The chlorine ion diffusion in potassium chloride

The diffusion coefficient of the chlorine ion in Harshaw potassium chloride crystals and in potassium chloride crystals containing strontium has been measured. The measurements were made with radioactive chlorine 36 and sectioning techniques. The chlorine ion diffusion coefficient of the Harshaw single crystals is well represented by D == Doexp(-W!kT) cm2/sec from 560°C to 760°C. The value of W was found to be 2.12 + 0.05 eV and D was found to be 61 cm 2 /sec. The un- ~ , 0 certainty in the value of W produces a corresponding uncertainty in Do from 34 cm2/sec to 110 cm2/sec. The diffusion data for the crystals containing strontium were not explicable on the basis of a single anion vacancy mechanism alone. The assumption that the diffusion of the chlorine ion occurs by a vacancy pair mechanism and a single anion vacancy mechanism is in good agreement with the experimental data and the diffusion parameters obtained are in good agreement with their theoretical values. Based on this assumption the diffusion coefficient of the chlorine ion in KC1 is expressed as D = Da n1.. on + D pal.. rs The following results were obtained: Danion = 36.51 exp(-2.l05 eV/kT) cm 2 /see D . = 8.561 x 10 3 exp(-2.654 eV/kT) cm 2 /see. pa1.rs This analysis also permitted the determination of the fractional concentration of vacancies in pure KCl, no' which was found to be n ;: 43.91 exp{-2.313 eV!2 kT). o The subtraction of the exponent in the no equation from the exponent in the Danion equation gives the jump activation energy of a single anion vacancy the value 0.948 eVe In this analysis the low temperature data from the regions where the log D versus 1fT curves have positive curvature were omitted. The regions of po~itive curvature were the Harshaw data for temperatures below 560°C and the data from the crystal containing 469 parts per million mole fraction strontium for temperatures below 645°C. The possibilities of this anomalous behavior arising from dislocation effects or impurity effects are discussed.U of I OnlyThesi