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 degrees C and led to the formation of CaSiO3 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-alpha)1/3]2 = kt, and the Ca2+ ion diffusion in CaSiO3 was concluded to be a rate-determining step.