Activated state in the lepidocrocite structure during thermal treatment

Gehring, A. U.; Karthein, R.; Reller, Armin

doi:10.1007/bf01131161

Cited by 28 publications

(30 citation statements)

References 7 publications

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“…Gehring et al (1990) pointed out that the formation of maghemite clusters occurs simultaneously with an enhanced structural distortion of FeO6 octahedra. This state, defined as an activated state in the lepidocrocite structure (Gehring et al, 1990), occurs in the same temperature range where the changes in d-OH modes were detected. Therefore, it is very likely that this activated state is created through weakening of Fe-OH and O-H bonds.…”

Section: Discussionmentioning

confidence: 99%

“…In a recent study, Gehring et al (1990) described an activated state on the molecular level within the lepidocrocite structure prior to the actual evolution of water and the subsequent formation of ferrimagnetic maghemite. This state has been explained as an enhanced distortion of FeO6 octahedra in the lepidocrocite structure caused by the dynamic rearrangement of the position of oxygen and hydrogen atoms.…”

Section: Introductionmentioning

confidence: 99%

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The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

Gehring

Hofmeister

1994

Clays and clay miner.

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118

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Abstract--Infrared (IR) spectroscopy, in combination with magnetic methods, was used to study the thermally induced transformation of synthetic lepidocrocite (3,-FeOOH) to maghemite (~-Fe203). Magnetic analyses showed that the thermal conversion began at about 175"C with the formation of superparamagnetic maghemite clusters. The overall structural transformation to ferrimagnetic'y-Fe203 occurred at 200"C and was complete around 300"C. At higher temperatures, the maghemite converted into hematite (a-Fe203). Observation of the transformation from 3,-FeOOH to "y-Fe203 using variable-temperature IR spectroscopy indicated that dehydroxilation on a molecular level was initiated between 145"C and 155*C. The lag time between the onset of the breaking of OH bonds and the release of H20 from lepidocrocite around 1750C can be explained by diffusive processes. Overall dehydroxilation and the subsequent breakdown of the lepidocrocite structure was complete below 219*(3. The comparison of the magnetic and IR data provides evidence that the dehydroxilation may precede the structural conversion to maghemite.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

Gehring

Hofmeister

1994

Clays and clay miner.

Self Cite

118

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“…Fe nI in an undistorted octahedral ligand field can cause resonance at g = 2 (Gehring et al 1990). Gainon and Lacroix (1962) found such a resonance for structure bound We III in a single crystal of a natural anatase.…”

Section: Electronic Environment Of Fementioning

confidence: 98%

Iron Substitution in Soil and Synthetic Anatase

Schwertmann

1995

Clays and clay miner.

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Abstract--Iron nI for Ti TM substitution in the structure of pedogenic and synthetic anatase of up to Fe/ (Ti+Fe) 0.1 mol/mol was indicated by an increase in unit cell size as measured by XRD line shifts. MiSssbauer-and electron paramagnetic resonance spectra at both, 298 K and 4.2 K supported this by the presence of signals typical for octahedrally coordinated Fe I11 in a diamagnetic matrix. Charge compensation was achieved by structural OH, as indicated by FTIR bands at 3360 and 960 cm -~, which were absent in pure anatase and which disappeared on heating. The weight loss on heating amounted to ca. 0.5 mol H20/mol Fe. At 600~ structural Fe was ejected, the unit cell size decreased to that of pure anatase, and pseudobrookite, Fe2TiOs, was formed.

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“…In addition, ESR spectroscopy was used to analyse the magnetic properties of the solid solution at low temperature. This spectroscopic method detects power absorption by the sample from the transverse magnetic microwave field as function of a dc field and can provide information on the coordination of paramagnetic species and on magnetic ordering [21][22][23]. The principles of this method can be found elsewhere [24,25].…”

Section: Samples and Methodsmentioning

confidence: 99%

“…Considering T c E260 K for the hemo-ilmenite solid solution as determined by ZFC-FC magnetization curves, the broad anisotropic signal at this temperature is explained by FM resonance due to the onset of long-range magnetic ordering [e.g 21,23,24]…”

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confidence: 99%