• 한국해양공학회지
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• 제27권2호
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• pp.8-12
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• 2013

Four kinds of silicon nitride composites with tri-laminate structure were prepared by stacking tapes with aligned ${\beta}-Si_3N_4$ whisker seeds. The composites were fabricated using a modified tape casting method for enhanced alignment of the whisker seeds. The relative densities of all four samples reached 99% at room temperature. The three-point flexural strengths of the samples according to the stacking sequences were measured at both room temperature and 1723 K. The high temperature strength of sample WWW was $457{\pm}14$ MPa. The fracture of sample WWW occurred mainly along the grain boundary. The room temperature strengths of samples OOO, OWO, WOW, and WWW were $430{\pm}32$ MPa, $470{\pm}19$ MPa, $700{\pm}14$MPa, and $940{\pm}14$ MPa, respectively.

• 한국결정성장학회지
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• 제24권3호
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• pp.127-132
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• 2014

$Y_2O_3$-BN 세라믹 복합체를 제작하기 위해서, 분말 입도 $3{\sim}10{\mu}m$인 $Y_2O_3$ 분말을 분산한 슬러리에 pH 조절제인 NaOH를 첨가하였으며 결합제로는 PVA, 가소제로는 PEG를, BN 분말과 혼합하고, 분무건조(spray drying)공정을 거쳐 $Y_2O_3$ 혼합 분말을 제조하였다. ${\O}14mm$ 크기의 $Y_2O_3$-BN 시편을 성형하고, $1550^{\circ}C$ 및 $1600^{\circ}C$에서 소결하여 $Y_2O_3$-BN 복합체를 제작하였다. BN 투입량과 소결온도의 변수에 따른 미세구조, 순도, 꺽임강도, 열팽창계수, 밀도, 체적저항, 내플라즈마 특성을 조사하였다.

• 한국세라믹학회지
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• 제39권2호
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• pp.145-152
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• 2002

상용 알루미나 분말(0.5, 2.8, 12, 45 ${\mu}m$)을 die-press법을 이용하여 1120$^{\circ}C$에서 2시간 1차 소결하여 다공성 전성형체를 제조하고 1100$^{\circ}C$에서 0∼2시간까지 $La_2O_3-Al_2O_3-SiO_2$계 유리를 용융 침투시켜 유리 침투 깊이와 침투 시간간의 kinetic을 조사하였다. 침투시간이 증가할수록 유리 침투깊이는 Washburn 식의 포물선 관계를 가지면서 증가하였으며 침투 상수인 K는 알루미나 입도가 증가할수록 증가하였다. 유리-알루미나 복합체의 강도값은 2.8${\mu}m$ 알루미나가 분산된 복합체까지 충진률의 증가로 인하여 증가하다가 알루미나 입도가 증가할수록 감소하였다. 파괴인성은 알루미나 입도가 증가할수록 균열 휨 현상과 균열과 알루미나 입자간 결합에 의하여 증가하였다.

• 한국세라믹학회지
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• 제40권8호
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• pp.751-757
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• 2003

10 wt% A1$_2$O$_3$-Y$_2$O$_3$-CaO를 첨가한 SiC-30 wt% TiC 분말을 스파크 플라즈마 소결(SPS) 방법을 사용하여 급속 치밀화 하였다. SPS 공정은 매우 빠른 승온 속도와 짧은 시간에 완전 치밀한 시편을 얻을 수 있다. 본 실험에서, 승온 속도와 압력은 $100^{\circ}C$/min과 40MPa이고, 소결 온도 범위는$1600^{\circ}C$~$1800^{\circ}C$이었으며, 10min 동한 유지하였다. $Al_2$O$_3$, $Y_2$O$_3$ 및 CaO를 첨가한 SiC-30 wt% TiC 복합체는 $1700^{\circ}C$ 이상 온도에서 스파크 플라즈마 소결 방법으로 완전 치밀화가 이루어졌다. 모든 SPS 공정 온도에서 탄화큐소으 상전이나 YAG 결정상의 형성 없이 3C-SiC와 TiC 만이 XRD에서 나타났다. 급속 소결한 SiC-30 wt% TiC 복합체의 미세구조는 비교적 작은 등축상 SiC 결정립과 비교적 큰 TiC 결정립으로 구성되었다. $1750^{\circ}C$에서 제조한 시편의 이축강도능 635.2MPa이고, 파괴인성은 6.12 MPaㆍ$m^{1/2}$이었다.

• 한국세라믹학회지
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• 제38권10호
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• pp.914-920
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• 2001

새로운 소결법인 방전플라즈마소결법(SPS: Spark Plasma Sintering)으로 제조된 $ZrB_2$-ZrC 복합체의 결정립 방위분포 및 결정입계의 특성을 EBSP(Electron Back-Scattered Pattern)법으로 분석하여 상압소결법(PLS, Pressureless Sintering)에 의한 시편과 비교하였다. 방전플라즈마 소결법으로 제조된 시편의 $ZrB_2$ 결정립은 상압소결된 시편과는 다르게 (0001)면이 시편표면에 수직한 배향(normal direction)을 나타냈으며, ZrC 결정립은 두 경우 무질서한 배향을 나타냈다. 결정입계 특성 분석에서 low angle $(<15^{\circ})$의 분포는 상압소결법인 경우 전체 입계 중 약 10%, 방전플라즈마 소결법은 8%로 두 소결체에서 큰 차이를 보이지 않았으나, CSL(Coincident Site Lattice) 입계의 분포에서는 방전플라즈마 소결법으로 제조된 복합체에서 $\Sigma$ 3,5,7,9,11의 CSL 분포가 상압소결법에 비해 높은 분율을 나타냈다.

• 한국세라믹학회지
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• 제40권1호
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• pp.37-45
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• 2003

$BaTiO_3$의 Ba 자리에 Ca, Ti 자리에 Zr을 첨가한 $(B a_{1-x}Ca_x)(Ti_{0.96-y}Zr_{y}Sn_{0.04})O_3$ $(0.15 {\leq} x{\leq}0.20,\; 0.09{\leq}y{\leq}$0.14) 조성에 2차상 형성을 유도하여 복합체를 만든 후 유전 및 소결 특성을 조사하였다. Ca량이 15mol% 이상 첨가됨에 따라 $CaTiO_3$를 주성분으로 하는 2차상이 석출하여 복합체가 형성되었으며, Ca량의 증가에 따라 2차상 분율이 증가하였다. Ca량의 증가는 큐리 온도를 mol%당 $1.7^{\circ}C$ 감소시키며, 저유전율 2차상의 영향으로 Ca량 증가에 따라 최대 유전율은 mol%당 200 감소하였다. Zr 첨가는 큐리온도를 mol%당 $10^{\circ}C$ 감소시키며, 확산형 상전이 현상을 증가시켜 최대 유전율을 217 감소시켰다. 2차상의 증가에 의하여 비정상 입성장이 억제되어 소결밀도, 내전압 특성이 향상되었으며, Zr 첨가에 의하여 커패시턴스의 온도 안정성을 제어하여 EIA 규격을 만족하는 고압, 고유전율 Y5U 콘덴서 조성을 개발하였다.

• 한국전기전자재료학회논문지
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• 제32권5호
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• pp.418-425
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• 2019

A piezoelectric ceramic fiber composite (PCFC) was successfully fabricated using $0.69Pb(Zr_{0.47}Ti_{0.53})O_3-0.31[Pb(Zn_{0.4}Ni_{0.6})_{1/3}Nb_{2/3}]O_3$ (PZT-PZNN) for use in small-scale wind energy harvesters. The PCFC was formed using an epoxy matrix material and an array of Ag/Pd-coated PZT-PZNN piezo-ceramic fibers sandwiched by Cu interdigitated electrode patterned polyethylene terephthalate film. The energy harvesting performance was evaluated in a custom-made wind tunnel while varying the wind speed and resistive load with two types of flutter wind energy harvesters. One had a five-PCFC array vertically clamped with a supporting acrylic rod while the other used the same structure but with a five-PCFC cantilever array. Stainless steel (thickness: $50{\mu}m$) was attached onto one side of the PCFC to form the PZT-PZNN cantilever. The output power, in general, increased with an increase in the wind speed from 2 m/s to 10 m/s for both energy harvesters. The highest output power of $15.1{\mu}W$ at $14k{\Omega}$ was obtained at a wind speed of 10 m/s for the flutter wind energy harvester with the PZT-PZNN cantilever array. The results presented here reveal the strong potential for wind energy harvester applications to supply sustainable power to various IoT micro-devices.

• 한국분말재료학회지
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• 제30권5호
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• pp.409-414
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• 2023

YSZ (Y₂O₃-stabilized zirconia)-based ceramics have excellent mechanical properties, such as high strength and wear resistance. In the application, YSZ is utilized in the bead mill, a fine-grinding process. YSZ-based parts, such as the rotor and pin, can be easily damaged by continuous application with high rpm in the bead mill process. In that case, adding WC particles improves the tribological and mechanical properties. YSZ-30 vol.% WC composite ceramics are manufactured via hot pressing under different pressures (10/30/60 MPa). The hot-pressed composite ceramics measure the physical properties, such as porosity and bulk density values. In addition, the phase formation of these composite ceramics is analyzed and discussed with those of physical properties. For the increased applied pressure of hot pressing, the tetragonality of YSZ and the crystallinity of WC are enhanced. The mechanical properties indicate an improved tendency with the increase in the applied pressure of hot pressing.

• 한국재료학회지
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• 제34권3호
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• pp.175-183
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• 2024

Geopolymer, also known as alkali aluminum silicate, is used as a substitute for Portland cement, and it is also used as a binder because of its good adhesive properties and heat resistance. Since Davidovits developed Geopolymer matrix composites (GMCs) based on the binder properties of geopolymer, they have been utilized as flame exhaust ducts and aircraft fire protection materials. Geopolymer structures are formed through hydrolysis and dehydration reactions, and their physical properties can be influenced by reaction conditions such as concentration, reaction time, and temperature. The aim of this study is to examine the effects of silica size and aging time on the mechanical properties of composites. Commercial water glass and kaolin were used to synthesize geopolymers, and two types of silica powder were added to increase the silicon content. Using carbon fiber mats, a fiber-reinforced composite material was fabricated using the hand lay-up method. Spectroscopy was used to confirm polymerization, aging effects, and heat treatment, and composite materials were used to measure flexural strength. As a result, it was confirmed that the longer time aging and use of nano-sized silica particles were helpful in improving the mechanical properties of the geopolymer matrix composite.

• 한국세라믹학회지
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• 제37권5호
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• pp.479-490
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• 2000

The microstructure of Ni-YSZ composite as an anode of SOFC was investigated as a function of Ni content(10-70 vol%) in order to examine the correlation between microstructural-and electrical property. Image analysis based on quantitative microscopy theory was performed to quantify the microstructural property. We could get the informations about the size and distribution, contiguity and interfacial area of each phase or between the phases from the image analysis. According to the image analysis, contiguity between the same phae was mainly dependent on the amount of the phase while the contiguity between different phases was additionally influenced by the microstructural changes, especailly by the coarsening of the Ni phase. The whole length of pores perimeter was increased as Ni content increased, which indicated the overall microstructural evolution was mostly related with the coarsening of Ni phase. Ni-Ni interfacial area was also gradually increased as Ni content increased but controlled by pore phase at low Ni content region and by YSZ phase at intermediate Ni content region. These quantified microstructural properties were used to characterize the electrical properties of Ni-YSZ composite.