Hemihydrate calcium sulfate

Calcium sulfate hemihydrate []0034-76-1 j 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 CaS04 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. [Pg.409]

Likewise, the calcination of gypsum drives away water. Calcinating gypsum (composed of hydrated calcium sulfate) causes that part of the water combined with the calcium sulfate to evaporate, leaving a solid, friable residue usually known as plaster of Paris (composed of calcium sulfate hemihydrate) plaster of Paris is used as a cement and mortar as well as an efficient casting material (see Textbox 35). [Pg.173]

Plaster of Paris has long been used as a casting material, a cement, and a mortar. If mixed with water, plaster of Paris forms a very soft and pliable mixture. After a very short time, lasting only 5-8 minutes, the wet, pliable mixture sets, that is, it hardens into a stable, firm solid. The setting process entails the incorporation of water molecules (a process known as hydration) into the calcium sulfate hemihydrate and the consequent formation and crystallization of hydrated sulfate of calcium. In other words, when water is added to plaster of Paris, the two combine, again forming gypsum, which soon crystallizes into a hard solid mass ... [Pg.175]

Calcium aluminate monosulfate hydrate CaNH4P04-8H20 Calcium sulfate hemihydrate CaS04 CaS04-2H20... [Pg.184]

The soluble sulfate versus time curve for the cement containing the natural anhydrite is radically changed when CLS is present [130, 131]. The rate of solution of natural anhydrite, which is much slower than that of gypsum or calcium sulfate hemihydrate, is further retarded in the presence of chemical admixtures, which leads to a sulfate-starved system in the concrete, often producing rapid set and an increase in rate of concrete slump loss (Fig. 7.42). Apparently the adsorption of the lignosulfonate by the natural anhydride plus the rapid reaction between the soluble SO3 and the... [Pg.525]

The calcium ion reacts with the sulfate ion and a half water molecule to form a calcium sulfate-hemihydrate. [Pg.463]

According to Hill [40], analyses of reaction products during the spray absorption drying shows that the reaction of the calcium hydroxide with the sulfur dioxide leads to calcium sulfate hemihydrate. The main reaction equation can be formulated as follows ... [Pg.463]

Calcium sulfate hemihydrate (see Section 17), is used in the preparation of plaster of Paris bandage, which is used for the immobilization of limbs and fractures it should not be used in the formulation of tablets or capsules. [Pg.105]

Calcium phosphate, dibasic anhydrous calcium phosphate, dibasic dihydrate calcium phosphate, tribasic calcium sulfate hemihydrate. [Pg.106]

E516 Calcium Sulfate Hemihydrate 106 E1505 Triethyl Citrate 796... [Pg.883]

The recrystallization in variant 3 can proceed either after the calcium sulfate hemihydrate had been filtered off or in situ. [Pg.69]

Calcium. sulfate occurs naturally as its dihydrate, (natural gypsum) as anhydrous anhydrite and rarely as its hemihydrate in the form of the mineral bassanite. Only the deposits of natural gypsum and anhydrite are of economic interest. For applications in the construction industry only the hardenable modifications, calcium sulfate hemihydrate (a- and P-form) and anhydrite, which are manufactured by dehydrating the dihydrate, are important. The properties and formation conditions of the different calcium sulfate modifications are given in Table 5.3-11. [Pg.416]

The monohydrate is formed by zeolithic take up of water by calcium sulfate hemihydrate... [Pg.418]

Anhydrite II is formed at higher temperatures from anhydrite III or calcium sulfate hemihydrate and is identical to naturally occurring anhydrite. It occurs in three different intermediate forms. The rehydration rates of these intermediate forms depend upon temperature. The flooring plaster (Estrichgips) obtained above 7()0°C partly consists of CaO, since decomposition of anhydrite begins above 600°C ... [Pg.418]

Plaster. setting is the reaction of calcium sulfate hemihydrate, anhydrite II or anhydrite III with water i.e. the opposite reaction to the manufacture of plaster ... [Pg.423]

Setting" i.s the rchydralion ot calcium sulfate hemihydrate or anhydrite... [Pg.423]

Keeping the temperature low is necessary to avoid the precipitation of anhydrite (anhydrous calcium sulfate) or calcium sulfate hemihydrate (CaS04 O.5H2O) which tend to form at high operating temperatures. Both... [Pg.302]

TABLE 2—The effea drying on changes in composition of p calcium. sulfate hemihydrate. [Pg.49]

FIG. 2—Microwave drying curves for calcium sulfate hemihydrates. [Pg.54]

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