• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1994.04a
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• pp.23-26
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• 1994

130mm D.B. 추진기관의 고온 시험에서 나타난 극심한 이상 연소 현상을 해결하기 위해 미세한 고체 입자들을 연소 가스에 분산시켜 불안정 연소를 억제하는 particulate damping 효과를 연구하였다. 고체 입자로서 효과적인 것으로 알려진 $K_2$$SO_4$. ZrC, Graphite를 CTPB, HTPB 고분자 물질에 충진시켜 epoxide, isocyanate 반응기와 가교 반응을 일으킴으로써 고무상의 탄성체 성질을 갖게 하는 $K_2$$SO_4$/CTPB, ZrC/Graphite/HTPB, ZrC/Graphite/AP/HTPB, ZrC/AP/HTPB 조성의 연소 안정제를 개발하였다. 이 연소 안정제는 외경 17mm, 길이 1000mm의 안정봉 형태로 제작하여 모타의 중심 cavity에 조립한 후 지상 연소 시험을 통하여 성능을 확인하였다. 시험 결과, 조성에 AP를 포함시켜 연소 안정제에 일정한 연소 속도를 부여하여 추진제 grain 연소 동안 고체 입자를 연소 가스에 분산되게 설계한 ZrC/Graphite/AP/HTPB, ZrC/AP/HTPB 조성의 연소 안정제가 불안정 연소 억제에 효과적인 것으로 나타났다.

• Journal of Powder Materials
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• v.25 no.2
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• pp.151-157
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• 2018

In this study, the compound $Li_3BO_3$ (LBO) is intended to be prepared by a polymeric complex method as a sintering aid for the densification of $Li_7La_3Zr_2O_{12}$ (LLZ) solid electrolyte. A polymeric precursor containing Li and B is heat-treated in an air atmosphere at a temperature range between $600^{\circ}C$ and $800^{\circ}C$. Instead of LBO, the compound $Li_{2+x}C_{1-x}B_xO_3$ (LCBO) is unexpectedly synthesized after a heat-treatment of $700^{\circ}C$. The effect of LCBO addition on sintering behavior and ion conductivity of LLZ is studied. It is found that the LCBO compound could lead to significant improvements in the densification and ionic conductivity of LLZ compared to pure LLZ. After sintering at $1100^{\circ}C$, the density of the LLZ-12wt%LBO composite is $3.72g/cm^3$, with a high Li-ion conductivity of $1.18{\times}10^{-4}Scm^{-1}$ at $28^{\circ}C$, while the pure LLZ specimen had a densify of $2.98g/cm^3$ and Li-ion conductivity of $5.98{\times}10^{-6}Scm^{-1}$.

• Journal of the Korean Ceramic Society
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• v.23 no.3
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• pp.21-26
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• 1986

In this study the system of $Pb(Mn_{1/3} Nb_{2/3})O_3-PbTiO_3-PbZrO_3$ piexoelectric ceramics was made in the radial mode disk and attenuation characteristic of the desinged ladder type filter was investigated. What is more temperature dependance of resonant frequency and variation of resonant frequency was examined by chan-ging the electrode diameter of piezoelectric resonator. (A Group : De=11mm, B Group : De=7.5mm and C Gro-up : De=5.5mm) Upon investigation it was the following. The center frequency of A, B and c filter showed up in the 200KHz, 270KHz and 380KHz respectively. As the electrode diameter decreased center frequency in creased abruptly. As the Co_2/Co1 increased attenuation characteristics and selectivity was improved. As the x=50. resonant frequ-ency invaried with variation of temperature.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.471-478
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• 2011

Investigations of crystal structure and phase transition of $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics doped with A-site substitution impurity (La, Nd) or B-site substitution impurity (Sb, Nb) at 2 mol% concentration were carried out. X-ray diffraction patterns of impurities doped $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics have been measured at pressures up to ~5 GPa with diamond anvil cell and synchrotron radiation. The patterns were obtained at room temperature using methanol-ethanol mixture as pressure-transmitting media. In order to refine the crystal structure, Rietveld analysis has been performed. The structures of impurities doped $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics are tetragonal in space group P4mm at ambient pressure and are transformed into a cubic phase in space group Pm$\bar{3}$m as the pressure increases. In this study, when A-site substitution donor $La^{3+}$ or $Nd^{3+}$ ion was added to $Pb(Zr_{0.52}Ti_{0.48})O_3$ ceramics, the phase transition phenomena showed up at the pressure of 2.5~4.6 GPa, but when B-site substitution donor $Nb^{5+}$ or $Sb^{5+}$ ion was added to it, the phase transition appeared at relatively lower pressure of 1.7~2.6 GPa.

• Composites Research
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• v.30 no.2
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• pp.94-101
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• 2017

Ultra-high temperature ceramics (UHTC) such as $ZrB_2$, ZrC, $HfB_2$, HfC and TaC has been recently actively investigated for the application as components such as nose-cone, rocket nozzle and leading edge of hypersonic systems. However, the application has been limited by various reasons. The brittleness of the materials and consequent low thermal shock resistance is one of the reasons. The property can be improved through the fabrication of ceramic matrix composites. In this paper, the concept of UHTC and the fabrication process and testing of UHTC-based ceramic matrix composites (UHTC-CMC) were briefly reviewed. Also, international activities regarding the fabrication of UHTC-CMC were summarized and a UHTC-CMC project, which was performed in Korea, was introduced.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.306-310
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• 1992

Effects of hafnium, boron and zirconium on the ductility of Ni$_3$(Al, Fe) intermetallic compounds were studied using tensile test and SIMS analysis. Ni$_3$(Al, Fe) alloy with 0.1 at.% Hf, 0.05 at.% B and 0.1 at.% Zr additions showed maximum elongations of about 30% at 300K, 10% at 300K and 14% at 473K, respectively. The fracture mode of the alloy without the additive was the mixture of intergranular and transgranular fractures, but the addition of Hf, Zr or B changed the fracture mode to transgranular only. SIMS analysis showed that the beneficial effects of Hf, Zr or B segregation on the grain boundary strength are consistent with the grain boundary cohesion theory.

• The Korean Journal of Ceramics
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• v.2 no.2
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• pp.76-82
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• 1996

PLZT ceramics having two nominal compositions, $Pb_{1-3x/2}La_xV_{x/2}(Zr_{03}Ti_{03})O_3$ and $Pb_{1-x}La_x(Zr_{0.2}Ti_{0.5})_{1-x/4}V_{x/4}O_3$ (V: vacancy) with x=0.00~0.30, were prepared. The physical, structural, and dielectric properties were investigated by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and measurements of bulk density and dielectric constant. The two series with A-stie and B-site vacancies showed different physical, structural, dielectric properties, and, specially, Curie temperature. In comparison to PLZT with B-site vacancies, PLZT with A-site vacancies showed high Curie temperatures and low maxima of dielectric constant. Consequently, it is evident that the properties of PLZT ceramics depend on the vacancy formula adopted as a batch composition in preparation.

• Journal of Magnetics
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• v.4 no.1
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• pp.1-4
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• 1999

The microstructure and magnetic properties of$ Fe_{87}Zr_7Si_4B_2$ nanocrystalline alloys were studied by magnetization measurements and M ssbauer spectrometry over a wide temperature range. Three well resolved spectral components have been found and attributed to bcc-Fe grains (with almost pure iron structure), residual amorphous matrix enriched with solute elements and interfaces formed at the grain-matrix boundaries. It has been shown that, contrary to the expectation, during crystallization the atomic segregation occurs leading to the formation of primary bcc-Fe grains and the partition of Si atoms into the residual amorphous matrix.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.45-48
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• 1997

ZrO$_2$ coated flake graphite powders were prepared by the controlled hydrolysis of zirconium oxichloride. The stirring process plays an important role in the coating process. There are two types of coated ZrO$_2$ particles: (a)primary particles with few nm size were obtained by the direct formation of the shell by precipitation of the surface of the graphite and (b) Secondary particles of ZrO$_2$ with ∼0.1$\mu\textrm{m}$ size were obtained by the independent formation of primary particles ZrO$_2$ and subsequent heterocoagulation at the graphites surface.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.1-6
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• 1996

A single phase Ba2(Ti8,472Zr0.528)O20 was prepared by the oxalate method from aqueous solution of BaCl2 TiCl4 and ZrOCl2. The structure ananlysis has been carried out by Rietveld analysis method at room temperature. Powder X-ray data of Ba2(Ti8,472Zr0.528)O20 was indexed with the triclinic lattice(a=7.4587 $\AA$ b=14.0672 $\AA$, c=13.3327 $\AA$, $\alpha$=89.87, $\beta$=79.45 ${\gamma}$=84.46) The R (Residual) values of structure refinement were in a range between 10.00 and 8.00 This analysis proved that the added Zr occupied Ti sites in th structure of Ba2Ti9O20. Ba2(Ti8,472Zr0.528)O20 has excellent dielectric properties(dielectric constant K=40.49 at 5.42 GHz Q=4621) so that it can be used as good microwave dielectric materials.