Stress-Controlled Catalysis via Engineering Nanostructures
[Technical Report, Final Report]
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The need to control either enhancing or retarding - chemical reactions is ubiquitous across a range of technologies, including chemical synthesis via catalysis, chemical sensing via adsorption and reaction, chemical embrittlement in structural materials, and microstructure and precipitate evolution in structural materials. It is commonly thought that mechanical energies cannot compete with chemical energies, so that Chemistry and Mechanics have little overlap. Roughly, chemical energies are on the order of eV while the mechanical energies are on the order of meV, as loosely estimated by where p is typical mechanical load 100 MPa and a typical misfit volume few A3 for a reaction process. However, mechanical energy can be harvested from a large volume by relaxing elastic strains or, equivalently, be concentrated near a defect such as a crack tip or dislocation, generating stresses approaching the theoretical material strengths 10 GPa and thus provide energies that can alter chemical reactions. More subtly but of equal importance is the fact that mechanical energy can tip the energy landscape to drive reactions or diffusive processes preferentially in one direction. The role of stress or strain in influencing reactions appears across a broad range of materials applications such as strained-layer superlattice, self-organization of quantum dot structures in Si-Ge, dynamic strain aging in Al-Mg alloys, and stress corrosion cracking. The role of stress in modifying reactions, broadly construed, is thus well-founded within materials science. Why is gaining active control over catalytic reactions so important The application of stress can both tune and modulate reactions, and therefore may overcome the barrier implied in Sabatiers Principle that is manifested in the Volcano Effect, two widely held concepts in catalysis.
- Physical Chemistry