| Popis: |
Controlled atmosphere electron microscopy has been used to study the influence of calcium on the graphite-oxygen and graphite-steam reactions. Direct observation of the specimen surface has enabled us to establish that the high catalytic activity of calcium for graphite oxidation is associated with the ability of the alkaline earth to wet and spread along the graphite edges, which subsequently undergo gasification by the edge recession mode. We have found that in the presence of steam, calcium-coated graphite edges would occasionally deactivate, and this behavior became more pronounced as the temperature was increased. A decrease in rate of gasification was found when nickel was added to calcium, this is attributed to a fundamental difference in the mechanisms by which these two elements catalyze the graphite-steam reaction. |
