Thermodynamic implications of drawing rectilineal phase boundaries

For illustrative and explanatory purposes, liquidus and solidus are frequently drawn as straight lines in textbooks. Thermodynamic consequences of sketching rectilineal phase boundaries are analyzed. It is shown that although thermodynamics does not prohibit such boundaries, they result in peculiar temperature dependencies of components׳ lattice stabilities. An idiosyncrasy of these functions and restrictions imposed by them are worth keeping in mind if it is intended to pencil a T-x section on which all phase boundaries are straight lines.