(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.