Key Engineering Materials Vols. 609-610

Abstract: Springback is an important factor influencing forming precision in bending process, which becomes more complex for micro metal foil due to the size effect existing. Bending springback is studied through the micro bending experiments designed with different grain sizes and foil thicknesses using T2 purple copper in this paper. The accurate stress-strain relationships are obtained based on the copper foil tensile experiments; the bending process of micro-component is simulated based on both dynamic explicit and static implicit codes. Comparison of simulation results with experimental results shows that: thickness can serve as an important parameter effecting on the springback; the trend of springback amount rising with a thickness diminishing enhances in small size; sheets with same thickness exhibit phenomenon of springback angle reducing with an increasing grain size. Bending springback of micro metal foil indicates obvious size effect on foil thickness and grain size.

Abstract: The effect of galvanic interaction between the evolving facets of the etch front on the Si {100} surface smoothness during wet anisotropic etching in surfactant-added tetramethylammonium hydroxide (TMAH) is studied by etching different mask patterns. Triton X-100, with formula C₁₄H₂₂O(C₂H₄O)_n, where n=9-10, is used as the surfactant. The different smoothness of wet etched Si {100} surfaces, evaluated by atomic force microscope (AFM) and optical microscope, indicates that the wet etched Si {100} surfaces could become extremely smooth after the onset of the electrochemical etching contribution. A model to account for the galvanic interaction between the evolving facets is proposed, demonstrating that the chemical etching can be significantly surpassed by the electrochemical etching when the relative area of the exposed {100} surfaces are relatively small in comparison to that of the developed {111} sidewalls. Additionally, silicon beams with smooth surfaces are presented in the fabrication of a sandwich micro accelerometer to avoid the risk of device invalidation. This study is useful for engineering applications where the fabrication of microstructures for high quality devices should contain smooth surfaces.

Abstract: nanoTiO₂/cellulose composite gels have been uniformly blended during the dissolving process of cellulose in ionic liquids (ILs). After the regeneration process, the obtained hydrogel was finally dried through supercritical CO₂ to obtain the TiO₂/cellulose composite aerogel. The structure and properties of the composite aerogel were characterized by XRD, SEM, FT-IR, UV-vis, and photocatalytic degradation tests. The porous structure and hydroxyl groups in the regenerated cellulose matrix provided cavities and affinity for the immobilization of TiO₂ in the cellulose gels through electrostatic and hydrogen bonding interactions. The TiO₂/cellulose composite gels exhibited a good photocatalytic activity for photodegradation of Rhodamine B (RhB) under UV light irradiation. This research highlights another opportunity for the development of the portable and flexible photocatalyst.

Abstract: Direct current (DC) magnetron sputtering method was used to deposit vanadium oxide thin films on ordinary glass substrates from a vanadium metal target and a five factors four levels orthogonal experimental method was used to find the best combination of sputtering pressure, sputtering power, oxygen/argon flow ratio, substrate temperature and deposition time for fabricating high temperature coefficient of resistance (TCR) vanadium oxide film. The results indicate that a good combination of these parameters should be 1Pa, 160W, 1.5/25, 280°C and 60 minutes. And the film fabricated using this parameters combination is mainly composed of V₂O₅ and has a resistance range of 80.3kΩ to 40kΩ while its temperature changed from 20°C to 80°C.

Abstract: In this work, optical K9 glass surface has been flattened by nanoparticle colloid jet machining, which is an ultra-smooth surface processing technique utilizing surface chemical effect between work surface atoms and nanoparticles in alkaline colloid to remove the uppermost surface atoms. The surface removal process of nanoparticle colloid jet machining has been investigated through K9 glass polish experiments. And the characterizations of ultra-smooth K9 glass surface polished by nanoparticle colloid jet machining have also been studied in this paper. Surface profiler and atomic force microscopy (AFM) are used to observe the surface microscopic morphological characteristics of K9 glass sample before and after polishing by nanoparticle colloid jet machining. The measurement results of processed surface prove that the primary scratches on the original surface have been completely wiped off by nanoparticle colloid jet machining and the roughness of the K9 glass surface has been improved to be less than 1 nm (Rq). Autocovariance (ACF) is investigated along a cross section of the K9 glass surface to determine the dominant spatial frequencies. The ACF curves show that the surface morphology of K9 glass processed by nanoparticle colloid jet machining is completely different from the preprocessed surface. The final K9 glass surface has been flattened by nanoparticle colloid jet machining. The microscopic morphological profile of the final K9 glass surface becomes increasingly smooth and eventually close to a flat state.

Abstract: By applying ultrasonic solidification, gypsum based micro casting mold with different chemical compositions were sintered at different temperatures. The influence of processing parameters and sintering temperature on the microstructure and surface roughness were investigated. Meanwhile, the effect of sintering temperature on the bending strength was studied. The result showed that the nucleation rate of gypsum can be significantly improved under high temperature and pressure, which was caused by the effect of ultrasonic cavitation. Under the frequency of 100 KHz and the power of 200 W, 20 min, the morphology of gypsum transfers from flake and needle into near spherical after 20 min, and the grain size can be refined to around 500 nm. The value node of surface roughness occurs at the sintering temperature of 600 °C. The surface roughness is the lowest when the gypsum content is 60% and under the sintering temperature of 600 °C, which can reach Ra ~ 0.22 um. The bending strength of mold roughly increased with the increase of content of gypsum. There is no obvious rule for the mold strength with the change of sintering temperature. The mold strength reaches the highest value when the sintering temperature is 600°C.

Abstract: In this paper, ZnO thin films were prepared on ITO conductive glass by direct current magnetron sputtering and the Cu electrodes were evaporated on ZnO/ITO by electric beam evaporation to get transparent Cu/ZnO/ITO resistive random access memory. The crystal structure and surface morphology were investigated by X-ray diffraction and atomic force microscopy, respectively. The transmittance spectra of ZnO/ITO in the visible region were measured by UV-VIS spectroscopy. The resistive switching characteristics of the fabricated devices were investigated by the voltage sweeping method, which showed that the transparent Cu/ZnO/ITO device had good resistive switching characteristics.

Abstract: Mesophase microbeads were prepared by thermal condensation in the presence of heterogeneous and homogeneous systems. Morphologies and sizes of mesophase microbeads are characterized by scanning electronic microcopy (SEM), polarized light optical microphotography (PLOM) and laser particle size analyzer. SEM and PLOM results exhibit that mesophase microbeads have a narrow size distribution and many large particle in heterogeneous system. In homogeneous system, there are a great deal of smaller mesophase microbeads and a very little of larger mesophase microbeads. The laser particle size analysis results show that size distribution of mesophase microbeads in heterogeneous system is quite different from that in homogeneous system. There are multi-peaks on volume distribution curve in heterogeneous system. Larger mesophase microbeads are mainly in tens micron peak of size distribution curve. In homogeneous system, particle size of mesophase microbeads has a wide distribution and only single peak on size distribution curve. Moreover, sulfur concentration in reaction system makes the size of mesophase microbeads increase and the size distribution curve move to larger particle diameter. But sulfur concentration can not affect the curve pattern of size distribution.

Abstract: Aiming at the special requirements for filter film of the optical prismatic system, basing on the design theory, and choosing the appreciate film materials, a high reflectance film and a splitter film are designed respectively. The films can satisfy with the optical requirement perfectly, when the incidence light is P polarized at the 25 angle in the range of the visible wavelengths (450nm~650nm). During the preparation process, the optical film absorption is solved by continually optimizing the process parameters, such as temperature, rate of evaporation and ion assisted deposition parameters, etc. Meanwhile, the error produced in the process of preparation is analyzed and revised through several repeated tests and researches, so that the control precision of layer thickness is improved. Finally the high-reflective film with average reflectance over 99.5% in the 450~500nm band and the beam splitting film with transmittance and reflectance ratio of 1:1 and 1:2 are prepared respectively (both errors are below 1%) in the 450~650nm band. After the spectrum testing and analyzing, the spectrum curve shows that all the parameters meet the basic requirements for usage.

Abstract: In order to apply nanofluids to ammonia-water absorption refrigeration, several groups of nanofluids mixing with rutile TiO₂(r-TiO₂) and ammonia-water were perpared by an optimizing method. Observation tests were carried out to investigate the effects of the kind and mass fraction of dispersant, mass fraction of ammonia-water basefluid and durations of supersonic vibration on the dispersion stability of nanofluids. The results show that, all three factors have influences on the dispersion. The optimal dispersing condition of 0.1wt% r-TiO₂ nanofluids was 0.1% of PAA in 25% ammonia water basefluid with 10 minutes of ultrasonic vibration.