Low-Temperature Nucleation of Rutile Observed by Raman Spectroscopy during Crystallization of TiO2

The thermal evolution of amorphous TiO₂ powders, consisting of spherical particles and prepared by hydrolysis of a titanium ethoxide aerosol, was studied by using Raman spectroscopy. On calcination at 350°C, the solid crystallized, giving anatase as a major phase. A small amount of rutile was also detected and attributed to small seeds localized at the particle outlayer. The nucleation of rutile at so low a temperature was ascribed to the presence of organic impurities in the powders. The transformation of anatase into rutile was clearly observed after heating at 660°C.     

Facile synthesis of mesoporous titanium dioxide nanocomposites with controllable phase compositions by microwave-assisted esterification

Mesoporous titanium dioxide nanocomposites with controllable phase compositions and high surface areas were synthesized through convenient, fast, and one-step microwave-assisted esterification method. The introduction of microwave in the synthetic reactions not only accelerates the esterification reaction but also promotes the fast crystallization. By changing reaction temperature, microwave irradiation time, the amount of staring materials and the composition of solvents, pure anatase, pure rutile or mixed phase titanium dioxide nanocomposites were obtained in minutes. Meanwhile, the size of crystallite can be controlled by the reaction temperature. The as-synthesized materials display significative photocatalytic activities without any further disposal, among which the material with 3.6% rutile shows the best effect in degradation of methylene blue under UV-light irradiation. Moreover, the nitrogen adsorption–desorption results illustrate the obtained samples are mesophases. It is also interesting that the pure rutile has specific surface area as high as 210 m² g^?1 calculated by BET equation. The method can control the hydrolysis of TiCl₄ well and dramatically shorten the preparation time of titanium dioxide.     

Low-Temperature Growth of Monolayer Rutile TiO2 Nanorod Films

Low-temperature growth of well-crystallized titania thin films with controlled nanofeatures are of great interest because of their potential uses in catalysts, gas sensors, photovoltaic cells, photonic crystals, etc. This paper reports the synthesis of a well-crystallized, pure rutile monolayer consisting of well-aligned nanorods with average diameters of ca. 25 nm and an aspect ratio of ca. 6 through a simple solution approach at a low temperature of 80°C. The monolayer nanorods precipitate from the precursors that were obtained through the reaction between metallic titanium and hydrogen peroxide solutions at 80°C for 24–60 h. The nanoporous titania thin layer derived by oxidizing the titanium substrate with hydrogen peroxide at 80°C for 10 min facilitates the growth of the monolayer rutile TiO₂ nanorod films.     

Titanium and Alloy Surfaces for Adhesive Bonding

The nature of the oxide on the surface of titanium and the Ti-6Al-4 V alloy after a number of recommended treatments has been examined by x-ray and electron diffraction. No evidence for material other than titania in its rutile form was obtained even though anatase and fluoride have been reported. The most efficient surface for adhesive bonding is a rough surface of the black oxide such as is produced by treatment of the metal in alkaline hydrogen peroxide.     

Titanium and Alloy Surfaces for Adhesive Bonding

The nature of the oxide on the surface of titanium and the Ti-6Al-4 V alloy after a number of recommended treatments has been examined by x-ray and electron diffraction. No evidence for material other than titania in its rutile form was obtained even though anatase and fluoride have been reported. The most efficient surface for adhesive bonding is a rough surface of the black oxide such as is produced by treatment of the metal in alkaline hydrogen peroxide.     

Phase Formation and Microstructure of Titanium Oxides and Composites Produced by Thermal Plasma Oxidation of Titanium Carbide

The phase formation and microstructure of titanium oxides and composites produced by Ar–O₂ thermal plasma oxidation of titanium carbide powders were investigated in detail by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Relationships between the phase compositions and microstructures of the oxides were established by combined structural and phase analyses, in correlation with synthesis conditions and phase formation mechanisms. It is revealed that vapor condensation favored the formation of anatase, which existed as smaller particles, while liquid/solid oxidation favored the formation of rutile, which appeared as larger particles or composites. A higher oxygen input in the plasma gases (Ar + O₂) enhanced the formation of anatase due to impeded oxidation and evaporation. A small amount of Ti₄O₇ and Ti₃O₅ was detected in the larger particles coexisting with rutile or TiC. These suboxides were formed as intermediates in solid oxidation of TiC or precipitated from the Ti–C–O melt during cooling. Furthermore, extensive cracks, dislocations and stresses were observed in the monolithic rutile and composites, in association with the rapid quenching in this high-temperature in-flight oxidation process.     

Conditions for the production of pigmentary titanium dioxide of rutile and anatase modifications by ilmenite processing with ammonium fluoride

The process of ammoniac precipitation of hydrated titanium dioxide from a solution of ammonium hexafluorotitanate obtained during ilmenite processing by ammonium fluoride with the further sublimation separation of titanium tetrafluoride has been studied. The dehydration of hydrated titanium dioxide has been studied. The phase structure of titanium dioxide, depending on the thermal treatment and precipitation conditions, has been investigated. The size of the sample particles has been studied with the method of electron microscopy. The conditions of rutile and anatase pigments production have been determined.     

Photooxidation of organic compounds in a solution containing hydrogen peroxide and TiO2 particles under visible light

Cyclohexane was oxidized under visible light in a titanium dioxide suspension containing hydrogen peroxide. Cyclohexanol and cyclohexanone were detected as products. Under similar experimental conditions, nonyl aldehyde was oxidized to nonylic acid. The reaction rate for the oxidation on rutile particles was faster than that on anatase particles. When hydrogen peroxide was added to suspensions of these particles, both rutile and anatase particles became yellow-colored due to the formation of peroxide complexes on their surfaces. The difference between the reaction rates for rutile and anatase particles suggests that the properties of the peroxide complexes formed on these particles are different. The properties of these complexes were studied by UV–vis spectroscopy.     

TiO2, TiO2/Ag and TiO2/Au photocatalysts prepared by spray pyrolysis

TiO₂, TiO₂/Ag and TiO₂/Au photocatalysts exhibiting a hollow spherical morphology were prepared by spray pyrolysis of aqueous solutions of titanium citrate complex and titanium oxalate precursors in one-step. Effects of precursor concentration and spray pyrolysis temperature were investigated. By subsequent heat treatment, photocatalysts with phase compositions from 10 to 100% rutile and crystallite sizes from 12 to 120 nm were obtained. A correlation between precursor concentration and size of the hollow spherical agglomerates obtained during spray pyrolysis was established. The anatase to rutile transformation was enhanced with metal incorporations and increased precursor concentration. The photocatalytic activity was evaluated by oxidation of methylene blue under UV-irradiation. As-prepared TiO₂ particles with large amounts of amorphous phase and organic residuals showed similar photocatalytic activity as the commercial Degussa P25. The metal incorporated samples showed comparable photocatalytic activity to the pure TiO₂ photocatalysts.     

TiCl_4气相氧化法制备金红石型TiO_2的工艺

以粗TiC l4(98.0%)为主要原料,通过白矿物油除钒提纯处理后,采用气相氧化法制备出金红石型TiO2,并分析了粉体的相关性能。研究表明,制备的金红石型TiO2具有较高的晶型转化率(100.0%)、白度(102.08%)和消色力(123%),且粒度适宜(258 nm)、粒度分布较窄、近似球形、分散性好等优异性能。A lC l3蒸气在气相反应中起到了晶型转化剂的作用。当A lC l3加入量增加至2.6%以上时,TiO2的晶型转化率达到了最大值100.0%。     

Low-Temperature Preparation of Anatase and Rutile Layers on Titanium Substrates and Their Ability To Induce in Vitro Apatite Deposition

Surface modification of titanium and its alloys to induce apatite deposition within a short period is of practical importance in clinical applications. In this study, titanium substrates were treated with hydrogen peroxide solutions at low temperatures to yield titania layers consisting of anatase and rutile. Those titania layers, regardless of the fraction of anatase and rutile, were bioactive to induce deposition of apatite in Kokubo's simulated body fluid within 24 h. The bioactivity was attributed to both the epitaxial effect and the abundant Ti–OH group of the titania layer.     

改性电炉钛渣矿相解构法制备富钛料新工艺研究

以氧化后的钛精矿电炉冶炼渣为研究对象,采用一段氟化氢铵浸出-二段盐酸浸出的新工艺制备可用于沸腾氯化生产的富钛料原料,从浸出反应热力学和改性钛渣浸出行为两方面进行了系统的研究。氟化氢铵浸出热力学研究表明,氟化氢铵浸出可分解硅酸盐和部分黑钛石,并形成CaMg2Al2F12, CaF2和AlF3沉淀,浸出后杂质元素硅主要以(NH4)2SiF6的形式进入到浸出液中。氟化氢铵浸出实验表明,在氟化氢铵浓度为15wt%、液固比为10:1、温度20℃、浸出时间2 h的条件下,Si, Al, Ti, Fe, Ca和Mg元素的浸出率分别为93.55wt%, 28.03wt%, 3.88wt%, 20.50wt%, 3.40wt%和2.45wt%。浸出渣中主要的物相为金红石、黑钛石和钙镁氟化盐。氟化浸出残渣的盐酸浸出热力学表明,CaMg2Al2F12, CaF2, AlF3沉淀和剩余的黑钛石可溶解于盐酸溶液中。盐酸浸出实验表明,在盐酸浓度为20wt%、液固比为8:1、温度120℃、浸出时间2 h的条件下,Ca, Al, Mg, Ti, Si和Fe的浸出率分别为86.78wt%, 62.33wt%, 92.31wt%, 18.08wt%, 40.23wt%和75.36wt%。盐酸浸出后浸出渣主要物相为金红石,TiO2品位95.20wt%、CaO含量为0.49wt%、MgO含量为0.48wt%,满足沸腾氯化法对原料成分的要求。     

Ion implantation of oxygen and nitrogen in CpTi

A study of the plasma ion implantation (PIII) of commercially pure titanium (CpTi) at a low voltage (<4 kV) is presented. The processed samples were treated in divers mixtures of O and N in order to achieve biocompatible oxidized and nitrided layers as well as to enhance their superficial hardness. In this way, the low wearing resistance of CpTi can be avoided while creating a biocompatible rutile phase titanium oxide layer for a better bone integration. A form of synergy associated to the dependence of microhardness on the implanted layer disposition is identified. Thus, an upper rutile layer is immediately followed by another one, in which titanium, a nitride (TiN_0.26) and rutile coexist. The latter leads to a superior microhardness performance. Most of all these surface treatments of titanium, when applying an 80%N–20%O mixture, yield higher corrosion resistance parameters with respect to the main metallic materials used in prosthetics, including the Co–Cr–Mo alloys, albeit excluding CpTi.     

熔盐法处理富钛渣制备金红石型TiO_2

工业生产钛白粉的方法主要有硫酸法和氯化法两种,但这两种方法都存在环境污染严重的问题。本文提出了一种常压、低温下钠碱熔盐分解富钛渣制备金红石型二氧化钛的新工艺,从生产源头消除了对环境的污染,实现钛资源的可持续发展。介绍了该反应的制备、水洗、固相离子交换-水解耦合和煅烧过程。实验结果表明,该工艺可以制得理想的金红石型二氧化钛,二氧化钛含量为96.66%。     

Low temperature synthesis of visible light responsive rutile TiO2 nanorods from TiC precursor

A nano-structured TiO₂ with rutile phase was synthesized by using the hydrothermal method from a titanium carbide (TiC) nano-powder precursor at low temperature to produce a stable visible light responsive photocatalyst. The rutile phase was formed at temperature as low as 100°C, and both synthesis time and temperature affected its formation. The rutile particles showed a faceted nano-rod structure, and were tested for absorption and photo-degradation ability under visible light. Particles with shorter synthesis times showed higher visible light absorption and corresponding photo-degradation ability, while those synthesized at lower temperatures had lower, but still evident, degradation ability under visible light.     

Growth and Phase Transformation of Nanometer-Sized Titanium Oxide Powders Produced by the Precipitation Method

We report an in situ TEM investigation of the growth and transformation in nanometer-sized titania powders. The powders were produced through precipitation of titanium tetrachloride under different pH conditions. The initial phase of the produced powders was amorphous or was a mixture of anatase and brookite according to the pH conditions. During calcination, the anatase particles grew and transformed into rutile. The transformation temperature increased with increasing pH value. In situ TEM observations showed that the anatase particles were absorbed into rutile, and then rutile particles grew by coalescence. Furthermore, small pores were observed to form in samples prepared with high pH from the effects of hydroxyl ions and zeta potential. Pore formation increased the surface area, which delayed the transformation and nucleation of rutile. This explains the difference of growth and transformation of titania powders produced under different pH conditions during calcination.     

Conversion Efficiency of Alkoxide Precursor to Oxide Films Grown by an Ultrasonic-Assisted, Pulsed Liquid Injection, Metalorganic Chemical Vapor Deposition (Pulsed-CVD) Process

Polycrystalline coatings of an oxide, with a columnar grain morphology, were grown on metal substrates from metalorganic precursors using the pulsed-CVD process. In a model study, films of the rutile phase of titanium dioxide were grown on nickel by thermal decomposition of titanium isopropoxide. Growth rates of up to 0.3 µm/min were obtained with conversion efficiencies (mole oxide per mole precursor) approaching 100%. The high growth rates and conversion efficiencies portend the application of this method for the manufacture of films and coatings on large surface areas, as, for example, required in the deposition of zirconium dioxide on nickel-based superalloys to serve as thermal barrier coatings on turbine blades.     

Characterization of titanium-boron binary oxides and their photocatalytic activity for stoichiometric decomposition of water

A titanium-boron binary oxide has been prepared by sol–gel method and used as a photocatalyst for the decomposition of water. The structure of titanium oxide species in the Ti/B binary oxide was amorphous before and crystal after calcination in O₂, while the boron oxide species maintained its amorphous state. With increasing calcination temperature, the crystalline structure of titanium oxides changed from an anatase phase to a rutile phase. Pt-loaded Ti/B photocatalysts decomposed water stoichiometrically in aqueous suspension system. Their photocatalytic activity decreased markedly with increase in the calcination temperature, indicating that the photocatalytic activity of the Ti/B binary oxide was strongly dependent on the crystal phase of the titanium oxide in the Ti/B binary oxide. A remarkable yield in the reaction of water decomposition was obtained when Na₂CO₃ was added in the Pt-loaded Ti/B binary oxide suspension.     

Titania Nanoflowers with High Photocatalytic Activity

Titania with nanostructures has attracted considerable attention due to its potential use in catalysts, gas sensors, photovoltaic cells, photonic crystals, etc. This paper reports the synthesis of titania nanoflowers by simply oxidizing pure titanium with hydrogen peroxide solutions containing hexamethylenetetramine and nitric acid at a low temperature of 353 K. Titania nanoflowers with the crystal structure of anatase or a mixture of anatase and rutile were obtained after a subsequent thermal treatment to crystallize the as-precipitated amorphous structure. Photocatalytic tests revealed an excellent photocatalytic property of the titania nanoflowers.     

攀枝花钛精矿氧化改性研究

根据目前钛资源综合利用发展方向,采用XRD、矿物扫描电镜和热重-差热分析方法对攀枝花钛精矿加热过程中氧化效果及物相结构转化进行分析,得出了攀枝花钛精矿起始氧化温度、氧化率增长趋势及物相转化情况（在氧化过程中钛精矿主要物相由钛铁矿相依次向铁板钛矿相、金红石相、假板钛矿相转化）。为攀枝花钛精矿氧化改性生产高品质钛原料提供了理论基础。