• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.12
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• pp.762-767
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• 2017

Mullite ($3Al_2O_3{\cdot}2SiO_2$) has emerged as a promising candidate for high-temperature structural materials due to its erosion resistance, chemical and thermal stabilities, relatively low thermal expansion coefficient, excellent thermal shock and creep resistances, and low dielectric constant. However, since the pure mullite sintering temperature is as high as $1,600{\sim}1,700^{\circ}C$, there is an increasing need for a sintering additive capable of improving the strength characteristics while lowering the sintering temperature. Herein we have tried to obtain the optimal sintering additive composition by adding MgO, $Cr_2O_3$, and $Y_2O_3$ to mullite, followed by sintering at $1,325{\sim}1,550^{\circ}C$ for 2 h. With additives of 2 wt% of MgO, 2 wt% of $Cr_2O_3$, 4 wt% of $Y_2O_3$, A density of $3.23g/cm^3$ was obtained for the sintered body at $1,350^{\circ}C$ upon using 2 wt% MgO, 2 wt% $Cr_2O_3$, and 4 wt% $Y_2O_3$ as additives. The three-point flexural strength of that was 275 MPa and the coefficient of thermal expansion (CTE) was $4.15ppm/^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.6
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• pp.493-501
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• 2000

The microstructure and electrical properties of ZnO-Pr$_{6}$/O$_{11}$-CoO-Er$_{2}$/O$_{3}$ based varistors were investigated with Er$_{2}$/O$_{3}$ additive content of the range 0.0 to 2.0 mol%. Most of the added Er$_{2}$/O$_{3}$ were segregated at the nodal points and grain boundaries and it coexisted with Pr$_{6}$/O$_{11}$ in the bulk intergranular layer. The average grain size was decreased in the range of 7.44 to 5.62${\mu}{\textrm}{m}$ at 130$0^{\circ}C$ and 18.36 to 9.11 at 135$0^{\circ}C$ with increasing Er$_{2}$/O sub 3/ additive content. The density of ceramics was in the range 4.87 to 5.08 g/cm$^3$ at 130$0^{\circ}C$ and 5.35 to 5.62 g/cm$^3$at 135$0^{\circ}C$. At 130$0^{\circ}C$ the varistors without Er$_{2}$/O$_{3}$ exhibited 29.66 in the nonlinear exponent and 28.23 $\mu$A in the leakage current whereas the varistors with 0.5 mol% Er$_{2}$/O$_{3}$ exhibited a high nonlinearity which is 52.78 in thenonlinear exhibited and 9.75 $\mu$A in the leakage current. At 135$0^{\circ}C$ the varistors without Er$_{2}$/O$_{3}$ exhibited a very poor nonlinearity indicating 2.08 in the nonlinear exponent and 133.79 $\mu$A in the leakage current whereas the varistors with 1.0mol% Er$_{2}$/O$_{3}$ exhibited a relatively high nonlinearity which is 36.79 in the nonlinear exponent and 5.92 $\mu$A in the leakage current. Therefore Er$_{2}$/O$_{3}$ was additive which greatly improve the nonlinearity. It is believed that ZnO-0.5 mol% Pr$_{6}$/O$_{11}$-1.0 mol% CoO-0.5 mol% Er$_{2}$/O$_{3}$ based ceramicss will be usefully used as a basic composition to develop the advanced pr$_{6}$/O$_{11}$-based ZnO varistors.ristors.ristors.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.122-126
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• 2010

In this article photoluminescence of the $Al_2O_3:xCr_2O_3$ solid solutions prepared by solid state reaction method are represented. The effect of $Cr_2O_3$-activator concentration and heat treatment time on the PL characteristics have been discussed in conjunction with microstructure of phosphor samples. The $Al_2O_3:xCr_2O_3$ phosphors show the highest PL intensity at x=0.003 mole when the samples are reacted at $1600^{\circ}C$ for 5 h. The PL emission and absorption spectra show the maximum peaks at 698 nm and at 398 nm respectively. The CIE color coordinate is (x=0.646, y=0.316) at 0.003 mole $Cr_2O_3$, which value is very close to the NTSC coordinate of red color. This characteristic feature of $Al_2O_3:xCr_2O_3$ has been applied for an additive to improve the color characteristic of other red phosphor $LiEuW_2O_8$ which has a relatively poor color purity with an emission peak centered at 615 nm and with a CIE coordinate (x=0.530, y=0.280). The $Al_2O_3:0.003Cr_2O_3$ phosphor has been mixed with the $LiEuW_2O_8$ phosphor powder and the PL characteristics and CIE color coordinates are characterized. The $Al_2O_3:xCr_2O_3$ phosphor was found effective for improving the CRI (color rendering index) of $LiEuW_2O_8$ phosphor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.657-661
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• 2002

PZT powder was prepared by partial oxalate method using $(Zr_{0.53}Ti_{0.47})O_2$, $Pb(NO_3)_2$ and $(COOH)_2{\cdot}2H_2O$ as a precipitant. $Nb_2O_5$ additive effect on microstructure and piezoelectric properties of PZT ceramics were investigated. The coexistence of rhombohedral and tetragonal phases of PZT ceramics at the sintering temperature of $1100^{\circ}C$ was revealed from the X-ray diffraction patterns. The grain size PZT ceramics was decreased with the increase $Nb^{5+}$. and the sinterbility of PZT ceramics was decreased with the increase $Nb^{5+}$ addition. The electromechanical coupling factors $K_p$ show above 0.60 at $1100^{\circ}C$ sintering temperature by $Nb_2O_5$ addition above 0.6mol%.

• 연구논문집
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• s.30
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• pp.111-119
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• 2000

Sintering of alumina powder was studied in the presence of Y-Si oxide and oxynitride additives. The main crystalline phase of the sintering aids pre-reacted at $1400^{\circ}C$ was $\alpha$ - $Y_2$$SiO_2$>$O_7$. Y-N apatite was co-existed in the Si-40N sintering aid because of its high content of N. During the sintering process, liquid phases were formed by the reaction between additives and alumina, and these liquid phases promote the densification of alumina. SEM micrographs showed that uniform grain growth occurred in the system with oxide additive(Si-0N). In the case of oxynitride additive system(Si-20N and Si-40N), bimodal microstructure was observed due to the exaggerated grain growth, As the nitrogen content in the additive system increased the exaggerated grain growth occurred extensively. Bloating, which seemed to be originated by the liberation of $N_2$ gas, occurred un the Si-40N oxynitride additive system.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2000.11a
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• pp.93-96
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• 2000

In this study, we investigated the electromagnetic properties of Mn-Zn ferrite doped with rare earth oxide (Dy$_2$O$_3$, Er$_2$O$_3$). The main composition is 52mo1% $\alpha$-Fe$_2$O$_3$, 25mo1% Mn$_3$O$_4$23mo1% ZnO and doped with them(0.05wt%~0.25wt%, step:0.05wt%). An experimental process has advanced by conventional ferrimagnetism manufacturing that was prepared by standard ceramic techniques. The XRD pattern of all doped sample were observed spinel and secondary phase. The density of sample were measured nearly constant value. As increased the additive, resistivity, initial permeability and real component of the series complex permeability increased with setting limits each other. In case of Mn-Zn ferrite excess doped with them, resistivity, initial permeability and real component of the series complex permeability decreased and magnetic loss increased in proportion to increasing the additive.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.93-96
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• 2000

In this study, we investigated the electromagnetic properties of Mn-Zn ferrite doped with rare earth oxide (Dy$_2$O$_3$, Er$_2$O$_3$). The main composition is 52mo1% ${\alpha}$-Fe$_2$O$_3$, 25mol% Mn$_3$O$_4$ 23mo1% ZnO and doped with them(0.05wt% ∼ 0.25wt%, step:0.05wt%). An experimental process has advanced by conventional ferrimagnetism manufacturing that was prepared by standard ceramic techniques. The XRD pattern of all doped sample were observed spinel and secondary phase. The density of sample were measured nearly constant value. As increased the additive, resistivity, initial permeability and real component of the series complex permeability increased with setting limits each other. In case of Mn-Zn ferrite excess doped with them, resistivity, initial permeability and real component of the series complex permeability decreased and magnetic loss increased in proportion to increasing the additive.

• Journal of the Korean Ceramic Society
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• v.21 no.3
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• pp.259-265
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• 1984

As the effect of Al-powder as an additive on the sintering of $Al_2O_3$ was found satisfacotry in the range of 1350-155$0^{\circ}C$ this experiment was carried out at higher temperature(1600-180$0^{\circ}C$) at which the commerical $Al_2O_3$ body is sintered. Some phsical properties were measured and the micostructures of the specimens were observed by SEM. Although some measured physical properties of the specimens were improved through the addition of Al powder to $Al_3O_2$ powder the systematic changes in microsturces of the specmens could not be observed by SEM.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.458-462
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• 2006

A simple pressing process using a SiC powder, $Al_2O_3-Y_2O_3$ sintering additive, and polymer microbeads for fabricating cellular SiC ceramics is demonstrated. The strategy for making the cellular ceramics involves: (i) forming certain shapes using a mixture of a SiC powder, $Al_2O_3-Y_2O_3$ sintering additive, and polymer microbeads by pressing; (ii) heat-treatment of the formed body to burn-out the microbeads; and (iii) sintering the body. By controlling the microsphere content and sintering temperature, it was possible to adjust the porosity in a range of 16% to 69%. The flexural and compressive strengths of cellular SiC ceramics with $\sim$40% porosity were $\sim$60 MPa and $\sim$160 MPa, respectively.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.48-53
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• 2002

$Al_2O_3-SiC$ and $Al_2O_3-SiC$-TiC composite powders were prepared by SHS process using $SiO_2,\;TiO_2$, Al and C as raw materials. Aluminum powder was used as reducing agent of $SiO_2,\;TiO_2$ and activated charcoal was used as carbon source. In the preparations of $Al_2O_3-SiC$, the effect of the molar ratio in raw materials, compaction pressure, preheating temperature and atmosphere were investigated. The most important variable affecting the synthesis of $Al_2O_3-SiC$ was the molar ratio of carbon. Unreactants remained in the product among all conditions without compaction. The optimum condition in this reaction was $SiO_2$: Al: C=3: 5: 5.5, 80MPa compaction pressure under Preheating of $400^{\circ}C$ with Ar atmosphere. However there remains cabon in the optimum condition. The effect of $TiO_2$ as additive was investigated in the preparations of $Al_2O_3-SiC$. As a result of $TiO_2$ addition, $Al_2O_3-SiC$-TiC composite powder was prepared. The $Al_2O_3$ powder showed an angular type with 8 to $15{\mu}m$, and the particle size of SiC powder were 5~$10{\mu}m$ and TiC powder were 2 to $5{\mu}m$.