| Abstract Scope |
The term “extreme conditions” implies conditions far from those we normally encounter. But the effect of a given condition on different materials may range from minor to catastrophic. A more useful definition is that for a given material, a condition is extreme if it causes substantial changes in physical and chemical properties. Thus 4 K is extreme for helium, while 2000 K has little effect, on alumina. Alumna shows only normal compressibility over a wide range of pressure, while complex oxides show structural and electronic transformations. Alumina is stable under electron irradiation, while silica and many silicates readily amorphize. Radiation damage is a balance between initial damage and relaxation and annealing, with complex intermediate states. Survival under harsh chemical conditions is controlled long-term by thermodynamics and short-term by kinetics, often involving surface passivation. Several examples are presented to better define “extreme”. |