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多嵌段聚氨酯脲硬段模型化合物的合成和结构研究 总被引:2,自引:0,他引:2
多嵌段聚氨酯脲硬段模型化合物的合成和结构研究罗宁,王得宁,应圣康(华东理工大学材料科学研究所,上海,200237)关键词3,5-二乙基甲苯二胺,4,4′-二苯基甲烷二异氰酸酯,氢键,微晶,热分析3,5-二乙基甲苯二胺(DETDA)是目前反应注射成型(... 相似文献
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碳化硅 ( Si C)由于其高度的共价键结合特性而具有高硬度、耐磨性和高化学稳定性等优异性能而成为热机、高温环境和化学化工等领域的研究应用对象 .碳化硅材料的无压烧结最早是由 Prochazka[1] 实现的 .2 0世纪 80年代初期 ,Omori[2 ] 通过采用氧化物 ( Al2 O3,Y2 O3和稀土氧化物等 )添加剂的手段大大降低了无压烧结的温度 .这些氧化物具有较低的共熔点 ,在高温下易形成液相 ,从而促进了碳化硅的晶粒重排和晶体生长 .2 0世纪 90年代以来 ,氮化物和氧化物的混合添加剂 (如 Al N- Y2 O3) [3]被广泛应用于碳化硅的液相烧结 .这是因为氮在… 相似文献
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E. M. Kazaryan L. S. Petrosyan H. A. Sarkisyan 《Physica E: Low-dimensional Systems and Nanostructures》2001,11(4)
The energy levels of electrons in a narrow band gap semiconductor microcrystal under the influence of magnetic field are investigated. The confinement potential of microcrystal is approximated as parabolic, and the electron dispersion law is considered within the framework of two-band Kane model. It has been shown that nonparabolicity of dispersion law results in the appearance of the “anharmonic” term in Hamiltonian. The values of magnetic field at which the “anharmonic” term can be considered as perturbation are found. Results of electron energy of nonperturbed Hamiltonian dependencies on values of magnetic field and frequency of microcrystal confinement potential are presented. A comparison of the obtained results with the other cases has been done. 相似文献
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Takeharu Tsuge Yoshihiro Hamada Satoshi Tomizawa Hideki Abe 《Polymer Degradation and Stability》2010,95(8):1345-1348
Polyhydroxyalkanoate (PHA) copolymers consisting of (R)-3-hydroxybutyrate (3HB) and medium-chain-length (R)-3-hydroxyalkanoate (3HA), P(3HB-co-3HA), are usually solved in chloroform. However, we found that some of the P(3HB-co-3HA) aged for more than 1 month under ambient conditions were not solved in chloroform, but instead swelled when the 3HA fraction was over 14 mol%. On the basis of differential scanning calorimetry and wide-angle x-ray diffraction analyses, we predicted that swellable P(3HB-co-3HA) contained numerous P(3HB) microcrystals, which may form physical crosslinks between adjacent PHA polymer chains. 相似文献
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Xueying Wu 《Journal of solid state chemistry》2007,180(11):3288-3295
Single-crystalline BaMoO4 microcrystals with uniform shuttle-like morphology have been successfully prepared via a facile aqueous solution mineralization process at room temperature. It was found that the pH value and the reaction temperature had important influences on the formation of the BaMoO4 microcrystals. The shuttle-like microcrystals can be obtained in alkaline aqueous solution (pH=9-14), and when the pH value was adjusted to 6-7, cocoon-like microcrystals appeared. A possible two-stage growth process has been proposed, and the Ostwald ripening was responsible for the formation of the shuttle-like BaMoO4 microcrystals. The products were characterized by XRD, XPS, FESEM, HRTEM and Raman spectroscopy. Room-temperature photoluminescence indicated that the as-prepared BaMoO4 microcrystals had a strong blue emission peak centered at 438 nm. 相似文献
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The nitridosilicate chloride Ba1.63La7.39Si11N23Cl0.42:Ce3+ was synthesized by metathesis reaction starting from LaCl3, BaH2, CeF3 and the product of the ammonolysis of Si2Cl6. The title compound is stable towards air and moisture. Diffraction data of a microcrystal were recorded using microfocused synchrotron radiation. X‐ray spectroscopy confirms the chemical composition of the crystal. IR spectra corroborate absence of N–H bonds. The compound is homeotypic to Ba2Nd7Si11N23 and crystallizes in space group Cmmm with a = 11.009(3), b = 23.243(8), c = 9.706(4) Å and Z = 4, R1(all) = 0.0174. According to bond valence sum calculations, some crystallographic positions show complete occupancy by Ba or La whereas others contain significant amounts of both elements. In contrast to the structure prototype Ba2Nd7Si11N23, Ba1.63La7.39Si11N23Cl0.42:Ce3+ contains chloride ions in channels of the SiN4 tetrahedra network, hinting at various substitution possibilities of the complex zeolite‐like structure. 相似文献
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本论文测定了碘含量对板状碘溴化银微晶的光吸收的影响,并利用Dember光电效应、低温荧光、高低照曝光等光物理方法研究所制备微晶的固体物理性质,发现微晶中碘含量的增加使光吸收增加。在低照曝光时,所有的乳剂均发生低照互易律失效,而在高照曝光时仅是碘含量为18 mol%的乳剂发生高照互易律失效。板状碘溴化银微晶乳剂的Dember效应和低温荧光的实验结果表明,微晶中的碘含量增加使Dember光生电压值下降,光电压表减时间变短,荧光强度下降,说明碘离子掺入量的增加使微晶中的缺陷数目增加,导致电子陷阱数和填隙银离子的浓度增加,造成光电子被捕获。 相似文献
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Avrami’s equation was found to be the best kinetics theory to describe the high-Tc Bi-2223 crystal formation so far. There are three parameters (exponential index n, activation energy E and parameter k) in the equation. A series of research works have been done on the determination of parameters n and E, but few on another parameter k are to be found. The purpose of the approach was to determine and study the role of k in the formation of Bi-2223 crystals. The analysis in the research showed that the parameter k could describe the exhausting speed of reactants, and determine reaction probability and mean lifetime of reactants. The growth mechanism of the 2223 polycrystals was found to show some differences from the prediction of the Avrami’s theory model. At the initial duration, the 2223 crystal growth was much lower than the theoretical prediction; especially there was a mature duration to be found at the last growth duration, at which the 2223 crystal almost did not increase, but its crystal grains obviously became larger. This was a typical morphological transformation. The morphological transformation was the first time to be reported for the growth of the 2223 phase. 相似文献
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The bismuth basic nitrate [Bi6O4(OH)4](NO3)6 crystallizes in a rhombohedral hexagonal unit cell with parameters , , , Z=6, space group R-3. The synthesis, formula determination, thermogravimetric analysis and nitrate assay, and finally, its crystal structure refinement determined at 150(2) K by synchrotron X-ray microcrystal diffraction are reported. Its structure is built from [Bi6O4(OH)4]6+ polycations, six per unit cell, disordered over two positions. Two oxygen atoms are common to the two antagonist polycations (full occupancy) while the remaining six are partially occupied. The [Bi6O4(OH)4]6+ hexanuclear clusters form columns along the c-axis. The cohesion between polycationic entities is effected by nitrate anions through either OH-ONO2 hydrogen bonds or Bi-ONO2 bonds. One of the two independent [NO3]− groups is also disordered over two positions. Only a local order in the columns is obtained by formation of pairs of ordered [Bi6O4(OH)4]6+ polycations. 相似文献