Effect of Cooling Rate on Thermal Shock Behavior of Alumina Ceramics

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J. Korean Ceram. Soc. > Volume 34(7); 1997 > Article

Journal of the Korean Ceramic Society 1997;34(7): 767.

$Al_2O_3$ 세라믹스 열충격에 미치는 냉각 조건의 영향

한봉석, 이홍림, 전명철¹

연세대학교 세라믹공학과
¹포항산업과학연구원 기능세라믹스팀

Effect of Cooling Rate on Thermal Shock Behavior of Alumina Ceramics

ABSTRACT

Thermal shock behavior of alumina ceramics were studied by quenching the heated alumina specimen into the water of various temperatures over 0~10$0^{circ}C$. The critical thermal shock temperature difference ( Tc) of the specimen decreased almost linearly from 275$^{circ}C$ to 20$0^{circ}C$ with increase in the cooling water temperature over 0~6$0^{circ}C$. It is probably due to the increase of the maximum cooling rate which is dependent of the convection heat transfer coefficient. The convection heat transfer coefficient is a function of the temperature of the cooling water. However, the critical thermal shock temperature difference( Tc) of the specimen increased at 25$0^{circ}C$ over 80~10$0^{circ}C$ due to the film boiling of the cooling water. The maximum cooling rate, which brings about the maximum thermal stress of the specimen in the cooling process, was observed to increase linearly with the increase in the quenching temperature difference of the specimen due to the linear relationship of the convection heat transfer coefficient with the water temperature over 0~6$0^{circ}C$. The critical maximum cooling rate for thermal shock fracture was observed almost constant to be about 260$pm$1$0^{circ}C$/s for all water temperatures over 0~6$0^{circ}C$. Therefore, thermal shock behavior of alumina ceramics is greatly influenced by the convection heat transfer coefficient of the cooling water.

Key words: Thermal shock, Cooling rate, Thermal stress, Convection heat transfer coefficient