• 한국분말재료학회지
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• 제10권6호
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• pp.443-447
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• 2003

Nano-sized $TiB_2$ was in situ synthesized in copper matrix through self-propagating high temperature synthesis (SHS) with high-energy ball milled Ti-B-Cu elemental mixtures as powder precursors. The size of $TiB_2$ particles in the product of SHS reaction decreases with time of preliminary mechanical treatment ranging from 1 in untreated mixture to 0.1 in mixtures milled for 3 min. Subsequent mechanical treatment of the product of SHS reaction allowed the $TiB_2$ particles to be reduced down to 30-50 nm. Microstructural change of $TiB_2$-Cu nanocomposite during spark plasma sintering (SPS) was also investigated. Under simultaneous action of pressure, temperature and electric current, titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a interpenetrating phase composite with a fine-grained skeleton.

• 대한금속재료학회지
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• 제47권10호
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• pp.660-666
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• 2009

The consolidation of mechanical alloyed $Ti_5Si_3$ powder by electro-discharge-sintering has been investigated. A single pulse of 2.5 to 8.0 kJ/0.34 g was applied to each powder mixture using 300 and $450{\mu}F$ capacitors. A bulk-like solid with $Ti_5Si_3$ phase has been successfully fabricated by the discharge with an input energy of more than 2.5 kJ in less than $160{\mu}sec$. Micro-Vickers hardness was found to be higher than 1350, which is significantly higher than that of a conventional high temperature sintered sample. The formation of $Ti_5Si_3$ and consolidation occurred through a fast solid state diffusion reaction.

• 한국분말재료학회지
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• 제23권5호
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• pp.379-383
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• 2016

A thick film of $Li_7La_3Zr_2O_{12}$ (LLZO) solid-state electrolyte is fabricated using the tape casting process and is compared to a bulk specimen in terms of the density, microstructure, and ion conductivity. The final thickness of LLZO film after sintering is $240{\mu}m$ which is stacked up with four sheets of LLZO green films including polymeric binders. The relative density of the LLZO film is 83%, which is almost the same as that of the bulk specimen. The ion conductivity of a LLZO thick film is $2.81{\times}10^{-4}S/cm$, which is also similar to that of the bulk specimen, $2.54{\times}10^{-4}S/cm$. However, the microstructure shows a large difference in the grain size between the thick film and the bulk specimen. Although the grain boundary area is different between the thick film and the bulk specimen, the fact that both the ion conductivities are very similar means that no secondary phase exists at the grain boundary, which is thought to originate from nonstoichiometry or contamination.

• 한국분말재료학회지
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• 제25권2호
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• pp.109-119
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• 2018

The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to $135.48kJ{\cdot}mol^{-1}$ by adding the Al/V particles because the activation energy for the diffusion of Al in ${\alpha}-Ti$ ($77kJ{\cdot}mol^{-1}$) is much lower than that of the self-diffusion of ${\alpha}-Ti$. The coarser Ti powders increase the energies from 135.48 to $181.16kJ{\cdot}mol^{-1}$ because the specific surface areas of Ti decrease.

• 한국세라믹학회지
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• 제44권12호
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• pp.696-702
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• 2007

The family of (Sr,Mg)-doped $LaGaO_3$ compounds, which exhibit high ionic conductivity at $600-800^{\circ}C$ over a wide range of oxygen partial pressure, appears to be promising as the electrolyte for intermediate temperature solid oxide fuel cells. Conventional synthesis routes of (Sr,Mg)-doped $LaGaO_3$ compounds based on solid state reaction have some problems such as the formation of impurity phases, long sintering time and Ga loss during high temperature sintering. Phase stability problem especially, the formation of additional phases at the grain boundary is detrimental to the electrical properties of the electrolyte. From this point of view, we focused to synthesize single phase (Sr,Mg)-doped $LaGaO_3$ electrolyte at the stage of powder synthesis and to apply relatively low heat-treatment temperature using novel synthesis route based on combustion method. The synthesized powder and sintered bulk electrolytes were characterized by XRD, TG-DTA, FT-IR and SEM. AC impedance spectroscopy was used to characterize the electrical transport properties of the electrolyte with the consideration of the contribution of the bulk lattice and grain boundary to the total conductivity. Finally, relationship between synthesis condition and electrical properties of the (Sr, Mg)-doped $LaGaO_3$ electrolytes was discussed with the consideration of phase analysis results.

• Journal of Electrochemical Science and Technology
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• 제2권1호
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• pp.39-44
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• 2011

Sub-micrometer $La_{0.8}Ca_{0.2}CrO_3$ powders for ceramic interconnects of solid oxide fuel cells were synthesized by the aqueous combustion process. The materials were prepared from the precursor solutions with different glycine (fuel)-to-nitrate (oxidant) ratios (${\phi}$). Single-phase $La_{0.8}Ca_{0.2}CrO_3$ powders with a perovskite structure were obtained after combustion when ${\phi}$ was equal to or larger than 0.480. Especially, the stoichiometric precursor with ${\phi}$ = 0.555 yielded the spherical $La_{0.8}Ca_{0.2}CrO_3$ particles with 150-250 nm diameters after calcination at $1000^{\circ}C$. When compared with the powders synthesized by the solid-state reaction, the combustion-derived, fine powders exhibited improved sinterability, leading to near-full densification at $1400^{\circ}C$ in oxidizing atmospheres. Moreover, a small quantity of glass additives was used to reduce the sintering temperature, and considerable densification was indeed achieved at temperatures as low as $1100^{\circ}C$.

• 한국레이저가공학회지
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• 제3권1호
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• pp.21-28
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• 2000

Selective Laser Sintering (SLS) can produce three-dimensional objects directly from a CAD solid model without part-specific tooling. In this study, a simple rapid prototyping through selective laser sintering on brass powder is investigated using a Nd-YAG laser. Experiments are conducted to produce single lines on a powder-packed bed for various process parameters. Also, temperature distribution in the powder bed and the thickness of a melted line are predicted by finite element analysis. In the numerical analysis, the thermal conductivity of the brass powder which is obtained as a function of state and temperature is used.

• 한국세라믹학회지
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• 제51권3호
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• pp.208-217
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• 2014

$La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.2-x}Zn_xO_{2.8}$(LSGMZ, X=0-0.05) was prepared using a solid state reaction method. Two secondary phases ($LaSrGaO_4$ and $LaSrGa_3O_7$) of powders were identified by X-ray diffraction analysis. The relative amount of these secondary phases depended on the calcination conditions (temperature and time) and Zn content. The sintering density of LSGMZ was enhanced by increasing the Zn content and calcination temperature at the low sintering temperatures ($1250-1300^{\circ}C$). The relationship between the sintering density of LSGMZ and the synthesis conditions was discussed considering the phase analysis results.

• 한국전기전자재료학회논문지
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• 제30권4호
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• pp.218-222
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• 2017

In this paper, in order to develop excellent composition ceramics for a piezoelectric energy- harvesting device, we synthesized $0.99(Na_{0.52}\;K_{0.443}\;Li_{0.037})(Nb_{0.883}\;Sb_{0.08}\;Ta_{0.037})O_3$ + $0.01(Sr_{0.95}Ca_{0.05})TiO_3$ + $0.3\;wt%\;Bi_2O_3\;+\;0.3\;wt%\;Fe_2O_3\;+\;0.3\;wt%\;CuO$ (abbreviated as NKN-SCT) ceramics with different sintering times, using the ordinary solid-state reaction method. The effect of sintering time on the microstructure and piezoelectric properties was investigated. The ceramics with the sintering time of 7 h have the optimum values of the piezoelectric constant ($d_{33}$), piezoelectric voltage constant ($g_{33}$), planar piezoelectric coupling coefficient (kp), mechanical quality factor (Qm), and dielectric constant (${\varepsilon}r$): $d_{33}=314[pC/N]$, $g_{33}=20.07[10^{-3}mV/N]$, kp = 0.442, Qm = 93, ${\varepsilon}r=1,768$, all being suitable for a piezoelectric energy-harvesting device.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2289-2294
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• 2021

In the present study, an original spark plasma sintering-reactive synthesis (SPS-RS) method for minerallike ceramic materials based on SrAl₂Si₂O₈ feldspar-like skeleton structure was used for the first time, promising solid-state matrices for reliable immobilization of high-energy ⁹⁰Sr. The method is based on the "in-situ" reaction of a mixture of SrO, Al₂O₃ and SiO₂ oxides when heated by a unipolar pulsed current under compacting pressure. The phase and elemental composition structure were studied. The dynamics of the consolidation of the reaction mixture of oxides was studied in the range of 900-1200 ℃. The study found the temperature of the high-speed (minutes) SPS-RS formation of single-phase SrAl₂Si₂O₈ composition ceramic in the absence of intermediate reaction products with a relative density of up to 99.2% and compressive strength up to 145 MPa and a strontium leaching rate of 10^-4g/cm²·day.