• Journal of the Korean Magnetics Society
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• v.6 no.4
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• pp.204-210
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• 1996

M type hexa-ferrites were prepared by means of a solid state reaction using mill scale, $Fe_{2}O_{3}$, and the mixture of mill scale and $Fe_{2}O_{3}$. The mixture of powders were calcined at $1150^{\circ}C$ for 2 hrs. and sintered at $1250^{\circ}C$ for 2 hrs, with varing the mole ratio of $Fe_{2}O_{3}$/$BaCO_{3}$, by 5.2~6.0. And the magnetic properties and morphologies of Baferrites with impurities such as $SiO_{2},\;Al_{2}O_{3},\;MgO,\;CaO\;and\;Na_{2}O$ in the mill scale were investigated. The magnetic properties were worsened by the addition of $Na_{2}O because of non-reacted iron oxide and intermediate compound of $BaFe_{2}O_{4}$ but they were improved apparently by the addition of $Si_{2}$ and $Al_{2}O_{3}$ in the composition of $BaO.5.6Fe_{2}O_{3}$. Moreover, $M_{s}$ decreased but $_{B}H_{C}$ increased through the addition of $Al_{2}O_{3}$ in Ba-ferrite. ${(BH)}_{max}$ of sintered BM($BaCO_{3}$, mill scale mixture) and BFM($BaCO_{3}$, $Fe_{2}O_{3}$, and null scale mixture) were 0.86 and 1.04 MGOe, respectively, and the magnetic properties were changed around $440^{\circ}C$.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.114-115
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• 2013

$Ti_3AlC_2$ was corroded between 800 and $1100^{\circ}C$ in an Ar-0.2% $SO_2$ gas atmosphere according to the equation: $Ti_3AlC_2+O_2{\rightarrow}rutile-TiO_2+{\alpha}-Al_2O_3$ + (CO or $CO_2$). The scales that formed on the $Ti_3AlC_2$ were thin and rich in ${\alpha}-Al_2O_3$, whose growth rate was exceedingly slow. The $TiO_2$ was present either as the outermost surface scale or a mixture inside the ${\alpha}-Al_2O_3$-rich scale. In the $Ti_3AlC_2$, the activity and diffusivity of Ti were low, whereas those of Al were high. This was the main reason for the superior corrosion resistance of $Ti_3AlC_2$ over TiAl.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.219-219
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• 2003

HVOF(High Velocity Oxygen Fuel)법을 사용한 MCrAlY(M=Ni, Co, Fe)계 열차폐 코팅(thermal barrier coating)은 열기관 내부의 극심한 환경 부하에 대해 구조물 표면에 열적, 화학적 장벽을 형성함으로써 구조물의 내구성을 향상시킨다 이와 동시에 열차폐 효과는 구조물의 온도상승 없이 내부 가동 온도를 높일 수 있게 함으로써 열효율을 상승시키고 연료 효율을 높여 가동비용 절감을 이룰 수 있는 동시에 고 연소를 통한 오염원의 배출을 감소시킬 수 있다. 본 연구에서는 $H_2O$$_2$=5:1 분위기 하에서 HVOF법을 사용하여 Hastelloy-X 기판위에 125$\mu\textrm{m}$의 두께로 다음 5종류의 (Ni, Co, Cr)계 MCrAlY 코팅을 용사시켰다. 준비된 (Ni, Co)-Cr-Al-(Y, Ta, Re), (Ni, Co)-Cr-Al-(Y, Re), (Ni, Co)-Cr-Al-(Y, Ta), (Ni, Co)-Cr-Al-Y, (Ni,Co)-Cr-Al-Ir 코팅시편에 대한 산화성질을 조사하기 위해 대기 중 1000, 1100, 120$0^{\circ}C$에서 50, 100, 150, 200시간 등온실험(Isothermal oxidation)을 실시하였고, XRD, SEM/EDS, EPMA를 이용하여 생성된 산화막과 코팅 시편의 조직 변화를 조사하였다. 산화온도와 산화시간이 증가할수록 산화막의 박리가 많이 발생하였으며, 분석 결과 미세하게 분포된 a-Al$_2$O$_3$ 입자, NiCr$_2$O$_4$스피넬 상, 미세한 Cr$_2$O$_3$가 관찰되었고, 코팅 조성 변화에 따라 형성되는 이들 산화물의 존재비가 달라졌으며, 산화온도가 높아질수록 산화속도가 가속화되었다.

• Bulletin of the Korean Chemical Society
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• v.31 no.1
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• pp.47-51
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• 2010

A powder, containing 80 percent of blue cobalt aluminate $(CoAl_2O_4)$ crystallites, was synthesized at $210 ^{\circ}C$ using a (metal nitrate-malonic acid-ammonium hydroxide-ammonium nitrate) system. The optimal amount of concentrated ammonia water and initial decomposition temperature were determined for the blue $CoAl_2O_4$ crystallites preparation. Three $CoAl_2O_4$ precursor pastes, corresponding to the various amounts of concentrated ammonia water, were prepared by evaporating the initial solutions in an electric furnace fixed at $80 ^{\circ}C$ under a vacuum of 25 torr. The initial solution was used to dissolve the starting materials. The powder with the maximum content (80%) of blue $CoAl_2O_4$ crystallites was prepared when the prepared precursor was decomposed at $210 ^{\circ}C$. The blue $CoAl_2O_4$ crystallite content in the prepared sample decreased with increasing initial decomposition temperature. For 0.2 mole of the $Al^{3+}$ ion, the chemical compositions of the precursor corresponded to molar ratios of 0.4, 1.40, 2.56 and 2.00 for the $Co^{2+}$ ion, malonic acid, ammonia and ammonium nitrate per mole of the $Al^{3+}$ ion, respectively. The blue $CoAl_2O_4$ crystallite content in the sample decreased with the amount of ammonia deviated from the optimal value. The characteristics of the powders were examined using X-ray diffraction, optical microscopy, Fourier transformation infrared spectroscopy and the Brunauer-Emmett-Teller technique.

• Proceedings of the Korean Ceranic Society Conference
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• 2000.04a
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• pp.74.1-74.1
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• 2000

• Journal of Hydrogen and New Energy
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• v.23 no.6
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• pp.581-587
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• 2012

Thermal aging effect on NSR kinetics was studied over Pt/Co/Fe/Ba/$Al_2O_3$ catalyst. The amount of $NO_x$ uptake over Pt/Co/Fe/Ba/$Al_2O_3$ calcined at $400^{\circ}C$ increased with increasing NSR temperature from $200^{\circ}C$ to $400^{\circ}C$, where amount of $NO_x$ uptake is the highest at $400^{\circ}C$ with mol ratio of $NO_x$/Ba = 0.5. Thereafter, the amount of $NO_x$ uptake at $400^{\circ}C$ decreased with the higher calcination temperature, where Pt/Co/Fe/Ba/$Al_2O_3$ catalyst calcined at $700^{\circ}C$ showed an amount of $NO_x$ uptake with the mol ratio of $NO_x$/Ba=0.062. Result of XRD and NSR showed that Fe addition into Pt/Co/Fe/Ba/$Al_2O_3$ suppressed sintering of Pt crystallites and make $NO_x$ uptake larger, compared to no addition of Fe into Pt/Co/Fe/Ba/$Al_2O_3$ catalyst. From BET result, it was found that the change of specific surface area was relatively small by the thermal aging process. Therefore, it was found that the sintering of Pt crystallites caused the decrease of $NO_x$ uptake during NSR reaction and Fe played a role to suppress the sintering process of Pt crystallites caused by thermal aging.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.2
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• pp.244-252
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• 1997

The pseudo-spinel type solid solution, $LiAl_{2.5}/Fe_{2.5}O_8$ was prepared by reaction of $LiCO_3, Al_2O_3, Fe_2O_3$ mixture at 1620K, which can be used for cathode material in lithium batteries. Its structure was investigated by Rietveld profile-analysis of XRD in detail. The space group of solid solution is $P4_3$32(a=8.1293$\AA$) and the final residual index of structure refinement was about 5%. Cations $Al^{3+}, Fe^{3+}$ are located at both tetra- and octahedral-coordination and $Li^+$ ions are occupied in the octahedral 4b-, 12d-site of the inverse spinel.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.727-730
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• 2009

Highly active and stable nano-sized Ni catalysts supported on MgO-$Al_2O_3$ calcined from hydrotalcite-like materials have been successfully developed with a strong metal to support interaction (SMSI) to enhance the coke resistance in combined $H_2O$ and $CO_2$ reforming of $CH_4$ (CSCRM) for syngas ($H_2$/CO=2) production. The change of the surface area and NiO crystallite size with varying the pre-calcination temperature of support and Mgo content was investigated in relation to the coke resistance. As increasing the pre-calcination temperature, the surface area decreases and the metal to support interaction becomes weak. As a consequence, the coke deposition was more severe on catalysts pre-calcined at high temperature. It was concluded that highly dispersed Ni metal in the surface of Ni/MgO-$Al_2O_3$ catalyst (MgO=30 wt%) pre-calcined at $800^{\circ}C$ had a strong metal to support interaction (SMSI) resulting in an increase of coke resistance and high activity.

• Journal of Electrochemical Science and Technology
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• v.8 no.2
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• pp.101-106
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• 2017

$Li_2SiO_3$ was used as a coating material to improve the electrochemical performance of $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$. $Li_2SiO_3$ is not only a stable oxide but also an ionic conductor and can, therefore, facilitate the movement of lithium ions at the cathode/electrolyte interface. The surface of the $Li_2SiO_3$-coated $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ was covered with island-type $Li_2SiO_3$ particles, and the coating process did not affect the structural integrity of the $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ powder. The $Li_2SiO_3$ coating improved the discharge capacity and rate capability; moreover, the $Li_2SiO_3$-coated electrodes showed reduced impedance values. The surface of the lithium-ion battery cathode is typically attacked by the HF-containing electrolyte, which forms an undesired surface layer that hinders the movement of lithium ions and electrons. However, the $Li_2SiO_3$ coating layer can prevent the undesired side reactions between the cathode surface and the electrolyte, thus enhancing the rate capability and discharge capacity. The thermal stability of $Li[Ni_{0.8}Co_{0.15}Al_{0.05}]O_2$ was also improved by the $Li_2SiO_3$ coating.

• Corrosion Science and Technology
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• v.12 no.3
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• pp.119-124
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• 2013

Nano-multilayered, crystalline AlTiSiN thin films were deposited on WC-TiC-Co substrates by the cathodic arc plasma deposition. The deposited film consisted of wurtzite-type AlN, NaCl-type TiN, and tetragonal $Ti_2N$ phases. Their oxidation characteristics were studied at 800 and $900^{\circ}C$ for up to 20 h in air. The WC-TiC-Co oxidized fast with large weight gains. By contrast, the AlTiSiN film displayed superior oxidation resistance, due mainly to formation of the ${\alpha}-Al_2O_3$-rich surface oxide layer, below which an ($Al_2O_3$, $TiO_2$, $SiO_2$)-intermixed scale existed. Their oxidation progressed primarily by the outward diffusion of nitrogen, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.