Effect of Adsorbed Iron on Thermoluminescence and Electron Spin Resonance Spectra of Ca-Fe-Exchanged Montmorillonite

Lelia M. Coyne and Amos Banin
Department of Chemistry, San Jose State University San Jose, California 95192 and NASA-Ames Research Center, Mail Stop 239-4 Moffett Field, California 94035
Seagram Center for Soil and Water Sciences The Hebrew University, Rehovot, Israel, and Department of Chemistry, San Francisco State University San Francisco, California 94132

Abstract: The electron spin resonance (ESR) spectra and the natural and gamma-induced thermoluminescence (TL) glow curves of a series of variably cation-exchanged Fe-Ca-clays prepared from SWy-1 montmorillonite were examined. The ESR signal (g = 2) intensity associated with the surface Fe was found to increase linearly with surface Fe content up to a nominal concentration of 50% exchangeable Fe. At > 50% exchangeable Fe, no appreciable increase in the signal was noted. The TL intensity decreased linearly with increasing surface Fe up to 50% nominal exchangeable Fe. At > 50%, the signal was not appreciably further diminished. The natural TL showed only a high-temperature peak, but irradiation produced an additional low-temperature peak. One month after gamma-irradiation, the integrated TL signal was still 10–100 times higher than that from the non-irradiated material. Thus, (1) surface iron clusters may form above a certain critical Fe concentration; (2) the Fe clusters are probably less effective in quenching TL than are single Fe atoms, implying interaction between surface Fe and the stored energy content of the material; and (3) the electronic energy stored in the material as the result of gamma-irradiation is only slowly dissipated.

Key Words: Electron spin resonance • Iron • Montmorillonite • Surface adsorption • Thermoluminescence

Clays and Clay Minerals; December 1986 v. 34; no. 6; p. 645-650; DOI: 10.1346/CCMN.1986.0340604
© 1986, The Clay Minerals Society
Clay Minerals Society (www.clays.org)