title: Luminescence and ESR studies of relationships between O(-)-centres and structural iron in natural and synthetically hydrated kaolinites.
abstract: Luminescence, induced by dehydration and by wetting with hydrazine and unsymmetrically substituted hydrazine, and related ESR spectra have been observed from several kaolinites, synthetically hydrated kaolinites, and metahalloysites.  The amine-wetting luminescence results suggest that intercalation, not a chemiluminescence reaction, is the luminescence trigger.  Correlation between hydration-induced luminescence and g = 2 ESR signals associated with O(-)-centres in several natural halloysites, and concurrent diminution of the intensity of both these signal types as a function of aging in two 8.4 angstroms synthetically hydrated, kaolinites, confirm a previously-reported relationship between the luminescence induced by dehydration and in the presence of O(-)-centres (holes, i.e., electron vacancies) in the tetrahedral sheet.  Furthermore, the ESR spectra of the 8.4 angstroms hydrate showed a concurrent change in the line shape of the g = 4 signal from a shape usually associated with structural Fe in an ordered kaolinite, to a simpler one typically observed in more disordered kaolinite, halloysite, and montmorillonite.  Either structural Fe centres and the O(-)-centres interact, or both are subject to factors previously associated with degree of order.  The results question the long-term stability of the 8.4 angstroms hydrate, although XRD does not indicate interlayer collapse over this period.  Complex inter-relationships are shown between intercalation, stored energy, structural Fe, and the degree of hydration which may be reflected in catalytic as well as spectroscopic properties of the clays.
authors.affiliation: Department of Chemistry, San Jose State University, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Coyne
authors.forename: P M
authors.initials: PM
authors.lastname: Costanzo
authors.forename: B K
authors.initials: BK
authors.lastname: Theng
mesh_terms: D000538:Aluminum Silicates / Q000032:analysis* / Q000737:chemistry; D000588:Amines; D000077215:Clay; D004127:Dimethylhydrazines / Q000032:analysis / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D019418:Evolution, Chemical; D006834:Hydrazines / Q000032:analysis / Q000737:chemistry*; D007501:Iron / Q000032:analysis / Q000737:chemistry*; D007616:Kaolin / Q000032:analysis* / Q000737:chemistry; D008163:Luminescent Measurements; D013052:Spectrometry, X-Ray Emission; D014025:Titanium / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D000588:Amines; D004127:Dimethylhydrazines; D006834:Hydrazines; C009495:titanium dioxide; D007616:Kaolin; C029424:hydrazine; D014025:Titanium; D007501:Iron; D000077215:Clay