Thermophysical properties of undercooled liquid cobalt

The surface tension of undercooled liquid cobalt has been measured by the oscillating-drop technique combined with electromagnetic levitation. The accuracy of the method was verified by measurements of the surface tension of liquid nickel. The liquid cobalt was undercooled by up to 231K (0.13T m), and its surface tension determined to be σCo =1875 0.348(T-T m)mNm-1. From this result, the viscosity, self-diffusion coefficient, density and thermal diffusivity of undercooled liquid cobalt were derived. Using these thermophysical parameters, the growth velocity of cobalt dendrite is calculated and shown to agree well with experimental results. Furthermore, the Marangoni number and the Rayleigh number are calculated; these increase slowly with increasing degree of undercooling.