Glass
Glass is a noncrystalline material that can maintain indefinitely, if left undisturbed, its overall form and amorphous microstructure at a temperature below its glass transition temperature. more...
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Glass synthesis is achieved by quenching a glass forming liquid through its glass transition temperature, resulting in the formation of an amorphous solid. Amorphous solids may also be formed by methods other than melt quenching, such as vapour deposition or the sol-gel method. Silica glass may be produced by using sand as a raw material (or \"quartz sand\") that contains almost 100 % crystalline silica in the form of quartz. The most common method for glass pane production is using molten tin, where the molten glass floats on top of the perfectly flat molten tin, thus giving it the name \"float glass\".
The Physics of Glass
The standard definition of a glass (or vitreous solid) requires the solid phase to be formed by rapid melt quenching. Glass is therefore formed via a supercooled liquid and cooled sufficiently rapidly from its molten state through its glass transition temperature, Tg, that the supercooled disordered atomic configuration at Tg, is frozen into the solid state. Generally, the structure of a glass exists in a metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase . By definition as an amorphous solid, the atomic structure of a glass lacks any long range translational periodicity. However, by virtue of the local chemical bonding constraints glasses do possess a high degree of short-range order with respect to local atomic polyhedra.
Glass versus undercooled liquid
Glass is generally treated as an amorphous solid rather than a liquid, though different views can be justified since characterizing glass as either 'solid' or 'liquid' is not an entirely straightforward matter. However, the notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis.
From a more commonsense point of view, glass should be considered a solid since it is rigid according to everyday experience
Some people believe glass is a liquid due to its lack of a first-order phase transition where certain thermodynamic variables such as volume, entropy and enthalpy are continuous through the glass transition temperature. However, the glass transition temperature may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous. Despite this, thermodynamic phase transition theory does not entirely hold for glass and hence the glass transition cannot be classed as a genuine thermodynamic phase transition.
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