ESR-SPECTRA OF OXYGEN RADICAL-IONS IN KAOLINITE

The oxygen adsorbed on the surface of oxide systems may be stabilized as O{sub 2}{sup {minus}} radical-ions. This form of stabilization has been studied extensively by ESR spectroscopy for various catalytic systems. These radical-ions may also be stabilized in the structure of crystals as point defects. The existence of paramagnetic sites in kaolinite has long been known. Various workers have studied ESR spectra in kaolinites. However, no uniform opinion has emerged concerning the nature of the paramagnetic sites. Mank has carried out a detailed study of ESR spectra in kaolinites. The observed ESR signals were assigned to the paramagnetic form of oxygen O{sup {minus}}, stabilized on Al{sup 3+} and the hydroxyl radical. The possibility of other paramagnetic oxygen forms distributed in defects of the mineral structure was also noted. In light of the importance of the study of defects in the structure of silicate systems, the authors investigated the ESR signals of natural kaolinites in order to elucidate the fine details of these spectra and elucidate the nature of the point defects. 7 refs., 2 figs.