Strong evidence of an isotope effect in the diffusion of a NaCl and CsCl solution

Abstract

The existence of isotope effect in liquid diffusion is thoroughly investigated in aqueous solutions of NaCl and CsCl. The tracer difFusion coefFicients with difFerent isotopes of the same species are measured by the sliding-cell technique. The experimental data shower strong evidence of the existence of an isotope efFect in the difFusion of a NaCl and CsCl solution.The phenomenon of diffusion, a fundamental rate process occurring in every physicochemical reaction, is a subject of great topical interest. There is a well-known controversy about the existence of the isotope effect in liquid diffusion and still today it is not known whether this effect can be neglected or not. Many experimental investigations were carried out in this field, but none of them could provide conclusive evidence in favor of the isotope effect. The radioactive tracer technique is one of the sensitive tools which involves the use of isotopically labeled radioactive species for the measurement of the diffusion coeKcients in liquids. If the isotope effect has any contribution, the mass change due to the labeling of the molecules with suitable radioactive isotopes will cause the measured tracer diffusion coefFicient to differ from the true self-diffusion coefFicient. This aspect needs a thorough investigation with different liquid systems. We chose the aqueous solution of the two most interesting binary electrolytes, NaCl and CsCl, in one of which the cations (Na) has a structure-forming capacity and other (Cs) has a structure-breaking capacity. This enables us to study the isotope effect in binary electrolytes of opposite cationic properties. An appreciable difference in the tracer diffusion coefFicients of different isotopes for the same system at the same concentration is found which provides strong evidence for the existence of the isotope effect in the diffusion of aqueous NaCl and CsCl.A critical survey through the literature about previous studies on the isotope effect reveals that Miller's work of isotopic separation of lithium isotopes by diffusion in an aqueous solution leads to the conclusion that the lighter isotope ( Li) diffuses more rapidly than the heavier isotope ( Li). The observation is congruent with the findings of some other groups from their work on liquid Li and Li. The ratios of the self-diffusivities of Li and Li are found to be significantly greater than the square root of the inverse mass ratio. Feinauer et Ol. have parametrized the isotope effect from diffusivity studies on Li and Li. Their values are compatible with the ratio of self-diffusivities of Li and "Li as obtained from a quantum mechanical calculation by Omini based on the pseudopotential method. Pikal studied the diffusion coefficient ratio of the ions Na and Na in a 0.1M NaCl solution and found that the lighter isotope diffused slightly more rapidly than the heavier one, the ratio of the diffusion coefFicient of Na to Na being 1.002. He also found that the ratio to be 1.004 for sodium diffusion in 10M LiBr solution. These works show (Dt -Dh) Conc.

Glass transition temperature of Pd–Cu–Ni–P thin film metallic glass—a 2D approach

“…Far above the glass transition temperature liquid like viscous flow prevails via atomic collisions. Studies of the isotope effect of diffusion [33] reveal a transition from large isotope effects in the ordinary liquid state [34] to very small ones in the supercooled state, similar to those observed by experiments in the glassy state. A thorough literature survey reveals that the logarithm of the pre-exponential factors and the activation enthalpies for diffusers bear a linear relationship for solute diffusion in crystalline metals.…”

Isotopic mass dependence of metal cation diffusion coefficients in liquid water

“…From a geochemical perspective, our results further suggest that, if nano-confinement attenuates hydrodynamic modes, isotope fractionation may be enhanced in water-filled nanopores, an effect already apparent in available data on CH 4 diffusion in smectite clays (Pernaton et al, 1996) vs. sandstone (Schloemer and Krooss, 2004) and on Li + diffusion in dialysis membranes (Fritz, 1992) or grain boundaries (Teng et al, 2006) vs. bulk liquid water (Richter et al, 2006). (Chakrabarti, 1995;Rodushkin et al, 2004) were not included in Table 1. Simulation values of β were obtained by linear regression of log D vs. log m as in Fig.…”

Comment on “Modeling sulfur isotope fractionation and differential diffusion during sulfate reduction in sediments of the Cariaco Basin” by M.A. Donahue, J.P. Werne, C. Meile and T.W. Lyons

“…(Chakrabarti, 1995;Rodushkin et al, 2004) or D i /D j values estimated by fitting an assumed transport model to geochemical data (Desaulniers et al, 1986;Groen et al, 2000;Gussone et al, 2003) or to data on coupled advection and diffusion through semi-permeable membranes (Fritz, 1992). a D heavy /D light estimated by Richter et al (2006) from the ionic conductivity data of Kunze and Fuoss (1962).…”