Kinetics of Potassium Chloride and Chlorine on Tungsten

Abstract

The kinetics of adsorbed layers of potassium chloride on tungsten and of chlorine on tungsten have been investigated in the range 300°—1900°K by means of the field electron microscope. Data are interpreted as showing that KCl in the presence of tungsten at room temperature forms a W–KCl complex to which the potassium is weakly bound. Activation at approximately 500°K results in the desorption of potassium leaving a tungsten chloride (WCl_x) layer which is stable to about 1100°K. Work functions, patterns and critical temperatures for KCl on tungsten and chlorine on tungsten are indistinguishable in the range 1100°—1900°K. Limiting processes above 1100°K are believed to be the formation and subsequent desorption of tungsten chloride and atomic chlorine. Temperature‐dependent processes, such as migration, desorption, and structure change, associated with experimentally determined activation energies of ∼10 to 80 kcal, are discussed. The behavior of chlorine on tungsten is shown to be similar to that of oxygen on tungsten in the temperature range studied.