• 한국결정성장학회지
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• 제15권1호
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• pp.16-20
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• 2005

고체 산화물 연료전지 전해질 재료인 8YSZ(yttria stabilized zirconia)세라믹 소재의 전기 전도도와 기계적 특성을 동시에 향상시키기 위하여 첨가제로서 Al₂O₃를 사용하고, 방전 플라즈마 소결법을 적용하였다. 제조된 소결체는 1200℃의 소결 온도에서 96% 이상의 밀도를 보이며, 1 ㎛ 이하의 균일한 크기의 결정립들로 구성된 미세구조를 보여주고 있다. 첨가된 Al₂O₃는 순수한 8YSZ의 결정립성장을 억제하여 파괴인성 및 굽힘강도 등 기계적 물성을 향상시키고, 또한 결정립 내부 전도도는 일정하게 유지한 채, 결정립계 전도도를 향상시켜 전체 이온 전도도를 증가시킴을 확인하였다. 이는 방전플라즈마 소결법이 비교적 낮은 온도에서 소결이 가능하여 기존의 소결 방법에서 문제시 되었던 8YSZ내로 Al₂O₃가 용해되는 것이 억제 되었을 뿐 아니라, 결정립계에 존재하는 SiO₂가 Al₂O₃와 반응하여 Al/sub 2-x/Si/sub l-y/O/sub 5/상으로 결정화되면서 결정립계 전도도를 향상시킨 결과로 사료된다.

• 한국결정성장학회지
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• 제32권6호
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• pp.231-238
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• 2022

Al₂O₃ 다공체는 필터 및 촉매 담체 등으로 활용되며 그 기능성과 내구성을 확보하기 위해서는 다공성 구조의 기계적 강도가 중요하다. 소결 중 치밀화 및 입자성장을 유리하게 제어하는 것이 기계적 강도 향상에 필수적이며, 본 연구에서는 그 일환으로 La을 첨가하여 동결주조로 성형된 Al₂O₃ 다공체의 입자성장 양상을 분석하였다. 즉, 250 ppm의 La을 첨가한 계에서 1400℃에서 1600℃에 이르는 온도 범위 내에서 소결 시간 및 온도에 대한 평균입도 변화를 관찰하여 G_tⁿ-G₀ⁿ = kt 관계로부터 exponent(n 값)은 3으로, k = k₀exp(-E_a/RT)로부터 입자성장에 대한 활성화 에너지(E_a)는 489.09 kJ/mol로 각각 계산되었다. 이러한 결과는 입자성장에 대한 La의 첨가 효과를 나타내며, La이 Al₂O₃의 입계 이동속도를 늦춰 입자성장의 억제에 효과가 있음을 방증하므로 기계적 강도에 이롭다. 한편, 향후 원료 분말에 함께 포함되어 있는 미량의 불순물 작용을 관찰하면 La의 기여를 명확히 구분할 수 있으며, 이러한 접근은 향후 다공성 Al₂O₃에서 입자성장을 제어하는데 사용될 수 있는 첨가제를 선택하는 데 유용하게 사용될 수 있다.

• 한국세라믹학회지
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• 제15권3호
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• pp.157-167
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• 1978

The batch compositions and physical properties of slag-ceramics were studied with respect to their formability from the molten state and conditions of nucleation and crystal growth treatment. The selected batch compositions for nucleation and growth studies were slag, 56%; silica sand, 28%; $Na_2O＋MgO$, 8% and $TiO_2＋$chromite, 8%. The optimum nucleation condition was the temperature of 75$0^{\circ}C$ with 6 hrs. holding time and the optimum growth condition was the temperature 975$^{\circ}C$ with zero holding time. The slag-ceramics prepared under the above conditions showed the best developed microtexture. The grown crystals were identified as diopside with the average grain size of 5.7$\mu\textrm{m}$, and the amount of crystal grown were about 53% by weight. The prepared specimens of slag-ceramics showed the microhardness, 793kg/$\textrm{mm}^2$; MOR, 1,050 kg/$\textrm{cm}^2$ and thermal expansion coefficient, $85{\div}10^{-7}$cm/cm/$^{\circ}C$($25^{\circ}C$~$700^{\circ}C$).

• Corrosion Science and Technology
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• 제23권1호
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• pp.64-71
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• 2024

The objective of this study was to investigate corrosion and cavitation-erosion characteristics of the electroless nickel plating layer with heat treatment. The crystallization temperature of the electroless nickel plating layer was about 410 ℃. The phase transformation energy was confirmed to be 12.66 J/g. With increasing heat treatment temperature, the amorphous electroless nickel plating layer gradually changed to crystalline Ni and Ni₃P. At the same time, the crystal grain size was also increased. Additionally, when heat treatment was performed at a temperature above 400 ℃, NiO phase was observed due to oxidation phenomenon. As a result of the electrochemical polarization experiment, the corrosion resistance of the heat-treated electroless nickel plating layers was superior to that of the as-deposited plating layer. This was because crystal grains became larger and grain boundaries decreased during heat treatment. The cavitation-erosion resistance of heat-treated plating layers tended to be superior to that of as-deposited plating layers due to increased microhardness.

• 한국표면공학회지
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• 제46권2호
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• pp.55-60
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• 2013

Superhard TiN coatings were fabricated by DC and ICP (inductively coupled plasma) assisted magnetron sputtering techniques. The effect of ICP power, ranging from 0 to 300 W, on coating microstructure, preferred orientation mechanical properties were systematically investigated with HR-XRD, SEM, AFM and nanoindentation. The results show that ICP power has a significant influence on coating microstructure and mechanical properties of TiN coatings. With the increasing of ICP power, coating microstructure evolves from the columnar structure of DC process to a highly dense one. Grain sizes of TiN coatings were decreased from 12.6 nm to 8.7 nm with increase of ICP power. The maximum nanohardness of 67.6 GPa was obtained for the coatings deposited at ICP power of 300 W. Preferred orientation in TiN coatings also vary with ICP power, exerting an effective influence on film nanohardness.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.682-683
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• 2006

Thermoelectric conversion efficiency of thermoelectric elements can be increased by using a structure combining n-type and p-type semiconductors. From the above point of view, attention was directed at ZnO as a candidate n-type semiconductor material and investigations were made. As the result, a dimensionless figure of merit ZT close to 0.28 (1073K) was obtained for specimens produced by the PCS (Pulse Current Sintering) method with addition of specified quantities of $TiO_2$, CoO, and $Al_2O_3$ to ZnO. It was found that the interstitial $TiO_2$ in the ZnO restrains the grain growth and CoO acts onto the bond between grains. The influence of the inclusion of $TiO_2$ and CoO onto the sintering behavior also was investigated.

• 한국표면공학회지
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• 제33권4호
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• pp.273-280
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• 2000

Silver was deposited on glass by electroless plating and electroplating. Surface properties were investigated using the AFM. Crystal structure of deposit layers was confirmed by TEM and XRD. Electroplating is performed by DC plating and pulse plating, respectively. This study resulted in followings, first, deposit of electroless plating showed fine grain and was similar to the amorphous structure. Second, electrodeposit on the electroless layer was revealed following results ; (1) more uniform layer and finer grains were obtained with increasing frequency (2) more isotropic structure was obtained with increasing frequency (3) finer grains at 25% duty cycle was obtained (4) grain size and roughness of the silver deposit was decreased with increasing frequency.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.19-22
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• 1997

The surface modificaion of alumina by $Al_2$O$_3$/SiC nanocomposite coating was studied in terms of processing and microstructure. A powder slurry of 5 vol% SiC composition was dipcoated onto presintered alumina bodies and pressurelessly sintered at 1$700^{\circ}C$ for 2 h in $N_2$. The used of organic binder and plasticizer in the slurry preparation, and the control of the density of presintered alumina body were found to be necessary to avoid cracking and warping during processing. The nanocomposite coating well bonded to the alumina body with thickness about 110 ${\mu}{\textrm}{m}$. The average grain size of coating (2 ${\mu}{\textrm}{m}$) was much finer than that of alumina body (13 ${\mu}{\textrm}{m}$). Fracture surface observations revealed mostly transgranular fracture for the coating, whereas intergranular fracture for the alumina body. Some pores (about 6%) were observed in the coating layer, although the alumina body showed fully dense microstructure.

• 한국세라믹학회지
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• 제54권1호
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• pp.33-37
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• 2017

Single phase niobium nitride (NbN) coatings were deposited using asymmetric bipolar pulsed dc sputtering by varying pulse frequency and duty cycle of pulsed plasmas. Crystal structure, microstructure, morphology and mechanical properties were examined using XRD, FE-SEM, AFM and nanoindentation. Upon increasing pulse frequencies and decreasing duty cycles, the coating morphology was changed from a pyramidal-shaped columnar structure to a round-shaped dense structure with finer grains. Asymmetric bipolar pulsed dc sputtered NbN coatings deposited at pulse frequency of 25 kHz is characterized by higher hardness up to 17.4 GPa, elastic modulus up to 193.9 GPa, residual compressive stress and a smaller grain size down to 27.5 nm compared with dc sputtered NbN coatings at pulse frequency of 0 kHz. The results suggest that the asymmetric bipolar pulsed dc sputtering technique is very beneficial to reactive deposition of transition-metal nitrides such as NbN coatings.

• 한국세라믹학회지
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• 제19권3호
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• pp.205-214
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• 1982

The method of lowering the sintering temperature and enlarging the range of sintering temperature in the manufacture of forsterite porcelain as a high frequency insulator was investigated. The four kinds of forsterite chamotte were calcinated at $1400^{\circ}C$. The forsterite bodies produced by adding $BaCO_3$ as a flux and 5% Kaolin as a bonding agent were heated in the range of sintering temperature. Sintering temperature tended to increase almost straightly as MgO exceded without $BaCO_3$. The range of sintering tem was at least $140^{\circ}C$. Specimens of MF-2-0, MF-2-A had superior mechanical strength and dielectric properties. The growing of the forsterite crystal was restricted and thus their grain size became fine and also the amount of crystal formation tended to decrease rapidly as $BaCO_3$ increased excessively.