Methods of eliminating expansion and embrittlement during firing of products based on chamotte from rotary furnaces

Conclusions We established the mechanism of expansion in the firing of articles made on the basis of grog obtained from rotary furnaces. The cause of the expansion is the incompleteness of the process of vitrification (sintering) during rapid heating, giving rise to the formation of closed pores. During repeat firing the expansion of the gaseous phase trapped in the closed pores gives rise to an increase in the volume of the grains.The expansion of the grog may be eliminated or substantially mitigated by breaking up the closed pores by means of an addition to the original batch of nonplastic materials or kaolins which are not prone to form expanding grog.Translated from Ogneupory, No. 4, pp. 36–41, April, 1967.