Papers by Author: Lian Meng Zhang

Abstract: A new kind of functionally graded materials (FGM) with density gradient has come to show great potentials as flier-plates for creating quasi-isotropic compression waves. In order to meet the demand of lower density in the front face and wider density range for such flier-plate, Mg with a density of 1.74g/cm3 and W of 19.3g/cm3 are selected to make Mg-W system density graded materials. Mg-W alloys with various mass fractions of Mg and W were sintered by spark plasma sintering (SPS) technique at low temperatures, and the processing of densification is mainly investigated. It is found that, up to 92wt%W, the Mg-W alloys can be fully densified at 873K due to the conglutination of Mg particles. The Mg-W alloys still exist as a mechanical mixture of Mg and W. Finally, the Mg-W density graded materials with a density change from 1.74g/cm3 to 10.55g/cm3 have been successfully prepared.

Abstract: In this work, Fe and Si powders were used to fabricate 6.5% Si silicon steel. The mixing powder was rolled into strip and then treated at 900°C in Ar. Sn was added into the mixing powder to investigate the effect of Sn on the sintering. The density, composition, and structure were examined. The results show that Fe almost does not react with Si at 900°C. But with the addition of Sn, Fe reacts with Si to produce Fe3Si at 900°C. Increasing the amount of Sn accelerates this reaction. When the amount of Sn addition is excessive, there will leave many pores in the alloy because the reaction rate is too fast to shrink. The proper amount of Sn addition can decrease the sintering temperature and shorten the sintering time.

Abstract: In this paper, silicon nitride (Si3N4) ceramics by aligning α-Si3N4 whiskers were prepared via tape casting, hot-press sintering technique using Y2O3 and MgO as sintering additives. Aligned α-Si3N4 whiskers were realized by modifying the tape casting technique. After tape casting, Si3N4 tape with good flexibility and uniform pores can be obtained. Microstructures of the tape, green body and sintered sample were observed by SEM images. The results show α-Si3N4 whiskers in Si3N4 tape and green body were aligned preferentially along the tape casting direction. Si3N4 ceramics with aligned elongated grains are developed by hot-press sintering technique based on the reaction between Si3N4 and the sintering additives which lead to the liquid phase.

Abstract: α-Al2O3 nanopowders were prepared by a novel synthesis process, using the nanosized α-Al2O3 obtained from pyrolyzing ammonium aluminum carbonate hydroxide as seeds and the self-dispersed nanosized AlOOH crystal powders as precursors. Based on their good self-dispersion in water, the α-Al2O3 seeds were dispersed evenly into the AlOOH sol by the new homodispersion mixing technique. This process enables the conversion of AlOOH to alumina at 190°C (hydrothermal temperature), in which the alumina is calcined to nanosized alpha-alumina having an average length to diameter ratio of 60nm:15nm at 930°C. In the synthesis reaction for transforming the AlOOH to alumina, the effect of superfine pulverization and self-dispersion of the precursors was studied.

Abstract: In this study, K3Li2-xNb5+xO15+2x (KLN) thin films were prepared by laser-ablated a sintered ceramic target. For an optimum deposition condition, in-situ post annealing method was employed on as-deposited films. XRD measurements showed that KLN films with (310) preferred orientation were obtained on fused quartz substrate. Surface morphology studies indicated that in-situ post annealing could improve the surface quality of KLN thin films. The average transmittance of as-deposited and annealed films in the visible range was nearly 80% to 90%.

Abstract: The porous ceramic support was prepared from cordierite by adjusting the phase composition, grain size of aggregate, additions of pore-forming material and binder. The porous ceramic support had excellent chemical stability and relative high strength with a porosity of 48％and pore size of 128μm. Factors that affected the properties of the support material were analyzed. The pore size of the porous ceramic support was directly proportional to the grain size of the aggregate around firing temperature. The strength of the support material increases with a rise in amount of the binder and firing temperature. The porosity of the support material increases while the strength decreases with a rise in amount of the pore-forming agent.

Abstract: Potassium lithium niobate (KLN: K3Li2Nb5O15) films have been deposited on quartz glass by Pulsed laser deposition (PLD) technique using a stoichiometric KLN target as starting materials. By investigating the effects of both the oxygen pressure and the substrate temperature on the structure of KLN films, optimum parameters have been identified for the growth of high-quality KLN films. At 10Pa oxygen ambient pressure, tetragonal tungsten-bronze-type structure of KLN films with (310) preferred orientation can be achieved at substrate temperatures in the range of 700-800°C. Optical studies indicate that the films are highly transparent in the visible-near-infrared wavelength range.

Abstract: A series of zirconia porous ceramics with different density are fabricated with commercial zirconia powder and zirconia hollow balls by pressureless sintering technology. The microstructure and phase transformation are characterized respectively by SEM and XRD testing methods. The result indicates that the density and compressive strength depend greatly on zirconia powder content at the same sintering temperature, and elevating sintering temperature just has a little effect on the density and compressive strength for the samples of the same zirconia powder content. The XRD diffraction patterns analysis shows that elevating sintering temperature is helpful to eliminate monoclinic zirconia and the best sintering temperature should be beyond 1700°C.

Abstract: In the present study, α-Si3N4 is prepared by using MgO and Al2O3 as the sintering additives and spark plasma sintering (SPS) technique. The SPS sintering mechanism is discussed. The relationship between the content of sintering additives, sintering temperature and relative densities of the samples is analyzed. The results suggest that when the sintering temperature is 1300-1500°C, the content of sintering additives is 6wt.%-10wt.%, the relative density of sintered samples is 64%-96%. When the sintering temperature reaches 1400°C, the content of sintering additives is 10%, the samples can be fully dense sintered and the relative density can be up to 95%. The sintering mechanism is liquid phase sintering. The bending strength of the sintered samples is 50-403MPa and has a close correlation with the relative density.

Abstract: In this paper, a three-phase composite with electrically conductive carbon black (ECCB) and piezoelectric ceramic particles, PMN, embedded into butyl (PMN/ECCB/IIR) was prepared by simple blend and mold-press process. Dynamic mechanical properties with various ECCB loading were tested by dynamic mechanical analysis (DMA). DMA shows that the ECCB loading has remarkable effect on the dynamic mechanical properties of the three-phase composite. The temperature range of loss factor (tanδ) above 0.3 the composite was broadened by almost 100°C and the maximum of loss factor shifts to higher temperature in the testing temperature range respectively with increasing the ECCB loading. The piezoelectric damping theory was used to explain the experimental results. The three-phase composites with proper composition can be used as high damping polymer materials.