• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.343-350
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• 1997

To fabricate the ceramic/metal(SiC/ Al alloy) composite, SiC preform was prepared by Pressureless Powder Packing Forming Method and 6061 Al alloy was infiltrated into the preform. Uniform compact having an average pore size of 10 ${\mu}{\textrm}{m}$ and narrow pore size distribution was prepared. Phenolic resin solution(40 wt%) was penetrated into the SiC compact, and then the compact was preheated at the temperature of 120$0^{\circ}C$. The pore size distribution and the microstructure of the preform were not changed by preheating. An uniform microstructure without any crack in the preform was obtained in SiC-Al alloy composite. The infiltration of 6061. Al alloy into the preform began at the temperature of 130$0^{\circ}C$ and the amount of infiltration increased in proportion to the infiltration temperature and the soaking time. The increasement rate of the infiltration amount decreased after 3 h. As a result of the infiltration at 140$0^{\circ}C$ for 4 h, Al alloy was well distributed in the interparticle channels and the relative density of the composite was above 98%. The strength and the fracture toughness of the composite were 303 MPa and 21.65 MPam1/2, respectively.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.390-395
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• 2011

The objective of our study was to produce an imitation bone material consisting of hydroxyapatite with a compact and spongy structure. This study shows the ideal content of $SiO_2$ and the sintering temperature to produce imitation bone that has the mechanical properties of natural bone. On the basis of our determination of the ideal conditions, a compact part was produced and its mechanical properties were tested. A compact part made of 0.5 wt% $SiO_2$ and sintered at $1350^{\circ}C$ showed excellent mechanical properties. The bioactivity of the compact part under this condition was tested, and it was found to be bioactive. The porous part was produced by controlling the powder size, and the dual structure was manufactured by combining the compact and porous parts. A water permeability test confirmed that the dual structure had an interconnected pore structure. Therefore, this dual-body structure is feasible for use in the creation of implants.

• 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.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.164-169
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• 2020

Use of SiPM has been considered as an alternative to PMT, because of its compact size, low-operating voltage, non-sensitive to electromagnetic, low costs and so on. The main limitation for the use of SiPM is due to its small sensitive area compared to PMT that limits the light collection, and therefore the sensor energy resolution. In this article we studied the effect of increasing the number of SiPM by connecting them in parallel to increase the active detection area. This allowed us to compare the different energy resolution measurements. ¹³⁷Cs has been selected as reference to study the energy resolution for 662 keV gamma-rays. Another investigation was to compare the minimum detectable gamma energy under various SiPM configurations. It has been found that the use of 4 SiPM arrays can greatly improve the energy resolution up to 4% than only one SiPM array, meanwhile use of more than 2 SiPM arrays does not increase the energy resolution significantly. Thus we can conclude that for a large area of cylindrical scintillator (3 × 3 inches), the use of SiPMs are limited to a certain number or certai active area depending on the commercial SiPMs, and its cost should be less than traditional PMT for the cost-effective and compact size considerations. It is well known that the gain of SiPM varies with temperature. In this article, we also calibrated gain to guarantee the same position of photoelectric peak in response of different temperatures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.7
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• pp.4835-4841
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• 2015

The effect of particle size and compaction pressure on the thermoelectric properties of n-type $FeSi_2$ was investigated. The starting powders with various particle size were pressed into a compact (compaction pressure; $70{\sim}220kg/cm^2$). The compact specimens were sintered at 1473 K for 7 h and annealed at 1103 K for 100 h under Ar atmosphere to transform to the semiconducting ${\beta}$-phase. The microstructure and phases of the specimens were observed by SEM, XRD and EDS. The electrical conductivity and Seebeck coefficient were measured simultaneously for the same specimen at r.t.~1023 K in Ar atmosphere. The electrical conductivity increased with decreasing particle size and hence the increases of relative density of the sintered body and the amount of residual metallic phase ${\varepsilon}$-FeSi due to a increase of the electrical conductivity. The Seebeck coefficient exhibited the maximum value at about 700~800 K and decreased with decreasing particle size. This must be due to a increase of residual metallic phase ${\varepsilon}$-FeSi. On the other hand, the change of compaction pressure appeared to have little effect on the thermoelectric properties. Consequently, the power factor would be affected more by particle size than compaction pressure.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.63-64
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• 2016

This paper deal with single module design of 13.2kVrms/10kVA solid state transformers exchanging conventional transformer. We can design compact hardware system to reduce size and get higher switching frequency by using SiC devices. As a result by comparing simulation results with experiment result, it is verified.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.39-40
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• 2006

The relationship between the powder particle size change and a mechanical property of the Metal Injection Molding (MIM) product was examined in detail. The XRD results indicate that the diffraction peaks of BCC appeared in compacts of powder particle size of 4 to $10{\mu}m$ as well as the bulk SUS630. However, the diffraction peaks from both BCC and FCC were observed in the compact with powder size less than $3{\mu}m$. TEM observation revealed that the powder with those BCC/FCC two phase structure have a finely dispersed $SiO_2$ precipitates. Because the Si is ferrite stabilizing element, decrease of Si composition in the matrix phase by the $SiO_2$ precipitation resulted in formation of the retained austenite. Therefore, controlling the elements such as Si as well as oxygen decrease is very important to obtain a normal microstructure in ultra-fine powder $(<3{\mu}m)$ injection molding.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.325-329
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• 1994

This paper describes a compact design and control method of PWM inverter-mounted induction motor especially designed for reducing the size and weight considerably, which may be applied to the speed control system such as air conditionr,conveyor and textile mill, etc. To obtain higher power density without derating performance, a new mechanical configuration unifying the inverter circuit and motor is proposed. Also, through the use of current minimization control method during V/f operation it is possible to reduce the size of heat-sink related to the losses of power circuit. By the proposed design method, a compact inverter-mounted induction motor system of 1Hp is built and its validity can be verified through the experimental results.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.363-368
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• 2012

Nitriding and post-sintering behavior of powder mixture compacts were investigated. As mixture compacts are different from simple Si compacts, the fabrication of a sintered body with a mixture composition has engineering implications. In this research, in specimens without a pore former, the extent of nitridation increased with $Si_3N_4$ content, while the highest extent of nitridation was measured in $Si_3N_4$-free composition when a pore former was added. Large pores made from the thermal decomposition of the pore former collapsed, and they were filled with a reaction product, reaction-bonded silicon nitride (RBSN) in the $Si_3N_4$-free specimen. On the other hand, pores from the decomposed pore former were retained in the $Si_3N_4$-added specimen. Introduction of small $Si_3N_4$ particles ($d_{50}=0.3{\mu}m$) into a powder compact consisting of large silicon particles ($d_{50}=7{\mu}m$) promoted close packing in the green body compact, and resulted in a stable strut structure after decomposition of the pore former. The local packing density of the strut structure depends on silicon to $Si_3N_4$ size ratio and affected both nitriding reaction kinetics and microstructure in the post-sintered body.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.63-69
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• 1983

It is know that $Si_3-N_4$ bonded SiC has almost all the valuable properties needed for the high temperature material and thus has bery wide range of applicability. Si powder and two different sized SiC powder were used as the raw mateials. Specimens were prepared by heating the green compact mode of the raw materials with polyvinyl alcohol binder in the nitrogen atmosphere. The bond-ing of SiC particles is brought about with the formation of reaction bonded silicon nitride phase between the particles he influences of the variation of the relative amounts of the raw materials and the amount of the organic binder on the density and the bend strength of the specimens were investigated. It was shown that the calculation of the amount of the nitridation of Si is somewhat complicated matter since some portion of the organic binder reacts with the Si during the firing process. Fixing the Si amount to 20w/o the distributions of the size of the SiC particles that gives the maximum density and the maximum strnegth were obtained through experiments. It was observed that the two distributions were not equal to each other. As the amount of Si increased the amount of Si reacted with nitrogen and the strength increased. The fracture mode was intergranular for the most part and the transgranular fracture was scarcely observed.