Calcium sulfate properties

Table 2 Hsts the physical properties of calcium sulfate.

Fillers (calcium carbonate, calcium sulfate, aluminum oxide, bentonites, wood flour) increase the solid content of the dispersion. They are added up to 50%, based on PVAc. The purpose of the addition is the reduction of the penetration depth, provision of thixotropic behavior of the adhesive, gap filling properties and the reduction of the costs. Disadvantage can be the increase of the white point and a possible higher tool wear. 

Calcium sulfate a-hemihydrate, 4 582 manufacture, 4 590-591 Calcium sulfate anhydrous (anhydrite), 4 582, 583t manufacture of, 4 591 physical properties of, 4 585t uses of, 4 599... 

TABl.F. I. TERMINOLOGY AND PROPERTIES OF CALCIUM SULFATE-WATER COMPOUNDS... 

The relative reactivity of the different mineral phases of cement with water is usually given as C A>C S>C S>C AF. Aluminate phases and their hydration products therefore play an important role in the early hydration process. Because of the high reactivity of calcium aluminate, the aluminate hydration reaction is carried out in the presence of sulfate ions. The latter provide control of the reaction rate through the formation of mixed aluminum sulfate products (ettringite and monosulfoaluminate) Calcium sulfate which is added to the cement clinker hence controls the properties of the aluminate hydration products. Sulfates thus play a crucial role in cement hydration and the influence of chemical admixtures on any process where sulfates are involved may be expected to be significant [127],... 

In addition to water, which is always the product of a neutralization reaction, the other product is calcium sulfate, CaS04. This compound is a salt composed of Ca2+ ions and SO4 ions held together by ionic bonds. A salt, consisting of a cation other than H+ and an anion other than OH, is the other product produced in addition to water when an acid and base react. Some salts are hazardous substances and environmental pollutants because of their dangerous or harmful properties. Some examples include the following ... 

X-ray Diffraction Analysis. The inorganic components of paper are the most suitable ones for quantitative X-ray diffraction analysis. Most of these compounds are minerals and are present as fillers, coatings and pigments (often whiteners) which are added to improve the properties of the paper. Examples of compounds commonly added to paper are alumina, aluminum silicate, barium sulfate, calcium carbonate, calcium sulfate, calcium sul-foaluminate, iron oxide, magnesium silicate, silica, titanium dioxide, zinc oxide, and zinc sulfide (28). Some of these, e.g., calcium carbonate and titanium dioxide, may be present in any of... 

The most popular thin layer is silica gel, and it is estimated that about 90% of TLC separations are performed on standard TLC silica plates a common size is 20 cm square and 250 g,m thick. Binders, in amounts up to 15%, are usually used to produce a stable layer and good adherence to the backing plate, but plates can be made without binders. Calcium sulfate (gypsum, designated with a G in the name, e.g., silica gel G) and polyvinyl alcohol (PVA) are most common. The PVA plates are very stable and will withstand rather rough handling. While it is not difficult to make one s own plates, most laboratories prefer commercially prepared plates, especially those made with PVA. It must not be forgotten, however, that both binders will modify the adsorption properties of the silica and can produce somewhat different separations. 

The one exception where certain fillers can provide electrical property improvement is in arc resistance. Here hydrated aluminum oxide and hydrated calcium sulfates will improve arc resistance if cure is sufficiently low to prevent dehydration of the filler particles. Electrical-grade fillers generally improve the arc resistance of cured epoxy systems, as indicated in Table 9.10. 

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). 

Calcium sulfate dihydrate is used in the formulation of tablets and capsules. In granular form it has good compaction properties and moderate disintegration properties. 

The crucial step in the digestion of apatite is the formation of calcium sulfate. Its properties, in particular, its ability to be filtered, are very important e.g. for throughput optimization. The incorporation of phosphate into the crystal lattice of calcium sulfate reduces the phosphate yield and can render the calcium sulfate unusable in the building industry. 

Activation of the latent hydraulic properties of foundry sand can also be achieved with gypsum (sulfate activation). Mixtures of foundry sand with a high aluminum oxide and lime content with ca. 15% calcium sulfate (as raw gypsum or natural anhydrite) are known as supersulfated cement. 

Calcium. sulfate occurs naturally as its dihydrate, (natural gypsum) as anhydrous anhydrite and rarely as its hemihydrate in the form of the mineral bassanite. Only the deposits of natural gypsum and anhydrite are of economic interest. For applications in the construction industry only the hardenable modifications, calcium sulfate hemihydrate (a- and P-form) and anhydrite, which are manufactured by dehydrating the dihydrate, are important. The properties and formation conditions of the different calcium sulfate modifications are given in Table 5.3-11. 

Properties Miscible with water but insoluble in organic solvents. It possesses sequestering, dispersing, and deflocculating properties and precipitates proteins. In very low concentration, it inhibits corrosion of steel and prevents the precipitation of slightly soluble, scale-forming compounds such as calcium carbonate and calcium sulfate. 

Fillers are used in these products to improve mechanical properties or impart flammability resistance. Fillers are frequently silane-treated to further improve mechanical properties. Fillers must have a low moisture (below 0.1%), a low absorption of resin, and are expected to impart thixotropic properties. There are special cases. For example, if peroxyketals are used as initiators, basic fillers have to be used because acidic fillers interfere with cure times and the shelf-life of the composition. Shape and particle size distribution must be considered in filler selection to impart the desired rheological properties. Calcium carbonate is the most popular filler but aluminum trihydrate, anhydrous calcium sulfate, and silica are also frequently used. Barite is well suited to this application, especially if acid... 

The conditions under which the free water is removed arc as important to proper drying as the physical and chemical properties of the sample. These two factors must be considered simultaneously when designing a drying procedure. Drying by controlling the temperature alone would not be reliable because of the effect the relative humidity (RH) has on the amount of water desorbed from the solid surface. However, drying under controlled conditions of temperature and relative humidity may be effective in free water removal only when a pure calcium sulfate is present. 

Properties and reactivity of a calcium sulfate 3-hemihydrate are widely dependant on the preparation procedure. Although kinetical studies on the hydration reaction are done by a number of researchers, there is no standard procedure to elaborate a stable, reproducible calcium -hemihydrate specimen. This paper presents a very simple apparatus and an experimental procedure setup to elaborate a specimen that is stable and allows kinetical studies even after a long time of conservation. This apparatus also allows the simultaneous determination of the hydration rate for six different species of incompletely hydrated plasters and demonstrates experimentally that the amount of heat involved in the hydration... 

Ingo, G.M., Riccucci, C., and Chiozzini, G., Origin of gas porosity in gold-based alloys cast in calcium sulfate-bonded investment and influence of metal oxide acid-base properties on calcium sulfate thermal stabihty, J. Am. Ceram. Soc., 84, 1839, 2001. 

At the Shawnee Test Facility, major emphasis has been placed on the use of adipic acid in conjunction with forced oxidation of calcium sulfite to calcium sulfate, since this system results in better sludge dewatering properties and reduced waste solids disposal costs. Furthermore, the more tightly closed liquor loop,... 

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