Catálogo de publicaciones - libros

Since ancient times smelting of ore has been a primary task of the foundrymen, and the modern chemical engineer faces a thermodynamically similar task when he refines oil and natural gas. Nature offers her resources mostly as mixtures and man mostly wants them in the pure form, or at least in enriched form. It has long since been learned that the recipe for enrichment is smelting or destillation, but the thermodynamic knowledge behind the tricks governing these processes are more recent. They consist of outwitting the entropy of mixing, and sometimes the heat of mixing can promote that purpose.

In chemical reactions the additive constants in the internal energies and entropies of the constituents play a significant role. To be sure, it is not the constants themselves that matter but certain combinations, which we may call the heat of reaction and the entropy of reaction. These values can be determined experimentally and have been tabulated.

The balance of the heat of reaction and the entropy of reaction goes a long way in determining whether a reaction can proceed and in which direction it proceeds. We give some examples: Dissociation of oxygen, ammonia synthesis and photosynthesis of glucose. The latter appears to be impossible, if we did not know better.

The rich thermomechanical properties of shape memory alloys result from an austenitic-martensitic phase transition of the metallic lattice and from a twinning deformation in the low temperature phase, the martensite.

The thermodynamicist is interested in the phenomena, because — once again like in all phase transitions — they provide a non-trivial example for the competition between energy and entropy, with entropy gaining the upper hand at high temperatures. Recognizing this we are able to produce a model for shape memory behaviour which is capable of simulating all the observed features, at least qualitatively. Actually we describe several models, a thermodynamic one, a kinetic one and a numerical one. The latter employs molecular dynamics; it is particularly instructive and the accompanying CD permits the reader to view the crystalline rearrangement by observing the atoms shifting between their potential wells.

Shape memory alloys have found numerous small technical applications, and applications in the medical field. We start the chapter with a selective review.