Peculiarities of Diffusion Mass Transfer in System Fe[Cr]-Pb[O]
Process of high-temperature (650°С) interaction of Cr(Si)-containing steel EP-823 with stagnant Pb melt containing oxygen (CО[Pb] » 10-5 - 10-6 mass.%) was theoretically and experimentally investigated. The structure and composition of oxide layer formed on the steel surface during exposure to Pb melt was examined. It is determined that thin (£ 1000 Å) Cr(Si) - rich oxide layer is formed on the steel surface in the early stages of oxidation. Oxide layer is being formed intensively over the grain boundaries followed by a lateral diffusion of Cr and spreading of Cr2O3 over alloy surface. Iron diffuses through the Cr(Si) - rich continuous oxide layer in the course of time. The formed oxide layer protects the steel against liquid metal penetration. Kinetics of iron diffusion dissolution in the liquid Pb is analytically described taking into account the chemical interaction between iron and oxygen. It is assumed that oxygen ions serves as a “traps” for iron ions and eliminates them from the diffusion flux. Fe−O complexes are considered as separate slowmoving components of the melt. In order to formulate the diffusion problem equations with additional parameter describing the volume reaction between Fe and O in melt and boundary conditions involved the time dependence of oxygen concentration at the interface of both melt and solid metal sides were used. Result is obtained in analytical form using the Laplace transformation. Analysis of obtained relations allow to assert that in the case of dissolution of iron in the lead melt containing “oxygen traps” the diffusion zone are less than that in the conditions of dissolution (without “traps”). However, the total concentration of iron both on surface of oxide layer and in the contact zone of melt is increased.
M. Danielewski, R. Filipek, R. Kozubski, W. Kucza, P. Zieba, Z. Zurek
Y. Matychak et al., "Peculiarities of Diffusion Mass Transfer in System Fe[Cr]-Pb[O]", Defect and Diffusion Forum, Vols. 237-240, pp. 733-738, 2005