Design And Application Of A Device Based On Electromagnetic Induction Principle For Electrical Resistivity Measurement Of Liquid Metals

Both theories and experimental findings have shown that there is close relation between the structure of liquid metals and the electrical resistivity of them. Therefore, the structure of liquid metals can be speculated by measuring their electrical resistivity, which has been a significant method for the research of the structure of liquid metals. In addition, the contactless measurement is a practicable method for measuring the electrical resistivity of liquid metals in undercooled liquid state. It is highly helpful to study the correlation of the structure and its evolvement of the liquid metals during the cooling process as well as solidification mechanism. This work has a very important significance in promoting the fundamental study on solidification and the optimization of casting processes.In the present work, the author detailedly represented a contactless measuring device for electrical resistivity of liquid metals, which is based on electromagnetic induction principle. The form of its sensor is similar to a differential transformer, the two AC (alternating current) signals from the sensor can be commutated, filtered and converted DC (direct current) signals respectively. When input the differential amplifier, the two signals are successively processed and converted single-channal signal. Using the device, the electrical resistivity of metals can be measured qualitatively from liquid to solid states, at the same time, the temperature of samples can be measured by an pyrometer. At last, the relation between electrical resistivity and temperature is acquired.The device was adjusted without sample after being finished. The circuit was solely given a scrutiny by testing each circuit unit respectively and was modified repeatedly, and the stable signals were obtained. A perfect insulating scheme was instituted for eliminating effects of heat on sensor after comparing several insulating materials and methods. Then, the device put out satisfying experimental data. Finally, the changes of electrical resistivity of pure Zn, Sb and hypereutectic Zn-70wt.%Sb alloy with temperature decreasing were measured with the device. Comparing the experiment data with interrelated references as well as phase diagram, the author concluded that the different structure transition in liquid state, solidification and the solid state of materials can be characterized according to the changes of the electrical resistivity. The device can not only measure the changes of the electrical resistivity of liquid metals in real-time during the cooling process, but also be operated easily and expediently. In particular, it can easily realize the measurement of the changes of electrical resistivity with temperature of undercooled liquid metals due to the contactless inductive technique for electrical resistivity measurement. Therefore, the device can be considered a significant tool for investigating the relation of the electrical resistivity and structure of liquid metals especially undercooled melts, and that is important for exploring the solidification mechanism.