• Journal of the Korean Ceramic Society
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• v.31 no.4
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• pp.347-358
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• 1994

Creep densification and grain growth of alumina powder compacts during high temperature processing were investigated. The creep densification and grain growth of alumina powder compacts during various sintering processes were analyzed by employing the consitutive model by Kwon and Kim. Theoretical results from the constitutive model were compared with various experimental data of alumina powder compacts in the literature including pressureless sintering, sinter forging and hot pressing. The proposed constitutive equations were implemented into finite element analysis program (ABAQUS) to simulate densification for more complicated geometry and loading conditions. The effects of friction between die and powder compact or punch and powder compact during sinter forging and hot pressing are investigated by using the finite element method. Also, high temperature forming processing of alumina compact with complicated shape was simulated.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.204-209
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, $SiC_f/SiC$ composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of $SiC_f/SiC$ composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 $^{\circ}C$, 1780 $^{\circ}C$, 1800 $^{\circ}C$ and 1820 $^{\circ}C$ under 20 MPa using $Al_2O_3-Y_2O_3$ system as sintering additives in order to low sintering temperature. The starting powder was high purity ${\beta}-SiC$ nano-powder with an average particle size of 30 nm. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 nm to 200 nm.

• Korean Journal of Materials Research
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• v.16 no.6
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• pp.341-345
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• 2006

[ $Ni_2Si$ ] mixed powders were mechanically alloyed by a ball mill and then processed by hot isostatic pressing (HIP) and spark plasma sintering (SPS). In the powder that was mechanically alloyed for 15minutes(MA 15 min), only Ni and Si were observed but in the powder that was mechanically alloyed for 30minutes(MA 30 min), $Ni_2Si$, Ni and Si were mixed together. Some of the MA 15 min powder and MA 30 min powder were processed by HIP under pressure of 150MPa at the temperature of $1000^{\circ}C$ for two hours and some of them were processed by SPS under pressure of 60 MPa at the temperature of $1000^{\circ}C$ for 60 seconds. Both methods completely compounded the powders to $Ni_2Si$. The maximum density of sintered lumps by HIP method was 99.5% and the maximum density of the sintered lump by SPS method was 99.3%. with the hardness of HRc 66 with the hardness of HRc 63. Therefore, the SPS method that can sinter in short time at low cost is considered to be more economical that the HIP method that requires complicated sintering conditions and high cost and the sintering can produce target materials in desired sizes and shapes to be used for thin film.

• Journal of the Korean Ceramic Society
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• v.16 no.1
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• pp.13-20
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• 1979

High purity alumina has been extracted form low grade Korean alunite. Alunite ore was treated by 15% $NH_4OH$ solution, followed by 10% $H_2SO_4$ leaching and metallic impurities such as Fe and Ti were removed by solvent extraction method. Alumina prepared by the extraction process was 99.9% in purity. Hot Petroleum Drying Method has been employed for the preparation of uniformly fine alumina powder, using chemical reagent aluminum sulfate and ammonium aluminum sulfate extrated from Korea alunite. The sinterability of alumina powder prepared by Hot Petroleum Drying Method was shown to be improved in comparison with the one treated by other methods such as ball milling method, but dry pressing was difficult due to the agglomeration of calcined powder. The best slip of alumina powder prepared by Hot Petroleum Drying Method contained a lower soild content than the one treated by other methods. The alumina body formed by soild and drain casting with the former alumina powder showed a higher sintered density.

• Tribology and Lubricants
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• v.24 no.5
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• pp.269-274
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• 2008

Carbon nanotube composite is considered to be a good candidate material for composite material because of its excellent mechanical property and low density under high temperature as well as good wear and frictional properties. In this study, tribological characteristics of carbon nanotube aluminum composite were evaluated using pin-on-disk wear tester. Spark Plasma Sintering method is more effective than Hot Pressing method in terms of wear and friction. The composite with 1% CNT has the lowest friction and wear characteristic.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.2
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• pp.49-54
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• 2010

The n-type $Bi_2(Te,Se)_3$ powders were fabricated by melting/grinding method and were hot-pressed in order to compare thermoelectric properties of the hot-pressed specimens with those of the $Bi_2(Te,Se)_3$ ingot. Effects of mechanical milling treatment of the $Bi_2(Te,Se)_3$ powders on thermoelectric characteristics of a hot-pressed specimen were also examined. The hot-pressed $Bi_2(Te,Se)_3$ exhibited power factors of $27.3{\sim}32.3{\times}10^{-4}W/m-K^2$ which were superior to $24.2{\times}10^{-4}W/m-K^2$ of the ingot. The $Bi_2(Te,Se)_3$, hot-pressed after mechanical milling treatment of the powders, possessed a non-dimensional figure-of-merit of 1.02 at $100^{\circ}C$ and exhibited extrinsic-intrinsic transition at $130^{\circ}C$.

• Journal of Hydrogen and New Energy
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• v.24 no.1
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• pp.70-75
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• 2013

It has fabricated membrane electrode assemblies (MEA) for proton exchange membrane fuel cell by hot-pressing method. The hot-pressing was used for the fabrication of MEA which is composed of commercial platinum electrode on carbon paper. The performance of MEA was studied with different fabrication conditions of temperature, pressure and torque. As the temperature increased, the performance of MEA was increased. and started to decrease l after arrived at the maximum performance of MEA. This is related with good contact between electrode and polymer electrolyte membrane at high temperature and microstructural change at much higher temperature. Similarly, as the pressure increased, the performance of the MEA increased up to highest values and start to decrease. According to the our results, the maximal performance of the MEA was at the temperature of $140^{\circ}C$ and the pressure of $1.5{\times}10^3$ kPa. The optimal torque to assemble the single stack was 3.2 N m.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.516-518
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• 1996

Bimuth telluride type thermoelectrics are prepared by AC current applied got pressing method. It is possible to minimize the defects arising from the vaporization of Te, because of the very short processing time. The optimum conditions for the got pressing of 95mol% $Bi_2Te_3$-5mol%$Bi_2Se_3$ themoelectrics are sintered at $400^{\circ}C$, for 2min. with 1500 kgf/$cm^2$ from the particle size of 125 to 250 $\mu$m rang of powder. the resulted Z value (figure of merit) was 2.2$\times$10-3deg-1.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.4
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• pp.1-5
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• 2000

Properties of AC applied hot pressed ($Pb_{1-x}Sn_{x}$) Te thermoelectrics were investigated. Mechanical alloying process used to produce alloyed powder to reduce the inhomogeneity and to avoid vaporization of constituents. It showed an increase in the mechanical alloying time with increasing of Sn contents in ($Pb_{1-x}Sn_{x}$)Te. ($Pb_{1-x}Sn_{x}$)Te were sintered at 873 to 923K for 1-4 minutes, under 150 kgf/$\textrm{cm}^2$ by AC applied hot pressng method. The short sintering time of AC applied hot pressing process could reduce the vaporization of Te. The density of ($Pb_{1-x}Sn_{x}$) Te was more dependent on the sintering temperature than the sintering time. The p-n transition was observed at x=0.1 but only p type conduction behavior was observed at more than 20 mol% of Sn compositions. The maximum value of Seebeck coefficient is 250 $\mu$V/K for x=0.2 at 500K. As the amount of Sn increases, the peak value of Seebeck coefficient drops and shifts to higher temperature and the peak value of electrical conductivity decreased with increasing temperature.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1512-1515
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• 1996

Dense $SiC-ZrB_2$ electro-conductive ceramic composites were obtained by hot pressing for high temperature structural application. The influences of the $ZrB_2$ additions an the mechanical and electrical properties of $SiC-ZrB_2$ composites were investigated. Samples were prepared by adding 15, 30, 45 vol.% $ZrB_2$ particles as a second phase to a SiC matrix. Sintering of monolithic SiC and $SiC-ZrB_2$ composites were achieved by hot pressing under a $10^{-4}$ torr vacuum atmosphere from 1000 to $2000^{\circ}C$ with a pressure of 30 MPa and held for 60 minutes at $2000^{\circ}C$. SiC and $SiC-ZrB_2$ samples obtained by hot pressing were fully dense with the relative densities over 99%. Flexural strength and fracture toughness of the samples were improved with the $ZrB_2$ contents. In the case of SiC sample containing 30vol.% $ZrB_2$, the flexural strength and fracture toughness showed 45% and 60% increase, respectively compared to those of monolithic SiC sample. The electrical resistivities of $SiC-ZrB_2$ composites were measured utilizing the four-point probe method and they decreased significantly with Increasing $ZrB_2$ contents. The resistivity of SiC-30vol.% $ZrB_2$ showed $6.50{\times}10^{-4}{\Omega}{\cdot}cm$.