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 degreesC 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 are also measured at 0.8 Pa of O-2. The reactivity ratio order is 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 has been determined and some tentative data are given on the reactivities of the other planes. The reactivity at higher oxygen partial pressures was also measured for TiC(111) and in these conditions a well-defined TiC-rutile ceramic to ceramic joint has been obtained. The reactivity and iii situ electrical resistivity measurements on polycrystalline TIC and ZrC, both as received and high temperature, high vacuum treated, are presented. Large differences in the reactivity hystereses were found. The same result was not found in the behavior of the resistivity. (C) 2001 The Electrochemical Society.