共查询到17条相似文献,搜索用时 187 毫秒
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用浸渍法制备了一系列不同Mo含量的MoO3/Al2O3催化剂.测量了这些样品的正电子湮没寿命谱(PALS)与符合多普勒展宽(CDB)谱,以研究其孔洞结构以及Mo分散.正电子寿命测量结果表明,Al2O3载体中存在两种不同尺寸的孔洞.掺入MoO3之后,Mo原子主要进入Al2O3的大孔中,使孔洞体积减小.符合多普勒展宽谱结果表明,当MoO3的质量含量仅为3%时,多普勒展宽谱即发生了显著的改变.这表明Mo已分散至Al2O3的孔洞中,使得正电子测量所得到的电子动量分布发生改变.在MoO3含量达到18%之后,Al2O3中大孔的体积减小到尺寸与小孔相当,此后正电子寿命和多普勒展宽谱不再随MoO3含量变化,表明Mo分散逐渐达到饱和. 相似文献
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测量了磁性纳米Fe3O4颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe3O4颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe3O4颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe3O4<
关键词:
正电子
3O4')" href="#">Fe3O4
寿命谱
多普勒展宽谱 相似文献
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本文用中国第一台正电子湮没辐射一维角关联实验装置,测量了非晶锂离子导体B2O-0.7Li2O-0.7LiCl-xAl2O3(x=0.15;0.10;0.05)晶化过程中各条正电子湮没辐射的一维角关联曲线,并对归一化的电子动量分布进行了线形参数的计算,从其S参数同样能推测出该离子导体在晶化过程中缺陷浓度的变化。非晶离子导体B2O3-0.7Li2O-0.7LiCl-xAl2O3的实验结果表明,Al2O3组分不同,对非晶态样品在室温下一维角关联曲线的S参数亦无较大影响。完全晶化后,一维角关联曲线的S参数均有很大下降。在晶化过程最初期,无论Al2O3含量多少,S参数都明显略增;到晶化温度附近,仅对Al2O3含量较多的非晶,S参数反常增高。这些结果验证和补充了测正电子平均寿命得出的结论。由此初步证实了界面层有大量缺陷的物理图象。
关键词: 相似文献
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采用溶胶-凝胶(sol-gel)工艺制备0.1 mol% Er3+掺杂Al2O3体系和SiO2-Al2O3复合体系粉末. 实验结果表明:5 mol%的SiO2复合加入Al2O3抑制γ→θ和θ→α相转变. 掺0.1 mol%Er3+:Al2O3体系粉末,900℃烧结,在1.47—1.63μm波段内光致发光(PL)谱为中心波长1.53 μm、半高宽56 nm的单一宽峰,1000—1200℃烧结,劈裂为多峰PL谱. 掺0.1 mol%Er3+:SiO2-Al2O3复合体系粉末,在高达1200℃烧结,仍保持中心波长1.53 μm的单一宽峰PL谱,由于—OH更完全的脱除,PL强度较900℃烧结Al2O3体系,SiO2-Al2O3复合体系均提高1个数量级.
关键词:
2-Al2O3复合体系')" href="#">SiO2-Al2O3复合体系
掺铒
溶胶-凝胶工艺
光致发光 相似文献
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利用正电子湮没技术研究了10 at.% Co掺杂的Co3O4/ZnO纳米复合物中退火对缺陷的影响. 利用X射线衍射(XRD)测量了Co3O4/ZnO纳米复合物的结构和晶粒尺寸. 随着退火温度升高,Co3O4相逐步消失,ZnO晶粒尺寸也有显著增加. 经过1000 ℃以上退火后,Co3O4相完全消失,并出现了CoO的岩盐结构. 正电子湮没寿命测量显示出Co3O4 /ZnO纳米复合物中存在大量的Zn空位和空位团. 这些空位缺陷可能存在于纳米复合物的界面区域. 当退火温度达到700 ℃后Zn空位开始恢复,空位团也开始收缩. 900 ℃以上退火后,所有空位缺陷基本消失,正电子寿命接近ZnO完整晶格中的体态寿命值. 符合多普勒展宽谱测量也显示Co3O4 /ZnO纳米复合物经过900 ℃以上退火后电子动量分布与单晶ZnO基本一致,表明界面缺陷经过退火后得到消除.
关键词:
ZnO
界面缺陷
正电子湮没 相似文献
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采用传统的固相反应法,在1400–1500 ℃下烧结,制备得到Al2O3-Y2O3-ZrO2三相复合陶瓷.样品的结构、形貌和电性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)及介电谱表征.XRD表明此三相复合体系无其他杂相,加入Y2O3及ZrO2后使得Al2O3成瓷温度降低;SEM表明此体系晶粒直径为200–500 nm,并且样品随烧结温度的升高而变得更加致密,晶界更加清晰;介电损耗谱中出现峰值弛豫现象,根据Cole-Cole复阻抗谱得出其为非德拜弛豫.
关键词:
2O3-Y2O3-ZrO2三相陶瓷')" href="#">Al2O3-Y2O3-ZrO2三相陶瓷
介电弛豫
阻抗谱
热导率 相似文献
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C. Li 《Applied Surface Science》2010,256(22):6801-6804
Fe2O3/Al2O3 catalysts were prepared by solid state reaction method using α-Fe2O3 and γ-Al2O3 nano powders. The microstructure and surface properties of the catalyst were studied using positron lifetime and coincidence Doppler broadening annihilation radiation measurements. The positron lifetime spectrum shows four components. The two long lifetimes τ3 and τ4 are attributed to positronium annihilation in two types of pores distributed inside Al2O3 grain and between the grains, respectively. With increasing Fe2O3 content from 3 wt% to 40 wt%, the lifetime τ3 keeps nearly unchanged, while the longest lifetime τ4 shows decrease from 96 ns to 64 ns. Its intensity decreases drastically from 24% to less than 8%. The Doppler broadening S parameter shows also a continuous decrease. Further analysis of the Doppler broadening spectra reveals a decrease in the p-Ps intensity with increasing Fe2O3 content, which rules out the possibility of spin-conversion of positronium. Therefore the decrease of τ4 is most probably due to the chemical quenching reaction of positronium with Fe ions on the surface of the large pores. 相似文献
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Abstract Diffuse Reflectance Infrared Fourier Transform (DRIFT) and FT-Raman spectra have been used to investigate the interactions between molybdena and ceria in MoO3/CeO2 samples with different Mo loadings. The spectra exhibit a weak Mo=O broad band of surface species at ca. 920–970 cm?1, which reveals that the interaction between dispersed molybdena and ceria could be mainly ionic in nature. With the increasing of Mo loadings, the observed Mo=O band broadening and frequency shifting are due to the overlapping and condensation of different hydrated surface species. On the basis of the measured surface dispersion capacity of morybdena and the structure of the preferentially exposed (111) plane of ceria, it is reasonable to suggest that the Mo6+ cations and the accompanying O2- anions are incorporated into the surface available vacant sites of CeO2, accordingly the dispersed molybdena species are interacted electrostatically with the support instead of only physically dispersed on the surface of it. 相似文献
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Ag/Al2O3 nano-array composite structures were obtained by alternating current (AC) electrodeposition of Ag into the pores of anodic alumina membrane (AAM). The ordered wire-grid structure of Ag nanowires formed along a preferential direction, typically 20 nm in diameter, was fabricated. XRD revealed that Ag2O is also preserved in the pores of AAM. Optical properties of Ag/Al2O3 prepared at different annealing temperatures were measured by using spectrometer. Transmission spectra indicate that the transmittance of Ag/Al2O3 increases obviously with the increasing of annealing temperature. Polarization spectra indicate that Ag/Al2O3 has good polarization in the range of 900–2000 nm, and the extinction ratio increases with the increasing of the annealing temperature or incident angle. 相似文献
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A coating method with precipitating process was developed to reduce the particle size and to improve the particle dispersion of Y3Al5O12:Tb3+ phosphor prepared by sol-gel method. The particle morphology was observed by using SEM and TEM; and the particle size and its dispersion was measured by using laser scattering technique. Several coating materials were tested. Among them, Al2(SiO3)3 coating not only reduced the particle size from several micrometers to ∼1 μm and improved the particle dispersion, but also well kept luminescent intensities and improved the duration of the phosphor under the bombardment of cathode ray. The mechanism of the particle size reduction was proposed. 相似文献
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The ceria-zirconium-modified alumina-supported palladium catalysts are prepared using impregnation method with H2PdCl4 as Pd source, hydrazine hydrate as reducing agent. The physicochemical properties of these catalysts are characterized by BET surface area (BET), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), temperature programmed reduction (H2-TPR) and temperature programmed oxidation (O2-TPO) techniques, and their catalytic activities for the combustion of methane are examined. The results show that the palladium mainly exist in a highly dispersed PdO species on Ce-Zr-rich grains as well as Al2O3-rich grains surfaces, and a stable PdO species due to the strong interaction between PdO and CeO2-ZrO2 on the Ce-Zr/Al2O3 surfaces. The catalytic activity is strongly related to the redox behavior of PdO species highly dispersed on Ce-Zr-rich grains and Al2O3-rich grains surfaces, and the higher the reducibility of the PdO species, the higher the catalytic activity. The presence of Ce-Zr in Pd/Al2O3 catalyst would inhibit the site growth of PdOx particles and decomposition of PdO to Pd0, and the reoxidation property of Pd0 to PdOx is significantly improved, which obviously increases thermal stability and catalytic activity of Pd/Ce-Zr/Al2O3 catalyst for the methane combustion. 相似文献
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SMA-g-MPEG comb-like polymer is first employed as the dispersant of Al2O3 suspensions in this paper. The comb-like polymer has anionic polycarboxylate backbone, which makes the polymer easily absorbed on the cationic surface of Al2O3 particles; on the other hand, the comb-like polymer has hydrophilic MPEG side chains, which extend into the solution to provide steric repulsion after the comb-like polymer is absorbed on the surface of Al2O3 particles. The adsorption behavior, zeta potential, apparent viscosity, granularity and TEM images of the Al2O3 suspensions using SMA-g-MPEG as dispersant are investigated. The addition of SMA-g-MPEG improves the dispersibility and decreases the apparent viscosity of the Al2O3 suspension observably. The impacts of the length of side chains on the dispersion of Al2O3 suspensions are particularly discussed. The adsorbed molecular number of the dispersant decreased by increasing the length of side chains. The zeta potential of Al2O3 suspension is more negative by using comb-like polymer with shorter side chains. Based on the steric repulsion and adsorbed molecular number, SMA-g-MPEG with moderate length of side chain is found to have the best dispersibility for Al2O3 suspension. 相似文献
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Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献