Hexagonal faces

Fig. 2. In the centre of this drawing there is shown a dodecahedral complex. The polyhedra that surround it are tetrakaidecahedra, each having two hexagonal faces...

We have already illustrated rotation axes in 2.1.6. Plane symmetry involves symmetry such as that of the hexagonal faces given above in 2.2.5. We will now examine inversion or mirror symmetry. One type mirror symmetry is shown in the following diagram, given as 2.2.6. on the next page. 

The objective of this study is to determine the mechanism of growth of zeolite L and thereby control the crystal habit. AFM was applied to study the surface features on both the (100) side walls, and the (001) hexagonal faces of zeolite L and the likely mechanism of growth was determined. Crystals with modified habits were also studied, and found to exhibit different surface features from one another. 

Figure 3 Cross-section depicting the smallest steps present on the surface of each face of crystals with aspect ratios 1.5. Where 1 i) shows the position of the cross-section, lii) shows the cross-section and the corresponding heights and 1 iii) shows a schematic of the possible cancrinite unit of attachment onto the hexagonal face. Where 2i) shows the position of the cross-sections, 2ii) and iv) show the cross-sections and the corresponding heights and 2iii) and v) show schematics of the possible cancrinite unit of attachment onto the side walls.

In summary, zeolite L was found to grow via cancrinite cage incorporation, although different mechanisms of incorporation were observed depending on the face of the crystal. When the crystal habit was modified, the features observed on the hexagonal face varied considerably, suggesting growth had been modified. It is possible that this was caused by the occurrence of defects in the crystal. 

In general the foam density reduces as the amount of blowing agent is increased, with a lower limit set by foam stability. It is possible to model the factors which affect the final density Mahapatro and co-workers (206) used a regular Kelvin foam model to analyse the expansion of PE foams. The foam has uniform sized cells, each with eight hexagonal faces and four square... 

Figure 5, having hexagonal faces and square faces. 

The crystal structure of the faujasite is built up by linking the sodalite cages tetrahedrally through their hexagonal faces forming connecting hexagonal prisms. 

Fig. 26. Y-Fe2Si04 (high-pressure spinel form) projected on (001) of the cubic cell Fe and Si atoms only. Large circle = Si, small circle = Fe, heights in units of c/8. The f.c.c. unit cell is dotted, the equivalent b.c.t. unit cell (c, = cj outlined with broken lines. The SiFci2 truncated tetrahedra are drawn top right. Si at 3/4 bottom right. Si at 1/2 bottom left. Si at 1/4 top left. Si at 0. (Note that the Fe which appear to be at the centres of hexagonal faces are not. They form the lower edge of the truncated tetrahedron concerned.)...

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