On synthesis of Fe2SiO4/SiO2 and Fe2O3/SiO2 composites through sol-gel and solid-state reactions

Major processing factors in forming Fe2SiO4/SiO2 and Fe2O3/SiO2 powders via sol-gel synthesis followed by solid-state reactions are investigated. The results clearly indicate that the chemical compositions of the precursors, the ratio of the precursors, the nature of the catalyst used, and the gas atmosphere during solid-state reactions can all affect the outcome of the reaction product(s). The formation of Fe2SiO4/SiO2 is enhanced by using the precursor iron(III) acetylacetonate as the Fe source with the precursor ratio of iron(III) acetylacetonate to tetraethyl orthosilicate being 1:1 and the addition of formic acid. Otherwise, crystalline Fe and Fe3C are formed in place of Fe2SiO4. By altering the gas atmosphere during solid-state reactions from argon to oxygen, the reaction products change from Fe2SiO4/SiO2 to Fe2O3/SiO2. All of the observed phenomena can be rationalized via the degree of mixing of the Fe-O and Si-O domains at the molecular level in the gel network during sol-gel reactions and the presence of a reducing or oxidizing atmosphere during the solid-state reaction.