Ti掺杂及退火处理对水热合成WO_3纳米晶粒结构及气敏性能的影响

采用水热法制备了不同掺杂浓度的WO3∶Ti纳米晶粒,并在350℃下退火1 h。采用SEM、XRD表征了材料的形貌与结构,并测试了用退火前后合成材料制成的薄膜气敏传感器件在200℃下对NO2的气敏性能。结果表明,Ti掺杂可以有效抑制WO3晶粒的生长,减小晶粒尺寸;退火处理使材料的晶相发生了改变,晶粒尺寸进一步减小,晶粒分散性变好。薄膜传感器件的测试结果显示,适量Ti掺杂和退火处理均可提高器件对NO2的灵敏度,退火后Ti掺杂2%样品制成的器件的灵敏度最大,其值达到了15.38,响应恢复时间分别为2.2和1.5 min,且具有良好的可重复性和稳定性。     

Synthesis and photochromic properties of EDTA-induced MoO3 powder

In this study, the photochromic MoO₃ powder with novel morphology has been synthesized via hydrothermal method, using ethylene diamine tetraacetice acid (EDTA) as organic inducing agent. The influence of EDTA on the morphology, structure and photochromic properties of MoO₃ powder has been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as ultraviolet and visible spectroscopy (UV-vis) and color difference meter. When the molar ratio of EDTA/Mo⁶⁺ is 0.05:1, the EDTA-induced MoO₃ powder is found to have 3D flower-like morphologies and excellent photochromic properties. Furthermore, the possible growth mechanism of the flower-like structure and the photochromic mechanism of MoO₃ powder are also discussed in detail.     

pH值对纳米W03粉体结构及光致变色性能的影响

以钨酸钠为钨源,采用水热法在不同pH值条件下制备纳米WO3粉体,通过XRD、SEM、BET等分析手段对产物的晶型结构、形貌和比表面积进行了表征,并利用紫外-可见光漫反射吸收光谱仪和测色计对所制备的样品进行光致变色性能测试.结果表明,pH=1.0和2.0时合成的产物分别为六方晶型和立方晶型的WO2粉体.其中,六方晶型的WO2所具有的规则孔道结构为光生质子H+的传递提供了良好的通道,有利于WO3粉体产生良好的光致变色性能;而立方晶型的WO3所具有的复杂的网络结构不利于光生质子H+的传递,因而光致变色性能较差.且pH=1.0时合成的刺猬状WO3粉体颗粒大小均匀,具有较大的比表面积和较高的反应活性,这也有利于粉体光致变色性能的提高.     

热处理对WO3薄膜光学性质的影响

直流反应磁控溅射法制备了WO3薄膜,薄膜在723K纯N2气中被退火处理.热处理前WO3薄膜为无定形态,热处理后为多晶态.采用透射谱和单谐振子模型获得了薄膜的折射率和消光系数,得到退火前后谐振子能量分别为5.77和5.28eV,色散能为19.9和15.9eV.分析表明退火前后吸收边附近均表现出间接带隙的两段线性关系,间接带隙分别为3.14和2.96eV,声子能量为32和149meV,退火后带隙减小推测可能是由于退火薄膜晶化,氧填隙粒子导致的带尾态效应消失的结果.     

Crystal structure and spontaneous magnetism of BiFeO3 powder synthesized by hydrothermal method

Single-phase BiFeO3 powder was successively synthesized by a low-temperature hydrothermal method. Scanning electron microscopy and transmission electron microscopy results showed that BiFeO3 powder had several hundred nanometers to micrometer-sized particles with a broad size distribution. BiFeO3 powder showed weak-ferromagnetic behavior with a small magnetization value (Ms approximately 20 memu/g) at room temperature. Rietveld refinement results for the crystal structure show the displacive disorder of the Fe-site(6a); the Fe-site(6a) splits into two pairs, Fe(1) and Fe(2) displaced by 0.9 angstroms from each other and these sites are partially occupied. Hence the O-site(18b) also splits into the two partially occupied sites forming a distorted FeO6 octahedras. The weak ferromagnetism observed in the hydrothermal BFO powder is ascribed to the displacive disorder of FeO6 octahedras resulting in an incomplete counterbalance between the antiferromagnetic sublattices of the Fe-ions.     

Effect of hydrothermal growth temperature on structural and optical properties of TiO2 nanoparticles

TiO₂ nanoparticles have been prepared by hydrothermal method at different temperatures. The X-ray diffraction results showed that anatase TiO₂ nanoparticles with grain size in the range of 7–27 nm has been obtained. HRTEM images show the formation of TiO₂ nanoparticles with grain size ranging from 7 to 26 nm. The Raman spectra exhibited peaks corresponding to the anatase phase of TiO₂. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increasing hydrothermal temperature.     

颗粒尺寸及温度对羰基铁粉磁化性能的影响

为了揭示颗粒尺寸及温度对羰基铁粉磁化性能的影响规律,利用振动样品磁场计分别测试了两种不同粒径羰基铁粉在室温条件下的磁化特性曲线,并以粒径为7μm的颗粒为对象,研究了温度对其磁化性能的影响。结果表明,粒径较大的颗粒具有更为优良的磁化性能,相同磁场作用下,其磁化强度较大而矫顽力却较小;温度升高将导致颗粒达到相同磁化强度所需磁场强度减小且对应磁化强度值降低,并且这种影响随温度的升高而逐渐加剧;当长期处于高温下工作后,由于表面氧化层的形成,颗粒磁性将会出现较大程度的减弱。     

Tungsten powder from carbon coated WO3 precursors

This paper deals with the formation of tungsten powder from carbon coated tungstic oxide precursors. This study makes use of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). TGA data allowed for calculation of the activation energy as 626 ± 18.2 kJ/mol. XRD characterized the products resulting from the reaction of the carbon coated WO₃ for each isotherm. These diffraction patterns support the hypothesis that reduction to W proceeds through the formation of lower oxidation states. This is the first isolation of a metal powder using the carbon coated precursor process.     

Structural change of hydrothermal BaTiO3 powder

Formation rate of tetragonal BaTiO₃ powder by hydrothermal synthesis and its dielectric property were studied. Submicron tetragonal BaTiO₃ powders were prepared hydrothermally, using Ba(OH)₂ · 8H₂O, TiO₂ (anatase) and KOH as starting chemicals. Characterization via X-ray diffractometry, Field Emission Scanning Electron Microscopy confirmed that increasing calcination temperature (from 1100 to 1300°C) promotes the formation of tetragonal BaTiO₃. Tetragonal BaTiO₃ ceramics obtained from optimum condition (Tetragonal BaTiO₃ powders calcined at 1200°C for 3 h after hydrothermal synthesized at 200°C for 168 h) exhibited submicron size of 0.5–0.7 m, monodispersed type and high relative permittivity.     

Effect of calcination temperature on the textural properties and photocatalytic activities of highly ordered cubic mesoporous WO3/TiO2 films

Highly organized cubic mesoporous WO3/TiO2 films were successfully prepared by evaporation-induced self-assembly (EISA) process, employing triblock copolymer as template. The characterization results by XRD, SEM, TEM, UV-Vis. spectrophotometry, and nitrogen adsorption-desorption isotherms reveal that the mesoporous films are made up of well-defined 3-D cubic (lm3m space group) mesoporous structure and nanocrystalline anatase frameworks with high surface area, uniform pore sizes and excellent optical transparency. Photocatalytic properties of the mesoporous WO3/TiO2 films in decomposing gaseous 2-propanol to CO2 were analyzed as a function of calcinations temperature. The highest photocatalytic activity was obtained for the films calcined at 450 degrees C, which possess an appropriate crystallinity and relevant ordering of mesoporous structure. It was found that that long-range ordering of mesopores is one of the important factors in determining the photocatalytic degradation of gaseous organics.     

The formation of WO3 nanorods using the surfactant-assisted hydrothermal reaction

Monoclinic tungsten oxide (WO₃) nanorods were grown using the hydrothermal method on a seeded W foil. The seed layer was formed by thermal oxidation of W foil at 400°C for 30 min. Cetyltrimethylammonium bromide (CTAB) or hexamethylamine (HMT) was used in the reactive hydrothermal bath, along with sodium tungstate dihydrate (Na₂WO₄.2H₂O) and hydrochloric acid (HCl). The concentration of CTAB was varied from 0.01 M to 0.07 M and the concentration of HMT was varied from 0.01 M and 0.05 M. The result showed that CTAB-assisted hydrothermal reaction produced WO₃ nanorods with 4–7 nm diameter, and provided that CTAB concentration was less than 0.07 M. WO₃ nanorods could not be obtained when CTAB concentration was 0.07 M. Columnar structured WO₃ was produced with the presence of HMT in the hydrothermal bath. This was due to decomposition of HMT to form hydroxyl ions (OH^?) that inhibited the growth of nanorods. Cyclic voltammetry (CV) analysis showed better electrochromic property of WO₃ nanorods compared to columnar structured WO₃.     

抗氧剂/光稳定剂对3D打印光致变色木塑复合材料性能的影响

功能性光致变色木塑复合材料(PWPC)使用寿命通常较短,因此本研究将抗氧剂1010和光稳定剂770引入到PWPC中,以改善复合材料的力学和耐光疲劳等性能.采用熔融共混法制得杨木粉/聚乳酸(WF/PLA)基光致变色复合材料,通过熔融沉积技术(FDM)打印成型,对制备的WF/PLA复合材料力学、界面相容性、热稳定性和耐光疲...     

纳米三氧化钨材料的制备及其结构分析

通过不同方法制备纳米WO3,材料,利用透穿电子显微镜和XRD,观察材料晶粒大小,形状,研究材料的结构特性.分别通过热分解法,溶胶-凝胶法,电弧气相法制备纳米WO3材料,研究上述制备方法对材料的影响.实验发现,通过热分解法,适量加入SiO2材料,可以大幅度减小WO3材料尺寸,改善分散特性.溶胶一凝胶法制备的WO3材料,在某一晶面方向生长明显,呈现片状结构;采用气相热分解法制备WO3材料,出现较为规则的几何形状.因此,通过选择制备方法,控制纳米WO3材料形状及大小,改变其性能.     

Effect of humidity treatment on the structure and photocatalytic properties of titania mesoporous powder

In the work presented here, mesoporous titania (MT) powders is synthesized by sol–gel method using amphiphilic triblock copolymer as a template at two different levels of relative humidity (RH); 20 and 80%. Various techniques such as small angle X-ray diffraction (SAXRD), wide angle X-ray diffraction (XRD), UV–visible spectroscopy, high resolution transmission electron microscopy (HRTEM), Fourier transformed infra red (FTIR) spectroscopy and N₂-adsorption/desorption analysis were utilized to study the prepared samples. Further, the photocatalytic activities of the prepared samples were evaluated from the photo-degradation analysis of methylene blue (MB). For the sample treated with 80%RH the formation of an ordered mesoporous structure with a high specific surface area (172 m²g⁻¹), mesoporosity (48%) and enhanced photocatalytic activity were obtained compared to those of the sample subjected to 20%RH. The observed increased MB degradation for the latter is mainly attributed to the formation of higher specific surface area and mesoporosity. The availability of highly ordered open pore channels could provide increased contacts between reactants in the solution and the active sites on the surfaces of MT particles.     

A dramatic increase of photochromic sensitivity in the case of hydrogen photochromism in WO3

The use of two hydrogen-containing molecules with different functions (donor of hydrogen atoms and provider of proton surface diffusion) enables one to dramatically increase the photochromic sensitivity at hydrogen photoinjection in both films and bilayer structures of WO₃. Application of a bilayer structure of WO₃ films enables one to unambiguously prove the effect of proton diffusion on the photochromic sensitivity at hydrogen photochromism.     

WO3纳米微粒的制备及气敏特性研究进展

综述了近年来国内外对WO3纳米微粒作为气敏材料时的制备方法进展,对WO3的气敏机理进行了探讨,并总结了不同化合物的掺杂对其气敏性能的影响。     

Low temperature preparation of bismuth-related ferroelectrics powder and thin films by hydrothermal synthesis

Bi(4)Ti(3)O(12) (BIT) thin films were prepared by low temperature hydrothermal synthesis on Pt/TiO(x)/SiO(2)/Si. Bi(4)Ti(3)O(12) or TiO(2) gel solution was formed and annealed at 350 degrees C. The BIT thin films were crystallized as a Bi-layer structural ferroelectric. During the hydrothermal treatment, the TiO(2) anatase (101) peak appears and seems to play the role as an intermediate layer. Randomly oriented BIT thin films were obtained. As a result, the BIT thin films have ferroelectric property. The as-deposited BIT thin films include spherical grains with the grain size of 120 nm.     

Effect of ZnSe doping on the photochromic and thermochromic properties of MoO3 thin films

The photochromic and thermochromic properties of molybdenum oxide (MoO₃) thin films doped with zinc selenide (ZnSe) were studied. The films were deposited on glass substrates by thermal evaporation of MoO₃-ZnSe powder mixtures. The characteristic optical absorption band attributed to color center formation indicated an enhanced photochromic effect for MoO₃ films doped with ZnSe 5 mol% relative to undoped MoO₃ samples. In addition, the thermochromic effect was most pronounced for ZnSe 5 mol% samples annealed at 23-125 °C, and for undoped samples annealed at 125-225 °C. The chromogenic properties were essentially suppressed for MoO₃ doped with ZnSe 10 mol%.