Mechanochemical Reaction Kinetics—A Theoretical Modeling and Experimental Study

Mechanochemical reactions represent a class of chemical processes triggered by mechanical energy, widely recognized for their efficiency, solvent-free nature, and environmental benefits. They are increasingly applied in synthetic chemistry, a branch of science focused on creating new chemical compounds through controlled laboratory reactions. However, the mechanisms underlying mechanical activation remain poorly understood, primarily due to the difficulty in quantifying energy transfer during milling, where solid reactants are ground together using a ball mill. This thesis aims to bridge the gap in understanding the relationship between mechanical parameters and reaction kinetics by developing and validating a theoretical framework based on dimensional analysis, physical modeling, and experimental evaluation. A predictive, dimensionless model was derived integrating physical impact theory and Hertzian contact mechanics to relate ball mill parameters—frequency, ball diameter, and material properties—to the mechanical contribution and, consequently, to the activation energy. This model was experimentally validated through mechanochemical synthesis of imidazole and zinc oxide, a reaction selected for its reproducibility and complete solvent-free nature. High-speed video recordings were employed to directly visualize ball motion in an empty acrylic jar, enabling identification of on-phase motion, skewed figure-eight trajectories, and the frequency dependent nature of impact dynamics. Reaction progress was monitored in situ using Raman spectroscopy, and kinetic profiles were extracted by tracking reactant and product Raman peaks over time. Experimental parameters (milling frequency and ball size) and pre-treatment of reactants were systematically varied to evaluate their influence on reaction rate and homogeneity. The experimental results support the theoretical prediction that the reaction rate increases with milling frequency, in agreement with the proposed scaling of mechanical activation energy. This study provides both mechanistic insights and practical guidelines for designing efficient mechanochemical processes. The combination of experimental observation, kinetic modeling, and dimensional analysis offers a foundational framework for further exploration of solid-state reactivity under mechanical force.