Preparation and characterization of Si3N4/SBR nanocomposites with high performance

In this work, native silicon nitride (Si₃N₄) nanoparticles were modified by macromolecular coupling agent (LMPB-g-MAH) which was designed and synthesized according to the chain structure of styrene butadiene rubber (SBR), and Si₃N₄/SBR nanocomposites were prepared by two-segment mixing process. The structure and surface properties of modified Si₃N₄ nanoparticles were characterized by Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR), size distribution analyzer, and contact angle measuring instrument. The effect of different dosage of nano-Si₃N₄ on Si₃N₄/SBR nanocomposites was also systematically studied. It can be got that LMPB-g-MAH can effectively inhibit the agglomeration and improve the hydrophobic property of Si₃N₄ nanoparticles. It also can be found that modified Si₃N₄ nanoparticles brings well physical and dynamic mechanical properties, aging resistance, oil resistance, wear resistance, and low rolling resistance to SBR, especially, when the dosage is 0.5–1.5 phr, the best overall performance of Si₃N₄/SBR nanocomposites can be achieved.     

The dielectric properties of epoxy/AlN composites

In this paper, AlN ceramic powder is chosen to be mixed with epoxy to form epoxy/AlN composites, the effects of the content of AlN filler on the physical and dielectric properties of epoxy/AlN composites are developed. From the SEM observation, the particles of self-synthesized AlN powder, obtained by using combustion method, is less uniformity and the average particle size is about 3.12 μm. Only the AlN phase can be detected in the XRD patterns of the epoxy/AlN composites. The more AlN powder is mixed with epoxy, the higher crystal intensity of AlN phase will exist in the XRD patterns. As the content of AlN powder in the epoxy/AlN composites increases from 5 to 40 wt.%, the dielectric constant increases from 6.52 to 7.28 (measured at 1 MHz). The loss tangent of epoxy/AlN composites is slightly increased as the measured frequency increases. Moreover, the epoxy/AlN composites in this investigation show less pores as compared to other literatures. The results indicate that the fabrication process has an apparent effect on the decrease of porosities, and the composites with a low porosity will lead to a low loss tangent.     

Brown ceramic pigments based on chromium(III)-doped titanite obtained by spray pyrolysis

Cr-doped titanite (CaTiSiO₅) pigments were synthesized through spray pyrolysis of aerosols generated from aqueous solutions containing colloidal silica, calcium chloride, titanium(IV) oxychloride and chromium(III) nitrate. This process yielded amorphous powders with spherical morphology and broad size distribution (<10 μm) after thermal decomposition at 600 °C. The titanite phase was obtained by further calcination at 800 °C without any addition of flux agents. The brown color of the pigments can be attributed mainly to the existence of Cr(IV) ions occupying both, octahedral positions of Ti(IV) and tetrahedral position of Si(IV), together with a small amount of Cr(III) present as Cr₂O₃. The optimum pigment obtained by this method corresponded to a Cr/titanite mole ratio of 0.04.     

Mathematical modelling of the heat behaviour in the ceramic chamber furnaces at different temperature baking curves

Herewith an algorithm for a determination of the shortest baking regime for ceramic articles in chamber furnaces is proposed. It is based on mathematical modelling and numerical investigation of the baking process. The algorithm is tested through an example solution for a real working furnace.     

One-step,in situ growth of unmodified graphene – magnetic nanostructured composites

Development of composite materials that combine the superior electronic properties of graphene with magnetic functionality is highly desirable as can open new doors for graphene applications. However, attempts to grow such structures typically result in significantly reduced graphene quality due to processing required for the graphene formation and/or magnetic functionalization. We report a magnetic graphene material consisting of 2–5 graphene layers encapsulating magnetic nanoparticles, produced in one step without any chemical modification or post-treatment, using a dual-action ferrofluid catalyst/carbon chemical vapor deposition (CVD) precursor. The resulting composite exhibits high quality, as evidenced by Raman spectroscopy, since the properties of as grown pure graphene are fully preserved, coupled to magnetic sensitivity, as evidenced by Mossbauer and magnetic measurements, originated from the encapsulated Fe-based nanoparticles. Notably, the material is stable due to particle encapsulation by the graphene layers, while the fabrication is simple and carried out by CVD which is widely used in the microelectronics industry thus favoring scalability towards applications that include magnetoelectronics, high-density data storage, magnetic nanodevices, and electrochemical energy storage and supply.     

The numerical analysis of the radial sleeve bearing with combined surface slip

In order to improve the carrying capacity and reduce the temperature rise in high speed and precise spindle systems, a combined surface radial sleeve bearing using the interfacial slip technique was discussed. An extended Reynolds equation was derived based on the modified slip length model considering the limiting shear stress. By means of the finite differential methods, the characteristic analysis and optimization of the slip region of the combined surface sleeve bearing were carried out, and it has been proved that there is still a considerable large load support in a parallel sliding gap. Comparing with the general journal bearing, the load capacity and end leakage rate of the combined surface sleeve bearing can be increased greatly and the load capacity can be increased by 1.75 times. The attitude angle, friction drag, temperature rise of the combined bearing can be decreased distinctly and the temperature rise can be decreased by 92.4%.     

Nano-explosion synthesis of multi-component ceramic nano-composites

Here we demonstrate a unique processing technique which is based on engineering multi-component ceramic nanopowders and composites with precise morphology by nano-explosive deagglomeration/calcination. Multiple nano-explosions of impregnated cyclotrimethylene trinitramine deagglomerate the nanopowder due to the highly energetic impacts of the blast waves, while the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during the nano-explosions. We applied this technique to produce nanosize agglomerate-free ceria–gadolinia solid solution powder with uniform morphology and an average aggregate size of 32 nm, and 8 mol% yttria-doped zirconia aggregates with an average size of 53 nm impregnated with platinum (2–14 nm).     

纳米压痕技术在材料力学测试中的应用

近年来,材料纳米级力学测试日益引起广大研究者的重视。纳米压痕仪凭借极高的载荷和位移分辨率,广泛应用于材料表面的微纳米级力学性能的测试,包括硬度、弹性模量、塑性应变、薄膜界面结合强度以及材料疲劳特性等。综述了几种纳米压痕和纳米冲击技术测试材料力学性能的方法和原理,介绍了纳米压痕技术在材料力学性能测试方面的若干先进应用实例及其测试机理,以及原子力显微镜和扫描探针显微镜在力学测试方面的原理和应用。最后,提出了纳米压痕仪存在的若干问题,并对纳米压痕技术的发展进行了展望,认为纳米压痕技术结合有限元模拟建立材料疲劳断裂模型,是纳米压痕在力学测试方面发展的必然趋势。     

Exploring the potential of the fabrication of large-size mirror facet for semiconductor laser bar utilizing mechanical cleavage

While mechanical cleavage technology is an ideal alternative approach to fabricate large-size mirror facets for high-power laser bar, there has been little scientific understanding of mechanical cleavage mechanisms. To fill this gap, cleavage experiments were designed according to the Taguchi method for analyzing the main effects of three parameters. Surface and subsurface cracks and cleavage plane morphology are analyzed as well. The results show that scribing load has significant impact on the scratch morphology as compared with other parameters, and quadratic polynomial models are formulated to predict kerf width and maximum damage width values. For scribing along the [0−1−1] direction on the (100) GaAs wafer, the subsurface cracks are TLC and LC which propagate along [0-11] direction and MC which propagates along [100] direction. The achieved optimal combination of parameters are scribing load of 10 g, scribing speed of 20 mm/s and scribing length of 0.6 mm. The undamaged length of cleaved planes can reach 11.77 mm. Our results demonstrate that mechanical cleavage is a powerful technique which could guide actual production and manufacturing field of high-power GaAs-based laser bars.