Effects of composition and atmosphere on reactive metal penetration of aluminium in mullite

Abstract Ceramic-metal composites can be made by reactive penetration of dense ceramic preforms by molten Al. Molten Al will reduce mullite to produce a composite of Al 2 O 3 , Si and Al. The reaction can be written as 3Al 6 Si 2 O 13 + (8 + x )Al → J3Al 2 O 3 + Al x Si y + (6 − y )Si. The penetration is driven by the strongly negative Gibbs free energy for reaction. In order to assess the influence of atmosphere and temperature in the penetration process, reaction couples of molten Al on mullite were heated at temperatures from 950 to 1150 °C, and at p ( O 2 ) from ~10 −10 to ~10 −20 atm. In this range p ( O 2 ) has little influence on reaction kinetics; the reaction rate is controlled by the rate of Si diffusion out of the preform to the external Al source.