Synthesis of Nanocrystalline Titanium Nitride Powders by Direct Nitridation of Titanium Oxide

Nanocrystalline TiN powder has been synthesized by the direct nitridation of nanocrystalline TiO₂ powder. Powder XRD patterns indicated that the TiN nanocrystalline powder could be obtained by nitridation at 800°C for 5 h. TEM micrographs showed that the synthesized TiN powders consisted of uniform spherical particles with an average diameter of ∼20 nm. The effect of the nitridation temperature and holding time on the powder properties is discussed.     

Low-Temperature Creep of Nanocrystalline Titanium(IV) Oxide

Nanocrystalline TiO₂ with densities higher than 99% of rutile has been deformed in compression without fracture at temperatures between 600° and 800°C. The total strains exceed 0.6 at strain rates as high as 10⁻³ s⁻¹. The original average grain size of 40 nm increases during the creep deformation to final values in the range of 120 to 1000 nm depending on the temperature and total deformation. The stress exponent of the strain rate, n , is approximately 3 and the grain size dependence is d ^{− q} with q in the range of 1 to 1.5. It is concluded that the creep deformation occurs by an interface reaction controlled mechanism.     

钛基贵金属氧化物涂层电极的应用进展

与传统的铅基合金阳极、石墨阳极相比,钛基贵金属氧化物涂层电极具有较高的电催化活性、更好的化学稳定性。介绍了贵金属氧化物涂层钛电极的分类、优点,综述了涂层钛电极的典型应用,指出了应用中存在的问题,并展望了涂层钛电极未来的发展方向。     

钛基金属氧化物电极的制备方法及性能表征

电化学催化氧化技术作为一种环境友好技术,近年来在环境污染治理方面越来越受到人们的重视。文章系统评述了以金属钛为基体金属氧化物作为活性层的DSA电极的制备工艺,还介绍了利用最新纳米技术的制备的电极材料,总结了表征DSA电极性能指标的常用方法。最后,讨论了该技术存在的主要问题和今后发展的方向。     

染料敏化纳米晶体光电池

对染料敏化纳米晶体太阳能电池(Dye—Sensitized Nanocrystalline Photovdtaic Sollr Cells)的结构、工作原理进行了介绍,概述了它的研究现状及存在问题,指出它是一种非常有前途的清洁太阳能装置,具有结构简单,成本低廉,易于制造等优点,对光强度变化和温度变化不敏感,光电转换效率高,光稳定性好,对环境无污染,自1991年问世以来,引起了人们的广泛关注。并对这一研究领域的前景进行了展望。     

Performance Evaluation of Doped Titanium Oxide for Low‐Voltage Applications

Varistors are the electronic devices which are used in various industries to protect the electrical and electronic systems from sudden surges. In this research, the electrical properties of titanium dioxide (TiO₂) doped with tantalum pentoxide (Ta₂O₅), tungsten trioxide (WO₃), cobalt oxide (Co₃O₄), and bismuth oxide (Bi₂O₃) and fired at different temperatures were investigated for low‐voltage applications. The adequate amount of dopants at suitable sintering temperature had beneficial effect in improving the properties of TiO₂. The relative density was found to be more than 97% of theoretical density when samples sintered between 1300°C and 1400°C for all composition compared to undoped samples. On the other hand, the addition of dopants enhanced hardness and compressive strength of varistor disks. The average grain size was also increased with the dopants system, making it suitable for low‐voltage application. Furthermore, the current–voltage characteristic of the TiO₂ revealed a significantly high value of nonlinearity of 19.6. A high dielectric constant of 10⁴ with minimum dissipation factor of 0.002852 at 1 kHz was also obtained, thereby making it suitable for low‐voltage application.     

纳米晶体太阳能电池及染料敏化剂

介绍了纳米晶体太阳能电池(Nanocrystalline Photovoltaic Cells，简称NPC)的结构和工作原理，概述了NP电池所用染料敏化剂的研究现状及问题。     

Field-Assisted Sintering of Nanocrystalline Titanium Nitride

Nanosized TiN powder was densified via field-assisted sintering at temperatures of 1150°–1350°C and a pressure of 66 MPa under vacuum. A maximum relative density of ∼97% and a maximum mean grain size of 150–200 nm were obtained. Densification and microstructural evolution have been discussed, in terms of superplasticity and electric-field effects.     

Kinetics of Electrophoretic Deposition for Nanocrystalline Zinc Oxide Coatings

An integrated process combining the preparation of ZnO nanoparticles and the formation of ZnO coatings using electrophoretic deposition (EPD) is reported. The work focuses on the deposition kinetics of nanocrystalline ZnO coatings on copper electrodes during EPD by direct measurement of the thickness of the deposited layer. The experimental results show that the EPD process is a powerful route to fabricate uniform coatings with desired thickness and excellent surface smoothness, which might be attributed to small particle size and narrow size distribution. On the other hand, the deposition kinetics changes with applied voltage and deposition time. The deposition thickness increases with increasing applied voltage and deposition time. In a short deposition time, the deviation of deposition rate between the theoretical and experimental values is caused by voltage drops during deposition, and the discrepancy increases with the applied voltage. Moreover, the increasing voltage drop and depletion of the suspension lead to decreasing current and lower deposition rate after longer deposition time. The critical transition time of deposition kinetics is found to exponentially decrease with increasing applied voltage.     

纳米陶瓷及其发展趋势

纳米陶瓷改变了传统陶瓷的脆性，大幅度提高了材料的强度、韧性和超塑性，同时对传统陶瓷材料的电学、热学、磁学、光学等性能产生了重要影响。本文综述了纳米陶瓷的性能以及发展趋势。     

纳米分子筛的合成与应用

纳米分子筛因具有大的外表面积和短的孔道结构而显示独特的催化活性和选择性,近年来成为催化领域研究的热点。在总结国内外相关研究的基础上,文章介绍了纳米分子筛的特点,系统综述了纳米分子筛的合成方法,以及其在催化领域、微生物领域和特殊水体系中的应用。     

Modeling Oxygen Gas Diffusion Electrodes for Various Technical Applications

In gas diffusion electrodes (GDEs), electrocatalysts are in contact with gas and electrolyte ensuring a large active three‐phase boundary. GDEs are used for important technical applications in energy transformation and chemical synthesis. This review gives an introduction into the vast range of existing models for GDEs and their specific purpose, with an emphasis on oxygen reduction electrodes. After introducing the processes occurring in GDEs, modeling approaches are described according to their dimensionality (from 0D to 3D to multiscale) and perspectives for future research are discussed.     

Low Cost and Efficient Photovoltaic Conversion by Nanocrystalline Solar Cells

Solar cells are expected to provide environmentally friendly solutions to the worlds energy supply problem. Learning from the concepts used by green plants we have developed a molecular photovoltaic device whose overall efficiency for AM 1.5 solar light to electricity has already attained 10 %. The system is based on the sensitization of nanocrystalline oxide films by transition metal charge transfer sensitizers. In analogy to photosynthesis, the chemical solar cell achieves the separation of the light absorption and charge carrier transport processes. Extraordinary yields for the conversion of incident photons into electric current are obtained, exceeding 90% for transition metal complexes within the wave-length range of their absorption band. The use of molten salt electrolytes together with coordination complexes of ruthenium as sensitizers has endowed these cells with a remarkable stability making practical applications feasible. Quite aside from their intrinsic merits as photovoltaic device, the mesoscopic oxide semiconductor films developed in our laboratory offer attractive possibilities for a number Of Other applications. Thus, the first example of a briefly discussed.     

Sulfonated Poly (Ether Ether Ketone) / Barium Strontium Titanium Oxide Polymer Nanocomposite Membranes for Fuel Cell Applications

ABSTRACT

Polymer nanocomposite membranes based on sulfonated poly (ether ether ketone) (SPEEK) and barium strontium titanium oxide (BSTO) have been prepared by solution casting technique. The SPEEK was obtained by direct sulfonation of poly (ether ether ketone) using concentrated sulfuric acid. The degree of sulfonation of SPEEK was determined by ¹H NMR spectroscopy. The composite membranes showed higher water uptake capacity when compared to SPEEK. The ion-exchange capacity of the composite membranes was found in the range between 1.48 and 1.62 meq. g^?1. The thermal stability of composite membrane was found to be good enough to use in fuel cell.     

Temperature Dependence of the Hardness of Nanocrystalline Titanium Dioxide

Vickers hardness of nanocrystalline ( N -) TiO₂ was measured in the temperature range 25° to 1200°C and it was compared with that of polycrystalline ( P -) TiO₂ in the same temperature range. N -TiO₂ showed a lower hardness than P -TiO₂ at temperatures up to 800°C which resulted in the lack of indentation crack traces for N -TiO₂ presumably implying more plasticity.     

纳米TiO_2膜电极上乙醛酸的电催化合成研究

运用电化学循环伏安法 (CV)对纳米TiO2 膜电极 (Ti/nano TiO2 )在硫酸和草酸溶液中的电化学行为进行了研究。在c(H2 SO4 ) =1mol/L溶液中的循环伏安图上Epac1=- 0 .5 6V(vs.SCE)和Epac2 =- 0 96V(vs.SCE)处 ,出现两对可逆氧化还原峰 ,而在相同扫描速度下草酸溶液中的循环伏安曲线上 ,这两对电极反应氧化峰基本消失 ,还原峰电流增大 ,表明Ti/nano TiO2 膜电极对电还原草酸成为乙醛酸的反应具有较高的电催化活性和选择性。常温常压下 ,控制电位Epc=- 1 0V左右电解合成乙醛酸 ,乙醛酸的产率和电流效率分别达到 96 5 %和 90 %。     

Microwave Dielectric Loss of Titanium Oxide

The dielectric loss (tan δ) of titanium dioxide (TiO₂) disks has been measured at a frequency of 3 GHz. High-purity TiO₂ sintered to almost-full density exhibits a very high tan δ, which is interpreted to be due to oxygen deficiency. To counter this, doping with stable divalent and trivalent cations, such as Mg and Al, leads to a low tan δ, probably by preventing Ti⁴⁺ reduction. The tan δ of polycrystalline TiO₂ doped with divalent and trivalent ions with ionic radii in the range of 0.5–0.95 Å at 3 GHz can be very low: 6 × 10⁻⁵ ( Q ∼ 17 000) at a temperature of 300 K. The tan δ of undoped pure TiO₂ disks increases when the disks are cooled from 300 K to ∼100 K. At temperatures <100 K, the tan δ decreases rapidly, which is interpreted as carrier freeze-out. The tan δ for all the high- Q doped TiO₂ polycrystalline samples smoothly decrease to ∼5 × 10⁻⁶ ( Q ∼ 200 000) at 15 K, comparable to that of single crystals.     

Electrooxidation of Aqueous p-Methoxyphenol on Lead Oxide Electrodes

Oxidation of p-methoxyphenol (pmp) in aqueous solution on bismuth-doped lead oxide was studied, and the effects of the initial pmp concentration, applied potential and hydrodynamic conditions upon the oxidation rate were identified. Under all conditions studied, the concentration decay of pmp during electrooxidation follows first—order reaction kinetics. Through analysis of rotating ring-disc currents, the faradaic efficiencies for oxidation at various concentrations of pmp in solution were determined. Using u.v.—vis. and H¹RMN spectroscopy for solution analysis, it is shown that partial oxidation of pmp occurs in chloride-free aqueous solutions. The principal products were p-benzoquinone and maleic acid, with low production of CO₂ up to 1000 C dm^–3 charge. Mineralization to CO₂ was considerably improved upon addition of chloride ions to the solution. In situ FTIR spectra of the electrode surface during electrolysis indicated that the presence of chloride ions enhances the mineralization of pmp by reaction of benzoquinone with anodically generated hypochlorite.     

Synthesis and Kinetics for Nanocrystalline Titanium Carbide upon Metallothermic Reduction of Liquid Chlorides

Nanosized titanium carbide particles were synthesized by the reaction of liquid magnesium and vaporized TiCl₄ + C_xCl₄ (x = 1, 2) solution. Fine titanium carbide particles about 50 nm in size were successfully produced by combining Ti and C atoms released by the chloride reduction of magnesium, and a vacuum was then used to remove the residual phases of MgCl₂ and excess Mg. Small amounts of impurities such as O, Fe, Mg, and Cl were detected in the product, but such a problem can be solved by more precise control of the process. The lattice parameter of the product was 0.43267 nm, which is near the standard value. With respect to the reaction kinetics, the activation energy for the reactions of TiCl₄ + C₂Cl₄ and Mg was found to be 69 kJ/mol, which was about half of the value of the reaction with TiCl₄ + CCl₄, and the higher reactivity of the former contributed to an increase in the stoichiometry to the level of TiC_0.96 and to a decrease in the free carbon content to below 0.3 wt %.Original English Text Copyright © 2005 by Fizika i Khimiya Stekla, Lee, Alexandrovskii, Tolochko, D. Kim, B. Kim.This article was submitted by the authors in English.