Thermocell studies of sulfate mixtures and melts relevant for aluminium electrolysis

摘要

Classical thermodynamics gives no information about local heat effects in electrochemical systems, only the total entropy or enthalpy of the reaction, and it is not applicable where there is transport of heat, electricity or matter inside and across the borders of the system. The theory of irreversible thermodynamics describes interacting transport processes, and is much more suited to analyze such situations. Theory of thermocells (irreversible thermodynamics) has been applied to the aluminium electrolysis. Reversible heat changes at the electrodes have been calculated using assumptions about transported entropies and literature data. For a total current of 245 kA, the reversible heat production and cathode surface was calculated to be 23 kJ/s. The reversible heat production at anode surface was calculated to be -193 kJ/s, the negative sign means that it is consumed and represent a cooling. The reversible heat effects at the electrodes are of the same magnitude as other local heat effects (Joule heating and heating due to overpotentials). The method is well suitable to analyze the electrolysis. The theory gives a more accurate description of the cell voltage. Furthermore, the theory gives information about heat effect which can not be located by equilibrium thermodynamics. In spite of uncertainties in the assumptions made, we conclude that there is a reversible heat consumption at the anode surface. 54 refs., 32 figs., 22 tabs.