a-ODPA共聚的耐高温热塑性聚酰亚胺的研究

以2,3,3',4'-二苯醚四甲酸二酐(a-ODPA)为单体,与不同配比的4,4'-二氨基二苯醚(4,4'-ODA)和1,4-苯二胺(1,4-PDA)共聚,制备了一系列的聚酰亚胺(PI)。结果表明,随着1,4-PDA摩尔分数的增加,Tg(玻璃化转变温度)从279℃逐渐上升到328℃,同时比浓对数黏度从110 mL/g逐渐下降到40 mL/g(DMAc,25℃)。当1,4-PDA的摩尔分数不超过0.4的时候,该PI在DMAc、DMF、NMP、DMSO和γ-丁内酯中具有良好的溶解性,塑料样条在220℃的高温下,力学性能的保持率良好。     

工艺条件对中温裂纹釉的影响

以钠长石、石英、硅灰石、方解石、龙岩高岭土、白云石为原料,采用氧化气氛在1 200~1 230℃制备中温裂纹釉。研究了工艺条件对中温裂纹釉的影响。实验结果表明:在配方组成不变的情况下,工艺条件对裂纹釉有着重要的影响。当球磨时间为9min时,釉浆浓度均匀易于裂纹釉的形成;同时当浸釉时间为6~9s,烧成温度为1 200~1 220℃,保温时间为20min时,釉面平整光滑,呈现大片开裂。     

改性纤维素材料对金属离子吸附研究进展

纤维素在地球上含量十分丰富,且表面含有大量的羟基,可以通过羟基一系列的衍生反应,对纤维素进行改性,将纤维素制成离子型的吸附剂。本文就纤维素改性,综述了近些年来国内外以纤维素为原料改性制得的吸附剂相关的研究进展。     

O/W型微乳液应用于三线态湮灭上转换介质研究

光子上转换是吸收低能量（长波长）的光发射高能量（短波长）光的过程,在太阳能光伏、光催化等领域具有潜在应用价值而受到广泛研究,然而通常介质采用有机溶剂及绝氧处理都大大限制了上转换的实际应用.本文报道了可用于三线态湮灭上转换过程的新介质-O/W型微乳液,该体系制备简单、无毒环保,无需除氧脱气条件下,上转化发光稳定,具有未来实际应用的潜力.     

丝杠用1Cr15Ni4Mo2CuN不锈钢热处理温度场的有限元数值模拟

基于ANSYS有限元平台,结合热物性参数的温度敏感性和现行热处理工艺对1Cr15Ni4Mo2CuN钢不同尺寸丝杠工件在淬火加热和深冷处理过程中的温度场变化规律进行了模拟,通过显微组织观察、XRD和硬度测试分析了不同深冷处理时间下工件的残留奥氏体含量。结果表明,?40、?45和?50 mm工件在1070℃加热时的温度均一时间分别为1100、1294和1446 s;?40 mm工件在-196℃深冷79 s时整体温度降至Mf点以下,此时工件中的残留奥氏体已大量转变为马氏体,硬度明显升高,残留奥氏体含量随深冷时间延长而降低,但深冷1800 s后,继续延长深冷时间时残留奥氏体含量变化不明显。     

Enantioselective One‐Pot Reaction: Organocatalyzed Synthesis of Fully Functionalized Oxabicyclo[2.2.2]octanes with Seven Contiguous Stereocenters

An enantioselective one‐pot Michael/Michael/Henry/hemiacetalization reaction between α,β‐unsaturated aldehydes, α‐ketoamides, and nitroalkenes under mild conditions catalyzed by a diarylprolinol silyl ether has been developed. The sequential methodology provides a direct approach to a wide range of fully substituted chiral oxabicyclo[2.2.2]octanes with seven contiguous stereocenters in moderate to excellent yields (up to 99%), high to excellent diastereoselectivities (up to >25:1 dr), and high to excellent enantioselectivities (up to 99% ee).

     

Copper‐Catalyzed Difunctionalization of Terminal Alkynes with Diazo Esters and Amines to Construct β‐Enamino Esters

An operationally simple and efficient copper‐catalyzed three‐component tandem reaction of terminal alkynes, diazo compounds and amines to yield β‐enamino esters is described. This straightforward protocol takes place rapidly with a wide range of substrates and gives the desired β‐enamino esters in good to excellent yields. Preliminary mechanistic studies suggested that the reaction probably proceeds through Cu‐catalyzed formal C–H insertion to produce an alkynoate intermediate, which was then trapped by amines to give the β‐enamino esters.

     

可液化地基单桩基础离心机模型试验的三维数值分析

文章通过三维水土耦合动-静一体有限元程序DBLEAVES对饱和砂土地基（Dr=40%）单桩基础的离心机模型试验进行模型试验相对应的原型三维有限元数值模拟和分析。对比分析小震（峰值加速度0.08g）和大震（峰值加速度0.47g）情况下的土体加速度、超静孔隙水压、沉降位移以及桩身弯矩等变化规律。其中,地基土的性质采用应力诱导各向异性的交变移动弹塑性模型模拟,基桩采用弹性梁单元模型模拟。结果表明：①超静孔隙水压会“隔断”振动波的传递,当土体接近完全液化时,土表面峰值加速度会明显小于输入波峰值加速度,而当超静孔隙水压比较小时,土表面加速度相对于输入波则可能会放大;②地震时所达到的最大超静孔隙水压比是地基土沉降量的主要因素之一,且一大部分沉降发生在震后的孔压消散期;③数值模拟与模型试验结果的对比分析表明,交变移动模型可以较好地反映土体在交变荷载下的动力响应特性,验证了所采用的DBLEAVES程序和有限元方法的有效性。     

Coverage and Substrate Effects on the Structural Change of FeOx Nanostructures Supported on Pt

Structural changes of FeO_x nanostructures supported on Pt(111) and Pt foil with response to oxidation and reduction treatments in O₂ and H₂ atmospheres upto 1.0 bar have been investigated by using X-ray photoelectron spectroscopy and scanning tunneling microscopy. We show that submonolayer O–Fe bilayer (FeO) structure on Pt(111) can be transformed to O–Fe–O trilayer (FeO₂) upon oxidation in 5.0 × 10^?6 mbar O₂, while the FeO to FeO₂ transformation happens over the full FeO film only with the O₂ partial pressure above 1.0 × 10^?3 mbar. Reduction of the submonolayer FeO₂ structure back to the FeO structure occurs when exposed to 1.0 mbar H₂ at room temperature (RT). In contrast, the full FeO₂ structure can be kept even under 1.0 bar H₂ exposure condition. The FeO_x coverage and FeO_x/Pt boundary play a critical role in the redox behavior of the supported FeO_x nanostructures. Furthermore, we show that the FeO_x nanostructures supported on Pt foil can be oxidized in a similar way as those on the Pt(111) surface. However, the Pt foil supported FeO₂ nanostructures can be more deeply reduced to the state close to metallic Fe in 1.0 mbar H₂ at RT. The close-packed Pt(111) surface exhibits a stronger confinement effect on the FeO overlayer than the open polycrystalline Pt surface.     

Influences of heat-treatment on the microstructure and properties of silica–titania composite aerogels

Silica–titania composite aerogels were synthesized via ambient pressure drying by using water glass and titanium tetrachloride as raw materials. The influences of heat-treatment at different temperature with different heating rate on the microstructure and properties of the composite aerogels were investigated by differential thermal analyzer, Fourier transform infrared spectrometer, X-ray diffraction, nitrogen adsorption–desorption, scanning electron microscope and transmission electron microscope analysis. The results indicate that the silica–titania composite aerogels heat-treated at 250 °C exhibited highest specific surface area, pore volume and average pore diameter. When the heat-treatment temperature was higher than 450 °C, the –CH₃ groups on the surface of silica–titania composite aerogels would transform into –OH groups gradually, and in the meantime, the composite aerogels network structure would be destroyed gradually and the crystallinity of TiO₂ would be improved with the increase of heat-treatment temperature. Particularly, heat-treatment at temperatures above 750 °C would cause serious damage to the network structure of the composite aerogels. The adsorption/photocatalytic activity experiments showed that the composite aerogels heat-treated at 550 °C exhibit highest darkroom adsorption efficiency, and the 650 °C-heat-treated samples exhibited highest efficiency for removing the Rhodamine B from water.