Crystal structures and voids in diesel waxes

Abstract

Diesel waxes containingn-alkanes in the rangen\,=\,9–30 show only two types of X-ray diffraction pattern. When indexed these are seen to belong to the orthorhombic space groupsBb21mandFmmm; they are isostructural with two binary phases, one phase havingn\,=\,24 and 26 and the othern\,=\,22 and 24. We designate these the low-disorder (LD) and high-disorder (HD) phases, respectively. From the long spacings shown in the XRD patterns, it is possible to calculate the percentage of void space present in the wax crystals. It is found that the larger the spread ofnvalues in the wax composition (i.e.the larger the variance in chain length), the greater the tendency to crystallize in the HD form and the more extensive the voids.