The Columnar Zone

Figure 4.5 Section through a solidification ingot showing the various solidification zones. The equiaxed zone forms near the mold walls. In the interior is the columnar zone, where crystal growth is in the direction of heat flow. (After Lalena and Cleary, 2005. Copyright John Wiley Sons, Inc. Reproduced with permission.)...

The columnar crystals develop predominantly from the chill zone and show a strong preferred ciystallographic orientation which corresponds with the preferred crystallographic directions of dendritic growth. " Some few grains appear in the columnar zone which... 

Variation of the length of the columnar zone with the alloy content for comtantpouring temperature (Chalmers ). 

The regions of positive segregation have two characteristic forms. The outer bands are referred to as A-segregates and are arranged as rope-like stringers of segregation located on the surface of cones with their bases at the base of the ingot. They occur predominantly in a zone near and almost parallel to the end of the columnar zone. 

Cervical cancer arises in the transitional zone that marks the junction of the squamous epithelium of the external cervix with the columnar epithelium of the cervical canal. This zone is usually located on the portio in younger women, which is where cervical cancer usually occurs with exophytic growths. In contrast, older women with retraction of the transformation zone into the cervical canal typically develop cervical cancer with an endocervical growth pattern (Fig. 7.13). This growth type usually gives rise to the typical barrel-shaped configuration of the cervix as the tumor increases in size or an endocervical ulcer develops when there is necrosis. 

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