Crystallization by annealing

To erase information by the transition amorphous — crystalline, the amorphous phase of the selected area must be crystallized by annealing. This is effected by illumination with a low power laser beam (6—15 mW, compared to 15—50 mW for writing/melting), thus crystallizing the area. This crystallization temperature is above the glass-transition point, but below the melting point of the material concerned (Eig. 15, Erase). 

A well-defined amount of co-crystallization is possible across the interface of two adjacent crystals by annealing two stacked, completely wetted, solution-cast films of UHMW-PE [32]. It was found that doubling of the lamellae across the interface enhances the peel energy to such a level that the films could not be separated anymore. By contrast, pre-annealing one side of the film prohibited co-crystallization across the interface and these films could still be separated easily. It was therefore concluded that a limited amount of chain diffusion across the interface occurs during doubling of the lamellae, as facilitated by the well-defined structure of the interphase due to the adjacent reentry that occurs upon crystallization from solution. 

Samples of PET/PEN copolymers with 10, 20, 30, 50, 80 and 100 mol% PEN have been synthesized. Amorphous films of the samples were obtained by melt pressing above the melting point and quenching in ice-water. The samples were then crystallized by annealing the glassy materials at various temperatures. The degree of crystallinity was calculated from the amorphous density measured on quenched samples and from the crystal density derived from the crystal unit cell. 

Experimentally we can determine the equilibrium shapes of crystals by annealing small single crystal particles at high temperature in an inert atmosphere or by annealing small voids (inverse particles) in a crystal. 

No comparable work has been done on semiconducting glasses. Tauc et aL (1969) and,Chittick (1969) reported an observation of a band at 0.23 eV in a-Ge films which disappeared upon crystallization by annealing simultaneously with the band observed at 0.07 eV (560 cm" ) which was ascribed to vibrations of a defect characteristic of a-Ge (Section 4.2.3). The band at 0.23 eV was tentatively ascribed to an electronic transition on the same defect. 

The crystallization temperature of 2GT has been investigated in relation to fibre spinning, as has the melting behaviour and the mosaic block structure of the crystalline layers in 2GT crystallized by annealing in the highly oriented state. DTA studies have also been made on 2GT fibres, and the relationship between peak area of drawn fibres and the crystalline, intermediate, and amorphous phase indices, obtained by X-ray analysis, have been evaluated. ... 

The behavior of PaAA-8 was found to be remarkably different from that of PaAA-6 in spite of the fact that the alkyl sidechain is only two methylenes longer [36], Casting from chloroform solutions produces a partially disordered stmcture (similar to that adopted by PaAA-6) that could be crystallized by annealing. The crystal structure consists of a layered arrangement of chains with... 

Fischer E W and Fakirov S (1976) Structure and properties of poly(ethylene terephthalate) crystallized by annealing in the highly oriented state. Part 1. Morphological structure as revealed by SAXS, J Mater Sci 11 1041-1065. 

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