Process for preparing acicular iron oxide particles
AssigneeEastman Kodak Company
InventorBernard J. Pingaud
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Abstract
This disclosure relates to a process for preparing acicular magnetic iron oxide particles by (a) adding an aqueous solution of a ferrous salt to an aqueous solution of a stoichiometric excess of alkaline hydroxide while substantially avoiding local excesses of the ferrous salt, to form an aqueous dispersion of ferrous hydroxide particles, (b) oxidizing these particles to form non-magnetic alpha ferric oxide hydrate particles, and (c) converting the non-magnetic particles to magnetic iron oxide particles by dehydration and reduction or dehydration, reduction and oxidation. The ferrous salt solution is subjected to reducing conditions prior to and/or during the addition to the alkaline hydroxide solution to reduce contaminating ferric ions that are normally present to ferrous ions.
Claims23
In a process for preparing acicular magnetic iron oxide particles comprising (a) adding an aqueous solution of ferrous salt to an aqueous solution of a stoichiometric excess of alkaline hydroxide while substantially avoiding local excesses of said ferrous salt, to form an aqueous dispersion of ferrous hydroxide particles, (b) oxidizing said particles to form non-magnetic alpha ferric oxide hydrate particles, and (c) converting said non-magnetic particles to magnetic iron oxide particles by dehydration and reduction or dehydration, reduction and oxidation, the improvement wherein said ferrous salt solution is subjected to reducing conditions prior to or during said addition to reduce contaminating ferric ions present therein to ferrous ions.
Dependencies are inferred from the claim text.