• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.35-42
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• 1985

$eta$-Sialon powders were prepared by reduction-nitridation from mixture of Wando pyrophyllite and graphite as a reducing agent at 135$0^{\circ}C$ in 80% $N_2$-20% $H_2$ atmosphere. As the reaction products $Si_2ON_2$, $\beta$-$Si_3N_4$ a--$Si_3N_4$ and $\beta$-SiC were observed. Additive agents of MgO, CaO, $Y_2O_3$ were used for promoting the reduction and nitridiation aeaction. The present study was conducted to investigate the effects of silica-carbon ratio ($SiO_2$/C=weight ratio), raction time gas flow rate pellet size and powder packing on synthesis of $\beta$-Sialon from Wando pyropyllite.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.167-170
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• 1989

Al2O3/SiC composite-material was synthesized by the birth-spread mechanism through the carbothermal reduction reaction of SiO2 in Ha-Dong Kaolin with carbon powder under H2 gas atmosphere at 1300~140$0^{\circ}C$. Average diameter of synthesized SiC whiskers were 1${\mu}{\textrm}{m}$ and aspect ratio (c/a) was 10~100. Al2O3 particles and SiC whiskers were mixed homogeneously in the reacted pellet.

• Journal of the Korean Ceramic Society
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• v.56 no.1
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• pp.84-90
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• 2019

The varistor properties and stability against dc-accelerated stress of $V_2O_5-Mn_3O_4-Co_3O_4-Dy_2O_3-Nb_2O_5-Bi_2O_3$ (VMCDNB)-doped zinc oxide ceramics sintered at $850-925^{\circ}C$ were investigated. Increasing the sintering temperature increased the average grain size from 4.6 to 8.7 mm and decreased the density of the sintered pellet density from 5.54 to $5.42g/cm^3$. The breakdown field decreased from 5919 to 1465 V/cm because of the increase in the average grain size. Zinc oxide ceramics sintered at $875^{\circ}C$ showed the highest nonlinear coefficient (43.6) and the highest potential barrier height (0.96 eV). Zinc oxide ceramics sintered at $850^{\circ}C$ showed the highest stability: the variation rate of the breakdown field was -2.0% and the variation rate of the nonlinear coefficient was -23.3%, after application of the specified stress (applied voltage/temperature/time).

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.198-201
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• 2012

The electrolytes in thermal batteries are nonconductive solids at ambient temperature, which prevent the self-discharge and corrosion. To meet severe environmental requirements and guarantee acceptable handling yields, all the pellets in cells should have adequate strength, especially for the cathodes due to their poor binding properties among FeS2 particles. By modifying the surface microstructure of FeS2 through molten-salt heat treatment, the inter-particle binding strength is greatly increased, resulting in the enhanced pellet strength and yield. The addition of Li2O also promoted the soft salt coating coverage of hard FeS2 particles, which can be explained by the enhanced wettability of the molten salt.

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.648-652
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• 2009

Ceramic fiber separator is the promising material for thermal battery system because it reduces the production cost and offers the potential to a new application compared to a pellet type electrolyte. The electrolyte separator for thermal battery should be easily handled and loaded a large amount of the molten lithium salt. Ceramic fibers were used as an electrolyte separator and the lithium based molten salts were infiltrated into the ceramic filters. Leakage of molten salt (several lithium salts) leads to short-circuit during the thermal battery operation. In this study, a uniform and fine SiOC mat with fibers ranging from 1 to 3 ${\mu}m$ was obtained by electrospinning of polycarbosilane and pyrolysis. The optimum spinning conditions for obtaining fine diameters of SiOC fiber were controlled by the solution composition and concentration, applied voltage and spinning rate, release rate by porosity. The pore structures of the ceramic filter and the melting properties of the lithium salts affected to the electrolyte loading and leakage. The importance of the fiber size and porosity and their control was discussed and the mechanical properties were also discussed.

• Journal of Powder Materials
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• v.24 no.5
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• pp.364-369
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• 2017

Ceramic powder, such as MgO, is added as a binder to prepare the green compacts of molten salts of an electrolyte for a thermal battery. Despite the addition of a binder, when the thickness of the electrolyte decreases to improve the battery performance, the problem with the unintentional short circuit between the anode and cathode still remains. To improve the current powder molding method, a new type of electrolyte separator with porous MgO preforms is prepared and characteristics of the thermal battery are evaluated. A Spherical PMMA polymer powder is added as a pore-forming agent in the MgO powder, and an organic binder is used to prepare slurry appropriate for tape casting. A porous MgO preform with $300{\mu}m$ thickness is prepared through a binder burnout and sintering process. The particle size of the starting MgO powder has an effect, not on the porosity of the porous MgO preform, but on the battery characteristics. The porosity of the porous MgO preforms is controlled from 60 to 75% using a pore-forming agent. The batteries prepared using various porosities of preforms show a performance equal to or higher than that of the pellet-shaped battery prepared by the conventional powder molding method.

• Journal of the Korean Ceramic Society
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• v.41 no.12 s.271
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• pp.907-914
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• 2004

The nitridation mechanism of Si by SHS at $Si-NaCl-NH_{4}Cl-NaN_3$ system was investigated in this work. It was revealed that NaCl as a diluent was helpful to the perfect nitridation reaction by retarding the growth of Si particle resulted from the melting of Si at the initial stage of the nitridation reaction. And $NH_{4}Cl\;and\;NaN_3$ formed NaCl through decomposition and combination, and the preheating of pellet was helpful to the nitridation reaction in this process. The main nitridation mechanism of this system was liquid-gas reaction. The optimum porosity of the pellet for the nitridation of ${\alpha}-Si_{3}N_4$ was $67-69\%$.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.567-572
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• 2004

The variation of the sintered density and grain size of UO$_2$ as a function of the Li$_2$O amount and sintering atmosphere was observed. Li$_2$O enhanced the grain growth of the UO$_2$ pellet in H$_2$, but rather hindered it in $CO_2$ atmosphere. Grain size of the UO$_2$ and UO$_2$-0.1 wt%Li$_2$O pellets was, respectively, 8 $\mu$m and 100 $\mu$m at 168$0^{\circ}C$ in the H$_2$ atmosphere, and that of each pellet was, respectively, 24 $\mu$m and 17 $\mu$m at the same temperature in the $CO_2$ atmosphere. As-received Li$_2$O powder, which had been composed of Li$_2$O and LiOH, was converted to the Li$_2$CO$_3$ phase after heating to 80$0^{\circ}C$ in $CO_2$. On the other hand, the Li$_2$O and LiOH phases remained unchanged in H$_2$ atmosphere. In the H$_2$, the as-received Li$_2$O powder began to evaporate at about 105$0^{\circ}C$ and then about 20 wt% residue was left at 150$0^{\circ}C$. But, most of the Li elements evaporated at 150$0^{\circ}C$ in the $CO_2$ atmosphere.

• Journal of the Korean Ceramic Society
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• v.54 no.4
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• pp.278-284
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• 2017

In this work, Ta-substituted $Li_7La_3Zr_{2-x}O_{12}$ (LLZTO) powder and pellets with garnet cubic structure were fabricated and characterized by modified and optimized sol-gel synthesis. Ta-substituted LLZO powder with the smallest grain size and pure cubic structure with little pyrochlore phase was obtained by synthesis method in which Li and La sources in propanol solvent were mixed together with Zr and Ta sources in 2-methoxy ethanol. The LLZTO pellets made with the prepared powder showed cubic garnet structure for all conditions when the amount of Li addition was varied from 6.2 to 7.4 mol. All the X-ray peaks of the pyrochlore phase disappeared when the Li addition was increased above 7.0 mol. When the final sintering temperature was varied, the LLZTO pellet had a pyrochlore-mixed cubic phase above $1000^{\circ}C$. However, the surface morphology became much denser when the final sintering temperature was increased. The sol-gel-driven LLZTO pellet with a sintering temperature of $1100^{\circ}C$ showed a lithium ionic conductivity of 0.21 mS/cm when Au was adopted as electrode material for the blocking capacitor. The results of this study suggest that modified sol-gel synthesis is the optimum method to obtain cubic phase of LLZTO powder for highly dense and conductive solid electrolyte ceramics.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.637-642
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• 1994

Using SHS(Self-propagating High-temperature Synthesis) method, the optimum synthetic condition of titanium carbonitride was established by controlling the parameters such as relative density of mixture (Ti+C), nitrogen pressure, additive amounts of titanium hydride(TiH1.924) and protecting heat loss. Under 1 atm nitrogen pressure, nitridation ratio with changing relative density of the sample compacts has a maximum (87.2%) at about 55%, and in the case of enveloping the pellet with a quartz tube, the highest nitridation ratio of 90% was obtained at about 68%. At relative density of 55%, nitridation ratio with the nitrogen pressure has a miximum (87.3%) at 7 atm. As the amounts of additive titanium hydride increased, nitridation ratio decreased at below 7 atm nitrogen pressure and, increased at above this pressure until percent of addition percent reached 15 wt% and decreased abruptly upon futher increases in titanium hydride. In the synthesis of TiCxNy by combustion reaction, heat transfer from combustion zone to preheating zone and nitrogen gas penetration into the compact were found to be important factors affecting the TiCxNy formation. It was difficult to obtain high nitridation ratio when the conbustion temperature was either too high or too low, and it seems that the retention of high temperature after a combustion wave sweeped through the reactant mixture pellet is critical to obtain a satisfactory nitridation ratio.