Silicon monoxide
| General | ||||||||||||||||
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| Surname | Silicon monoxide | |||||||||||||||
| other names |
Silicon (II) oxide |
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| Molecular formula | SiO | |||||||||||||||
| Brief description |
dark brown odorless solid |
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| External identifiers / databases | ||||||||||||||||
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| properties | ||||||||||||||||
| Molar mass | 44.09 g · mol -1 | |||||||||||||||
| Physical state |
firmly |
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| density |
2.13 g cm −3 |
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| Melting point |
> 1702 ° C |
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| boiling point |
1880 ° C |
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| solubility |
almost insoluble in water |
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| safety instructions | ||||||||||||||||
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||
Silicon monoxide (also silicon monoxide ) is a compound of silicon and oxygen in which silicon is in the + II oxidation state. Since the preferred oxidation state of silicon is + IV, low-valent oxides such as SiO or Si 2 O 3 are also referred to as suboxides. SiO exists in various modifications , but only one of them is of commercial importance. This is a dark brown to anthracite-colored, amorphous solid.
Silicon monoxide does not occur in any of the known modifications on earth but has been detected spectroscopically in interstellar space and is therefore the most common oxide of silicon in the universe in terms of quantity. On earth, however, it does not occur in any of the known modifications, but is exclusively produced synthetically.
Silicon monoxide is thermodynamically stable only in the gas phase and disproportionates when cooled in silicon and silicon dioxide. Spectroscopic investigations on SiO have so far not been able to provide evidence that silicon in the + II oxidation state is present in the condensed phase. After analyzing Friede's structural investigations with the help of XANES spectroscopy, high pressure investigations, NMR, radial distribution function from energy-dispersive X-ray diffraction and pair distribution function from electron diffraction data, commercially available SiO is better described as a mixture of silicon and silicon dioxide that is disproportionate at the atomic level. During the vapor deposition process, gaseous silicon monoxide evidently disproportionates into Si and SiO 2 as it cools , at the atomic level in such a way that neither silicon nor silicon dioxide domains can be detected directly. The dark brown product has chemical and physical properties that differ significantly from those of a mixture of Si and SiO 2 and are therefore of great importance for technical applications. The difference to a mixture is expressed e.g. B. in reactions that aim at the cleavage of Si – Si bonds and Si – O bonds. In the case of SiO, they did not lead to success.
Extraction and presentation
If silicon dioxide is heated with elemental silicon in a vacuum to at least 1250 ° C, gaseous, monomolecular SiO is formed, which disproportionates again into the starting materials on cooling . By quenching the gas on cold surfaces, however, the dark, amorphous form of SiO can be obtained as a solid.
properties
Physical Properties
The dark brown, amorphous modification of silicon monoxide (SiO) x consists of polymeric Si – O chains and is glassy and brittle. The structural disproportionation of this coke-like modification in clusters of the phases Si and SiO 2 was demonstrated.
The molecular silicon monoxide SiO is isostatic to the carbon monoxide CO. As a monomer, it can only be isolated in a noble gas matrix. The enthalpy of formation is −99.6 kJ / mol and the Si – O distance 0.1509 nm.
There is also a yellow, powdery and a black, fiber-like modification.
Chemical properties
Silicon monoxide is a powerful reducing agent. Even at room temperature, it reacts quickly with atmospheric oxygen to form silicon dioxide .
A silicon dioxide layer formed on the surface protects the SiO underneath by passivation , so that the material can be kept unchanged for many years. In contrast, SiO in a very fine distribution is pyrophoric . SiO can be completely converted to SiO 2 by melting with a mixture of alkali carbonate and alkali nitrate .
Silicon monoxide is completely dissolved by hydrofluoric acid , but less easily than silicon dioxide. From around 600 ° C (SiO) x breaks down into SiO 2 and silicon. The rate of disintegration increases with increasing temperature.
use
Silicon monoxide is in a large scale as a material for compensation of optical lenses used. SiO is evaporated in a PVD process in a vacuum (whereby monomolecular SiO is formed in the gas phase) and deposited in a thin layer on the lenses. Depending on the oxygen partial pressure set in the process, the layer is deposited as SiO, Si 2 O 3 or SiO 2 . The lenses are hardened in this way or - in combination with layers of other vapor deposition materials - anti-reflective.
Furthermore, silicon monoxide is also used as a starting material for the synthesis of other silicon compounds, e.g. B. of silicon carbide or silicon nitride .
Historical
The first description of the discovery of silicon monoxide was published in 1887.
Individual evidence
- ↑ a b c d e silicon monoxide data sheet (PDF) from Merck , accessed on March 15, 2010.
- ↑ a b Datasheet Silicon monoxide, pieces, 3-10 mm, 99.99% trace metals basis from Sigma-Aldrich , accessed on February 26, 2013 ( PDF ).
- ↑ Peter Jutzi and Ulrich Schubert (2003) Silicon chemistry: from the atom to extended systems. Wiley-VCH ISBN 3-527-30647-1
- ↑ M. Nagamori, J.-A. Boivin, A. Claveau: Gibbs free energies of formation of amorphous Si 2 O 3 , SiO and Si 2 O . In: Journal of Non-Crystalline Solids . tape 189 , no. 3 , September 1995, p. 270-276 , doi : 10.1016 / 0022-3093 (95) 00239-1 .
- ^ B. Friede, New Contributions to the Representation and Structure of Subvalent Silicon, Germanium and Tin Chalcogenides, Dissertation University of Bonn 1999
- ↑ U. Schubert, G. Donhärl, Diploma thesis G. Donhärl, University of Würzburg 1994
- ↑ Achim Hohl: Investigations into the structure of amorphous silicon monoxide . Dissertation, Darmstadt 2003 ( PDF )
- ^ A b c Charles F. Mabery: On the composition of certain products from the Cowles electrical furnace . In: Ira Remsen (Ed.): American chemical journal . tape 9 . Baltimore 1887, p. 11–15 ( online at the University of Illinois University Library pages at Urbana-Champaign).
literature
- Entry to silicon monoxide. In: Römpp Online . Georg Thieme Verlag, accessed on August 23, 2015.
- AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 .
- RH Doremus: Diffusion of reactive molecules in solids and melts . Wiley-IEEE, 2002, ISBN 9780471385455 , p. 241, chapter Diffusion of Oxygen and Silicon in Silicon: Silicon Monoxide Model ( limited preview in the Google book search).