"The diffusion of ¹³¹I in single crystals and along the tilt grain boundaries of pure and calcium chloride doped (142±5 ppm) bicrystals of sodium chloride, grown by Czochralski technique, was investigated using a microtome sectioning technique. Results on bulk diffusion in pure NaCl agree well with the results of earlier investigators and are represented by the D=(504 cm²/sec)exp (-2.27 ev/kT). Enhanced diffusion of ¹³¹I is observed along the grain boundaries and the presence of the dopant lowers the grain boundary diffusivity over the entire temperature range of 430ºC - 570ºC studied in the present investigation. Thermal activation and electrical polarization effects, acting simultaneously on the diffusing ion, determine the magnitude of the grain boundary diffusivity in these ionic bicrystals. In the low temperature range of 430ºC - 490ºC, the diffusion of ¹³¹I along the grain boundaries is described by the relationship where (D'δ) = (D'δ)ooexp(-Qb/kT), where (D'δ)o has values of 8.45 x 10⁻⁵ and 0.39 cm³/sec for the pure and the doped bicrystals, respectively. Qb is observed to be 1.36 and 1.93 eV for the same two cases. In the high temperature range of 490ºC - 570ºC, grain boundary charge and ionic polarization cause distinct but similar diffusion anomalies in the grain boundary diffusivity plots of both the pure and the doped bicrystals, depending upon the proximity of the measuring temperature to the isoelectric temperature. Grain boundary diffusion seems to occur by movement of ions in the grain boundary core by an "interstitial" motion of iodine ions"--Abstract, pages ii-iii.
Ownby, P. D.
Weart, H. W. (Harry Waldron), 1927-
Clark, J. B. (J. Beverley)
Moore, Robert E., 1930-2003
Materials Science and Engineering
Ph. D. in Metallurgical Engineering
United States. Defense Advanced Research Projects Agency
University of Missouri--Rolla
vii, 79 pages
© 1972 Kulwant Singh Sabharwal, All rights reserved.
Dissertation - Open Access
Kirkendall effect -- Mathematical models
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Sabharwal, Kulwant Singh, "Grain boundary diffusion in ionic crystals" (1972). Doctoral Dissertations. 204.