SELF-DIFFUSION OF Ag$sup +$ AND Na$sup +$ IN MOLTEN Ca(NO$sub 3$)$sub 2$-- KNO . Page: 6 of 34
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on a short tine scale must be found. One possibility would be the MMR
pulse echo method which has been used to follow diffusion coefficients to very
low values in supercooled o-terphenyl (Lo). However, this technique requires
considerable specialized equipment. An alternative approach for short time
scale diffusion coefficient determinations is provided by electrochemical
methods in which electrodeposition rztes of a suitable 4lectroactive species
are limited by its diffusivity. A convenient electrochemicaL technique which
has been applied to molten salts by a number of authors (LLY is chronopoten-
tionetry, in which one determines the tine taken, during passage of a constant
current, for the potential. of the electrode to rise above the value for the
There has, however, been some doubt that electrochemical methods have
been free from all sources of systematic error (12) in their application to
molten salts. It has been found (13,14) that deviations from the Sand
equation (15) can occur due to kinetic complications for the electrodeposition
reaction, as well as the normal design and mass transfer considerations (11).
However, Laity and McIntyre (16) have 'demonstrated that in absence of the
kinetic complications diffusion coefficients determined by chronopoten-
tiometry should be identical with self-diffusion coefficients providing the
required experimental precautions are taken.
In this work we have $tudied the diffusion of Ag in molten Ca(1O83)2 -
KI)S in stabLe and supercooLed conditions using both tracer and chrono-
potentiometric techniques. We show that in the temperature range in which
tracer methods arc practicabLe the chronopotentioxetric data agree with the
tracer data !ithia, the uncertainty limits of the two techniques. Using the
electrochemical technique, however, we have been abLe to extend the
diffusivity data by an order of magnitude, covering in total values from
7.61 -5 Cm see down to xl&"l cm sec'. Tracer data for the Na ion,
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Welch, B. J. & Angell, C. A. SELF-DIFFUSION OF Ag$sup +$ AND Na$sup +$ IN MOLTEN Ca(NO$sub 3$)$sub 2$-- KNO ., report, January 1, 1970; Lafayette, Indiana. (https://digital.library.unt.edu/ark:/67531/metadc1029789/m1/6/: accessed May 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.