分子模拟纳米ZnO/丁腈橡胶复合材料的摩擦学行为

采用分子模拟的方法研究了纳米ZnO/丁腈橡胶（NBR）复合材料的摩擦学行为,考察了纳米ZnO/NBR复合材料的回转半径、原子相对浓度和剪切行为,探讨了纳米ZnO/NBR复合材料摩擦学行为的微观机制。结果表明:与纯NBR材料相比,纳米ZnO/NBR复合材料具有更小的回转半径,橡胶分子链的柔顺性下降;与纳米ZnO/NBR复合材料相比,纯NBR材料摩擦界面具有更高的原子相对浓度,纯NBR材料上下摩擦表面的原子浓度峰值比纳米ZnO/NBR复合材料分别高了6.4%和4.3%。说明纳米ZnO的存在提高了纳米ZnO/NBR复合材料分子链的刚性,减小了能量耗散,从而改善了纳米ZnO/NBR复合材料的摩擦性能。      

基于逆变技术的200 A弧焊电源变压器设计

为了促进弧焊技术的快速发展,提高弧焊电源变压器的工作效率与动态响应速度显得至关重要.基于逆变技术设计研发出一套200 A中频弧焊电源变压器,讨论了逆变弧焊电源变压器的结构和工作特点.根据弧焊电源的电路结构和工作原理,选择了弧焊电源电路,研究了不同铁芯材料对变压器电磁性能的影响,提出了变压器铁芯的设计方法,并对变压器性能的影响因素进行了分析与计算.结果表明,所提设计方法的元器件消耗量较小,但可实现性较高.     

喷涂粒子飞行路径的高速摄像分析及计算模拟

为了满足采用等离子喷涂时获得最佳喷涂质量的要求,利用高速摄像系统对等离子喷涂过程中粒子的飞行路径进行拍摄,将得到的图片进行分析研究,得到粒子的运动速度和轨迹,与计算模拟结果相对比,以确定最优化的喷涂工艺参数.结果表明:随着喷涂电流的增加,喷涂粒子的速度升高; 而随着喷涂主气流量的降低,喷涂粒子的速度有所下降.图片分析结果与计算结果相符合,为选择等离子喷涂的最佳工艺参数和获得高质量的涂层提供了理论依据.     

Roll-formability of cryo-rolled ultrafine aluminium sheet

Ultrafine-grain aluminium sheet was produced by rolling at cryogenic (CR) and at room temperature (RTR). Commercial purity aluminium plate was reduced in 30 passes from an initial material thickness of 10 mm to a final thickness of 2 mm (80% reduction). Tensile stress and strength were significantly increased while total elongation was drastically reduced. It was found that despite the low tensile elongation both materials are able to accommodate high localised strains in the neck leading to a high reduction in area. The formability of the material was further investigated in bending operations. A minimum bending radius of 6 mm (CR) and 5 mm (RTR) was found and pure bending tests showed homogeneous forming behaviour for both materials. In V-die bending the cryo-rolled material showed strain localisations across the final radius and kinking of the sample. It has been found that even if the total elongation in tension is close to zero leading to early failure in V-die bending, ultra-fine grained and low ductile sheet metals can be roll formed to simple section shapes with small radii using commercial roll forming equipment.     

S-scheme g-C3N4/TiO2/CFs heterojunction composites with multi-dimensional through-holes and enhanced visible-light photocatalytic activity

A novel multi-dimensional through-holes structure of g-C₃N₄ with adjustable pore size was prepared by controlling the mass ratio of oxamide (OA, structure guiding agent) to urea during one-step calcination process, and a break-rearrangement mechanism was explored. Then, a series of porous g-C₃N₄/TiO₂ (CT) composites with uniformly deposited TiO₂ nanoparticles were prepared based on the multi-dimensional framework by a facile hydrothermal method. The results show that a new S-scheme heterojunction with multi-dimensional through-channel structure was obtained, which is particularly desired for enhancing the visible-light utilization, reducing the carrier recombination rate and enhancing redox capacity. The CT composite obtained at hydrothermal treatment time of 2 h has a specific surface area of 180.15 m² g^-1, which shows high degradation capability (99.99%) for tetracycline hydrochloride (TC·HCl) under 350 W Xe lamp irradiation for 90 min. In addition, CT nanostructures was in-situ growth on carbon fiber (CFs), the degradation rate constant is 0.1566 min^-1, and 90% of the degradation efficiency can be maintained even after 5 consecutive cycles. It is expected to provide an effective reference for solving the problems of recovery difficulty and low reuse rate of powder photocatalytic materials.     

Synthesis and photocatalytic activity of nano-sized iron oxides

Nano-sized iron oxide powder with average crystallite sizes 35, 100 and 150 nm was prepared by thermal evaporation and co-precipitation techniques. The synthesized powders were characterized by X-ray diffraction analysis technique, transmission electron microscope (TEM) and scanning electron microscope (SEM). The prepared powders were tested as catalysts for the photo catalytic decomposition of Congo red dye. The effect of crystal size of iron oxides on the rate of decomposition of Congo red dye was investigated in visible light as well as in the absence of light. The experimental results show that both iron oxides with crystallite size 35 and 150 nm cause complete decomposition of Congo red dye while iron oxide particles with crystallite size 100 nm were unable to decompose the dye.     

Electrochemical Cycled Structure of MnV2O6 Nanoribbons Synthesized via Hydrothermal Route

1 Introduction Low-dimensional nanostructures, such as nanorods, nanowires, and nanotubes, have received much attention for their superior optical, electrical, catalytic and magnetic properties.     

Influence of electroless nickel-plating on fracture toughness of pitch-based carbon fibre reinforced composites

Nickel-Pitch-based carbon fibres (Ni-PFs) were prepared by electroless nickel-plating to enhance fracture toughness of Ni-PFs reinforced epoxy matrix composites (Ni-PFs/epoxy). The surface properties of Ni-PFs were determined by scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), and X-ray diffraction (XRD). The fracture toughness of the Ni-PFs/epoxy was assessed by critical stress intensity factor (K_IC) and critical strain energy release rate (G_IC). The fracture toughness of Ni-PFs/epoxy was enhanced compared to those of PFs/epoxy. These results were attributed to the increase of the degree of adhesion at interfaces between Ni-PFs and matrix resins in the composites.     

Microstructural and mechanical properties of jointed ZrO2/Ti–6Al–4V alloy using Ti33Zr17Cu50 amorphous brazing filler

Ceramic ZrO₂ and metallic Ti–6Al–4V alloy are jointed by using a Ti₃₃Zr₁₇Cu₅₀ (at.%) amorphous alloy as a solder at 1123–1273 K in a high vacuum. It is demonstrated that the microstructure and mechanical properties are significantly influenced by the brazing temperature, the heat time and the cooling rate. The brazing seam jointing ZrO₂ with Ti–6Al–4V is composed of ZrO₂/Cu₂Ti₄O, (Ti,Zr)₂Cu/TiO, Ti₂O/CuTi₂, (Ti,Zr)₂Cu/CuTi₂/Ti–6Al–4V alloys and compounds, of which the increasing thickness weakens the shear strength as the brazing temperature, the heat time the cooling rate increase. The maximum shear strength of the brazing joints reaches 162 MPa with the optimal technical parameters: the brazing temperature of 1173 K, the heat time of 10 min and the cooling rate of 5 K/min. The fracture of the joint occurs in the brittle seam layer nearby the side of ZrO₂.     

混沌流微混合器的性能优化

为提高低雷诺数层流条件下被动式微混合器的效率,依据"三维马蹄变换"数学模型,对流体进行"挤压拉伸""弯曲折叠""二次折叠"和"逆变换-交集"操作,得到了一款包含6个混合单元,总长度为15 mm的混沌流微混合器.仿真研究表明:在"低流速-扩散主导"阶段u=2×10-4 m/s时,t=300 s后混合器进入稳定混合状态,出...