Magnetic pulps loaded with ferrite (M
2+OFe
23+O
3) in the pulp lumen were prepared by
in situ synthesis. First the basic conditions for preparation of manganese-ferrite, zinc-ferrite and manganese-zinc ferrite by in situ synthesis were clarified; alkali was added to a pulp suspension containing ferrous salt and divalent metal ion, followed by oxidization of the pulp suspension through air-bubbling at temperature lower than 100°C. The amount of divalent metal ion added was stoichiometrically controlled for coprecipitation of the ferrite. New procedures to prepare ferrite-loaded pulps at their lumen were then developed on the basis of the obtained conditions.
Manganese-ferrite was formed at temperature of more than 50°C 60°C and 80°C when the equivalent value of the alkali added was about 1.0, 1.5 and 2.0 times, respectively, as much as that of the ferrous salt present in the pulp suspension. Meanwhile, zinc-ferrite and manganese-zinc-ferrite were formed in a narrow range of the alkali addition level at temperature of more than 50°C where the equivalent value of the alkali required was approximately 1.0-1.1 times as much as that of ferrous ion.
The contents of manganese-ferrite, zinc-ferrite and manganese-zinc-ferrite in the loaded pulps were 30.9±2wt%, 32.4±2wt% and 36.2±2wt%, respectively. These contents were close to or slightly higher than that of magnetite-loaded pulps reported in our previous paper. The lumen-loaded pulp with 30.9% manganese-ferrite content had saturation magnetization, remnant magnetization and coercive force values of 15.8emu/g (based on the manganese-ferrite-loaded pulp), 3.2emu/g and 107 Oe, respectively. On the other hand, the lumen-loaded pulp with 36.2% manganese-zinc-ferrite content had the corresponding values of 21.4emu/g, 4.7emu/g and 119 Oe, respectively.
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