Résumé
The present paper reports the preparation of non-oxide ceramic fibers through the Polymer-Derived Ceramics (PDCs) route. The poly[beta-(methylamino)borazine]-derived boron nitride (BN) ceramic fibers and modified C-B-C-bridged polysilazanes-derived silicoboron carbonitride (SiBCN) ceramic fibers were used as models. The chemical tailoring of BN or SIBCN molecular and polymeric precursors, achieved by the introduction of plasticizing pendent groups such as Si-CH3 and NCH3/N(H)CH3 in the structure, has been shown to improve the melt-spinnability of preceramic polymers. Such pendent groups allowed of controlling both melt-viscoelastic properties and thermal reactivity, and then to produce high quality fine-diameter endless green fibers via a stable melt-spinning process. Fibers were subsequently cured through a chemical process using ammonia as curing agent. As-cured fibers were then pyrolyzed in a controlled atmosphere depending on the desired ceramics. BN fibers were prepared by pyrolysis in an ammonia atmosphere at 1000 degrees C to remove the carbon elements from the materials, then in a nitrogen atmosphere at 1800 degrees C to microstructurally design the boron nitride phase and produce polycrystalline ceramic fibers. SiBCN fibers were obtained through pyrolysis of as-cured fibers at 1400 degrees C in a nitrogen atmosphere. Ceramic fibers are delivered in a controlled chemical composition with form retention.