Lead glass
In the case of the type of glass called lead crystal glass, the alkaline earths contained in many glasses, such as calcium oxide, are replaced by lead (II) oxide (PbO) during production by melting . The proportion for real lead crystal glass must be at least 24%. Cut lead glass is often referred to as lead crystal . Lead crystal glass is clear even in thick-walled vessels and is easy to grind. It is characterized by a high refractive index , high dispersion , i.e. strong splitting of white light into rainbow colors, colorless transmission, gloss and a beautiful sound. The high density of 3.5-4.8 g / cm 3 is also characteristic .
The designation pressed lead crystal is used for a glass with at least 18% PbO. If more than 30% lead oxide is contained, one speaks of high lead crystal.
The definition of lead glass results from Zschimmer's rule, alkali content = (76% -% PbO) × 0.27 , with the predominant alkali content being brought in by K 2 O.
Applications
A lead glass with a very high lead oxide content (> 40%) is the flint glass used in optics . Its desired high refractive index enables high refractive lenses even with a comparatively small surface curvature. However, the high dispersion of lead glass is undesirable in optical devices. Since lead glass has only a moderately higher refractive index than crown glass , but a much larger dispersion, a so-called achromat could be produced from around 1883 by combining these two early types of optical glass , which refracts blue and red light equally. For a converging achromatic lens, a converging crown glass lens is combined with a diffusing flint glass lens by cementing together.
Lead glass of a suitable composition has a low softening point , which is why it was suitable for the manufacture of pressed glass at an early stage .
For the manufacture of laboratory equipment, only platinum can be melted into ordinary glass, and chrome - nickel wire into lead glass.
For environmental reasons, lead glass should no longer be used for optics and ornaments, since garbage has to be incinerated and / or disposed of and one wants to avoid potentially toxic lead in the environment. Alternative glasses with little or no lead oxide content, both with high dispersion and with a low softening point (“soft glass”), have been developed.
The rhinestone used as a gemstone substitute is also a special lead glass.
Due to the high atomic mass of lead, which manifests itself in a high density, windows with lead glass are used to shield radiation sources in radiology , nuclear medicine , engineering and in the manufacture of cathode ray tubes (e.g. in television sets), where a clear View into the radiation area or onto the generated image is necessary.
Lead glass is used in nuclear and particle physics as a detection medium and for determining the energy of fast, charged elementary particles . Lead glasses are layered in the form of blocks, typically 20 to 30 centimeters long, to form walls, on the back of which the Cherenkov radiation generated in the lead glass is converted into electrical voltage signals with photomultipliers . Such lead glass walls can consist of several thousand blocks and thus cover areas of several square meters. Because they are used to measure the energy of electrons , positrons and photons , lead glass walls are also classified as electromagnetic calorimeters . An example of a detection detector with large lead glass walls is the universal detector of the UA2 experiment that was in operation at CERN to investigate proton - antiproton collisions.
Health hazard
Like ceramics with a lead glaze, lead glass is not suitable for drinking and eating vessels. In particular, acidic attack by acetic acid contained in some dishes - lead acetate is the only relevant water-soluble salt of lead - dissolves lead from the glass, which should not be absorbed into the body.
Web links
Individual evidence
- ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 945.
- ↑ Crystal Glass Labeling Act KrGlasKennzG at www.gesetze-im-internet.de .
- ↑ Leo Grätz: Die Physik, 1917, 636 p., P. 426 of the partial view . Reprint, BoD - Books on Demand, 2017, ISBN 978-9-925058-389 .
- ↑ Konrad Bernhauer: Introduction to organic-chemical laboratory technology, Springer Verlag, 1934, digitized April 9, 2013, accessed September 11, 2018. S.153
- ↑ Annette Kniffler: Glass as a material pc-magazin.de, colorfoto.de, February 15, 2008, accessed September 11, 2018.
- ↑ The UA2 Collaboration: Inclusive pi0 production at the CERN p-_p_-Collider ( English , PDF; 328 kB) CERN. May 27, 1982. Retrieved Jan 15, 2010.