Porous silicon nitride (Si3N4) and silicon carbide (SiC) are technologically important ceramic materials, because of their chemical inertness, thermal stability, and mechanical toughness. Applications span across diverse areas from catalysis to metallurgy, aerospace, biomedicine etc. Herein, we introduce the carbothermal synthesis of porous Si3N4 and SiC from a single source: compressed compacts of cross-linked (X-) silica aerogels, i.e., silica aerogels whose skeletal frameworks had been coated with a carbonizable polymer (polyurea). Those X-silica compacts were carbonized at 800 °C followed by pyrolysis at 1495 °C under flow of N2 to yield porous monolithic Si3N4. Unreacted carbon was removed at 650 oC in air. The resulting Si3N4 discs contained a small amount of amorphous silica (1.61% w/w) and a Si3N4:SiC mol ratio of 7.14. Porous SiC was prepared by pyrolyzing carbonized X-silica compacts at 1500 °C under flow of Ar. Unreacted carbon was removed at 800 oC in air. Samples of Si3N4 had higher porosities (up to 74% v/v) than SiC (52% v/v) and higher surface areas (146 m2g-1 vs. 15 m2g-1, respectively). Pd was deposited in the pores of Si3N4 and the resulting Pd@Si3N4 discs were used to catalyze 5 successive batches of Heck coupling reactions without significant loss of activity.

One-step synthesis of highly porous silicon nitride and silicon carbide from polymer-crosslinked silica aerogels

251st National Meeting (2016)

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