Gypsum plaster, properties

Calcined Anhydrite. Soluble anhydrite, or second-settle stucco, has physical properties similar to those of gypsum plaster. It hydrates to the dihydrate rapidly in water. Its outstanding property is its extreme affinity for any moisture, which makes it a very efficient drying agent (see Desiccants). In ambient moisture-laden air, it readily hydrates to hemihydrate. Soluble anhydrite, under the trade name Drierite, is widely used as a desiccant in the laboratory and in iadustry. A small amount is also used as an insecticide carrier. Small amounts of soluble anhydrite are unintentionally produced in most commercial calciners during hemihydrate production. 

Construction Soil stabilization water absorber water retention aids in cements, grouts, and tiles improvement of mechanical properties of cement and gypsum plasters and water based paints... 

REFERENCE Koslowski. T. and Ludwig. U.. Retardation Gypsum Plasters with Citric Add Mechanism and Properties/ The Chemistry and Technology of Gypsum. ASl STP S6J, R. A. Kuntze, Ed.. American Society for Testing and Materials. 1984. pp. 97-104. 

The object of this research work is the investigation of the mechanism of retardation of gypsum plaster by the addition of citric acid and its influence on the properties of the fresh and hardened mortar. The significance of this work lies in the explanation of the retardation mechanism and its close connection with the microstructure and hence with the mortar properties. 

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. 

Gypsum has useful fire-resistant properties due to its water of crystallization (20.9 %). Gypsum plaster is widely used as an insulating material for protecting columns and beams of wooden materials from the high temperatures that develop during a lire. 

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. 

Plaster is the rehydrated calcined gypsum. The American Dental Association classifies five types of dental plaster according to the physical properties type 1, impression plaster type 11, model plaster type 111, dental stone type IV, high-strength dental stone and type V, high-strength. 

In this chapter the terms plaster and plaster material refer to the existing wall preparation regardless of its analyzed composition. We assume that the original plaster material in the tomb of Nefertari was predominantly gypsum based, not only because this material would have the desired binding properties, but also because the formation of calcium sulfate dihydrate is kinetically favored under the conditions of formation just described (38). 

The concept of fire-retardancy is remarkably old. The Greek historian, Herodotus, in 484-431 BC recorded that the Egyptians imparted fire-resistance to wood by soaking it in a solution of alum (potassium aluminum sulfate) [Browne, 1958]. The Romans added vinegar to the alum for the same purpose. Vitruvius in the first century BC described the natural fire-retardant properties of the larch tree and some military applications of fire retardant materials such as plaster of clay reinforced with hair [Vitruvius, I960]. In 1638, Circa recorded that Italian theaters were painted with a mixture of clay and gypsum (potassium aluminum silicate and hydrated calcium sulfate) to protect them from fire. Wild was issued a British patent in 1735 for his process of treating wood with a mixture of alum, ferrous sulfate and borax (sodium tetraborate decahydrate). And Gay-Lussac in 1821 showed that a solution of ammonium phosphate, ammonium chloride and borax acts as a fire-retardant for wood. 

CHEMICAL PROPERTIES stable under ordinary conditions of use and storage hazardous polymerization will not occur very hygroscopic (i.e., absorbs moisture from the air) reacts with water to from Gypsum and Plaster of Paris FP (NA) LFL/UFL (NA) AT (NA) HF (-1434.5 kJ/mol crystal at 25°C) Hf (28.03 kJ/mol at 1723K). 

Gypsum, the raw material for Plaster of Paris, occurs in several varieties. The Greeks used a form of gypsum as windows for their temples. What particular property would be important for this application What form of gypsum would be most suitable ... 

Chem. Descrip. Methyl slllconate In water Uses Water repellent, hydrophobic sealer for low-fired clay prods, (roof tiles, facing bricks, flower pots), aerated concrete, post-treatment of gypsum boards, light fillers such as perlite, vermicullte, and aerated concrete granules additive to whitewash and water-based paints, primer for emulsion paints and plasters Features Water-based VOC compliant Properties Colorless to yel. sp.gr. 1.29 pH = 13 42% solids Environmental Environmentally friendly... 

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