Conversion of potassium titanate nanowires into titanium oxynitride nanotubes

Tunnel-structured potassium titanate with a K(3)Ti(8)O(17) phase was synthesized by direct oxidation of titanium powder mixed with KF(aq) in water vapor at 923 K. The reaction conditions were adjusted so that uniform single crystalline potassium titanate nanowires with [010] growth direction (length: 5-30 μm, diameter: 80-100 nm) were obtained. Nitridation of the nanowires by NH(3)(g) at 973-1073 K converted the titanate nanowires into rock-salt structured cubic phase single crystalline titanium oxynitride TiN(x)O(y) nanotubes (x = 0.88, y = 0.12, length = 1-10 μm, diameter = 150-250 nm, wall thickness = 30 - 50 nm) and nanorods (x = 0.5, y = 0.5, length = 1-5 μm, diameter = 100-200 nm) with rough surfaces and [200] growth direction. The overall conversion of the titanate nanowires into the nanotubes and the nanorods can be rationalized by Ostwald ripening mechanism. We fabricated an electrode by adhering TiN(x)O(y) nanotubes (0.2 mg) on a screen-printed carbon electrode (geometric area: 0.2 cm(2)). Electrochemical impedance spectroscopy demonstrated its charge transfer resistance to be 20Ω. The electrochemical surface area of the nanotubes on the electrode was characterized by cyclic voltammetry to be 0.32 cm(2). This property suggests that the TiN(x)O(y) nanostructures can be employed as potential electrode materials for electrochemical applications.     

Molten salt synthesis of single-crystalline K2Ti6O13 annular nanostructures

Single-crystalline K2Ti6O13 ring-like structures have been synthesized via a simple molten salt method without any templates and surfactants. The annular structures have several different types, such as nanoring, wheel-like and diskette-like ring. Each type of rings was characterized individually by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). These annular structures are formed by the loop-by-loop self-coiling of K2Ti6O13 nanobelts in the ring plane. The driving force of self-coiling is suggested to minimize the local electrostatic energy introduced by spontaneous polarization.     

Synthesis of GaN nanowires through Ga2O3 films' reaction with ammonia

GaN nanowires were synthesized by ammoniating Ga₂O₃ films on Ti layers deposited on Si (111) substrates at 950 °C. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM). The XRD, FTIR and HRTEM studies showed that these nanowires were hexagonal GaN single crystals. SEM observation demonstrated that these GaN nanorods with diameters ranging from 50 nm to 100 nm and lengths up to several micrometers intervene with each other on the substrate.     

One-dimensional TiO2 nanomaterials: preparation and catalytic applications

This work reports on the syntheses of one-dimensional (1D) H2Ti3O7 materials (nanotubes, nanowires and their mixtures) by autoclaving anatase titania (Raw-TiO2) in NaOH-containing ethanol-water solutions, followed by washing with acid solution. The synthesized nanosized materials were characterized using XRD, TEM/HRTEM, BET and TG techniques. The autoclaving temperature (120-180 degrees C) and ethanol-to-water ratio (V(EtOH)/V(H2O) = 0/60 approximately 30/30) were shown to be critical to the morphology of H2Ti3O7 product. The obtained H2Ti3O7 nanostructures were calcined at 400-900 degrees C to prepare 1D-TiO2 nanomaterials. H2Ti3O7 nanotubes were converted to anatase nanorods while H2Ti3O7 nanowires to TiO2(B) nanowires after the calcination at 400 degrees C. The calcination at higher temperatures led to gradual decomposition of the wires to rods and phase transformation from TiO2(B) to anatase then to rutile. Photocatalytic degradation of methyl orange was conducted to compare the photocatalytic activity of these 1D materials. These 1D materials were used as new support to prepare Au/TiO2 catalysts for CO oxidation at 0 degrees C and 1,3-butadiene hydrogenation at 120 degrees C. For the CO oxidation reaction, Au particles supported on anatase nanorods derived from the H2Ti3O7 nanotubes (Au/W-180-400) were 1.6 times active that in Au/P25-TiO2, 4 times that in Au/Raw-TiO2, and 8 times that on TiO2(B) nanowires derived from the H2Ti3O7 nanotubes (Au/M-180-400). For the hydrogenation of 1,3-butadiene, however, the activity of Au particles in Au/M-180-400 was 3 times higher than those in Au/W-180-400 but similar to those in Au/P25-TiO2. These results demonstrate that the potential of 1D-TiO2 nanomaterials in catalysis is versatile.     

MgH_2-K_2Ti_6O_(13)-Ni球磨复合体系的微观结构与解氢性能

采用机械球磨法制备了K_2Ti_6O_(13)晶须单独掺杂、以及K_2Ti_6O_(13)晶须与Ni粉复合掺杂的MgH2储氢复合体系,并通过XRD,SEM,DSC等检测手段对其微观结构与解氢性能进行表征。结果表明:当K_2Ti_6O_(13)晶须单独掺杂于MgH2时,K_2Ti_6O_(13)晶须起到助磨细化MgH2晶粒的作用,同时还抑制了MgH2颗粒的团聚,有效降低了MgH2基体的解氢温度,且当K_2Ti_6O_(13)与MgH2质量配比为3∶7时,MgH2解氢性能的改善效果尤为明显,其解氢温度较纯MgH2球磨体系降低了近75℃;此外,当K_2Ti_6O_(13)晶须和Ni粉末复合掺杂于MgH2时,得益于K_2Ti_6O_(13)晶须的助磨细化MgH2晶粒以及Ni固溶于MgH2晶格致使其结构稳定性降低的双重作用,从而使得MgH2基体的解氢温度较K_2Ti_6O_(13)晶须单独掺杂时进一步降低,相对于纯MgH2球磨体系降低了近87℃。     

Thermal Growth and Nanomagnetism of the Quasi-one Dimensional Iron Oxide

Quasi-one dimensional iron oxide nanowires with flat needle shape were synthesized on the iron powders by a rather simple catalyst-free thermal oxidation process in ambient atmosphere. The characterization by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman and high-resolution transmission electron microscopy (HRTEM) revealed that these nanostructures are single crystalline α-Fe2O3. The various dimensions with 40-170 nm in width and 1-8 μm in length were obtained by tuning the growth temperature from 280 to 480℃. A surface diffusion mechanism was proposed to account for the growth of quasi-one dimensional nanostructure. The typical α-Fe2O3 nanowires synthesized at 430℃ had a reduced Morin temperature TM of 131 K in comparison with their bulk counterpart. The coercivitis Hc of these nanowires are 321 and 65 Oe at 5 and 300 K, respectively. The temperature of synthesis also has important effects on the magnetic properties of these nanowires.     

Synthesis and characterization of srilankite nanowires

We describe the synthesis and characterization of srilankite (Ti2ZrO6) nanowires. The nanowires are produced via hydrothermal synthesis with a TiO2/ZrO2 mixture under alkaline conditions. The zirconium titanate nanowires have median diameters of 60 nm and median lengths of 800 nm with the (022) axis along the length of the nanowire. Electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, and electron diffraction are used to characterize the phases and compare nanowires produced with varying molar ratios of Ti and Zr. Electron diffraction patterns produced from single nanowires show highly crystalline nanowires displaying a compositional-ordering superlattice structure with Zr concentrated in bands within the crystal structure. This is in contrast to naturally occurring bulk srilankite where Zr and Ti are randomly substituted within the crystal lattice. Streaking is observed in the electron diffraction patterns suggesting short-range ordering within the superlattice structure.     

The structure and photoluminescence properties of Bi2O3-core/SnO2-shell nanowires

Bi2O3-core/SnO2-shell nanowires have been prepared by using a two-step process: thermal evaporation of Bi2O3 powders and sputtering of SnO2. The crystalline nature of the Bi2O3-core/SnO2-shell nanowires has been revealed by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). TEM analysis and X-ray diffraction (XRD) results indicate that the Bi2O3-core/SnO2-shell nanowires consist of pure tetragonal alpha-Bi2O3-phase momocrystalline cores and tetragonal SnO2-phase polycrystalline shells. The photoluminescence (PL) measurements show that Bi2O3 nanowires have a broad emission band centered at around 560 nm in the yellow-green region. On the other hand, the Bi2O3-core/SnO2-shell coaxial nanowires with the sputtering times of 4 and 8 min have a blue emission band centered at around 450 nm. In contrast, those with a sputtering time of 10 min have a broad emission band centered at approximately 550 nm again. The origin of this yellow-green emission from the core/shell nanowires, however, quite differs from that from Bi2O3 nanowires, i.e., it is not from the Bi2O3 cores but from the SnO2 shells.     

Growth mechanism of titanium dioxide nanowires for dye-sensitized solar cells

Mesoporous films made of titanium dioxide nanowires are desirable for dye-sensitized solar cells because nanowires provide direct conduction pathways for photogenerated electrons. Anatase titanium dioxide nanowires with polycrystalline microstructure were synthesized on titanium foil using a three-step process. First, the top surface of the titanium foil was transformed to Na(2)Ti(2)O(4)(OH)(2) nanotubes through hydrothermal oxidation in NaOH. Next, the Na(2)Ti(2)O(4)(OH)(2) nanotubes were converted to H(2)Ti(2)O(4)(OH)(2) nanotubes by ion exchange. Finally, the H(2)Ti(2)O(4)(OH)(2) nanotubes were converted to polycrystalline anatase nanowires through a topotactic transformation. The film morphology evolution, crystal structure transformations and growth mechanism are described in detail. Titanium foil reacts with NaOH to form Na(2)Ti(2)O(4)(OH)(2) sheets, which exfoliate and spiral into nanotubes. The Na(2)Ti(2)O(4)(OH)(2) nanotubes are immersed in HCl solution to replace the Na(+) ions with H(+) ions. During the topotactic transformation of H(2)Ti(2)O(4)(OH)(2) nanotubes to anatase TiO(2) nanowires, the sheets made of edge bonded TiO(6) octahedra in the H(2)Ti(2)O(4)(OH)(2) nanotubes dehydrate and move towards each other to form anatase crystals oriented along the nanotube axis which creates a polycrystalline nanowire. These mesoporous TiO(2) nanowire films were suitable for use as dye-sensitized solar cell photoanodes.     

纤维及晶须增强PTFE复合材料的摩擦磨损性能研究

利用MHK－500型环－块磨损试验机,对炭纤维,玻璃纤维及钛酸钾（K2Ti6O13)晶须增强聚四氟乙烯（PTFE）复合材料在干摩擦条件下与GCr15轴承钢对磨时的摩擦学性能进行了较为系统的研究,并利用扫描电子显微镜（SEM）和光学显微镜对其磨屑和摩擦表面进行了观察。结果表明,炭纤维,玻璃纤维及K2Ti6O13晶须虽增大了PTFE的摩擦系数,但均可将PTFE的磨损量降低2个数量级,其中玻璃纤维的减磨效果最好,K2TiO13晶须的减磨效果最差,由于K2TiO13晶须的承载能力较差,致使K2Ti6O13晶须增强PTFE复合材料的磨损表面发生了明显的挤压变形,因而该复合材料具有较高的摩擦和磨损。     

Filling double-walled carbon nanotubes with WO3 and W nanowires via confined chemical reactions

Carbon nanotubes filled with metals and semiconductors have been regarded as one of the most promising materials for nanodevices. Here, we demonstrate a simple and effective method to produce tungsten trioxide (WO3) and tungsten (W) nanowires with diameters of below 4 nm inside double-walled carbon nanotubes (DWCNTs). First, the precursors, i.e., phosphotungstic acid (HPW, H3PW12O40) molecules, are successfully introduced into DWCNTs. Subsequent decomposition and reduction lead to the formation of WO3 and W nanowires inside DWCNTs. The products were carefully characterized by high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. FTIR spectra provide a direct proof that the HPW molecules enter the DWCNTs as an ionic state, i.e., PW12O40(3-) and H+, instead of the molecular state. HRTEM analysis shows that the diameter of the WO3 nanowires inside DWCNTs is 1.1-2.4 nm with the average length of 16-18 nm, and that for W nanowires is 1.2-3.4 nm with the average length of 15-17 nm. Meanwhile, DWCNTs are doped by the encapsulated WO3 and W nanowires. Tangential band shift in Raman spectra revealed the charge transfer between the nanowires and carbon nanotubes.     

Microstructure and superconductivity of highly ordered YBa(2)Cu(3)O(7-δ) nanowire arrays

In order to explore the fundamental properties of one-dimensional nanostructured high-temperature superconductors and enhance their promising applications, a universal and general method for the synthesis of high-quality YBa(2)Cu(3)O(7-δ) (YBCO) nanowire arrays is developed, which involves the combination of a novel sol-gel process to lower the crystallization temperature of YBCO, and porous anodic alumina (PAA) as an effective morphology-directing hard template. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results indicate that the as-prepared YBCO nanowires have average diameters of about 50?nm and lengths up to several microns. The structures of the samples were analysed by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDX) and inductively coupled plasma (ICP) analysis, which indicate that the nanowires are well crystallized with orthorhombic YBCO-123 structure. The magnetization measurement under zero-field-cooled (ZFC) mode indicates that the superconducting transition temperature (T(c)) of the nanowires is about 92?K, which is in agreement with that of a bulk YBCO sample.     

KDC法合成钛酸钾纤维的研究

本文研究了ＫＤＣ法合成钛酸钾纤维的过程、生长反应和合成条件;应用ＫＤＣ法合成了Ｋ２Ｔｉ２Ｏ５,Ｋ２Ｔｉ４Ｏ９、Ｋ２Ｔｉ６Ｏ１３等纤维状物质。     

无铅Ba(Ce,Ti)O_3陶瓷的电卡效应

本文使用标准固相烧结法制备了Ba(Ti_(1-x)Ce_x)O_3(x=0.10,0.15,0.20)陶瓷,通过XRD分析发现这些陶瓷中除了Ba(Ti_(1-x)Ce_x)O_3主相外,还存在少量的杂相。利用Rietveld拟合的方法,获得了Ba(Ti_(1-x)Ce_x)O_3主相中的Ce/Ti实际比例。介电温谱表明这些陶瓷均存在一个明显的介电峰,且随着x的增加,峰值温度下降,介电峰宽展宽。利用不同温度下的电滞迴线,给出了不同温度和电场强度下的极化值,通过间接法获得了这些陶瓷的电卡效应。结果表明,BaTi_(0.9)Ce_(0.1)O_3的电卡效应最强,其DT值在403K和40kV/cm的电场下达到最大值,为0.48K,电卡强度为0.12×10~(-6)K·m/V。     

C@K2Ti6O13分级纳米材料对Cr(VI)的吸附去除

Cr(VI)具有非常大的生物毒性, 去除溶液中的Cr(VI)是当前的一个研究热点。本研究制备了C@K₂Ti₆O₁₃分级纳米材料, 并用不同表征手段对材料的物相和结构等进行表征, 进一步探究了初始pH、吸附时间、离子强度等对C@K₂Ti₆O₁₃复合纳米结构吸附Cr(VI)的影响。实验结果表明C@K₂Ti₆O₁₃复合纳米结构对Cr(VI)有较强的吸附能力, 1 h内去除率能够达到50%以上, 其吸附动力学符合准二级动力学模型, 吸附热力学符合Langmuir等温吸附模型, 表明这种分级纳米材料在环境治理方面应用潜力巨大。     

氨化Si基Ga2O3/Ti制备GaN纳米线

采用磁控溅射技术先在硅衬底上制备Ga2O3/Ti薄膜,然后在950℃时于流动的氨气中进行氨化反应制备GaN薄膜.X射线衍射(XRD)、傅立叶红外吸收光谱(FTIR)、选区电子衍射(SAED)和高分辨透射电子显微镜(HRTEM)的结果表明采用此方法得到了六方纤锌矿结构的GaN单晶纳米线.通过扫描电镜(SEM)观察发现纳米线的形貌,纳米棒的尺寸在50～150nm之间.     

Effect of the microstructure on the cutting performance of superhard (Ti,Si,Al)N nanocomposite films

A d.c. reactive magnetron sputtering technique was used to deposit (Ti,Si,Al)N coatings onto WC-Co cutting tools. The microstructure of the coatings was analysed using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) measurement. Before the cutting experiments, the XRD results revealed a structure indexed to an fcc TiN. The results obtained by the XRD tests, with detector variation in asymmetric mode (rocking curves) showed a decrease in the quality of the fiber texture in the (111) grains with the change on deposition chamber geometry (two magnetrons in place of four magnetrons). Cross-sectional HRTEM images of the (Ti,Al)N sample showed grains with a diameter between 16 and 30 nm, while for the (Ti,Si,Al)N samples grains with a diameter between 6 and 10 nm were observed. Furthermore, through the visualization of bright field images it was possible to discern a columnar structure. For samples prepared at high deposition rates (2 μm/h), HRTEM micrographs revealed the formation of the multilayer stacking of (Ti,Si)N/(Ti,Al)N.     

化学气相沉积法制备GaN纳米线和纳米棒

采用浸渍法在未抛光的硅衬底上涂抹一层NiCl2薄膜,通过化学气相沉积法(CVD)制备出高质量的GaN纳米线和纳米棒.X射线衍射(XRD)、傅立叶红外吸收光谱(FTIR)、选区电子衍射(SAED)和高分辨透射电子显微镜(HRTEM)的分析结果表明,采用此方法得到了六方纤锌矿结构的GaN单晶纳米线.通过扫描电镜(SEM)观察发现纳米线的形貌,纳米线的直径在50～200nm之间,纳米棒的直径在200～800nm之间.     

Gallium nitride nanowires doped with magnesium

GaN nanowires doped with Mg have been synthesized on Si (111) substrate through ammoniating Ga₂O₃ films doped with Mg under flowing ammonia atmosphere. The Mg-doped GaN nanowires were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL). The results demonstrate that the nanowires were single crystalline with hexagonal wurzite structure. The diameters of the nanowires ranged 20-30 nm and the lengths were about hundreds of micrometers. The intense PL peak at 359 nm showed a blueshift from the bulk band gap emission, attributed to Burstein-Moss effect. The growth mechanism of the crystalline GaN nanowires is discussed briefly.     

Strain-induce shift of the crystal-field splitting of SrTiO₃ embedded in scandate multilayers

Strained SrTiO? layers have become of interest, since the paraelectric-to-ferroelectric transition temperature can be increased to room temperature. A linear relationship between strain and energy splitting of the fundamental transitions in the fine structure of Ti L(?,?) and O K edges is observed, that can be exploited to measure strain from electronic transitions, complementary to measuring local strain directly via high-resolution transmission electron microscopy (HRTEM) images. In particular, for both methods, the geometrical phase analysis performed on high-resolution images and the measurement of the energy splitting by energy loss spectroscopy, tensile strain of SrTiO? layers was measured when grown on DyScO? and GdScO? substrates. The effect of strain on the electron loss near edge structure (ELNES) of the Ti L(?,?) edge in comparison to unstrained samples is analyzed. Ab initio calculations of the Ti L(?,?) and O K edge show a linear variation of the crystal field splitting with strain. Calculated and experimental values of the crystal field splitting show a very good agreement.