Diffusion induced recrystallization

When the difference in concentration between the parent phase and a new solid solution is high, diffusion-induced recrystallization (DIR—also called... 

Two effects cause the low production capacity of large-grained catalyst. First, large grain size retards transport of the ammonia formed inside the catalyst into the bulk gas stream. This is because the ammonia transport proceeds by slow diffusion through the pore system. The second effect is a consequence of the fact that a single catalyst grain in the oxide state reduces from the outside to the interior of the particle. The water vapor produced inside the catalyst by reduction comes into contact with already reduced catalyst on its way to the outer surface of the catalyst. This induces a severe recrystallization. As an example, if the particle size increases from about 1 to 8 mm, the inner surface decreases from 11 to 16 m2/g to 3 to 8 m2/g74. Therefore the choice of catalyst requires the optimization of 1) catalyst size versus catalyst activity, 2) catalyst size versus pressure drop across the converter and 3) the impact of 1 and 2 on... 

In order to obtain dense shapes and fine microstructures, hot pressing has been applied to induce grain boundary sliding, twinning, creep, and bulk diffusion accompanied by recrystallization [410-412]. 

McGrath, Robeson, and Matzner investigated block copolymers and homopolymer-copolymer blends of bisphenol-A polysulfone and nylon-6 (7). They found improved ESCR as the content of the crystalline nylon-6 block increased. Similarly, Viswanathan, al. prepared random block copolymers of bisphenol-A pFTysulfone and the partially crystalline hydroquinone polysulfone (8). ESCR improved markedly as the hydroquinone content increased. However, while the copolymers "as made" are semicrystalline, the compression molded specimens used for ESCR studies are amorphous. Hence, recrystallization from the melt was quite slow. The improvement of ESCR is attributed to solvent-induced crystallization of the surface layers, which was presumed to restrict diffusion of the liquid into the bulk. 

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