Carl-Axel Sjöblom

Effect of Frit Material on External Transport Numbers in Molten Salts

Abstract Molten salt external transport numbers have been examined with respect to the possible in-fluence of the frit material. Improved measuring techniques revealed a slight temperature dependence for the transference of PbCl2 in Pyrex frits over the range 529 to 610°C, but generally con-firmed the values obtained by most of the earlier workers who used porous glass or related mate-rials. Within experimental error the figures were found to be identical in Pyrex frits of two different pore sizes. On the other hand, significant deviations were detected when a boron nitride frit was used. These experiments confirm that the transport properties of the interfacial layer between the melt and the solid depend on the nature of the solid.

Plastic deformation of supersonic conductors

Abstract Stress relaxation has been used to investigate the plastic deformation of the supersonic conductors AgI, Li 2 SO 4 , and Li 2 SO 4 - K 2 SO 4 mixtures rich in Li 2 SO 4 . The activation volume for flow is inversely proportional to the effective initial stress, and the proportionality constant is about 50% smaller than in “normal” substances. This fact is attributed to an order-disorder transition in AgI and to the weak steric hindrance for rotation of the lattice units in Li 2 SO 4 (and similar mixtures). The order-disorder transition in AgI is also confirmed by measurements of the maximum shear stress versus shear rate.

Gravimetrie Interdiffusion Studies of the NaNO3—AgNO3 and NaNO3-RbNO3 Fused Salt Mixtures

The interdiffusion coefficient has been measured over the whole range of compositions in the NaNO3 -AgNO3 and NaNO3 - RbNO3 molten salt mixtures, using an improved version of the gravimetric interdiffusion technique. At 340 °C the interdiffusion coefficient is about 2.3 × 10-5 cm2 s-1 in mixtures with a high NaNO3 content. It increases slightly with increasing AgNO3 content and decreases with increasing RbNOs content. Good agreement is found with data obtained with other methods. There is evidence that the interdiffusion coefficient is inversely proportional to the cation radii in the melt. Interionic friction coefficients are calculated. Only three ionic species are present in dilute solutions of AgNO3 and RbNO3 in NaNO3 but there is evidence of “complex ion formation” in dilute solutions of NaNO3 in AgNO3 and in RbNO3.

Self-diffusion in Molten Silver Iodide

Abstract The self-diffusion coefficients of the cation (D+) and of the anion (D-) have been measured in molten silver iodide be tween 580 °C and 620 °C with the porous-frit technique. At 610 °C it is found that D+ = D-=5A × 10-5 cm2 s-1. At the melting point (556 °C) D+ melt (4.4 × 10-5 cm2 s-1) is very close to D+ solid (4.3 × 10-5 cm2 s-1) . The Klemm friction coefficients do not indicate the existence of complex entities. D+ and D- calculated according to the Nernst-Einstein equation agree with observed data within 20%.

Thermal Expansion of Alkali Sulphate Mixtures

The linear thermal expansivities of polycrystalline samples of mixtures of Li2SO4 with K2SO4 and with Na2SO4 have been measured with a “Fused-Quarz Tube” apparatus 1. Phase transitions are accompanied by changes in the expansion coefficient and also by volume changes. The observed expansion coefficient is constant over wide temperature intervals. Simple crystal structures show higher expansivities than more complex structures. The “pre-melting” phenomenon in Li2SO4 does not measurably influence the thermal expansion. A method has been devised to correct the observations for the plastic flow of the crystals close to the melting points

Interdiffusion in Dilute Solutions of Silver Nitrate in Alkali Nitrates

The ordinary diffusion coefficients in dilute solutions of AgNO8 molten in LiNO8, NaNO8, KNO8, RbNO8, and CsNO8 have been measured with a porous frit technique. The results can be summarized in Arrhenius equations: Solvent: LiNO3 DV12 = 7.00 × 10-3 exp{-7270/RT} (272-399°C) NaNO3 DV12 = 2.23 × 10-3 exp{5430/RT} (310-382°C) KNO3 DV12 = 0.354 × 10-3 exp{-3530/RT} (337-386°C) RbNOO3 DV12 = 4.00 × 10-3 exp{-6670/RT} (317-384°C) CsNOO3 DV12 = 2.88 × 10-5 (428°C) where DV12 is expressed in cm2 s-1, R in cal mole-1 degree-1, and T in degrees Kelvin. The results are in good agreement with chronopotentiometric data on the AgNO3—NaNO3 and AgNO3—CsNO3 systems 1 and also with some recent data on the AgNO3—NaNO3, AgNO3—KNO3, and AgNO3 — RbNO3 systems obtained with an optical method 2. Interionic friction coefficients are calculated. Only three ionic species are present in the AgNO3—LiNO3, AgNO3—NaNO3, and AgNO3—KNO3 mixtures while there is evidence of “complex ions” in AgNO3—RbNO3 and AgNO3—CsNO3.

Interdiffusion and Selfdiffusion in Binary Mixtures of Molten Salts

Mutual diffusion coefficients in two fused salt systems have been measured with the gravimetric porous frit technique. The system AgNO3—KNO3 has been investigated for the composition range 50 — 75 mole % AgNO3, and the system AgNO3—NaNO3 for mixtures rich in NaNO3. The selfdiffusion coefficient of the Ag+-ion in AgNO3—KNO3 has been measured with the porous frit technique. A comparison with results obtained by other workers is made.

Notizen: On the Validity of Inter- and Self-Diffusion Measurements in Molten Salts by Methods Applying Multiporous Fritted Discs

A gravimetric method has been used to study interdiffusion in binary mixtures of AgNO3 and KNO3 over the range 50 -75 mole % AgNO3 at tem peratures below 200°C. The obtained cation diffusion coefficients are of the order of 2 × 10-6 cm2 sec-1 i.e. considerably lower than what might have been expected from other diffusion m easurements. It has previously been found that there is a tendency for self-diffusion coefficients obtained with fritted discs to be lower than those obtained with the conventional open-end capillary technique. Some possible sources of error are discussed.

Selbstdiffusion in geschmolzenen Halogeniden

Durch Diffusions-Austausch zwischen einem großen Salzvolumen und radioaktivem Salz in einer feinporigen, gesinterten Platte wurden folgende Selbstdiffusionskoeffizienten gemessen: D+ = 0,080 exp [(-16 900 ± 990) /RT] für ZnBr2 im Bereich 449-555°C und D+ = 0,024 exp [ (-10 150 ± 290) /RT] bzw. D- = 0,017 exp [ (9310 ± 300) /RT] für TlCl im Bereich 437-548°C. Dabei ist D in cm2 sec-1 und R in cal Mol-1 Grad-1 gemessen, und die angegebenen Fehler sind Standardabweichungen. Während das Ergebnis für ZnBr2 in guter Übereinstimmung mit früheren Messungen mit anderen Methoden steht, sind die beiden Aktivierungsenergien des TlCl zweimal größer als nach früheren Messungen. Bei ZnBr2 zeigen sowohl die jetzigen als auch ältere Messungen, daß die sogen. Aktivierungsenergie mit wachsender Temperatur kleiner wird. Die Fehlerquellen der verschiedenen Methoden zur Messung der Selbstdiffusion werden diskutiert, und es werden die KLEMMschen Reibungskoeffizienten für sämtliche bisher untersuchten Halogenide berechnet. Das einfache Modell mit nur zwei Komponenten scheint für die Alkalihalogenide am besten zu passen.