Papers by Author: Zhi Peng Xie

Abstract: Mixtures of two grades of hexagonal boron nitride (h-BN) powder differing in their grain size and crystallinity were spark plasma sintering in a vacuum. The influences of the mixing ratio of h-BN powders on the densification, microstructure and mechanical properties were investigated in detail. The results show that the smaller grain size, the lower crystallization degree and the higher density and mechanical properties. While the orientation degree of flake h-BN grains can be greatly enhanced by using h-BN powder with larger particle size. As the increasing of nanometer h-BN powder adding amount, the relative density has the same “V” shape changing trends with mechanical properties. In addition, the orientation of boron nitride grains varied widely, and a nearly isotropic material was prepared from a mixture containing 90wt.% nanometer powder.

Abstract: The thermal barrier coating samples of different thickness with alumina coated zirconia and zirconia as coating materials were prepared on the surface of heat resistant alloy steel substrate after activation treatment with NiCoCrAlY as adhesive transition layer by plasma spraying method and spray gun quick spraying process. The bonding strength and thermal insulation property of two kinds of ceramic coating with the same thickness were compared by the test results of bonding strength, high temperature heat insulation and microstructure, and the relationship between the coating thickness and heat insulation effect were investigated. The results indicate that the structure and property of thermal barrier coating using nanoAl₂O₃ coated ZrO₂-Y₂O₃ powder are superior to that using single zirconia powder. The thermal insulation property of the thermal barrier coating increased with the increasing of coating thickness, and the advantage is more obvious with temperature increasing.

Abstract: Use starch, corn meal and activated carbon as pore-making agent, Ni-YSZ/YSZ composite ceramic green body was prepared by multiple gel-tape casting with acryloyl ammonium-polyvinyl alcohol. The specimen was sintered at 1450°C for 4h, then reduced in hydrogen atmosphere at 800°C for 4h, Ni-YSZ/YSZ composite ceramic disk was obtained, the porosity, thermal expansion coefficient, electrical properties and microstructures of the specimen was tested. The results showed that the porosity of Ni-YSZ/YSZ composite ceramic disk reaches about 30% when use starch as pore-making agent, expansion coefficient is proportional to porosity, both of them reduced with the temperature increased. The YSZ is continued and compact with network structure, Ni particulates are well distributed in it, suitable for intermediate temperature solid oxide fuel cell anode materials. Image analysis of SEM micrograph showed that the structure is loose, porous, uniform and compact in Ni/YSZ/YSZ multi-layer composite ceramics, which meet the requirement of intermediate temperature SOFC.

Abstract: The sp³C doped SiC superhard nanocomposite films had been deposited on stainless steel (SS) substrates at different temperature by electron beam-physical vapor deposition (EB-PVD). The sp3C doped SiC film was studied by grazing incidence X-ray asymmetry diffraction (GIAXD), and X-ray photoelectron spectroscopy (XPS). The results of GIAXD showed that the sp³ doped SiC nanocomposite films were not perfect crystalline, which was composed with fine SiC nanocrystals, and a second phase very similar with diamond like carbon (DLC). XPS analysis showed that the excess C existing in films and turned from diamond into DLC from the surface to inner of film.

Abstract: ZnO nanopowder have been prepared by chemistry liquid-phase method with the water soluble polymer and the surfactant as additive in [Zn (OH)₄]^2- precursor solution. The Character of spectroscopy and microstructure and phase composition was studied by X-ray diffraction, transmission electron microscopy and UV–Vis absorption spectroscopy. The possible influence like reaction time, reaction temperature, reactant ratios and so on was investigated. At the same time, the inorganic granule coring and the crystal growth affected by the water-soluble polymer and the surfactant were discussed. Studies have shown the ZnO nanopowder with the diameter of 50nm has the structure such as the good crystal state and well-defined crystallographic surfaces. The ZnO nanopowder have strong absorption in the UV region with the wavelength of 200 ~ 300 nm.

Abstract: The self-catalytic role of zirconium n-propoxide has been investigated with respect to the synthetic parameters of ZrO₂/Y₂O₃-CeO₂ compound powders. When zirconium n-propoxide is prehydrolyzed, the gelation time is prolonged, resulting in a more transparent gel. It is found that gelation time can be shortened with a high concentration of tetraethoxysilane in the presence of a small amount of zirconium n-propoxide. On the basis of the synthetic data, a mechanism for the zirconium n-propoxide catalytic reactions has been discussed. A linear correlation between the mixing level and metal content holds up to 45 mol% of ZrO₂/Y₂O₃ under the studied conditions.

Abstract: Ni/YSZ cermet is the most widely used anode material for solid oxide fuel cell. In this paper, the NiO/YSZ green body was prepared by gel-tape casting, using 15%wt. starch as pore-forming agent, in the mixed polyvinyl alcohol and acrylamide systems. Ni/YSZ anode material was obtained after sintered at 1450°C for 2h and reduced at 800°C in H2 atmosphere for 4h. The anode porosity, XRD, TGA and microstructures were measured. YSZ formed a continuous network structure and Ni particles were dispersed homogeneously in the YSZ network. It is suitable to fabrication of anode material for solid oxide fuel cell.

Abstract: Particular attention is paid in this paper to understanding the surface characteristics and aqueous dispersibility of as-received commercial powders. The different production methods and specific pulverization processes used for the four powders studied (FD1, FD2, M11, UBE) result in obvious differences in such powder properties as surface groups, aqueous dispersibility, and water-soluble ions.

Abstract: An innovative processing route for fabricating porous zirconia ceramics has been developed based on traditional injection molding method. Azodicarbonamide (AC) was used as the foaming agents and mixed with the zirconia powder and conventional binders (polypropylene, ethylene/vinyl acetate, paraffin wax and stearic acid). There were three stages in the foaming course: (1) Small bubbles nucleated when AC decomposed into N2 and CO in the barrel. (2) Viscosity and pressure drop led to the growth of the bubbles when the melt feedstock was injected into the die cavity. (3) The porous structure was kept in the solidified body. The AC content and injection parameters were optimized to control the pore density and size. The porous green body was debinded at the heating-up rate of 0.5 °C /min to 450°C and sintered at 1550°C. Samples with porosity of 40%-50% and pore sizes from 200-250μm were prepared when the addition of AC was 0.3% by weight. The results showed that ceramic injection molding method was also suitable for fabricating the porous ceramics.

Abstract: Water debinding is an important debinding technique for ceramic injection molding. However cracks or blisters usually generate during water extraction. In this paper, two types of multi-component binder systems were studied: (1) a major fraction of polyethylene glycol (PEG), and a minor fraction of polyvinyl butyra (PVB) and other additives. (2) a major fraction of PEG, and a minor fraction of polymethyl methacrylate (PMMA) and other additives. Mechanism of defects generation was investigated, and PEGs with various molecular weights were introduced to avoid cracks or blisters during the process. Further more, the compatibilities of PEG/PVB and PEG/PMMA were studied. The results showed that PEG and PMMA exhibited better compatibility, with the feedstock more homogeneous and sintered ceramic parts higher strength.