不同酸化条件下水热合成V2O5粉末的结构和电化学性能

为了研究酸化条件对V2O5粉末结构和电化学性能的影响,利用HNO3和H2C2O4酸化NH4VO3溶液,经水热和后续热处理制备了V2O5粉体。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和电化学工作站等对V2O5粉体的微观结构与电化学性能进行了测试。结果表明,所得粉体为纯V2O5相,前驱体溶液的pH值和酸化所用酸的酸根阴离子影响了最终粉体的晶体发育和微观结构。其中,利用HNO3酸化NH4VO3溶液至pH值=3制得的粉体为直径约100nm的纳米棒,在0.5和1C的放电速率下循环30次后,放电比容量仍有150mAh/g左右,且大电流放电性能更好。     

PEO／V2O5纳米复合薄膜的变色特性研究

为改善V2O5薄膜的电致变色性能，采用溶胶-凝胶法将具有高离子电导率并具有水溶性的聚环氧乙烷（PEO）直接嵌入V2O5层间，制备了PEO／V2O5纳米复合薄膜。采用标准三电极法从0．5mol／L LiClO4的PC电解质溶液向PEO／V2O5纳米复合薄膜注入锂离子，测量了纳米复合薄膜在注入不同数量锂离子时的可见光透射光谱以及对应的颜色变化，并运用循环伏安法测试其电化学性能。实验结果表明，PEO／V2O5纳米复合薄膜的循环伏安图出现了2对氧化还原峰，并且具有稳定的循环可逆性。随着应用电压的不同，薄膜呈现黄色、绿色和蓝色的多色可逆变化。PEO／V2O5纳米复合薄膜的电化学稳定性和机械性能都优于V2O5干凝胶薄膜，可以作为电致变色材料得到应用。X射线光电子能谱（XPS）成分分析表明PEO／V2O5纳米复合薄膜的电致变色效应与V、O的化合价和化学环境密切相关。     

V2O5促进六钛酸钾晶须的合成

六钛酸钾晶须是一种连锁风洞结构的具有优良物理机械性能和稳定化学性能等特点的新型材料。目前KDC法合成六钛酸钾晶须所需的煅烧温度高,且晶须长径比较小,而采用V2O5为添加剂的改进KDC法可以降低其煅烧温度,提高晶须长径比,使长径比>20。实验通过TG-DSC曲线说明V2O5的加入可以降低其煅烧温度,通过XRD确定了六钛酸钾晶须的合适煅烧温度、煅烧时间和钒酸盐的加入量,通过SEM说明晶须的长径比、形貌等。结果表明,当煅烧温度为800℃、煅烧时间为5h、V2O5的加入量为2%时,合成的六钛酸钾晶须平均长径比可达到22,且晶体结晶性好,形貌均匀。     

堇青石改性V2O5-WO3/TiO2催化剂性能影响研究

采用固液混合方法,利用改性堇青石制备蜂窝式V2O5-WO3/Cordierite-TiO2脱硝催化剂,通过扫描电子显微镜(SEM)、热分析(DSC-TG)、X射线衍射分析仪(XRD)、模拟烟气分析装置和磨损装置,考察其表面形貌、热稳定性、晶相变化、耐磨损性能和催化剂活性。结果表明,改性堇青石的引入,制备的催化剂具有表面微气孔多和热稳定性好的特点,700℃煅烧后,V2O5和WO3的仍呈现无定形态或微晶状态;引入10%的堇青石制备的催化剂磨损率低,尤其在250～460℃反应时,脱硝率可以保持在80%以上。     

纳米YMn2O5半导体可见光催化剂

采用改进的聚丙烯酰胺凝胶法合成了YMn2O5纳米颗粒.XRD分析结果表明,合成的纳米颗粒主要为正交YMn2O5相,兼有少许的六方YMn2O5相,无其它杂质相存在.SEM观察显示,制得的YMn2O5纳米颗粒粒度均匀、形貌规整、呈类球形,平均颗粒尺寸约为45nm.利用紫外—可见光漫反射光谱研究了YMn2O5纳米颗粒的光吸收特性及带隙,获得的光学带隙值为1.21eV.以一种典型的偶氮染料甲基红为目标降解物,研究了YMn2O5纳米颗粒的光催化活性.结果表明,在紫外光和可见光辐照下纳米颗粒均表现出了良好的光催化活性.实验确定了光催化降解率的最佳条件:甲基红的初始浓度为～15mg/L,催化剂的加载量为～1.2g/L.     

V2O5-B2O3-TeO2体系低熔点玻璃形成规律及特性

较详细地研究了V2O5-B2O3-TeO2三元体系的熔化温度、冷却熔体的相组成及玻璃形成规律;并测试分析了V2O5-B2O3-TeO2三元体系玻璃的热性能和特征温度。结果表明,V2O5-B2O3-TeO2三元体系具有较低的熔化温度,存在3个不同的结晶区域和一个较广阔的玻璃形成区,其玻璃形成区域为:V2O50%～70%、B2O30%～30%、TeO230%～100%(均为摩尔分数);V2O5-B2O3-TeO2系玻璃具有较低的熔化温度和封接温度,是无铅低温封接玻璃的理想体系之一。     

CoAl2O4/Al2O3纳米复合陶瓷的结构与表征

利用溶胶-凝胶方法制备了的CoAl2O4/Al2O3纳米复合陶瓷,并用X-ray分析(XRD)、红外光谱(IR)和扫描电镜分析(SEM)对其结构进行了分析.结果表明,随Al2O3含量增多,CoAl2O4尖晶石相从CoAl2O4/Al2O3凝胶中的析晶温度升高.SEM形貌也说明,随Al2O3含量增多,CoAl2O4/Al2O3陶瓷中形成一定的层状结构.     

热处理对V2O5-TiO2复合薄膜表面结构与光学性能的影响

以钛酸丁脂、V2O5粉末为前驱体,采用溶胶-凝胶法制备了V2O5-TiO2复合薄膜,并采用X射线光电子能谱(XPS)和Uv-vis-nir分光光度计等方法研究了热处理对薄膜性能的影响.结果表明,随热处理温度的升高,复合薄膜中钛离子的价态不变,仍为Ti4 ;而V4 离子逐渐被氧化为V5 离子;并采用氢氧基团、碳氧键与多种钒离子进行叠加拟合,拟合结果与实验曲线非常符合;V2O5-TiO2复合薄膜在紫外光波段的透射率减小,吸收带边出现红移.     

复合持续时间对P2O5-Al2O3异相复合玻璃结构和力学性能的影响

近年来,分相玻璃以其独特的结构以及优异的物理化学性质引起了广泛关注。本研究结合气动雾化加料和机械搅拌,采用熔融冷却法制备了纳米SiO₂-Na₂O高硅玻璃颗粒增强的P₂O₅-Al₂O₃玻璃。通过改变复合持续时间,研究了玻璃的结构与力学性能之间的关系。结果表明,异相复合玻璃的杨氏模量高于P₂O₅-Al₂O₃玻璃,并且随着复合持续时间由10s增大到8min,玻璃的杨氏模量呈现先升高后降低的趋势,在复合持续时间为6min时,杨氏模量达到最大值80.7GPa。相比于P₂O₅-Al₂O₃玻璃,杨氏模量提高了18%。引入SiO₂-Na₂O高硅玻璃颗粒不仅能够在基体玻璃中形成第二相,而且会改变P₂O₅-Al     

聚合物嵌入V2O5干凝胶纳米复合材料的合成研究

本文采用溶胶-凝胶方法,将聚合物(PEO)嵌入到V2O5干凝胶层间,制备出(PEO)xV2O5·nH2O纳米复合薄膜材料,利用XRD、TG/DTA、SEM等测试手段分析了复合薄膜的合成过程和状态.结果表明:V2O5干凝胶是在c轴方向有序而a、b轴方向无序的一种层状结构.当PEO嵌入到V2O5干凝胶层间形成纳米复合薄膜材料时,使得V2O5干凝胶层间距明显增大.经热处理后,其层间距由x=0时的11.154A增大到x=2时的14.246A.当x=0.5～1时,PEO嵌入较完全,且复合薄膜表面均匀,无裂纹和孔洞.     

Structural and optical properties of pulsed laser deposited V2O5 thin films

Pulsed laser deposited nanocrystalline V₂O₅ thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and optical spectroscopy. The films were deposited on amorphous glass substrates, keeping the O₂ partial pressure at 13.33 Pa and the substrate temperature at 220 °C. The characteristics of the films were changed by varying the laser fluence and repetition rate. XRD revealed that films are nanocrystalline with an orthorhombic structure. XPS shows the sub-stoichiometry of the films, that generally relies on the fact that during the formation process of V₂O₅ films, lower valence oxides are also created. From the HRTEM images, we observed the size evolution and distribution characteristics of the clusters in the function of the laser fluence. From the spectral transmittance we determined the absorption edge using the Tauc plot. Calculation of the Bohr radius for V₂O₅ is also reported.     

Hydrogen insertion compounds of V6O13 and V2O5

Hydrogen insertion compounds H_xV₆O₁₃ (0<x?7.3) have been synthesised and characterised. Unit-cell dimensions, determined from powder X-ray analysis, indicate that the hydrogen-insertion reaction proceeds topotactically. In addition, a low-hydrogen-content phase of H_xV₂O₅ of similar structure to V₂O₅ has been prepared.     

Hydrothermal growth of V2O5 photoactive films at low temperatures

It is shown that the surface morphology and the photoactivity of hydrothermally grown V₂O₅ films at 95 °C are greatly affected by the deposition time. Well-defined phase of V₂O₅ films grown for a deposition period of 2 h were found to exhibit significant photocatalytic activity, degrading stearic acid by 57%. The films presented a relatively porous structure, appearing as a wall-like network. The correlation of deposition period with the structure, morphology and the photoinduced properties of the materials are discussed.     

Structural and optical studies of nanocrystalline V2O5 thin films

We report the structural and optical properties of nanocrystalline thin films of vanadium oxide prepared via evaporation technique on amorphous glass substrates. The crystallinity of the films was studied using X-ray diffraction and surface morphology of the films was studied using scanning electron microscopy and atomic force microscopy. Deposition temperature was found to have a great impact on the optical and structural properties of these films. The films deposited at room temperature show homogeneous, uniform and smooth texture but were amorphous in nature. These films remain amorphous even after postannealing at 300 °C. On the other hand the films deposited at substrate temperature T_S > 200 °C were well textured and c-axis oriented with good crystalline properties. Moreover colour of the films changes from pale yellow to light brown to black corresponding to deposition at room temperature, 300 °C and 500 °C respectively. The investigation revealed that nanocrystalline V₂O₅ films with preferred 001 orientation and with crystalline size of 17.67 nm can be grown with a layered structure onto amorphous glass substrates at temperature as low as 300 °C. The photograph of V₂O₅ films deposited at room temperature taken by scanning electron microscopy shows regular dot like features of nm size.     

Low temperature chemical vapor deposition of nanocrystalline V2O5 thin films

Spatially uniform, carbon-free thin films of V₂O₅ were deposited on silicon by chemical vapor deposition using vanadium oxide triisopropoxide and water as gaseous precursors, in the temperature range of 100-300 °C. Films with substantial crystallinity were obtained for deposition temperatures as low as 180 °C. The “neat” chemistry that nominally leaves no fragments of ligand or water in the solid promotes film purity and reduces the deposition temperature needed for crystallization. Such deposition temperatures also open up additional possibilities for using crystalline vanadia on fragile substrates such as polymers for electronics and optical applications.     

Surface and electrical studies of CuO:V2O5 thin films

Results from the studies of multicomponent CuO:V₂O₅ bulk material and thermally evaporated thin films of highly conducting bulk composition prepared at different substrate temperatures are thus compared and discussed. The electronic conductivity is enhanced on increase in the substrate temperature T_s and reaches a maximum value of 12.3 × 10⁻⁶Ω⁻¹ cm⁻¹ for T_s = 423 K. X-ray photoelectron spectroscopy studies indicate an increase in the reduced states of vanadium and copper ions in going from the bulk glass to the thin film. Dynamic secondary-ion mass spectroscopy studies on thin films over a depth of 3000 Å show a strong dependence of T_s on the Cu-to-V intensity ratio. Even though stoichiometric values for thin films are achievable by varying the T_s, the oxidation states of Cu in these films are predominantly monovalent. The electrical behaviors of these materials and their thin film counterparts are finally being discussed in relation to the surface analysis data.     

Morphology characterization and friction coefficient determination of sputtered V2O5 films

The morphology of V₂O₅ low-friction coatings on MgO (001) substrates synthesized by unbalanced reactive magnetron sputtering was investigated using atomic force microscopy. Analyzing the height-height correlation function, the evolution of the surface roughness parameters root mean square roughness (rms), lateral correlation length, and the Hurst parameter were determined. Studying samples of V₂O₅ grown at temperatures from 25 °C to 300 °C, a transition from amorphous to crystalline growth at 80 °C was observed. The rms roughness increased from 0.7 nm at 26 °C to 21 nm at 300 °C. Furthermore, a method to quantitatively determine friction coefficients via friction force microscopy was applied. The surface contact forces were calculated via the cantilever's spring constants determined using the Sader method. At scan speeds of 1.25 μm/s and 3.13 μm/s, friction coefficients of 0.60 ± 0.02 and 0.63 ± 0.01, respectively, have been obtained.     

Growth and structure of electron beam evaporated V2O5 thin films

The growth, structure and room temperature electrical conductivity of electron beam evaporated V₂O₅ thin films were studied in detail as a function of deposition temperature. The films deposited at T_s≈553 K and subsequently annealed in oxygen atmosphere at 693 K exhibited orthorhombic layered structure.     

Microdurete de monocristaux de V2O5

Microhardness measurements of V₂O₅ single crystals were undertaken in order to study the anisotropy of their mechanical properties. Results are presented for both Vickers and Knoop hardness values on (100), (010) and (001) planes of orthorhombic V₂O₅ single crystals.A strong anisotropy is observed in each plane. As expected, hardness appears to be particularly small when the diamond indenter is parallel to the clivage directions in the (100) and (001) planes. A remarkably small value is observed along the [100] direction in the (001) plane, which could be related to the model proposed by Gillis in order to explain the structural charge into V₆O₁₃ occuring in non-stoichiometric V₂O₅.     

Conversion of V2O5·xH2O into orthorhombic V2O5 single-crystalline nanobelts

Orthorhombic V₂O₅ single-crystalline nanobelts have been synthesized by hydrothermal treating V₂O₅·xH₂O precipitate derived from aqueous solution of V₂O₅ and H₂O₂. The synthetic method is facile, fast, environmental friendly, and easy to scale up. The V₂O₅ single-crystalline nanobelts are 30-80 nm in width, 30-40 nm in thickness, and lengths up to several tens of micrometers. The V₂O₅·xH₂O precursor is crucial for the formation of orthorhombic V₂O₅ single-crystalline nanobelts. The influences of synthetic parameters, such as reaction time and reaction temperature, on the crystal structures and morphologies of the resulting products have been investigated. Time-dependent experiments show that V₂O₅·xH₂O are dehydrated gradually and converted into orthorhombic V₂O₅ single-crystalline nanobelts. High reaction temperature also favors the formation of orthorhombic V₂O₅ nanobelts.