Gypsum-bonded investment and dental precision casting (IV) transformation of III-CaSO4 to II-CaSO4.
The degree of III-CaSO4 to II-CaSO4 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 degrees C furnace until a specimen temperature of 200 degrees C to 700 degrees C was reached. The estimation was made by measuring mass changes of the specimens before and after heating. The transition reached 39% at 350 degrees C. The same estimation method, when applied to a previous study, showed no transition to this temperature in dry specimens heated slowly (5 degrees C/min). The large difference in transition found between the wet and dry specimens was attributed to the formation of alpha- and beta-hemihydrate, respectively. At 350-450 degrees C, 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.
Aghajani
Farzaneh
F
Biomaterials Science Unit, Faculty of Dentistry, The University of Sydney, 2 Chalmers Street, Surry Hills, NSW 2010, Australia.
Hasratiningsih
Zulia
Z
Mori
Toshiko
T
D002133:Calcium Sulfate / Q000737:chemistry*; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique; D003890:Desiccation; D004055:Differential Thermal Analysis; D006361:Heating; D044367:Phase Transition; D013816:Thermodynamics; D017155:Wettability
D003734:Dental Casting Investment; D002133:Calcium Sulfate