Effect of rare earth Th on thermophysical properties of ternary Co–Fe–Th liquid alloy

By Monte Carlo method with EAM potentials, the thermophysical properties, including the surface tension (σ), the viscosity (η), and the diffusion coefficient (D) of liquid Co–50at%Fe and Co–48.5at%Fe–3at%Th alloys at different temperatures are calculated. The effect of Th on the thermophysical parameters is examined. Over the temperature range from 1500 to 2000 K, the surface tension decreases from σb = 1.795−5.140 × 10−4(T − Tm) N/m to σb = 1.630−6.433 × 10−4(T – T0) N/m, and the viscosity increases from ηb=1.173e15,169RTmPas to ηt=1.159e16,660RTmPas after Th was added. Meanwhile, with the addition of Th, the diffusion coefficients of Fe and Co decrease 9.2% and the diffusion activation energy increases 3.8% from 29,997 to 31,165 J mol−1. It is the addition of Th element which has bigger atomic radius, larger atomic mass, and complex arrangement of extranuclear electron, leads to the reduced surface tension, increased viscosity, and enhanced diffusion activation energy. The underlying mechanism of the contribution of the Th to the diffusion coefficient should be ascribed to the formation of different short and medium range order structures in liquids.

► Surface tension, viscosity, and diffusion coefficient are calculated by Monto Carlo method when Th is added in Fe–Co alloy.
► Surface tension decreases when Th is added.
► Diffusion coefficient decreases whereas viscosity increases with Th.
► The contribution of Th on diffusion coefficient is due to the variation of liquid structure.