Rutile Modification Research Articles

Structure dependence of reflection spectra of TiO2 single crystals

Polarized reflection spectra of three crystalline modifications of titanium dioxide, rutile, anatase and brookite, were measured for the photon energy range of 2–25 eV using synchrotron orbital radiation. The difference in the spectral feature of the reflection bands is discussed on the basis of the modifications in crystal structure.

Composition, binding states, structure, and morphology of the corrosion layer of an oxidized Ti0.46Al0.54N film

A metastable, single-phase, polycrystalline Ti0.46Al0.54N film was deposited on a HSS substrate by reactive magnetron sputtering ion plating and oxidized in synthetic air at 800°C. The build-up of the oxidic overlayer formed during 1 h of oxidation was analyzed with the followign results: Scanning electron microscopy (SEM) micrographs taken at the inner profile of a crater sputtered through the oxide overlayer showed a glassy morphology of the near surface region and, between the near surface region and the nitridic film, a sublayer consisting of crystals embedded in a glassy matrix. Electron probe microanalysis (EPMA) crater edge linescan analysis revealed that the oxide overlayer consists of two sublayers, which differ significantly in the Al and Ti content. At the surface and in the near surface toplayer the composition corresponds to Al2O3, whereas with increasing depth a composition conforming with Al2O3 and TiO2 was detected. The binding states of the components Al, Ti, O, and N were determined with increasing depth by high resolution Auger electron spectroscopy (AES) multipoint analysis as the inner profile of the crater. Evaluation of the spectra revealed that oxygen is present in two binding states. In the toplayer, oxygen is bonded to Al in Al2O3, and in the underlying layer, to Al in Al2O3 and to Ti in TiO2−y. Transmission electron microscopy (TEM) and high energy electron diffraction (HEED) analyses revealed that the Al2O3 rich toplayer is present in an amorphous state. With structure analysis by thin film X-ray diffraction (XRD), two modifications of TiO2, namely anatase and rutile, were detected.

Metal/semiconductor electrocomposite photoelectrodes: behavior of [formula omitted] photoanodes and comparison of photoactivity of anatase and rutile modifications

Metal/semiconductor electrocomposite photoelectrodes: behavior of [formula omitted] photoanodes and comparison of photoactivity of anatase and rutile modifications

Double chemical modification of the rutile surface

The successive adsorption of some aliphatic amines and carboxylic acid on titanium dioxide (rutile modification) from their vapors and toluene solutions has been studied. It was found that the efficiency of double modification of TiO2 with different modifiers depends on the sequence of their adsorption. From adsorption measurements and mass-spectroscopic thermal analysis, it has been shown that when the rutile surface is modified with vapors of n-butylamine and acetic acid, it is possible for the two substances to interact in the surface layer. As a result, the order in which the amine and the acid are adsorbed affects the structure and properties of the resulting adsorbed layers. Both the displacement of the previously adsorbed substance and the formation of new surface compounds are observed. It has been established that the modifying amine layer on rutile with preadsorbed carboxylic acid is the densest. This layer consists of molecules of both the modifiers and the product of their surface reaction.

Composition and structure of the anodic films on titanium in aqueous solutions

Surface-enhanced Raman spectra of the amorphous film on titanium have been obtained for the first time. The anodic corrosion film at low potentials is identified to be highly disordered TiO 2 with some Ti 2O 3 also present. The presence of the anatase and rutile modifications of TiO 2 at high voltages (⩾ 80V) is confirmed.

Effect of preparative pH and ageing media on the crystallographic transformation of amorphous TiO 2 to anatase and rutile

A study of the various parameters affecting the crystallographic transformation of amorphous titania gels (prepared from TiCl 3) to anatase and rutile has been conducted. Analysis of the effect of the preparative pH (3.0, 7.5 and 11.0) and of the ageing media (HCl, H 2O, air and NH 4OH) suggests that coordinated water as well as the presence of chloride ions (bulk or surface) play an important role in the transformation of amorphous titania gels to the anatase and rutile modifications. The formation or depletion of anion vacancies as well as the presence of interstitial ions seem to be the crucial parameters controlling the rate of transformation of anatase to rutile. A higher heating temperature as well as a higher preparative pH generally lead to an accelerated conversion. In most cases first-order kinetics are followed. A nucleation process with high k n predominates with NH 4OH and H 2O as ageing media, whereas with air a propagation-growth process in general controls the kinetics of the transformation. Ageing in HCl gives ill-defined kinetic curves. A notably low activation energy for nucleation (≈52 kcal mol −1) was observed in the case of the low pH gels aged in ammonia.

Characterization of molybdenum oxide catalysts supported on anatase and rutile polymorphs of titania by low-temperature oxygen chemisorption

Oxygen chemisorption (at -78°C, reduced state) and methanol oxidation activity have been measured for molybdenum oxide catalysts supported on anatase and rutile modifications of TiO 2 . The resutls suggest that molybdenum oxide forms a monolayer with a high degree of dispersion of the active component. Anatase-supported catalysts show better dispersion and activity than the corresponding rutile-supported ones. A correlation has been found between oxygen chemisorption and activity of the catalysts toward partial oxidation of methanol

Low temperature oxygen chemisorption: a facile technique for characterization of vanadium oxide catalysts supported on anatase and rutile polymorphs of TiO2

Oxygen chemisorption at –78 °C has been determined on the reduced surface of vanadium oxide catalysts supported on anatase and rutile modifications of TiO2; a correlation is found between oxygen chemisorption capacities with the activity of the catalysts for vapour-phase oxidation of methanol to formaldehyde.

ChemInform Abstract: An Investigation of Phases in the Titanium‐Antimony‐Oxygen System.

Abstract The nature of solid phases formed in the titanium-antimony-oxygen system by the calcination of precipitates in air has been investigated by powder X-ray diffraction, electron microscopy, Mossbauer spectroscopy, thermal analysis, and temperature programmed reduction techniques. The amorphous solids formed by mild temperature dehydration are converted to crystalline, and frequently multiphasic, materials when calcined at temperatures exceeding ca. 500 °C. The nature of the crystalline materials depends on the relative concentrations of the titanium and antimony cations in the initial precipitates and the calcination temperature. Antimony(V) in monophasic low-antimony content solids induces the structural transformation of the anatase form of titanium dioxide to the rutile modification at a lower temperature than is normally expected. Materials containing an excess of ca. 30% antimony and heated at temperatures exceeding ca. 500 °C are usually multiphasic and contain an antimony-containing rutile related phase. Evidence has been found for the occurrence of the mixed oxide of composition Sb3Ti2O10 in some multiphasic materials. Titanium-antimony oxides calcined at high temperatures in air may be described as solid solutions of low concentrations of antimony(V) in rutile titanium(IV) oxide. The tolerance of rutile titanium dioxide for the incorporation of antimony depends on the temperature and duration of thermal treatment.

An investigation of phases in the titanium-antimony-oxygen system

The nature of solid phases formed in the titanium-antimony-oxygen system by the calcination of precipitates in air has been investigated by powder X-ray diffraction, electron microscopy, Mössbauer spectroscopy, thermal analysis, and temperature programmed reduction techniques. The amorphous solids formed by mild temperature dehydration are converted to crystalline, and frequently multiphasic, materials when calcined at temperatures exceeding ca. 500 °C. The nature of the crystalline materials depends on the relative concentrations of the titanium and antimony cations in the initial precipitates and the calcination temperature. Antimony(V) in monophasic low-antimony content solids induces the structural transformation of the anatase form of titanium dioxide to the rutile modification at a lower temperature than is normally expected. Materials containing an excess of ca. 30% antimony and heated at temperatures exceeding ca. 500 °C are usually multiphasic and contain an antimony-containing rutile related phase. Evidence has been found for the occurrence of the mixed oxide of composition Sb 3Ti 2O 10 in some multiphasic materials. Titanium-antimony oxides calcined at high temperatures in air may be described as solid solutions of low concentrations of antimony(V) in rutile titanium(IV) oxide. The tolerance of rutile titanium dioxide for the incorporation of antimony depends on the temperature and duration of thermal treatment.

Photocatalytic degradation of phenol in aqueous titanium dioxide dispersions

The results of a study of photocatalytic degradation of phenol using aqueous oxygenated TiO2 (anatase) suspensions in a batch Pyrex photoreactor are reported. The influence on the photodegradation rate of various parameters as pH, phenol and TiO2 content, oxygen partial pressure, anions present in the dispersions was investigated. A complete oxidation of phenol was observed. Intermediate compounds, catechol and quinone, were detected. It was observed that the photodegradation also proceeded with sunlight radiation. A mechanistic and kinetic model, which accounts for the results obtained, is given. Likely reasons for inactivity of the rutile modification for this reaction are also given.

O-xylene oxidation on V 2O 5 - TiO 2 oxide system : II. ESR studies of the catalysts

The ESR spectra of V 2O 5 deposited in different quantities on the surface of anatase or rutile modification of TiO 2 have been registered. The reduced vanadia on both TiO 2 modifications is present in the form of (V=O) 2+ groups dispersed on the TiO 2 surface and V 4+ ions in V 2O 5 phase. (V=O) 2+ groups on anatase containing samples are densely placed, and resistant to oxidation in an oxygen atmosphere. Those on rutile are more scarcely dispersed and are, in contrast to anatase samples, easily oxidized. Comparison of total reduction degree with that determined by the ESR method suggests, moreover, the presence of lower vanadium oxides on rutile containing samples.

O-xylene oxidation on the V 2O 5-TiO 2 oxide system : I. Dependence of catalytic properties on the modification of TiO 2

O-xylene oxidation and isopropanol decomposition have been studied on V 2O 5-TiO 2 oxides prepared by decomposition of a vanadia phase on anatase and rutile modifications of titania under conditions in which the solid state reactions involving formation of solid solutions of vanadium in rutile are excluded. It has been shown that anatase-containing catalysts show higher activity and selectivity in o-xylene oxidation, lower reduction degree of the catalyst in the stationary state of catalytic reaction, and lower dehydration/dehydrogenation ratio as compared with rutile-containing samples. Properties of the rutile-containing catalysts resemble those of pure vanadia: the modifying action of anatase is observed even at low vanadia concentration (XXX 1.0 mole %) and it is ascribed to the formation of a special structure of vanadia of possibly a monolayer type on the anatase surface which exhibits the isopropanol dehydrogenation centres and has low acidity.

Light scattering by SiO x and TiO x films

The scattering intensities of vapour-deposited SiO x films ( x ⪅2) are of the order of 10 -4 if the incidence intensity is unity. This is of the same order of magnitude as the scattering intensity from highly polished optical glass surfaces. The low level of scattering results from the nearly amorphous film structure. Reactively evaporated TiO x films also exhibit a very low scattering intensity, whereas for reactively sputtered TiO 2 films the scattering intensity is strongly dependent on the partial pressure of oxygen in the sputtering gas. For films sputtered in 100% O 2 the scattering level amounts to a few per cent. This is due to the large grain sizes of up to i μm in these films. For low plasma oxygen concentrations TiO 2 films sputtered under unbiased conditions show microcrystalline structures of the anatase modification. However, when the oxygen partial pressure is increased and a bias voltage is applied to the substrate the rutile modification is produced.

Porous titania glass as a photocatalyst for hydrogen production from water

The rutile modification of TiO2 in the form of a powder suspended in water shows promise as a photocatalyst for the production of hydrogen from water1,2. Although hydrogen production was reported3 from pure rutile powder suspended in an aqueous solution, subsequent work1,2 revealed that sustained hydrogen production required Pt or RuO2 on the rutile surface. This limiting usefulness of crystalline rutile in photocatalytic applications has prompted us to investigate the photocatalytic properties of amorphous titania in the form of a porous glass. Here we report an inexpensive method of forming monolithic porous titania glass (PTG) and some properties that make it uniquely suited to photocatalytic applications such as its inexpensive fabrication, its high surface area, and its spontaneous photo-formation of H2 from water without the need for precious metals.

The growth and habit modification of rutile crystals using Li2WO4–WO3 flux

The single crystals of rutile were grown from the flux of the system Li2WO4–WO3. Their growth habits varied through three types, {110}>{101}, {110}>{111} and {111}>{110}≈{253}, with increasing WO3 in the flux melt. TiO2 solubility was measured to determine the reactivity between TiO2 and WO4 or WO6 species in the flux melt. The heat of solution of TiO2 into the Li2WO4 melt was determined to be 49 kcal/mol, and decreased markedly by adding WO3 owing to the large reactivity of TiO2 with WO3 (or WO6).It is inferred that the habit modification of rutile was attributed to the steric interaction of WO6 species which were epitaxially adsorbed on the growing surfaces.

Growth Characteristics of Rutile Film by Chemical Vapor Deposition

Thin film rutile has been grown by the chemical vapor deposition reaction of and O2 on silicon and a variety of oxide substrates over a range of temperatures (673°–1320°K) and reactant partial pressures . At high oxygen partial pressures between 990° to 1100°K, the films have been found to contain the rutile modification of almost exclusively. Polycrystalline deposits on silicon, fused quartz, and amorphous silica (thermally grown or chemically vapor deposited) substrates displayed some preferred growth orientation (fiber texture). Epitaxial films were obtained on (001)‐, (110)‐ and (111)‐rutile, , and (0001)‐sapphire substrates at elevated temperatures.

Enthalpy of Transformation of a High-Pressure Polymorph of Titanium Dioxide to the Rutile Modification

The enthalpy of transformation of a high-pressure form of titanium dioxide, which has the alpha lead dioxide structure, to the rutile modification was measured by the method of "transposed temperature-drop calorimetry." For the reaction, titanium dioxide (alpha lead dioxide form) transforming to rutile, the change in the heat content is -0.76 +/- 0.17 kilocalorie per mole. From this value and the volume change (+ 2.8 percent) associated with the transformation, we estimate the equilibrium pressure at 294 degrees K to be 60 +/- 20 kilobars.

The aging of some pigmented polymeric films

Pigmented films based on different polymers and their blends have been prepared on pine-wood and low-carbon steel substrates, and exposed in laboratory and out-of-doors. In the high humidity cabinet, films based on pentaerythritol alkyd modified with 65% linseed oil and applied to a pine-wood surface, deteriorated by blistering, except those pigmented with titanium dioxide. A blend of the same medium with stabilized chlorinated rubber showed good resistance to degradation in high humidity conditions as well as in marine and industrial environments. In the latter system, especially the combined pigmentations zinc oxide/rutile behaved very well on aging. However, in linseed oil varnish, the combined pigmentation zinc oxide/rutile/basic lead carbonate protected the exposed films very well. The rutile modification of titanium dioxide protects a polymeric film by absorbing ultraviolet light which would otherwise damage it. Also, zinc oxide indicates complete absorption of the shorter wavelengths, and basic lead carbonate transmits much more ultraviolet light. Nevertheless, lead and zinc soap formation with free acids might affect various film properties in the above pigment combination. The highest retention of whiteness was exhibited by the film samples exposed to a marine environment, and the lowest by those exposed to an industrial atmosphere.

Sorption and chemical reaction kinetics in intimate mixtures of a gas with a fluidized particulated catalyst of homogeneous surface

The successive adsorption of some aliphatic amines and carboxylic acid on titanium dioxide (rutile modification) from their vapors and toluene solutions has been studied. It was found that the efficiency of double modification of TiO2 with different modifiers depends on the sequence of their adsorption. From adsorption measurements and mass-spectroscopic thermal analysis, it has been shown that when the rutile surface is modified with vapors of n-butylamine and acetic acid, it is possible for the two substances to interact in the surface layer. As a result, the order in which the amine and the acid are adsorbed affects the structure and properties of the resulting adsorbed layers. Both the displacement of the previously adsorbed substance and the formation of new surface compounds are observed. It has been established that the modifying amine layer on rutile with preadsorbed carboxylic acid is the densest. This layer consists of molecules of both the modifiers and the product of their surface reaction.