• Applied Chemistry for Engineering
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• v.23 no.6
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• pp.534-538
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• 2012

$Na^+$-beta-alumina solid electrolyte was synthesized by solid state reaction using $Li_2O$ and MgO as a phase stabilizer, and the effect of stabilizers on the phase formation and sintering density was investigated. In order to determine the phase fraction according to the synthesizing temperature, the molar ratio of [$Na_2O$] : [$Al_2O_3$] was fixed at 1 : 5, and calcination was conducted at temperatures between $1200{\sim}1500^{\circ}C$ for 2 h. In the $Li_2O$-$Na_2O$-$Al_2O_3$ ternary system, ${\beta}^{{\prime}{\prime}}$-alumina phase fraction considerably increased by the secondary phase transition at $1500^{\circ}C$, whereas it maintained similarly in the MgO-$Na_2O$-$Al_2O_3$ system. Additionally, the disc-type specimens of $Na^+$-beta-alumina were sintered at the temperature between $1550{\sim}1650^{\circ}C$ for 30 min, and relative sintering densities, phase changes, and microstructures were analyzed. In case of $Li_2O$-stabilized $Na^+$-beta-alumina, ${\beta}^{{\prime}{\prime}}$-phase fraction and relative density of specimen sintered at $1600^{\circ}C$ were 94.7% and 98%, respectively. Relative density of MgO-stabilized $Na^+$-beta-alumina increased with a rise in sintering temperature.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.128-128
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• 1994

• Korean Journal of Materials Research
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• v.6 no.3
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• pp.297-304
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• 1996

15 vol% ZrO2가 첨가된 Na $\beta$"-alumina 복합재를 1단계와 2단계 소결법을 사용하여 제조하였다. ZrO2는 효율적으로 Na $\beta$"-alumina에 비해 약 51%정도 증가하였으며 열처리 시간에 따른 Klc값의 큰 변화는 관찰되지 않았다. 그러나 이들 복합재의 굽힘 강도 값은 열처리 시간이 60분을 초과함에 따라 점차 감소하는 경향을 나타냈다. 2단계 소결법으로 제조한 Na 복합재의 전기 전도도는 1단계 소결법으로 제조된 시편과 달리 열처리 시간에 따른 전도도 값의 분산성이 거의 없었으며, 그 값은 다결정 Na $\beta$"-alumina의 전도도와 거의 동일하였다. Na 복합재 및 이온교환법에 의해 제조한 K 복합재의 전기전도도 값은 30$0^{\circ}C$에서 각각 1.3x 10-1과 5.9x20-2Scm-1로 측정되었다.2Scm-1로 측정되었다.

• Korean Journal of Materials Research
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• v.20 no.2
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• pp.55-59
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• 2010

$Na^+$ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric $Na^+$ $\beta$-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric $Na^+$ $\beta$-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric $Na^+$ $\beta$-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric $Na^+$ $\beta$-alumina.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.35-41
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• 1999

In this study we investigated the effects of process variables on the bond strength, and its dependency upon the interfacial chemistry when the joined $ZrO_2$ toughened $Na\beta$"-alumina to $\alpha$-alumina using B$_2$$O_3$-$SiO_2$-Al$_2$$O_3$-CaO glass sealant. We observed that bond strength is mainly determined by the strength of the glass, which, in turn, depends on the glass composition established after joining reaction. Joining at $950^{\circ}C$ for 15min yielded the highest average bond strength of 66MPa. Different types of interfacial reaction seem to occur at each interface. After joining at $950^{\circ}C$ for 15min we found that Ca and Si diffuse much deeper(~15$\mu\textrm{m}$) into the $\beta$"-alumina composite than into the $\alpha$-alumina(<1$\mu\textrm{m}$) as a result of ion exchange reaction and more effective grain boundary diffusion. Thermal expansion coefficient of the glass was found to have changed more closely to those of the $\beta$"-alumina composite and $\alpha$-alumina, which put the glass under a slight compressive stress.ressive stress.

• Journal of the Korean Electrochemical Society
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• v.25 no.4
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• pp.191-200
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• 2022

Na-β"-Al₂O₃ has been widely employed as a solid electrolyte for high-temperature sodium (Na) beta-alumina batteries (NBBs) thanks to its superb thermal stability and high ionic conductivity. Recently, a vapor phase conversion (VPC) method has been newly introduced to fabricate thin Na-β"-Al₂O₃ electrolytes by converting α-Al₂O₃ into β"-Al₂O₃ in α-Al₂O₃/yttria-stabilized zirconia (YSZ) composites under Na⁺ and O^2- dual percolation environments. One of the main challenges that need to be figured out is lowered conductivity due to the large volume fraction of the non-Na⁺-conducting YSZ. In this study, the effect of lithia addition in the β"-Al₂O₃ phase on the grain size and ionic conductivity of Na-β"-Al₂O₃/YSZ solid electrolytes have been investigated in order to enhance the conductivity of the electrolyte. The amount of pre-added lithia (Li₂O) precursor as a phase stabilizer was varied at 0, 1, 2, 3, and 4 mol% against that of Al₂O₃. It turns out that ionic conductivity increases even with 1 mol% lithia addition and reaches 67 mS cm^-1 at 350 ℃ of its maximum with 3 mol%, which is two times higher than that of the undoped composite.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.398-405
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• 2021

To fabricate a full-scale pilot model of the cost-effective Na-(Ni,Fe)Cl₂ cell, a Na-beta-alumina solid electrolyte (BASE) was developed by applying a one-step synthesis cum sintering process as an alternative to the conventional solid-state reaction process. Also, Fe metal powder, which is cheaper than Ni, was mixed with Ni metal powder, and was used for cathode material to reduce the cost of raw material. As a result, we then developed a prototype Na-(Ni,Fe)Cl₂ cell. Consequently, the Ni content in the Na-(Ni,Fe)Cl₂ cell is decreased to approximately (20 to 50) wt.%. The #1 prototype cell (dimensions: 34 mm × 34 mm × 235 mm) showed a cell capacity of 15.9 Ah, and 160.3 mAh g^-1 (per the Ni-Fe composite), while the #2 prototype cell (dimensions: 50 mm × 50 mm × 335 mm) showed a cell capacity of 49.4 Ah, and 153.2 mAh g^-1 at the 2^nd cycle.

• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.136-142
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• 1988

β-Al2O3, which is used for solid electrolyte membrances in sodium-sulfur batteries, was prepared by sol-gel process. Sodium-n-propoxide NaOC3H7 and aluminum-isopropoxide Al(OC3H7)3 were hydrolyzated in the solution at pH 3, pH 7, pH 9 and pH 11, respectively. The sol-gel processed samples were calcined at several temperature steps, respectively and analysed by thermal analyser(DT-TGA), infrared spectrum analyser and X-ray diffraction analyser. The gelling rate of solution at pH 7 was much higher than that of the solution at pH 3. Thermal exchanging behavior of the gels at pH 3 were similar to Na2O·Al2O3·6H2O and, above pH 7, were similar to Na2O·Al2O3·3H2O. When samples' composition ratio was 9.13 : 90.87 [NaOC3H7:Al(OC3H7)3] at pH 7, β-Al2O3 was formed at 1100℃.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.455-461
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• 1995

To investigate the synthesis of $\beta$-Al2O3 and its crystallization behavior by oxalate coprecipitation method, the optimum pH range for oxalate coprecipitates has been theoretically calculated from the solubility products and the equilibrium constans of each metal ionic species and their solubility diagram wa obtained. The optimum pH range for oxalate coprecipitates at room temperature was estimated as <4. In experiment, we found that the optimum condition for oxalate coprecipitates was pH<1, which was not doped with pH controller. The Na+ ions were easily exchanged for the NH4+ ions of NH4OH which was used as pH controller, and those NH4+ ions were supposed to affect the crystallization behavior of $\beta$-Al2O3. The thermal decomposition of all complexes was almost complete below 40$0^{\circ}C$. The primary product of the decomposition process was m-Al2O3, which transformed to $\beta$"- or $\beta$-Al2O3 at temperature higher than 100$0^{\circ}C$. We found that the powder prepared at 120$0^{\circ}C$ had only $\beta$"- and $\beta$-Al2O3.EX>-Al2O3.

• Journal of Sensor Science and Technology
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• v.23 no.3
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• pp.170-172
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• 2014

$CO_2$ sensor was used only one solid electrolyte in many cases. To improve the sensing characteristics of $CO_2$ sensors, solid electrolyte $CO_2$ sensor has been developed by bi-electrolyte type sensor using Na-Beta-alumina and YSZ. However, in many further studies, bi-electrolyte type sensor was made by pellet pressed by press machine and additional treatment for formation of interface. In the aspect of mass production, using thick film and additional treatment is not suitable. In this study, $CO_2$ sensor was fabricated by bi-electrolyte structure which was made by an NBA paste layer deposited on YSZ pellet and fired at $1650^{\circ}C$ for 2 hour. The formation of stable interface between YSZ and NBA were confirmed by SEM image. When the type IV electrochemical cell arrangement represented by $CO_2,O_2,Pt{\mid}Li_2CO_3-CaCO_3{\parallel}NBA{\parallel}YSZ{\mid}O_2,Pt$ is used to measure the $CO_2$ concentration in air. This sensor EMF should depend only on the concentration of $CO_2$ by logarithmic. Also, sensor shows $P_{CO_2}$ and EMF relationship like nerstian reaction at a temperature of $450^{\circ}C$.