Dynamical Considerations for Kinetic Methods in Thermal Analysis

• Relaxation dynamics can impact both isothermal and non-isothermal kinetic methods.
• Isothermal methods should include models for first-kind dispersive kinetic conversions.
• Non-isothermal methods can be affected by first-kind and second-kind dispersive kinetics.
• Second-kind effects are due to distributed reactivity caused by rapid sample heating/cooling.
• A complete treatment (isothermal/non-isothermal) of the Avrami-Erofe'ev mechanism is put forth.

Popular kinetic methods of thermal analysis (TA) typically do not properly account for system dynamics (relaxation processes) that give rise to distributed reactivity, referred to here as “dispersive kinetics of the first kind”. In this work, new thermoanalytical relationships are put forth that allow more rigorous treatment of dispersive kinetics via the well-known Avrami-Erofe’ev (A–E) model, as it applies to both isothermal and non-isothermal (fixed heating/cooling rate) conditions. Simulated data is provided to highlight the errors that can arise from combining classical (non-dispersive, Arrhenius-based) kinetic treatments with the (dispersive) A–E mechanism. Lastly, “dispersive kinetics of the second kind” is discussed in the context of heating (cooling) a sample faster than it can thermalize. As shown by simulated data, doing so can impart dynamical effects even to conversions that would otherwise exhibit classical Arrhenius behavior.