In a simple binary phase diagram, according to the phase rule,
>
> #Phase + #Freedom = #Component + 1 (pressure is fixed).
>
> Then, the eutectic point will have 0 degree of freedom.
>
> Does this rule apply to a spinodal decomposition as well?
Only once you have reached the final equilibrium concentrations, and it does not apply to the interfaces, which are nonequilibrium structures.