Decomposition of Gypsum Bonded Investments

Decomposition of gypsum bonded investments was investigated by means of TG-DTA and X-ray diffraction. The decomposition began at about 900°C and led to the formation of CaSi03 as a major product and Ca2SiO4 as a minor one. CaO was not formed during the decomposition of any of the investments. The decomposition process followed Jander's equation, [1-(1-α)1/3]2 = kt, and the Ca2+ ion diffusion in CaSi03 was concluded to be a rate-detennining step.