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

Abstract

Thermal diffusion in the molten systems LiNO3—AgNO3, KNO3—AgNO3, RbNO3—AgNO, and CsNO3—AgNO3 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 AgNO3 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 LiNO3— AgNO3 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 KNO3—AgNO3 system, and about 1.3 × 10-3 degr.-1 over the investigated ranges for the RbNO3—AgNO3 and CsNO3—AgNO3 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 6Li—7Li as well as for 39K—-41K, which is in agreement with previous investigations.