Porous and foamed ceramics, based primarily on Si_3N_4, have been developed using a simple air-atmosphere sintering procedure. This approach entails enveloping the samples being sintered within a protective Si_3N_4 powder bed, such that subsequent heating in an air atmosphere furnace results in oxidation of the outer regions of the powder bed. The outer SiO_2 scale that is formed then protects the enclosed Si_3N_4 samples from subsequent oxidation. In the present work two families of material have been developed. The first is based on porous β-Si_3N_4 ceramics prepared through partial sintering, in this instance using single, rare-earth sintering additions to minimize densification. The second group of ceramics is based on a novel Si_3N_4-Si_2N_2O-Bioglass～? composite, which foams during the sintering heat-treatment. The effects of the sintering treatment on each material are highlighted, from the perspectives of microstructure development and phase transformation behavior.
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