THE ROLE OF EXTERNAL DIFFUSION IN THE OXIDATION OF STRUCTURAL STEELS IN HEAVY LIQUID-METAL COOLANTS

Authors & Affiliations

Niyazov S.-A.S., Ivanov K.D., Lavrova O.V., Askhadullin R.Sh., Legkikh A.Yu.
A.I. Leypunsky Institute for Physics and Power, Obninsk, Russia

Abstract

From the point of view of chemical kinetics and thermodynamics of the system, including the interaction of iron with oxygen, the partial pressure of which provide pecials at the level of the operating range of the oxidation potential of heavy liquid metal technologies (TGMT). The interaction of structural steels with liquid melts {Pb-Bi} or {Pb} are excluded from analysis in order to simplify the system and determine the effect of only one factor - the partial pressure of oxygen. The analysis led to the following conclusions: In the initial period passivation of structural materials in the molten lead or lead-bismuth front of the oxidation reaction may be located within the outer diffusion (liquid) sublayer in the relative distance from a solid surface. The degree of removal of the reaction front from a solid surface in this period is determined by the partial pressure of oxygen or its concentration in the melt. The result of the removal of the reaction front from a solid surface is prevailing volumetric condensation of the reaction products (magnetite) above the surface condensation and formation of porous coatings of greater thickness, but lower density. In the limiting case, the reaction products can condense in the dispersed particles are withdrawn from the diffusion layer to the external environment (regular loss). In the non-isothermal contours reactor plants with TIMT always implemented conditions for mass transfer of the components of the structural materials in the hot zone of steel in the coolant, since the residual (equilibrium) activity of iron in the formation of magnetite is significant value (aFe = 10-2 ÷ 10-1). This means that not all that came out were the iron can be placed in the oxide film. In the limit when moving reaction front at the external border of the oxide film almost all of the iron can go to the coolant. The presented approach can be extended to other elements included in the composition of the steel. However, the reaction zone will gradually shift into solid material and the total process to transition control of oxygen diffusion in the solid-house material.

Keywords
liquid metal coolants, external diffusion, structural steel, oxidation, thermodynamics, non-isothermal contours, oxide film, dispersed particles, oxygen concentration, equilibrium activity of iron, losses, magnetite

Article Text (PDF, in Russian)

References

UDC 621.039.534.6

Problems of Atomic Science and Technology. Series: Nuclear and Reactor Constants", issue 1, 2014