Advanced Materials Research Vols. 476-478

Abstract: In order to develop a new middle dielectric constant LTCC materials, the effects of BaO–ZnO–TiO₂–B₂O₃–SiO₂(BZTBS) and/or BaCu(B2O5)(BCB2) on the phase composition, microstructure and microwave dielectric properties of BaO–ZnO–TiO2 ceramics were investigated by solid-state reaction. It was found that BCB2 mainly worked as sintering aids to lower the sintering temperature and the key role of BZTBS was to affect the phase composition in favour of showing a high Q×f value. Therefore, when 5wt% BZTBS+6wt% BCB2 were co-doped, the sintering temperature was down to 850°C, and the microwave dielectric properties were improved significantly because the densification and grain size distribution were not only improved but also the phase composition was controlled. At last, this ceramics sintered at 850°C for 0.5 h showed good microwave dielectric properties: ε_r=28.4, Q×f=8,030 GHz and τ_f=2 ppm/°C. Also, it was compatible with Ag electrodes, so it was a promising candidate for LTCC application.

Abstract: Spherical gold colloidal nanoparticles were prepared used traditional liquid phase method and the corresponding nonlinear absorption properties were investigated by open aperture Z-scan technique using 8 ns laser pulses of 532 nm. The gold colloidal nanoparticles exhibited a transform from saturable absorption (SA) to reverse saturable absorption (RSA) at relatively higher irradiation intensities. The SA behavior presumably owes to the bleach of ground-state surface plasmon resonance (SPR) absorption, while the RSA might result from high excited-stated free carrier absorption.

Abstract: Ba(Ti0.95Sn0.05)O3 ceramics were prepared using BaCO3, SnO2 and TiO2 et al as crude materials, La2O3 as dopant, and their dielectric properties are investigated. The morphology analysis of sintered samples was conducted by SEM. It is found that for 0.1 wt% La2O3 doped BTS5 ceramics sintered at 1290oC has the highest dielectric constant. It can also be seen that the samples sintered at 1260oC have higher dielectric loss, which can result from the existence of the pore. Meanwhile, in the terms of dielectric loss, 0.1 wt% La2O3 doped BTS5 ceramics has lower value and the dielectric loss is more stable with temperature varying.

Abstract: Generally, high thermal conductivity of SiC ceramics is required. However, in some circumstances, low thermal conductivity SiC is also needed, for example, for good thermoelectricity or heat insulation. In this work, the product of pyrolysis of polycarbosilane (PCS) is chosen as raw materials. The microwave sintering process was applied to obtain low thermal conductivity at a relatively low sintering temperature. The microwave sintering processes were performed at 1200 °C under Ar atmosphere with dwelling time of 10, 20 and 30 min. The morphology and phases were analyzed by electric microscopy and X-ray diffraction (XRD), respectively. The thermal diffusivities, specific heat and thermal conductivities were measured by laser-flashed method using a thermal analyzer. The thermal conductivity of samples is within the range from 0.81 to 1.37 W/m•K. The sample with dwelling time of 30 min shows potential for multiple applications, due to its good crystallization in XRD spectra and relatively low thermal conductivity in the considered temperature range. The results also suggest a phase transformation at a dwelling time near 20 min that may have occurred.

Abstract: This paper presents the dual fuzzy neural network, designed the decisional autonomy flight controller for civil aviation aircraft in approach and landing phase. Real-time learning method was applied to train the neural network using the gradient-descent of an error function to adaptively update weights. Adaptive learning rates were obtained through the analysis of Lyapunov stability to guarantee the convergence of learning. Conventional automatic landing system (ALS) can provide a smooth landing, which is essential to the comfort of passengers. However, these systems work only within a specified operational safety envelope. When the conditions are beyond the envelope, such as turbulence or wind shear, they often cannot be used. The objective of this paper is to investigate the use of dual fuzzy neural network in ALS and to make that system more intelligent.

Abstract: ZnNb2O6 ceramics doped with V2O5 were prepared by conventional mixed solid method. The effects of V2O5 addition on the microstructure and the microwave dielectric properties of ZnNb2O6 ceramics were investigated systematically. The sintering temperature of ZnNb2O6 ceramics with 1.0wt.% V2O5 addition can be effectively reduced from 1150°C to 1050°C. The secondary phase ZnV2O6 was observed in sintered samples with V2O5 addition content higher than 1.0wt.%. For 0.3–3wt.%V2O5-doped ZnNb2O6 ceramics, The dielectric constants (εr) of densified samples were higher than that of undoped ZnNb2O6 ceramics. The temperature coefficient of resonant frequency (τf) were shifted toward zero direction with the increase of V2O5 addition, However, the dielectric loss (tanδ=1/Q) increased. The 1.0wt.% V2O5-doped ZnNb2O6 ceramics sintered at 1050°C for 3h have the optimum microwave dielectric properties: εr=28, tanδ=0.0006 and τf=-42.5 ppm/°C.

Abstract: This paper constructs a dynamic model of a four-wheel drive electric vehicle, which contains a vehicle model and a brushless DC motor model. In order to improve the starting and acceleration performance of the electric vehicle, we design a speed and current double closed-loop speed control system based on the constructed dynamic electric vehicle model. The starting and acceleration process of the electric vehicle is simulated and analyzed by CarSim-Matlab/Simulink co-simulation. The effectiveness of the speed control system is evaluated by the co-simulation results. In addition, the robustness of the speed control system is also analyzed for different vehicle masses.

Abstract: Ni-Cu bulk alloys were successfully prepared with spark plasma sintering (SPS) technique from nanopowders obtained by the arc plasma evaporation method. The tensile tests indicated that the tensile strength of Ni-Cu bulk alloy sintered by SPS at 600°C was the highest among the Ni-Cu bulk alloys sintered at different temperature and much higher than that of bulk ingots. Through investigating the fractographs of the bulk alloy, the intrinsic reasons for the tensile strength of the sintered specimens were discussed.

Abstract: In order to study the ion effect on titania phase structure, crystallite size, and photocatalytic activity, Rb+-doped TiO2 nanoparticles were prepared via a modified sol-gel method and characterized by means of X-ray diffraction, Energy Dispersive X-rays spectroscopy and transmission electron microscopy. The photocatalytic activity of the elaborated powders was studied following the degradation of methyl orange. The results indicate that doping Rb+ increases the BET surface area of TiO2 crystals, decreases the crystal size, reduces the diminishing rates of surface area with increasing calcinations temperature, raises the temperature at which anatase changes into rutile phase, and so significantly increases the photocatalytic activity of TiO2. The kinetics of the methyl orange degradation fits Langmuir-Hinshelwood kinetics model well.

Abstract: Soil surface electrochemical properties may have an important effect on soil fertility and genesis. Few researches are available on the changes of surface electrochemical properties of purple soils during the pedogenesis. In present work, four purple rocks and their derived soils under arable, orchard, forest and grass were collected to determine surface electrochemical properties including surface specific area, surface charge quantity, surface charge density, electric field strength, and surface potential using the kinetic method. The results indicated that soil surface specific area and surface charge quantity of soils were both significantly higher than their parent rocks. There were similar trends in surface potential, surface charge density and electric field strength of soils and parent rocks, soils derived from Shaximiao Formation (J2s) and Suining Formation (J3s) were higher than those of parent rocks, whereas the reverse trends existed in Feixianguan Formation (T1f) and Penglaizhen Formation (J3p). At the same time, surface potential of soil samples collected from four sites with different land utilization, i.e., Arable, Orchard, Forest and Grass, were determined to illustrate the various trends of soil electrochemical properties change. Under different land use patterns, the descending orders of soil surface potential in Shaximiao Formation (J2s) and Suining Formation (J3s) were both as follows: orchard > forest > arable > grass; the order in Feixianguan Formation (T1f) and Penglaizhen Formation (J3p) were as: orchard > forest > grass > arable. On the other hand, the value of soil surface charge quantity was increased with clay content and soil acidity because of the intensive physical weathering and slight chemical weathering. Therefore, the surface electrochemical properties may have some agreements with the weathering extent of the purple soils. Soil surface potential, surface charge quantity, surface charge density, electric field strength, and surface specific area could be employed as reference criteria for pedogenesis of purple soils.