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用共沉淀法制备了不同比例的MoCrTeO、MoCoTeO和MoCrTeCoO复合氧化物催化剂,考察其对丙烷选择氧化制丙烯醛反应的催化性能,并对反应温度、空速、原料气比例等条件进行优化,得到丙烯醛最高产率为22.96%.实验结果表明,Te元素的添加对提高丙烯醛的选择性和产率起了十分重要的作用,但过高的Te含量却不利于丙烷的转化率.X射线衍射表征结果表明,催化剂中正交系TeMo5O16相可能是丙烷选择氧化制丙烯醛反应的重要的活性相.  相似文献   
2.
Sr2ScAlO5:Eu^2+, a red oxide phosphor with a perovskite-type structure, has been synthesized through a solid-state reaction and its luminescence properties have been investigated. An absorption band centering at 450 nm is observed from the diffuse reflection spectra and the excitation spectra, indicating that the phosphor can match perfectly with the blue light of InGaN light-emitting diodes. A broad red emission band at 620 nm is found from the emission spectra, originating from the 4f^65d-4f^7 transition of the Eu^2+ ions. The best doping content of Eu in this material is about 5%. S Sr2ScAlO5:Eu^2+ is a highly promising red phosphor for use in white light-emitting diodes.  相似文献   
3.
A single-phased silicate compound (Ba1-xCex)9(Sc1-yMny)2Si6O24 was prepared by solid-state reaction at high temperature. From powder X-ray diffraction (XRD) analysis, the formation of Ba9Sc2Si6O24 with an R3 space group was confirmed. In the photoluminescence spectra under ultraviolet (UV) ray excitation, the Ba9Sc2Si6O24:Ce3+,Mn2+ phosphor emits two distinctive color light bands: a blue one originating from Ce3+and a red one caused by Mn2+. The energy transfer process from Ce3+ to Mn2+ was confirmed, the critical radius as well as the transfer efficiency was calculated, and the energy transfer mechanism was discussed. In addition, the decay-time testing indicates that the energy transfer efficiencies from Ce(1) to Mn2+ and Ce(2) to Mn2+ are different. The emission chromaticity of Ba9Sc2Si6O24:Ce3+,Mn2+ phosphor could be tuned from blue to red by altering the Ce3+/Mn2+ concentration ratio.  相似文献   
4.
采用平面波超软赝势方法研究了纤铁矿型TiO_2纳米片层结构的稳定性和电子结构.结果显示该结构具有较高的稳定性,其带隙比锐钛矿型TiO_2要大0.59 e V,带隙内没有出现表面态.通过对空位缺陷形成能的比较,结果显示这在还原性气氛下纤铁矿型TiO_2纳米片层表面Ti空位的形成能明显低于O空位的形成能,确定出最容易出现的缺陷是-4价的Ti空位,该空位缺陷的出现会使带隙中产生表面缺陷态.与体相内缺陷不同,表面缺陷态可以促进电子和空穴的分离,这些发现可以合理的解释最近的实验结果 .  相似文献   
5.
一种声发射信号方位角自适应监测算法*   总被引:1,自引:1,他引:0       下载免费PDF全文
四阶累积量可用于声发射信号处理,结合盲波束形成算法可对声发射信号的方位角进行估计。由于四阶累积量的计算量较大,采用迭代计算的思想,提出一种基于四阶累积量的自适应声发射信号方位角监测算法。与改进前的算法相比,自适应算法的计算复杂度和所需存贮空间均显著降低,可用于声发射信号的方位估计和监测。计算机仿真及实测数据分析均验证了算法的有效性。  相似文献   
6.
Trivalent cerium-doped yttrium aluminum garnet(YAG:Ce3+) phosphors are synthesized by solid-state reaction method through using(Y1-xCex)2O3 solid solutions as precursors. Solid solubility limits of Ce3+replacing Y3+in Y2O3and YAG are determined to be 40% and 7.5%, respectively, based on the relationship between the lattice parameter and chemical composition. Using(Y1-xCex)2O3 as precursors we synthesize YAG:Ce3+single phase at 1450°C and N2atmosphere. However, under the same conditions using CeO2there exists a second phase YAlO3as impurity. The photoluminescence intensity of YAG:Ce3+increases monotonically with the increase of Ce concentration until it reaches a maximum at solid solubility limits of Ce3+in YAG.  相似文献   
7.
周天亮  宋振  宋西平  边柳  刘泉林 《中国物理 B》2010,19(12):127808-127808
Sr2ScAlO5:Eu2+,a red oxide phosphor with a perovskite-type structure,has been synthesized through a solid-state reaction and its luminescence properties have been investigated.An absorption band centering at 450 nm is observed from the diffuse reflection spectra and the excitation spectra,indicating that the phosphor can match perfectly with the blue light of InGaN light-emitting diodes.A broad red emission band at 620 nm is found from the emission spectra,originating from the 4f 6 5d-4f 7 transition of the Eu 2+ ions.The best doping content of Eu in this material is about 5%.Sr2ScAlO5:Eu2+is a highly promising red phosphor for use in white light-emitting diodes.  相似文献   
8.
Trivalent cerium-doped yttrium aluminum garnet (YAG:Ce3+) phosphors are synthesized by solid-state reaction method through using (Yl-xCex)203 solid solutions as precursors. Solid solubility limits of Ce3+ replacing y3+ in Y203 and YAG are determined to be 40% and 7.5%, respectively, based on the relationship between the lattice param- eter and chemical composition. Using (Y1-xCex)203 as precursors we synthesize YAG:Ce3+single phase at 1450 ~C and N2 atmosphere. However, under the same conditions using CeO2 there exists a second phase YA103 as impurity. The photoluminescence intensity of YAG:Ce3+ increases monotonically with the increase of Ce concentration until it reaches a maximum at solid solubility limits of Ce3+ in YAG.  相似文献   
9.
基于混合编码遗传算法和有限元分析的压电结构载荷识别   总被引:1,自引:0,他引:1  
与传统的优化算法相比,遗传算法不需要计算目标函数的导数信息,便于迭代,可实现全局寻优.因此,本文提出一种采用混合编码的遗传算法与有限元分析相结合,对复合材料层合板、壳进行载荷识别的新方法.在遗传算法求解过程中,设计变量的编码方法选择是其重要环节,二进制编码容易产生连续函数离散化时的映射误差,且其求解精度与染色体的编码长度紧密相关,过长的染色体描述虽可提高精度,但会显著降低算法的求解效率.为此,本文提出采用混合编码的方法进行载荷识别,即用二进制编码表征载荷作用位置,浮点数编码表示载荷的大小.这一方法大大降低了染色体的长度,并显著提高了计算效率和精度.  相似文献   
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