Fused Silica and Other Glasses

Source Data from refs. 6 and 9. Less than 1 ppm total metals. 

TABLE 3.4 Typical Impurities Present in Fused Silica 

Although quartz tubing is available commercially, its metal oxide content (10 to 100 ppm) is considered to be too great for use in capillary gas chromatography (10). Metal oxides are Lewis acids and can serve as adsorptive sites for electfon-donor species such as ketones and amines and as an active site for species with //-bonding 

TABLE 3.5 Physical and Mechanical Properties of Fused Silica 

Synthetic fused silica is formed by introducing pure silicon tetrachloride into a high-temperature fiame followed by reaction with the water vapor generated in the combustion (9, 11). The process can be described by the reaction 

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H. 6. Jennings, "Comparison of Fused Silica and Other Glass Columns in Gas Chromatography", Huethig, Heidelberg, 1981. 

W. G. Jennings, Comparisons of Fused Silica and Other Glasses Columns in Gas Chromatography, Heuthig, Heidelberg, 1986, p. 12. 

The widespread use of fused silica as a column material for capillary GC may be attributed to the more inert inner surface texture compared to other glasses. The interested reader may refer to the book by Jennings (9) for a comparison of fused silica with other glasses, such as soda-lime, borosilicates, and lead, that have been used as column materials where the proposed structure of fused silica (Figure 3.4) may also be found representative metal oxide concentration data are... 

The two most common substrates for thin film electrodes are various types of glass—soda-lime, Pyrex, and various forms of quartz or fused silica—and silicon wafers that have been treated to produce an insulating surface layer (typically a thermally grown oxide or nitride). Other possible substrates include mica, which can be readily cleaved to produce an ordered surface, and various ceramic materials. All of these materials can be produced in very flat, smooth... 

Glassware that has bends and/or has been fused to other pieces of glass will be either common laboratory borosilicate glass or fused silica. Any soft glass made into laboratory apparatus is for special application or, more likely is very old (and ought to be in a museum). 

Elemental silicon is central to the vast industry of solid-state electronics. Appropriately doped with other elements, it forms a variety of semiconductors that constitute most transistors and integrated circuits. Other elements and compounds such as germanium or gallium arsenide have also found a niche as semicondnctors in electronics, but silicon occupies the prime position. How fortunate that it is the second most abundant element in the Earth s crust. Its compounds with the most abundant crustal element, oxygen, are equally central in many different aspects of chromatography. Silica, silica gel, glass, qnartz, fused silica, and silicones all have a remarkable variety of key roles to play in chromatography. Let us familiarize ourselves with some of their relevant properties. 

Columns of aluminum-clad fused silica, " and metal-clad fused silica support temperatures up to 500°C, representing an advantage in comparison with borosUicate glass columns, with a temperature limit to 450°C, and columns of polyimide-clad fused silica for high temperature, limited temperature to 400-420°C. On the other hand, aluminum-clad fused silica columns present leakage, principally in the connections, after a... 

Frit. A ceramic composition that has been fused, quenched to form a glass, and granulated. Frits form an important part of the batches used in compounding enamels and glazes the purpose of this pre-fusion is to render any soluble and/ or toxic components insoluble by causing them to combine with silica and other added oxides. 

Fused silica and some other single-component glasses such as Zn(P03)2, BeF2, and GeOj display anomalous negative thermal expansion coefficient in the vicinity of absolute zero temperature. The exact cause of this behavior is not clearly understood. 

When silica is fused,. silica glass is formed. This has advantages over ordinary glass in that it is much less easily fused (it softens at about 1800 K). and has a very low coefficient of expansion. It is. therefore, used for crucibles and other articles required to be infusible... 

MMVF are synthetic fibers with glasslike structures. The term usually refers to silicate-based glass fibers, because these compositions form the largest volume of fibers produced. However, in addition to fiberglass and fused silica (Si02), there are other amorphous fibers used in commerce alumina (AI2O3) and silica combinations, rock and slag wool, as well as fibers with nonsilicate compositions such as carbon. Many of these amorphous fibers have proprietary names. 

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