• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
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• pp.7-11
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• 2012

Plasma electrolytic oxidation of magnesium alloys is a well known technique to produce corrosion and wear resistant coatings. The addition of particles to the electrolyte provides a possibility to produce coatings with an increasing range of composition by in-situ incorporation of those particles into the coating. An extensive literature review has revealed that the mode of incorporation depends mainly on the melting point of the used particles and the energy provided by the discharges of the PEO process. The spectrum ranges from inert to partly reactive incorporation, but a complete reactive incorporation and a formation of a new single phase coating was not observed so far. Thus a new approach in PEO processing is introduced using specific particles as a kind of sintering additive, changing not only the composition but lowering the melting temperature and increase the liquid phase fraction during the discharges, resulting in a new amorphous coating.

• 한국세라믹학회지
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• 제39권7호
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• pp.617-621
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• 2002

Calcium aluminosulfate (3CaO.3Al$_2$O$_3$.CaSO$_4$or $C_4$A$_3$S) was prepared by chemical synthesis from the nitrate salts and aluminum sulfate. $C_4$A$_3$S was the main phase after calcination at 110$0^{\circ}C$. The specific surface areas after calcination at 110$0^{\circ}C$ and 130$0^{\circ}C$ were about 2.5 and 1.0 $m^2$/g, respectively. Hydration was investigated by XRD, DSC, SEM, EDS, conduction calorimetry and analysis of the liquid phase. Calorimetry showed that the induction period was longer than that of a sample prepared by conventional solid state sintering and this was attributed to the formation of amorphous coatings in abundance of $Al_2$O$_3$ and SO$_3$. Crystalline hydration products, principally calcium monosulfoaluminate hydrate and Al(OH)$_3$, appeared subsequently.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권10호
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• pp.500-503
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• 2001

The mechanical and electrical properties of the hot-pressed and pressureless annealed SiC+39vol.%$TiB_2$electroconductive ceramic composites were investigated as a function of the liquid additives of $Al_2O_3+Y_2O_3$. The result of phase analysis for the SiC+39vol.%$TiB_2$composites by XRD revealed $\alpha$-SiC(6H), $TiB_2$, and $YAG(Al_5Y_3O_{12})4 crystal phase. The relative density of SiC+39vol.%$TiB_2$ composites was increased with increased $Al_2O_3+Y_2O_3$. contents. The fracture toughness showed the highest value of $7.8 MPa.m^{1/2}$ for composites added with 12 wt % $Al_2O_3+Y_2O_3$. additives at room temperature. The electrical resistivity and the resistance temperature coefficient showed the lowest value of $7.3\times10_{-4}\Omega.cm\; and\; 3.8\times10_{-3}/^{\circ}C$ for composite added with 12 wt% $Al_2O_3+Y_2O_3$. additives at room temperature. The electrical resistivity of the SiC+39vol.%$TiB_2$composites was all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C\; to\; 700^{\circ}C$.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권2호
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• pp.92-97
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC+39vol. %ZrB2 electroconductive ceramic composites were investigated by adding 1, 2, 3wt% Al2O3+Y2O3(6:4wt%) of the liquid forming additives. In this microstructures, no reactions were observed between $\beta-SiC$ and ZrB2. The relative density is over 90.8% of the theoretical density and the porosity decreased with increasing Al2O3+Y2O3 contents. Phase analysis of the composites by XRD revealed $\alpha-SiC(6H, 4H)$, ZrB2 and $\beta-SiC$(15R). Flexural srength showed the highest of 315.5MPa for composites added with 3wt% Al2O3+Y2O3 additives as room temperature. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed 5.5MPa.m1/2 and 5.3MPa.m1/2 for composites added with 2wt% and 3wt% Al2O3+Y2O3 additives respectively at room temperature. The area fraction of the elongated SiC grain in the etched surface of sample showed 65% and 65.1% for composite added with 2wt% and 3wt% Al2O3+Y2O3 additives respectively. The electrical resistivity at room temperature. The electrical resistivity of the composites wall all positive temperature coefficient(PTCR) against temperature up to $700^{\circ}C$.

• 한국전기전자재료학회논문지
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• 제11권1호
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• pp.48-56
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• 1998

Pr\ulcornerO\ulcorner-based ZnO varistors were fabricated in the range of $Y_2$O$_3$additive content from 0.5 to 4.0mol%, and its microstructure and electrical properties were investigated. Yttrium was distributed nearly in the grain boundaries and the cluster phase formed at nodal point but more in cluster phase. The average grain size was decreased markedly from 34.9 to 8.6${\mu}{\textrm}{m}$ with increasing $Y_2$O$_3$additive content. It is believed that the decrease of grain size is attributed to the formation of cluster phase and the weakening of driving force for liquid sintering. As a result, $Y_2$O$_3$was acted as the inhibitor of the grain growth. With increasing $Y_2$O$_3$additive content, the varistor voltage, the activation energy, and the nonlinear exponent increased whereas the leakage current decreased, especially 4.0mol% $Y_2$O$_3$-added varistor exhibited very good I-V characteristics; nonlinear exponent 87.42 and leakage current 46.77nA. On the other hand, as $Y_2$O$_3$additive content increases, the varistor showed tendency of the salient decrease for donor concentration and the increase for barrier height. Conclusively, it is estimated that ZnO:Pr varistor compositions added more than 2.0mol% $Y_2$O$_3$are to be used to fabricate useful varistors.

• 한국결정성장학회지
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• 제24권4호
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• pp.176-182
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• 2014

상온 압축 성형 후 고상 반응 소결 공정을 통하여 $Mg_3Sb_2$ 소결체를 제조하고자 하였다. Mg과 Sb의 성분의 몰비와 반응온도에 따른 결정상의 변화를 조사하였다. 773~843 K에서 얻어진 고상반응 소결체들은 전형적인 $Mg_3Sb_2$ 결정상을 형성하였으나 소결체의 위치에 따라 약간 다른 상적 구성을 보였다. 소결체 하단 부위에서 전형적으로 얻어지는 결정상이 얻어졌으며 823 K 온도에서는 Mg : Sb = 3.15 : 1.85 조성일 때, 843 K 온도에서는 Mg의 몰 수가 3.10 이상인 모든 조성에서 ${\alpha}-Mg_3Sb_2$ 상과 정확히 일치하는 결정상이 얻어졌다. 미량 남아있는 Mg 성분은 응고 후 냉각 시 ${\alpha}-Mg_3Sb_2$ 상으로부터 석출된 것으로 보인다.

• 한국세라믹학회지
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• 제53권2호
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• pp.129-133
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• 2016

$MnO_2$ was added to the $0.95(Na_{0.5}K_{0.5})NbO_3-0.05CaTiO_3$ (NKN-CT) ceramics in order to promote the densification and improve the poling efficiency by increasing the resistance of the specimens. Densification and abnormal grain growth occurred in the $MnO_2$-added NKN-CT ceramics sintered at $1020^{\circ}C$, indicating that $MnO_2$ assisted the liquid-phase sintering of these materials. $Mn^{3+}$ ions were considered to enter the A-site of the matrix, thereby producing the free electrons, which interacted with the holes resulting from the evaporation of alkali ions. This interaction results in an increase in the resistance of the specimens. The increased resistance improved the poling efficiency and, hence, the dielectric and piezoelectric properties of the NKN-CT ceramics. A few of the $Mn^{3+}$ ions that entered the B-site of the NKN-CT matrix led to a slight increase in the mechanical quality factor.

• 자원리싸이클링
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• 제9권2호
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• pp.33-39
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• 2000

생물여과법에 의한 유해성 유기물 제거용 저밀도 담체로 사용하기 위하여 석탄회를 출발물질로 이용하여 세라믹 담체를 제조하였다. 석탄회에 기공 조절용 및 탄소함량 조절용으로 밀가루를 첨가하여 약환원성 분위기를 유지하여 $1200^{\circ}C$에서 소결한 결과 1.6~1.8 g/$\textrm{cm}^3$의 겉보기 밀도를 얻을 수 있었다. 소결 시 공기를 차단하고 급속히 승온하여 시편 조성의 일부를 환원시킴으로써 액상을 형성할 수 있었으며, 이렇게 형성된 액상은 시편의 표면부근에 폐기공을 형성하여 밀도를 낮추었다.

• 한국분말재료학회지
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• 제24권5호
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• pp.406-413
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• 2017

A Nanosized $WO_3$ and CuO powder mixture is prepared using novel high-energy ball milling in a bead mill to obtain a W-Cu nanocomposite powder, and the effect of milling time on the structural characteristics of $WO_3-CuO$ powder mixtures is investigated. The results show that the ball-milled $WO_3-CuO$ powder mixture reaches at steady state after 10 h milling, characterized by the uniform and narrow particle size distribution with primary crystalline sizes below 50 nm, a specific surface area of $37m^2/g$, and powder mean particle size ($D_{50}$) of $0.57{\mu}m$. The $WO_3-CuO$ powder mixtures milled for 10 h are heat-treated at different temperatures in $H_2$ atmosphere to produce W-Cu powder. The XRD results shows that both the $WO_3$ and CuO phases can be reduced to W and Cu phases at temperatures over $700^{\circ}C$. The reduced W-Cu nanocomposite powder exhibits excellent sinterability, and the ultrafine W-Cu composite can be obtained by the Cu liquid phase sintering process.

• 한국결정성장학회지
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• 제24권2호
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• pp.77-83
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• 2014

본 연구는 순환자원인 저회, 잔사회 그리고 준설토로 인공 경량골재를 제조할 때 철분의 종류와 양이 발포기구에 미치는 영향을 분석하는 것이다. 원료의 화학적 특성을 X선 회절 분석과 X선 형광 분석으로 측정하였다. 준설토 50 %, 저회 15 % 그리고 잔사회 35 %를 무게비로 혼합하고 철분함량을 5 % 단위로 30 %까지 첨가하였으며, 철분의 종류는 $Fe_2O_3$와 $Fe_3O_4$로 선정하였다. 성형된 골재는 급속 소성법으로 $40^{\circ}C$ 간격으로 $1060^{\circ}C$에서 $1180^{\circ}C$까지 소결하고, 비중과 흡수율을 측정하였다. 인공 경량골재는 철분 함유량이 10~15 %일 때 가장 낮은 비중을 보이며, 철분량이 증가할수록 액상 소결이 되어 비중이 증가하였다.