Synthesis and Properties of Nanocrystalline δ-FeOOH

For fabricating pure δ-FeOOH, Fe(OH)2 was first precipitated by reacting FeCl2(aq) with NaOH(aq) and then oxidized by an oxidant, such as NaClO(aq) or H2O2(aq). When using NaClO(aq) as the oxidant, with various amounts of NaClO(aq) and NaOH(aq), four phase regions were found, i.e. (a) amorphous region, (b) α-FeOOH+δ-FeOOH+Fe3O4 phase region, (c) δ-FeOOH +α-FeOOH phase region, and (d) very high purity δ-FeOOH phase region. When using H2O2(aq) as the oxidant, with various amounts of H2O2(aq) and NaOH(aq), three phase regions were found, i.e. (a) amorphous region, (b) δ-FeOOH+Fe3O4 phase region, and (c) δ-FeOOH phase region. The study on the microwave properties of pure δ-FeOOH showed that the electron spin resonance linewidth was 3 kOe and the external resonance magnetic field with the maximum absorption was at 2.5 kOe