

[0012] However, despite all the economic and environmental attractiveness, the use of this electrolyte has a number of difficulties:

[0013] - all components are dissolved separately, after which solutions of potassium ferrocyanide and potash are boiled and added to silver salt, then all three components are boiled again, this process should exclude exposure to daylight;

[0014] - formation of iron(III) hydroxide Fe(OH)3, which retains a hidden portion of silver chloride AgCl, which can cause significant silver loss during electrolyte preparation. Therefore, the precipitate must be filtered and dissolved in hydrochloric acid.

[0015] Such problems are common to iron cyanide electrolytes and, despite the high current densities, make the use of such electrolytes impractical due to the difficulties in working with them.

[0016] Currently known dicyanoargentate-rhodanite electrolytes provide an insufficiently high current density at a level of up to 5 A / dm 2 .

[0017] A dicyanoargentate electrolyte developed by Vilnius Kapsukas State University [3] is known from the prior art, the general composition of which is presented below, g / l:

[0018] Ag (as KAg(CN)2) 20-80 KSCN 150-400 K2CO3 10-30

[0019] At a temperature of 18-25°C and a cathode current density of 0.5-5 A / Dm 2 .

[0020] This electrolyte is suitable for silver plating wire. K2CO3 increases the stability of the dicyanoargentate complex in the electrolyte, improves the conductivity and dissipation capacity of the electrolyte, and the electrolyte itself is easy to manufacture and adjust its composition. However, the disadvantages of the aforementioned dicyanoargentate electrolyte [3], in addition to insufficient current density, include low wear resistance and hardness of the resulting coating.

[0021] In order to eliminate these shortcomings, a well-known dicyanoargentate-thiocyanate electrolyte [4] was created, which is closest in composition to the claimed silvering electrolyte, selected as a prototype, containing, g / l:

[0022] silver (as KAg(CN)2) 23-27 potassium thiocyanate (KCNS) 250-270 Rochelle salt (NaKC4H4O6) 70-80 alizarin oil (C14H8O4) 40-45 tetrahydrofurfuryl alcohol (C5H10O2) 70-75 antimony (in the form of potassium antimonate SbOKC4H4O6) 11-13

[0023] The cathode current density of the prototype is 0.2-0.4 A / dm 2 , temperature 18-25°C.

[0024] The disadvantage of the prototype is the low operating current density.

[0025] Disclosure of the essence of the invention

[0026] The technical problem of the invention is the development of a dicyanoargentate-rhodium silvering electrolyte that provides a fine-crystalline homogeneous structure of the coating, the possibility of applying a coating with a thickness of up to 50 μm, sufficient plasticity of the coating and resistance to delamination during further deformation processing, capable of operating at current densities of more than 5 A / dm 2 .

[0027] The technical problem is solved due to the fact that the claimed silvering electrolyte contains dicyanoargentate, potassium thiocyanate, potassium carbonate, potassium sodium tartrate tetrahydrate, potassium antimony tartrate, alizarin oil and tetrahydrofuryl alcohol in the following ratio of components, g / l:

[0028] dicyanoargentate 30-50 (in terms of metallic silver) potassium thiocyanate 100-250 potassium carbonate 40-70 potassium sodium tartrate tetrahydrate 10-80 potassium antimony tartrate no more than 0.7 alizarin oil no more than 45 tetrahydrofuryl alcohol no more than 75

[0029] The technical result of the invention, in comparison with the prototype, is to provide a fine-crystalline homogeneous structure of the coating and the possibility of depositing a coating with a thickness of up to 50 μm, sufficient plasticity of the coating and resistance to delamination during further deformation processing, as well as the possibility of silvering at high current densities of 5-8 A / Dm 2 , making it suitable for industrial applications.

[0030] Implementation of the invention

[0031] Cyanide-free dicyanoargentate electrolyte for depositing silver on copper wire and bronze wire BrKhTsrK contains dicyanoargentate, potassium thiocyanate, potassium carbonate, potassium sodium tartrate tetrahydrate, potassium antimony tartrate, alizarin oil and tetrahydrofuryl alcohol in the following ratio of components, g / l:

[0032] - dicyanoargentate (KAg(CN)2) 30-50 in terms of metallic silver;

[0033] - potassium thiocyanate (KCNS) 100-250;

[0034] - potassium carbonate (K2CO3) 40-70;

[0035] - potassium sodium tartrate 4-aqueous (KNaC4H4O6⋅4H2O) 10-80;

[0036] - potassium antimony tartrate not more than 0.7;

[0037] - alizarin oil not more than 45;

[0038] - tetrahydrofuryl alcohol not more than 75.

[0039] The claimed electrolyte ensures operation at a high current density of 5 to 8 A / dm 2 The operating temperature of the electrolyte is 40-60°C. The maximum coating thickness reaches 50 µm.

[0040] The presence of potassium carbonate (K2CO3) at a concentration of 40-70 g / l increases the stability of the dicyanoargentate complex in the electrolyte, improves the conductivity and dissipation capacity of the electrolyte, especially at increased current densities up to 8 A / Dm 2 .

[0041] To prevent passivation of silver anodes and ensure electrolysis at increased current densities, potassium sodium tartrate tetrahydrate (KNaC4H4O6⋅4H2O Rochelle salt) was introduced at a concentration of 10-80 g / l and potassium thiocyanate (KCNS) at a concentration of 100-250 g / l.

[0042] To increase wear resistance and hardness, it is recommended to add antimony to the dicyanoargentate electrolyte in the form of potassium antimony tartrate with Rochelle salt [5]. The addition of antimony in an amount of no more than 0.7 g / l ensures high-quality adhesion of the silver coating to the copper base due to the change in internal stresses from tensile to compressive [6], without affecting the electrical conductivity of silver-plated copper wire and bronze wire.

[0043] Alizarin oil refines the structure of the silver coating [5], which reduces the coating's "looseness" and increases its density, which is especially critical in surface layers for subsequent compaction. The formation of a finer structure allows for the application of silver coatings up to 50 µm thick.

[0044] Industrial "pass-through" silver plating of wire poses the problem of silver-containing deposits forming on the cathode elements. These deposits impede wire passage through the machine and indicate a loose coating, which contributes to wire breakage during the silver plating stage and subsequent drawing. In addition to adding alizarin oil and antimony, this problem can be solved by using tetrahydrofuryl alcohol, a primary monohydric alcohol that quickly volatilizes and promotes the formation of hard, shiny deposits [5], which increases wire sliding as it passes through the cathode.

[0045] Increasing the operating temperature of the electrolyte and increasing the silver concentration facilitates the operation of the electrolyte at higher current densities; during the silver electrodeposition process, active mixing occurs due to currents and wire movement.

[0046] Thus, the proposed technical solution has the following advantages:

[0047] - the quality of silver plating is comparable to that of cyanide electrolyte;

[0048] - the use of dicyanoargentate electrolyte causes significantly less harm to the environment compared to cyanide electrolyte;

[0049] - a successful combination of electrolyte additives provides a fine-crystalline, uniform structure, which allows for the application of a coating up to 50 microns thick and makes the coating sufficiently plastic and resistant to peeling during further deformation processing.

[0050] This electrolyte composition has been successfully tested at JSC OKB KP using copper wire and BrKhTsrK bronze wire. Silver-plated copper wire and silver-plated BrKhTsrK bronze wire, produced by silver plating, including subsequent drawing, are suitable for use in cable and wire products. The electrical resistance of copper wire and BrKhTsrK bronze wire after silver plating and drawing complies with current regulatory and technical documentation and does not exceed 0.0180 μOhm⋅m and 0.0200 μOhm⋅m, respectively.

[0051] Literature

[0052] 1. Edited by Doctor of Technical Sciences, Professor M.A. Shluger. Galvanic Coatings in Mechanical Engineering. Volume 1. Moscow "Mashinostroenie", 1985.

[0053] 2. Patent RU 2652681 C2. Silver plating electrolyte, Kamsky Kabel LLC.

[0054] 3. Interindustry information leaflet. No. 44-73, series 10-12. LitNIINTI, 1973.

[0055] 4. https: / / impgold.ru / articles / 5692 / ?ysclid=lupvqcjdhw934370772 [electronic resource, accessed 04 / 07 / 2024]

[0056] 5. T.Yu. Yankauskas, V.E. Daujotis, V.A. Kaikaris. On increasing the gloss and hardness of silver coatings. Knowledge Society of the RSFSR, Moscow House of Scientific and Technical Propaganda named after F.E. Dzerzhinsky. GALVANIC AND CHEMICAL COATINGS WITH PRECIOUS AND RARE METALS, 1978.

[0057] 6. A.G. Putaykina, G.K. Burkat. "The Possibility of Using an Ag-Based Composite Coating to Increase the Wear Resistance of Electrical Contacts." On the 100th Anniversary of Domestic Tank Building, 2020.

Claims

A silvering electrolyte containing dicyanoargentate, potassium thiocyanate, potassium sodium tartrate tetrahydrate, potassium antimony tartrate, alizarin oil and tetrahydrofuryl alcohol, characterized in that it additionally contains potassium carbonate in the following ratio of components, g / l: dicyanoargentate 30-50 (in terms of metallic silver) potassium thiocyanate 100-250 potassium carbonate 40-70 potassium sodium tartrate tetrahydrate 10-80 potassium antimony tartrate no more than 0.7 alizarin oil no more than 45 tetrahydrofuryl alcohol no more than 75