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高岭石矿物表面化学的量子化学研究   总被引:7,自引:1,他引:6  
用量子化学的理论和计算方法,研究高岭石表面的化学状态、表面化学活性位置及其成键特征、结果表明,高岭石分子簇的最高占据轨道基本上是由上、下表面的一些氧原子组成的,且具有较高的能态,说明这些位置具有较高的化学活性,易于与获得电子能力较强的物质形成化学键。而其最低空轨道则主要由硅、铝和少量的侧面O原子组成.相对而言,能级较低,易于与提供电子的体系作用,其化学反应活性较大。因此,当高岭石与带负电荷的离子或离子基团作用时,可能在侧面的位置形成表面化合物。Al和Si都是组成LUMO分子轨道的主要成分,但Al原子的化学活性要大于Si原子,因此,当高岭石表面与提供电子的体系发生化学作用时,最可能的位置应该是八面体的Al原子。  相似文献
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Electronic Structure and Chemical Bond of Titanium Diboride   总被引:7,自引:7,他引:0  
1 IntroductionTitaniumdiboride (TiB2 )hasattractedmuchatten tionrecentlybecauseofitshighmeltingpoint,hardnessandchemicalstability .Ontheotherhand ,TiB2 hasfineelectricalproperty ,soitmaybeusedinwide rangingfields[1-3 ] .Aswellknown ,thepropertiesofmaterialsaredecidedbythestructures .Obviously ,thespecialpropertyofTiB2 isrelatedtoitsstructuresofcrystalandelectrons .However ,thereislessstudyonstructuresofvalenceelec tronsandtypeofchemicalbondofTiB2 .JiJia mingetal[4] studiedtheelectronicst…  相似文献
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柠檬酸盐溶胶凝胶法合成Ca3Co2O6陶瓷粉末   总被引:5,自引:0,他引:5  
Ca3Co2O6是一种很有潜力的氧化物热电材料。研究了柠檬酸盐溶胶凝胶法制备Ca3Co2O6氧化物粉末,并应用TG/DSC、XRD和sEM等方法进行了测试研究。干凝胶在700℃煅烧就可以生成片状的Ca3Co2O9晶体,随着煅烧温度的升高,在850℃保温2h的条件下,Ca3Co4O9可以全部转化为条状的Ca3Co2O6晶体。pH值、乙二醇的加入与煅烧温度是影响制备过程的主要因素。乙二醇的使用可以减轻团聚现象,有利于预烧阶段的自燃烧,对晶相的生成没有多大影响。  相似文献
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聚合物基纳米复合材料热导率计算   总被引:3,自引:0,他引:3  
讨论了聚合物基高导热高绝缘纳米复合材料的导热机理与常用的导热理论模型。考虑到填充率、温度等的影响,用不同的理论模型计算了氧化铝纳米颗粒填充环氧树脂的热导率,并结合相关研究实验对不同的导热理论模型进行分析比较。通过添加高导热填料可显著提高聚合物材料的热导率,且热导率随填料填充率的增大而显著增大。热导率随在300 K到373 K的范围内,复合材料的热导率随着温度的升高而增大;而当温度超过373 K,复合材料的热导率则随着温度的升高缓慢下降。  相似文献
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Structure and Chemical Bond of Thermoelectric Ce-Co-Sb Skutterudites   总被引:2,自引:2,他引:0  
The correlations among composition, structure, chemical bond and thermoelectric property of skutterudites CoSb3 and CeCo5Fe3Sb12 have been studied by using density function and discrete variation (DFT-DVM) method. Three models for this study were proposed and calculated by which the "rattling" pattern was described. Model 1 is with Ce in the center, model 2 is with Ce away the center and near to Sb, and model 3 is also with Ce away the center but near to Fe. The calculated results show that in model 3, the ionic bond is the strongest, but the covalent bond is the weakest. Due to the different changes between ionic and covalent bond, there is less difference in the stability among the models 1, 2 and 3. Therefore, these different models can exist at the same time, or can translate from one to another more easily. In other words, the "rattling" pattern has taken place. Unfilled model of CoSb3, without Ce and Fe, is called model 4. The covalent bond of Co-Sb or Fe-Sb in models 1, 2 and 3 is weaker than that of  相似文献
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ELASTOPLASTIC OPTIMUM DESIGN OF Ni/TiC FUNCTIONAL GRADIENT MATERIAL   总被引:1,自引:0,他引:1  
The thermal residual stresses developed in a disk-shaped.Ni/TiC functionally gradient material (FGM) during its fabricationare investigated by an elastic-plastic finite element numerical ap-proach.Constitutive relations for the graded Ni-TiC composite interlayers between pure metal Ni and ceramic TiC are estimated by usingan effectiv-medium approach,and effective plastic strain and stressdistributions are computed for simulated cooling from an assumed fab-rication temperature.Analyses are performed for a fixed specimen ge-ometry and the graded region is treated as a series of perfectly bondedequal-thick layers.The restults are compared with those obtained by on-ly considering elastic material response to assess the effect of plasticityon the optimum fabrication design of the Ni/TiC FGM.It is demon-strated that the consideration of plasticity is of critical importance foroptimization of the metal/ceramic gradient materials.  相似文献
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温度对V2O3系材料电子结构的影响   总被引:1,自引:0,他引:1  
采用自洽场离散变分Xα(SCC-DV-Xα)方法对(V0.9950Cr0.0025Al0.0025)2O3体系分别处于25℃及200℃时的电荷分布、态密度、能级结构等进行了研究。结果表明,温度对电子结构的影响导致材料的电导率发生显著变化,变化趋势与实验结果相一致,对钒系PTC材料的进一步研制具有理论指导意义。  相似文献
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The relation among electronic structure, chemical bond and property of Ti2AlC, Ti3AlC2 and doping Si into Ti2AlC was studied by density function and the discrete variation (DFT-DVM) method. After adding Si into Ti2AlC, the interaction between Si and Ti is weaker than that between Al and Ti, and the strengths of ionic and covalent bonds decrease both. The ionic and covalent bonds in Ti3AlC2, especially in Ti-Al, are stronger than those in Ti2AlC. Therefore, in synthesis of Ti2AlC, the addition of Si enhances the Ti3AlC2 content instead of Ti2AlC. The density of state (DOS) shows that there is mixed conductor characteristic in Ti2AlC and Ti3AlC2. The DOS of Ti3AlC2 is much like that of Ti2AlC. Ti2SixAl1-xC has more obvious tendency to form a semiconductor than Ti2AlC, which is seen from the obvious difference of partial DOS between Si and Al 3p.  相似文献
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1 IntroductionKaoliniteisoneofthemostwide spreadphyllosili catesintheearthcrust.Thegoldiscloselyrelatedtoclayinmanysubmicrometergoldminerals .Itisimportanttostudytheinterrelationbetweengoldandclayforunder standingthecloseassociationofgoldandclaymineralsa…  相似文献
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