Structural and Mechanical Behavior of Boron Nitride Fibers Derived from Poly[(Methylamino)Borazine] Precursors: Optimization of the Curing and Pyrolysis Procedures

Abstract

A series of boron nitride fibers were prepared by varying the tension applied on a same lot of poly(methylamino)borazine fibers during their pyrolytic conversion at 1800°C. Their microstructure/microtexture was studied by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy investigations. Such analyses showed that ceramic fibers presented good crystallinity, but crystallites oriented along the fiber axis with fiber stress. It is most interesting that stretching was essentially effective during the pyrolysis to 1000°C, preventing fiber crimping, and decreasing the fiber diameter. Therefore, the fiber strength increased, while the fiber modulus also increased because of an improvement of the basal layer orientation along the fiber axis.

Fabrication and properties of borazine derived boron nitride matrix wave-transparent composites reinforced by 2.5 dimensional fabric of Si–N–O fibers

“…When the final pyrolysis temperature was elevated to 1300 ºC, the strength values declined to 106.2 MPa and 70.4 MPa, respectively. Nevertheless, the obtained composites still showed a favorable 13 non-brittle fracture behavior (Fig.8a). The reduction of mechanical strengths, however, was believed to be mainly caused by fiber degradation.…”

“…However, the crystallization-prone nature of quartz fiber often leads to a low preparation temperature of the composites, typically 800 ºC [11], which in turn generates unstable matrix structure and causes rapid strength reduction at higher temperatures [12]. Al 2 O 3 fiber is a well-established oxide fiber with its mechanical strength being stable up to 1300 ºC within air, whereas its high dielectric constant (9~13) restricts it from many practical applications [13]. BN fiber also displays excellent high-temperature resistance and dielectric properties.…”

Polymer-Derived Boron Nitride: A Review on the Chemistry, Shaping and Ceramic Conversion of Borazine Derivatives

“…The main motivation to implement the PDCs route lies in the special advantages that are offered by molecular or polymeric precursors in controlling ceramic compositions and micro-/nanostructures (amorphous, crystalline or nanocomposite) and in processing materials in particular shapes and morphologies (dense or porous) that are difficult, or even impossible to obtain by conventional routes. As an illustration, this synthesis method has been applied to the preparation of simple carbides, nitrides of various main groups and transition elements [25,26,27] as well as homogeneous mixtures or solid solutions of pseudo-binary combinations of ceramics and nanocomposites [28,29,30,31]. It represents a synthetic approach in which the chemistry of molecular precursors is designed at atomic scale to deliver the desired inorganic polymer (called preceramic polymer) composition.…”

Nearly stoichiometric BN fiber by curing and thermolysis of a novel poly[(alkylamino)borazine]

“…Due to these small defects, single tensile strength and Young's modulus of the fiber were determined as approximately 600 MPa and 30 GPa, respectively. Considering the dependence of fiber tensile strength on the diameter and crystallinity, great improvement could be achieved by increasing pyrolysis temperature, applying tension on fiber during pyrolysis process [28], etc. A detailed investigation of the BN fiber microstructure was investigated by high resolution transmission electron microscopy (HRTEM) with selected-area electron diffraction (SAED), as Fig.…”