Abstract
The products and kinetics of the reaction between Si3N4 and iron were studied at 1173 to 1573K under both nitrogen and argon. The following results were obtained:(1) An Fe-Si solid solution was produced at low temperatures, which with an increase in temperature changed to iron silicides in the following order of occurrence: Fe3Si, Fe5Si3 and FeSi.(2) As the reaction proceeded, the lattice constant of the bcc crystal structure successively decreased throughout α-Fe, the Fe-Si solid solution and Fe3Si.(3) The incubation period was long at low temperatures, but shortened markedly with increasing temperature.(4) The initial stage followed a linear rate of reaction. Below 1373K, the activation energies were 626kJ/mol under a nitrogen atmosphere and 477kJ/mol under argon atmosphere. The reaction rate is thought to be controlled by a chemical process. At 1373K and above, an activation energy of 106kJ/mol was obtained under both atmospheres. The rate is thought to be determined by the combination of gas-phase diffusion through interparticle pores and chemical reaction.(5) On producing iron silicides, the reaction kinetics could be described by a parabolic rate law. The activation energy was estimated to be 217kJ/mol under an argon atmosphere. The reaction rate is thought to be determined by solid-state diffusion through the reaction layer. However, the parabolic rate law was unapplicable to the rate data produced under a nitrogen atmosphere, because of the approach to the reaction equilibrium.
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