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Electrochemical and Metallographical Characterization

Electrochemical and Metallographic Characterization of Inhibitor Variation in Copper Refining Electrolysis
Z. Mubarok, I. Filzwieser*, P. Paschen Department of Metallurgy, University of Leoben Franz-Josef-Strasse 15, A-8700 Leoben, Austria * METTOP GmbH Augartenweg 1, A-8700 Leoben, Austria

Abstract
The objective of the present paperis to discuss the polarization and microstructure behaviour of copper electrodeposit from the electrolytic refining with various additives compositions in the electrolyte. The effect of the concentration of glue and thiourea and the concentration ratio of glue/thiourea at different current densities and temperatures on the cathode polarization has been investigated by galvanostatic polarizationmethod. Thiourea was found to have cathodic polarizing effect at a current density of 300 Am-2 and a depolarizing effect at higher current densities (600 and 900 Am-2). Glue was identified as a cathodic polarizer under current densities of 300 to 900 Am-2. The polarizing effect of glue was reduced significantly at a temperature of 70 oC and after 12 and 24 hours exposures. Test series with variousglue/thiourea ratios in the electrolyte were also conducted at 65 oC, for 48 hours, under current densities of 350 Am-2. As the results of short term galvanostatic polarization, a higher glue/thiourea ratio resulted in a higher cathode polarization during copper deposition. The metallographic analysis of the copper deposit indicated the growth of basisoriented reproduction (BR) crystal followed bylarge columnar crystals of field isolated crystal (FI) type at a high ratio of glue/thiourea. The extensive growing of copper grain at extremely high cathode polarization during electrolysis was identified in correlation with the growth of dendritic cathode and nodulation.

Proceedings of EMC 2005

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Mubarok, Filzwieser, Paschen

1

Introduction

The optimization of the additives inthe copper tank house remains a topic of concern in producing good quality of cathode with the increase of the current density applied. The research efforts are focusing on the determination of the appropriate concentration of the mostly used additives, monitoring and control of the actual additives activity in the electrolyte as well as the use of alternative additives [4,6,14]. The most commonadditives currently used in the electrorefining of copper are thiourea, glue, and chloride. Although the glue and thiourea have been used nearly as long as the application of copper electrorefining, the behaviour and inhibition mechanism are not yet completely understood. Basically, a combination of several addition agents, such as glue, thiourea and chloride is necessary for optimal control ofcopper electrocrystallization [9]. An inhibitor is needed to slow down the rate of electrocrystallization but there must also be some possibility to reactivate the process by means of nucleation. Overall control of the electrodeposition process is thus achieved by the use of two counteractive regulators. Improper concentration and concentration ratio of the additives can lead to cathode nodulation[6,10]. The optimum concentration and concentration ratio of the inhibitor depends on the electrolysis parameters, mainly current density, anode composition, temperature and hydrodynamic behaviour of electrolyte. Those parameters often vary considerably over the electrolysis time. In this regard, a system for monitoring of actual inhibitor activity is necessary to be esta- blished. Electrochemicalmeasurement techniques have been widely used in laboratory for investigating the additives behaviour during copper electrolytic deposition, such as potentiodynamic polarization, cyclic voltammetry, current transient and galvanostatic method [3,5,7]. Among the available techniques, galvanostatic technique is a rapid one that can be used to evaluate the additives performance during electrodeposition...
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