Low Temperature Preparation of Ferrite Magnetic Materials by the Addition of a Little Amount of Boric Acid and Their Characteristics

Abstract

Recently, magnetite (Fe₃O₄) of ferrite magnetic materials has attracted attentions arising from the scientific inter-est in clarifying material properties and its potential applications. However, its industrial applications have been limited by the need of high temperature (ca. 1500°C) sintering under reduced pressure or vacuum. So the purpose of this study is to fabricate the magnetite sintered body with high-strength and soft magnetism at relatively mild condi-tions. The manufacturing procedures are as follows: fine magnetite powder was synthesized under a CO₂ atmo-sphere at 500°C from the oxalic acid iron by liquid phase sedimentation using iron chloride and ammonium oxalate; subsequently, a small amount of boric acid [H₃BO₃] was added to the powder, and then the magnetite powder com-pact was prepared with Newton press and CIP methods. Finally, the Fe₃O₄ sintered body was fabricated by sintering at 1050°C under a CO₂ atmosphere which is lower in comparison with the traditional manner. By this method, we obtained magnetite sintered body with 0.5 mass% boric acid additive being of high strength (400 MPa), high satura-tion magnetization value and low coercive force.