Amorphous and Crystalline Titanium and Iron-Titanium Oxides in Synthetic Preparations, at Near Ambient Conditions, and in Soil Clays

Abstract--The form under which Ti occurs in kaolinitic materials from various environments has been investigated using second derivative diffuse reflectance spectroscopy. The position of the absorption edge may be used as a diagnostic band to determine Ti-phases (anatase, futile, Ti-gels). Ti-oxides may be detected in kaolins, down to 0.1 wt. % Ti02. Diffuse reflectance spectra show the presence of Ti-gel-like phases occluded in sedimentary kaolinite particles. These phases, which record conditions at the time of kaolinite growth, constitute the first direct evidence of Ti mobility at the scale of mineral assemblages and question the substitution of Ti for AI in kaolinite. The nature of the Ti-oxides associated with kaolinite particles gives some constraints on the temperature conditions of hydrothermal kaolins, the evolution of sedimentary kaolin during basin diagenesis and the source of parental material in soil kaolins.

Section: Methodsmentioning

confidence: 99%

Spectroscopic Approach for Investigating the Status and Mobility of Ti in Kaolinitic Materials

Malengreau

Müller

Calas

1995

“…Conversion of goethite to hematite took place at 200~ in these samples and at 300~ in the others. of Fitzpatrick et al (1978) and Taylor and Schwertmann (1978) for both Ti-and AI-substituted goethites (Figure 3). Between compositions of 20 and 40 mole % AI, a large decrease in MCD took place.…”

Section: Physical Properties Of the Productsmentioning

confidence: 99%

Synthesis and Properties of Poorly Crystalline Hydrated Aluminous Goethites

Fey

1981

Abstraet--AI-substituted goethites were prepared by rapid oxidation of mixed FeCI2-AICI 3 solutions at pH 6.8 in the presence of CO2 at 25~ A combination of AI substitution and adsorption of CO2 reduced crystal size (except for an increase at small additions of AI) and produced unusual thin, porous particles. Product goethites had surface areas up to 283 mZ/g and unit-cell expansions induced by hydration. Substitution of AI for Fe reduced the 111 spacing and increased infrared OH-bending vibrational frequencies. A1 substitution split the goethite dehydroxylation endotherm during differential thermal analysis into a doublet and increased the temperature of all reactions. Both cold and hot alkali solutions dissolved AI from the goethite structure.After drying the product in vacuo at 110~ X-ray powder diffraction data indicated minimal deviation from Vegard's law for the goethite-diaspore solid solution up to about 30 mole % AI substitution. Goethite prepared in the presence of 40 mole % AI had a 111 spacing of 2.403/~ corresponding to 36 mole % structural AI if Vegard's law was obeyed. Rapid oxidation of mixed FeCI2-AICI 3 solutions appears to be conducive to a higher degree of AI substitution in goethite than alkaline aging of hydroxy-Fe(III)-Al coprecipitates.

“…To the best of our knowledge, the literature holds no proof of Fe-for-Ti substitution in natural anatase except that Fe has been noted as a trace constituent (Deer et al 1962). Fitzpatrick et al (1978) synthesized Ti-Fe-mixed phases from coprecipitates at 70~ and obtained anatase as the sole phase between Ti/(Ti+Fe) ratios of 0.7 and 1.0. The Fe was no longer oxalate extractable, and the XRD peaks became broader as Fe content increased.…”

Section: Introductionmentioning

confidence: 99%

Iron Substitution in Soil and Synthetic Anatase

Schwertmann

1995

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.