Influence of different stress types on the mechanochemical CaCO3-synthesis

Mechanochemistry is considered a green alternative to conventional wet-chemistry. Several reactions have been reported to be feasible via the mechanochemical route, while detailed insight in the mechanistic background of mechanochemical reactions is still elusive. Certain is a significant role of the mechanical stress applied, but the influence of the stress type is rarely addressed. This study uses different simple setups to apply isolated impact, compressive and shear stress to the reactants of the mechanochemical CaCO₃-synthesis. Measuring of the energy inputs and modelling of the stressing conditions allowed correlation of the specific energies in the setups with the chemical conversion of the inorganic model reaction. For the same specific energy, impact stressing was found to be most successful in yielding product and the stress intensity could be identified to play a crucial role. A lower stress intensity was beneficial during initiation of the reaction, whereas a progressed reaction state could take advantage of higher stress intensities. This change is ascribed to the energy utilisation, which is limited in the beginning, but rises in an advanced reaction state due to the formation of product layers and an increased local temperature. Based on the results, a hypothesis on the influencing factors and procedure of the mechanochemical CaCO₃-synthesis was formulated.