ORNL-1816 - the Molten Salt Energy Technologies Web Site

for self-diffusion of the thallous ion is greater than
that for electrical conduction. These results are
in accord with the concept that the application
of an electrical field lowers the potential barrier
restricting migration of charged ions in the ap-
propriate direction of the applied field. The self-
diffusion coefficient of a given ion can be used in
conjunction with the Nernst-Einstein equation 36
to calculate the contribution of that particular ion
to the total equivalent conductance of the salt.
When this is done, it is observed for sodium nitrate
and thallous chloride that, in each case, the cation
accounts for about 95% of the equivalent con-
ductance of the respective molten salt at temper-
atures about 25OC above the melting point, This
indicates that the transport numbers of these
cations relative to their anions in these two salts
are approximately 0.95.
Viscosity Measurements
F. A. Knox F. Kertesz
V. Smith
Mat hemistry Divisio
The automatic capillary viscometer, which was
used previously37 for determining the viscosity of
36R. 2
= D.z F /RT, where is the equivalent con-
I I
ductonce, D the self-diffusion coefficient, z the charge
of ions, F the Faraday constant, R the gas constant,
and T the absolute temperature.
PERlOD ENDING DECEMBER 10, 7954
fluoride melts, has been modified and pBaced in
operation for viscosity determinations of alkali
nitrate melts. Effort has been concentrated on
determining viscosity changes immediately above
the melting points as an adjunct to the work being
done by Van Artsdalen to establish the signifi-
cance of ion size on physical properties (see
section above). In view of the low melting points
of the salt mixtures being studied, a glass instru-
ment is used, but it is planned to use an (ill-metal
apparatus when the investigation is extended to
chloride and fluoride melts.
The salt mixtures studied included pure sodium
and potassium nitrates as well as mixtures of the
two in 12.5 w-t % steps. The values obtained for
the pure salts were about 0.3 centipoise above the
data reported by DantumaIf8 who determined the
viscosity by the logarithmic decrement method.
The viscosities of the mixtures nearly overlap at
higher temperatures, being located between the
viscosity curves of the pure components. A plot
of reciprocal temperatures vs the log of viscosity
gave an apparent deviation from linearity near the
melting point of most of the mixtures, while the
pure salts showed a direct linear correlation.
37F. A. Knox, N. V. Smith, and F. Kertesr, ANP
Quar. Prog. Rep. Sept. 10, 1952, ORNL-1375, p 145.
38R. S. Dantuma, 2. anorg. u. allgem. Chem. 175,
33-4 (1928).
75