• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.305-307
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• 1997

Gd-doped $CeO_2$, ultrafine powders were synthesized by the glycine-nitrate process and then their sintering and electrical characteristics were analysed using the dilatometric and AC impedance measurements. In the dilatometric measurements green bodies from the synthesized powders after milling shrinked to about $1470^{\circ}C$ in appearance and then expanded thermally with the increase of the heating temperature, whereas those from the synthesized powders before milling continuously shrinked to the temperatures of $1600^{\circ}C$. It may be due to the change of the packing density of the synthesized powders by milling. In the AC impedance measurements, the electrical resistivity of the Gd-doped $CeO_2$ bodies from the as-milled powders, sintered at $1500^{\circ}C$ with the increase of the sintering time, showed the minimum value at the sintering time of 10h. The minimum total resistivity of the Gd-doped $CeO_2$ bodies sintered at $1500^{\circ}C$ for 10h seems to result from the lowest activation energy by the combination between the activation energies for the resistivities at the grain interior and grain boundary.

• 한국분말재료학회지
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• 제11권2호
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• pp.165-170
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• 2004

Growth behavior of two different types of grains, faceted and rounded, in a liquid matrix has been studied in the (75WC-25TiCN)-30Co system. Powder samples were sintered above the eutectic temperature for various times under a carbon saturated condition. (Ti,W)(C,N) grains with a rounded shape and WC grains with a faceted shape coexisted in the same Co based liquid. With increasing sintering time, the average size of (Ti.W)(C,N) grains increased continuously and very large WC grains appeared. The growth of rounded (Ti,W)(C,N) grains followed a cubic law, r^3-r^3_0$=kt, where r is the average size of the grains, $r_0$ the initial average size, k the proportionality constant and t the sintering time. indicating a diffusion-controlled growth. On the other hand, the growth of the faceted WC grains resulted in a bimodal grain size distribution, showing an abnormal grain growth. These observations show that the growth behavior of different types of grains is governed by their shape, faceted or rounded, even in the same liquid matrix.

• 한국분말재료학회지
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• 제28권5호
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• pp.403-409
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• 2021

In this study, Ti-Mo-EB composites are prepared by ball milling and spark plasma sintering (SPS) to obtain a low elastic modulus and high strength and to evaluate the microstructure and mechanical properties as a function of the process conditions. As the milling time and sintering temperature increased, Mo, as a β-Ti stabilizing element, diffused, and the microstructure of β-Ti increased. In addition, the size of the observed phase was small, so the modulus and hardness of α-Ti and β-Ti were measured using nanoindentation equipment. In both phases, as the milling time and sintering temperature increased, the modulus of elasticity decreased, and the hardness increased. After 12 h of milling, the specimen sintered at 1000℃ showed the lowest values of modulus of elasticity of 117.52 and 101.46 GPa for α-Ti and β-Ti, respectively, confirming that the values are lower compared to the that in previously reported studies.

• 소성∙가공
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• 제31권4호
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• pp.240-245
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• 2022

In this study, to achieve good electrical conductivity of a charging terminal component in electric vehicles, we investigated the microstructure evolution of pure-Cu subjected to metal injection molding by controlling the sintering variables, such as temperature and time. Thus, three samples were sintered at temperatures ranging from 1000 ℃ to 1050 ℃ near to the melting temperature of 1085 ℃ for 1 and 10 h after thermal evaporation of binder at 730 ℃. Both procedures were made using a unified furnace under Ar+H₂ gas with high purity. The structural observation displayed that the grain size as well as the compactness (a reciprocal of porosity) increased simultaneously as temperature and time increased. This gave rise to high thermal conductivity of 90% IACS together with high density, which was mainly attributed to decrease in fractions of grain boundaries and micro-pores working as effective scattering center for electron movement.

• 한국전기전자재료학회논문지
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• 제33권1호
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• pp.37-44
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• 2020

This study investigated the microstructure and piezoelectric properties of lead-free 0.74(Bi_1/2Na_1/2)TiO₃-0.26SrTiO₃ (BNST26) piezoelectric ceramics sintered using a microwave furnace. For comparison, specimens were also prepared using a conventional furnace sintering (CFS). Average grain sizes of 2.4 ㎛ and 3.2 ㎛ were obtained in the sample sintered at 1,100℃ for 5 min using microwave sintering (MWS) and at 1,175℃ for 2 h using CFS, respectively. To quantify the changes in the microstructures and electrical properties according to the sintering conditions, the polarization hysteresis, bipolar and unipolar strain curves, and temperature dependence of permittivity were evaluated. As a result, it was determined that the P_max (maximum polarization), P_r (remanent polarization) and S_max (maximum strain) values tend to increase with the average grain size. Based on these results, it is concluded that the MWS method can produce lead-free ceramics with superior performance in a relatively short time compared to the conventional CFS method.

• 한국전기전자재료학회논문지
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• 제27권9호
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• pp.561-565
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• 2014

Thermoelectric materials have been the topic of intensive research due to their unique dual capability of directly converting heat into electricity or electrical power into cooling or heating. Bismuth telluride ($Bi_2Te_3$) is the best-known commercially used thermoelectric material in the bulk form for cooling and power generation applications In this work we focus on the large scale synthesis of nanostructured undoped bulk nanostructured $Bi_2Te_3$ materials by employing a novel bottom-up solution-based chemical approach. Spark plasma sintering has been employed for compaction and sintering of $Bi_2Te_3$ nanopowders, resulting in relative density of $g{\cdot}cm^{-3}$ while preserving the nanostructure. The average grain size of the final compacts was obtained as 200 nm after sintering. An improved NS bulk undoped $Bi_2Te_3$ is achieved with sintered at $400^{\circ}C$ for 4 min holding time.

• 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.

• 한국세라믹학회지
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• 제46권2호
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• pp.200-210
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• 2009

It is necessary to minimize the mismatch of sintering shrinkage between dielectric ceramic and Ni inner electrode layers for the purpose of developing the ultra high-capacity multi layered ceramic condenser(MLCC). Thus, low temperature sintering of dielectric $BaTiO_3$ ceramic should be precedently investigated. In this work, the influence of the milling condition on sintering behavior and electrical properties of $BaTiO_3$ ceramics was investigated in the $BaTiO_3$(BT)-Mg-Dy-Mn-Ba system with borosilicate glass as a sintering agent. As milling time increased, specific surface area(SSA) of the powder increased linearly, while both sinterability and dielectric property were found to be drastically decreased with an increasing SSA. It was also revealed that the sinterability of the excessively milled $BaTiO_3$ ceramics could be recovered by increasing Ba content, rather than increasing glass addition. These results suggest that the sintering behavior of $BaTiO_3$ ceramics under the high SSA was more strongly dependent on the transient liquid phase caused by Ba addition, than the liquid phase from additional glass.

• 한국산학기술학회논문지
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• 제9권6호
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• pp.1555-1559
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• 2008

$5{\sim}150{\mu}m$의 오스테나이트계 304(Fe-18%Cr-12%Ni) 및 316L(Fe-18%Cr-13%Ni-2.4%Mo)미립 분말을 사용하여 소결 특성을 평가한 결과, 다음과 같은 결론을 얻었다 (1) 3.6ks의 소결 시간으로는 어느 경우에 있어서나 소결조건에 관계없이 소결체의 상대밀도는 $95{\sim}98%$에서 포화하여 완전 치밀화된 소결체를 얻을 수 없었다. (2) $5{\mu}m$분말을 진공소결 하였을 경우, ts=57.6ks에서 거의 완전 치밀화된 소결체가 얻어졌다. (3) 소결 분위기에 상관없이 304 및 316L소결체에는 $0.5{\sim}0.6%$정도의 산소가 잔류하였다. (4) 진공 소결의 경우, 탄소분 첨가에 의해 소결체의 잔류 산소량은 무첨가 소결체에 비하여 0.375이상 감소하였고, 조직적으로도 산화물은 거의 관찰되지 않았다. 또한 탄소 첨가는 소결체의 밀도 향상 효과로 작용하여 목적하는 완전 치밀화된 고성능 소결체를 제조하는 것이 가능하게 되었다.

• 대한금속재료학회지
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• 제49권11호
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• pp.845-852
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• 2011

The Spark Plasma Sintering(SPS) method offers a means of fabricating a sintered-body having high density without grain growth through short sintering time and a one-step process. A titanium compact having high density and purity was fabricated by the SPS process. It can be used to fabricate a Ti sputtering target with controlled parameters such as sintering temperature, heating rate, and pressure to establish the optimized processing conditions. The compact/target(?) has a diameter of ${\Phi}150{\times}6.35mm$. The density, purity, phase transformation, and microstructure of the Ti compact were analyzed by Archimedes, ICP, XRD and FE-SEM. A Ti thin-film fabricated on a $Si/SiO_2$ substrate by a sputtering device (SRN-100) was analyzed by XRD, TEM, and SIMS. Density and grain size were up to 99% and below $40{\mu}m$, respectively. The specific resistivity of the optimized Ti target was $8.63{\times}10^{-6}{\Omega}{\cdot}cm$.