• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.995-1004
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• 1994

Phase relation and microwave dielectric properties of the system BaO.(Nd1-xSmx)2O3.TiO2 (n=4, 5) were studied. With n=5 (1 : 1 : 5), Ba2Ti9O20 and TiO2 formed in case of X$\leq$0.7, and Ba2Ti9O20 and Sm2Ti2O7 formed at X=1.0 as the second phases dispersed in fine-grained orthorhombic matrix phase. With n=4 (1 : 1 : 4). on the contrary, only fine grains of an ortho-rhombic phase were observed irrespective of Nd/Sm ratio. The compositions of these two stable orthorombic phases having distinct lattic constants even with the same Nd/Sm ratio were estimated as 4BaO.5(Nd1-xSmx)2O3.18TiO2 and BaO.(Nd1-xSmx)2O3.4TiO2 with n=5 and n=4 in the system BaO.(Nd1-xSmx)2O3.TiO2, respectively. Consequently the composition BaO.(Nd1-xSmx)2O3.5TiO2 lies in the compatible triangle of 4BaO.5(Nd1-xSmx)2O3.18TiO2 and the second phases mentioned above. The microwave dielectric properties (~4 GHz) of BaO.(Nd1-xSmx)2O3.5TiO2 can be controlled effectively by adjusting Sm content : with increasing X from 0 to 0.7, both dielectric constant and the temperature coefficient of resonant frequency decreased monotonically from 82 to 65 and from 91 (ppm/$^{\circ}C$) to -19(ppm/$^{\circ}C$), respectively, while unloaded Q(Qo) remained constant at about 2,600.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.06a
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• pp.285-291
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• 2004

As a part of assessment of the structural material for the molten salt handling system, corrosion behavior of Inconel 718, X-750, Haynes 75 and Haynes 263 alloys in the molten salt of LiCl-Li$_2$O-O$_2$was investigated in the range of temperature; $650^{\circ}C$, time; 24~168h, $Li_2O$; 3wt%, mixed gas; Ar~10%$O_2$. In the molten salt of LiCl-$Li_2O-O_2$, the order corrosion rate was Haynes 263 ＜ Haynes 75 ＜ Inconel X-750 ＜ Inconel 718. Haynes 263 alloy showed the highest corrosion resistance among the examined alloys. Corrosion products of alloys were as fellows: Haynes 75: $Cr_2O_4$, $NiFe_2O_4$, $LiNiO_2$, $Li_2NiFe_2O_4$, Inconel 718; $Cr_2O_4$, $NiFe_2O_4$, Haynes 263; $Li(Ni,Co)O_2$, $NiCr_2O_4$, $LiTiO_2$, Inconel X-750; $Cr_2O_3$, $NiFe_2O_4$,$FeNi_3$, (Al,Nb,Ti)$O_2$. Haynes 263 showed local corrosion behavior and Haynes 75, Inconel 718 and Inconel X-750 showed uniform corrosion behavior.

• Journal of the Korean Applied Science and Technology
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• v.34 no.4
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• pp.746-755
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• 2017

In this study, $CeO_2/TiO_2$ nanoparticle with structure of core and shell was synthesized by growing $TiO_2$ onto the surface of $CeO_2$ according to hydrolysis of $Ti(SO_4)_2$. Reaction time, temperature, concentration of $CeO_2$ slurry, pH control of $Ti(SO_4)_2$ were optimized about synthesis of $CeO_2/TiO_2$ core-shell nanoparticle. It was found that optimal mole ratio range of $CeO_2:TiO_2$ was 1:0.2~1.1, the optimal concentration of $CeO_2$ slurry was 1 %, and the optimal reaction temperature was $50^{\circ}C$. The optimal concentration of $CeO_2$ slurry could be increased up to 10 % by adjusting the pH of $Ti(SO_4)_2$ to 1 using $NH_4OH$ and adding to $CeO_2$ slurry. If reaction was carried at $80^{\circ}C$ or higher, the separated $TiO_2$ particles were obtained instead of $CeO_2/TiO_2$ core-shell nanoparticles. The optimal reaction temperature was $50^{\circ}C$ at which good shaped core-shell structure of $CeO_2/TiO_2$ was obtained.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.2
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• pp.70-76
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• 2014

$Zn_2TiO_4$, using an anatase form of $TiO_2$ on zinc crystalline glaze, was shown as effective nuclear agent. Thus the effects on glaze were studied with synthesized $Zn_2TiO_4$ at low temperature. First, the chromophore elements were employed in synthesized $Zn_2TiO_4$ then add them in the zinc crystalline glaze. Crystal creation and development of color by $Zn_2TiO_4$ addition on the zinc crystalline glaze were more effective. Addition of $Zn_2TiO_4$, which is developed in low range temperature, is effected as zinc crystalline nuclear in the willemite glaze. When 5 wt% of synthesized $Zn_2TiO_4$ was added to the willemite glaze, nuclear creation increases and steadily retains. Therefore addition of respectively doped $Zn_2TiO_4$ with CoO, NiO, and CuO would increase doped effects in the glaze, various color willemite crystal were obtained.

• Journal of the Korean Ceramic Society
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• v.14 no.3
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• pp.187-192
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• 1977

For the purpose researching to the influence of tetrahedral and octahedral preference of cations of $Ni^{2+}$, $Ti^{4+}$ upon the formation and the color development of the $ZnO-SnO_2$ spinel containing $Ni^{2+}$ and $Ti^{4+}$ ions, the gradual substitution of $Ni^{2+}$ ions for $Zn^{2+}$ ions and of $Ti^{4+}$ ions for $Sn^{4+}$ ions of the spinel in NiO-ZnO-$SnO_2$-$TiO_2$ system was carried out. On samples prepared by calcining the oxide and basic cabonate mixtures at $1300^{\circ}C$ for 2 hours, the X-ray analysis, measurement of reflectance and the test of their stabilaity as a glaze pigment were also carried out. The results are summarized as follows 1) Single spinel was formed completely to x=1 in the $xNiO\cdot(2-x)ZnO\cdot{SnO}_2$system, and gave brilliant lightgreen hue. Moreover, $NiO\cdot{ZnO}\cdot{SnO}_2$ formed easily spinel than $NiO\cdot{MgO}\cdot{SnO}_2$ because Zn^{2+}$ ions had more strong tetrahedral preference than $Mg^{2+}$ ions. 2) As the gradual substitution of $Ti^{4+}$ ions for $Sn^{4+}$ ions in $NiO\cdot{MgO}\cdot{SnO}_2$ system, the spinels formed well and was nearly not changed in the hue. 3) The results of glaze test. (1) As the gradual substitution of $Ni^{2+}$ ions for $Zn^{2+}$ ions, the color changed from dull white to graish broun gradually in calcium-zinc glaze and calcium glaze, and from white to beige in tile glaze. (2) As the gradual substitution of $Ti^{4+}$ ions for $Sn^{4+}$ ions in $NiO-ZnO-SnO_2-TiO_2$ system, the color was become dull generally and was not change in tile glaze.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1541-1543
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• 2003

The microwave dielectric properties of $0.6Mg_4Ta_2O_9-0.4TiO_2$ ceramics were investigated. All sample of $0.6Mg_4Ta_2O_9-0.4TiO_2$ ceramics were prepared by the conventional mixed oxide method, and sintered in the temperature of $1350^{\circ}C{\sim}1450^{\circ}C$. The structural properties of $0.6Mg_4Ta_2O_9-0.4TiO_2$ ceramics were investigated by the X-ray diffraction meter. According to the X-ray diffraction patterns of $0.6Mg_4Ta_2O_9-0.4TiO_2$ ceramics, the major phase of the hexagonal $0.6Mg_4Ta_2O_9-0.4TiO_2$ were presented, In the case of $0.6Mg_4Ta_2O_9-0.4TiO_2$ ceramics sintered at $1400^{\circ}C$ for 5hr., the dielectric constant, quality factor and temperature coefficient of resonant frequency were 12.19, 109.411GHz, -17.21ppm/$^{\circ}C$, respectively.

• Journal of Powder Materials
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• v.21 no.5
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• pp.377-381
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• 2014

This work describes the coloration, chemical stability of $SiO_2$ and $SnO_2$-coated blue $CoAl_2O_4$ pigment. The $CoAl_2O_4$, raw materials, were synthesized by a co-precipitation method and coated with silica ($SiO_2$) and tin oxide ($SnO_2$) using sol-gel method, respectively. To study phase and coloration of $CoAl_2O_4$, we prepared nano sized $CoAl_2O_4$ pigments which were coated $SiO_2$ and $SnO_2$ using tetraethylorthosilicate, $Na_2SiO_3$ and $Na_2SiO_3$ as a coating material. To determine the stability of the coated samples and their colloidal solutions under acidic and basic conditions, colloidal nanoparticle solutions with various pH values were prepared and monitored over time. Blue $CoAl_2O_4$ solutions were tuned yellow color under all acidic/basic conditions. On the other hand, the chemical stability of $SiO_2$ and $SnO_2$-coated $CoAl_2O_4$ solution were improved when all samples pH values, respectively. Phase stability under acidic/basic condition of the core-shell type $CoAl_2O_4$ powders were characterized by transmission electron microscope, X-ray diffraction, CIE $L^*a^*b^*$ color parameter measurements.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.314-319
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• 2000

Microstructueral development and electrical properties in ZnO-Bi2O3-ZnAl2O4 system were investigated with ZnAl2O4 content(0.1~1.0 mol%). The shrinakge of specimens started around $700^{\circ}C$ and finished at 110$0^{\circ}C$, reaching a maximum shrinkage rate at 80$0^{\circ}C$. The shrinkage rate is strongly related to the fromation of a Bi-rich liquid. The increase of the ZnAl2O4 content inhibited the grain growth of ZnO. Most of ZnAl2O4 particles located at the grain boundaries were about 2~3${\mu}{\textrm}{m}$. ZnO grain size changed little up to 110$0^{\circ}C$, but increased markedly above 115$0^{\circ}C$, especially at lower ZnAl2O4 content. Drastic decreasing in breakdown voltage(Vb) with increasing temperature is expected to be dependent on the ZnO grain size and the distribution of the largest grains between the electrode. The nonlinear I-V characteristic was significantly influenced by the ZnAl2O4 content, which exhibited a maximum value at about 15${\mu}{\textrm}{m}$ of ZnO grain size.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.4
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• pp.756-760
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• 2007

The $(1-x)Mg_4Ta_2O_9-xwt%TiO_2\;(x=5\sim20)$ microwave dielectric ceramics were prepared by solid-state reaction method and sintered at $1450^{\circ}C$. According to the X-ray diffraction data, the $Mg_4Ta_2O_9-xwt%TiO_2$ ceramics had main phase of $Mg_4Ta_2O_9$ and $MgTi_2O_5$ peaks were added by increasing of $TiO_2$ addition. Microwave dielectric properties of the $Mg_4Ta_2O_9-xwt%TiO_2$ ceramics were influenced by $MgTi_2O_5$ phase and properties of $TiO_2$. There was a little decrement of the quality factor from 116,800GHz of pure $Mg_4Ta_2O_9$ to 100,100GHz of 15wt% $TiO_2$ added one. But there was excellent improvement in temperature coefficient of the resonant frequency (TCRF) by addition of 15wt% $TiO_2$. The dielectric constant quality factor and TCRF of the $Mg_4Ta_2O_9-xwt%TiO_2$ ceramics sintered at $1450^{\circ}C$ were $13.08\sim16.41,\;45,000\sim165,410GHz,\;-24.82\sim+3.88ppm/^{\circ}C$, respectively, depending on the value of x. Simulated dielectric resonator (DR) with $Mg_4Ta_2O_9-15wt%TiO_2$ ceramics had the operating frequency of 11.97GHz and $S_{2,1}$ of -35.034dB.

• Journal of the Korean Ceramic Society
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• v.35 no.11
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• pp.1130-1140
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• 1998

Thin films of $Bi_4Ti_3O_{12}\;nBaTiO_3(n=1&2)$ were prepared using sols erived Ba-Bi-Ti complex alkoxides. The sols were spin-cast onto $Pt/Ti/SiO_2/Si$ substrates and followed by pyrolysis for 1 hr at $620^{\circ}C,\;700^{\circ}C\;and\;750^{\circ}C$ In the thin films a pyrochlore phase seemed to be formed at a lower temperature and then tran-formed to the layered perovskite phase as the heating temperature increased. In the thin films pyrolyzed at formed to the layered perovskte phase as the heating temperature increased. In the films pyrolyzed at $750^{\circ}C$ the amount of $Bi_4Ti_3O_{12}{\cdot}BaTiO_3$ reached to 94% while $Bi_4Ti_3O_{12}{\cdot}BaTiO_3$ was 77% in composition. This result shows that the formation of the layered pervoskite phase becomes difficult as the amount of complexing $BaTiO_3$ increases. The microstructures and the electrical properties of the thin films were gen-erally improved with the incease of the heating temperature. However the presence of the pyrochlore phase could not be removed effectively. Our study showed that the electrical properties of $Bi_4Ti_3O_{12}{\cdot}BaTiO_3$ were pronouncedly improved with complexing with BaTiO3 when compared to those of $Bi_4Ti_3O_{12}$ while the presence of the pyrochlore phase was detrimental to the those of $Bi_4Ti_3O_{12}{\cdot}2BaTiO_3$.