Deriving thermophysical properties of liquid Nb by containerless electrostatic levitation

Abstract

Containerless solidification of Nb was carried out by the electrostatic levitation process in which a bulk sample was electrostatically levitated and melted by laser irradiation in high vacuum. A t(T) function in a time-temperature profile was analytically determined to describe the radiative cooling curves of Nb in the liquid state to estimate the ratio of constant pressure specific heat to hemispherical total emissivity, c P (T)/ε T (T), and further to derive ε T (T) and c P (T). The cooling behavior of liquid Nb was found to be well described by an inverse biquadratic polynomial of t(T). With the analytical t(T) function, the derivative dt/dT was easily obtained and the c P (T)/ε T (T) ratio was readily estimated from the radiative cooling curve. The estimated c P (T)/ε T (T) and the derived ε T (T) and c P (T) agreed well with the reference data in the literature. This implies the rationale behind the analytical approach taken in this study was reasonable and can be applied to estimating c P (T)/ε T (T) and further deriving c P (T) or ε T (T) of materials in the liquid state.