Transformation of Trace Element-Substituted Maghemite to Hematite

Sidhu, P. S.

doi:10.1346/ccmn.1988.0360105

Cited by 102 publications

(66 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Hanesch and Scholger (2005) (Jordanova and Jordanova, 1999). The transformation of goethite or ferrihydrite to maghemite takes part during heating (Nørnberg et al, 2004) at temperatures as low as 220°C (Sidhu, 1988). Zanelli et al (in press) observed in-situ formation of maghemite up to 0.5 m deep in soils affected by forest fires in Southern Switzerland.…”

Section: Charred Organic Matter As Colouring Agentmentioning

confidence: 99%

Pedogenesis of Chernozems in Central Europe — A review

Gerlach²,

et al. 2007

View full text Add to dashboard Cite

Since Dokuchaev's investigations of Russian Chernozems, Central European Chernozems were established as steppe soils, with their pedogenesis dominated by humus accumulation as a result of dry continental climate and steppe vegetation, with carbonaceous parent material and bioturbation as other prerequisites. The WRB-FAO classification defined Chernozems by their morphological characteristics, but was biased by the climo-genetic formation model. However, the assumption that modern Central European Chernozems are relics of steppe soils conflicts with palaeobotanical evidence from an early reforestation that started in the Late Glacial, and also with pedological studies that dated Chernozem formation to the Early Holocene. In this review we compile the most important literature on pedogenesis of Central European Chernozems since the 1920s, according to the soil forming factors climate, time, vegetation, relief and man. Our review demonstrates that there is no consensus on the factors controlling the formation, conservation and degradation of Central European Chernozems in published literature. We found that (1) no absolute time of formation could be stated so far, and that (2) Central European Chernozems formed not only under steppe but also under forest vegetation; (3) the spatial distribution of Chernozems and Phaeozems did not correlate with climate conditions or topographic position, and (4) until now no other factors were considered to be responsible for Chernozem development. Recent studies showed that these unknown factors could include anthropogenic activity and vegetation burning as they could form black soils or strongly affect the composition of soil organic matter. We concluded that not all soils classified as Chernozems in Central Europe are steppe soils and thus, as they do not necessarily reflect past climate, the classification may be misleading. Pedogenesis of Chernozems inCentral Europe -A review Eileen Eckmeier a AbstractSince Dokuchaev's investigations of Russian Chernozems, Central European Chernozems were established as steppe soils, with their pedogenesis dominated by humus accumulation as a result of dry continental climate and steppe vegetation, with carbonaceous parent material and bioturbation as other prerequisites. The WRB-FAO classification defined Chernozems by their morphological characteristics, but was biased by the climo-genetic formation model. However, the assumption that modern Central European Chernozems are relics of steppe soils conflicts with palaeobotanical evidence from an early reforestation that started in the Late Glacial, and also with pedological studies that dated Chernozem formation to the Early Holocene.In this review we compile the most important literature on pedogenesis of Central European Chernozems since the 1920s, according to the soil forming factors climate, time, vegetation, relief and man.Our review demonstrates that there is no consensus on the factors controlling the formation, conservation and degradation of Central European Chernozems in pub...

show abstract

Section: Charred Organic Matter As Colouring Agentmentioning

confidence: 99%

Pedogenesis of Chernozems in Central Europe — A review

Gerlach²,

et al. 2007

View full text Add to dashboard Cite

show abstract

“…Increasing χ LF values may be due to remnant maghemite components that maintain magnetism, although XRD data only points to the presence of hematite. Increasing Al IS changes the temperature of the solid phase thermal transformation from maghemite to hematite (Sidhu, 1988); therefore even long exposure of maghemites to 500 °C temperature was not able to completely transform maghemite to hematite, and this effect was more pronounced as IS increased.…”

Section: Mass Specific Magnetic Susceptibilitymentioning

confidence: 98%

“…This temperature was chosen based on differential thermal analysis (DTA) and on literature results (Sidhu, 1988). The mullite refractories were placed on a steel tray and then heated.…”

Section: Maghemite-to-hematite Transformationmentioning

confidence: 99%

“…The samples remained in the furnace for different times: 0,5,10,16,64,128,192,360,720,2160,3600,5040, and 6480 min. After that, they were withdrawn and immediately cooled (the tray was placed on ice) to interrupt further reactions (Sidhu, 1988) and then kept in plastic containers.…”

Section: Maghemite-to-hematite Transformationmentioning

confidence: 99%

“…This increasing resistance to color change with increasing IS and the differences in the initial (maghemite) and final (hematite) colors follow the same reasoning used to explain phase alteration. It is evident that higher temperatures (Sidhu, 1988) or longer heating periods are necessary for the solid state maghemite-to-hematite transformation when the minerals have undergone isomorphic substitution.…”

Section: Colormentioning

confidence: 99%

See 2 more Smart Citations

Thermal Transformation and Characterization of Synthetic Al-Substituted Maghemites (γ-Fe2-xAlxO3)

Nonaka

Batista

Inoue

et al. 2016

Rev. Bras. Ciênc. Solo

View full text Add to dashboard Cite

ABSTRACT:Burning is a common practice in tropical areas and related changes in mineralogy might affect the chemical and physical behavior of soils. Maghemite is a common iron oxide in soils formed from basic rocks in tropical regions. This mineral and hematite are the main pigments in these soils and exhibit high magnetization stemming from the precursor magnetite formed during the weathering process of primary minerals. The objective of the present study was to analyze changes in color, magnetic suceptibility values, Fourier transform infrared spectroscopy (FTIR) spectra, and available Fe and Al contents extracted with 1 mol L -1 KCl during the process of thermal transformation of synthetic Al-maghemites into Al-hematites. Synthetic substituted maghemites with different degrees of Al-substitution (0.0, 1.0, 2.0, 2.9, 3.8, 5.6, 6.7, 10.0, 12.0, and 17.1 mol% Al) were subjected to a temperature of 500 ± 10 °C for 0, 5, 10, 16, 64, 128, 192, 360, 720, 2160, 3600, 5040 and 6480 min. The color of the samples was analyzed by a Munsell system in a colorimeter. Mass-specific magnetic susceptibility (χ LF ) was measured at low-frequency. Available Fe and Al contents were estimated by a 1 mol L -1 KCl solution. Fourier transform infrared spectroscopy (FTIR) spectra were obtained through use of a Bruker Vertex 70X FTIR spectrophotometer at a spectral resolution of 4 cm -1 . Contents of Fe and Al extracted by 1 mol L -1 KCl in Al-hematites were not detected. All samples analyzed exhibited YR hue. Hue proportion decreased with increased heating time, and color changed from brown to red. The increase in isomorphic substitution (IS) led to increased hue values from maghemite to hematite, and the latter then became yellower. The χ LF values decreased with an increase in heating time, indicating transformation from a ferrimagnetic phase (maghemite) to an antiferrimagnetic phase (hematite). With increasing IS, the maghemite χ LF values decreased. Bands of the initial members (time 0) in the FTIR spectra were indexed as maghemites. The end members after completion of the heat treatment were identified as hematites. The IS of Fe by Al in maghemite influenced the thermal transformation to hematite, as well as the color and χ LF of the minerals. The χ LF proved to be very efficient in detecting maghemites remaining after thermal processing. Fe and/or Al were not ejected from the hematite crystalline structure after heat treatment.

show abstract

Simultaneously Enhancing Stability and Activity of Maghemite via Site‐Specific Ti(IV) Doping for NO Emission Control

Chen

et al. 2018

ChemCatChem

View full text Add to dashboard Cite

Maghemite (γ‐Fe2O3) is an environmentally benign catalyst for selective catalytic reduction (SCR) of NO with NH3, but its poor stability and low activity hamper its application in real NO emission control. Herein, we developed a stable Ti4+ doped γ‐Fe2O3 catalyst (Ti‐γ‐Fe2O3) by site‐specific Ti4+ doping at the octahedral sites rather than tetrahedral active sites (Fe3+Td), as substantiated by synchrotron room‐temperature X‐ray diffraction (SXRD) data. In situ SXRD and thermogravimetric analysis (TG) data demonstrate that Ti4+ cations occupying part of the octahedral sites lead to enhanced thermal stability of Ti‐γ‐Fe2O3 with respect to γ‐Fe2O3, thus enabling Ti‐γ‐Fe2O3 to stably operate at 400 °C under simulated normal SCR conditions. Fe L3‐edge and O K‐edge X‐ray absorption spectra show that the high‐valence Ti4+ doping lengthens the Fe3+Td‐O bonds, and activates the lattice oxygen species, thus improving the SCR activity. This work provides a feasible strategy for designing environmentally benign Fe2O3‐based SCR catalysts with significant stability and high catalytic activity.

show abstract

Transformation of Trace Element-Substituted Maghemite to Hematite

Cited by 102 publications

References 14 publications

Pedogenesis of Chernozems in Central Europe — A review

Pedogenesis of Chernozems in Central Europe — A review

Thermal Transformation and Characterization of Synthetic Al-Substituted Maghemites (γ-Fe2-xAlxO3)

Simultaneously Enhancing Stability and Activity of Maghemite via Site‐Specific Ti(IV) Doping for NO Emission Control

Contact Info

Product

Resources

About