Ramasami, N. (1969) Electrified interfaces – electrocrystallisation of calomel an ellipsometric kinetic study. PhD thesis, University of Madras.

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Abstract

The role of electrified interfaces in determining the course of electrochemical reactions and the similarity and dissimilarity between chemical and electrochemical reactions have been discussed. Concepts of electrocrystallisation as applied to electrochemical studies and various factors that govern nucleation and growth are briefly summarized. The types of anodic crystallization reactions, the influence of film properties on subsequent reactions and the mechanism of film formation are also surveyed. The principle of various electrochemical techniques used for studying anodic crystallization reactions is discussed. Stressing on the suitability of using physical mathods for this purpose. The application of the ‘insitu’ physical method namely ellipsometry in electrochemical studies and the limitations of these methods under dynamic conditions and the latest trend in the development of ellipsometers are also reviewed. The present state of knowledge of the electrocrystallisation of calomel and the work done by various workers in this field are reviewed. The fabrication of ellipsometer and nephalometer for electrocrystallisation and precipitation studies are discussed. Ellipsometric and nephalometric studies have been carried out using different concentrations of KCl at different current densities. Oscillographic potential transients are also recorded for all these current densities. In naphalometric measurements, the precipitations of AgCl from a solution of KCl by the addition of AgNO3 have been studied for different concentrations of KCl. A new equation has been derived by combining the Rayleigh equation with the equation for three dimensional nucleation to interpret the nephalometric data. The precipitation of AgCl has been shown to proceed through the intermediate species (AgCl)- in solution. The results of ellipsometric and potential transients have been processed and plotted as i(1/2) vs i graphs for all concentrations studied. Values of equilibrium constants Kf, rate constants K+ and K- and critical concentration c* for precipitations of the precursor species have been calculated. It has been observed that experimental results obtained in the present study cannot be explained by the model put forth by Bockris, Devanathan and Reddy. A new model based on (HgCl4)-2 complex is proposed to explain various facts like the concentration of dependence of c* on Cl- ion concentration, the minimum current density, imin for precipitation etc. The reason for the absence of plateau in the OT1/2 vs i curves for aerated solutions is given. A semi quantitative calculation of the rate constant for the oxidative removal of the complex [Hg2Cl4]-2 has been made. Ellipsometer is used to detect the instant of nucleation and the subsequent increase of photovoltage measures the growth. The equation for growth on a highly slipped surface has been applied in the electrocrystallisation of calomel under galvanostatic conditions. The dependence of growth rate on the square of the galvanotechnic current i predicted by the above basic growth equation has been confirmed for three concentration of KCl. From imax and equation for growth, the current for crystal building process is evaluated and formula for calculating current efficiency is provided. Results are interpreted using the concept of imax and imin for electrocrystallisation

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Electrocrystallisation of calomel
Subjects:	Electrodics and Electrocatalysis
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	13 Jun 2012 04:55
Last Modified:	13 Jun 2012 04:55
URI:	http://cecri.csircentral.net/id/eprint/2830

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