The theory of thermal shock in heterogeneous refractory materials

Conclusions Increases in the thermal shock resistance with the addition of high-molecular organic liquids to the grog, proven experimentally, is confirmed by calculations of the factors for thermal-shock resistance of fireclay articles according to the theory of maximum stresses.The established reduction of thermal resistance with the addition of organic liquids in the bond is not reflected by the calculations. Hence, the theory of maximum stresses, although it can in certain cases be applied to bodies which are heterogeneous, it is not universal.On account of the growth in microcracks, the experimentally determined thermal-shock resistance for firebrick increases with chaotic orientation of the microcracks, and with their distribution over the grog grains, but diminishes when the microcracks are located in the bond parallel to each other.In this and other cases, the coefficient of homogeneity of the material diminishes, and the associated probability of destruction (calculated by Weibull) increases. Thus, the statistical theory of strength evolved by Weibull cannot be used to account for the effect of the orientation of microcracks in the structure on the distribution of cracks developed in the material during thermal shock.Calculation of the developed thermal stresses, as a function of the Biot and Fourier criteria, established that with the addition to the grog grains in the fireclay mass of organic liquids, these stresses diminish by a factor of 3–4; there is an increase in the time period and difference in temperature at which the cracks develop, and also the depth of the development of the latter. However, the distribution of the developing thermal cracks is limited when the microcracks are arranged chaotically and around the grog grains. This also increases the thermal resistance of the fireclay refractories when the high-molecular organic liquids are added to the grog grains.