Synthesis of Spinel Ferrites from Ferrous Hydroxide by the Schikorr Reaction in Hot Water, and Accompanied Hydrogen Generation Property

The preparation of ferrite particles from Fe (OH)2 aqueous suspension is studied in high temperaturehydrothermal condition accompanied with the Schikorr reaction. The well crystalized magnetite particle grew in larger size in this reaction system, compared to the usual co-precipitating or wet-oxidizing methods. The addition of KNO3 as an oxidizing reagent prior to the hydrothermal treatment was useful to control the nucleation of magnetite and this led to reduce the particle size. The addition of excess amount of KNO3 led to hematite formation. When Mn2+ or Ni2+ ion was mixed in starting ferrous solution, respective ion partially entered into spinel phase. In this case, manganese or nickel ferrite with stoichiometric composition was not obtained and the maximum value of x in the MxFe3-xO4 (M: divalent metal ion) seemed to be 0.4 for Mn, and very small for Ni. The amount of H2 generated during the reaction decreased by adding Ni2+. Also, Ni metal phase was observed by XRD in the series of Ni adding experiments. Although, when KNO3 solution was added into the starting solution, Mn2+ or Ni2+ were easily incorporated into the spinel phase to give respective stoichiometric ferrite.