High oxidation and thermal stable carbon-ceramic electrospun nonwovens

Authors: Jakob Denk, Xiaojian Liao, Günter Motz, Seema Agarwal

Abstract

Electrospinning is a method for processing of polymer fibers with diameters in the nanometer scale from respective solutions. By using preceramic polymers, the fibers can afterwards be converted into ceramic fibers by pyrolysis. The resulting fiber mats are interesting, for example, for catalysts and filtration. In this study various nonwovens composed of polymer blends of polyacrylonitrile (PAN) and different amounts of the commercial available organosilazane Durazane 1800 were synthesized. Subsequent stabilization and pyrolysis transformed the polymer fibers into ceramic C/SiCON hybrid fibers. The characterization of the microstructure and elemental distribution of the fibers with high-resolution HAADF and STEM-EDS led to a “sea-island” nanostructure. Using various analytical methods such as FTIR, WAXS and solid state NMR, the chemical structure of the hybrid material was analyzed. The carbon phase is mainly amorphous, the ceramic phase consists of different amorphous SiCxOy, SiNxOy, and SiCxNy environments.

Compared with pure carbon films, the oxidation and flame stability of the material is significantly improved by adding organosilazanes. The ceramic phase (islands) serve as a protective layer and prevent the carbon phase (sea) from reacting with oxygen. Therefore, the limiting oxygen index (LOI) increased from 80% to 100%, and the time for the fibers to resist a flame and remain intact increased significantly.

This properties and their foldability and mechanical flexibility make these nonwovens interesting for real-world applications such as flame protection, catalyst support, high temperature filtration or as a possibility to increase the oxidation stability of carbon fibers, making them interesting for further applications, e.g. in ceramic matrix composites (CMCs).

Keywords: carbon fibers, ceramic fibers, electrospinning, sea-island nanostructure, oxidation stability, flame stability