Abstract: Magnetite (Fe3O4) of ferrite magnetic materials has attracted attentions arising by the chip coil electronic material. However, its industrial applications have been limited by the need of high temperature sintering under reduced pressure or vacuum. In order to develop the process method of low-cost and energy saving with high strength and high magnetism of the magnet, a new low temperature sintering method during CO2 gas and adding small amount of boric acid (H3BO3) are proposed. Here, the superfine magnetite powder was fabricated by decomposition from ferrous oxalate at 500℃ in CO2 gas. The ferrous oxalate was synthesized using iron chloride and ammonium oxalate with the liquid phase precipitation. The magnetite powder compact was produced by Newton press and CIP (cold isostatic press) after adding small amount of boric acid. In this study, the effects of the additive on the mechanical and magnetic properties of the sintered magnet were also evaluated. By characteristic evaluation of the magnet, the validity of the proposed new low-temperature sintering process and the optimal process conditions were confirmed.

Key words: Ferrite magnet, Superfine powder, Low-temperature sintering, Boric acid