Weak interaction of oxygen with some refractory carbides

The reactivity of NbC (single crystal and polycrystalline), TiC (single crystal and polycrystalline), and polycrystalline ZrC in the temperature range from ambient to 1020 C and at oxygen partial pressures from 0.07 to 9 Pa is reported. The reactivities of the principal (hkl) planes of TiC as well as the polycrystal were measured at 0.8 Pa of O2. The reactivity ratio order was 1.0, 1.2, and 1.9, respectively, for (111), (100), and (110) planes. Under these conditions, laths at right angle of epitaxial rutile were observed. The comparison of the reactivity between NbC(100) and polycrystalline NbC was determined and some tentative data are given on the reactivities of the other planes. The reactivity at higher oxygen partial pressures was measured for TiC(111) and, in these conditions, a well-defined TiC-rutile ceramic-to-ceramic joint was obtained. The reactivity and in situ electrical resistivity measurements on polycrystalline TiC and ZrC, both as received and high temperature, high vacuum treated, are presented. There were differences in the reactivity hystereses. The same result was not found in the behaviour of the resistivity. 16 refs.