• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.125-133
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• 2016

With the aim of using a filler material in a conductive paste, fine Cu nanoparticles were synthesized through the high-speed chemical reaction between cuprous oxide ($Cu_2O$) powder and sulfuric acid in distilled water. Under external temperature of $7^{\circ}C$, sulfuric acid concentration of 48%, and $Cu_2O$ amount of 30 g, the $Cu_2O$ particles were eliminated and slightly aggregated Cu nanoparticles were synthesized. Futhermore, Cu nanoparticles of 224 nm, in which the aggregation between particles was obviousiy much suppressed, were synthesized with the choice of an additive. In the particle sample, occasionally there are coarse particles formed by the aggregation of fine nanoparticles and weak linkages between the nanoparticles. However, the coarse particles were destroyed and the linkages were broken after mixing with a resin formulation, indicating the behavior of untangling the aggregation between nanoparticles.

• Journal of Surface Science and Engineering
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• v.50 no.1
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• pp.46-54
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• 2017

Marcel Pourbaix에 의해 만들어진 Eh-pH 도표는 화학적으로 안정한 상을 pH와 전위 (Potential or Eh)의 관점으로 도시한 것으로서 수용액 내에서 일어나는 화학반응을 부식-방식의 관점에서 이해하데 유용하게 사용되어 왔다. pH (potential of hydrogen)는 수소이온의 농도의 함수이며, Eh는 표준수소전극 (SHE, standard hydrogen electrode) 에 대한 전위를 나타낸다. 수용액에서의 도금 반응은 부식반응의 역반응이라 할 수 있으므로 도금반응도 이 도표를 이용하면 반응에 대한 열역학적 예측이 가능하다. 국내외 전기화학 및 표면공학 관련 교재들을 보면 Eh-pH 도표로 대표되는 열역학이나 분극곡선으로 대표되는 속도론에 대한 설명은 주로 부식의 관점에서 설명이 되어있어 도금을 공부하는 학생들에게는 직접적인 이해가 쉽지 않은 것이 사실이다. 저자는 출연연구소에 근무하면서 새로 들어오는 학연생(대학원생)들의 Eh-pH 도표에 대한 이해도를 알아보면 이 도표를 이해하고 이용할 줄 아는 학생이 거의 없다는 점을 안타깝게 여겨왔다. 최근에는 단순한 금속 도금이 아니라 나노 분말 합성, 반도체 물질 합성 등 여러 가지 공정기술과 응용기술이 수용액에서의 산화-환원 반응을 이용하고 있기 때문에 Eh-pH 도표의 중요성은 더해가고 있음을 느끼고 있었다. 그러던 중, 일본의 표면 처리 학술지인 표면기술(表面技術) (2013년, 64권 2호)에 'Eh-pH 도표의 표면기술에의 응용'이라는 제하의 소특집이 발간되었다. 이 소특집은 6편의 논문으로 되어 있었다. 저자는 이 소특집을 읽는 순간 이 논문들을 번역하여 표면공학회지에 소개를 하면 도금이나 전기화학을 공부하는 학생들에게 큰 도움이 될 것이라는 생각을 하였다. 본 기술해설 논문은 저자가 이 소특집에 게재된 논문을 번역하고 일부 내용은 저자의 의견으로 가감하여 표면공학회 학생 회원 및 기업의 연구원들에게 소개하기 위하여 저역을 한 것이다. 이 논문은 매 호 한편씩 소개할 예정이며, 원문을 읽고 싶다면 표면기술(表面技術)을 참조하길 바란다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.4
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• pp.160-166
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• 2019

Cerium oxide ($CeO_2$, often called as Ceria) is one of the valuable rare earth oxide materials, which has been widely used for high temperature applications such as solid oxide fuel cells, automotive three-way catalysts and oxygen storage capacity. Considering those application, it is important to improve high redox and thermal stability with high surface morphology because the high surface area of $CeO_2$ could improve the catalytic reactivity at high temperature conditions. Herein we successfully fabricated hierarchical flower-like $CeO_2$ deposited via controlling pathway of precipitation reaction to supply carbonate ion lead to the flower-like morphology. The hexagonal lattice system of precipitated precursor shows better thermal stability then orthorhombic one during thermal cycling condition.

• Applied Chemistry for Engineering
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• v.17 no.4
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• pp.420-425
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• 2006

Nano sized mixed metal hexagonal ferrite powders with improved magnetic properties have been prepared by sol-gel method using propylene oxide as a gelation agent. To obtain the desired ferrite, two different metal ions were used. One of the ions has only +2 formal charge. The key step in the processes is that hydrated $Ba^{2+}$ or $Sr^{2+}$ ions are hydrolyzed and condensed at the surface of the previously formed $Fe_{2}O_{3}$ gel. In this processes, all the reaction can be finished within a few minutes. The magnetic properties of the produced powder were improved by heat treatment. The highest values of the magnetic properties were achieved at temperature $150^{\circ}C$ lower than those of the previously published values. The highest observed values of coercivity and the saturation magnetization of Sr-ferrite and Ba-ferrite powder were 6198 Oe, 5155 Oe and 74.4 emu/g, 68.1 emu/g, respectively. The ferrite powder annealed at $700^{\circ}C$ showed spherical particle shapes. The resulting spheres which were formed by the aggregation of nanoparticles with size 3~5 nm have diameter around 50 nm. The powder treated at $800^{\circ}C$ showed hexagonal-shaped grains with crystallite size above 500 nm.

• Korean Chemical Engineering Research
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• v.46 no.1
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• pp.99-105
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• 2008

Core-shell structured $BaTiO_3$ powders were produced via nano-coating of $Cr_2O_3$ and $Mn_2O_3$ to barium titanate powder system for MLCCs. From preliminary experiments, the optimal solution reaction condition employing using $KMnO_4$, $K_2Cr_2O_4$ and sulfur was established. Not only powders of $Cr_2O_3$ and $Mn_2O_3$ were synthesized but also their coating on $BaTiO_3$ powders were peformed under the same reaction condition. The coating was carried out in two ways, one-step and two-step, and its results were characterized for comparison. Conclusively speaking, two oxide additives were coated onto the $BaTiO_3$ powder surface with high quality and excellent reaction yield even under mild condition, which indicates that the contents as well as the properties of additive shell layer can be precisely controlled with rather ease.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.252-258
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• 2002

Transparent $TiO_2$ thin films prepared by sol-gel process using the modification of titanium(IV) alkoxide showed improved thermal stability and high refraction index. Compared to the pure $TiO_2$ film, the modified $TiO_2$ films show the increased index of refraction under proper condition at pH 2.5. Transparency of these $TiO_2$ thin films were more than 80% in the visible region. It has been demonstrated that the reaction occurs in the amorphous phase: an exchange of phase results in anatase before and after 400$^{\circ}C$, in rutile over 700$^{\circ}$C form the XRD results. The particle sizes, shapes and structures of these nanoclusters in the $TiO_2$ films have been identified through a SEM and XRD. The physical properties and structures of their powders have also been studied through a SEM, XRD, TGA and DSC. The thickness and index of refraction have been determined by the analysis of ellipsometric spectra.

• Journal of Powder Materials
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• v.28 no.2
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• pp.143-149
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• 2021

In this study, (GaN)_1-x(ZnO)_x solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa₂O₄) to a (GaN)_1-x(ZnO)_x solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)_1-x(ZnO)_x nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700℃. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)_1-x(ZnO)_x, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.

• Journal of Powder Materials
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• v.29 no.1
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• pp.47-55
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• 2022

Tungsten carbide is widely used in carbide tools. However, its production process generates a significant number of end-of-life products and by-products. Therefore, it is necessary to develop efficient recycling methods and investigate the remanufacturing of tungsten carbide using recycled materials. Herein, we have recovered 99.9% of the tungsten in cemented carbide hard scrap as tungsten oxide via an alkali leaching process. Subsequently, using the recovered tungsten oxide as a starting material, tungsten carbide has been produced by employing a self-propagating high-temperature synthesis (SHS) method. SHS is advantageous as it reduces the reaction time and is energy-efficient. Tungsten carbide with a carbon content of 6.18 wt % and a particle size of 116 nm has been successfully synthesized by optimizing the SHS process parameters, pulverization, and mixing. In this study, a series of processes for the high-efficiency recycling and quality improvement of tungsten-based materials have been developed.

• Journal of the Korean Ceramic Society
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• v.41 no.4
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• pp.334-339
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• 2004

Microstructures and mechanical properties of SPSed monolithic HAp, HAp-Ag, and HAp-ZrO$_2$sintered bodies were investigated by the XRD, SEM, and TEM techniques. The nano-sized HAp powders were successfully synthesized by precipitation of Ca(NO$_3$)$_2$4$H_2O$ and (NH$_4$)HPO$_4$solution. In the HAp-Ag composite, the shrinkage cavities were observed at the interfaces between HAp and large sized Ag particles due to the mismatch of their thermal expansion coefficients. However, no found the defect at the interfaces between HAp and fine-sized Ag particles. In the HAp-ZrO$_2$composite. nano-sized ZrO$_2$particles were almost dispersed at the grain boundaries of HAp phase. The fracture toughness of HAp-Ag and HAp-ZrO$_2$ composites were increased due to the plastic deformation and phase transformation mechanisms of the dispersed fine Ag and ZrO$_2$phase in the HAp matrix, respectively.

• Journal of the Mineralogical Society of Korea
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• v.22 no.1
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• pp.63-72
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• 2009

Carbon-coated lithium iron phosphate ($LiFePO_4/C$) composites are synthesized by the modified mechanical activation method (modified MA process) and studied by the Rietveld structural refinement. Rietveld indices of $LiFePO_4/C$ indicate good fitting with $R_p=8.14%,\;R_{wp}=11.1%,\;R_{exp}=9.09%,\;R_B=3.88%$, and S (GofF, Goodness of fit) = 1.2, respectively. $LiFePO_4/C$ with a space group Pnma shows a = 10.3229(3)${\AA}$, b = 6.0052(2) ${\AA}$, c = 4.6939(1) ${\AA}$, and V = 290.98(1) ${\AA}^3$ in dimension, indicating good agreements with those of previous works. Synthetic powders are nano-sized ($65{\sim}90nm$) homogeneous particles with high purity. Thus the modified MA method will be an efficient process to get a high quality cathode material for commercial lithium batteries.