Spindle-shaped goethite particles, spindle-shaped metal magnetic particles composed mainly spindle-shaped hematite particles, and iron, as well as methods for their production

摘要

PROBLEM TO BE SOLVED: To produce a metallic magnetic grain good in dispersibility and having excellent weather resistance and coercive force distribution by specifying the crystallite size and shape of a goethite grain containing Co and Al in a specific proportion based on the total Fe. SOLUTION: This spindle-shaped goethite grain comprises =0.5 and 8 atomic% of Co based on the total Fe and 5-10 atomic % of Al and has 0.18-0.30 m average major axial length, =0.22 size distribution (standard deviation/major axial length), 0.025-0.045 m average minor axial length, 5-10 average axial ratio, 1.8-2.4 crystallite size ratio D020/D110, 1.05-1.20 crystallite size ratio D020/D020 (seed crystal grain) for the seed crystal grain and 1.02-1.10 crystallite size ratio D110/D110 (seed crystal grain) for the seed crystal grain. The spindle-shaped goethite grain is produced by mixing an aqueous solution of an alkali carbonate with an aqueous solution of an alkali hydroxide, reacting an aqueous solution of a ferrous salt therewith, aging an aqueous suspension containing the resultant iron(II)-containing precipitate, then aerating the aqueous suspension with an oxygen-containing gas, producing a spindle-shaped goethite seed crystal grain and adding Co and Al thereto.