MANUFACTURE OF NEEDLE-SHAPED ALPHA-FEOOH FOR MAGNETIC RECORDING MATERIAL

摘要

PURPOSE:To produce needle-shaped particles low in size distribution, with less branching and higher axial ratio, by a method wherein a specified quantity of phosphoric ions is in existence during the crystal producing stage and the quantity to be produced is prescribed to be 5-25g/l in terms of Fe, in the production of needle-shaped alpha-FeOOH. CONSTITUTION:A ferrous salt solution with some phosphoric acid or phosphate in the mother liquor is partially neutralized with an alkali for the transformation by oxidation of a part of the Fe component into alpha-FeOOH crystals. The concentration in the ferrous solution is set at 30-100g/l and the quantity of the phosphoric acid to be added is set in terms of P at 0.05-0.6 weight % of the total alpha-FeOOH nuclei precipitation to be produced. The quantity of alkali addition is to be as large as to cause Fe ions in the mother liquor to precipitate at a rate of 5-25g/l. During the crystal forming stage, the reaction temperatures are to be kept at 50-100 deg.C, and pH at 3-8. Further, the growth rate of nuclei is controlled to be 1.5-3.5 times higher. The magnetic tape manufactured of this material is provided with an excellent coercive force and square ratio.