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排序方式: 共有449条查询结果,搜索用时 31 毫秒
101.
In this study, we investigate the interfacial mechanical characteristics of carbon nanotube (CNT) reinforced epoxy composite using molecular dynamics (MD) simulations. The second-generation polymer consistent force field (PCFF) is used in the MD simulations. In particular, we compare MD results with those obtained by atomistic-based continuum (ABC) multiscale modeling technique, which makes use of the appropriate constitutive relations derived solely from interatomic potentials. The results of our comparative investigation suggest that (i) the ABC multiscale model and MD simulation provides almost identical predictions for the interfacial properties of the nanocomposite for smaller diameter of CNTs, (ii) the ABC model slightly over predict the interfacial properties of the nanocomposite for larger diameter of CNTs, and (iii) the MD simulations represents the real nanocomposite structure with the minimum assumptions compared to that of the ABC multiscale model but with much greater computer requirements and limited length scale. 相似文献
102.
《Journal of the European Ceramic Society》2007,27(11):3331-3337
Commercial nanocrystalline yttrium aluminum garnet (nc-YAG) powders were used for fabrication of dense and transparent YAG by spark plasma sintering (SPS). Spherical 34 nm size particles were densified by SPS between 1200 and 1500 °C using 50 and 100 MPa pressures for 3, 6, and 9 min durations. Fully dense and transparent polycrystalline cubic YAG with micrometer grain size were fabricated at very moderate SPS conditions, i.e. 1375 °C, 100 MPa for 3 min. Increase in the SPS duration and pressure significantly increased the density especially at the lower temperature range. The observed microstructure is in agreement with densification by nano-grain rotation and sliding at lower densities, followed by curvature driven grain boundary migration and normal grain growth at higher densities. Residual nanosize pores at the grain boundary junctions are an inherent microstructure feature due to the SPS process. 相似文献
103.
《Applied Catalysis A: General》2007,316(2):240-249
The anodic oxidation under spark discharge (ANOF technique) is presented as a promising alternative for the preparation of catalytic oxide layers on metallic supports. The influence of the substrate (Al, Ti, and Mg), electrolyte composition and the treatment time to obtain egg-shell catalysts with tailor-made properties for the effective oxydehydrogenation (ODH) of cyclohexane to cyclohexene is studied. Chromium, molybdenum and nickel were chosen as precursors for active species in order to obtain catalysts able to perform the substrate oxidation by electrophilic (chromium oxide), nucleophilic (molybdena) or both kind of oxygen species (nickel oxide). It was found that compared to nickel oxide, the chromium oxide containing egg-shell catalyst was less selective while the molybdenum oxide showed very high selectivity, but lower activity. The intrinsic activity of nickel containing egg-shell catalysts is an order of magnitude higher than that of a classic alumina supported nickel oxide catalyst obtained by impregnation. The selectivity to the intermediate cyclohexene is also favored on the egg-shell catalyst with a regular pore structure. Moreover, the selectivity performance of the catalysts can be improved by designing catalysts with shorter pores. 相似文献
104.
《Inorganic chemistry communications》2007,10(11):1325-1329
Two heterometallic Cu/Mn complexes [Cu(Me2en)2][Mn2(ox)3] · 2H2O (1) (Me2en = N,N-dimethylethylenediamine, H2ox – oxalic acid) and [Cu(1,3-pn)(ox)(H2O)][Mn(ox)(H2O)2] · H2O (2) (1,3-pn = 1,3-diaminopropane) are prepared by the one-pot reaction of copper powder, tetrabutylammonium permanganate, oxalic acid and N-chelating ligands. Their structures are investigated by single-crystal X-ray analysis that reveals interesting variation in bridging motives of the oxalate groups composing the Mn-polymeric fragments. 相似文献
105.
《International Journal of Hydrogen Energy》2020,45(41):21473-21482
In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates Fe2P phase at 300 °C and FeP phase at 350 °C. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were carried out at elevated temperatures. Annealing at 500 °C under reductive atmosphere induced structural changes in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500 °C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe2P/FeP−500 °C). Pure Fe2P films was prepared under argon atmosphere at 450 °C (Fe2P−450 °C). The electrocatalytic activities of heat-treated Fe2P−450 °C, Fe3P−500 °C, and Fe2P/FeP−500 °C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H2SO4. The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm−2 was achieved with Fe2P/FeP−500 °C catalyst. 相似文献
106.
107.
目的 提高燃气轮机叶片材料镍基高温合金GH80A的抗高温氧化性能。方法 利用强流脉冲电子束(High-Current Pulsed Electron Beam, HCPEB)技术对GH80A合金进行表面处理。研究HCPEB辐照前后GH80A的微观结构变化及在850 ℃恒温氧化后的氧化动力学行为及氧化机制。利用光学显微镜、X射线衍射仪和扫描电子显微镜对HCPEB诱发的微观结构和氧化产物进行了表征。结果 HCPEB辐照后,GH80A合金表面发生熔化,形成厚约3 μm的重熔层,重熔层内形成大量的位错滑移,且晶粒明显得到细化。850 ℃高温氧化实验结果表明,氧化100 h后,原始样品氧化增重最大,生成的氧化膜较厚,且存在大量裂纹,所生成的Cr2O3发生了挥发,导致氧化膜疏松多孔,基体发生了严重的内氧化。HCPEB辐照20次后,样品氧化增重最小,100 h氧化后形成的氧化膜主要由外层TiO2和内层Cr2O3构成。外层连续致密的TiO2抑制了保护性氧化膜Cr2O3的挥发,因此生成的Cr2O3氧化膜连续、致密、无剥落,对基体起保护作用。结论 HCPEB辐照后,GH80A合金的抗高温氧化性能明显提升,20次辐照样品的抗高温氧化性能最佳。 相似文献
108.
WC-7Co硬质合金放电等离子烧结工艺 总被引:1,自引:0,他引:1
采用放电等离子烧结(spark plasma sintering,SPS)技术制取WC-7Co硬质合金。研究了烧结温度、烧结压力对烧结WC-7Co硬质合金力学性能的影响,探讨了最佳烧结热压比,分析了粉末烧结致密化过程和晶粒长大机制。结果表明,WC-7Co硬质合金在1150℃烧结时,随着压力的增加,烧结致密性呈现先增加后降低的变化趋势,在30 MPa时可获得最佳烧结致密性。在升温速率为100℃/min,保温时间为5 min,烧结温度为1150℃,热压比为38℃/MPa的工艺条件下,利用SPS技术可制备组织致密、综合力学性能良好的WC-7Co硬质合金。 相似文献
109.
Qing Yuan Nan Li Wangchang Geng Yue Chi Xiaotian Li 《Materials Research Bulletin》2012,47(9):2396-2402
A simple and efficient method has been developed to fabricate core–shell structured Fe3O4@SiO2@meso-TiO2 nanocomposites with enhanced photocatalytic activity in this paper. The as-made core–shell structure is composed of a central magnetite core with a strong response to external fields, an interlayer of SiO2, and an outer layer of TiO2 nanocrystals with mesoporous structure. Fe3O4@SiO2 was obtained through a sol–gel process. To avoid magnetic loss caused by magnetite core phase transition and particle reunion, we adopt a mild synthetic method to get anatase shell instead of traditional high-temperature calcination. The structure of resulting composites was characterized and their photocatalytic activities were also tested. Fe3O4@SiO2@meso-TiO2 composite exhibits higher photocatalytic activities than Fe3O4@SiO2@solid-TiO2 for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the high surface area and pore volume created by mesoporous anatase shell. 相似文献
110.
The dielectric properties and electrical response of grain boundaries of Na1/2La1/2Cu3Ti4O12 ceramics were investigated as a function of temperature. High dielectric permittivity (6.1–8.7 × 103) and low loss tangent (0.032–0.038 at 10 kHz) were observed in Na1/2La1/2Cu3Ti4O12 ceramics. Through analyses using complex impedance and electric modulus, it was found that the dielectric properties of Na1/2La1/2Cu3Ti4O12 ceramics are closely related to the electrical response of grain boundaries. The investigation of non-Ohmic characteristics at various temperatures suggests that the potential barrier at the grain boundaries of Na1/2La1/2Cu3Ti4O12 ceramics is due to the Schottky effect. The giant low frequency dielectric response in Na1/2La1/2Cu3Ti4O12 ceramics is attributed to Maxwell–Wagner polarization at the grain boundaries. 相似文献