• 한국재료학회지
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• 제30권6호
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• pp.321-325
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• 2020

The present study demonstrates the effect of magnetic pulse compaction and spark plasma sintering on the microstructure and mechanical property of a sintered W body. The relative density of green specimens prepared by magnetic pulse compaction increases with increase in applied pressure, but when the applied pressure is 3.4 GPa or more, some cracks in the specimen are observed. The pressureless-sintered W shows neck growth between W particles, but there are still many pores. The sintered body fabricated by spark plasma sintering exhibits a relative density of above 90 %, and the specimen sintered at 1,600 ℃ after magnetic pulse compaction shows the highest density, with a relative density of 93.6 %. Compared to the specimen for which the W powder is directly sintered, the specimen sintered after magnetic pulse compaction shows a smaller crystal grain size, which is explained by the reduced W particle size and microstructure homogenization during the magnetic pulse compaction process. Sintering at 1,600 ℃ led to the largest Vickers hardness value, but the value is slightly lower than that of the conventional W sintered body, which is attributed mainly to the increased grain size and low sintering density.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.58.1-58.1
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• 2011

WC-Co and other similar cemented carbides have been widely used as hard materials in industrial cutting tools and as mould metals; and a number of techniques have been applied to improve its microstructural characteristics, hardness and ear resistance. Cobalt is used primarily to facilitate liquid phase sintering and acts as a matrix, i.e. a cementing phase between WC grains. A uniform distribution of metal phase in a ceramic is beneficial for improved mechanical properties of the composite. WC-Co, starting from initial powders, is vastly used for a variety of machining, cutting, drilling, and other applications because of its unique combination of high strength, high hardness, high toughness, and moderate modulus of elasticity, especially with fine grained WC and finely distributed cobalt. In this study, that started with two different compositions of initial powders, WC-7.5wt%Co and WC-12wt%Co with initial powder size being 1~3 ${\mu}m$, magnetic pulsed compaction followed by subsequent vacuum sintering were carried out to produce consolidated preforms. Magnetic Pulsed Compaction (MPC), a very short duration (~600 ${\mu}s$), high pressure (~4 Gpa), high-density preform molding method was used with varied pressure between 0.5 and 3.0 Gpa, in order to reach an initial high density that would help improve the sintering behavior. For both compositions and varied MPC pressure, before and after sintering, changes in microstructural behavior and mechanical properties were analyzed. With proper combination of MPC pressure and sintering, samples were obtained with better mechanical properties, densification and microstructural behavior, and considerably improved than other conventional processes.

• 한국결정성장학회지
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• 제5권2호
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• pp.135-141
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• 1995

마이크로파 (2.45 GHz) 에너지를 이용한 PZT계 세라믹스의 소결특성과 전기적 특성을 조사하였다. 소결은 $1050 ~ 1130^{\circ}C$ 범위에서 5분간 행하였다. 소결온도가 높아질수록 소결밀도가 높은 치밀한 소결체를 얻을 수 있었으며, 전기적 특성이 증가하는 경향을 보였다. 그러나 소결온도가 $1090^{\circ}C$이상으로 증가하게 되면 PbO의 휘발로 인하여 소결밀도가 감소하였으며, 이에 따라 유전율과 전기기계결합계수 값도 감소하였다. PbO 분위기 조절없이 마이크로파로 $1090^{\circ}C$에서 소결한 시편의 전기적 특성은 유전율, 기계적품질계수, 전기기계결합계수 등의 값이 각각 1900, 80, 0.53으로 일반적인 전기로에 의한 소결과 비교하여, 비슷한 특성을 나타내었다. 마이크로파 에너지를 이용하여 소결공정을 20분 안에 끝마칠 수 있는 급속소결법으로 공정시간과 에너지를 크게 절감할 수 있었다.

• 한국분말재료학회지
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• 제17권4호
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• pp.289-294
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• 2010

For the aim of low-temperature co-fired ceramic microwave components, sintering behavior and microwave properties (dielectric constant ${\varepsilon}_r$, quality factor Q, and temperature coefficient of resonant frequency ${\tau}_f$) are investigated in $Bi_{18}O(Ca_{0.725}Zn_{0.275})_8Nb_{12}O_{65}$ [BCZN] ceramics with addition of $V_2O_5$. The specimens are prepared by conventional ceramic processing technique. As the main result, it is demonstrated that the additives ($V_2O_5$) show the effect of lowering of sintering temperature and improvement of microwave properties at the optimum additive content. The addition of 0.25 wt% $V_2O_5$ lowers the sintering temperature to $890^{\circ}C$ utilizing liquidphase sintering and show the microwave dielectric properties (dielectric constant ${\varepsilon}_r$ = 75, quality factor $Q{\times}f$ = 572 GHz, temperature coefficient of resonance frequency ${\tau}_f\;=\;-10\;ppm/^{\circ}C$). The estimated microwave dielectric properties with $V_2O_5$ addition (increase of ${\varepsilon}_r$, decrease of $Q{\times}f$, shift of ${\tau}_f$ to negative values) can be explained by the observed microstrucure (sintered density, abnormal grain structure) and possibly high-permittivity $Bi_{18}Zn_8Nb_{12}O_{65}$ (BZN) phase determined by X-ray diffraction.

• 구강회복응용과학지
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• 제32권3호
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• pp.246-254
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• 2016

Direct metal laser sintering (DMLS) 방식은 3D 프린팅 중 한 방식으로, 재료를 쌓아가면서 레이저를 이용하여 선택적으로 sintering하는 방식이다. 이는 주조 방식에서 문제되는 결손과 뒤틀림을 방지할 수 있으며 절삭 가공 방식으로 제작하기 어려운 복잡한 구조물을 제작할 수 있다. 본 증례들은 DMLS 방식을 이용하여 지대치 간 길이가 긴 고정성 보철물, 포스트 등 다양한 고정성 보철물을 제작하여 수복하였고, 주기적인 관찰 결과 심미적, 기능적으로 만족할만한 결과를 얻었기에 이를 보고하는 바이다.

• 한국세라믹학회지
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• 제37권4호
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• pp.395-401
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• 2000

In this study, we chose the basic composition which indicated the best electrical properties by change of x content(0, 0.05, 0.1, 0.15, 0.2, 0.25 mol respectively) in xPb(Mn1/3Sb2/3)O3-(1-x)Pb(Zr0.52Ti0.48)O3 ceramics. And we substituted Cd2+ for Pb2+ site, then observed the sintering behavior, microstructure and electrical propertties according to the various sintering temperature. The basic composition was the 0.05PMS-0.95PZt, and it showed single perovskite phase and excellent properties. In case of Cd2+ substitution, we were able to sinter at 90$0^{\circ}C$ which was lower than conventional sintering temperature(1200~130$0^{\circ}C$). Especially, when the 2mol% substituted PMS-PZT specimens were sintered at 90$0^{\circ}C$ for 2h, we obtained the p=7.6g/㎤, kp=56%, Qm=520 and made sure of a position of Cd2+ substitution by observing lattice parameter, phase transition temperature. From this results, we could infer that because Cd2+ substituted fro A-site, low temperature sintering of Cd2+ substituted PMS-PZT without any loss of electrical properties shows its applicability for the piezoelectric ceramic transformer.

• 한국세라믹학회지
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• 제49권6호
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• pp.608-613
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• 2012

We investigated the property changes of MgO powders sintered at temperatures ranging from $700^{\circ}C$ to $1900^{\circ}C$ for 5minutes at a pressure of 2.7 GPa for a high-pressure high-temperature(HPHT) diamond synthesis process. The physical properties of the sintered MgO powders were characterized by optical microscopy, field emission scanning electron microscopy (FE-SEM), Vickers hardness tests, and by the apparent density, and X-ray diffractometry. An optical micro-analysis showed that white MgO powders became black after sintering due to carbon contamination from the graphite heat source. FE-SEM revealed the growth in the grain size of the MgO powders from $0.3{\mu}m$ to $50{\mu}m$ after sintering at $1700^{\circ}C$. The hardness and apparent density increased to $1800^{\circ}C$ while the samples were dedensified at $1900^{\circ}C$ due to the growth of isolated pores. According to the XRD analysis, no phase transformation occurred in the MgO powders. These results suggest that HPHT-sintered MgO powders can show an accelerated sintering process characterized by grain neck growth, pore connections, isolated pore growth and dedensification in 5 minutes, while these processes with the conventional sintering process take at least 5 hours.

• 전기학회논문지
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• 제56권3호
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• pp.556-560
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• 2007

In this study, both structural and microwave dielectric properties of the $Mg_5B_4O_{15}$ (B=Ta, Nb) cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were prepared by the conventional mixed oxide method and sintered at $1400^{\circ}C{\sim}1500^{\circ}C$. The bulk density and quality factor of the $Mg_5B_4O_{15}$ (B=Ta, Nb) ceramics were increased with increasing sinterning temperature in the range of $1400^{\circ}C{\sim}1450^{\circ}C$, but these were decreased the sintering temperature of above $1450^{\circ}C$. The dielectric constant of the $Mg_5Ta_4O_{15}$ ceramics was increased continuously with increasing sintering temperature. And the dielectric constant of the $Mg_5Nb_4O_{15}$ ceramics was increased in as the sintering temperature increasesfrom $1400^{\circ}C{\sim}1450^{\circ}C$ but was decreased at the temperatures above $1475^{\circ}C$. In the case of the $Mg_5Ta_4O_{15}\;and\;Mg_5Nb_4O_{15}$ ceramics sintered at $1450^{\circ}C$ for 5h, the dielectric constant, quality factor, and temperature coefficient of the resonant frequency (TCRF) were 8.2, 259,473 GHz, $-10.91ppm/^{\circ}C$ and 14, 37,350 GHz, $-52.3ppm/^{\circ}C$, respectively.

• 한국세라믹학회지
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• 제45권2호
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• pp.94-98
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• 2008

Silicon nitride($Si_3N_4)$ is one of the most widely used structural ceramic materials. However silicon nitride is difficult to sinter because of its strong covalent bonding characteristics. In this study, $Si_3N_4$ ceramics were fabricated by spark plasma sintering process with $Y_2O_3$ and $Al_2O_3$ addition to improve the sinterability and the mechanical properties and their phase transformation behavior, microstructure and mechanical properties were evaluated. Fully densified $Si_3N_4$ ceramics could be obtained by spark plasma sintering process at a lower temperature than conventional sintering method. The formation of network microstructure was affected by the addition of $Al_2O_3$ because it could accelerate a to ${\alpha}$ to ${\beta}$ phase transformation of $Si_3N_4$. As a result, the mechanical properties depended on amounts of $Al_2O_3$ addition. The hardness value increased with increasing ${\alpha}$-phase fraction, but fracture toughness value increase with increasing ${\beta}$-phase fraction.

• 한국세라믹학회지
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• 제54권4호
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• pp.292-297
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• 2017

${\beta}-SiAlON$, based on its high fracture toughness, good strength and low abrasion resistance, has been adopted in several industrial fields such as bearings, turbine blades and non-ferrous metal refractories. In general, ${\beta}-SiAlON$ is fabricated by reactive sintering using expensive $Si_3N_4$ and AlN as starting materials. On the other hand, in this study, a cheaper ${\beta}-SiAlON$ starting powder synthesized by SHS was employed to improve price competitiveness compared to that of the reactive sintering process. ${\beta}-SiAlON$ ceramics with various content of the sintering additive $Y_2O_3$ up to 7 wt% were fabricated by conventional pressureless sintering at $1800^{\circ}C$ for 2 to 8 h under $N_2$ pressure of 0.1 MPa. The specimen with 3 wt% $Y_2O_3$ exhibited the best mechanical properties: hardness of 14 GPa, biaxial strength of 830 MPa, fracture toughness of $5MPa{\cdot}m^{1/2}$ and wear rate of about $3{\times}10^{-6}mm^3/N{\cdot}m$.