GLASS IS MADE PRIMARILY OF SILICATES

Ss noted earlier, the prime component of slag is silicates, and as early as 500 B.C. metal workers noticed that solidified slag had properties not unlike tho.se of the highly prized volcanic gjlass obsidian. This prompted people to heat all sorts of rocks in various combinations. 51ags of many colors were pro- 

Glass is an amorphous material. In such a substance, submicroscopic units are randomly oriented relative to one another. This is distinguished from a crystal, in which submicroscopic units arc arranged in a periodic and orderly fiishion (Section 6.3). Glajss can have a variety of chemical composition-s. Common glass is a mixture of sodium silicate, NajSiO, and calcium silicate, CaSi03. It is formed by heating a blend of sodium carbonate, calcium carbonate, and silica  

Eyeglasses, a telescope, and a distillation apparatus—pivotal glass inventions. 

Information-bearing light pulsas travel through the glass of fiberoptic cables, a revolution in longdistance communication. 

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But not all ceramic materials are clay (glass is made of sand], and they don t all behave the same way. They are, it turns out, far more interesting and versatile than one might imagine. For years, ceramics were generally defined as inorganic, nonmetallic materials, are known primarily as silicate bearing, that is, composed of the natural minerals that make up most of the rocks in the earth s crust. 

Since the Earth s cmst is primarily made up of silicates, we can understand why all ceramics that come close, by near or by far, to terra cotta are silicate materials. Silicate ceramics form, in tormage, the majority of the world of ceramics. They are often described as traditional ceramics, a term which we do not endorse because it may be understood as opposed to progress and technical improvements - whereas many silicate ceramics are sophisticated materials - but which is justified by history it was only at the end of the 19 century that non-siUcate ceramics came to the scene, with specific uses that explain their other name, technical ceramics. Our choice here is to use silicate ceramics and non-silicate ceramics , rather than opposing tradition and advanced technology. We may note that almost all industrial glasses and cements are also sihcate compounds. 

If the compositional difference along the diffusion direction is primarily in one component, and the difference in other components is due to the dilution effect, then diffusion of this component (not necessarily the other components) may be treated as effective binary, and the EBDC can be applied reliably to similar situations. Some examples are a diffusion couple made of dry rhyolite on one half and hydrous rhyolite on the other half, the hydration or dehydration of a silicate melt, and adsorption of a gas component by a glass. 

His experiments were primarily upon a single soda-lime silicate, which was chosen because it had been studied extensively in the literature and can be made in small amounts with fair optical quality. The decay for this glass with 0.8 per cent Nd203 added is shown in Fig. 33. It is quite clearly not a single exponential. One finds that the slope changes by a factor of three over the range examined and that the curvature increases with neodymium concentration. The measurements made at long times were done with a mechanical shutter that shielded the photomultiplier tube from the initial intense fluorescence. When this was not done, hysteresis in the photomultiplier tube led to spurious results. 

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