Oxygen Evolution and Chemical State Changes of Iron during Firing of Red Clay Bodies at Low Oxygen Pressure.

TAKAHASHI Hidenori, TAKEUCHI Nobuyuki, ISHIDA Shingo, WAKAMATSU Mitsuru

doi:10.2109/jcersj.108.1260_705

A red clay body containing 7mass% Fe₂O₃ was fired at PO₂=0.1kPa and its bloating and blackening mechanisms were investigated.<br>Blackening started at around 1100°C and the Fe²⁺/total Fe ratio in the fired body was about 5%. The disappearance of open pores started at about 1200°C, and the sealed porosity began to increase above 1200°C. The Fe²⁺/total Fe ratio in the body fired at 1200°C was 16%, indicating that a considerable amount of oxygen had been released. Although the evolution of oxygen started at around 1100°C as judged from the results of chemical analysis of Fe, the evolution of oxygen was detected only at around 1080°C and at the soaking temperatures probably due to the high heating rate (5°C/min).<br>The results of thermodynamic calculations suggested that oxygen evolution was caused or at least assisted by the reaction of iron oxides with Al₂O₃ to form FeAl₂O₄, a stable spinel. It is, however, assumed that FeAl₂O₄ reacted with silicate compounds during sintering at high temperatures.

Oxygen Evolution and Chemical State Changes of Iron during Firing of Red Clay Bodies at Low Oxygen Pressure.

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