glass

Glass is a non-crystalline solid made primarily from silica (silicon dioxide) and various additives that act as fluxes or stabilizers. It is typically transparent and can be molded into a wide range of shapes. Glass is usually amorphous, meaning it lacks the long-range atomic order found in crystals, which contributes to its distinctive combination of hardness, brittleness and optical properties.

Most common glass is soda-lime glass, comprising roughly 70-74% SiO2 with alkali oxides (such as Na2O from soda ash) and lime (CaO) as stabilizers. Other formulations include borosilicate glass, which adds boron oxide to reduce thermal expansion, and lead glass, which increases refractive index and density. Glass can contain colorants or opacifiers to produce green, brown, blue or opaque varieties. The microscopic structure consists of a network of SiO4 tetrahedra linked in three dimensions, with modifiers disrupting the network to adjust properties such as durability and melting temperature.

Manufacture involves melting raw materials at high temperatures and forming the molten glass into desired shapes, followed by cooling and annealing to relieve stresses. The float glass process, developed in the mid-20th century, produces flat, uniform sheets by floating molten glass on a bath of molten tin. Other methods include blowing, pressing, and lamination. Tempered glass is rapidly cooled to increase strength and safety, while laminated glass stacks glass with interlayers such as polyvinyl butyral for additional resilience and security.

Applications span windows, bottles, cookware, laboratory vessels, electrical displays, and fiber-optic systems. Glass recycling is common and helps reduce energy use and raw material demand.