Anhydrous gypsum plaster

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. 

Synonyms anhydrous calcium sulfate-anhydrite muriacite karstenite anhydrous gypsum anhydrous sulfate of lime hemihydrate-plaster of Paris annalin dried gypsum dried calcium sulfate dihydrate-gypsum alabaster satin spar mineral white terra alha satinite light spar selenite precipitated calcium sulfate native calcium sulfate... 

Synonyms/Trade Names Anhydrous calcium sulfate, Anhydrous gypsum, Anhydrous sulfate of lime. Calcium salt of sulfuric acid [Note Gypsum is the dihydrate form Plaster of Paris is the hemihydrate form.]... 

Synonyms Anhydrite (natural form) Anhydrous calcium sulfate Anhydrous gypsum Calcium sulfate (1 1) Calcium sulfonate Gypsum Plaster of Paris Sulfuric acid, calcium salt Sulfuric acid, calcium salt (1 1) Classification Inorganic salt Empirical CaOjS Formula Ca H2O4S... 

When gypsum (CaS04.nH20) is heated to a temperature of 170°C, it loses three quarters of its water of crystallization, becoming calcium sulphate hemi-hydrate, or plaster of Paris. Anhydrous calcium sulphate forms at higher temperatures. These two substances are the chief materials used in plasters. Gypsum plasters have now more or less replaced lime plasters. 

Estrlch, m. plaster floor layer of mortar, -gips, m. estrich gypsum, flooring plaster (a form of anhydrous calcium sulfate similar to Keene s cement), -stein, m, a kind of paving brick. 

Synonyms Anhydrous calcium sulfate anhydrous sulfate of lime gypsum (CaS04-2H20 plaster of paris (CaS04-l/2H20)... 

Your team needs to develop a procedure to experimentally determine the correct empirical formulas for both hydrates of this anhydrous compound. You will use gypsum samples from the mine and samples of the plaster of Paris product. 

The second process is a two-step reaction sequence (Reactions 3.5 and 3.6). The process is highly adaptable—one of three forms of calcium sulfate [gypsum (dihydrate), plaster of paris (hemihydrate), or anhydrate]—may be used. The advantage of this process is the avoidance of a sulfuric acid intermediary. 

Both the anhydrous and dihydrate forms of calcium sulfate occur naturally in the form of the minerals anhydrite, angelite, muriacite, and karstenite (CaS04) and gypsum (CaS04-2H20). These minerals have been known to humans and used by them for thousands of years. The method for converting natural gypsum to the hemihydrate (plaster of... 

Calcium sulfate is commonly found in three forms, i.e. anhydrous (called anhydrite), hemihydrate (plaster of Paris) and dihydrite (gypsum). The mid-infrared spectra of each of these forms are shown below in Figure 5.2. Comment on the differences between these spectra. 

Anhydrite - drIt [Gr Anhydrite fr. Gk any-dros] (ca. 1823) n. The mineralogical name for native anhydrous calcium sulfate which is often associated in nature with calcium sulfate dehydrate or gypsum. It occurs occasionally as an impurity in gypsum and plaster of Paris. 

Whether anhydrous or in solution (beryllium or magnesium sulphate), these sulphates have no action on aluminium. Calcium and barium sulphate are insoluble. It is well known that plaster, which mainly contains calcinated calcium sulphate (gypsum) does not attack aluminium (see Section G.4.2). 

---