TEM characterization of the reaction products in aluminium–fly ash couples

The reaction products region formed between molten aluminium and dense, mainly amorphous, precipitator fly ash substrate, produced by hot pressing in argon, was investigated by transmission electron microscopy and energy-dispersive X-ray spectroscopy. The observations proved the oxy-redox reactions between Al and such fly ash constituents as SiO2, Fe2O3, Fe3O4 and mullite. It results in the formation of two interpenetrating crystalline networks, i.e., α-Al2O3 particles surrounded by a continuous metallic phase (Si or Al–Si alloy, reinforced with iron aluminade precipitates). The CaO does not react with Al and its fine crystallites were observed either inside or between the α-Al2O3 particles.