Mechanochemical reaction kinetics scales linearly with impact energy

Inelastic collisions of the milling media in ball milling provide energy to the reaction mixture required for chemical transformations. However, movement of the milling media also results in physical mixing of reactants, which may enable a chemical reaction too. Separating the two contributions is challenging and gaining a direct insight into the purely mechanochemically driven reactivity is accordingly hindered. Here, we have applied in situ reaction monitoring by Raman spectroscopy to a suitable, purely mechanically activated, chemical reaction and combined kinetic analysis with numerical simulations to access experimentally unattainable milling parameters. The breadth of milling conditions allows us to establish a linear relationship between the reaction rate and the energy dose received by the sample. Consequently, different kinetic profiles in time scale to the same profile when plotted against the energy dose, which increases with the ball mass, the average ball velocity and the frequency of impacts, but decreases with the hardness of the milling media due to more elastic collisions. The fundamental relationship between kinetics and energy input provides the basis for planning and optimisation of mechanochemical reactions and is essential for transferability of mechanochemical reactions across different milling platforms.

Automated summary

Inelastic collisions in ball milling provide energy for chemical transformations and also enable physical mixing of reactants. This study uses in situ reaction monitoring and numerical simulations to reveal the relationship between kinetics and energy input, providing a basis for planning and optimizing mechanochemical reactions.