• Electrical & Electronic Materials
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• v.5 no.2
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• pp.182-188
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• 1992

코디에라이트 그라스 세라믹은 다충 IC 기관과 IC 팩키지용 그라스 세라믹의 재료로 크게 각광을 받고 있다. 보강용 휘스커량과 열처리 온도는 시료의 경도와 이성에 직접적인 영향을 미치며 경도와 인성은 휘스커량과 열처리 온도에 따라 증가하였다. 약 15 vol.%의 휘스커를 포함한 시료를 950.deg.C로 열처리 하였을 때에 경도나 인성 같은 기계적 특성이 가장 좋았다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.473-480
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• 1997

$\beta-SiC$powder with or without the addition of 1-3 wt% of $\beta-SiC$ whiskers (seeds) was hot-pressed at $1850^{\circ}C$ for 1 h using $Al_2O_3$ and $Y_2O_3$ as sintering aids. The hot-pressed materials were subsequently annealed at $1950^{\circ}C$ to enhance grain growth. The introduction of $\beta-SiC$ whiskers into $\beta-SiC$ does not affect the microstructure as well as mechanical properties significantly because the whiskers are not viable in the presence of liquid phase during hot-pressing. The strengths and fracture toughnesses of the hot-pressed and subsequently 5 h-annealed materials with 1 wt% $\beta-SiC$ whiskers and without $\beta-SiC$ whiskers were 465 MPa and 5.8 MPaㆍ$m^{1/2}$, and 451 MPa and 5.5 MPaㆍ$m^{1/2}$, respectively.

• Journal of the Korean Ceramic Society
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• v.33 no.12
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• pp.1380-1386
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• 1996

The effects of urea addition and reaction conditions were examined in the prepareation of zirconia coated SiC whiskers through surface precipitation taking place during high-temperature aging of Zr(SO4)2 solutions containing the whiskers. More dense zirconia-hydrate was precipitated on the surfaces of the whiskers in the presence of urea. The ratio of the concentration of Zr(SO4)2 to the amount of added whiskers was the most important factor to confine the precipitation of zirconia-hydrate only at the surfaces of the whiskers The from of the coating layers was unchanged after heat-treatment leading to the dehydration and crystallization of the layers.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.561-569
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• 1988

Mixtures of very small amounts of additive, carbon and silica(about 0.46${\mu}{\textrm}{m}$) which synthesized by the hydrolysis of ethyl silicate, the molar ratio of SiO2/C was fixed to 1/10, was nitrided at 145$0^{\circ}C$. It was considered that the optimum amount of additive to promote the nitridation reaction was below 2.0wt%. By the addition of additive, the nitridation reaction was promoted and formation of $\beta$-Si3N4 was promoted at 145$0^{\circ}C$ for 1hour, but, the nitridation reaction was decreased and the ratio of $\alpha$/$\beta$ of Si3N4, was increased at 145$0^{\circ}C$ for 5 hours. The crystal phase was $\alpha$ phase and the nitridation reaction was promoted and the particle size of silicon nitride was become smaller by the addition of $\alpha$-Si3N4, but silicon nitride of whisker-like form was produced by the addition of transition elements. There was a difference in the lattice constants of $\alpha$-Si3N4, but no difference in its of $\beta$-Si3N4 according to kinds of added substance and reaction time.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.188-192
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• 2006

The microstructures and mechanical properties of continuously porous $SiC-Si_3N_4$composites fabricated by multi-pass extrusion were investigated at different Si levels added. Si-powder with different weight percentages (0%, 5%, 10%, 15%, 20%) was added to the SiC powder to make the raw mixture powders, with $6wt%Y_2O_3-2wt%Al_2O_3$ as sintering additives, carbon ($10-15{\mu}m$) as a pore-forming agent, ethylene vinyl acetate as a binder and stearic acid ($CH_3(CH_2)_{16}COOH$) as a lubricant. In the continuously porous $SiC-Si_3N_4$ composites, $Si_3N_4$ whiskers like the hairs of nostrils were frequently observed on the wall of the pores. In this study, the morphology of the $Si_3N_4$ whiskers was investigated with the silicon addition content. In the composites containing of 10 wt% Si, a large number of $Si_3N_4$ whiskers was found at the continuous pore regions. In the sample to which 15 wt% Si powder was added, maximum values of about 101 MPa bending strength and 57.5% relative density were obtained.

• Korean Journal of Materials Research
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• v.15 no.10
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• pp.644-651
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• 2005

The thermal analysis of $Al(OH)_3-SiO_2-AIF_3$ system was done. The thermal behaviors of components and the effect of moisture on the formation of mullite were investigated via TG-DTA and XRD analysis. The mixture of $Al(OH)_3,\;SiO_2,\;AIF_3$showed two endothermic peaks with drastic weight loss and one exothermic peak. Fluorotopaz was formed at $800^{\circ}C$ and turned into mullite completely at $1100^{\circ}C$. But the mixture $Al_2O_3$ of or dehydrated $Al(OH)_3$ and $SiO_2$ could not form mullite even at $1200^{\circ}C$ in which the crystalline phases were $\alpha-Al_2O_3$ ana cristobalite. It was found that the synthesized mullite was aciculate shaped single crystalline whisker.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.199-202
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• 2006

In this study, SiC whiskers were grown on a porous SiC diesel particulate filter for nanoparticle filtering. To grow the whiskers at the inner pore without closing the pores, we used chemical vapor infiltration with a solution source and a dilute. As the deposition time increased, the whiskers grew and formed a network structure. After 180 min of deposition, the mean diameter of the whiskers was 174 nm and the compressive strength was 58.4 MPa. The pores shrank from $10{\mu}m\;to\;0.4{\mu}m$ and, because the whiskers filed the inner pores, the gradient of permeability decreased as the deposition time increased. However, by using the network structure of whiskers deposited for 120 min and 180 min, we obtained a diesel particulate filter with pores of $0.98{\mu}m\;and\;0.4{\mu}m$, respectively. Furthermore, the filter shows better permeability than a porous body with pores of $1{\mu}m$. In short, by filtering the nanoparticulate materials, the network structure of whiskers improves the strength, reduces the pore size and minimizes the permeability drop.

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.457-464
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• 1990

This paper presents the influence of the loading rate on the room temperature fracture toughness of a brittle Al2O3 and a SiC whisker reinforced Al2O3 composite. Dynamic fracture toughness tests were conduced using compressive fatigue pre-cracked notched round bars loaded in tension to produce a stress intensity rate K1=106 MPa√m/sec. The experimental results show that for each loading rate the fracture toughness values obtained for the ceramic matrix composite are higher than the corresponding values for the single phase alumina. In addition, both the reinforced and unreinforced ceramic are singnificantly tougher under dynamic loading than static loading. This dynamic and quasi-static fracture initiation behaviro can be interpreted by identifying quantitatively the mode of fractuer initiation as a function of loading rate.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.330-336
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• 1994

High strength cement composites (W/C=0.1) were prepared by using various blending materials such as SiC whisker and white carbon (hydrated silica: SiO2·nH2O). The effect of various blending materials on the microstructure and strength of the hardened cement paste were investigated in the view of fracture mechanics. The plain specimen showed 101 MPa of flexural strength, 81 GPa of Young's modulus and 1.32 MPam1/2 of fracture toughness. When the blending materials were added to the composites, their values were enhanced to about 110∼138 MPa, 95∼146 GPa and 1.32∼1.87MPam1/2 respectively. The improvement of the mechanical strength for the hardened cement paste may be due to the removal of macropores, the reduction of total porosity, pozzolanic reaction and the increase of various fracture toughening effect.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.511-516
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• 1992

In this study, SiC powder and Si powder were used as the raw materials. Mixture was prepared with addition of Al2O3 and Fe2O3 at 0.1~0.5wt% respectively. After this step, the mixture was pressed and nitrided for 30 hrs at 140$0^{\circ}C$ under NH3-N2 atmosphere. Mechanical properties of sintered specimens were investigated from measurement of porosity, bulk density and three point bending test. nitration reaction extent was observed at the change of mass before and after reaction, and the microstructure and the change of $\alpha$-Si3N4 and $\beta$-Si3N4 were observed by XRD and SEM. In the current work, the results are as follows 1. When Fe2O3 added, the nitridation increased with the content of Fe2O3, and the bending strength was increased from 0.1 wt% to 0.3 wt%, and decreased to 0.5 wt%. 2. When Al2O3 added, the nitridation and the bending strength increased little by little with the content of Al2O3 3. The bending strength of the specimen added with Fe2O3 were higher than that with Al2O3. Because the specimens contained Fe2O3 had much more the whisker type crystal of Si3N4 contributing to strength than contained Al2O3.