PURPOSE: To enhance holding power, etc., by a method wherein after alkali is added to a mixed solution to obtain a pH necessary to make iron hydroxide and cobalt hydroxide to be precipitated, it is made to form a uniform colloid solution by adding dilute sulfuric acid, and alkali is added again to make colloid nuclei to grow.
CONSTITUTION: The mixed solution of iron and cobalt is made using iron salt and cobalt salt, and acicular core crystals of ferromagnetic iron oxide powder is added and stirred to make the core crystals to be dispersed. Alkali, such as caustic soda, etc., is added to obtain the pH of 12W 13 necessary to make iron hydroxide and cobalt hydroxide to be precipitated, and then pH is made to descend to 3W5 by adding dilute acid, such as dilute sulfuric acid, etc., to convert the precipitation into a uniform colloid solution to make it as nuclei to induce uniform cobalt ferrite, etc., moreover alkali sufficient to make the nuclei to grow is added, heat of the grade not to make cobalt to disperse inside of the core crystals is applied and is stirred, and cobalt compound, etc., are made to be deposited uniformly to the core crystals and to cover the surface of the unit core crystals uniformly. Accordingly high holding power can be obtained and distribution of holding power can be improved remarkably.
MIYAMOTO SOUICHI
TOKUNAGA HIDEAKI
| JPS525494A | 1977-01-17 |