Papers by Author: Lian Meng Zhang

Abstract: In this paper, the raw SiC powder is oxidized at high temperature (1000 °C for 4h), and a layer of SiO₂ oxide film is formed on the surface of SiC particles. By adding phosphoric acid, phosphoric acid reacts with SiO₂ at lower temperatures to form phosphate. Phosphate decomposition produces gas to create pores. At 1200 °C, the phosphate is completely decomposed into SiO₂, and a large amount of gas is produced to prepare porous SiC ceramic with high porosity and high strength. The effects of H₃PO₄ content on the phase composition, microstructure, porosity and mechanical properties of the prepared porous SiC ceramic were investigated. With the increase of H₃PO₄ content, the porosity increased and the bending strength decreased. The results suggest that at the sintering temperature of 1200 °C, the porosity of the samples can reach 58.3%~71.2%, while the bending strength of them can reach 8.72~31.09 MPa.

Abstract: Copper thin films were deposited on single crystal sapphire substrate via metal-organic MOCVD using Cu (acac)₂ as precursor. X-ray diffraction (XRD) and Scanning Electronic Microscope (SEM) were employed for studying preferred orientation and microstructure. Atomic Force Microscope was utilized in order to characterize roughness of copper thin layer. By calculation of the Gibbs free energy, the reactions have been deeply understood. Depositions were carried out at various substrate temperatures in the rage 473K to 673K. It has been revealed that temperature determined the orientation and microstructure of copper films. At 673K, copper films have exhibited preferred orientation, smooth surface and connected grains, which proved that this copper thin film can act as precursor. Based on the study of epitaxial growth of copper films, a schematic diagram of epitaxial growth relationship is suggested for the step by step depositions processes.

Abstract: Ferroelectric BiFeO₃ (BFO) thin films were prepared on Pt (111)/Ti/SiO₂/Si substrates by pulsed-laser deposition under various oxygen partial pressures (P_O2). The effects of P_O2 on the phase, orientation, surface morphology, and ferroelectric properties of the films were investigated, particularly in regard to relationships between structure and properties. It was found that the crystallographic orientation and surface morphology of the BFO thin films strongly depended on P_O2. Films prepared at P_O2=10 Pa had a high degree of (111) orientation and densely packed grains. A maximum of twice the remanent polarization for the BFO thin film was 68 μC/cm².

Abstract: In this paper, silicon nitride porous ceramics with high porosity and bimodal pore structure were prepared using pressureless sintering at 900~1100°C. In these porous ceramics, zirconium phosphate (ZrP2O7) was used as a binder and starch and naphthalene powders were used as pore forming agents. The obtained results showed that the porosity could be controlled in the range of 34 % to 70 % by changing the content of pore forming agents. The pores were formed by the continuous reaction of ZrP2O7 at ~250 °C and burnout of starch at ~550 °C (when starch was used as a pore forming agent), or sublimation of naphthalene at 80°C (when naphthalene was used as a pore forming agent). The bimodal pore structure was produced with pore size of less than 0.5m and ~10 m when using starch as a pore forming agent and the pore size of less than 0.5m and ~30μm when using naphthalene as a pore forming agent.

Abstract: Mo and Cu Were Bonded Successfully by Means of Vacuum Diffusion Bonding. The Interfacial Structure of the Joints Was Studied by Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), Energy Dispersive X-Ray Spectrometer (EDS) and X-Ray Diffraction (XRD), the Mechanical Property Is Tested by Tensile Strength Measurement. The Results Showed that the Differentatoms Diffused to each other in the Bonding Process. A Mo-Cu Solid Solution Was Formed in the Joint and with No Intermetallic Compounds. The Tensile Strength of the Joint Increased with the Increasing of Temperature, however, while the Holding Time Increased, the Strength Increased in the First Stages and then Decreases. It Were Observed that the Fracture Mode of the Joints Was a Brittle Fracture.

Abstract: Hot-Press Sintering, a Method that Could Effectively Decrease the Densification Temperature due to the Applied Pressure, Was Employed to Prepare a New Kind of Ho³⁺ Doped Bi₄Ti₃O₁₂ Ceramics, Bi_3.6Ho_0.4Ti₃O₁₂. The Effect of Preparation Parameters on the Crystal Phase, Density and Microstructure of the Ceramics Were Investigated. at First, Single-Phased Bi_3.6Ho0.4Ti3O12 Powders Were Synthesized from Bi2o3, Tio2 and Ho2o3 Raw Powders by Solid-State Reaction and the Optimum Calcined Temperature Should Be 900 °C. The as-Synthesized Powders Were Further Densified at 750-900 °C to Prepare Bi_3.6Ho_0.4Ti₃O₁₂ Ceramics. Dense (relative Density Was 99.4 %) Bi_3.6Ho_0.4Ti₃O₁₂ Ceramics with a Compact Texture Were then Obtained by Hot-Press at 850 °C, about 150-200 °C Lower as Compared with Pressureless Sintering.

Abstract: In this Paper, Silicon Nitride Porous Ceramics with Hierarchical Porosity Were Prepared Using Pressureless Sintering and their Mechanical Properties as a Function of Porosity and Pore Size Were Analyzed. In these Porous Ceramics, Macro-Pores with the Pore Size of 0.1 µm Were Formed by the Continuous Reaction of ZrP₂O₇ at ~250 °C and Macro-Cellular Pores with the Pore Size of 10~30μm Were Formed by the Burnout of Starch at ~550 °C or the Sublimation of Naphthalene at 80 °C. The Flexural Strength Decreased from 105 MPa to 6 MPa with the Porosity Increased from 35% to 65%. The Obtained Results Showed that the Flexural Strength Was Fit for the Equation of σ=σ₀exp(-bP), where σ₀ Is the Bending Strength of Nonporous Body of the same Material, P Is the Porosity and b Is the Factor Determines by Pore Structure. The Difference of Pore Size Was Determined by the Different Value of b and the Value of b Increased with the Increasing of Pore Size. Macro-Pores with the Pore Size of 0.1 µm Referred to a b Value of 4.3 and Macro-Cellular Pores with the Pore Size of 10 μm and 30 μm Referred to a b Value of 5.1 and 6.0 Respectively.

Abstract: High Density Antimony-Doped Tin Oxide (ATO) Ceramic Targets Are the Crucial Materials for Preparation of High Quality Transparent Conductive ATO Thin Films in Sputtering Process. In the Present Work, ATO Nanopowders with Different Sb₂O₃ Doping Content (0~10 mol%) Were Used to Fabricate the ATO Nanoceramics by Spark Plasma Sintering (SPS) Technique, which Can Reduce the Densification Temperature and Restrain a Grain Growth. And the Effect of Sb₂O₃ Doping Content (0~10 mol%) on the Density and Microstructure Had Been Investigated. the Results Showed that with the Sb2o3 Doping Content Increase, the Relative Density of ATO Nanoceramics Is Increased and the Resistivity Is Decreased. When the Sb₂O₃ Doping Content Is 10 mol%, the Relative Density Is 97.2% and the Resistivity Is 7.9×10^-2 Ω•cm.

Abstract: In this Paper, Five Fundamental Effective Thermal Conductivity Structural Models (Series, Parallel, Two Forms of Maxwell-Eucken and Effective Medium Theory) Were Used to Analyze and Design Silicon Nitride Porous Ceramics. Then α-Si₃N₄ Matrix Porous Ceramics Were Prepared with ZrP₂O₇ as a Binder and Thermal Conductivity of ZrP₂O₇ Bonded Si₃N₄ Porous Ceramic Was Evaluated. ZrP₂O₇ Bonded Si₃N₄ Porous Ceramic Had Open and Interconnected Pore Structure which is either in EMT or in Maxwell-Euken 2. The Thermal Conductivity of ZrP₂O₇ Bonded Si₃N₄ Porous Ceramics Changes from 2.0 to 0.5 W/m•K with Increasing the Porosity from 20% to 51%. The Obtained Results Showed that the External Porosity Material with Maxwell-Euken 2 Structure Had the Lowest Thermal Conductivity in All Porous Materials. The Open and Interconnected Pore Structure of ZrP₂O₇ Bonded Si₃N₄ Porous Ceramics Provided much Lower Thermal Conductivity.

Abstract: Transparent Conducting Antimony Doped Tin Oxide (ATO) Films Have Been Prepared on Quartz Substrate by Pulsed Laser Deposition (PLD) Technology. Despite of Extensive Researches of ATO Films Prepared by other Methods, the Study of PLD Technology Is Relatively few. PLD Technology Is Distinctive to Maintain the Elemental Components between the Targets and the Obtained Thin Flms under Optimal Conditions Contributing to Precise Control of Composition and Doping Ratio of ATO Films. The Effect of Sb₂O₃ Doping on the Electrical and Optical Properties of the ATO Films Was Investigated with Various Sb₂O₃ Doping Ratio (mol%) as 2, 4, 6, 8, 10 at 500 °C in an Oxygen Pressure of 8 Pa. The Results Suggest that the Electrical Resistivity Is Firstly Decreased and then Increased with the Increase of Sb₂O₃ Doping Ratio. When the Sb₂O₃ Doping Ratio Is about 6 mol%, the Optimal Electrical Resistivity Is 3.5×10-3 Ω.cm and the Average Optical Transmittance Is 83.1%. It Is Significant to Clarify the Impact Mechanism of Sb₂O₃ Doping Ratio to Get the Best Electrical and Optical Physical Properties. it Is Supposed that the Carrier Concentration Dominates at a Low Sb₂O₃ Doing Ratio while a Scattering Effect Is Performed at a High Sb₂O₃ Doing Ratio.