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Synthesis of Fe(Ni) nanoparticles by calcination and hydrogen reduction of metal nitrate powders
Oh, Sung-Tag,Joo, Min-Hee,Choa, Yong-Ho,Kim, Ki Hyeon,Lee, Sang-Kwan Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139
<P>The calcination and hydrogen reduction behavior of Fe- and Ni-nitrate powders has been investigated by using thermal analysis and microstructure observation. Fe-oxide/NiO composite powder was prepared by calcination at 350 °C for 2 h of Fe- and Ni-nitrate. Microstructural observation revealed that FeNi<SUB>3</SUB> particles with an average size of 40 nm were formed by hydrogen reduction at 320 ° C of calcined powders. Changes of the DSC curve and the XRD pattern with the increase in reduction temperature were explained as presumably due to the phase transformation of Fe(Ni) powders.</P>
Wear Behavior of Nano-Sized Metal Particle Dispersed Al<sub>2</sub>O<sub>3</sub> Nanocomposites
Oh, Sung Tag,Yoon, Se Joong,Choa, Yong Ho,Jeong, Young Keun,Niihara, Koichi Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.317 No.-
<P>The microstructure and mechanical properties including wear resistance of Al2O3-based nanocomposites with 5 vol% of Cu and Ni-Co dispersions were investigated. Al2O3/Cu and Al2O3/ Ni-Co nanocomposites were fabricated by hydrogen reduction and sintering process using metal oxide and metal nitrates. The composites showed homogeneous microstructures with nano-sized metal dispersions and enhanced fracture strength and toughness compared with monolithic Al2O3. In particular, high toughness and hardness were measured for the Al2O3/Ni-Co nanocomposite consolidated by PECS. A minimum wear coefficient of 2.33 x 10-5 mm3/Nm was obtained for the Al2O3/Ni-Co nanocomposite, while the monolithic Al2O3 showed a value of 2.0 x 10-5 mm3/Nm. Wear behavior is discussed in terms of microstructure and mechanical properties of the nanocomposites.</P>
Fabrication of Nanocomposites by Atmosphere-controlled Sintering and Their Properties
Oh Sung-Tag,Kim Young-Do,Lee Jeong-Keun 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
The microstructure and mechanical property of hot-pressed nanocomposites with a different temperature for atmosphere changing from to Ar have been studied. When the atmosphere changed from to Ar gas at , the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when the atmosphere changed at a lower temperature of , a more homogeneous microstructure and higher fracture strength was observed.
Processing of Nano-Sized Metal Alloy Dispersed Nanocomposites
Oh Sung-Tag,Seok Namkung,Lee Jai-Sung,Kim Hyoung-Seop,Tohru Sekino 한국분말야금학회 2001 한국분말야금학회지 Vol.8 No.3
An optimum route to fabricate the ferrous alloy dispersed nanocomposites such as /Fe-Ni and /Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of 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 , forming nanocomposite powder. The sintered /Fe-Ni composite showed the formation of Fe phase, while the reaction phases were not observed in /Fe-Co composite. Hot-pressed /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.
Oh, Sung-Tag,Kim, Young Do,Song, Young-Jun,Suk, Myung-Jin Materials Research Society of Korea 2016 한국재료학회지 Vol.26 No.11
In order to examine how the solid-liquid interface responds to temperature variation depending on the materials characteristics, i.e. faceted phase or nonfaceted phase, the moving solid-liquid interface of transparent organic material, as a model substance for metallic materials (pivalic acid, camphene, salol, and camphor-50wt% naphthalene) was observed in-situ. Plots of the interface movement distance against time were obtained. The solid-liquid interface of the nonfaceted phase is atomically rough; it migrates in continuous mode, giving smooth curves of the distance-time plot. This is the case for pivalic acid and camphene. It was expected that the faceted phases would show different types of curves of the distance-time plot because of the atomically smooth solid-liquid interface. However, salol (faceted phase) shows a curve of the distance-time plot as smooth as that of the nonfaceted phases. This indicates that the solid-liquid interface of salol migrates as continuously as that of the nonfaceted phases. This is in contrast with the case of naphthalene, one of the faceted phases, for which the solid-liquid interface migrates in "stop and go" mode, giving a stepwise curve of the distance-time plot.
Microstructure and Properties of Nano-Sized Ni-Co Particulate Dispersed Matrix Nanocomposites
Oh Sung-Tag,Mutsuo Sando,Koichi Niihara 한국분말야금학회 1998 한국분말야금학회지 Vol.5 No.4
In purpose of introducing the inverse magnetostrictive properties into the structural ceramics, based nanocomposites dispersed with nano-sized Ni-Co particles were studied. The composites were fabricated by the hydrogen reduction and hot-pressing of and NiO-CoO mixed powders. The mixtures were prepared by using Ni- and Co-nitrate as source materials for the Ni-Co particles. Microstructural observations revealed that nano-sized Ni-Co particles were dispersed homogeneously at grain boundaries. High strength above 1 GPa was obtained for the wt% Ni-Co nanocomposite fabricated by a controlled powder preparation process. The inverse magnetostrictive response to applied stress was obtained due to the presence of dispersed Ni-Co particles, which indicates a possibility to incorporate new functions into the structural ceramics without loosing the mechanical properties.
Oh, Sung-Tag,Lee, Sung-Il American Scientific Publishers 2010 Journal of Nanoscience and Nanotechnology Vol.10 No.1
<P>The processing conditions to prepare nano-sized Cu and Mo dispersed Al2O3 (Al2O3/Cu and Al2O3/Mo) composites by pressureless sintering were explored. The composite powders of Al2O3/Cu and Al2O3/Mo were obtained by the hydrogen reduction of Al2O3/CuO and Al2O3/MoO3 powder mixtures and consolidated by pressureless sintering using infrared heating furnace with a heating rate of 200 degrees C/min. SEM and TEM analyses for the composite showed that the nano-sized metal particles were well distributed and situated on the grain boundaries of the Al2O3 matrix. The nanocomposites, sintered at 1300 to 1500 degrees C for 4 min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in Al2O3/Cu nanocomposites with sintering additive of 1 wt% MgO. The sintered nanocomposites exhibited the enhanced fracture toughness of above 4.5 MPa x m(1/2), compared with monolithic Al2O3. The mechanical properties were discussed in terms of observed microstructural characteristics.</P>