• 한국세라믹학회지
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• 제24권5호
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• pp.453-460
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• 1987

β'-sialon(Z=2.7) specimens with <30%wt. graphite as a reducing agent were decomposed at 1350°up to 1,450℃ under the atmosphere of 90% N2-10%H2. The decomposition of β'-sialon was calculated from the change in Z-value, and the formation of new minerals was identified from X-ray diffraction patterns. The decomposition reactions of sialon were considered to yield a stable sialon close to β-silicon nitride and some aluminum compounds according to the following equations; β'-sialon(s)＋C(s)＋N2(g)→β2-sialon(metastable)＋β3-sialon(stalbe phase) β2-sialon(s)＋C(s)＋N2(g)→β3-sialon(s)＋AlN(s)＋α-Al2O3(s)＋15R(s)＋SiO(g)＋Al2O(g)＋CO(g) Z-value; β2( 3.5)>β'( 2.7)>β3( 0.5) The decomposition rate of sialon was controlled by two mechanisms ; One was characterized by the interface area of contact, corresponding to an apparent activation energy of 50.5Kcal/mol in the initial stage, and the other by the diffusion, corresponding to that of 104.3Kcal/mol in the final stage of the decomposition.

• 한국세라믹학회지
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• 제30권11호
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• pp.941-948
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• 1993

The powder mixture of Si3N4-AlN-Y2O3, Si3N4-AlN-CeO2 and Si3N4-AlN-Y2O3-CeO2 system was hot-pressed at 175$0^{\circ}C$ for 2h in N2 to prepare $\alpha$-Sialon ceramics. The mechanical property and oxidation behaviour of the prepared $\alpha$-Sialon ceramics were investigated. At 120$0^{\circ}C$, oxidation resistance was best for the Y2O3 added $\alpha$-Sialon ceramics and oxidation rate increased when the amount of CeO2 increased. But when the mixture of Y2O3 and CeO2 added $\alpha$-Sialon ceramics showed a good oxidation resistance. Fracture toughness of (Y2O3＋CeO2) added $\alpha$-Sialon ceramics was higher than Y2O3 added $\alpha$-Sialon ceramics.

• 한국세라믹학회지
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• 제26권3호
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• pp.402-408
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• 1989

$\beta$-Sialon powder was synthesized by the simultaneous reduction and nitridation of the mixed powder of Hadong kaolin and Kimcheon quartzite, using graphite as a reducing agent. The synthesized $\beta$-Sialon powder (Z=1) was hot-pressed at 175$0^{\circ}C$, for 90min under 30MPa in N2 atmosphere, after Yttria and YAG composition material were added as sintering agents. The effects of grain-boundary crystallization on high-temperature mechanical properties of $\beta$-Sialon ceramics were investigated. Strength degradation was observed at above 1,00$0^{\circ}C$ for the $\beta$-Sialon (Z=1)-8wt% Y2O3 composition, but it was not observed up to 1,20$0^{\circ}C$ for the $\beta$-Sialon-8wt% YAG composition which was annealed at 1,40$0^{\circ}C$ for 4 hours in N2 atmosphere. After the $\beta$-Sialon-8wt% YAG composition was annealed, the decrease of fracture toughness was observed.

• 한국세라믹학회지
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• 제25권2호
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• pp.143-153
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• 1988

김천규석으로부터 합성한 질화규소와 시약급의 AIN과 $Y_2O_3$를 출발원료로 하여 $Si_3N_4-0.1Y_2O_3-0.9AIN$의 tie line에서 X=0.6, 0.4(금속고용량)인 조성으로부터 AIN 의 양을 감소시킨 조성과 $Y_2O_3$를 증가시키는 조성으로 1750~1800도에서 소결시켜 부분 안정화 $\alpha$-Sialon을 제조하였다. $\alpha$-Sialon 생성에는 $Y_2O_3$ 첨가량보다 AIN 첨가량에 밀접하게 관련되며 AIN은 $\beta$단위격자 보다 $\alpha$ 단위격자로 우선적으로 고용되었으며 $Y_2O_3$가 과잉으로 첨가된 조성에서는 melillite 형성과 입자 조대화 및 $\alpha$-Sialon의 분배로 인하여 yttrium silicide 와 금속 Si를 형성하였으며 기계적 물성은 저하하였다. 본 실험에서 얻은 기계적 물성의 최고 값은 모두 1780도에서 얻어졌으며 그 값은 꺽임강도 723MPa, 파괴 인성 4.5MN/m^3/2, 경도 19.3GPa이었다.

• 한국세라믹학회지
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• 제49권4호
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• pp.375-379
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• 2012

Nitride phosphors are now attracting significant attention of material scientists and phosphor engineers, because they promise red-shifted photoluminescence spectra, small Stokes shift, high quantum efficiency and low thermal degradation. A number of interesting nitride phosphors have been developed and practiced for producing white light with LED chips. In this paper, the applications of nitride phosphors in highly reliable wLEDs will be overviewed.

• 한국세라믹학회지
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• 제24권4호
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• pp.349-356
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• 1987

${\beta}$-Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350$^{\circ}C$ in N2-H2 atmosphere, using graphite as a reducing agent. The synthesized ${\beta}$-Sialon powder was pressurelessly sintered over 1450-1850$^{\circ}C$ in nitrogen atmosphere. The average particle size of ${\beta}$-Sialon powder was about 4.5$\mu\textrm{m}$. The relative density, M.O.R., fracture toughness and micro-hardness of ${\beta}$-Sialon ceramics sintered at 1800$^{\circ}C$ for 1 hour were 92%, 36 kpsi, 2.8MN/㎥/2 and 13.3 GN/㎡, respectively. The critical temperature difference (ΔT) in water quench thermal shock behavior showed about 375$^{\circ}C$ for the synthesized ${\beta}$-Sialon ceramics.

• 한국세라믹학회지
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• 제31권11호
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• pp.1259-1264
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• 1994

$\beta$-Sialon has been regarded as one of promising materials showing high strength, fracture toughness, corrosion resistence and wear resistence. The improvement of the fracture toughness and tribological properties of $\beta$-Sialon (Z=1) has been attempeted by fabricating the $\beta$-Sialon/ SiC whisker composite. Each of green body composed of following ingredients, i.e., Si3N4, AlN, Y2O3 nd SiC, respectively, was first fired at 178$0^{\circ}C$ for 3hrs in N2 atmosphere and then post-HIPed at 173$0^{\circ}C$ for 1 hr under 170 MPa for N2 gas pressure. The fracture toughness, flexural strength and tribological properties increased with increasing SiC whisker content, despite the reduction of the relative density and hardness. $\beta$-Sialon/15 vol% SiC whisker showed a significant enhancement of wear resistance compared to the monolithic $\beta$-Sialon. The addition of SiC whisker caused the reduction of the density and hardness, but induced the increment of wear resistance.

• 한국세라믹학회지
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• 제23권2호
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• pp.1-6
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• 1986

The mixture of (opalit+Al) powder was ignited by electric shock for the preparation of sialon powder by changin the contents of Al. The formation reaction of sialon was investigated by heating the specimens of ignited mixture (opalit+Al) in nitrogen atmosphere at various temperature. The phases existing inthe specimens nitrided between 1400 and 1$600^{\circ}C$ were found $\beta$-sialon 15R-sia-lon $Al_2O_3$ and AlN but the mixture $\beta$-sialon and 15R-sialon was finally acquired by heating the ignited mixture of (Al 50%+opalit) at 175$0^{\circ}C$ for 3hours in nitrogen atmosphere.

• 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.

• 한국세라믹학회지
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• 제28권12호
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• pp.961-968
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• 1991

The nature and composition of the surfaces of silicon nitride and β-Sialon powders were investigated using high voltage and high resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). β-Sialon powder was produced from Hadong kaolin by the carbothermic reduction and simultaneous nitridation. XPS showed that Al was contained in the surface of β-Sialon powder besides Si, N and O components, which is different from that of silicon nitride. It was supposed that Al in the surface of β-Sialon was bonded with oxygen from the oxygen-nitrogen ratio and the measurement of Al 2p binding energies. After both silicon nitride and β-Sialon powders were oxidized at 800℃ for 24h in air, nitrogen didn't exist in the surfaces and the depth of the oxide layer increased. The measurement of Si 2p binding energies showed that the chemical shifts occurred from Si3N2O and/or Si2N2O to SiO2 phase.