用扫描电镜及透射电镜研究MTO催化剂——ZSM-5沸石分子筛

进入21世纪，石油价格不断攀升，在石油的持续供给无法保障的情况下，人们开始寻找其它替代资源来生产石油化工产品。其中以甲醇制烯烃（MTO）反应的研究相当活跃，并取得了一些突破性进展，反应所用的催化剂就是沸石分子筛。     

Co-Ru与Pd两种负载分子筛催化剂的SEM研究

催化剂的表面形貌及活性金属的分布等对表面催化反应的活性具有重要的影响。活性金属分布的越均匀催化剂的活性越高 ,金属颗粒度越小活性越高。对其微观结构和性质的了解 ,对于改进原有催化剂 ,发展新型催化剂 ,有重要的意义。实验材料与方法实验使用的Ｃｏ Ｒｕ负载分子筛催化剂经离子交换法制备而成 ,Ｐｄ负载分子筛催化剂经浸渍法制备而成。制备好的催化剂样品部分进行了催化反应 ,其中Ｃｏ Ｒｕ负载分子筛催化剂使用 30 0ｈ ,Ｐｄ负载分子筛催化剂使用 30ｈ。使用中科科仪的ＫＹＫＹ 2 80 0扫描电子显微镜和ＫｅｖｅｘｌｅｖｅｌⅡＸ 射…     

负载型Ni—B／SiO2催化剂硫中毒显微结构与表面结构的研究

用化学还原法制备的负载型Ni-B/SiO2催化剂对于石油制品的加氢和加氢脱硫反应具有良好的催化活性和选择性[1],然而,困扰该类催化剂严重的问题之一是硫中毒[2].本工作将透射电镜(TEM)、高分辨电镜(HREM)和X射线光电子谱(XPS)等技术结合起来,研究了新鲜和硫中毒后的负载型Ni-B/SiO2催化剂的显微结构和表面结构特征.     

ZSM-5沸石结构的高分辨电子显微学研究

ZSM-5是石油化工领域中使用的一种重要的择形催化剂，ZSM-5中掺杂进过渡族金属会促进烷烃的脱氢反应。ZSM-5为正交结构，点阵参数a=2.01，b=1.99，c=1.34nm，空间群Pnma，沿[010]方向的直线型孔道是椭圆形开口，长轴为0.58nm，短轴为0.478nm，每个十元环被8个五元环和2个六元环包围，沿[100]方向的正弦型孔道开口近似为正十元环，直径为0.53nm。     

快凝Fe60Cr27Al13合金显微结构的电镜分析

快凝Ｆｅ＿（６０）Ｃｒ＿（２７）Ａｌ＿（１３）合金显微结构的电镜分析孟祥敏，章靖国，吴玉琨（中国科学院金属研究所固体原子像实验室，快凝非平衡合金实验室，沈阳１１００１５；冶金部上海钢铁研究所）电热材料Ｆｅ－Ｃｒ－Ａｌ合金用快凝法制备时因大幅度提高Ｃｒ...     

Fe85Ga15合金的电子显微结构研究

磁致伸缩材料广泛应用于各种各样的传感器和伺服机构器件,Fe-Ga合金以其作为磁致伸缩材料的潜在应用前景已经引起研究人员的注意。Fe-Ga合金的磁致伸缩效应很强,归因于晶体中存在着Ga原子的不对称形状团簇,其导致的四方格子结构在Fe-Ga合金的磁致伸缩特性中起了关键的作用。     

V2O5-TiO2系催化剂载体钠迁移的扫描电镜和能谱分析

V2O5-TiO2体系(简称V-Ti系)负载型催化剂，在某些烃类选择氧化反应中，因其具有较好的选择性，已被广泛采用。但我们在研究工作中遇到一些催化剂经长期反应后活性、选择性有所下降的问题。为探讨其原因，用扫描电镜和能谱仪对催化剂反应前后的形貌和组成进行了分析。     

高铌TiAl合金的氧化及其显微结构研究

TiAl基合金具有高的比强度和比刚度以及密度低等特点，在航空、汽车、能源工业具有广泛的应用前景。但由于其室温脆性及高温抗氧化性不强抑制了它的应用。当前，其室温塑性可通过全片层组织的调整得到改善。因此，其高温抗氧化性能变为该材料应用的瓶颈，尤为突出。材料的抗氧化性能     

扫描电镜和EDS研究钯的加入对SAPO—5分子筛合成及结构的影响

在硅磷酸铝反应物凝胶中采用引入钯盐共晶化的方法，一步合成了ＰｄＳＡＰＯ－５分子筛。通过不同温度的水热处理来对分子筛材料进行改性，用扫描电子显微镜观察处理前后样品的晶形变化，用ＥＤＳ分析不同晶粒上的元素组成。     

负载于碳纳米管上的新型金纳米催化剂

与传统催化剂载体材料相比，碳纳米管因其具有新颖的微观结构和独特的综合性能，更适合作为催化剂的载体材料。本研究采用一种简单的化学镀工艺，制备了负载于碳纳米管上的新型金纳米催化剂，并用高分辨透射电镜(PhilipsTecnai-20，200kV)对所获得的材料进行了表征。     

As-synthesized ZSM-5 zeolite as a suitable support for increasing the photoactivity of semiconductors in a typical photodegradation process

To increase the photocatalytic activity of NiO it was supported onto ZSM-5 zeolite (NiO–ZSM-5). After characterization of the obtained photocatalyst by FT-IR, XRD, SEM and TG/DTG methods, it was used for the photodecolorization of methyl green dye aqueous solution. Decolorization extent of the dye was followed by UV–vis spectroscopy. The optimal experimental conditions were achieved at: pH 9, 80 °C, 40 mg L⁻¹ of the dye concentration and 0.8 g L⁻¹ of the catalyst. Un-supported NiO showed lower degradation efficiency than the supported one.     

Structural and magnetic properties of Dy3+ doped Y3Fe5O12 for microwave devices

The Dy³⁺ doped Y_3−xDy_xFe₅O₁₂ (x=0–3) nanopowders were prepared using microwave hydrothermal route. The structural and morphological studies were analyzed using transmission electron microscope, X-ray diffractometer and field emission scanning electron microscope. The nanopowders were sintered at 900 °C/90 min using microwave furnace. Dense ceramics with theoretical density of around 95% was obtained. Ferro magnetic resonance (FMR) spectrum and microwave absorption spectrum of Dy³⁺ doped YIG were studied, the signal exhibits a resonance character for all Dy³⁺ variations. It was observed that the location of the FMR signal peak at the field axes monotonically shifts to higher field with increasing Dy³⁺ content. The dielectric and magnetic properties (ε′, ε′′, µ′ and µ′′) of Dy³⁺ doped YIG were studied over a wide range of frequency (1–50 GHz). With increase of Dy³⁺ both ε′ and µ′ decreased. The low values of dielectric, magnetic properties and broad distribution of FMR line width of these ceramics are opening the real opportunity to use them for microwave devices above K- band frequency.     

Fe2+掺杂中红外固体激光器技术综述

总结了目前可实现中红外激光输出的技术途径,介绍了各种类型中红外激光器的优缺点。重点分析了Fe2+掺杂中红外固体激光器实现的技术途径,介绍了国际上处于技术领先水平的几个实际系统。总结了中红外激光器的技术现状和未来发展趋势。     

Magnetic ordering effects in heavily doped GaAs:Fe crystals

The exchange coupling of Fe centers in GaAs crystals is studied by electron spin resonance (ESR). Transitions to a superparamagnetic state and to an impurity ferromagnetism domain are analyzed. A study of a system of single-domain magnetically ordered regions in GaAs:Fe with the transition to a ferromagnetic state occurring at the temperature T_C1 = 460 K is described. It is shown that impurity ferromagnetism with a transition temperature T_C2 of 60 K in a disordered system of Fe centers randomly distributed among superparamagnetic regions exists in GaAs:Fe.     

Microstructural evolution of nickel nanoparticle catalysts supported on gadolinium-doped ceria during autothermal reforming of iso-octane

The microstructure and composition of a nanoparticle Ni catalyst supported on gadolinium-doped ceria (Ce_1−xGd_xO_(4−x)/2) were studied using transmission electron microscopy (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The support of the fresh catalyst exhibits a homogenous aggregation of crystalline grains, with sizes ranging between 20 nm and 50 nm. The crystalline structure of the fresh catalyst support is of the CeO₂ phase, in which gadolinium atoms exist in a solid solution of CeO₂. Nickel in the fresh catalyst is highly dispersed and forms granular crystals that are 5–30 nm in size on the surface of the ceria support. The support of the used catalyst exhibits a bimodal distribution of grains in which smaller grains have similar structure and morphology as those in the fresh catalyst, while the larger sized grains appear dull and exhibit nonfaceted crystal morphology resulting either from the sintering of a number of CeO₂ grains or by the occupation of highly defective crystals of Ce₂O₃ and CeO phases. A thin amorphous layer of carbon also covers most of the larger grains in the used catalyst. The Ni particles could not be imaged by TEM in the used catalyst, but energy dispersive x-ray spectroscopy (EDX) detected their presence. The XPS analysis of the catalyst samples suggests the participation of lattice O atoms from the ceria support in the catalytic reaction. The XPS data also show the presence of carbonate species and a higher hydrocarbon concentration in the used catalyst.     

Humidity sensing properties of spray deposited Fe doped TiO2 thin film

In the present work,ferrite (Fe) doped TiO2 thin films with different volume percentage (vol％) were synthesized us-ing a spray pyrolysis technique.The effect of Fe doping on structural properties such as crystallite size,texture coefficient,mi-crostrain,dislocation densities etc.were evaluated from the X ray diffratometry (XRD) data.XRD data revealed a polycrystalline anatase TiO2 phase for sample synthesized up to 2 vol％ and mixed anatase and rutile crystalline phase for sample synthesized at 4 vol％ Fe doped TiO2.The crystalline size was observed to decrease with increase in Fe dopant vol％ and also other structur-al parameters changes with Fe dopant percentage.In the present work,electrical resistance was observed to decrease with a rise in Fe dopant vol％ and temperature of the sample.Thermal properties like temperature coefficient of resistance and activa-tion energy also showed strong correlation with Fe dopant vol％.Humidity sensing properties of the synthesized sample altered with a change in Fe dopant vol％.In the present paper,maximum sensitivity of about 88.7％ for the sample synthes-ized with 2 vol％ Fe doped TiO2 and also the lowest response and recovery time of about 52 and 3 s were reported for the same sample.     

Impedance and dielectric analysis of polycrystalline undoped and Fe doped SnS2

Polycrystalline Sn_1−xFe_xS₂ samples with (x=0, 0.125, 0.250 and 0.375) have been prepared by the molten salt solid state reaction method. The X-ray diffraction (XRD) shows that all the samples crystallize in the hexagonal structure, with P-3m1 space group in preferred orientation of (011). The electrical properties have been studied by complex impedance spectroscopy over the frequency range (20 Hz up to 1 MHz) at room temperature. The Nyquist plot for all samples have been fitted using ZMAN software. The impedance analysis showed that all samples exhibit both bulk and grain boundary contributions and it was found that by increasing the iron content, the resistance increases, but, the dielectric constant and dielectric loss tangent decrease which leads to decrease in conduction. The absorption coefficient (α) has been calculated from the complex dielectric constant. Interestingly, there was a significant correlation between the electromagnetic wave absorption and the reduction in the peak intensity of the XRD patterns indicating that when the iron content increases the sample seems to be a good absorber of electromagnetic waves.     

A study of S doped ZnSb

We report on S-doping of ZnSb for S concentrations ranging from 0.02 at% to 2.5 at%. There are no previous reports on S-doping. ZnSb is a thermoelectric material with some advantages for the temperature range 400 K–600 K. The solid solubility of S in ZnSb was estimated to be lower than 0.1% from observations of precipitates by scanning microscopy. Hall and Seebeck measurements were performed as a function of temperature from 6 K to 623 K. The temperature dependence of the electrical properties suggests that S introduces neutral scattering centers for holes in the p-type material. An increase in hole concentration by S is argued by defect reactions involving Zn vacancies.     

Comparative study of Fe doped ZnO based diluted and condensed magnetic semiconductors in wurtzite and zinc-blende structures by first-principles calculations

Magnetic semiconductors with simultaneous semiconducting and magnetic characteristics are significant for applications in next generation spintronic devices. However, efficiency of these materials strongly relies on the selection of the proper host and dopant/alloying materials. In this work, we explore magnetic semiconductors based on the most appropriate materials namely ZnO doped with Fe in wurtzite (w) and zinc-blende (zb) structures. For comprehensive analysis, Fe has been doped into ZnO for several Fe concentrations such as 6.25%, 12.5%, 18.5% and 25%. Investigations are achieved using density functional theory (DFT) based full potential linearized augmented plane wave plus local orbital FP-L(APW+lo) method. The exchange correlation energy has been determined using Perdew et al. proposed generalized gradient approximations (GGA) with additional Hubbard (U) parameter as well. Our results show that; in w-structure, Fe:ZnO favors antiferromagnetism (AFM) at ground state, whereas in zb structure, ferromagnetism (FM) is dominated at 6.25% and 12.5% dopant concentration. However, for 18.75% and 25% dopant concentration, AFM interactions are dominated over FM, possibly is caused by the occurrence of anti-ferromagnetic secondary phases. Moreover, effect of mismatching ionic radii of Fe and Zn atoms, and formation of secondary phases is noticed on lattice parameters of Fe:ZnO with Fe concentration. The electronic and magnetic properties of Fe:ZnO endorse them suitable for applications in spin based electronic devices.     

Microstructural study of SnO2-based nanoparticles by X-ray diffractometry

Two tin dioxide samples undergone to different thermal treatments have been studied by X-ray diffraction profile analysis, using the modified Williamson-Hall and Warren-Averbach methods. Assuming <10-1>{101} slip system and screw dislocations, the area and volume-weighted average particle sizes have been evaluated for both samples. The assumed log-normal particle size distribution has been calculated from these values. This distribution is in good agreement with the derived from SEM micrographs for the sample with lower particle size. Values of the dislocation densities were estimated around 10¹⁴ m⁻² for the sample with lower grain size and around 10¹² m⁻² for the sample with greater grain size. The difference in the results for the analyzed samples could be explained from the difference between the treatments after synthesis.