Preparation of Nanosized Rutile TiO2 from an Aqueous Peroxotitanate Solution

A new facile method for direct preparation of well-crystallized rutile TiO₂ nanoparticles without any ionic impurities was reported. The nanosized TiO₂ was prepared by aging a peroxotitanate solution at 100°C for 0–12 h, formed by reaction of H₂O₂ and titanium tetraisopropoxide (TTIP). The method involves hydrolysis of TTIP and simultaneous digestion of hydrolyzed precipitates, and hydrothermal treatment into crystalline phases. It was found that the TTIP/H₂O₂ molar ratio in the preparation of peroxotitanate as a precursor for TiO₂ was crucial in the formation of a rutile phase. Transmission electron microscope observation for sols showed rod-like shapes with average particle sizes of around 100 nm in the elongated direction.     

Nitridation of the Sol–Gel-Derived Titanium Oxide Films by Heating in Ammonia Gas

Dip-coated sol–gel-derived TiO₂ films on an alumina substrate were converted to nonstoichiometric titanium nitride (TiN _x ( x ≦ 1)) films by heating at approxmately 1000°C in NH₃ gas. TiO₂ films made from TiO₂ sols prepared from Ti(O– i -C₃H₇)₄ and stabilized by diethanolamine were more easily nitrided than those from sols containing HCl as a deflocculant reagent. This appears to be a result of the more porous structure of the former films.     

Effects of Thermal Annealing on Formation of Micro Porous Titanium Oxide by the Sol–Gel Method

We investigated the structural and optical properties of microporous titanium oxide (TiO₂) fabricated by the sol–gel method using templates of colloidal crystals with polystyrene spheres when the annealing temperature was changed between 600° and 1000°C. From X-ray diffraction patterns and SEM images, the rutile TiO₂ annealed at a high temperature did not form periodic porous bodies, while the anatase TiO₂ annealed at lower than 800°C formed periodic porous bodies. The porous TiO₂ obtained acts as an air-sphere/TiO₂ photonic crystal with an FCC structure. It is suggested that TiO₂ sol annealed at a lower temperature do not lead to phase transition from the anatase phase to the rutile phase to obtain the air-sphere/TiO₂ photonic crystal by the sol–gel method using templates of colloidal crystals.     

Homogeneous Precipitation of TiO2 Ultrafine Powders from Aqueous TiOCl2 Solution

Crystalline TiO₂ powders were prepared by the homogeneous precipitation method simply by heating and stirring an aqueous TiOCl₂ solution with a Ti⁴⁺ concentration of 0.5 M at room temperature to 100°C under a pressure of 1 atm. TiO₂ precipitates with pure rutile phase having spherical shapes 200-400 nm in diameter formed between room temperature and 65°C, whereas TiO₂ precipitates with anatase phase started to form at temperatures >65°C. Precipitates with pure anatase phase having irregular shapes 2-5 µm in size formed at 100°C. Possibly because of the crystallization of an unstable intermediate product, TiO(OH)₂, to TiO₂ x H₂O during precipitation, crystalline and ultrafine TiO₂ precipitates were formed in aqueous TiOCl₂ solution without hydrolyzing directly to Ti(OH)₄. Also, formation of a stable TiO₂ rutile phase between room temperature and 65°C was likely to occur slowly under these conditions, although TiO₂ with rutile phase formed thermodynamically at higher temperatures.     

Fabrication and Microstructure Characterization of Continuous Porous TiO2/Al2O3 Composite Membrane

Using a multipass extrusion process, continuous porous Al₂O₃ body (∼41% porosity) was produced and used as a substrate to fabricate continuous porous TiO₂/Al₂O₃ composite membrane. The diameter of the continuous pores of the porous Al₂O₃ body was about 150 μm. The TiO₂ nanopowders dip coated on the continuous pore-surface Al₂O₃ body existed as rutile and anatase phases after calcination at 520°C in air. However, after aging of the fabricated continuous porous TiO₂/Al₂O₃ composite membrane in 20% NaOH at 60°C for 24 h, a large number of TiO₂ fibers frequently observed on the pore surface. The diameter of the TiO₂ fibers was about 150 nm having a high specific surface area. However, after 48-h aging period, the diameter of the TiO₂ fibers increased, which was about 3 μm. Most of the TiO₂ fibers had polycrystalline structure having nanosized rutile and anatase crystals of about 20 nm.     

Immiscibility Area in the System TiO2–ZrO2–SiO2

A furnace for use in conjunction with the X-ray spectrometer was developed which was capable of heating small powdered specimens in air to temperatures as high as 1850°C. This furnace was also used for the heating and quenching of specimens in air from temperatures as high as 1850°C. An area of two liquids coexisting between 20 and 93 weight % TiO₂ above 1765°± 10°C. was found to exist in the system TiO₂–SiO₂, which is in substantial agreement with the previous work of other investigators. The area of immiscibility in the system TiO₂–SiO₂ was found to extend well into the system TiO₂–ZrO₂–SiO₂. The two liquids were found to coexist over a major portion of the TiO₂ (rutile) primary-phase area with TiO₂ (rutile) being the primary crystal beneath both liquids. The temperature of two-liquid formation in the ternary was found to fall about 80°C. with the first additions of ZrO₂ up to 3%. With larger amounts of ZrO₂ the change in the temperature of the boundary of the two-liquid area was so slight as to be within the limits of error of the temperature measurement. Primary-phase fields for TiO₂ (rutile), tetragonal ZrO₂, and ZrTiO₄ were found to exist in the system TiO₂–ZrO₂–SiO₂. SiO₂ as high cristobalite is known to exist in the system TiO₂–ZrO₂–SiO₂.     

Identification of α-Al2O3 Precipitates in Rutile Single Crystals

After high-temperature reaction between Al₂O₃ and TiO₂ crystals, precipitates found in rutile were characterized by electron microprobe and X-ray diffraction methods and by optical and electron microscopy. The precipitates were identified as α-Al₂O₄. Geometric and crystallographic orientation relations with the TiO₂ matrix constitute a reverse case of rutile precipitation in star sapphire .     

Synthesis of Nanocrystalline TiO2 Particles by Hydrolysis of Titanyl Organic Compounds at Low Temperature

Fourier transform infrared analysis, nuclear magnetic resonance, and thermogravimetric analysis show that most of the solid product prepared from the reaction of Ti(OC₄H₉)₄ and excess (CH₃CO)₂O is a mixture of titanyl organic compounds. Nanocrystalline TiO₂ particles, which include anatase TiO₂, rutile TiO₂, and a mixture of anatase and rutile, can be obtained from hydrolysis of the titanyl organic compounds under normal pressure at 60°C. The particle size, shape, and formation process of the crystals have been studied using X-ray diffraction and transmission electron microscopy. The specific-surface-area data for a rutile TiO₂ sample and the powders obtained after calcination at different temperatures have been measured by the Brunauer–Emmett–Teller method.     

Anatase-to-Rutile Transformation in Titania Powders

Titania (TiO₂) is an important electronic ceramic material for use in diverse applications such as gas sensors, catalysts, dielectrics, and ceramic membranes. TiO₂ exists as several polymorphic phases, most commonly as rutile or anatase. This paper investigates the microstructural evolution of anatase-based commercial TiO₂ powders, with an average size of 100 nm, at high temperatures. These powders transform to the rutile structure at 1000°C. The characteristics of the anatase-to-rutile transformation have been studied using transmission electron microscopy analysis, and new information regarding the nature and mechanisms of this polymorphic reaction has been revealed.     

Dopants in Flame Synthesis of Titania

The effect of dopants on the characteristics of titania particles made by oxidation of TiCl₄ in a laminar diffusion flame reactor is presented. Introduction of dopant SiCl₄ inhibits the transformation of anatase to rutile, due to the formation of interstitian solid solution of SiO₂ and TiO₂. Silica decreases the sintering rate of titania and decreases the primary particle size, and, as a result, the specific surface area increases. Intruduction of SnCl₄ enhances the transformation of anatase to rutile, due to the similar crystalline structure of SnO₂ and rutile titania. However, the presence of SnO₂ and rutile titania. However, the presence of SnO₂ does not affect the primary particle size or the specific surface area of titania particles. Introduction of AICI₃ enhances the transformation of anatase to rutile, due to the formation of excess oxygen vacancies as Al₂O₃ and TiO₂ form a substitutional solid solution.     

Antibacterial Activity of Photocatalytic Titanium Dioxide Thin Films with Photodeposited Silver on the Surface of Sanitary Ware

The antibacterial activity of photocatalytic titanium dioxide (TiO₂) thin films with photodeposited silver on the surface of sanitary ware was studied. Samples were prepared by coating a TiO₂ sol that was calcined at 880°–980°C and photodeposited with silver ions onto the glazed layer of the sanitary ware. The relationships between the antibacterial activity and the fabrication conditions were investigated by X-ray diffractometry, scanning electron microscopy, and colorimetry. The phase of TiO₂ identified in the thin films was a mixture of anatase and rutile. The amount of rutile phase increased as the calcination temperature increased, and grain growth of the TiO₂ particles was observed. The activity was dependent on the TiO₂ thickness, the calcination temperature, and the amount of silver. These results suggest that the antibacterial activity was strongly affected by the amount of anatase in the thin films.     

Thermal Treatment of Titanate Derivatives Synthesized by Ion-Exchange Reaction

TiO₂ fibers were formed by thermal treatment of layered H₂Ti₄O₉ (hydrous titanium dioxide) and KHTi₄O₉ synthesized by ion-exchange reactions. The calcination of the former at 900° and 1050°C for 3 h yielded TiO₂ fibers with anatase and rutile phases, whose length and diameter were 15–20 and 2–5 μm and 10–15 and 3–5 μm, respectively. The thermal treatment of the latter at temperatures of 250° to 500°C yielded pure K₂Ti₈O₁₇, which tended to decompose to K₂Ti₆O₁₃ and TiO₂ at temperatures >600°C. At 1050°C, K₂Ti₆O₁₃ phase was formed with rutile TiO₂ fibers, whose length and diameter were 10–20 and 1–3 μm, respectively.     

Preparation of Necklace-Structured TiO2/SnO2 Hybrid Nanofibers and Their Photocatalytic Activity

TiO₂/SnO₂ nanonecklace-structured hybrid nanofibers have been prepared via an electrospinning method. These hybrid nanofibers are characterized with SnO₂-rich beads and pure TiO₂ chains. It is found that TiO₂ in the beads shows a rutile structure, and the one in the chains is entirely composed of anatase phase. This novel microstructure enhanced the photocatalytic activity, as well as its ideal recyclable character. We believe that this fire-new type of nanofiber may potentially serve as a new generation photocatalyst in environmental remediation.     

Subsolidus Phase Relationships in the Ga2O3–Al2O3–TiO2 System

Subsolidus phase relationships in the Ga₂O₃–Al₂O₃–TiO₂ system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO₂ (rutile), Ga_{2−2 x} Al_{2 x} O₃ ( x ≤0.78 β-gallia structure), Al_{2−2 y} Ga_{2 y} O₃ ( y ≤0.12 corundum structure), Ga_{2−2 x} Al_{2 x} TiO₅ (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga_{4−4 x} Al_{4 x} Ti _{n −4}O_{2 n −2} ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work.     

Synthesis of a Visible-Light Active TiO2−xSx Photocatalyst by Means of Mechanochemical Doping

A visible-light active TiO_{2− x} S _x in rutile structure has been synthesized by means of a mechanochemical method. The method is composed of two steps: the first is grinding the mixture of sulfur and TiO₂, and the second is calcining the ground sample at 673 K in an inert gas flow. XPS analysis confirms that sulfur has been successfully doped into TiO₂. The calcined sample under irradiation of visible light with wave-length over 510 nm has shown good performance for NO gas destruction, suggesting its high photograph-reactivity.     

Structural and Optical Characterization of Flower-Like Rutile Nanostructures Doped with Fe3+

Flower-like agglomerates with sizes of 200–400 nm of pure and Fe³⁺-doped TiO₂ with rutile crystalline structure were synthesized by the coprecipitation method. The morphology of the agglomerates was determined by electron microscopy (TEM and HRTEM). TiO₂ agglomerates consist of nanorods with clearly visible crystalline faces, parallel to the axis of elongation whose direction was along the [101] direction of pure TiO₂ and the [111] direction of doped TiO₂. Furthermore, nanorods consist of "chains" of spherical particles, most likely interconnected through the so-called oriented attachment or grain-rotation-induced grain coalescence (GRIGC) process. UV/Vis reflection measurements revealed that the absorption of pure TiO₂ was significantly shifted from UV toward the visible spectral region upon the incorporation of Fe³⁺ into the TiO₂ host.     

Origin of Microwave Dielectric Loss in ZnNb2O6-TiO2

(1− x )ZnNb₂O₆· x TiO₂ ceramics were prepared using both anatase and rutile forms of TiO₂. At a composition of x = 0.58, a mixture region of ixiolite (ZnTiNb₂O₈) and rutile was observed and the temperature coefficient of resonant frequency (τ_f) was ∼0 ppm/°C. We found that although ɛ_r and τ_f were comparable, the quality factor ( Q × f , Q ≈ 1/ tan δ, f = resonant frequency) of 0.42ZnNb₂O₆·0.58TiO₂ prepared from anatase and rutile was 6000 and 29 000, respectively. The origin of the difference in Q × f of both samples was investigated by measuring electrical conductivity and by analysis of the anatase–rutile phase transition. The anatase-derived sample had higher conductivity, which was related to the reduction of Ti⁴⁺. It is suggested that the increase of dielectric loss originates from an increase in Ti³⁺ and oxygen vacancies due to an anatase–rutile phase transition.     

Direct Formation of Iron(III)-Doped Titanium Oxide (Anatase) by Thermal Hydrolysis and Its Structural Property

Anatase-type TiO₂ (titania) doped with iron up to 19.8 mol% was directly formed as nanometer-sized particles from acidic precursor solutions of TiOSO₄ and Fe(NO₃)₃ by simultaneous hydrolysis, under mild hydrothermal conditions at 180°3C. Iron content in the anatase-type TiO₂ was much less than that of the starting composition of the precursor solutions because of slower hydrolysis rate of Fe(NO₃)₃ than that of TiOSO₄ at 180°3C. The XRD data, TEM selected-area diffraction patterns, and Mössbauer effect measurement showed that iron(III) formed a solid solution in the anatase-type TiO₂ precipitates and that there was no iron oxide precipitated as secondary phase without making a solid solution with TiO₂ present in the precipitates. Doping of Fe₂O₃ into TiO₂ shifted the phase transformation from anatase-type to rutile-type structure to a low temperature. On the phase transformation from anatase to rutile, iron oxide was precipitated as Fe₂TiO₅ (pseudobrookite) phase. When the iron content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV-light region and in the visible-light region over 400–600 nm clearly appeared in the diffuse reflectance spectra of the as-prepared Fe(III)-doped TiO₂.     

Characterization and Tribological Investigation of Sol–Gel Titania and Doped Titania Thin Films

Titania (TiO₂) and doped TiO₂ ceramic thin films were prepared on a glass substrate by a sol–gel and dip-coating process from specially formulated sols, followed by annealing at 460°C. The morphologies of the original and worn surfaces of the films were analyzed with atomic force microscopy (AFM) and scanning electron microscopy. The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of TiO₂ and doped TiO₂ thin films sliding against Si₃N₄ ball were evaluated on a one-way reciprocating friction and wear tester. The AFM analysis shows that the morphologies of the resulting films are very different in nanoscale, which partly accounts for their tribological properties. XPS analysis reveals that the doped elements exist in different states, such as oxide and silicate, and diffusion took place between the film and the glass substrate. TiO₂ films show an excellent ability to reduce friction and resist wear. A friction coefficient as low as 0.18 and a wear life of 2280 sliding passes at 3 N were recorded. Unfortunately, all the doped TiO₂ films are inferior to the TiO₂ films in friction reduction and wear resistance, primarily because of their differences in structures and chemical compositions caused by the doped elements. The wear of the glass is characteristic of brittle fracture and severe abrasion. The wear of the TiO₂ thin film is characteristic of plastic deformation with slight abrasive and fatigue wear. The doped TiO₂ thin films show lower plasticity than the TiO₂ thin film, which leads to large cracks. The propagation of the cracks caused serious fracture and failure of the films.     

Preparation of 〈110〉-Textured BaTiO3 Ceramics by the Reactive-Templated Grain Growth Method Using Needlelike TiO2 Particles

Dense, highly 〈110〉-textured BaTiO₃ ceramics were prepared by the reactive-templated grain growth method. Needlelike TiO₂ (rutile) particles with their needle axis parallel to 〈001〉 were used as reactive template particles. Slurry containing an equimolar mixture of TiO₂ and BaCO₃ was tape cast to form a green compact, in which TiO₂ particles were aligned with their needle axis parallel to the casting direction. Calcination of the green compact changed TiO₂ particles into BaTiO₃ grains with their 〈110〉 direction parallel to the casting direction, for which the topotaxial relation of was responsible. Sintering yielded a dense, highly textured BaTiO₃ compact.