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Title of Thesis

Amtul Naseer
Institute/University/Department Details
Department of Chemistry/ Quaid-i-Azam University Islamabad
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
passivated copper surfaces, impedance spectroscopy, alternating current electrodynamics, electrochemical impedance, cyclic voltammogram

In the present work two electrochemical techniques were used to study passivation of a clean copper surface. Cyclic voltammetry was employed to see the oxide formation on metal. Electrochemical impedance spectroscopy (EIS) was used to investigate the oxide formation and the changes that take place in them as a result of imposing static potential in the range of -0.3 V to 0.9 V in aqueous buffer solutions of pH values 9.2, 8.5, and 8.0.

The response of an electrode using EIS, initially at equilibrium to an applied potential is modeled with equivalent circuits. Equivalent circuits have been pro posed for different potential regions which completely illustrate the Cu/oxide/electrolyte systems and their properties in terms of two interfaces. The component values of the equivalent circuit are determined from experimental data using an NLLS-FIT algorithm. Mainly three stages are identified in the whole working potential range on the basis of these circuit topologies. The model characterizing the initial and final stage potential is valid for reactions that are slow in comparison with the time constant of the decay of the charging current. The stability (thickness and resistance) of the oxides/hydroxide film is pH dependent and it has been found to increase in a specific potential region, while diffusion plays its role in another potential region. These potential regions are strongly pH dependent. It is observed that an increase in the imposed potential also significantly reduces impedance of the systems under study after a specific potential value of 0.3 V. Criteria for the applicability of equivalent circuit models are discussed.

Diffusion coefficients of ions in the film calculated from the EIS data which are of the order of 10-9, 10-6 and 10-5 for the buffer solutions of pH 9.2, 8.5, and 8.0 respectively. On the basis of this parameter the concentration of the mobile species is calculated which is of the order of 10-9 mol/ml and it decreases with pH. The effect of compressive stress that developes in the oxide films is also discussed both from Bode as well as the Warburg plots. Results obtained for film grown by potentiostatic methods widely differ from the results obtained for the film grown by potentiodynamic methods.

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4320 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
233.49 KB
2 1 Introduction 1
186.38 KB
  1.1 Relevant Work 1
  1.2 Objective 5
3 2 Impedance Spectroscopy 8
178.73 KB
  2.1 Advantages Of The Is Test Methods 9
  2.2 Earlier Impedance Work 10
  2.3 Recent Applications 11
4 3 Theoretical 15
797.03 KB
  3.1 General 15
  3.2 Principles Of Alternating Current Electrodynamics 17
  3.3 Electrochemical Impedance Spectroscopy 30
  3.4 Methods For Analysis Of Electrochemical Impedance 37
  3.5 Point Defect Model 48
5 4 Experimental 60
127.96 KB
  4.1 Instrumentation 60
  4.2 Chemicals 61
  4.3 System Preparation 62
6 5 Results And Discussion 67
2769.81 KB
  5.1 Cyclic Voltammetric (CV) Studies Of Copper 68
  5.2 Cyclic Voltammogram (CV) Of Copper Surface In Buffer Of pH 9.2 68
  5.3 Cyclic Voltammogram (CV) Of Copper Surface In Buffer Of pH 8.5 69
  5.4 Cyclic Voltammogram ( CV) Of Copper Surface In Buffer Of pH 8.0 71
  5.5 Electrochemical Impedance Spectroscopic (EIS) Studies Of Copper Surface 72
  5.6 Effect Of Applied Potential On The Electrode Surface At Constant pH 75
  5.7 EIS Studies Of Copper In Buffer Of pH 9.2 77
  5.8 EIS Studies Of Copper In Buffer Of pH 8.5 96
  5.9 EIS Studies Of Copper In Buffer Of pH 8.0 105
  5.10 Effect Of pH At Constant Potential 112
  5.11 Discussion 133
  5.12 References Cited 183
7 6 The First Appendix 193
62.09 KB
8 7 The Second Appendix 198
75.82 KB