In-situ synthesis of ternary layered Y3Si2C2 ceramic on silicon carbide fiber for enhanced electromagnetic wave absorption

A novel ternary layered ceramic of Y₃Si₂C₂ was successfully in-situ synthesized on the surface of home-made third-generation KD-SA SiC fiber for the first time by molten salt method aimed at improving the electromagnetic wave (EMW) absorption. After in-situ synthesis of Y₃Si₂C₂ ceramic layer on SiC fiber (SiC_f/Y₃Si₂C₂), significantly improved EMW absorption performance was obtained. The minimum reflection loss (RL_min) of ?16.97 dB was reached in SiC_f/Y₃Si₂C₂ composites at the thickness of only 2.19 mm, and the effective absorption bandwidth (EAB) was up to 5.44 GHz (12.56–18 GHz) at a thin thickness of 2.64 mm. The improvement in EMW absorption of SiC_f/Y₃Si₂C₂ is mainly attributed to enhanced dielectric loss and conduction loss resulting from increased heterogeneous interfaces and multiple reflections and scattering originating from net structure. The SiC_f/Y₃Si₂C₂ could be a promising EMW absorber for application in high-performance EMW absorbing materials.     

Hardness of Re-, Ru-, Os-based borides and metal substituted aluminum diborides of MgB2 type M0.5Al0.5B2

A generalized bond-strength model of hardness was applied to of Re₃B, Re₇B₃, ReB₂, Ru₇B₃, RuB, Ru₂B₃, RuB₂, OsB, Os₂B₃, OsB₂, and metal substituted aluminum diborides of MgB₂ type M_0.5Al_0.5B₂ (M = Li, Na, Mg, K, Ca, Sc, Ti, V, Y, Zr, Nb, Mo, Tc, Ru, Hf, Ta, W, Re, and Os). The resulting hardness of transition metal borides was found to be within the range of 14.3–28.2 GPa, and metal substituted aluminum diborides 7.2–21.1 GPa. Comparing the results with other semiempirical results and available experimental data shows the applicability of different methods.     

Digital light processing of SiC ceramic from allylhydridopolycarbosilane with limited acrylate monomers

Digital light processing of ceramic precursor was used to prepare SiC rich ceramic parts in this study. In order to achieve appropriate light curing rate, the ceramic precursor allylhydropolycarbosilane (LHBPCS) was mixed with acrylate monomers tripropylene glycol diacrylate and trimethylolpropane triacrylate. The content of acrylate monomers was optimized to increase the ceramic yield and reduce the shrinkage during pyrolysis. According to the results of thermogravimetric analysis and photolithography experiment, 15 wt% acrylate monomers was appropriate. 330 mJ/cm² UV irradiation dose was selected for every layer with a thickness of 25 μm, and green bodies with different shapes were successfully printed. During pyrolysis, these printed parts changed from transparent yellow to black accompanying uniform shrinkage. At 1000 °C, the shrinkage was 24.0–26.0%, and crack-free SiC rich ceramic parts with density of 2.11 g/cm³ and chemical formula of SiC_1.31O_0.26 were obtained.     

Large-area reduced graphene oxide thin film with excellent thermal conductivity and electromagnetic interference shielding effectiveness

In this work, we fabricated reduced large-area graphene oxide (rLGO) with maximum surface area of 1592 μm² through a cost-effective chemical reduction process at low temperature. The product revealed large electrical conductivity of 243 ± 12 S cm⁻¹ and thermal conductivity of 1390 ± 65 W m⁻¹ K⁻¹, values much superior to those of a conventional reduced small-area graphene oxide (with electrical conductivity of 152 ± 7.5 S cm⁻¹ and thermal conductivity of 900 ± 45 W m⁻¹ K⁻¹). The rLGO thin film also exhibited not only excellent stiffness and flexibility with Young’s modulus of 6.3 GPa and tensile strength of 77.7 MPa, but also an efficient electromagnetic interference (EMI) shielding effectiveness of ∼20 dB at 1 GHz. The excellent performance of rLGO is attributed to the fact that the larger area LGO sheets include much fewer defects that are mostly caused by the damage of graphene sp² structure around edge boundaries, resulting in large electrical conductivity. The manufacturing process of rLGO is an economical and facile approach for the large scale production of highly thermally conducting graphene thin films with efficient EMI shielding properties, greatly desirable for future portable electronic devices.     

含石墨烯胞室结构的铜复合材料及其耐腐蚀性能

目的 开发一种石墨烯在铜基复合材料中的均匀分散结构,制备出兼具高导电和强抗刻蚀性能的石墨烯/铜复合材料。方法 采用化学气相沉积原位生长法结合分散剂工艺,制备分散均匀石墨烯/铜基粉体复合材料。利用制备的石墨烯/铜粉体材料,采用真空热压工艺,制备了石墨烯/铜块体材料,然后用拉曼光谱、X射线粉末衍射仪和金相显微镜,考察石墨烯/铜试样的质量和形貌,最后用数字便携式涡流电导仪测量其电导率。利用自主设计的石墨烯/铜在过硫酸铵中刻蚀的实验装置,测试石墨烯/铜的抗刻蚀性能。结果 利用石墨烯/铜粉体制备的石墨烯/铜块体和铜具有相同的(111)、(200)和(220)晶面,多层石墨烯以立体胞室结构均匀分布在铜晶粒的晶界处。石墨烯/铜块体的导电率为96%IACS,明显优于文献报道的以其他方法制备的石墨烯/铜块体,并且在过硫酸铵溶液中浸泡90 min后,石墨烯/铜块的质量损失为126.6 mg, 石墨烯/铜比纯铜的抗刻蚀能力提高了37.6%,具有比铜更强的抗刻蚀性能。结论 以CVD原位生长法和真空热压法制 备的石墨烯/铜复合材料,石墨烯以立体胞室结构均匀分散在铜界面处,并且兼具高的导电性和强的抗刻蚀性能。     

Synthesis,densification and oxidation study of lanthanum hexaboride

This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB₆. LaB₆ was synthesized by boron carbide reduction of La₂O₃. Effect of temperature on product quality was investigated. Pure LaB₆ powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB₆ powder resulted in a density of only 85.1% of the theoretical value. Hot pressing resulted in near theoretical density at the same operating temperature. Hardness and fracture toughness of the dense LaB₆ was measured as 20 GPa and 3.02 MPa m^1/2 respectively. Oxidation study by thermogravimetry revealed that oxidation starts slowly at 500 °C and accelerates at 700 °C. Isothermal oxidation study revealed that protective oxide layer forms on LaB₆ surface on oxidation at 900 °C. The presence of protective continuous oxide layer on the surface was observed even after 64 h exposure in air atmosphere.     

基于海藻制备超级电容器用三维多孔石墨烯

以海藻作为固相碳源,利用海藻对金属离子具有吸附性能的特点,在未进行生物质材料改性的条件下,实现海藻生物质材料对催化剂金属离子的均匀吸附.本文结合原位高温金属催化和化学活化的方法制备三维多孔石墨烯,并研究了其作为超级电容器电极材料的电化学性能.通过扫描电镜、透射电镜、X射线衍射、拉曼光谱、氮气吸附等手段对三维多孔石墨烯的形貌与结构进行表征分析.研究结果表明,制备的三维多孔石墨烯具有片层状三维网络结构,且片层较薄,并具有较高的石墨化程度,其比表面积达到1 700 m~2/g,孔径分布主要在2~10 nm.以该三维多孔石墨烯材料作为超级电容器电极材料,进行电化学性能表征,发现在较低的电压扫速下得到的比电容量为90 F/g,同时,该材料还具有较高的能量密度和功率密度.以海藻为固相碳源制备得到的三维多孔石墨烯材料在超级电容器领域具有一定的应用前景.     

Adoption of wide-bandgap microcrystalline silicon oxide and dual buffers for semitransparent solar cells in building-integrated photovoltaic window system

We focused on developing penetration-type semitransparent thin-film solar cells (STSCs) using hydrogenated amorphous Si (a-Si:H) for a building-integrated photovoltaic (BIPV) window system. Instead of conventional p-type a-Si:H, p-type hydrogenated microcrystalline Si oxide (p-μc-SiO_x:H) was introduced for a wide-bandgap and conductive window layer. For these purposes, we tuned the CO₂/SiH₄ flow ratio (R) during p-μc-SiO_x:H deposition. The film crystallinity decreased from 50% to 13% as R increased from 0.2 to 1.2. At the optimized R of 0.6, the quantum efficiency was improved under short wavelengths by the suppression of p-type layer parasitic absorption. The series resistance was well controlled to avoid fill factor loss at R = 0.6. Furthermore, we introduced dual buffers comprising p-a-SiO_x:H/i-a-Si:H at the p/i interface to alleviate interfacial energy-band mismatch. The a-Si:H STSCs with the suggested window and dual buffers showed improvements in transmittance and efficiency from 22.9% to 29.3% and from 4.62% to 6.41%, respectively, compared to the STSC using a pristine p-a-Si:H window.