Hematite particles for non-magnetic undercoat layer for magnetic recording medium, process for producing the same, non-magnetic undercoat layer and magnetic recording medium

摘要

High-density acicular hematite particles for a nonmagnetic undercoat layer for a magnetic recording medium have an average major axial diameter of not more than 0.3 mu m, a major axial diameter distribution in geometrical standard of not more than 1.50 and a BET specific surface area of not less than 35 m<2>/g; show a pH of not less than 8; and contain not more than 300 ppm of soluble sodium salt, calculated as Na, and not more than 150 ppm of soluble sulfate, calculated as SO4.