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A series of iron/titanium oxide nanocrystalline particles with Fe/Ti molar ratios up to 0.15 were synthesized by a modified sol-gel technique using Ti(IV)-isopropoxide and anhydrous Fe(II)-acetate. The precursors were mixed and subsequently hydrolyzed with water molecules generated in situby an esterification reaction between acetic acid and ethanol. As-synthesized samples were amorphous for XRD, independently of the relative amount of doped iron. The undoped samples and samples with the molar ratio Fe/Ti = 0.01, treated at up to 500°C, contained anatase as the dominant phase and rutile as the minor phase. The samples with the Fe/Ti molar ratio of 0.15, treated at the same temperature, contained anatase (major phase), rutile (minor phase) and a very small amount of an unidentified phase. The crystallite size of the dominant phase in the samples was estimated from the XRD line broadening using the Scherrer formula. Thermogravimetric analysis showed that weight loss was accelerated and completed at lower temperatures as the relative concentration of iron in the Fe-TiO2samples increased. The strong exothermic peak in the DTA curve between 300 and 450°C in the undoped TiO2sample shifted to the lower temperatures and became much more asymmetrical with increased iron doping. This DTA peak corresponded to the amorphous-to-anatase-transition and it included several steps such as (i) the thermal degradation of strongly bound organic molecules, (ii) the condensation of unhydrolyzed –OR groups, (iii) the sintering and growth of particles and (iv) the rearrangement of newly formed chemical bonds. The center of the most intense Raman band of the Egmode at 143.8 cm−1in the undoped TiO2sample continually shifted to higher wave numbers and the full-width at half maximum increased with iron doping. Transmission electron microscopy revealed decrease of the mean particle size from 16.3 nm in undoped sample to 9.7 nm in the highest iron doped sample. The particle size distribution becomes narrower with iron doping. The narrowest particle size distribution was found in sample with the Fe/Ti molar ratio of 0.05, calcined at 500°C. Scanning electron microscopy of undoped samples calcined at 580°C showed irregular aggregates having a relatively flat surface. On the contrary, the samples doped with 15 mol% of iron and treated at the same temperature exhibited a non-uniform sponge-like surface with distributed micrometer holes.

Chemical and structural properties of oxide precipitates formed from FeSO4 solution were investigated using X-ray diffraction and57Fe Mössbauer spectroscopy. The hydrolysis of urea at elevated temperature was used for the generation of OH- ions during the precipitation process. The formation of particular oxide phase in the precipitate is strongly dependent on the concentrations of FeSO4 and urea, as well as on the rate of oxygenation. The phase analysis of precipitates showed the presence of different oxide phases, such as goethite, lepidocrocite, hematite and magnetite, and in one sample of a small amount of siderite. Only substoichiometric magnetite, Fe3-xO4, was detected. Significant differences in the Mössbauer spectrum of goethite were observed, due to a very small particle size, the degree of crystallinity and/or different content of structurally bonded water. The correlation between the Mössbauer spectra of precipitated goethite and goethite formed during the atmospheric corrosion of steel is discussed.

Chemical and structural properties of the rust formed by corrosion of steel in aqueous solutions were studied by X-ray diffraction and Fourier transform infrared (FT-IR) spectroscopy. The corrosion products of steel were generated in aqueous solutions of different electrolyte compositions at room temperature (20 °C) or in an autoclave at 120 °C. X-ray diffraction analysis showed the presence of different oxide phases in the rust, such as lepidocrocite, magnetite, ferrihydrite, goethite and haematite. In all samples, the presence of an amorphous fraction was detected. Ferrihydrite was detected only in the rust samples formed at 120 °C, The characteristic properties of the FT-IR spectrum of the ferrihydrite component in the rust were investigated. Phase compositions of the corrosion products depended on the formation temperature and the electrolyte composition of the aqueous solutions. The influence of chloride, nitrate or sulphate anions on the phase composition of the rust is discussed.

Nanosized TiO2 was prepared using the sol–gel procedure. The prepared powder was thermally treated up to 1000°C. X-ray diffraction (XRD) measurements showed that the starting powder and the samples obtained after heating this powder up to 500°C were mixtures of anatase, as the dominant phase, and brookite. The crystallite sizes of the samples were estimated using the Scherrer equation. A new approach to the size determination of nanosized TiO2, by low-wavenumber Raman scattering, was also applied. The particle sizes, determined by low-wavenumber Raman scattering, were in agreement with the crystallite sizes measured by XRD. Rutile was produced by heat treatment of the starting powder at 850°C and higher temperatures. © 1997 John Wiley & Sons Ltd.

Abstract: Glasses are suitable host matrices for the immobilization of high-level radioactive wastes. The corrosion behaviour of nuclear waste glass in water is of considerable importance, since a potential route for returning of radionuclides to the biosphere is their leaching from the waste form into groundwater and subsequent transport by the groundwater to the surface. In this study, the preparation and characterization of borosilicate glasses of different chemical composition were investigated. Borosilicate glasses were doped with simulated nuclear waste oxides. The chemical corrosion in water of these glasses was followed by measuring the leach rates (g·cm–2·day–1), as a function of time. It was found that a simulated nuclear waste glass with the chemical composition (weight %), 15.61% Na2O, 10.39% B2O3, 45.31% SiO2, 13.42% ZnO, 6.61% TiO2 and 8.66% waste oxides, is characterized by low melting temperature and with good corrosion resistance in water. Influence of passive layers on the leaching behaviour of nuclear waste glasses is discussed.

Abstract: The effects of iron on the structural properties of Zn-borosilicate glass and Pb-metaphosphate glass were studied using X-ray diffraction,57Fe Mössbauer spectroscopy and IR spectroscopy. Zn-borosilicate glass was prepared with varying amounts of Fe2O3 (up to 30% wt.). It was found that the chemical form of added iron (agr-FeOOH, agr-Fe2O3 or Fe3O4) affects the Fe3+/Fe2+ ratio, as well as the distribution of iron ions at different coordination sites. At high concentration of iron the crystallization of zinc ferrite in the glass matrix takes place. X-ray diffraction and57Fe Mössbauer spectroscopy showed that the amount of zinc ferrite in Zn-borosilicate glass decreases with the following order of addition: agr-FeOOHrarragr-Fe2O3rarrFe3O4. In Pb-metaphosphate glass doped with high concentration of agr-Fe2O3, the crystallization of Fe3(PO4)2 is pronounced. The assignments of IR band positions and the corresponding interpretation are given. The importance of this study for the technology of vitrification of high-level radioactive wastes is emphasized.

Structural properties of lead vanadate glasses containing La3+ or Fe3+ ions were investigated using X-ray diffraction, Fourier transform infrared spectroscopy and laser Raman spectroscopy. Crystalline Pb2V2O7 was formed for the molar composition 66.7PbO-33.3V2O5. Incorporation of greater quantities of La3+ into lead metavanadate glass caused the crystallization of Pb2V2O7. Fourier transform infrared and laser Raman spectra also suggested the presence of LaVO4. Incorporation of Fe3+ ions into lead metavanadate glass, up to 20 wt% Fe2O3, did not cause crystallization inside the glass matrix. Changes in the vibrational spectra are discussed.

The structural properties of precipitates formed by hydrolysis of Fe3+ ions in aqueous solutions, containing N03-and Cl- ions, were investigated. The reactions of hydrolysis were performed in glass autoclaves at 120 °C. X-ray diffraction showed that a-FeOOH and a-Fe2O3 were present in hydrolytical products formed in solutions containing N03-ions, while ß-FeOOH and a-Fe2O3 were typical hydrolytical products in solutions containing Cl- ions. In the mixed Fe(N03)3+FeCl3 solutions, the phase composition of the hydrolytical products was determined by the concentration of the dominant Fe(III)-salt. Fourier transform infrared spectroscopy and Mössbauer spectroscopy were also used for the structural characterizations of the hydrolytical products. Transmission electron microscopy showed a diversity of shapes of the particles, which depended strongly on the experimental conditions. All types of particle, observed by transmission electron microscopy, were interpreted.