Influence of ε-Fe₂O₃ Synthesis Conditions on Particle Properties in Silica Xerogels

Abstract

Xerogels were prepared from mixed aqueous ethanol solutions of Tetraethyl orthosilicate (TEOS) and hydrated iron nitrate, and their properties were investigated using XRD, TEM, FTIR, and VSM. As the heat treatment temperature of the iron oxide particles increased, the γ-Fe₂O₃ and the ε-Fe₂O₃ were precipitated, and the particle diameters increased.

For heat treatment at 1100°C, the α-Fe₂O₃ was observed when the Si/Fe ratio was 1.5, while the ε-Fe₂O₃ was formed when the Si/Fe ratio was 2.8, 5.7, and 11.4. The particle diameter of the ε phase increased with decreasing Si/Fe ratio. By adding yttrium, crystal growth of the iron oxide particles was promoted, and the particle diameters and the coercivity consequently became larger than that of the sample without yttrium present.