ZrC及びZrN粉末と高温高圧水との反応

概要

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The reactions of ZrC or ZrN powder and H_2O have been studied at 190゜-400℃ wader 100 MPa. The reaction of ZrO_2 with H_2O above 240℃ for 3 h yielded monoclinic ZrO_2, and CH_4, while the reaction of ZrN above 190℃ for 3 h yielded monoclinic ZrO_2, NH_3, and H_2. The oxidation rate calculated from the weight gain or the integrated peak intensity of the X-ray diffraction was compared with various model functions. A nucleation- controlled model was the best fitted one, while a core-shirinking model fitted as well. This suggested that the reaction was controlled by phase boundary reactions. TEM observation showed that the ultrafine particles about 10 nm nucleated on the surface of ZrN or ZrC grains of about 1-3 μm. These Zr_2 fine particles did not from a protective layer on ZrN or ZrC particles, but formed clusters of particles because of large volume expansions about 40% during the oxidation. An Arrhenius plot of the rate constants gave apparent activation energies of 99 kJ/mol and 78 kJ/mol for the oxidation of ZrC and ZrN by H_20, respectively, on the basis of the nucleation-controllod model. The difference of about 20 kJ/mol in the activation energies for ZrC and ZrN might be explained by the difference in the formation energy between the C-H bonding and N-H bonding.
社団法人日本セラミックス協会の論文
1988-02-01