The influence of the various transport properties of the nitriding atmosphere on the formation of reaction-bonded Si3N4
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The thermal conductivities of nitrogen gas containing various second component gases have been calculated, and the importance of the gaseous phase in thermal conduction during nitridation has been described. Thermal segregations by thermal diffusion inside the nitriding furnace containing the various binary gas mixtures have also been calculated and the influence this effect has on the formation of reaction-bonded Si3N4 is discussed. In N2-H2 and N2-He gas mixtures, nitrogen diffuses down the temperature gradient, leading to a lower concentration of nitrogen and a higher concentration of hydrogen or helium around the silicon compact than expected from the initial composition, whereas in N2-Ar gas mixtures argon diffuses down the temperature gradient, leading to opposite results from the above; such phenomena affect the overall reaction rate and other transport properties. The conclusions obtained have been used in explaining previous experimental results obtained under various nitriding atmospheres.
KeywordsThermal Conduction Temperature Gradient Thermal Diffusion Transport Property Opposite Result
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