مرکز منطقه ای اطلاع رساني علوم و فناوري -

چكيده لاتين :

Compositions ofA120j+Si, Si02+AI and AI+Si systems were prepared to study the effect ofreaction bonding process on the mulliteformation. The composition ofeach system was adopted according to mullite stoichiometery and sintered in 700-1600°C range. Results showed that the formation of reaction bonded mullite starting from AI20j+Si mixtures, proceeded in two partially overlapping steps, the oxidation ofSi to Si02• and the reaction of SiO: and Al203 to form mullite. In this system, up to 1400°C, conversion ofSi to Si02 was taken place and cristobalite formed, but mullite formation was not observed. Mullite phase started toform at 1450°C. Results indicated that complete reaction was not occurred up to 1600°C and 2 hours soaking time. XRD patterns ofsamples in Al+Si02 system showed that the reaction through sequences:(a) reduction of Si02 by AI, (b) formation of a-A1203 and Sial-derived Si oxidation, and (c) mullite formation. X-ray diffraction patterns ofheat-treated Al+Sisystem showed that reaction between Al and oxygen at 900°C was occurred with the reaction product being a-AI20j. Oxidation of Si and formation ofmullite were not detected in this system. SEM micrographs showed that both AI203+Si and Si02+Al systems have similar microstructures. which consisted of a-AI203, mullite and free Si. The microstructures of the samples in Al+Si system consisted ofa-AI20 j. free Al and Si with intermetallic Al-Si compound.