Fischer‐tropsch waxes. I. An infra‐red method for the determination of crystallinity

Crystallinity is, ideally, the fraction or percentage of perfectly crystalline matter in a material which is partially crystalline. Because transition structures can exist, however, measured crystallinity will depend largely on the method used. The differences in the infra‐red spectra of the same substance in the crystalline and amorphous states can be exploited for quantitative measurement. Methods based on bands that appear only in the ‘amorphous spectrum’, such as the method described here, have definite advantages over those based on ‘crystalline bands’. While testing the method it was found that the rate of cooling has only a small effect on the crystallinity of Fischer–Tropsch waxes. Surface effects play an important role, however. Thin slices cut from the central parts of thick discs were used for measurements. Before they were sampled, certain waxes had to be homogenised by melting. Results were reproducible within ± 1·5 to ±6 per cent for different waxes. Because of the dependence of crystallinity upon the method used, however, the value of this method lies in its use in comparative studies.