Quartz glass

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Surname Quartz glass
other names fused silica , fused silica
Molecular formula SiO 2
Brief description Pure SiO 2 glass
Physical Properties
density 2.201 g / cm³
Tensile strength (strongly dependent on
shape and surface quality)
approx. 50 N / mm²
hardness 5.3-6.5 Mohs; 8.8 GPa
Speed ​​of sound , longitudinal 5930 m / s
Speed ​​of sound , transversal 3750 m / s
Impurities typ. 10-1000 ppm
Optical properties
transmission 170-5000 nm
Refractive index 1.46 at 589.3 nm
Brewster angle 55.58 °
Thermal properties
Thermal expansion coefficient 0… 600 ° C 0.54 10 −6 K −1
Specific heat capacity 0… 900 ° C 1052 J / (kg K)
Thermal conductivity (20  ° C ) 1.38 W / (m K)
Phonon thermal conductivity (2000 ° C) 15 W / (m K)
Transformation point 1130 ° C
Littleton temperature 1760 ° C
Processing temperature > 2000 ° C
boiling point 2230 ° C

Quartz glass , also referred to as silica glass , is a glass that, in contrast to conventional glasses, does not contain any additions of sodium carbonate or calcium oxide . H. consists of pure silicon dioxide (SiO 2 ). Industrially produced quartz glass has different concentrations of impurities, depending on the raw material and production process, which are in the ppm or, for synthetic silica glass, in the ppb range.

It can be obtained by melting and resolidifying quartz (quartz sand or artificially produced), hence the name quartz glass and the English name fused quartz or fused silica .

Naturally occurring quartz glass is called lechatelierite .

Richard Küch (1860–1915), physicist and chemist, discovered in 1899 that silicon dioxide can be melted in an oxyhydrogen flame without bubbles and in the highest purity, and made quartz glass usable as a mass product for industry.



High-purity quartz glass is transparent in the wavelength range from 190 nm to 3.5 µm, but normally has an absorption band of around 2.5 to 3 µm caused by OH - groups. Improved infrared transmission at wavelengths of 2.2 to 3 µm is achieved through a reduced hydroxyl group ( OH group ) content. The normal value is 100  ppm , with improved IR transmission below 1 to 3 ppm.

By doping with titanium , UV-C absorption can be achieved; by doping with cerium , absorption in the entire ultraviolet range can be achieved (UV-blocking halogen lamps ).

Quartz glass wafer with microchannel structure as a preliminary product for a lot size nanoliter cuvette

In instrumental analysis , quartz glass cuvettes are used to measure volumes below 50  nl . It is only the special properties of quartz glass that enable measuring equipment and supply channels with a diameter of less than 100 µm.
Because of the sometimes very low specific absorption of the samples, the layer thickness cannot be reduced at will. It follows from this that ever smaller cross-sections of the measuring equipment and the supply channels down to a diameter of less than 100 µm are required. In this way, measuring volumes of less than 50 nl are achieved. The production takes place by means of microlithography and etching . Further important properties of quartz glass for the production of cuvettes are its high degree of transmission between approx. 200 nm and 4 µm, its good chemical resistance and its low electrical conductivity .

The disadvantage is that quartz glass is difficult to process.

The very low expansion coefficient of quartz glass makes it highly resistant to temperature changes. This and the high softening temperature of the quartz glass allow components, tubes and vessels to be manufactured that can withstand temperatures of up to max. Withstand 1400 ° C.

Individual evidence

  1. Thomas Jüstel, Sebastian Schwung: Phosphors, light sources, lasers, luminescence . Springer-Verlag, Berlin, Heidelberg 2016, ISBN 978-3-662-48455-5 , pp. 207 ( limited preview in Google Book search).
  2. Product information page of the manufacturer Heraeus Conamic , www.heraeus-conamic.de
  3. H. Scholze: Glass. Nature, structure and properties . 1988, ISBN 3-540-18977-7 , pp. 154 .
  4. Chemical purity of quartz glass , www.heraeus-conamic.de
  5. ^ Richard Küch and Heraeus: Creating Innovations , press release from Heraeus Holding GmbH
  6. Product information page of the crystal dealer Korth Kristalle , www.korth.de, accessed on June 21, 2012
  7. H. Scholze: Glass. Nature, structure and properties . 1988, ISBN 3-540-18977-7 , pp. 213 f .