Gypsum (plaster)
HYDRATED CALCIUM SULPHATE
Chemistry
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Volatiles
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Miscellaneous
- Family: Other
- Region: None
- Mined At: Unspecified
- Raw Mineral: No
- Generic: No
Notes
Specific Gravity: 2.3
Hardness: 3
Plaster (gypsum, alabaster) is calcium sulphate CaSO4 2H2O. It is the crystalline mineral from which plaster is made. Gypsum has three different decomposition cycles, depending on temperature. At 120-200C and 500C water is liberated, at 1000-1100C it decomposes completely.
Plaster is not practical as a source of CaO in glazes because its decomposition produces large amounts of sulpfur trioxide which is dangerous to health.
Plaster reacts with sodium silicate and soda ash in a calcium-for-sodium ion exchange, and this process will eventually clog the pore structure of a mold. The use of polyacrylate deflocculants will prevent this (and have other advantages).
Data
- Specific Gravity: 1200.00
- Specific Gravity: 1200.00
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
XML
<?xml version="1.0" encoding="UTF-8"?>
<material name="Gypsum (plaster)" descrip="HYDRATED CALCIUM SULPHATE" generic="0" rawmineral="0" searchkey="" loi="67.40">
<families>
<family name="Other"/>
</families>
<oxides>
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="*" percent="32.600" tolerance=""/>
</oxides>
<volatiles>
<volatile symbol="" name="" percent="67.400" tolerance=""/>
</volatiles>
<suppliers>
<supplier name="Generic" country="" url="" label=""/>
</suppliers>
<notes>
<note>Specific Gravity: 2.3
Hardness: 3
Plaster (gypsum, alabaster) is calcium sulphate CaSO4 2H2O. It is the crystalline mineral from which plaster is made. Gypsum has three different decomposition cycles, depending on temperature. At 120-200C and 500C water is liberated, at 1000-1100C it decomposes completely.
Plaster is not practical as a source of CaO in glazes because its decomposition produces large amounts of sulpfur trioxide which is dangerous to health.
Plaster reacts with sodium silicate and soda ash in a calcium-for-sodium ion exchange, and this process will eventually clog the pore structure of a mold. The use of polyacrylate deflocculants will prevent this (and have other advantages).</note>
</notes>
<testdata>
<testitem testname="0" value="1200.00"/>
<testitem testname="0" value="1200.00"/>
</testdata>
</material>
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