Fused quartz and fused silica are the amorphous forms of quartz chemically known as SiO₂ Fused quartz is made from purifying and melting natural crystalline quartz, usually natural quartz sand. Fused silica is a purer version of fused quartz that is made from various silicon glasses.

We supply large quantities of Semiconductor Grade Fused Quartz such as “Vitreosil”, GE 124 and “Infrasil” machined into a myriad of shapes and sizes of up to 600mm in diameter and optically polished windows in both Fused Quartz and “UV grade” Fused Silica such as “Spectrosil” and “Suprasil” as well as water free quartz if required.

Main Characteristics

Both materials have an extremely low coefficient of expansion making them far more shock resistant than any other refractory material.

Semiconductor Grade Fused Quartz will transmit between 220 nanometers up to 3 microns whereas many types of Fused Silica will transmit as low as 175 microns.

They will withstand a continuous maximum of 900⁰C to 1100⁰C, depending on the size and shape of the part and can even be used up to 1400C for short periods of time.

Material Parameters

These materials can be supplied machined to as large as Ø600mm and to lengths of several metres on smaller diameters.

They can be machined into bars, tubes, sheets and complex components.

They are non-wetting, odourless and non-outgassing with zero porosity.

They do not creep or deform like ductile materials.

They can be machined to tight tolerances, allowing for complicated shape design (optimal performances up to +/- 0.013 mm for dimensions, < 0.5 µm for ground surfaces) and can also be polished flat to optical standards.

These materials have a very low thermal conductivity and dielectric constant and the lowest loss tangent of almost all known materials.

Typical Properties of Clear Fused Silica

Density g/cm³ 2.203
Hardness Mohs scale 5.3–6.5
Tensile strength MPa 48.3
Compressive strength GPa >1.1
Bulk modulus GPa ~37
Rigidity modulus GPa 31
Young’s modulus GPa 71.7
Poisson’s ratio 0.17
Coefficient of thermal expansion °C (average from 20°C to 320°C) 5.5×10−7
Thermal conductivity W/(m·K) 1.3
Specific heat capacity J/(mol·K) 45.3
Softening point °C c. 1665
Annealing point °C c. 1140
Strain point °C 1070
Electrical resistivity Ω·m >1018
Dielectric constant @ 20°C 1 MHz 3.75
Dielectric loss factor @ 20°C 1 MHz < 0.0004
Dielectric strength kV/cm at 20°C 250–400
Index of refraction @ 587.6 nm (nd) 1.4585
Change of refractive index with temperature (0 to 700°C) 1.28×10−5/°C (between 20 and 30°C)