Thermochemical Arsenide-Oxide Equilibria in the System Ni–As–O Determined Electrochemically between 438 and 866°C

Abstract

An electrochemical technique has been developed for the determination of solid-solid-gas equilibria in metal-bearing arsenic-oxygen systems which are of significance in pyrometallurgy and for which few thermomechanical data are available.Equilibrium electrochemical potentials were measured in an oxygen concentration cell which consisted of (a) an oxygen reference electrode, (b) a solid zirconia-calcia electrolyte and (c) an arsenide-oxide mixture over which was passed argon containing a known partial pressure of As4O6.The technique has been used to determine the free energies of reaction of rammelsbergite (NiAs2), niccolite (NiAs), maucherite (Ni11Asg) and Ni5As2 with oxygen to form bunsenite (NiO) and As4O6 in the temperature range 438–866°C. The thermodynamic functions for these compounds were also calculated from the measurements; those for NiAs are in good agreement with literature values.The literature on the electrochemical determination of thermodynamic equilibria at elevated temperatures in M–S–O systems was also reviewed.