Silicon-carbon alloy films

An SiC film formed by pyrolysis of polysiloxane gave IR preaks due to pSi-CHs vibrations in the range 790-810 cm". The FTIR spectra of silicon-carbon alloys synthesised by electron cyclotron resonance CVD include a band at 1180 cm", assigned as an SiC stretch, corresponding to an SiC bond order of 1.5. ° Raman spectra of Sii-yCy films formed by low-temperature CVD include a band at 607 cm", assigned to C atoms at Si substitutional sites. IR spectra of such films show a similar band, together with features at 475 and 810 cm 1312 methods were used to calculate the wavenumbers of substitu-... 

The high-chromium irons undoubtedly owe their corrosion-resistant properties to the development on the surface of the alloys of an impervious and highly tenacious film, probably consisting of a complex mixture of chromium and iron oxides. Since the chromium oxide will be derived from the chromium present in the matrix and not from that combined with the carbide, it follows that a stainless iron will be produced only when an adequate excess (probably not less than 12% of chromium over the amount required to form carbides is present. It is commonly held, and with some theoretical backing, that carbon combines with ten times its own weight of chromium to produce carbides. It has been said that an increase in the silicon content increases the corrosion resistance of the iron this result is probably achieved because the silicon refines the carbides and so aids the development of a more continuous oxide film over the metal surface. It seems likely that the addition of molybdenum has a similar effect, although it is possible that the molybdenum displaces some chromium from combination with the carbon and therefore increases the chromium content of the ferrite. 

Hydrogen atoms are bonded with silicon and carbon as well in the films over a wide range of alloy composition, as is clearly seen in the infrared absorption spectra of Fig. 2. One thing to be noted is that hydrogen, once introduced into the film during the low-temperature deposition, tends to remain there even at high temperatures, probably owing to the more stable nature of the C-H bond compared to the Si-H bond (Munekata et al, 1980). 

Richman EK et al (2008) Ordered mesoporous silicon through magnesium reduction of polymer templated silica thin films. Nano Lett 8(9) 3075-3079 Shen L et al (2012) Magnesiothermically reduced diatomaceous earth as a porous silicon anode material for lithium ion batteries. J Power Sources 213 229-232 Shen X et al (2013) Si/mesoporous carbon composite as an anode material for lithium ion batteries. J Alloys Compounds 552 60-64... 

Carburization, as such, is not a corrosion phenomenon. However, it forms chromium carbides that reduce the chromium matrix, and it reduces the efficacy of the prior oxide film. Higher silicon contents will reduce the rate of carburization. Nickel in the iron-chromium-nickel alloys will improve the resistance to carburization by lowering the solubility of carbon, but not to the same degree that silicon and chromium do. 

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