• 한국표면공학회지
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• 제30권2호
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• pp.93-103
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• 1997

High temperature materials used in the elevated temperature and corrosive atmosphere must have the good oxidation resistance and preserve their own mechanical properties simultaneously. For the oxidation resistance, it is very important to form a protective oxide scale such as $Al_2O_3$ or $Cr_2O_3$ on the substrate. However, the additions of protective oxide forming elements such as Cr and Al in the alloy to enhance its oxidation resistance are limited due to the deleterious effects on their mechanical properties. PECVD(P1asma Enhanced Chemical Vapor Deposition) coating processes were employed to improve the oxidation resistance at high temperature. Cr and/or A1 were coated on the substrates of Ni and Inconel 600 at various temperatures of 400, 500, $600^{\circ}C$ and at different conditions of specimen surfaces. Then, coated specimens were exposed to isothermal and cyclic oxidation conditions in air at 1000 and $1100^{\circ}C$. In order to enhance the adhesion between the substrate and coated layer, heat treatments of the coated specimens were conducted in a vacuum. At isothermal oxidation experiments, Al-coated Ni specimen showed better oxidation resistance than pure Ni. At cyclic oxidation experiments at $1000^{\circ}C$. Cr and Al-coated specimen showed better oxidation resistance. Cr-coated Inconel 600 had also showed better oxidation resistance due to Cr in the substrate. By PECVD coating process, oxidation resistance could be improved, but it was not improved as expected due to the weakness of the adhesion between the substrate and the coated layer.

• 마이크로전자및패키징학회지
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• 제6권3호
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• pp.37-43
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• 1999

고주파에서 사용하기 위한 $SiO_2-TiO_2-Bi_2O_3$-RO계(RO:BaO-CaO-SrO)를 주성분으로 하는 결정화 유리와 세라믹 충진재로서 $Al_2O_3$를 혼합하여 제조한 저온 소성용 Glass/Ceramic 유전체 모재와 Ag-thick film의 동시 소결시 발생할 수 있는 소결 부정합과 그 해소 방안을 연구하였다. 적층된 Glass/Ceramic 유전체 sheet와 Ag-thick film의 동시 소결시에 소결체는 sheet와 film의 densification rate 차 등에 의해 큰 camber 현상과 그로 인해 Ag-film에 crack이 발생하였다. 이를 교정하기 위해 유리 성분과 $Al_2O_3$성분이 혼합된 유전체 분말에 $B_2O_3$를 6, 8, 10, 12, 14 vol% 첨가한 결과를 보면 $B_2O_3$첨가량이 증가함에 따라 소결체의 camber 현상은 점점 크게 줄어들었으며 14 vol% 첨가된 경우에는 거의 관찰되지 않았다. 또한 $BaO_3$첨가량이 증가함에 따라 유전율($varepsilon_{r}$)은 점점 감소하였고 Q$\times$f 값은 크게 증가하는 경향을 나타내었으며 $\tau_{f}$ 값은 양(+)의 값으로 점점 크게 변하였다.

• 공업화학
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• 제30권3호
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• pp.345-351
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• 2019

본 연구에서는 $TiO_2$를 기반으로 한 중공사형 흡착제를 제조와 다양한 금속산화물 첨가에 따른 비소 흡착 특성을 평가하였다. 실험 결과 $TiO_2$ 중공사형 흡착제가 가장 우수한 비소 흡착 성능을 보였으며, 금속산화물을 첨가한 경우 금속산화물이 $TiO_2$ 표면의 산점을 막음으로 인해 오히려 비소 흡착 성능이 저하되었다. 그러나 장시간 비소 흡착 성능을 비교한 결과 $Al_2O_3$를 첨가한 중공사형 흡착제의 비소 흡착 성능이 증진되었다. 또한 비표면적 및 기공 크기가 상대적으로 클수록 비소 흡착 성능이 우수하였으며, 루이스 산점과 브뢴스테드 산점이 풍부하게 존재할수록 흡착에 유리한 사이트가 제공됨을 확인하였다. 이를 통해 기존 파우더 형태의 상용 $TiO_2$를 담체 형태로도 제조하여 소규모 정수처리 시설에 적용이 가능할 것으로 판단된다.

• 한국세라믹학회지
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• 제17권1호
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• pp.27-34
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• 1980

The synthesis of glass-ceramic materials from glasses based on industrial wastes or natural rocks their physical properties were studied. Glasses of composition, CaO14.7∼16.1, MgO7.4∼9.0, Al2O38.3∼19.3, SiO2 48.9∼51.0wt% were prepared from domestic blast furnace slag, serpentine, sea sand and etc. with additions of chromic oxide, and fluoride as nucleating agent. The glasses were subjected to controlled heat treatments and yielded fine microstructure of glass-ceramics which were composed of monocrystalline phase of aluminous diopside. X-ray diffraction techniques were adopted to identify the crystalline phases and to determine the degree of crystallization quantitatively. Density, coefficient of thermal expansion, young's modulus, microhardness and modulus of rupture were measured and the resulting properties were discussed in terms of the heat-treatment conditions, the degree of crystallization, species of crystaline phase, the microstructures formed in glass-cramics and the chemical compositions of mother glasses.

• 한국세라믹학회지
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• 제21권4호
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• pp.361-365
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• 1984

This study has been carried out to sinter silicon nitride with additives and to show the effect of surface finishments on its strength and Weibull modulus which are two most important factors for its applications into structural ceramics. Silicon nitride was sintered with the additions of $Al_2O_3$ and $Y_2O_3$ under pressureless cond-ition. The optimum properties were obtained by sintering at 1, 75$0^{\circ}C$ for 3hrs under $N_2$ atmosphere and the strength showed 6, 500kg/$cm^2$ at room temperature and 3, 300kg/$cm^2$ at 120$0^{\circ}C$. The effects of surface treatment on the strength of sintered $Si_3N_4$ were studied and the results showed that fine surface treatment increased the strength by up to 50% The Weibull analysis showed that its modulus was increased with increasing fineness of surface finishments. It was concluded that the mechanical properties of sintered silicon nitride could be improved by fine surface grinding which implied the brittle-fracture nature of sintered silicon nitride.

• 한국환경과학회지
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• 제19권11호
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• pp.1385-1390
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• 2010

Repeated additions of untreated slurry to soil affected ecology and caused high levels of heavy metal in soil and ground water. The objective of this study was to evaluate heavy metal from hanwoo slurry with ferrous sulfate ($FeSO_4{\cdot}7H_2O$), aluminum sulfate [$Al_2(SO_4)_3{\cdot}14H_2O$, alum] and aluminum chloride ($AlCl_3{\cdot}6H_2O$) as a way to improve environmental management in hanwoo industry. The treatment rates, which were incorporated totally within the hanwoo slurry, were 1.0 g and 1.5 g of ferrous sulfate, alum and aluminum chloride/25 g of hanwoo slurry. The various rates of chemical additives significantly increased dry matter (9.98~13.94%) and decreased pH (3.48~6.52) compared with the controls. The use of chemical additives decreased Fe (11~29%), Al (7~12%), Zn (13~36%), and Cu (4~32%) contents, except for Fe in hanwoo slurry with ferrous sulfate and Al in hanwoo slurry with alum and aluminum chloride. In addition, the reduction in heavy metal should be associated with reduction in pH. In conclusion, the results of this study suggest that alum and aluminum chloride additives at rate of 1.5 g were cost-effective management practice that significantly reduces heavy metal from hanwoo slurry, while it may be improved environmental management.

• 한국주조공학회지
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• 제21권2호
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• pp.127-134
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• 2001

Misch metal (rare earth element, Ce, La, Nd, Pr) which has large influence on high-temperature stability and toughness was added to the Al-5%Ni-5%Mg alloy, and squeeze casting was used for Al-5%Ni-5%Mg-(Mm) alloys. The effect of applied pressure and misch metal additions on mechanical properties in Al-5%Ni-5%Mg alloy by direct squeeze casting has been investigated. The applied pressure were 0 MPa(gravity casting), 25, 50 and 75 MPa. Squeeze-cast Al-5%Ni-5%Mg-(Mm) alloys had better mechanical properties than those of non-pressurized cast alloys because of the increased cooling rate by the application of pressure during solidification. By the addition of misch metal in Al-5%Ni-5%Mg alloy, better combination of strength and elongation was obtained. The addition of 0.3%Mm in Al-5%Ni-5%Mg alloy improved the heat resistant property due to the formation of fine eutectic phases.

• 한국세라믹학회지
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• 제28권6호
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• pp.457-464
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• 1991

Aluminum nitride (AlN) has excellent properties such as high thermal conductivity and electrical resistivity, whereas it has some disadvantages such as low sinterability and tendency to be hydrolyzed by moisture at room temperature. In the present work, the relative density, modulus of rupture and microhardness were examined for pressure-less-sintered AlN (synthetic and commercial) bodies which were prepared under the conditions of various sintering temperatures, holding times and additions of CaCO3 which showed the best effect on sinterability among the various sintering aids. As a result, the AlN bodies with 1.0 wt% CaCO3 (0.56wt% CaO) which were sintered at 1800$^{\circ}C$ for 20 min showed good densification. In this case, the relative densities were 95.9% and 95.2%, and microhardnesses were 10.3 GPa and 9.8 GPa for synthetic and commercial AlN respectively. And as the holding time at 1800$^{\circ}C$ was increased from 10 min to 60 min, the relative density was increased from 91.9% to 96.5%. It was considered that impurities of metals and oxygen promoted the densification of AlN at low temperature (1600$^{\circ}C$).

• 한국분말재료학회지
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• 제3권2호
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• pp.97-103
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• 1996

The densification of the compacts of pure Co, Fe+50%.Co and Fe+25% Co sintered under H$_2$ gas or in vacuum was investigated. The effects of AL, Nb, Ti, and V additions on the densification were also studied. The sintered compact of Co was fully-dense when the density of the compact was lower than $Dg^c$. However, above $Dg^{c}$, it was never fully-dense regardless of sintering atmosphere, temperature, and time. The densification of sintered compacts of Fe-50% Co and Fe-25% Co were always incomplete. While the addition of AL made all compacts fully-dense, the addition of Ti was effective for the compacts of Co and Fe-25% Co. V was effective only for the Fe-25% Co. These results tell us that the particle size of Co powder, the amount of Fe, and the amount of additives forming stable oxides play on important role for the complete densification. Therefore it is desirable to reduce or eliminate the equilibrium pressure of H$_{2}$O or CO in isolated pores to obtain a fully-dense sintered compact.

• 한국주조공학회지
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• 제15권5호
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• pp.469-476
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• 1995

The effects of Cr, Mo or B additions were investigated on $B2{\leftrightarrow}DO_3$ structural transition temperature $(T_C)$ and mechanical properties of Fe-28at.%Al. The raw materials were arc-melted in vacuum and then subjected to the following heat-treatments to maximize the $DO_3$ ordered structure : $1000^{\circ}C/7days$, slowly cooled to $500^{\circ}C$ and then held for 5 days. In the effect on the grain refinment, the addition of alloying element B was the most effective. The addition of Cr or Mo had little effect. When 1at.%Mo was added, $T_c$ increase about $30^{\circ}C$, but Cr had a very little effect on $T_c$. On the contrary, when B was added, $T_c$ was apt to come down minutely. In the additional effect of alloying element on the mechanical properties, Cr was apt to decrease the microvickers hardness and yield strength, Mo and B didn't have much effect. In the case of compressure strength test, the effect of the environment on the yield strength was contrary to the result of the tensile strength test.