Pure tungsten with ultra-fine grain size has been fabricated by a novel sintering method combined resistance sintering with ultra high pressure in the absence of any additives. The relative density of the fabricated material is 97.9% and the average grain size is less than 1 μm. the density of the sintered sample is mainly contributed by the applied ultra high pressure, while the resistance sintering benefit for high mechanical properties of the sintered material. Compared to another fast resistance sintering technology spark plasma sintering, resistance sintering under ultra high pressure shows the advantage of not only retaining the fine grain size, but also further refining the grain size during consolidation.
The free–standing transparent TiO2 nanotube array membranes were prepared by anodization of titanium foil in ethylene glycol organic electrolyte containing water, ammonium fluoride, and sodium molybdate. The membrane was amorphous TiO2 and its thickness was about 10μm. It was found that the amorphous TiO2 nanotubes could be transformed to anatase structure after a hydrothermal treatment at 120oC while the integrity structure of the membranes was well remained. It is found that the transmittance of such transparent membrane is determined by the surface structure and its crystal structure. The TiO2 nanotube array membranes can be expected to be used in dye sensitized solar cells.
Nanoparticles of Yb3+, Er3+-codoped sodium yttrium fluoride were prepared by solventthermal method. The properties of the prepared materials were characterized. The up-conversion luminescent properties of the NaYF4 : Yb3+, Er3+ nanoparticles were investigated. The effect of deionized water and ethanol as reaction medium on the performance of the up-conversion materials was studied. The results showed that the up-conversion nanoparticles had relatively high up-conversion effect when ethanol was used as reaction medium and simultaneously ethylenediaminetetraacetic acid (EDTA) was also added. The up-conversion phosphors emit visible light which could be well utilized by solar cells.
The semi–solid thixo–extruding feasibility of AlSi7MgBe alloy cast by near–liquidus semi–continuous casting (NLSC) process was studied by analyzing the microstructures and properties of extruded bars. The results shown that the microstructure of AlSi7MgBe alloy billets cast by NLSC consists mainly of the homogeneous, fine rosette–shaped grains. The microstructures of the billets, reheated and held at 575oC, are stable and near–spherical grains which are suitable for semi–solid thixoforming. The semi–solid thixoextruded bars of the AlSi7MgBe alloy billet are facial–smoothed, microstructure–fined and homogeneous. Treated by the solution at 540oC for 5 hours and aging at 175oC for 10 hours, the tensile strength of the semi–solid extruded bars is above 325 MPa and the elongation rate is above 14.6%.
The Ti–Fe alloy compound was prepared by FFC in the molten salts at 700oC . The preformed cathode feed was fabricated with the slurry of mixing TiO2 and Fe power. The graphite rod was used as the anode in the corundum crucible. At cell voltage of 3.4 V, electro–deoxidation was carried out. With different stoichiometric ratios of Fe and TiO2 powder, different currency–time plots were gotten, which showed that the more Fe addition, the quicker the reaction speed is during the first 7 hours deoxidation.
A 2D carbon fiber preform (bulk density 0.43 g/cm3) was infiltrated by novel ICVI in temperature 1080–1200 oC, pressure 10 KPa, gas residence time 0.01 s, using natural gas as carbon source, N2 as diluent gas, and the C/C composites were obtained. The flexural strength was measured by three–point bonding tests, the microstructures of pyrocarbon matrix and the morphologies of fractured surfaces were observed by polarized light microscopy (PLM) and scanning electron microscopy (SEM). The results show that the bulk density of 2D–C/C composites manufactured in 150 h is 1.75 g/cm3, its texture is pure rough laminar, flexural strength and flexural modulus are 164.77 MPa and 21.34 GPa respectively. The fracture of C/C composites exhibits a pseudo–plastic failure behavior.
A novel method to prepare metallic structure with hemisphere layer formed by metal sheet plastic processing and connect it to novel porous metal in certain ways is proposed. The strength of structure composed of interconnected flat plate layers is greater than that of structure composed of accumulative metallic balls with air core in the same condition. This structure has high strength and can absorb energy, and the thickness and porosity of aluminum sheet have obvious effect on it's compressive property.
The phase transition of crystalline in poly(vinylidene fluoride) from α anti-ferroelectric to β ferroelectric phase achieved by electric poling treatment with a high temperature has been investigated. It was found that the ferroelectricity of polymer was improved and the polarization depended on increasing poling electric field was non-linear. The phase transition of PVDF in electric field was theoretical simulated based on dynamical equilibrium. The results show that the effective electric field affected on the crystalline is 50 MV/m, which accords with the coercive field of ferroelectric PVDF. At the same time, the effective electric field affected on the amorphous is close to starting electric field of the phase transition. It demonstrates that the method of dynamical equilibrium simulated phase transition of crystalline in PVDF is feasible.
Mg and a Mg–Ca alloy were heat treated at 773 K for 10h and self–assembled in stearic acid alcohol solution of 0.5mol/L for 1.5 h to improve the corrosion properties and biocompatibility of bio–magnesium materials. And then comparison research was carried out for the bio–magnesium materials with and without modification by putting in simulated body fluid and in vivo animal test. Electronic balance, SEM, EDS, XRD FTIR, digital electronic pH meter and atomic absorption spectrometry were used to analyse the corrosion process, corrosion rate and the products. The results showed that the corrosion resistance and bioactivity of the bio–magnesium materials with heat–self–assembled monolayer were improved. The corrosion rate of Mg changed from 0.11 mm/y to 0.05 mm/y, and that of Mg–Ca alloy from 0.38 mm/y to 0.32 mm/y. The diameter of Mg in thigh bone of the tested rabbit for 12 weeks decreased from 0.97 mm to 0.20 mm, and thickness of new bone increased from 2.563 mm to 3.135 mm.
Assisted by the advanced LMC process and an optimum composition design, a highperformance second-generation directionally solidified superalloy DZ59 with low Re content has been developed. The high temperature creep properties of the superalloy are better than first-generation single crystal alloys and is close to the level of second-generation single crystal alloys. The microstructure and creep rupture feature of the DZ59 alloy have been analysed in detail by SEM and TEM. The SGRZ was first discovered in the second-generation directionally solidified superalloys. The results showed that SGRZ is controlled by the temperature and stress. Because SGRZ increases the area of transverse grain boundary, creep voids may initiate and propagate in the SGRZ location under high stress.
Chitosan microspheres, used as template to prepare polyelectrolyte microcapsule, were prepared by high voltage electrostatic method. Polyelectrolyte membrane made of chitosan and sodium alginate was constructed layer–by–layer assembly. A little residual chitosan template can induce sediment of molecule with negative charge. Acetic acid aqueous solution was used to dissolve the chitosan template. The concentration of sodium fluorescein in the microcapsules linearly increased with time, and embeded concentration became saturated after 15 min. When concentration of sodium fluorescein solution is 2 mg/L, the saturated embeded oncentration of sodium fluorescein arrived at 10.2 mg/L. The release behavior is mainly affected by microcapsule's wall and the structure of template, but concentration of NaCl has little influence on the release behaviour.
Porous aluminium with controlled periodic pore structures was processed by infiltration method. The results of sounds absorption within the range tested, which have been obtained by standing wave tube method around, are basically consistent with the simulation results. Based on the model, the relationship between pore structure parameters (periodic number, ratio with different layers, packing order) and sound absorption coefficient were studied. It is suggested that sound-absorption behavior (>2 kHz) is strongly affected by pore size distribution, but no apparent correlation in low frequency.
Triclosan and silver antibacterial agent were incorporated into polyethylene by blending. The antimicrobial efficacy of modified samples and inhibitory effect of antimicrobial agent on biofilm formation on the LDPE surface were investigated. The results showed that both of modified LDPE samples exhibited excellent antimicrobial performance against S. aureus and E. coli. The formation of biofilm could be described as a three–stage process: adhesion, proliferation and biofilm maturation. The adhesion and propagation of bacteria were evidently reduced by triclosan added into LDPE, thereby the formation of biofilm was prevented. However, the amount of bacteria on the surface of LDPE adding silver antimicrobial agent was no less than that on the control sample. Silver antimicrobial agent could not make much difference in biofilm formation on surfaces.
Micro-indentation method was used to study deformation and fracture behavior of Si, Ge, GaAs, InP single crystals. In-plane microhardness, critical indentation size and fracture toughness of the [100] oriented crystals were measured to analyze anisotropic mechanical properties of these materials. The results show that under the indentation load, Si and Ge deformed through the formation of shear faults, while the activation of slip systems accommodated the deformation of GaAs and InP. The microhardness, elastic modulus and fracture toughness exhibit anisotropic at different extent. The relationship between crack length and indent size shows that the critical indent size and the linearly-fitted slope of the crack length vs. indent size of Si and Ge single crystals are smaller than that of GaAs and InP. The variations of the critical indent size and the linear slope are consistent with that of the hardness and fracture toughness.
MoSi2 composites with different Si 3N 4(p) and SiC(w) volume contents are prepared by means of wet mixing and heat pressing process. The morphology, grain size, hardness, fracture toughness, bending strength of the MoSi2–Si3N4(p)/SiC(w) composites were investigated by means of scanning electron microscope (SEM), polarizing microscopy, vickers hardness tester, and universal material testing machine in this paper. It is shown that mechanical properties of the prepared composites are much higher than that of MoSi2, and its grain size is finer than that of MoSi2, more over it is declined with the increasing of strengthening phases. MoSi2–20% Si3N4(p)–20% SiC(w) composite has better mechanical properties, and its bending strength and room fracture toughness are 427 MPa and 10.4 MPa·m1/2, respectively. The strengthening mechanism of MoSi2– Si3N4(p)/SiC(w) composites are fine grain strengthening and dispersion strengthening, and the toughening mechanism are fine grain toughening and crack deflection toughening.
AZ91D magnesium alloy was treated by micro-arc oxidation (MAO) in electrolyte system including NaAlO2 and (NaPO3)6 in this paper. Effects of tungstate and some other additives on the structure, property and component of the MAO coatings were investigated and the electrolyte subsequently was optimized with the orthogonal experimental design approach. The results show that the composite additives (Na2EDTA1g/L, CH3(CH2)11SO 3Na0.5g/L) could constrain the ruinous micro-arc, which makes the porosity and microarc channel diameter of the coatings and the arcing voltage decrease; the coatings compositions mainly include MgO, Mg3(PO4)2, MgAl2O4 and AlPO4; ceramic coatings exhibited excellent anticorrosion property; the anticorrosion property of the MAO coatings was improved greatly with the composite electrolyte additives.
MCM–41 mesoporous molecular sieves containing heteroatoms (Zn, Ni, Fe, Al, Cu, Ce) (T–MCM–41) were synthesized by direct hydrothermal process and were applied in the synthesis of dioctyl phthalate (DOP) in this paper. The effects of different heteroatoms incorporation on structure, specific surface area and pore volume, aciditity and catalytic activity of T–MCM–41 were investigated. The results show that T–MCM–41 which still remains the well–ordered hexagonal mesostructure of MCM–41 has high surface area (550–900 m2/g), large pore diameter (∼3 nm). Meanwhile, it has high catalytic activity and selectivity in DOP synthesis because heteroatoms incorporation can produce acid centers. When T–MCM– 41 (T=Zn, Fe, Al, Cu) is used as the catalyst, the conversion of phthalic anhydride (PA) reaches above 95.5% and DOP selectivity reaches above 96.5% in 5 h. Moreover, T–MCM–41 has good stability and Al–MCM–41 holds good catalytic activity after being reused five times.
The dealumination course of framework of Silicon-Aluminum molecular sieves (SAMS) was simplified as the diffusion of aluminium atoms in the framework as well as the formation and migration of vacancy sites. Based on this simplification in this paper, and the instantaneous concentration of aluminum atoms have been determined as a function of time and location according to Fick's Second Law. The critical parameters affecting the dealumination process was also discussed. The accuracy of the formulae is verified as the calculation results agree with the ratio of silicon to aluminum in Mordenite and ZSM-5 framework measured by XPS and infrared spectra and 27Al-NMR.
In this paper the tensile properties and fracture behaviour of aluminum alloy 2009 reinforced with silicon carbide particulates (SiCp) fabricated via elemental powder metallurgical technique were presented. The results indicate that the strength of 15%SiC/2009Al composite decrease with increasing particulates size, but ductility inversely. When particulates were 1.5μm, the breakage is due to tearing of matrix near interface. The failure of composites with 20μm particulate results from crack of SiCp. When particulates are between above sizes, the failure of composite results from tearing of matrix near interface and crack of SiCp.
Sulfonated poly(phthalazinone ether ketone ketone)s (SPPEKK) with pendent sulfonate groups were synthesized via aromatic nucleophilic substitution and composite membranes have been prepared from SPPEKK and solid inorganic proton conductive BPO4 in situ process. 1H–NMR and FT–IR were used to characterize the structures of the SPPEKK and its composite membranes. The results show that the effects of BPO4 content on mechanical stability, thermo–stability and proton conductivity were investigated. The proton conductivity of the composite membrane was measured to increase to 6.3×10−2S·cm−1(90℃). The conductivity of the composite membrane was improved clearly while holding the better mechanical and thermo property.
Ceramic coatings were prepared on the surface of Mg–5%Li alloy in three kinds of optimized electrolytes by single-polar pulsed micro-arc oxidation (MAO). Thickness, microstructure, phase composition and corrosion resistance of the ceramic coatings were investigated. The results showed that all the MAO coatings were composed of MgO, and their corrosion resistance was improved distinctly. The coating gained in Na3PO4 system contained MgF3, and was the thickest with a great deal of cracks; the coating from Na2SiO3 system included olivine Mg2SiO4, and had the best pitting corrosion resistance; the coating from Na2SiO3–Na3PO4 system contained MgSiO3, showed the most compact micro-surface, and owned the best uniform corrosion resistance.
