New insights on the crystalline forms in binary systems of n-alkanes: Characterization of the solid ordered phases in the phase diagram tricosane + pentacosane

X-ray diffraction analyses of the pure components n-tricosane and n-pentacosane and of their binary mixed samples have enabled us to characterize the crystalline phases observed at low temperature. On the contrary to what was announced in literature on the structural behavior of mixed samples in odd-odd binary systems with D n = 2, the three domains are not all orthorhombic. This work has enabled us to show that two of the domains are, in fact, monoclinic, (Aa, Z = 4) and the other one is orthorhombic (Pca21, Z = 4). The conclusions drawn in this work can be easily transposed to other binary systems of n-alkanes

From concept to application. A new phase change material for thermal protection at-11 degrees C

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Ordered phases in n-heptacosane (C27H56). Structure determination of the Mdci phase

n-Heptacosane (C27H56) is known to have a rich polymorphism. With increasing temperature, the following phase transitions are observed:  Oi → Odci → Mdci → RIII ···> RIV → L. The Mdci form is known to be isomorphous with the modification B in n-tritriacontane (C33H68). Two possible space groups were given in the literature for the B-form of C33H68: monoclinic (Aa) and orthorhombic (A21am). We have determined the structure of the n-heptacosane at 325 K combining lattice energy minimization calculations and Rietveld refinement using accurate X-ray diffraction data. We have shown that the Mdci form of heptacosane is monoclinic (Aa, Z = 4). Moreover, at each phase transition Oi → Odci → Mdci, a substantial decrease in intensity of the 0 0 l reflections and an increase in the interlayer spacing due to end-gauche defects are observed. In addition, each phase transition is characterized by subtle appearance and disappearance of reflections observed at large angles of diffraction. These characteristics are powerful tools for phase identification in binary or ternary phase diagrams of n-alkanes

n-alkane binary molecular alloys

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