Magnetic Measurements of NiFe₂O₄ Formation from Iron Hydroxides and Oxide in High Temperature Water

Abstract

Formation of NiFe₂O₄ from iron hydroxides and an oxide has been studied in high temperature water by in situ measurements. The five kinds of Fe compounds used in the experiments are known as components of Fe crud in BWR condensate water. Among the reactants and products, only NiFe₂O₄ shows ferromagnetism. An in situ method, using a magnetic balance, was developed to measure the mass of NiFe₂O₄ in high temperature water. The lower detection limit of this method is 0.01 mg of NiFe₂O₄ with a maximum detection error of ±2%. The iron hydroxides react with Ni(OH)₂ to form NiFe₂O₄ and α-Fe₂O₃ through a dehydration reaction in 553 K water. Amorphous iron hydroxide and γ-FeOOH react rapidly, reaching saturated values of the conversion to NiFe₂O₄ within a few hours at 553 K. The dissolved oxygen has no influence on the NiFe₂O₄ formation. The amount of generated NiFe₂O₄ decreases with the reduction of the pH value, due to dissolution of the reactant. The rate of NiFe₂O₄ formation increases with reaction temperature, while the saturated value of formed NiFe₂O₄ decreases.

KEYWORDS:

• chemical preperation
• nickel ferrite
• iron hydroxides
• iron oxides
• hematite
• magnetic balance
• magnetic susceptibility
• dehydration
• pH value
• temperature dependence