• Journal of the Korean Ceramic Society
• /
• v.49 no.3
• /
• pp.247-252
• /
• 2012

Crystal structure and chemical compositions of Plasma electrolytic oxidized layer of A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for plasma electrolytic oxidation was mixture of distilled water, $Na_2P_2O_7$, Cu, Cr metal salts and KOH. ${\eta}$-Alumina, as well as ${\alpha}$-alumina, was main crystal phase. Another crystals such as $(Al_{0.948}Cr_{0.052})_2O_3$ and $(Al_{0.9}Cr_{0.1})_2O_3$ were also formed in the oxide layer. It was thought that the effect of electrolyte compositions on the physical properties and crystal system of PEO layers was greater than the effect of Al alloy composition variation.

• Journal of the Korean Ceramic Society
• /
• v.49 no.3
• /
• pp.241-246
• /
• 2012

Physical properties of plasma electrolytic oxidized layers of 8 different kinds of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for plasma electrolytic oxidation was mixture of distilled water, $Na_2P_2O_7$, KOH and some metal salts. Growth rate of oxide layer was slower in $Na_2P_2O_7$ electrolyte system than in $Na_2SiO_3$ system, and Ra50 surface roughness of oxidized layer was below $1.2{\mu}m$. Surface hardness in $Na_2P_2O_7$ electrolyte system is higher than in $Na_2SiO_3$ system, and roughness was lower in $Na_2P_2O_7$ electrolyte system than in $Na_2SiO_3$ system.

• Journal of the Korean Ceramic Society
• /
• v.46 no.1
• /
• pp.86-93
• /
• 2009

The crack formation and the resistance of ITO film on PET substrate with a thickness of 20 nm were investigated as a function of strain. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Electrical resistance increased at the strain of 1.6% at the strain rates below $10^{-4}/sec$ while it increased at ${\sim}2%$ at the strain rates above $10^{-3}/sec$. The critical strain at which the cracks were formed is close to the proportional limit. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. However, the effect of the strain rate on the crack density was less pronounced in ITO/PET with 20 nm ITO thickness than ITO/PET with 125 nm ITO thickness, the strength of ITO film is thought to increase as the thickness on ITO film decreases. The absence of cracks on ITO film at a strain as close as 1.5% can be attributed to the compressive residual stress of ITO film which was developed during cooling after the coating process. The higher critical strain for the onset of the resistance increase and the crack initiation of ITO/PET with a thinner ITO film (20 nm) can be linked with the higher strength of the thinner ITO film.

• Journal of the Korean Ceramic Society
• /
• v.45 no.9
• /
• pp.549-555
• /
• 2008

The thermal barrier coating must withstand erosion when subjected to flowing gas and should also maintain good stability and mechanical properties while it must also protect the turbine component from high temperature, hot corrosion, creep, and oxidation during operation. In this study we investigated the influence of subsurface layer, $Al_2O_3$ or NiCrCoAIY bond coat layer, on the indentation damage behavior of YSZ thermal barrier coating layers deposited by electron beam physical vapor deposition (EB-PVD). The bond coat is deposited using different process such as air plasma spray (APS) or spray of high velocity oxygen fuel (HVOF) and the thickness is varied. Hertzian indentation technique is used to induce micro damages on the coated layer. The stress-strain behaviors are characterized by results of the indentation tests.

• Journal of the Korean Ceramic Society
• /
• v.34 no.3
• /
• pp.314-322
• /
• 1997

The thin film processing and the applicability as a IMD material of SiO2 aerogels providing ultralow dielec-tric properties were studied. The SiO2 aerogel films with 0.5g/㎤ density (78% porosity) and 4000~21000$\AA$ thickness could be prepared at 25$0^{\circ}C$ and 1160 psig by supercritical drying of wet-gel films, which were spin-coated at the spin rate of 1000~7000 rpm on p-Si(111) wafer under the isopropanol atmosphere. The optimum viscosity of polymeric SiO2 sols for spin coating was in the range of 10~14 cP. The main fac-tors being able to control the film thickness and microstructures were found to be sol concentration, spin rpm, and aging time of wet-gel films. The dielectric constant of the SiO2 aerogel thin film was around 2.0 low enough to be applied to the next generation semiconductor device beyond the giga level.

• Journal of the Korean Ceramic Society
• /
• v.39 no.10
• /
• pp.981-987
• /
• 2002

Monodispersed colloidal silica was prepared by Stober process. We have synthesized monodispersed colloidal silica of carious sizes (100 nm, 200 nm, 300 nm) by controlling volume ratios of TEOS(Tetraethylorthosilicate), $NH_4OH$, Ethanol and D. I. water. Shape and monodispersity of the synthesized colloidal particles were observed by Scanning Electron Microscopy(SEM) and laser light scattering particle analyzer. Self-assembled monolayer of monodispersed colloids was achieved by dipping Si substrate into a well-dispersed silica suspension. It was determined that uniformity and spatial extent of the self-assemble monolayer of monodispersed colloids are significantly influenced by the experimental parameters such as concentration, pH and surface tension of the colloidal suspension. We have observed a hexagonally well-ordered packing colloidal monolayer in a relatively large area (1.5 mm ${\times}$ 1.5 mm) as confirmed by SEM.

• Journal of the Korean Ceramic Society
• /
• v.45 no.8
• /
• pp.472-476
• /
• 2008

The surface region of commercial stainless steel 304 and 316 plates has been modified through deposition of the multi-layered coatings composed of titanium film ($0.1{\mu}m$) and gold film ($1-2{\mu}m$) by an electron beam evaporation method. XRD patterns of the stainless steel plates deposited with conductive metal films showed the peaks of the external gold film and the stainless steel substrate. Surface microstructural morphologies of the stainless steel bipolar plates modified with multi-layered coatings were observed by AFM and FE-SEM images. The stainless steel plates modified with $0.1{\mu}m$ titanium film and $1{\mu}m$ gold film showed microstructure of grains of under 100 nm diameter. The external surface of the stainless steel plates deposited with $0.1{\mu}m$ titanium film and $2{\mu}m$ gold film represented somewhat grain growth of Au grains in FE-SEM image. The electrical resistance and water contact angle of the stainless steel bipolar plates modified with multi-layered coatings were examined with the thickness of the gold film.

• Journal of the Korean Ceramic Society
• /
• v.41 no.10 s.269
• /
• pp.788-791
• /
• 2004

We have studied the fabrication of silver micro lines using the silver nano sol on ITO substrate by an ink-jet method. The average particles size of $10wt\%$ silver nano sol synthesized with polyelectrolytes was smaller than 10 nm. The pattern formation of silver nano sol on the substrate closely related with the contact angle of the silver nano sol. The dot shaped of silver nano sol on bare ITO substrate was formed due to the high contact angle of silver nano sol. When ITO substrates was treated with 100 ppm polyethylenimine for silver nano sol patterning, fine silver micro lines of $60{\sim}100{\mu}m$ width was fabricated by ink-jet method.

• Journal of the Korean Ceramic Society
• /
• v.38 no.3
• /
• pp.261-266
• /
• 2001

적색 CaTiO$_3$:Pr 형광체 막을 졸-겔법으로 제조하고 형광체의 결정상 및 발광특성에 미치는 열처리 조건 및 Pr 첨가량의 영향에 대하여 연구하였다. CaTiO$_3$:Pr sol로부터 제조된 CaTiO$_3$:Pr 분말은 30~60nm 크기의 입자들이 0.3~0.5$mu extrm{m}$ 크기로 응집된 상태를 나타내었으며, 한편 sol을 borosilicate 기판 위에 4000rpm의 속도로 3회 스핀 코팅하고 열처리하였을 경우 두께 1.2$\mu\textrm{m}$의 CaTiO$_3$:Pr 박막이 형성되었다. CaTiO$_3$:Pr gel 분말을 여러 온도에서 열처리한 경우, $600^{\circ}C$ 이하에서는 비정질이지만, 온도가 증가하면서 erovskite 결정상이 생성되기 시작하여 90$0^{\circ}C$에서는 우수한 perovskite 결정상이 발달되었다. 반면, 박막의 경우에는 80$0^{\circ}C$의 열처리 온도에서는 결정성이 우수한 perovskite 상이 관찰되었으며 이러한 온도는 기존의 분말법의 소결온도에 비하여 300~40$0^{\circ}C$나 낮은 것이다. 0.2 mol% Pr이 첨가되고 90$0^{\circ}C$로 열처리된 분말시편은 최적의 Photoluminescence (PL) 특성을 나타낸 반면, 박막의 경우에는 80$0^{\circ}C$에서 열처리된 시편이 최적의 PL 특성을 나타내었다. 제조된 CaTiO$_3$:Pr 박막에 대하여 Cathodoluminescence (CL) 분석을 행한 결과, 6100$\AA$에서 폭이 좁고 강도가 큰 스펙트럼을 나타냄으로서, 본 실험에서 제조된 박막이 FED(field emission display)등의 적색형광체로 사용될 수 있음을 확인하였다.

• Journal of the Korean Ceramic Society
• /
• v.42 no.8 s.279
• /
• pp.554-560
• /
• 2005

The engineering ceramic needs the properties of high strength, hardness, corrosion-resistance and heat-resistance in order to withstand thermal shock or applied nonuniform stresses without failure. The densely coated porous ceramics can be used for machine component, electromagnetic component, bio-system component and energy-system component by their high-performances from superior coating properties and light-weight characteristics due to the structure including pore by itself. In this study we controlled the porosity of silica and alumina, $8.2\~25.4\%$ and $23.4\~36.0\%$, respectively, by the control of sintering temperature and starting powder size. We made bilayer structures, consisting of a transparent glass coating layer bonded to a thick substrate of different porous ceramics by a thin layer of epoxy adhesive, facilitated observations of crack initiation and propagation. The elastic modulus mismatch could be controlled using different porous ceramics as the substrate layer. Then we applied 150 N force using WC sphere with a radius of 3.18 mm by Hertzian indentation. As a result, the crack initiation in the coating layer was delayed at lower porosity in the substrate layer, and the damage in the coating layer was relatively smaller at the bilayer structure coated on higher elastic substrate.