| The thermodynamics of liquid surfaces and interfaces are discussed. Surfaces are treated as separate phases with a thickness corresponding to a monolayer. The introduction of surface chemical potentials allowed the development of equations for the calculation of surface concentrations and surface tensions of both miscible and immiscible liquid mixtures. This model, which incorporates Good's equation, was tested on many systems and the calculated values compared excellently with reported literature data.; The interfacial tensions between different metals and sodium fluxes were measured using the sessile drop technique combined with X-ray radiography. The interfacial tension was calculated from a series of coordinate points of the drop profile, using a computer program based on a numerical solution of the Laplace equation. From the Dupre's equation, it is predicted that the interfacial tension may be larger than the largest of the surface tensions of the two phases. This was confirmed for the metal-flux systems involving Ag, Bi, Pb and Sn.; The interfacial tensions between aluminum and cryolite melts with different salt additions were then measured. The interfacial tension between aluminum and cryolite at 1031(DEGREES)C is 481 mN/m and is strongly dependent of the NaF/AlF(,3) ratio. Additions of AlF(,3), Al(,2)O(,3) and LiF increased the interfacial tension. The change in interfacial tension with composition is explained by sodium enrichment of the Al/melt interface. The interfacial tension between aluminum and electrolytes containing 5 wt% AlF(,3), 5 wt% CaF(,2) and 5 wt% Al(,2)O(,3), is 690 mN/m for cathodic current densities between 0.1 and 0.6 A/cm('2).; The developed model for calculation of interfacial tension was successfully applied to the Al/cryolite system. The fractional surface coverage of sodium is only 0.33 at the cryolite composition as compared to complete coverage, as predicted from Gibb's adsorption equation.; The wetting behaviour of graphite anodes was studied during electrolysis. The wetting of the graphite anode by the electrolyte depended strongly on the cell polarity. Both the mechanisms for the initiation of the anode effect and the current transport during the anode effect are discussed. A gas film covers the base of the anode and it is estimated that a 30 (mu)m thick gas film covers the sides of the anode during the anode effect. |
