Expansion of phosphate-bonded investments: Part II--Thermal expansion.

This study investigated the thermal expansion of phosphate-bonded investment materials. Three investments were mixed with either distilled water or their special liquids and allowed a setting time of 1 or 24 hours. Hydration and thermal expansions were measured with a vertical dilatometer and were analyzed for interactive and main effects. The amount of expansion attributed to hydration was minimal, whereas thermal expansions varied and were of greater magnitudes. Material I exhibited the greatest thermal expansion. Materials II and III recorded smaller thermal expansions that increased when the materials were mixed with their special liquids. Setting time did not substantially influence hydration expansions but did influence thermal expansions, and heating the materials to 800 degrees C instead of 700 degrees C did not dramatically elevate expansions.