关键词： 单分散二氧化硅   小粒径   改进Stöber法   日用化学产品   生物医药  

摘要： 二氧化硅纳米粒子是一种极其重要的无机材料,具有比表面积大、表面吸附能力强、无毒、物理化学稳定性强等一系列优点,在吸附、陶瓷、催化、医药、日用化工等领域具有巨大应用潜力而受到广泛关注。Stöber法是一种非常有效的溶胶-凝胶策略,常被用作生产具有高度可定制尺寸和表面性能的均匀单分散二氧化硅纳米粒子。不同尺寸的二氧化硅纳米粒子理化性质有所变化,根据不同领域的需求,对二氧化硅纳米粒子的粒径有着不同要求,因此,为满足这些需求,逐渐在Stöber法的基础上发展出了许多改进方案,以获得尺寸范围更大、粒径更加均一、形态更多样化的二氧化硅纳米粒子。本文在简要介绍二氧化硅纳米粒子的基础上,重点介绍了Stöber法和其改进方案,以及基于改进Stöber法合成的二氧化硅纳米粒子在日用化学工业和生物医药方面的应用。旨在为相关领域提供一些参考。

关键词： 黏土   纤维素   植物胶   防渗漏材料   渗水率  

摘要： 为提高水利工程的储水效果,试验将偏高岭土作为黏土材料,分别与羟丙基甲基纤维素和田菁胶植物胶复合,制备纤维素/黏土防渗漏材料以及植物胶/黏土防渗漏材料,并研究其性能。结果表明,在防渗漏材料中添羟丙基甲基纤维素和田菁胶植物胶均可以增大其粒径,使其具备防渗漏能力。当以0.6%纤维素和1.0%植物胶分别制备防渗漏材料时,900 h渗水率基本为0.00%,且30 d储存水质良好。其中,pH值分别为7.20、7.28,COD_(Mn)分别为3.315、2.744 mg/L,氨氮含量分别为0.352、0.375 mg/L,浑浊度分别为2.241、2.018 NTU。且这些30 d储存水质情况均达到相关国家标准,储存效果优于HDPE土工膜,在水利工程应用中有一定潜在价值。

关键词： 铝基复合材料   粉末冶金   摩擦学行为   磨损机制  

摘要： 采用真空热压烧结制备了不同Mo_(2)BC含量的Al基复合材料,并进一步分析了Mo_(2)BC含量对Al基复合材料摩擦学性能的影响。研究表明:随着Al基体中Mo_(2)BC陶瓷颗粒含量的增加,材料体系的硬度得到了明显的提升,这是因为高硬度的Mo_(2)BC陶瓷颗粒在复合材料中能够表现出显著的钉扎效应,使得基体在受力过程中产生的塑性变形能够得到抑制。当Mo_(2)BC陶瓷颗粒的质量分数提高到30%时,复合材料的硬度较纯Al提升了约130%,其硬度值高达72.5HV_(0.2)。此外,随着Mo_(2)BC陶瓷颗粒含量的增加,复合材料的摩擦磨损性能得到了明显的改善。对于纯Al和添加Mo_(2)BC质量分数为10%的Al基复合材料,当其与GCr15轴承钢进行配副时,磨损机制主要表现为二体磨粒磨损和黏着磨损,此时材料基体具有较高的磨损率(1.43×10^(-4)mm^(3)·N^(-1)·m^(-1))和摩擦系数(0.84)。随着添加的Mo_(2)BC陶瓷颗粒质量分数逐渐增加至30%,复合材料的磨损率降低至2.35×10^(-3)mm^(3)·N^(-1)·m^(-1),摩擦系数降至0.56,表现出一定的减摩润滑特性。这是由于Mo_(2)BC的添加能够使材料体系摩擦表面通过摩擦氧化作用生成具有润滑性能的摩擦氧化物层,有效抑制了二体磨粒磨损和黏着磨损,起到了一定的抗磨减摩效应。

关键词： 复合材料层合板   代表性体积单元   多尺度   弹道侵彻   刚度退化  

摘要： 针对纤维增强复合材料层合板结构设计和抗侵彻数值仿真需要大量材料参数和动态试验数据的问题,以碳纤维增强复合材料层合板为研究对象,采用多尺度模拟方法,实现了纤维丝-纤维束-层合板的微观-介观-宏观力学性能和抗侵彻能力的全流程数值仿真预测。首先,建立微观代表性体积单元(representative volume elements,RVE),基于最大应力准则,预测出纤维束的力学性能;然后,根据编织结构的空间特征建立介观RVE模型,采用Hashin和Hou的失效准则,预测出宏观等效力学性能;最后,根据已发表的试验数据,建立了宏观弹道侵彻数值模型,提出了一种考虑材料应变率效应的改进Hashin失效准则,进而研究了弹道侵彻作用下纤维增强复合材料层合板的剩余速度和损伤特征。结果表明:试验与仿真得到的剩余速度的相对误差在5%以内,宏观数值模型准确捕捉到了纤维断裂、层间分层等损伤模式,验证了多尺度模拟方法的合理性和准确性;拟合得到了弹道极限速度随板厚变化的关系式,两者呈线性关系,且相关系数达0.97以上。研究结果有助于实现纤维增强复合材料层合板抗侵彻的低成本、短周期结构设计,对纤维增强复合材料层合板的正向性能预测和逆向结构设计均具有重要的科学和工程应用价值。

关键词： Aluminum alloys  

摘要： This study designed laser engraving, atmospheric pressure plasma spraying and resin pre-coating (RPC) on aluminum alloy surface to construct quasi-Z-directional "epoxy-pins" for improving bonding strength with carbon fiber reinforce polymer (CFRP). The laser engraving treatment was used to create pitted structure on the aluminum alloy surface, higher wettability was acquired and greater vertical spaces were formed to impregnate epoxy resin for stronger mechanical interlocking. Atmospheric pressure plasma spraying was then utilized to remove surface contaminants of aluminum alloy surface and increase the quantity of adsorbed polar functional groups. RPC technique was further adopted to guide high-viscosity epoxy resin into pits to minimize defects between the resin and the substrate and reinforce the mechanical interlocking. The bonding strength of the specimen with the combined treatments of L0.08-1 yielded up to 130.5% increment than the base in bonding strength. The failure modes of composites were changed from adhesive failure of aluminum alloy surface to delaminationdominated failure of laminated CFRP composites. Simple and effective combined treatment method is expected to gain application in the development of high performance of heterogeneous material bonding. © 2025 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.

关键词： Plasma CVD  

摘要： Objective Light emitting diodes (LEDs) have gained widespread adoption in high-resolution display technology due to their superior characteristics, including high contrast ratio, high brightness, and high energy efficiency. While GaN-based LEDs are commonly fabricated on sapphire substrates, these conventional configurations face significant challenges regarding crystal quality and luminous efficiency. Patterned sapphire substrate (PSS) has emerged as an effective solution to enhance both GaN crystal quality and light extraction efficiency (LEE) of LEDs. However, when applied to small-size LED applications, conventional microscale PSS demonstrates inherent constraints, particularly in achieving optimal LEE and uniform light distribution. Recent investigations have demonstrated that LEE can be significantly improved through enhancing diffraction effects after reducing pattern dimensions to the nanoscale. Additionally, after the introduction of patterned Al2O3 - SiO2 substrate, which is termed multi-material substrate (MMS), the LED performance can be optimized by increasing axial luminescence intensity and reducing the luminous angle. We fill the research gap in the optical design and optimization of nanoscale patterned substrate. Through optical simulations and calculations, the underlying mechanisms by which the nanoscale MMS enhances the optical performance of flip-chip LEDs have been revealed. Moreover, we aim to design the optimal parameters of nanoscale MMS patterns for flip-chip LEDs. The designed nanoscale MMS has been successfully fabricated by employing semiconductor manufacturing techniques. Methods We employ two simulation methods. First, the wave optics method in COMSOL software is used to simulate the transmittance of MMS with different pattern periods. By calculating the transmittance at different incident angles and wavelengths of plane waves, the influence of pattern periods on the transmittance is analyzed. Second, the Monte Carlo ray-tracing method

关键词： Dielectric properties  

摘要： The lithium-based silicate microwave dielectric ceramics with ultra-low permittivity show great potential as substrate materials in the fifth-generation wireless communication technology. However, the residual stress caused by higher sintering temperatures leads to increased dielectric loss, thereby deteriorating the microwave dielectric performance. In this work, B3+ was introduced into LiAlSi2O6 ceramics to reduce Al3+ content, aiming to improve their sintering temperature and microwave dielectric performance. LiBxAl1–xSi2O6 (0≤x≤0.20) microwave dielectric ceramics were prepared using a combination of solid-state reaction and cold isostatic pressing techniques. Effects of B3+ doping on the sintering characteristics, phase structure, microstructure, and microwave dielectric properties of the materials were characterized. The results show that with a gradual increase in the doping concentration, sintering temperature of the ceramics decreases significantly from 1400 to 1000 °C. Meanwhile, the relative permittivity (Εr) decreases from 3.95 to 3.69, the quality factor (Q×f) increases significantly from 24300 to 30560 GHz, and the temperature coefficient of resonant frequency (τf) increases from –45.9×10–6 to –20.9×10–6 °C–1. Specifically, the change in Εr is mainly influenced by intrinsic polarization, lattice vibrations, and covalent bond strength of the material;the improvement in Q×f is closely related to the increase in packing fraction (PF) and the decrease in damping coefficient;the increase in τf is strongly correlated with the bond valence of oxygen (VO). Furthermore, the composition with x = 0.20 exhibits the best microwave dielectric performance with Εr = 3.69, Q×f = 30560 GHz, and τf = –20.9×10–6 °C–1. Findings of this study on LiBxAl1–xSi2O6 provide important theoretical guidance and practical insights for development and application of high-performance microwave dielectric ceramics in the future. © 2025 Science Press. All rights reserved.

关键词： Fracture toughness  

摘要： SiC/SiC composites have emerged as essential thermal structure materials for development of hypersonic vehicles and high thrust-to-weight ratio aero-engines. Design and utilization of boron-containing ceramic precursors as impregnation agents for precursor infiltration and pyrolysis (PIP) to introduce self-healing components into matrix represent a key strategy for enhancing the antioxidant properties of SiC/SiC composites. Here, borane pyridine or borane triethylamine were utilized as boron sources and subsequently mixed with a solid polycarbosilane (PCS) xylene solution to prepare different boron-modified PCS solutions. These solutions were used as PIP impregnation agents to fabricate various boron-modified SiC/PyC (pyrolytic carbon)/SiC composites. The physicochemical properties of boron-modified PCS-derived ceramics, along with the physical and mechanical properties of SiC/PyC/SiC composites before and after matrix boron modification, were investigated. Results demonstrated that addition of appropriate amounts of borane pyridine and borane triethylamine as boron sources in solid PCS solutions effectively introduced boron as a heterogeneous element into the derived SiC ceramics. Compared to PCS, the boron-modified PCS solutions (BP-1 and BP-2) exhibited increased ceramic yields. The derived ceramics exhibited a semi-crystalline β-SiC structure, with boron element contents of 1.7% and 2.2% (in mass), respectively. In contrast to unmodified composite, the boron-modified SiC/SiC composites exhibited negligible changes in density, apparent porosity, and fracture toughness. However, the flexural modulus increased from 116 GPa to 132 GPa. Furthermore, the flexural strength of the modified composite using borane pyridine alone as boron source was 658 MPa, comparable to the unmodified composite's strength of 643 MPa, but with a reduced dispersion coefficient. All above data demonstrate that borane pyridine can be used as boron source for preparation of boron-modified SiC