Voids appearence

These experiments confirm that scatters (presumably voids) appear during deformation as L decreases (Fig. 9.). Moreover, they emphasise the difference in the cavitation processes encountered in the modified amorphous and semi-cristalline PET. In the case of semi-cristalline blends the onset of cavitation is quasi-simultaneous to the yielding of the material (Fig. 9a). Conversely, for the amorphous materials, cavitation only appears after yielding of the matrix (Fig. 9b). 

Scanning electron microscopy of the anodic film formed in the dilute phosphoric acid electrolyte at 170 V reveals the typical porous film morphology, including well-defined barrier layer and pores of about 80 nm in diameter (Fig. la). Scrutiny of the cell material reveals bubble-shaped features located at the cell boundaries with an occasional disturbances to the parallel-sided pore walls. After further chemical dissolution in phosphoric acid, resulting in pore widening to 150 nm, numerous voids become evident in the cell material adjacent to the pore. The mouths of the voids appear circular, and the defects pass into the cell material in a tubular manner (Fig. lb). The defects are oriented approximately perpendicular to the pore walls and are separated from each other by about 200 nm. The void diameters are approximately 70 nm. 

Figure 4.19 shows the meridional SAXS intensity curves for PT OX post-polymerized in air. The original sample shows a very broad intensity maximum at about 13 of 20, the position of which shifts to the lower angle side by annealing the sample at a higher temperature. This indicates an increase in the sparing of the void appearance by the annealing. 

Figure 10.32 Formation of a new boundary on the tip of the void appearing in the two-step grown samples.

There were several types of genuine porosities observed by various researchers. The first type was a void observed in the magnetite layers formed on iron and steel at temperatures below 570°C [91,93], where the gas used could be moist air, dry air or CO2. The voids were very fine in size and were observed at grain boundaries as well as inside magnetite grains. This type of porosity is also known as Kirkendall voids [100]. The formation of voids appeared to be associated with the formation of a duplex scale structure [101]. Recently, some theoretical treatments using conventional diffusion theories were made by Maruyama etal. [102] and Ueda etal. [92] to provide a semi-quantitative and quantitative explanation of their formation mechanism and their location in the scale. 

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