Characterization and thermal transformation of ferric oxide hydrate gel

Saraswat, I. P.; Vajpei, A. C.; Garg, V. K.; Sharma, Vijay Kumar; Prakash, Nam

doi:10.1016/0021-9797(80)90083-1

Cited by 33 publications

(14 citation statements)

References 11 publications

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“…Therefore what is seen on the SEM image is probably rounded aggregates with large internal surface areas. The calculated mean spherical diameter of the 2-line ferrihydrite of 6.6 nm is in the same range as that found by other workers from TEM images (6,7,15). For goethite and lepidocrocite, the equivalent spherical diameter proves a poor measure of the crystal dimensions.…”

Section: Figsupporting

confidence: 52%

“…The calculated equivalent spherical diameter of 6.6 nm (Table 3) is, however, less than the observed diameter of 35-50 nm. Other workers have found that synthetic 2-line ferrihydrite is heavily aggregated, and single crystals are difficult to identify (7,8,15). Therefore what is seen on the SEM image is probably rounded aggregates with large internal surface areas.…”

Section: Figmentioning

confidence: 93%

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BET Measurements: Outgassing of Minerals

Clausen

Fabricius

2000

Journal of Colloid and Interface Science

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Section: Figsupporting

confidence: 52%

Section: Figmentioning

confidence: 93%

BET Measurements: Outgassing of Minerals

Clausen

Fabricius

2000

Journal of Colloid and Interface Science

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“…From the current study and other studies (Fischer and Schwertmann, 1975;Barron et al, 1984;Serna and Iglesias, 1986;Serna et al, 1987;Sidhu, 1988), the IR vibrations of hematite are dependent on the panicle size and morphology of the product. The pseudohematite reported by Saraswat et al (1980) and Cornejo (1987) may actually be a small particle size or lesscrystalline hematite. The particle size and morphology of the hematite product of any transformation reaction is dependent on the precursor (including mineral form and the presence of coprecipitated or adsorbed phases) and the conditions of transformation.…”

Section: Discussionmentioning

confidence: 88%

“…Rendon and Serna (1981) found that hematite formed by the thermal transformation of goethite at 300~ gave IR bands at 650, 525, 440, and 300 cm -t, and that the hematite formed by heating goethite at 600~ gave an additional band at 400 cm -l. Serna et al (1987), using classical theory of absorption of IR radiation by small particles, concluded that the differences in IR bands of hematite were largely dependent on particle morphology. Saraswat et al (1980) reported the formation of an intermediate-phase pseudohemarite upon heating ferrihydrite to 250 ~ to 3000C, based on the comparison of the IR bands to those of wellcrystallized hematite formed at temperatures > 350~ Corjeno (1987) also suggested the name pseudohematite for a product formed by heating ferrihydrite at 150~ for 24 hr.…”

Section: Introductionmentioning

confidence: 99%

Infrared Vibrations of Hematite Formed from Aqueous- and Dry-Thermal Incubation of Si-Containing Ferrihydrite

Vempati

1990

Clays and clay miner.

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Abstract--Ferrihydrite samples having Si/Fe molar ratios ranging from 0 to 1 were synthesized by the reaction of Fe2(SO4)3 and Na2SiO3 with NaOH to an equilibrium pH of 8.2. Hematite formed by incubating the ferrihydrite (Si/Fe molar ratios <-0.05) at pH 12.5 and 91~ for 36 hr had a globular morphology. Hematite formed from Si-free ferrihydrite gave infrared (IR) bands at 548, 471, 397, and 337 cm -l, whereas, hematite formed from Si-containing ferrihydrite having 0.001 to 0.05 Si/Fe molar ratios gave broad IR bands at about 550, 450, and 330 cm -~. Ferrihydrite having Si/Fe molar ratios >-0.10 did not transform to hematite following the aqueous-thermal treatment.The ferrihydrite samples were thermally treated for 2 hr at consecutive 100*C intervals from 100 ~ to 8000C. The Si-free ferrihydrite transformed at 300"C to poorly crystalline hematite. Transmission electron microscopic analyses indicated that the hematite consisted of aggregates of spheroidal particles of 20-80 /~ cross sections. Broad IR bands were observed at 529 and 452 cm-l; however, after heating the sample to 800~ the particle cross sections increased to about 150--600 A, and additional IR bands were present at 378 and 325 cm -~. The differences in the IR patterns of hematite formed from ferrihydrite at 300 ~ and 800~ were probably due to increases in particle size and aggregation and improved crystallinity of the hematite particles following the higher temperature treatment. The hematite formed by the thermal transformation of the ferrihydrite having a 0.01 Si/Fe molar ratio was also spheroidal, and IR vibrations were present at about 528 and 443 cm -~. An increase in the temperature of the thermal treatment, however, did not result in additional IR bands.Differences in the IR vibrations of hematite formed during aqueous-and dry-thermal treatments of the ferrihydrite samples were probably due to differences in the particle size and morphology of the product. The Si content, due to its effect on particle size of the precursor and the prevention of sintering and particle growth of hematite, influenced the IR pattern of the product. Particle morphology and IR spectroscopy may therefore be useful indicators of the precursor of hematite and the conditions of hematite formation in soil.

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“…The immediate precursors of hematite obtained from goethite decomposition have been noted by Wolska [9] as protohematite and hydrohcmatite, with their nominal formulae given by Fez.m(OH)~O3., with 1 _> x > 0.5 (for protohematite) and 0.5 -> x > 0 (for hydrohematite). Similar intermediate phases have been identified by Saraswat et aL [16,17] during the thermal transformation of iron(III) oxide hydrate precipitates. In the present study the DSC curve of sample 7 of aged iron(III) hydroxide is characteristic of finely divided protoferrihydrite as a major phase [5,6], along with a small fraction of goethite, which gives a separate .I.…”

Section: Study Of Aged Iron(iii) Hydroxide and Chromium(ill) Hydroxidmentioning

confidence: 70%