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With judicious heating, gypsum converts to the partially dehydrated mineral called bassanite or plaster of Paris. This material has the formula CaSO 4 ·( n H 2 O), where 0.5 ≤ n ≤ 0.8. [ 8 ] Temperatures between 100 and 150 °C (212–302 °F) are required to drive off the water within its structure.
The plaster is not pure plaster of Paris, but rather has additives to improve green strength, dry strength, permeability, and castability.For instance, talc or magnesium oxide are added to prevent cracking and reduce setting time; lime and cement limit expansion during baking; glass fibers increase strength; sand can be used as a filler. [1]
Gypsum is moderately water-soluble (~2.0–2.5 g/L at 25 °C) [13] and, in contrast to most other salts, it exhibits retrograde solubility, becoming less soluble at higher temperatures. When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate ( bassanite , often simply called "plaster") and, if heated ...
Gypsum plaster, [12] also known as plaster of Paris, [13] is a white powder consisting of calcium sulfate hemihydrate. The natural form of the compound is the mineral bassanite . [ 14 ] [ 15 ]
There are several different filler materials used in ceramics including plaster of Paris and other commercially available putties and fillers. Plaster of Paris is a material that consists of calcium sulphate hemihydrate power and is produced by heating gypsum to 120 °C.
Gypsum mortar, also called plaster of Paris, was used in the construction of many ancient structures. It is made from gypsum, which requires a lower firing temperature. It is therefore easier to make than lime mortar and sets up much faster, which may be a reason it was used as the typical mortar in ancient, brick arch and vault construction.
Paredes coated the mantel and chimney breast in black Venetian plaster to add “something dramatic” amid the snowy slopes and all-white walls. Chris Mottalini Parisian Fireplace
However, plaster of Paris casts take too long to fully dry and limits patient mobility for up to 74 hours — if the patient walks on the cast during this time, the shape will change, and the cast will not protect the foot and wound correctly. [10] Fiberglass casts were introduced in the 1980s or 1990s.