Glass composition, 548

Relatively smaller amounts of very high purity A1F. are used ia ultra low loss optical fiber—duotide glass compositions, the most common of which is ZBLAN containing tirconium, barium, lanthanum, aluminum, and sodium (see Fiber optics). High purity A1F. is also used ia the manufacture of aluminum siUcate fiber and ia ceramics for electrical resistors (see Ceramics AS electrical materials Refractory fibers). 

There are three key variables in the design of a glass-ceramic the glass composition, the glass-ceramic phase assemblage, and the nature of the crystalline microstmcture. 

AH commercial as well as most experimental glass-ceramics are based on siUcate bulk glass compositions. Glass-ceramics can be further classified by the composition of thek primary crystalline phases, which may consist of siUcates, oxides, phosphates, or borates. 

In addition, the phenoHc glass composite has a UL-94 VO rating, whereas the polyester SMC bums (see Polyesters, unsaturated). 

The process of pulverized cuUet reduction yields a product having near-batch equivalent sizing (—12 mesh (<1.7 mm mm)) and in a furnace-ready condition. Foil-backed paper, lead and other metals, and some tableware ceramics can be removed in an oversized scalping operation after the first pass through the system. Other contaminants are reduced to a fine particle size that can be assimilated into the glass composition during melting. 

A typical range of glass compositions for this type of photochromic system is given in Table 2 (11). 

When the catalyst is triethylamine, the yield is nearly 100% cycHc oligomers but if pyridine is used, the polymer is nearly 100% linear. A basic catalyst in the second step, such as lithium stearate or an organic titanate [bis-(acetylacetonato)diisopropoxytitanium], produces a polycarbonate with a molecular weight of 250,000—300,000 when polymerized at 300°C for 30 min. A fiber glass composite has been prepared using this basic procedure (39). 

The electrical conductivity also increases with increasing metal oxide content, due to the high mobility of the metal ions. For example several glass compositions have been used as solid electrolytes in galvanic cells in which other metal ions apart from the alkaline and alkaline earth ions have been incorporated. The electrochemical cell... 

Due to these virtues, solid state NMR is finding increasing use in the structural analysis of polymers, ceramics and glasses, composites, catalysts, and surfaces. 

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