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991.
纳米Y2O3/钴基合金激光熔覆层的组织 总被引:6,自引:0,他引:6
利用5 kW CO2激光器,在Ni基高温合金表面,熔覆纳米稀土氧化物(Y2O3)/钴基合金复合材料,制备了涂层.利用光学显微镜、扫描电镜及透射电镜分析了熔覆层的组织结构.结果表明: 熔覆层的主要相组成为γ-Co,ε-Co,Cr23C6和Y2O3;加入纳米Y2O3,凝固组织由细长的柱状树枝晶转变为较短的树枝晶;纳米Y2O3含量增大至1%时整个断面获得等轴晶组织;纳米Y2O3作为异质形核的核心,细化了组织;纳米Y2O3在熔覆层中分布不均匀,促进了γ-Co向ε-Co的转变;熔覆层的亚结构为堆跺层错.对熔覆层等轴组织形成机制进行了分析. 相似文献
992.
Synthesis and utilization of monodisperse hollow polymeric particles in photonic crystals 总被引:3,自引:0,他引:3
We developed a process to fabricate 150-700 nm monodisperse polymer particles with 100-500 nm hollow cores. These hollow particles were fabricated via dispersion polymerization to synthesize a polymer shell around monodisperse SiO(2) particles. The SiO(2) cores were then removed by HF etching to produce monodisperse hollow polymeric particle shells. The hollow core size and the polymer shell thickness, can be easily varied over significant size ranges. These hollow polymeric particles are sufficiently monodisperse that upon centrifugation from ethanol they form well-ordered close-packed colloidal crystals that diffract light. After the surfaces are functionalized with sulfonates, these particles self-assemble into crystalline colloidal arrays in deionized water. This synthetic method can also be used to create monodisperse particles with complex and unusual morphologies. For example, we synthesized hollow particles containing two concentric-independent, spherical polymer shells, and hollow silica particles which contain a central spherical silica core. In addition, these hollow spheres can be used as template microreactors. For example, we were able to fabricate monodisperse polymer spheres containing high concentrations of magnetic nanospheres formed by direct precipitation within the hollow cores. 相似文献
993.
994.
合成了硫氰酸合希土酸四丁基季铵盐配合物,测定了它们的远红外光谱及部分配合物的中红外光谱,结果表明,配合物中的NCS-是以氮原子与Ln3+配位。用X射线单晶衍射法测定了[(n-C4H9)4N]3Nd(NCS)6晶体的结构,结果表明,该晶体属单斜晶系,Cc空间群,晶胞参数为:a=25.188(8)Å,b=13.320(6)Å,c=25.322(8)Å,β=121.30(2)°,晶胞体积V=7258.9Å3,每一晶胞中有四个配合物分子,中心离子Nd3+与六个来自NCS-的氮原子配位,这六个氮位于配位正八面体的六个顶角上,构成配阴离子Nd(NCS)63-,它与三个[(n-C4H9)4N]+以静电引力结合成中心分子,所以晶体为离子型晶体。 相似文献
995.
996.
CO2选择性氧化甲烷制C2烃催化剂La2O3/ZnO的氧化还原和CO2吸附性能 总被引:6,自引:0,他引:6
La2O3/ZnO催化剂体系在以二氧化碳作为氧化剂的甲烷氧化偶联反应中具有很高的C2烃选择性和稳定性.采用CO2-TPD-MS和TPR技术考察了La2O3/ZnO对CO2的吸附性质及其氧化还原行为.结果表明:(1)La2O3/ZnO催化剂体系存在着强、弱两种碱中心,其中弱碱中心数量随样品中La2O3含量增加而减少,强碱中心强度随样品中La2O3含量增加而增强.(2)由于组分相互作用,高温下,La2O3/ZnO易产生晶格氧空位,使之对CO2的吸附增强,吸附后的CO2与晶格氧作用形成立方晶型La2O2CO3.(3)La2O3/ZnO表面的La3+和Zn2+可以部分被还原,由于组分间的相互作用,使得二者的还原都较单一组分存在时更难.(4)H2-CO2-H2氧化还原循环实验表明,La2O3/ZnO表面被部分还原后,CO2可以将部分被还原的表面再氧化.在此基础上对La2O3/ZnO催化剂上甲烷与CO2转化为C2烃的机制也进行了讨论. 相似文献
997.
SynthesisandStructureoftheHexanuclearDiazenido-oxomolybdate[(n-C_4H_9)_4N]_3[Mo_6O_(18)(N_2C_6H_4-p-NO_2)]LiHai-Lian;YouXiao-Zeng;... 相似文献
998.
Melt extrusion was used to prepare binary nanocomposites of ethylene copolymers and organoclay and trinary nanocomposites of low-density polyethylene (LDPE), ethylene copolymer and organoclay. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to analyze the structure of the clay phase and the morphology of the nanocomposites. Influences of the comonomer in the copolymer and the content of the copolymer on the morphology of the resulting nanocomposites were discussed. The binary and the trinary composites may form intercalated or exfoliated structures depending on the interaction between the copolymer and the clay layers and the content of the copolymer. 相似文献
999.
Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane
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The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature (excluding 800 ℃). The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature.The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking. 相似文献
1000.
Various two-dimensional (2D) NMR techniques are reported on a bent-core mesogen 4,6-dichloro-1,3-phenylenebis[4'-(9-decenyloxy)-1,1'-biphenyl] carboxylate in its nematic and solid phases in order to unambiguously assign its carbon-13 NMR spectrum. The (13)C chemical shifts from the molecular core were studied as a function of temperature to extract its molecular geometry and orientational order tensor. To this end, the chemical shift anisotropy tensors of some carbon sites were measured in the solid state of this mesogen using a recent method called the separation of undistorted powder patterns by effortless recoupling (SUPER). The average bending angle subtended by the two arms of the bent-core structure is determined to be 148.7 degrees. The C-H dipolar couplings obtained from the separated local field (SLF) experiment for the aromatic rings are used to find the local order parameter tensors. 相似文献