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By glass (of Germanic glasa "the shining, resplendent one ", also for "amber ") one understands an amorphous not crystalline solid. Materials, which one is called glass in the everyday life life (for example drinking and television disks and lamps) only one cutout from that variety of the glasses.
Glass is an amorphous, i.e. essentially not crystalline substance. In addition, usually glass is produced by melts, the formation of glass is possible by the heating up of Sol gel and by shock waves. Thermodynamically glass is called frozen, undercooled liquid. This definition applies to all substances, which are melted and cooled down accordingly fast. That means that with the solidification of the melt to the glass incipient crystals form, for the crystallization process however sufficient time does not remain. The solidifying glass is fast too firm, in order to permit still another crystallization. The transformation range, that is the transient area between melt and solid, lies with many types of glass around 600 "°C.
Despite the not defined melting point glass is a solid body. Even if it deformed under long-term application of force, one might not call it liquid. The slow deformation under a constant Kraft appears also in crystalline solids and as creeping is designated. Reports of flowing Kirchenfenstern cannot be confirmed and the idea of the liquid glass seem on a wrong translation to decrease/go back.
Hydrocarbon connections such as plexiglass are not glass, but a plastic. Plastics possess organic compounds, even Silikone are saturated and as more or less out-differentiated chains structured with organic remainders.
Those generally linguistic usage meaning-basic characteristic of glass is transparency. The optical characteristics are as various, as the number of glasses. Beside clear which are permeable in a broad volume for light, one can block the permeability by addition from special materials to the melt. For example one can make optically clear glasses for infrared light undurchdringbar, those for radiant heat is blocked. The most well-known controlling of the permeability is the colouring. The most diverse colors can be obtained. On the other hand there is obscure glass, which already is due to its main components or the addition of opak.
Customs glass has a density of approx. 2.5 g/cm The mechanical characteristics vary very strongly. The fragility of glass is proverbial. The breaking strength is determined strongly by the quality of the surface. Glass is to a large extent resistant to chemicals. An exception is hydrofluoric acid, it loosens the silicon dioxide and changes it to Generally glass has a high electrical resistance.
Although glass belongs to the oldest materials of mankind, still ambiguity exists in many questions of the atomic structure and its structure. Meanwhile the generally recognized interpretation of the structure is the network hypothesis, which was set up by Zachariasen 1932. This means that in the glass in principle the same connection conditions are present as in the crystal. With silikatischen thus in the form of SiO4-Tetraedern.
As the two-dimensional illustrations of the quartz and quartz glass show, the difference is appropriate for lattices and there a network in the regularity of the structure - here. The fourth oxide connection, which points to the third dimension, is not represented to the better descriptiveness. The connection angles and distances in the glass are not regular and the tetrahedrons are distorted. The comparison shows that glass has exclusively a short-range order in form of the tetrahedrons, however no crystalline long-range order exhibits. This missing long-range order is also responsible for the very heavy analysis of the glass structure. In particular the analysis middle range, thus the connections of several basic forms (here the tetrahedrons) is the subject of the current research and among the today's largest problems of physics is ranked.
One calls the material, which determines this essential structure of the glass, non-columnar. Beside the mentioned silicon oxide also different materials can be such as boron oxide and not-oxidic like Arsensufid non-columnar. Single-component glasses are however the exception and quartz glass are the only economically meaning. Further materials merge themselves differently into the network structure. Here network transducers and stabilizers are differentiated.
Network transducers are built into the stand formed by the non-columnar. For usual customs glass - lime alkali glass (more however the closer term is Kalk-Natron-Glas) - are this sodium and/or potassium oxide and calcium oxide. These network transducers tear the network architecture up. The bridge oxygen of the silicon oxide tetrahedrons is blown up. In place of the firm atomic bond a weaker electrovalence of soda with the oxygen steps.
Intermediate oxides such as alumina and lead oxide can function as non-columnar and - transducers. However they are not alone capable of the glass formation.
Usually a melt crystallizes when falling below the melting point. So from water in falling below of 0 "°C ice and silicon dioxide kritallisiert at 1727 "°C to Cristobalit. The melting point is defined exactly and with its under or excess changes numerous characteristics such as viscosity and density abruptly.
In contrast to the transition from melt to crystal is more gradual from melt to amorphous solid (thus glass). Here one speaks transformations not of a melting point but of '' a range ''
further aggregates are among other things:
Below a table with the approximate compositions of important glasses. The percentage figures are in weight percentage.
| Type of glass | SiO2 | Al2O3 | Na2O | K2O | MgO | CaO | [[Bor|B2O3]] | PbO | TiO2 | F | As | SE | Ge | Width unit |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Quartz glass | 100 % | "– | "– | "– | "– | "– | "– | "– | "– | "– | "– | "– | "– | "– |
| Container glass | 72 % | 2 % | 14 % | - | - | 10 % | - | - | - | - | "– | "– | "– | "– |
| Floating glass | 72 % | 1,5 % | 13,5 % | - | 3,5 % | 8,5 % | ||||||||
| Lead crystal glass | 60 % | 8 % | 2,5 % | 12 % | - | - | - | 17,5 % | - | - | "– | "– | "– | "– |
| Laboratory glass | 80 % | 3 % | 4 % | 0,5 | - | - | 12,5 % | - | - | - | "– | "– | "– | "– |
| E-glass | 54 % | 14 % | - | - | 4,5 % | 17,5 % | 10 % | - | - | - | "– | "– | "– | "– |
| Enamel | 40 % | 1,5 % | 9 % | 6 % | 1 % | |||||||||
| Chalkognidglas 1 | "– | "– | "– | "– | "– | "– | "– | "– | "– | "– | 12 % | 55 % | 33 % | "– |
| Chalkognidglas 2 | "– | "– | "– | "– | "– | "– | "– | "– | "– | "– | 13 % | 32 % | 30 % | 25 % |
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