DEHYDRATION OF GYPSUM

P-Hemihydrate. The dehydration of gypsum, commonly referred to as calcination in the gypsum industry, is used to prepare hemihydrate, or anhydrite. Hemihydrate is generally called stucco in North America and plaster in many other continents. In North America, plaster is differentiated from hemihydrate or stucco by the inclusion of additives to control intended use properties, eg, rehydration time, density, coverage, strength, and viscosity. 

Anhydrite. In addition to ketde calcination (Fig. 1), soluble anhydrite is commercially manufactured in a variety of forms, from fine powders to granules 4.76 mm (4 mesh) in size, by low temperature dehydration of gypsum. 

Mack s cement). A group of cements that consist essentially of calcium sulfate and are produced by the partial dehydration of gypsum to the hemihyd-rate CaS04 l/2I I2(). They usually contain additions... 

The clinker formation process is initiated by the dehydration of gypsum to anhydrite at around 100-120°C, followed by a decomposition of clay minerals at around 300-600°C. The decaibonization of the calcium carbonate that is present starts at about 700°C, and is completed before the temperature reaches 900°C. 

The only known commerdal process for produdng alpha hemihydrate from phosphogypsum is the Giulini process that wm developed in West Germany [281 and was used in two plants in that country and one in fre-land. As mentioned previously, alpha hemihydrate is formed by dehydration of gypsum in an aqueous suspension in an autodave. 

Plaster of Paris (calcium sulfate hemihydrate) is produced by the partial dehydration of gypsum... 

DTA results of C3A + 25% gypsum mixtures hydrated with 0% and 1% TEA are shown in Fig. 11. The unhydrated mixture exhibits an endothermal doublet between 100 and 150°Cduetoastepwise dehydration of gypsum. Hydration seems to start from the first minute of contact of water with the sample. At 5 minutes, a larger amount of gypsum disappears from... 

Figure 28. Dehydration of gypsum (solid line) associated with Ca-montmorillonite (dashed line) previously heated to 80°C for 60 min in a flow of N2 gasJ ...

Dehydration of gypsum when grinding Portland cement... 

Check if your material is altered by the grinding process (e.g. dehydration of gypsum). 

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