Fused quartz
Fused silica, also called silica glass is a glass which, in contrast to the conventional glass contains no additions of sodium carbonate or calcium oxide, that of pure silicon dioxide ( SiO2) is. Industrially produced quartz glass has depending on the starting material and manufacturing process, different concentrations of contaminants that are in the ppm or for synthetic quartz glass in the ppb range.
It can be recovered by melting and re- solidification of quartz ( silica sand or artificially ), hence also known as fused silica and fused quartz or the English name of fused silica.
Naturally formed quartz glass is referred to as Lechatelierite.
Richard Küch (1860-1915), physicist and chemist, discovered in 1899 that silica in an oxyhydrogen flame is free of bubbles and melt in the highest purity, and made of quartz glass used for the industry as a mass product.
Properties
- Transmittance for infrared to ultraviolet radiation (about 170 nm to 5000 nm wavelength)
- A low thermal expansion coefficient and high thermal shock resistance
- High chemical resistance: Quartz glass is attacked with the exception of hydrofluoric acid and hot phosphoric acid and of none is neutral over many other materials.
- The dielectric strength is about 40 kV / mm, which makes the material a good insulating material in electrical components such as optocouplers.
- The softening temperature is significantly higher than that of other glasses.
Applications
- Window and lens materials for ultraviolet optics ( excimer laser, photolithography )
- Isolation layer in semiconductor devices ( MOS technology )
- Piston for tungsten halogen lamps
- Discharge vessels for mercury vapor lamps ( high and very high pressure lamps, and low pressure lamps when UV emission is desired )
- Material investments in the semiconductor manufacturing
- Cells for instrumental analysis
- Material for fiber optic cable ( laser beam transmission, communications technology )
- Window of the Space Shuttle
- Visual and measuring window in hot environments (furnaces, motors, gas turbines)
- Insulating material in electrical components such as optocouplers
Exceptional purity quartz glass is transparent for wavelengths of 190-3500 nm, but usually has a problem caused by OH groups absorption band at about 2500-3000 nm Enhanced infrared transmission between wavelengths of 2200-3000 nm is reduced by hydroxyl groups ( achieved OH- ) content. The normal value is 100 ppm, with an improved IR transmission to fall to 1-3 ppm.
By doping titanium can UVC absorption by cerium doping may be accomplished absorption (UV - blocking halogen lamps ) in the entire ultraviolet range.
In the instrumental analysis of quartz glass cuvettes are used for the measurement of volumes less than 50 nl. Only the special properties of the silica glass allowing Messaperturen and feed channels less than 0.1 mm in diameter. Because of the sometimes very low specific absorption of the samples, the layer thickness can not be reduced indefinitely. It follows that more and lower cross sections of the feed channels and Messaperturen are required to less than 0.1 mm in diameter. As the measurement volume can be achieved of less than 50 nl. Production is carried out by micro- lithography and etching. Another important characteristics of silica glass for the production of cells are to be a high internal transmittance is between about 200-4000 nm, having a good chemical resistance and low electrical conductivity.
The disadvantage is that quartz is difficult to process.
The very low coefficient of expansion of quartz glass causes its high thermal shock resistance. This and the high softening temperature of the quartz glass allow the production of components, pipes and vessels that can withstand temperatures up to 1,400 ° C.