Showing papers on "Rutile published in 1995"
TL;DR: Using the self-consistent orthogonalized linear-combination-of-atomic-orbitals method in the local-density approximation, the electronic structure and the optical properties of three phases of titanium dioxide have been studied.
Abstract: Using the self-consistent orthogonalized linear-combination-of-atomic-orbitals method in the local-density approximation, the electronic structure and the optical properties of three phases of titanium dioxide have been studied. For rutile, the calculated band structure, equilibrium lattice constant, and bulk modulus are in good agreement with other recent calculations and with experimental data. The results on the ground-state properties of anatase and brookite are reported. Compared with the rutile phase, anatase has similar ground-state properties except for a larger band gap, whereas brookite has relatively smaller bulk modulus. The optical properties of these three phases are also calculated using the band-structure results and compared with the available measurements. For the rutile phase, the anisotropic properties of the dielectric function are in good agreement with the reflectance spectroscopy. For the anatase phase, there are very limited experimental optical data for comparison. For the brookite phase, no experimental data are available. Our calculations show subtle differences in the optical properties of these three phases.
941 citations
744 citations
TL;DR: In this paper, an anatase-type TiO2 catalyst with large band gap and numerous surface OH groups showed high efficiency for the formation of CH4 and CH3H.
448 citations
TL;DR: In this article, the semi-empirical MO method SINDO1 was used for the investigation of molecular and dissociative adsorption of water at titanium dioxide surfaces rutile (110) and anatase (001).
180 citations
TL;DR: In this paper, the structure parameters, the concentration of each phase, and their average crystallite size were obtained from x-ray powder diffraction, and the conditions for obtaining single-phase samples that could be used as precursors for making up titania single phase thin films.
Abstract: We prepared sol-gel titania by using different hydrolysis catalysts, and characterized it by x-ray powder diffraction. The structure of the crystalline phases—brookite, anatase, and rutile—in the samples annealed between 70 and 900 °C was refined by using the Rietveld technique. From the refinement we obtained the structure parameters, the concentration of each phase, and their average crystallite size. These quantities and their evolution with temperature depended on the hydrolysis catalyst. Anatase and rutile were deficient in Ti, suggesting that their crystalline structure contained hydrogen atoms, forming OH− ions inside. In anatase this deficiency depended on its crystallite size, but it was constant in rutile. When anatase was annealed, it dehydroxylized, producing either crystallitc growing up or its conversion into rutile. From the analysis we also found the conditions for obtaining single-phase samples that could be used as precursors for making up titania single-phase thin films.
177 citations
TL;DR: The characterization results suggest that the photocatalyst consists of individual single crystal particles of the rutile and anatase phases of titania; no amorphous titania particles could be identified conclusively.
149 citations
TL;DR: In this paper, the crystal structure of natural hydrous rutile from a mantle eclogite nodule has been refined from single-crystal neutron diffraction data collected at 24 K.
Abstract: The crystal structure of natural hydrous rutile from a mantle eclogite nodule has been refined from single-crystal neutron diffraction data collected at 24 K. The chemical composition was 95.52 wt% Ti02, 0.74 wt% Fe203, 0.68 wt% A1203, 1.16 wt% Cr203, 1.86 wt% Nb205, and 0.04 wt% MnO, with approximately 13000 ppm OH-, as estimated by IR spectroscopy. The position of the H atom was located by examining the negative residuals in the difference Fourier maps. The refined position is near the shared edge of the cation octahedron at xl a = 0.42(1), ylb = 0.50(1), and zlc = 0 with a site occupancy of 2.7%, which is consistent with the H concentration estimated by IR spectroscopy. The O-H bond distance is 1.05 A and the OH vector is in the (001) plane, which is consistent with the strong w-polarization of the OH absorption observed in the IR spectra. Single-crystal X-ray data were collected from a synthetic anhydrous rutile crystal and a hydrous rutile crystal from the same mantle nodule as the sample used in the neutron study. The detailed X-ray structures of both rutiles were compared and no significant differences were found; the ale ratios and the 0 position were identical within error. Therefore, we conclude that the addition of H into rutile for the purpose of charge-balancing excess 3 + cations does not significantly change the structure.
126 citations
TL;DR: In this paper, the effect of dopants on the characteristics of titania particles made by oxidation of TiCl{sub 4} in a laminar diffusion flame reactor is presented.
Abstract: The effect of dopants on the characteristics of titania particles made by oxidation of TiCl{sub 4} in a laminar diffusion flame reactor is presented. Introduction of dopant SiCl{sub 4} inhibits the transformation of anatase to rutile, due to the formation of interstitial solid solution of SiO{sub 2} and TiO{sub 2}. Silica decreases the sintering rate of titania and decreases the primary particle size, and, as a result, the specific surface area increases. Introduction of SnCl{sub 4} enhances the transformation of anatase to rutile, due to the similar crystalline structure of SnO{sub 2} and rutile titania. However, the presence of SnO{sub 2} does not affect the primary particle size or the specific surface area of titania particles. Introduction of AlCl{sub 3} enhances the transformation of anatase to rutile, due to the formation of excess oxygen vacancies as Al{sub 2}O{sub 3} and TiO{sub 2} form a substitutional solid solution.
125 citations
TL;DR: In this paper, an explanation base on the thermodynamics and kinetics of nucleation growth type of transformations is given for the observed difference between the crystallite sizes of anatase and rutile phases during the initial stage of the phase transformation.
Abstract: Anatase-to-rutile transformation in titania system is a metastable-to-stable irreversible transformation. Transformations of this type are very important both from a scientific as well as from a technological point of view. In this paper, an explanation base on the thermodynamics and kinetics of nucleation-growth type of transformations is given for the observed difference between the crystallite sizes of anatase and rutile phases during the initial stage of the phase transformation. Two situations are considered here, pure titania and the titania phase in the titania-alumina nanocomposites. It is postulated that the critical nuclei size of rutile phase may be much larger than the transforming anatase particles.
122 citations
TL;DR: In this paper, annealing in 1 × 10−6 Torr O2 at temperatures ranging from 500°C to 700°C leads to a three-fold symmetric structure with a unit cell of 18.2 A × 13.9 A which is observed at coverages of 1.0 to 1.5 ML.
105 citations
TL;DR: In this paper, a titanium dioxide thin film doped with nitrogen was deposited at 420°C on p-type silicon substrate by metalorganic chemical vapor deposition using titanium tetraisopropoxide and nitrous oxide.
Abstract: Titanium dioxide thin film doped with nitrogen was deposited at 420 °C on p‐type silicon substrate by metalorganic chemical vapor deposition using titanium tetra‐isopropoxide and nitrous oxide. From an x‐ray diffraction result, when deposited at 420 °C, only the anatase (101) peak and (200) peak were observed. Raman spectroscopy confirmed the presence of anatase phase without any rutile or TiN phase. X‐ray photoelectron spectrum revealed that nitrogen was doped into the lattice of TiO2 anatase. In the bulk of the film nitrogen peak was observed, and the spectrum of Ti 2p core level confirmed titanium–nitrogen bonding due to nitrogen incorporation into the anatase lattice.
TL;DR: In this paper, methanol, ethanol, and 2-propanol were adsorbed at room temperature on anatase and rutile powders and temperature-programmed desorption spectra were obtained in a high-vacuum microbalance system.
TL;DR: In this article, the authors compared the catalysts of various titanium oxide containing compounds in photocatalytic decomposition of phenol and found that anatase and titanium oxide impregnated over silica gel were the most active catalysts with regard to the degradation rate of phenols, while carbon dioxide formation was fastest over the latter catalyst.
01 Jan 1995
TL;DR: Anatase-to-rutile phase transition has been studied on high-area TiO2-anatase and bicomponent systems containing molybdena and, for comparison, cobalt oxide, copper oxide, vanadia and corresponding TiO 2 rutile based systems, using TG-DTA, XRD and surface-area measurements.
Abstract: Anatase-to-rutile phase transition has been studied on high-area TiO2-anatase and bicomponent systems containing molybdena and, for comparison, cobalt oxide, copper oxide, vanadia and corresponding TiO2-rutile based systems, using TG–DTA, XRD and surface-area measurements. These materials were prepared by impregnation and (co)precipitation methods. Conversion to rutile and crystal size growth strongly depend on the minority phase oxide. It is found that, while Cu and V oxides speed up both phase transition and particle sintering, Mo and Co oxides inhibit them. Moreover, the rutile particles obtained by phase transition are always much larger than both the starting and residual anatase particles. A mechanism of rutile formation by coalescence and phase transformation of anatase particles is proposed.
TL;DR: Transmission electron microscopy was used to identify the crystal structure and morphology of the oxide film on commercially pure titanium specimens before and after immersion in simulated physiologic fluids, and shows that the oxide layer is composed mainly of anatase and rutile, both of which are tetragonal in structure.
Abstract: The passivating surface oxide on titanium is one of the elements considered in the explanation of the favorable biologic response of this metal in implant applications. In the present study, transmission electron microscopy was used to identify the crystal structure and morphology of the oxide film on commercially pure titanium specimens before and after immersion in simulated physiologic fluids. The results show that the oxide layer is composed mainly of anatase and rutile, both of which are tetragonal in structure. Although the simulated physiologic fluids did not induce an observable change in the crystal structure for the immersion times investigated, the results indicate an immersion-induced change in microstructure from a fine-grained to a coarser-grained structure. The grain growth observed could be attributed to the growth of the native oxide crystals; however, it most likely results from the formation of a new oxide layer. The results also support oxide thickening as one of the processes associated with passive dissolution of titanium.
TL;DR: In this article, a new method for metalorganic chemical vapor deposition has been developed in which a precursor solution is directly injected into a reaction chamber and vaporization of short pulses of liquid is facilitated by atomization with a piezoelectrically operated nozzle.
Abstract: A new method for metalorganic chemical vapor deposition has been developed in which a precursor solution is directly injected into a reaction chamber. The vaporization of short pulses of liquid is facilitated by atomization with a piezoelectrically operated nozzle. The system has been used successfully to grow oriented, thin TiO 2 (rutile) films on sapphire substrates with the crystalline relationship (101)[010] R ∥ (1120)[0001] s . A film growth rate of approximately 2.5 monolayers of TiO 2 (rutile) per pulse was achieved at 650°C for a reactant impingement rate of about 250 monolayers of Ti(OPr i ) 4 per pulse.
TL;DR: For the U.S., this paper reported the following results: 106/436, 441, 106/499, 438, 439, 442, 443, 444, 446, 447, 501/12, 134, 423/608, 610, 616, 598, 424/59, 428/403, 404, 252/309, 313.1; 210/348, 429/111 Germany, 195 43 204.5
Abstract: (51) Int. Cl." ....................................................... C09C 1/36 52 U.S. Cl. .......................... 106/436; 106/438: 106/439; 106/441; 106/442; 106/443; 106/444; 106/446; 106/447; 423/598; 423/610; 423/616; 252/309; 252/313.1; 424/59; 429/111; 428/403 58 Field of Search ..................................... 106/436, 441, 106/499, 438, 439, 442, 443, 444, 446, 447; 501/12, 134; 423/608, 610, 616, 598; 424/59; 428/403, 404; 252/309, 313.1; 210/348; 429/111 Germany ........................ 195 43 204.5
15 Jun 1995
TL;DR: In this article, the acidity of industrial titania has been investigated using potentiometric titration and microelectrophoretic mobility measurements, and it was shown that the surface of rutile is more acidic than anatase.
Abstract: The rutile, anatase, and industrial titania (used in catalysis as support and consisting of rutile and anatase)-water solution interfaces were studied using potentiometric titration and microelectrophoretic mobility measurements. Concerning the simple oxides it was found that specific adsorption of the ions of the background electrolyte (NH4NO3) does not take place. The electrical double layer developed in the anatase/aqueous solution and rutile/aqueous solution interfaces is described by the diffuse layer model. On the basis of this model the surface acidity constants, the point of zero charge, and the concentration of the various surface hydroxyls in the pH range 4-8 were calculated using a computer program called SURFEQL. It was confirmed that the surface of rutile is more acidic than the surface of anatase. Concerning industrial titania used in catalysis as support it was demonstrated that its surface has a patchwise structure consisting of rutile (10%) and anatase (90%) regions. The acid-base behavior of this material is identical to a mechanical mixture of rutile and anatase of the same composition. Taking into account its patchwise structure we calculated the variation, with pH, of the concentration of each surface hydroxyl of industrial titania [TirOH+2, TiIOH, TirO-, TiaOH+2, TiaOH, and TiaO-; a, r stand for anatase and rutile, respectively]. These variations allow one to model the deposition of species containing catalytically active ions on the surface of industrial titania.
TL;DR: The results of periodic Hartree-Fock calculations on the adsorption of oxalic acid on rutile and anatase TiO2 structures were presented in this article.
TL;DR: The surface concentration of Sb in doped TiO2 rutile ceramics has been measured by means of angle-resolved core level X-ray photoelectron spectroscopy (AR-XPS).
TL;DR: In this article, sintered samples of rutile have been submitted to the irradiation of a 355 nm laser beam and X-ray absorption spectroscopy at the Ti K-edge and Xray photoelectron spectrograms were used to provide evidence in favour of Ti3+ ion formation in the near surface region of the samples.
TL;DR: In this paper, a microprobe Raman spectroscopy was used to examine physical vapor deposited TiN coatings oxidized by solar beam heat treatment in air, and the results indicated incipient oxidation by the presence of anatase TiO2 and showed a broadband feature around the forbidden TiN vibrational mode.
Abstract: Physical vapor deposited TiN coatings oxidized by solar beam heat treatment in air were examined by microprobe Raman spectroscopy. The Raman spectra of TiN treated at 400 °C indicated incipient oxidation by the presence of anatase TiO2 and additionally showed a broadband feature around the forbidden TiN vibrational mode. Inhomogeneous mixtures of rutile TiO2 and small amounts of anatase polymorph (< 10%) were detected for the treatments at 600 °C only during the initial stage of oxidation. Prolonged treatment at 600 °C resulted in a complete anatase-to-rutile conversion. Rutile was identified as the single product of oxidation of the TiN samples treated at 800 °C. Peak analysis of the rutile spectra revealed no substantial spectral shifts, demonstrating an oxide growth of nearly stoichiometric rutile with an estimated composition in the range of TiO2±0.02. The Raman scattered light intensity could be correlated with the rutile layer thickness.
TL;DR: In this article, the surface morphology has a granular structure for electropolished titanium and for titanium evaporated on mica at low substrate temperature (570 K), but changes to flat terraces for the films evaporated at higher temperature (770 K).
Abstract: Oxidized titanium surfaces resulting from various processes have been structurally characterized by means of scanning force microscopy, x‐ray photoemission spectroscopy (XPS), x‐ray diffraction, and electron energy‐loss spectroscopy (EELS) with losses in the 0–100 eV range. It has been found that the surface morphology has a granular structure for electropolished titanium and for titanium evaporated on mica at low substrate temperature (570 K), but changes to flat terraces for the films evaporated at higher temperature (770 K). Angular‐dependent XPS has revealed the presence of a Ti2O3 suboxide at the Ti/TiO2 interface for electropolished titanium. Dry oxidation has been performed at 770 and 970 K on both weakly and highly crystallized evaporated titanium films oriented along (0001). In the case of underlying crystallized metallic titanium, the resulting TiO2 films are crystallized with the anatase (004) orientation for oxidation at 770 K and with rutile (200) orientation for oxidation at 970 K. EELS spectra interpreted in terms of the molecular orbitals of a (TiO6)8− cluster show that the local octahedral environment of titanium atoms is preserved on native oxides, even if these oxides are not crystallized.
TL;DR: In this article, X-ray absorption spectroscopy of bulk amorphous TiO2 and the crystalline phases obtained by heat treatments are investigated by X-Ray absorption spectrograms.
Abstract: Sol-gel-derived bulk amorphous TiO2 and the crystalline phases obtained by heat treatments are investigated by X-ray absorption spectroscopy. The environment of the Ti atoms in the amorphous phase shows a residual from the alkoxide precursor and the presence of anatase crystallites. Thermal treatments up to 350°C give crystalline anatase and the pure rutile phase is obtained at 750°C. Near-edge absorption measurements confirm the octahedral coordination of Ti in all the phases investigated.
TL;DR: In this article, the interaction between Pt and ideal and oxygen-defective TiO2(rutile)(110) surfaces is studied by ab initio SCF methods, and it is shown that the interaction is very strong; the bond energy reaches 16.5 eV for the ideal surface and 23.0 eV in the oxygen-poor TiO 2(rural) surface.
TL;DR: In this paper, the Raman spectra of nanophase titanium dioxide were examined for different particle sizes and after successive annealing temperatures, and all the normal modes at 152, 230-250, 422, 612, 702 and 796 cm-1 were assigned comparing with assignments for rutile, anatase structures and other nanophases TiO2.
Abstract: Raman spectra of nanophase titanium dioxide are examined for different particle sizes and after successive annealing temperatures. All the normal modes at 152, 230-250, 422, 612, 702 and 796 cm-1 are assigned comparing with assignments for rutile, anatase structures and other nanophase TiO2. Oxygen deficient effect, grain-size effect and critical selection rule are specially discussed, which are related to special properties of the modes concerned.
TL;DR: In this paper, cyclic voltammetry was used to study properties of the (110) surface of a rutile (TiO 2 ) monocrystal and its interaction with vanadium(V) species at conditions simulating typical preparation procedures for catalysts.
Abstract: Cyclic voltammetry was used to study properties of the (110) surface of a rutile (TiO 2 ) monocrystal and its interaction with vanadium(V) species at conditions simulating typical preparation procedures for catalysts. It was found that vanadium enters the crystal lattice of rutile as a tetravalent ion and cannot be electrochemically oxidized to pentavalent but can easily be reduced to the trivalent oxidation state. A second vanadium species may also appear on the surface of rutile, which may be both reduced from +5 through +4 to +3 and oxidized from +3 through +4 to +5 oxidation state.