Wetting testing of wettable cathodes for aluminium production
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The aim of this work has been to assess the wettability of a set of carbon-TiB2 composites towards aluminium. In order to do so, further improvements to the immersion-emersion method, a method used to assess the wetting properties of electrodes during aluminium electrolysis, was made. The method was tested for its validity and compared to the sessile drop test. Samples of composite cathode materials were supplied by an external manufacturer and tested. Pure graphite and TiB2 were used as benchmarks. Furthermore, the tested TiB2-samples were characterised in SEM and EDS.It was found that results from the immersion-emersion varies greatly across parallels and are not consistent with those from sessile drop testing. None of the tested composites show significant wetting, but the particle size of TiB2 has an influence on the properties of the material. Polarisation increases wetting for the materials, but the improvement is not sustained after polarisation is removed. The alumina concentration in the electrolyte was found to influence the wetting of the cathode, also after compensation for the electrolyte meniscus. Carbide formation was observed on most sample to a larger extent than previously seen, and was attributed to the increased duration of the immersion-emersion testing.Further work should include a more detailed investigation of this carbide formation and the processes occurring on the surface of the samples during polarisation. Additionally, a modification to the apparatus, involving an inner, insulating crucible, has been suggested in order to eliminate polarisation of the metal bath. Minor changes to the immersion-emersion procedure has also been suggested. These should be incorporated and applied to a larger number of parallels in the next stage of the project.