Work function of the zirconium carbide-oxygen system

The effect of O2 on ZrC work function has been investigated by thermionic emission and thermodesorption in the range of oxygen pressure 3x10-5-3x10-9 torr and cathode temperatures 1300-1550 K. Under these conditions two stationary states are formed on ZnC surface. In the first one the work function phi=3.2-3.3 eV. It is preserved only in vacuum, and is destructed at 1600 K, which is close to the temperature of zirconium oxicarbide homogenization. It is shown that the first stationary state is monolayer of ZrCsub(x)Osub(y). In the second state phi=4.25-4.15 eV. It appears after absorption of 4.6x1015 molecules/cm2, and is preserved only in oxygen atmosphere and presents a layer of oxygen adatoms on the ZrCsub(x)Osub(y) monolayer. Adsorption coating formation and oxygen penetration into the sample take place in Zr-O2 system with comparable speed and simultaneously. Adhesion coefficient is equal to 6x10-4+-3x10-4 and does not depend on coating. The oxydation rate of ZrC is limited by the adsorption rate of oxygen molecules