US 5,399,278 AGranted

Process for producing acicular goethite particles and acicular magnetic iron oxide particles

AssigneeToda Kogyo Corporation

InventorsKatsumi Yamashita, Tosiharu Harada, Haruki Kurokawa, Kazuhisa Inaba, Hideaki Sadamura, Tomohisa Moriya, Junichi Kawano

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Abstract

Disclosed herein are a process for producing acicular goethite particles comprising the steps of: blowing an oxygen-containing gas into a ferrous salt reaction solution containing colloidal ferrous hydroxide or iron-containing colloidal precipitates which is obtained by reacting an aqueous ferrous salt solution with less than one equivalent of an aqueous alkali hydroxide solution and/or an aqueous alkali carbonate solution based on Fe.sup.2 + in said aqueous ferrous salt solution so as to oxidize said colloidal ferrous hydroxide or iron-containing colloidal precipitates and to produce acicular goethite nucleus particles, adding to the resultant aqueous ferrous salt reaction solution containing said acicular goethite nucleus particles not less than one equivalent of an aqueous alkali carbonate solution based on Fe.sup.2 + in said aqueous ferrous salt reaction solution, and blowing an oxygen-containing gas into the mixed aqueous ferrous salt reaction solution so as to grow said goethite nucleus particles; and a process for producing acicular magnetic iron oxide particles by reducing the acicular goethite particles obtained in the above process to produce acicular magnetite particles, and if necessary, oxidizing the acicular magnetite particles to obtain acicular maghemite particles, and if necessary, modifying the acicular magnetite or maghemite particles with Co or Co and Fe.sup.2 +.

Claims9

Dependent claims

A process for producing acicular goethite particles having an aspect ratio of not less than 20 comprising the steps of

(a) blowing an oxygen-containing gas into a ferrous salt reaction solution containing either colloidal ferrous hydroxide which is obtained by reacting an aqueous ferrous salt solution with less than one equivalent of an aqueous alkali hydroxide solution based on Fe.sup.2+ in said aqueous ferrous salt solution or iron-containing colloidalprecipitates which are obtained by reacting an aqueous ferrous salt solution with less than one equivalent of an aqueous alkali carbonate solution or aqueous alkali hydroxide and alkali carbonate solution based on Fe2+ in said aqueous ferrous salt solution so as to oxidize said colloidal ferrous hydroxide or iron-containing colloidal precipitates and to produce acicular goethite nucleus particles;
(b) adding to the resultant aqueous ferrous salt reaction solution containing from 10 to 90 mol % of said acicular goethite nucleus particles based upon the total amount of goethite particles produced in the process, not less than one equivalent of an aqueous alkali carbonate solution based on Fe.sup.2+ in said aqueous ferrous salt reaction solution;
and
(c) blowing an oxygen containing gas into the mixed aqueous ferrous salt reaction solution so as to grow said nucleus goethite particles
wherein the reaction temperature for producing goethite nucleus particles, the oxidization temperature and the reaction temperature for growing goethite nucleus particles are not higher than 80.degree. C.

2 more elements

Dependencies are inferred from the claim text.