2023-08-14 ノースカロライナ州立大学(NCState)
◆保護層は炎の熱に反応して変化し、酸素のアクセスを制御し、材料の加熱速度や化学反応をコントロールできる。この方法により、炭素チューブの生成など幅広い応用が期待されている。
＜関連情報＞
- https://news.ncsu.edu/2023/08/taming-fire/
- https://onlinelibrary.wiley.com/doi/10.1002/anie.202308822
熱的にモーフィングされた表面付加体を介した空間的指向性熱分解 Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts
Chuanshen Du, Paul Gregory, Dhanush U. Jamadgni, Alana M. Pauls, Julia J. Chang, Rick W. Dorn, Andrew Martin, E. Johan Foster, Aaron J. Rossini, Martin Thuo
Angewandte Chemie International Edition Published: 19 July 2023
DOI:https://doi.org/10.1002/anie.202308822
Graphical Abstract
Taming fire: Using morphing surfaces to control ignition and mass transport turns combustion to pyrolysis, hence slows rate of thermal degradation. Pyrolysis leads to incomplete combustion, hence graphitic tubes. This being a surface process, nm to μm wide tubes are produced.
Abstract
Combustion 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.
