Si-Ti-C-O繊維結合型セラミックスにおける遊離炭素層の酸化挙動の定量解析

概要

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A model for the oxidation kinetics and mechanisms of Si-Ti-C-O fiber-bonded ceramics was newly developed to evaluate the oxidation behavior quantitatively at temperatures ranging between 773 and 1473 K in air. The model considers the geometry changes of pores resulting from consumption by oxidation of the free carbon layer, and the oxygen consumption due to oxidation of the pore walls. A differential equation for the oxygen concentration profile along the pore was derived and solved numerically. For materials with very thin carbon layer, the geometry change of the pore has a significant effect on the oxygen concentration profile. The relative mass changes due to oxidation of (1)the external surface, (2)the carbon layer and (3)the pore walls were respectively calculated and thermogravimetric analysis (TGA) curves of the materials derived from their sum. The calculated TGA curves well agreed with the experimental data. The length of carbon layer consumed by oxidation was calculated as a function of time and temperature. At low temperatures, the rates of the carbon consumption were low, but pores took place proceeded for long time. At high temperature, in contrast, the oxidation of the carbon layer was inhibited in a short time due to the quick sealing of the pore entrance by silica layer. Thus, the oxidation damage is limited only in the vicinity of the material surface.
社団法人日本セラミックス協会の論文
2001-02-01