What drives reactions in ball mills? - Qualification and Quantification of the forces in mechanochemical reactions

• Applicants: Professor Lars Borchardt, Ph.D.; Professorin Dr.-Ing. Sandra Breitung-Faes
• Subject Area: Mechanical Process Engineering ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 462608944

Mechanochemistry has been nominated as one of the emerging technologies of the future. It allows chemical reactions to be conducted in the absence of solvents, to proceed swiftly, and to often outperform conventional wet-chemical reaction pathways with respect to time-, energy, and resource-efficiency. Mechanochemistry utilizes mechanical forces to break and recreate chemical bonds, and thus, facilitate chemical reactions. These reactions are often conducted in media mills, where rotating or vibrating vessels are filled with grinding media which collide and transfer their kinetic energy to the added reactants. Over the last decades several theories have been proposed, aiming to explain the mechanistic background of mechanochemical reactions. However, the various observations made and the huge variety of possible reactions conducted by mechanochemistry all over the world cannot be explained by one single of these theories exclusively. The key question is: “What initiates a chemical reaction mechanochemically? Is mechanochemistry only mixing and reactions run via well-known thermally-controlled conditions or is there any special mechanical force initiating a reaction?Within this proposal, we aim to contribute to this key question by quantifying and qualifying these “mechanical forces” within media mills. We target this question from an experimental, numerical and theoretical side by developing a simulation for the milling process on two different scales and by using model reactions in different milling setups. Combining simulation data with experimental observations will allow us to differentiate between different stress mechanisms in mills, i.e. shear, compression or impact, to quantify their contribution in different mill types, and correlate them to the conversion of model reactions. Furthermore, performing these reactions under isotherm conditions using either home built or cryo mill setups will help us to uncouple thermal from mechanical impact in mechanochemical reactions. For that reason, we have formed an interdisciplinary team of experimental chemists (AK Borchardt) and engineers (AK Breitung-Faes) to target this question from these two important perspectives.

• DFG Programme: Research Grants