X-Ray Scattering Data as Criteria for Complete Stabilization

The diffraction of X-rays by crystalline matter is described by the Bragg relationship 

For a given wave length (generally Cu Ka radiation, with A = 156 pm), the sinus of the angle of diffraction 0 is the smaller, the larger is the separation d of the diffracting lattice planes. 

PAN fibers give a typical wide angle diffractogram, which undergoes characteristic changes during stabilizing heat treatment of the fiber (Uchida ). Fig. 10 shows 

Uchida has attributed the new reflection to the sheet-like structure of arromatized 

Although AI values may be useful to estimate the progress of the oligomerization of the nitrile groups and the subsequent oxidation and dehydrogenation processes, they cannot be recommended as a criterion for optimum stabilization, unless a careful investigation has been made as to which lA value is actually optimum for a particular precursor. AI values close to unity may easily be obtained by prolonged heat treat- 

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