• 한국세라믹학회지
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• 제26권1호
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• pp.13-20
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• 1989

After sintering Si3N4 containing 20wt% of variable composition ratio of Y2O3 and Al2O3 at 1$600^{\circ}C$, the specimens were annealed at 125$0^{\circ}C$ and 135$0^{\circ}C$ for 5, 10, 15 hours in order to crystallize the remanining oxynitride glass phases. The main grain-boundary crystalline phases in the Si3N4-Y2O3-Al2O3 system were melilite and YAG. By annealing 15hrs. at 125$0^{\circ}C$, almost all of the glasses were crystallized. During the growth of melilite, lattice volyume of $\beta$-Si3N4 was increased as Al3+ and O2- ions in the oxynitride glass diffuse into $\beta$-Si3N4 lattice, but during the growth of YAG, lattice volume of $\beta$-Si3N4 was decreased by reverse diffusion of Al3+ and O2- ions. In case of crystallization of glass phase to melilite, thermal expansion of sample was decreased, but in case of crystallization to YAG, inverse phenomen on was observed.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권9호
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• pp.516-522
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta-SiC-ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of$Al_2O_3+Y_2O_3$ Phase analysis of composites by XRD revealed $\alpha-SiC(6H) ZrB_2\; and YAG(Al_5Y_3O_{12})$ The relative density of composites were increased with increased Al2O3+Y2O3 contents. The Flexural strength showed the highest value of 390.6MPa for composites added with 20wt% Al2O3+Y2O3 additives at room temperature. Owing to crack deflection crack bridging phase transition and YAG of fracture toughness mechanism the fracture toughness showed the highest value of 6.3MPa.m1/2 for composites added with 24wt% Al2O3+Y2O3 additives at room temperature. The resistance temperature coefficient showed the value of$ 2.46\times10^{-3}\;, 2.47\times10^{-3},\; 2.52\times10^{-3}/^{\circ}C$ for composite added with 16, 20, 24wt% Al2O3+Y2O3 additives respectively. The electrical resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $256{\circ}C\; to\; 900^{\circ}C$.

• 한국세라믹학회지
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• 제33권2호
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• pp.169-176
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• 1996

The specimens which were prepared from $\alpha$-Si3N4 with additions of YAG(3Y2O3.5Al2O3)-10 wt% and various AlN contents were sintered in N2 atmosphere at 1$700^{\circ}C$ The effect of $\alpha$,$\beta$-solid solution contents and sintering time on mechanical properties were investigated. As the content of $\beta$-solid solution and sintering time increased the hardness is reduced but the hardness of specimen sintered over 10 hours is constant irrespective of sintering time. While the fracture toughness increased with increasing of $\beta$-solid solution and sintering time. The fracture toughness of specimen with 80% $\beta$-solid solution content increased from 3.89 to 6.66 MPam1/2 with sintering sintering up to 20 hours/ But the amount of increased fracture toughness of specimen with below 20% $\beta$-solid solution content is not significant.

• 한국세라믹학회지
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• 제25권2호
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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℃.

• 한국세라믹학회지
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• 제26권2호
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• pp.201-209
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• 1989

Fine Si-Al-OH coprecipitate powders were prepared from Si- and Al-alkoxides by the hydrolysis method. $\beta$-Sialon powder was obtained from prepared Si-Al-OH coprecipitate by the simultaneous reduction and nitridation method. The syntehsized Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 90 min in N2 atmosphere. The characterization of the Sialon powder was performed with XRD, BET, SEM, TEM and particle size analysis. The sinterability and mechanical properties of sintered bodies were investigated in terms of relative density, M.O.R., fracture toughness, hardness and the morphology of microstructure. The highest values of their mechanical properties were obtained for the $\beta$-Sialon ceramics at Z=1 and those values are as follows : M.O.R., KIC and HV of $\beta$-Sialon ceramics(Z=1) are 499.1 MPa, 5.9MN/m3/2 and 18.7GPa, respectively.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권2호
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• pp.92-97
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC+39vol. %ZrB2 electroconductive ceramic composites were investigated by adding 1, 2, 3wt% Al2O3+Y2O3(6:4wt%) of the liquid forming additives. In this microstructures, no reactions were observed between $\beta-SiC$ and ZrB2. The relative density is over 90.8% of the theoretical density and the porosity decreased with increasing Al2O3+Y2O3 contents. Phase analysis of the composites by XRD revealed $\alpha-SiC(6H, 4H)$, ZrB2 and $\beta-SiC$(15R). Flexural srength showed the highest of 315.5MPa for composites added with 3wt% Al2O3+Y2O3 additives as room temperature. Owing to crack deflection and crack bridging of fracture toughness mechanism, the fracture toughness showed 5.5MPa.m1/2 and 5.3MPa.m1/2 for composites added with 2wt% and 3wt% Al2O3+Y2O3 additives respectively at room temperature. The area fraction of the elongated SiC grain in the etched surface of sample showed 65% and 65.1% for composite added with 2wt% and 3wt% Al2O3+Y2O3 additives respectively. The electrical resistivity at room temperature. The electrical resistivity of the composites wall all positive temperature coefficient(PTCR) against temperature up to $700^{\circ}C$.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.400-403
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• 1999

The mechanical and electrical properties of hot-pressed and annelaed $\beta$-SiC+39vol.% $ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_2O_3+Y_2O_3$(6:4 wt%). In this microstructures, no reactions and elongated $\alpha$-SiC grains with equiaxed $ZrB_2$ grains were observed between $\beta$-SiC and $ZrB_2$. The properties of the $\beta$-SiC+39vol.%$ZrB_2$ composites with 4wt% $Al_2O_3+Y_2O_3$ at R.T. are as follows: fracture toughness is 6.37 MPa.m1/2, electical resistivity is $1.51\times10^{-4}\Omega \cdot\textrm{cm}$ and the relative density is 98.6% of the theoretical density. The fracture toughness of the $\beta$-SiC+39 vol.% $ZrB_2$ composites were weakly decreased with increasing amount of $Al_2O_3+Y_2O_3$ additives. Internal stresses due to the difference of $\beta$-SiC and $ZrB_2$ thermal expansion coefficient and elastic modulus mismatch appeared to contribute to fracture toughening in $\beta$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권2호
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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 $700^{\cire}C$.

• Macromolecular Research
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• 제16권5호
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• pp.441-445
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• 2008

A series of aluminum complexes supported by $\beta$-ketoamino, ligand-bearing, 3-position substituents $LAlEt_2$ ($L=CH_3C(O)C(Cl)=C(CH_3)NAr\;(L_1)$, $L=CH_3C(O)C(H)=C(CH_3)NAr\;(L_2)$, $L=CH_3C(O)C(Ph)=C(CH_3)NAr\;(L_3)$, and $L=CH_3C(O)C(Me)=C(CH_3)NAr\;(L_4)$, $Ar=2,6-^iPr_2C6H_3$) were synthesized in situ and employed in the ring-opening polymerization (ROP) of $\varepsilon$-caprolactone ($\varepsilon$-CL) and cyclohexene oxide (CHO). The 3-position substituents on the $\beta$-ketoamino ligand backbone of the aluminum complexes influenced the catalyst activity remarkably for both ROP of $\varepsilon$-CL and CHO. Aluminum $\beta$-ketoamino complexes displayed different catalytic behavior in ROP of $\varepsilon$-CL and CHO. The order of the catalytic activity of $LAlEt_2$ was $L_1AlEt_2$>$L_2AlEt_2$>$L_3AlEt_2$>$L_4AlEt_2$ for ROP of $\varepsilon$-CL, being opposite to the electron-donating ability of the 3-position substituents on the $\beta$-ketoamino ligand, while the order of the catalytic activity for ROP of CHO was $L_1AlEt_2$>$L_3AlEt_2$>$L_4AlEt_2$>$L_2AlEt_2$. The effects of reaction temperature and time on the ROP were also investigated for both $\varepsilon$-CL and CHO.

• 한국세라믹학회지
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• 제32권9호
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• pp.1040-1046
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• 1995

The formation free energy of Y2Cu2O5 was measured by the partial ion exchanged (Cu2+, Na+)-$\beta$/$\beta$"-Al2O3 as solid state electrolyte. The formation cell was built as follows: Pt(O2)/Y2Cu2O5＋Y2O3//(Cu2+, Na+)-$\beta$/$\beta$"-Al2O3//CuO/(O2)Pt The virtual formation formation formula, and the calculated formation free energy of Y2Cu2O5 as a function of temperature are as follows: 2CuO＋Y2O3=Y2Cu2O5 ΔfG0/kJ.mol-1=13.19-16.25*10-3T/K.5*10-3T/K.