3. Alteration mechanisms

What is a glass?

Glass is a non-crystalline solid formed by the three-dimensional concatenation of basic units: silica tetrahedra. Silicon is considered a forming or vitrifying element. In addition to silicon, aluminum, boron, phosphorus, iron and arsenic can act as glass-forming elements.

Alkali or alkaline-earth oxides, known as modifiers or fluxes, are added during the glassmaking process to lower the melting temperature of silica from 1,700-2,000°C to 1,200-1,500°C. Their introduction breaks the bonds between tetrahedra and reduces the liquid's viscosity.

The durability of a glass depends on its chemical composition; to a first approximation, this decreases with the addition of modifiers. For alkalis, glass reactivity increases in the following order:...