THERMODYNAMICS AND KINETICS OF LIQUID LEAD INTERACTIONS WITH REFRACTORY METALS AND COMPOUNDSProfs. M.A. Dayananda and D. R. Gaskell
School of Materials Engineering
In recent years there has been a renewed interest in the use of high-temperature liquid lead as a coolant in advanced nuclear reactors. The successful development of these reactor concepts will depend on a fundamental understanding of the interactions between liquid lead and structural materials. Unfortunately, many of the thermodynamic phase diagrams of lead with common transition metals are poorly understood and even less is known about the kinetics of these systems. The scope of the proposed research is to determine the thermodynamics and kinetics of interaction between high-temperature liquid lead and key structural materials that may be used in advanced lead-cooled reactor designs. The project has three objectives:
- to determine phase relationships between Pb and the transition metals, Nb, Mo, Ta, Re, Zr and Cr at temperatures up to 1000oC;
- to study rates of interaction and interdiffusion between liquid lead and the metals Nb, Mo, Re, Ta, Zr and Cr and their alloys;
- to examine the silicides of Mo, Nb and Re as possible coating materials to improve compatibility.
Coupons of transition metals will be immersed in liquid lead at selected temperatures and will be brought to a state of equilibrium. The equilibrium phases will be examined at room temperature by optical and scanning electron microscopy, x-ray diffraction and electron microprobe analysis. The phase relationships at temperatures between room temperature and 1000oC will be determined by differential thermal analysis at controlled rates of heating and cooling in an inert atmosphere. Kinetic studies will be carried out with solid-liquid diffusion couples assembled with coupons of refractory metals and their alloys in contact with liquid lead for various times at selected temperatures between 750o and 1000oC and letting the liquid solidify. Cross sections of the diffusion couples will be examined by SEM-EDS and electron microprobe analysis for characterization of reaction layers and their growth with time. Identification of the resulting intermetallic phase layers will complement the differential thermal analysis experiments in the construction of phase diagrams.