• Journal of the Korean Ceramic Society
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• v.28 no.5
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• pp.399-405
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• 1991

Mullite-PSZ powders were synthesized by the sol-gel process using Al(sec-OC4H9)3, Si(OC2H5)4, ZrOCl2$.$8H2O and YCl3 solution and the characteristics of synthesized powders were studied. The sinterability and mechanical properties of powder compacts sintered at 1670$^{\circ}C$ for 4hr were also studied for various PSZ contents. ${\gamma}$-Al2O3(Al-Si spinel) formed at 980$^{\circ}C$ from amorphous dried gel, and mullite as well as ZrO2 formed above 1200$^{\circ}C$. At the room temperature, ZrO2 was a mixture of tetragonal and monoclinic phases. The specimens were densified to 97∼98% except the specimen containing 25 vol% PSZ which showed the relative density of 94%. The K1c value increased with the PSZ content and showed a maximum value of 4.1 MN/m3/2 at 25 vol% PSZ; this value was about 50% higher than that of the mullite without PSZ. Flexural strength had a maximum value of 280 Mn/㎡ at 20 vol% PSZ. In contrast, at 25 vol%, the flexural strength was even lower than that of the mullite possibly due to higher porosity of 6%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.55-55
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• 2008

이차전지의 음극 중 $LiC_6$는 높은 용량을 보이나 완충하는 프로세스 동안에 금속리튬에 가까운 potential을 갖게 되어 조작에 어려움이 있다. 이러한 대용물질로서 $Li_4Ti_5O_{12}$ spinel은 가볍고 높은 에너지 밀도를 가지고 있고 낮은 전압영역이 가능하여 이차전지의 음극 물질로서 유용하다. 그러나 $Li_4Ti_5O_{12}$ 물질 자체가 insulation이며, 고상합성법을 사용하게 되면 좋은 특성을 나타내기가 어렵다. 이번 실험에서는 고상합성을 통하여 $Ba^{2+}$와 $Sr^{2+}$이온을doping한 후 전기화학적 특성이 어떻게 향상되었는가를 연구하였다. Ba와 Sr을 첨가한 $Li_4Ti_5O_{12}$는 첨가하지 않은 물질에 비하여 보다 안정적인 평탄구역을 갖게 되었으며 방전용량이 $40mAhg^{-1}$의 향상을 가져왔다. 또한 Li half cell에서 100cycle 진행하는 동안 보다 안정적인 전극구조를 유지하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.432-436
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• 2006

The $ZnGa_2O_4$ and Mn, Cr-doped $ZnGa_2O_4$ Phosphors were synthesized through conventional solid state reactions. The XRD patterns show that the $ZnGa_2O_4$ has a (3 1 1) main peak and a spinel phase. The emission wavelength of $ZnGa_2O_4$ showed main peak of 420 nm and maximum intensity at the sintering temperature of $1100^{\circ}C$. In the crystalline $ZnGa_2O_4$, the Mn shows green emission (510 nm, $^4T_1-^6A_1$) with a quenching concentration of 0.6 mol%, and the Cr shows red emission (705 nm, $^4T_2-^4A_2$) with a quenching concentration of 2 mol%. These results indicate that $ZnGa_2O_4$ Phosphors hold promise for potential applications in field emission display devices with high brightness operating in full color regions.

• Corrosion Science and Technology
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• v.6 no.1
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• pp.1-6
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• 2007

Ferritic stainless steels for the SOFC interconnect applications are required to possess not only a good oxidation resistance, but also a high electrical conductivity of the oxide scale that forms during exposure at the SOFC operating environment. In order to understand the effects of alloying elements on the oxidation behavior of ferritic stainless steels and on the electrical properties of oxide scales, two kinds of commercial ferritic stainless steels, STS 430 and STS 444, were investigated by performing isothermal oxidations at $800^{\circ}C$ in a wet air containing 3% $H_{2}O$. The results showed that STS 444 was superior to STS 430 in both of the oxidation resistance and the area specific resistance. Although STS 444 contained a less amount of Mn for the $(Mn,Cr)_{3}O_{4}$ spinel formation than STS 430, the minor alloying elements of Al and Mo in STS 444, which were accumulated in the base metal region adjacent the scale, were suggested to reduce the scale growth rate and to enhance the scale adherence to the base metal.

• Journal of Magnetics
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• v.10 no.1
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• pp.23-27
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• 2005

The crystallographic and magnetic properties of a series of substitutions in nickel ferrite where the Fe³⁺ is replaced with In³⁺ have been investigated using X-ray diffraction (XRD) and Mössbauer spectroscopy. Information on the exact crystalline structure, lattice parameters, bond lengths and bond angles were obtained by refining their XRD profiles by a Rietveld method. All the crystal structures were found to be cubic with the space group Fd/3m. The lattice constants increased with In³⁺ concentration. The expansion of the tetrahedron was outstanding, indicative of the tetrahedral (A) site preference of larger indium ion. The Mossbauer spectra showed two sets of sextuplet originating from ferric ions occupying the tetrahedral sites and the octahedral (B) sites under the Neel temperature T_N. Regardless of the composition x, the electric quadrupole splitting was zero within the experimental error. At x = 0.2, the magnetic hyperfine fields increased slightly, which meant that the nonmagnetic indium ions occupied preferentially the A-site. At the same time, the intensity of the B-site sub-spectra decreased markedly at the elevated temperature, indicating that the occupation of the A site by indium induced a considerable perturbation on the B site.

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.295-299
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• 1998

The magnetic thin films can be prepared without vacuum process and under the low temperature(<100 $^{\circ}C$) by ferrite plating. We have performed ferrite plating of $Ni_xFe_{3-x}O_4$ (x=0.162~0.138) films on cover glass at the substrate temperature 80 $^{\circ}C$ and pH range of the oxidizing solution, 7.1~8.8. the crystal structure of the samples has been identified as a single phase of polycrystal spinel structure by x-ray diffraction technique. The deposition rate and the grain size of the film increased with the pH of oxidizing solution. The coercive force (H_C)$ decreased with the pH of oxidizing solution.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1445-1453
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• 2013

$Zn_{(1-x)}Ni_xAl_2O_4$ (x = 0.0-1.0) spinels were prepared at $800^{\circ}C$ by co-precipitation method and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The specific surface area was determined by BET. SEM image showed nano sized spherical particles. XPS confirmed the valence states of the metals, showing moderate Lewis character for the surface of materials. The powders were successfully used as new heterogeneous catalysts of Biginelli's reaction, a one-pot three-component reaction, leading to some dihydropyrimidinones (DHPMs). These new catalysts that produced good yields of DHPMs, were easily recovered by simple filtration and subsequently reused with persistent activity, and they are non-toxic and environmentally friendly. The optimum amount of catalyst is 20% by weight of benzaldehyde derivatives, while the doping amount has been found optimal for x = 0.1.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.43-47
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• 2014

NiO-doped hibonite pigments were synthesized by the solid state method to get stabilized blue color pigment in both oxidation and reduction atmospheres. Optimum substitution condition with NiO for hibonite blue pigment was investigated. Experimental results were comparable to those of previous cobalt-minimization studies performed with other phosphate- or oxide-based cobalt-containing ceramic pigments (having olivine ($Co_2SiO_4$), spinel ($CoAl_2O_4$), or with co-doped willemite ($(Co,Zn)_2SiO_4$) structures). Composition was designed varying the NiO molar ratio increasing with $SnO_2$. The optimum substitution content is 0.93 mole NiO with 0.75mole $SnO_2$. The characteristics of the synthesized pigment were analyzed by XRD, Raman spectroscopy, SEM, and UV-vis. Synthesized pigment was applied to a lime-barium glaze with 10 wt% each and fired at an oxidation atmosphere of $1250^{\circ}C/1h$ and a reducing atmosphere $1240^{\circ}C/1h$. Blue color was obtained with $L^*a^*b^*$ values at 43.39, -6.78, -18.20 under a reducing atmosphere and 41.66, -6.36, -14.7 under and oxidation atmosphere, respectively.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.3
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• pp.119-123
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• 2005

Lithium titanium oxide as anode material for energy storage prepared by novel synthesis method. Li$_{4}$Ti$_{5}$O$_{12}$ based spinel-framework structures are of great interest material for lithium-ion batteries. We describe here Li$_{4}$Ti$_{5}$O$_{12}$ a zero-strain insertion material was prepared by novel sol-gel method and by high energy ball milling (HEBM) of precursor to from nanocrystalline phases. According to the X-ray diffraction and scanning electron microscopy analysis, uniformly distributed Li$_{4}$ Ti$_{5}$O$_{12}$ particles with grain sizes of 100nm were synthesized. Lithium cells, consisting of Li$_{4}$ Ti$_{5}$O$_{12}$ anode and lithium cathode showed the 173 mAh/g in the range of 1.0 $\~$ 3.0 V. Furthermore, the crystalline structure of Li$_{4}$ Ti$_{5}$O$_{12}$ didn't transform during the lithium intercalation and deintercalation process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.369-372
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• 2000

ZnO varistor is studied to sintering condition and mixing condition for the improvement to non linear of electrical characteristics. In this paper, ZnO varistor, ZnO-Bi$_2$O$_3$-Y$_2$O$_3$-MnO-Cr$_2$O$_3$-Sb$_2$O$_3$series, is fabricated with Sb$_2$O$_3$mol ratio(0.5~4[mol%]) and sintered at 1250[$^{\circ}C$] for 2 hours. The grain size to Sb$_2$O$_3$moi ratio was measured by fractal mathematics. The ZnO varistors that Sb$_2$O$_3$mot ratio is 1[mol%] were shown small grain size because of spinel phase. The fractal dimension were increased with increasing of Sb$_2$O$_3$mo ratios. The capacitance of ZnO varistors with increasing of Sb$_2$O$_3$additive in voltage-capacitance characteristics was decreased by small grain size.