Quartz and Silicas
Lilian P. Davila, Subhash H. Risbud, and James F. Shackelford
Abstract Silica is the most ubiquitous mineral in the earth’s crust, existing in a wide variety of crystalline and noncrystalline forms due to the flexibility of the linkage among SiO4 tetrahedra. The thermodynamically stable, room temperature form of silica is quartz, which is itself a widely available mineral and ingredient in many commercial ceramics and glasses. In addition to historically abundant raw material sources, crystalline and noncrystalline silicas can be produced by a wide range of synthetic routes. For example, synthetic quartz can be produced by hydrothermal growth in an autoclave, and synthetic vitreous silica can be produced from silicon tetrachloride by oxidation or hydrolysis in a methane-oxygen flame. Pure silicas serve as model systems in the study of ceramics and glasses, but at the same time, are used in a wide and steadily increasing variety of sophisticated technological applications, from piezoelectric crystals to optical fibers to waveguides in femtosecond lasers. Increased understanding of these ubiquitous materials is aided by improved experimental tools such as new neutron scattering facilities and increasingly sophisticated computer simulation methods.