![]() There are mainly three types of plaster of paris, which are described below At a temperature of more than 373 K, it forms anhydrous calcium sulphate, which is called dead burnt plaster of paris.It tends to expand slightly after setting.It is water-resistant in nature, so it is widely used for making pottery and medical casts.For example, it forms gypsum crystals (hard mass) when water is added to it. It changes into a hard mass when it is wet or water is added to it.At high temperatures, it undergoes decomposition to produce poisonous sulphur dioxide.Although it is chemically less reactive, it can act as an oxidising agent.It is a non-combustible and non-inflammable white powder.In this case, it is called dead burnt plaster as it cannot be used like POP by adding water to it. ![]() ![]() If Gypsum is heated at a temperature of more than 373K, it loses all water molecules and thus gets converted into anhydrous calcium sulphate (CuSO4). When water is added to POP, it changes itself into a hard substance, this property makes it suitable to be used to make statues, decorative items, etc. However, half of the water molecule still remains with the plaster of paris so, it is called hemihydrate. The gypsum (CaSO 4.2H 2O) when heated at 373 K loses water molecules and forms plaster of paris. Its chemical name is Calcium Sulphate Hemihydrate and its chemical formula is CaSO 4.1/2H 2O. It is commonly used to make the false ceiling, as a sculpturing material and in plasters used in the treatment of fractured bones. Plaster of paris is also known as the Gypsum plaster as it is made of gypsum. ![]()
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