Vijayavalli, R. (1980) Polarisation studies of metals and alloys in aqueous electrolytes. PhD thesis, Madurai-Kamaraj University.

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Abstract

The main theme of work revolves around the investigations on the behavior of lead and its alloys under the influence of an a.c. ripple superimposed over the electrolyzing d.c. This is of specific importance due to the fact that lead and its alloys find a large application in the field of lead acid batteries, the other major application being in the field of cable sheathing especially for underground buried communication lines. Corrosion of lead and its alloys merits attention and serious consideration due to the magnitude of the problem of corrosion involved in both the applications. Investigations have been carried out on lead, tin, silver and their binary and ternary alloys with lead as the major component. Both the galvanostatic and potentiostatic polarization techniques have been adopted for the study. Anodic and cathodic behavior of these electrodes has been studied under different conditions a.c. superimposition. On the basis of the results the following conclusions were drawn: Superimposed a.c. acts as a powerful depolarizer and reduces electrochemical passivity, the effect being dependent on the percentage of a.c, d.c. density and the system under study. Whereas in the case of lead flattening of passivation peak was observed at high percentages of a.c., sharp passivation peaks were obtained in the case of silver. AC was found to bring out effective leaching of antimony from antimony containing alloys and the attack was found to be selective at regions as indicated by a number of pits. Formation of Alpha PbO2 by superimposed a.c. is another important observation which indicates attack of the base metal leading to the direct conversion to lead dioxide. Increase in the formation of alpha PbO2 with the increase in percentage of a.c. superimposed also points out that the effect is partly due to increase in pH adjacent to the electrode surface. The remarkable change in the Tafel slope observed during the cathodic prevention indicates that the reaction mechanism for hydrogen evolution is altered with the superimposed a.c. In the case of silver, it was observed that the slope with 100% a.c. is 0.03 whereas the same with d.c. and lower a.c. superimposition is 0.12. Behaviour of tin has been found to be very peculiar corrosion pattern in all the cases was found to be changed by superimposed a.c. depending on the metal or the alloy. An explanation has been offered for the effects brought out by superimposed a.c.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Polarisation studies; Metals and alloys
Subjects:	Electrodics and Electrocatalysis
Divisions:	UNSPECIFIED
Depositing User:	Dr. N Meyyappan
Date Deposited:	13 Jun 2012 05:30
Last Modified:	13 Jun 2012 05:30
URI:	http://cecri.csircentral.net/id/eprint/2837

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