THE MULTISTRUCTURE OF OXIDIZED REDUCED TUNGSTEN CARBIDE SURFACE(S)

The XPS of bulk tungsten carbide, partially oxidized WC surfaces at 37 3 and 573 K as well as tungsten trioxide have been reported. Bulk WC h as been prepared from WO3 as a starting material in a mixture of CH4 ( 20%) and H-2 (80%) at 1150 K for 4 h, while partially oxidized WC surf aces were prepared by oxygen chemisorption on a clean WC surface at 20 0 K, then the temperatures were raised to 373 and 573 K respectively. The XPS of a freshly prepared WC reveals the presence of a small amoun t of WO3 on the surface and a slightly higher concentration in the bul k. The oxygen-exposed fresh WC surfaces and surfaces treated at temper atures higher than 373 K show the presence of WO3 in a considerable qu antity depending on the length and the treatment temperature. Ar+ bomb ardment of this partially oxidized surface reduces WO3 to WO2 and W(0) , while WC is partially reduced to W(0). Isomerization reactions of al kanes on oxygen-exposed WC surface occurs in reality on a composite su rface structure containing WC, WO3, WO2 and elemental W(0).