Chromium nitride and carbide nanofibers: from composites to mesostructures

This work describes an easy two-step approach for metal nitride/carbide nanocomposite ceramic nanofibers via heat treatment of electrospun precursor fibers. Possibilities to tune their composition, carbon scaffold organization and texture depend on the calcination temperature, and yield two different types of fiber structures. Fiber mats with various morphologies were obtained from polyacrylonitrile-chromium chloride precursor electrospun fibers, while well defined rod-like fiber non-woven mats were obtained when a methylated polyurea was used as an additive to the previous system. It was observed that the use of a two component organic system, involving a fiber stabilizing polymeric template (PAN) and a specific nitrogen/carbon donor (PUF), enables to maintain the morphology of the initial fibers during heat treatment and prevents the system from forming sintered membranes at high humidity conditions. The chromium content found for PAN-free and PAN-containing was 9 and 12 wt%, respectively. Moreover, thermal treatment at temperatures higher than 1000 degrees C led to graphitization of the carbon subphase of both series. Nitrogen sorption studies revealed that the graphitization process increases the specific surface area of the fibers, which possess a pore system with a wide diameter distribution and inkbottle-shaped pores. Conductivity studies revealed that the fiber systems are suitable for electrochemical applications.