Structure transformation coalescence

A common feature of the dehydroxylation of all iron oxide hydroxides is the initial development of microporosity due to the expulsion of water. This is followed, at higher temperatures, by the coalescence of these micropores to mesopores (see Chap. 5). Pore formation is accompanied by a rise in sample surface area. At temperatures higher than ca. 600 °C, the product sinters and the surface area drops considerably. During dehydroxylation, hydroxo-bonds are replaced by oxo-bonds and face sharing between octahedra (absent in the FeOOH structures see Chap. 2) develops and leads to a denser structure. As only one half of the interstices are filled with cations, some movement of Fe atoms during the transformation is required to achieve the two thirds occupancy found in hematite. 

In conclusion, the combination of structural and biochemical results using enzyme from a variety of sources is beginning to coalesce around a unified mechanism for the critical and complex transformation of glucose 6-phosphate to MIP catalyzed by MIP synthase. 

Comprehensive structural study of Ti-3Al-5Zr-Si-alloys, as-cast and deformed, confirmed the features found with the binary Ti-Si-system described above. The transition from polygonal to dendritic structure takes place between 2- and 4-wt.% Si. Alloy with 2-wt.% Si fails with intergranular (but ductile) mode whereas alloys with 4- and 6-wt.% fail with mixed mode where dendritic structure may be recognized. In any case, eutectic areas, in contrast to dendrite or polygonal bodies, which are of a-phase failing with cleavage microcracking, fail with ductile mode - with voids coalescence (Fig. 8). Hot plastic deformation transforms the alloys studied into ductile or semi-ductile materials, which fail only with ductile void coalescence mode [1],... 

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