• 한국세라믹학회지
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• 제35권4호
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• pp.311-318
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• 1998

The reaction bonded alumina ceramics with reinforced particles which have low shrinkage were pro-duced by blending of SiC or TiC or ZrO2 powders to the mixture of Al metal and Al2O3 powder. The powd-ers were attrition milled isostantically pressed and preheated tio 110$0^{\circ}C$ with a heating rate of $1.5^{\circ}C$/min The specimens were then sintered at the temperature range 1500 to 1$600^{\circ}C$ for 5 hours with a heating rate of 5$^{\circ}C$/min. The specimens showed 5-9% weight gain and 2-9% dimensional expansion through the complete oxidation of Al after preheating up to 11--$^{\circ}C$ the overall dimensional change of the specimens after the reaction sintering at 1500-1$600^{\circ}C$ was 6-12% The maximum densities were 92% theoretical. The fine grain-ed(average grain size :0.4 ${\mu}{\textrm}{m}$) microstructure were observed in the specimen with ZrO2 and SiC. But the microstructure of specimen with TiC was relatively coarse.(average grain size : 2.1 ${\mu}{\textrm}{m}$) The mullite phase was formed by the reaction of Al2O3 and SiO2 in a specimen with SiC. In the TiC contained specimen TiC was oxidized into TiO2 and finally reacted with Al2O3 to form Al2TiO5 during sintering.

• 한국산학기술학회논문지
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• 제20권11호
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• pp.217-223
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• 2019

복합 형상 부품 제작 및 제작 공정의 일체화 장점으로 3D 프린팅 기술의 적용 분야가 확대되고 있으며, 지속적인 연구 개발에 의해 다양한 기술방안들이 등장하고 있다. 대표적인 기술로는 파우더 형태의 소재 위에 레이저를 조사함으로써 원하는 영역을 소결 및 적층 제작하는 방식의 SLS 기술이 있으며, 고성능의 엔지니어링 플라스틱을 활용하여 실제 사용할 수 있는 부품을 제작하는 사례가 늘어나고 있다. 본 연구에서는 활용도가 높은 고분자 소재인 폴리아미드 12 소재 및 글라스 비드가 보강된 폴리아미드 12 소재를 대상으로 인장시편을 제작하여 시편 제작 방향 및 인장 시험 온도에 따른 특성 결과를 비교 분석하였다. 시편 제작방향은 작업 평면 기준으로 0°, 45°, 90° 로 구분하였으며, 인장시험온도는 -25℃, 25℃, 60℃로 조건을 구분하였다. 시험 결과로부터 제작 방향이 90°에 가까울수록 두 소재 모두 탄성률의 미세한 감소를 보였으며, 인장강도는 PA12보다 글라스 비드 보강 PA12가 제작방향에 대한 의존성을 명확하게 보였다. 또한 시험 온도 증가에 따라 탄성률 및 인장강도의 저하를 확인할 수 있었다.

• 한국재료학회지
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• 제21권1호
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• pp.21-27
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• 2011

A nano-porous structure of tin oxide was prepared using an anodic oxidation process and the sample's electrochemical properties were evaluated for application as an anode in a rechargeable lithium battery. Microscopic images of the as-anodized sample indicated that it has a nano-porous structure with an average pore size of several tens of nanometers and a pore wall size of about 10 nanometers; the structural/compositional analyses proved that it is amorphous stannous oxide (SnO). The powder form of the as-anodized specimen was satisfactorily lithiated and delithiated as the anode in a lithium battery. Furthermore, it showed high initial reversible capacity and superior rate performance when compared to previous fabrication attempts. Its excellent electrode performance is probably due to the effective alleviation of strain arising from a cycling-induced large volume change and the short diffusion length of lithium through the nano-structured sample. To further enhance the rate performance, the attempt was made to create porous tin oxide film on copper substrate by anodizing the electrodeposited tin. Nevertheless, the full anodization of tin film on a copper substrate led to the mechanical disintegration of the anodic tin oxide, due most likely to the vigorous gas evolution and the surface oxidation of copper substrate. The adhesion of anodic tin oxide to the substrate, together with the initial reversibility and cycling stability, needs to be further improved for its application to high-power electrode materials in lithium batteries.

• 한국재료학회지
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• 제17권6호
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• pp.318-322
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• 2007

Porous ${\beta}-tricalcium$ phosphate $({\beta}-TCP)$ bioceramic was fabricated by pressureless sintering using commercial HAp and different volume percentages of PMMA powders (30-60 vol.%). The range of spherical pore size was about $200-250\;{\mu}m$ in diameter. By increasing the PMMA content, the number of pores and their morphology were dramatically changed as well as decreased the material properties. In case of using 60 vol.% PMMA content, network-type pores were found, due to the necking of the PMMA powders. The values of relative density, elastic modulus, bending strength and hardness of the 60 vol.% PMMA content sample, sintered at $1500^{\circ}C$, were about 46%, 22.2 GPa, 5MPa and 182 Hv respectively. Human osteoblast-like MG-63 cells and osteoclast-like Raw 264.7 cells were well grown and fully covered all of the porous ${\beta}-TCP$ bodies sintered at $1500^{\circ}C$.

• 한국재료학회지
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• 제26권10호
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• pp.570-576
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• 2016

Using the ultrasonic pyrolysis method, spherical $SiO_2$ powders were synthesized from aqueous $SiO_2$ sol as a starting material. The effects of pyrolysis conditions such as reaction temperature, $SiO_2$ sol concentration, and physical properties of precursor were investigated for the morphologies of the resulting $SiO_2$ powders. The particle size, shape, and crystallite size of the synthesized $SiO_2$ powders were demonstrated according to the pyrolysis conditions. Generally, the synthesized $SiO_2$ particles were amorphous phase and showed spherical morphology with a smooth surface. It was revealed that increased crystallite size and decreased spherical $SiO_2$ particle size were obtained with increases of the pyrolysis reaction temperature. Also, quantity of spherical $SiO_2$ particles decreased with the decrease in the concentration and surface tension of the precursor.

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1706-1713
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• 2020

Functionally gradient material (FGM) is promisingly effective in mitigating the thermal stress between plasma facing materials (PFM) and structural materials. However, the corresponding research with respect to W/V FGM has not been reported yet. In this work, we firstly report the successful fabrication of W/V FGM by a combined technology of mechanical alloying (MA) and spark plasma sintering (SPS). The microhardness and microstructure of the consolidated sample were both investigated. W/V stacks show significantly enhanced microhardness (>100%) compared with pure W plate, which is beneficial to the integral strength of the hybrid structure. Furthermore, we clarify that the different ductility of W and V should be carefully considered, otherwise W/V powder might aggregate and lead to the formation of compositional segregation, and simultaneously unmask the impact of V proportion on the distribution of second phase in W-V binary alloy system. This work provides an innovative approach for obtaining W-V connections with much better performance.

• 한국해양공학회지
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• 제22권4호
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• pp.59-64
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• 2008

The mechanical properties of liquid phase sintered (LPS) SiC materials, with the addition of oxide powder, were investigated, in conjunction with a detailed analysis of their microstructures. LPS-SiC materials were fabricated at a temperature of 1820 $^{\circ}C$ under an argon atmosphere, using three different starting sizes of SiC particles. The sintering additive for the fabrication of the LPS-SiC materials was an $Al_2O_3-Y_2O_3$ mixture with a constant composition ratio ($Al_2O_3/Y_2O_3$: 1.5). The particle sizes of the commercial SiC powderswere 30 nm, 0.3 $\mu$m, and 3.0 $\mu$m. The flexural strength of the LPS-SiC materials was also examined at elevated temperatures. A decrease in the starting size of the SiC particles led to an increase in the flexural strength of the LPS-SiC materials, accompanying a highly dense morphology with the creation of a secondary phase. Such a secondary phase was identified as $Y_3Al_2(AlO_4)2$. The flexural strength of the LPS-SiC materials greatly decreased with an increase in the test temperature, due to the creation of a large amount of pores.

• 한국세라믹학회지
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• 제47권2호
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• pp.199-204
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• 2010

A dual-phase ceramic membrane consisting of gadolinium-doped ceria (GDC) as an oxygen ion conducting phase and $MnCo_2O_4$ as an electron conducting phase was fabricated by sintering a GDC and $MnCo_2O_4$ powder mixture. The $MnCo_2O_4$ was found to maintain its spinel structure at temperatures lower than $1200^{\circ}C$. (Mn,Co)(Mn,Co)$O_4$ spinel, manganese and cobalt oxides formed in the sample sintered at $1300^{\circ}C$ in an air atmosphere. XRD analysis revealed that no reaction phases occurred between GDC and $MnCo_2O_4$ at $1200^{\circ}C$. The electrical conductivity did not exhibit a linear relationship with the $MnCo_2O_4$ content in the composite membranes, in accordance with percolation theory. It increased when more than 15 vol% of $MnCo_2O_4$ was added. The oxygen permeation fluxes of the composite membranes increased with increasing $MnCo_2O_4$ content and this can be explained by the increase in electrical conductivity. However, the oxygen permeation flux of the composite membranes appeared to be governed not only by electrical conductivity, but also by the microstructure, such as the grain size of the GDC matrix.

• 한국세라믹학회지
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• 제39권2호
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• pp.199-203
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• 2002

소결 분위기가 금속입자분산 세라믹스기 복합체의 미세 조직 및 물성에 미치는 영향에 대하여 조사하고자 화학적 방법으로 합성한 $Al_2O_3$/Fe-Ni 나노복합분말을 수소 및 아르곤 가스 분위기, 또한 소결온도 등으로 제어하여 열간가압 소결하였다. 수소분위기에서 소결한 복합체는 아르곤분위기의 경우보다 반응상 $FeAl_2O_4$의 형성이 억제되었으며, 증가된 파괴강도 및 인성 값을 나타내었다. 또한, 소결 온도를 낮추었을 경우 기지상 및 금속 분산상의 미세화와 향상된 기계적 성질을 얻을 수 있었다. 소결 조건에 따른 기계적 특성의 변화는 주로 반응상의 형성과 관련된 미세조직 특성에 의존하는 것으로 해석하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제19권2호
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• pp.19-24
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• 2017

Cryogenic milling which is a combined process of low-temperature treatment and mechanical milling was applied to fabricate high critical current density $(J_c)MgB_2$ bulk superconductors. Liquid nitrogen was used as a coolant, and no solvent or lubricant was used. Spherical Mg ($6-12{\mu}m$, 99.9 % purity) and plate-like B powder (${\sim}1{\mu}m$, 97 % purity) were milled simultaneously for various time periods (0, 2, 4, 6 h) at a rotating speed of 500 rpm using $ZrO_2$ balls. The (Mg+2B) powders milled were pressed into pellets and heat-treated at $700^{\circ}C$ for 1 h in flowing argon. The use of cryomilled powders as raw materials promoted the formation reaction of superconducting $MgB_2$, reduced the grain size of $MgB_2$, and suppressed the formation of impurity MgO. The superconducting critical temperature ($T_c$) of $MgB_2$ was not influenced as the milling time (t) increased up to 6 h. Meanwhile, the critical current density ($J_c$) of $MgB_2$ increased significantly when t increased to 4 h. When t increased further to 6 h, however, $J_c$ decreased. The $J_c$ enhancement of $MgB_2$ by cryogenic milling is attributed to the formation of the fine grain $MgB_2$ and a suppression of the MgO formation.