Papers by Author: Lian Meng Zhang

Abstract: In this work, ZrB2 powder coated with ZrO2 (ZrB2 @ ZrO2) were applied to promote the densification of ZrB2 prepared by pulsed electric current sintering (PECS). The coating process and sintering behavior were investigated. While the pH value was about 9, the ZrB2 particles were successfully coated with ZrO2 by co-precipitation methods. The thickness of ZrO2 layer was about 3-5nm. The coated powder was sintered at 1600°C ~1950°C by PECS in vacuum. For comparison, the pure ZrB2 powder was sintered at the same conditions. The relative density of the sample coated with ZrO2 was 97.8% at PECS 1950°C, which was higher than that of sample without coating. The densification process can be divided into three stages. The ZrO2 coating layer plays an important role on the densification of ZrB2.

Abstract: Barium dititanate (BaTi2O5) films were prepared on MgO (100) substrate by pulsed laser deposition under various laser energy densities. The effect of laser energy on crystallinity, orientation and surface morphology was investigated. The preferred orientation of the as-deposited films changes from (710) to (020) with decreasing laser energy, and the surface morphology is different depending on laser energy too. The b-axis oriented BaTi2O5 film could be obtained at the laser energy density of 2J/cm2, where the film shows a dense surface with an elongated granular texture.

Abstract: In this paper, the molten aluminum erosion resistance of Al2TiO5/Al2O3 composites which were soaked in molten aluminum for long-time were characterized by cross section of microstructure and element distribution of samples. The results show that Al2TiO5/Al2O3 composites have good erosion resistance to molten aluminum.

Abstract: Surface coating has been used to prepare nano-particle BN-AlN composite powder. Nano-BN was synthesized via in-situ reaction, coating on the surface of AlN particles. The effects of coated nano-BN on the microstructure and properties of BN-AlN composites have been investigated. Results indicate that the microstructure and properties of BN-AlN composites are very different from the origin composite powders. Nano-BN particles cause the homogeneous microstructure and reinforce the grain boundary of BN-AlN composites. They exhibit similar regularity of reinforce effect of ceramic nano-particle and enhances remarkably the composites’ mechanical strength. But nano-BN will introduce more grain interfaces, more oxygen-related defects in grain lattice to increase phonon scattering and reduce the thermal conductivity of BN-AlN composites.

Abstract: The purpose of this study was to investigate the oxidation of ZrB2/ZrO2 (ZZ) and ZrB2/ZrO2/SiC (ZZS) ceramics. The ceramics were fabricated by spark plasma sintering (SPS) at 1900°C and exposed to ten-minute oxidation cycles in stagnant air at 1200°C in a box furnace with molybdenum disilicide heating elements. Results of relative density, surface phase change and the rate of weight growth show that the addition of ZrO2 improved the sintering properties of ZrB2 ceramics. While the resistance to oxidation declined with the increase content of ZrO2. And the addition of SiC improved the resistance to oxidation of ZrB2/ZrO2 composites significantly.

Abstract: 0-3 piezoelectric ceramic PMN/conductive carbon black(CB)/epoxy resin(EP) composites were prepared by resin casting method. The electric and damping properties of PMN/CB/EP composites were detected. The volume resistivity of the composites decreases with the addition of conductive carbon black, and the composites experience transition from insulator to semiconductor when the CB content is 6% weight of the resin in the composites. Damping loss factor-temperature curves scanned by DMA showed that the peak value of damping loss factor(tanmax), the loss factor area(TA) and the damping temperature range(T) of the composites increase and reach to maximum values when CB content is 6% weight of EP resin, then drop a little with CB contents further increasing. When CB was just at threshold content 6% of epoxy weight the composite converts from insulator to semiconductor with the volume resistivity being about 108 Ωm and piezo-damping mechanism plays efficiently.

Abstract: The single phase of Bi-doped Mg2Si0.5Sn0.5 compounds have been successfully fabricated by solid state reaction-spark plasma sintering (SPS). The effect of Bi doping concentration on the thermoelectric properties of Mg2Si0.5Sn0.5 is mainly investigated. The doping of Bi atom introduces impurity energy to Mg2Si0.5Sn0.5 compounds, which results in the increase of carrier concentration ( ), meanwhile it causes the increase of crystal distortion, enhancing the scatter of phonon. The results show that with the increasing of Bi doping content, the electrical conductivity (σ) increase, the absolute Seebeck coefficient ( ) and thermal conductivity ( ) decrease slightly in the measuring temperature range between 300 K and 800K. When the doping concentration of Bi is up to 2.5at% (nominal molar percent), the sample shows a maximum value of the figure of merit, ZT, is 0.78 at 800K.

Abstract: The radome performance is evaluated by means of a computer aided design (CAD) for the wall structure of multilayer ceramic radome in accordance with the microwave propagation theory. The calculation model for the ceramic radome with A-sandwich structure is built. By optimizing the thickness of the whole wall and the thickness and dielectric constant of skins and core layer, the power transmission efficiency at a broadband frequency of A-sandwich structure ceramic radome is calculated especially. The calculation results suggest that when the wall thickness is 6 mm, the thickness ratio of surface layer to core layer is 1:15 and dielectric constant of core layer is less than 2.5, the maximal broadband transmission efficiency is obtained.

Abstract: A group of boron-carbon ceramic material was in-situ synthesized and densified simultaneously via Spark Plasma Sintering (SPS) technique from carbon and boron element powders with different molar ratio. The phase structures of samples with different B/C molar ratio were characterized by X-ray Diffraction (XRD). The B/C atomic ratio of the sintered materials was calculated from X-ray photoelectron spectroscopy (XPS) measurement data. Meanwhile, the chemical analysis (CA) method had also been taken to verify the B/C atomic ratio. Finally, the experience equation had been obtained to control the B/C atomic ratio of sintered samples.

Abstract: Nanocomposites and heavy doping both are regarded as effective way to improve materials’ thermoelectric properties. 0.7at% Bi-doped Mg2Si nanocomposites were prepared by spark plasma sintering. Results of thermoelectric properties tests show that the doping of Bi atom effectively improves the electrical conductivity of Mg2Si，and the nanocomposite structures are helpful to reduce thermal conductivity and increase Seebeck coefficient, hence improving the thermoelectric performance. A maximum dimensionless figure of merit of 0.8 is obtained for the Bi-doped Mg2Si nanocomposite with 50 wt % nanopowder inclusions at 823K, about 63% higher than that of Bi-doped Mg2Si sample without nanopowder inclusions and 119% higher than that of microsized Mg2Si sample without Bi-doped, respectively.