Effect Of Nickel On Copper Anode Passivation In A Copper Anode Passivation In A Copper Sulfate Solution By Electrochemical Impedance Spectroscopy
Páginas: 29 (7179 palabras)
Publicado: 14 de noviembre de 2012
Journal of Applied Electrochemistry (2006) 36:691–701 DOI 10.1007/s10800-006-9130-2
Ó Springer 2006
Effect of nickel on copper anode passivation in a copper sulfate solution by electrochemical impedance spectroscopy
G. JARJOURA and G.J. KIPOUROS* Materials Engineering Programme, Dalhousie University, P.O. Box 1000, Halifax, NS, B3J 2X4, Canada (*author for correspondence, e-mail:Georges.kipouros@dal.ca)
Received 5 June 2005; accepted in revised form 23 January 2006
Key words: anode passivation, copper, diffusion coefficient, electrorefining, electrochemical Impedance Spectroscopy, surface oxides
Abstract Electrochemical Impedance Spectroscopy (EIS) was applied on Cu–Ni samples passivated in a specially designed flat electrochemical cell which was heated at 60 °C. The electrolyteconsisted of 160 g l)1H2SO4, 40 g l)1 Cu2+ and 0, 10, 20, 30 or 40 g l)1 Ni2+ and the copper anodes contained nickel ranging from 0 w% to 10 w%. The oxygen content of the anodes and the electrolyte was also measured. An AC excitation signal of 10 mV and of 1mHz– 100 MHz frequency was applied at the open circuit potential as well as at a passivation potential, the latter having been determinedpreviously. The results indicate that nickel ion additions to the electrolyte increased the resistance of the electrolyte and altered the porosity, thickness and constituents of the passivation layer formed. The equivalent circuit models generated from the data acquired during the EIS experiments and the values for the electrical components were in the predicted range. The results are supported bysupplementary XRD and SEM findings.
1. Introduction High purity copper is produced by electrorefining of copper anodes containing at least 99.5% copper which are cast from fire refined blister copper [1]. Copper ions dissolve at the anode, enter the electrolyte and then selectively deposit onto the cathode under the force of an applied direct current. Impurities in the anode either dissolve into theelectrolyte and circulate with it or remain at the anode and become part of the anode slimes. Among the impurities are also precious metals the recovery of which contribute into the financial success of the operation. Nickel in the anode in concentrations less than 3000 ppm dissolves virtually 100% into the electrolyte whereas in excess of that amount result in the formation of some NiO upon thesolidification of the anode. Nickel oxide being a refractory, does not dissolve in the electrolyte and remains in the anode slimes. The slimes will either settle to the bottom of the cell or circulate with the electrolyte or remain attached to the copper anode forming a relatively thick porous layer of impurities. The slimes layer adds to the resistance of the diffusion layer and may contribute to theeffect known as anode passivation i.e. a sharp increase in anode potential while the current applied is unchanged. During anode passivation further dissolution of the anode ceases, the electrorefining process is prematurely terminated and the remaining
undissolved anode is removed and remelted. To avoid passivation the applied current density is limited to around 30 mA cm)2 [1]. Theinterpretation of the mechanism by which the anode is passivated is still an issue of disagreement. Some researchers [2] have attributed the anode passivation to the low solubility of copper sulphate in the electrolyte that causes precipitation of copper sulfate crystals at the copper anode, which in turn is insulated and the passage of current through the electrochemical cell is prevented. Other researchers[3] have postulated that passivation is due to the formation of a cuprous oxide film on the anode, formed by the following reactions: Dissolution Reactions Cu ! Cuþ þ eÀ ðfastÞ Cuþ ! Cu2þ þ eÀ ðslowÞ Passivation Reactions 2Cuþ þ H2 O ! Cu2 O þ 2Hþ 2Cu þ H2 O ! Cu2 O þ 2Hþ þ 2eÀ ð3Þ ð4Þ ð1Þ ð2Þ
According to this theory high current densities result in the build up of Cu+ ions at the anode...
Ó Springer 2006
Effect of nickel on copper anode passivation in a copper sulfate solution by electrochemical impedance spectroscopy
G. JARJOURA and G.J. KIPOUROS* Materials Engineering Programme, Dalhousie University, P.O. Box 1000, Halifax, NS, B3J 2X4, Canada (*author for correspondence, e-mail:Georges.kipouros@dal.ca)
Received 5 June 2005; accepted in revised form 23 January 2006
Key words: anode passivation, copper, diffusion coefficient, electrorefining, electrochemical Impedance Spectroscopy, surface oxides
Abstract Electrochemical Impedance Spectroscopy (EIS) was applied on Cu–Ni samples passivated in a specially designed flat electrochemical cell which was heated at 60 °C. The electrolyteconsisted of 160 g l)1H2SO4, 40 g l)1 Cu2+ and 0, 10, 20, 30 or 40 g l)1 Ni2+ and the copper anodes contained nickel ranging from 0 w% to 10 w%. The oxygen content of the anodes and the electrolyte was also measured. An AC excitation signal of 10 mV and of 1mHz– 100 MHz frequency was applied at the open circuit potential as well as at a passivation potential, the latter having been determinedpreviously. The results indicate that nickel ion additions to the electrolyte increased the resistance of the electrolyte and altered the porosity, thickness and constituents of the passivation layer formed. The equivalent circuit models generated from the data acquired during the EIS experiments and the values for the electrical components were in the predicted range. The results are supported bysupplementary XRD and SEM findings.
1. Introduction High purity copper is produced by electrorefining of copper anodes containing at least 99.5% copper which are cast from fire refined blister copper [1]. Copper ions dissolve at the anode, enter the electrolyte and then selectively deposit onto the cathode under the force of an applied direct current. Impurities in the anode either dissolve into theelectrolyte and circulate with it or remain at the anode and become part of the anode slimes. Among the impurities are also precious metals the recovery of which contribute into the financial success of the operation. Nickel in the anode in concentrations less than 3000 ppm dissolves virtually 100% into the electrolyte whereas in excess of that amount result in the formation of some NiO upon thesolidification of the anode. Nickel oxide being a refractory, does not dissolve in the electrolyte and remains in the anode slimes. The slimes will either settle to the bottom of the cell or circulate with the electrolyte or remain attached to the copper anode forming a relatively thick porous layer of impurities. The slimes layer adds to the resistance of the diffusion layer and may contribute to theeffect known as anode passivation i.e. a sharp increase in anode potential while the current applied is unchanged. During anode passivation further dissolution of the anode ceases, the electrorefining process is prematurely terminated and the remaining
undissolved anode is removed and remelted. To avoid passivation the applied current density is limited to around 30 mA cm)2 [1]. Theinterpretation of the mechanism by which the anode is passivated is still an issue of disagreement. Some researchers [2] have attributed the anode passivation to the low solubility of copper sulphate in the electrolyte that causes precipitation of copper sulfate crystals at the copper anode, which in turn is insulated and the passage of current through the electrochemical cell is prevented. Other researchers[3] have postulated that passivation is due to the formation of a cuprous oxide film on the anode, formed by the following reactions: Dissolution Reactions Cu ! Cuþ þ eÀ ðfastÞ Cuþ ! Cu2þ þ eÀ ðslowÞ Passivation Reactions 2Cuþ þ H2 O ! Cu2 O þ 2Hþ 2Cu þ H2 O ! Cu2 O þ 2Hþ þ 2eÀ ð3Þ ð4Þ ð1Þ ð2Þ
According to this theory high current densities result in the build up of Cu+ ions at the anode...
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