Key Engineering Materials Vols. 562-565

Abstract: In order to study on the effect of the content of Zn to phase morphology and photocatalytic performance of ZnO/TiO2 composite material, we prepare ZnO particle finishing with surface chemistry and make tubular TiO2 with hydrothermal. Using characterization methods like XRD,SEM,TEM to explore how various conditions such as different incineration temperature, atomic ratio, etc can interfere with morphology, structure and photocatalytic performance of composite. In this experiment, the surface of TiO2 nanotubes combusted under the temperature of 673K for 2h are smooth;Zn:TiO2=1:4 to achieve uniformly and firmly distributed nano composite particles which grain size is 11nm on the surface of TiO2 nanotubes,including 2-3nm ZnO particles on tubes; 0.1mol/L sodium hydrate-ethanol solution as precipitant to obtain ZnO/tubular TiO2 composite materials which are highly dispersed and deposited on the surface of tube-shaped TiO2; Zn:Ti=1:4 reach the best catalytic result.

Abstract: As a renewable, clear and inexhaustible energy, solar energy receives much more attention and has partly substituted traditional energies in many fields. Multi-crystalline silicon plays an important role for its low cost, abundant reserves and excellent photoelectric conversion in solar cells. Mixed acid etching is an effectively method to texture the morphology on the surface of mc-Si, While stochastic etching between silicon and acids results in irregular texturing and high reflectivity. In this paper, ultrasonic standing wave is introduced into acid solution, which aid wet etching to texture on the surface of mc-Si by controlling distribution of atoms of acids. Scanning electron microscope experiment shows that the morphology on the surface of mc-Si textured by this method is similar to that of mono-crystalline silicon. And the average reflectivity is 8%, much lower than mixed acid etching.

Abstract: Polyesteramides (PEA) has both good heat resistance and degradability properties. In recent years, the Preparation of carbon nanotubes have became relatively advanced, but the reports of degradable nanocomposites and patents are less. In this paper, PEA/MWNTs (multi-walled carbon nanotubes) were synthesized using the in situ polymerization method, and the degradation in the air and alkaline was studied. The results show that MWNTs can be uniformly dispersed in the composited polyesteramides, the addition of MWNTs reduced the thermal properties of the PEA/MWNTs in the air. The PEA/MWNTs heat resistance and degradation rate in an alkaline solution were apparent changed in the content of the MWNTs is 0.7wt%.

Abstract: In this paper, a novel lapping method based on regulating the position of carrier centroid is proposed to modify interfacial normal pressure uniformity. Eight special points are selected to represent carrier weight. This lapping process can be divided into initial stage, regulated stage and stable stage. The purpose of initial stage is calculating the position of carrier centroid according to the equivalent mass of eight points. The regulated stage is to decrease total thickness variation (TTV) by regulating the position of weight. Finally, the stable stage will keep uniformity of material removal rate (MRR) uniform at each point. A 3-inch and 400 μm thickness silicon wafer is lapped to demonstrate the feasibility of this method. We can find that TTV of this wafer decreases from initial stage 20 μm to 3 μm and remain constant. Therefore, the uniformity of MRR has been greatly improved by this novel lapping method.

Abstract: In this paper a novel and sensitive electrochemical sensor for the detection of formaldehyde was developed based on the platinum nanoparticles and L-alanine modified glassy carbon electrode. The sensor was fabricated by two steps. Platinum nanoparticles were immobilized on the electrode via electrodeposition method firstly, then the L-alanine was modified on the electrode by self-assembly method. The structure and morphologies of the Platinum nanoparticles were characterized by SEM and TEM. The electrocatalytic activity of the PtNP-L-alanine/GC electrode for formaldehyde detection in alkaline media was investigated via a series of electrochemical measurements. The PtNP-L-alanine/GC electrode show very high electrochemical activity toward formaldehyde. The oxidation peak current had a linear relationship with the formaldehyde concentration in the 0.3 µmol dm-3 to 4.0 mmol dm-3 range (R=0.9998), while the detection limit was estimated to be 34 nmol dm-3 (S/N=3). Such high sensitivity was attributed to the large surface area of the highly dispersed nanoparticles for electrocatalytic reaction and the fast electron transfer in the composite electrode. It demonstrated that glassy carbon electrode modified by platinum nanoparticles and L-alanine was suitable for the determination of formaldehyde.

Abstract: A series of three-dimensional molecular dynamics (MD) simulations of nanoindentation are conducted to investigate the deformation behavior and phase transformation of monocrystalline silicon with different size hemispherical diamond indenters on (010) crystal plane. The technique of coordination number (CN) is employed to elucidate the detailed mechanism of phase transformation in the monocrystalline silicon. The simulation results show that the phase transformation varies according to the different radii indenters. In the phase transformation region beneath the indenter, the crystalline structures of Si-II, Si-XIII, and amorphous phase structures are observed. In addition, the results indicate that phase transformation with large indenters is not same with the small indenter. The six-coordinated silicon phase, Si-XIII, transformed from Si-I is identified. The phases of Si-II and Si-XIII, which have the same coordinate number, are successfully extracted from the transformation region during nanoindentation and amorphous phase will emerge upon unloading.

Abstract: The characterization technique of glass-ceramics by TEM was discussed by comparing the effects of single layer carbon film technique and double layers carbon film technique on the microstructure of Li-Al-Si glass-ceramics. The results show that double layers carbon film technique can improve glass-ceramics sample’s conductivity, reduce the induction of elctron beam on glass-ceramics, and avoid the temperature increasing of glass-ceramics particles caused by the charges aggregation on the particles’ surface when TEM electron beam hit down, prevent glass-ceramics from crystallization and the transformation of microstructurec. So, compared with single layer carbon film technique, double layers carbon film technique is more suitable for the research of microsture of glass-ceramics by TEM.

Abstract: A Platinum nanoparticles modified Au electrode has been successfully fabricated by using an in situ growth method. In this method, the Platinum nanoparticles could be grown on the Au electrode surface via the one-step immersion into the mixture of H2PtCl6 (analytical grade, 1g/L), NaBH4 (analytical grade) and polyvinylpyrrolidone K30 (PVP, analytical grade). A certain amount of PVP was added into the reaction system to prevent the coagulation of the Platinum nanoparticles, which obtained by the chemical redox reaction of H2PtCl6 and NaBH4. The structures and morphologies of the Platinum nanoparticles were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) . The direct electrochemical behavior of ascorbic acid in 0.3 mol/L NaCl medium at the Platinum nanoparticles modified electrode has been investigated in detail. Compared to a bare Au electrode, a substantial decrease in the overvoltage of the ascorbic acid was observed at the Platinum nanoparticles modified electrode with oxidation starting at ca. 0.20 V vs. SCE (saturated KCl). At an applied potential of 0.18V, this modified electrode produced high and reproducible sensitivity to ascorbic acid and linear responses were obtained over a concentration range from 0.600 to 3.267 μmol/L with a detection limit of 1.9 nmol/L(S/N=3). The fabrication method of this sensor, which has highly sensitive, low working potential, and fast amperometric sensing to ascorbic acid, is simple and without using complex equipment. In addition, the sensor has been successfully used to detect ascorbic acid in real sample, thus is promising for the future development of ascorbic acid sensors.

Abstract: A composite nanofibers of modified konjac glucomannan (MKGM)/PBS were prerared by electrospinning process. The property of electrospinning solution and nanofibers were characterized by rheology, conductivity, surface tension and SEM. The diameter of nanofibers changed with addition of PBS, and the optional ratio for mixing MKGM with PBS is 6:4. The diameter of the nanofibers obtained at that ratio ranged from 236 to 1495nm, and the average diameter was 432nm.

Abstract: Thermal conductivities of the titanium carbide thin films with thickness ranging from 58 to 158 nm were measured at room temperature using the transient thermoreflectance technique. The results show that thermal conductivities of these films are lower than corresponding bulk material values. The reduction in the thermal conductivity can be attributed to the material microstructure brought by the thin film fabrication process. Both the film thickness and the atom ratio of Ti/C are the important factors. The thermal conductivity increases with the increasing film thickness and atom ratio of Ti/C. It also indicates that the material beneficial to thermal management and thermal design could be fabricated by improvement of the deposition techniques.