Noncontact electrical resistivity measurement technique for molten metals

Abstract

A noncontact technique of measuring the changes in electrical conductivity (or resistivity) of conducting liquids is reported. The technique is based on a conducting drop that is levitated by the high-temperature electrostatic levitator in a high vacuum. This technique, which utilizes the principle of the asynchronous induction motor, measures the relative changes in torque as a function of temperature by applying a rotating magnetic field to the sample. Changes in electrical resistivity are related to the changes in measuredtorque using the formula developed for the induction motor. Validity of this technique was demonstrated using a pure aluminum sample around its melting temperature. When the measurement results were calibrated by a literature value of resistivity at the melting point, our resistivity data around the melting point could be expressed by r liq =24.19+1.306×10 −2 (T−T m ) μΩ cm over T m ∼1160 K , r solid =10.77+1.421×10 −2 (T−T m ) μΩ cm over 700 K ∼T m , and the thermal conductivity as determined by the Wiedemann–Franz–Lorenz law from the resistivity data was given by κ liq (T)=94.61+4.41×10 −2 (T−T m ) W m−1 K−1, κ solid (T)=211.13−7.57×10 −2 (T−T m ) W m−1 K−1. Both electrical resistivity and thermal conductivity are in close agreement with the literature, confirming the validity of the present technique.