• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.343-350
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• 1995

A Abstract Systematic studies of the effects of crystalline forms of starting powders and p processing variables on the texture of hot - pressed silicon carbide are described. The results I indicate that hot - pressing of $\beta$ - SiC can produce strong textures and composite type duplex microstructure due to the ${\beta} {\rightarrow} {\alpha}$ phase transformation of SiC. The texture variations d during post - annealing have been observed. In the case of using a - SiC as starting pow¬d ders, the degree of preferred orientation by hot - pressing is relatively weak.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.260-265
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• 1999

$SiC/Si_3N_4$ composites were prepared by mixing ${\alpha}-Si_3N_4$ powder to $\alpha$-SiC powder in the range of 10 to 30 vol% with 10 vol% interval. 6 wt% of $Al_2O_3$ and $Y_2O_3$ were also added respectively as sintering aids. Then, pressureless sintering was performed at 1,78$0^{\circ}C$ for 2 hours in $N_2$ gas. In the case of adding 20 vol% of ${\alpha}-Si_3N_4$ powder, the relative desity to theoretical value and the flexutal strength were 92 % and 3,560 MPa, respectively. The smallest relative worn amount thereof was $2.68{\times}10^{-3}\;mm^2$ for 20 vol% ${\alpha}-Si_3N_4$. The composite containing 30 vol % of ${\alpha}-Si_3N_4$ powder showed the highest fracture toughness $(K_{1c})$ of $4.9\;MN/m^{3/2}$, although the reduction of the wear resistance due to the effect of the pores was observed.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.283-286
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• 2006

We have studied the role of ${\alpha}-Al_{2}O_{3}$ buffer layer as a diffusion barrier in the Ba-ferrite/$SiO_{2}$ magnetic thin films for high-density recording media. In the interface of amorphous Ba-ferrite $(1900-{\AA}-thick)/SiO_{2}$ thin film during annealing, the interfacial diffusion started to occur at ${\sim}700^{\circ}C$. As the annealing temperature increased up to $800^{\circ}C$, the interfacial diffusion abruptly proceeded resulting in the high interface roughness and the deterioration of the magnetic properties. In order to control the interfacial diffusion at the high temperature, we introduced ${\alpha}-Al_{2}O_{3}$ buffer layer ($110-{\AA}-thick$) in the interface of Ba-ferrite/$SiO_{2}$ thin film. During the annealing of Ba-ferrite/${\alpha}-Al_{2}O_{3}/SiO_{2}$ thin film even at ${\sim}800^{\circ}C$, the interface was very smooth. The magnetic properties, such as saturation magnetization and intrinsic coercivity, were also enhanced, due to the inhibition of interfacial diffusion by the ${\alpha}-Al_{2}O_{3}$ buffer layer. Our study suggests that the ${\alpha}-Al_{2}O_{3}$ buffer layer act as a useful interfacial diffusion barrier in the Ba-ferrite/$SiO_{2}$ magnetic thin films.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.243-249
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• 1993

Coated type Al2O3-SiC composite powders were synthesized by surface modification method. Transformation temperature to $\alpha$-Al2O3 of Al2O3 monolith was 115$0^{\circ}C$ whereas increased to 1200, 1250, 130$0^{\circ}C$ with increment of SiC content to 5, 15, 25wt%. Transformation temperature to $\alpha$-Al2O3 was lowered by $\alpha$-Al2O3 seeding. FTIR data analysis and electron micrographs showed that Al2O3 particles were effectively coated on SiC particles.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.502-508
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• 1988

The $\alpha$ to $\beta$ phase transformation of $\alpha$-Si3N4 whisker and related microstructural changes have been investigated. When only $\alpha$-Si3N4 whisker was heat treated in the range 1650~175$0^{\circ}C$, the $\alpha$ to $\beta$ phase transformation occured. In this case, it eas suggested that the oxygen content in $\alpha$-Si3N4 whisker affected the transformation behavior. Although $\alpha$-Si3N4 whisker with Si was heat treated under the same condition, however, the variation of $\beta$- fraction had a similar tendency with heat treating time. Therfore, it was considered that the oxygen content in $\alpha$-Si3N4 whisker affected the transformation behavior dominently rather than the content of added Si. The added $\beta$ phase did not affect the transformation behaviro of $\alpha$-Si3N4 whisker.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.7
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• pp.352-357
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• 2004

The composites were fabricated, respectively, using 61vol.% SiC - 39vol.% TiB$_2$ and using 61vo1.% SiC - 39vo1.% WC powders with the liquid forming additives of 12wt% $Al_2$O$_3$＋Y$_2$O$_3$ by pressureless annealing at 180$0^{\circ}C$ 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$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-TiB$_2$, and SiC(2H), WC and YAG(Al$_{5}$Y$_3$O$_{12}$) crystal phase on the SiC-WC composites. $\beta$\$\longrightarrow$$\alpha$-SiC phase transformation was ocurred on the SiC-TiB$_2$, but $\alpha$\$\longrightarrow$$\beta$-SiC reverse transformation was not occurred on the SiC-WC composites. The relative density, the vicker's hardness, the flexural strength and the fracture toughness showed respectively value of 96.2%, 13.34GPa, 310.19Mpa and 5.53Mpaㆍml/2 in SiC-WC composites. The electrical resistivity of the SiC-TiB$_2$ and the SiC-WC composites is all positive temperature coefficient resistance(PTCR) in the temperature ranges from $25^{\circ}C$ to 50$0^{\circ}C$. 2.64${\times}$10-2/$^{\circ}C$ of PTCR of SiC-WC was higher than 1.645${\times}$10-3/$^{\circ}C$ of SiC-TiB$_2$ composites.posites.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.999-1006
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• 1993

Si3N4(p)-SiC(p) composites were prepared by gas pressure sintering at 190$0^{\circ}C$ for 1 hour. $\alpha$-SiC with average particle size of 0.48${\mu}{\textrm}{m}$ were dispersed from zero to 50vol% in $\alpha$-Si3N4 with average particle size of 0.5${\mu}{\textrm}{m}$. Y2O3-Al2O3 system was used as sintering aids. When 10vol% of SiC was added to Si3N4, optimum mechanical properties were observed; relative density of 98.8%, flextural strength of 930MPa, fracture toughness of 5.9MPa.m1/2 and hardness value of 1429kg/$\textrm{mm}^2$. Grain growth of $\beta$-Si3N4 was inhibited as the amount of added SiC was increased. SiC particles were found inside the $\beta$-Si3N4 intragrains in case of 10, 20 and 30vol%SiC added composites.

• Journal of the Korean Ceramic Society
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• v.36 no.10
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• pp.1102-1107
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• 1999

SiC-Si3N4 composites were prepared by mixing $\alpha$-Si3N4 powder to $\alpha$-SiC powder in the range of 10 to 30 vol% with 10vol% interval. 6wg% Al2O3 and 6wt% Y2O3 were respectively added as sintering aids. Hot pressing was performed at 1,80$0^{\circ}C$ for 1 hour with 25 MPa pressure. In the case of adding 20vol% of $\alpha$-Si3N4 powder the relative density to theoretical value and the flexural strength were 99.1% and 34,420 MPa respectively and the worn amount was 2.09$\times$10-3 mm2 which were the highest values in the all range of he composition. Although the composite containig 10 vol% of $\alpha$-Si3N4 powder showed the highest fracture toughness(KIC) of 4.65MN/m3/2 the reduction of the wear resistance in this composite is likely to be affected by the homogeneity and the uniformity of the grain coalescence and growth during the sintering process.

• The Korean Journal of Ceramics
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• v.2 no.4
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• pp.226-230
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• 1996

A small amount of fine particle graphite was added to $\alpha$-SiC and $\beta$-SiC having certain particle distributions, and they were mixed clay and frit. After forming, they were sintered at 140$0^{\circ}C$ for 3 hours. Tribological properties of sintered $\alpha$-SiC-$\beta$-SiC-graphite-clay (frit) system showed that kinetic friction coefficient was 0.108, specific wear rate was 1.3${\times}10^-8\;mm^2$.$kgf^1$, and torque was 0.01kgf.cm at the wrench torque of 100 kgf.cm.

• Journal of the Korean Ceramic Society
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• v.37 no.11
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• pp.1091-1096
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• 2000

본 연구에서는 기상 반응법을 이용하여 TMS(Tetramethylsilane:Si($CH_3$)$_4$)와 NH$_3$그리고 H$_2$의 혼합기체로부터 반응 온도 1000~120$0^{\circ}C$ 및 입력비(NH$_3$/Si($CH_3$)$_4$) 1~3의 조건에서 초미분의 SiC-Si$_3$N$_4$복합 분말을 합성하였다. 합성되어진 복합 분말들의 결정상의 변화와 평균 입경을 알아보기 위해 XRD와 TEM 분석을 행한 결과, 구형의 비정질 분말이 형성되었으며, 입자의 크기는 약 70~130nm이었다. 입자의 크기는 입력비에 관계없이 거의 일정하였으나 반응 온도가 증가함에 따라서 감소하였다. FT-IR과 EA 분석 결과, 합성되어진 분말은 Si, N, C, 그리고 H로 이루어진 화합물임을 확인할 수 있었다. 또한 입력비가 다른 조건에서 합성되어진 분말을 $N_2$분위기 하에서 155$0^{\circ}C$로 2시간 열처리를 행한 결과, 낮은 입력비인 경우 $\beta$-SiC, $\alpha$-Si$_3$N$_4$와 $\beta$-Si$_3$N$_4$의 결정상들이 혼재하였으나, 높은 입력비인 경우는 결정화 후 $\alpha$-Si$_3$N$_4$상만이 존재하였다.