聚乙烯拉伸过程中晶态变化及形变机理

用红外光谱和X-射线衍射研究了室温拉伸的聚乙烯,结果显示单斜晶存在于室温拉伸的聚乙烯中。对Hendra等关于拉伸过程机理的“微熔融”理论及其所根据实验结果提出异议,而本文的,实验结果支持了Peterlin模型。     

X-ray, Raman and FTIRS studies of the microstructural evolution of zirconia particles caused by the thermal treatment

Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO₃)₂ solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 °C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO₂. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) already after a mild calcination at 500 °C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600-650 °C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM.     

碲化镓纳米片中单斜晶相和六方晶相共存的光谱特征（英文）

快速发展的二维层状材料为构建新型高效的微纳发光器件和光电探测器件提供了新的平台.其中碲化镓纳米片备受关注,这是因为碲化镓从少层到块体都具有极强的发光性能,因而可以降低二维微纳器件的制备条件.然而碲化镓纳米片具有单斜和六方等多种晶相,使其发光特性和光谱结构异常复杂,目前还缺少对不同厚度碲化镓纳米片荧光光谱的系统研究.本文研究了不同厚度碲化镓纳米片的荧光光谱和拉曼光谱,以及荧光光谱从低温(4 K)到室温的演化行为.通过光谱分析,发现单斜晶相和六方晶相可能同时共存于多层碲化镓纳米片中.为了阐述相关实验结果,构建了如下原子结构模型:其中六方晶相位于纳米片的顶层与底层,而单斜晶相位于纳米片的中间位置.基于温度依赖的荧光光谱,可以获得六方晶相的光学带隙为1.849 eV,且该激子峰只能在较高温度(>200 K)下和声子辅助下才能表现出显著的荧光发射行为.进一步的实验结果确定了六方晶相的激子-声子相互作用强度约为1.24 meV/K.本工作证实了碲化镓纳米片中单斜晶相与六方晶相共存的实验现象,为研究碲化镓纳米片的晶相变化和激子动力学,以及探究碲化镓的奇异物理化学特性,提供了新的见解.     

Analysis of silica fume produced by zircon desilication

Novel chemical methods have been developed to allow for the determination of the components of silica fume produced by zircon desilication. Hitherto, no methods have been described for the analysis of this material. The amorphous silica is first removed by treatment with sodium hydroxide. The residue from the hydroxide treatment may then be subjected to a suite of reagents to determine the zircon, the total zirconia, the monoclinic zirconia and the tetragonal zirconia content of the fume. The zircon content of the fume is determined by treatment of the hydroxide residue with concentrated hydrofluoric acid (HF). The total zirconia content of the fume is determined by digestion of the hydroxide residue with fuming sulphuric acid (oleum), while the relative amounts of monoclinic and tetragonal zirconia may be found by treatment of the hydroxide residue with 10%w/v HF, which attacks the less stable tetragonal phase. Both X-ray diffraction and particle size analysis were used to validate the steps in the analytical procedure. An explanation of the presence of tetragonal zirconia in the fume is proposed. A greater understanding of the composition of the fume led to the installation of a separator in the company's production line to remove the zircon. Australian Fused Materials (AFM) now produces a vastly superior grade of fume marketed under the code SF-98.     

Global structural behaviour of thin and moderately thick monoclinic spherical shells using a mixed shear deformation model

Summary The static and dynamic responses of anisotropic spherical shells under a uniformly distributed transverse load are investigated. Analytical solutions using the mixed variational formulation are presented for spherical shells subjected to various boundary conditions. Numerical results of a refined mixed first-order shear deformation theory for natural frequencies, critical buckling, center deflections and stresses are compared with those obtained using the classical shell theory. A variety of simply-supported and clamped boundary conditions are considered and comparisons with the existing literature are made. The sample numerical results presented herein for global structural behaviour of monoclinic spherical shells should serve as references for future comparisons.     

聚合所得初生聚乙烯的晶型

聚合所得初生聚乙烯的晶型伍青，张启兴，卢泽俭，王海华，欧阳巍，林尚安，张光华（中山大学高分子研究所，广州，５１０２７５）（中国科学院广州化学研究所）关键词聚乙烯，结晶，单斜晶，颗粒形态热力学稳定的聚乙烯晶型为正交晶系［１］．当聚乙烯受一定应力作用时如...     

Study of the effect of precipitant on the high-temperature phase stability of SrO-ZrO2 prepared by n-butanol soft-template method

SrO doped zirconia (20%) was synthesized by n-butanol soft-template method using both NaOH and ammonia solution as precipitants. The high-temperature phase stability was investigated following further heat treatment at 1000°C for 2 h. XRD and Raman spectra were used to characterize the crystal form of zirconia. In addition, TEM was used to characterize the dispersibility of SrO doped zirconia. The results indicated that the concentration of OH^? introduced into the ZrO₂ lattice was the main factor controlling the crystal form of nanosized zirconia. The NaOH solution precipitant could improve the dispersibility of SrO doped t-ZrO₂, and could also prevent the phase transformation of zirconia from t-ZrO₂ to m-ZrO₂ effectively.     

单斜层状LiMn0.97Al0.03O2-x(PO4)x材料的合成及其电化学性能

以Na₂CO₃, (CH₃CO₂)₂Mn·4H₂O, Al₂O₃, Na₃PO₄·12H₂O和CH₃COOLi·2H₂O为原料, 通过2次高温固相法和一步水热离子交换法得到一系列铝和磷掺杂的LiMn_0.97Al_0.03O₂, LiMnO_1.99(PO₄)_0.01和LiMn_0.97Al_0.03O_2-x(PO₄)_x(x=0.01, 0.03, 0.05)化合物. 用X射线衍射(XRD)表征了前驱体及交换产物的晶体结构, 用扫描电镜(SEM) 测定了晶体的形貌. 通过X射线光电子能谱(XPS)、傅里叶红外光谱及恒电流充放电测试, 研究了掺杂离子对合成材料结构及电化学性能的影响. 研究结果表明, Al-PO₄复合掺杂综合了Al³⁺掺杂提高材料的电化学反应活性和减低材料的电化学反应阻抗以及PO₄^3-掺杂增大材料的晶胞体积的特点, 提高材料中Li⁺的扩散能力, 有效地抑制了材料由于Jahn-Teller效应引起的结构畸变, 改性后的LiMnO₂正极材料既保持了较高的容量又获得了良好的电化学循环性能.     

单斜仲钨酸铵热分解的热化学测定

The heat of the thermal decomposition of monoclini c ammonium paratungstate, (NH4)10H2W12O42•4H2O, was measured in a HT-1000 microcalorimeter using three-step calorimetry and suitable thermochemical cycle. The standard enthalpy of the thermal decomposition reaction at 298.15 K and the standard enthalpy of formation at 298.15 K for monoclinic ammonium paratung-state were obtained to be (430.1± 10.2) kJ•mol－ 1 and－ (13 423.7±14.8) kJ•mol－ 1, respectively.     

Sol-gel modified Pechini method for obtaining nanocrystalline KRE(WO4)2 (RE = Gd and Yb)

KRE(WO₄)₂ (RE = Gd and Yb) nanocrystalline powder was obtained by the modified sol-gel Pechini method. The precursor powder was calcined between 923 and 1023 K for a maximum of 6 h at air atmosphere. DTA-TG of the precursor powder shows that the temperature for total calcination is around 800–850 K. Molar ratio between the complexing agent and the metal ions in the first step of the method and molar ratio between the complexing agent and the ethylene glycol in the second step of the method were studied to optimize the preparation process. X-ray diffraction and IR spectroscopy were used to study the transformation from precursor powder into a crystalline monoclinic phase. Raman spectroscopy was used to study the vibrational structure of the nanoparticles. The Scherrer formula was used to confirm the grain sizes visualized by SEM and TEM techniques. Small nanoparticles in the range of 20–50 nm of monoclinic KREW have been successfully obtained by this methodology.