Zr／Ti比对PLZT陶瓷显微结构的影响及机制

在锆钛铅镧(简称PLZT)透明铁电陶瓷的研究中,往往通过改变Zr/Ti比来调节材料的相变温度和有关特性,从而改善陶瓷的物性。为此,经常使用电子显微术和选区电子衍射,对PLZT中Zr/Ti比的变化所引起的显微结构差异进行观测和研究。大量的观察结果表明,     

过氧化合物法PLZT纳米粉体的制备和表征

掺镧的锆钛酸铅固溶体（Pb1-x,Lax）(Zry,Ti-y)1-x/4O3（简称PLZT）是一种有重要用途、性能优良的电光陶瓷材料[1]。为避免局部组成变化引起散射和保证良好的电光性能,材料的组成和均匀性非常重要。用传统的固相法制备PLZT粉体耗能大,生成的粉体颗粒大,组成均匀性差,不能满足现代高科技应用的要求。近年来研究的溶胶．凝胶[2]、柠檬酸法[3]、EDTA凝胶法[4]等湿化学法有许多优点,受到人们的关注,但这些方法需用较贵原料。而在众多的湿化学法中,以共沉淀法最为经济,并且它比传统的固相法好,能够制得均匀性好的纳米粉体。但该…     

新试剂7-(2,4,6-三羟基苯偶氮)-8-羟基喹啉-5-磺酸光度法同时测定微量锆和铪

本文研究了新试剂7-(2,4,6-三羟基苯偶氮)-8-羟基喹啉-5-磺酸(THBAQS)与锆、铪的显色反应.酸性条件下锆、铪均可形成 M-THBAQS-CTMAB三元络合物,ε_(315nm)~(Zr)=3. 27×10~4,ε_(515nm)~(HI)=3.8×10~4,适量H_2O_2使锆络合物吸光度显著降低,据此实现了锆铪的同时测定.本法简便快速、适用范围为0～30μgZr/25 mL,0～25μg Hf/25 mL,且X_(Zr)+X_(Hf）<35μg/25 mL.     

几种钙钛矿型晶体极化性能的从头算分子动力学研究

对具有钙钛矿结构的钛酸钡(BT)、钛酸铅(PT)、锆酸铅(PZ)、三种钛/锆比例的锆钛酸铅(PZT)和镁铌酸铅(PMN)的部分构型建立了复晶胞模型, 并运用从头算分子动力学方法CPMD对其极化性能进行了模拟. 计算结果表明自发极化强度与B格点原子类型和其偏离所处氧笼中心距离有关; d₃₃/χ_e最大值: 25%/75% (Ti/Zr)的PZT的出现在(111)方向, 其它晶体均出现在(001)方向; PZ, PZT, PMN的d₃₃/χ_e值较高; g₃₃×χ_e最大值出现在(001)或(110)方向; PT和PZT的 g₃₃×χ_e值较大.     

一种修饰钙掺杂钛酸铅湿敏纳米薄膜的新方法——钾修饰薄膜的制备、湿敏特性和结构表征

为了使感湿性能很差的钛酸铅湿敏改性，选取Ti(O-n-Bu)_4，Pb(OAc)_2和Ca (OAc)_2为起始物，采用溶胶-旋涂法以及烧结晶化过程，在镀有Ag-Pd合金叉指电 极的α-Al_2O_3基片上制备了钾修饰的钙掺杂钛酸铅纳米湿敏薄膜(K~+-Ca_xPb_ (1-x)TiO_3，缩写为K-CPT)。在(20 ± 0.1) ℃常温下、相对湿度RH=8.0%～93.6 之间5个检测点上测试了K-CPT的阻-温特性，并与纯钛酸铅薄膜（PT）、钙掺杂钛 酸铅薄膜(CPT)以及锂修饰的钙掺杂钛酸铅薄膜(Li-CPT)进行了比较，对工艺进行 了正交实验和研究。结果表明：在x = 0.35，K~+含量为1%(K/Ti, mol/mol)，以及 850 ℃/1h的烧结晶化成瓷条件下，所制得的陶瓷薄膜在RH=8.0%～93.6%的实测范 围内，灵敏度S=3.3*10~3，感湿响应时间τ=15s，湿滞 ≤ ±2%；而在RH=0%～ 100%的全湿范围内，总的电阻值降低值约为10~4 kΩ，即全湿范围内的灵敏度可达 四个数量级；S=10~4kΩ/100△RH(%)。通过XRD，SEM和TEM手段对薄膜的晶相结构 及显微结构进行了表征，薄膜为四方多晶，具有网状孔道和岛形晶界，晶粒呈极度 化定向排列的电畴结构，粒度为10nm，岛的平均面积为4μm*5μm。     

锆钛酸铅(PZT)陶瓷的应用与发展

一、引言 锆钛酸铅压电陶瓷于1955年由美国的B.Jaffe等人发现之后,由于它具有机械耦合系数高、温度特性好、居里温度高(～300℃)等优点,大大推进了压电陶瓷的实用化。用Sr、Ca、Mg等元素取代Pb或添加Nb、La、Sb、Cr、Mn、Fe、Co、Ni等元素进行改性,可以得到许多不同用途的 PZT系压电陶瓷,如PZT-4,PZT-5,PZT-6,PZT-7及PZT-8等,利用它们各自不同的效应可以应用在不同的方面。     

EFFECT OF La AND Zr ON THE CATALYTIC PERFORMANCE OF SUPPORTED COPPER CATALYST FOR DEHYDROGENATION OF METHANOL TO METHYL FORMATE

The catalytic dehydrogenation of methanol over supported Cu/SiO_2and Cu/Al_2O_3 prepared by impregnation and by ion-exchange (Cu/SiO_2(im),Cu/Al_2_3(im) and Cu/SiO_2(ex)), La_2O_3 and ZrO_2 promoted Cu/SiO_2 or Cu/Al_2O_3 catalyst has been studied in a fixed bed microreactor at 250℃ and atmo-spheric pressure. The Cu/SiO_2 (ex) catalyst was found to be very active and se-lective toward methyl formate (MF). However, Cu/SiO_2(im) catalyst wasless active and selective among the studied catalysts. The catalytic activity, MFselectivity and MF yield over Cu/SiO_2 And Cu/Al_2O_3 are greatly improved byLa and Zr. XPS and XRD results suggest that the crystallite size of copper wasreduced by coating La and Zr, the surface Cu/Si or Cu/Al atomic ratio in-creased. TPR results show when the support was coated with La and Zr thepeak temperatures of catalysts significantly decreased.     

Pd/Ce0.8Zr0.15La0.05Oδ整体催化剂甲苯催化燃烧性能的研究

采用一次浸渍法分别制备了 Pd/Ce0.8Zr0.15La0.05Oδ及Pd/Ce0.8Zr0.2O2整体式蜂窝陶瓷催化剂,考察了不同温度焙烧的两类整体催化剂甲苯催化燃烧性能.通过X射线粉末衍射(XRD)、比表面积、拉曼光谱(Raman)、程序升温还原(H2-TPR)、PdO分散度等表征结果与催化活性进行关联.结果表明,随着焙烧温度升高,催化剂比表面积下降,Raman图谱CeO2及PdO峰强度增加,H2-TPR中Ce4+还原峰向高温方向移动,同时PdO分散度下降,相应甲苯催化氧化活性下降.与CeO0.8Zr0.2O2涂层催化剂相比,La3+掺杂催化剂在高温焙烧时,其比表面积下降较小,Raman光谱表明其氧缺位比铈锆涂层催化剂多,H2TPR谱图中Ce4+还原峰低约60～80℃,PdO分散度亦比末掺杂催化剂高.1000℃焙烧下的甲苯氧化反应活性远高于未掺杂催化剂,说明镧的掺杂提高了铈锆涂层催化剂的高温反应活性及热稳定性.     

超细粉Pb_(0.75)Ca_(0.25)[(Ni_(1/3)Nb_(2/3))_(0.08)Ti_(0.912)Mn_(0.008)]O_3的制备与表征

报道了用化学共沉淀法制备掺杂 Ca、Ni、Nb、Mn钛酸铅超细陶瓷粉末的方法。制得的粉料化学式为 :Pb0 .75Ca0 .2 5[(Ni1 / 3 Nb2 / 3 ) 0 .0 8Ti0 .91 2 Mn0 .0 0 8] O3 ,粒径小于 0 .1μm,所有的掺杂元素均能定量掺入。     

CeO2掺杂MgO-ZrO2陶瓷的阻抗特性

利用共沉淀法合成了CexMg0.06Zr（1-x）O1.94（x=0～16%）超细粉体,压制成型后分别在1300,1400,1500,1600 ℃下,保温3 h烧结.对烧结样品用XRD研究了相组成.在不同温度下（700～1200 ℃）测试了CexMg0.06Zr（1-x）O1.94陶瓷的交流阻抗谱.结果表明： 随着CeO2掺入量的增加,促进了CexMg0.06Zr（1-x）O1.94陶瓷立方相结构的形成,扩展了氧离子迁移的通道,降低了导电相粒子间的接触电阻,减低了氧离子的迁移阻碍,从而使得 CexMg0.06Zr（1-x）O1.94陶瓷的导电性能提高.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.