Thermal stability and chemical-physical features of gypsum-bonded investment with regard to burnout cycle

Thermal stability, mechanical properties and chemical and physical characteristics of a type of gypsum bonded investment commonly used for the preparation of moulds for investment casting have been studied, with regard to the burnout cycle. Scanning electron microscopy coupled with micro-chemical analysis by X-ray energy dispersion (SEM + EDS), X-ray diffractometry (XRD), differential thermal analysis coupled with thermogravimetry (DTA - TG), porosimetry and compressive strength evaluation have been used for this research. The results show a remarkable effect of burnout cycle temperature and duration on mechanical properties and thermal stability of the investment. These variations have been correlated with thermal expansion, porosity, size pore distribution produced by the parameters of the burnout cycle in the two components of the material, silica and gypsum, respectively. From the point of view of the technology, the results show the possibility of managing the final properties of gypsum based investment in the best way, by suitable adaptation of burnout cycle time, maximum temperature, heating and cooling rate.