• 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.

• The Journal of Advanced Prosthodontics
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• 제9권2호
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• pp.130-137
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• 2017

PURPOSE. The purpose of this study was to evaluate the effect of nano-structured alumina surface coating on shear bond strength between Y-TZP ceramic and various dual-cured resin cements. MATERIALS AND METHODS. A total of 90 disk-shaped zirconia specimens (HASS CO., Gangneung, Korea) were divided into three groups by surface treatment method: (1) airborne particle abrasion, (2) tribochemicalsilica coating, and (3) nano-structured alumina coating. Each group was categorized into three subgroups of ten specimens and bonded with three different types of dual-cured resin cements. After thermocycling, shear bond strength was measured and failure modes were observed through FE-SEM. Two-way ANOVA and the Tukey's HSD test were performed to determine the effects of surface treatment method and type of cement on bond strength (P<.05). To confirm the correlation of surface treatment and failure mode, the Chi-square test was used. RESULTS. Groups treated with the nano-structured alumina coating showed significantly higher shear bond strength compared to other groups treated with airborne particle abrasion or tribochemical silica coating. Clearfil SA Luting showed a significantly higher shear bond strength compared to RelyX ARC and RelyX Unicem. The cohesive failure mode was observed to be dominant in the groups treated with nano-structured alumina coating, while the adhesive failure mode was prevalent in the groups treated with either airborne particle abrasion or tribochemical silica coating. CONCLUSION. Nano-structured alumina coating is an effective zirconia surface treatment method for enhancing the bond strength between Y-TZP ceramic and various dual-cured resin cements.

• 한국표면공학회지
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• 제27권1호
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• pp.29-35
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• 1994

The effects of coating of 3$\mu\textrm{m}$ thickness on the mechanical property of alumina after heat treatment at 100$0^{\circ}C$ for 30minutes under $10^{-6}$torr vacuum was quantified in terms of modulus of rupture(MOR) using Weibull plot. While the copper coating did not change MOR of alumina due to the nonwetting behavior of Cu on $Al_2O_3$, the reactive titanium metal coating caused a noticeable 29% reduction in averaged MOr strength. This was related with the combined effects of microcracks in coating formed during heat treatment and good bonding character between Ti and $Al_2O_3$. The effect of cosputtering of Ti and Cu, bilayer coatings of Cu/Ti and Ti/Cu were also investigated. It was found that Ti, cosputtered, Cu/ti and Ti/Cu coatings reduced MOR strength of alumina in the order listed. This was correlated with the amount of Ti at coating/alumina inter-face associated with a coated layer or segregation of Ti during heat treatment.

• 한국세라믹학회지
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• 제36권5호
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• pp.513-520
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• 1999

Alumina-coated SiC whiskers wee prepared by the calcination (1150$^{\circ}C$, 1h, Ar) of the alumina hydrate layer which was precipitated homogeneously on whisker surface from a solution of Al2(SO4)3 and urea as a precipitant. In addition carbon coated SiC whiskers were prepared by the pyrolysis (1000$^{\circ}C$, 4h Ar) of phenolic resin coated whisker. The effects of coating conditions on the thickness and morphology of the coated layers were examined by SEM and TEM. It was found that Al2O3-coating layers become thinner and more uniform with decreasing the Al2(SO4)3 concentration. Thin (0.075-0.1$\mu\textrm{m}$) and uniformly alumina-coating layers were obtained at the Al2(SO4)3 concentration 0.010mol/l. On the other han carbon-coating layers were uniform but very thin (5-16 nm) in thickness. For thicker carbon-coating layers ethanol as a disperse medium was found to be more efficient compared tousing acetone.

• 한국표면공학회지
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• 제22권4호
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• pp.185-196
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• 1989

The surface modification of a mild and stainless steel by alumina sprayed coating were studied. The effects of surface roughness and bond coating layer on the adhesive strengthy and durability of sprayed specimens were also investiated. The adhesive strength of ceramic coating was affected by surface roughness and bond coating layer thinkness. That showed excellent undergrit blast time and bond coating layer; 60 sec and 0.15-0.33mm, respectively. The adhesive strength and densification of sprayed coating with air pressure were superior to those of without and fracture was mainly occured at alumina-bond coating interface. Under ambient atmosphere at $800^{\circ}C$, the oxides existed within bond coating layer promote diffusion of oxygen to lower durability of sprayed specimens. In this case, fracure was occured at sudstrate-bond coating interface.

• 한국세라믹학회지
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• 제36권10호
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• pp.1087-1093
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• 1999

Bioglass which is one of the surface active bionmaterials has a good biocompatibility but a poor mechanical strength, In the present work therefore two types of fluoride-containing bioglasses were coated on an alumina to improve mechanical strength. Crystallization of the coating layer and the hydroxyapatite formation on the bioactive glass coatings in tris-buffer solution were studied. When bioactive glass coated alumina was heat-treated Na2CaSi3O8 crystal was formed on the layer at lower temperature while wollastonite(CaSIO3) was obtained at higher temperature. Hydroxyapatite forming rate on the coating layer with Na2CaSi3O8 crystal was delayed with SiO2 contents in glass composition. However the hydroxyapatite was developed in 20minutes regardless SiO2 contents when the coating layer crystallized into wollastonite. More amount of P3+ ions were leached out of the coating layer with wollastonite than that with Na2CaSi3O8 crystal while Na+ and Ca2+ ions were leached out more easily from the Na2CaSi3O8 crystal containing coating layer.

• 한국해양공학회지
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• 제10권2호
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• pp.88-97
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• 1996

The pupose of this study is to improve the mechanical properies and to evaluate the residual stresses of flame-sprayed Alumina ceramic coating layer. The first work in this study is to investigate the effects of strengthening heat treatments on the mechanical properties of coating layer. Strengthening heat treatments for sprayed specimens were carried out in vaccum furnace. The mechanical properties such as microhardness, thermal shock resistance, adhesive strength and erosion resistance were tested for the sprayed specimens after strengthening heat treatments. And it was clear that the mechanical properties of coating layer were much improved by strengthening heat treatments. The second work in this study is to evalute the residual stresses in coating lsyer by numerical analysis. FDM and FEM were used to analyze temperature distribution and residul stresses in coating layer. It was proved that are tensile stresses in coating layer and that residual stresses can be controlled by the appropriate selection of the spraying parameters such as preheat temperature, coating thickness and bond coat thickness.

• 한국광물학회지
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• 제26권2호
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• pp.101-110
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• 2013

나노크기 매킨나와이트(nanocrystalline mackinawite, FeS)는 높은 비표면적을 지닌 반응성 높은 광물로, 오염된 지하수나 토양의 복원을 위해 널리 사용된다. 또한 매킨나와이트는 혐기성 부식반응에 대해 열역학적으로 안정하고, 황산염 환원미생물의 대사에 의해 재생된다는 장점이 있다. 하지만 매킨나와이트 나노입자는 지하수 흐름에 의해 멀리 확산되거나 입자집적이 일어나 대수층 공극을 막는다. 따라서 현장복원을 위한 투과반응벽(permeable reactive barrier)의 설치를 위해서 나노크기 매킨나와이트에 대한 변형이 필요하다. 이를 위해 본 연구에서는 코팅법을 활용해 매킨나와이트 나노입자를 알루미나(alumina, $Al_2O_3$) 및 활성알루미나(activated alumina) 표면에 증착시켰다. 매킨나와이트의 코팅량은 pH에 따라 현저히 달랐으며, 두 종의 알루미나 모두 약 pH 6.9에서 최대 코팅이 관찰되었다. 이 pH에서 알루미나와 매킨나와이트는 반대의 표면전하(surface charge)를 띠어 두 광물 간 정전기적 인력이 발생하고, 이로 인해 효율적인 코팅이 일어났다. 이 pH에서 알루미나 및 활성 알루미나에 의한 코팅량은 각각 0.038 $mmol{\cdot}FeS/g$과 0.114 $mmol{\cdot}FeS/g$이었다. 혐기성 조건에서 코팅되지 않은 알루미나 및 활성 알루미나, 그리고 최적 pH에서 코팅된 알루미나 및 활성 알루미나를 사용해 아비산염(arsenite) 흡착실험을 수행했다. 코팅되지 않은 활성 알루미나는 코팅되지 않은 알루미나와 비교해 단위질량당 높은 아비산염의 제거를 보여주었으나, 매킨나와이트의 코팅에 의한 흡착량 증가를 보이지 않았다. 활성 알루미나는 높은 비표면적을 지니고 있어 반응성 높은 수산화작용기(hydroxyl functional group)가 다수 존재했고, 이로 인해 코팅된 매킨나와이트에 의한 아비산염의 제거가 중요하지 않았다. 반면 알루미나는 매킨나와이트 코팅에 의해 향상된 아비산염의 제거율을 보였는데, 이것은 알루미나에 존재한 수산화작용기가 아비산염과의 표면배위결합(surface complexation)에 소모되고, 코팅된 매킨나와이트에 의한 부가적인 흡착이 일어났기 때문이다. 코팅된 알루미나는 이전에 연구된 코팅된 실리카와 비교해보면 단위 비표면적당 매킨나와이트의 코팅량이 약 8배 높았으며, 더 높은 아비산염에 대한 흡착력을 보였다. 따라서 본 연구의 결과는 코팅된 알루미나는 투과반응벽의 설치에 적합한 물질이고, 특히 아비산염으로 오염된 지하수의 정화에 유용하게 적용될 수 있음을 지시하고 있다.

• Korean Chemical Engineering Research
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• 제54권6호
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• pp.767-774
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• 2016

졸-겔법에 의해 출발물질로 aluminum isopropoxide를 사용하여, 메탄올용매 내에서 가수분해 시킨 후 해교제인 초산, 질산 또는 염산을 각각 첨가하여 해교 시켜 3종류의 alumina sol을 제조하였다. 또한 이 sol에 실란커플링제인(3-glycidyloxypropyl) trimethoxysilane을 첨가하여 코팅 용액을 제조한 후, 이용액을 polycarbonate 기재 위에 담금 코팅 후 열 경화시켜 코팅 도막을 형성하였다. 이 과정 중 해교제의 종류 변화가 코팅 도막의 물성에 미치는 영향을 연구하였다. 그 결과 해교제로서 강산인 염산이나 질산을 사용한 코팅 도막은 H나 2H의 연필경도와 5B의 부착력을 나타내어 우수한 물성을 나타내었다. 반면에 해교제로서 약산인 초산을 사용한 경우에는 HB의 연필경도와 3B의 부착력을 보여 좋지 못한 물성을 나타내었다.

• 한국세라믹학회지
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• 제31권11호
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• pp.1271-1282
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• 1994

The surface of commercial alumina fibers used for reinforcing the MCFC matrix has been coated with ${\gamma}$-LiAlO2 being the same material as the matrix, by the sol-gel method in order to enhance the corrosion resistivity of alumina fibers. Stable LiAlO2 complex polymeric sols for coating was synthesized by mixing aluminum alkoxide polymeric sols with LiNO3 solution. It was found that the LiAlO2 polymeric sol prepared by adding the mixed chelate of acethylacetone and triethanolamine (the mole ratio of AA/TEA = 0.125/0.75) to the 1 mole of the aluminum alkoxide had the excellent stability and coating behavior. The crystalline structure of the dried gel from the ${\gamma}$-LiAlO2 sol was completely transformed into the ${\gamma}$-LiAlO2 at $600^{\circ}C$. The optimum viscosity of the sol for coating the alumina long fibers was 30~40 cP, while it was 12~20 cP in case of the short fiber coating. The ${\gamma}$-LiAlO2 coated alumina fibers without defects fully densified when heat-treated at 120$0^{\circ}C$.