Thermal Diffusion in Molten Binary Mixtures of Silver Nitrate with Alkali Nitrates

Thermal diffusion in the molten systems LiNO 3 —AgNO 3 , KNO 3 —AgNO 3 , RbNO 3 —AgNO, and CsNO 3 —AgNO 3 was detected by means of chemical analysis. Two types of cells were used: the elementary effect was measured directly in cells with vertical temperature gradients, and the coefficient of thermal diffusion (D') was estimated from the steady-state separation obtained in convection cells (horizontal temperature gradient). A discussion of possible sources of error shows for both methods that the results might be systematically lower than corresponding to ideal conditions. In all systems AgNO 3 was enriched at the cold side. There are indications that the SORET-coefficient varies with the composiiton of the mixture and the temperature. Thus for the LiNO 3 — AgNO 3 system, depending on the conditions, the SORET coefficient ranged from 2 × 10 -3 to 5.5 × 10 -3 degr. -1 , while it was about 1.8 × 10 -3 -5 degr. -1 over a wide concentration range for the KNO 3 —AgNO 3 system, and about 1.3 × 10 -3 degr. -1 over the investigated ranges for the RbNO 3 —AgNO 3 and CsNO 3 —AgNO 3 systems. Also isotope effects were measured with the convection cell, giving SoRET-coefficients of the order of 10 -5 to 4 × 10 -5 degr. -1 for 6 Li— 7 Li as well as for 39 K— -41 K, which is in agreement with previous investigations.