Effect of nitriding atmosphere on the morphology of AlN nanofibers from solution blow spinning

High purity AlN fiber is a promising thermal conductive material. In this work, AlN fibers were prepared using solution blow spinning followed by nitridation under N₂ or NH₃ atmosphere. Soluble polymer, such as polyaluminoxane, and allyl-functional novolac resin were adopted as raw materials to form homogeneous distribution of Al₂O₃ and C nanoparticles within the fibers, which could inhibit the growth of alumina crystal and promote their nitridation process. The effect of nitriding atmosphere on the fiber morphology was investigated. XRD results showed that complete nitridation was achieved at 1300 °C in the NH₃ or at 1500 °C in the N₂ atmosphere. Hollowed fiber structure was observed when fiber was nitrided in N₂ at high temperature, which was caused by gaseous Al gas diffusion, and this phenomenon was eliminated in NH₃ atmosphere. The nitridation mechanisms in different atmosphere were analyzed in detail. It was demonstrated that the nitridation of Al₂O₃ fibers in the NH₃ atmosphere offered the favored AlN morphology and chemical quality. Flexible AlN fiber with O content of 0.7 wt% was achieved after nitriding in NH₃ at 1400 °C. The high quality AlN can be used in thermal conductive composite materials.     

综合设计性实验在药物分析学实验中对学生综合能力的培养

《药物分析学实验》是药学专业的一门独立必修课程,是药学科学领域中的一个重要组成部分,具有较强的实践性和综合性,旨在培养学生综合运用所学知识分析药品质量的能力.综合设计性实验作为《药物分析学实验》的重要组成部分,对学生实践操作能力,发现问题、分析问题、解决问题的能力,创新能力,应用能力,团结协作能力,劳动素养等综合能力的培养具有极其重要的意义.     

Numerical simulation analysis and experimental validation on wear/fracture mechanisms of polycrystalline cubic boron nitride superabrasives in high-speed grinding

In this study, a two-dimensional finite element model is proposed to investigate the wear/fracture mechanisms of polycrystalline cubic boron nitride (PCBN) superabrasives in high-speed grinding process. The special geometric microstructures of PCBN grains are constructed by using the classic Voronoi tessellation technique, and cohesive elements are embedded into the geometric model of PCBN grains as the potential crack propagation paths for simulating the wear/fracture behaviours of PCBN grains under grinding loads. The effects of uncut chip thickness per grain (a_gmax) on the stress distribution characteristics and wear/fracture behaviours of PCBN grains during grinding are discussed in detail. Results show that the wear behaviour of PCBN grains during grinding mainly occurs around the grain vertex region; however, the fracture behaviour, leading to the quick failure of PCBN grains, is prone to appear around the grain–filler bonding interface, which is usually on the opposite side of the in-feed direction. Moreover, to separate the PCBN grains from the macro-fracture during grinding, the uncut chip thickness per grain should be kept smaller than 1.0?µm to prevent the unfavourable fracture behaviour from appearing around the grain–filler bonding interface. Furthermore, the corresponding single-grain grinding trials are performed to validate the numerical simulation results by evaluating the wear/fracture morphologies of the PCBN superabrasives in the actual grinding operation.     

光诱导作用对木霉菌产孢量的影响研究

通过固体发酵和液体发酵,对比研究了光诱导作用对8株木霉菌菌株产孢量的影响。结果表明,在固体发酵条件下,50～200 Lux蓝光照射能显著提高菌株Tr673、TL02、Tr25、Tr775的产孢量(P≤0.01);菌株Tr673、TL02、Tr25、Tr775在避光处理36 h后再进行蓝光照射的产孢量较持续光照显著降低(P≤0.01)。在液体发酵条件下,菌株Tr673、TL02、Tr25、Tr775在100～200 Lux白光或蓝光照射下的产孢量较避光处理提高数倍(P≤0.01),较其它光源照射提高2～8倍;100～200 Lux蓝光照射能显著提高Tr673、TL02、Tr775的产孢量(P≤0.01),但对Tr25的产孢量提高不明显。     

Enhancement of density and ionic conductivity for garnet-type Li5La3Ta2O12 solid electrolyte by self-consolidation strategy

Garnet-type Li₅La₃Ta₂O₁₂ (LLTaO) solid electrolyte is a potential candidate component for future all-solid-state batteries due to its extraordinary stability against the reaction with molten lithium. In contrast with traditional cold isostatic pressing (CIP) method, which generally pursues ultra-high pressure, this paper tries to enhance the density and ionic conductivity of LLTaO by self-consolidation strategy without the assistance of any pressing operations. A LLTaO bulk with a relative density of 95% is obtained. SEM images reveal that the bulk sample is assembled by large dense particles in size of tens of microns indicating that the interstitial space among the particles has been dramatically minimized. Accordingly, the total ionic conductivity and the bulk ionic conductivity at 30?°C are promoted up about one order of magnitude higher to 2.63?× 10^?5 S?cm^?1 and 1.41?×?10^?4 S?cm^?1, respectively. Moreover, the lithium ionic migration network in the crystalline unit cell of LLTaO is first explored from its assembled way. A hexagon-like basic unit with tetrahedral Li1 joint sites and Li1- - Li1 edges is identified. The tetrahedral Li1 sites act as crucial junctions for the transportation of lithium ions. This work would significantly stimulate the development of LLTaO electrolyte membrane technology.     

Effects of Al2O3 crystal types on morphologies,formation mechanisms of mullite and properties of porous mullite ceramics based on kyanite

Porous mullite ceramics with different crystal shapes of mullite are fabricated by in-situ reaction with middle-grade kyanite as raw material, Al(OH)₃, γ-Al₂O₃, ρ-Al₂O₃ and α-Al₂O₃ as alumina sources. Effects of Al₂O₃ crystal types on morphology evolution and formation mechanisms of mullite, and properties of porous ceramics are investigated. Results show that mullite in the sample with Al(OH)₃ mainly shows acicular morphology, because its (001) plane has the minimum interplanar crystal spacing and maximal attachment energy, it grows fast along [001] direction by screw dislocation mechanism. With a successive slowdown in reactivities of Al(OH)₃, γ-Al₂O₃, ρ-Al₂O₃ and α-Al₂O₃, the amount and aspect ratio of mullite reduce, its growth mechanism gradually transforms into two-dimensional nucleation. Acicular mullite not only reinforces samples, but makes effective pore sizes smaller, which enable the sample with Al(OH)₃ to present low bulk density, high apparent porosity and linear changes, small average pore size and good mechanical strength.     

Preparation of composites based on recycled polypropylene and automotive shredder residue

In past research, mechanical recycling of automotive shredder residue (ASR) has led to serious deterioration of material performance, and real‐scale application in this way still remains a challenge. Here, we report a sustainable approach called solid‐state shear milling (SSSM) for the production of high‐performance polypropylene (PP)/ASR composites with robust mechanical performance on a commercial scale. After the SSSM process, the obtained 50/50 wt% PP/ASR composite exhibited a 41.3% increase in tensile strength, 32.9% increase in flexural strength and 55.0% increase in impact toughness when compared with corresponding composites made by traditional direct melt blending. In particular, the toughness of the material can be improved by further addition of PP grafted with maleic anhydride with toughness comparable to that of recycled PP, and a 325% increase in toughness can be obtained with addition of styrene–butadiene–styrene block copolymer grafted with maleic anhydride. This PP/ASR composite shows good processability and high thermal stability, and meets the requirements of many applications for nonstructural products. The approach presented in this paper highlights a novel technique for ASR recycling. © 2018 Society of Chemical Industry     

电子束诱导沉积钴微米线及其铁磁性

通过电子束诱导沉积的方法制备了钴(Co)微米线,并利用扫描电子显微镜(SEM)、原子力/磁力显微镜(AFM/MFM)以及物性测量系统(PPMS)等手段对Co微米线的沉积尺寸、微结构、铁磁性和电学性质进行了测试和分析。研究结果表明:Co微米线轮廓清晰、均匀性好。在不同的沉积条件下,微米线的实际长度与设定长度基本一致;实际宽度数据呈类梯形分布,半高宽是设定值的2~10倍;实际厚度低于设定厚度的60%。沉积电流对Co微米线的铁磁特性有重要影响。当沉积电流大于0.5 nA时,样品呈现出良好的铁磁特性。另外,电学性能测试结果显示Co微米线呈现绝缘特性。成功制备了室温铁磁绝缘Co微米线,这将有助于深入开展微纳尺度的结构与器件的研究和应用。