By means of the combined use of different analytical techniques, the chemical-physical properties of gypsum-bonded investment are studied as a function of burnout parameters such as temperature, atmosphere and thermal treatment time. The attention has been focused on the measurement of the temperature of the CaSO4 thermal decomposition that is strictly related to the origin of gas porosity and on gaining further insight into the micro-chemical and micro-structural structure of the thermal treated CaSO4-bonded investment. The results confirm that the decomposition temperature - about 1000° C for an investment prepared and fired according to the producer's directions - can be increased by varying the procedures, the duration and the temperature of the burnout cycle.

Author: Dr. G.M. Ingo, G. Chiozzini, Dr. Valerio Faccenda, C. Riccucci, C. Veroli