| Popis: |
Controlled atmosphere electron microscopy studies have demonstrated that both chromium and copper are extremely active catalysts for the graphite-oxygen reaction over the range 550–800°C. Under these conditions the active catalytic entities are probably Cr 2 O 3 and CuO, respectively. The behavior of chromium is quite unique, not fitting into the well established patterns, i.e. pitting or channeling. Instead, particles remain motionless throughout the oxidation sequence and the action is seen as an acceleration of edge recession all over the specimen. In contrast, copper exhibited conventional channeling activity, which diminished at higher temperatures (>700° C ) due to the wetting and spreading of active particles along graphite edges. Such edges underwent rapid recession following this phenomenon. Neither metal showed any tendency to catalyze gasification of graphite in the presence of steam. Copper was found to be an active catalyst for graphite hydrogenation at temperatures in excess of 800°C, but chromium remained inactive. |
