Analogy Between Allophane Aggregates and Synthetic Gels

Analogy Between Allophane Aggregates and Synthetic Gels 

Surface area several hundred m /g Fractal stmcture (D not known) High water content Irreversible shrinkage during drying 

Surface area several hundred w /g Fractal structure D — 1.8-2.4) High liquid content (H2O, alcohol) Irreversible shrinkage during drying 

A synthetic gel of silica is a two phase solid-liquid material, amorphous and extremely porous (70-99% of porosity). The bulk density of the solid phase is typically in the range of 0.5-0.1 g/cm and the specific surface area is several hundred of m /g [13,14]. The gel network can be described as an assembly of clusters ( 50 nm). The clusters can be fractal (D/ l. 8-2.4), each being composed by aggregates of small particles ( l-2 nm) [20-22] (Chap. 2). 

The literature explains that allophane aggregates come from the leaching of amorphous volcanic materials (glass and ashes) [25], the weathering leading to oversaturated 

---