Cooling Cross hatching

A transformation from monoclinic to triclinic on cooling from high temperatures is also observed in anorthoclase and gives rise to a cross-hatched microstructure, which is observed in b c sections. However, this... 

Figure 12.14 Overlap between the co-crystal domain at the temperature of isolation (arbitrarily set at 25 °C) and the liquid-to-solid phase boundary through which the co-crystal domain is initially accessed (cross-hatched area). In the black areas the co-crystal phase can be accessed directly via cooling, whereas in the grey area the co-crystal phase is only reached after passing through the solid state phase of crystalline B.

Secondary crystallization in isotactic polypropylene occurs in a peculiar way. On cooling additional crystallites are formed, however, many of them are oriented oblique to the primary lamellae rather than p lrallel as is normally observed. As explained by Lotz and Wittmann [8], this cross-hatching is caused by an epitaxial growth mechanism. If cross-hatching occurs the one-dimensional model used so far in the analysis of SAXS data becomes invalid. There is a simple check which shows the deviations. For a stack of crystallites one expects... 

From the three distinct 2D cross-sectional views (7.41a), (7.42), (7.43) of the P-T-x surface, we can now visualize the full 3D form of the surface as shown in Fig. 7.8. The surface is seen to resemble a curved envelope, clipped at each end to reveal the inside of the envelope through the hatched holes. Viewed toward the P—T plane, only the curved edge of the envelope is seen, as in (7.41a). However, viewed toward the P-xB plane or the T-xB plane, the inside of the envelope is seen as the hatch marks in (7.42) or (7.43), respectively. The upper P-T-x surface of the envelope is called the bubble-point surface, in reference to the first vapor bubbles that are seen as the liquid is heated to its boiling point. The P-T-xBap underside of the envelope is correspondingly called the dew-point surface, in reference to the first dewy droplets of liquid as the vapor is cooled to its condensation temperature. Although we normally see only the flat P-T, P-xB, or T-xb projections on the blackboard or book page, it is useful to keep in mind the full 3D form of the P-T-xB surface that underlies these 2D projections of the / = 3 system. 

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