• Journal of Powder Materials
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• v.19 no.6
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• pp.429-434
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• 2012

With increase in operating temperature of gas turbine for higher efficiency, it is necessary to find new materials of TBC for replacement of YSZ. Among candidate materials for future TBCs, zirconate-based oxides with pyrochlore and fluorite are prevailing ones. In this study, phase structure and thermal conductivities of $(La_{1-x}Gd_x)_2Zr_2O_7$ oxide system are investigated. $(La_{1-x}Gd_x)_2Zr_2O_7$ system are comprised by selecting $La^{3+}/Gd^{3+}$ as A-site ions and $Zr^{4+}$ as B-site ion in $A_2B_2O_7$ pyrochlore structures. With powder mixture from each oxide, $(La_{1-x}Gd_x)_2Zr_2O_7$ oxides are fabricated via solid-state reaction at $1600^{\circ}C$. Either pyrochlore or fluorite or mixture of both appears after heat treatment. For the developed phases along $(La_{1-x}Gd_x)_2Zr_2O_7$ compositions, thermal conductivities are examined, with which the potential of $(La_{1-x}Gd_x)_2Zr_2O_7$ compositions for TBC application is also discussed.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.67-72
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• 2003

Graphite powders were coated with ZrO₂ by the controlled hydrolysis of a DI water, ethanol and DI water+ethanol solutions. The hydrolysis process was carried out with temperature control because of the low wettability of Zr ions to the surface of the graphite. PVA was added to the solution for the enhancement of metal ion adsorption. The surface of the graphite powders coated with ZrO₂ was observed by SEM and TEM. There are two types of ZrO₂ particles with the condition of ZrOCl₂°§8H₂O aqueous solutions were used; (a) primary particles a few nm in size and (b) secondary particles with ∼0.1 ㎛ size were obtained. The graphite powders coated in 50% ethanol-50% DI water solution of Zr(SO₄)₂ㆍ4H₂O have the relatively uniform coating layer and the starting temperature of oxidation was 100℃ higher than the raw graphite.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.8
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• pp.675-680
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• 2000

In this study the temperature coefficient of resonant frequency(TC $F_{r}$) dielectric and piezoelectric properties of Pb[(S $b_{1}$2//N $b_{1}$2/)$_{0.065}$)-(Z $r_{x}$, $Ti_{1-x}$ )$_{0.90}$] $O_3$ceramics were investigated with Zr/Ti ratio. The compositions near the morphotropic phase boundary (MPB) appeared when Zr/Ti ratio was 49.5/50.5 The dielectric constant and electromechanical coupling factor( $k_{p}$) also showed the highest values of 1,257, 0.653 respectively when the Zr/Ti ratio was 49.5/50.5 Moreover the mechanical quality factor( $Q_{m}$) showed th lowest value of 713 when the Zr/Ti ratio. The temperature coefficient of resonant frequency(TC $F_{r}$) abruptly change at the morphotropic phase boundary(MPB) which existed between the rhombohedral phase with highly negative TC $F_{r}$ of -106ppm/$^{\circ}C$ and the tetragonal phase with highly positive TC $F_{r}$ of +64pp $m^{\circ}C$ as Zr/Ti ratio varied from 50/50 to 49.5/50.5.50.5..50.5.

• Journal of Magnetics
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• v.21 no.2
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• pp.164-167
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• 2016

The effect of the B additions on glass formation and magnetic properties is reported for the $Fe_{(87-x-y)}Co_yTi_7Zr_6B_x$ (x = 2, 4, 6 and y = 35, 40) alloy system. The ribbon samples with the width of 2 mm for each composition were prepared by the melt spinning technique; furthermore, their phase information was obtained from X-ray diffraction. Glass formation and magnetic properties were measured using differential scanning calorimetry and vibrating sample magnetometer respectively. The $Fe_{45}Co_{40}Ti_7Zr_6B_2$ (x = 2 and y = 40) system has the nanocrystalline phase identified as ${\alpha}-Fe$, as well as the amorphous phase, whereas all other alloys are fully amorphous. It is associated with the role of B on the glass formation. The widest supercooled liquid region is obtained as 71 K at x = 4 (both y = 35 and 40). The saturation magnetization decreases with the increase of the amount of the B addition, and the highest value is 1.59 T as x = 2 and y = 35 for this alloy system.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.3-8
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• 1985

$ZrO_2$ single crystals were grown by slow cooling flux method using Borax $(Na_2B_4O_7)$ and KF as flux agent. The morphology of grown crystals was observed under a petrographic microscope. And the results obtained from grow crystals were as follows : 1. $ZrO_2$ crystals grown in the present work are morphologically divided into two shapes ; tabular and den-dritic crystals. 2. The maximum size of the crystals grown reaches to $4{\times}15{\times}2mm$ on edge into length at $ZrO_2$ 15mole% Borax 50mole% and KF 35mole% 3. $ZrO_2$ single crystals grown by flux method have monoclinc structure. 4. The content of KF as flux agents was limited by 60mole% KF. Since alumina crucible was heavily damaged by increasing KF content.

• Bulletin of the Korean Chemical Society
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• v.22 no.11
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• pp.1231-1235
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• 2001

Pseudotetragonal ZrO0.75S whose space group is P212121 was synthesized and the cell dimensions were a=5.110(2) $\AA$, b=5.110(7) $\AA$, and c=5.198(8) $\AA.$ The space group P212121 seems to be resulted from lowering the symmetry of cubic ZrOS structure with P213 space group by lattice distortion due to the oxygen defects. In the distorted structure, bond shortening between metal-nonmetal by reduction of cell volume and alternation of Zr-Zr distance were observed. Dielectric constant and loss data of the bulk material in temperature range -170 to 20 $^{\circ}C$ and frequency range 50 Hz to 1 MHz showed that there was dielectric transition at around -70 $^{\circ}C$ originated from the relaxation of Zr-S segment. Comparing with ZrO2 exhibited the dielectirc constants, 9.0 at room temperature, ZrO0.75S showed high dielectric constant, k = 200.2 at 100 kHz. The activation energy of relaxation time due to dielectric relaxation of Zr-S was 0.47 eV (11.3 kcal/mole). According to the impedance spectra, ZrO0.75S showed more parallel circuit character between the resistance and capacitance components at the temperature (-70 $^{\circ}C)$ that the Zr-S dielectric relaxation was observed.

• Korean Journal of Materials Research
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• v.10 no.5
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• pp.343-349
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• 2000

Fabrication of various carbide fibers from carbon fibers and elementary powders of Ti, Zr, Nb, Zi, W, B, and Mo by self-propagating high temperature synthesis was attempted. It was found the almost pure phase of TiC, ZrC, NbC, SiC, $B_4$C, and $Mo_2$C carbides were successfully produced. The three types of morphologies were ob-served, TiC, ZrC, NbC, and $B_4$C had a hollow-type fibrous shape. SiC had fiber shape consisting of smaller particles and fine whiskers. WC and $Mo_2$C had non-fibrous shapes. The reason for the different morphologies was explained. The formation mechanism of hollow fibers was suggested.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.491-495
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• 1995

The crystallization behaviors and magnetic properties for $Fe_{81-x}Al_{4}B_{10}Zr_{5}Cu_{x}$ (x=0, 1, 2 at%) alloys is investigated. By the addition of 1~2 Cu, the temperature range, where a single bcc phase exists, expands largely over 200 K and the grain size of bcc phase represents to less than 10 nm. For the optimally annealed Cu-added alloys, the high $\mu_{e}$ (1 kHz) above 20000 combined with the high $B_{10}$ of about 1.4 T is obtained in nanocrystalline state. The low core loss of 95.8 W/kg at 0.1 T and 100 kHz is confirmed for the nanocrystalline $Fe_{80}Al_{4}B_{10}Zr_{5}Cu_{1}$ alloy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.259-259
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• 2007

The low temperature sintering of dolomite type borates, $CaZr(BO_3)_2$[CZB] ceramics and their microwave dielectric properties were investigated The sintering temperature of CZB ceramics could be reduced from $1150^{\circ}C$ to $925^{\circ}C$ by the addition of sintering additive. $CaZrO_3$, $ZrO_2$ and $CaB_2O_4$ second phases were found in the CZB ceramics. The syntheses, sintering properties, microstructures, and dielectricnproperties of dolomite-type borates were examined by XRD, thermal analysis, electron microscopy, network analyzer, and the results are discussed intensively. The compatibility with silver electrode was also explored.

• Macromolecular Research
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• v.12 no.3
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• pp.316-321
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• 2004

We have performed copolymerizations of ethylene with 1-hexene using various ansa-metallocene compounds in the presence of the non-coordinative [CPh$_3$][B(C$\_$6/F$\_$5/)$_4$ion pair as a cocatalyst. The metallocenes chosen for this study are isospecific metallocene diamide compounds, rac-(EBI)Zr(NMe$_2$)$_2$ [1, EBI = ethylene-l ,2-bis(1-indenyl)], rac-(EBI)Hf(NMe$_2$)$_2$ (2), rac-(EBI)Zr(NC$_4$H$\_$8/)$_2$ (3), and rac-(CH$_3$)$_3$Si(1-C$\_$5/H$_2$-2-CH$_3$-4-$\^$t/C$_4$H$\_$9/)2 Zr(NMe$_2$)$_2$ (4), and syndiospecific metallocene dimethyl compounds, ethylidene(cyclopentadienyl)(9-fluorenyl) ZrMe$_2$ [5, Et(Flu)(Cp )ZrMe$_2$] and isopropylidence (cyclopentadienyl)(9-fluorenyl)ZrMe$_2$ [6, iPr(Flu)(Cp)ZrMe$_2$]. The copolymerization rate decreased in the order 4 ＞1-3＞2 ＞5＞6. The reactivity of I -hexene decreased in the order 2 ＞6＞1- 3-5＞ 4. We characterized the microstructure of the resulting poly(ethylene-co-l-hexene) by $\^$l3/C NMR spectroscopy and investigated various other properties of the copolymers in detail.