Properties of TiO2 film prepared from titanium tetrachloride

The properties of TiO₂ film prepared by titanium tetrachloride were investigated with respect to annealing temperatures in terms of phase change, crystallite size, and band gap energy. The TiO₂ film dried at room temperature exhibited an amorphous phase, while films calcined above 281 and at 990°C displayed anatase TiO₂ and a mixture of anatase and rutile, respectively. The TiO₂ film was transformed to an anatase phase through three stages during the annealing processes: (1) removal of water, (2) decomposition of a peroxo group, and (3) amorphous-anatase phase transformation. It was also found that the bandgap energy of TiO₂ film was changed with increasing annealing temperature. This is attributed to the quantum size effect in the range of 475–675°C and to the formation of rutile phase having lower band gap energy than anatase in the range of 675–990°C.     

Optimization of Oxidation Temperature for Commercially Pure Titanium to Achieve Improved Corrosion Resistance

Thermal oxidation of commercially pure titanium (cp-Ti) was carried out at different temperatures, ranging from 200 to 900 °C to achieve optimum corrosion resistance of the thermally treated surface in simulated body fluid. Scanning electron microscopy, x-ray diffraction, Raman spectroscopy and electrochemical impedance spectroscopy techniques were used to characterize the oxides and assess their protective properties exposed in the test electrolyte. Maximum resistance toward corrosion was observed for samples oxidized at 500 °C. This was attributed to the formation of a composite layer of oxides at this temperature comprising Ti₂O₃ (titanium sesquioxide), anatase and rutile phases of TiO₂ on the surface of cp-Ti. Formation of an intact and pore-free oxide-substrate interface also improved its corrosion resistance.     

Effects of Calcination on Structural, Photocatalytic Properties of TiO2 Nanopowders Via TiCl4 Hydrolysis

Photocatalytic degradation of methyl orange (MO) in water was examined using TiO₂ nanopowders under solar irradiation. These photocatalysts were successfully synthesized by hydrolysis of titanium tetra chloride (TiCl₄) in the temperature range of 70-95 °C and calcined at higher temperatures of between 400 and 900 °C. The samples prepared were characterized using x-ray powder diffraction, scanning electron microscope (SEM) and Fourier transform infrared spectrophotometer (FTIR). UV-Vis spectrometer was used for analyzing the concentration of MO in solution at different time intervals during the photodegradation experiment. Parameters affecting the photodegradation rate such as catalyst crystallinity, concentration of the catalyst, MO concentration, and pH of the solution have been investigated. The results indicate that TiO₂ nanopowder was antase at low calcination temperatures in the range of 400-500 °C. The sample calcined at 600 °C is composed of both anatase and rutile phase. Further increase in the temperature enhanced the intensities of diffraction peaks of the rutile phase. The size of the crystallites for all the samples prepared were found to be in the 6-13 nm range and from SEM micrographs it was in the range of 19-43 nm. The mixture of both phases exhibited a higher photoactivity in comparison with pure anatase or rutile catalysts.     

The improvement of high-temperature oxidation of Ti–50Al by anodic coating in the phosphoric acid

The high temperature cyclic oxidation resistance of Ti–50Al can be improved by anodic coating in phosphoric acid aqueous solution (4 wt% H₃PO₄) at 18°C. Sparking occurs sporadically on the surface as the voltage is over 300 V and the instantaneous current density after 45 min of anodization increases with increasing voltage. The anodic films are amorphous and contain substantial amount of phosphorus. Cyclic oxidation test indicates that the anodization can remarkably reduce the oxidation in air at 800°C and the improvement increases with increasing anodizing voltage up to 400 V, at which the parabolic oxidation rate constant can be reduced to about 1/600 of that for as-homogenized Ti–50Al. Raman spectra show that the anodic film can slow down the formation of rutile and α-Al₂O₃ during oxidation. The doping effect of phosphorus ions in titanium oxide accounts for the improvement of high temperature oxidation of Ti–50Al.     

Structure of calcium titanate/titania bioceramic composite coatings on titanium alloy and apatite deposition on their surfaces in a simulated body fluid

In this study, TiO₂-based coatings containing Ca and P ions were prepared on titanium alloy surfaces by microarc oxidation (MAO). After soaking in aqueous NaOH solution and subsequent heat treatment at 700 and 800 °C, calcium titanate/titania bioceramic composite (CTBC) coatings were obtained. The results show that the outer layers (0–1.5 μm) of the CTBC coatings are mainly composed of Ca, Ti, O and Na constituents with a uniform distributions with increasing the depth near the surfaces. The surface phase compositions of the CTBC coating formed at 700 °C are anatase, rutile and CaTi₂₁O₃₈ phases, as well as a few CaTiO₃, while those of the CTBC coating formed at 800 °C are anatase, rutile and CaTiO₃. When incubated in a simulated body fluid (SBF), apatite was deposited on the CTBC coatings probably via formation of hydroxyl functionalized surface complexes on the CTBC coating surfaces by ionic exchanges between (Ca²⁺, Na⁺) ions of the CTBC coatings and H₃O⁺ ions in the SBF. The CTBC coating formed at 800 °C seems to facilitate the deposition of Ca and P probably due to the good crystallographic match between perovskite CaTiO₃ and HA on specific crystal planes.     

Preparation of titanium dioxide nanotube arrays on titanium mesh by anodization in (NH4)2SO4/NH4F electrolyte

The self‐organized titanium dioxide (TiO₂) nanotube arrays on titanium mesh were prepared by electrochemical anodization with the neutral electrolyte containing ammonium sulfate and ammonium fluoride in a two‐electrode electrochemical cell. The effects of the fluoride ion concentration, the anodic potential, and the oxidation time on the formation of the titanium dioxide nanostructures on titanium mesh with complex geometry were investigated. The anodized titanium mesh was characterized by field emission scanning electron microscope and in situ high temperature X‐ray diffraction. The results show that the titanium dioxide nanotube arrays are grown in a radially outward direction around the titanium wire. The optimized anodization condition for preparing titanium dioxide nanotube arrays with superior architecture on the titanium mesh is 0.5 wt% of ammonium fluoride, 20 V of applied potential, and 20 min of oxidation time. The amorphous titanium dioxide nanotubes on titanium mesh turn to anatase phase at 400 °C and further to rutile phase at 650 °C.     

Preparation and crystalline phase of a TiO2 porous film by anodic oxidation

Anatase titanium dioxide is an active photocatalyst, but it is difficult to immobilize on the substrate. A crystalline TiO2 porous film was prepared directly on the surface of pure titanium by anodic oxidation in this work. Constant voltage and constant current anodic oxidation were adopted with sulphuric acid used as the electrolyte, pure titanium as the anode and copper as the cathode. The morphology and structure of the porous film on the substrate were analyzed with the aid of Field Emission Scanning Electron Microscopy （FESEM） and X-ray Diffraction （XRD）. The effects of the parameters of anodic oxidation （such as voltage, the concentration of sulphuric acid, anodization time and current density） on the aperture and the crystalline phase of the TiO2 porous film were systematically investigated. The results indicate that the increase of current density facilitates the augment of the aperture and the generation of anatase and mille. In addition, the forming mechanism of anatase and mille TiO2 porous films was discussed.     

Increasing the Upper Temperature Oxidation Limit of Alumina Forming Austenitic Stainless Steels in Air with Water Vapor

A family of alumina-forming austenitic (AFA) stainless steels is under development for use in aggressive oxidizing conditions from ~600?C900 °C. These alloys exhibit promising mechanical properties but oxidation resistance in air with water vapor environments is currently limited to ~800 °C due to a transition from external protective alumina scale formation to internal oxidation of aluminum with increasing temperature. The oxidation behavior of a series of AFA alloys was systematically studied as a function of Cr, Si, Al, C, and B additions in an effort to provide a basis to increase the upper-temperature oxidation limit. Oxidation exposures were conducted in air with 10% water vapor environments from 800?C1000 °C, with post oxidation characterization of the 900 °C exposed samples by electron probe microanalysis (EPMA), scanning and transmission electron microscopy, and photo-stimulated luminescence spectroscopy (PSLS). Increased levels of Al, C, and B additions were found to increase the upper-temperature oxidation limit in air with water vapor to between 950 and 1000 °C. These findings are discussed in terms of alloy microstructure and possible gettering of hydrogen from water vapor at second phase carbide and boride precipitates.     

Comportement des revetements de carbonitrure de titane en atmosphere oxydante—premiere partie: Action de l'oxygene

The oxidation rate of a titanium carbonitride film formed on titanium by pure oxygen has been followed between 600 and 950°C. The product of the reaction is porous dioxide TiO₂ (rutile). After an approximately parabolic first stage, the reaction rate remains constant until the complete disappearance of the carbonitride film. This rate lies in the same range as that of the oxidation of the metal. The influence of the pressure has been investigated between 10 and 400 torrs.     

Oxidation Behavior of Tribaloy T-800 Alloy at 800 and 1,000 °C

The oxidation behavior of Co-based Tribaloy T-800 alloy has been studied isothermally in air at 800 and 1,000 °C, respectively. The results showed that the oxidation mechanism was dependent on the exposure temperature. The oxidation of the alloy followed subparabolic oxidation kinetics at 800 °C. The oxide scale at this temperature exhibited a multi-layered structure including an outer layer of Co oxide, a layer composed of complex oxide and spinel, a nonuniform Mo-rich oxide layer, an intermediate mixed oxides layer and an internal attacked layer with different protrusions into Laves phase. During 1,000 °C exposure, it followed linear kinetics. The oxidation rendered a relatively uniform external Cr-rich oxide layer coupled with a thin layer of spinel on the top surface and voids at local scale/alloy interface and intergranular region together with internal Si oxide at 1,000 °C.     

钛铁矿（FeTiO3）粉末的氧化过程中的物相转变、微观形貌及其氧化机制

探讨钛铁矿氧化过程中的物相转化、形貌改变及其氧化机理。在700~800°C时,钛铁矿(FeTiO3)转变为赤铁矿(Fe2O3)和金红石(TiO2),当温度高于900°C时,三价铁板钛矿开始形成。原始的钛铁矿粉末呈现顺磁性,但是经过中温(800~850°C)氧化后,氧化产物呈现弱铁磁性。同时,讨论钛铁矿的氧化机理。通过对微结构的观察,发现在中温氧化过程中颗粒表面出现大量微孔,其在氧化过程中能够强化氧的传质。     

Oxidation of Ag–Sn–La Alloy Powders

The gas atomized Ag-9.26wt%Sn-0.44wt%La alloy powders were oxidized in air between 400 and 900 °C. The oxidation thermodynamics, kinetics and microstructure of the alloy were investigated. We suggested that the addition of La may accelerate oxidation of Sn and prevent the formation of the dense SnO₂ film. The suitable oxidation temperature of the alloy powders is 800 °C in air. After internal oxidation, many cracks were observed on the surface of the alloy powders. In addition, the whole oxidation process of the alloy powders is controlled by the oxygen diffusion. The diffusion coefficient of oxygen in the alloy powders at 800 °C is about 1.5 times larger than that at 700 °C on the initial stage of internal oxidation, while that is 4.5 times on the subsequent stage.     

纯钛TIG焊接接头的高温氧化行为

对纯钛氩弧焊焊接接头在550 ℃下氧化不同时间（2,4,6,8 h）以及在不同温度（650,750,850,950 ℃）下氧化4 h的氧化动力学、氧化形态和氧化产物进行了研究。结果表明,在550 ℃下,氧化时间对焊接接头氧化行为的影响有限,而氧化温度对纯钛焊接接头的氧化行为有显著影响,且温度越高,氧化越严重。在低温下,纯钛焊接接头的氧化动力学接近准线性定律,随着温度升高,氧化速率呈指数增长。此外,焊接接头表面产生的氧化产物是具有锐钛矿和金红石结构的TiO₂,温度对TiO₂的类型没有明显影响。纯钛焊接接头的氧化过程可描述为：氧气在表面被吸收;氧化物优先在缺陷区形核;氧化物横向生长、增厚。在较高温度下,氧化膜中出现裂纹或空隙,成为O原子传输通道,导致O和Ti原子的高扩散速率和氧化速率。     

钛合金切削过程氧化膜特性研究

高速切削钛合金时，在加工表面会产生氧化膜，对钛合金的力学性能造成影响。对钛合金Ti-6Al-4V进行单因素车削试验，研究切削表面变形特性并对氧化膜表面进行物相分析。结果表明：切削表面会产生严重塑性变形，变形层的厚度随着进给量的增大而增大，切削表面发生氧化反应，形成氧化膜，表面呈现不同的颜色，其成分主要为Al2O3、锐钛矿型 TiO2 和金红石型 TiO2。     

Effect of a phosphoric acid treatment on the high temperature oxidation behaviour of γ-TiAl: An overall mechanism

TiAl coupons were dipped in a low-concentration phosphoric acid solution, air dried, then heated up to 700 °C or 800 °C before discontinuous oxidation under laboratory air at these temperatures. At the end of the heating ramp, surfaces of TiAl samples were covered by a layer made of a pyrophosphate compound, resulting from reaction between the deposited acid and oxidized titanium. This layer strongly adhered to the substrate surface and allowed to greatly improve the resistance of TiAl to oxidation. After a certain time, a transition period occurred during which pyrophosphate compound disappeared to be changed into TiO₂ rutile. For experiments carried on at 800 °C, it was shown that the phosphorus coming from the pyrophosphate group was present in this titanium oxide and that sample mass gain was still lowered. Performed analyses (XRD, SEM, EDS, μ-Raman spectroscopy) allowed to propose an overall mechanism to account for the “phosphorus effect”.     

Effect of substrate temperature on structural properties and photocatalytic activity of TiO2 thin films

Titanium dioxide （TiO2） films with anatase structure were prepared on quartz glass substrates by pulse laser ablating titanium （99.99%） target under oxygen pressure of 10 Pa at substrate temperature of 500-800 ℃. The structural properties of the films were characterized by X-ray difffactometry（XRD）, X-ray photoelectron spectroscopy（XPS） and field emission scan electron microscopy（FESEM）. The results show that, as the substrate temperature is increased from 600 ℃ to 800 ℃, the anatase structure of the films changes from random growth to （211）-oriented growth. The absorption edge tested by UV-Vis Spectrometer has a blue shift. The photocatalytic activity of the films was tested on the degradation of methyl orange. It is found that the film with random growth structure exhibits better photo-degradation efficiency than that with （211）-oriented growth structure.     

Phase formation of nano-TiO<Subscript>2</Subscript> particles during flame spraying with liquid feedstock

The nanostructured TiO₂ photocatalytic coatings were synthesized through flame spraying with liquid feedstock under different conditions. The nanostructured TiO₂ deposit of substantial anatase phase was annealed at different temperatures. X-ray diffraction analysis showed that significant transformation from anatase to rutile occurred at a temperature above 600 °C. However, thermal analysis suggested that the phase transformation from anatase to rutile started at a temperature from 400 to 500°C. It was found that the grain size of rutile phase was larger than that of anatase. The deposits annealed at temperatures lower than 450°C were photocatalytically active. However, the deposit annealed at 500°C, which contained 95% anatase crystalline, became photocatalytically inactive. Based on the experimental findings, a model is proposed to explain the phase transformation of the nano-TiO₂ particles and the phase formation in flame-spraying of nanostructured TiO₂ deposit with liquid feedstock. The original version of this paper was published as part of the DVS Proceedings: “Thermal Spray Solutions: Advances in Technology and Application,” International Thermal Spray Conference, Osaka, Japan, 10–12 May 2004, CD-Rom, DVS-Verlag GmbH, Düsseldorf, Germany.     

Structural Characterization and Corrosion Behavior of Stainless Steel Coated With Sol-Gel Titania

Sol-gel titania films were prepared from hydrolysis and condensation of titanium (IV) isopropoxide. Diethanolamine was used as chelant agent in titania synthesis. 316L stainless steel substrates were dip-coated at three different withdrawal speeds (6, 30, and 60 mm/min) and heated up to 400 °C. Thermogravimetry and differential thermal analyses of the titania gel solution evinced a continuous mass loss for temperatures up to 800 °C. The transition of anatase to the rutile phase begins at 610-650 °C, being the rutile transformation completed at 900 °C. The thicknesses of the films were determined as a function of the heat treatment and withdrawal speed. It was observed that their thicknesses varied from 130 to 770 nm. Scanning electron microscopy images of the composites revealed the glass-like microstructure of the films. The obtained sol-gel films were also characterized by energy dispersive spectroscopy. The chemical evolution of the films as a function of the heating temperature was evaluated by Fourier transform infrared spectroscopy (specular reflectance method). After performing the adhesion tests, the adherence of the titania films to the stainless steel substrate was excellent, rated 5B according to ASTM 3359. The hardness of the ceramic films obtained was measured by the Knoop microindentation hardness test with a 10 g load. We observed that the titania film became harder than the steel substrate when it was heated above 400 °C. The corrosion rates of the titania/steel composites, determined from potentiodynamic curves, were two orders of magnitude lower than that of the bare stainless steel. The presence of the sol-gel titania film contributed to the increase of the corrosion potential in ca. 650 mV and the passivation potential in ca. 720 mV.     

Characterization of surface oxide films and cell toxicity evaluations with a quenched titanium surface

This study characterizes the surface of the oxide film that forms on titanium metal through the use of thermal and quenching treatments in cold water and investigates the effects of the surface characteristics and cellular interactions of a modified titanium surface. A range of sample groups were prepared in heat treatments of pure titanium at 600°C, 700°C, 800°C, 900°C, and 1000°C and subsequent quenching in cold water. The surface topography, roughness, crystallite size and crystal intensity were found to depend on the heating temperature. An increased surface roughness was observed with increases in the heating temperature and the quenching. The surface roughness was in the range of 0.15 μm–1.07 μm. In vitro cell responses were evaluated with mouse osteoblast MC3T3 cells in terms of cell proliferation and differentiation. MTT assays showed an increase in the living cell density and proliferation upon heating and quenching the titanium surface. The results of this study indicate that the cell toxicity was sensitive to the surface roughness and that it decreased as the roughness of the Ti increased.     

废弃SCR脱硝催化剂与废NaCl盐焙烧回收催化剂中的钛、钒、钨（英文）

通过废弃选择性催化还原(SCR)脱硝催化剂与废NaCl盐焙烧,可以将催化剂中的钨和钒与钛分离。在最佳浸出条件下(焙烧温度900℃,焙烧时间3 h,废盐与废催化剂的质量比为0.5,浸出温度80℃,反应时间60 min),钨和钒的浸出率分别达到84.63%和66.42%,同时钛的损失率仅为1.3%。废NaCl盐和焙烧温度可以促进锐钛矿型TiO₂转化为金红石型TiO₂,反应后得到了金红石型TiO₂。金红石型TiO₂中的钛的价态为四价,晶格氧和化学吸附氧分别占57.26%和42.74%。该方法可以同时解决2种废弃物的处置问题。