Pressureless-Sintering and Hot-Pressing of β-SiC Powders Prepared by Carburization of Shirasu Glass

• Published in: Journal of the Ceramic Association, Japan Vol. 92; no. 1063; pp. 126 - 134
• Main Authors: HIRATA, Yoshihiro, SUEKAWA, Yukihiro, SHIMADA, Kinji
• Format: Journal Article
• Language: Japanese
• Published: The Ceramic Society of Japan 01.03.1984
• Subjects: Densification; Hot-pressing; Pressureless-sintering; Shirasu; Silicon carbide; Strength; Vickers hardness
• ISSN: 0009-0255; 1884-2127
• DOI: 10.2109/jcersj1950.92.1063_126

Pressureless-sintering in the temperature range 1600°-2100°C and hot-pressing at 1900°C under Ar atmosphere were performed on β-SiC powders (average particles size: 0.34μm) prepared by carburization of Shirasu glass with carbon black. The SiC powders, whose purity is 84.4%, contains the glass enriched with Al2O3. Little densification of the compacts occurred in the pressureless-sintering owing to the presence of the glass phase and large weight loss during heating even when several sintering aids were added. On the other hand, undoped or C-added (2%) SiC powders were densitied up to relative densities of 85-90%, based on the density of raw powders (3.32g/cm3), by hot-pressing under a pressure of 200kg/cm2 at 1900°C for 30min. The relative densities of SiC hot-pressed with the additives such as Al (2%), B (2%), Al+C (2+2%), B+C (2+2%) or Al+B+C (2+2+2%) were 93-95%. Increase in the sintered density under the pressure is mainly attributed to the rearrangement of SiC particles promoted by the liquid phase from the Al2O3-enriched glass. Room temperature strengths of the hot-pressed SiC depend upon both size and shape of grains. Strengths were less than 35kg/mm2 in the specimen containing B or B+C and were 40 to 50kg/mm2 in the other specimens. The Vickers hardness of hot-pressed specimens increases remarkably with an increase in the relative density and reaches 2090±150kg/mm2 at the density of 97%.