The reaction between chromium oxide and chromium carbide was caused in a high vacuum of 1.01–0.10 Pa at temperatures ranging from 1323 K to 1593 K. Mixture of 1 mol of Cr
7C
3 and 1 mol of Cr
2O
3 was prepared in a form of pellet and reduced under the above mentioned conditions. The results are as follows;
(1) The reduction products of this reaction system were Cr
23C
6 and metallic chromium. At these experimental conditions, the reaction process producing Cr
23C
6 was assumed by considering possibility of uniform reaction model. However, the ensuing reaction process from the surface to the inside of the pellets formed metallic chromium. That means that the formed metallic chromium layer is considered to be caused by the topo-chemical reaction.
(2) At the earlier stage of the reaction, a rate equation for interfacial reaction control was applicable to the formation of metallic chromium from Cr
23C
6, and moreover it was presumed that the reaction rate was controlled by the interfacial reaction, from the proportionality of the rate constant to the reciprocal particle diammeter of Cr
7C
3, but at the later stage of reaction, the rate determining step was obserbed to be the diffusion reaction.
(3) Judging from the isothermal TGA and the formed metallic layer of section of pellets, the apparent activation energy was estimated to be 247–277 kJ/mol, from the Arrhenius plot under the interfacial reaction.
(4) It may be concluded from the experimental results of this investigation that the chain reaction was controlled by supply of CO
2 and CO gases.
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