Spatially Directed Pyrolysis via Thermally Morphing Surface Adducts

Area of Science:

• Materials Science
• Chemical Engineering
• Combustion Science

Background:

• Combustion reactions are challenging to control spatially, often leading to runaway reactions.
• Existing methods lack precise control over reaction kinetics and spatial progression.

Purpose of the Study:

• To develop a method for spatially directing ignition and controlling combustion-pyrolysis transitions.
• To fabricate functionalized carbon fibers with tuneable properties.

Main Methods:

• Coupling pyrolytic chemical transformation with mass transport and reaction rates (Damköhler number).
• Grafting alkysilanes onto cellulose fibers and controlled pyrolysis.
• Utilizing surface modification with SiO2 to control flame propagation.
• Incorporating additives (MnCl2 or KCl) to modulate pyrolysis.

Main Results:

• Achieved spatially directed ignition with a switch from combustion to pyrolysis.
• Demonstrated 'surface-then-core' ignition order and controlled burning rates.
• Fabricated graphitic tubes via inside-out thermal degradation.
• Created magnetic, paramagnetic, and oxide-containing carbon fibers with tuneable wall thickness.
• Produced nm- and μm-diameter tubes from appropriately sized fibers.

Conclusions:

• The developed approach offers precise control over ignition and pyrolysis, enabling the fabrication of advanced carbon materials.
• This method allows for the creation of functionalized carbon fibers with tailored magnetic and structural properties.
• The technique is scalable for producing carbon tubes of varying diameters.