[Phase diagrams in the binary system]

The properties of pharmaceutical formulations are profoundly influenced by physico-chemical interactions, particularly those occurring between a drug and an excipient. The prediction and comprehension of these interactions provide information to use during the development of a dosage form. Thermal analysis methods are commonly utilized to obtain data from which phase diagrams can be easily constructed for a number of binary systems. The aim of this review is the classification of the phase diagrams of binary systems, as a function of two fundamental factors: 1) the relative strength of interaction between similar (UAA, UBB) and different atoms (UAB); 2) the limiting permissible degree of deformation of the energy field. The main binary phase diagrams have been analyzed starting from the simplest case, in which the two components are virtually incapable of dissolving each other either in the liquid and in the solid states, to the case where the formation of unlimited solid solutions both in the liquid and in the solid states can be observed.