• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.2
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• pp.90-98
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• 2021

Piezoelectric ceramic fiber composite (PCFC) was fabricated using a planar electrode printed piezoelectric ceramic fiber driven in transverse mode for small-scale wind energy harvester applications. The PCFC consisted of an epoxy matrix material and piezoelectric ceramic fibers sandwiched by interdigitated electrode (IDE) patterned polyimide films. The PCFC showed an excellent mechanical performance under a continuous stress. For the fabrication of PCB cantilever harvester, five -PCFCs were vertically attached onto a flexible printed circuit board (PCB) substrate, and then PCFCs were serially connected through a printed Cu circuit. The energy harvesting performance was evaluated applying an inverted structure, which imples its free leading edge located at an open end but the trailing edge at a clamped end, to enhance strain energy in a wind tunnel. The output voltage of the PCB cantilever harvester was increased as the wind speed increased. The maximum output power was 17.2 ㎼ at a resistance load of 200 ㏀ and wind speed of 9 m/s. It is considered that the PCB cantilever energy harvester reveals a potential use for wind energy harvester applications.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.643-651
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• 2006

The Pb-Ag-Bi-S system minerals such as galena-matildite solid solutions, cosalite and heyrovskyite occur in the Nakdong As-Bi deposits. Galena-matildite solid solutions commonly coexisting with native bismuth fill in microfractures of pyrite grains and form irregular shapes. Cosalite forms composite grains including native bismuth, heyrovskyite and Bi-Te-S system minerals in the matrix of quartz vein. Matildite from the Nakdong deposits has an end member composition, $Ag_{1.07-1.11}Bi_{1.12-1.20}S_2$, and an excess concentration of $0.3{\sim}2.4$ mole % $Bi_2S_3$ compared to the stoichiomeoic value. PbS concentrations in $PbS-AgBiS_2$ solid solutions do not exceed 54 mole %. The average chemical composition of cosalite in the study area is $Pb_{1.79}Bi_{2.29}Ag_{0.12}S_5$. Pb is slightly depleted compared to the ideal composition, but the concentrations of Ag and Cu reach as much as 1.47 wt.% and 0.27 wt.%, respectively. Heyrovskyite has the chemical formula of $Pb_{5.01}Ag_{0.26}Bi_{2.70}S_9$ suggesting that there occurs the coupled substitution of $2Bi^{3+}$ for $3Pb^{2+}$ as well as that of $Ag^++Bi^{3+}$ for $2Pb^{2+}$. The genetic condition of Pb-Ag-Bi-S system minerals can be confined to the temperature of $220{\sim}270^{\circ}C$ and the pressure below 200 bars.

• 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.