An electrochemical and electron spectroscopic investigation of the galena/diethyl dithiophosphate system

Abstract

The galena/diethyl dithiophosphate system has been studied using electrochemical and electron spectroscopic techniques. Voltametric investigations of the oxidation of dithiophosphate at a gold electrode were interpreted in terms of the formation of a chemisorbed layer, the disulfide and gold dithiophosphate. Voltametry with a lead electrode indicated that dithiophosphate was chemisorbed at potentials below that at which lead dithiophosphate was formed. At high potentials, where high lead ion concentrations develop at the interface, lead dithiophosphate dissolved. Voltamograms recorded with a galena electrode in the presence of dithiophosphate show no evidence for chemisorbed species and suggest that lead oxidation products have a significant solubility. Cathodic stripping voltametry carried out with a galena electrode after immersion in dithiophosphate solutions in equilibrium with air showed no evidence of surface dithiophosphate species for contact times below 1 h. For longer immersion periods the results were inconclusive. X-ray photoelectron spectra and X-ray induced Auger electron spectra indicated that dithiophosphate is not present on fresh fracture surfaces of galena after exposure to dithiophosphate solutions in equilibrium with air for periods of 1 h or less. Some dithiophosphate was detected after extended exposure periods and the resulting coverage depended on immersion time rather than dithiophosphate concentration.