Quartz properties

Quartz Properties Microcrystalline quartz, structure confirmed by XRD, BET specific surface area 6 m /g [429], external specific surface area used in calculations was 1.7 mVg [428,429],... 

Definition Amorphous mineral consisting of fused sodium potassium aluminum silicate, with variable chemical composition and <1% quartz Properties Lt. gray to glassy black transparent solid wh. or grayish-wh. fluffy or glassy-wh. particulate (expanded perlite) mod. sol. in NaOH si. sol. in min. acids (expanded) very si. sol. in water (expanded) dens. 2.2-2A, 0.05-0.3 (expanded perlite) m.p. > 1093 C, > 2000 F (expanded perlite) nonflamm. 

Uses Suspending agent, emulsifier, plasticizer used in industrial prods, such as asphalt emulsions and rockwool insulation Features General purpose contains minor amounts of feldspar, calcite, and quartz Properties Vise. 15 cps min. 6.25% solids pH 8.0-10.0 5% solids 12% moisture... 

The reports were that water condensed from the vapor phase into 10-100-/im quartz or pyrex capillaries had physical properties distinctly different from those of bulk liquid water. Confirmations came from a variety of laboratories around the world (see the August 1971 issue of Journal of Colloid Interface Science), and it was proposed that a new phase of water had been found many called this water polywater rather than the original Deijaguin term, anomalous water. There were confirming theoretical calculations (see Refs. 121, 122) Eventually, however, it was determined that the micro-amoimts of water that could be isolated from small capillaries was always contaminated by salts and other impurities leached from the walls. The nonexistence of anomalous or poly water as a new, pure phase of water was acknowledged in 1974 by Deijaguin and co-workers [123]. There is a mass of fascinating anecdotal history omitted here for lack of space but told very well by Frank [124]. 

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

Silica. SiHca (qv) comes in various forms including quartz [14808-60-7]. It has found wide use as an abrasive in the past, particularly as an inexpensive coated abrasive for woodworking. The term sandpaper is stiU used as a generic term for coated abrasives in many quarters although the use of sand in coated abrasives has been almost entirely elkninated because of the hazard of siHcosis to the user and its inferior grinding properties (especially for metals). 

Hardness. The hardness (qv), or related property abrasiveness, is an important filler property. Hardness is determined by comparison to materials of known hardness on the Mohs scale. On this nonlinear scale, diamond is rated 10, quartz 7, calcite 3, and talc 1. The abrasiveness of a filler is also dependent on psd and the presence of impurities, eg, ka olin clay (Mohs hardness of 3) can be quite abrasive because of the presence of quartz impurities. 

Table 3. Thermodynamic Properties of Quartz, Cristobalite, and Liquid Si02...

In the absence of a suitable soHd phase for deposition and in supersaturated solutions of pH values from 7 to 10, monosilicic acid polymerizes to form discrete particles. Electrostatic repulsion of the particles prevents aggregation if the concentration of electrolyte is below ca 0.2 N. The particle size that can be attained is dependent on the temperature. Particle size increases significantly with increasing temperature. For example, particles of 4—8 nm in diameter are obtained at 50—100°C, whereas particles of up to 150 nm in diameter are formed at 350°C in an autoclave. However, the size of the particles obtained in an autoclave is limited by the conversion of amorphous siUca to quartz at high temperatures. Particle size influences the stabiUty of the sol because particles <7 nm in diameter tend to grow spontaneously in storage, which may affect the sol properties. However, sols can be stabilized by the addition of sufficient alkaU (1,33). 

Silicon dioxide [7631-86-9] Si02, exists in both crystalline and glassy forms. In the former, the most common polymorph is a-quartz (low quartz). All commercial appHcations of crystalline quartz use a-quartz, which is stable only below ca 573°C at atmospheric pressure. Some of the properties of a-quartz are Hsted in Table 1. 

Silicone foam thus formed has an open ceU stmcture and is a relatively poor insulating material. Cell size can be controlled by the selection of fillers, which serve as bubble nucleating sites. The addition of quartz as a filler gready improves the flame retardancy of the foam char yields of >65% can be achieved. Because of its excellent dammabiUty characteristics, siUcone foam is used in building and constmction fire-stop systems and as pipe insulation in power plants. Typical physical properties of siUcone foam are Hsted in Table 10. 

Because of their unique combination of physical and chemical properties, manufactured carbons and graphites are widely used in several forms in high temperature processing of metals, ceramics, glass, and fused quartz. A variety of commercial grades is available with properties tailored to best meet the needs of particular appHcations (45). Industrial carbons and graphites are available in a broad range of shapes and sizes. 

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