• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.5
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• pp.210-216
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• 2007

Porous nickel membrane far high precision gas filter was prepared by in-situ reduced/sintered process of NiO with an addition of polymer(PMMA; polymethyl methacrylate). It showed that the porosity of Ni membrane was approximately 52%. It is similar to metal membrane which prepared using metal fiber as raw materials. The average pore diameter and porosity of Ni membrane increased as content of added polymer and decreased as elevating reduced/sintered temperature from $800^{\circ}C$ to $1000^{\circ}C$. Increase of porosity at $800^{\circ}C$ was associated with surface diffusion mechanism that leads to initial sintering, while decrease of porosity at $1000^{\circ}C$ was associated with lattice diffusion and grain boundary diffusion.

• Journal of the Korean Applied Science and Technology
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• v.31 no.2
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• pp.183-189
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• 2014

On the basis of our previous research results concerning a batch Teflon coating process on the surface of basalt fiber which has superior fire-resistance and chemical resistance, we have tried to set up suitable operating conditions for continuous polytetrafluoroethylene(PTFE) coating process. The basalt fiber was continuously pre-treated with 7.5 wt%(6.5% of DPU) of triethoxytrifluoropropylsilane(TMTFPS) and then coated with 20 wt% of PTFE dispersions containing 0.25 wt% of penetrating agent sodium bis(2-ethylhexyl)sulfo succinate (DOS-Na) to get the highest tensile and loop strengths. After dipping process, the PTFE coated basalt fiber was dried under 2 m drying chamber at $120^{\circ}C$ with 12 m/min of winding speed and consequently sintered under 2 m sintering chamber at $380^{\circ}C$ for 40 s. Conclusively, PTFE coated basalt fiber whose tensile and loop strengths were to $3.4g_f/D$ and $2.3g_f/D$, respectively, applicable to high temperature sewing thread could be continuously prepared with our pilot scale process under optimum conditions.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.602-606
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• 2015

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of $WO_3$ and spherical PMMA of 20 vol% were frozen at $-25^{\circ}C$ and dried for the sublimation of the camphene. The green bodies were heat-treated at $400^{\circ}C$ for 2 h to decompose the PMMA; then, sintering was carried out at $1200^{\circ}C$ in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about $400^{\circ}C$, and $WO_3$ was reduced to metallic W at $800^{\circ}C$ without any reaction phases. The sintered bodies with $WO_3$-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.165-170
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• 2015

Ceramics biomaterials are useful as implant materials in orthopedic surgery. In this study, porous HA(hydroxyapatite)/${\beta}$-TCP(tricalcium phosphate) composite biomaterials were successfully fabricated using HA/${\beta}$-TCP powders with 10-30 wt% $NH_4HCO_3$ as a space holder(SH) and $TiH_2$ as a foaming agent, and MgO powder as a binder. The HA/${\beta}$-TCP powders were consolidated by spark plasma sintering(SPS) process at $1000^{\circ}C$ under 20 MPa conditions. The effect of SH content on the pore size and distribution of the HA/${\beta}$-TCP composite was observed by scanning electron microscopy(SEM) and a microfocus X-ray computer tomography system(SMX-225CT). These microstructure observations revealed that the volume fraction of the pores increased with increasing SH content. The pore size of the HA/${\beta}$-TCP composites is about $400-500{\mu}m$. The relative density of the porous HA/${\beta}$-TCP composite increased with decreasing SH content. The porous HA/${\beta}$-TCP composite fabricated with 30%SH exhibited an elastic modulus similar to that of cortical bone; however, the compression strength of this composite is higher than that of cortical bone.

• Journal of the Korean Ceramic Society
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• v.26 no.3
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• pp.423-437
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• 1989

Al2O3/ZrO2 composites were prepared by precipitation method using Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O as starting materials and NH4OH as a precipitation agent. Al2O3/ZrO2 composites(series A) were prepared by mixing Al2O3 powder obtained by single precipitation method with ZrO2(＋3m/o Y2O3) powder obtained by co-predipitation method. Al2O3/ZrO2 composites (series B) were prepared by co-precipitation method using the three starting materials. In all cases, the composition was controlled as Al2O3-15v/o ZrO2(＋3m/o Y2O3). The composites of series A showed higher final relative densities than those of series B and tetagonal ZrO2 in all cases was retained to about 95% at room temperature. ZrO2 particles were coalesced more rapidly in grain boundary of Al2O3 than within Al2O3 grain. ZrO2 particles were located at 3-and 4-grain junction of Al2O3 and limited the grain growth of Al2O3. It was observed that MgO contributed to densification of Al2O3 but limited grain growth of Al2O3 by MgO was not remarkable. In all Al2O3/ZrO2 composites, exaggerated grain growth of Al2O3 was not observed and Al2O3/ZrO2 composites were found to have homogeneous microstructures.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.625-629
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• 2010

This study investigates the effects of porosity on the thermal stability and the thermal shock resistance of a porous nozzle used for blowing an inert gas. The samples of $Al_2O_3-SiO_2-ZrO_2$ system, which had the apparent porosity of 16~30% and bulk density of $2.6{\sim}3.2g/cm^3$, were prepared by adding different graphite contents (5, 10, 20 wt%) as a pore-forming agent. The thermal shock test was conducted at ${\Delta}T=500$, 1000, and $1400^{\circ}C$ also and the thermal stability was also carried out at 1550, 1600, and $1650^{\circ}C$ for 5 hrs. The specimen contained 10 wt% graphite had uniform pore size distribution, whereas the specimen with 20 wt% graphite showed non-uniform pore size distribution. As a result of thermal shock test, the specimen containing 10 wt% graphite appears to have higher mechanical strength than the other specimens (5, 20 wt% graphite). Both the 5 wt% and 20 wt% graphite specimens developed a non-uniform pore size distribution and cracks that were generated by intensive thermal stress.

• Korean Journal of Materials Research
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• v.22 no.9
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• pp.476-481
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• 2012

Among the various roll-to-roll printing technologies such as gravure, gravure-offset, and reverse offset printing, reverse offset printing has the advantage of fine patterning, with less than 5 ${\mu}m$ line width. However, it involves complex processes, consisting of 1) the coating process, 2) the off process, 3) the patterning process, and 4) the set process of the ink. Each process demands various ink properties, including viscosity, surface tension, stickiness, and adhesion with substrate or clich$\acute{e}$; these properties are critical factors for the printing quality of fine patterning. In this study, Ag nano ink was developed for reverse offset printing and the effect of polyvinylpyrrolidone(PVP), used as a capping agent of Ag nano particles, on the printing quality was investigated. Ag nano particles with a diameter of ~60 nm were synthesized using the conventional polyol synthesis process. Ethanol and ethylene glycol monopropyl ether(EGPE) were used together as the main solvent in order to control the drying and absorption of the solvents during the printing process. The rheological behavior, especially ink adhesion and stickiness, was controlled with washing processes that have an effect on the offset process and that played a critical role in the fine patterning. The electrical and thermal behaviors were analyzed according to the content of PVP in the Ag ink. Finally, an Ag mesh pattern with a line width of 10 ${\mu}m$ was printed using reverse offset printing; this printing showed an electrical resistivity of 36 ${\mu}{\Omega}{\cdot}cm$ after sintering at $200^{\circ}C$.

• Resources Recycling
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• v.13 no.3
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• pp.3-11
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• 2004

Basic studies have been conducted regarding the crystal formation of hydroxyapatite which was produced in the treatment process of phosphate-containing wastewater using calcium ions as the precipitating agent for its employment as the material for artificial bones. The precipitation of hydroxyapatite were conducted in the synthetic solution which simulating human body fluid for its increased applicability. Ca($NO_3$)$_2$$.$$4H_2$O and ($NH_4$)$_2$$HPO_4$ were employed for the precipitation of hydroxyapatite and its composition was analyzed after drying at 80oC. The thermal behavior of precipitate was investigated by examining the change in its crystalline structure according to the sintering temperature. DTA/TG analysis showed that the escape of moisture from the precipitate occurred at ca. $100^{\circ}C$ and the decomposition of ammonia and the evaporation of lattice water were brought about at around $250^{\circ}C$. X-ray diffraction analysis indicated that the thermally treated precipitate consisted mainly of hydroxyapatite. For dried precipitate, the bonds in the component materials which used for the precipitate formation were observed by FT-IR, and after thermal treatment the major bonds in the precipitate were shown to be $OH^{-}$, $PO_4^{3-}$ , and $CO_3^{ 2-}$ , which were main comprising bonds of hydroxyapatite.

• Journal of the Korean Ceramic Society
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• v.40 no.1
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• pp.81-86
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• 2003

Microwave dielectric properties have been investigated in the$(1-x)CaTiO_3-xYAlO_3$ (x=0.1~1.0) solid solution system. The mixtures of $CaTiO_3$ and $YalO_3$using solid state method were sintered at various temperatures. Their dielectric constants and related temperature coefficients were strongly depend on the composition of the solid solution. The optimum properties were recorded as for ${\varepsilon}_r=47,$ $Q{\times}f_0$=35000 and ${\tau}_f=+11ppm/^{\circ}C$ without sintering agent. Even at $1200^{\circ}C$ full densification has been achieved with addition of $CaB_2O_4$ in the $0.75CaTiO_3-0.25YalO_3$ composition. The sample of $0.3 wt%-CaB_2O_4$ added $ 0.75CaTiO_3-0.25YalO_3$ sintered at $1300^{\circ}C$ for 3 h showed optimum microwave dielectric properties of ${\varepsilon}_r=47$, $Q{\time}f_0=37000$ and ${\tau}_f=+17ppm/^{\circ}C$, which demonstrates the promising candidates for microwave dielectric materials covering 5~7 GHz range.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.259-279
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• 1996

최근 정보·전자산업의 발전으로 고 신뢰성 전자재료에 대한 수요가 증대되고 있으며 이러한 첨단산업의 기반의 될 신소재 중 전자세라믹스가 차지하는 비중이 그 대부분을 차지하고 있으며 이에 대한 수요와 기대가 점점 커지고 있다. 이러한 전자세라믹스는 유전재료, 자성재료, 압전재료, 도전성 재료 등으로 나뉘게 된다. 어떠한 분류에 들어가든 그 조성은 금속의 산화물 형태가 일반적이며 미세한 분말의 성형체를 소결(sintering) 함으로써 최종제품으로 완성된다. 이러한 전잣라믹스가 최근 요구되는 고 신뢰성, 고 밀도화를 달성하기 위해선 원료 분말 제조단계부터 제어가 필요하다. 원료분말의 균일·균질성과 그 입도는 소결특성 뿐만아니라 전기적 특성에도 큰 영향을 미치기 때문이다. 세라믹스의 분말제조 방법 중 일반적으로 사용되는 방법으로는 고상 산화물을 혼합하여 하소(calcination)한 후 분쇄하는 '고상합성법'과 금속의 염 또는 alkoxide 용액을 이용하여 화학적으로 제조하는 '습식 화학적 합성법'이 있다. 고상합성법은 합성온도가 높고 기계적 분쇄와 혼합에 의존하므로 균일·균질성이 떨어지고 분말크기를 1㎛ 이하로 만들기 힘들다. 반면에 습식화학적 합성법은 기계적인 분쇄와 혼합에선 얻을 수 없는 원자 혹은 분자단위의 균일한 혼합과 submicron 이하의 미세한 분말을 얻을 수 있다. 따라서 이러한 습식 화학적 합성으로 얻은 분말을 사용하면 미세한 입자의 특성으로 인해 소결온도를 낮출 수 있으며 균일한 미세구조와 균질한 조성을 갖게되어 기계적·전기적 물성증진도 가져올 수 있게 된다. 습식 화학적 분말합성법은 전술하였듯이 alkoxide의 가수분해를 이용하는 sol-gel 법과 금속의 염(salt) 용액을 이용하여, 화학적으로 화합물 침전을 얻거나 또는 공침전물(coprecipitate) 형태의 분말을 얻는, 침전법으로 나뉠 수 있다. 침전법의 근본원리는 pH 및 pCO3 등에 따른 이온종의 용해도 차이를 이용하는 것으로써 각 이온종에 따른 solubility product(ksp)를 이용하여 설명된다. 본 연구에서는 침전법을 사용한 Ba-, Pb-계 전자세라믹스의 분말합성에 대한 이론적 고찰과 공정개발 및 실험을 통한 물성증진 효과에 대해 알아보았다. 본 실험상의 전자세라믹스 조성은 강유전체, 세라믹반도체, 압효과에 대해 알아보았다. 본 실험상의 전자세라믹스 조성은 강유전체, 세라믹 반도체, 압전재료로 널리 사용되는 BaTiO3, PZT(PbZrO3-PbTiO3)와 수직 자기기록매체로 큰 가능성이 있으며 hard ferrite로 널리쓰이는 Ba-feerite(BaFe12O19)로써 수산화물 형태의 침전에 대한 기구(mechanism)와 물성에 대해 살펴보았다. 이러한 침전법에 의한 분말합성 과정에는 소결체의 물성에 영향을 미치는 pH 조절제나 원료에서 혼입될 수 있는 Na+, K+, Cl-, SO4- 등의 제거(washing 혹은 filtering)가 필수적이다. 그러나 침전법에서 얻게 되는 분말은 매우 미세하여 colloid를 형성하게 되며, 이러한 colloid 상태의 미세한 침전입자가 filtering media에 끼이게 되어 견고하면서도 상당한 부피를 가지는 filter cake을 형성하기 때문에 filtering에 많은 시간과 다량의 filtering agent (본 실험의 경우엔 증류수)가 필요하게 된다. 따라서 이러한 문제점을 해결하기 위하여 colloid 상태의 침전물을 얼렸다 녹이는 freezing process를 개발, 적용하여 그 원리 및 효과, 그로인한 분말형태를 관찰하여 보았다.