Gypsum-bonded Investment and Dental Precision Casting (IV) Transformation of III-CaSO_4 to II-CaSO_4

概要

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The degree of III-CaSO_4 to II-CaSO_4 transition was estimated on wet specimens, 25 mm in diameter and 50 mm high, prepared from a gypsum-bonded investment for quick casting. After 30 min from mixing the specimens were heated in a 700℃ furnace until a specimen temperature of 200℃ to 700℃ was reached. The estimation was made by measuring mass changes of the specimens before and after heating. The transition reached 39% at 350℃. The same estimation method, when applied to a previous study, showed no transition to this temperature in dry specimens heated slowly (5℃/min). The large difference in transition found between the wet and dry specimens was attributed to the formation of α - and β-hemihydrate, respectively. At 350-450℃, the transition was 3% and 48%, respectively. The pronounced latter transition, generally identified by differential thermal analysis of gypsum, appears as the major investment shrinkage demonstrating its dry dehydration process.
日本歯科理工学会の論文