Equilibrium adsorption of fluorides from the gaseous phase on tungsten single crystals

Abstract

This paper is devoted to a theoretical analysis of equilibrium adsorption of the components of the W-F system on the basal planes of a tungsten single crystal. A complete data bank of thermochemical constants has been compiled for tungsten fluorides in the monomeric and oligomeric forms and for fluorine. Equilibrium pressures of gaseous components of the W-F system have been calculated in a wide temperature range; the gaseous phase has been shown to mainly contain WF6, WF3, WF4, and F. Equilibrium parameters of adsorption for all components on W (100) and (110) planes have been calculated to show that these planes are saturated mostly by tungsten pentafluoride and elementary fluorine. The degree of coverage depends only moderately on the temperature and the total pressure of the reaction mixture. There is a specific feature of the adsorbed layer in fluoride systems in the existence of very strong lateral interactions between the adsorbed fluorides and fluorine.