Preparation and oxidation of Al 4 SiC 4
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Single-phase Al4SiC4 was successfully synthesized by heating the powder mixture of aluminum, silicon, and carbon black in the molar ratio corresponding to the chemical composition of Al4SiC4 with a small amount of triethanolamine (TEA) above 1200 °C in argon gas. Without TEA, two phases of Al4C3 and SiC were formed, irrespective of the heating temperature. The marked mass gain by oxidation of Al4SiC4 was observed with forming Al2O3 and SiO2 in the range of 850 to 1150 °C, which slightly increased above 1150 °C. At 1600 °C, mullite was formed by the reaction between Al2O3 and SiO2.
I. INTRODUCTION
Carbon–carbon composites (C/C composites) are attractive materials for many applications at high temperatures exceeding 2000 °C.1 Therefore, they have been used as the structural materials at high temperatures, such as rocket noses and leading edges of space shuttles, etc.2 However, their uses have been restricted below 500 °C in air, because carbon is easily oxidized above 500 °C. Therefore, the improvement of the oxidation resistance of C/C composites is one of the important problems to be solved. Two effective methods for improving the oxidation resistance have been proposed, the dispersion of fine particles of carbides such SiC and B4C in the C/C composites and the coating of thin films of ceramics such SiC, zircon, and mullite on the composites.3–10 In these methods, the improvement of oxidation resistance is supposed to be due to the protective oxide layer on the surface of composites. The structure of oxide films on the surface was known to govern the oxidation resistance of the composites; mullite (3Al2O3 ⭈ 2SiO2) has a higher performance than SiO2–B2O3 glass.7,10 It might be more effective if fine particles of Al4SiC4 can be dispersed in C/C composites, because mullite is expected to be formed directly by their oxidation. However, the reports on the synthesis of Al4SiC4 are few11–13 and its single phase has never been obtained so far. As the first step of the research for making the C/C composite dispersed with Al4SiC4 powder, we tried to prepare single-phase Al 4 SiC 4 from the mixture of
aluminum, silicon, and carbon black. The preparation condition of a single phase of Al4SiC4 and its oxidation behavior are studied in this work. II. EXPERIMENTAL A. Preparation of Al4SiC4
Aluminum (purity, 99.99%; particle size, 0.5 m), silicon (purity, 99.99%; particle size, 0.5 m), and carbon black (purity, 99.95%; particle size, 1 m) were used as starting materials. These powders were collected at a molar ratio corresponding to the chemical composition of Al4SiC4, and triethanolamine [TEA, N(CH2CH2OH)3; purity, 98%] was added with a molar ratio (TEA/Al) of 3. The powders were mixed in a planetary ball mill with the rate of 200 rpm for 1 h and then dried at 200 °C for 72 h. The powder mixtures thus prepared were pressed under a pressure of 22.4 MPa to the disk of 10 mm × 2 mm size. The compressed disk was placed in a graphite crucible and then heated for 6 h in a high-purity argon gas (purity, 99.999%) at the temperat
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