Solid−Solid and Solid−Liquid Equilibria in the Heneicosane−Docosane Binary System

Abstract

The experimental phase diagram of the binary system implying the nonisomorphous consecutive n-alkanes heneicosane (C 21 H 44 ) and docosane (C 22 H 46 ) has been determined by combining X-ray diffraction and microcalorimetric methods. The phase diagram is very complex. X-ray experiments performed on powder samples at 288 K have shown the presence of five monophasic domains at "low temperature": three orthorhombic (Oi, Odci, and Op), one monoclinic (Mdci), and one triclinic (Tp). With increasing temperature occur successively the rotator forms RV, RI, and RII. No less than ten solid-solid and two solid-liquid biphasic domains are observed, as well as three peritectoid, one eutectoid, and one peritectic invariants. Moreover, cell parameters of mixed samples corresponding to the forms Odci (space group Pnam), Mdci (Aa), and Op (Pca2 1 ) have been determined at 288 K.

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

“…Indeed, experimental results on this system and on other binary systems and, in particular, on C 26 1 C 28 (the subject of another paper) have enabled us to characterize for the first time the three intermediate forms and to propose, therefore, a new phase diagram for the binary system C 23 -C 25 . The scope of this work is even wider since these phases are also observed in other binary systems [31][32][33][34][35][36][37][38][39][40][41] of n-alkanes [with a chain-length difference ͑Dn͒ equal to 1 or 2]. In other words, this paper leads to a complete characterization of all solid ordered forms observed in all binary systems of n-alkanes (the components belonging to the range C 16 to C 28 ).…”

“…The study of binary phase diagrams (temperature versus composition) has revealed a complex structural behavior of the mixed samples [28][29][30][31][32][33][34][35][36][37][38][39][40][41] where other forms than those seen in the components are observed and which are stabilized by mixing. The earliest binary phase diagram showing multiple one-phase domains at low temperature (temperature domain where the ordered phases are observed) is that of Lüth et al 28 for the system C 20 -C 22 .…”

“…Polymorphism of n-alkanes (C n H 2n12 ; hereafter denoted by C n ) and determination of binary phase diagrams [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] in the alkane family have been reported on in recent years in numerous publications. The polymorphism of n-alkanes is rather well known where many solid-solid phase transitions have been observed as a function of temperature.…”

Lubricating and Waxy Esters. VI. Effect of Symmetry about Ester on Crystallization of Linear Monoester Isomers

“…This may be due to a rotational disorder of the molecule along the c long axis and its subsequent order, analogous to the phase transition occurring in n-alkanes from a disordered to an ordered orthorhombic form [24]. The change in lattice parameters with temperature in fact occurs to accommodate a better order in the a,b plane and seems to be occurring at the expense of some disorder in the c-axis.…”

Clasificación y selección de materiales de cambio de fase según sus características para su aplicación en sistemas de almacenamiento de energía térmica

“…Por tanto, se trata de un material "termoajustable", que permite modular la temperatura de almacenamiento y restitución de la energía a partir de su composición. Sobre este aspecto se puede encontrar abundante información en las referencias (27), (18,19,28,29).…”