Influence of Gas-Flow Conditions on the Evolution of Thermally Insulating Si₃N₄ Nano-Felts

This paper discusses the role of nitrogen (N₂) gas flow conditions on the formation of silicon nitride (Si₃N₄) 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 Si₃N₄ 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 Si₃N₄ 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.