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排序方式: 共有102条查询结果,搜索用时 10 毫秒
31.
Characterization of ZnO Based Varistor Derived from Nano ZnO Powders and Ultrafine Dopants 总被引:1,自引:0,他引:1
Weizhong YANG Dali ZHOU Guangfu YIN Runsheng WANG Yun ZHANG College of Material Science Engineering Sichuan University Chengdu China 《材料科学技术学报》2005,21(2):183-186
Nanosized ZnO powders were prepared with a two-step precipitation method. The average size of ZnO particles was about 80 nm and their size distribution was narrow. Combining with ultrafine additive powders, ZnO base varistor was produced via an oxide mixing route. ZnO varistor derived from normal reagent grade starting materials was investigated for comparison purpose. Outstanding microstructure of the ZnO varistor derived from nanosize ZnO powders and ultrafine dopants was obtained: uniform distribution of fine ZnO grains (less than 3 microns), grain boundary and the dopant position. Higher varistor voltage (U=492 V/mm) and nonlinear coefficient (α=56.2) as well as lower leakage current (TL=1.5 μuA) were achieved. The better electrical properties were attributed to the uniform microstructure, which in turn led to stable and uniform potential barriers. Also this improved technique is more feasible for producing ZnO nanopowders and resulting varistor in large scales. 相似文献
32.
《Ceramics International》2019,45(14):17521-17528
The nanopowders of zirconia toughened alumina (ZTA) as soft spherical granules were directly synthesized by combining co-precipitation with spray drying (CPSD). The co-precipitation of alumina (Al2O3) and yttria-stabilized zirconia (YSZ) was performed together in one step to obtain the ZTA precipitate. Spray drying, which is the most preferred industrial processing way to produce the nanopowders as spherical granules, was used to atomize, dry and granulate the suspension like milk prepared from the synthesized ZTA precipitate under previously optimized spray drying conditions. However, the important and complex processing parameters of spray drying such as the solid-liquid ratio and the feeding rate of the suspension, the inlet temperature and the flow rate of the hot air have to be optimized depending on the moll mass and volume of the component in the prepared suspension. The ZTA nanopowders containing 4–20 wt% YSZ synthesized by the CPSD method have a crystalline structure of alumina and YSZ, an average nanoparticle size between 26.64 and 46.70 nm with a very high specific surface area (SSA) between 77.43 and 112.41 m2 g−1 in a soft spherical granule form, which were determined by XRD, BET and SEM, respectively. The preparation and drying conditions of the synthesized precipitate, the solid-liquid ratio of the suspension and the molar mass ratio of YSZ in Al2O3 matrix have a significant effect on the crystallinity, morphology, particle size, SSA, and granule form of the synthesized ZTA nanopowders. 相似文献
33.
Yaqian Chen Huanping Wang Xiaoting Zhang Zhen Xiao Qinghua Yang Ruoshan Lei Degang Deng Lihui Huang Shiqing Xu 《中国稀土学报(英文版)》2018,36(5):468-473
(Y_(0.87)La_(0.1)Zr_(0.03))_2O_3 nanopowders doped with various concentrations of Tm~(3+) and Ho~(3+) were prepared by the citrate method. The standard cubic Y_2O_3 phase can be matched in the Tm~(3+)/Ho~(3+) co-doped(Y_(0.87)La_(0.1)Zr_(0.03))_2 O_3 nanopowders. The nanopowders exhibit average particle sizes of 40,60, 80 and 100 nm after calcinated at 900,1000,1100 and 1200℃,respectively. The energy transfer from Tm~(3+) to Ho~(3+) and the optimum fluorescence emission around 2 μm were investigated. Results indicate that the emission bands at around 1.86 and 1.95 μm correspond to ~3 F_4→~3 H_6 transition of Tm~(3+) and ~5 I_7→~5 I_8 transition of Ho~(3+), respectively.Better spectral properties were achieved in Tm~(3+)/Ho~(3+) co-doped(Y_(0.87)La_(0.1)Zr_(0.03))_2O_3 nanopowders with the average size of 100 nm obtained at the conditions of the treatment of precursors calcinated at 1200 ℃ for 2 h doped with 1.5 mol% Tm~(3+) and 1 mol% Ho~(3+). 相似文献
34.
In this paper, the catalytic effect of Zn nanopowders on thermal decomposition of ammonium perchlorate (AP) as well as those of Zn micropowders has been investigated using differential thermal analysis (DTA). The results show that both nanometer and micrometer Zn powders show similar excellent catalytic effect on the decomposition of AP, while the total heat releases of AP added by Zn nanopowders are generally higher than those of AP added by Zn micropowders. In addition, an attempt has been made to explain the observed results with the help of theoretical considerations and data generated during this work. 相似文献
35.
Samir Hamrit Kamal Djessas Kahina Medjnoun Idris Bouchama Mohammad Alam Saeed 《Ceramics International》2021,47(16):22881-22888
RF-magnetron sputtering has been carried out at room temperature to deposit vanadium-doped zinc oxide (VZO) nanostructured thin films onto flexible PEN substrates. The sputtering targets of compacted VZO nanopowder have been prepared using a rapid and inexpensive Sol-Gel synthesis followed by a supercritical drying process. Structural and morphological study of VZO particles in the targets has been carried out via X-ray diffraction and Transmission Electron Microscopy (TEM). The nanostructured thin films have been characterized to analyze the structural, morphological, electrical and optical properties as a function of vanadium content from 0 to 4 at.%. Structural characterization of VZO thin films revealed that the deposited thin films have been grown preferentially along (002) and exhibit the hexagonal wurtzite structure. The cross-sectional and microstructural analysis performed by Scanning Electron Microscopy (SEM) confirms the columnar growth of nanostructures. The deposited thin films exhibit transparent behavior with transmission >70% in the visible region. It has been observed that nanostructured thin films with vanadium content of 2% have demonstrated the lowest resistivity (6.71 × 10?4 Ω cm) with Hall mobility of 10.62 cm2 V?1 s?1. The deposited vanadium doped nanostructured thin films would have potential applications in electronic and optoelectronic devices. 相似文献
36.
S. Mittal 《Integrated ferroelectrics》2020,205(1):122-130
AbstractSolid state synthesis route was employed to form Ba0.85Ca0.15Zr0.1Ti0.9O3 powder. The calcined powder was high energy ball milled at different milling speeds to get powders of different particle sizes. XRD pattern of the ceramics made from these powders show the presence of pure perovskite. This paper deals with a systematic study of the pyroelectric and the fatigue properties of the ceramics. The room temperature pyroelectric coefficient (p) attains the minimum value p?=?0.119X10?8 C cm?2 K?1 for the ceramic made from the powder milled at 250?rpm. The fatigue was also found to be minimum for the same ceramic samples. 相似文献
37.
《Advanced Powder Technology》2017,28(7):1739-1744
Nanometric powders of stoichiometric compositions in the Mo-Nb-W ternary system were produced by Self-propagating High-temperature Synthesis (SHS) using magnesium to reduce their oxides, in presence of sodium chloride. The influence of Mg and adiabatic temperature on the phase compositions of the final products were determined. After reaction, samples were analyzed by XRD, SEM, and BET.Results demonstrate the possibility to obtain high purity nanostructured products in the 20–800 nm range, with an average equivalent diameter, from specific surface measurements, of 66 nm. For moderate excess Mg amounts, due to the low Mg boiling temperature, niobium is not completely reduced and forms complex compounds with MgO, whereas reduction is near-complete for the highest Mg amounts. 相似文献
38.
A. Cabot J. Arbiol J. R. Morante U. Weimar N. B rsan W. G pel 《Sensors and actuators. B, Chemical》2000,70(1-3):87-100
In order to clarify the role of the noble metal additives in the gas sensing mechanisms, three of the most common catalytic additives, such as Pd, Pt and Au, have been introduced in a sol–gel obtained tin oxide base material. The additives nominal weight concentrations used were 0.2% and 2%, and they were introduced in the precipitated tin oxide. A posterior calcination treatment was carried out, during 8 h, at the temperatures of 250°C, 400°C, 450°C, 600°C, 800°C and 1000°C. Structural and surface analysis of these nanopowders have been performed. Identification and localisation of metallic, 2+ and 4+ oxidised states of the used noble metals are discussed, and experimental evidences about their effects on the sensor performance are presented. Likewise, effects of their presence on the nanoparticle characteristics, and also on the material sensitivity to CO and CH4, are analysed and discussed. 相似文献
39.
In this work, the BaF2 nanopowders with different particle size were synthesized by precipitation in the ethanol/water mixed solvents. Five kinds of compositions of mixed solvents, including pure water, 25 vol.%, 50 vol.%, 67.5 vol.%, and 75 vol.% of ethanol were used. The effects of aging and the volume percentage of ethanol in the mixed solvents on the resultant BaF2 nanoparticles were under investigation. The size and morphology of the BaF2 particles were characterized by TEM, FSEM and XRD analyses. The results show that after aging for 2 h the particle size of the BaF2 precipitates in the 50% mixed suspension changes little. The prepared BaF2 particles all exhibit cubic fluorite structures no matter what kind of composition is used. In pure water environment, the size of BaF2 particles is about 70 nm, whereas it reduces to 33 nm in the 75% mixed solution. As the vol.% of ethanol increases the particle size decreases, and other properties such as the size distribution, dispersion, oriented growth et al. are also modulated. These alterations can be interpreted by varying the dielectric constant of mixed solvent. 相似文献
40.
The phase and structure evolution during synthesis of vanadium carbide (V8C7) nanopowders by thermal processing of the precursor were investigated using X-ray diffraction (XRD). The morphology of the reactant was characterized by transmission electron microscopy (TEM). Simultaneous thermogravimetric and differential thermal analysis (TG-DTA) were made on the precursor. The results indicate phase evolution sequences are NH4VO3→V2O5→VO2→V5O9+V4O7→V2O3→VC1−X→V8C7. The single phase V8C7 powders can be prepared at ∼1100 °C for 1 h, and the powders show good dispersion and are mainly composed of uniformly sized spherical particles with the majority diameters of 20-50 nm. 相似文献