A metastable chromium carbide powder obtained by carburization of a metastable chromium oxide

A metastable Cr3C2-x carbide powder is prepared by carburization of a metastable chromium oxide in H2-CH4 atmosphere under the appropriate conditions (temperature, dwell time and CH4 content). A very high specific surface area (greater than 210 m2 g-1) of the starting oxide is necessary to avoid the formation of the sole stable Cr3C2 phase. The transformation from the stable Cr3C2 to the metastable Cr3C2-x is observed for the first time. The driving force could be an epitaxial effect between Cr3C2-x and the surrounding graphite layer. This is consistent with the observation that the formation of graphite layers by CH4 cracking is easier in the Cr3C2-x-containing powders. (orig.)