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91.
A,X,P型分子筛的原位制备与结构控制 总被引:1,自引:0,他引:1
以天然矿物红辉沸石为原料,采用"酸处理红辉沸石--碱--铝酸钠--水"水热反应体系,在晶化温度95℃,晶化时间为7h条件下,根据不同分子筛相应结构比,通过控制SiO2/Al2O3,SiO2/Na2O和H2O/Na2O的摩尔比,制备出A、X、P型分子筛,并通过X射线衍射、扫描电子显微镜、Fourier红外光谱和热重--差热分析仅分析相应结构和性能特征。结果表明,生成的A、X、P型分子筛分别为立方四面体,立方八面体和四方晶系结构,结晶度分别高达97%,96%和97%,体积粒径范围分别为3.5~4μm、2~3μm和1~3μm,脱水活化能分别达到35.48、30.03和19.11kcal/mol,产率分别为94.7%、91.4%和90.2%。 相似文献
92.
《Journal of the European Ceramic Society》2014,34(12):2997-3006
Lead-free perovskite [(Bi1/2Na1/2)0.95Ba0.05]1−xLaxTiO3 (x = 0.00–0.10) ceramics were fabricated via the solid state reaction method and their crystal structures and electrical properties were systematically studied. Transmission electron microscopy examination reveals a transition from a rhombohedral R3c phase with micron-sized complex domains to a mixture of rhombohedral R3c and tetragonal P4bm phases with nanodomains as La content was increased. X-ray diffraction analysis on bulk samples, however, indicates a pseudocubic structure in La-doped compositions. Electrical poling seems to transform the pseudocubic structure to a rhombohedral phase in compositions with 0.00 < x < 0.03. With La addition, the depolarization temperature (Td) is observed to decrease and the dielectric constant (ɛr) within 100–350 °C becomes more temperature independent, promising for applications in high-temperature capacitors. Electric field-induced polarizations and strains display complex changes with respect to La concentration, with the highest strain of 0.35% achieved in the composition x = 0.04 under 70 kV/cm at room temperature. The piezoelectric coefficient d33 initially increases with La content, reaching a maximum value of 151 pC/N in the composition x = 0.02, and then diminishes. 相似文献
93.
《Journal of the European Ceramic Society》2014,34(7):1741-1753
Among the family of temperature-compensated microwave dielectric ceramics, BaMg1/3Ta2/3O3 shows the lowest dielectric loss and remains a material of choice for state-of-the-art airborne and land-based communication systems. We report on the compositional stability range, microwave dielectric properties, and the degree of atomic order of the title compound within the BaO–MgO–Ta2O5 ternary diagram. In most cases an atomic order is robust to the deviation from stoichiometry with an exception of Ba-rich and/or Ta-deficient samples which favor (partial) disorder. We further demonstrate that the dense, atomically ordered BaMg1/3Ta2/3O3 ceramic shows large variation of dielectric loss within a single phase composition region – a clear message that the dielectric loss in practical ceramics is dominated by extrinsic sources and that the cation order alone is insufficient to achieve a minimum dielectric loss in BaMg1/3Ta2/3O3. The low-temperature dielectric relaxation studies suggest that the extrinsic dielectric loss in the title compound is due to the ‘rattling’ of the off-centered Mg2+ ions misplaced at the Ba sites. Controlled deviation from the BaMg1/3Ta2/3O3 stoichiometry toward the Mg-deficient region leads to suppression of the extrinsic dielectric loss as a result of the reduced chemical activity of Mg ion. 相似文献
94.
Fa‐Ai Zhang Ming Luo Zheng‐Ji Chen Zhi‐Bo Wei Thomas J. Pinnavaia 《Polymer Engineering and Science》2014,54(12):2746-2752
Rod‐like and spherical mesoporous SBA‐15 silica particles were synthesized as pure silicas and surface modified by organosilane coupling agents firstly, and then the effects of these mesoporous materials on the critical micelle concentration (CMC) of sodium dodecylsulfate (SDS), the stabilities of batch and semi‐continuous MMA emulsion polymerizations, and the molecular weights and molecular weight distributions of the polymer products were studied. The incorporation of both unmodified and silane‐modified forms of the mesoporous silica particles in the polymerization reaction increased the CMC of SDS. The presence of the unmodified mesoporous silica in the polymerization process led to instability in the batch emulsion polymerization process, as indicated by the formation of increased amounts of coagulum, and a decrease in the molecular weight of the polymer product. However, in comparison to the polymer formed in the absence of particle additives the molecular weight of the PMMA polymer increased with the amount of emulsifier and the addition of silane‐modified SBA‐15 particles, suggesting the growth of the polymer chains is facilitated at least in part by reaction in the pores of the particles. The improvement in molecular weight indicates that semi‐continuous MMA emulsion polymerization is best suited for the preparation of PMMA–mesoporous silica composites. POLYM. ENG. SCI., 54:2746–2752, 2014. © 2013 Society of Plastics Engineers 相似文献
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