Ansa-metallocene derivatives .2. Syntheses and structures of tetramethyldisiloxandiyl bis(1-indenyl and tetrahydroindenyl) zirconium dichlorides

The ansa-zirconocene derivative tetramethyldisiloxandiyl bis(1-indenyl) zirconium dichloride (1) has been prepared by the reaction of the dilithium salt of 1,3-bis(l-indenyl) tetramethyldisiloxane with ZrCl4 . 2THF, After catalytic hydrogenation, the corresponding tetrahydroindenyl complex (2) has been formed. Both 1 and 2 have been shown by H-1 NMR spectra to be the mixture of the cis(meso) and trans(rac) isomers, The pure trans isomers 1(l), 2(l) and cis isomer 2(c) were obtained by recrystallization, The crystal structures of 1(l) and 2(c) were determined by X-ray diffraction. Both crystals of 1(l) and 2(c) are monoclinics, belonging to space groups P2(1)/n(1(l)) and P2(1)/c(2(c)). In the unit cell of 2(c), one of the six-membered rings of the tetrahydroindenyl Ligands has two different conformations which have the same probabilities.

SYNTHESIS AND MOLECULAR-STRUCTURE OF THE 5-COORDINATE ZIRCONIUM COMPLEX (CH3C5H4)2ZRCL(ALPHA-C10H7COO)

Bis(methylcyclopentadienyl)chloro(alpha-naphthoyloxy)zirconium, (CH3C5H4)2Zr Cl(alpha-C10H7COO), has been synthesized by the reaction between (MeCp)2ZrCl2 and equimolar sodium alpha-naphthoate in toluene at room temperature. The molecular structure of the title complex was determined by X-ray diffraction. The molecules have a five-coordinate bent metallocene structure in which the alpha-naphthoxyligand is bidentate [Zr-O, 2.317(2), 2.260(2) angstrom]. The remaining distances are [Zr-Cl, 2.521(1) angstrom; Zr-C, 480-2, 565 angstrom; Zr-cent-CH3C5H4 2.217 and 2.230 angstrom].

Investigation of ideal zirconium-doped perovskite-type ceramic membrane materials for oxygen separation

Zirconium-doped perovskite-type membrane materials of BaCo0.4Fe0.6-xZrxO3-delta (x = 0-0.4) with mixed oxygen ion and electron conductivity were synthesized through a method of combining citric and EDTA acid complexes. The results of X-ray diffraction (XRD), oxygen temperature-programmed desorption (O-2-TPD) and hydrogen temperature-programmed reduction (H-2-TPR) showed that the incorporation of proper amount of zirconium into BaCo0.4Fe0.6O3-delta could stabilize the ideal and cubic structure of perovskite. Studies on the oxygen permeability of the as-synthesized membrane disks under air/He gradient indicated that the content of zirconium in these materials had great effects on oxygen permeation flux, activation energy for oxygen permeation and operation stability. The high oxygen permeation flux of 0.90 ml cm(-2) min(-1) at 950degreesC, the single activation energy for oxygen permeation in the range of 600-950 degreesC and the long-term operation stability at a relatively lower operational temperature of 800 degreesC under air/He gradient were achieved for the BaCo0.4Fe0.4Zr0.2O3-delta material. Meanwhile, the effect of carbon dioxide on structural stability and oxygen permeability of this material was also studied in detail, which revealed that the reversible stability could be attained for it. (C) 2002 Elsevier Science B.V. All rights reserved.

Novel and ideal zirconium-based dense membrane reactors for partial oxidation of methane to syngas

A novel and ideal dense catalytic membrane reactor for the reaction of partial oxidation of methane to syngas (POM) was constructed from the stable mixed conducting perovskite material of BaCo0.4Fe0.4Zr0.2O3-delta and the catalyst of LiLaNiO/gamma-Al2O3. The POM reaction was performed successfully. Not only was a short induction period of 2 h obtained, but also a high catalytic performance of 96-98% CH4 conversion, 98-99% CO selectivity and an oxygen permeation flux of 5.4-5.8 ml cm(-2) min(-1) (1.9-2.) mumol m(-2) S-1 Pa-1) at 850 degreesC were achieved. Moreover, the reaction has been steadily carried out for more than 2200 h, and no interaction between the membrane material and the catalyst took place.

A novel zirconium-based perovskite-type membrane material for oxygen permeation

A novel zirconium-based membrane material of BaCo0.4Fe0.4Zr0.2O3-6 with cubic perovskite structure was synthesized for the first time through a method of citric and EDTA acid combined complexes. The structural stability was characterized by XRD, O-2-TPD and H-2-TPR techniques respectively. The high oxygen permeation flux of 0.873 mL/cm(2) min at 950 degreesC was obtained under He/Air gradient. Meanwhile, the single activation energy for oxygen permeation and the long-term steady operation of 200 h at 800 degreesC were achieved.

表面纳米化Zr的拉伸性能

利用表面机械研磨处理(SMAT)技术在Zr片状拉伸样品表面施加剧烈变形,获得超细/纳米晶粒组织的变形细化表层,其中Zr板厚度1 mm,两侧变形层厚度均为100μm.拉伸实验结果表明,表层细化组织提高了屈服强度和抗拉强度,使加工硬化能力及伸长率下降.应变速率在10~(-4)～10~(-3)s~(-1)范围时,拉伸强度随应变速率的提高而提高;应变速率增大至10~(-2)s~(-1)量级时,抗拉强度下降.扫描电镜观察显示出韧性韧窝状断裂特征.

Microstructure of Zr-alloyed coating using pulsed laser

Coatings were synthesized by laser alloying of zirconium (Zr) particles using a pulsed Nd:YAG laser on an austenite stainless steel. The distribution of Zr is uneven, in a depth of 18 mum just below the surface of the pool. The coating consisted of duplex microstructures, i.e. metallic glass (MG) and austenite. The MG formed in Zr-contained regions, with the Zr composition ranging from 7.6 to 16.8 at.%. The formation of the MG was attributed to an increase in glass-forming ability by Zr addition.

Effect of Pb Volatilization on Dielectric Properties of 0.77PbMg1/3(Nb0.9Ta0.1)2/3O3-0.23PbTiO3

Lead magnesium niobate-lead titanate (PMN-PT) is an intriguing candidate for applications in many electronic devices such as multi-layer capacitors, electro-mechanical transducers etc. because of its high dielectric constant, low dielectric loss and high strain near the Curie temperature. As an extension of our previous work on Ta-doped PMNT-PT aimed at optimizing the performance and reducing the cost, this paper focuses on the effect of Pb volatilization on the dielectric properties of 0.77Pb(Mg1/3(Nb0.9Ta0.1)2/3)O3-0.23PbTiO3. The dielectric constant and loss of the samples are measured at different frequencies and different temperatures. The phase purity of this compound is determined by X-ray diffraction pattern. It is found that the volatilization during sintering does influence the phase formation and dielectric properties. The best condition is sintering with 0.5 g extra PbO around a 4 g PMNT-PT sample.

Mechanisms of thermal shock failure for ultra-high temperature ceramic

The materials considered in our analysis were ZrB2 ceramic matrix composites. Effect of two different additives (graphite and AlN) on thermal shock stability for the materials was measured by water quench test. It showed that it may provide more stable thermal shock properties with additives of graphite. It was explained by different thermal properties and crack resistance of the two materials in detail. Surface oxidation was one of main reasons for strength degradation of ceramic with additives of graphite after quenched in water, and surface crack was one of main reasons for strength degradation of ceramic with additives of AlN after quenched in water. It was presented that it was a potential method for improving thermal shock stability of ZrB2 ceramic matrix composites by introducing proper quantities of graphite.

基于PLZT的电光偏转器的特性研究

采用具有高二次电光效应的掺镧锆钛酸铅陶瓷材料（PLZT），设计和制备了一种基于折射率随外加电压发生变化的电光偏转器。构建了测试系统，测得PLZT的电光系数是R33=2.1