The video shows a phase front separating a single high-temperature phase that is decomposing into a two-phase low temperature lamella structure. This decomposition is typical of eutectic or eutectoid invariant reactions for which a single phase g -> a + b.

The process is controlled by the diffusion of a component in the region of the phase front in order to give the two final phases their required composition. This composition is such that the chemical potential of the two phases in equilibrium has the same value: m_a = m_b