Binary mixtures of n-alkanes. Phase diagram generalization: Intermediate solid solutions, rotator phases

At ''low temperatures'', the binary mixtures of the consecutive [even-numbered: even-numbered]; [even-numbered: odd-numbered] and [odd-numbered: odd-numbered] n-alkanes (19 < n < 27) do not form a continuous homogeneous solid solution. This study shows the existence of terminal solid solutions which have the pure n-alkanes structures and many intermediate solid solutions, denoted beta(n)' and beta(n) '' (n = 1 or 2): these intermediate phases have an orthorhombic cell as the odd-numbered n-alkanes, but they ate not isostructural with the pure n-alkanes nor with their terminal solid solutions. On the basis of powder X-ray diffraction photographs, the phases beta(1)' and beta(2)' are indistinguishable in all the binary systems. The X-ray behavior of the phases beta n '' is also identical. The succession of the solid solutions is described when varying the concentration. With increasing temperature, the intermediate phases undergo the same solid-solid transitions as the odd-numbered n-alkanes (n-tricosane), and the rotator phases appear at ''high temperatures'' below the solidus line. The phase diagrams of n-C-22: n-C-23, n-C-23: n-C-24, n-C-22: n-C24 and n-C-24: n-C-26 are presented.