Key Engineering Materials Vols. 645-646

Abstract: A simple composite bonding that combines dielectric barrier discharge (DBD) plasma activation with anodic bonding has been developed to achieve strong silicon/glass bonding at low temperature. The realization of low temperature bonding is attributed to enhance the hydrophilicity and smooth of silicon and glass surfaces and form lots of free radical after the DBD plasma (including-OH, -H, O, and heat) reacts with the interfaces. And these further reduce the difficulty of chemical bond switching, and improve the speed of the intimate contact formation. The experimental result show that the bonding temperature strongly decreased 100°C by using composite anodic bonding with DBD pretreatment which strength kept constant, and 10MPa bonding strength was obtained at 250°C/900V after the bonding interface was treated for 10s under the conditions of AC1.5KV/25KHz and the clearance 100μm.

Abstract: SiC molds have excellent performance for high-temperature molding optical lenses. The stable physical and chemical properties of SiC results in the difficulty of manufacture high precision SiC molds. Using etching method can manufacture SiC molds apace and accurately, which is used for Micro-embossing needs to study the suitable selectivity ratio of SiC and the anti-etch layer-epoxy resin. The etching gas is SF₆ and O₂. Under different ICP power, bias voltage, the gas mixing ratio and other parameters, it has studied the influence of various factors on the etching ratio, the etching rate and the etching quality. Experiments show that under the parameters of SF₆ flow of 80sccm, O₂ flow of 5sccm, ICP power of 1200w, bias power of 70w, temperature of 30 °C, and pressure of 30mTorr, the SiC etching rate is 246.44nm/min, and the epoxy etching rate is 616nm/min. The SiC/epoxy resin etching ratio is stable at 1:2.5. The roughness of SiC is 1.2nm (Sa= 1.2nm). The anisotropic of etching is good.

Abstract: N-doped TiO₂ nanoparticle powders were prepared efficiently by the sol-gel method using triethylamine and ammonium hydroxide as composite N precursor. The as-prepared N-doped TiO₂ precursor powders were calcined at 300°C in air for 3 h and subsequently annealed at 300°C in air for 2.5 h. The samples were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy. The visible light photocatalytic activities of as-prepared samples were evaluated by photodecomposition of methyl orange (MO). The results show that the as-prepared samples have high visible light photocatalytic activities. Triethylamine produces the N-species doped in TiO₂ lattice responsible for the high visible light photocatalytic activity. Ammonium hydroxide makes the gel of the TiO₂ nanoparticles nitrided by triethylamine gelate further and facilitates significantly the centrifugation of the gel. An annealing treatment can eliminate effectively the outer N species caused by ammonium hydroxide and the surface organic residues, improve effectively crystallinity, and retain the N species caused by triethylamine.

Abstract: This paper describes the fabrication, characterization and the application of the photocatalytic TiO₂ nanofiber as the photocatalyst for the digestion of total phosphorus (TP). The nanoTiO₂ fibers were fabricated by the electro-spinning technique on silicon substrate. Under the conditions of room temperature (25 degrees Celsius) and humidity less than 40%, the TiO₂ fabricated by the electro-spinning presents a silky coagulation appearance, which can be converted to the nanofiber appearance by annealed in the muffle furnace at 450 degrees Celsius for 10 hours. X-ray diffraction (XRD) examination shows that the silky coagulation can be converted to anatase-type TiO₂. The absorbance values of different phosphate concentrations after exposure in UV light at the intensity of 7000μW/cm² were tested in this paper. Sodium tripolyphosphate solutions serve as the water sample of TP, and five standard concentrations (by weight of P) are 0.0mg/L, 1.0mg/L, 2.0mg/L,3.0mg/L and 4.0mg/L, respectively. The digestion rate exhibits satisfied linearity ranges from 0.0mg/L to 4.0mg/L with acceptable linearity R² of calibration curve, in both digestion temperature of 25 degrees Celsius and 50 degrees Celsius.

Abstract: Based on the design theory of film stack,H4 and SiO2 were selected as the high and low refractive index materials respectively. Through optimization by Macleod and TFCalc software, plus considering the internal electric field intensity distribution of film and laser induced damage threshold as well,the beam-splitting film with Tp=65±5% and Ts=30±5% in the 600-700 band in condition of 45 °± 3 ° incident angle has been achieved. Adopting electron beam ion assisted deposition system to development, the deposition parameters of materials has been optimized via orthogonal matrix experiment. The fabrication of thin film for laser polarization beam splitter has been succeeded. Its optical properties, mechanical properties and resistance to environmental test of the film have been approved to meet all using requirements.

Abstract: Dissimilar materials between TiNi shape memory alloy (SMA) and stainless steel of 200μm mm thick were butt welded by micro impulse laser and the electrochemical behavior of the weld joints was studied. The results show that the crack sensitivity of the welded joint is very high and good joining between TiNi SMA and stainless steel can be realized with pure Ni wire as filler material presented between TiNi SMA and stainless steel. The tensile strength of the welded joint with pure Ni wire as filler material is 580MPa. The electrochemical tests of the welded joints in different concentrations of NaCl solutions and different pH value solutions show that, the maximum of the corrosion potential Ecorr in the three typical corrosion systems (0.9%NaCl, pH=7.3; 3.5%NaCl, pH=7.3; 0.9%NaCl, pH=4) is the weld seam, which indicates that the corrosion tendency of the weld is smaller than that of TiNi alloy and stainless steel in the three corrosion systems. The pitting corrosion potential of TiNi alloy, stainless steel and the weld gradually decreased with the increase of Cl-concentration; the pitting corrosion potential decreased with the increase of H+ concentration, while TiNi alloy decreased faster than that of the weld and stainless steel, the surface stability of TiNi alloy is low when pH value dropped below 7.

Abstract: A multi-scale method was developed, which utilized intrinsic relationships among zeta potential of particles, rheological properties of suspensions and particle size distribution (PSD), to analyze dispersion behavior of nanoparticles in concentrated suspensions. It was found that PSD of a kind of nanoceria particles by dynamic light scattering (DLS) method in solution A with concentration 5 wt% accorded well with that by direct TEM analysis, which meant the particles had been dispersed well. However, there had a significant difference when the concentration was increased to 20 wt%. When particles concentration increased from 5 wt% to 20 wt%, zeta potential in solution A changed from-150 mV to-100 mV, while zeta potential in solution B changed from-35mV to-45 mV. Variations of zeta potential of particles accorded well with rheological properties of suspensions too, from phenomenological models. When the suspensions composed by solution A and the nanoparticles with concentration about 20 wt% was diluted with its original solution to 5 wt%, the PSD of nanoceria could be measured indirectly, which accorded well with both that of a suspension prepared directly with near concentration and that from TEM images. Then a method to measure PSD of nanoparticles in concentrated suspension was brought forward.

Abstract: The mechanical properties of SiC thin films deposited by chemical vapor deposition process on silicon substrate are studied using nanoindentation techniques. The SiC thin films are of three different thicknesses: 1.6μm、4.5μm、9μm. In this study, nanoindentation method is preferred due to its reliability and accuracy on determining mechanical properties from indentation load-displacement data. The mechanical properties of elastic modulus and hardness are characterized. 1.6μm SiC thin film has the following values: E=345.73Gpa, H=33.71Gpa; 4.5μm SiC thin film has the following values: E=170.18Gpa, H=10.33Gpa; 9μm SiC thin film: E=167.96Gpa, H=9.48Gpa

Abstract: In the micro electroforming process, the existence of electroforming layer defects caused by macro internal stress seriously limits the application and development of the micro electroforming technology. Currently, some studies have shown that ultrasonic can reduce the internal stress. But the formation process of the internal stress and the mechanism of ultrasonic stress relief in micro electroforming layer are still unclear now. In this paper, the relationship between dislocation density and internal stress under ultrasonic was studied. The results show that the ultrasonic can make the dislocation density increase and the compressive stress decrease. When the ultrasonic power is 200W, the dislocation density and the compressive stress culminate 3.8×10^-15m^-2 and-144.4MPa, respectively. The ultrasonic can excite the movement of dislocation proliferation, pile-up and opening, which leads to a micro plastic deformation in the crystal, and thereby releases the internal stress.

Abstract: Ultra High Toughness Cementitous Composites (UHTCC) is a unique class of the ultra-ductile fiber reinforced cementitious composites. To meet the increasingly high requirements for materials in the construction, nanoSiO₂, polyvinyl alcohol (PVA) and steel (ST) fibers were added into UHTCC to improve the mechanical property and control the crack width. Multiple effects of nanosilica and hybrid fibers on the flexural properties of UHTCC under three-point bending are evaluated. The results show that nanoSiO₂ can increase flexural strength of UHTCC while equivalent deformability is guaranteed. When the addition of nanoSiO₂ is 5%, the highest flexural strength is 15.77MPa. Moreover, hybrid steel-PVA fibers effectively mitigate negative influence from nanoSiO₂ which induce the wider cracks of UHTCC as the stronger matrix. Comparing with mono fiber composites, hybrid fibers composites exhibit remarkably higher flexural strength and slightly lower deformation. The best performance are 24.85MPa and 2.34% at maximum volume of hybrid fibers.