Structure of glass-ceramic from Fe-Ni wastes

Due to the elevate amounts of iron and magnesium oxides and the presence of ∼2 wt % chromium oxides in the composition, the crystallization process is peculiar and the final structure of glass-ceramic is complex. Some preliminary Fe-Mg-Cr spinel crystals with size of few microns precipitate during the melt cooling. Then, these crystals act as centres for the growth of a pyroxene phase; thus, 15-20 vol% of the glass-ceramic structure is formed. The major amorphous phase, where Cr2O3 concentration becomes negligible, is characterized with a high immiscibility trend, leading to the formation of Fe-rich droplets with size of 50-70 nm. Subsequently, these droplets are transformed into nano magnetite crystals, which provoke crystallisation of the main pyroxene phase. This “second” new pyroxene phase differs by the one, already formed on the preliminary Fe-Mg-Cr spinel, and is composed by mono-crystals with size of 150-200 nm.