• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.2
• /
• pp.59-64
• /
• 2014

Crystallographic phases of Plasma electrolytic oxidized Al alloy, A1050, were investigated. The electrolyte of PEO was $Na_2Si_2O_3$ and KOH. Unipolar pulse, $ 2000{\mu}sec$ with $400{\mu}sec+420V$ impulse, were applied for 2 min, 5 min, 15 min, and 30 min. ${\gamma}-Alumina$, as well as ${\alpha}-alumina$, was main crystal phase. ${\gamma}-Alumina$ was appeared in the beginning, then the amount of ${\alpha}-alumina$ was increased with time, but the amount of ${\gamma}-Alumina$ remained constant without any increasing. So, it is concluded that plasma gas produce ${\gamma}-Alumina$ at the first, and then ${\gamma}-Alumina$ transform ${\alpha}-alumina$ finally. During the transformation, high temperature of micro plasma gives transformation energy.

• Journal of the Korean Ceramic Society
• /
• v.29 no.12
• /
• pp.970-980
• /
• 1992

${\gamma}-alumina$ membranes were prepared by sol-gel dip coating or pressurized coating of boehmite sols on slipcasted ${\gamma}-alumina$ support tubes. The particle size of sols synthesized via the modified Yoldas-method could be controlled below 5 mn according to the mole ratio of nitric acid/aluminumtri-sec-butoxide (0.07~1.0). The reproducible crack-free composite membranes were produced by the 2nd dip coating or the pressurized coating technique using very stable sols with the particle size of 45 nm. Nitrogen gas permeability through the top-layer in the composite membrane was about $70~55{\times}10^{-7}\;mol/m^2{\cdot}s{\cdot}Pa$. The thermal stability of the top layer was proved to be good enough upto the heat-treatment temperature of $500^{\circ}C$.

• Analytical Science and Technology
• /
• v.24 no.2
• /
• pp.61-68
• /
• 2011

Ni-coated alumina was prepared by sonochemical method. To increase an efficiency of Ni coating on alumina, amorphous alumina was prepared by sol-gel method and Ni was coated to fine particles of alumina. Ni-coated alumina was prepared from various calcination temperatures ($500^{\circ}C$, $1,000^{\circ}C$), concentrations of Ni solution (0.01 M~0.2 M) and sonochemical reaction times (30 min, 2h). The prepared fine particles were characterized by X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), and Particle Size Analyzer (PSA). The coating amount of Ni increased, as Ni concentration and ultrasonication time increased. The maximum amount of Ni was coated to fine particles of alumina, when Ni-coated alumina was prepared with 0.1 M concentration of Ni solution for 2 h of sonication time at $1000^{\circ}C$ of calcination temperature. The average particle size was in the range of 835.9 to 986.7 nm.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.9
• /
• pp.5758-5762
• /
• 2014

Electrostatically-actuated Micro device have been used widely in a variety of integrated sensors and actuators. Electrostatically-actuated micro devices with a gap of several micrometers or less between the electrodes have shown failure problems by electrostatic adhesion. To improve this adhesion phenomenon, micro devices of varying lengths and widths in electrodes were fabricated, and an alumina coating was then deposited using atomic layer deposition technology. The effects of improving adhesion phenomenon were compared by measuring the pull-in voltage before and after the coating process. The pull-in voltage increased with increasing length of the upper electrode after the coating. An increase in the electrode area results in an increase in the pull-in voltage after coating. The alumina coating method applied to improve the adhesion on an electrostatically-actuated micro device was observed as an effective method.

• Journal of the Korean Ceramic Society
• /
• v.31 no.4
• /
• pp.359-366
• /
• 1994

Tow types of supports were made using $\alpha$-Al2O3 powder and optimum conditions to prepare for supports were provided. Sol solution for coating was synthesized by sol-gel method with aluminum isopropoxide. Supports were coated and heat-treatemented, where the thickness of coating layer was controlled by dipping time. Flux and permeability of alumina membrane were measured by liquid and gas filtration apparatus and these were compared with the provided model. It was confirmed that the coating was done very well without micro~crack and defect.

• Journal of the Korean institute of surface engineering
• /
• v.32 no.3
• /
• pp.447-451
• /
• 1999

Silver has the highest electrical conductivity of all metals and consequently this property is an attractive feature which makes it a leading candidate for use in electronic devices. The research conducted was focused primarily on the development of a process for obtaining a deposited silver-coating onto alumina, for applications related to electrical-conducting devices and, ancillarily, catalysts. Alumina balls and plane substrates were utilized for the investigation. The coating process employed an aqueous ammoniacal silver-nitrate electrolytes with a formaldehyde solution as the reductant. Modifying additives-an activator which would be expected to promote good deposition-characteristics onto the (dielectric) substrate and an inhibitor which would obviate homogeneous reduction (precipitation) of silver was observed when the activator-containing silver-electrolyte reductant constituents were combined. However, the silver-electrolyte/reductant system with inhibitor could be employed (at 8$0^{\circ}C$) to achieve a viable (subject to future research optimization) coating on alumina. The influence of the processing temperature on the deposition process was delineated during the course of the research. The morphology of the deposited-silver on the alumina balls was assessed by SEM imaging. A tape-peel test was employed, with the plane substrates, to semi-quantitatively characterize the adhesion to the alumina.

• 연구논문집
• /
• s.22
• /
• pp.107-113
• /
• 1992

The $\alpha$-alumina/fused alumina/$\beta$"-alumina specimens were fabricated by addition of fused alumina to $\alpha$-alumina/$\beta$"-alumina system. The sintered densities with and without fused alumina were almost same. But, the bending strength was decreased due to the presense of defects caused by the inhomogeneous dispersion of large fused alumina particles. And the fracture toughness was also decreased because the crack propagated through the fused alumina particles due to the imperfection of $\beta$"-alumina coating around them.

• Journal of the Korean Ceramic Society
• /
• v.35 no.12
• /
• pp.1257-1265
• /
• 1998

Hertzian contact tests were used to investigate the evolution of fracturedamage in the coating layer as functions of contact load and coating thickness by studying crack patterns in porcelain on glass-infiltrated alumina bilayer system conceived to simulate the crown structure of a tooth. Cone cracks initiated at the coating top surface without delamination at interface and crack propagation to substrate. Preferentially the cracks made multi-cracks at the coating top surface rather than proceeding to interface. The cracks were highly stabilized with wide ranges between the loads to initiate first cracking and to cause final failure im-plying damage-tolerant capability. Finite element modelling was used to evaluate the stress distribution. Maximum tensile stress were responsible for the cracking at the coating layer and had a profound influence on the crack pattern and fracture damage in the layered structure materials.

• Journal of the Korean Vacuum Society
• /
• v.7 no.s1
• /
• pp.50-56
• /
• 1998

Ion beam assisted deposition (IBAD) was successfully used to produce a dense and ultra-adherent Hydroxyapatite (HA) film on titanium alloy and alumina. Recently it is also proved that the HA coatings on alumina substrate treated with 20 ppm $AgNO_3$ had the structure of $(Ag, Ca)_10(PO_4)6(OH)_2$, which exhibited excellent antimicrobial effects. The present paper aims to morphlogically characterize the adhesion of macrophages on newly developed Ag-HA coated alumina and Ti6A14V substrates and to evaluate the biocompatibility of the coatings in vitro. It can be found that the cell number on alumina of the concentration of $AgNO_3$ in the treatment, the cell number on Ag-HA coatings decreased. Up to 20 ppm $AgNO_3$ by Ag-treatment, the morphological development of the cells on Ag-HA coating was similar to that of the cells on HA coating, suggesting the biotolerance of the Ag-HA coatings.

• New & Renewable Energy
• /
• v.1 no.1 s.1
• /
• pp.64-71
• /
• 2005

The stability of alumina-coated NiO cathodes was studied in $Li_{0.62}/K_{0.38}$ molten carbonate electrolyte. Alumina was effectively coated on the porous Ni plate using galvanostatic pulse plating method. The deposition mechanism of alumina was governed by the concentration of hydroixde ions near the working electrode, which was controlled by the temperature of bath solution. Alumina-coated NiO cathodes were formed to $A1_2O_3-NiO$ solid solution by the oxidation process and their Ni solubilities were were than that of NiO up to the immersion time of 100h. However, their Ni solubilities increased and were similar to that of the bare NiO cathode after 100h. It was because aluminum into the solid solution was segregated to $\alpha-LiAlO_2$ on the NiO and its Product did not Play a role of the Physical barrier against NiO dissolution.