Direct Evidence Of Chemical Reactions Induced By Shear-Strains

Abstract

ABSTRACTAfter a brief review of the history of mechanochemistry, and of the theoretical principles of chemical reactivity, four examples are described of reactions that demonstrate the importance of elastic shear strains compared with hydrostatic compressive strains (volume changes). Techniques for separating shear strains from volume changes, and for isolating elastic strains from plastic deformation are described. The latter (isolation) is achieved simply by localizing a strained region making it too small for dislocation nucleation. Shear strain acts by reducing the chemical hardness (activation energy) of a reactant. The four examples are: (1) “hammer chemistry” in which physisorped methane is struck by argon atoms with enough kinetic energy to cause chemisorption; (2) enhanced oxidation of silicon at stressed crack tips; (3) selective dissolution of crystals at screw dislocations; and (4) increased rates of catalyzed reactions when surface acoustic waves are passed through the catalyst.