Papers by Keyword: Polytitanocarbosilane

Abstract: Liquid phase sintering based on the dissolution-precipitation mechanism was applied to densify a 0.8 μm SiC powder with alumina (1.2 vol%)-yttria (0.9-3.3 vol%) additives. To uniformly distribute the sintering additives around the SiC particles, a heterocoagulated particle network was formed among negatively charged SiC particles, positively charged 0.2 μm alumina and yttrium ions in an aqueous suspension at pH 5. Yttrium ions were electrostatically adsorbed on the negatively charged SiC surfaces. The consolidated green compacts were highly sintered to 97-99 % of theoretical density by hot-pressing at 1950 °C. Four-point strength, fracture toughness and Weibull modulus were highly enhanced when a bimodal particle size system of SiC (75 vol% 0.8 micrometer-25 vol% 30 nanometer SiC) was sintered. The maximum strength reached 1.1 GPa. The fracture toughness was about 6 MPa•m1/2 and the Weibull modulus was 5.9. When a small amount of SiC precursor polymer was infiltrated in the green compact, the strength and Weibull modulus were further improved.

Abstract: A bimodal powder system of 800 nm SiC (75 vol%) - 30 nm SiC (25 vol%) was dispersed at 20 vol% solid in a 0.3 M Y(NO3)3 solution containing 0.2 μm Al2O3 and 1.0 mg/m2 polyacrylic acid (PAA: dispersant). The SiC (97.6 vol%)-Al2O3 (1.2 vol%)-Y2O3 (1.2 vol%)-PAA system suspension was consolidated by casting in a gysum mold. Polytitanocarbosilane (PTC) of 3 vol% was infiltrated into the SiC compact calcined at 800 °C to increase the mechanical properties and Weibull modulus. Both the calcined powder compacts with and without PTC were hot-pressed to relative density above 97 % at 1950 °C. The hot-pressed SiC with or without PTC provided the following excellent mechanical properties: average four-point flexural strength of 911 and 812 MPa, fracture toughness of 5.2 and 6.0 MPa·m1/2, and Weibull modulus 11.3 and 5.8 for PTC addition and no addition, respectively. The PTC addition was effective to decrease the shape factor of flaw and increased the strength and Weibull modulus.

Abstract: In this paper, 3D Cf/Si-Ti-C-O composites were prepared with a polytitanocarbosilane (PTC) via polymer infiltration and pyrolysis (PIP) process, and accordingly the mechanical, oxidation resisting and thermal shock resisting properties were investigated. The composites with density of 1.93g·cm-3 show rather high flexural strength (485.3MPa) and fracture toughness (19.95MPa⋅m1/2), and typical non-brittle fracture failure mode. After oxidation treatment at 1300°C for 10 minutes in air, the flexural strength of the samples is 306.2MPa, with 63% strength retention. After 5 times of thermal shock tests from room temperature to 1300°C, the flexural strength of the samples is 408.9MPa, about 85% strength retention. SEM observation also testifies non-brittle failure because many fibers are pulled out on the fracture surface. After oxidation treatment, the matrix shows no changes from XRD measurement.

Abstract: A polytitanocarbosilane (20-30 mass%)-xylene solution was infiltrated into a porous laminated composite with 35-40 vol% Si-Ti-C-O fabric of 11 diameter fiber and 15-25 vol% mullite filler, and decomposed at 1000°C in an Ar atmosphere. This polymer impregnation and pyrolysis method was repeated 8 times to produce the composites of 76-82 % theoretical density. The yarn (662-765 filament / yarn), fabric and composite provided the following average strengths : 1240 MPa for the yarn; 768 MPa for the fabric; 117 MPa for the composite. The fracture probability of the yarn, fabric and composite was well fitted by the normal distribution function. The tensile strength of the composite was interpreted by the product of the effective fiber content, the Young's modulus of the fiber and elongation of the composite.