• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.628-634
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• 2016

The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starting powders were prepared by conventional spray dry method with different additive and process parameter conditions. As a result, large- and small-size spherical-type particles and Donut-type particles were obtained. Dense structure of 8YSZ coating was produced when small size spherical-type or Donut-type particles were used. On the other hand, 8YSZ coating with a porous structure was formed from large-size spherical-type particles. Furthermore, a segmented coating structure with vertical cracks was observed after post heat treatment on the surface of dense structured coating by argon plasma flame at an appropriate gun distance and power condition.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.453-460
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• 2019

To reduce residual pores of composites and obtain a dense matrix, SiC_f/SiC composites were fabricated by chemical vapor deposition (CVI) using SiC nanorods. SiC nanorods were uniformly grown in the thickness direction of the composite preform when the reaction pressure was maintained at 50 torr or 100 torr at 1,100℃. When SiC nanorods were grown, the densities of the composites were 2.57 ~ 2.65 g/㎤, higher than that of the composite density of 2.47 g/㎤ for non-growing of SiC nanorods under the same conditions; grown nanorods had uniform microstructure with reduced large pores between bundles. The flexural strength, fracture toughness and thermal conductivity (room temperature) of the SiC nanorod grown composites were 412 ~ 432 MPa, 13.79 ~ 14.94 MPa·m^1/2 and 11.51 ~11.89 W/m·K, which were increases of 30%, 25%, and 25% compared to the untreated composite, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.320-321
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• 2008

Ferroelectric $SrBi_2Ta_2O_9$(SBT) ceramics were deposite on Pt/Ti/SiO2/Si substrates using a sintered SBT target and then were annealed in the oxygen atmosphere at $750^{\circ}C$, the most excellent characteristics were shown, and the remnant polarization ($2P_r$) value and the coercive electric field ($E_c$) were respectively about 12.40[${\mu}C/cm^2$] and 30[kV/cm]. Moreover, the excellent fatigue characteristic t was little aged even after $10^{10}$ cycles of switchings. The leakage current density and the dielectric constant of the SBT capacitor annealed in the oxygen atmosphere were respectively approximately $2.13\times10^{-9}$ [A/$cm^2$] and 340.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.6-12
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• 2013

Aerosol deposition(AD) coating that enable fabricate films at low temperature have begun to be widely researched for the integration of ceramics as well to realize high-speed deposition rates. For application of ceramic thick film by AD to display and electronic ceramic industry, fabrication of dense structure with a no cracking is required. In this study, to fabricate dense ceramic thick film, the effect of crystal phase of starting powder was investigated. For this study, amorphous and crystalline $SiO_2$ powders were used as starting powders. Two types of $SiO_2$ powders were deposited on glass substrate by AD. In the case of amorphous $SiO_2$ powder, the deposited films had extremely incompact and opaque layer, irrespective of particle size. In contrast to amorphous powder, in the case of crystalline powder, porous structure layer and dense microstructure with no cracking layer were fabricated depending on the particle size. The optimized starting powder size for dense coating layer was $1{\sim}2{\mu}m$. The transmittance of film reached a maximum of 76% at 800 nm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.4
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• pp.235-240
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• 2017

The effect of particle sizes on the aerosol deposition (AD) of Cu films is investigated in order to understand the deposition behaviors of metal powder during the AD process. The Cu coatings fabricated by using $2{\mu}m$ Cu powders had a dense microstructure, a high deposition rate ($1.6{\pm}0.2{\mu}m/min$), and low resistance ($9.42{\pm}0.4{\mu}{\Omega}{\cdot}cm$) compared to that from using Cu powder with a particle size greater than $5{\mu}m$. Also, from estimating the internal micro-strain of Cu films, the Cu coatings fabricated by using $2{\mu}m$ Cu particles exhibited a high micro-strain value of $3.307{\times}10^{-3}$. On the other hand, the strain of Cu coatings fabricated with $5{\mu}m$ particles was decreased to $2.76{\times}10^{-3}$. These results seem to show that the impacted Cu particles are compressed and flattened by shock waves, and that their bonding is associated with the high internal micro-strain caused by plastic deformation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.2
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• pp.236-241
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• 2004

New electrolytes of cubic L $a_2$M $o_2$-x Nbx $O_{9-}$$\delta$/(x=0, 0.05, 0.1, 0.2) were fabricated by a solid-state reaction method and their sintered densities were approximately 93％ of theoretical density. X-ray diffraction analysis and microstructure observation for the sintered specimens were performed. The at complex impedance were measured at 34$0^{\circ}C$ to 93$0^{\circ}C$ in air and fitted with a Solatron ZView program. Their impedance spectra showed big difference below and over the phase transition temperature (58$0^{\circ}C$). The electrical conductivity of L $a_2$M $o_2$ $O_{9}$ was 1.36${\times}$10$^{-2}$ S$cm^{-1}$ / at 817$^{\circ}C$. Comparing to undoped L $a_2$M $o_2$ $O_{9}$ , Nb-doped specimen showed the increase of electrical conductivity due to the aliovalent doping effect..

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.5-6
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• 2006

Using the $(Ba_{0.5}Sr_{0.5}){TiO_3}$(BST) powders prepared by the Sol-Gel method, the EST thick films were fabricated on the ${Al_2}{O_3}$ substrates coated with Pt by the screen printing method. Compared with pure EST thick films, the structural and dielectric properties of the EST thick films doped with 1${\sim}$10 wt % MgO were investigated. It was observed that the Mg substitution into EST causes a shift in the cubic-tetragonal EST phase transition peak to a lower temperature. The microstructure of the EST substituted with Mg was homogeneous and dense. Mg substitution into EST had a significant effect on the grain size reduction. Dielectric constant was decreased with increasing the MgO content and temperature. In the case of EST thick films doped with 1 wt% MgO, the relative permittivity and dielectric loss were 158] and 1.4 % at 1 MHz.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.55-59
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• 2009

The epoxy resin without hardener can harden by a ring-opening reaction in the presence of the alkalies produced by the hydration of cement in epoxy-modified mortars and concretes. This paper investigates the effect of curing conditions on the strength improvement of polymer-modified mortars using bisphenol A-type epoxy resin without hardener. The polymer-modified mortars using epoxy resin are prepared with various polymer-cement ratios, and subjected to ideal, water, dry and heat cures. In the heat cure, the epoxy-modified mortars are sealed or unsealed with a PVDC (polyvinylidene chloride) film. The epoxy-modified mortars are tested for flexural and compressive strengths at desired curing methods. The microstructures of the epoxy-modified mortars are also observed by scanning electron microscope. The effects of curing conditions on the strength development of the epoxy-modified mortars are examined. From the test results, the marked effectiveness of the heat cure under the PVDC film sealing against the development of the strength of the epoxy-modified mortar without the hardener is recognized. The flexural and compressive strengths of 7-day-90℃ heat-cured, PVDC film-sealed epoxy-modified mortars without hardener reach 7 to 17MPa and 24 to 44MPa respectively, and are two to three times of Unmodified mortar. Such high strength development of the epoxy-modified mortars may be achieved by the dense microstructure formation by cement hydrates and the hardening of the epoxy resin in the mortars.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.10a
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• pp.106-108
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• 2003

We fabricated Ni and Ni-W alloys for use as a substrate in YBCO coated conductor applications and evaluated the effect of W in Ni on texture, microstructure and surface morphology, and hardness of substrate. Pure Ni, Ni-2 at.％W, and Ni-5at.％W alloy substrates were prepared by plasma arc melting, cold rolling, and the recrystallization heat treatment at various temperature (700- 130$0^{\circ}C$). It was observed that Ni-W alloy substrates had stronger cube texture and maintained it at higher annealing temperature, compared to pure Ni substrate : The full-width at half- maximums of in-plane texture was 13.40$^{\circ}$ for Ni substrate and 4.42$^{\circ}$-5.57$^{\circ}$ for Ni-W substrate annealed at 100$0^{\circ}C$. In addition, it was observed that the Ni-W substrate had smaller grain size, shallower boundary depth, and higher hardness, compared to those of pure Ni substrate.

• Advances in nano research
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• v.4 no.4
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• pp.281-294
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• 2016

The advantages of nano-scale materials (size 1-99 nm in at least in one dimension) could be realized with their potential applications in diversified avenues. Herein, we report for the first time on the successful synthesis of homogeneous epoxy coatings containing phytogenic silver nanoparticles (Ag) on PVC and glass substrates by room-temperature curing of fully mixed epoxy slurry diluted by acetone. Alstonia scholaris bark extract was used to reduce and stabilize the silver ions. The surface morphology and mechanical properties of these coatings were characterized using the techniques like, UV-Vis (UV-Visible) spectrophotometry, X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FT-IR), Epifluorescence microscopy and scanning electron microscopy (SEM). The effect of incorporating Ag nanoparticles on the biofilm (scale) resistant epoxy-coated PVC was investigated by total viable counts ($CFU/cm^2$) from epoxy coating from (Initial) $1^{st}$ day to $25^{th}$ days. The phytogenic Ag nanoparticles were found to be significantly improving the microstructure of the coating matrix and thus enhanced the anti-biofilm performance of the epoxy coating. In addition, the antimicrobial mechanism of Ag nanoparticles played an important role in improving the anti-biofilm performance of these epoxy coatings.