In situ measurement and simulation of temperature and stress gradients during sintering of large ceramic components

A special thermooptical measuring system was used to determine mechanical, thermal and sintering properties during firing simultaneously. Combining customary and novel in situ measuring methods, a complete dataset was obtained which includes elastic and viscous moduli, thermal conductivity and coefficients of heat transfer, specific heat, reaction and sintering data and gas permeability. Using finite element methods (FEM) the temperature fields in large components were simulated for various time temperature cycles. From the temperature field local reaction and shrinkage rates were calculated. The corresponding stresses were obtained using FEM again. The time temperature cycle was optimized taking into account both a sufficient safety margin to the respective strength of the sintering material and the economic requirement for a short firing cycle. The use of the methods was demonstrated considering as example a large high voltage porcelain insulator, which undergoes a number of phase transformations during firing.