The characterization and thermal transformations of coprecipitated iron(III)-chromium(III)-hydroxide systems☆

VAJPEL, A; Rousset, A.; Uma,; Chandra, K.; Saraswat, I. P.; Mathur, V.K.

doi:10.1016/0167-2738(89)90353-6

Cited by 5 publications

(3 citation statements)

References 9 publications

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“…It is probable that, in this case, V 3+ cations do not replace Fe 3+ to form the complex hydroxide leading to crystallized magnetite, but they induce the formation of amorphous hydroxides. This is similar to the substitution of Fe 3+ by Cr 3+ ions, where it has been reported that incorporation of chromium modifies the microstructure of the precipitates and leads to amorphization, tending to form larger aggregates with a decrease in the size of the primary particles …”

Section: Resultssupporting

confidence: 80%

Synthesis and Stability Region of Stoichiometric Nanocrystalline Vanadium−Iron Spinel Powders

Nivoix

Gillot

2000

Chem. Mater.

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Vanadium−iron spinels with nanometric sizes have been synthesized by a soft chemistry route. This way of elaboration consists of a coprecipitation followed by thermal treatments at low temperatures. The last thermal annealing is performed under a reducing atmosphere in order to obtain the exact oxygen stoichiometry (four oxygen atoms for three metal atoms in AB2O4). Because of the low temperatures used, very low oxygen partial pressures (between 10-20 and 10-30 Pa) have to be applied. For this purpose, a reducing setup has been used. It consists of H2/N2/H2O gas mixtures, creating a reducing atmosphere with low oxygen partial pressure. This atmosphere can be applied to a sample in a thermobalance, so the mass variations are correlated with the oxygen content (or oxygen stoichiometry) in the sample. Thermal annealing under low oxygen partial pressure allows one to obtain stoichiometric spinels of Fe3 - x V x O4 (0 ≤ x ≤ 2).

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Section: Resultssupporting

confidence: 80%

Synthesis and Stability Region of Stoichiometric Nanocrystalline Vanadium−Iron Spinel Powders

Nivoix

Gillot

2000

Chem. Mater.

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“…Information obtained regarding the Fe:Cr ratio (from DCP analysis) was incorporated in the compositions used for PDF normalization. Vajpei et al studied the thermal behavior of coprecipitated Fe(III)−Cr(III) hydroxide series with a synthesis method similar to ours and found gradual changes in weight loss due to hydration within the series. Assuming that the total weight loss is due to the removal of surface or structural water, total hydration information (from TG weight loss analysis) of the Fe end member (Fe10), Cr end member (Cr10), and intermediate composition sample (Fe5Cr5) is used for these three samples as well as for estimating the hydration states of all other samples.…”

Section: Methodsmentioning

confidence: 65%

Structural Properties of the Cr(III)−Fe(III) (Oxy)hydroxide Compositional Series: Insights for a Nanomaterial “Solid Solution”

et al. 2010

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Chromium(III) (oxy)hydroxide and mixed Cr(III)−Fe(III) (oxy)hydroxides are environmentally important compounds for controlling chromium speciation and bioaccessibility in soils and aquatic systems and are also industrially important as precursors for materials and catalyst synthesis. However, direct characterization of the atomic arrangements of these materials is complicated because of their amorphous X-ray properties. This study involves synthesis of the complete Cr(III)−Fe(III) (oxy)hydroxide compositional series, and the use of complementary thermal, microscopic, spectroscopic, and scattering techniques for the evaluation of their structural properties. Thermal analysis results show that the Cr end member has a higher hydration state than the Fe end member, likely associated with the difference in water exchange rates in the first hydration spheres of Cr(III) and Fe(III). Three stages of weight loss are observed and are likely related to the loss of surface/structural water and hydroxyl groups. As compared to the Cr end member, the intermediate composition sample shows lower dehydration temperatures and a higher exothermic transition temperature. XANES analysis shows Cr(III) and Fe(III) to be the dominant oxidation states. XANES spectra also show progressive changes in the local structure around Cr and Fe atoms over the series. Pair distribution function (PDF) analysis of synchrotron X-ray total scattering data shows that the Fe end member is nanocrystalline ferrihydrite with an intermediate-range order and average coherent domain size of ∼27 Å. The Cr end member, with a coherent domain size of ∼10 Å, has only short-range order. The PDFs show progressive structural changes across the compositional series. High-resolution transmission electron microscopy (HRTEM) results also show the loss of structural order with increasing Cr content. These observations provide strong structural evidence of chemical substitution and progressive structural changes along the compositional series.

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“…Solubility and structure studies have also suggested that the Cr(III)-Fe(III)-hydroxide phase is stable during the fast precipitation of Cr(III) and Fe(III) aqueous ions (Sass and Rai, 1987;Vajpei et al, 1989;Amonette and Rai, 1990;Tang et al, 2010). We are not aware of any study reporting separate Cr(III)-and Fe(III)-hydroxide phases during the redox reaction between Cr(VI) and Fe(II) or the co-precipitation of Cr(III) and Fe(III).…”

Section: Reaction Products In the Presence Of Cr(vi)mentioning

confidence: 94%

Siderite dissolution in the presence of chromate

Tang

Martin

2011

Geochimica et Cosmochimica Acta

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The characterization and thermal transformations of coprecipitated iron(III)-chromium(III)-hydroxide systems☆

Cited by 5 publications

References 9 publications

Synthesis and Stability Region of Stoichiometric Nanocrystalline Vanadium−Iron Spinel Powders

Synthesis and Stability Region of Stoichiometric Nanocrystalline Vanadium−Iron Spinel Powders

Structural Properties of the Cr(III)−Fe(III) (Oxy)hydroxide Compositional Series: Insights for a Nanomaterial “Solid Solution”

Siderite dissolution in the presence of chromate

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