Phase Diagram of n-Tricosane and n-Pentacosane Mixtures

The phase diagram of the mixtures n-C23H48:n-C25H52 has been established by joint calorimetric and structural analyses. This study indicates the existence of nine solid single-phase domains of equilibrium : four terminal solid solutions, denoted beta 0(C-23), beta'0(C-23), beta'0(C-25) and beta 0(C-25) with the n-t ricosane and npentacosane structures, three orthorhombic intermediate solid phases, called beta"(1), beta'(1) and beta"(2) (beta"(1) and beta"(2) on both sides of beta'(1) are isostructural), with increasing temperature, two total miscibility fields : beta, with the orthorhombic structure Fmmm, above the intermediate solid solution regions (a second order transition which ischaracterized by the Rotator RI state is observd in this phase) and below the solidus line alpha-RII with the rhombohedral structure R (3) over bar m. These results complete the literature diagrams which only presented two solid single-phase domains.