(b)
Fig – 4: Vapor pressure as a function of temperature for various rare earths metals (a) Saturated vapor pressure of Tb, Mn and Cr, (b) vapor pressure of other rare earth metals [17]
Cell efficiency
Cell efficiency may be calculated by measuring the concentration of reactant and product species in electrolyte. An excellent study documents these in Cerium [18]. Interested reader is referred to it for further details.
Mass transfer
Mass transfer coefficients, solubility of rare earth oxides in molten fluorides, oxide solubility determinations, oxide solubility diagrams. Prior to the proper oxide solubility determinations and diagram development, the equilibration time for oxide source dissolution, e.g., Dy2O3 and Dy2(CO3)3, was determined. It was determined by adding a certain amount of the oxide source (below solubility limit) and sample analysis thereafter at certain intervals. The time of equilibrium dissolution is measured by noting time at which the analyzed oxide content becomes constant. Below figures (Fig – 5) show the results obtained when Dy2O3 was added to the DyF3-LiF melts at different compositions, i.e., DyF3 (50 mol pct)-LiF (50 mol pct) and DyF3 (20 mol pct)-LiF (80 mol pct), at a working temperature of 1323 K (1050 C). The results showed that in the case of the eutectic composition longer dissolution times than in the equimolar composition are needed, in which case, all Dy2O3 added is dissolved well within 30 minutes.