Materials Science Forum Vols. 675-677

Abstract: The effects of melting condition on the dephosphorization behavior in metallurgical grade silicon (MG-Si) by electron beam melting (EBM) were investigated in this study. Experiment results showed that phosphorus content decreased by evaporation with the increase of melting time, and evaporation rate increased with the increase of electron beam power. Phosphorus content decreased to below 0.1 ppmw by EBM treatment at 21 kW for 1800 seconds. The dephosphorization reaction was found to follow the first order kinetics. Dephosphorization rate was controlled by free evaporation.

Abstract: Proton conductivity of the natural diatomite was studied by AC complex impedance technique. At room temperature, the highest proton conductivity was found to be 4.5　10-7 S·cm-1. By hydrating the diatomite, the proton conductivity was increased by two orders of magnitude. The room temperate proton conductivity of the hydrated diatomite (5.5　10-5 S·cm-1) was comparable to other hydrated solid proton conductors. Based on these results, the natural diatomite could be used as solid proton conductor for various electrochemical applications such as fuel cells, gas sensors, humidity sensors, and pH sensors.

Abstract: In this paper, the structure and composition of multicrystalline silicon ingots prepared by directional solidification with different pulling rates were analyzed to investigate the effect of pulling rate on the multicrystalline silicon ingot. The results showed that the lower pulling rate will make the site taking place constitutional supercooling move to the upper part of ingots and make the high purity area become larger. Lowering the pulling rate will decrease the impurity effective segregation coefficient and the solid-liquid interface curvature.

Abstract: The olivine-type LiFePO4 powder was prepared by a chemical method using the synthesized FePO4⋅2H2O, LiOH and glucose as raw materials. The synthesized FePO4⋅2H2O powder was obtained by co-precipitation method. FePO4⋅2H2O and LiFePO4 powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed the synthesized FePO4⋅2H2O powder at pH of 2.05 was in a single phase and nearly spherical in shape. Using the synthesized powders to prepared LiFePO4 at 600 °C in vacuum for 2 h was nearly spherical in shape and whose size was in the range of 0.1-0.5μm.

Abstract: In order to investigate flowability and drying shrinkage of ECC, mini-slump flow deformation test and drying shrinkage are employed to analyse the influence of fly ash on the flowability and shrinkage of ECC. The water-binder ratio is kept at 0.25. The replacement ratio of cement by fly ash is 50%, 60%, 70% and 80%, respectively. The experimental results show that fluidity of fresh cment paste increases obviously as the fly ash becomes larger. The drying shrinkage of ECC specimens is greatly reduced as the content of fly ash increases from 50% to 80%. The measured drying shrinkage strian of ECC specimens with 80% fly ash at 28 days is less than 1000×10-6. 25% reduction of drying shrinkage of ECC is found when the fly ash content increases from 50% to 80%.

Abstract: The real times Electrochemical Impedance Spectroscopy (EIS) analysis which corresponds to the charge and discharge process was reported in order to evaluate the relationships between impedance and potential for new high specific energy electrochemical double-layer capacitors (EDLC). Also the Niquist plots were presented and the impedance of the EDLC was discussed in terms of complex capacitance. It was found that the high frequency impedance changed with its potential in charging or discharging process, the medium frequency impedance Rct belonged to the resistance of ions diffusion into micro pore or the inner of electrode material decreased with increasing charge voltage and had a certain capacitance of about 1F.

Abstract: Copper hydroxyphosphate,as self-assembled nanoparticles, was synthesized by using a hydrothermal method,with cupric acetate (Cu(CH3COO)2·H2O) and diammonium hydrogen phosphate ((NH4)2HPO4) as raw materials. Physical property of copper hydrophosphate was characterized by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and Ultraviolet obvious diffuse reflection(UV-vis DRS). No surfactants or templates were added in the procedure of preparation. By simply adjusting the pH from 3 to 9, the morphology of copper hydrophosphate varied from microrods to walnutshaped microspheres. Photocatalytic activity of the samples was also investigated. Photo decoloration of Rhodamine B in water under visible light irradiation shows that copper hydrophosphate (pH=7) have the best photocatalytic activity: Photodecoloration activity of 100 mL Rhodamine B (10 mg/L) was 98 % under illumination for 30 min.

Abstract: To improve current matching in a tandem solar cell, a strain-compensated InGaAs/GaAsP multiple quantum-wells (MQWs) structure was grown within the middle GaAs PN junction, using metal organic vapor phase epitaxy (MOVPE) on GaAs substrate. Aiming at an accurate design of adsorption edge and precise control of crystal quality in MQWs, post- and in situ characterization was applied in such a fabrication process. Here, we report some applications of some post-characterization such as: X-ray scanning and reciprocal mapping in clarifying composition and crystal quality in these structures; photoluminescence (PL) and FTIR in determining adsorption edge and even indicate some irradiative recombination features as well. By employing an in situ optical surface reflectivity measurement, we established a way of and evaluating an instant of strain relaxation in the course of MOVPE, which deteriorates crystal quality significantly. When strain balancing was incomplete, surface reflectivity dropped during the growth of MQWs, indicating lattice relaxation. The accumulated strain, which is defined as the average strain per period of QW multiply the number of stacking for MQWs , was roughly constant for all the MQWs samples in our experiment. Therefore, it may indicate that this overall strain may be used as a tentative criterion of critical value for lattice relaxation or to predict the maximum number of MQWs for a given value of the average strain per QW period. Combining both post and in situ characterizations, we can effectively adjust the overall strain to get defects free growth for MQWs, and also significant features can be observed for better understanding the heterostructure management.

Abstract: Nano-sized precursor FePO4·xH2O particles were obtained by oxidation co-precipitation using FeSO4⋅7H2O, H2O2 and ammonia. The powder was characterized by differential thermal analysis (DTA) and thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The TG-DTA results determined the content of crystal water of FePO4·xH2O, i.e. x = 1.5. The SEM observation suggested that FePO4·xH2O particles were spherical in shape and its grain size was about 150 nanometers. The dispersion of the synthesized powder was improved through the addition of surfactant. The XRD analysis indicated that the synthesized FePO4·xH2O was amorphous. After being calcined at 720 °C for 10 hrs, the synthesized FePO4·xH2O at pH of ~3.5 was crystallized and FePO4 in a single phase was obtained. According to the test results, the optimized preparation process parameters were determined.

Abstract: La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) thin film electrolytes were fabricated on La0.7Sr0.3Cr0.5Mn0.5O3-δ (LSCM) porous anodes by radio-frequency (RF) magnetron sputtering. The formation and microstructure of LSGM thin films were characterized by X-ray diffraction(XRD) and scanning electron microscopy (SEM). The effects of different sputtering conditions, such as Ar gas pressure, substrate temperature and sputtering power, on the performance of LSGM electrolyte film were estimated. Dense LSGM thin film electrolytes with thickness of about 2μm, which are compatible with LSCM-based anodes and without crack, have been successfully fabricated on LSCM-based anode supports by RF magnetron sputtering when sputtering power density is 5.2W·cm-2, Ar gas pressure is 5Pa and substrate temperature is 300°C. It is found that high sputtering power density and high Ar gas pressure, as well as high substrate temperature, are beneficial to deposition of dense electrolyte thin film, close bonding of electrolyte thin film with anode substrate, and formation of large three phase boundaries between anode and electrolyte.