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김성호,ZhengYi Fu,Koichi Niihara,이수완 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.3
To apply a thermal barrier coating, the coating materials must satisfy the basic requirements. This paper explains composite powder processing and the characterization of sintered materials. The composite powders were prepared by two types of method: conventional ball-milling and chemical precipitation. The morphology of the powder differed with the processing method. In chemically precipitated powder, the surface of zirconia was coated with LaPO4. The samples were fabricated from these powders, using the PECSed method. The flexural strength of the nanocomposites was decreased with an increase in the amount of LaPO4 due to its poor mechanical properties. However, the thermal properties, such as thermal conductivity and high temperature stability, were lower and more stable than that of the monolith.
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Optical, Mechanical and Tribological Properties of Boronnitride Dispersed Silicon Nitride Ceramics
Joshi, Bhupendra,Fu, Zhengyi,Niihara, Koichi,Lee, Soo-Wohn Materials Research Society of Korea 2010 한국재료학회지 Vol.20 No.8
Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline $Si_3N_4$ ceramics were affected by the density, ${\alpha}:{\beta}$-phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of $\alpha-Si_3N_4$, AlN, MgO, and h-BN at $1850^{\circ}C$. The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped $Si_3N_4$ ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.
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AlN matrix composites fabricated by the spark plasma sintering –reactive synthesis method
Tiekun Jia,Weimin Wang,Zhengyi Fu,Hao Wang 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.6
A mixture of Al and BN powders was adopted to synthesize AlN matrix composites using the spark plasma sintering-reactive (SPS) synthesis method. The crystalline phases of sintered samples were characterized by X-ray diffraction (XRD). Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the microstructure revealed that the BN phase was homogeneously distributed in the matrix of synthesized AlN. The effect of sintering temperature on the microstructure and properties of sintered samples was investigated. The results showed that densification of sintered samples was improved and the thermal conductivity exhibited a significant increase with an increase of the sintering temperature. A mixture of Al and BN powders was adopted to synthesize AlN matrix composites using the spark plasma sintering-reactive (SPS) synthesis method. The crystalline phases of sintered samples were characterized by X-ray diffraction (XRD). Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the microstructure revealed that the BN phase was homogeneously distributed in the matrix of synthesized AlN. The effect of sintering temperature on the microstructure and properties of sintered samples was investigated. The results showed that densification of sintered samples was improved and the thermal conductivity exhibited a significant increase with an increase of the sintering temperature.
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Study of co-excited green emission of Tb3+, Ce3+ and Gd3+ in yttrium aluminum garnet
Fei Huang,Limin Dong,Hao Wang,Weimin Wang,Yucheng Wang,Zhengyi Fu 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.6
YAG : Tb3+, Ce3+, Gd3+ nano-phosphors derived from a sol-gel chemistry have been successfully synthesized and characterized by TG/DTA, XRD, SEM, and spectrometer. The results show that the phosphors have a uniform particle size distribution ranging 30-50 nm. The value of the lattice constant increased with an increase of the Gd3+ content. Tb3+ →Ce3+, Ce3+ →Tb3+ and Gd3+ →Ce3+ energy transfer existed in the co-excited system. The luminescence intensity was controlled by the concentration and ratio of the co-dopants. A small quantity of Gd3+ and Ce3+ evidently increased the green emission (5D4→7F5) of Tb3+. YAG : Tb3+, Ce3+, Gd3+ nano-phosphors derived from a sol-gel chemistry have been successfully synthesized and characterized by TG/DTA, XRD, SEM, and spectrometer. The results show that the phosphors have a uniform particle size distribution ranging 30-50 nm. The value of the lattice constant increased with an increase of the Gd3+ content. Tb3+ →Ce3+, Ce3+ →Tb3+ and Gd3+ →Ce3+ energy transfer existed in the co-excited system. The luminescence intensity was controlled by the concentration and ratio of the co-dopants. A small quantity of Gd3+ and Ce3+ evidently increased the green emission (5D4→7F5) of Tb3+.
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Bi2InTaO7 compounds as promising photocatalysts for marine plankton removal
Leticia M. Torres-Martínez,Isaías Juárez-Ramírez,Juan S. Ramos-Garza,Francisco Vázquez-Acosta,Ricardo Gómez,ZhengYi Fu,Soo Wohn Lee 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.1
The removal of marine plankton, red (Amphidium carterae), and green (Tetraselmis suecica) tide algae, by heterogeneous photocatalysis was carried out using pyrochlore-type semiconductors. The semiconductor, Bi2InTaO7 , was prepared by the solgel method and a solid state reaction. The XRD patterns evidence formation of the pyrochlore phase in the sol-gel materials calcined at low temperatures (600-800 oC). Nanostructured sol-gel materials were observed by SEM. The sol-gel preparation allowed the formation of the pyrochlore-type compound with specific surface areas (7-13 m2g−1) higher than the solid obtained by solid state preparation (< 5 m2g−1). Band gap (Eg) values between 2.1-2.7 eV determined by UV-Vis spectroscopy were obtained. Bi2InTaO7 photocatalysts prepared by the sol-gel method were able to eliminate Tetraselmis suecica and Amphidium carterae algae totally after 50 minutes of UV-irradiation, whereas Bi2InTaO7 by solid state preparation needed more than 1 h.
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