Electron Spin Resonance Studies of Iron Oxides Associated with the Surface of Kaolins

Angel, B. R.

doi:10.1346/ccmn.1978.0260402

Cited by 82 publications

(51 citation statements)

References 25 publications

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“…A similar reso nance was recognized in some clays and clay minerals (HALL et al, 1974;MEADS and MALDEN, 1975;ANGEL and VINCENT, 1978), micas (KEMP, 1971(KEMP, , 1972 and organic materials containing Fe(III) (WICKMAN et al, 1965;CHESHIRE et al ., 1977;SENESI et al, 1977).…”

Section: Mentsupporting

confidence: 56%

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Electron spin resonance and distribution of some elements in shales

1981

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Five types of ESR signals were observed in shales. The resonance composed of six lines near geff = 2 (type A) is attributed to Mn(II). Type A resonance is divided into two groups on the basis of its line shape; one exhibits six sharp lines (type A-1), and another shows relatively broad lines (type A-2). The geff = 2 broad resonance (type B) may be attributed to Fe(III). The geff = 2 sharp resonance line (type C) probably results from stable organic free radicals. The geff = 4.1 resonance (type D) can be attributed to high spin Fe (III) occupying sites of orthorhombic symmetry in clay minerals. Some of the shales show an inclined signal covering a wide magnetic field (type E).Combination of ESR measurements and leaching experiments made it possible to survey the distribu tion and states of some elements in shales. In shales which exhibit type A-1 resonance overlapped with type A-2 resonance, Mn (II) is randomly distributed both in calcite and clay minerals. In shales which exhibit only type A-2 resonance, Mn (II) is associated mainly with clay minerals. Most of the iron in shales is bound to clay minerals. A part of the iron in clay minerals is present as Fe (III) which shows type D resonance.

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Section: Mentsupporting

confidence: 56%

“…In particular, a number of ESR studies have been made on clay minerals and related materials (KEMP, 1971(KEMP, , 1972ANGEL and HALL, 1973;HALL et al, 1974;MEADS and MALDEN, 1975;ANGEL and VINCENT, 1978). However, ESR spectra of the shale, which is composed of some minerals in cluding clay minerals, have not been examined yet.…”

Section: Introductionmentioning

confidence: 99%

Electron spin resonance and distribution of some elements in shales

1981

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“…Strong baseline perturbations arose from the presence of iron oxides which are always associated with natural kaolinites (Malengreau et al 1994). These oxides are responsible for a broad resonance (AB > 1000 G) which superimposes on the investigated EPR signal, whenever the oxides occur as distinct phases or as coatings (Angel and Vincent 1978;Bonnin et al 1982). Fe oxides have thus been eliminated prior to irradiation, using the complexing dithionite-citrate-bicarbonate (DCB) method (Mehra and Jackson 1960), which has no influence on the kaolinite structure nor the shape and the intensity of the RID spectra (Muller and Calas 1989).…”

Section: Methodsmentioning

confidence: 99%

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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“…In addition, the EPR technique has been applied to the study of clay minerals (Meads and Malden, 1975;Angel and Vincent, 1978;Hall, 1980); dolomites (Lumsden and Lloyd, 1988;Granwehr et al, 2004), volcanic ashes (Pawse et al, 1998), sedimentary organic matter (Aizaenshtat et al, 1986;Díaz et al, 2000;Gonzalez et al, 2002) and marine sediments (Otamendi et al, 2006).…”

Section: Sampling and Experimental Techniquesmentioning

confidence: 99%

Hydrocarbon-induced magnetic contrasts in some Venezuelan and Colombian oil wells

et al. 2006

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In this work we present a review of our current research on the subject of near-surface hydrocarbon-induced magnetic contrasts. Samples are drill cuttings from number of Venezuelan and Colombian oil fields, and some soils from an oil prospective area. Results from rock magnetic, electronic paramagnetic resonance (EPR), extractable organic matter (EOM) and scanning electron microscopy (SEM) are discussed in light of new experiments. Two types of magnetic susceptibility (MS) anomalies have been recognized in oil well samples (i.e. A and B-like). A-like anomalies are probably associated to a reducing environment caused by the underlying reservoirs, whereas B-like anomalies might reflect lithological contrasts. Samples from A-like anomalous levels reveal the restrictive presence of authigenic spherical aggregates of submicronic Fe-rich magnetic crystals. Peaks of organic matter free radical concentration (OMFRC) and EOM are also observed at depth levels that lie close to those with A-like anomalies. Hysteresis ratios J rs /J s and H cr /H c could be used as additional criteria to recognize A-like magnetic contrasts. In soil samples, MS and OMFRC anomalies coincide with peaks of ethane concentration and an area underneath where source rock has reached appropriate conditions of pressure and temperature to generate hydrocarbons (Cretaceous kitchen). Different types of crude oils and subsurface structures could have also a direct effect on the observed amplitude of A-like anomalies.

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Electron Spin Resonance Studies of Iron Oxides Associated with the Surface of Kaolins

Cited by 82 publications

References 25 publications

Electron spin resonance and distribution of some elements in shales

Electron spin resonance and distribution of some elements in shales

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

Hydrocarbon-induced magnetic contrasts in some Venezuelan and Colombian oil wells

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