Solid Hydrogel Transformation Mechanism

Another name for solid hydrogel transformation mechanism is solid-phase mechanism, while solution-mediated transport mechanism is also called liquid-phase mechanism. The main difference in explaining the formation process of zeolites by these two mechanisms lies in whether the liquid component is involved during the crystallization of zeolites. The views of these two mechanisms are opposite to each other and have their own experimental supporting evidence. To date, the liquid-phase mechanism has more experimental support than does the solid-phase mechanism. 

In 1968, Breck and Flanigen for the first time proposed the solid-phase mechanism based on their studies of the crystallization of aluminosilicate. They found that the formation and transformation of amorphous aluminosilicate hydrogel always happened during the crystallization process of zeolites and that the composition of the hydrogel was similar to that of the resultant zeolites. 

In a word, in the solid-phase mechanism, it is believed that neither the dissolution of solid gel nor the direct involvement of the liquid phase happened for the nucleation and growth of zeolite crystals during the crystallization process of zeolites. The nucleation and growth of zeolite crystals came from the structural rearrangement of the framework of solid aluminosilicate gel under hydrothermal crystallization conditions. 

In the early 1970s, McNicol et al. monitored the entire crystallization process of zeolite A by using molecular spectrum techniques and obtained experimental evidence that supported the solid-phase mechanism.[21] 

Based on an analysis of the results of Raman and phosphorescence spectra, McNicol claimed that, during the crystallization process of zeolites A, the composition of the 

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In a series of papers, Nicolaon and Teichner (318) have described the methods of preparation, the transformation of hydrogels to alcogels, the mechanical and thermal stability, and the chemical structure of aerogels. An aerogel is probably the lightest (lowest density) coherent solid that can be made. 

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