The Gibbs Phase Rule

Materials are made up of regions of space that are homogeneous in structure and properties, called phases. The number of different phases in a material depends on its temperature, pressure and composition, as given when the material is at equilibrium by the Gibbs phase rule. This was discovered by the American scientist J. Willard Gibbs during his ground-breaking investigations in the late 19th century into the thermodynamics of heterogeneous materials. This chapter explains the differences between solutions, mixtures and compounds; the use of phase diagrams to determine the structure of a material; and the way in which phase transformations can be used to change the structure of a material. Gibbs grew up in an academic family at Yale University in New Haven at the time of the American Civil War. He was the first person to receive an engineering doctorate in the United States, and he later became a fundamental theoretician of thermodynamics, statistical mechanics and vector fields.