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| | Calcium sulfate hemihydrate Basic information | | Description |
| | Calcium sulfate hemihydrate Chemical Properties |
| alpha | +6.5°(D/20℃ | | density | 2.69 g/cm3 | | form | Solid | | color | White with a blue, gray or red hue | | Water Solubility | sets to hard mass when mixed with H2O [MER06]; g/100g solution H2O: 1.23 (0°C), 0.71 (25°C), 0.189 (100°C); solid phase, CaSO4 · 1/2H2O [KRU93] | | Stability: | Stable. Hygroscopic. | | CAS DataBase Reference | 10034-76-1 | | EPA Substance Registry System | Calcium sulfate hemihydrate (10034-76-1) |
| | Calcium sulfate hemihydrate Usage And Synthesis |
| Description | Calcium sulfate hemihydrate (CaSO4 • 0.5H2O) is the dehydrated product of gypsum, calcium sulfate dihydrate (CaSO4•2H2O). It is obtained by heating gypsum to approximately 150°C. It is known as gypsum plaster or plaster of Paris (POP). On adding water, it solidifies by an exothermic reaction into hydrated calcium sulphate. It is commonly used to precast and hold parts of ornamental plasterwork placed on ceilings and cornices. Plaster of Paris casts can be used as a treatment of fractures to immobilize the limb. It is also used as a desiccant, and in medicine as a tablet excipient.
| | Chemical Properties | white or slightly off-white powder or granules | | Definition | ChEBI: Calcium sulfate hemihydrate is a calcium salt and a hydrate. | | Industrial uses | Gypsum is the most common sulfate mineral,characterized by the chemical formulaCaSO4 · 2H2O; it shows little variation from thiscomposition.
Gypsum is one of the several evaporite minerals.This mineral group includes chlorides,carbonates, borates, nitrates, and sulfates. Theseminerals precipitate in seas, lakes, caves, andsalt flats due to concentration of ions by evaporation.When heated or subjected to solutionswith very large salinities, gypsum converts tobassanite (CaSO4.H2O) or anhydrite (CaSO4).Under equilibrium conditions, this conversionto anhydrite is direct. The conversion occursabove 42°C in pure water.
Gypsum is used for making building plaster,wallboard tiles, as an absorbent for chemicals,as a paint pigment and extender, and forcoating papers. Natural gypsum of California,containing 15 to 20% sulfur, is used for producingammonium sulfate for fertilizer. Gypsumis also used to make sulfuric acid by heatingto 1093°C in an air-limited furnace. Theresultant calcium sulfide is reacted to yield limeand sulfuric acid. Raw gypsum is also used tomix with portland cement to retard the set.Compact massive types of the mineral are usedas building stones. | | Purification Methods | Its solubility in H2O is 0.2parts/100 at 18.75o. It dehydrates completely >650o. Dry it below 300o to give a solid with estimated pore size ca 38% of volume. Anhydrous CaSO4 (Drierite) has a high affinity for H2O and will absorb 6.6% of its weight of H2O to form the hemihydrate (gypsum). It sets to a hard mass with H2O; hence it should be kept in a tightly sealed container. The solubility of gypsum in H2O is unusual: 0.176% at 0o, 0.209% at 30o, 0.210 at 40o, 0.204 at 50o and 0.200 at 60o. [Hulett J Am Chem Soc 27 49 1905, James & Partington J Chem Soc 107 1019 1915, Namba J Soc Chem Ind 40 2797 1920.] |
| | Calcium sulfate hemihydrate Preparation Products And Raw materials |
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