Investigation into microstructure of carbon nanotube multi-yarn

Structural analysis at the nano and micro scale was performed on a carbon nanotube (CNT) multi-yarn. The yarns were made by a process of drawing CNTs into a ribbon and twisting the ribbon into a yarn. Scanning electron microscopy (SEM) was used to view the exterior of the yarn. Polarized microscopy was used to examine details of the 1-yarn, and it also identified ribbon–ribbon boundaries. Further examination of interior structure was done by NanoCT scans which showed that folding of the ribbons had occurred causing complicated structures. The interior folding was found by milling into the yarn with a focus ion beam gun (FIB) and imaging with SEM. These different methods thus provided various microstructural details (structure, ribbon–ribbon boundary, folding and void fraction) of CNT multi-yarn which could be used to compare with other yarns fabricated with different procedures/sources as well to provide parameters for analytical tools. Further, these microstructural details can be related to macro mechanical and physical properties.     

An efficient and secure cipher scheme for images confidentiality preservation

In this paper, a novel image encryption scheme based on two rounds of substitution–diffusion is proposed. Two main objectives have guided the design of this scheme: (a) robustness against the most known type of attacks (statistical, chosen/known plaintext, ciphertext-only and brute force attacks) and (b) efficiency in terms of computational complexity (i.e., execution time reduction) in order to meet recent mobiles’ applications’ requirements. First, a dynamic key, changed for every input image is generated and used as the basis to construct the substitution and diffusion processes. Then, the encryption process is performed by the transmitter based on a non-linear S-box (substitution) and a matrix multiplication (diffusion), applied on each sub-matrix of the image. At the destination side, decryption is applied in the reverse order. We have conducted several series of experiments to evaluate the effectiveness of the proposed scheme. The obtained results validated the robustness of our scheme against all considered types of attacks and showed an improvement in terms of execution time reduction compared to the recent existed image-encryption schemes.     

Tristable switching of the electrical conductivity through graphene quantum dots sandwiched in multi-stacked poly(methyl methacrylate) layers

Tristable switching nonvolatile memory (NVM) devices based on graphene quantum dots (GQDs) sandwiched between multi-stacked poly (methyl methacrylate) (PMMA) layers were fabricated on indium-tin-oxide (ITO)-coated glass substrates by using a solution-processed method. Current-voltage (I-V) curves at 300 K for the silver nanowire/PMMA/GQD/PMMA/GQD/PMMA/ITO/glass devices showed tristable switching currents with high-resistance, intermediate-resistance, and low-resistance states. The device's cycling endurance of the three resistance states remained stable with a distinguishable value for each resistance state over 1000 cycles, and the obtained retention results showed well-distinguished resistance states without degradation for up to 1 × 10⁴ s. Schottky emission, Poole-Frenkel emission, trapped-charge limited-current, and ohmic conduction were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I-V characteristics. The described energy-band diagrams confirm the proposed conduction band mechanisms.     

基于RSM与GA的汽车后备箱盖板成形工艺参数多目标优化

针对某车型的后备箱盖板拉延成形时出现的破裂和起皱现象,首先,基于DYNAFORM建立后备箱盖板的有限元模型;其次,探究压边力x1、拉延筋1的阻力x2和拉延筋2的阻力x3对后备箱盖板拉延成形的综合影响,建立中心复合试验设计(CCD)方案,通过中心复合试验设计方案构建了影响成形的工艺参数的二阶响应面法(RSM)模型,以板料的最大减薄率y1和最大成形力y2为优化目标,建立多目标优化函数;运用改良型的遗传算法(GA)进行模型寻优,获得影响后备箱盖板成形的最佳工艺参数组合,即x1=520.05 kN,x2=80.03 N·mm,x3=82.18 N·mm;最后,对最佳工艺参数组合进行试验验证,试验结果表明,提出的方法可有效地提高汽车后备箱盖板的成形质量,同时对类似覆盖件的成形质量控制具有一定的指导意义。     

Polyaniline-graphene composites with a three-dimensional array-based nanostructure for high-performance supercapacitors

The ordered three-dimensional arrays conjugative polyaniline–graphene composites were fabricated through in-situ chemical oxidative polymerization of aniline in the presence of amino-functionalized graphene sheets (AFG), in which polyaniline (PANI) polymerization is initiated by those amino groups on graphene. Therefore, the resulting PANI nanorod arrays are integrated into a large conjugative frame based on chemical covalent bond incorporation. The structure and properties of these resulting composites were characterized and evaluated by combining Fourier transform infrared spectroscopy, Ultraviolet–visible absorption spectroscopy, Raman spectroscope, X-ray diffraction spectroscopy analyses and electrochemical techniques. Morphology was studied by scanning electron microscopy. It was found that the density and size of ordered PANI nanorod arrays can be manipulated by simply varying the amount of AFG. Such resultant composite exhibits high special capacitance, together with low electrical resistance and excellent cycling stability attributed to conjugative covalent bonds and ordered PANI nanorod arrays. Meanwhile, a new time-dependent heterogeneous nucleation mechanism was proposed and investigated in detail.     

Rapid diffusion bonding of WC-Co cemented carbide to 40Cr steel with Ni interlayer: Effect of surface roughness and interlayer thickness

WC-Co cemented carbides were rapidly diffusion bonded to 40Cr steels with pure Ni as interlayers by utilizing plasma activated sintering (PAS). The bonding was carried out at 750 °C for 13 min under a pressure of 40 MPa. It was found that the roughness of the initial surfaces still plays an important effect on the microstructure and mechanical behavior of the joints diffusion bonded by PAS irrespective of the electric current applied during bonding. The adoption of smoother original surfaces was significantly favorable to eliminate the interfacial interstices and microvoids. Correspondingly, the shear strength of the diffusion bonded joints increased with decreasing surface roughness. Additionally, the effect of interlayer thickness on the shear strength of the joints was also evaluated, and the results showed that the strength decreased sharply when thicker interlayer was employed. A maximum value of shear strength, 293.07 MPa, was obtained when the original surfaces was ground with P1200 grit SiC paper and at the same time 50 µm thick interlayer was used. In this case, the fracture initiated and run predominantly along the bonding interfaces instead of in the WC-Co substrate.     

持久疏水涂层织物的制备及其油水分离性能研究

以甲基三乙氧基硅烷（ MTES）为原料,采用溶胶 -凝胶法,在 MTES溶胶中引入端羟基聚二甲基硅氧烷（ PDMS-OH）柔性疏水链段,制得聚硅氧烷凝胶,研究了柔性疏水链段对聚硅氧烷凝胶的柔韧性及疏水性的影响;采用浸渍涂覆的方法,在聚酯织物表面负载聚硅氧烷凝胶,固化后制备得到涂层织物。采用红外光谱（ FT-IR）、抗弯模量和水接触角,对聚硅氧烷凝胶及织物涂层的结构、柔韧性、疏水稳定性及其耐久性进行表征。结果表明： PDMS-OH能够大幅提高涂层织物的柔韧性和疏水性,在聚硅氧烷溶胶中,加入 0. 10 mol端羟基含量为 8. 5%的 PDMS-OH时,涂层织物的静态水接触角可达到（ 138±2）°,且具有持久的稳定性;同时,油水分离实验结果表明,制备的涂层织物可以实现以正己烷、苯和苯胺为代表的烷烃、芳香烃类等油水混合物的有效分离。     

Sintering of high-entropy nanoparticles obtained by polyol process: A case study of (La0.2Y0.2Nd0.2Sm0.2Gd0.2)2Ce2O7-δ

High-entropy (HE) ceramics nanoparticles have received much attention due to their interesting properties. However, very limited studies have been conducted on their sintering. Here, we report the sintering behavior of HE A₂B₂O₇ type rare earth oxide nanoparticles obtained by polyol process. HE cerate (HECe) (La_0.2Y_0.2Nd_0.2Sm_0.2Gd_0.2)₂Ce₂O_7-δ is chosen as an exemplary case, which is considered as a good candidate for thermal insulation. HECe nanoparticles with size of 2.6–7.1 nm can be synthesized through polyol process followed by annealing in air at 300–700 °C. HECe nanoparticle compact can be densified by directly sintering at 1500 °C. The sintering temperature could be further decreased using a two-step sintering process, i.e., 1500 °C 5 min-1300 °C 5 h. Our results show that fine particle and abundant oxygen vacancies probably dominate the densification process. By controlling the sintering regime, we can tune the microstructure of HECe ceramics and thermal conductive properties accordingly.     

增塑熔纺聚丙烯腈纤维的预氧化过程

以增塑熔纺聚丙烯腈(PAN)纤维为研究对象,借助于傅里叶变换红外光谱对其结构以及预氧化过程中官能团的变化进行了分析研究,并进一步研究了预氧化温度和时间对反应程度的影响。研究结果表明:熔纺PAN纤维在纺丝过程中已发生了部分环化,其环化度为0.18;反应程度随着预氧化温度的升高逐渐增大,但在230℃之后变化不明显;预氧化时间对预氧丝的反应程度具有类似的影响,在预氧化20 min时反应程度迅速增大,但进一步延长预氧化时间,预氧丝的反应程度增幅较小。     

Highly active nitrogen-doped few-layer graphene/carbon nanotube composite electrocatalyst for oxygen reduction reaction in alkaline media

In this work the electrocatalysis of oxygen reduction on nitrogen-doped few-layer graphene/multi-walled carbon nanotube (FLG/MWCNT) composite catalyst has been investigated. These composite materials were prepared from different nitrogen precursors, acid-treated MWCNTs and graphene oxide (GO), which was synthesised from graphite by the modified Hummers’ method. Urea and dicyandiamide were used as nitrogen precursors and the doping was achieved by pyrolysing the mixture of GO and MWCNTs in the presence of these nitrogen-containing compounds at 800 °C. The N-doped composite catalyst samples were characterised by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was studied in 0.1 M KOH on glassy carbon electrodes modified with N-doped FLG/MWCNT electrocatalysts employing the rotating disk electrode (RDE) method. The RDE results indicated that these metal-free nitrogen-doped nanocarbon catalysts possess remarkable electrocatalytic activity towards the ORR in alkaline media similar to that of commercial Pt/C catalyst. The results obtained in this work are particularly important for the development of non-Pt cathode catalysts for alkaline membrane fuel cells.