It is very difficult to prepare full-densified aluminum nitride-boron nitride （AIN/BN） composite ceramics with homogeneous microstructure and high thermal conductivity. Spark plasma sintering （SPS） was used to ful...
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It is very difficult to prepare full-densified aluminum nitride-boron nitride （AIN/BN） composite ceramics with homogeneous microstructure and high thermal conductivity. Spark plasma sintering （SPS） was used to fully densify the AIN/BN composites in this work. Microstructure, mechanical properties and thermal conductivity of the SPS sintered AIN/BN composites with 5-30 vol% BN were investigated. The results show that the microstructure of composites is fine and homogenous, and the AIN/BN composites exhibit high mechanical properties. To promote the growth of AIN grains and modify the distribution of grain boundary in AIN/BN composites, a heat treating methodology was introduced through gas pressure sintering （GPS）. This processing was significantly beneficial to enhancing the thermal conductivity of the specimen. The thermal conductivity of AIN/BN composites with 5-30 vol% BN reached 60 W/m K after the samples were treated by GPS.
In order to investigate the influence of gas diffusion layer (GDL) structure on the drainage, electric and gas conductivity of proton exchange membrane fuel cell(PEMFC), such factors as electrochemical reaction, phase...
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In order to investigate the influence of gas diffusion layer (GDL) structure on the drainage, electric and gas conductivity of proton exchange membrane fuel cell(PEMFC), such factors as electrochemical reaction, phase change, transfer of water and oxygen, and water transfer in membrane are investigated, and GDL with spacing porosity in plane is also studied. Results show that the performance of PEMFC with GDL with spacing porosity is better than that of PEMFC with normal GDL. GDL with spacing porosity in plane can improve the transfer of liquid water and gas and then improve the performance of PEMFC.
The thermoelectric energy conversion efficiency of the thermoelectric generator devices not only depends on the figure of merit of the materials, but also on the temperature distribution in the device. However, each s...
The thermoelectric energy conversion efficiency of the thermoelectric generator devices not only depends on the figure of merit of the materials, but also on the temperature distribution in the device. However, each single thermoelectric material is only suitable for a narrow range of temperature and no single thermoelectric material is suitable for use over a very wide range of temperatures (∼300–800 K). Recently, the concept of integrating new thermoelectric materials into a segmented thermoelectric unicouple has been introduced. In the present paper, the thermal stresses of CoSb3/Bi2Te3 thermoelectric unicouple subjected to thermal cyclic loading are simulated by finite element method. The results show that the maximum thermal tensile stress would reach about 180 MPa or even higher because of the mismatch of the theromechanical properties of the CoSb3 and Bi2Te3. This means that the device cannot work as the tensile strength of CoSb3 is about 100 MPa. In order to improve the performance, the graded interlayers are inserted to reduce the thermal stresses. It is shown that the thermal stresses in the thermoelectric device with graded interlayers would reduce to about 100 MPa.
In this paper, a one-dimensional model of a thermoelectric generator was created. The output power and efficiency were analyzed by using the thermcxlynamic theory. The effect of thermal conductance of the component an...
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In this paper, a one-dimensional model of a thermoelectric generator was created. The output power and efficiency were analyzed by using the thermcxlynamic theory. The effect of thermal conductance of the component and the contact layer on output power and efficiency was discussed. The results showed that, the output power and the efficiency increased with the increase of the contact layer's thermal conductance, but increased more slowly. The output power and the efficiency also increased with the decrease of the generator's thermal conductance, and increased faster. This research would be an important reference to design.
Potassium lithium niobate (KLN:K3Li2Nb5O15) thin films have been deposited on quartz glass by pulsed laser deposition (PLD) technique using a stoichiometric KLN target, which was prepared by solid reaction with K2CO3,...
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Potassium lithium niobate (KLN:K3Li2Nb5O15) thin films have been deposited on quartz glass by pulsed laser deposition (PLD) technique using a stoichiometric KLN target, which was prepared by solid reaction with K2CO3, Li2CO3, and Nb2O5 powders as starting materials. X-ray diffraction (XRD) and Raman studies have revealed that tetragonal tungsten-bronze-type structure of KLN films with (310) preferred orientation could be achieved at the substrate temperature of 700°C and the oxygen partial pressure of 10 Pa. The average transmittance of as-deposited thin films in the visible range was nearly 90%.
KNbO 3 films were prepared on Si (100) substrates by pulsed laser deposition. The effect of experimental parameters on the films structure and composition was investigated. Well crystallized and single-phase KNbO 3 fi...
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KNbO 3 films were prepared on Si (100) substrates by pulsed laser deposition. The effect of experimental parameters on the films structure and composition was investigated. Well crystallized and single-phase KNbO 3 films were obtained at the substrate temperature of 650 °C, laser energy of 7.5 mJ/pulse and target-substrate distance of 40 mm, but a severe potassium-deficient was observed in the deposited films. The mechanism of K deficiency in films was explored and a method to control the composition was designed. The experimental results indicate that the composition of films can be well controlled by adjusting the oblique angle of substrates from the axial direction of plume. The stoichiometric KNbO 3 films with K/Nb molar ratio of 0.98 were obtained by locating the substrate at an oblique angle of 3–12° from the plume axis.
To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 wer...
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To reuse roller waste as a raw material of high performance green ceramic balls, three kinds of white alumina ceramic balls whose wear resistance were 2-3 times of the best high alumina ceramic ball with 90% Al2O3 were prepared, and the Al2O3 content of the prepared balls was 75%. It is found that the effect of calcia and magnesia on the wear resistance of ceramic balls is contrast to the accepted one： the wear rate of the ceramic balls prepared in CaO-Al2O3-SiO2 system is the lowest and the wear rate of the ceramic balls prepared in MgO-Al2O3-SiO2 is the highest. The main crystal phase of the ceramic ball is mullite and corundum. The ceramic ball granular is uniform and fine with 4-5 μm average size. The pore diameter is about 2 μm. The wear way of the ceramic balls is mainly transcrystalline fracture.
A novel process was introduced in this paper for the diameter-controlling synthesis of carbon nanofibers (CNFs) in the ethanol flames. The carbon nanofibers were grown on a nanocrystalline Fe layer, which was electro-...
A novel process was introduced in this paper for the diameter-controlling synthesis of carbon nanofibers (CNFs) in the ethanol flames. The carbon nanofibers were grown on a nanocrystalline Fe layer, which was electro-deposited on a substrate using periodic reverse (P.R.) pulse plating. It was found that the quality of the plating nanocrystalline and the corresponding carbon nanofibers was related with two plating parameters: output pulse frequency ( f ) and duty cycle ( r ). In addition to that the straight and helical carbon nanofibers were selectively synthesized by addition of different additives in plating bath. In this paper, the base-growth mechanism of carbon nanofibers was clearly discussed.
Based on the theory of photonic crystal and its characteristic, which was known as photonic band gap (PBG), the finite-difference time-domain (FDTD) method, including absorbing boundary condition and periodic boundary...
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Based on the theory of photonic crystal and its characteristic, which was known as photonic band gap (PBG), the finite-difference time-domain (FDTD) method, including absorbing boundary condition and periodic boundary condition, was used to simulate transmission characteristic of two-dimensional photonic crystal, which has periodic Al2O3 cylinder array structure. Incident wave was presumed as s-polarized wave. In two incident angles which were 0° and 30°, electric field, phase and transmissivity in the range of 1-30 μm were calculated. Numerical simulation results showed that PBG of photonic crystal existed in the range 12-18 μm (infrared waveband), and it may be used to develop infrared wave-guide.
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