Affiliation:
1. Materials Science and Engineering Iowa State University Ames IA 50011 USA
2. Materials Science and Engineering North Carolina State University Raleigh NC 27695 USA
3. US Department of Energy Ames National Laboratory Ames IA 50011 USA
4. Department of Chemistry Iowa State University Ames IA 50011 USA
5. Department of Chemical and Biological Engineering University of British Columbia Vancouver V6T 1Z3 BC Canada
Abstract
AbstractCombustion is often difficult to spatially direct or tune associated kinetics—hence a run‐away reaction. Coupling pyrolytic chemical transformation to mass transport and reaction rates (Damköhler number), however, we spatially directed ignition with concomitant switch from combustion to pyrolysis (low oxidant). A ‘surface‐then‐core’ order in ignition, with concomitant change in burning rate,is therefore established. Herein, alkysilanes grafted onto cellulose fibers are pyrolyzed into non‐flammable SiO2 terminating surface ignition propagation, hence stalling flame propagating. Sustaining high temperatures, however, triggers ignition in the bulk of the fibers but under restricted gas flow (oxidant and/or waste) hence significantly low rate of ignition propagation and pyrolysis compared to open flame (Liñán's equation). This leads to inside‐out thermal degradation and, with felicitous choice of conditions, formation of graphitic tubes. Given the temperature dependence, imbibing fibers with an exothermically oxidizing synthon (MnCl2) or a heat sink (KCl) abets or inhibits pyrolysis leading to tuneable wall thickness. We apply this approach to create magnetic, paramagnetic, or oxide containing carbon fibers. Given the surface sensitivity, we illustrate fabrication of nm‐ and μm‐diameter tubes from appropriately sized fibers.
Funder
North Carolina State University
National Science Foundation
Canada Foundation for Innovation
Subject
General Chemistry,Catalysis