• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.7
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• pp.602-608
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• 2002

In this study, microstructural and piezoelectric characteristics of PNW-PMN-PZT ceramics manufactured using attrition milling method were investigated. Sintering temperature of the ceramics was varied from $1080^{\circ}C$ to $1240^{\circ}C$. With increasing sintering temperature, dielectric constant increased. In the specimen sintered at $1120^{\circ}C$, electromechanical coupling factor(Kp) and density showed the maxinum values of 0.546 and 7.78[$g/\textrm{cm}^3$], respectively. In the specimen sintered at $1160^{\circ}C$, mechanical quality factor(Qm) also showed the maxinum value of 1,943. Contour vibration mode piezoelectric transformer with the size of $27.5{\times}27.5{\times}2.5mm$ using PNW-PMN-PZT ceramics was manufactured and its driving characteristics for T5 fluorescent lamp was investigated. Taking into consideration temperature rise of 6.8[$^{\circ}C$] and efficiency of 98.23%, it can be concluded that the transformer is suitable for driving the T5 fluorescent lamp.

• Journal of Biosystems Engineering
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• v.25 no.1
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• pp.39-46
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• 2000

This work was conducted to study the operating characteristics of a grinding system designed to obtain fine rice husk ash powder. To find better utilizing of rice husk, a valuable by-product from rice production, once the rice husk was incinerated and the thermal energy was recovered from the furnace, the ash was fed and pulverized in the grinding system resulting a fine powder to be used as a supplementary adding material to the portland cement manufacturing . The rice husk ash grinding system consisted of a high speed centrifugal fan for the preliminary coarse milling and a dry-type stirred ball mill for the subsequent fine grinding . Total grinding time 9 5, 15, 30, 45 min), impeller speed (250, 500, 750 rpm) , and mixed ratio (4.8, 7.9, 14.9) were three operating factors examined for the performance of a stirred ball mill used for the fine grinding of ash. With the stirred ball mill used in this study, the minimum attianable mean diameter of rice husk ash powder appeared to be 2 ${\mu}{\textrm}{m}$. During the find grinding, the difference in specific surface area of powder showed an increase and the grinding energy efficiency decreased with the increase in total grinding time, impeller speed ,and mixed ratio. For the operating conditions employed , the resulting mean diameter of fine ash powder, specific energy input, and grinding energy efficiency were in the range of 1.79 --16.04${\mu}{\textrm}{m}$, 0.072-5.226kWh/kg, an d1.11-12.15$m^2$/Wh, respectively. Grinding time of 30 min , impeller speed of 750 rpm, and mixed ratio of 4.8 were chosen as the best operating conditions of the stirred ball mill for fine grinding . At these conditions, mean particle diameter of the fine ash, grinding energy efficiency, grinding throughtput, and specific energy input were 2.73${\mu}{\textrm}{m}$, 3.95$m^2$/Wh, 0.25kg/h, and 1.22kWh/kg, respectively.

• Journal of the Korean Wood Science and Technology
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• v.45 no.3
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• pp.268-277
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• 2017

In this study, lignocellulose nanofibrils (LCNFs) were prepared from Pussy willow wood powder by disk-milling after pretreatment using the cosolvent of 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) and N,N-dimethylformamide (DMF) with different mixing ratios for different time. All pretreated samples showed native cellulose I polymorph and cellulose crystallinity was lowest when cosolvent of DMF with 30% [EMIM]Ac was used. Average crystallite size of raw material and the pretreated product by MDF and its cosolvent with 10% [EMIM]Ac was found to be about 3.2 nm and decreased with increasing pretreatment time at the DMF cosolvent with 30% [EMIM]Ac. Defibrillation efficiency was improved by loosening wood cell wall structure by the pretreatment using co-solvent system of [EMIM]Ac and DMF.

• Resources Recycling
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• v.11 no.1
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• pp.9-18
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• 2002

Printed wiring boards(PWBs) of the obsolete computers are composed of various organic and inorganic compounds as well as metals and alloys. As convinced that the valuable metals obtained from the PWBs are effectively utilized as secondary resources when recovered by economical methods, in this study, an investigation for characterizing the physical separation techniques is conducted. For the recovery of them, the sockets and chips dismantled from PWBs by scraping and residual resin boards are subjected to the appropriate separation processes according to the physical properties of each part. In the case of crushed socket scraps size ranged from -2.36 mm to +1.18 mm, approximately 97 wt% of the product obtained by magnetic separation consists of metallic compounds. In the case of chip scraps, 97% of Fe-Ni alloy and 95% of Cu metal are recovered by the combined process of air classification and dry magnetic separation in the size range from -2.36 mm to +0.15 mm. Ball milling is adopted in order to improve the removal efficiency of the thin-printed metallic materials on the residual resin boards and approximately 77% of Cu metal is recovered by zigzag separation after ball milling.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.534-543
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• 2017

$Gd_2O_3:Eu^{3+}$ red phosphors were prepared by template method from crystalline cellulose impregnated by metal salt. The crystallite size and photoluminescence(PL) property of $Gd_2O_3:Eu^{3+}$ red phosphors were controlled by varying the calcination temperature and $Eu^{3+}$ mol ratio. The nano dispersion of $Gd_2O_3:Eu^{3+}$ was also conducted with a bead mill wet process. Dependent on the time of bead milling, $Gd_2O_3:Eu^{3+}$ nanosol of around 100 nm (median particle size : $D_{50}$) was produced. As the bead milling process proceeded, the luminescent efficiency decreased due to the low crystallinity of the $Gd_2O_3:Eu^{3+}$ nanoparticles. In spite of the low PL property of $Gd_2O_3:Eu^{3+}$ nanosol, it was observed that the photoluminescent property was recovered after re-calcination. In addition, in the dispersed nanosol treated at $85^{\circ}C$, a self assembly phenomenon between particles appeared, and the particles changed from spherical to rod-shaped. These results indicate that particle growth occurs due to mutual assembly of $Gd(OH)_3$ particles, which is the hydration of $Gd_2O_3$ particles, in aqueous solvent at $85^{\circ}C$.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.1
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• pp.6-10
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• 2001

In this study, we investigated the optical properties of sub-wavelength a-Si thin film transmission gratings, especially the polarization effect, the phase difference and the birefringence by using linearly polarized He-Ne laser beam (632.8nm). The a-Si transmission grating of the thickness $of < 0.1 \mum$ with four-type period($\Lambda = 0.4 \mum and 0.6 \mum$ for sub-wavelength and $\Lambda = 1.0 \mum and 1.4 \mum$ for above-wavelength) on quartz substrates have been fabricated using 50 KeV Ga+ Focused-Ion-Beam(FIB) Milling and $CF_4$Reactive-Ion-Etching(RIE) method. Finally, we obtained the trating array of a-Si thin film with a period $0.4 \mum, 0.6 \mum, 1.0 \mum, 1.4 \mum$ which have nearly equal finger spacing and width, sucessfully. Especially, for gratings with $\Lambda = 0.6 \mum(linewidth=0.25 \mum, linespace=0.35\mum), the \etamax at \theta_в=17.0^{\circ}$ is estimated to be 96%. As the results, we believe that the sub-wavelength grating arrayed a-Si thin film has the applicability as the optical device and components.

• Journal of the Korean Electrochemical Society
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• v.12 no.2
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• pp.162-166
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• 2009

The carbon-coated Si/Cu powders were synthesized by mechanical ball-milling and hydrocarbon gas decomposition methods at high temperature. The carbon-coated Si/Cu powder was used as anode for lithium secondary battery and its electrochemical behavior was investigated. In addition, the carbon-coated Si/Cu/graphite composite anode material was prepared using natural graphite powder and their electrochemical characteristics were compared with natural graphite anode. The specific capacity of carbon-coated Si/Cu anode increased to the initial 10 cycles. The carbon-coated Si/Cu/graphite composite anode exhibited the reversible specific capacity of 450mAh/g and the first cycle efficiency of 81.3% at $0.25mA/cm^2$. The cycling performance of the composite anode was similar to that of pure graphite anode except the reversible specific capacity value.

• Korean Journal of Materials Research
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• v.25 no.5
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• pp.215-220
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• 2015

The effect of Al content on the processing of reaction-bonded $Al_2O_3$ (RBAO) ceramics using 40v/o ~ 80v/o Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processes that use ~ 40v/o pure Al powder. The influence of high Al content in starting $Al_2O_3$-Al alloy powder mixtures on its particulate characteristics, reaction-bonding, microstructure, physical and mechanical properties was revealed. Starting $Al_2O_3$-Al alloy powder mixtures with 40v/o ~ 80v/o Al alloy powder were milled, reaction-bonded, post-sintered, and characterized. With an increasing Al alloy content, the milling efficiency of Al alloy powder was lowered, resulting in a larger particle size after milling. However, in spite of the larger particle size of Al alloy powder, the oxidation, i.e., reaction-bonding, of the Al alloy was successfully completed via solid and liquid state oxidation, in which the activation energy of the oxidation was nearly the same regardless of Al alloy content. After reaction-bonding and post-sintering at $1600^{\circ}C$, RBAO ceramics from 80v/o Al alloy content showed a relative density of ~97% and a flexural strength of 251 MPa compared to ~ 96% and 353 MPa for RBAO ceramics from 40v/o Al alloy content, respectively. The lower flexural strength at 80v/o Al alloy content was due to the weak spinel phase that formed from Zn, Mg alloying elements in Al.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.648-653
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• 2012

Hybridization of dense ceramic membranes for hydrogen separation with an electronically conductive metallic phase is normally utilized to enhance the hydrogen permeation flux and thereby to increase the production efficiency of hydrogen. In this study, we developed a nickel and proton conducting oxide ($BaCe_{0.9}Y_{0.1}O_{3-{\delta}}$: BCY) based cermet (ceramic-metal composites) membrane. Focused on the general criteria in that the hydrogen permeation properties of a cermet membrane depend on its microstructural features, such as the grain size and the homogeneity of the mix, we tried to optimize the microstructure of Ni-BCY cermets by controlling the fabrication condition. The Ni-BCY composite powder was synthesized via a solid-state reaction using $2NiCO_3{\cdot}3Ni(OH)_2{\cdot}4H_2O$, $BaCeO_3$, $CeO_2$ and $Y_2O_3$ as a starting material. To optimize the mixing scale and homogeneity of the composite powder, we employed a high-energy milling process. With this high-energy milled composite powder, we could fabricate a fine-grained dense membrane with an excellent level of mixing homogeneity. This controlled Ni-BCY cermet membrane showed higher hydrogen permeability compared to uncontrolled Ni-BCY cermets created with a conventionally ball-milled composite powder.

• Journal of Dental Rehabilitation and Applied Science
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• v.39 no.3
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• pp.158-167
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• 2023

As digital technology has advanced in the field of dentistry, the use of computer-aided design/computer-aided manufacturing (CAD/CAM) has brought changes to the stages of dental treatment. The use of CAD/CAM technology in dental restoration offers clinical efficiency and convenience by reducing production time and appointment intervals, while also simplifying the fabrication process to reduce errors. In this case, digital replication and printing of temporary teeth were used to aid a patient with complex medical histories and physical disabilities. The final impression obtained with silicone impression material included information on the vertical dimension, centric relation, and the angle and length of the anterior teeth, which shortened the production time and appointment intervals and increased patient satisfaction. The final restoration was fabricated using milling and monolithic disc techniques, demonstrating appropriate stability, retention, and support, resulting in functional and aesthetic satisfaction.