钕的添加对V2O5-MoO3/TiO2平板式脱硝催化剂性能的影响

本研究制备了一系列不同Nd含量的V₂O₅-MoO₃-Nd₂O₃/TiO₂平板式脱硝催化剂。采用XRD、N2-吸附脱附、XPS、H2-TPR、拉曼光谱、NH3-TPD和红外光谱等表征手段对催化剂进行分析。结果表明:适量的Nd2O3(0.25%、0.5%,质量分数)可以增强V₂O₅-MoO₃/TiO₂催化剂的还原性能,增加了催化剂的Oα/(Oα+Oβ)比率,从而提升了催化剂的脱硝活性。然而,过量Nd₂O₃(0.75%、1%)的添加,会导致催化剂酸性性能的显著降低,造成催化剂脱硝性能的下降。此外,过量Nd的添加还会对催化剂的耐磨性能有负面影响。各催化剂中,VMoN d(0.5%)/Ti催化剂显示了最佳的脱硝活性。并且,该催化剂还显示了优良的抗SO₂、H₂O性能。     

New Pt–Ru solid compounds as precursors of anodic catalysts for direct methanol fuel cell

This research is aimed to increase the activity of platinum–ruthenium alloy catalysts, thus to lower the catalyst loading in anodes for methanol electrooxidation. The DMFC catalyst consisting of Pt–Ru/C were prepared from (NH₄)₂PtCl₆ and Ru(OH)₃ as solid precursors at different temperatures and times of duration during their reduction. Their performances were examined by cyclic voltammograms and chronoamperometric curves. The particle size and its distribution in the catalysts were determined by means of TEM and XRD. It is found that the XRD patterns of the catalyst prepared from (NH₄)₂PtCl₆ and Ru(OH)₃ as precursors show Pt reflexions with f.c.c. crystal structure. There are diffraction peaks indicating the presence of either pure Ru or a Ru-rich h.c.p. phase, which has not been alloyed with Pt in Pt–Ru/C. The activity of the Pt–Ru/C catalysts prepared from (NH₄)₂PtCl₆ and Ru(OH)₃ as precursors is higher than those obtained from H₂PtCl₆ and RuCl₃ by chemical or thermal reduction. The activity of Pt–Ru/C catalysts prepared at 360 °C is higher than those prepared at 320 and 400 °C. After 1 h of reduction at 360 °C its particle size is small, about 7.5 nm, and its catalytic activity is higher than those obtained after 2 and 3 h of reduction.     

Oxidation behavior of ceramic coatings on Ti–6Al–4V by micro-plasma oxidation

Compound ceramic coatings prepared on Ti–6Al–4V alloy by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO₂ solution were oxidized under different temperature in air. The phase composition and surface morphology of the coatings before and after oxidation were investigated by X-ray diffractometry and scanning electron microscopy, respectively. Meantime, the weight gains and the high temperature oxidation characteristics of the coated samples were investigated. The results show that the coatings prepared by MPO were composed of a large amount of Al₂TiO₅ and a little -Al₂O₃ and rutile TiO₂. And the oxidation process of the coated samples included the decomposition of the Al₂TiO₅ in the coating, the oxidation of the substrate and the changes of the coating structure. After high temperature oxidation, the increase of -Al₂O₃ in the coating was due to the decomposition of Al₂TiO₅, whereas the increase of rutile TiO₂ in the coating was attributable to both the decomposition of Al₂TiO₅ and the oxidation of the Ti substrate. The main crystalline of the coatings became rutile TiO₂ after the oxidation of 1000 °C for 1 h. The decomposition of Al₂TiO₅ in the coating occurred at 900 and 1000 °C, and its half decomposition time was less than 1 h at 1000 °C. Increasing oxidation temperature or extending oxidation time, the weight gains of coated samples was increased to different extent. However, the weigh gains of the coated samples was much lower than that of the substrate, so the ceramic coatings improved the oxidation resistance of Ti alloy greatly under the experimental conditions.     

Comparative studies of adsorbed CO and methanol electrooxidation on carbon supported Pt and PtRu catalysts in acid solution

1. Introduction Direct methanol fuel cells (DMFCs) have con-siderable advantages compared to gas feed (H2/air) polymer electrolyte membrane (PEM) fuel cells [1-2]. The hydrogen PEM fuel cells use gaseous hy-drogen as fuel. But there is no source and infra-structure established yet for hydrogen distribution and storage, neither as a liquid nor as a gas. How-ever, the DMFC, similar to a proton exchange membrane fuel cell (PEMFC), uses methanol fuel directly for electric power generation …     

High temperature oxidation behavior of Ti3SiC2-based material in air

The oxidation behavior of Ti₃SiC₂-based material in air has been studied from 900°C to 1200°C. The present work showed that the growth of the oxide scale on Ti₃SiC₂-based material obeyed a parabolic law from 900°C to 1100°C, while at 1200°C it followed a linear rule. The oxide scale was generally composed of an outer layer of coarse-grained TiO₂ (rutile) and an inner layer of fine-grained TiO₂ and SiO₂ (tridymite) above 1000°C. A discontinuous coarse-grained SiO₂ layer was observed within the outer coarse-grained TiO₂ layer on the samples oxidized at 1100°C and 1200°C. Marker experiments showed that the oxidation process was controlled by the inward diffusion of oxygen, outward diffusion of titanium and CO or SiO, and that internal oxidation predominated. The TiC content in Ti₃SiC₂ was deleterious to the oxidation resistance of Ti₃SiC₂.     

Effects of the solution temperature and the pH on the electrochemical properties of the surface oxide films formed on Alloy 600

The surface oxide films on Alloy 600 have been investigated as a function of the solution temperature and the pH by using a cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and a depth profiling by Auger electron spectroscopy (AES). H₃BO₃, Na₂SO₄ and NaOH aqueous solutions with temperatures in the range of 30–300 °C were used as the test solutions. As the solution temperature of the 0.5 M H₃BO₃ increased, the thickness of the passive film increased but the resistance of the passive film was diminished, which is coincident with a solution temperature dependency of the passive current in the potentiodynamic curve. The inner oxide film on Alloy 600 was distinguishable from the Cr-rich outer oxide film above 100 °C. From the Mott–Schottky relation, the oxide formed in 0.5 M H₃BO₃ at 300 °C showed a p-type semiconductor property, accompanied by a Cr-rich oxide film throughout the whole oxide film unlike the n-type oxide films up to 250 °C. The oxide resistance of the passive film decreased in the order of 0.5 M H₃BO₃, 0.1 M NaOH and 0.5 M Na₂SO₄, which is consistent with the pH dependency of the passive current. Ni-rich oxide films of a p-type were formed in the 0.5 M Na₂SO₄ or 0.1 M NaOH.     

Effect of TiO2 on high-temperature thermoelectric properties of ZnO

The as-sintered Zn_1−xTi_xO (0.01 ≤ x ≤ 0.05) samples contained a solid solution of Zn_1−xTi_xO with a wurtzite structure and a small amount of the cubic spinel Zn₂TiO₄. The amount of Zn₂TiO₄ increased with an increase in TiO₂ content. The density and grain size increased with the small TiO₂ content (≤0.01), and then they decreased gradually by further increasing the TiO₂ content. The addition of TiO₂ to ZnO led to a significant increase in the electrical conductivity and a decrease in the absolute value of the Seebeck coefficient, resulting in an increase in the power factor. The highest value of power factor (7.6 × 10⁻⁴ W m⁻¹ K⁻²) was attained for Zn_0.98Ti_0.02O at 1073 K. It is demonstrated that the TiO₂ addition is fairly effective for enhancing thermoelectric properties.     

Crystal structure analysis and thermoelectric properties of p-type pseudo-binary (Al2Te3)x–(Bi0.5Sb1.5Te3)1−x (x = 0 0.2) alloys prepared by spark plasma sintering

Sm³⁺-doped TiO₂ nanocrystalline has been successfully prepared by low temperature combustion synthesis (LCS). Results showed that the samarium doping was found to be able to significantly inhibit the anatase–rutile phase transformation. Photocatalytic degradation experiments indicated that doping samarium ions in TiO₂ could enhance photocatalytic activity in photocatalytic degradation of methylene blue. The increase in photocatalytic activity is probably due to prevention of electron–hole recombination and the existence of a synergistic effect between anatase and rutile. The highest enhancement in photoreactivity was obtained at 0.5 mol% samarium ions doping, which may be in favor of the most efficient separation of the charge carriers. It has been found that the photocatalytic activity is drastically increased under the presence of a small amount of anatase phase (only 5.9% anatase) compared to pure rutile, and the sample calcined at 600 °C with 51.61% rutile shows the highest photocatalytic activity, which suggests the existence of a synergistic effect between anatase and rutile powders in the Sm³⁺-doped TiO₂, which is similar to that of undoped TiO₂.     

Induced crystallization and physical properties of Li2O–CaF2–P2O5:TiO2 glass system: Part I. Characterization, spectroscopic and elastic properties

Li₂O–CaF₂–P₂O₅ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 0.8 mol%) were crystallized at 500 °C. The samples are characterized by X-ray diffraction, scanning electron microscopy and differential thermal analysis techniques. Spectroscopic properties (IR and Raman) and elastic properties (viz., Young's modulus E, shear modulus G and micro-hardness H) at room temperature are studied. The X-ray diffraction and the scanning electron microscopic studies revealed the presence of lithium phosphate, lithium titanium phosphate and titanium phosphate crystal phases. The differential thermal analysis traces of these samples exhibit three crystalline temperatures. The IR and Raman spectra of these samples have exhibited bands due to TiO₄ and TiO₆ structural units in addition to the conventional bands due to various phosphate structural groups. The analysis of these results indicated that the sample crystallized with 0.6 mol% of TiO₂ possesses the highest density, high mechanical strength and more compact network.     

Structure and electrochemical properties of Li(Ni0.5Mn0.5)1-xTixO2 prepared by one-step solid state reaction

The layered compound Li(Ni_0.5Mn_0.5)_1-xTi_xO₂ powders were prepared with Ni(OH)₂, MnCO₃, Li₂CO₃ and TiO₂ by one-step solid state reaction. The effect of doping Ti on the structure and electrochemical properties was studied. The XRD results indicate that the powders with 0≤x≤0.05 have good layered structure and trace of impurity appears in the samples with x≥0.1. The SEM photographs show that the particle size distributes homogeneously and the sample with x=0.15 has larger particle size than other samples. The charge-discharge tests show that Li(Ni_0.5Mn_0.5)_0.95Ti_0.05O₂ synthesized at 800 °C for 36 h exhibits good electrochemical properties. It firstly delivers 173 mA·h/g and maintains 90% of the initial discharge capacity after 30 cycles. The cyclic voltammetry and differential capacity vs voltage curves show that the major oxidation and reduction peaks are around 3.95 V and 3.75 V, respectively, assigned to Ni²⁺/Ni⁴⁺ oxidation-reduction process. A weak peak around 4.5 V is found during the oxidation process in the first cycle, which can be regarded as the main reason of the large drop of discharge capacity in the initial cycle.     

Effect of Cu on the magnetic properties and reducibility of Fe2TiO5

Ferrites have been studied for several years due to their wide use as magnetic materials for telecommunications, audio and video, power transformers and many other applications.

Equimolar mixtures of Fe₂O₃ and TiO₂ were fired in a muffle furnace at 1200 °C for 4 h. Mixed samples were prepared by replacing TiO₂ with calculated amounts of CuO (x = 0.2, 0.4, 0.6, 0.8 and 1 mol). The synthesized samples were characterized with X-ray diffraction and their magnetic properties were measured using vibrating-sample magnetometer. The microstructure of the sample was examined using reflected light microscope and scanning electron microscope. The formation of Fe₂TiO₅, Fe₅CuO₈, Cu₂TiO₃ and CuFeO₂ phases were detected whereas their magnetic properties increased with increasing the added mole ratio of Cu²⁺ ions. The isothermal reduction kinetics of synthesized nanocrystallites Ti–Cu mixed ferrite compacts were studied at 500 °C using hydrogen gas. It was found that the reduction rate and the reduction extent increased with increasing the extent of Cu²⁺ (0.2–1) whereas the maximum reduction extent (100%) was detected for pure Cu ferrite (Cu²⁺) while the minimum reduction extent (12%) was detected for pure iron titanate (Cu²⁺ = 0). The magnetic properties showed a drastic improvement upon reduction with hydrogen gas.     

Eco-friendly one-pot synthesis of acetals and ketals by heterogeneously catalyzed liquid-solid phase reaction

Twelve classes of acetals and ketals were synthesized from aldehyde/ketone and glycol using ZiSiW12O40/TiO2 as a novel eco-friendly catalyst. The physical characterizations were carried out by TG/DTA, FT-IR, XRD, and ^1H NMR spectra. The results indicated that the catalyst showed excellent catalytic activity for the condensation reactions. The yield of 12 classes of acetals and ketals reached 56.3%-96.3% under the typical reaction conditions （the molar ratio of aldehyde/ketone and glycol was 1：1.5, the quantity of catalyst was 0.5% of feed stock, the reaction time was 1.0 h, and the reaction temperature was 80-116℃）. The catalyst was easily recovered and reused to give almost the same yield of the product as that given by fresh TiSiW12O10/TiO2.     

Effect of sintering temperature on the structure and properties of cerium-doped 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 piezoelectric ceramics

Phase structure, microstructure, dielectric and piezoelectric properties of 0.4 wt% CeO₂ doped 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ (Ce-BNT6BT) ceramics sintered in the temperature range from 1120 to 1200 °C have been investigated as a candidate for lead-free piezoelectric ceramics. Tetragonal phase played an important role in improvement of electrical properties and the density of the ceramics. Dielectric constant decreased slightly with the increase of sintering temperature in ferroelectric region but a reverse phenomenon occurred in antiferroelectric and paraelectric regions, suggesting that interfacial polarizations were improved with the increase of sintering temperature and domain walls of ferroelectricity became active after depolarization. At room temperature, Ce-BNT6BT ceramics sintered at 1180 °C showed good performances: dielectric constant was 914 at 1 kHz, thick coupling factor k_t was 0.52, and the ratio of k_t/k_p was 2.3. The ceramics were suitable for narrowband filters and ultrasonic transducers in commercial applications.     

Fabrication of anatase-type TiO2 films by reactive pulsed laser deposition for photocatalyst application

TiO₂ films having anatase crystal structure were prepared on glass substrates by reactive pulsed laser deposition using a metallic Ti target in an O₂ gas ambient. At a fixed substrate temperature of 400 °C, the crystalline structure, surface morphology, optical properties and photocatalytic activity of the TiO₂ films were greatly affected by the O₂ gas pressure. It was found that nearly pure anatase-phase TiO₂ film can be obtained under an O₂ pressure of 15 Pa, which had smallest grain size among the films deposited under various O₂ gas pressure from 5 to 30 Pa. This film also showed good optical transmittance between the wavelength of 200 and 800 nm and high photocatalytic efficiency on the decomposition of methylene blue in aqueous solution. Discussions were given to explain the experimental phenomena.     

Synthesis of iron（Ⅲ）-doped nanostructure TiO2/SiO2 and their photocatalytic activity

Iron(Ⅲ)-doped nanostructure TiO2-coated SiO2 (TiO2/SiO2) particles were prepared using the layer-by-layer assembly technique and their photocatalytic property was studied. TiO2 colloids were synthesized employing the sol-gel method with TiCl4 as a precursor. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), SEM, EDS, XPS, and XRD. The experimental results show that TiO2 nanopowders on the surface of SiO2 particles are well distributed, the amount of TiO2 is increased with the adding of coating layers, the pure anatase-TiO2 coating layers are synthesized at 500℃, and the photocatalytic activity of Fe3 -doped TiO/SiO2 is higher than tnat of undoped TiO2/SiO2.     

Growth kinetics and oxidation behavior of WSi2 coating formed by chemical vapor deposition of Si on W substrate

The growth kinetics of WSi₂ coating formed by chemical vapor deposition (CVD) of Si on a W substrate at temperatures between 1000 and 1200 °C using SiCl₄–H₂ gas mixtures was investigated and its isothermal oxidation resistance in 80% Ar–20% O₂ atmosphere was evaluated at temperatures between 800 and 1300 °C. WSi₂ coating grew with a parabolic rate law after an initial incubation period, indicating the diffusion-controlled growth. The activation energy for growth of WSi₂ coating was about 42.5 kcal/mol. The isothermal oxidation rate of WSi₂ coating increased with increasing oxidation temperature but rapidly decreased at 1300 °C. The oxidation product of WSi₂ coating was composed of the WO₃ particles embedded in the amorphous SiO₂ matrix at below 1200 °C but consisted of only SiO₂ phase at 1300 °C. The fast oxidation behavior of WSi₂ coating at below 1200 °C was attributed to the formation of many cracks and pores, i.e. short-circuit diffusion path of oxygen, within the oxide scale, which resulted from the internal stress generated both by the large volume expansion caused by the oxidation reactions of WSi₂ and by the evaporation of WO₃ phase. The slow oxidation behavior of WSi₂ coating at 1300 °C was due to the exclusive formation of a slow-growing continuous SiO₂ scale by the rapid evaporation of WO₃ phase.     

二氧化钛包覆微细金刚石的制备及表征

以聚乙烯吡咯烷酮（PVP）为偶联剂,钛酸四丁酯（TBOT）为TiO₂前驱体,氨水为催化剂,通过St?ber法制备核-壳结构的二氧化钛包覆微细金刚石（UFD@TiO₂）,研究溶液pH值、氨水及去离子水的加入量对UFD@TiO₂的影响。采用XRD、SEM及DSC-TG等手段对UFD@TiO₂进行表征,利用三点弯曲法测定添加UFD或UFD@TiO₂的陶瓷结合剂试样的抗折强度,通过SEM观察陶瓷结合剂试样断口的微观形貌。实验结果表明:当溶液pH值约为8,氨水体积分数为0.8%,去离子水体积分数为0.8%时,TBOT水解生成的TiO₂易在金刚石表面异质形核,可获得致密均匀的TiO₂膜层;UFD@TiO₂的起始氧化温度为650℃,比UFD的起始氧化温度583℃提高了67℃;UFD@TiO₂-陶瓷结合剂试样的抗折强度比UFD-陶瓷结合剂试样的抗折强度提高了20.9%。      

Induced crystallization and physical properties of Li2O–CaF2–P2O5:TiO2 glass system: Part II. Electrical, magnetic and optical properties

The results of various physical properties namely, dielectric properties (dielectric constant, loss tan δ, ac conductivity σ, over a wide range of frequency and temperature and dielectric breakdown strength in air medium at room temperature), optical absorption, electron spin resonance (ESR) at liquid nitrogen temperature and magnetic susceptibility at room temperature of Li₂O–CaF₂–P₂O₅:TiO₂ glass-ceramics have been reported. The optical absorption and magnetic susceptibility studies indicated that the titanium ions exist in Ti³⁺ state in addition to Ti⁴⁺ state in these samples. However, the reduction seems to be the lowest in the sample containing 0.6 mol% of TiO_2. The dielectric constant and loss variation with the concentration of TiO₂ have been explained on the basis of space charge polarization mechanism. The dielectric relaxation effects exhibited by these samples have been analyzed by a pseudo Cole–Cole plot method and the spreading of dielectric relaxation has been observed. The ac conductivity in the high temperature region seems to be related both with electronic and ionic movements. The low temperature (or the nearly temperature independent) part of conductivity could be explained on the basis of quantum mechanical tunneling model. The studies on dielectric breakdown strength indicated the highest insulating strength for the sample containing 0.6 mol% of TiO₂.     

Structural and electrical properties of SrBi2(Ta0.5Nb0.5)2O9 thin films

SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBTN) thin films were obtained by polymeric precursor method on Pt/Ti/SiO₂/Si(1 0 0) substrates. The film is dense and crack-free after annealing at 700 °C for 2 h in static air. Crystallinity and morphological characteristic were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The films displayed rounded grains with a superficial roughness of 3.5 nm. The dielectric permittivity was 122 with loss tangent of 0.040. The remanent polarization (P_r) and coercive field (E_c) were 5.1 μC/cm² and 96 kV/cm, respectively.     

Low-temperature synthesis and characterization of (Zn,Ni)TiO3 ceramics by a modified sol–gel route

Hexagonal ilmenite-type (Zn_1−xNi_x)TiO₃ (x = 0, 0.85–1.0) ceramic powders were successfully synthesized by a sol–gel route with low temperature (800 °C) sintering, which was modified by using the two-step heat treatment so as to obtain pure products. The thermal stability of the hexagonal (Zn,Ni)TiO₃ was enhanced with the increasing amount of nickel addition. FE-SEM observations demonstrated that the average crystallite sizes of (Zn_1−xNi_x)TiO₃ remarkably decreased from more than 200 nm to less than 100 nm with the increasing solubility x. The dielectric properties of (Zn_1−xNi_x)TiO₃ were measured at different frequencies and the results showed that there existed maximum values both for the dielectric constants and the loss tangents at x = 0.85.