Porosity control in silicon nitride‐based support materials toward enhanced gas permeability

Abstract Porous Si 3 N 4 materials in tubular geometry are prepared by slip casting before partial sintering. A variety of material‐ and process‐specific variables and their respective effects on densification and resulting pore morphology are systematically evaluated, focusing on starting powder type, amount of sintering additives, and sintering parameters including temperature and time. An increased β ‐Si 3 N 4 content in the starting powder was found to promote the formation of a network of elongated grains exhibiting increased pore diameters, as opposed to a more finely featured pore network obtained from starting materials consisting of α ‐Si 3 N 4 . Following an iterative evaluation of processing variables, materials exhibiting a characteristic diametral compression strength (C‐ring test) of 163 MPa and a Darcian permeability of 4.7 ⋅ 10 −15 m 2 at a total porosity of 41% were obtained, corresponding to an increase of over 40% in strength and of over 600% in permeability in comparison to materials obtained by α ‐Si 3 N 4 powders at comparable porosities. These results demonstrate that the composition of Si 3 N 4 powders significantly affects the resulting pore structure, and by combining the respective selection of starting materials with finely tuned sintering parameters, materials with superior performance in terms of mechanical properties as well as permeability characteristics are accessible.