Pure Silica Quartz Glass

Vycor will deform and melt about 100°C lower than fused silica, and it is a poor transmitter of uv light. In the early years of Vycor production, Vycor was significantly less expensive than pure quartz glass. However, as the manufacturing techniques of pure quartz glass have become more efficient, Vycor is now the more expensive material. 

Transparent silica glass is pure Si02 in the vitreous state the alternative name quartz glass is derived from a modification of Si02, quartz, which is the usual raw material. Current commercial types of transparent silica glass contain roughly 10" of impuri-... 

CAS 14808-60-7 EINECS/ELINCS 238-878-4 Synonyms Agate Amethyst Chalcedony Crystalline silica Flint Free crystalline silica Onyx Pure quartz Quartz glass Rose quartz Sand Sea sand Silica Silica, crystalline quartz Silica flour Silica glass Silica, quartz Silicic anhydride Silicon dioxide Classification Inorg. silicon compd. 

Temperatures above 1800°C would be required to contain a fiber forming silica melt in a bushing. A requirement like this would by far exceed the practical capability of most precious metal and/or other practical alloy materials. As a result, pure silica glass fibers are downdrawn from solid silica preform rods (Figure 14). Gas flame or electrical furnaces soften the ends of the quartz rods, and thereby facilitate the formation of continuous silica fibers. Preforms made from natural silica contain 99.99% Si02 and impurities include 20-50 ppm Al, <5 ppm OH", and <4 ppm Na. Preforms made by oxidation of SiCl4 in a plasma flame [60] afford even purer silica fibers (<1 ppm Al, <0.1 ppm OH, <1 ppm Na, and <50 ppm Cl). 

The three lasers that have been commonly used in the past for laser surgery are the CO2, the Nd YAG, and the Ar ion lasers. These are also the lasers that were tried first with fiberoptic delivery systems. The Ar laser radiation (X = 514 nm) is in the visible spectral range, and its radiation is readily transmitted by pure silica glass (i.e., quartz) fibers. The same is true for the Nd YAG laser, whose radiation is in the NIR (X = 1.06 /u.m). Fibers of diameters... 

Fig. 1.8. Schematic 2D representation of a network of silica tetrahedra in a pure silica or quartz glass. A fourth bridging oxygen would be located directly below or above the silica [546,574]...

The need for temperature cycling should be taken into account when designing or conducting tests. The nature of the test vessel should be considered for tests in aqueous solutions at temperatures above about 60°C since soluble constituents of the test vessel material can inhibit or accelerate the corrosion process. An inhibiting effect of soluble species from glass, notably silica, on the behaviour of steel in hot water has been shown . Pure quartz or polymeric materials are often more appropriate for test vessel construction. 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

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