Microwave thermogravimetry as a tool to evaluate the drying of refractory castables – The effects of volumetric heating

Refractory castables present special features that render them unique and the most appropriate solution for lining specific high-temperature industrial equipment. Hydraulic bonded monolithics develop mechanical strength at room temperatures due to the hydration of some of its constituents, such as calcium aluminate cement. Their most significant drawback is the drying step, which takes place before firing and requires several hours of slow heating rates and plateaus to reduce the likelihood of facing explosive spalling. This phenomenon is a result of water vapor pressurization, as well as thermomechanical stresses. As an alternative to reduce the time and CO2 generation, microwave heating can be a promising solution as the volumetric nature of the temperature increase can make this process safer. Besides this benefit, the likelihood of using green energy and the higher efficiency of this method add to the potential benefits. The present work analyses the mass loss of refractory castables by proposing a microwave thermogravimetry equipment. The results suggest that water removal occurs at earlier temperatures and, in total, nine-fold less energy consumption estimation Numerical model results showed the distinct thermal gradients and the resulting drying profiles, highlighting the importance of properly controlling the microwave power during drying. Thus, these findings indicate that the microwave process might be a valid strategy for a safer, greener and faster drying of castable refractories