Silicates and Silica

Addition of silica to a rubber compound offers a number of advantages such as improvement in tear strength, reduction in heat buildup, and an increase in compound adhesion in multicomponent products such as tires. Two fundamental properties of silica and silicates influence their use in rubber compounds ultimate particle size and the extent of hydration. Other physical properties such as pH, chemical composition, and oil absorption are of secondary importance. 

To illustrate the influence of surface hydroxyl groups and hydration levels on rubber properties, Wagner (1976) took a series of silicas of different surface areas, hydroxylated to different extents, and then added them to an SBR compound at 50phr (Table 9.19). The author concluded that a reduction in silanol level as a result of an increase in absorbed water will decrease cure time, tensile strength, and abrasion resistance. 

Silicas can be divided into three groups or classes. These include standard or conventional silicas, semi-highly dispersible (semi-HD) or easily dispersible silica, and the latest group developed, termed highly dispersible silica or HDS 

TABLE 9.19 Effect or Surface Hydration on Silica Properties 

Conventional Tire casing. Nontire internal and external Tire treads. Tire casings and nontire products Tire treads and nontire external components for  

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Aqueous hydrogen fluoride is a weak acid (see above) and dissolves silica and silicates to form hexafluorosilicic acid hence glass is etched by the acid, which must be kept in polythene bottles. 

Chemical Economics Handbook Marketing Pesearch Peport, Silicas and Silicates, SRI International, Menlo Park, Calif., 1993. 

Chrome ore Chromite from. silica and. silicates Roll 120 -0.85 ... 

For electrical insulation china clay is commonly employed whilst various calcium carbonates (whiting, ground limestone, precipitated calcium carbonate, and coated calcium carbonate) are used for general purpose work. Also occasionally employed are talc, light magnesium carbonate, barytes (barium sulphate) and the silicas and silicates. For flooring applications asbestos has been an important filler. The effect of fillers on some properties of plasticised PVC are shown in Figure 12.21 (a-d). 

There is one particular type of filler whose value can be in no doubt. This is the so-called thixotropic filler exemplified by certain fine silicas and silicates which appear to increase the viscosity of the resin on standing. These are useful in minimising drainage of resins from vertical and near-vertical surfaces during hand lay-up operations. 

Silica is normally present in most sources of MU water, although not to any significant level as soluble Si02 but rather as both colloidal amorphous silica and silicate salts. In any particular water, such... 

Because of the problems relating to silica and silicates, silica levels in the FW and BW must be strictly controlled. This normally is not a problem in higher pressure boilers because various methods of pretreatment are typically employed to reduce the concentration of silica in the FW as much as possible. Automatic monitoring and alarm systems are also provided. 

Table 7.4 Summary notes silica and silicate crystalline scales and deposits affecting boiler section waterside surfaces.

Table 8.54 indicates the main characteristics of X-ray powder diffraction. Powder samples of lmg or greater can be analysed. The principal advantage is that substances (e.g. BaS04) can be identified directly, and not indirectly via their elements (e.g. Ba and S). This is particularly advantageous if both silica and silicates (kaolin, talc) are present. Detection limits are matrix dependent, but ca. 3% in a two-phase mixture, with synchrotron radiation ca. 0.1 %. 

The susceptibility of hardness measurements of silica and silicate glasses to environmental factors is consistent with the effects of water on the deformation of quartz. The load effect and indentation size effect appear to be a result of the frictional forces at the indenter-specimen interfaces. 

Compounding ingredients which bring about reinforcement of rubbers. The most widely used are carbon black, silica and silicates, zinc oxide, treated whitings, high styrene resins and phenolic resins. 

Amorphous silica, 21 780t 22 380-406. See also Amorphous silica and silicates Amorphous silicon (a-Si) Vitreous silica... 

See also Analytical test methods for anthropogenic silicas and silicates, 22 470... 

Anthraquinonoid soluble dyes, 7 373t Anthrone soluble dyes, 7 373t Anthropogenic mercury releases, trends in, 16 47-49 Anthropogenic silicas and silicates, 22 451-480... 

See also DOT entries U.S. Department of Transportation (DOT) anthropogenic silicas and silicates and, 22 467... 

Food and beverage processing, reverse osmosis in, 21 650-651 Food and Drug Administration (FDA), 10 848 11 47 18 682 21 568. See also FDA entries U.S. Food and Drug Administration (FDA) anthropogenic silicas and silicates and, 22 468... 

Gravimetric methods, tellurium determination by, 24 415 Gravimetric techniques. See also Acoustic wave gravimetric technique for anthropogenic silicas and silicates, 22 470... 

Permissible exposure limits (PEL), 10 509 12 281 21 837. See also Personal exposure limit (PEL) for anthropogenic silicas and silicates, 22 467... 

Silicate minerals, 25 56t Silicate modifications, via silylation, 22 696 Silicate products, prices of, 22 468t Silicates, 26 145-146, 5 640. See also Anthropogenic silicas and silicates commercial soluble, 22 451-452... 

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