RESEARCH PAPER

Research Paper

Acknowledgment

We are grateful to Mr. Javed Iqbal helping in preparation of copper discs.

Abstract

Cyclic voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were used to investigate the oxide formation by anodic polarization from -0.3 V to 0.9 V on copper surface in buffer of pH 8.5. Mechanism of passive film formation and its breakdown were explored thus unraveling the facts not explained by cyclic voltammetry.

The reaction of an electrode using EIS, initially at equilibrium to an applied potential is then modeled with equivalent circuits which were proposed for different potential regions that completely illustrated the Cu/oxide/electrolyte systems and their properties in terms of two interfaces. Criterion for the applicability of equivalent circuit models was discussed. Changes in the film/metal interface as a function of potential were also probed at 30 MHz using Nyquist plots. Diffusion coefficient and concentration of mobile ions in the film calculated from the EIS data came out of the order of 10-6 cm2 s-1 and 10-6 mmol/ml respectively.

Table of content

Introduction1

Experimental2

Results and Discussion2

EIS studies of copper surface3

Initial stage4

Middle stage7

Final stage9

Variation in Z/ and Z// at 30 mHz11

Conclusion12

Research paper

Introduction

The growth pattern of passive film formation and breakdown was investigated earlier in buffer solution of pH 9.2.1. Thin films formed over copper surface mostly consist of a barrier layer of Cu2O and a duplex film CuO/Cu (OH)2. Feng. et.al. showed the strong reliance of film texture on the pH of the solution and since the film formation has attracted considerable interest in many areas of research to study phenomena of corrosion, electro catalysis and double layer structures, therefore, it is useful to study its anodic behavior in aqueous media of weakly acidic or alkaline pH. Nevertheless, in the past, passive layers on copper metal have been investigated with full concentration. Recently, studies of corrosion of micro and nano particles of copper and pre-patinated copper have been reported.

The degree of protection against corrosion or oxidation afforded by the oxide film on a metal surface depends on its integrity, its thickness, and the diffusion constants in the oxide film. Relatively a large number of surface analytical and electrochemical tools have been used to explore its corrosion behavior. Electrochemical impedance spectroscopy is a powerful situ technique that is used in the present work to explain the mechanism responsible for the growth of passive film under applied potential and ultimately breakdown of this layer in buffer solution, pH 8.5.

Experimental verification

Buffer solution of pH 8.5 was prepared in triply distilled water by mixing 0.3 M H3BO3 with 0.075 M Na2B4O7 in required volumes and monitoring the hydrogen ion concentration with pH meter. A standard three electrode cells were used for electrochemical measurement. Before recording CV, the electrodes were pretreated at -1.4 V for 45 seconds using PAR 173 potentiostat/ Galvanstat and cyclic voltammogram was recorded at a scan rate of 50 mV/s in the potential range -1.2V to 1.0V.

After recording the CV of copper surface, the system was connected to impedance analyzer TFA2000. A platinum wire electrode serving as anode via ...