EFFECT OF ALKALI-METAL AND SOME QUATERNARY-AMMONIUM CATIONS ON THE ANODIC-DISSOLUTION OF P-SI IN FLUORIDE MEDIA

A systematic study of the anodic dissolution rate upon changing the ca tions of the supporting electrolyte has been performed for a wide rang e of electrolyte compositions. The usable range of fluoride concentrat ions is limited by the solubility of the fluoride salt in the case of Li+, and by the solubility of the hexafluorosilicate salt in the case of K+, Rb+ and Cs+. When limitations due to solubility are avoided, th e anodic dissolution rate has been found to depend markedly upon the c oncentration of the supporting electrolyte and the nature of its catio n (alkali-metal or quaternary-ammonium). Changing the cation may resul t in variations in anodic currents of more than one order of magnitude . This variation appears entirely due to a variation of the kinetic co ntribution to the anodic current, and is associated with a catalytic e ffect in the dissolution rate of the interfacial oxide by the fluoride species.