Key Engineering Materials Vols. 317-318

Abstract: A cordierite filter was fabricated by an extrusion method and it was loaded with LaCoO3 catalyst by a vacuum impregnation method. The simultaneous removal efficiency of NOx/SOx was measured by passing NO and SO2 through the catalyst-loaded ceramic filter. The cordierite porous filter had an apparent porosity of 61.6%, compressive strength of 12.3 MPa, and a pressure drop of 1200 Pa at a face velocity of 5 cm/sec, at 400
. These values are sufficient to apply the filters for the removal of hazardous gas in incineration systems, etc. NOx & SOx simultaneous removal efficiency of LaCoO3 loaded on the porous cordierite filter was about 98% of NOx and over 90% of SOx between 600
and 650
. We could find no poisoning of the catalyst by SO2.

Abstract: The contact deformation mechanisms of a superplastic ceramic, 3Y-TZP (3mol % yttria-partially stabilized tetragonal zirconia polycrystals) are examined in indentation creep tests at high temperatures. A large discrepancy between the uniaxial compression and the pyramidal indentation contact behaviors is observed. The indentation creep curves exhibit a hardening behavior, i.e., the penetration rate decreases as the penetration depth and/or the creep time increases. This fact implied that the cooperative grain-boundary sliding (CGBS) in a microscopically localized region, such as the sub-surface contact region beneath a pyramidal indenter, is very limited through the microscopic processes of localized grain interlocking.

Abstract: Much attention has been paid to unidirectionally solidified ceramic composites as a candidate for a high-temperature structural material. We have recently developed eutectic composites, which are named as Melt Growth Composites (MGCs). The binary MGCs (Al2O3/YAG and Al2O3/GAP binary systems) have a novel microstructure, in which continuous networks of single-crystal Al2O3 phases and single-crystal oxide compounds (YAG or GAP) interpenetrate without grain boundaries. Therefore, the MGCs have excellent high-temperature strength characteristics, creep resistance, superior oxidation resistance and thermal stability in an air atmosphere at very high temperatures. Manufacturing processes for the MGCs are being examined under a Japanese national project, scheduled from 2001 - 2005. To achieve higher thermal efficiency for gas turbine systems, a bowed stacking nozzle vane has been fabricated on an experimental basis.

Abstract: An 8000 kW class Hybrid Gas Turbine (HGT) project, administered by the New Energy and Industrial Technology Development Organization (NEDO), was completed in March 2004. The targets of this project were improvement in thermal efficiency and output power by using ceramic components, and early commercialization of the gas turbine system. The ceramic components were used for stationary parts subjected to high temperature. It became clear that silicon nitride material showed significant recession under combustion gas. Kyocera and Central Research Institute of Electric Power Industry developed new EBCs to suppress this recession. These EBCs were evaluated by exposure test, heat cycle test and actual HGT engine test. One of the EBCs showed slight defects after the actual engine tests. However, all EBCs showed high corrosion resistance and good adhesion. It was confirmed that the all EBCs worked effectively.

Abstract: Polymer impregnation pyrolysis method (PIP method) has some advantages to fabricate SiC fiber /SiC composite with large or complex form. However polymer derived SiC contains some amount of excess carbon and porosity. In particular the excess carbon is easy to be oxidized in air at high temperature. Therefore reliability of the composite is not sufficient for long term use, because the oxidized matrix makes strong bonding between the fiber and the matrix. In this study, TiO2 as a reactive filler was added into polymer to consume the excess carbon by chemical reaction. Polycarbosilane (PCS) was used as a precursor polymer to synthesize a SiC matrix. It was confirmed that TiO2 was formed TiC on reaction with PCS over 1673 K by preliminary study. SiC fiber, Hi-Nicalon®, was used as reinforcement. Al2O3 powder was coated on surface of SiC fiber as interface layer of fiber/matrix. TiO2 added PCS/hexane solution was compounded with the fiber tow by filament winding. SiC fiber/SiC composite was synthesized at 1673 K for 3.6 ks in Ar. The composite was densified by reinfiltration of TiO2 added PCS solution and pyrolysis at 1673 K. Though densification behavior of the composite with TiO2 is slower than composite without TiO2, it was suggested that composition of synthesized SiC is close to stoichiometric one by apparent density. Fracture behavior of the composite indicated that addition of TiO2 was increase bonding strength between fiber and matrix. Bending strength of composite was increased after oxidation test at 1473 K for 360 ks in air atmosphere.

Abstract: Porous ceramic fiber composites were coated with pyrolytic carbon by the decomposition of infiltrated phenolic resin in a nitrogen atmosphere at 800
. The amount of carbon coating was varied to tailor the electrical conductivity of the carbon-coated composites. The electrical and thermal conductivity of the composites were measured at room temperature using a two-point method and a hot-wire one, respectively. Up to 30 wt% pyrolytic carbon, the electrical conductivity σ shows linearly increasing tendency and is fitted by the effective conductivity according to the parallel rule of a mixture σeff = ΣΧi ·σi with an effective conductivity of pyrolytic carbon σc= 0.42 S/cm. The thermal conductivity of the coated composites is in the range 0.05-0.08 W/mK and increases with carbon content.

Abstract: Thick oxide coatings have wide-ranged applications typically thermal barrier coatings. Although high speed deposition processes, often plasma spray or electron-beam physical vapor deposition, have been employed for these applications, another route has been pursued to improve the performance of coatings. We have proposed laser chemical vapor deposition (LCVD) for high-speed and thick oxide coatings. Conventional CVD can fabricate coatings at deposition rates of several to several 10 μm/h, and conventional LCVD has been mainly focused on thin film coatings and low temperature deposition. In the present LCVD, high-speed deposition rates ranging from 300 to 3000 μm/h have been achieved for several oxide coatings such as yttria stabilized zirconia (YSZ), TiO2, Al2O3 and Y2O3. This paper describes the effect of deposition conditions on the morphology and deposition rates for the preparation of YSZ and TiO2 by LCVD.

Abstract: Effect of La2O3 addition on thermal conductivity and high temperature stability of YSZ coating produced by EB-PVD was investigated. La2O3 was selected as an additive because it had a significant effect on suppressing densification of YSZ. The developed coating showed extremely low thermal conductivity as well as high resistance to sintering. Microstructural observation revealed that the coating had fine feather-like subcolumns and nanopores, which contributed to limit thermal transport. These nanostructures were thought to be formed by suppressing densification during deposition.

Abstract: This paper presents the work on the development of ceramic coating processing. Nano-structured zirconia coating has been developed with functions; substrate temperature and oxygen gas change in chamber by electron beam physical vapor deposition (EB-PVD). The microstructure of the coating layer has been characterized with FE-SEM, and SEM. The crystalline phase of the coating layer has been also characterized with XRD. The zirconia coating by EB-PVD had not monoclinic zirconia phase as shown in XRD pattern and Raman spectra and the thickness of coating were quite homogeneous. The fracture microstructure of the coating layer for a thickness of ~15 μm showed columnar or non-columnar structure and had nano-structure with nano scaled grain as shown in micrograph by FE-SEM.

Abstract: ZrO2-4mol% Y2O3 coatings on zirconia substrate were deposited by EB-PVD. Influence of the coating thickness on thermal conductivity and thermal diffusivity of coated samples is examined. The fractured surface of the coated samples reveals a columnar microstructure consisting of feather-like structure. We have adopted a laser flash method for thermal diffusivity and specific heat capacity of coated samples. It was found that the thermal conductivity of the coating layers was strongly dependent on coating thickness. The thermal conductivity of coating layers shows increasing tendency with increasing the coating thickness.