Study on polysiloxane resins as matrix precursors for ceramic composites
Teresa Gumuła*, Stanisław Błażewicz*, Kei Enomoto** *Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, ul. Reymonta 23, 30-059 Kraków **Tohoku University, Departament of Materials Science and Engineering, Japan
Annals 2 No. 4, 2002 pages 259-262
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abstract One of the most advanced and promising engineering materials is the carbon fibres-reinforced carbon matrix composite, often termed as carbon-carbon composite. Their desirable properties including high-tensile modulus and tensile strength that are retained to temperatures in excess of 2000oC, resistance to creep, and relatively large fracture toughness values. Furthermore, carbon-carbon composites have low coefficients of thermal expansion and relatively high thermal conductivities; these characteristics, coupled with high strengths, give rise to a relatively low susceptibility to thermal shock. Their major drawback is a propensity to high-temperature oxidation. This occurs at temperatures above 500oC. Much effort is done in order to protect carbon-carbon composite against air-oxidation and to enable their use for high temperature application. Several methods have been developed to improve oxidation resistance. Ceramic matrix composites reinforced with carbon fibres are potential candidates for applications requiring high strength and modulus at elevated temperatures. Subject of this work is usability of [methyl(phenyl)siloxane] resins as matrix fibre-reinforced composites. The used resins were compared from point of view of mass losses after heat treatment and of oxidation resistance in air at 600oC. The investigations were realized in the following stages: 1. Investigation of two types of [methyl(phenyl)siloxane] resins (designations: L 150X and L 901) as matrix precursors. 2. Preparation of composite samples with various types of fibres. 3. Investigation of composites. In this study [methyl(phenyl)siloxane]-based resins, type L 150X and L 901, produced by Lučební závody, Kolin (Czech Republic) and various types of fibres (carbon fibres T 300 (Torayca) without sizing, carbon fibres T 300 (Torayca) with sizing, SiC fibres NICALON) were used. Resins were used as the substrates for receiving matrices of composites. The resins varied in chemical structure, physical properties and type of solvent. The unidirectional composite samples (1D) were manufactured by wet-winding (prepreg) technique. Method of preparation is shown in Figure 1. The oxidation resistance for all samples was determined by mass losses measurement after heating in air atmosphere at 600oC for 2 hours. Mass losses after heat treatment for resin L 901 were 15,7% (Fig. 2). This result indicates that composite with L901 resin as a matrix precursor should have lower porosity in comparison to composite with matrix received by heat treatment of L 150X resin (50.2%). Hence, the L 901 resin heat treated at 900oC has lower mass losses after oxidation then L 150X resin (after heat treatment at the same conditions) (Fig. 2). Carbon fibres T 300 surface treated (with sizing)/resin composite after heat treatment at 900oC (Fig. 4) has distinctly lower oxidation resistance in comparison to the same composite after heat treatment at 1500oC (Fig. 5). It can be explained by SiC forming in the matrix after additional treatment at 1500oC, which inhibits the oxidation process. As it indicates from Figures 3 and 4 carbon fibres T 300 reinforced with resin matrix and subject to heat treatment at 900oC have relative low oxidation resistance. SiC fibres/resin composite (Fig. 6) has comparable oxidation resistance to the carbon fibres with sizing/resin composite after heat treatment at 1500oC (Fig. 5). Composites with L 901 resin-based matrix have lower mass losses after heat treatment in comparison to composites with L 150X resin-based matrix. Such a low value of mass losses can be useful for receiving the composites, which should have higher density, lower porosity and probable should have better mechanical properties. The highest oxidation resistance have carbon fibres T 300 with surface sizing/ resin composite after heat treatment at 1500oC and SiC fibres/resin composite heat treated at 900oC.