Non-contact measurements of thermophysical properties of niobium at high temperature

Four thermophysical properties of both solid and liquid niobium have been m easured using the vacuum version of the electrostatic levitation furnace de veloped by the National Space Development Agency of Japan. These properties are the density, the thermal expansion coefficient, the constant pressure heat capacity, and the hemispherical total emissivity. For the first time, we report these thermophysical quantities of niobium in its solid as well a s in liquid state over a wide temperature range, including the undercooled state. Over the 2340 K to 2900 K temperature span, the density of the liqui d can be expressed as rho (L) (T) = 7.95 x 10(3) - 0.23 (T - T-m)(kg . m(-3 )) with T-m = 2742 K, yielding a volume expansion coefficient alpha (L)(T) = 2.89 x 10(-5) (K-1). Similarly, over the 1500 K to 2740 K temperature ran ge, the density of the solid can be expressed as rho (s)(T) = 8.26 x 10(3) - 0.14(T - T-m)(kg . m(-3)), giving a volume expansion coefficient alpha (s )(T) = 1.69 x 10(-5) (K-1). The constant pressure heat capacity of the liqu id phase could be estimated as C-PL(T) = 40.6 + 1.45 x 10(-3) (T - T-m) (J . mol(-1) . K-1) if the hemispherical total emissivity of the liquid phase remains constant at 0.25 over the temperature range. Over the 1500 K to 274 0 K temperature span, the hemispherical total emissivity of the solid phase could be rendered as epsilon (TS)(T) = 0.23 + 5.81 x 10(-5) (T - T-m). The enthalpy of fusion has also been calculated as 29.1 kJ . mol(-1). (C) 2001 Kluwer Academic Publishers.