Tin-containing granular magnetic oxide particles and process for producing the same

Tin-containing granular magnetic oxide particles comprising spinel-type crystal represented by the formula:

• Fe3-xSnxO4
• wherein x is 0.14 to 0.48, and
• having an average particle diameter of 0.1 to 0.3 μm, a Fe2+ content of 17 to 22% by weight, a lattice constant of 8.41 to 8.49 Å, a magnetization value of 20 to 50 Am2/kg when measured under an applied magnetic field of 79.6 kA/m, a blackness (a* value) of not more than +1.5, and a depth of a groove of not more than 40 μm at which three or more continuous lines each having a length of not less than 10 mm are developed in a pigment dispersion test using a grind-meter when measured by Hoover's muller method according to JIS K5101 (1991) 9.1.

A process for producing tin-containing granular magnetic oxide particles, comprising:

• mixing an aqueous ferrous salt solution, an aqueous solution containing a tin compound in an amount of 10 to 30 mol %, calculated as Sn, based on ferrous iron contained in the ferrous salt and an aqueous alkali solution to obtain Fe- and Sn-containing precipitates;
• and
• subjecting the Fe- and Sn-containing precipitates to hydrothermal treatment.

A process for producing tin-containing granular magnetic oxide particles, comprising:

• mixing an aqueous ferrous salt solution containing a ferrous salt in an amount of 0.1 to 10 M, calculated as an anhydride of the ferrous salt, an aqueous solution containing a tin compound in an amount of 10 to 30 mol %, calculated as Sn, based on ferrous iron contained in the ferrous salt and an aqueous alkali solution in an amount of the aqueous alkali solution is not less than 1 equivalent per ferrous and tin in the aqueous solution;
• and
• hydrothermally treating the obtained Fe- and Sn-containing precipitates at a temperature of 101 to 300° C. for 0.5 to 48 hours.