Coatings Systems: Chromium Carbide, Nitride and Carbonitride
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The process of the chemical deposition from vaporous implies the adsorption of the mobile atoms (monomers) on the substrate surface, their migration with embryos and stable nucleus formation, followed up by further growth through the adsorption of new atoms on the surface and also by the nucleus coalescence. The final structure of the deposed layer is given by various effects such as, the adsorption of impurities, the incorporation of gaseous, the co-deposition of another elements, the crystallization, etc. The ultimate properties of the coatings are further dependent on the nature and composition on the substrate. Therefore, in theory a vast number of substratecoating combinations is possible, with its own set of physical and chemical characteristics. If the vapor chemical deposition takes place within a tubular continuous reactor, a gas carrying the reacting species is passed over the substrate. At the substrate surface, the reacting elements undergo a number of chemical reactions leading to the product formation. Part of the products are deposited on the substrate and part of it goes back to the gas stream . Before examining the vapor chemical deposition reactions it must be determined if the reaction is possible thermodynamically, if the calculated concentrations (partial pressures) of the reactants under equilibrium conditions are less than their initial values.
- 2005 fascicula9 nr1