Paracrystallinity theory, development

The average d-spacings of the iron diffraction peaks are very close to those of pure elemental iron as indicated in Fig. 2.15. This result is in good agreement with the conclusions reached from the other two methods of structural analysis discussed above. There is one difference, however, between the diffraction patterns of pure iron powder and that of the catalyst, namely, the line shape is significantly and reproducibly different. The theory of paracrystallinity was developed " from this line shape effect, which is the only experimental evidence in support of the idea that the bulk of an active ammonia synthesis catalyst may be different from iron powder. 

A second important event was the development by Hosemann (1950) of a theory by which the X-ray patterns are explained in a completely different way, namely, in terms of statistical disorder. In this concept, the paracrystallinity model (Fig. 2.11), the so-called amorphous regions appear to be the same as small defect sites. A randomised amorphous phase is not required to explain polymer behaviour. Several phenomena, such as creep, recrystallisation and fracture, are better explained by motions of dislocations (as in solid state physics) than by the traditional fringed micelle model. 

Szwarc discovers the living polymers by anionic polymerisation Theory of paracrystallinity developed by Hosemann... 

The concept of paracrystallinity introduced by Hosemann et al. in 1966 was used earlier to describe the phenomenon of ammonia iron. They developed the theory of paracrystallinity from XRD data which seemed to explain the special properties of the activated iron catalyst. A three-dimensional, endotactic incorporation of hercynite (FeAl204) motives into the a-iron lattice was thought to create substitutional point defects in the crystal lattice leading to a modified bulk and surface structure of the activated catalyst material. The interplanar spacings change... 

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