Turk J Chem (2020) 44: 378 – 392 © TÜBİTAK doi:10.3906/kim-1907-80 Turkish Journal of Chemistry http://journals.tubitak.gov.tr/chem/ Research Article A comparative study of silver electrodeposition from pyrophosphate-cyanide and high concentration cyanide electrolytes in the presence of brighteners Hatice Kübra AKBEN 1,2, ∗ , Servet İbrahim TİMUR 1  1 Department of Metallurgical and Materials Engineering, İstanbul Technical University, İstanbul, Turkey 2 Department of Metallurgical and Materials Engineering, Engineering Faculty, İstanbul Gedik University, İstanbul, Turkey Received: 08.08.2019 • Accepted/Published Online: 28.01.2020 • Final Version: 01.04.2020 Abstract: A study of the electrodeposition of silver from 2 diferent types of electrolytes; (1) neutral pyrophosphate- cyanide 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. Infuence 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 efective for silver electrodeposition. The rapid increase in current density at the same potential interval related to grain refnement efect of potassium antimony tartrate was shown. The cyclic organic compound, 2- mercaptobenzothiazole, polarizes the reduction to high cathodic potential in pyrophosphate electrolyte. However, the sufcient levelling efect required for the mirror-bright appearance seems to be related to the high polarizing efect of the high concentration cyanide content. In the case of pyrophosphate electrolytes, sufcient 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 difusion-controlled growth in high concentration cyanide electrolyte. Key words: Electrodeposition, silver, cyanide, brighteners, potassium antimony tartrate, 2-mercaptobenzothiazole 1. Introduction Electrodeposition of silver is a common industrial process in the manufacture of mirrors, in decorative ap- plications, electronic applications, bearings, hot gas seals, and many other applications because of the high refectivity of the surface and the highest electrical and thermal conductivity of all metals. The signifcant tech- nological 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. To overcome these problems, researches on less toxic compounds for silver electroplating have been receiving great attention. Electroplating baths of nitrate [1–4], uracil [5], thiourea [6], 2-hydroxypyridine [7,8], 5,5-dimethylhydantoin [9,10], ferrocyanide-thiocyanide [11,12], ionic liquids [13–15] have been proposed. However, 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 bufer salt and metal-cyanide complex ion as a source of metal ∗ Correspondence: kubra.akben@gedik.edu.tr This work is licensed under a Creative Commons Attribution 4.0 International License. 378