| Reliable estimation of the hydrate vapour pressure of molten reactive halide systems important to electrolysis and metallothermic reduction Georges Kipouros1; 1MATERIALS ENGINEERING, DALHOUSIE UNIVERSITY, Halifax, Canada; PAPER: 131/Molten/Keynote (Oral) SCHEDULED: 14:50/Thu. 24 Oct. 2019/Ambrosia A (77/RF) ABSTRACT: Most of reactive metals and their alloys are produced by fused salt electrolysis or metallothermic reduction in molten salts. The feed material for both of these processes is the anhydrous chloride of the metal under consideration produced by the dehydration of the form of hydrate. A critical step in the production of most reactive metals requires rigorous thermodynamic analysis. Thermodynamic data for most of the reactive metal chloride hydrates have not been measured. Improper dehydration of the metal chloride hydrate may lead to a prohibitive amount of hydroxychloride, oxychloride, and finally oxide. To prevent hydrolysis, a certain pressure of hydrogen chloride must be maintained to supress or reverse hydrolysis. In this investigation, it is demonstrated that by careful application of the phase rule, sigma function, and utilization of prediction and estimation techniques will lead to a reliable technique for the estimation of the hydrate vapour pressure. These techniques will also lead to prediction of the necessary hydrogen chloride presence to avoid hydrolysis. Thermodynamic data, including heat capacities, standard entropies, and enthalpies, are estimated/predicted for all conceivable intermediate hydrate compounds. Estimations are based on published data, as well as trends proven in similar systems. The thermodynamic estimations and predictions have been published for magnesium chloride, neodymium trichloride, dysprosium chloride and is a continuous program for rare earth metal chlorides. References: 1. G.J. Kipouros and D.R. Sadoway, "The Chemistry and Electrochemistry of Magnesium Production" in Advances in Molten Salt Chemistry, Vol. 6, Edited by G. Mamantov, C.B. Mamantov and J. Braunstein, Elsevier, Amsterdam, pp. 127-209 (1987). 2. R.J. Roy and G.J. Kipouros, "Estimation of Vapour Pressures of Neodymium Trichloride Hydrates", Thermochimica Acta, 178, 169-183 (1991). 3. Judge and G.J. Kipouros, “Prediction of hydrogen chloride pressure to avoid hydrolysis in the dehydration of dysprosium trichloride hexahydrate (DyCl3.6H2O).” Can. Metall. Quart., 52,(3), 303-310 (2013). 4. G.J. Kipouros, “Dehydration of Magnesium Chloride Hexahydrate”, Ralph Lloyd Harris Memorial Symposium, Ed. Cameron L. Harris, Sina Kashani-Nejad and Matthew Kreuh, Materials Science and Technology (MS&T) 2013, 11-23 (Invited, keynote), (2013). |
