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Evolution of structural features and mechanical properties during the conversion of poly[(methylamino)borazine] fibers into boron nitride fibers

Abstract : Poly[(methylamino)borazine] (PolyMAB) green fibers of a mean diameter of 15 μm have been pyrolyzed under ammonia up to 1000°C and heat treated under nitrogen up to 2000°C to prepare boron nitride (BN) fibers. During the polymer-to-ceramic conversion, the mechanical properties of the green fibers increase within the 25–400°C temperature range owing to the formation of a preceramic material and remain almost constant up to 1000°C. Both the crystallinity and the mechanical properties slightly increase within the 1000–1400°C range, in association with the consolidation of the fused-B3N3 basal planes. A rapid increase in tensile strength (σR) and elastic modulus (Young's modulus E) is observed in relation with crystallization of the BN phase for fibers treated between 1400°C and 1800°C. At 2000°C, “meso-hexagonal” BN fibers of 7.5 μm in diameter are finally obtained, displaying values of σR=1.480 GPa and E=365 GPa. The obtention of both high mechanical properties and fine diameter for the as-prepared BN fibers is a consequence of the stretching of the green fibers on a spool which is used during their conversion into ceramic.
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Submitted on : Monday, May 25, 2020 - 9:44:51 AM
Last modification on : Saturday, June 13, 2020 - 7:34:06 AM

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Samuel Bernard, Khaled Ayadi, Marie-Paule Berthet, Fernand Chassagneux, David Cornu, et al.. Evolution of structural features and mechanical properties during the conversion of poly[(methylamino)borazine] fibers into boron nitride fibers. Journal of Solid State Chemistry, Elsevier, 2004, 177 (6), pp.1803-1810. ⟨10.1016/j.jssc.2004.01.004⟩. ⟨hal-02617050⟩

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