Phil cook window tinting3/30/2023 ![]() Where certain thermodynamic variables such as volume, entropy and enthalpy are discontinuous through the glass transition range. Glass is sometimes considered to be a liquid due to its lack of a first-order phase transition Generally, a glass exists in a structurally 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. This ability can be predicted by the rigidity theory. The tendency for a material to form a glass while quenched is called glass-forming ability. Formation from a supercooled liquidįor melt quenching, if the cooling is sufficiently rapid (relative to the characteristic crystallization time) then crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at T g. Though a material viscosity on the order of 10 17–10 18 Pa s can be measured in glass, such a high value reinforces the fact that glass would not change shape appreciably over even large periods of time. The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis (see viscosity in solids). Due to chemical bonding constraints, glasses do possess a high degree of short-range order with respect to local atomic polyhedra. As in other amorphous solids, the atomic structure of a glass lacks the long-range periodicity observed in crystalline solids. Although the atomic-scale structure of glass shares characteristics of the structure of a supercooled liquid, glass exhibits all the mechanical properties of a solid. However, the term "glass" is often defined in a broader sense, to describe any non-crystalline ( amorphous) solid that exhibits a glass transition when heated towards the liquid state. The standard definition of a glass (or vitreous solid) is a solid formed by rapid melt quenching. Main article: Structure of liquids and glasses Extruded glass fibres have application as optical fibres in communications networks, thermal insulating material when matted as glass wool so as to trap air, or in glass-fibre reinforced plastic ( fibreglass). ![]() The refractive, reflective and transmission properties of glass make glass suitable for manufacturing optical lenses, prisms, and optoelectronics materials. Glass can be coloured by adding metal salts or painted and printed with vitreous enamels, leading to its use in stained glass windows and other glass art objects. In its most solid forms, it has also been used for paperweights and marbles. Due to its ease of formability into any shape, glass has been traditionally used for vessels, such as bowls, vases, bottles, jars and drinking glasses. The earliest known glass objects were beads, perhaps created accidentally during metalworking or the production of faience. Archaeological evidence suggests glassmaking dates back to at least 3,600 BC in Mesopotamia, Egypt, or Syria. Some objects, such as drinking glasses and eyeglasses, are so commonly made of silicate-based glass that they are simply called by the name of the material.ĭespite being brittle, buried silicate glass will survive for very long periods if not disturbed, and many examples of glass fragments exist from early glassmaking cultures. The term glass, in popular usage, is often used to refer only to this type of material, although silica-free glasses often have desirable properties for applications in modern communications technology. Soda–lime glass, containing around 70% silica, accounts for around 90% of manufactured glass. The most familiar, and historically the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica (silicon dioxide, or quartz), the primary constituent of sand. Glass is most often formed by rapid cooling ( quenching) of the molten form some glasses such as volcanic glass are naturally occurring. Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics.
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