After determining the activation energy ($E_a$) with a model-free isoconversional method, the Master Plot technique allows for the determination of the most probable reaction model, $f(\alpha)$.
The technique is based on comparing the experimental data, transformed into a dimensionless "master curve," with a series of theoretical master curves. The fundamental equation of kinetics can be rearranged into a separable form:
$$ \frac{g(\alpha)}{g(0.5)} = \frac{\int_0^T e^{-E_a/RT} dT}{\int_0^{T_{0.5}} e^{-E_a/RT} dT} $$The left side represents the **theoretical master curve** (dependent only on the reaction model form, $g(\alpha)$), while the right side is the **experimental master curve** (dependent on experimental T-vs-$\alpha$ data and the $E_a$). By plotting both sides against $\alpha$, the model whose theoretical curve best matches the experimental one can be identified.
This tool first calculates an average $E_a$ using the OFW method, then generates the experimental master curve and compares it against a library of 10 common solid-state reaction models to find the best fit.