To obtain good rates of reaction you typically need the diffusion coefficient to be larger than
~ 10-12 cm2 /s.
The diffusion coefficient increases with temperature, rapidly as you approach the melting point. This concept is leads to Tamman's Rule : Extensive reaction will not occur until the temperature reaches at least 2/3 of the melting point of one or more of the reactants.
Rates of Reaction are controlled by three factors: