Preparation,surface modification and microwave characterization of magnetic iron fibers

In this paper, magnetic iron fibers of 3–10 μm diameter and an adjustable aspect ratio were synthesized successfully by a method involving pyrolysis of carbonyl under a magnetic field. A surface modification technology was also investigated. The electromagnetic parameters of the iron-fiber–wax composites were measured using the transmission/reflection coaxial line method in the microwave frequency range of 2–18 GHz. The results show that the prepared iron-fiber–wax composites exhibit high magnetic loss that can be further improved after phosphating. On the other hand, the complex permittivity was significantly decreased after phosphating. As a result, this kind of iron fiber may be useful for thin and lightweight radar-absorbing materials.     

关于不含k-C-圈的n阶γ-一致超图的若干结果

主要讨论了不含k-C-圈的n阶γ-一致超图,对不同的k, 分别得出了它的极大边数的一个下界,并且得出在有些情况下它的下界是最大的.另外,我们得到了Krn含k-C-圈的一个充分必要条件.     

La2／3Ca1／3—xSrxMnO3系列锰氧化物材料的Rietveld结构分析

用固相反应法制备了La2/3Ca1/3-xSrxMnO3系列样品，利用Rietveld方法精修晶体结构，结果表明，当x≥0.15时，样品由正交结构（Pnma)转变为六方结构（R－3c)。本文详细介绍了Rietveld精修方法并分析了Sr^2 ,Ca^2 对材料结构的影响。     

不同剂量C离子注入Si单晶中Si1-xCx合金的形成及其特征

室温下在单晶Si中注入 (0 6— 1 5 ) %的C原子 ,利用高温退火固相外延了Si1-xCx 合金 ,研究了不同注入剂量下Si1-xCx 合金的形成及其特征 .如果注入C原子的浓度小于 0 6 % ,在 85 0— 95 0℃退火过程中 ,C原子容易与注入产生的损伤缺陷结合 ,难于形成Si1-xCx 合金相 .随注入C原子含量的增加 ,C原子几乎全部进入晶格位置形成Si1-xCx 合金 ,但如果注入C原子的浓度达到 1 5 % ,只有部分C原子参与形成Si1-xCx 合金 .升高退火温度 ,Si1-xCx 合金相基本消失 .     

Numerical studies of the vibrational isocoordinate rule in chalcogenide glasses

Many properties of alloyed chalcogenide glasses can be closely correlated with the average coordination of these compounds. This is the case, for example, of the ultrasonic constants, dilatometric softening temperature and the vibrational densities of states. What is striking, however, is that, at a given average coordination, these properties are nevertheless almost independent of the elemental composition. Here, we report on some numerical verification of this experimental rule as applied to the vibrational density of states. We find that this rule is not exact but holds qualitatively well over a wide range of compositions and local chemical correlations. Received 25 April 2000     

Investigation of silica particle structure containing metallocene immobilized by a sol-gel method

A series of homogeneous metallocenes (Cp₂ZrCl₂, (nBuCp)₂ZrCl₂, (iBuCp)₂ZrCl₂, (tBuCp)₂ZrCl₂, Cp₂TiCl₂, Cp₂HfCl₂, EtInd₂ZrCl₂ and Et(IndH₄)₂ZrCl₂) were immobilized within a silica matrix during its preparation using a non-hydrolytic sol-gel method. Supported metallocenes were characterized by small angle X-ray scattering (SAXS) and nitrogen adsorption. The results show that the silica particle was formed by the aggregation of primary structures having a diameter of about 160 nm. This was a result of the aggregation process, which was affected by the metallocene. This result suggests that the metallocene is surrounded by primary particles deep inside the silica matrix. The low polymer productivity exhibited by the less active metallocene catalysts could be related to the problems of particle fragmentation due to monomer mass transfer limitations along the partially fragmented particle, which would subsequently affect catalytic activity.     

NOx储存催化剂Pt／Ba—Al—O的结构与性能研究

采用共沉淀和浸渍法,制备了不同烧温度,不同Al/Ba原子比的Pt/Ba-Al-O系列催化剂样品,BET结构表明,所得样品具有较高的比表面积,若烧温度相同,同昆表面积随着样品中Ba含量的减小而增加,XRD结果表明,载体Ba-Al-O经过1000℃焙烧后,Ba主要以BaAl2O4形式存在,所含BaCO3较少,于空气中陈放10个月后,样品中BaAl2O4的衍射强度显著下降,而BaCO3的衍射峰明显增强,陈化样品经800℃焙烧2h报,BaAl2O4相明显再生,NO－TPD和NSC结果均表明,新鲜的催化剂样品对NOx具有良好的储存性能,在有氧和较高温度（200℃）下,NO更易于被氧化,并以硝酸盐的形式储存起来。     

MnOx／Al2O、MnOx／BaO—Al2O3催化剂的制备、表征及其对甲烷低温燃烧的催化活性

改变锰的负载最及前驱体,制备了MnOx/Al2O、MnOx/BaO-Al2O3系列催化剂;采用X-射线衍射（XRD）、程序升温还原（TPR）对催化剂进行表征,并考察了BaO的加入对CH4低温燃烧催化活性的影响。结果表明,用醋酸锰作前驱体与用硝酸锰制备的催化剂相比,其活性组分分散性好、氧中心活性高,催化CH4低温燃烧的活性高。在Al2O3载体中掺入BaO,催化剂的氧中心数目的没有明显变化,但氧中心活性有所下降,因而降低了对CH4低湿燃烧的催化活性。