Graduate Thesis Or Dissertation
 

A study of simultaneous diffusion of Ca²⁺ and Sr²⁺ in alkali chlorides

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  • The simultaneous diffusion of Ca 2+ and Sr 2+ ions in purified single crystals of KC1 and NaC1 was studied over the temperature ranges from 451°C to 669°C in KC1 and from 448°C to 683°C in NaCl. A radioactive tracer technique was used in two types of measurements: diffusion from a deposited surface layer of CaC12 and SrC12 at temperatures below 580° C (the lowest melting eutectic) in the KC1 system and below 500° C in the NaC1 system, and diffusion from CaC12 and SrC1 vapors above 580° C in KC1 and above 500° C in NaCl. The saturation diffusion coefficients, enthalpies and entropies of impurityvacancy association were calculated using the common ion model for simultaneous diffusion of divalent ions in alkali halides. The saturation diffusion coefficients Ds(Ca) and Ds(Sr) in KC1 are given by Ds (Ca) = 9.93 x 10-5 exp( -0.592 eV/kT) cm2/sec and Ds(Sr) = 1.20 x 10 3 exp(-0.871 eV /kT) cm2/sec for calcium and strontium, respectively. The Gibbs free energy ofassociation of the impurity-vacancy complex in KC1 for calcium can be represented by G(Ca) = -0.507 eV + (2. 25 x 10 -4 eV /°K)T and that for strontium by G(Sr) = -0.575 eV + (2.90 x 10-4 eV /°K)T. In NaC1 the saturation diffusion coefficients D s(Ca) and Ds(Sr) and are given by Ds(Ca) = 1.14 x 10-3 exp(-0.851 eV/kT)cm2/sec Ds(Sr) = 2.30 x 10-3 exp( -0. 925 eV /kT)cm2/secs for calcium and strontium, respectively. The Gibbs free energy of association of the impurity-vacancy complex in NaC1 for calcium can be represented by G(Ca) = -0.572 eV + (2. 69 x 10-4 eV/°K)T and that for strontium by AG(Sr) = -0.671 eV + (3.35 x 10 -4 eV/°K)T.
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