A Comprehensive Study of Thermo-Physical Properties of Investment Shells

Investment shell molds are typically built up with metastable amorphous silica binder and may include fused (amorphous) silica flour as filler and crushed fused silica grains as stucco.  These metastable amorphous (non-crystalline) materials can crystallize (devitrify) at elevated temperature during industrial process and the amount of transformed amorphous phase depends on temperature, time at temperature, and the presence of mineralizers.  The degree to which these amorphous phase materials devitrify during the process will affect the thermo-mechanical properties, which controls the solidification and ceramic shell integrity.  In this article, influences of firing temperature on the thermo-mechanical properties of silica-based shell molds were investigated.  The thermal properties were also correlated to the degree of phase transformations, which can occur during sequential heating/cooling cycles in investment casting processing.