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

• Composites Research
• /
• v.22 no.4
• /
• pp.50-53
• /
• 2009

This paper mainly describes the armor materials, especially the ceramic materials for the personal protection. In the ceramic armor materials, B4C ceramics and SiC ceramics are the most popular materials. The $B_4C$ ceramics which consists of 4 atoms of boron and I atom of carbon is very light and strong. It is usually used to personal protection armor and chair protection in the helicopter. This material must be sintered at very high temperature because it melts at $2400^{\circ}C$. In order to have a good armor property, it must have very high density which is achieved by hot press or subsidiary sintering aid methods such as reducing the particle size of raw materials or mixing the sintering agents to the raw materials.

• Journal of Korean Ophthalmic Optics Society
• /
• v.5 no.2
• /
• pp.207-210
• /
• 2000

The SiC-TiC composites materials for glasses lens cutting were fabricated by hot-pressing and annealing. The amount of TiC was 0, 10, 20, 30wt% in the mixture of ${\beta}-SiC$. The microstructure of materials for glasses lens cutting was very dependent on the TiC amount. The introduction of larger amount of TiC improved fracture toughness, optical microscope and XRD analysis of the surface of samples were carried out. An in situ-toughened microstructure, consisted of distributed elongated SiC, matrix like TiC grains was developed by using ${\beta}-SiC$. Typical hardness and fracture toughness of materials for spectacle lens cutting were 14.9 GPa and $5.7MPa{\cdot}m^{1/2}$, respectively.

• Journal of Korean Ophthalmic Optics Society
• /
• v.11 no.2
• /
• pp.85-89
• /
• 2006

To research of the improved mechanical properties of materials for spectacle lens cutting, SiC and TiC were used as the main powder. Also, $Al_2O_3$ and $Y_2O_3$ was included as a sintering additive. The weight ratio of the alumina($Al_2O_3$) to yttria($Y_2O_3$) was set to 1:1. The materials for spectacle lens cutting were fabricated by hot-pressing at $1810^{\circ}C$ for 1h and subsequently annealed at $1860^{\circ}C$ for 3, 6 and 12h to initiated grain growth. The longer annealing time is, the bigger the grain size is. The microstructures were observed by scanning electron microscopy (SEM). The SEM images were quantitatively analyzed by image analysis (Image-Pro Plus, Media Cybernetics, Maryland, U.S.A.). Crack deflection by elongated SiC grains was most frequently observed as the dominant toughening mechanism. Crack deflection was generally observed for elongated SiC grains with aspect ratio(AR) > 2.5 and grain thickness < $2.3{\mu}m$. Crack bridging was also observed as one of the operating toughness mechanism.

• Journal of Korean Ophthalmic Optics Society
• /
• v.5 no.1
• /
• pp.61-65
• /
• 2000

${\beta}$-SiC powder and ${\alpha}$-SiC powders of different particle sizes, containing 5.7wt% $Al_2O_3$ and 4.3wt% $Y_2O_3$ as sintering aids, were hot-pressed at $1780^{\circ}C$ and subsequently annealed at $1950^{\circ}C$ to initiate grain growth. All the hot-pressed and annealed materials consisted of large SiC grains and elongated SiC grains. Typical hardness and fracture toughness of materials for spectacle lens cutting were 15.6 GPa and $5.7MPa{\cdot}m^{1/2}$, respectively.

• Journal of Korean Ophthalmic Optics Society
• /
• v.7 no.1
• /
• pp.25-27
• /
• 2002

To improve the properties of materials for spectacle lens cutting. AIN was included as a sintering additive. The amount of AIN was 0, 1, 3, 5 wt% and materials for spectacle lens cutting were fabricated by hot-pressing at $1830^{\circ}C$ for 2h. Microstructure was consisted of equiaxed SiC and elongated TIC. Typical fracture toughness and hardness of materials for spectacle lens cutting with AIN $4.8MPa{\cdot}m^{1/2}$ and 15.3 GPa, respectively.

• Applied Chemistry for Engineering
• /
• v.16 no.5
• /
• pp.648-652
• /
• 2005

A super ionic conductor, $K^+$-beta-aluminas, which is known to be difficult to obtain in the form of dense sintered density under atmospheric pressure, was pulverized to 350 nm mean particle size using attrition mill. The sample were pressed into tablet form by uniaxial pressing. The specimen was sintered under atmospheric pressure in powder form. Sintering temperature range was $1400^{\circ}C$ to $1650^{\circ}C$ at $50^{\circ}C$ intervals. Additionally, zone sintering was carried out to control the growth grain at high temperature ($1600^{\circ}C$). The density of specimens that were sintered at $1600^{\circ}C$ and $1650^{\circ}C$, and sintered at $1600^{\circ}C$ by zone sintering were about 93% and 95%, respectively. In the case of the lengthened sintering time to 2 h, the density of specimen was reduced to lower than 90%, since the particles were grown to the duplex microstructure.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.18 no.6
• /
• pp.237-241
• /
• 2008

Hot-press sintering of AlN ceramics were carried out with $Y_2O_3$ as sintering additive at a sintering temperature $1,750{\sim}1,850^{\circ}C$. The effect of $Y_2O_3$ addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. $Y_2O_3$ added AlN showed noticeably higher denazification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of $Y_2O_3$ in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because $Y_2O_3$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% $Y_2O_3$ added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.

• Journal of the Korean Ceramic Society
• /
• v.38 no.1
• /
• pp.22-27
• /
• 2001

$\beta$-Si$_3$N$_4$종자입자 첨가가 소결조제로 Y-Mg-Si-Al-O-N계 oxynitride glass를 사용하여 일축가압 소결을 행한 SiC-Si$_3$N$_4$복합재료의 미세구조와 기계적 특성에 미치는 영향을 고찰하였다. 길게 자란 $\beta$-Si$_3$N$_4$입자들과 등방성의 $\beta$-SiC 입자들이 균일하게 분포된 미세구조를 얻었다. $\beta$-Si$_3$N$_4$종자입자 함량이 증가함에 따라 SiC-Si$_3$N$_4$복합재료의 강도와 파괴인성이 증가하였고, 이는 복합화에 기인하는 결함크기의 감소와 길게 자란 $\beta$-Si$_3$N$_4$입자에 의한 균열가교 및 균열회절 등에 기인하였다. SiC-70 wt% Si$_3$N$_4$복합재료의 대표적인 강도와 파괴인성은 각각 770 MPa과 6.2 MPa.m$^{1}$2/ 이었다.

• Journal of Korean Ophthalmic Optics Society
• /
• v.5 no.1
• /
• pp.55-59
• /
• 2000

In this study, materials for spectacle lens cutting were fabricated by hot-pressing and annealing SiC powders with $Al_2O_3$ and $Y_2O_3$. A microstructure that consisted of uniformly distributed, large SiC grains and elongated SiC grains was developed by using ${\alpha}$-SiC powders. The microstructure was observed by scanning electron microscope(SEM). By hot-pressing and subsequent annealing, elongated ${\beta}$-SiC grains were grown via ${\beta}{\rightarrow}{\alpha}$ phase. This is caused the crack deflection as toughening mechanism. Typical hardness and fracture toughness of materials for spectacle lens cutting were 13.3 GPa and $4.8MPa{\cdot}m^{1/2}$, respectively.