| abstract |
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 µm, 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 SO 4 . |