Gypsum heated

Gypsum, heated at 130°C forms plaster of Paris (2CaS04.H20). Anhydrite and gypsum are used in the manufacture of sulfuric acid. 

Table 3. Influence of gypsum heat activation on mortar mechanical performance (immersion at 20°C)...

CaSO4-0-5HiO, prepared by heating gypsum at 130 "C, is used as plaster of Paris. Gypsum and anhydrite are used for H2SO4 production and gypsum is used as a soil additive and as an inert additive to pharmaceuticals and insecticides. 

Cements are commonly made by heating a mixture of limestone and clay to about 1700 C. The product is ground with gypsum. Chemically cements consist of a mixture of calcium silicates and aluminates with some sulphate present. World production 1976 730 megatonnes. 

A number of modifiers are employed to prevent most of the shrinkage of gypsum when it is heated above 300°C. Among these are boric acid (118) and sodium and other chlorides (119,120). A review of the development and composition of some investments is given (121). 

Cellulose liner material absorbs water and needs to be wet for at least 30 s prior to investing to prevent Uquid from being extracted from the investment. The ceUulose liner bums when heated in air and is eliminated completely from the mold at burnout temperatures of 700°C (123). To ensure retention of the mold within the casting ring, a ceUulose liner should be kept short of each end. For gypsum investments a liner that is 12 mm shorter than the height of the ring should be used. 

Water is mainly used as noncontact cooling water, scrubbing water, and in the transportation of gypsum as slurry to the wastewater treatment facility. The water in the heat exchangers is used to... 

Gypsum Building making plaster of Paris Calcium sulfate Easily shaped and polished decomposed by heat... 

When Plaster of Paris, CaSC>4 5H2O (s), is mixed with water, solid gypsum, CaS04- 2 H2O (s), is formed in an exothermic reaction, that is, a heat-releasing reaction. Thus, as the cast hardens, the plaster cast becomes warm ... 

Brenden and Chamberlain (6) measured heat release rate from wall assemblies having fire-retardant-treated studs and gypsum board as interior finish in the FPL fire endurance furnace using three methods (a) the substitution method, by which the amount of fuel required to maintain the ASTM E-119 time-temperature curve for a... 

Heat Release Rate of Wail Assemblies. As examples, heat release rates are shown for series B because these tests lasted for longer times than the tests in series A and C (Figures 5-8). In walls B-3 and B-4, which had gypsum as the interior finish, combustion was complete throughout the entire runs. The concentration of CO was negligible. 

For those walls protected by gypsum (walls B-3 and B-4), furnace heat release rate and heat release rates from the fuel gas (Eq. (12)) and the wall (Eq. (13)) are shown in Figures 7 and 8. Similar to the noncombustible wall, the gypsum provided very little heat, except for a small peak in the beginning, which could have been caused by the gypsum paper. Heat release rates from walls B-3 and B-4 rose slowly as a result of the gypsum opening up at the seams or cracks. 

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