The Trouble with Activation Energies

ChEMS Seminar

Featuring Dr. Peter E.D. Morgan
Consultant
Fellow of the American Ceramic Society
Ph.D., Imperial College, London University  - Inorganic Chemistry

Location: Engineering Tower 204

Abstract:
The concept of activation energy (AE) is simple, but, it can only sensibly be applied to simple situations; most solid state processes are complex.  For a simple unimolecular decomposition or change; for a simple bimolecular reaction etc., things are fairly straightforward. Even when a molecule must change shape (as for enzymatic processes) to interact, and a series of sequential processes occur in any particular temperature regime, it is normally understood that the slowest process in that regime is rate determining and the associated activation energy may be measured. On the other hand, when parallel processes occur the situation changes, and this will be seen to be quite common in solid state kinetic processes as in the cases of sintering, with or without densification, grain-growth, creep and so forth. Examples will be given from the literature of what the problem is, and how it can be tackled, so that unrealistically high AE (higher than any known diffusional processes) can be understood.

About the Speaker:
Research activities centered on chemical synthesis and processing of ceramics and included silicon nitride (ultimately intended for bearings, turbines, etc.), molybdenum disilicide, oxides for composites, and sulfides for IR windows; new directions in Si-S-N-C chemistry, new alkoxide polymers (by thermolysis as well as sol-gel), and fused salt techniques have been explored. Interests are maintained in the following: phrase diagrams, the effects of phase transformations on various solid state processes in metals, polymers and ceramics, the effect of chemical reactions, eutectic liquids and decomposition on sintering and grain growth; hot pressing and HIPing phenomena, creep etc.; general high temperature chemistry; crystal structures and chemical bonding; and fine particle technology (nanophase materials and superplasticity), spray-dry-roasting, especially as applied to energy-related phenomena, including nuclear waste disposal in ceramic wasteforms. Work on superconducting ceramics (and others) has included working in and collegial relations are maintained at Universities of Osaka and Kyoto. The discovery that monazite seems to form weak interfaces with most oxides, and is, therefore, enabling of debonding in CMCs is a highlight.