Production of ε-Fe2O3 Nanoparticles in Matrices Constituted by Closely Packed Silica Spheres

Mixtures of iron(III) oxide polymorphs with a high content of e-Fe2O3 were obtained by the decomposition of iron(III) nitrate in voids of a close packing of silica spheres. It was shown that the phase composition of Fe2O3 nanopowders can be controlled by using silica spheres of various sizes. The critical sizes of Fe2O3 nanoparticles that correspond to the γ-Fe2O3 → e-Fe2O3 and e-Fe2O3 → α-Fe2O3 transitions were determined to be 10 ± 2 and 28 ± 3 nm, respectively. The maximum e-Fe2O3 content is reached at a silica sphere size of 110 nm and is 83%.