A comparative study of silver electrodeposition from pyrophosphate-cyanide and high concentration cyanide electrolytes in the presence of brighteners.

Hatice Kübra Akben,Servet İbrahim Ti̇mur

doi:10.3906/kim-1907-80

Abstract

A study of the electrodeposition of silver from 2 different types of electrolytes; (1) neutral pyrophosphatecyanide electrolyte and (2) alkaline high concentrated cyanide electrolyte in the presence of a variety of additives such as 2-mercaptobenzothiazole, potassium selenocyanate, and potassium antimony tartrate was performed. Influence of additives and cyanide concentration on microstructure and kinetics of the cathodic processes were studied. A brightener couple, 2-mercaptobenzothiazole and potassium antimony tartrate, were combined within this investigation and detected to be highly effective for silver electrodeposition. The rapid increase in current density at the same potential interval related to grain refinement effect of potassium antimony tartrate was shown. The cyclic organic compound, 2-mercaptobenzothiazole, polarizes the reduction to high cathodic potential in pyrophosphate electrolyte. However, the sufficient levelling effect required for the mirror-bright appearance seems to be related to the high polarizing effect of the high concentration cyanide content. In the case of pyrophosphate electrolytes, sufficient levelling cannot be achieved, so semigloss coatings are obtained. The low cathodic potential electrodeposition of silver in pyrophosphate electrolyte, which is found to proceed by 3D instantaneous nucleation, is polarized to high cathodic potentials and grows into 3D progressive nucleation and diffusion-controlled growth in high concentration cyanide electrolyte.

Highlights

Electrodeposition of silver is a common industrial process in the manufacture of mirrors, in decorative applications, electronic applications, bearings, hot gas seals, and many other applications because of the high reflectivity of the surface and the highest electrical and thermal conductivity of all metals
The significant technological concern is to achieve a compact, adherent, and smooth silver electrodeposition. This type of silver coating is still achieved by electrodeposition in baths if highly concentrated cyanide, though this process poses the problems of high toxicity of cyanide and high cost of wastewater treatment
This research has compared and presented the effect of organic and inorganic brighteners used in cyanideand pyrophosphate-based silver electrolytes

Summary

Introduction

Electrodeposition of silver is a common industrial process in the manufacture of mirrors, in decorative applications, electronic applications, bearings, hot gas seals, and many other applications because of the high reflectivity of the surface and the highest electrical and thermal conductivity of all metals. The significant technological concern is to achieve a compact, adherent, and smooth silver electrodeposition. Today, industrially, this type of silver coating is still achieved by electrodeposition in baths if highly concentrated cyanide, though this process poses the problems of high toxicity of cyanide and high cost of wastewater treatment. This type of silver coating is still achieved by electrodeposition in baths if highly concentrated cyanide, though this process poses the problems of high toxicity of cyanide and high cost of wastewater treatment To overcome these problems, researches on less toxic compounds for silver electroplating have been receiving great attention. Industrial use of these baths is still restricted because their use does not achieve coating of high brightness, compactness, and adhesion; the baths lack stability and the complexing agents are expensive. The other type of electrolyte, pyrophosphate-cyanide, contains pyrophosphate buffer salt and metal-cyanide complex ion as a source of metal

Methods

Results

Conclusion