Effect of temperature on the thermal spalling behaviour of MgO-C brick and a crack progress behaviour is investigated from the view point of fracture mechanics. As a result, it was found that the number of heating/ quenching cycles for the generation of small cracks and large cracks became smaller when the carbon content in the bricks decreased. It was also found that the number of heating/quenching cycles for the generation of small cracks and large cracks decreased with increasing temperature. Apparent activation energy for crack propagation was derived from the analysis of fracture mechanics. Apparent activation energy incleased with increasing carbon content in brick. And it was higher than glass material and lower than Si3N4 and ZrO2. Furthermore, the interpretation of apparent activation energy for crack propagation was discussed from the viewpoint of bond energy although it might be qualitative. As a result, the apparent activation energy for crack propagation would have something to do with dispersion energy for the covalent bond between graphite and amorphous carbon.

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