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《Journal of the European Ceramic Society》2007,27(10):3161-3170
The influence of Al2O3 doping in the range 0.00–0.83 mol% on the microstructure and current–voltage characteristics of ZnO-based varistor ceramics sintered at 1200 °C for 2 h was studied. The threshold voltage VT (V/mm) increased up to a dopant level of about 0.08 mol% Al2O3; the nonlinear coefficient α was significantly increased by additions of up to 0.04 mol% Al2O3, although larger additions of Al2O3 caused it to decrease; and the leakage current increased sharply with increasing amounts of Al2O3. Doping with Al2O3 up to about 0.12 mol% Al2O3 resulted in a significantly decreased ZnO grain size, which is mainly responsible for the significantly increased threshold voltage, VT. No ZnAl2O4 spinel phase was detected in any of the samples, and EDXS and WDXS analyses showed that most of the added Al2O3 distributed between the Zn7Sb2O12 spinel phase and the ZnO phase, while only trace amounts were detected in the Bi2O3-rich phase. The spinel phase incorporates an appropriate amount of Al2O3; however, with an increasing amount of added Al2O3, more of it remains outside the spinel phase in the Bi2O3-rich liquid, where it can incorporate into the growing ZnO grains at the sintering temperature. The amount of Al in the ZnO grains was determined. A mechanism for the grain growth inhibition resulting from the small amounts of Al2O3 in the Bi2O3-rich liquid phase is also proposed. 相似文献
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为提高纳米α-Al2O3粒子在有机体系中的分散性和相容性,对纳米α-Al2O3进行了有机表面改性.首先制备了纳米α-Al2O3水分散液,然后把纳米Al2O3水分散液转移到溶有硬脂酸的正丁醇溶液中,升温到一定温度,将纳米Al2O3浆体中的水分蒸馏出去,使纳米Al2O3在有机相中进行表面改性,使得纳米Al2O3有机表面改性和防团聚处理一步完成,得到了团聚程度较小的纳米Al2O3粉体.采用红外光谱(IR)、热分析(TG-DTA)、透射电镜(TEM)、润湿性实验、分散性实验等手段对表面改性前后的纳米Al2O3进行表征.红外光谱和TEM表明,在纳米Al2O3表面包覆有硬脂酸的有机层,并且可能有硬脂酸铝的生成.热分析显示,包覆量约为16.7%.润湿性实验及分散性实验表明,经硬脂酸改性的纳米Al2O3的表面性质由亲水变为疏水. 相似文献
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Patrick D. Burton David Lavenson Michael Johnson David Gorm Ayman M. Karim Travis Conant Abhaya K. Datye Bernadette A. Hernandez-Sanchez Timothy J. Boyle 《Topics in Catalysis》2008,49(3-4):227-232
Heterogeneous catalysts composed of Pd nanoparticles on zinc oxide (ZnO) and aluminum oxide (Al2O3, alumina) were synthesized and tested for catalytic activity. Palladium nanoparticles were synthesized via solution-precipitation methods and deposited on aluminum oxide and zinc oxide supports. The particles were synthesized by decomposing a palladium precursor (Pd(Mes)2) in a solution of trioctylphosphine [TOP route] or palladium acetate (Pd(OAc)2) in a solution of octylamine [amine route] at 300 °C. The particles were washed and suspended in hexane, whereupon they were deposited on an oxide powder. Supported nanoparticle powders were subjected to CO oxidation tests to determine catalytic activity. Particle sizes ranged from 2.4 ± 0.4 nm average diameter when prepared using trioctylphosphine to 4 ± 1 nm using the amine route. No significant size change was observed after removal of the surfactant and catalytic testing by CO oxidation. The highest conversion of CO to CO2 occurred with a calcined sample, indicating that the removal of surfactant increases activity. 相似文献
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The addition of B2O3 to a Cu/ZnO/Al2O3 catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The
stability of the B2O3-containing Cu/ZnO/Al2O3 catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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采用表面接枝和表面印迹技术,以正硅酸乙酯改性后的Al2O3粉末为载体、壳聚糖为功能单体,制备了Cu2+印迹复合材料(IIP/Al2O3),用于选择性分离Cu2+. 研究了IIP/Al2O3对Cu2+的动态吸附,利用Thomas, Yoon-Nelson和Wolborska模型分析IIP/Al2O3吸附Cu2+过程,考察了动态条件下Cu2+的最佳洗脱条件. 结果表明,当Cu2+浓度100 mg/L、柱高37.25 mm、流速1.0 mL/min和pH=5时,IIP/Al2O3的穿透吸附容量和动态吸附容量分别为4.03和15.68 mg/g,Cu2+去除率为45.55%;Thomas和Yoon-Nelson模型能很好地拟合IIP/Al2O3对Cu2+的吸附;在柱高37.25 mm、洗脱液流速1.0 mL/min的条件下,15 mL 0.6 mol/L盐酸溶液对Cu2+的脱附率高达99.54%,脱附作用时间短,Cu2+易回收. 相似文献
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为了提高PVDF膜的亲水性和力学强度,利用硅烷偶联剂乙烯基三甲氧基硅烷和碱液分别对Al2O3粒子和聚偏氟乙烯(PVDF)进行了改性,并以改性后产物为制模材料,以过氧化苯甲酰(BPO)为引发剂,将改性纳米Al2O3粒子引入到PVDF中,通过热致相变法制备了双改性Al2O3/PVDF杂化膜。随后,考察了硅烷偶联剂对Al2O3粒子粒径及不同碱浓度和碱处理时间对PVDF结构的影响,并对制备的双改性膜做了性能测试。结果表明,当添加的硅烷偶联剂的质量分数为33%时,Al2O3粒子的粒径降为43.47 nm,在此基础上,当添加的改性Al2O3粒子的质量分数为5%时,杂化膜的截留率为83.1%,通量为621.5 L/m2.h,膜的拉伸强度达到5.01Mpa,改性纳米Al2O3粒子的引入,是杂化膜通量和力学强度提高的主要原因。 相似文献
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Gwénaël Gouadec Karim Makaoui Loïc Perrière Philippe Colomban Léo Mazerolles 《Journal of the European Ceramic Society》2012,32(10):2145-2151
The fluorescence from (naturally present) Cr3+ impurities was used to measure the residual stress in the alumina phase of six melt-grown ceramic eutectic composites associating gadolinum aluminum perovskite (GAP), erbium aluminum garnet (EAG) or yttrium aluminum garnet (YAG) with α-alumina and cubic zirconia. Such measurements are reported for the first time in the GAP containing eutectics.In the usual hydrostatic assumption, we conclude to a residual compression in the range of ~70–400 MPa depending on the sample composition. The validity of the hydrostatic assumption is questioned when a microscope is used for the measurements. 相似文献
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《Journal of Catalysis》2005,229(1):213-226
The simultaneous hydrodenitrogenation (HDN) of alkylamines and hydrodesulfurization (HDS) of alkanethiols, with the NH2 and SH groups attached to primary, secondary, and tertiary carbon atoms, were studied at 270–320 °C and 3 MPa over sulfided NiMo/Al2O3, CoMo/Al2O3, and Mo/Al2O3 catalysts. Pentylamine and 2-hexylamine reacted by substitution with H2S to form alkanethiols and with another amine molecule to form dialkylamines. Alkenes and alkanes were not formed directly from pentylamine and 2-hexylamine, but indirectly by elimination and hydrogenolysis of the alkanethiol intermediates, as confirmed by their secondary behavior and the similar alkene/alkane ratios in the simultaneous reactions of amines and thiols. Only 2-methyl-2-butylamine, with the NH2 group attached to a tertiary carbon atom, produced alkenes as primary products by E1 elimination. NiMo/Al2O3 and CoMo/Al2O3 have a higher activity for the HDS of alkanethiols than does Mo/Al2O3; H2S has a negative influence. This shows that the thiols react on vacancies on the catalyst surface (Lewis acid sites). Mo/Al2O3 is the best HDN catalyst; H2S has a positive influence on the HDN of amines with the NH2 group attached to a secondary and a tertiary carbon atom. This indicates that the HDN of alkylamines occurs on Brønsted acid sites. 相似文献
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真空条件下,以Al2O3和Al为原料,通过Al2O歧化法制备微细Al2O3/Al复合粉体.XRD和SEM分析表明:在反应温度为1200~1400℃时,随着温度的升高,粉体中氧化铝含量升高;冷凝温度约为550~750℃时,复合粉体中的氧化铝包括稳定晶型和不稳定晶型;冷凝温度约为1100~1300℃时,复合粉体中的氧化铝全部为稳定晶型;冷凝温度约为550~650℃时,复合粉体的平均粒径小于0.5μm;冷凝温度约为750℃时,铝熔化、微粒团聚;冷凝温度约为1100~1200℃时,铝形成铝珠,氧化铝为不规则状、平均粒径小于2μm;冷凝温度约为1300℃时,氧化铝为片状.因此,通过选取合适的反应温度、冷凝温度,可以控制Al2O3/Al复合粉体中氧化铝的含量、晶型和粒径. 相似文献
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XPS measurements have shown that tin oxides are more readily reduced to metallic tin by hydrogen in Ni/Al2O3 systems than on pure Al2O3. During the reductive activation of Sn doped Ni/Al2O3 catalysts, surface segregation of the dopant was observed. This finding may explain that tin enhances the selectivity of the steam reforming catalysts only when added in very low concentrations and that it acts as a poison at higher loadings. 相似文献
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以一氧化碳和乙炔为探针分子,采用原位红外光谱技术研究了Pd-Ag/ Al2O3和Pd/ Al2O3催化剂上乙炔加氢反应以及催化剂本身的表面形态,动态考察了乙炔加氢的气相反应行为、CO吸附以及催化剂表面吸附物种的变化。结果表明,在Pd-Ag/ Al2O3催化体系中,由于Ag的加入而受到几何效应和电子效应的共同影响,引起了催化剂表面形态的改变从而改变了催化剂的性能。另外,乙炔加氢反应会导致钯催化剂表面形成由长分子链的饱和烃组成的碳氢化合物层,该碳氢化合物层有可能是加氢反应形成的绿油。 相似文献
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Glass ceramics are the result of controlled crystallisation of one or more crystalline phases embedded in the glass matrix, which usually results in better mechanical properties than conventional glasses. Crystalline phases precipitated in the vitrified bond improve mechanical strength and provide new functions that are not present in the original glass. The most widely encountered issue in standard composites is the presence of inclusions, generated during the process of thermal treatment, of finely dispersed crystalline phases, which are spread in the amorphous phase.Another way of increasing the mechanical properties of composites is via surface crystallisation of the binder. The mechanical strength can be significantly and permanently increased by inducing compressive stress at the glass surface. In the case of the binder designed here, the generated crystalline phase is willemite (Zn2SiO4), which is characterised by a low coefficient of thermal expansion (CTE). Zn2SiO4 usually crystallises at the glass surface, which results in the development of favourable compressive stresses in the glass-crystalline binder.Transition metal oxides significantly affect the crystallisation characteristics, thus influencing the thermal behaviour of glass ceramics. The majority of current publications focus on studies of the influence of copper on certain properties, and mainly the optical and photonic properties, and the influence of copper on the mechanical properties of silicate systems is still poorly recognised. This article investigates the mechanical and physical properties of porous Al2O3 composites with a glass-ceramic bond doped with nanocopper. 相似文献
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Guojun Zheng Jianhong Wu Zhousu Xu Zaijin Fang Xiaofeng Liu Jianrong Qiu 《Journal of the American Ceramic Society》2021,104(7):3139-3148
Transparent polycrystalline ceramics (TPCs) are crystalline materials with single-crystal-like transparency, which, however, have to rely on fabrication processes with a relatively high cost. Here, we produced lab-scale TPCs based on the typical refractory Y2O3-Al2O3 system, through full congruent crystallization of the parent glass prepared by aerodynamic levitation melting method. Doping of the glass and TPCs by rare-earth (RE) ions (Ce3+, Tb3+, Nd3+, and Yb3+) and transition-metal (TM) ions (Cr3+) results in strong visible and near-infrared (NIR) photoluminescence with high quantum yield. The dominance of Stark splitting of the emission band for RE and TM ions in the TPCs as compared with that of the glass confirms crystallization of the parent glasses. 相似文献
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Al2O3/Al2O3 ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al2O3/Al2O3 CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y2O3 is considered a candidate EBC material for Al2O3/Al2O3 CMC. Up to 1 mm thick Y2O3 coatings were deposited by means of air plasma spraying (APS) on Al2O3/Al2O3 CMC with a reaction-bonded Al2O3 bond-coat (RBAO). APS Y2O3 coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y2O3/RBAO interface. The reaction zone between Y2O3 and Al2O3 comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively. 相似文献