The quaternary ammonium salts of chitosan (HACC) were synthesized with two different degrees of substitution (DS: 29%, 48%) of quaternary ammonium by reacting chitosan with glycidyl trimethylammonium chloride. Characterization of HACC was analyzed with IR spectra and HNMR spectroscopy. A biomimetic coating was codeposited on the surface of AZ91 magnesium alloy by adding HACC of two DS into simulated body fluid (SBF). The CaP/HACC coatings were analyzed by scanning electron microscopy (SEM) and X ray diffraction (XRD). The coatings have different crystal types. The results of antibacterial assays show that the CaP/HACC coatings have more antimicrobial activity to Staphylococcus aureus than CaP/CS coatings. The absorbances at the 6th hour show that the bacterial inhibition rate of four samples exceeds 90%. The absorbances at the 24th hour show that the samples obtained by adding the HACC of lower concentration into simulated body fluid have better antimicrobial effect and their bacterial inhibition rate reaches 98%.
Different proportional polypropylene (PP)/intumescent flame retardant (IFR)/organic montmorillonite (OMMT)/MCM–41 (without template) nano–composites were obtained by the melting method. Effect of nano–layered OMMT and dual nano–structured MCM–41 (with nano–sized spherical particle and nano–sized hexagonal channel) on the properties of polypropylene composites was investigated. The results show that the flame retardancy properties of PP matrix can be improved obviously with the combination of OMMT, MCM–41 and IFR. A synergistic effect in flame retardancy is best when the ratio of OMMT/MCM–41 was 1:1. The tensile strength and impact strength reached the maximum, meanwhile, the LOI value was 34.2 and increased by 50% compared with pure PP. Furthermore the UL–94 rating rose to V–0 and the thermal stability was improved significantly compared with that of PP/IFR composite.
By rapid thermal process, the initial thermal oxidation of single-side polished silicon wafer has been accurately obtained at 800 by oxygen switching for 15, 30 and 60 min oxidation time to form ultra thin silicon oxide layers. The ultra thin silicon oxidation layers were analyzed. The results show that the main composition of these layers is silicon dioxide, and the thicknesses are (4.1±0.4) nm, (6.2±0.6) nm and (9.6±0.5) nm, respectively. The incomplete oxides of Si2O3, SiO and Si2O all less than 5% of total oxidation layer formed at the interface between Si and SiO2. For those silicon oxide layers with the thickness of 4.1 and 6.2 nm, the difference of the binding energy between SiO2 and Si increases with decrease of graze angles, and the kinetic energy of photoelectron is affected by the build-in potential in the surface of the n-type silicon substrate. However, for the layers with 9.6 nm thick silicon oxide, the kinetic energy of photoelectron is dominated by the positive charge in the silicon oxide.
Effect of tempering temperature on mechanical properties and microstructure of a lowalloy quenched and tempered steel was investigated. The results show that the as-quenched status is lath martensite with self-tempered precipitates, which possesses both good strength and toughness. The amount of plate-like precipitates increases when tempered at around 250℃, and the yield strength gets a certain rise thereby. Carbide film precipitated along lath boundaries at 400℃ inducing tempered martensite embrittlement. The lath morphology still remains generally after high temperature tempering, while laths in some local areas have merged to block ferrite grains. A large amount of nano-scale carbide precipitates was observed above 550℃, and cementite particles were coarsened apparently. Fine grain strengthening and precipitation strengthening are the main strengthening mechanisms of the steel. The microstructure evolvement and precipitation characteristics influence the tensile curve shape and n value directly.
La0.7Sr0.3MnO3 (LSMO) nanoparticles were synthesized by a polyacrylamide gel technique. X-ray diffraction and scanning electron microscope were adopted to characterize the as-prepared samples. The results show that single-phase LSMO nanoparticles can be prepared by calcination at 600℃ using citric acid, tartaric acid, acetic acid, oxalic acid and ethylenediamine-tetraacetic acid (EDTA) as the chelating agent, respectively. The particles prepared using the five chelating agents are like spheres, and the citric acid-derived particles exhibit the best particle shape. The average particle size of five samples is 24, 28, 36, 38, and 50 nm, respectively. The photocatalytic properties of LSMO particles were evaluated by degradation of methyl red (MR) in ethanol/water solution under irradiation of visible-light tungsten lamp. The results show that the adsorption and photocatalytic degradation of MR are highly dependent on the H2O content in the reactive mixture. Among the samples, the citric acid-derived particles exhibit the highest photocatalytic activity. The direct hole oxidation is suggested to be the main mechanism toward the MR degradation.
SiCp were nickel-plated by means of chemical deposition to investigate the effects of the plating treatment on mechanical properties of SiCp/Fe composites. It was found that the coating thickness on SiCp can be controlled by amount of total input nickel chloride in the chemical solution. When the molar ratio of the nickel chloride versus hypophosphite is 1:3 and the temperature is within 93–95℃, the reduction of nickel chloride on the surface of the particles approaches to near 100%. When SiCp size is 45μm and the volume fraction is 10%, tensile strength of the composite is the best increased by 22.9%. After SiC particle surface nickel plated, the final elongation of SiCp/Fe composite is also improved significantly. The elongation is increased up to 30% with the plating when the particle size is 21μm and the volume fraction is 15% for nickel plated.
The nanocomposites of BaTiO3 and BaFe12O19 were prepared by sol-gel process, and the (BaTiO3+BaFe12O19)/PANI was prepared by in situ polymerization method. The structure, morphologies and electromagnetic properties of the samples were characterized by means of powder X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectrometer, transmission electron microscope (TEM), scanning electron microscope (SEM), four-point probe instrument(SDY-4) and vibrating sample magnetometer (VSM). The results show that with the increasing of PANI contents, the magnetization of the composites decreases, and the electrical conductivity increases, the microwave reflectivity absorption strength increase, maximum reflection loss is −27.73 dB, the absorption frequency shift to two-level (high-frequency and low-frequency) direction, and the infrared absorption performance increases.
Pb–0.3%Ag/Pb–Co3O4 composite inert anodes were prepared on the surface of Pb–0.3%Ag substrates, the electrochemical properties of the composite inert anodes obtained under different forward pulse average current densities from 2 A/dm2 to 5 A/dm2 and different Co3O4 concentrations from 10 g/L to 40 g/L in bath were investigated. The anodic polarization curves, cyclic voltammetry curves and Tafel polarization curves were measured in a synthetic zinc electrowinning electrolyte of 50 g/L Zn2+ and 150 g/L H2SO4 at 35 , the kinetic parameters of oxygen evolution, voltammetry charge, corrosion potential and corrosion current were obtained. The results show that Pb–0.3%Ag/Pb–Co3O4 composite inert anode obtained under forward pulse average current density of 3 A/dm2 and Co3O4 concentration of 30 g/L in bath, possess higher electrocatalytic activity, lower overpotential of oxygen evolution, better reversibility of electrode reaction and corrosion resistance in a synthetic zinc electrowinning electrolyte. The overpotential of oxygen evolution of the composite inert anode is 0.891 V under 500 A/m2, and it is 280 mV lower than that of Pb–1%Ag alloy; the surface voltammetry charge q∗ is 0.725 C·cm−2, and is 26.5% higher than that of Pb–1%Ag alloy; the corrosion current is also lower than that of Pb–1%Ag alloy. Large active surface areas and active substance numbers on the surface of the composite inert anode improve the electrocatalytic activity for oxygen evolution in [ZnSO4+H2SO4] solution. Fine and uniform grains, compact microstructures and fewer surface defects increase the corrosion resistance of the composite inert anode.
Microstructural evolution and mechanical properties of a solution-treated 0Cr13 ferritic stainless during the process of equal-channel angular pressing (ECAP) for 1–4 passes at room temperature were investigated. The results showed that the microstructural refinement of 0Cr13 steel during ECAP process presented as the grain subdivision by the induced deformation bands in mesoscale, and the crystal disintegration through dislocation segmentation model in microscale. As a result, a homogeneous ultrafinegrained structure developed in the 4-pass ECAP sample, and the corresponding average grain size is about 349 nm. Tensile and impact tests at room temperature showed that the strength of the tested steel increased and its ductility decreased after ECAP deformation for a single pass. However, further pressings (2nd, 3rd and 4th) resulted in a certain degree of improvement in impact toughness with enhancing strength simultaneously. The impact toughness of the multi-pass (3 and 4 passes) samples approximately returned to about 30% of the pre-pressing level. The enhanced static toughness and the changes in fracture mechanism resulted from grain refinement and dynamic recovery are responsible for the improved impact toughness of the multi-pass ECAP samples.
La1−xCex(Fe0.92Co0.08)11.4Si1.6 (x=0, 0.1, 0.3, 0.5) alloys were prepared by arc meltspinning. The structure and magnetic entropy change of annealed La1−xCex(Fe0.92Co0.08)11.4Si1.6 alloys (1000℃ for 3 h) were investigated using by X-ray diffraction (XRD) and magnetic properties. The results show that partial substitution of Ce for La in La1−xCex(Fe0.92Co0.08)11.4Si1.6 (x=0, 0.1, 0.3, 0.5) alloys, the cubic NaZn13-type structure phase is more easily formed, α–Fe phase is significantly reduced, Curie temperature is reduced to some extent, and the magnetic entropy change increases greatly. However the impurity phases appear when Ce substitution is up to 0.5, the magnetic entropy change decreases. The maximum isothermal magnetic entropy change of La1−xCex(Fe0.92Co0.08)11.4Si1.6 alloy with x=0.3 near room temperature is superior to that of Gd, suggesting that La1−xCex(Fe0.92Co0.08)11.4Si1.6 alloy with x=0.3 is promising to be low-cost, high efficiency magnetic refrigeration materials at room temperature.
CBS/Al2O3 glass–ceramic was prepared by using CaO–B2O3–SiO2 (CBS) glass and Al2O3 powders as the raw materials with the mass ratio of 50/50, and the influence of the additive of Li2CO3 on the sintering property, dielectric property and mechanical properties of CBS/Al2O3 composites was investigated. The results show that the additive of Li2CO3 can lower the softening point and viscosity of CBS glass by modifying the structure of CBS glass, and can react with Al2O3 to form low melting phase of Li2AlO2, which can promote the sintering process of CBS/Al2O3 glass–ceramic and result in lowering down the sintering temperature to 830 . However, the excess Li2CO3 can deteriorate the dielectric property and mechanical properties of CBS/Al2O3 glass–ceramic because of the volatilization of Li–compounds. With 0.50% Li2CO3 addition, the CBS/Al2O3 glass–ceramic could be sintered at 830℃ and obtained excellent properties.
The fatigue tests were performed for 2A12 aluminum alloys specimens at various stresses and stress ratios, and the microstructure of fatigue fractography was observed by optical microscope and scanning electron microscope. The microstructure features of crack nucleation and propagation were revealed. The results show that the fatigue cracks usually initiate in the larger second phase particles near the free surfaces or the defects in corner angle of the specimen. The distance between the crack initiation and the surface is related to stresses and stress ratios, and fatigue crack propagation zone is also related to stresses and stress ratios. The phenomenon of crack intergranular propagation and crack transgranular propagation under smaller stresses or higher stress ratios is particularly obvious. A small (large) crack-nucleating particle on fatigue fractography results in a short (long) life of specimen. Micro crack nucleation life play an important role in the calculation of holistic fatigue life.
Colloidal crystals templates, comprising polystyrene (PS) microspheres of diameter ca. 340 nm, were prepared by two-substrate vertical deposition method from aqueous colloidal suspensions of PS microspheres. Inverse opal three-dimensional ordered macroporous (3DOM) CeO2was synthesized by using PS colloidal crystal templates. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscope (AFM) and N2 adsorption–desorption. And the low-temperature reducibility of the obtained 3DOM-CeO2 was analyzed by hydrogen temperature-programmed reduction (H2-TPR). FESEM and AFM results show that the PS colloidal crystal template microspheres are arranged on a face-centered cubic lattice. The formed CeO2 inverse opals exhibit a three-dimensional ordered structure with macroporous framework, which is composed of loosely packed CeO2 nanoparticles. The hole spaces of the 3DOM–CeO2 is about 280–300 nm, and the thickness of the porous walls is ca. 40 nm. H2–TPR results indicate that the low-temperature reducibility of 3DOM–CeO2 is much better than that of ceria standard samples.
Pyrrole was polymerized into HDI trimer modified silicone polyurethane (HESO) foam by in–situ adsorption polymerization process in order to manufacture conductive silicone polyurethane (PPy/HESO). The effects of different preparative conditions including feeding ratios, feeding sequences and reaction conditions were investigated. The results show that the optimum preparative conditions arepyrrole to HESO mass ratio 12.5:100, ferric chloride and anthraquinone –2–sulfonate(AQS) to pyrrole molar ratio of 2.2 : 1.2 : 1, feeding sequence: HESO–Pyrrole–AQS–FeCl3, reaction temperature 0℃, pH=3 of the reaction solution. Effect of the Si and polypyrrole on electrochemical properties has a concertedness. It is more conducive to PPy/HESO, and forming a continuous core–shell–type conductive polymer in the HESO latex surface or at the interface.
Al2O3/TiC–Al2O3/TiC/CaF2 laminated composite ceramic material was prepared by vacuum hot pressing sintering. The Vickers hardness is 20.7 GPa and the fracture toughness is 4.5 MPa·m1/2. The bending strength has little difference in the vertical direction and parallel direction which is respectively for 323 MPa and 353 MPa. Sliding wear tests against chilled 45# steel were performed on the ceramic composites using ring-disc method in dry conditions, worn morphology was observed by the scanning electron microscope (SEM) and the composition was investigated by energydispersive X-Ray spectroscopy (EDS). Results show that the friction coefficient and wear rate decline with the increase of the load and rotating speed. The material has self-lubricated property. The main wear mechanisms of laminated composite are abrasive wear and adhesive wear.
The cold-rolled polycrystalline molybdenum strip was laser shocked by the Thales laser with the maximum output laser pulse energy of 12.5 J, and the microhardness and microstructure of shocked specimens were analyzed. The results show that laser shock at high strain rate can achieve a double effect of forming and modification of brittle polycrystalline cold-rolled molybdenum strip. The microhardness on the surface of the polycrystalline molybdenum strip in the half-lap region of laser shock processing accorded with variation of the Gaussian function, and the peak range was HV265-310. The thermostability of laser shocked molybdenum strip was improved.
WC–Co surface reinforced composite was formed by V–EPC (vacuum– expendable pattern casting), and the microstructure of the matrix in the composite was investigated. The results show that the Co addition caused the appearance of granular pearlite and troostite in the matrix, therefore the brittle tendency of the composite was lightened. After the molten steel infiltrating into the preform, the counter–diffusion in matrix decreased from the substrate to the surface of composite, the composition of the matrix became more uneven, and the formation of the spheroidal pearlite and troostite were facilitated. When the atomic concentration of W and C in the matrix increased, Co3W3C, η type carbide, was easier to be separated out. Before the temperature of the composite drop to 1200℃, Co3W3C could precipitate in the interface reaction between the matrix and the tungsten carbide particles, the hardness of the matrix would be increased, and then the abrasive resistance of the composite could be improved.
The sintering characteristics of block magnesite with different sizes were investigated. The results show that after firing in 400–800℃, the smaller size of the specimens, the higher the decomposition rate and activity of the specimens, as well as the faster decreasing of the bulk density. Sintering of the specimens did not start when fired in 800–1000℃. The sintering speed of the specimens is slow fired in 1000–1300℃, the bulk density increases to 2.00 g/cm3, because magnesite pseudomorph impedes the diffusion of particle during solid sintering. However, the sintering speed increases in 1300–1600℃, the solid sintering turns to liquid sintering, and the bulk density increases to 2.60 g/cm3. Sintering speed of the specimens increases rapidly fired at 1600℃ or higher. The specimens are densified in the completely liquid sintering, bulk density increases to 3.27 g/cm3. The size of specimens have little effect on the final bulk density fired at 1800℃.
