The effect of early heating on the expansion of a phosphate bonded investment

A bstract — The setting expansion of a phosphate bonded investment continued for more than six hours at room temperature. Specimens heated to about 100°C within six hours of mixing expanded rapidly, the degree of expansion increasing with reduction of time between mixing and heating and with increase in colloidal silica concentration of the liquid. The rapid expansion on heating was considered to be a combination of thermal and accelerated setting expansion. Time between mixing and heating could be an important variable with regard to obtaining optimal expansion.