ALTERNATIVE VERSION ON THE NATURE OF THE ANODE EFFECT IN ELECTROLYSIS OF CRYOLITE-ALUMINOUS MELTS

Abstract

The paper gives prove the new hypothesis concerning the causes of the anode effect, which is manifested in the electrolytic production of aluminum. The nature of the anode effect is contradictory. The first version of the causes of its origin is based on the notions of the determining influence of the surface tension change on the boundary of the melt with a graphite electrode. The second version explains the increase in the operating voltage and sparking on the electrolyzer by the formation of the low conductive layer of the non-fluoride compounds with low wettability on the electrode surface. The new hypothesis is based on the taking into account the composition change of the electrolyte anode layer and the formation of cryolite-aluminous melt layer on the surface of the electrode. For its substantiation, the estimating calculations taking into account the density of the anode current in electrolysis and the dynamics of voltage increase on the electrolysis bath in the period between two anode effects have been carried out in the paper. Based on the provisions of the theory of mass transfer in near-electrode layers at the direct current flow, as well as Maxwell relations, describing the electrical conductivity of heterogeneous systems, the possibility of a heterogeneous phase formation at the electrode surface with electrical conductivity which is at least two orders lower than that of the initial cryolite-aluminous melt has been shown. The considered version does not contradict the phenomenon of the gaseous shirt formation around the anode, because the determining factor of this is not the wettability of electrode in the melt, but the consistency of the near-electrode layer of the electrolyte. Unlike other versions, it also explains the progressive voltage growth on the electrolysis just before the anode effect.