• Journal of the Korean Applied Science and Technology
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• v.41 no.1
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• pp.46-57
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• 2024

In this study, the various process conditions for high-power DC Magnetron Sputtering (DCMS) on the surface roughness of carbon thin films were investigated. The optimal conditions for Si/C coating were 40min for deposition time, which does not deviate from normal plasma, to obtain the maximum deposition rate, and the conditions for the best surface roughness were -16volt bias voltage and 400watt DC power with 1.3x10-3torr chamber pressure. Under these optimal conditions, an excellent carbon thin film with a surface roughness of 1.62nm and a thickness of 724nm was obtained. As a result of XPS analysis, it was confirmed that the GLC structure (sp² bonding) was more dominant than the DLC structure (sp³ bonding) in the thin film structure of the carbon composite layer formed by DC sputtering. Except in infrequent cases of relatively plasma instability, the lower bias voltage and applied power induces smaller surface roughness value due to the cooling effect and particle densification. For the optimal conditions for Graphite/C composite layer coating, a roughness of 36.3 nm and a thickness of 711 nm was obtained under the same conditions of the optimal process conditions for Si/C coating. This layer showed a immensely low roughness value compared to the roughness of bare graphite of 242 nm which verifies that carbon coating using DC sputtering is highly effective in modifying the surface of graphite molds for glass forming.

• Korean Journal of Metals and Materials
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• v.50 no.8
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• pp.575-582
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• 2012

Medium carbon steel was aluminized by hot dipping into molten Al or Al-1 at% Si baths. After hot-dipping in these baths, a thin Al-rich topcoat and a thick alloy layer rich in $Al_5Fe_2$ formed on the surface. A small amount of FeAl and $Al_3Fe$ was incorporated in the alloy layer. Silicon from the Al-1 at% Si bath was uniformly distributed throughout the entire coating. The hot dipping increased the microhardness of the steel by about 8 times. Heating at $700-1000^{\circ}C$, however, decreased the microhardness through interdiffusion between the coating and the substrate. The oxidation at $700-1000^{\circ}C$ in air formed a thin protective ${\alpha}-Al_2O_3$ layer, which provided good oxidation resistance. Silicon was oxidized to amorphous silica, exhibiting a glassy oxide surface.

• Journal of Surface Science and Engineering
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• v.50 no.4
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• pp.244-250
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• 2017

Effects of plating conditions (dispersant concentration, plating time, and ultrasonication) on electroless Cu plating on SiC fabric woven by crossing of SiC continuous fibers vertically were studied. The ultrasonic dispersion treatment not only did not improve the dispersion of the SiC fibers, but also did not change the plating thickness. The ultrasonication in the pretreatment step of electroless plating did not improve the dispersion of the fibers, while the ultrasonication in the plating step enhanced the dispersion of the fibers and decreased the thickness of the Cu films. It was possible to control the thickness of the Cu coating layer as well as the dispersion of the fibers in the fabric by changing the plating conditions such as dispersant concentration, plating time, and ultrasonication, but it was very difficult to coat copper on the intersection of vertical fibers in the fabric.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.398-404
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• 2001

Effects of coating treatment of metallic Cu film on SiC for Al/SiC composite were studied. The Copper was deposited on SiC by electroless plating method. Al/sic composite was fabricated at temperature range of $670^{\circ}C$ to 90$0^{\circ}C$ under vacuum atmosphere. The wetting behavior of Al/SiC composite were analysed by SEM and XRD. The coating treatment on SiC improved wettability of Al melt on SiC considerably comparing to the non coated SiC. This improved wettability seems strongly concerned to the increase of chemical reactivity between coated layer and Al matrix. The improvement of wettability of Al melt on the Cu coated SiC was closely related to in the initial stage of reaction. The metallic film played an important role in reducing the interfacial free energy and breaking down the aluminum oxide film through the reaction with Al melt. The wetting behavior of the as-received SiC with Al melt was not uniform, indicated by the contact angles from less than $97^{\circ}$to more than $97^{\circ}$.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2162-2166
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• 2013

The tailored surface modification of electrode materials is crucial to realize the wanted electronic and electrochemical properties. In this regard, a dexterous carbon encapsulation technique can be one of the most essential preparation methods for the electrode materials for lithium rechargeable batteries. For this purpose, DL-malic acid ($C_4H_6O_5$) was here used as the carbon source enabling an amorphous carbon layer to be formed on the surface of Si nanoparticles at enough low temperature to maintain their own physical or chemical properties. Various structural characterizations proved that the bulk structure of Si doesn't undergo any discernible change except for the evolution of C-C bond attributed to the formed carbon layer on the surface of Si. The improved electrochemical performance of the carbon-encapsulated Si compared to Si can be attributed to the enhanced electrical conductivity by the surface carbon layer as well as its role as a buffering agent to absorb the volume expansion of Si during lithiation and delithiation.

• Journal of Surface Science and Engineering
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• v.29 no.1
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• pp.26-35
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• 1996

The Ni-SiC composite plating was performed in a Watt nickel solution and the wear resistance of the composite layer was studied on a pin-on-flat type wear tester. The volume losses and friction coefficients were measured. It was found that the quantity of SiC powder in the composite layers was affected by SiC concentration, pH, temperature, and agitation speed in the Watt nickel solution. The hardness and wear resistance of the coatings increased with SiC content. The quantity of SiC powder in the coating from a nickel sulfamate solution is larger than that of the Watt nickel solution, because the amount of nickel ions absorbed on the SiC powder in the nickel sulfamate solution is greater than that in the Watt's solution.

• Carbon letters
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• v.4 no.3
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• pp.133-139
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• 2003

Carbon/carbon composites are ideal candidates for a number of aerospace applications including structural materials for advanced vehicles, leading edges, structures of re-entry and hypersonic vehicles and propulsion systems. One serious defect for such application of the carbon/carbon composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating was employed to protect the composites from oxidation. It is mechanically and chemically stable under extreme thermal and oxidative environments, provides good adhesion to the substrate, and offers good thermal shock resistance. The SiC layer on the nozzle machined from the carbon/carbon composites was formed by pack-cementation method. Then, erosion characteristic of SiC coated carbon/carbon nozzle was examined by combustion test using a liquid rocket motor. The erosion rates were measured as function of combustion pressure, ratio of oxygen to fuel, combustion time, density of the composites and geometry of reinforced carbon fibre in the composites. The morphology change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.

• Composites Research
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• v.30 no.2
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• pp.84-93
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• 2017

This study investigates thermal and mechanical characterization of environmental barrier coating on the $SiC_f-SiC$ composites. The spherical environmental barrier coating (EBC) powders are prepared using a spray drying process for flowing easily during coating process. The powders consisting of mullite and 12 wt% of Ytterbium silicate are air plasma sprayed on the Si bondcoat on the LSI SiC fiber reinforced SiC composite substrate for protecting the composites from oxidation and water vapor reaction. We vary the process parameter of spray distance during air plasma spray of powders, 100, 120 and 140 mm. After that, we performed the thermal durability tests by thermal annealing test at $1100^{\circ}C$ for 100hr and thermal shock test from $1200^{\circ}C$ for 3000 cycles. As a result, the interface delamination of EBC never occur during thermal durability tests while stable cracks are prominent on the coating layer. The crack density and crack length depend on the spray distance during coating. The post indentation test indicates thermal tests influence on the indentation load-displacement mechanical behavior.

• Journal of the Korean Ceramic Society
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• v.32 no.8
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• pp.909-914
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• 1995

From alumina powder and TEOS, $\alpha$-Al2O3/SiO2 composite powder for reaction-sintered mullite was synthesized by heterogeneous coagulation and surface coating, and investigated the mullitization reaction and sintering behavor of these powders. In $\alpha$-Al2O3/SiO2 composite powder prepared by heterogeneous coagulation, each alumina particles were surrounded by silica particles of 50~60 nm in size. And the alumina particles in composite powder prepared by surface coating were coated by uniform silica layer with thickness of 50 nm. In both methods, mullitization reaction was completed at 1$650^{\circ}C$ for 3h, and specimen sintered above 145$0^{\circ}C$ was about 95% fo the theoretical relative density. Mullite grains formed from the reaction with composite powders showed spherical shape with a size of 1~2${\mu}{\textrm}{m}$.

• Journal of the Korean Society for Heat Treatment
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• v.20 no.6
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• pp.299-305
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• 2007

The effect of spray deposition of oxide particles on oxidation behaviors of as-cast Mo-14.2Si-9.6B (at%) alloys at $1200^{\circ}C$ up to for 100 hrs has been investigated. Various oxide powders are utilized to make coatings by spray deposition, including $SiO_2,\;TiO_2,\;ZrO_2,\;HfO_2$ and $La_2O_3$. It is demonstrated that the oxidation resistance of the cast Mo-Si-B alloy can be significantly improved by coating with those oxide particles. The growth of the oxide layer is reduced for the oxide particle coated Mo-Si-B alloy. Especially, for the alloy with $ZrO_2$ coating, the thickness of oxide layer becomes only one fifth of that of uncoated alloys when exposed to in air for 100 hrs. The reduction of oxide scale growth of the cast Mo-Si-B alloy due to oxide particle coatings are discussed in terms of the change of viscosity of glassy oxide phases that form during oxidation at high temperature.