Gel des solutions concentrees en milieux poreux et application au procede Hall-Heroult (French text).

摘要

At the basis of this work, there is a fundamental need from the aluminium industry, which is to better understand the degradation mechanisms of electrolysis cells' lining in order to improve their conception. One of the problems that preoccupy this industry is cathode blocks heaving. The hypothesis that a phenomenon related to frost heaving in soils could also contribute to cathode heaving remains present without being thoroughly investigated. Thus, the objective of the present study is to try to determine the probability that such phenomenon could intervene to cathode heaving.; It was decided to study the frost heaving obtained with aqueous solutions and in particular concentrated solutions, for which the behaviour should be closer to the fluoride solutions used in the Hall-Heroult process.; The frost heaving behaviour of a fine inert powder saturated with concentrated aqueous solutions served as a physical model in the experimental portion of the study.; The main contributions of the present thesis are the following: (1) First detailed description of the visual evolution obtained with concentrated solutions. (2) Presentation of a proposition stating that the heaving kinetics during thermal steady state is mainly governed by the solute diffusion toward the unfrozen zone. (3) Derivation of an equation rationalising the particle clusters migration across the segregation zone, as well as the heaving kinetic during thermal steady state. (4) Proposition of a simple modelling for the liquid content evolution with temperature in porous media containing concentrated solutions and capable of rationalising the behaviour observed when an eutectic transformation is reached. (5) Numerical simulations of solutes transport during freezing tests. (6) Experimental evidences that the solute concentration has no effect on the maximum pressure under a threshold concentration. (7) Proposition of an explanation rationalising the evolution of maximum pressure as a function of solute concentration. (8) Proposition of an explanation rationalising the effect of salt on the heaving kinetic which does not necessitate a decrease of the hydraulic conductivity. (9) Theoretical derivation based on the proposed phenomenological model of the temperature interval in which frost heaving-type segregation is possible in presence of concentrated solutions. (Abstract shortened by UMI.)