Effect of heating rates on the synthesis of Al2O3-SiC composites by the self-propagating high-temperature synthesis (SHS) technique

Various aspects of in situ formation of Al2O3-SiC composites by the self-pr opagating high-temperature synthesis (SHS) technique have been investigated using thermal analyses (TG/ DTA) of a powder mixture (4Al, 3SiO(2), 3C) an d pellets in an argon atmosphere at different heating rates. Both the react ion initiation and peak temperatures are found to increase with the heating rates. At lower heating rates, the powder samples do not reveal any exothe rmic peak possibly because of poor reactivity and sluggish exothermic react ion. The appearance of exothermic peaks in the DTA plots after melting of a luminum indicates reduction of silica by liquid aluminum. Conversion of alu minum is found to decrease marginally with an increase in heating rates. Th e apparent activation energy of the process compares well with the interdif fusion activation energy of silicon and oxygen, indicating that oxygen diff usion in Si formed at the reaction front may be the rate-controlling factor for this SHS process. From SEM studies it appears that the formation of Si C whiskers is through liquid-phase mass transfer.