Oxidation Mechanism of Steels in Liquid–Lead Alloys

Abstract

The oxidation mechanism of steels in liquid-lead alloys (lead or lead-bismuth) was studied. Parametric dependencies of oxidation, including oxygen-concentration effects, oxidation-rate constant and corrosion-rate effects, are analyzed. An oxidation model is developed based on the assumptions that the chemical reactions are at equilibrium locally, and scale removal is due to mass-transfer corrosion. The model shows that outward-iron diffusion in the solid phase (oxide layer) controls the oxide growth and mass-transfer rate in the flowingboundary layer determines the corrosion-product transport in the liquid phase (liquid-lead alloy). The oxide thickness depends on both the parabolic oxidegrowth-rate constant and the mass-transfer-corrosion rate. For long-term operation, the outer layer of a duplex-oxide layer can be completely removed by flowing lead alloys and it is expected that a pure-chromium-oxide layer forms underneath the Fe-Cr spinel if iron is heavily depleted. The oxide thickness and steel weight change are very different from those of the pure parabolic law and they are classified into distinct and universal categories. The model is validated partially by application to interpreting the measured oxide behavior of several steels in a lead-bismuth eutectic-test loop.

Buoyancy-Enhanced Oxygen Transport in the Experimental Liquid Lead Bismuth Eutectic Container

“…The oxygen diffusion coefficient in LBE is estimated to be on the order of 10 À8 m 2 /s at 500 C and no accurate experimental data are available so far. 7,8,27) Three oxygen diffusivity values, 1:0 Â 10 À8 , 2:0 Â 10 À8 , and 5 Â 10 À8 m 2 /s with corresponding Schmidt numbers (Sc ¼ 3:6, 6.8, and 2.72, respectively) are considered. For simplicity, Sc ¼ 2:72 is taken as an example, the oxygen concentration distributions at different moments (t ¼ 500, 1,500, 5,000, 10,000, and 3,000 s) are shown in Figs.…”

“…The main driving force for LBE corrosion is the chemical potential for dissolution of steel elements into LBE at the solid surfaces in contact with LBE. 6,19) The main types of corrosion of liquid metal are illustrated in Fig. 1.…”

“…Oxygen was assumed to be transported along the grain boundaries, or some other pores and vacancies by some unclear mechanisms. 27) The mass transport of oxygen can be treated as an effective diffusion which will follow the diffusion equation but with a much higher diffusivity as a sum of the lattice tracer self-diffusion coefficient and the diffusion coefficient along the grain boundary. 6,7) It is reasonable to assume that the transport rates of iron (diffusion) and oxygen (effective diffusion) are of the same order, and both the transport rates of iron and oxygen control oxidation rate.…”

Effects of alloying on oxidation and dissolution corrosion of the surface of γ-Fe(111): a DFT study

“…Globally, the technological and economic losses caused to industry by corrosion soak up 3~4 % of the annual GDP, which has led to intensive efforts to minimize its adverse effects. Although new stainless steels with greatly improved abilities to resist corrosion have been created by adding different proportions of alloying elements to the iron, localized corrosion may still take place due to the activity of Fe and damage to or even removal of the passive film on the alloy surface, which is mainly composed of an Fe-Cr spinel and magnetite [1][2][3], under certain conditions. Local etching such as pitting and galvanic corrosion impact alloy performance significantly.…”

Kinetic Features of Iron Oxidation in Liquid Lead Saturated with Oxygen Below and Above the Chaudron Point (570 °C)

“…The main task of this technology consists in supplying and controlling the optimal oxygen concentration in the lead melts to an form in situ protective oxide layer Me 3 O 4 (Me:Fe, Cr) on the steel surface and to minimize in this way the solubility of steel's components (Ni, Cr, Fe) in the liquid-metal medium [4]. An understanding of passivation of steels in heavy-metal melts is complicated since the systems investigated (Fe[Cr, Ni, Si]/ Pb [O] or PbBi [O]) are very complex in order to gain an insight into the oxidation process [5][6][7][8]. In addition, there are many factors affecting corrosion processes, i.e.…”