Search

High-aspect-ratio (HAR) micro-electroforming is a significantly challengeable implementation to manufacture metallic microstructures and microparts mainly due to mass transportation limitation effect. In this paper, flow pattern and flow rate change characteristics within HAR micro-cavity during electroforming under magnetic field are investigated, and evaluations of the electroformed micro-sized HAR nickel features under the improved magnetohydrodynamic (MHD)-governed condition are carried out. It was found that, five electrolyte flow-pattern zones can be formed within the horizontally placed micro-cavity under the MHD condition and favorable mass transfer effects can be created when the current field applied is perpendicular to the gravity field; HAR (≥ 7) nickel microstructure with good surface quality and few plating defects can be produced at a relatively high current density (up to 11 A/dm2) under the combined actions of MHD-driven convection and external forced-convection; MHD-assisted nickel micro-electroforms have a higher microhardness, better surface morphologies and fewer defects than the ones obtained without the superimposition of the magnetic field. MHD-driven convection benefits the desirable implementation of HAR micro-electroforming processes.

For developing the hypersonic vehicle with high lift-to-drag performance, the design based on waverider is an effective approach. Because of the limit of aerodynamic heating, the sharp leading of hypersonic vehicle needs to be blunted in practical applications. Considering the advantages and disadvantages of waverider comprehensively, a kind of quasi-waverider hypersonic vehicle body is designed and a kind of bluntness method is carried out. According to the characteristics of the quasi-waverider, the leading edge and the sharp side edge are blunted, respectively. A method of increasing material was used to blunt the leading edge, of which the blunt curve is a circular curve. A blunt method for increasing material based on cubic Bezier curve is proposed for the sharp side edges. At the basis, the sharp side edges of top and bottom are blunted simultaneously, which not only ensuring a continuous smooth side surface, but also increasing volume of the quasi-waverider. The effect of bluntness on the aerodynamic force and aerodynamic heating of the configuration is studied by numerical simulation. Numerical calculation results show that aerodynamic force is influenced less by bluntness, while aerodynamic heating is influenced greater. The lift-drag ratio reduced about 11% due to blunt leading edge, while maximum heat flux decrease about 59% and aerodynamic heating performance is improved. The reason for the loss of the aerodynamic force is the bow shock wave produced by bluntness, resulting in the high pressure airflow of lower surface leaks to upper surface and lift coefficient reduce. The shock drag of edge increases greatly due to bluntness, causing drag coefficient increase. Investigation shows that the aerodynamic force and aerodynamic heating performance of quasi-waverider hypersonic aircraft are well balanced under this blunt method and the method can be used for the configuration design of hypersonic vehicle.

The garnet-type lithium ion conductor, nominal Li7La3Zr2O12 (LLZO) has received a lot of interest as they are considered usable as solid electrolytes in lithium battery. The Li+ migration bottleneck size of garnet-type Li7La3Zr2O12 (LLZO) solid electrolyte are posed significant effect on Li+ transportation property. However, the regulation mechanism of the bottleneck size on the Li+ migration activation energy is not clear. In the study, equivalent substitution of tetravalent M4+ (M4+ = Ge4+, Ti4+, Sn4+, Hf4+ and Te4+) ions on Zr site of Li7La3M0.25Zr1.75O12 is designed to regulate the bottleneck size. X-ray absorption fine structure (XAFS) is applied to detect the quantitative structural information of M-doped LLZO. Experimental and calculations results show that the M4+ substitution regulate the Li+ migration bottleneck size via changing M–O bond length. The M–O bond length increases with the increase of M4+ doping ion radius which results in the increase of the bottleneck size. However, larger bottleneck size is not necessarily favorable for Li+ migration. Ge4+ and Ti4+ doped LLZO have smaller bottleneck size than the un-doped LLZO, which is more suitable for Li+ migration (corresponds to lower Ea of 0.28 eV, 0.29 eV, respectively). This study is of great significance for obtaining optimum lithium ion migration channel size for LLZO, and the regulation mechanism is universality for crystal ion conductors.

An experimental study on the circulation control around a modified NCCR1510-7067N airfoil is presented. The plasma-induced wall jet is achieved by the use of Dielectric Barrier Discharge plasma actuators, which are placed around the curved circular trailing edge. A wind tunnel test is performed in order to quantify the effects of applied voltage and actuator position on the lift enhancement. The lift and pressure measurements are taken using micro pressure electronic scanning valve. Additionally a smoke flow visualization test is performed in order to elucidate the fundamental working principles of the concept. Preliminary results indicate that the variation of the lift coefficient with the applied voltage was nonlinear, the short laminar separation bubble appeared at the leading edge in advance with applied voltages above 8 kV; consequently, the optimal applied voltage was 8 kV. The lift coefficient was increased by 0.154 and the lift augmentation efficiency reached 108.7 with a single actuator on the lower surface. A smoke flow visualization showed the delay of separation position and the formation of virtual flap effect.

Using graphene oxide as substrate and stabilizer for the silver nanoparticles, silver nanoparticles-graphene oxide (Ag NPs/GO) composites with different Ag loading were synthesized through a facile solution-phase method. During the synthesis process, AgNO3on GO matrix was directly reduced by NaBH4. The structure characterization was studied through X-ray diffraction (XRD), atomic force microscopy (AFM), high-resolution transmission electron microscope (HRTEM), ultraviolet-visible spectroscopy (UV-Vis), and selected area electron diffraction (SAED). The results show that Ag nanoparticles (Ag NPs) with the sizes ranging from 5 to 20 nm are highly dispersed on the surfaces of GO sheets. The shape and size of the Ag NPs are decided by the volume of initial AgNO3solution added in the GO. The antibacterial activities of Ag NPs/GO nanocomposites were investigated and the result shows that all the produced composites exhibit good antibacterial activities against Gram-negative (G−) bacterial strainEscherichia coli(E. coli) and Gram-positive (G+) strainStaphylococcus aureus(S. aureus). Moreover, the antibacterial activities of Ag NPs/GO nanocomposites gradually increased with the increasing of volume of initial AgNO3solution added in the GO and this improvement of the antibacterial activities results from the combined action of size effect and concentration effect of Ag NPs in Ag NPs/GO nanocomposites.

To improve the deposition accuracy and surface quality of the deposited micro-features, a novel compressed air-film encircling Jet ECD was proposed. In the proposed Jet ECD, a high-speed compressed air-film is coaxially encircling the impinging electrolytic jet. Numerical model describing the coupled field of electric field and flow field was established, and some auxiliary observation and measurement experiments were conducted to investigate the distribution characteristics of electric field and hydrodynamics characteristics in the concerned regions as well as the change of the electrolyte jet diameter. And the effect of air-film formation parameters and hydrodynamic parameters of the electrolyte jet on the electrodeposition behaviors during forming patterns and high aspect ratio micro-features were studied. Deposition accuracy and surface quality of the microstructures fabricated by the compressed air-film encircling Jet ECD were evaluated. It was demonstrated that, compared with the traditional Jet ECD, the proposed Jet ECD has a higher deposition accuracy and faster deposition rate (up to 1 μm/s) as well as better surface quality. In addition, the newly developed Jet ECD has an admirable additive manufacturing ability and a 370±3 μm-diameter smooth column with the aspect ratio of about 20 was successfully manufactured.

Modified calcite CaCO3 (M-CaCO3) was synthesized from calcium nitrate, sodium carbonate, ethylene diamine tetraacetic acid and sodium dodecyl sulfate. Then, poly(L-lactic acid) (PLLA)/ M-CaCO3 composites were fabricated using melt blending and hot-press forming technologies. The effect of M-CaCO3 on the thermal and mechanical performance of PLLA was investigated. The results showed that the crystallization temperature and M-CaCO3 content significantly affected the crystallization of PLLA but the effect of M-CaCO3 on the crystallization of PLLA was very complicated. Compared to neat PLLA, 1 % M-CaCO3 decreased the t1/2 from 3999.4 s to 342.7 s at 100 °C. The melt index measurements indicated that a small amount of M-CaCO3 could block the fluidity of PLLA. However, the addition of a high content M-CaCO3 increased the fluidity of PLLA. The results of tensile strengths and elongation at break of PLLA/M-CaCO3 composites showed that both M-CaCO3 content and defective modification CaCO3 affected the mechanical performance of the PLLA/M-CaCO 3composites.

CeO_2-ZrO_2 and CeO_2-ZrO_2-La_2O_3 catalysts with mass ratios of 60:40 and 60:30:10 were prepared by co-precipitation method,respectively.The catalytic activity in oxidation of the soluble organic fraction(SOF) in diesel exhausts was studied using thermogravimetric-differential thermal analysis(TGDTA).The results indicate that the catalytic activity of the La-modified CeO_2-ZrO_2 catalyst is better than that of the CeO_2-ZrO_2 catalyst;the light-off temperature of SOF is 164 ℃,and the weightlessness fastest point temperature is 212 ℃,whereas for CeO_2-ZrO_2,these temperatures are 168 and 221 ℃,respectively.X-ray diffraction(XRD) shows that modification with La is beneficial to decrease the growth rate of the crystallite size relative to that of CeO_2-ZrO_2 after high-temperature ageing.N_2 adsorption-desorption results suggest that the addition of La enlarges the surface area.O_2-temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy(XPS) show that modification with La increases the amount of chemisorbed oxygen on the CeO_2-ZrO_2 catalyst.The CeO_2-ZrO_2-La_2O_3 catalyst shows better activity and ageing resistance than the CeO_2-ZrO_2 catalyst.

Conventional circulation control technology presents problems in certain situations. Pulsed jet circulation control appears to be a feasible alternative to solve such problems, especially for the high-frequency pulsed jet (HFPJ). To acquire the aerodynamic characteristics of the HFPJ and reveal the mechanism behind it, numerical simulation is conducted using a verified computational fluid dynamics (CFD) method. The action mode of the pulsed jet characterized by equilibrium and oscillation is proposed according to the analysis of a dynamic procedure. Lift and drag characteristics are obtained, defining the critical frequency to demarcate high and low frequencies. An oscillation function is also established to illustrate the difference between the characteristics of the HFPJ and a low-frequency pulsed jet (LFPJ) by analyzing the simulation results. The pressure distribution and flow field in the simulation results explain the stall characteristic of the HFPJ. Series results indicate the HFPJ demonstrates superior lift augmentation and drag reduction compared to the LFPJ and steady jets.

In order to improve the performances of urea–formaldehyde (UF) resin adhesive and reduce formaldehyde emission, the isocyanate was applied to modify the UF resin adhesive. The effects of the composition ratio of the isocyanate/UF resin on the thermal stability and molecular structure of the composite adhesive were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyzer. The results showed that the appropriate addition of the isocyanate into the UF resin is favorable to improve the performances of the composite adhesive due to the chemical cross-linking reaction of the isocyanate with UF. Furthermore, the reaction mechanism of the UF resin adhesive with isocyanate was analyzed in detail. These research results can be applied to aid materials engineering design for the development of new adhesive, quality assurance, and characterization assessment of durability.

In order to improve the storage modulus and water resistance of poly (vinyl acetate), the vinyl acetate and poly (vinyl alcohol) (PVA) were respectively used as monomers and protective colloid to prepare a new kind of polyvinyl acetate emulsion adhesive by continuous emulsion polymerization. The dynamic mechanics, particle distribution, glass transition temperature, polymer emulsion structure of both polymerized and copolymerized emulsion were analyzed by SEM, DMA and XPS, respectively. The results indicated that the copolymerized emulsion has the appropriate particle size and the uniform particle distribution, the glass transition temperature increased from 50 °C to 70 °C, compared with poly (vinyl acetate). It could be seen from XPS spectra of copolymerized emulsion that key characteristic peak of C O was still existent. X-ray photoelectron spectra revealed that the addition of EVA did not generate the new bond, whereas the maximum percentage increases in ester was determined in the composite film with the introduction of EVA of 25%, which indicated that the composite film has copolymer structure. The storage modulus and water resistance of poly (vinyl acetate) were improved due to the introduction of the EVA.

This paper studied the production process, synthetic material structure and performance characterization of the polyurethane composite adhesive, which is modified by organic montmorillonite (OMMT). The experiments mainly contain three parts. First; try to use the organic inserted layer method to modify the inorganic MMT, then to get the organic nano-meter montmorillonite. Second, Control the proportion of –NCO, –OH and the -OH in PEG and DMPA and the amount of OMMT, using of three factors of three levels orthogonal experiment to synthetize nine kinds of polyurethane adhesive modified by OMMT. Finally, orthogonally experimental analysing the relevant representative data of the performance to conclude the best ratio of each performance glue. Again, analyses the structure and properties of the polyurethane adhesive modified by OMMT by using thethermo gravimetric analysis (TGA) and Scanning electron microscope(SEM). The experiment’s results show that various performance indicators of the polyurethane adhesive modified by OMMT have a certain degree of improvement.It was clearly seen form the SEM micrograph of adhesive interface oak, the fracture surface of adhesive were uniform distribution.

A series of Co-modified Ce0.5Zr0.5O2 catalysts with different concentrations of Co (mass %: 0, 2, 4, 6, 8, 10) was investigated for diesel soot combustion. Ce0.5Zr0.5O2 was prepared using the coprecipitation method and Co was loaded onto the oxide using the incipient wetness impregnation method. The activities of the catalysts were evaluated by thermogravimetric (TG) analysis and temperature-programmed oxidation (TPO) experiments. The results showed the soot combustion activities of the catalysts to be effectively improved by the addition of Co, 6 % Co/Ce0.5Zr0.5O2 and that the 8 % Co/Ce0.5Zr0.5O2 catalysts exhibited the best catalytic performance in terms of lower soot ignition temperature (Ti at 349°C) and maximal soot oxidation rate temperature (Tm at 358°C). The reasons for the improved activity were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). These results revealed that the presence of Co could lower the reduction temperature due to the synergistic effect between Co and Ce, thereby improving the activity of the catalysts in soot combustion. The 6 % Co catalyst exhibited the best catalytic performance, which could be attributed to the greater amounts of Co3+ and surface oxygen species on the catalyst.

Cubic phase cobalt (Co), which can be used as a key component for composite materials given its excellent ductility and internal structure, is not easy to obtain at room temperature. In this study, oxalic acid and cobalt nitrate are used as raw materials to synthesize the cobalt oxalate precursor, which has a stable structure with a five-membered chelate ring. Cobalt oxalate microspheres, having a high internal energy content, were prepared by using mechanical solid-state reaction in the presence of a surfactant, which can produce spherical micelles. The thermal decomposition of the precursor was carried out by maintaining it in a nitrogen atmosphere at 450°C for 3 h. At the end of the procedure, 100 nm cubic phase-Co microspheres, stable at room temperature, were obtained. Isothermal and nonisothermal kinetic mechanisms of cobalt grain growth were investigated. The cubic-Co grain growth activation energy, Q, was calculated in this study to be 71.47 kJ/mol. The required reaction temperature was low, making the production process simple and suitable for industrial applications.

Using the common natural cellulose substance (filter paper) and triblock copolymer (Pluronic P123) micelles as dual templates, porous titania nanotubes with enhanced photocatalytic activity have been successfully synthesized through sol-gel methods. Firstly, P123 micelles were adsorbed onto the surfaces of cellulose nanofibers of filter paper, followed by hydrolysis and condensation of tetrabutyl titanate around these micelles to form titania layer. After calcination to remove the organic templates, hierarchical titania nanotubes with pores in the walls were obtained. The sample was characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption/desorption, Fourier Transform Infrared Spectroscopy (FT-IR), Ultraviolet-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS), and X-ray photoelectron spectroscopy (XPS). As compared with commercial P25 catalyst, the porous titania nanotubes prepared by this method displayed significantly enhanced photocatalytic activity for degrading methyl orange under UV irradiation. Within 10 minutes, the porous titania nanotubes are able to degrade over 70% of the original MO, while the value for the commercial Degussa P25 is only about 33%.

The enhancement of crystallization performance is very important in semicrystalline polymers for broadening their practical application. In this study, N,N'-bis(1H-benzotriazole) adipic acid acethydrazide (BA) was synthesized from 1H-benzotriazole and adipic acid in order to evaluate the heterogeneous nucleating performance of poly(L-lactic acid) (PLLA). Through the investigation of non-isothermal crystallization behavior of PLLA containing different BA content using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), it was clear that BA was able to significantly promote the crystallization of PLLA compared to pristine PLLA, and the addition of BA resulted in an increase in the onset and peak crystallization temperatures and in the non-isothermal crystallization enthalpy. Furthermore, 1 wt% BA was found to be the optimal concentration, achieving the best nucleating effect for PLLA. The cooling rate was a key factor affecting the non-isothermal crystallization peak. The set final melting temperature also affected crystallization, as a result of the solubility of BA in the PLLA matrix and the thermal decomposition of PLLA at the set temperature. Comparative study of the melting behavior of PLLA and PLLA/BA further confirmed the nucleating interaction of BA with PLLA. Differences in melting behavior were largely dependent on the competition between the crystallization rate and the relevant heating or cooling rate.

The nano-silver flake with about 30 nm, was prepared by a chemical reduction method. Cetyltrimethyl ammonium bromide (CTAB) was used to prevent agglomeration of the nanoparticles by its steric hindrance. However, an excessive amount of CTAB will impede the growth of silver nanoparticles, and thus it is not beneficial to the formation of the desired morphology. When the mass ratio of CTAB to silver nitrate is 0.8, the nano-silver with flaky structure can be obtained. At temperature of 20 °C, the solubility of CTAB is low, and it is difficult to retard the agglomeration effectively. At the same time, the low reaction rate will lead to large and nonuniform nanoparticles. When the temperature is 40 °C, the increased solubility of CTAB promotes the forming of nanoparticle. Nevertheless, when the temperature reaches 60 °C, the reaction is so fast that the nucleation rate increases and thus tiny particles are formed eventually. High pH value will lead to promote the reaction and ensure the complete consumption of Ag+, but too high pH may cause damage to the double-layer electronic structure of silver particles, resulting in collapse and agglomeration of the formed particles. When the pH value is around 6, stable nano-silver flakes can be obtained in a uniform dispersed form.

The effects of dioctyl phthalate (DOP) on performances of poly(L-lactic acid) (PLLA) were investigated in detail using optical depolarizer, X-ray diffraction, melt index instrument, and electronic tensile tester. Crystallization performance showed that the half time of overall PLLA crystallizationt1/2decreased with increasing of crystallization temperature (80°C to 105°C), but thet1/2of PLLA/DOP composites firstly decreased and then increased, andt1/2of PLLA/DOP exhibited minimum value at 85°C. Compared to neat PLLA, 20%DOP made thet1/2decrease from 7258.3 s to 265.4 s. X-ray diffraction experiment further confirmed that DOP could accelerate the crystallization of PLLA. The fluidity of PLLA/DOP composites indicated that the melt mass flow rate firstly decreased and then greatly increased with increasing of DOP content. The mechanical performance showed that DOP could improve the general mechanical performance, and the elongation at break of PLLA/25%DOP was about 30 times longer than that of neat PLLA.

We report on a three-color InAs/GaAs quantum dot infrared photodetector grown by molecular beam epitaxy. The InAs quantum dots with AlGaAs inserting layers are formed on an InGaAs quantum well layer as an absorber region. The detector is an nin-type device, and three photocurret peaks at 6.3, 10.2 and 11 m are observed at 77 K, respectively. Each peak is designated and the physical mechanism is discussed. The dependences of the intensities of the three peaks on the applied bias voltage are different for the positive and the negative bias conditions due to the asymmetric structure of the absorber region. The peak arising from the transition between the quantum dot ground state and a continuum state becomes weaker when the bias voltage is larger than a certain value. The physical reason is attributed to the decrease of the wavefunction overlap between the two quantum states.

Formamide and urea were used as plasticizers for corn starch to prepare formamide plasticized-thermoplastic starch (FPTPS) and urea plasticized-thermoplastic starch (UPTPS), respectively. The properties of thermoplastic starch (TPS) were tested by scanning electron microscope (SEM), x-ray diffraction (XRD), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and mechanical testing machine. Scanning electron microscope result shows that both formamide and urea can make corn starch plasticized form uniform continuous phase, but plasticizing effect of formamide was better than that of urea. X-ray diffraction exhibits that the crystallization peaks of FPTPS were disappeared, and a reduction minish for UPTPS, the crystallinity of FPTPS was smaller than UPTPS. The gelatinization temperature of two kinds of thermoplastic starches was basically the same, but the gelatinization enthalpy of FPTPS was much less than UPTPS. Formamide was better plasticized than urea for corn starch, which made the TGA inflection temperature and residual quantity of FPTPS was lower than UPTPS. FPTPS tensile strength was lower than UPTPS, but the elongation at break was much bigger than UPTPS.

[Abstract] Bi2Te 3 nanoparticles of 15∼25nm were prepared via solvothermal processes in which pyridine, absolute ethanol and distilled water were used as reaction medium respectively. The XRD and TEM have been applied to analyze the samples, and the grain sizes have also been calculated by Scherrer Equation. The results showed that in these experiments, all of the reaction products' purity, crystallization, grain size and tropism increased with dielectric constant and polarity of the solvent. A novel Bi2Te3 nanowires with several tens to a hundred nanometers diameter and up to more than ten microns length have been prepared when distilled water was used as reaction medium.

Na2O-B2O3-SiO2 glasses doped with semiconductor PbS quantum dots were fabricated via a sol-gel routine in this paper. The influence of different heat treatment on microstructure of glass were made, and characterization of the micro-crystals doped in glass matrix were made by varies methods. The result of N2 adsorption-desorption shows that the diameter of pores in the interior of glass diminishes, with increasing temperature, and the pores totally disappear at last. IR spectra indicate that network structure of glass is form at low temperature, and becomes compact at higher temperature. The PbS crystals are found in the glass matrix by both X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM), and the average size of the crystallites is 3.5nm in diameter. Comparing with the bulk PbS, the absorption edge in the optical absorption spectra of glass containing PbS quantum dots exhibits a blue shift and shows obvious quantum size effect. The nonlinear refractive index (γ) of the glass doped with PbS micro-crystals was determined by Z-scan technology to be -1.6×10-11cm2/GW.

The diamond-like carbon (DLC) films were deposited under different deposition parameters by using arc technology. The detailed relationship of sp3 structure with the D peak of the DLC films' Raman spectra is discussed. In aid of the discussion, X-ray photoelectron spectroscopy was used to determine the DLC films' C1s binding energy. By comparing the binding energy with the Raman shift of the films, it can be found that the intensity of D peak decomposed from the Raman shift can be increased not only by the graphite cluster, but also by higher content of sp3 bonds. Higher sp3 content of DLC films can be obtained by using 90 degree magnetic filter. The study shows that the C1s binding energy of DLC films, whose Raman spectra have higher intensity of D peak, can be 284.15 or 285.50 eV, which reveals that the DLC films may have higher graphite-like or diamond-like structure, respectively.