OXYGEN AND POTASSIUM ADSORPTION ON A CARBIDE-MODIFIED STEPPED-W(100) IN CONTACT WITH THE CARBON SOLID SOLUTION: AN AES AND WF STUDY AT 300 K AND AT ELEVATED TEMPERATURES

Abstract

The adsorption of oxygen and potassium on the two-phase system: carbide-modified stepped- W (100) surface (CMT) in contact with the solid solution of carbon in bulk tungsten, was investigated by AES and WF measurements. The CMT surface shows metallic behavior judging from its interaction with K . The expected dissociative adsorption of oxygen appears to occur with 1 - θ kinetics, possibly via a molecularly chemisorbed state. The "dispersed phase — two-phase" model is clearly applicable when oxygen adsorbs on the K -pre-covered carbide. The initial sticking coefficient of oxygen increases drastically from the dispersed to the condensed phase, at least four-fold with respect to s0 on the clean carbide. It is proposed that this two-phase carbon system can be advantageous compared with the bulk carbide since it can easily regenerate the surface if the latter is depleted from carbon.