An integrated micro- and nano-scale investigation of green aluminosilicate materials: New insight into the gel network after natural weathering

The microstructures of most of the geopolymers synthesized from different starting materials are composed of a mixture of (semi)-crystalline and amorphous phases. In this work we aim to investigate in dept the nanoscale morphology and composition of the gel phase of two volcanic- (Mt. Etna, Sicily) and metakaolin-based geopolymers. The main technique used is high-resolution transmission electron microscopy (HRTEM), with energy dispersive X-ray compositional analysis (STEM-EDS) and selected area electron diffraction (SAED). The results were compared with those obtained on a larger scale. For the first time, a focus at the micro- and nanoscale of geopolymers synthesized with these binary mixtures was achieved. The effect of weathering on the geopolymer network, the crystalline phases and the chemical composition was also evaluated showing, with the convergence of the results of complementary methods, that environmental exposure affects the products made with one type of precursor ( ghiara ) more than the other (volcanic ash). • Binary mixtures geopolymers of volcanic precursors / metakaolin were studied. • Behavior of geopolymers after natural weathering was evaluated at the nanoscale. • The different materials are differently affected by the environmental exposure. • Volcanic ash- based materials are less affected than ghiara paleosoil-based ones.