Characteristics of Porous B4C-Al2O3Composites Fabricated by the Combustion Synthesis Technique

Abstract

The Combustion Synthesis or Self-propagating High Temperature Synthesis (SHS) technique has been used to produce porous B4C-Al2O3 composites. The effects of the green density of the pellet on the combustion characteristics and porosity were studied. The combustion synthesis reaction was highly exothermic, generating significant vapor at the combustion front. The evolution of the vapor led to a large degree of expansion in the direction of the combustion waves, which in turn led to the formation of highly porous (mostly open pores) B4C-Al2O3 composites. Two kinds of pores, termed as macro pores and micro pores had formed in the sample. The macro pores had a size of 300–400 μm and were oriented in the radial direction, and the micro pores had an average size about 1/10 of that of the macro pores and were situated between the macro pores. Samples containing macro pores exhibited low strength. By eliminating these macro pores, samples with improved properties, i.e., higher compressive strength and more uniform distribution of pores, have been produced.