Silicon monoxide
Silicon- (II ) oxide
Dark brown odorless solid
Fixed
2.13 g · cm -3
> 1702 ° C
1880 ° C
Insoluble in water
Attention
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Silicon monoxide ( and silicon monoxide ) is a compound of silicon and oxygen present in the silicon in the oxidation state II. Because the preferred oxidation of silicon IV, low-valent oxides such as SiO or Si2O3 are also known as sub-oxides. SiO exists in different modifications, of which only one is of commercial importance. This is a dark brown to charcoal gray, amorphous solid.
Silicon monoxide is found in none of the known modifications in nature, but is exclusively produced synthetically.
Silicon monoxide is thermodynamically stable only in the gas phase, and upon cooling disproportionated silicon and silicon dioxide. Spectroscopic investigations of SiO could not provide evidence to date that is present in the condensed phase silicon in the oxidation state II. After analyzing the structural studies of peace by means of XANES spectroscopy, high-pressure studies, 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 disproportionated at the atomic level mixture of silicon and silicon dioxide. During the gas separation process, gaseous silicon monoxide disproportionation apparent upon cooling in Si and SiO2, and that at the atomic level in the mold, that neither silicon nor silica domains can be directly detected. The dark brown product here has chemical and physical properties that differ from those of a mixture of Si and SiO2 significantly and thus are of great importance for technical applications. The difference to a mixture manifests itself eg in reactions that target the cleavage of Si-Si bonds and Si -O bonds. They did not lead to success in the case of SiO.
Production and representation
Silica is heated with elemental silicon in a vacuum to at least 1250 ° C, the result gaseous monomolecular SiO, which disproportionates into the starting materials during cooling. By quenching of the gas on the cold surfaces, however, the dark, amorphous form of the SiO 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 coke-like modification in the cluster phases Si and SiO2 has been demonstrated.
The molecular silicon monoxide SiO is isosteric to carbon monoxide CO. It can be isolated as a monomer in an inert gas only matrix. The enthalpy of formation is -99.6 kJ / mol and the Si - O bond length 0.1509 nm
Further, there is a yellow powder, and a black fibrous modification.
Chemical Properties
Silicon monoxide is a strong reducing agent. It reacts at room temperature with atmospheric oxygen to form silicon dioxide on quickly.
However, a silicon dioxide layer formed on the surface protects the underlying SiO by passivation, so that the material remains stable for many years. SiO in a very fine distribution, however, is pyrophoric.
From about 600 ° C decomposes ( SiO) x in SiO2 and silicon. The rate of decay increasing with increasing temperature.
Use
Silicon monoxide is used on a large scale as a material for compensation of optical lenses. This SiO is in a PVD process in vacuum evaporated ( with mono -molecular SiO in the gas phase is formed ) and depressed in a thin layer on the lenses. Depending on the partial pressure of oxygen in the process set the layer separates as SiO, Si2O3 and SiO2 from. The lenses are so hardened or - in combination with layers of other evaporation materials - non-reflective.
Silicon monoxide also is used as a starting material for the synthesis of other silicon compounds such as silicon carbide or silicon nitride.