Applications gypsum plasters

Cement is a binder that sets and hardens by itself or binds other materials together. The most widely known application of cements is in construction a second one is the area of bone cements. Cements used in construction are characterized as hydraulic or nonhydraulic and mostly for the production of mortars and concrete. Hydraulic cements set and harden after combining with water. Most construction cements are hydraulic and based on Portland cement, which consists of calcium silicates (at least 2/3 by weight). Nonhydraulic cements include the use of nonhydraulic materials such as lime and gypsum plasters. Bone cements and bone cement composites refer to compounds that have a polymer matrix with a dispersed phase of particles. For instance, polymethylmethacrylate (PMMA) is reinforced with barium sulphate crystals (for radio-opacity) or with hydroxyapatite... 

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. 

Following are the applications using purely gypsum plaster (save some minor additions of other ingredients sometimes). 

Plasterboard is made of a gypsum plaster core with a paper facing. It is a widely used construction material for applications such as forming partitions, lining walls and ceilings. Over 2.5 million tonnes of plasterboard are manufactured and used in the UK each year, and this is increasing. 

At this point, Lavoisier was primarily interested in doing research that would impress the academicians. He read his first paper to the Academy as a visiting scientist (that is, a non-member) on February 27,1765. It dealt with a topic that had been pursued by some of the chemists in the Academy and was titled The Analysis of Gypsum. Gypsum was the mineral from which plaster was made, so it was a topic with practical applications. The two referees appointed by the Academy to judge the paper reported favorably on it and recommended it for inclusion in the Academy s Savants etrangers collection. It is probable that some sort of behind-the-scenes deal had been made because both referees were friends of Lavoisier s father. 

Although the maximum pore radius distribution in conventional gypsum microstructures usually lies within the range of capillary suction action (100 nm to 1 mm) [44, 52], the roughly 50% water absorption that occurs in untreated gypsum is often reduced to less than 5 wt% [44, 45] at standard market application rates of just 0.3 - 0.5 wt% H-siloxane. The optimum amount to use depends upon the gypsum raw material, the fineness of the grain in the plaster of Paris, its specific sur ce area, and the reaction temperature. 

An advantage of the system is that CaS04-2H20, gypsum, is non-toxic and is not a waste product it has a number of commercial applications, for example in the production of plaster of Paris (see Section 11.7) and cement. 

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. 

Plaster of Paris is employed extensively for the making of moulds for slip-casting in this application, the porosity of the set product is important, since water is removed locally from the casting-slip by the capillary action of the pores. Gypsum products however have many other uses, notably in the cement and building industries, and in dentistry and surgery. 

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 ... 

The plaster found wide application in ancient Egypt [2], It was applied as mortar and to stucco decoration, for example in Tutankhamen s tomb, for firnshing the tombstones of calcite (called alabaster). As mortar it was used in pyramids, in Giza. The beginning of its application is not establish it is regarded that it falls in the period from 5,000 to 3,400 year before Christ [2], The plaster application, instead of lime Jaworski explains by the lack of fuel, because the limestone are more easily accessible than gypsum raw materials [2]. 

Poly (2-hydroxyethyl, Et) ether Ethyl hydroxyethyl cellulose. Etulos. EMEC [9004-58-4] Useful in solvent coating applications, inks, paints and as an additive to cement and gypsum based plasters and mortars Laxative. 

Nonhydraulic cements are the most ancient type of cement. Most of these cements derive from the simple calcination of gypsum or calcium carbonates such as limestones. They harden when the calcine obtained is mixed with a given amount of water but the hardened products then produced when put in direct contact with water again are subject to dissolution and hence they are not resistant to water. Gypsum cement is still widely used in modern countries as plaster of Paris for interior applications like insulation panels. The transformation of natural gypsum to the calcium sulfate hemihydrate is obtained by moderate heat treating at 130-150 C and it is described by the following chemical reaction ... 

The plaster physical-chemical production, the application of gypsum industry association France-gypstun (Yang Kim translated). China construction industry press, 1987.pl33-141... 

The use of gypsum, or plaster of Paris as it is caUed, for different objects - figurines, bowls, stucco work and so on - has been described in the historical section. In our time the most important - and very large - application is for producing gypsum wall-board (drywall), which has almost replaced other waU coverings in buildings. 

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