Electron spin resonance studies of doped synthetic kaolinite. II

Jones, J. P. E.; Angel, B. R.; Hall, Peter G.

doi:10.1180/claymin.1974.010.4.04

Cited by 75 publications

(52 citation statements)

References 18 publications

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“…They have been noted Si-O--centers by reference to the Marfunin's systematics (Marfunin 1979). The Q-band orientation dependance demonstrates that the g~ component is oriented perpendicular to the (ab) plane (Figure 6), as stated previously from X-band spectra by Jones et al (1974). While the g-values for A-centers remain constant in natural kaolinites, the half-width of the g// component varies slightly among the samples within 0.7-1.3 roT.…”

Section: Evidence For One Type Of Al-o--al Center (B-center)supporting

confidence: 74%

Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works

Clozel

Allard

Müller

1994

Clays and clay miner.

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Abstract--A new appraisal of radiation-induced defects (RID) in natural kaolinite, i.e., positive trapped holes on oxygen atoms, has been undertaken using Q-band EPR spectra, recorded at 93 K, of irradiated annealed and oriented kaolinite samples originating from various environments. Three different centers were identified. Two of the centers, A-and A'-centers, are trapped holes on oxygen from Si-O bonds. They have a distinct signature and orthogonal orientation, i.e., perpendicular and parallel to the (ab) plane, respectively. The third center, the B-center, is a hole trapped on the oxygen bonding A1 in adjacent octahedral positions (Alv~-O--Alw bridge). This confirmed some previous assignments from the literature, some others are no longer considered as valid.A least squares fitting procedure is proposed to assess the RID concentration in any kaolinite. It allows a quantitative approach of the thermal stability of RID. Isochronal annealing shows that the thermal stability of the centers decreases in the order A, A', B over the temperature range 0-450~ (1) B-center is completely annealed above 300~ (2) A'-center can be annealed by heating at 400~ for more than two hours; (3) A-center is stable up to 450~ The activation energy and the magnitude of the mean halflife for A-center is evaluated through isothermal annealing at 350, 375 and 400*(2, with Ea = 2.0 eV + 0.2, and tv, > l0 ~2 years at 300 K. The stability of A-center seems to decrease with increasing crystalline disorder. Nevertheless, it is high enough for radiation dosimetry using kaolinites from any environment on the Earth's surface.

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Section: Evidence For One Type Of Al-o--al Center (B-center)supporting

confidence: 74%

Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works

Clozel

Allard

Müller

1994

Clays and clay miner.

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“…The ESR features of the clays studied (Fig. 7a, b) do not resemble those generally reported for kaolinite Jones et al, 1974;Meads & Malden, 1975;Herbillon et al, 1976;Mestdagh et al, 1980) and halloysite (Meads & Malden, 1975;Carr et al, 1977;Nagasawa & Noro, 1987;Chaikum & Carr, 1987). A broad g2 band is observed on all the spectra while a weak g4 band only appears on some ESR diagrams.…”

Section: Esr Spectramentioning

confidence: 53%

Surface properties and clay mineralogy of hydrated halloysitic soil clays. II: Evidence for the presence of halloysite/smectite (H/Sm) mixed-layer clays

Delvaux¹,

Herbillon

Vielvoye

et al. 1990

Clay miner.

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A B S TRACT:Six clays from volcanic ash soils at different stages of weathering differ in their relative halloysite content with respect to kaolinite and several surface properties, namely CEC, and exchange selectivity for K +. These three parameters are related to each other in that they all decrease with increasing soil weathering stage. XRD data show that the hydrated 1 : 1 layer-silicates in these clays combine with smectite to form interstratified H/Sm clay minerals. In these mixed-layers, the content and layer charge of smectitic units decrease as the relative halloysite content in the clay decreases. These clays thus depict a weathering sequence that is parallel to the weathering sequence of the soils from which they originate. It is also shown that the smectites in the H/Sm minerals have the distinctive composition and ESR spectrum of Fe-rich 2:1 clay minerals belonging to the beidellite-nontronite series. The information obtained explains why these clays have high CEC and distinct affinities for K + . It is hoped that this study will help to clarify the controversy concerning the CEC and related surface properties attributed to hydrated halloysite.

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“…Electron paramagnetic resonance (EPR) and Mrssbauer spectroscopy have been used frequently to study Fe 3+ in kaolinite (Boesman and Schoemaker, 1961;Jones et al, 1974;Meads and Malden, 1975;Jefferson et al, 1975;Angel et al, 1977). The present work attempts to relate the type of EPR spectrum observed to the form of iron in the kaolinite (iron in ionic substitution; adsorbed iron on the surface of kaolinite plates; separate iron minerals as impurities).…”

Section: Introductionmentioning

confidence: 99%

Application of Electron Paramagnetic Resonance and Mössbauer Spectroscopy in the Investigation of Kaolinite-Group Minerals

Komusinski¹,

Stoch²,

Dubiel

1981

Clays and clay miner.

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Abstract--Samples of nacrite, dickite, kaolinite, and halloysite were investigated using X-band electron paramagnetic resonance (EPR) and Mbssbauer spectroscopy. Fe 3+ gave rise to EPR signals at g = 4 which differed with the individual polytype. Only nacrite had no resonance in this region of the spectrum, but it had one at g ~ 2. Dickite had a quadruple line, kaolinite a triple line, and halloysite a single line in this region. The EPR spectra of these minerals are apparently dependent also on the orientation of adjacent layers in the structures. Other resonances were attributed to (1) clusters of ferric ions giving rise to broad resonance near g = 2, (2) trapped holes, and (3) free radicals linked with organic matter. The Mbssbauer spectroscopic results suggest that iron occurs in the ferric state (except in nacrite where Fe 2+ is present also) as an ionic substitution (IS) in octahedral layers. This suggestion follows from the difference is the IS values between octahedral and tetrahedral symmetry sites occupied by Fe a+ equal to -0.4 mm/sec. Linewidths depend mainly on the way the layers stack; for monoclinic modifications represented by nacrite and dickite, the linewidths are narrow (F = 0.45 mm/sec and 0.56 mm/sec, respectively); pseudomonoclinic halloysites also gave narrow linewidths (F = 0.39 mm/sec and 0.48 mm/sec). The widest line was observed for triclinic kaolinite (F = 0.62 mm/sec and 0.71 mm/sec).

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Electron spin resonance studies of doped synthetic kaolinite. II

Cited by 75 publications

References 18 publications

Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works

Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works

Surface properties and clay mineralogy of hydrated halloysitic soil clays. II: Evidence for the presence of halloysite/smectite (H/Sm) mixed-layer clays

Application of Electron Paramagnetic Resonance and Mössbauer Spectroscopy in the Investigation of Kaolinite-Group Minerals

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