• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.97.2-97.2
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• 2018

This study formed a hard TiAlSiWN coating layer using Ti, Al, Si and W raw powders that were mechanically alloyed and refined. The TiAlSi and TiAlSiW coating targets were fabricated using a single PCAS process in a short time with the optimal sintering conditions. The coating targets were deposited on the WC substrate by forming coating layers using TiAlSiN and TiAlSiWN nitride nano-composite structures with an AIP process. The properties of the nitride nano-composite coating layers were compared according to the addition of W. The microstructure of the nitride nano-composite coating layer was analyzed, focusing on the distribution of the crystalline phases, amorphous phases ($Si_3N_4$), and growth orientation of the columnar crystal depending on the addition of W. The mechanical properties of the coating layers were exhibited a hardness of approximately $3,000kg/mm^2$ and adhesion of about 117.77N in the TiAlSiN. In particular, the TiAlSiWN showed excellent properties with a hardness of more than $4,300kg/mm^2$ and an adhesion of about 181.47N.

• The Korean Journal of Ceramics
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• 제5권2호
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• pp.142-147
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• 1999

The interaction between commercial $Si_3N_4$ powder and two types of additives (nitrate and oxide additives) during the sintering of $Si_3N_4$ was investigated. The nitrates solution or oxide particles were added as a sintering additives. The surface of mixed powder was observed with FT-IR, TG, and HREM. DTA was used to characterize the reactivity of the powders. The formation of crystalline phases and phase transformation were analyzed by XRD. The adsorption of the additives on the surface of silicon nitride was confirmed in the nitrate salts. It was shown that the adsorption occurred by interaction between the amorphous $SiO_2$ layer on the $Si_3N_4$ surface and metal cations $(Al^{3++\; and \;Y^{3+})$ and anions $(NO_3\;^-\; or\; OH^-)$, resulting in a higher degree of homogeneous distribution of additives.

• 전기화학회지
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• 제3권3호
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• pp.146-151
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• 2000

초 미립자 산화 코발트 건조겔 파우더가 졸겔 공정과 관련 있는 독특한 용액화학을 사용하여 제조되었다. 생성된 건조겔의 결정성, 입자구조에 대한 열처리의 효과 및 그에 부합하는 전기화학적 성질이 $160^{\circ}C$까지 $Co(OH)_2$로 무정형하게 존재하였다. 온도가 $200^{\circ}C$까지 증가함에 따라서, 무정형 $Co(OH)_2$가 결정성 $Co_3O_4$를 형성하기 위한 CoO를 이루기 위해 분해하기 때문에, 표면적과 세공부피가 급격히 감소한다. 결정성 및 입자구조에서의 변화는 상당히 중요한 것이고, 여기에 건조겔의 전기화학적 성질에 대한 영향을 연관시켜 연구하였다. 192F/g의 최대용량이 $150^{\circ}C$에서 소성된 $CoO_x$ 건조겔로 제조된 전극에서 얻어졌다 이 정전용량은 단지 표면 산화$\cdot$환원반응에만 기인한 것이다.

• 한국자기학회지
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• 제7권6호
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• pp.293-298
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• 1997

기계적합금법으로 Fe$_{5}$Si$_{x}$B$_{5-x}$ 분말을 제조하고, Si 치환에 따른 합성상의 변화 및 합성분말의 자기적 성질을 XRD, TEM, Mossbauer spectroscopy, VSM 등으로 조사하였다. 각 출발 원소들은 milling 초기에 .alpha. -Fe 구조로 고용되어 비정질(amorphous) 상태로 되며, 기계적합금화가 진행됨에 따라 최종 안정상이 석출되었다. Fe$_{5}$B$_{5}$ 조성의 경우(x=0) 250시간 볼밀 처리한 후 800 .deg. C에서 2시간 열처리하면 FeB와 Fe$_{2}$B 상이 혼재된 구조가 얻어 진다. B의 일부를 Si으로 치환하면 Fe$_{2}$B 상의 생성이 억제되는 반면에 여분의 Si이 Fe$_{5}$SiB$_{2}$, Fe$_{2}$Si$_{0.4}$B$_{0.6}$ 상 및 상자성 상을 형성한다. FeB 상은 800 .deg. C에서 열처리한 후에도 결정성이 높지 않아서 넓은 범위의 초미세자장 값을 갖는 반면에, 다른 상들은 결정화가 이루어져 일정한 초미세자장 값을 보였다. 포화자화 값은 Fe$_{2}$B 상이 가장 많이 함유된 Fe$_{5}$B$_{5}$ 조성에서 가장 크게 나타났다.다.

• 대한치과기공학회지
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• 제29권1호
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• pp.121-131
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• 2007

A preparation process's conditions of aqueous sol which contains anatase-type nano titania particles with photocatalyic properties was established by using Yoldas process, so called, DCS(Destabilization of Colloidal Solution) process in this study. And crystal size change and phase transformation of titania particles in aqueous titania sol depending on reaction conditions was investigated by a light scattering method and XRD analysis of frozen dried powders, respectively. This sol with photo catalytic nano titania particles was used to the following hydrophilic hybrid coating film's fabrication and its properties was evaluated. Subsequently, for coating film using the above mentioned aqueous titania sol, non-aqueous titania sol was prepared without any chemical additives and its time stability according to aging time was investigate. By using the above mentioned aqueous titania sol and non-aqueous sol, a complex oxide coating sol for metal and ceramic substrate and a organic-inorganic hybrid coating sol for polymer substrate was prepared and it's hydrophilicity depending on UV irradiation conditions was evaluated. As a conclusions, the following results were obtained. (1)Aqueous titania sol The average particle size of titania in formed aqueous titania sol was distributed between 20$\sim$90nm range depending on reaction conditions. And the crystal phase of titania powders obtained by frozen drying method was changed from amorphous state to anatase and subsequently transformed to rutile crystal phase and it is attributed to concentration gradient in aqueous sol. (2)Non-aqueous titania sol Non-aqueous titania sol was prepared using methanol as a solvent and a little distilled water for hydrolysis and nitric acid as a catalyst were used. The obtained non-aqueous titania sol was stable at room temperature for 20 days. Additionally, non-aqueous titania sol with addition of chealating reagent such as acethylaceton and ethylene glycol prolonged the stability of sol by six months. (3)Complex sol and hybrid sol with super hydrophilicity The above mentioned aqueous titania sol as a main photocataylic component and non-aqueous titania sol as a binder for coating process was used to prepare a complex sol used for metal, ceramic and wood material substrate and also to prepare the organic-inorganic hybrid sol for polymer substrate such as polycarbonate and polyethylene, in which process APMS(3-Aminopropyltrimethoxysilane), GPTS(3-Glycidoxypropyl-trimethoxysilane) as a hydrophilic silane compound and HEMA(2-Hydroxyethyl methacrylate) as a forming network in hybrid coating film were used. The hybrid coating film such as prepared through this process showed a superhydrophilicity below 1$10^{\circ}$ depending on processing conditions and a pencil's hardness over 6 H.

• 한국광물학회지
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• 제18권4호통권46호
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• pp.289-299
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• 2005

알바이트 분말시료, 박편시료, TEM 시편용 시료를 이용하여 광학현미경 상에서 등온가열 실험을 수행하였다. 시료의 방향성은 광학현미경 및 XRD를 통하여 점검하였으며 TEM의 전자회절도형을 통해 확인하였다. 분말시료의 경우 $1030^{\circ}C$-12 hr에서, TEM 시편용 시료는 $1060^{\circ}C$-6 hr에서 부분 용융이 일어나며 이 이상의 온도에서는 용융으로 인한 시편두께 증가 및 비정질상으로의 변화로 인하여 알바이트 미세구조의 TEM 영상 획득이 어려웠다. 광학현미경과 TEM의 연계를 통한 알바이트 등온가열 실험 결과 알바이트 tweed 미세구조의 TEM 영상을 얻을 수 있는 최적 조건은 대기압 하에서는 $1050^{\circ}C$-12 hr로 파악되었다. 전자현미경 내 직접가열(in situ TEM heating) 실험의 경우 상기한 실험조건에 비해 고진공 상태임을 고려하면 $1050^{\circ}C$보다 다소 높은 온도에서 알바이트 tweed 미세구조를 직접 관찰할 수 있을 것으로 사료된다

• 한국재료학회지
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• 제23권8호
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• pp.441-446
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• 2013

There is increasing interest in zirconia as a dental material due to its aesthetics, as well as the exceptionally high fracture toughness and high strength that are on offer when it is alloyed with certain oxides like yttria. In recent years, many solution based chemical synthesis methods have been reported for synthesis of zirconia, of which the sol-gel method is considered to be best. Here, we synthesize zirconia by a sol gel assisted precipitation method using either PEG or PVA as a stabilizing agent. Zirconia sol is first synthesized using the hydrothermal method. We used NaOH as the precipitating agent in this method because it is easy to remove from the final solution. Zirconium and yttrium salts are used as precursors and PEG or PVA are used as stabilizers to separate the metal ions. The resulting amorphous zirconia powder is calcined at $900^{\circ}C$ for 2 h to get crystallized zirconia. XRD analysis confirmed the partially stabilized zirconia synthesis in all the synthesized powders. SEM was taken to check the morphology of the powder synthesized using either PEG or PVA as a stabilizing agent and finally the transparency was calculated. The results confirmed that the powder synthesized with 10 % PVA as the stabilizing agent had highest percentage of transparency among all the synthesized powder.

• 마이크로전자및패키징학회지
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• 제8권2호
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• pp.25-29
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• 2001

본 연구에서는 mesocarbon microbeads(MCMB)카본에 에폭시 수지(resin)를 코팅시킴으로 서 카본전극 표면개질에 따른 전지 성능의 개선효과에 관하여 고찰하였다. 에폭시 수지에 의한 카본의 표면코팅은 MCMB 분말을 에폭시 수지가 용해된 THF(tetrahydrofuran)용액에 넣어 혼합함으로서 표면에 에폭시 수지가 코팅 되도록 하였다. 이렇게 에폭시 수지가 코팅된 MCMB를 $1000^{\circ}C$이상의 온도로 열처리하여 고분해능 투과전자현미경으로 관찰한 결과, 코팅층은 비정질 카본 구조를 지님을 알 수 있었다. 또한, 에폭시 수지에 의하여 코팅된 MCMB는 코팅되지 않은 MCMB보다 더 높은 BET비 표면적을 나타내었으며, 더 우수한 충방전 용량과 싸이클 특성을 나타내었다. 카본표면에 코팅된 에폭시 수지가 얇은 비정질 막으로 표면에 존재함으로서 전해질과 카본결정과의 반응을 억제시키는 방지막 역할을 하기 때문에 전지특성이 개선된 것으로 해석된다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.409-412
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• 2001

The high purity manganese oxides were made from the dust, generated in AOD process that produces a medium-low carbon ferromanganese and collected in the bag filter. Manganese oxide content in the dust was about 90%, and its phase was confirmed as Mn₃O₄. In the extraction of manganese, because of remaining amorphous MnO₂, the dust was reduced to MnO by roasting with charcoal. The pulp density of the reduced dust can control pH of the solution more than 4 and then Fe ion is precipitated to a ferric hydroxide. Because a ferric hydroxide co precipitates with Si ion etc, Fe, Si ion was removed f개m the solution. Heating made water to be volatized and nitrates was left in reactor Then nitrates were a liquid state and stirring was possible. Among the nitrates in reactor, only the manganese nitrate which have the lowest pyrolysis temperature pyrolyzed into β-MnO₂powder and NO₂(g) at the temperature less than 200℃. When the pyrolysis of manganese nitrate has been completed about 90%, injection of water stopped the pyrolysis. Nitrates of impurity dissolved and the spherical high purity β-MnO₂powders were obtained by filtering and washing. Mn₂O₃or Mn₃O₄ powder could be manufactured from β-MnO₂powder by controlling the heating temperature. Lastly, a manufactured manganese oxide particle has 99.97% purity.

• Carbon letters
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• 제8권4호
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• pp.326-334
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• 2007

In this study, graphite composites were fabricated by warm press molding method to realize commercialization of PEM fuel cells. Graphite composites have been considered as alternative economic materials for bipolar plate of PEM fuel cells. Graphite powder that enables to provide electrical conductivity was selected as the main substance. The graphite powder was mixed with phenolic resin and the mixture was pressed using a warm press method. First of all, the graphite powder was pulverized with a ball mill for the dense packing of composite. As the ball milling time increases, the average size of particles decreases and the size distribution becomes narrow. This allows for improvement of the uniformity of graphite composite. However, the surface electrical resistivity of graphite composite increases as the ball milling time increases. It is due to that graphite particles with amorphous phase are generated on the surface due to the friction and collision of particles during pulverizing. We found that the contact electrical resistivity of graphite particles increases as the particle size decreases. The contact electrical resistivity of graphite powders was reduced due to high molding pressure by warm press molding. This leads to improvement of the mechanical properties of graphite composite. Hydrogen gas impermeability was measured with the graphite composite, showing a possibility of the application for bipolar plate in fuel cell. And, I-V curves of the graphite composite bipolar plate exhibit a similar performance to the graphite bipolar plate.