The SGTE Casebook PDF

Introduction

The real raison d'etre for the continuation of extensive experimental research in metallurgical thermochemistry is the potential application of its principles and data to practical, in particular industrial, problems. For this purpose the gathering of raw experimental data is obviously not enough. Missing numerical information must be supplemented by estimates ... Raw data must be sifted and critically evaluated to provide for every chemical system a consistent set of thermochemical properties ....

In practice, it is true, the knowledge of reaction rates is as important as that of equilibrium, if not more so, but the kinetic problems can only be tackled when the thermodynamic ones have been settled. It is also true that, in practice, metallurgical reactions are quite involved ... but with some effort it will be found that even complicated chemical processes may be broken up into simpler reactions which are accessible to normal thermodynamic evaluation.

The above points are made in the 5th edition of Metallurgical Thermochemistry by Kubaschewski and Alcock in 1979 [79Kub]. Elsewhere in the same book the term data-bank is used, albeit in quotation marks. Most of the statements are still relevant: computer supported calculations provide an enormous potential for the application of thermodynamic principles to the solution of practical problems. There is still the need for good estimates arising from the lack of data in certain fields of interest; and critical evaluation of raw experimental results to obtain consistent thermodynamic data sets for complete chemical systems is still of paramount importance. Nevertheless, the development of software for treating thermochemical problems has made some considerable advances in the past two decades and the questions that remain open can be tackled in a much more comprehensive way

The enormous effort involved in data collection and evaluation as carried out for example by Kubaschewski for pure substance data and by Kaufman [78Kau] in the field of alloy phases is now a somewhat less arduous task due to the availability to thermochemists of the computer. This has made it possible to treat thermochemistry in a completely new way. The computer, because of its data storage and management and its 'number-crunching' capabilities, has enabled us to look at the thermochemistry of a system as a whole, i.e. in many cases the user needs nothing more than a list of elements in his system and the values of the global variables temperature, pressure and element concentrations to carry out a theoretical study. Calculations can then be made of the phases stable at equilibrium, their amounts and compositions, and even information about the degree of instability of the phases not present at equilibrium can be provided. The flow sheet shown in Figure I may be used to illustrate the work procedure entailed in their activities.

The purpose of the present volume is to present some examples of such calculations and thus to demonstrate the enormous potential of this new technique. The computerised databases are still quite limited but a considerable effort is underway to expand them.

SGTE is making a major effort to provide comprehensive high-quality self-consistent, computerised thermodynamic databases both for pure substances and mixtures of all types and is playing a leading role in establishing methods for data evaluation and modelling of solution phases. Software for the storage and retrieval of assessed data has been developed and there are a number of application programs to treat different aspects of chemical equilibrium [70Kau, 80Bar,83Tur,84Sch, 85Sun, 85Tho, 85Tur,87Bar, 88Che, 88Din, 88Roi, 88Sun, 88Tho].

Edited by: K. Hack