Abstract: Exfoliated graphite with different expanding volume (EV) was prepared by two-step intercalation, in which the mixture of nitric acid and phosphoric acid, and that of nitric acid and acetic acid were employed as intercalating agent step by step, and potassium permanganate was used as oxidant. Its microstructure was analyzed by scanning electron microscope, and its millimeter-wave attenuation performance was measured by a static method. The results show that the exfoliated graphite forms more microcellular structures and its layers become thinner with the increasing of EV, the interlayers are fully opened and there are more tiny graphite flakes with size distribution between several microns and several ten microns. The millimeter-wave attenuation performance enhances with the increasing of EV, and the 3mm wave attenuation value rises from 5.7dB to 8.68dB When EV increases from 233ml/g to 450ml/g, which is mainly attributed to the full expansion of exfoliated graphite to form larger scattering cross section and the absorption of more tiny graphite flakes with size distribution between several microns and several ten microns.
Abstract: Mass fraction of 1.5%, 3% of the nanomontmorillonite (MMT) were separately added in the phenol prepolymer, phenolic resin/ MMT was synthesized by in-situ method (it is called PF/M). The PF/M was carried out TG analysis using thermal analyser, and the synthetic resin PF/M were as new resin matrix to prepare semimetallic friction material, tribological performance test was carried on XD-MSM fixed speed type friction-wear testing machine in accordance with the GB_5763-2008. The results show that the heat resistance of composite PF/M and tribological performance of friction material are best when nanoMMT is 3% in the resin, the Carbon residue rate of PF/M is an increase of 37% compared with PF without nanoparticles at 600°C, thermal recession temperature of sample by the preparation of PF/M increases above 100°C, and it has stable friction coefficient, overall wear rate decreases 26%, especially in high temperature stage at 350°C, the wear rate decreases significantly, its wear rate decreases 30%.
Abstract: Effects of different preparation parameters on the structural and mechanical properties of micro-arc oxidation coatings prepared in silicate electrolyte on 6063 alloy were investigated. The results show that the growth rate of ceramic coating increases with increasing current density and electrolyte concentration. The prepared coating had denser and smoother surface with few defects, higher micro-hardness values and better wear resistance when the current density was increased to 20A/dm2. The measurement properties were all up to their optimum values when the electrolyte concentration was in the range of 9-12g/l and oxidation time was 60min, respectively.
Abstract: In this manuscript, we report the simulation of electronic structures of TiO2 doped with Ag using first-principles calculation, based on the density functional theory (DFT) The mechanism to improve the visible-light photocatalytic activity for TiO2 doped with Ag. EF was displaced into the valence band (VB), narrowing the band gap. An independent energy band was also introduced above the VB and an energy band with the width of 0.9 eV is introduced under the conduction band (CB), also resulting in the narrowing of the band gap. New VB and CB were formed by three orbitals O-2p, Ti-3d and Ag-4d. Composite TiO2 nanotubes with Ag-doping were synthesized using the alkaline fusion and hydrothermal method under ambient atmosphere. XRD results indicated composite Ag-TiO2 nanotubes ranging from the single anatase phase to the anatase and rutile mixed phase. XPS showed an increase in the surface acidity and photo catalytic activity of TiO2 nanotubes due to the presence of OH radicals. Furthermore Ag-doping also facilitated the separation of photo-holes and photo-electrons and enhanced the optical properties.
Abstract: A removal of Cu (II) ions from aqueous solutions onto PAM/ATP has been investigated using batch adsorption technique, including the effect of pH, contact time, initial metal ion concentration, adsorption thermodynamics and kinetics. PAM/ATP was characterized with Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The equilibrium data were analyzed using Langmuir and Freundlich isotherms and the best interpretation was given by Langmuir. The maximum adsorption capacity was found to be 212 mg/g after 60 min when pH =3. Regeneration experiments showed that the investigated PAM/ATP could be reused without significant adsorption losses even after five adsorption-desorption cycles.
Abstract: By using scanning electron microscope and focused ion beam (SEM-FIB) dual beam system which was self-assembled, with xenon diflouride, nanograting structure has been successfully processed on the gilded silicon wafer. The grating period is 950 nm, and the width of single etched groove is 652 nm. Gas-assisted ion etching is also known as focused ion beam assisted etching (FIBAE). The working principle of FIBAE was analyzed firstly. The different experimental results of nanograting structures which were fabricated by FIBAE and FIB alone were investigated. And the effect of exposure time on nanograting structures was also studied detailed in the FIBAE process. The Results showed that FIBAE has the technology advantage of high reaction rate, saving time, reducing costs, and deep etching, and it provides an effective method for processing nanograting of high depth in the future.
Abstract: A novel micro spring with steel structures is described here. It can be fit into a specially designed microtensile apparatus, which is capable of carrying out a series of tests on micron scale freestanding thin films. This method is suitable for thin metal films or polymer layers with large strain and can be applied to samples with different thicknesses. The novel fabrication method uses the conventional lithography and electrochemical metal etching techniques. A single photomask is used to define the whole structure, resulting in a simple and inexpensive fabrication process. The method proposed here is promising for the low cost fabrication of micro spring based on steel. A micro spring of 100μm wide, 100μm thick, with 200μm diametric of the semicircle and 6 turns was prepared by this method; the elasticity of the spring is 147.3N / m. A gold wire was measured by this micro spring. The young's modulus and ultimate tensile strength of the gold wire were 30Gpa and 120Mpa, respectively.
Abstract: Cu2O, a p-type semiconductor, has broad potential applications, especially as a visible-light photocatalyst. This paper presents a simple water-bath reflux to prepare Cu2O micro/nanoparticles. The morphology evolution from intact octahedrons to surface-pitted spheres was obtained by adjusting reducing agent and additive. Reflectance spectra show similar photo-absorption intensity and the same range from 250 nm to 650 nm. However, they perform different photocatalytic activity. Intact octahedron has the best photodegradation ability and next is vertex-and edge-damaged octahedron, the lowest for vertex-free polyhedrons and surface-pitted spheres. The enhanced photocatalytic activity for intact octahedrons should to be attributed to its surface characteristics of high index. Our study not only provides a simple method for controllable preparation of Cu2O micro/nanoparticles with different morphologies but also confirms the effect of morphologies on photocatalytic activity.
Abstract: Becoming another key technology for system integration, GaAs based millimeter wave antenna is fabricated by MEMS technology, with high permittivity dielectric substrates. To obtain good performance, it is necessary to achieve the equivalent of low dielectric constant of the local area below microstrip patch antenna. The article describes deep etching fabrication and multiple etching with thick photoresist masking to creat air cavity under the microstrip patch which usually has the height from 70% to 80% of the original media substrate, thus it forms the air-mixed media substrate. Especially for precision control of the substrate thickness, use back thinning and high-precision polishing processes. At last realize back cavity depth of 227μm in the GaAs substrate and complete the process of Ka band MEMS patch antenna. The measurement results: the center frequency is 37.9 GHz, bandwidth is 4.4%, radiation efficiency above 50%.