The causes of expansion in fireclay products during firing

Conclusions The expansion of fireclay products during firing is due to the bloating of the grog. Bloating of the dry clays is observed during firing when they are fired in lumps with their natural structure intact.The expansion of the products depends on the conditions of firing the grog, the degree of firing, the time of firing, and the nature of the kiln atmosphere:increasing the temperature of maximum densification of the clay gives rise to bloating of the grog; firing the clay into grog with a fast cycle leads to a bigger expansion that with slow firing; maintenance of a reducing or weakly oxidizing atmosphere during the firing of the clays into grog contributes to a reduction in the growth of the articles.The expansion of the article depends on the firing temperature; in the preparation of grog from biscuit-dry clays, the expansion is noted at firing temperatures of more than 1380°C. The expansion of the articles as a rule is higher, the higher the content of the original raw materials and impurities contributing to sintering.An increase in the grog of fractions finer than 0.088 mm contributes to an increase in the expansion of the articles.The work was shared with O.T. Anosova, M.I. Ivanov, and V.A. Petrova.