Expansion of silica glass

The dilatometer method has been used for fused salts by heating in a hard glass or silica glass dilatometer (e.g. in a Lorenz furnace, 2.VI C) until the meniscus comes to a mark on the neck. The expansion of the glass must be taken into account that of silica glass is small (0 016 per cent of the volume for 100° C.) but can be introduced if necessary. 

When silica glass is heated to 1750K, it becomes plastic and can be worked in an oxy-hydrogen flame. Silica glass apparatus is highly insensitive to thermal shock owing to the low coefficient of thermal expansion of silica. Borosilicate... 

Another interesting property of silica glass fibers is their low coefficient of thermal expansion, a 0.5 X This value can be lowered and even rendered negative by adding TiOz to... 

The thermal expansion coefficient a of silica glasses depends on the following parameters ... 

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... 

Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda-lime-silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis. 

I il a soda-lime-silica glass, containing magnesia and boric oxide 1 than 1 per cent), made by the General Electric Co. It is often ibed as GEC X.8. or simply as X.8. The linear coefficient of Jial expansion between 20 and 350°C is 9-65 0-10 x 10-. This I il available as tubing and rod in a wide range of sizes. 

Thermal Expansion. Most manufacturers literature (87,119,136—138) quotes a linear expansion coefficient within the 0—300°C range of 5.4 x 10"7 to 5.6 x 10 7 /°C. The effect of thermal history on low temperature expansion of Homosil (Heraeus Schott Quarzschmelze GmbH) and Osram s vitreous silicas is shown in Figure 4. The 1000, 1300, and 1720°C curves are for samples that were held at these temperatures until equilibrium density was achieved and then quenched in water. The effect of temperature on linear expansion of vitreous silica is compared with that of typical soda—lime and borosilicate glasses in Figure 5. The low thermal expansion of vitreous silica is the main reason that it has a high thermal shock resistance compared to other glasses. 

Fig. 4. Effect of thermal history on low temperature thermal expansion of vitreous silica (143), where (---), (--), and (—) represent glasses having fictive...

Fig. 5. Comparison of thermal expansion of vitreous silica, A, to that of borosilicate glass, B, and soda—lime glass, C.

Thermal Expansion. The averaged value of the coefficient of linear thermal expansion of diamond over the range 20 to 100°C is 1.34 x 10-6 cm/cm/°C and3.14x 10-6 from 20 to 800°C. At room temperature the values for silica glass and diamond are 0.5 x 10-6 and 0.8 x 10-6, respectively. The relatively low expansion combined with the low reactivity of diamonds, except for carbide formation, leads to some challenges in making strong bonds between diamond and other materials. 

Silica Glass. A glass composed of silicon dioxide as the only constituent has a very high softening temperature and a very low thermal expansion. 

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