Hemihydrate gypsum

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. 

SYNONYMS calcium sulfate, hemihydrate, dried calcium sulfate, gypsum hemihydrate, hemihydrate gypsum, (note plaster of paris is the hemihydrate form of calcium sulfate and gypsum is the dihydrate form). 

Synonyms/Trade Names Calcium sulfate hemihydrate. Dried calcium sulfate, Gypsum hemihydrate, Hemihydrate gypsum [Note Plaster of Paris is the hemihydrate form of Calcium Sulfate Gypsum is the dihydrate form.] ... 

Anhydrous gypsum plaster contains -anhydrite (A-III ) as its main constituent. It is produced in a similar way to hemihydrate gypsum plaster, but at higher calcination temperatures. The binder is very hygroscopic, and tends to absorb water vapor rapidly from the air to convert to hemihydrate. The hemihydrate formed in this way hydrates rapidly to dihydrate, if mixed with water. The properties of this binder are similar to those of hemihydrate gypsum plaster. 

Alpha-hemihydrate gypsum plaster (autoclave gypsum)... 

Alpha-hemihydrate gypsum plaster has a distinctly lower water requirement than plaster of Paris and—at an equal consistency of the starting mix—exhibits a distinctly higher final strength. It is used in applications in which a high strength of the hardened material is essential, as in medical and dental applications, and in the production of molds for the ceramic industry. 

A air curing W underwater curing HH hemihydrate gypsum OPC ordinary Portland cement SRPC sulfate-resistant Portland cement MS microsilica D disintegration of samples Source Odler and Balzer (1992)... 

Fischer, K.W., and Uschmann, W. (1964) The production of -hemihydrate gypsum in technical salt solutions (in German). Silikattechnik 15, 361-366. 

Wirsching, F. (1962) The production of a-hemihydrate gypsum plaster from by-product gypsum in salt solutions (in German). Zement-Kalk-Gips 15, 439-441. 

Ztirz, A. et al. (1991) Autoclave-free formation of a-hemihydrate gypsum. Journal of the American Ceramic Society 74, 1117-1124. 

The product add at between 40% and 50% P2O5, depending on downstream requirements and hemihydrate gypsum, is separated by a horizontal vacuum filter... 

Gypsum is used as a paste with water for indoor decorations, partitions and plasters for the surface finish of walls and ceilings. When mixed with sand and lime, various kinds of mortar are obtained for non-structural and even structural elements. The compressive strength varies within large limits from 1.0 to 7.0 MPa for the plaster of Paris type and from 12 to 15 MPa for a-hemihydrated gypsum. Fibre reinforced gypsum is briefly described in Section 3.2.9. 

Figure 1.12 TGA of freshly bagged and artificially aged CEM I 42.5 N (storage at 90% relative humidity for 3 days). The corrected losses on ignition (without contribution of hemihydrate, gypsum and portlandite) as defined by Theisen and Johansen (1975) of the fresh and the aged cements are 0.18 and 1.8 wt.%, respectively. Fresh cements typically show values between 0.15 and 0.30 wt.%. (Adapted from Winnefeld, F., ZKG International, 61 (I I), 68-77, 2008.)...

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