Abstract
The present study analyzed the chemical adhesive phenomenon during casting between phosphate bonded investment components and surface oxides on non-precious dental casting alloys, e.g., Co-Cr alloys. Solid state reactions of MgO-Cr2O3 and NH4MgPO4・6H2O-Cr2O3 mixtures were analyzed by thermal analysis [thermogravimetric analysis (TG) & differential thermal analysis (DTA)] and the reaction products were identified by X-ray powder diffraction analysis.
Pichromite (MgCr2O4), which give rise to the chemical adhesive phenomenon, was formed in MgO-Cr2O3 in the temperature range of 610〜640℃, however, it was not formed in NH4MgPO4・6H2O-Cr2O3 below 1200℃. Magnesium pyrophosphate (Mg2P2O7), one of decomposition products of NH4MgPO4・6H2O, was converted from an amorphous to crystalline state at nearly 695℃.
