Comparison between microwave and thermal curing of a polyimide adhesive end-caped with phenylethynyl groups

Microwave energy was investigated to cure phenylethynyl-end-capped polyimide adhesive using an industrial microwave oven at a frequency of 2.45 GHz and the adhesive properties, thermal performance and curing mechanism for bonding stainless steel were evaluated. The results are compared with those of thermal cured samples. It was demonstrated that while the lap shear strength properties and thermal performance of microwave cured samples were almost as good as those cured via a thermal process, the microwave curing process resulted in a significant reduction in the process cycle time and power consumption. The Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis of the cured resin structures suggested that there was no obvious difference in the chemical reactions taking place during the microwave and the thermal cure processes.     

Strain sensitivity of nickel-containing amorphous hydrogenated carbon (Ni:a-C:H) thin films prepared by r.f. sputtering using substrate bias conditions

Thin films of nickel-containing amorphous hydrogenated carbon Ni:a-C:H were deposited by means of a reactive r.f. powered sputter process with different argon/ethene gas mixtures. The amount of incorporated nickel, measured by energy dispersive X-ray analysis (EDX) and the electrical conductivity of the films were obtained as a function of the ethene concentration in the processes, showing that the conductivity is strongly dependent on the nickel concentration in the films and may be varied over 8 orders of magnitude.The temperature coefficient of resistivity (TCR) and the strain sensitivity in terms of the gauge factor were measured for films under various process conditions. It turned out that low TCR values (300 ppm/K) and higher gauge factors of approx. 8 could be produced simultaneously, yet only with the help of an additional substrate r.f. bias power. In addition the long term stability of the produced resistors was improved by means of substrate bias sputtering. Therefore these films proved to be very promising candidates as strain gauge devices for sensors able to measure mechanical quantities such as pressure, force, weight and torque.     

莫来石/SiO2复合涂层的制备及微观组织研究

以天然红柱石为原料,采用高温煅烧使其发生莫来石化转变,然后经喷雾造粒、热处理,得到热喷涂用球形莫来石/SiO2复合粉末.采用大气等离子喷涂工艺在1Cr18Ni9Ti不锈钢上喷涂莫来石/SiO2粉末制得涂层,对涂层的微观组织、硬度和相成分进行了分析.研究结果表明:天然红柱石粉末莫来石化后,其相组成主要为莫来石和游离态SiO2喷雾造粒粉末在1 000℃热处理后,松装密度得到改善;涂层具有良好的微观形貌,表面显微硬度较高,主要由莫来石、石英和非晶玻璃相构成.     

芳纶纤维增强丁腈橡胶的摩擦性能

研究了芳纶纤维增强丁腈橡胶(NBR)复合材料的物理机械性能和摩擦性能,并用扫描电子显微镜分析了芳纶纤维增强NBR复合材料的磨损表面和磨屑形貌。结果表明,芳纶的加入提高了NBR的拉伸强度;随着芳纶用量的增大,复合材料的扯断伸长率降低;芳纶的加入降低了NBR的摩擦系数和磨损率;当芳纶用量为20份时,复合材料的综合性能最佳。加入芳纶对NBR摩擦磨损形式的改变是NBR摩擦性能提高的重要原因。     

季戊四醇油酸丙烯酸混合酯的合成及性能研究

以季戊四醇、丙烯酸、油酸为原料通过两步法合成一系列黏度可控的混合酯,利用红外光谱表征混合酯的化学结构,考察混合酯的黏温性能、摩擦磨损性能、热稳定性、挥发损失和铜片腐蚀性能。研究结果表明:所合成的混合酯黏度范围宽,40℃时的黏度在73~483 mm2/s之间,黏度指数约180,倾点在-36~-20℃之间;混合酯的分解温度超过400℃,挥发损失低,铜片腐蚀轻微,是一类性能优良的合成酯类油。     

Origin of frictional ageing by molecular dynamics simulation of a silicon tip sliding over a diamond substrate

In this paper, frictional ageing is investigated through simulating a silicon tip sliding over a diamond substrate with a molecular dynamics model. It is demonstrated that contact strengthening in ultra-high vacuum is mainly caused by surface dimerization. With the increase of temperature, tip-substrate contact evolves from incommensurate to commensurate due to the lattice transition from $\left(1\times 1\right)$ to $\left(2\times 1\right)$ lattice ordering. The combination effects of contact strengthening and thermal lubrication lead to a nonmonotonic variation of the mean friction force with temperature rise. However, the friction increase trend induced by the surface dimerization can be suppressed efficiently with the structural lubrication.     

The preparation of CeF3 nanocluster capped with oleic acid by extraction method and application to lithium grease

CeF₃ nanocluster surface-capped with oleic acid (coded as OA-CeF₃) were prepared using extraction method. The resulting OA-CeF₃ nanocluster was characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformation infrared spectrometry (FTIR), and X-ray photoelectron spectroscopy (XPS). The effect of the OA-CeF₃ nanocluster as an additive in synthetic lithium grease was investigated using a four-ball friction and wear tester. It was found that the as-prepared OA-CeF₃ nanocluster had a broad size distribution, with the average diameter to be about 20 nm, which was confirmed by both the XRD and TEM analytical results. The oleic acid as the capping agent was chemically bonded to the CeF₃ nanocores via strong chemical interaction. The OA-CeF₃ nanocluster as the additive led to an obvious improvement in the antiwear and extreme pressure properties of the synthetic lithium grease. However, the OA-CeF₃ nanocluster as the additive had little effect on the friction-reducing behavior of the lithium grease.     

钢/镍钛合金下乙二醇的摩擦化学反应研究

在万能摩擦试验机上采用钢/镍钛合金、钢/铝和钢/钢摩擦副进行乙二醇的摩擦化学反应研究;采用紫外光谱(UV)、傅立叶变换红外光谱(FT-IR)和核磁共振光谱(1HNMR)对摩擦产物进行分析.结果表明:乙二醇在钢/镍钛合金摩擦副表面发生摩擦化学反应,生成含有碳碳双键的化合物,而在钢/铝及钢/钢摩擦副表面不发生摩擦化学变化;在试验条件中,速度是影响摩擦化学反应的主要因素,而载荷对摩擦化学反应影响较小.     

Friction and wear properties of NBR/PVC composites

Acrylonitrial butadiene rubber (NBR)/Polyvinyl chloride (PVC) composites with different PVC content were prepared. The effect of PVC content on the mechanical strength and tribological properties of the NBR/PVC composites was investigated. The morphologies of the worn traces and debris of NBR/PVC composites and worn traces of mating ball were observed using a scanning electron microscope (SEM). It was found that the friction and wear of NBR/PVC was lower than that of NBR without PVC. The NBR/PVC composite with 30% PVC content showed the best synthetic mechanical and tribological properties. The inferior elastic properties and the lesser deformation under the applied load of composites with PVC resulted in hysteric force and adhesion force decrease, which leading to a lower friction and wear of NBR/PVC composites. The frictional failure unit of NBR70/PVC30 composite being smaller should be an important reason of the wear of the composite being lowest. The lubricating effect of PVC played an important role in decreasing the friction coefficient and wear of NBR/PVC composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007