炭素/B_4C/SiC/ZrB_2複合材料の湿潤空気雰囲気中における高温酸化と熱力学的考察

概要

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Oxidation of a carbon/B4C/SiC/ZrB_2 composite was in vestigated at 900℃ in moist air atmospheres. From mass change measurement, scanllillg electron micros copy (SEM) observation, X ray powder diffraction analysis and ion microprobe mass analysis before and after oxidations, the structure of oxidized layer was ex amined. The mass of the sarnple decreased with oxidation time and linearly with an increase in partial pres sure of the moisture. Cross sectional observation showed that the oxidized layer was formed on the sample and the oxidized layer was porous in comparison with the sample core. The oxidized layer consisted of SiC and ZrO_2, but carbon and boron were not detected. To discuss the formation process of the oxidized layer, thermodynanric calculations were performed. The equilibrium partial pressure of boric acids was calculat ed as a function of temperature or partial pressure of moisture. It is clarified that B_2O_3 (s, 1) formed from B4C and ZrB_2 by oxidation reacted with H_2O(g) to produce HBO_2 (g) , (HBO_2)_3 (g) and H_3B0_3 (g) at elevat ed ternperatures and the equilibrium partial pressure of these boric acids became high at 900℃ in H_2O(g) containing atmospheres. Based on the experimental results and thermodynamic considerations, the forma tion process of the oxidized layer at 900℃ in moist air was discussed.
社団法人日本セラミックス協会の論文
1994-10-01