Study On Silver Electroplating Technology

Silver, is a long history of precious metals, in the crust in the content is very small, only 0.07ppm, sterling silver is a beautiful silver-white metal, its jewelry and utensils have a good reflectivity, polished can To achieve a high brightness, in jewelry and home decoration in a wide range of uses. And in some metal surface coated with a layer of silver, you can also achieve the decorative effect of sterling silver, the appearance of bright and meticulous, wear, corrosion resistance, anti-color ability, and therefore has a wide range of applications. In the past, the use of non-bright Silver Electroplating process is poor appearance, low corrosion resistance, especially anti-sulfur anti-discoloration ability is poor, in order to light, usually using chemical polishing or copper brush brush and then dip silver, so that both waste of electricity and time , But also pollute the environment. In order to solve the above problems, the domestic commonly used two methods, one is the use of antimony potassium tartrate with organic additives (mostly sulfur compounds) to obtain bright Silver Electroplating, this method due to the impact of antimony and sulfur, the coating easy to color, Large, solderability is not ideal. The other is the use of cyanide bright silver, this method uses a sulfur-free organic brightener and the right amount of antimony potassium tartrate with the use of the whole bright silver layer, to solve the coating easy to change color, brittle, The problem is not ideal, while reducing the consumption of raw materials. However, this method because of the need for more organic complexes, making the factors affecting the plating increased, but also increased the process. In order to seek a time-saving and provincial method of raw materials, based on the original process on the basis of the reform, recommend an impact Silver Electroplating process, that is, at higher current density, in just a few seconds to complete the silver, silver Thin and uniform light, Silver Electroplating bath composition is simple, do not need other organic ingredients, the process once completed, the time is short, high production efficiency,

Saving raw materials (silver is only about 4% of the original cyanide bright silver).

1 Experimental methods and results discussed

1.1 Electrode and experimental conditions

Anode: stainless steel plate 10 × 2cm2;

Cathode: copper (several) 10 × 2cm2;

Temperature: no room temperature at room temperature.

1.2 Process flow

Silver Electroplating oil → hot water wash → cold water washing → chemical rust → washing → cyanide copper plating → washing → acid bright copper plating → washing → bright nickel plating → washing → impact Silver Electroplating → deionized water (or distilled water) wash → passivation → dip 400 organic film → drying → dip paint protective film → drying → inspection.

1.3 Electrolyte

The impact of Silver Electroplating electrolyte, including AgCN and KCN two kinds of electrolytes, so the number of AgCN and KCN on the impact of the plating within a short time the great impact on the plating method. The amount of fixed AgCN was 1.5 g / L, and the content of KCN in the electrolyte was changed to clarify the proper ratio of AgCN to KCN. Can be seen from Table 1, KCN in the electrolyte content of 80g / L the most appropriate, that is, with the AgCN ratio of 160: 3, when the silver coating bright and delicate, apparent as the ideal white, and KCN content is low In this content, the Silver Electroplating layer into the mist so that the silver coating blurred, lack of gloss, the coating is not detailed, if higher than this content, the coating yellow.

Agall and KCN to maintain this ratio is due to the impact of silver electroplating electrolyte of the main components of complex silver salt and free potassium cyanide. The formation reaction of the complex silver salt is as follows: AgCN + KCN = K [Ag (CN) 2]; dissociation reaction of complex silver salt: K [Ag (CN) 2] = K ++ [Ag (CN) 2]

Since the unstable constant of [Ag (CN) 2] - is very small (K unstable = 8 × 10-22), the concentration of Ag in the electrolyte is very low, so the deposition of silver layer on the workpiece is mainly [Ag (CN) 2] - direct reduction.

Potassium cyanide as a complexing agent in the electrolyte, combined with silver to form [Ag (CN) 2] -, because of its complex ability, so the stability of silver cyanide ions. The stability of [Ag (CN) 2] - complex ions can be ensured by maintaining a certain amount of potassium cyanide in the electrolyte, and the effect of cathodic polarization can be improved.

Electrolyte AgCN content is too high will lead to yellow coating, the content is too low silver ions and potassium cyanide complex instability, cathodic polarization is small, the coating is not detailed. This method can determine the requirement of impact plating when the content of AgCN is 1.5g / L on a large number of experiments, which saves the amount of silver and meets the requirements of decorative Silver Electroplating.