Abstract
The electrical resistivity of carbon anodes is an important parameter in the overall efficiency of the aluminum smelting process. The aim of this work is to explore the Van der Pauw (VdP) method as an alternative technique to the standard method, which is commonly used in the aluminum industry, in order to characterize the electrical resistivity of carbon anodes and to assess the accuracy of the method. For this purpose, a cylindrical core is extracted from the top of the anodes. The electrical resistivity of the core samples is measured according to the ISO 11713 standard method. This method consists of applying a 1 A current along the revolution axis of the sample, and then measuring the voltage drop on its side, along the same direction. Theoretically, this technique appears to be satisfying, but cracks in the sample that are generated either during the anode production or while coring the sample may induce high variations in the measured signal. The VdP method, as presented in 1958 by L.J. Van der Pauw, enables the electrical resistivity of any plain sample with an arbitrary shape and low thickness to be measured, even in the presence of cracks. In this work, measurements were performed using both the standard method and the Van der Pauw method, on both flawless and cracked samples. Results provided by the VdP method appeared to be more reliable and repeatable. Furthermore, numerical simulations using the finite element method (FEM) were performed in order to assess the effect of the presence of cracks and their thicknesses on the accuracy of the VdP method.
Highlights
The Hall–Héroult process [1,2] is used to perform the electrolysis of alumina
The results presented are a relative electrical resistivity, and a negative value refers to a measured electrical resistivity smaller a relative electrical resistivity, and a negative value refers to a measured electrical resistivity smaller than the average value obtained via standard method
The electrical resistivity of baked carbon anodes used in the aluminum industry was studied using both the ISO 11713 standard method and the Van der Pauw method
Summary
The Hall–Héroult process [1,2] is used to perform the electrolysis of alumina. To this end, an electrical current is applied through the electrolytic bath between carbon anodes and cathodes.The carbon anodes are used to provide carbon for the chemical reaction, as well as the electrical current necessary for the electrolysis. The Hall–Héroult process [1,2] is used to perform the electrolysis of alumina To this end, an electrical current is applied through the electrolytic bath between carbon anodes and cathodes. The quality control is performed on core samples, and usually extracted from the top of the anodes beside the stub holes. This location may lead to core samples having some structural flaws, especially at their bottom [7,8,9]. The electrical resistivity characterization of anode cores is achieved using the ISO 11713 standard method This method is merely an adaptation of ASTM B193-02, which is used as a test method for the resistivity of electrical conductor materials, this latter method requires a sample with neither cracks nor visible defects.
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