• Korean Journal of Materials Research
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• v.24 no.2
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• pp.81-86
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• 2014

The nitrogen solubility and nitride capacity of $CaO-SiO_2-Al_2O_3-MgO-CaF_2$ slag systems were measured by using gas-liquid equilibration at 1773K. The nitrogen solubility of this slag system decreased with increasing CO partial pressure, with the linear relationship between nitrogen contents and oxygen partial pressure being -3/4. This system was expected to show two types of nitride solution behavior. First, the nitrogen solubility decreased to a minimum value and then increased with the increase of CaO contents. These mechanisms were explained by considering that nitrogen can dissolve into slags as "free nitride" at high basicities and as "incorporated nitride" within the network at low basicities. Also, the basicity of slag and nitride capacity were explained by using optical basicity. The nitrogen contents exhibited temperature dependence, showing an increase in nitrogen contents with increasing temperature.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.189-199
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• 2009

The Powder characteristics and sintering behavior of $SiO_2$ coated $BaTiO_3$ were studied. $BaTiO_3$ powders were synthesized by the liquid mix method developed by Pechini, and silica coating was prepared by alkoxide hydrolysis method with TEOS and ethanol. The particle size of the $BaTiO_3$ powders was 35 nm and the thickness of the $SiO_2$ coating layer was 5 nm. As the $SiO_2$ content increased, the $SiO_2$ layers improved the powder dispersion by increasing electrostatic repulsion between the $BaTiO_3$ particles. Effects of MgO coating on microstructure and dielectric properties of $BaTiO_3$ have been studied compared with mechanically MgO mixed $BaTiO_3$. MgO coated $BaTiO_3$ particles were prepared by a homogeneous precipitation method using $MgCl_2\cdot 6H_2O$ and urea. MgO coated $BaTiO_3$ exhibited homogeneous microstructure compared with mixed samples. XRD analysis revealed that Mg substitution for the Ti site in the MgO mixed sample was much greater than in the coated one. Electrical properties of MgO mixed and coated $BaTiO_3$ were affected by the diffusion behavior of Mg in $BaTiO_3$ lattice.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1991.10a
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• pp.37-39
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• 1991

This paper is studies the effects of additives on the magnetic properties of Sr-ferrite. The specimens have been composed of SrO and Fe$_2$O$_3$with ratio of 1:5.9. As 1st additives, it is mixed to 0.2wt%, 0.7wt% and 1wt% of CaCo$_3$with 0.3wt% SiO$_2$. As 2nd addition, it is mixed to 0.5wt%, 1wt% of Na$_2$SiO$_3$, 0.5wt%, 1wt% of Cr$_2$O$_3$and 0.5wt%, 1wt% of Al$_2$O$_3$and sintering conditions was carried out at 1210$^{\circ}C$, 1230$^{\circ}C$ and 1250$^{\circ}C$. From experiments on the magnetic properties of specimen, the results were shown follows; (1) In case of additive SiO$_2$and CaO, it is stable magnetoplumbite structure for liquid phase grown, enhances mignetic propertics. (2) In case of basic compositions + 0.5wt% Al$_2$O$_3$, it is confirmed better properties by increasing of the coercivity than 0.5wt% Cr$_2$O$_3$additives. (3) In case of mixed additives of Cr$_2$O$_3$and Al$_2$O$_3$, magnetic propeties decrease with sintering density.

• Journal of the Korean Ceramic Society
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• v.36 no.10
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• pp.1094-1101
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• 1999

Liquid phase sintered silicon carbides were obtained by sintering of $\alpha$-SiC and $\beta$-SiC powders as starting materials at 2173K and 2273K respectively. The SiCplatelet seeds of different sizes were obtained by a repeated ball milling and sedimentation. Their mean size (d50) were 2.217 ${\mu}{\textrm}{m}$ 13.67 ${\mu}{\textrm}{m}$, 22.17${\mu}{\textrm}{m}$ respectively 6wt%Al2O3-4 wt% Y2O3 was used as the sintering additives for the liquid phase sintering. The two silicon carbides had a bimodal microstructure consisting of small matrix grains and large platelike grains when the SiCplatelet seeds were added. In the case of the $\beta$-SiC the appreciable phase transformation occurred as sintering temperature increased from 2173K to 2273K and resulted in matrix shape change from equiaxed into platelike grains. In contrast there was no shape change for the $\alpha$-SiC. The size of large grains in the $\alpha$-SiC of large grains in the $\alpha$-SiC was larger than that of the large grains in the $\beta$-SiC These results suggested that the growth of the $\alpha$-SiCplatelet in the $\alpha$-SiC matrix was more favored than that of the $\alpha$-SiCplatelet in the $\beta$-SiC matix. The three point flexural strength decreased as the added seed size increased. Fracture toughness values of samples sintered at 2273K were higher than those of samples sintered at 2173K.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.647-653
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• 2007

In ready mixed concrete factory, in case of using the high molecular additive in winter especially the liquid additive for the early strength, it is required to check the stability. In this research, the freezing and gelling characteristics of the liquid additive for the early strength is reviewed, the material and mechanical solution are proposed to that the practical quality control method will be suggested. As the result, the Freezing temperature of the liquid additive for the early strength is $-11.8^{\circ}C$, and it is the lower than the temperature at which the strength is shown. By making with sodium silicate of $37{\pm}0.5%$ designed by $SiO_2\;and\;Na_2O$ in 0.31 of mol ratio, it minimizes the gelling at the lower temperature. On the other hand, facilities for storing and supplying the material should be set at $40^{\circ}C$ so the temperature distribution is well spreaded for practical operation.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.660-664
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• 2000

Effect of various kinds of additive such as AlOOH, Al(OH)3, Al2Si2O5(OH)4, Nb2O5, TiO2 and MgO on the properties and microstructures of UO2 pellet has been examined. All the tested dopants had played a role to reduce sintered density and open porosity. It was revealed that the addition of TiO2 made pellet more stable thermally. UO2 pellet doped with 0.2wt% TiO2 was swelled rather than densified after annealing for 24 hrs at 1$700^{\circ}C$. It was attributed to large pore with spherical shape. Titinia and silicon coexisted with Al element were more effective to increase grain size than other additives. It could be also revealed that the formation of liquid phase was the main cause of grain growth.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.2
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• pp.98-103
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• 1999

The effect of $Al_2O_3$ additives to $\beta-SiC+39vol.%ZrB_2$ electroconductive ceramic composites by pressureless sintering on microstructural, mechanical and electrical properties were investigated. The $\beta-SiC+39vol.%ZrB_2$ ceramic composites were pressureless sintered by adding 4, 8, 12wt.% $Al_2O_3$ powder as a liquid forming additives at $1950^{\cire}C$ for 1h. Phase analysis of composites by XRD revealed mostly of $\alpha-SiC(6H), ZrB_2$ and weakly $\alpha-SiC(4H), \beta-SiC (15R)$ phase. The relative density of composites was lowered by gaseous products of the result of reaction between \beta-SiC and Al_2O_3$, therefore, porosity was increased with increasing $Al_2O_3$ contents, and showed the maximum value of 1.4197MPa.$m^{1/2}$ for composite with 4wt.% $Al_2O_3$ additives. The electrical resistivity of $\beta-SiC+39vol.%ZrB_2$ electroconductive ceramic composite was increased with increasing $Al_2O_3$ contents, and showed positive temperature coefficient resistance (PTCR) in the temperature range of $25^{\cire}C$ to $700^{\cire}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.67-70
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• 2002

The composites were fabricated 61vol% ${\beta}$-SiC and 39vol.% $TiB_2$ powders with the liquid forming additives of 8, 12, 16wt% $Al_2O_3+Y_2O_3$ by pressureless annealing at $1650^{\circ}C$ for 4 hours to form YAG. The result of phase analysis of composites by XRD revealed ${\alpha}$-SiC(6H), $TiB_2$, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density and the Young's modulus showed the highest value of 82.29% and 54.60 Gpa for composites added with 16wt% $Al_2O_3+Y_2O_3$ additives at room temperature.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1588-1590
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• 2004

The composites were fabricated, respectively, using 61vol.% SiC - 39vol.% $TiB_2$ and using 61vol.% SiC 39vol.% WC powders with the liquid forming additives of 12wt% $Al_2O_3+Y_2O_3$ by pressureless annealing at 1800$^{\circ}C$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, WC were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H), $TiB_2$ and YAG($Al_5Y_3O_{12}$) crystal phase on the SiC-$TiB_2$, and SiC(2H), WC and YAG($Al_5Y_3O_{12}$) crystal phase on the SiC-WC composites. ${\beta}{\rightarrow}{\alpha}$-SiC phase transformation was ocurred on the SiC-$TiB_2$, but ${\alpha}{\rightarrow}{\beta}$-SiC reverse transformation was not occurred on the SiC-WC composites. The relative density, the flexural strength showed respectively value of 96.2%, 310.19Mpa in SiC-WC composites. The electrical resistivity of the SiC-$TiB_2$ and the SiC-WC composites is all positive temperature cofficient resistance(PTCR) in the temperature ranges from 25$^{\circ}C$ to 500$^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.33 no.12
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• pp.1301-1310
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• 1996

Generally it requires high sintering temperatures more than 135$0^{\circ}C$ to make semiconductive BaTiO3 ceramics. Also it is very difficult to achieve a homogeneous mixing in solid-state reaction method. Therefore the liquid phase distributed to non-uniform dilute the characteristics of PTCR. In order to improve the uniformity this study is used the sol-gel coating method. Using this method we studied the new manufacturing process that had a high reproducibility and mass production capability. Tetraethyl orthosilicate (TEOS) was used as a source of Si. The semiconductive BaTiO3 ceramics which was produced by sol-gel method for the SiO2 addition and sintered between 124$0^{\circ}C$ and 130$0^{\circ}C$ showed almost same resistivity at room temperature among 125$0^{\circ}C$ and 130$0^{\circ}C$. As the results We could be sintered the semiconducting BaTiO3 ceramics at lower temperature even at 125$0^{\circ}C$ maintaining the same specific resistivity ratio ($\rho$max/$\rho$min) at 130$0^{\circ}C$. The specific resistivity both below and above the Curie temperature were increased by slow cooling and the steepness of the plots in the reasion of transition from low to high resistance increased as the cooling rate decreased.