Enhanced sound absorption properties of porous ceramics modified by graphene oxide films

Under the condition of constant thickness, improving the low-frequency sound absorption performance of conventional sound-absorbing materials is a challenging research topic. To address this issue, a new reduced graphene oxide/polyvinyl alcohol (RGO/PVA) porous composite ceramic was fabricated using freeze-drying and optimized by redesigning the internal connecting pores of porous ceramic matrixes with a reticular microstructure using RGO and PVA. The as-prepared porous structure showed significant enhancement in the low-frequency sound absorption band compared with pristine porous ceramics. In addition, the hybrid porous ceramics exhibited low thermal conductivity. These favorable properties indicate that the hybrid sound-absorbing ceramics have potential application prospects for noise reduction in the fields of construction and electrical and mechanical devices.     

纳米二氧化钛/聚丙烯酸酯复合乳液的研究进展

对纳米二氧化钛/聚丙烯酸酯复合乳液的制备方法进行了综述,并对其存在的问题和未来的发展前景进行了展望。     

Fabrication of polymer/ZnS nanoparticle composites by matrix-mediated synthesis

Zinc sulfide nanoparticles are obtained as primary particles in a polymer matrix by a matrix-mediated synthesis. Two types of matrix polymer are synthesized via the copolymerization of hydrophobic, cation-exchange, and cross-linking monomers. The ZnS nanoparticles are affected by the composition of the matrix polymer, and especially by its hydrophobicity. In a low-hydrophobicity copolymer matrix, aggregates of ZnS nanoparticles are observed in the matrix using transmission electron microscopy (TEM) and X-ray diffraction (XRD). In a high-hydrophobicity cation-exchange copolymer matrix, primary particles of ZnS with 2–5 nm diameters are observed in the matrix by TEM. However, the ZnS pattern is not distinguishable in XRD measurements because the particle sizes are too small to diffract X-rays.     

Evolution of microstructure and properties of Si3N4 whisker reinforced composites during densification by polymer infiltration and pyrolysis

Si₃N₄ whisker (Si₃N_4w) reinforced composites were prepared by a near-net shaping process, i.e., gel-casting of the Si₃N_4w preform followed by polymer infiltration and pyrolysis (PIP) densification using polysilazane as precursor. The densification process by PIP was described mathematically, after which several key parameters affecting densification efficiency were discussed. The small pore size (0.04 ～ 1 μm) of Si₃N_4w preform can cause filtration effect (low permeability of precursor with a molecular size bigger than pore size), which resulted in the density gradient of the composites. Porosity (P) dependence of flexural strength and elastic modulus of Si₃N_4w/Si₃N₄ followed a power law of (1 – P). With increasing density, the response of Si₃N_4w when confronting cracks transformed from whisker debonding to whisker fracture, which was supposed to be due to the increase of whisker/matrix interface strength. The Si₃N_4w/Si₃N₄ developed by us achieved a good balance between high strength and low dielectric constant, making it promising for high-temperature wave-transparent application.     

株洲体育中心超大跨度伸臂管桁架结构设计

介绍了某超大跨度伸臂立体管桁架结构的风洞试验、方案论证、结构计算分析、节点承载力验算、支座节点承载力验算和试验等。该结构建成后一段时期的正常使用表明,工程的主体桁架和下部承力结构具备较强的承载变形能力和可靠的安全度,满足设计规范和实际使用要求。     

双水相体系萃取分离熊猫豆蛋白质

采用Plackett-Burman（PB）实验、最陡爬坡实验、中心组合设计法对双水相萃取分离熊猫豆蛋白质的条件进行优化。首先,采用Plackett-Burman设计从影响萃取率的7因素中筛选出温度和水相pH两个显著影响因素。在此基础上,通过最陡爬坡实验逼近最大萃取率区域,然后通过中心组合实验对显著因素进行优化。得到最佳萃取条件为:PEG600质量分数为15%、硫酸铵质量分数为20%、氯化钠质量分数为0.05%、蛋白样品溶液加入量4mL,pH7.0,萃取温度为35℃,萃取时间为90min,萃取率可达43.69%,与预测值42.85%接近。说明本优化工艺具有可行性。      

AC+CRC复合式路面反射裂缝的有限元分析

为给复合式路面的使用寿命预估提供参考, 采用有限元软件建立了带裂缝的沥青混凝土罩面连续配筋水泥混凝土(AC+CRC)复合式路面结构应力分析模型, 对在正载和偏载作用下沥青面层正应力和剪应力分布进行了分析.计算了沥青层荷载型反射裂缝应力强度因子, 分析出结构层厚度、模量、配筋率、层间结合状态对AC层反射裂缝扩展的影响.分析结果表明, 增加AC层厚度及底基层模量、提高CRC层配筋率、改善层间结合状态等均能较好地抑制复合式路面反射裂缝的发展, 而CRC层厚度及模量、AC层模量对复合式路面反射裂缝的发展基本没有影响.研究结果可为AC+CRC复合式路面结构设计提供一定的理论依据.     

Polymer Electrolyte Membranes Containing Functionalized Organic/Inorganic Composite for Polymer Electrolyte Membrane Fuel Cell Applications

To mitigate the dependence on fossil fuels and the associated global warming issues, numerous studies have focused on the development of eco-friendly energy conversion devices such as polymer electrolyte membrane fuel cells (PEMFCs) that directly convert chemical energy into electrical energy. As one of the key components in PEMFCs, polymer electrolyte membranes (PEMs) should have high proton conductivity and outstanding physicochemical stability during operation. Although the perfluorinated sulfonic acid (PFSA)-based PEMs and some of the hydrocarbon-based PEMs composed of rationally designed polymer structures are found to meet these criteria, there is an ongoing and pressing need to improve and fine-tune these further, to be useful in practical PEMFC operation. Incorporation of organic/inorganic fillers into the polymer matrix is one of the methods shown to be effective for controlling target PEM properties including thermal stability, mechanical properties, and physical stability, as well as proton conductivity. Functionalization of organic/inorganic fillers is critical to optimize the filler efficiency and dispersion, thus resulting in significant improvements to PEM properties. This review focused on the structural engineering of functionalized carbon and silica-based fillers and comparisons of the resulting PEM properties. Newly constructed composite membranes were compared to composite membrane containing non-functionalized fillers or pure polymer matrix membrane without fillers.     

Comparative Study on Selected Properties of Modified Polyurethane Foam with Fly Ash

The aim of the article is to compare two types of fly ash (from the fluidized and pulverized coal combustion process) as a filler for rigid polyurethane foam. Pulverized fly ash (PFA) is widely used in building materials, while fluidized fly ash (FFA) is not currently recycled, but landfilled. The produced rigid polyurethane foams were reinforced with 5 and 10% by weight addition of fly ash from two different types of boilers. The foaming process, physical properties, morphologies and thermal degradation were subject to comparative analysis. The research indicated that fly ash intensifies the reactions of foam synthesis, most commonly, polyurethane (PU) foam with an addition of 10% PFA. What is interesting is that both ashes can be used in PU foam technology as they do not cause deterioration of the physical parameters. As shown, the addition of filler affects the morphology and impairs the brittleness. Additionally, the use of fly ash from coal combustion in the technology of polyurethane materials complies with the guidelines of the circular economy stated in the European Union legislation. Partial replacement of petrochemical components with waste filler also reduces the total energy consumption in the production of PU composites.