Polymorphism crystal lamella

Crystallization, by definition, implies that the initial structure be a glass, followed by the nucleation and growth of a crystalline phase, be it the equilibrium one or a metastable phase. The process is a first-order transformation and involves atomic diffusion, or at least atomic shuttles. Types of crystallization reactions that occur include polymorphous crystallization, which is a composition invariant transformation such as that in Fe-B, and eutectic crystallization, T, in FeNiPB glass, where line lamellae of iron-nickel austenite and mclastable (FeNiJj PB phases grow cooperatively. 

Polymorphic transformations in belite have been related to cooling rates in a recent study by Fukuda, Maki, and Ito (1997). These authors stated that rapidly cooled belites have a and a polymorphs, whereas slowly cooled belite is mainly the P polymorph, the latter crystal commonly showing remelting relationships with the parent grain. The rate of the remelting reaction was said to be dependent on temperature and the wetability of the a -phase lamellae by the exsolved liquid, determined by the kinds of impurities and Al/ Fe ratio in the parent a polymorph. 

The classification can be extended to amoeboid, dendritic, or dotlike types, but these terms are self-descriptive and need for alphabetic designations appears unnecessary. Thus one might symbolize a belite grain as Type AE, meaning that it has normal lamellae and they extend into the matrix or Type CF, indicating a complex internal structure and satellite crystals, etc. Designations of polymorph variety in the writer s classification are not intended, but polymorph variety and abundance are of major significance. 

Keywords epitaxy, isotactic polypropylene, syndiotactic polypropylene, crystal structure, crystal polymorphism, helical hand, nucleating agents, AFM, a-phase, 3-phase, lamellae. 

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