• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.2
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• pp.70-74
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• 2011

[ $(Ca,Mg)_{0.15}Zr_{0.7}O_{1.7}$ ]ceramics was investigated for the application to SOFC ceramic supporter with high porosity and mechanical strength. $ZrO_2$ powder was prepared by combustion method with glycine using the solution of $ZrO(NO_3)_2{\cdot}2H_2O$ dissolved into deionized water and calcination at $800^{\circ}C$ Porous $(Ca,Mg)_{0.15}Zr_{0.7}O_{1.7}$ ceramics was prepared by sintering the mixture of prepared $ZrO_2$ powder, dolomite and carbon black at $1200{\sim}1400^{\circ}C$ for 1 h. The open porosity ofthe $(Ca,Mg)_{0.15}Zr_{0.7}O_{1.7}$ ceramics sintered at $1300^{\circ}C$ was over 30 % and increased linearly with the amount of carbon black. The crystal structure of $(Ca,Mg)_{0.15}Zr_{0.7}O_{1.7}$ ceramics consisted of single cubic phase. The open pore of this ceramics was connected continuously and distributed well on the whole. This ceramics sintered at $1300^{\circ}C$ showed the porosity from 32 to 55 % and mechanical strength from 90 MPa to 30 MPa with increasing the content of added carbon black.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.481-490
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• 2005

The aim of this study was to investigate the relationship between the C-factor and shrinkage strain values of composite resin and examine the strain values in different incremental filling techniques. The strain gauge method was used for measurement of polymerization shrinkge strain. Experiment was divided two step. In a first experiment, we compared with strain value in three different depth (2mm, 3mm, 4mm) and microhardness of each samples after 24hours were measured. In a second experiment, we examined the strain values in five different filling techniques(Group 1: bulk filling, Group 2: oblique incremental filling, Group 3: horizontal incremental filling, Group 4: vertical incremental filling, Group 5: lining of flowable resin and bulk filling) The results of the present study can be summarized as follows: 1. Composite resin in acrylic molds showed the initial expansion at the early phase of polymerization. 2. Contraction stress was not revealed significant difference between depth of 2mm and 3mm(P>0.05). 3. Contraction stress in sample of 4mm was showed the lowest value(P<0.05). 4. Microhardness of specimen was revealed more difference between upper and lower surface in depth of 4mm than 2 and 3mm(P<0.05). 5. Lining of flowable resin and bulk filling (Group 5) was showed the lowest contraction stress, Group 2 and 3 was showed the highest contraction stress(P<0.05). On the basis above results, the stress that result from the polymerization shrinkage, when incremental curing techniques are used, showed that there is no advantage in incremental placement and curing.

• Journal of Powder Materials
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• v.15 no.5
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• pp.405-410
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• 2008

SOFC (Solid Oxide Fuel Cell) Ni-YSZ anode was fabricated by the spark plasma sintering (SPS) process and its microstructure and electrical properties were investigated in this study. The spark plasma sintering process was carried out at $800{\sim}1000^{\circ}C$ for holding time of 5 min under 40 MPa. To fabricate Ni-YSZ anode, the SPS processed specimens were reduced at $800^{\circ}C$ under $H_2$ atmosphere. The reduced specimens showed relative density of $48.4{\sim}64.8%$ according to sintering temperature. And also, the electrical conductivity of reduced specimens after sintering at 900 and $1000^{\circ}C$ showed $480{\sim}600$ (S/cm) values at the measuring range of $600{\sim}900^{\circ}C$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2004.05a
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• pp.21-25
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• 2004

The column for Steel Framed Reinforced Concrete Structure (SFRCS) and the column for Reinforced Concrete Structure (RCS) could be the most common building structure. The increasing of the need for massive space hasaffected the size of building components for supporting the massive structure. However, the changing of components size makes inefficient space of building. Hence, to meet the need for acquiring efficient space comparing the budget and cost the new structure method, Concrete Filled Tube Steel (CFT), was developed. CFT is the structure for which steel tube instead of other materials such as wood for holding concrete is used. The most benefit of this one is to help in reducing the size of the building components and local buckling because of tube steel holding concrete. For this reason, this research will examine the probability of applying CFT on construction sites by using the concrete (800kgf/$\textrm{cm}^2$) especially for CFT through the data from the real size mock-up.

• Journal of the Korean institute of surface engineering
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• v.50 no.3
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• pp.212-218
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• 2017

$Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrite powders were prepared by self-propagating high temperature synthesis followed by classifying with an ultrasonic wet-magnetic separation unit to get high pure nano-sized particles. The $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrites were well formed by using several powders like iron, nickel oxide, zinc oxide and magnesium oxide at 0.1 MPa of oxygen pressure. The ultrasonic wet-magnetic separation of pre-mechanical milled ferrite powders resulted in producing the powders with average size of 800 nm. The addition of a surfactant during the wet-magnetic separation process improved productivity more than twice. The coercive force, maximum magnetization and residual magnetization of the $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ nano-powders with 800 nm size were 3651 A/m, $53.92Am^2/kg$ and $4.0Am^2/kg$, respectively.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.1
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• pp.30-41
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• 2006

This paper shows mechanical Properties and behaviors of macrostructures for specimens welded by F.S.W according to welding conditions and tool dimensions with $6.35mm_t$ aluminum 7075-T651 alloy plate. It apparently results in defect-free weld zone in case transition speed was changed to 15mm/min 61mm/min and 124mm/min under conditions of tool rotation speed such as 800rpm. 1250rpm and 1600rpm respectively with tool's Pin diameter 40mm and 60mm. The optimum mechanical property, ultimate stress,${\sigma}_Y=470Mpa$ is obtained at the condition of 124mm/min of travel speed with 800rpm of tool rotation speed using full screw type pin. shoulder dia. $20{\phi}mm$ pin dia. $6{\phi}mm$ and pin length 6mm. The full-screw type and the half-screw type pin shows the similar behaviors of weldability. It is found that the size of nugget is depended on tool transition speed and tool dimension by macrostructures of the cross section of weld zone.

• Carbon letters
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• v.25
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• pp.89-94
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• 2018

In this study, we tried to prepare an isotropic spinnable pitch which can be useful to prepare the general purpose carbon fiber through the co-carbonization of biomass tar with ethylene bottom oil under two different preparation methods (atmospheric distillation, pressurized distillation). The results showed that the ethylene bottom oil added co-carbonization was very effective to decrease of the oxygen contents for obtaining a stable spinnable pitch. The pressurized distillation was more effective to reduce the oxygen functional groups of pitches than atmospheric distillation. The obtained spinnable pitch by the pressurized distillation showed higher pitch yield of 42% and lower oxygen content of 9.12% than the spinnable pitch by the atmospheric distillation. The carbon fiber derived from the pressurized distillation spinnable pitch by carbonization at $800^{\circ}C$ for 5 min showed that the higher tensile strength of carbon fiber was increased up to 800 MPa.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.348-358
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• 2005

This paper showed mechanical properties and behaviors of macrostructures for specimens welded by F.S.W according to welding conditions and tool with 6.35$mm_t$ aluminum 7075-T651alloy plate. It resulted in defect-free weld zone in case tool rotation speed was 800rpm, 1250rpm and 1600rpm respectively that transition speed was changed to 15mm/min, 61mm/min and 124mm/min with tool's pin diameter 4${\Phi}$mm and 6${\Phi}$mm. The optimum mechanical property, ultimate stress,${\sigma}_Y$=470Mpa was obtained at the condition of 124mm/min of travel speed with 800rpm of tool rotation speed using full screw type pin, shoulder dia. 20${\Phi}$mm, pin dia.6${\Phi}$mm and pin length 6mm. The full-screw type and the half-screw type pin showed the similar behaviors of weldability. It is found that the size of nugget was depended on tool transition speed and tool dimension by macrostructures of the cross section of weld zone.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2006.11a
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• pp.17-20
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• 2006

In the remote welding system using $CO_2$ laser, laser beam is rapidly deflected by moving mirrors of scanner system and has focusable distance over 1000mm from workpiece. From such arrangement, various advantages and disadvantages arise. Remote welding is a highly efficient laser process. As the mirrors of the scanner system allow positioning speeds exceeding 700m/s, it becomes possible to reduce the welding cycle time. On the other hand, as there no the provision of shielding gas which is normally required for beam powers exceeding 3kW, may become difficult task. Therefore, In this study, the influence of the various penetration of back bead by the different laser welding speed on the weld seam formation without shielding gas was investigated.

• Korean Journal of Materials Research
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• v.33 no.3
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• pp.101-105
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• 2023

A mixture of elemental Co₅₀Si₅₀ powders was subjected to mechanical alloying (MA) at room temperature to prepare a CoSi thermoelectric compound. Consolidation of the Co₅₀Si₅₀ mechanically alloyed powders was performed in a spark plasma sintering (SPS) machine using graphite dies up to 800 ℃ and 1,000 ℃ under 50 MPa. We have revealed that a nanocrystalline CoSi thermoelectric compound can be produced from a mixture of elemental Co₅₀Si₅₀ powders by mechanical alloying after 20 hours. The average grain size estimated from a Hall plot of the CoSi intermetallic compound prepared after 40 hours of MA was 65 nm. The degree of shrinkage of the consolidated samples during SPS became significant at about 450 ℃. All of the compact bodies had a high relative density of more than 94 % with a metallic glare on the surface. X-ray diffraction data showed that the SPS compact produced by sintering mechanically alloyed powders for 40-hours up to 800 ℃ consisted of only nanocrystalline CoSi with a grain size of 110 nm.