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. Laboratory measurements of room temperature glass flow do show a motion consistent with a material viscosity on the order of 10 17–10 18 Pa s. 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 as enamelled glass.
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 glass-making 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.Īlthough brittle, buried silicate glass will survive for very long periods if not disturbed, and many examples of glass fragments exist from early glass-making 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.