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111.
Seam tracking is important for butt joint laser welding. A magneto-optical imaging approach is proposed to detect the micro-gap weld whose width is less than 0.2 mm. The symmetry of the magnetic field above the weld joint is an important precondition to ensure the detection accuracy of the magneto-optical imaging method. However, in actual complex industrial scene, it is difficult to guarantee complete symmetry of the magnetic field. This paper proposes an effective method for solving the problem of magneto-optical imaging deviation under an asymmetric magnetic field. Two possible factors causing the asymmetry of magnetic field above weld joint are firstly investigated using finite element analysis. By analyzing the characteristics of the magneto-optic medium used in the sensor and measuring the magnetic field distribution of weld joint at different lift-off height and different excitation voltage, the prediction model of deviation between the weld position detected by magneto-optical imaging and the actual weld position is built by back propagation (BP) neural network. The experimental result of weld seam tracking based on magneto-optical imaging shows that the change of the lift-off height will affect the detection accuracy of the weld position, and sufficient accuracy can be ensured after correcting the deviation according to the prediction model of magneto-optical imaging deviation. 相似文献
112.
《Ceramics International》2017,43(13):10151-10157
Among dense ceramic membranes for H2 separation, the ceramic-ceramic composite ones have recently gained the interest of the scientific community thanks to their enhanced performances. However, the ceramic phases constituting the composite must show high chemical and thermomechanical compatibility to form a crack-free and robust membrane. This work reports the compatibility between the BaCe0.65Zr0.2Y0.15O3−δ (BCZY) proton conductive system and various electron conducting systems belonging to four different families: ceria-based (CeO2 and Ce0.8Gd0.2O1.9), lanthanum nickelate cobaltite (La0.95Ni0.6Co0.4O3−δ), strontium titanate (Sr0.9La0.1TiO3−δ) and the non-oxidic α-SiC. This work highlights how the coupling of BCZY with chemically different electron-conductive ceramics represents a challenging task, since La0.95Ni0.6Co0.4O3, Sr0.9La0.1TiO3 and α-SiC react with the proton conductive perovskite producing many secondary phases in air and in reducing atmosphere after 4 h of permanence at 1400 °C. As may be expected, BCZY is chemically compatible with CeO2 and Ce0.8Gd0.2O1.9 in air and in reducing atmosphere after 4 h of permanence at 1400 °C. Dilatometric results prove the thermomechanical compatibility between BCZY and the ceria-based systems in the operation temperature range. 相似文献
113.
《International Journal of Hydrogen Energy》2014,39(36):21053-21059
Sulfur-free hydrogen production is significant for sustainable energy such as fuel cell to avoid poisoning catalysts. The hollow fiber membrane is proposed as sulfur trapper for the hydrocarbon fuels. Hollow fiber membranes with polyimide (PI) matrix and adsorptive zeolites fillers are fabricated by dry–wet spinning with subsequent imidization process. By detailed investigation of FT-IR, thermal degradation cures, morphology and sulfur trapping performance, the molecular structure, thermostability and adsorption channels of membranes have been analyzed. The hollow fiber membranes have abundant pores, and the zeolites particles are incorporated in the three-dimension polymer matrix. The inlet fuel can be desulfurized to below 0.1 mg L−1, which means that the outlet fuel can be used as sulfur-free hydrogen source for fuel cell applications. Excellent sustainability of the system with hollow fiber configuration show attractive on-board application potential. 相似文献
114.
A hierarchically porous ZIF-67 was successfully synthesized by using non-ionic block copolymers P123 as a supramolecular templating surfactant and 1,3,5-trimethylbenzene (TMB) as a swelling agent. It was noted that TMB was an effective swelling agent to expand the pore size. Pore size distribution analyses reveal that the as-synthesized hierarchical ZIF-67 has a typical trimodal pore size distribution showing simultaneous micro-, meso- and macropore channel systems. Due to the effect of TMB and P123, the diameter of ZIF-67 nanoparticles was about twice of that synthesized with P123 only and larger pores were formed among the enlarged nanoparticles. This strategy is expected to be a facile and efficient method for the preparation of hierarchical ZIF-67. 相似文献
115.
A new bi-oxo capped molybdenum carboxylate, [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+, was synthesized by refluxing [Mo3(μ3-O)2(μ-O2CCH3)6(H2O)3]2 + in chloroacetic acid for 20 h (T = 110 °C). Using ion-exchange chromatography (0.5 M NaClO4 eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 °C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d4, substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is kobs298K = 5.3 × 10− 5 (± 0.3) s− 1 and activation parameters equal to ΔH3 = 130 (± 10) kJ mol− 1 and ΔS3 = 111 (± 33) J mol− 1 K− 1. From the kinetic data, we find that ligand substitution follows a dissociative pathway and that rates of substitution are faster than expected when compared to the molybdenum acetate analog. Herein, we report the synthesis, crystallographic study, and substitution reactivity of a new molybdenum bi-oxo capped cluster with bridging chloroacetate ligands. 相似文献
116.
《Carbon》2014
In order to improve their mechanical properties, carbon open-cell foams of two different pore sizes were infiltrated with pyrocarbon by chemical vapour deposition at reduced pressure and using pure propane as precursor. The optimal conditions in terms of deposition rate and uniformity in coating thickness, structure and anisotropy were first investigated. Foam specimens were infiltrated at various stages, with two pyrocarbons of distinct microtextures and their morphology, relative density and geometrical features were evaluated.Compressive crushing tests were conducted to determine the influence of the pore size, the pyrocarbon type and the relative density on the mechanical properties of the pyrocarbon-infiltrated foams. They retain their non-brittle and dissipating behaviour up to relative densities of 0.15. The stiffness, crushing strength and dissipated energy increase significantly with the relative density. The crushing behaviour of the pyrocarbon-foam specimens can be essentially explained using simple structural models and failure mechanisms, according to the Gibson & Ashby’s approach for brittle cellular solids. 相似文献
117.
《International Journal of Hydrogen Energy》2014,39(36):21601-21612
Direct methanol fuel cells are very promising power sources, but the easy poisoning of the platinum anode electrocatalyst by CO-like reaction intermediates, restricts their industrial application and commercialization. The development of Pt-based alloys or bimetallic catalysts, in which the second metal acts as Pt poisoning inhibitor, is one of the main promising solutions to this problem. In this work we have combined the use of unconventional methods to deposit the catalyst nanoparticles with unconventional carbon supports. Innovative electrodes made of platelet carbon nanofibers, directly grown on graphite paper, as substrate for electrodeposited platinum and gold bimetallic nanoparticles, have been developed. These electrodes allow having a single layer with both the diffusive and catalytic function, and a considerable decrease of noble metals amount (about five times), with consequent large cost reduction. Moreover, the replacement of the conventional ink deposition methods with electrodeposition for platinum and gold dispersion, considerably increases the catalytic activity. The electrocatalytic performance results were encouraging. Gold allows increasing the catalyst poisoning tolerance and then the electrode long term stability. The innovative electrodes show a performance improvement up to three times compared to a commercial carbon substrate electrode (Vulcan XC-72R) with ink-spray deposited PtRu nanoparticles as catalyst. 相似文献
118.
Spiky spherical nickel powders with sharp nanotips on their surface are excellent fillers for developing pressure-sensitive composites. The sharp nano-tips are responsible for generating field-assisted tunneling conduction, which leads to the strong responses of electrical conductivity of the composites to external force or deformation. The nanotip-induced ultrahigh pressure-sensitive composites can be used to develop new sensors, switches and controls for a wide range of applications including electronics, transport, space, medicine, defense, textiles, oil and gas, and civil engineering. In this paper, we examine a systematical review of research progress on the nanotip-induced ultrahigh pressure-sensitive composites, with attentions to mechanism of pressure-sensitivity, sensing performances, and applications of the composites. Future challenges in the development and application of the nanotip-induced ultrahigh pressure-sensitive composites are also discussed. 相似文献
119.
Mg matrix composites reinforced by carbon nanotubes (CNTs)-Al2O3 mixture, which was synthesized by in situ growing CNTs over Al2O3 particles through chemical vapor deposition (CVD) using Ni catalyst, were fabricated by means of powder metallurgy process, followed by hot-extrusion. By controlling synthesis conditions, the as-grown CNTs over Al2O3 particles possessed high degree of graphitization, ideal morphology, higher purity and homogeneous dispersion. Due to the ‘vehicle’ carrying effect of micrometer-level A2O3, CNTs were easy to be homogeneously dispersed in Mg matrix under moderate ball milling. Meanwhile, Al2O3 particles as catalyst carriers, together with CNTs, play the roles of synergistic reinforcements in Mg matrix. Consequently, the Mg matrix composites reinforced by CNTs-Al2O3 mixture exhibited remarkable mechanical properties. 相似文献
120.
Yu He Zhiwei Hu Mengda Ren Changkun Ding Peng Chen Qun Gu Qiong Wu 《Journal of materials science. Materials in medicine》2014,25(2):561-571
Two types of fibers were prepared by using bio-based materials: a mono-filament made from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and a multi-filament made from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactic acid (PLA) blend. The two fibers were evaluated for mechanical properties, biocompatibility and degradability for the potential application as medical sutures. The PHBHHx fiber showed remarkable biocompatibility by H.E. Stainning, with very little impact to the surrounding tissues. The degradation of the fiber was observed by SEM after implantation for 36 weeks, and the major degradation product was detected after 96 weeks. Consistently, the PHBHHx fiber maintained more than half of the mechanical properties after 96 weeks. The other fiber was prepared by twisting PHBV/PLA blend strands to a bunch, and showed high biocompatibility and relatively high degradability. The bunched structure loosed after 36 weeks of implantation. These low-cost and easily prepared fibers have great potential in medical applications, since they could avoid the formation of fibrous capsule, reduce the size of scar, and degrade into non-toxic and even beneficial products. 相似文献