Journal of Powder Materials

Fabrication of Metallic Particle Dispersed Ceramic Based Nanocomposite Powders by the Spray Pyrolysis Process Using Ultrasonic Atomizer and Reduction Process: Y.H. Choa, B.H. Kim, Y.K. Jeong, K.W. Chae, T.Nakayama, Kusunose T., T.Sekino, Niibara K.; J Korean Powder Metall Inst. 2001;8(3):151-156.

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Abstract PDF: MgO based nanocomposite powder including ferromagnetic iron particle dispersions, which can be available for the magnetic and catalytic applications, was fabricated by the spray pyrolysis process using ultra-sonic atomizer and reduction processes. Liquid source was prepared from iron (Fe)-nitrate, as a source of Fe nano-dispersion, and magnesium (Mg)-nitrate, as a source of MgO materials, with pure water solvent. After the chamber were heated to given temperatures (500~800°C), the mist of liquid droplets generated by ultrasonic atomizer carried into the chamber by a carrier gas of air, and the ist was decomposed into Fe-oxide and MgO nano-powder. The obtained powders were reduced by hydrogen atmosphere at 600~800°C. The reduction behavior was investigated by thermal gravity and hygrometry. After reduction, the aggregated sub-micron Fe/MgO powders were obtained, and each aggregated powder composed of nano-sized Fe/MgO materials. By the difference of the chamber temperature, the particle size of Fe and MgO was changed in a few 10 nm levels. Also, the nano-porous Fe-MgO sub-micron powders were obtained. Through this preparation process and the evaluation of phase and microstructure, it was concluded that the Fe/MgO nanocomposite powders with high surface area and the higher coercive force were successfully fabricated.

Processing of Nano-Sized Metal Alloy Dispersed Al_2O_3 Nanocomposites: Sung-Tag Oh, Namkung Seok, Jai-Sung Lee, Hyoung-Seop Kim, Sekino Tohru; J Korean Powder Metall Inst. 2001;8(3):157-162.

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Abstract PDF: An optimum route to fabricate the ferrous alloy dispersed Al_2O_3 nanocomposites such as Al_2O_3/Fe-Ni and Al_2O_3/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of Al_2O_3 and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded Al_2O_3, forming nanocomposite powder. The sintered Al_2O_3/Fe-Ni composite showed the formation of FeAl_2O_4 phase, while the reaction phases were not observed in Al_2O_3/Fe-Co composite. Hot-pressed Al_2O_3/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

Platinum Nano-Dispersion via In Situ Processing - Preparation and catalytic Property of Porous CaZrO_3/MgO/Pt Nanocomposite: Yoshikazu, Hae-Jin Hwang, Kondo Naoki, Ohji Tatsuki; J Korean Powder Metall Inst. 2001;8(3):163-167.

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Abstract PDF: A bulk porous CaZrO_3/MgO composite with plantinum nano-dispersion was synthesized in air atmosphere through the combination of several in situ reactions, including the pyrolysis of PtO_2. A mixture of CaMg(CO_3)_2(dolomite), ZrO_2, PtO_2 and LiF (0.5 wt%, as an additive) was cold isostatically pressed at 200 MPa and sintered at 1100°C for 2 h. The porous CaZrO_3/MgO/Pt composite (CaZrO_3/MgO : Pt=99 : 1 in volume) had a uniformly open-porous structure (porosity: 56%) with three-dimensional (3-D) network and a narrow pore-size distribution, similarly to the porous CaZrO_3/MgO composites reported before. Catalytic Properties (viz., NO direct decomposition and NO reduction by C_2H_4) of the CaZrO_3/MgO/Pt composite were investigated up to 900°C. In the absence of oxygen, the NO conversion rate reached ~52% for the direct decomposition and ~100% for the reduction by C_2H_4, respectively. The results suggest the possibility of the porous composite as a multifunctional filter, i.e., simultaneous hot gas-filtering and de-NO_x in one component.

Modelling Strength and Ductility of Nanocrystalline Metallic Materials: Hyoung-Seop Kim; J Korean Powder Metall Inst. 2001;8(3):168-173.

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Abstract PDF: The effect of grain refinement of the strength and ductility of metallic materials is investigated. A model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanisms: dislocation glide and mass transfer by diffusion. The model was exemplified by simulating uniaxial tensile deformation of Cu down to the nanometer grain size. The results confirm the observed strain hardening behaviour and a trend for reduction of ductility with decreasing grain size at room temperature.

Boron Nitride Dispersed Nanocomposites with High Thermal Shock Resistance: T. Kusunose, T. Sekino, Y.H. Choa, T. Nakayama, K. Niihara; J Korean Powder Metall Inst. 2001;8(3):174-178.

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Abstract PDF: The microstructure and mechanical properties of Si_3N_4/BN nanocomposites synthesized by chemical processing were investigated. The nanocomposites containing 15 vol% hexagonal BN (h-BN) were fabricated by hot-pressing alpha-Si_3N_4powders covered with turbostratic BN (t-BN). The t-BN coating on alpha-Si_3N_4particles was prepared by heating alpha-Si_3N_4 particles covered with a mixture of boric acid and urea in hydrogen gas. TEM observations of this nanocomposite revealed that nano-sized h-BN particles were homogeneously dispersed within Si_3N_4grains as well as at grain boundaries. The strength and thermal shock resistance were significantly improved in comparison with the Si_3N_4/BN microcomposites.

Microstructural Wear Mechanism of Al_2O_3-5 vol% SiC nanocomposite and Si_3N_4Ceramics: Doh-Hyung Riu, Yoon-Ho Kim, Soo-Wohn Lee, Niihara Koichi; J Korean Powder Metall Inst. 2001;8(3):179-185.

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Abstract PDF: Through the observation of wear scar of two ceramic materials, microstructural wear mechanisms was investigated. As for the Al_2O_3-5 vol% SiC nanocomposite, the grain boundary fracture was suppressed by the presence of SiC nano-particles. The intragranular SiC particles have inhibited the extension of plastic deformation through the whole grain. Part of plastic deformation was accommodated around SiC particles, which made a cavity at the interface between SiC and matrix alumina. On the other hand, gas-pressure sintered silicon nitride showed extensive grain boundary fracture due to the thermal fatigue. The lamination of wear scar was initiated by the dissolution of grain boundary phase. These two extreme cases showed the importance of microstructures in wear behavior.

Multifunctionality in Ceramic/Metal Nanocomposites: Tohru Sekino, Hiroki Kondo, Koichi Niihara; J Korean Powder Metall Inst. 2001;8(3):186-191.

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Abstract PDF: Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for Al_2O_3/Ni and ZrO_2/Ni nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.

Fabrication of Ag doped Hydroxyapatite and its Antimicrobial Effects with the Particle Size: Kyung-Sik Oh, Kyung-Ja Kim, Young-Keun Jeong; J Korean Powder Metall Inst. 2001;8(3):192-196.

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Abstract PDF: Ag doped Hydroxyapatite powder in nano-scale was successfully synthesized either by co-precipitation or by ion exchange route. The fabricated powder was successfully dispersed through freeze drying due to the prevention of secondary particles. The antimicrobial effects of nano-HAp against E.coli was superior to micron ones not only in its strength but also in duration.

Design of Nanocluster Based Material with Catalytic Properties: Nakayama Tadachika, Chang-Yeoul Kim, Sekino Tohru, Yong-Ho Choa, Kusunose Takafumi, Hayashi Yamato, Niibara Koichi; J Korean Powder Metall Inst. 2001;8(3):197-200.

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Abstract PDF: Modified inert gas condensation method was used to produce the nanocluster composites of CuO/CeO_2. High-resolution TEM, SEM and catalytic measurements have been used to characterize the samples and study the synergistic effect between the CuO phase and CeO_2(ceria) support. By varying the He pressure, the heating temperature and configuration of the heating boats inside the modified gas condensation chamber, nanoclusters of varying sizes, shapes and composition can be produced. The composition and nanostructured morphology were shown to influence the catalytic properties of the system. A copper content around 10 at% with a morphology that favors high-energy surfaces of ceria is shown to be beneficial for a high catalytic activity.

Fabrication of (La, Sr)MO_3 (M=Mn or Co)/YSZ Nanocomposite Thin Film Electrodes for the Exhaust Gas Purification by a Chemically-Modified Sol-Gel Process: H.J. Hwang, J.W. Moon, M. Awano, K. Maeda; J Korean Powder Metall Inst. 2001;8(3):201-206.

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Abstract PDF: >LaMnO_3, (La, Sr)MO_3, and (La, Sr)MO_3/YSZ gel films were deposited by spin-coating technique on scandium-doped zirconia (YSZ) substrate using the precursor solution prepared from La(O-i-C_3H_7)_3, Co(CH_3COO)_2or Mn(O-i-C_3H_7)_2,2-methoxyethanol, and polyethylene glycol. By heat-treating the gel films, the electrochemical cells, (La, Sr)MnO_3midScSZmidPt were fabricated. The effect of polyethylene glycol on the microstructure evolution of LaCoO_3and LaMnO_3thin films was investigated, and NOx decomposition characteristics of the electrochemical cells were investigated at 500°C to 600°C. By applying a direct current to the (La, Sr)MnO_3midScSZmidPt electrochemical cell, good NOx conversion rate could be obtained relatively at low current value even if excess oxygen is included in the reaction gas mixture.

Fabrication of Nanocomposite Powders by Sonochemical Method: Yamato Hayashi, Tohru Sekino, Koichi Niihara; J Korean Powder Metall Inst. 2001;8(3):207-209.

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Abstract PDF: Nano particles have recently been a major research interest, motivated by their unusual physical and chemical properties. Such particles can be synthesized using physical and chemical methods. The physical methods need expensive installation like vacuum induction furnace, whereas in chemical methods the process in generally very simple and low cost. In this study, simple and new fabrication process by using ultrasound was investigated to prepare the nano-sized metal particles on various powders at room temperature.

Novel Synthesis and Properties of Si_3N_4-based Nano/Nano-Type Composites: Masahi Yoshimura; J Korean Powder Metall Inst. 2001;8(3):210-213.

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Abstract PDF: Si_3N_4/TiN nano/nano-type composites were successfully fabricated by the combination of a mechano-chemical grinding (MCG) method and a short time sintering process, and their wear resistance was evaluated. Powder mixtures of alpha-Si_3N_4and Ti were prepared using mechano-chemical grinding process and the resulting nanocomposite powder mixtures were consolidated using pulsed electric current sintering (PECS). TEM observation showed that the nano/nano-type composites consisted of homogeneous and very fine matrix grains with the size less than 100 nm. The obtained Si_3N_4-based nano/nano-type showed high wear resistance and electric discharge machinability.

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