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How is plaster of Paris prepared?

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Plaster of paris is prepared by heating calcium sulfate dihydrate, or gypsum, to around 150 degree celcius. With an additive to retard the set, it is called hard wall, plaster, which can provide passive fire protection for interior surfaces.

Calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is called plaster of paris (plaster of paris). It is prepared by heating gypsum (CaSO4. 2H2O) at 120°C in rotary kilns, where it gets partially dehydrated.

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Sumit Saini

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