Stability Criteria for Self-Propagating Reaction Waves in Co/Al Multilayers.

Area of Science:

• Materials Science
• Chemical Engineering
• Physics

Background:

• Self-sustained formation reactions in Co/Al multilayers show design-dependent instability.
• Thin bilayers (<55 nm) yield stable waves, while larger periods react unstably, forming "spin bands."
• Previous studies linked instability to heat conduction away from the flame front, coupled with bilayer design.

Purpose of the Study:

• To decouple thermodynamic and kinetic contributions to wave stability in reactive multilayers.
• To investigate inert-mediated reactive multilayers for controlling reaction dynamics.
• To establish a stability criterion for Co/Al multilayers based on enthalpy loss.

Main Methods:

• Utilized inert-mediated reactive multilayers by depositing B2-CoAl within Co/Al reactant layers.
• Reduced stored chemical energy density in bilayer designs.
• Analyzed spin instabilities as a function of diluted volume and critical diffusion distance.

Main Results:

• Decoupled thermodynamic and kinetic factors influencing wave propagation stability.
• Demonstrated that inert-mediated designs allow spin instabilities to arise with changes in volume dilution and diffusion distance.
• Identified a stability criterion based on enthalpy loss from the reaction zone.

Conclusions:

• Inert-mediated reactive multilayers offer a new approach to control reaction propagation.
• The study provides a clearer understanding of the factors governing stability in Co/Al multilayers.
• Enthalpy loss is a key factor in determining the stability of these reactive systems.