• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.5
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• pp.525-530
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• 2023

Stretchable piezoelectric energy harvester (S-PEHs) based on composite materials are considered one of the potential candidates for realizing wearable self-powered devices for smart clothing and electronic skin. However, low energy conversion performance and expensive stretchable electrodes are major bottlenecks hindering the development and application of S-PEHs. Here, we fabricated the S-PEH by adopting the piezoelectric composites with enhanced stress transfer properties and kirigami-patterned textile electrodes. The optimum contents of piezoelectric BaTiO₃ nanoparticles inside the carbon nanotube/ecoflex composite were selected as 30 wt% considering the trade-off between stretchability and energy harvesting performance of the device. The final S-PEH shows an output voltage and mechanical stability of ~5 V and ~3,000 cycles under repeated 150% of tensile strain, respectively. This work presents a cost-effective and scalable way to fabricate stretchable piezoelectric devices for self-powered wearable electronic systems.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.156-168
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• 2023

This study investigates the high temperature oxidation behaviour of a Ni-20Cr-1.2Si (wt.%) alloy in steam from 1200 ℃ to 1350 ℃ by Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). The results demonstrate that exposed Ni-based alloy developed a thin oxide scale, consisted mainly of Cr₂O₃. The oxidation kinetics obtained from the experimental results was applied to evaluate the hydrogen generation considering a simplified reactor core model with different cladding alloys following an unmitigated Loss-Of-Coolant Accident (LOCA) scenario in a hypothetical Small Modular Reactor (SMR). Overall, experimental data and simulations results show that both Fe-based and Ni-based alloys may enhance cladding survivability, delaying its melting, as well as reducing hydrogen generation under accident conditions compared to Zr-based alloys. However, a substantial neutron absorption occurs when Ni-based alloys are used as cladding for current uranium-dioxide fuel systems, even when compared to Fe-based alloys.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2767-2774
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• 2024

In this study, investment casting shell waste successfully utilized to produce cordierite/mullite/zircon composites. Green pellets, consisting of investment casting shell waste, alumina, and magnesia, were prepared and sintered at temperatures between 1250 and 1350 ℃. The influence of the sintering temperature on the crystalline phase composition, densification behavior, flexural strength, microstructure, and radiation shielding properties of the cordierite/mullite/zircon composites is investigated. Phase analysis showed that characteristic cordierite peaks appear at 1250 ℃, but the complete conversation of silica from investment casting shell waste into cordierite requires a sintering temperature of at least 1300 ℃. Notably, the cordierite/mullite/zircon composite sintered at 1350 ℃ exhibited a sixfold increase in flexural strength compared to the ceramic composite directly fabricated from investment casting shell waste at the same sintering temperature. Furthermore, the effect of Y₂O₃ addition on composites' radiation shielding properties is investigated. The results show that the Y₂O₃ addition improves densification behavior, enhancing the shielding capabilities of the composites against fast neutron and gamma radiation. Our findings suggest that the developed ceramic composites show significant potential for gamma-ray and neutron shielding applications.

• Journal of Powder Materials
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• v.20 no.4
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• pp.269-274
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• 2013

The present work investigated the dispersion behavior of $Y_2O_3$ particles into AISI 316L SS manufactured using laser cladding technology. The starting particles were produced by high energy ball milling in 10 min for prealloying, which has a trapping effect and homogeneous dispersion of $Y_2O_3$ particles, followed by laser cladding using $CO_2$ laser source. The phase and crystal structures of the cladded alloys were examined by XRD, and the cross section was characterized using SEM. The detailed microstructure was also studied through FE-TEM. The results clearly indicated that as the amount of $Y_2O_3$ increased, micro-sized defects consisted of coarse $Y_2O_3$ were increased. It was also revealed that homogeneously distributed spherical precipitates were amorphous silicon oxides containing yttrium. This study represents much to a new technology for the manufacture and maintenance of ODS alloys.

• Korean Journal of Materials Research
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• v.8 no.2
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• pp.147-153
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• 1998

Tungsten nitride is very attractive as absorber for X-ray lithographic mask and as a diffusion barrier for interconnecting metallization in Si VLSI technology. Microstructure of tungsten nitride films prepared by RF magnetron sputtering has been investigated as a function of deposition parameter. The crystal structure of sputtered films on silicon nitride membrane depends strongly on the NJAr gas flow ratio(0~18%1, gas pressure(l0~43mTorr). RF power (60~150W), target-substrate distance(4~8cm). Tungsten nitride films deposited at the $N_2/Ar$ gas flow ratio(- 10%). gas pressure(~10mmTorr), RF power(~150W) and target-substrate distance(6cm) are amorphous, but at other conditions are almost rough -surfaced polycrystalline. Amorphous films are very smooth($3.1\AA$ rms) and expected to be excellent absorber for X-ray mask.

• Corrosion Science and Technology
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• v.10 no.2
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• pp.52-59
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• 2011

Corrosion of metallic materials occurs by the reaction with corrosive environment such as atmosphere, marine, soil, urban, high temperature etc. In general, reduction of thickness and cracking and degradation are resulted from corrosion. Corrosion in all industrial facilities and infrastructure causes large economic losses as well as a large number of accidents. Economic loss by corrosion has been reported to be nearly 1-6% of GNP or GDP. In order to reduce corrosion damage of industrial facilities, corrosion map as well as a systematic investigation of the loss of corrosion in each industrial sector is needed. The Corrosion Science Society of Korea in collaboration with 15 universities and institutes has started to survey on the cost of corrosion and corrosion map of Korea since 2005. This work presents the results of the survey on cost of corrosion by Uhlig, Hoar, and input-output methods, and the evaluation of atmospheric corrosion rate of carbon steel, weathering steel, galvanized steel, copper, and aluminum in Korea. The total corrosion cost was estimated in terms of the percentage of the GDP of industry sectors and the total GDP of Korea. According to the result of Input/output method, corrosion cost of Korea was calculated as 2.9% to GDP (2005). Time of wetness was shown to be categories 3 to 4 in all exposure areas. A definite seasonal difference was observed in Korea. In summer and fall, time of wetness was higher than in other seasons. Because of short exposure period (12 months), significant corrosion trends depending upon materials and exposure corrosion environments were not revealed even though increased mass loss and decreased corrosion rate by exposure time.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.519-523
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• 1995

The Fe-TM-C-N nanocrystalline films (TM : Hf, Zr and Nb) are investigated to examine the relation between microstructure and soft magnetic properties. In these films, as the atomic radius of TM element increases, $P_{N2}$ which was added to get good soft magnetic properties was decreased and the maximum value of the permeability shifted to the high Fe range in the composition diagram. The best soft magnetic properties achieved in these films are : Hc of 0.15 Oe, $\mu_{eff}$ of 7800 (1MHz) and $4{\pi}M_{s}$ of 17.5 kG in Fe-Hf-C-N film ; Hc of 0.06 Oe, $\mu_{eff}$ of 2750 (1MHz) and $4{\pi}M_{s}$ of 16.8 kG in Fe-Zr-C-N film and Hc of 0.31 Oe; $\mu_{eff}$ of 2100 (1MHz) and $4{\pi}M_{s}$ of 15.5 kG in Fe-Nb-C-N film. It was considered that the stronger the bonding force between TM and C(N), the finer TM(C,N) phase is precipitated and therefore, the finer $\alpha$-Fe grains are formed. The effective permeability of the Fe-Zr-C-N films and Fe-Nb-C-N films remains nearly constant up to 10 MHz.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.2
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• pp.79-93
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• 1991

With the advent of ULSI, many problems in previous metallization techniques and interconnection materials have become more serious. In this work, selective deposition of copper to fill the submicron contact has been tried. After forming electro-deposited copper films on p-type (100) silicon wafer using 0.75M $CuSO_4{\cdot}$5H_2O$ as an electrolyte, the effect of deposition time, current density and concentration of an additive on film properties were investigated. Film thickness, particle size and resistivity were analyzed by Alpha Step, SEM and 4 - point probe measurement respectively. The deposition rate was about $0.5-0.6\mu\textrm{m}$/min at $2A/dm^2$ and the particle size increased with increasing current density. The resistivities of electro-deposited copper films were about $3-6{\mu}{\Omega}{\cdot}$cm for the particle size above $4000{\AA}$. By the addition of 0.2 g/l gelatin, the particle size was reduced to less than $0.1{\mu}m $ and selective plugging of copper on submicron contacts could be successfully achieved.

• Journal of Sensor Science and Technology
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• v.10 no.2
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• pp.125-133
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• 2001

Conducting polymer sensors show high sensitivity when exposed to volatile organic compounds gases at room temperature. The 8 sensor array using by polypyrrole and polyaniline has been fabricated by chemical polymerization for measuring sensing characteristics of VOCs gases. Conducting polymer was polymerized by using distilled pyrrole, aniline as a monomer and ammonium persulfate (APS) as an oxidant and dodecylbenzene sulfonic acid (DBSA) as a dopant. Dedoped film was synthesized by reverse voltage and redoped film was synthesized by using 1-octanesulfonic acid sodium salt as another dopant in electrochemical cell. The sensitivity and reversibility were influenced by doping, dedoping, redoping and thickness for the polypyrrole and polyaniline. We investigated the relation between the structure of conducting polymer and sensitivity of these sensors through the analysis of scanning electron microscope (SEM), scanning probe microscope (SPM) and $\alpha$-step.

• Journal of Korea Foundry Society
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• v.11 no.6
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• pp.475-481
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• 1991

In this study the fabrication technology and mechanical properties of AC8A/$Al_2O_3$ Composites by squeeze casting process were investigated to develope for application as the piston materials that require good friction, wear resistance, and thermal stability. AC8A/$Al_2O_3$ composistes without a porosity and the break of preform were fabricated at the melt temperature of $740^{\circ}C$, the preform temperature of $500^{\circ}C$, and mold temperature of $400^{\circ}C$ under the applied pressure of $1200kg/cm^2$ as the results of the observation of microstructures. As the results of this study, the tensile strength of AC8A/$Al_2O_3$ composites was not increased linearly with $Al_2O_3$ volume fraction and so it seemed not to agree with the rule of mixture, which had been used often in metal matrix composite. Also the tensile strength after thermal fatigue test was little different from that before the test. Consequently it was thought that AC8A/$Al_2O_3$ composites fabricated under our experimental conditions had a good thermal stability and subsequently a good interface bonding. Wear rate(i.e., volume loss per unit sliding distance) of AC8A/$Al_2O_3$ composites was decreased with $Al_2O_3$ volume fraction and the sliding speed at both room temperature and $250^{\circ}C$ and so there was a good correlation between wear rate and hardness. Also the wear rate of AC/8A20% $Al_2O_3$ composities was obtained the value of $1.65cm^3/cm$ at sliding speed of 1.14m/sec as compared with about $3.0\;{\times}10^{-8}cm^3/cm$ hyereutectie Al-Si alloy(Al-16%Si-2%Cu-1%Fe-1%Ni), which applied presently for piston materials. The wear behavior of $Al_2O_3$ composites was observed to a type of abrasive wear by the SEM view of wear surface.