Calcium sulphate hemihydrate

Calcium sulphate hemihydrate [ 10034-76-1J M 145.2. Sol in H2O (0.2 parts/100 at 18.75 ). Completely dehydrated >650°. Dry below 300° to give a solid with estimated pore size ca 38% of vol. Anhydrous CaSOa has 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 should be kept in a tightly sealed container. 

Plaster of Paris, also known as calcium sulphate hemihydrate, is prepared by heating gypsum between 120° and 160°C -... 

Several assessments of experimental data from continuously operated precipitators, utilizing the population balance (section 8.1.1), are of particular interest, e.g. the MSMPR studies on calcium carbonate by Baker and Ber-gougnou (1974), calcium sulphate hemihydrate in phosphoric acid (Sikdar, Ore and Moore, 1980) and silver bromide in aqueous gelatin suspension (Wey, Terwilliger and Gingello, 1980). 

Gypsum plaster It is produced by mixing water with calcium sulphate hemihydrate, with the help of heat of about 300°F (150°C). When the dry plaster powder is mixed with water, it re-forms into gypsum. If plaster or gypsum is heated above 200°C, anhydrite is formed, which will also re-form as gypsum if mixed with water. 

S. Girgin, Crystallization of Alpha-Calcium Sulphate Hemihydrate by Aqueous Reaction of Calcium Chloride with Sulphuric Acid (PhD thesis, McGill University, 2006). 

M. El Moussaouiti, et al., Agglomeration Kinetics of Calcium Sulphate Hemihydrate Crystals in Sulpho-Phosphoric Solutions, Journal of Crystal Growth, 169 (1996), 118-123. 

Plaster of Paris. Calcium sulphate hemihydrate, CaS04. /2H20 prepared by heating gypsum (q.v.) at 150-160°C. There are two forms a, produced by dehydrating gypsum in water or saturated steam p, produced in an unsaturated atmosphere. Plaster usually contains both forms. It is used for making moulds (q.v.) in the pottery industry. 

Sidqui, M Collin, P Vitte, C Forest, N. Osteoblast adherence and resorption activity of isolated osteoclasts on calcium sulphate hemihydrate. Biomaterials, 1995, 17, 1327-1332. 

Calcium sulphate hemihydrate (CaSO4-0.5H2O), (CS), known as plaster of Paris, has been used for over a 100 years in a variety of pharmaceutical, dental, and orthopaedic applications. 

The dehydration and interconversion reactions of the various forms of calcium sulphate [dihydrate, hemihydrate (a and 3 pseudo morphs) and anhydrous salt (hexagonal and orthorhombic structures)] have been studied by Ball et al. [281,590,591] who compared their observations with the available rate and microscopic data. The important features of the complicated behaviour found are summarized in the scheme [281]... 

Calcium sulphate (anhydrous). (Prepared by heating the dihydrate or the hemihydrate in an oven at 235 for 2-3h it can be regenerated.) Available commercially as Drierite. It forms the hemihydrate, 2CaSO4.H2O, so that its capacity is fairly low (6.6% of its weight of water), and hence is best used on partially dried substances. It is very efficient (being comparable with phosphorus pentoxide and concentrated sulphuric acid). Suitable for most organic compounds. Solvents boiling below 100 can be dried by direct distillation from calcium sulphate. 

Badens, E., Veesler, S. Sc Boistelle, R. (1999). Ciystallization of gypsum from hemihydrate in presence of additives. Journal of Crystal Growth, 198/199, 704-709 Barton, F. M. Wilde, N. M. (1971). Dissolution rates of polyaystalline samples of gypsum and orthorhombic forms of calcium sulphate by rotating disk method. Transactions of the Faraday Society, 67, 3590-3597. 

The normal selenates of potassium, sodium, calcium and magnesium are very similar in properties to the corresponding sulphates, except that the potassium salt is much more soluble in water than potassium sulphate.3 Sodium selenate gives a decahydrate which effloresces, and the transition-point between this and the anhydrous salt is 31-8° C., above which point the solubility falls as the temperature rises. Calcium selenate gives a hemihydrate resembling plaster of Paris, and also a hydrate of composition CaSe04.l-5H2O.4... 

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