Papers by Author: Lian Meng Zhang

Abstract: Using the (100)-Oriented MgO Thin Film as the Buffer Layer, BaTi₂O₅ Films Were Deposited on Si(100) Substrates by Pulsed Laser Deposition under Various Oxygen Partial Pressures (P_O2). the Effects of P_O2 on the Crystal Phase, Orientation and Surface Morphology of the as-Deposited Films Were Investigated. Single-Phased Bati2o5 Films Were Obtained at P_O2 = 10-15 Pa, and the Preferred Orientation Changed from (710) to (020) with Decreasing P_O2. at P_O2 = 10 Pa, the BaTi₂O₅ Films with a Higher Degree of bItalic text-Axis Orientation and a Dense Texture Were Deposited on the Mgo(100)/Si(100) Substrates. The MgO Buffers Played an Important Role as Structural Templates for the Textured Growth of BaTi₂O₅ Films on Si Substrates.

Abstract: Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable tin oxide powder to be fully densified. Sintering without sintering aids is of great importance when SnO₂ ceramics are used as electrodes in the glass melting industry and aluminum electrometallurgy. Dense and good-conductive Antimony-doped SnO2 ceramics can be achieved by SPS at a lower sintering temperature and in a shorter time. When the Sb₂O₃ concentration is 1.0 mol%, the densities of the samples reach their maximum value, which is 98.2% of the theoretical value. When the content of Sb₂O₃ was 2.44mol%, SnO₂ ceramics with densities 97.6% can be obtained at 800°C-1000°C, and the resistivity was about 5.19×10^-2Ω.cm at the sintering temperature of 1000°C. Defined amount of Sb³⁺ used in our research are beneficial to low the sintering temperature and promote the densification of SnO₂ ceramics

Abstract: Bi_3.15Nd_0.85Ti₃O12 (BNT) thin films with different thicknesses (200, 270, 360, 450 and 540 nm) were prepared on Pt/Ti/SiO₂/Si substrates by sol–gel method. The effect of film thickness on the microstructure and ferroelectric properties of BNT thin films was investigated. All BNT thin films were consisted of a single phase of bismuth-layered perovskite structure. With increasing film thickness, grains gradually became larger, the remanent polarization (2P_r) firstly increased and then decreased, and the leakage current density showed opposite trend. The 360 nm-thick BNT film exhibited better electrical properties with 2P_r 26 µC/cm², coercive field (2E_c) 220 kV/cm, dielectric constant 345 (at 1 MHz) and low leakage current density.

Abstract: Reflective liquid-like films of silver nanoparticles simultaneously have metallic luster and the macroscopic properties of a fluid. Owing to their special properties, the films can be potential materials for the component of a new kind of liquid mirrors. The influence of different sizes of nanoparticles on the films reflectivity has been considered in this study. A great improvement on the reflectivity of the films has been found with the increase in the silver nanoparticles’ size. Additionally, the volume of the liquid substrate also has an effect on the reflectivity of the films. Characterization of the films by X-ray diffraction indicates that the liquid-like films are mainly composed of fcc silver nanoparticles rather than silver compounds.

Abstract: In this study, SnO2-based ceramics, with CuO as sintering aid and Sb2O3 as activator of the electrical conductivity, was obtained by pressure-less sintering at 1100°C ~ 1470°C. Addition of antimony leads to a higher densification temperature. Densification behavior and microstructure development are strongly dependant on CuO and Sb2O3. CuO gives rise to a liquid phase; Sb2O3 retards the formation of liquid phase and hinders the growth of grain. The electrical resistivities of SnO2-based ceramics vary in a wide range from 10-2 to 107 Ω•cm, depending on starting compositions and processing conditions. The electrical resistivities of samples with different amounts of CuO and Sb2O3 show different trends with the increasing of sintering temperature. The addition of antimony rapidly promotes electrical conductivity of SnO2-based ceramics containing CuO as the solid solution reaction of Sb2O3-SnO2. As the additions of CuO and Sb2O3 are the same, the electrical resistivity arrives the minimal value of 4.72×10-2 Ω•cm for 99%SnO2+0.5%CuO +0.5%Sb2O3 at 1470°C. More content of Sb2O3 than CuO causes the degression of density and the rising of electrical resistivity of ceramics.

Abstract: In this work, silicone/alumina composites with 33 wt.% silicone content are prepared by compression mould technique. TGA, XRD and SEM were used to characterize the ceramifying behavior when the samples were heated from 600 to 1600°C. XRD results suggest that the ceramic residue of SR could restrain the phase transformation of γ-Al2O3 below 1100°C, indicating that the chemical bonds preserve the mechanism strength of SR/Al2O3 composites under high temperature. The flexural strength increases from 18.19 MPa to 75.31 MPa with the increasing temperature from 600 to 1600°C, owing to the sintering reaction between SiO2 and Al2O3 forming mullite phase under higher temperature. It has low liner shrinkage after firing and nearly no macrocracks or deformation under any temperature, illustrating that the SR/Al2O3 composites can be used as organic fire-retardancy materials.

Abstract: Tape casting was used for the preparation of Mg-Cu systems density graded materials. A series of tapes with uniform compositions ranging from 100wt% Cu to 100wt% Mg were fabricated with sufficient strength to be handled during the post-processing stage. The effect of the tape casting process parameters on the properties of the tape were studied, such as the composition of the Mg-Cu and the solid loading. The rheology of the slurry of different Mg-Cu composition for tape casting was characterized by viscosity. The tapes characterized by microstructure, thickness and bulk density were outlined. The results demonstrated that the different Mg-Cu composition slurry with well-dispersed, high stability, certain solid loading from 45 ~70 wt% were obtained. The viscosity of the slurry and the density of the green tapes were increased with the increasing of the content of Mg. The thickness of tapes of compositions ranging from 100wt% Cu to 100wt% Mg with certain strength could be achieved 68-110μm and the density of the tapes was 0.74-2.42g/cm3. For 100wt% Cu tapes, when the solid loading was 68wt%, the high density tape was produced. The tapes with different thickness, density and different Mg-Cu compositions were obtained.

Abstract: FGMs with density gradient are of great interest in field of dynamic high-pressure physics. In this paper, tungsten particles reinforced epoxy resin composites, and FGMs with density gradient were prepared by calendering technique. Microstructures of tungsten-epoxy composites with various tungsten contents were analyzed, and the density distribution of the FGMs was characterized. The results show that the distribution of tungsten particles in tungsten-epoxy composites is homogeneous, and the combination of tungsten particles with epoxy matrix is good. The density of tungsten-epoxy composites varies from 1.26gcm-3 to 4.0gcm-3, and the thickness of each layer is about 200μm. Tungsten-epoxy FGMs with density gradient were obtained by laminating thin layers of tungsten-epoxy composites with different tungsten contents. The highly enough bonding strength between these transition layers and good parallelism were achieved. The density distribution of the tungsten-epoxy FGMs can meet the demand of the power function equation of density and thickness.

Abstract: Porous calcia stabilized zirconia ceramics (CSZC) with closed pores were presurelessly sintered by adding different contents of zirconia hollow balls. CSZC FGM with porosity gradient structure was then fabricated by laminating five layers with designed contents of zirconia hollow balls. The porosity, microstructure, and bending strength of the obtained CSZC samples were characterized. The results show that the hollow balls distribute uniformly and are well bonded with the matrix, and the porous structure is mainly composed of closed pores. The porosity of the CSZC increases linearly from 5.7 % to 31.6 % when the content of zirconia hollow balls increases from 0 % to 30 %, and the bending strength decreases rapidly from 297 MPa to 30 MPa. The thermal shock behavior of the CSZC and FGM was evaluated using air-quenching technique. It is shown that the residual bending strength of the quenched samples increases after several quenching cycles, and the samples are damaged by thermal shock after eight thermal cycles because of the production of monoclinic zirconia. FGM samples with porosity gradient structure can endure above twelve thermal shock cycles and exhibits better thermal shock resistance.

Abstract: A W/Cu system functionally graded material (FGM), which may be used as plasma facing component for fusion reactors, was prepared by inserting W-Cu layers with gradient composition between tungsten and copper alloy plates. W-Cu gradient layers were hot-press sintered from W-Cu powder mixtures added with zinc powder as the sintering aid, whose relative density increased with sintering temperature, reaching a value higher than 96% at 850°C. XRD and SEM measurements showed that the sintered W-Cu gradient layers were the mechanical mixtures of W and Cu. A wholly dense W/Cu system FGM was then obtained at 850°C by hot-press, whose composition and structure changed gradually. The finite element method (FEM) calculation showed that the residual stresses in the W/Cu FGM were effectively reduced as compared with the directly-bonded W/Cu joint.