Ion-adsorption by metallic powders.

The work described in this thesis consists of an investigation into the adsorption properties of gold and silver metal powders in some electrolyte solutions. The total adsorption at the Au/HCl , Au/KCl, Ag/HCl and Ag/KCl interfaces was determined conductimetrically, using an improved apparatus. In neutral salt solution,adsorption takes place instantaneously and is presumably due to weak physical forces. The process is much slower in acid solution and desorption experiments have shown that in this case adsorption onto a silver surface is irreversible in character. The adsorption from acid solution by gold is partly irreversible becoming more so as the equilibrium concentration of electrolyte is decreased . It is concluded that the adsorption from acid solution is mainly chemisorption. Some indication is given of the difficulty involved in determining the electrokinetic potential at the metal/solution interface. An electrckinetic study has been made of gold and silver suspensions in various electrolyte media , using the ultra microphoretic technique. The electrokinetic potentials and charges have then been calculated for these systems. The conductimetric and the electrokinetic data have been used to determine the distribution of adsorbed ions in the fixed and diffuse parts of the electrical double layer and hence to calculate the individual adsorption energies of the adsorbed ions. This work has shown that both cation and anion adsorption take place but that anions are preferentially adsorbed. Finally a potentiometric method for the determination of adsorption has been developed and some preliminary experiments are described,