Binary phase diagram of molecular alloys of the consecutive even-numbered n-alkanes n-tetracosane ( n-C 24H 50) and n-hexacosane ( n-C 26H 54)

Abstract

The phase diagram of molecular alloys of n-tetracosane ( n-C 24H 50) and n-hexacosane ( n-C 26H 54) has been established by a joint thermodynamic and structural study of twenty five compositions. At “low temperatures” it shows the existence of two limited domains of terminal solid solutions γ 0(C 24) and γ 0(C 26) and of three orthorhombic intermediate phases, denoted β′ 1, β″ and β′ 2. With increasing temperatures, these five solid solutions undergo the same solid-solid transitions as those observed in the even-numbered and odd-numbered pure n-alkanes and in the system n-docosane ( n-C 22H 46)- n-tetracosane ( n-C 24H 50), i.e.: γ 0(C 24) and γ 0(C 26) → Rotator phase α-RII (R3̄m) → Liquid β′ 1, β′ 2 and β″ → Rotator phase β-RI (Fmmm) å β-RII å Liquid