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

Balanand Santhosh,Gian Domenico Sorarù,Mattia Biesuz,Andrea Zambotti

doi:10.3390/ma15031068

Abstract

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.

Highlights

The development of thermally and chemically stable materials for thermal insulation, especially for application at elevated temperatures, is of pivotal significance in the present economic and technical scenario
The polymeric foam was converted into an amorphous silicon oxycarbide (SiOC) artefact during pyrolysis, which was transformed, at a higher temperature, into a Si3N4 felt through a reaction between the decomposition products of SiOC with N2
We focused our attention on the role of the flow rate on the synthesis of the Si3N4 felts

Summary

Introduction

The development of thermally and chemically stable materials for thermal insulation, especially for application at elevated temperatures, is of pivotal significance in the present economic and technical scenario. Ceramics-based materials are deployed for these purposes owing to their low thermal conductivity and unrivalled stability [1]. Advanced research [2,3,4,5] is being conducted to develop ceramics-based ultra-light materials with ‘super-insulation’ properties and with very low thermal distortion. Si3N4 nano-felts can be obtained by the polymer-derived ceramics (PDC) route [15,16,17] using polyurethane (PU) as templates [15]. This approach reported a simple, robust, and flexible synthesis route to develop ultra-light, well-shaped fibrous Si3N4 ceramics having ultra-low thermal conductivity [15]. The evolution process of nano-felts was reported to start with the release of SiO gas (reaction (1)) followed by the reaction of this SiO gas with the C from the ceramic foam and the N2 gas, leading to alpha-silicon nitride (α-Si3N4)

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Results

Conclusion