Preparation of broadband transparent Si3N4-SiO2 ceramics by digital light processing (DLP) 3D printing technology

Wave-transmitting materials are a kind of multi-functional materials that protect the normal operation of communication and guidance systems of spacecraft in harsh environments. In this paper, we fabricate a broadband microwave transparent Si₃N₄-SiO₂ composite ceramic with excellent performance through digital light processing (DLP) 3D printing technology. The influences of sintering temperature on the weight increase rate, density, dimensional shrinkage, phase composition, microstructure, bending strength and dielectric properties of Si₃N₄-SiO₂ ceramic were all systematically studied. The strength of Si₃N₄-SiO₂ ceramic sintered at 1350 ℃ was 77 ± 5 MPa. The relative permittivity of the ceramic is within the range of less than 4, and the loss tangent can be below 0.003. The 3D printed Si₃N₄-SiO₂ ceramic material exhibited excellent wave-transparent performance.     

基于ABAQUS的EBZ260掘进机切割部结构性能分析

针对EBZ260掘进机切割部运行过程中出现的结构失效问题,基于EBZ260掘进机的结构特点,建立切割部三维模型与仿真模型,对掘进机切割部运行过程中的结构性能进行仿真研究.研究结果显示:切割部中减速箱轴承座、前端支撑座、套环等区域是整个结构的薄弱部位,极易出现结构变形、开裂等失效现象,为此从多个角度开采了掘进机切割部的优化改进,以提高切割部的结构强度及使用寿命.     

The effect of alkali metal oxide on the properties of borosilicate fireproof glass: Structure,thermal properties,viscosity, chemical stability

The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R₂O–CaO–B₂O₃–SiO₂) systematically. Because the glass would emulsify when Li₂O was added to the glass batch, this article did not discuss Li₂O. The results showed that when the amount of Na₂O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na₂O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased.     

Large domain-wall currents in epitaxial Au/BiFeO3/SrRuO3 thin-film capacitors with modulated oxygen vacancy and wall densities

Large domain wall (DW) conductivity in an insulating ferroelectric plays an important role in the future nanosensors and nonvolatile memories. However, the wall current was usually too small to drive high-speed memory circuits and other agile nanodevices requiring high output-powers. Here, a large domain-wall current of 67.8 μA in a high on/off ratio of ~4460 was observed in an epitaxial Au/BiFeO₃/SrRuO₃ thin-film capacitor with the minimized oxygen vacancy concentration. The studies from read current-write voltage hysteresis loops and piezo-response force microscope images consistently showed remaining of partially unswitched domains after application of an opposite poling voltage that increased domain wall density and wall current greatly. A theoretical model was proposed to explain the large wall current. According to this model, the domain reversal occurs with the appearance of head-to-head and tail-to-tail 180° domain walls (DWs), resulting in the formation of highly conductive wall paths. As the applied voltage increased, the domain-wall number increased to enhance the on-state current, in agreement with the measurements of current-voltage curves. This work paves a way to modulate DW currents within epitaxial Au/BiFeO₃/SrRuO₃ thin-film capacitors through the optimization of both oxygen vacancy and domain wall densities to achieve large output powers of modern domain-wall nanodevices.     

Reusable Polyacrylonitrile-Sulfur Extractor of Heavy Metal Ions from Wastewater

Mercury, lead, and cadmium are among the most toxic and carcinogenic heavy metal ions (HMIs), posing serious threats to the sustainability of aquatic ecosystems and public health. There is an urgent need to remove these ions from water by a cheap but green process. Traditional methods have insufficient removal efficiency and reusability. Structurally robust, large surface-area adsorbents functionalized with high-selectivity affinity to HMIs are attractive filter materials. Here, an adsorbent prepared by vulcanization of polyacrylonitrile (PAN), a nitrogen-rich polymer, is reported, giving rise to PAN-S nanoparticles with cyclic π-conjugated backbone and electronic conductivity. PAN-S can be coated on ultra-robust melamine (ML) foam by simple dipping and drying. In agreement with hard/soft acid/base theory, N- and S-containing soft Lewis bases have strong binding to Hg²⁺, Pb²⁺, Cu²⁺, and Cd²⁺, with extraordinary capture efficiency and performance stability. Furthermore, the used filters, when collected and electrochemically biased in a recycling bath, can release the HMIs into the bath and electrodeposit on the counter-electrode as metallic Hg⁰, Pb⁰, Cu⁰, and Cd⁰, and the PAN-S@ML filter can then be reused at least 6 times as new. The electronically conductive PAN-S@ML filter can be fabricated cheaply and holds promise for scale-up applications.     

建筑工业化产品的系统论与装配式住宅设计

从建筑工业化产品的系统论出发,聚焦建筑设计方法与策略,结合装配式建筑系统集成特征,提出装配式建筑设计七个方面的设计策略,并分析其思路和相关手法.     

Facile construction of composition-tuned ruthenium-nickel nanoparticles on g-C3N4 for enhanced hydrolysis of ammonia borane without base additives

Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C₃N₄) as a NP support without additional stabilizing ligands. The optimized Ru₁Ni_7.5/g-C₃N₄ catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min^?1 and an activation energy of 28.46 kJ mol^?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru₁Ni_7.5/g-C₃N₄ is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru₁Ni_7.5/g-C₃N₄ has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru₁Ni_7.5/g-C₃N₄ should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen.     

寻找城中村与城市的罅隙——以广州市为例

随着城市的扩张,城中村不知不觉地被卷入这场城市化运动中.文章以广州城中村为例,寻找城中村与城市存在罅隙的原因,进一步具体阐释了其在物质形态、文化意识形态、经济社会结构方面与城市存在的罅隙,以找到解决问题的办法,达成城中村与城市融合共生的目的,不赞成以"一刀切"的方式进行大拆大建.     

Simple and novel synthesis of zirconia whiskers from a phosphate flux

High quality zirconia whiskers have been successfully prepared by molten salt method, using zirconium oxychloride (ZrOCl₂·8H₂O) and sodium phosphate tribasic dodecahydrate (Na₃PO₄·12H₂O) as precursor and molten salt, respectively. The effects of types of molten salt and heat treatment temperature on the formation of zirconia whiskers were characterized by XRD, Raman, DTA-TG, FE-SEM, TEM, SAED and HR-TEM. When Na₃PO₄·12H₂O is utilized as molten salt and the heat treatment temperature is 900?°C, the as-prepared zirconia whiskers with length ranging from 4?µm to 8?µm show an average aspect ratio of 25. The obtained ZrO₂ whiskers with monoclinic structure are elongated along [010] direction and exhibit a smooth surface with no distinct defects. The XRD and Raman results reveal that the phase transformation from tetragonal zirconia to monoclinic zirconia occurs with the increased crystal size and the water quenching treatment can significantly reduce the content of sodium zirconium phosphate [Na_9–4×Zr_x(PO₄)₃] in the final product. The growth mechanism of zirconia whiskers is supposed to be a dissolution-precipitation process. Since the sodium zirconium phosphate [Na_9–4×Zr_x(PO₄)₃] effectively promotes the dissolution of zirconia in liquid molten salt, zirconia can grow into zirconia whiskers according to its anisotropy.     

The peptides in oat and malt extracts that are preferentially absorbed by Lactobacillus plantarum and stimulates its proliferation in milk

Lactobacillus plantarum proliferates inefficiently in milk, mainly because of its lack of cell envelope proteases and its inability to hydrolyse proteins in milk. Our previous study showed that this strain could grow well in milk with the addition of oat and malt extracts. To investigate the usage and preference for polypeptides and oligopeptides for this strain, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), o-phthaldialdehyde (OPA), high-performance liquid chromatography (HPLC), plate counting and other methods were used in this study. The results showed that proteins in fermented milk cannot be absorbed and utilised by L. plantarum, whereas polypeptides and oligopeptides provide available nitrogen sources for their growth. Short-chain peptides were more conducive to absorption and utilisation than long-chain peptides. In particular, peptides with molecular weights in the range of 200–1400 Da in the oat extract and 100–700 Da in the malt extract were preferentially absorbed and utilised.