Silica glass workers

Individuals whose jobs expose them to unusually high particulate concentrations are especially susceptible to health problems from the pollutant. For example, men and women who work with the mineral asbestos are very prone to development of a serious and usually fatal condition known as asbestosis, in which fibers of the mineral become embedded in the interstices (the empty spaces within tissue) of the lung. Similar conditions are observed among coal workers who inhale coal dust (pneumoconiosis, or black lung disease) textile workers (byssinosis, or brown lung disease) those who work with clay, brick, silica, glass, and other ceramic materials (silicosis) and workers exposed to high levels of beryllium fumes (berylliosis). 

Gribanova, Chernoberezhsky, Friedrichsberg, and co-workers (Leningrad State University) (360-363) investigated the aggregative stability and electrical conductivity of quartz suspensions in aqueous electrolyte solutions, the dependence of contact angles on quartz and silica glass surfaces on the pH value of solutions, and so forth. 

Vitreous silica has the same solubility as other amorphous silica. Because of the small specific surface area of powdered silica glass in comparison with that of microamorphous or colloidal silicas, workers found it difficult to establish solubility equilibrium. Stober (144) found that at pH 8.4 in Ringer s solution (0.9% NaCI, 0.1% NaHCOj) at 25 C, at least 15 days was required to reach equilibrium when 20 m of silica surface was exposed per liter, regardless of particle size Without the use of this solution, which has an optimum catalytic effect, it would probably have been impossible to establish equilibrium. The solubility was found to be about 100 ppm. 

The studies on the sol-gel TiN film formation were followed by several workers. Kohno applied TiN films to silica glass tubes as an infrared reflectant coating (Kohno, 1991). 

This alternative hypothesis may explain the observational differences between different workers. Brune Smith (1982), unlike Wilson et al. (1972), found Si distributed throughout the cement but were uncertain whether it was due to Si in the matrix or the degradation of fine particles to silica gel. But Brune Smith (1982) used a normal glass powder while Wilson et al. (1972) removed fine particles to improve resolution. These differing observations are reconciled if the silicic acid which is formed migrates slightly before condensing to silica gel. 

L. B. Richardson and J. C. Woodhouse studied the absorption of mixtures of carbon dioxide and nitrous oxide by charcoal S. J. Gregg, the heat of adsorption D. H. Bangham and F. P. Burt, the adsorption of nitrous oxide by glass and W. A. Patrick and co-workers, by silica gel near the critical temp, of the gas. 

Extremely interesting infrared studies of physically adsorbed molecules were carried out by Sheppard and Yates (52). These workers studied the spectra of methane, ethylene, acetylene, and hydrogen on porous glass. They found that the perturbing effects of surface forces made it possible to detect bands which are found in the Raman spectra but are not observed in the normal infrared spectra. This indicates that the degree of symmetry of the adsorbed molecule is less than in the gaseous state because of the one-sided nature of the surface forces. This effect was discovered independently by Karagounis and Peter (52a) in studies 1,3,5-trichlorobenzene physically absorbed on silica. 

Many more measurements have been made of the recombination efficiencies of glass and silica than of any other materials, for the simple reason that most apparatuses are made of either glass or silica and the wall recombination efficiency is a natural by-product of most investigations. The recombination is predominantly first order and the more systematic measurements, for these recombination kinetics, are shown in Fig. 24 presently, we will see that, under some conditions, the recombination can be second order. Up to a threefold scatter in the values of 7 have been found even for the one apparatus (Melin and Madix [90]) depending on the history of the glass, but Fig. 24 demonstrates that there are also substantial systematic differences between the results obtained by different workers. 

Fig. 24. The efficiency of glass and quartz, at various temperatures, for the recombination of H atoms in the region of first-order kinetics. Pyrex A, Wood and Wise [91 ] +, Tsu and Boudart [64a] X (2), Smith [54] 0, Lede and Villermaux [69] (3), Tal roze and co-workers [92] (4), Villermaux and co-workers [93] (5), Pospelova and Myasnikov [61 ] , Lede and Villermaux [68 ]. Silica (1), Wood and Wise [91 ] (l ), Sancier and Wise [79] X (2 ), Smith [54] (3 ), Linnett and co-workers [94 ] (4 ), Kislyuk and Krylov [95] (5 ), Chery and Villermaux [67] (6 ), Villermaux and co-workers [96]. (Courtesy Lede and Villermaux [68].)...

A survey of the literature [28, 58-65, 71, 72, 74-80] indicates that the most frequent exposure to silicon involves exposure to silica and silicates mainly in their crystalline forms. Health risks associated with the exposure to other sihcon containing compounds were reported in the mortality study of 16.661 manmade mineral fiber workers employed during 1945 to 1963 at one of 17 U.S. manufacturing plants [75]. Fiber exposure in the plants producing fibrous glass or mineral wool, or both, was associated with increased... 

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