In order to obtain fundamental data on the behavior of iron oxide, titanium oxide and other impurities in the clay refractory at high temperatures, corhart particle was heatedd from 800° to 1300°C in oxygen, nitrogen or CO stream. The corhart particle used consisted of mullite, α-alumina and glass matrix.
The variation of lattice constant of α-Al₂O₃ and color change of the particle were examined and thermal stability of corhart particle was discussed. Results obtained were as follows:
1) a₀₃₀ of α-Al₂O₃ extracted from the corhart particle and heated in oxygen stream. was slightly smaller than those of ones heated in nitrogen and CO stream.
2) a₀₃₀ of α-Al₂O₃ in the corhart particle and in the mixture of α-Al₂O₃ and mullite showed different tendency from that of α-Al₂O₃ extracted from the corhart particle. a₀₃₀ of the former heated in oxygen or nitrogen gas decreased with the increase of temperature, while in CO gas it got smaller at 1100°C than at 1300°C.
c₀₀₂ of mullite heated at 1300°C in oxygen or nitrogen gas decreased as compared with one before heated. In the specimen heated in CO gas, c₀₀₂ was smaller at 1100°C than at 1300°C.
This tendency was in agreement with the color change and the result of the chemical analysis. Decomposition of the solid solution of impurities in the mixture of α-Al₂O₃ and mullite was observed at relatively low temperatures in a reducing atmosphere. This might be attributed to the effect of coexisting materials and the reducing atmosphere.
3) Thermal stability of the corhart particle containing glass matrix was similar to that of the mixture of α-Al₂O₃ and mullite, and decomposition of the solid solution of impurities in α-Al₂O₃ occured at about 500°C.