• Korean Journal of Materials Research
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• v.23 no.2
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• pp.135-142
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• 2013

The Ti-6Al-4V extra low interstitial (ELI) alloy has been widely used as an orthopedic implant material because of its excellent mechanical properties and biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity of the Al and V elements. Therefore, non-toxic biomaterials with a low elastic modulus need to be developed. A high energy mechanical milling (HEMM) process is introduced to improve the effect of sintering. Rapid sintering of spark plasma sintering (SPS) under pressure was used to make an ultra fine grain of Ti-25 wt.%Nb-7 wt.%Zr-10 wt.%Mo-(10 wt.%CPP) composites with bio-attractive elements for increasing strength. These composites were fabricated by SPS at $1000^{\circ}C$ at 60 MPa using HEMM powders. During the sintering process, $CaTiO_3$, TixOy, and CaO were formed because of the reaction between Ti and CPP. The effects of CPP content on the physical and mechanical properties of the sintered Ti-Nb-Zr-Mo-CPP composites were investigated. The biocompatibility and corrosion resistance of the Ti-Nb-Zr-Mo alloys were improved by the addition of CPP.

• Journal of Powder Materials
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• v.29 no.5
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• pp.382-389
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• 2022

A typical trade-off relationship exists between strength and elongation in face-centered cubic metals. Studies have recently been conducted to enhance strength without ductility reduction through surface-treatment-based ultrasonic nanocrystalline surface modification (UNSM), which creates a gradient microstructure in which grains become smaller from the inside to the surface. The transformation-induced plasticity effect in Fe-Mn alloys results in excellent strength and ductility due to their high work-hardening rate. This rate is achieved through strain-induced martensitic transformation when an alloy is plastically deformed. In this study, Fe-6%Mn powders with different sizes were prepared by high-energy ball milling and sintered through spark plasma sintering to produce Fe-6%Mn samples. A gradient microstructure was obtained by stacking the different-sized powders to achieve similar effects as those derived from UNSM. A compressive test was performed to investigate the mechanical properties, including the yielding behavior. The deformed microstructure was observed through electron backscatter diffraction to determine the effects of gradient plastic deformation.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.131.1-131.1
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• 2010

This study was conducted for engineering optimization for the gasification process which is the key factor for success of Taean IGCC gasification plant which has been driven forward under the government support in order to expand to supply new and renewable energy and diminish the burden of the responsibility for the reduction of the green house gas emission. The gasification process consists of coal milling and drying, pressurization and feeding, gasification, quenching and HP syngas cooling, slag removal system, dry flyash removal system, wet scrubbing system, and primary water treatment system. The configuration optimization is essential for the high efficiency and the cost saving. For this purpose, it was designed to have syngas cooler to recover the sensible heat as much as possible from the hot syngas produced from the gasifier which is the dry-feeding and entrained bed slagging type and also applied with the oxygen combustion and the first stage cylindrical upward gas flow. The pressure condition inside of the gasifier is around 40~45Mpg and the temperature condition is up to $1500{\sim}1700^{\circ}C$. It was designed for about 70% out of fly ash to be drained out throughout the quenching water in the bottom part of the gasifier as a type of molten slag flowing down on the membrane wall and finally become a byproduct over the slag removal system. The flyash removal system to capture solid particulates is applied with HPHT ceramic candle filter to stand up against the high pressure and temperature. When it comes to the residual tiny particles after the flyash removal system, wet scurbbing system is applied to finally clean up the solids. The washed-up syngas through the wet scrubber will keep around $130{\sim}135^{\circ}C$, 40~42Mpg and 250 ppmv of hydrochloric acid(HCl) and hydrofluoric acid(HF) at maximum and it is turned over to the gas treatment system for removing toxic gases out of the syngas to comply with the conditions requested from the gas turbine. The result of this study will be utilized to the detailed engineering, procurement and manufacturing of equipments, and construction for the Taean IGCC plant and furthermore it is the baseline technology applicable for the poly-generation such as coal gasification(SNG) and liquefaction(CTL) to reinforce national energy security and create new business models.

• Journal of Biosystems Engineering
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• v.9 no.1
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• pp.22-33
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• 1984

Husk separator is an indispensable equipment in rice milling plants. However, any basic research on the designing and operating criteria of the husk separator have rarely been conducted in Korea. According to the survey results reported recently, grain loss occurs in the process of rice husk separation at custom rice milling plants in Korea and the performance of husk separator has also not been identified. With this regard this study was conducted with a typical commercial husk separator to investigate the effect of the operational factors such as feed rate, blower speed and opening ratio on the velocity distribution in the air duct and the performance of the separator. The results are summerized as follows: 1. The average wind velocity in the primary air duct increased linearly with the blower rpm and the size of air inlet port in both cases of double type and single type operations. 2. The coefficient of variation in the horizontal wind velocities in the primary air duct was the minimum when the opening ratio was 0.22 ($0.052m^2$ of air inlet port) in both cases of single type and double type operations regardless of the blower speeds used in this test. The average wind velocity at the upper part of air duct was greater by 2-5 m/s than the velocity at the bottom part in double type operation. In case of single type operation, however, the average velocity in the middle part was greater than the upper or bottom part when the opening ratio was greater than 0.74. 3. The relationship between the overall effectiveness of separation(Ed for double type and Es for single type) and the average wind velocity (Va) in the primary air duct was expressed in the following quadratic functions. $$Ed=-190.84+106.18Va-10.052Va^2$$ ($r^2$ = 0.97782) $$Es=-223.76+106.23Va-9.1935Va^2$$ ($r^2$ = 0.97029) The average wind velocity required to obtain the overall effectiveness of separation more than 80% ranged from 4.04 m/sec to 5.84 m/sec in case of double type operation, and from 4.70 m/sec to 6.20 m/sec in case of single type. 4. An optimum wind velocity can be obtained with an increase in the blower speed or the size of air inlet port as presented in Figure 8. There was a tendency that the faster the blower speed, the narrower the control range of the air inlet port. 5. The feed rates (1850kg/hr and 2100kg/hr) adopted in this experiment did not bring about a significant difference in both the overall effectiveness of separation and the power consumption. 6. The energy consumption increased cubically with the blower speed but linearly with the size of the air inlet port. On the basis of the results described in items 1, 3, and 6, it would be more economic to adjust the size of the air inlet port larger with a relatively low blower speed than to adjust the size smaller with a relatively high speed.

• Korean Journal of Food Science and Technology
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• v.17 no.1
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• pp.25-32
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• 1985

Low-temperature in-bin paddy drying has been examined to study the limitations of this drying method under Korean weather conditions, the initial moisture content of the paddy, the bulk depth and the airflow rate. The results are reported and discussed with regard to drying time, energy requirements and costs, uniformity in the moisture content of the dried kernels and, finally, the quality of the paddy. The tests carried out during the paddy-drying period in 1981 and 1982 have shown that under Korean weather conditions paddy can be dried to safe storage conditions by continuous aeration with ambient air. Depending upon the initial moisture content of the kernels(19.2%-25.5% w.b.), the bulk depth(1.1-3.5m) and the airflow $(3.0-6.9m^3\;air/m^3\;paddy/min)$ the paddy could be dried within 5 to 17 days. The energy requirements and energy costs are shown to be considerably lower than for conventional high-temperature drying. No significant changes in the quality in terms of milling yield, cracking ratio, acid value and germination were observed.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.47-50
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• 2008

A new anode composition material comprising of SiO and Graphite has been prepared by adopting High energy ball milling (HEBM) technique. The anode material shows high initial charge and discharge capacity values of 1139 and 568 mAh/g, respectively. The electrode sustains reversible discharge capacity value of 719 mAh/g at 30th cycle with a high coulombic efficiency${\sim}99%$. Since the materials formed during initial charge process the nano silicon/$Li_4SiO_3$ and $Li_2O$ remains as interdependent, it may be expected that the composite exhibiting higher amount of irreversibility$(Li_2O)$ will deliver higher reversible capacity. In this study, constant current-constant voltage (CC-CV) charge method was employed in place of usual constant current (CC) method in order to convert efficiently all the SiO particles which resulted high initial discharge capacity at the first cycle. We improved considerably the initial discharge specific capacity of SiO/G composite by pretreatment(CC-CV).

• Progress in Superconductivity
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• v.10 no.2
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• pp.79-86
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• 2009

We successfully fabricated C-doped ex-situ $MgB_2$ wires using two different methods such as mechanical alloying(MA) and combined process(CP) of in-situ and ex-situ. In the MA, the precursor powder was prepared with a mixture of $MgB_2$ and 1 at% C powders by planetary ball milling for 0-100 h. In the CP, on the other hand, C-doped $MgB_2$ powder was prepared with Mg, B, and C powders by in-situ process via compaction, sintering, and crushing. The powders prepared by two methods were loaded into Fe tube and then the assemblages were drawn by a conventional powder-in-tube technique. The MA treatment of C-added $MgB_2$ decreased the particles/grains size and resulted in C-doping into $MgB_2$ after sintering, improving the critical current density($J_c$) in high external magnetic field. For the C-doped $MgB_2$ wire by MA for 25 h, the $J_c$ was $4.1{\times}10^3A/cm^2$ at 5 K and 6.4 T, which was 5.9 times higher than that of pure and untreated $MgB_2$ wire. The CP also provided C-doping into $MgB_2$ and improved the $J_c$ in high magnetic field; the C-doped $MgB_2$ wire fabricated by CP exhibited a $J_c$ being 2.3 times higher than that of the ex-situ wire used commercial $MgB_2$ powder at 5 K and 6.0 T($2.7{\times}10^3A/cm^2\;vs.\;1.2{\times}10^3A/cm^2$).

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.46 no.4
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• pp.1-10
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• 2014

In papermaking industry, inorganic fillers are widely used for the purpose of improving opacity, brightness, printability, uniformity and dimensional stability. They are also useful for production costs and energy savings. In the past, inorganic fillers in papermaking industry only focused on micro-scale but recently, new trials on nano-powdered technology are applying. Even nano-powdered fillers are rapidly utilized for improving the optical and surface properties in coating and surface sizing, there still have some problems in wet-end process due to poor dispersibility and retention. In this study, nano-particled calcium carbonate was produced by milling the PCC and its applicability between micro sized and nano sized calcium carbonated was compared in wet-end process, and finally the sheet properties were evaluated. Nano-PCC was not retained in sheet structure without applying retention system, but with retention system nano-powdered PCC was absorbed on fiber surface with expanding the fiber networks. The application of PAM-bentonite system has resulted in high ash retention and bulky structure for copier paper, and good optical properties in brightness and opacity. However, it required to solve the weakness of low tensile property due to interruption of hydrogen bonding by nano fillers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.97-102
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• 2004

용액 중에서 나노입자의 전기영동 특성을 이용한 전자종이용 잉크 제조를 위해 $TiO_2$ 나노입자를 저유전율 용매인 cyclohexane에 혼합한 후 용매와 용질의 비중차를 줄이기 위해 분말 상 polyethylen을 첨가하여 high energy milling의 방법으로 입자분쇄와 동시에 입자 표면에 고분자 풍을 코팅하였다. 용액내의 입자 분산성 향상과 용매 착색을 위하여 계면활성제와 oil-blue N을 첨가한 후 전자종이용 잉크를 제조하여 측정한 제타 전위 결과 cyclohexane 내에서 $TiO_2$의 제타전위는 -40mV 정도였으나 polyethylene으로 코팅한 후 계면활성제를 첨가하였을 경우 최대 -110mV 이상의 높은 값을 나타내었다. 실제 디스플레이 특성을 평가하기 위해 포토리소그래피를 이용하여 3인치 크기의 ITO glass 위에 $10{\mu}m$의 크기를 갖는 십자형의 격벽을 $40{\mu}m$의 높이로 균일하게 형성한 후 합성된 전자잉크로 주입하여 상부전극과 하부전극사이에 UV 경화제를 도포하여 UV 접합을 실시하였다. 격벽 내에서 입자의 mobility를 측정하여 환산된 전자잉크의 응답속도는 0.1cm/sec로 측정되었으나, 전기영동시 입자들의 움직임에 따른 반사광의 파형을 측정한 경우 0.07cm/sec의 응답속도를 나타내었다.

• Journal of Powder Materials
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• v.22 no.4
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• pp.283-288
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• 2015

Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-TiC composite powders which are fabricated by high-energy ball-milling. A powder mixture of Fe and TiC is prepared in a planetary ball mill at a rotation speed of 500 rpm for 1h. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts show incomplete densification with a relative denstiy of 86.1% after sintering at $1300^{\circ}C$ for 3h. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly complete densification of 98.6% relative density under the sintering pressure of 50 MPa.