Plaster Of Paris

Salient Features of Plaster of Paris :
Chem. Formula : CaSO4.1/2 H2O "Calcium Sulfate "
Grade : Commercial/Industrial
Physical Appearance : Pure White
Mesh Size : Very Fine a 0.2mm screen
Initial Setting Time: 3-8 minutes
Final Setting Time: 8-15 minutes
Flexural Strength: a Y2.5Mpa
Compressive strength: a Y5.0Mpa
Rigidity: a Y10N/mm2
Bulk density: 700a 1000kg/m3
Purity: Guaranteed high grade: 90 %
INFORMATIVE NOTE:
Plaster of Paris takes its name from Paris, France, where it was first widely used chemically, surgically and Constructionally. However, one of the earliest surgical uses was recorded in 1852 when A. Mathyson, a Dutch Army Surgeon, rubbed powdered plaster into cotton bandages to form splints.
Plaster of Paris, in its raw state, is termed gypsum hydrated calcium sulphate with impurities. The surgical form is pure anhydrous calcium sulphate. The essential chemical step is the heating of gypsum to 120 degree Celsius (250 degree F).
Adding water allows for a return to the original crystalline state of full hydration. Twenty percent of added water is incorporated into the hydrated crystal lattice but the other 80 percent of water eventually evaporates.
The absorption of water while setting gives out heat (an exothermic reaction) but not enough to cause discomfort or injury.