Influence of Gas-Flow Conditions on the Evolution of Thermally Insulating Si3 N4 Nano-Felts

This paper discusses the role of nitrogen (N2 ) gas flow conditions on the formation of silicon nitride (Si3 N4 ) nano-felts from polysiloxane-impregnated polyurethane (PU) foams. The polymeric foam was converted into an amorphous silicon oxycarbide (SiOC) artefact during pyrolysis, which was then transformed, at a higher temperature, into a Si3 N4 felt through a reaction between the decomposition products of SiOC with N2 . The study identified that a N2 flux of ~2.60 cm.min−1 at the cross-section of the furnace (controlled to 100 cm3 .min−1 at the inlet of the furnace using a flowmeter) substantially favored the transformation of the parent SiOC foam to Si3 N4 felts. This process intensification step significantly reduced the wastage and the energy requirement while considering the material production on a bulk scale. The study also inferred that the cell sizes of the initial PU templates influenced the foam to felt transformation.