Plaster of Paris And Gypsum Use Properties & Preparation

What is Plaster of Paris

The plaster of paris made of gypsum which is mainly found in paris. So it is called plaster of paris. It’s chemical formula is CaSO₄ H₂O. It is calcium sulphate hemihydrate.

Manufacturing of Plaster of Paris

Plaster of paris is prepared from gypsum. Gypsum is calcium sulphate dihydrate, CaSO₄. 2H₂O. That is, gypsum is calcium sulphate containing 2 molecules of water of crystallization.

Plaster of Paris is prepared by heating gypsum (CaSO₄.2H₂O) to a temperature of 100°C (373K). When gypsum is heated to a temperature of 100°C (373 K), it loses three–fourths of its water of crystallization and forms plaster of paris:

If heating will be uncontrolled then anhydrous calcium sulphate will be formed which is having no properties of plaster of paris.

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Properties Plaster of Paris

1. It is white powder having very fine crystals.
2. It gets hydrated, when treated with water with the liberation of large amount of heat energy, commonly, called heat of hydration. The gypsum crystals, so formed, tightly interlock with one another to form a solid mass within half an hour. Furthermore, on solidification, it slightly expands and hence, is excellent for making casts in moulds.

What is Gypsum

It is very soft mineral composed of calcium sulphate dihydrate with thechemical formulaCaSO₄·2H₂O

Physical Properties of Gypsum

Gypsum is moderately water–soluble (~2.0–2.5g/L at 25°C)

Gypsum crystals are found to containanion water andhydrogen bonding

Occurrence of Gypsum

Gypsum is a common mineral, with thick and extensiveevaporitebeds in association withsedimentary rocks.Gypsum is deposited from lake and sea water, as well as inhot springs, fromvolcanicvapours.

Uses of Gypsum:

Gypsum is used in a wide variety of applications:

1. Gypsum Boardprimarily used as a finish for walls and ceilings; known in construction as drywall.
2. Plaster ingredient.
3. As Fertilizer and soil conditioner.
4. As surgical splints; casting moulds; modelling.
5. A component of Portland cement used to prevent flash setting of concrete.
6. In foot creams, shampoos and many other hair products.
7. Impression plasters in dentistry.