• 한국분말재료학회지
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• 제16권3호
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• pp.209-216
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• 2009

A composite of rapidly solidified Al-6061 alloy powder with graphite particle reinforcements was prepared by ball milling and subsequent hot extrusion. The microstructure and mechanical properties of these composites were investigated as a function of milling time. With increasing milling time, the gas atomized initially and spherical powders became elongated with a maximum aspect ratio after milling for 30 h. Then, refinement and spheroidization were achieved by further milling to 70 h with a homogeneous and fine dispersion of graphite particles forming between the matrix alloy layers. The best compression and wear properties were obtained in the powder milled for 70 h, associated with the increased fine and homogeneous distribution of graphite particles in the aluminum alloy matrix.

• 한국세라믹학회지
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• 제14권3호
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• pp.163-168
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• 1977

As a wet chemical drying process "hot petroleum drying method" was applied and developed for preparing uniformly fine oxide powder with high purity and sinterreactivity. Using this method solution of sulfates was dried in hot petroleum bath (~17$0^{\circ}C$) to sulfate powder from which corresponding mullite doped by Fe3+ ion was formed. Particle size, shape, decomposition by heat, and phase identification of sulfate andoxide powders determined by DTA, TGA, X-ray diffraction, analysis and electron microscopy: sulfate powder prepared by this drying method is an intimate mixture of the amorphous form of uniformly and finely distributed spherical particles (0.05-0.1$\mu$). Mullitization with the sulfate powder occurs at 110$0^{\circ}C$ in air. The morphology of mullite particle made by firing the sulfate powder at 135$0^{\circ}C$ in oxygen atmosphere is granular of 0.1-0.3$\mu$ in size. This drying process proved to be a very effective method for preparing fine, homogeneous, and highly sinterreactive multicomponent oxide powder without conventional ceramic process of mixing, milling, and granulating. This process can be also applied for preparing electronic ceramic materials which are requisite for high purity and homogeneity.mogeneity.

• 열처리공학회지
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• 제11권3호
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• pp.168-176
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• 1998

The mechanical properties of mechanically alloyed Al-4wt%Mg alloys dispersed with $MgAl_2O_4$ dispersoilds at room and elevated temperatures were investigated. The powders in steady state during mechanical alloying consisted of Mg-supersatu rated Al solid solution and $Al_4C_3$ which resulted from the reaction of Al with C in process control agent (methanol). The hot-extruded materials consisted of uniformly dispersed fine $MgAl_2O_4$, ${\gamma}-Al_2O_3$, $Al_2O_3$ and matrix with extremly fine substructure. Tensile specimens prepared from the extruded bars were tested at room temperature to $400^{\circ}C$ under different strain rates. The tensile strength of alloys at room temperature ranged from 500 to 594MPa. At elevated temperatures, the tensile strengths and elongations decreased with increasing temperature. Adding 3% $MgAl_2O_4$ to Al-4wt%Mg increased the tensile strength of 50MPa at rowan temperature and 20MPa at $400^{\circ}C$.

• 한국분말재료학회지
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• 제12권3호
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• pp.174-178
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• 2005

This paper deals with the fabrication of titanium carbide using fine titanium hydride. The ratio of $TiH_2$ and C (Activated carbon) was 1:1 (mol) and milled in a planetary ball mill at a ball-to-powder weight ratio of 20:1. Thereafter, TGA was performed at $1400^{\circ}C$ to observe change of weight with milling time. Titanium carbide was obtained by using tempering the milled powders at $1100-1500^{\circ}C$. The microstructures of titanium carbide as well as the change of the lattice parameters and particle size have been studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

• 한국분말재료학회지
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• 제13권2호
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• pp.129-137
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• 2006

In this study, high purity fine $BaTiO_3$ powders were prepared by SHS (Self-propagating High-temperature Synthesis). We would examinate the study of sintering properties and characteristics as a function of temperature with various additives (binder, sintering agent). In separately binder addition, the green and sintered density of specimen were increased as binder content increases. The increased porosity resulted in fine grain size due to the inhibition of grain boundary moving. The $Al_{2}O_{3},\;TiO_{2}$ and MgO playa role of increasing dielectric constants at room temperature. These values were decreased at curie temperature. In case of $SiO_2$, the Curie temperature was decreased. In this study, a high dielectric ceramic capacitor material with temperature stability was synthesized by using various additives.

• 열처리공학회지
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• 제25권3호
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• pp.138-145
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• 2012

An ${\alpha}$-Ferrite (Fe) powder dispersed with 4 vol.% of $Al_2O_3$ was successfully produced by a simple miling at 210 K with a mixture of $Fe_2O_3$, Fe and Al ingredient powders, followed by 2 step high temperature consolidation: Hot Pressing (HP) at 1323 K and then Hot Isostatic Pressing at 1423 K. The microstructure of the consolidated material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEM-EDS analysis showed that the HIPed materials comprised a mixture of pure Fe matrix with a grain size of ~20 nm and $Al_2O_3$ with a bimodal size distribution of extremely fine (~5 nm) and medium size dispersoids (~20 nm). The mechanical properties of the consolidated materials were characterized by compressive test and micro Vickers hardness test at room temperature. The results showed that the yield strength of the ODS (Oxide Dispersion Strengthened) Fe alloy are as much as $674{\pm}39$ MPa and the improvement of the yield strength is attributed to the presence of the fine $Al_2O_3$ dispersoid.

• 열처리공학회지
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• 제6권4호
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• pp.204-212
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• 1993

The preparation of $TiO_2$ fine particles from $TiCl_4$ and oxygen by the vapor-phasereaction was investigated at $850^{\circ}C$ with an emphasis on the effect of its experimental conditions on the crystal type of the products. Anatase $TiO_2$ particles prepared by experiment were used to study anatase-rutile transition by calcination temperature, the additives and gas atmosphere. The results were as follows. The kinetics of anatase-rutile transition was well agreed with A vrami equation, and the activation energy of transition was 35kcal/mol. The addition of CuO in anatase $TiO_2$ particles accelerated the anatase-rutile transition, and its transition was retarded in vaccum.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2013년도 추계 학술논문 발표대회
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• pp.68-71
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• 2013

Reactive Powder Concrete (RPC) is an ultra high strength and high ductility cement-based composite material and has shown some promise as a new generation concrete in construction field. It is characterized by a silica fume-cement mixture with very low water-binder (w/b) ratio and very dense microstructure, which is formed using various powders such as cement, silica fume and very fine quartz sand (0.15~0.4mm) instead of ordinary coarse aggregate. However, the unit weight of cement in RPC is as high as 900~1,000 kg/㎥ due to the use of very fine sand instead of coarse aggregate, and a large volume of relatively expensive silica fume as a high reactivity pozzolan is also used, which is not produced in Korea and thus must be imported. Since the density of RPC has a heavy weight at 2.5~3.0 g/㎤. In this study, the modified RPC was made by the combination of ternary pozzolanic materials such as blast furnace slag and fly ash, silica fume in order to economically and practically feasible for Korea's situation. The fire resistance and structural behavior of the modified RPC exposed to high temperature were investigated.

• 한국기계가공학회지
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• 제20권1호
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• pp.103-109
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• 2021

Fine chips generated by machining have an impact on machine failure and quality of machined products, it is necessary to remove the chips, so the microchip collection and removal device by rotating conveyor belt with neodymium permanent magnets was developed. In this research, to solve the problem for reducing the existing microchips in the tank, a micro-chip removal device by rotating conveyor belt with neodymium permanent magnets developed. In the development of micro-chip removal device, 3D CATIA modeling was used, and the flow analysis and the electromagnetic force analysis were performed with COMSOL Multiphysics program. To evaluate the performance of the prototypes produced, design of experiments (DOE) is used to obtain the effect of neodymium conveyor movement speed on chip removal for the ANOVA analysis of recovered powders. An experiment was conducted to investigate the effect of the conveyor feed rate on the chip removal performance in detail. As a result of the experiment, it was confirmed that the slower the feeding speed of the fine chip removing device, the more efficient the chip removal.

• 대한화학회지
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• 제40권8호
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• pp.535-541
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• 1996

베시클을 이용한 알루미나 미분체 제조에 있어서 베시클 외부 분산계의 pH 변화, 즉 수산화이온의 농도변화가 베시클 내부에서 침전 반응기구 및 침전물의 입자 형태, 분포, 크기등에 미치는 영향을 고찰하고자 하였다. 투과전자현미경(TEM)과 탁도계로 관찰한 결과 분산계의 pH가 11.4 및 11.3에서부터 베시클내부에서 알루미늄 이온과 수산화이온이 반응하여 침전물이 생성되기 시작하였고 pH 12.0 에서 평균입자 크기가 50nm정도의 미세하고 균일한 구형의 침전물이 형성되었다. pH12.3 이상인 영역에서는 시간경과에 따른 베시클간의 응집 및 합체가 일어나 베시클 내부의 침전물이 pH12.0에서 생성된 침전물 크기에 비해 약 두 배 정도 성장함을 알 수 있었다.