Reactivity of finely dispersed iron (III) oxides and oxide hydroxides in solid-state reactions

The kinetics of the reaction of-Fe₂O₃ (hematite) with K₂CO₃ was studied at 600–800 °C for hematite samples prepared in different ways. The results demonstrated that the hematite reactivity is not a simple function of the specific surface area (or particle size), but depends significantly on the sample preparation history, especially at lower reaction temperature. The effect of low-temperature sintering on the hematite reactivity is discussed.

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Zusammenfassung Die Kinetik der Reaktion unterschiedlich präparierter-Fe₂O₃- (Hämatit-) Proben mit K₂CO₃ bei 600–800 °C wurde untersucht. Die Ergebnisse zeigen, dass die Reaktivität des Hämatits keine einfache Funktion der spezifischen Oberfläche (bzw. Teilchengrösse) ist, sondern deutlich von der Vorgeschichte der Probe, insbesondere bei tieferer Temperatur, abhängt. Der Einfluss des Tieftemperatursinterns auf die Reaktivität des Hämatits wird diskutiert.

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Structural and Magnetic Properties of NiFe2−2xSnxCuxO4

The substituted nickel ferrite (NiFe_2−2xSn_xCu_xO₄, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe³⁺ ions by Sn⁴⁺ and Cu²⁺ cations on the structural and magnetic properties of the ferrite was studied by means of ⁵⁷Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe₂O₄ adopts a fully inverse spinel structure of the type (Fe)[NiFe]O₄, Sn⁴⁺ and Cu²⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe_1−2xSn_xCu_x]O₄, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe_2−2xSn_xCu_xO₄ samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement.     

Perhydridosilicone films produced by IR laser‐induced chemical vapour deposition from disiloxane

Solid perhydridosilicone films have been produced by transversely excited atmospheric (TEA) and continuous‐wave CO₂ laser‐induced gas‐phase decompositions of H₃SiOSiH₃ controlled by elimination and polymerization of transient silanone H₂SiO and affording silane and hydrogen as side products. The decomposition mechanism is supported by evidence of scavenged intermediates and minor volatile products. The films are characterized by FT infrared and x‐ray photoelectron spectroscopy and by scanning electron microscopy and shown to undergo facile oxidation of the topmost layers in air and chemical changes upon argon ion sputtering. Copyright © 2000 John Wiley & Sons, Ltd.     

Thermal behaviour of natural and synthetic iron precipitates from mine drainage

TG–DTA, MS detections and XRD were used to characterize thermal behaviour of iron precipitates from acid mine drainage prepared by precipitation with urea and natural iron precipitates sampled from sludge bed (settling pit Sedem ?ien and old abandoned adit Hodru?a, mining area Banská ?tiavnica, Slovakia). The high-resolution transmission electron microscopy and scanning electron microscopy (SEM) techniques were used to characterize the surface microstructure and shape of the synthesized and sampled iron precipitates. The SEM micrographs of the iron precipitates (natural and precipitated with urea) show that the samples had formed into agglomerates, probably due to attractive forces of quite large surface area. During heating of the all samples up to 200 °C, physically adsorbed water was removed. On further heating in the range from 250 to 350 °C in natural iron precipitates, the less stable forms (goethite, ferrihydrite, and schwertmannite) transform to more stable forms like hematite. In case of synthetic samples, the transformation runs in two steps: first in the range from 250 to 350 °C, and second in the range from 600 to 750 °C.     

Emanation thermal analysis study of N-doped titania photoactive powders

Thermal behaviour of N-doped titania powders prepared by heat treatment of anatase in gaseous ammonia at 550 and 575°C, respectively, was characterized by emanation thermal analysis (ETA). The ETA results were used to assess transport properties of the samples subsurface using the mobility data of radon atoms previously incorporated into the samples to the depth of 60 nm. It was demonstrated that the radon permeability of anatase in the temperature range 50–500°C was enhanced for the N-doped titania as compared to the non-doped titania powder. Microstructure changes accompanying the anatase-rutile transition were pointed out from the decrease of the radon release rate in the temperature range 850–1000°C. The results of surface area and porosity measurements, DTA results as well XRD patterns supported the ETA results.     

La–Zn Substituted Hexaferrites Prepared by Chemical Method

La–Zn substituted M-type Ba hexaferrite powders were prepared by sol-gel (Mx) and organometallic precursor (Sk) methods with Fe/Ba ratio of 11.6 and 10.8, respectively. The compositions (LaZn) _x Ba_{1 ? x} Fe_{12 ? x} O₁₉ with 0.0 ≤ x ≤ 0.6 were annealed at 975°C/2 h. The cationic site preferences of nonmagnetic La³⁺ instead of Ba²⁺ ions and Zn²⁺ instead of Fe³⁺ ions were determined by Mössbauer spectroscopy. The La³⁺ ions substitute the large Ba²⁺ ions at 2a site and for x ≥ 0.4 also at 4f₂ site. The nearly all Zn²⁺ ions are placed at the 4f₁ sites. The thermomagnetic analysis of χ(?) confirms that only the small substitutions for x ≤ 0.4 can be taken as a single-phase hexaferrites. The coercivity H _c almost does not change at x = 0.2 for (Mx) samples and further decrease up to x = 0.6. For (Sk) samples at substitution x = 0.2 the values of H _c are decreasing and at higher x the values nearly do not change. The Curie points, T _c, slowly decrease with x for both (Mx) and (Sk) samples.     

Study of natural and ion exchanged vermiculite by emanation thermal analysis,TG, DTA and XRD

Emanation thermal analysis (ETA), thermogravimetry, DTA and XRD were used in thermal characterization of natural vermiculite (Santa Olalla, Huelva, Spain) and of Na^+- and - exchanged vermiculite samples during heating in air in the range 25-1100°C. A good agreement between the results of these methods was found. Changes in the radon release rate measured by ETA, which reflected the decrease and collapse of the interlayer space after the release of water as well as the formation of new crystalline phases were evaluated using a mathematical model. The model used for the evaluation was found suitable for the quantitative characterization of microstructure changes during in situ conditions of heating of vermiculite samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

IR laser‐induced breakdown in tetramethyltin adjacent to Ag or Au: deposition of β‐Sn nanograin‐containing amorphous Au–Sn/C and Ag–Sn/C films

Pulsed IR laser irradiation of metal (Au or Ag) target in gaseous tetramethyltin (TMT) results in metal ablation and adjacent dielectric breakdown (DB) in TMT and allows gas phase deposition of films containing metal (Au or Ag), Sn and C elements. Volatile products of DB of TMT were examined by FT‐IR spectroscopy and revealed as intermediates of gas phase carbonization reactions. The solid films were analyzed by FT‐IR and Raman spectroscopy, X‐ray diffraction and electron microscopy and shown as amorphous nanostructured Au–Sn/C and Ag–Sn/C phases containing β‐Sn nanograins. These Sn nanograins exhibit irreversible amorphization upon heating and melt below the melting point of bulk β‐Sn phase. Copyright © 2012 John Wiley & Sons, Ltd.     

IR laser‐induced decomposition of disiloxane for chemical vapour deposition of poly(hydridosiloxane) films

Continuous‐wave CO₂‐laser‐induced gas‐phase decomposition of H₃SiOSiH₃, dominated by elimination and polymerization of transient silanone H₂SiO and yielding silane and hydrogen as side‐products, represents a convenient process for chemical vapour deposition of poly(hydridosiloxane) films. Copyright © 1999 John Wiley & Sons, Ltd.     

Si/C phases from the IR laser-induced decomposition of divinylsilane

Transversely excited atmospheric (TEA) CO₂ laser-induced decomposition of divinylsilane in the gas phase yields unsaturated C₂–C₄ hydrocarbons, benzene and vinylsilane, and it represents a convenient process for chemical vapour deposition of thin solid films composed of silicon carbide and polycarbosilane. © 1998 John Wiley & Sons, Ltd.