微观结构对溶胶-凝胶法合成的La0.67Sr0.33MnO3电磁性能影响

采用溶胶-凝胶法制备了不同烧结温度的钙钛矿类锰氧化物La0.67Sr0.33MnO3样品。实验结果表明,在1573 K以上烧结的样品,晶粒出现异常长大,晶界效应明显。随着烧结温度的提高,磁化强度逐渐增大,但样品的居里温度基本不变。此外,在1173和1573 K温度下烧结的样品,均出现了低于居里温度的金属-半导体导电行为转变。在合适的烧结条件下,可以观察到隧道磁电阻(TMR)和超大磁电阻(CMR)2种磁电阻效应。实验表明,自旋电子的输运,不仅与样品平均粒径的大小和密度有关,而且与晶界的微观结构有密切关系。     

PREPARATION OF PARTICLE SIZE NARROWLY DISTRIBUTED LOW-DENSITY STYRENE DIVINYLBENZENE COPOLYMER MICROBEADS

In view of the importance of dispersion agent, the amount of the crosslinking monomer andthe diluent in suspension polymerization for the production of particle size narrowly distributedIow-density styrene divinylbenzene copolymer microbeads (LDPS), their actions are preliminarilyinvestigated in this paper. Experimental results indicate that when both the gelatine and polyvinylalcohol (PVA) are used as dispersion agents, the better effect is achieved. DVB is helpful to theformation of the lower density fine particles, the proportion of the DVB/St should be between1:1～1.5:1. Compared with toluene, gasoline is the more effective diluent for the above target.     

Crystal Structure and Characterization of a Dye with Two-photon Pumoed Frequency-upconverted Lasing Properties

The title compound, trans-4-[ p-( N-ethyl-N-(hydroxyethyl ) amino) styryl ]-N-methylpyridiniumtetraphenylborate (abbreviated as ESMT, C46H49N4OB) crystallizes in a space group P1- with a= 0. 983 23 (15)nm, b=1.410 73(16) nm, c=1.54 21(12) nm, a=95.252(13)°, β=91.959(17)°, γ= 107.421(12)°, Z=2, F(000)=712, μ= 0.1 mm-1 Mo Ka radiation, R=0. 093 8. The result shows that the cation of themolecule almost lies in one plane, the hydroxyethyl group is perpendicular to the plane, the anion takes a slightdistorted tetrahedral geometry. Also the thermal stability, two-photon fluorescence, two-photon pumped lasingproperty for the title compound were studied.     

高分子路易斯酸催化剂—阳离子交换树脂四氯化锡复合物

大孔强酸性聚苯乙烯系阳离子交换树脂与SnCl_4在CS_2中反应可生成一种稳定的高分子路易斯酸催化剂.其制备简单、易分离.这种催化剂不怕水,对酯化、缩醛、缩酮、醚化及付氏烷基化反应具有较好的催化作用,且催化性能稳定,至少可重复使用10次.     

Synthesis of Nicotinic Acid by Potassium Dichromate Oxidation

IntroductionNicotinic acid,whose IUPAC name is 3-pyridine formic acid,also known as Vitamine B5,ismainly used as an additive in food,drink andforage industry[1— 3 ] .In medical practice,it is usedto cure pellagra and other relative vitaminedeficiency illness. It is also an intermediate for thesynthesis of important medicines and chemicalmaterials[1,4] . In China,the demand of nicotinicacid is very big. However,there are manyproblems in the current preparation methods ofnicotinic acid,such…     

铝酸钠和含硅铝酸钠溶液结构和性质的研究

本文通过对铝酸钠和硅铝酸钠溶液的红外光谱、拉曼光谱、粘度、表面张力、丁达尔现象和聚沉等光谱和物理化学性质的研究测定,分析了硅在铝酸钠溶液中的行为.认为硅主要是取代Al-O-Al结构中的Al,形成Al-O-Si结构和Al-O-Si-O-Al-O结构等多种形式硅氧铝键以及由氢键相连的大分子结构.这种结构直接影响其物理化学性质,表现为随硅含量增加表面张力增加,粘度上升,具有丁达尔现象等.说明含硅铝酸钠溶液中存在大分子的胶性基团,属于无机高分子溶液,这种网络状"大分子"结构是硅铝酸钠溶液稳定的原因.     

电位滴定法测定半胱氨酸和胱氨酸的研究及应用

本文报道了以Hg^2 为滴定剂,涂丝Ag-Ag2S电极指示,电位滴定法测定复杂体系中半胱氨酸和胱氨酸的新方法。滴定终点突跃明显,检测下限1mg／L,回收率97％～99％。方法简便、快捷、灵敏。     

盐酸普拉克索关键中间体的合成

以1,4-二氧杂螺[4.5]癸-8-酮(2)为起始原料,经三甲基硅烯醚化、碘代反应、酸化后所得的产物,与硫脲发生环合、水解后制得2-氨基-6-氧代-4,5,6,7-氢苯并[1,2-d]噻唑(5,经氨化还原反应合成了2,6-二氨基-4,5,6,7-四氢苯并[1,2-d]噻唑(6)。5和6两种关键中间体的总收率分别为86%和71%,其结构经MS、¹H NMR和¹³C NMR确证,探索了合成盐酸普拉克索的两种关键中间体方法和工艺的影响因素。     

方酸构象和振动光谱的从头算研究

在6-31G^*^*水平上对方酸(3, 4-二羟基-3-环丁烯-1, 2-二酮)三种构象异构体进行了SCF计算。结果表明ZZ型异构体最稳定, ZE型次之。用等键反应能量分析方酸的稳定性, 并与苯作比较, 讨论方酸的芳香性。在6-31G水平上计算了方酸三种构象的振动频率。     

液相色谱-串联质谱法快速同时测定婴幼儿配方乳粉中氯霉素、三聚氰胺、甲硝唑和洛硝达唑

建立了婴幼儿配方乳粉中三聚氰胺、氯霉素、甲硝唑和洛硝达唑残留的高效液相色谱-串联四极杆质谱联用测定方法.样品经碱性乙腈提取,以MGⅢ-C18色谱柱(150 mm× 2.1 mm,5 μm)分离,流动相为60 mmol/L乙酸铵溶液(含0.4‰甲酸)和甲醇,梯度洗脱,流速为0.25 mL/min.采用多反应监测正离子或负离子模式,可以同时对婴幼儿配方乳粉中的三聚氰胺、氯霉素、甲硝唑和洛硝达唑进行快速定性和定量测定.在优化条件下,4种化合物检出限为0.3 ～ 50.0μg/kg,方法回收率为61.4％ ～ 96.2％,相对标准偏差(RSD)为1.8％ ～9.8％.采用本方法测定了多种市售婴幼儿配方奶粉.本方法操作简单、测定结果准确,可用于婴幼儿配方奶粉中三聚氰胺、氯霉素、甲硝唑和洛硝达唑残留的同时快速测定.