Glass, generally

Nessler tubes Cylinders of thin glass, generally graduated, used for comparing turbidities and colours of solutions. 

The attack of water is related to the leaching mechanism described for acids. Table 4 rates glasses based on their resistance to water attack. Low alkah, high alumina, or borosiUcate glasses generally have high water durabiUty. 

Because K is related to the polarizabiHty per unit volume, denser glasses generally have higher dielectric constants. The dielectric constant also increases with increasing temperature, because ionic motion becomes faster. Similarly, K is higher at lower frequencies, because the ions can foUow the oscillations more readily. 

This is the process of the crystallization of one or more of the constituents of glass. Generally a glass is thermodynamically unstable with respect to these crystals, but at ordinary temperatures the crystallization rate is quite negligible. Crystallization may occur when the glass is worked at high temperature. The crystals which appear in a supercooled melt are not necessarily those of the stable solid phase at the temperatiure concerned for example, cristobalite can appear at temperatures for which tridymite is the stable crystalline... 

Metals and glass generally support higher temperatures than polymers, which present a more or less plastic behaviour under stresses, leading to ... 

Chemical Properties. The chemical durability is a function of the durability of the crystals and the residual glass. Generally, highly siliceous glass-ceramics with low alkali residual glasses, such as glass-ceramics based on quartz and (3-spodumene, have excellent chemical durability and corrosion resistance similar to that obtained in borosilicate glasses. 

Ceramics are primarily compounds. Ceramics other than glasses generally have a crystalline structure, while silica-based glasses, a subclass of ceramic materials, are noncrystalline. In crystalline ceramic compounds, stoichiometry dictates the ratio of one element to another. Nonstoichiometric ceramic compounds, however, occur frequently. Some important ceramic materials are listed in Table... 

If a tensile stress is applied to a specimen in the direction of the x-axis, the specimen will elongate in that direction. This elongation will be accompanied by contraction in the y and z directions. The ratio of the transverse strain to the axial strain is called Poisson s ratio. Poisson s ratio for oxide glasses generally lies between 0.2 and 0.3, although the value for vitreous silica is only 0.17. The shear modulus, G, which relates shear strain, y, to shear stress, t, is given by the expression ... 

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