Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane

The morphologies of solvent-free, microporous, mechanically self-supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley & Sons, Inc.     

低密度聚乙烯光引发交联机理——Ⅱ.BNB自旋捕捉ESR研究

在光引发剂二苯甲酮(BP)存在下,紫外光辐照低密度聚乙烯(LDPE)所形成的自由基中间体已被自旋捕捉剂2,4,6-三特丁基亚硝基苯(BNB)所捕捉,其自旋加合物自由基已为电子自旋共振(ESR)所特征。现已检测和鉴定到二种自旋加合物:一种是叔碳自由基;另一种是仲碳自由基。它们分别是由BP的激发三重态从LDPE链的支化点和亚甲基团上夺氢所形成的自由基中间体同自旋捕捉剂BNB反应生成的。上述的证据表明:LDPE的光引发交联点主要发生在叔碳和仲碳原子上,且H-型交联点占主导地位。     

K2NiF4型结构的A2－xSrxBO4(A＝La, Dy, B＝Mn, Fe, Co, Ni)希土复合氧化物的合成

以典型的轻希土镧和重希土镝及碱土金属锶作为Ａ位离子，以过渡金属锰、铁、钴、镍作为Ｂ位离子，合成了Ｋ２ＮｉＦ４型结构的Ａ２－ｘＳｒｘＢＯ４希土复合氧化物，采用粉末Ｘ射线衍射技术考察了反应条件等因素对生成Ｋ２ＮｉＦ４型四方（Ｔ）结构上析影响，实现结果表明，四方结构的形成不仅与几何因素有关，而且与各组分的物理化学性质有关。各个不同的组成，生成四方相的温度范围也有所不同。适当地提高反应温度以及延长灼烧时间     

聚乙烯单晶的退火效应

用混合晶红外光谱法和ＳＡＸＳ、ＤＳＣ和ＬＡＭ等方法研究了聚乙烯单晶在７５℃、９０℃和１０５℃退火前后的结构变化，发现在９０℃以下和１０５℃以上退火，遵循不同的退火机制     

天然气和氧偶联制环氧乙烷催化剂的反应性能

研制了天然气和氧经偶联反应制环氧乙烷的Ａｇ－Ｂａ－Ｃｓ／Ａｌ２Ｏ３催化剂（ＮＥＯ－１）。用Ｎ２＋Ｏ２＋Ｃ２Ｈ４和偶联产物气加氧作原料气，在２５０℃，空速２５００ｈ＾－１时，乙烯转化率和ＥＯ选择性分别达到了３０％和８０％，ＮＥＯ－１催化具有适宜的比表面和孔结构，用ＸＰＳ分析发现，与新鲜的催化相比，经活化和反应后的催化剂表面的Ｂａ，Ｃｓ原子浓度增高，并具有较多的吸附氧物种。     

溶剂热还原合成Cr2O3纳米管(英)

Cr₂O₃ nanotubes with diameters of 80 nm and lengths of 550 nm were synthesized in a solvothermal reduction system at 180 ℃. The acetyl acetone (AcAc) and ethylene glycol (EG) were used as the chelate agent and the reductant respectively in the system. An intermediate compound-Cr(Ⅲ)(C₅H₇O₂)₃ was formed to force Cr₂O₃to crystallize along one direction.     

氧化铽团簇的表面修饰及对其荧光特性影响的研究

采用脉冲激光轰击浸于流动相中的氧化铽固体靶，考察了流动相及其流速、脉冲激光输出功率、修饰剂、添加修饰剂顺序等对所获得的氧化铽有机溶胶荧光性能的影响。UV-Vis和荧光光谱的测试表明：以含有修饰剂的无水乙醇作为流动相，可得到良好荧光性能的氧化铽乙醇溶胶，而环己酮与醋酸乙酯均不适合作为该体系的流动相;最佳流速为0.15 mL·s^-1；脉冲激光输出功率大有利于其荧光性能；最佳修饰剂为乙酰丙酮(acac)和2，2′-联吡啶(2，2′-bipy)，且应原位修饰。     

不同沉淀剂制备的Ag／TS－1催化丙烯直接气相氧化合成环氧丙烷

 在423K、常压固定床石英反应器中，以丙烯直接气相氧化为探针反应，考察了催化剂制备方法、沉淀剂的种类和浓度对制备的Ag／TS－1催化剂催化性能的影响，采用TEM，XRD和UV－Vis等表征手段对Ag／TS－1催化剂进行了分析．结果表明，沉积－沉淀法是最佳的催化剂制备方法，但浸渍法也可制得具有环氧丙烷选择性的催化剂．K2CO3是一种良好的沉淀剂．以K2CO3为沉淀剂，硅钛比为64的TS－1为载体制备的Ag／TS－1催化剂上的丙烯转化率为1．72％，环氧丙烷选择性为98．2％．少量单质银的存在有利于环氧丙烷的生成，除银粒子的分散状态外，银粒子与载体TS－1间的相互作用对提高催化剂的选择性具有决定性作用．     

LiCoO2中锂离子固相扩散系数随循环次数的变化

The solid diffusion coefficient of lithium-ion in LiCoO₂ cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. By SEM, XRD and FTIR techniques, the structure of LiCoO₂ was studied before and after charge-discharge cycles, and the relationship between solid diffusion coefficient and crystal structure was further discussed. CITT results show that the value of Li⁺ solid diffusion coefficient of LiCoO₂ is about 10^-12 cm²·s^-1. During the whole charge-discharge cycles, the Li⁺ solid diffusion coefficient decreased within the voltage of 4.0～4.3 V, which is attributed to the change of the structure of LiCoO₂.     

微波场中甲烷部分氧化制合成气 Ⅱ.Co/ZrO_2催化剂在微波场中的升温行为及催化活性

近年来，甲烷部分氧化制合成气（ＰＯＭ）的研究一直十分活跃［１，２］．前文报道了用于甲烷部分氧化制合成气的镍基催化剂（Ｎｉ／Ｌａ２Ｏ３）在微波场中的升温行为和催化活性［３］，发现在达到相同的ＣＨ４转化率时，微波活化方式下的催化剂床层温度比常规加热低得多...