The reaction of tungsten with sulphur vapour

Abstract

A thermogravimetric method has been used to investigate the kinetics of the reaction of both annealed and unannealed tungsten coupons with pure sulphur vapour at temperatures between 295 and 550 °C. The rates of sulphurization of both forms of metal were rapid and increased systematically with temperature to a rate maximum at 460–475 °C; thereafter the rates decreased. At temperatures below the rate maximum, the apparent activation energies were in the range 31–34 kcal/mole. For the annealed metal, the kinetics were essentially linear. The kinetics of sulphurization of the unannealed metal were linear above the rate maximum but, below this transition temperature, the reaction rate increased with time. For both forms of metal, the initial sulphurization rates increased in a complex manner with increasing sulphur pressure for temperatures below the rate maximum. Above this transition temperature, the rates increased directly with the partial pressure of S 2. Tungsten disulphide was the only reaction product detected under all experimental conditions.