Nanoscale observation of morphological transformation during ageing of silica and silica-alumina

摘要

Atomic force microscopy (AFM)was used for in-situ observation of nanoscale morphological transformations during the ageing step in sol-gel synthesis.Silica,alumina and silica-alumina samples with different Si/Al ratios were prepared from inorganic salt precursors and geled at low pH.Silica and silica-alumina samples formed branch-like gel network made of nanometer-sized clusters.During ageing at room temperature,the overall structure of the gel network remained unchanged but the clusters underwent phase trans-formation,coaslesence,coarsening,fragmentation,as well as dissolution resulting in the internal restructuring of the gel material.Morphological transformation associated with crystallization of pseudo-boehmite phase was observed for the alumina samples.These nanometer-scale processes are expected to play a key role in dictating the material properties of the final sol-gel product.