The need for basic thermodynamic data to guide process development

Abstract

The present paper concentrates on processes where the prediction of the energetics of reactions or the phase constitution of the products is likely to shorten or simplify the development programme. One of the earliest selfsustaining reaction synthesis processes was the Goldschmidt or Thermit process applied to welding rails. This is an example of a reaction where reasonable predictions of the outcome can be made on the basis of a very simple model of the process which can be justified a posteriori by a more complete analysis, including a consideration of the molten slag formed and the potential for forming Fe–Al alloys. A second example is an exploration of the feasibility of forming titanium diboride from titania, borax, and aluminium in the presence of an inert gas. In this instance, pressure is a useful variable which is quantitatively explored and compared with earlier work by Ray on the formation of titanium diboride from titania, boron trioxide, and aluminium. A more challenging problem is the choice of the most suitable reactants to form the 123 superconducting compound in the Y–Ba–Cu–O system. Here, attention is concentrated on the reaction enthalpies associated with the choice of different reactants, and predictions are compared with results obtained by Chen and Sharp. This problem is also used to support the case for high quality thermochemical data and models, particularly when control is required of, for example, oxygen stoichiometry to obtain good superconducting properties. Finally, consideration of the reinforcement of aluminium alloys with silicon carbide is used to show the importance of side reactions in affecting the quality of the final products.

MST/3378