MS Thesis Presentation by Audric Saillard
Friday, July 11, 2005

(Dr. Andrei Fedorov, Chair)

"Mercury Amalgam Electrodeposition on Metal Microelectrodes"

Abstract

Mercury amalgam microelectrodes, fabricated by electrodeposition of mercury onto platinum or gold inlaid disks, possess certain advantageous properties for scanning electrochemical microscopy (SECM) and electroanalysis. But as applications require more and more precision, fundamental questions concerning the exact shape and constitution of the amalgam can become important for interpreting SECM experimental data. The purpose of this study is to analyze in depth the formation of the amalgam, in order to provide a better understanding of the key physical processes, and so be able to judge of the accuracy of the currently used models, and refine them if necessary.

The amalgam formation is the result of several processes that occur at two different scales: the “global” scale, which is microscopic, and the “local” scale, of the order of few nanometers. On the global scale, the dominant physical process is the mass transport, driven almost entirely by diffusion, which determines the rate of mercury deposition. Other phenomena occur at the smaller local scale. Their understanding is essential to predict precisely the volume and shape of the amalgam at shorter times. Among these local phenomena, nucleation and droplet interactions appear critical. The former sets the formation rate and the size of the isolated mercury droplets that are formed at the surface of the electrode. An understanding of the latter is necessary to determine the droplet coalescence process.

Specific accomplishments of this Master thesis work:

1. time scale analysis of the “global” phenomena has been performed leading to the conclusion that quasi-steady state diffusion of mercury ions in the bulk solely defines the electrodeposition rate,

2. a series of analytical and numerical models of mass transport has been developed and implemented, and results were critically compared with experimental data,

3. mercury droplet nucleation and coalescence has been investigated in detail leading to the development of “regime” maps defining the shape of the electrode during the initial transient; and,

4. Finally, through analysis of theoretical predictions, a series of electroanalytical experiments have been proposed for the future validation of the suggested theoretical models.