Institute of Non-ferrous Metals and Materials Science, Siberian Federal University, Krasnoyarsk, Russia:

O. V. Yushkova, Leading Engineer of a Chair of Metal Science and Thermal Treatment named after V. S. Biront, e-mail: olga_yuskova_1954@mail.ru
P. V. Polyakov, Professor-Consultant

LLC “Engineering-Technological Center “RUSAL”, Krasnoyarsk, Russia.
G. V. Arkhipov, Director of a Project “Energy-saving constructions of electrolysers”

LLC “Scientific and Technical Center “Elter”, Krasnoyarsk, Russia:
A. M. Ivanova, Director of LLC “Scientific and Technical Center “Elter”

This paper shows the work to study the protective properties of graphite foil “GRAFLEKS”, proposed to protect the cast iron fill and collector bar from the electrolyte penetration, thus reducing the voltage drop in the cathode and increase the life time of the reduction cell. Samples from cathode blocks were prepared, while electrolysis in laboratory cells and measurements of elemental composition for the determination of electrolytes penetration degree with X-ray spectroscopy were performed. Total amount of fluorine and sodium was estimated in the shooting point before and after foil protection. There was carried out the analysis of microstructure and elemental composition of the samples on the microscope JSM-7001F with the microanalyzer system Oxford Instruments for the elemental composition determination and EVO 50 (ZEISS Company) for the porosity measurement. The cathode block’s sample that was not protected by the foil gets impregnated by electrolyte; and multiplication of foil layers improves their protective quality. One-layered (0.3 mm width) and three-layered materials with the foil protection reduced fluorine concentration, which testifies high protective quality of the foil. The analyses results in the form of graphics with the changes of elements content and photographs are presented. In consequence of foil porosity, tree-layered protection is recommended. Foil usage will prevent the electrolyte impregnation to the fill and collector bar and the formation of a layer of solid salt mixture between slotwall of the cathode block and fill. As a result, the structure, composition of casts and collector bars will not change, while the cast contact resistance (cathode block) will not increase during the life time of the cell. One of the foil functions consists in redistribution of thermal flows and currents with the absence of chemical reactions in the contact with the cell lining materials. Protection of the cast iron fills and collector bar from the penetration of the electrolyte with the graphite foil “GRAFLEKS” is recommended.
This article was written using the results of the works, carried out within the federal target program “Investigations and developments by the priority ways of development of the scientific-technological complex of Russia on 2014–2020”, according to the agreement No. 14.579.21.0032 “Development of the technology of aluminium obtaining with decreasing of the consumption of electric energy on operating electrolyzers on 300–1000 kW·h/t”, unique identifier RFMEFI57914X0032.

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