• 한국수소및신에너지학회논문집
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• 제16권1호
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• pp.49-57
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• 2005

[ $MO/Al_2O_3-ZrO_2$ ](M=Ni and Cu) mixed metal oxides were prepared using sol-gel method in order to investigate the applicability to the 2-step thermo-chemical water splitting process and their redox behaviors were studied by temperature programmed reaction(TPR) from room temperature to 900$^{\circ}C$ under 5% $H_2$/Ar for the reduction and $H_2O$/Ar for the oxidation, respectively. From the results, peaks of the reduction and the oxidation on temperature were shifted with the change of crystalline phases due to the addition of $Al_2O_3$ and $ZrO_2$. The intensities of the peaks were also increased with the increase of contents of NiO or CuO that could be considered as active species. In addition, based on the observation of SEM images before and after the redox test, it seemed that $Al_2O_3-ZrO_2$ added prevented high temperature sintering of active metal components such as Ni (or Cu) on the surface and played a role of dispersing the active species homogeneously in solid solution of mixed oxides.

• 한국세라믹학회지
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• 제29권7호
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• pp.511-516
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• 1992

In this study, SiC powder and Si powder were used as the raw materials. Mixture was prepared with addition of Al2O3 and Fe2O3 at 0.1~0.5wt% respectively. After this step, the mixture was pressed and nitrided for 30 hrs at 140$0^{\circ}C$ under NH3-N2 atmosphere. Mechanical properties of sintered specimens were investigated from measurement of porosity, bulk density and three point bending test. nitration reaction extent was observed at the change of mass before and after reaction, and the microstructure and the change of $\alpha$-Si3N4 and $\beta$-Si3N4 were observed by XRD and SEM. In the current work, the results are as follows 1. When Fe2O3 added, the nitridation increased with the content of Fe2O3, and the bending strength was increased from 0.1 wt% to 0.3 wt%, and decreased to 0.5 wt%. 2. When Al2O3 added, the nitridation and the bending strength increased little by little with the content of Al2O3 3. The bending strength of the specimen added with Fe2O3 were higher than that with Al2O3. Because the specimens contained Fe2O3 had much more the whisker type crystal of Si3N4 contributing to strength than contained Al2O3.

• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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• pp.6-10
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• 2003

Silver nano-powder was added to Ma $B_2$ to make (Ag)$_{(x)wt.%}$(Mg $B_2$)$_{(l00-x)wt.%}$ (A $g_{x}$-Mg $B_2$) (10 $\leq$ x $\leq$ 50) composite superconductors to investigate the effect of the Ag nano-powder on the vortex pinning. Pellets made out of the mixed powder were put inside stainless steel tubes, which were sintered at 85$0^{\circ}C$ in Ar atmosphere. No impurity phase was identified for as-rolled samples. However, both the Mg $B_2$ and the A $g_{x}$-Mg $B_2$ composite pellets, when sintered, contain small amount of Mg $B_4$ and MgAg impurity phases. From the magnetization study, it was found that the flux pinning was improved in the high magnetic field region (> 3 T) only when 10w/o Ag was added to Mg $B_2$. The "two step" structures in ZFC M(T) curve gradually increased as the amount of Ag added increased. Pinning centers can be created by adding a suitable amount of Ag nano-powder which is not too large to increase the decoupling between the Mg $B_2$ grains.crease the decoupling between the Mg $B_2$ grains.

• Journal of Electrochemical Science and Technology
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• 제11권1호
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• pp.60-67
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• 2020

In this study, copper (II) oxide powder for electroplating was prepared by recovering CuCl₂ from NaClO₃ type etching wastes via recovered non-sintering two step chemical reaction. In case of alkali copper carbonate [mCuCo₃·nCu(OH)₂], first reaction product, CuCo₃ is produced more than Cu(OH)₂ when the reaction molar ratio of sodium carbonate is low, since m is larger than n. As the reaction molar ratio of sodium carbonate increased, m is larger than n and Cu(OH)₂ was produced more than CuCO₃. In the case of m has same values as n, the optimum reaction mole ratio was 1.44 at the reaction temperature of 80℃ based on the theoretical copper content of 57.5 wt. %. The optimum amount of sodium hydroxide was 120 g at 80℃ for production of copper (II) oxide prepared by using basic copper carbonate product of first reaction. At this time, the yield of copper (II) oxide was 96.6 wt.%. Also, the chloride ion concentration was 9.7 mg/L. The properties of produced copper (II) oxide such as mean particle size, dissolution time for sulfuric acid, and repose angle were 19.5 mm, 64 second, and 34.8°, respectively. As a result of the hole filling test, it was found that the copper oxide (II) prepared with 120 g of sodium hydroxide, the optimum amount of basic hydroxide for copper carbonate, has a hole filling of 11.0 mm, which satisfies the general hole filling management range of 15 mm or less.

• 한국건설순환자원학회논문집
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• 제3권1호
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• pp.34-42
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• 2015

본 연구는 단순매립 및 소각처리 되고 있는 염색공단 슬러지의 재활용을 목적으로 Ti염과 Fe염으로 화학 처리된 염색공단 슬러지를 이용하여 인공경량골재를 제조하고, 인공경량골재로의 활용성 검토를 위하여 골재의 물리적 특성과 환경유해성 등을 평가하였다. 인공경량골재 제조는 점결제로 점토를 이용하여 점토와 슬러지 배합비율에 따른 성형성을 평가하여 최적 함수량을 선정하고, 최적 배합비를 기준으로 둥근 모양의 형태로 가공한 후 건조과정과 2단계의 소성과정을 거쳐 제조하였다. 제조된 경량골재는 KS F 2534 "구조용 경량 골재"를 기준으로 인공경량골재의 입도 및 조립률, 밀도 및 흡수율, 단위용적질량, 안정성 및 환경유해성 등을 평가하였다. 실험 결과 입도와 조립률에서 기준 범위를 일부 벗어났으나 다른 모든 물리적 특성은 기준 값을 모두 만족하는 것으로 나타났으며, 입도와 조립률도 향후 제조공정에서 충분히 해결할 수 있는 것을 확인할 수 있었다.

• 한국초전도ㆍ저온공학회논문지
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• 제4권2호
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• pp.16-20
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• 2002

Bi-axially textured Ni tapes for YBCO coated conductors were Prepared by cold rolling and heat treatment of Ni Powder compacts. The Ni powder used in this study was 5 urn in particle size and 99.99 % in purity. The process of this study consists of filling of hi powder into a rubber mold, cold-isostatically Pressing and sintering of the powder compacts at 110$0^{\circ}C$ for 6h in 96 % Ar - 4 % H$_2$ atmosphere. The sintered compacts were cold rolled with a 5 % step reduction ratio into a 100 micron-thick tapes and then heat-treated at 100$0^{\circ}C$ for various time periods. The (200) texture of Ni tape was successfully developed through the recrystallization heat treatment of the cold rolled Ni tapes. At 100$0^{\circ}C$, the degree of texture of the heat-treated Ni tapes seems not to be significantly affected by the heat-treatment time. The short heat treatment of S min was sufficient to develop the complete (200) cube texture. The degree of in-Plane and out-of-plane texture of the prepared Ni tapes was 8-10$^{\circ}$. The heat treated Ni tapes consisted of equiaxed grains with a size 50-70 microns. and the AFM sol-face roughness was as smooth as 3 nm.

• Korean Chemical Engineering Research
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• 제49권5호
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• pp.664-668
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• 2011

500 mL 교반탱크반응기 내에서 $AlCl_3$ 증기를 $H_2O$ 증기에 의해 부분 가수분해시켜 30~200 nm 크기의 $AlO_xCl_y(OH)_z$로 표시되는 구형의 알루미나 전구체 입자를 제조하였다. 반응시간, 교반속도, 반응온도가 생성된 입자의 형상, 크기 등에 미치는 영향을 조사하였다. 반응시간을 20, 60, 300 s로 변화시킨 결과 생성 입자의 형상 및 크기에 별다른 차이가 없었으며, 교반속도를 0, 300, 800 rpm으로 변화시킨 결과 0 rpm에서 입자의 크기가 최대값을 보였고, 반응온도를 180, 190, 200, $240^{\circ}C$로 변화시킨 결과 $190^{\circ}C$에서 제조된 입자의 크기가 가장 작게 나타났다. 가수분해 생성물 입자를 $10^{\circ}C$/min의 속도로 $1,200^{\circ}C$까지 가열하고 6 시간동안 하소시켜 45 nm 크기의 ${\alpha}$ 알루미나 입자를 얻었다. 하소과정에서 인접입자 사이의 소결에 의해 입자 형상이 구형에서 벌레모양으로 변환되었다. 하소온도를 $1,400^{\circ}C$로, 승온속도를 $50^{\circ}C$/min 로 증가시키고, 유지시간을 0.5 시간으로 감소시켜 급속 하소시킴으로써 인접입자의 소결을 상당히 감소시킬 수 있었다. $AlCl_3$의 가수분해 과정에서 소량의 $SiCl_4$ 또는 TMCTS(2,4,6,8-tetramethylcylosiloxane) 첨가에 의해 인접입자의 소결 방지 효과가 나타났으나, ${\alpha}$ 결정 이외에 ${\gamma}$ 결정, mullite 결정 등이 함께 생성되었다. 하소과정에서 $AlF_3$를 첨가한 결과 육각형 디스크 형상의 ${\alpha}$ 알루미나 입자가 생성되었다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.31.1-31.1
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• 2009

In an approach to acclimate ourselves torecent ecological consciousness trend, a lead-free piezoelectric material, bismuth sodium titanate (abbreviated as BNT) based bismuth sodium barium titanate (abbreviated as BNT-BT), was considered as an environment-friendly alternative for a lead based piezoelectric system. Ceramic specimens of0.94[(BixNa0.5)TiO3]-0.06[BaTiO3] (x = 0.500~0.515) compositions were prepared by a modified mixed oxide method. To increase the chemical homogeneity andre action activity, high energy mechanical milling machine and pre-milled nanosized powder has been used. In this method (BixNa0.5)TiO3 (x=0.500~0.515) andBaTiO3 were prepared separately from pre-milled constituent materials at low calcination temperature and then separately prepared BNTX (X=1, 2, 3 and 4) and BT were mixed by high energy mechanical milling machine. Without further calcination step the mixed powders were pressed into disk shape and sintered at $1110^{\circ}C$. Microstructures, phase structures and electrical properties of the ceramic specimens were systematically investigated. Highly dense ceramic specimens with homogenous grains were prepared in spite of relatively low sintering temperature. Phase structures were not significantly influenced by the excess amount Bi. Large variation on the piezoelectric and dielectric properties was detected at relative high excess Bi amounts. When $x{\leq}0.505$, the specimens exhibit insignificant variation in piezoelectric and dielectric constant though depolarization temperature is found to be decreased. Considerable amount of decrease in piezoelectric and dielectric properties are observed with higher excess of Bi amounts ($x{\geq}0.505$). This research indicates the advantages of high energy mechanical milling and importance of proper maintenance of Bi stoichiometry.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1018-1021
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• 2006

Powdered metal parts and components may be carburized successfully in a vacuum furnace by combining carburizing technology $VacCarb^{TM}$ with a hi-tech control system. This approach is different from traditional carburizing methods, because vacuum carburizing is a non-equilibrium process. It is not possible to set the carbon potential as in a traditional carburizing atmosphere and control its composition in order to obtain a desired carburized case. This paper presents test results that demonstrate that vacuum carburizing system $VacCarb^{TM}$ carburized P.M. materials faster than traditional steel with acceptable results. In the experiments conducted, PM samples with the lowest density and open porosity showed a dramatic increase in the surface carbon content up to 2.5%C and a 3 times deeper case. Currently the boost-diffusion technique is applied to control the surface carbon content and distribution in the case. In the first boost step, the flow of the carburizing gas has to be sufficient to saturate the austenite, while avoiding soot deposition and formation of massive carbides. To accomplish this goal, the proper gas flow rate has to be calculated. In the case of P.M. parts, more carbon can be absorbed by the part's surface because of the additional internal surface area created by pores present in the carburized case. This amount will depend on the density of the part, the densification grade of the surface layer and the stage of the surface. "as machined" or "as sintered". It is believed that enhanced gas diffusion after initial evacuation of the P.M. parts leads to faster carburization from within the pores, especially when pores are open . surface "as sintered" and interconnected . low density. A serious problem with vacuum carburizing is delivery of the carbon in a uniform manner to the work pieces. This led to the development of the different methods of carburizing gas circulation such as the pulse/pump method or the pulse/pause technique applied in SECO/WARWICK's $VacCarb^{TM}$ Technology. In both cases, each pressure change may deliver fresh carburizing atmosphere into the pores and leads to faster carburization from within the pores. Since today's control of vacuum carburizing is based largely on empirical results, presented experiments may lead to better understanding and improved control of the process.

• 한국전기전자재료학회논문지
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• 제26권3호
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• pp.246-251
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• 2013

Screen printing is commonly used to form the front/back electrodes in silicon solar cell. But it has caused high resistance and low aspect ratio, resulting in decreased conversion efficiency in solar cell. Recently the plating method has been combined with screen-printed c-Si solar cell to reduce the resistance and improve the aspect ratio. In this paper, we investigated the effect of light induced silver plating with screen-printed c-Si solar cells and compared their electrical properties. All wafers were textured, doped, and coated with anti-reflection layer. The metallization process was carried out with screen-printing, followed by co-fired. Then we performed light induced Ag plating by changing the plating time in the range of 20 sec~5min with/without external light. For comparison, we measured the light I-V characteristics and electrode width by optical microscope. During plating, silver ions fill the porous structure established in rapid silver particle sintering during co-firing step, which results in resistance decrease and efficiency improvement. The plating rate was increased in presence of light lamp, resulting in widening the electrode with and reducing the short-circuit current by shadowing loss. With the optimized plating condition, the conversion efficiency of solar cells was increased by 0.4% due to decreased series resistance. Finally we obtained the short-circuit current of 8.66 A, open-circuit voltage of 0.632 V, fill factor of 78.2%, and efficiency of 17.8% on a silicon solar cell.