Production method for metal oxide particles, metal oxide powder, and magnetic recording medium

Abstract

A production method for metal oxide particles includes: obtaining precursor particles of a metal oxide by performing a synthesis reaction of the precursor particles in the presence of an organic compound; and converting the obtained precursor particles into metal oxide particles by heating an aqueous solution containing the precursor particles to 300° C. or higher and pressurizing the aqueous solution at a pressure of 20 MPa or higher.

What is claimed is: 
     
         1 . A production method for metal oxide particles comprising:
 obtaining precursor particles of a metal oxide by performing a synthesis reaction of the precursor particles in the presence of an organic compound; and   converting the obtained precursor particles into metal oxide particles by heating an aqueous solution containing the precursor particles to 300° C. or higher and pressurizing the aqueous solution at a pressure of 20 MPa or higher.   
     
     
         2 . The production method for metal oxide particles according to  claim 1 ,
 wherein the heating and pressurization is performed while continuously feeding the aqueous solution.   
     
     
         3 . The production method for metal oxide particles according to  claim 1 ,
 wherein the synthesis reaction is performed in an aqueous reaction solution in a pH range of 5 to 14.   
     
     
         4 . The production method for metal oxide particles according to  claim 1 ,
 wherein an average particle size of the precursor particles is 25 nm or less.   
     
     
         5 . The production method for metal oxide particles according to  claim 2 ,
 wherein an average particle size of the precursor particles is 25 nm or less.   
     
     
         6 . The production method for metal oxide particles according to  claim 3 ,
 wherein an average particle size of the precursor particles is 25 nm or less.   
     
     
         7 . The production method for metal oxide particles according to  claim 1 ,
 wherein a coefficient of variation in the particle size of the precursor particles is 5% to 40%.   
     
     
         8 . The production method for metal oxide particles according to  claim 1 ,
 wherein, in the synthesis reaction, an iron salt, an alkali earth metal salt, and the organic compound are mixed with each other in an aqueous solution so as to cause precursor particles of hexagonal ferrite to precipitate.   
     
     
         9 . The production method for metal oxide particles according to  claim 1 ,
 wherein the conversion of the precursor particles into metal oxide particles is performed through the following steps including:   adding a precursor particle solution containing the precursor particles, which are obtained in the synthesis reaction, to a liquid feeding path to which water, which is heated to 300° C. or higher and is pressurized at a pressure of 20 MPa or higher, is continuously fed; and   converting the precursor particles into metal oxide particles by continuously feeding a mixed solution containing water and the precursor particle solution to the liquid feeding path while heating the mixed solution to 300° C. or higher and pressurizing the mixed solution at a pressure of 20 MPa or higher.   
     
     
         10 . The production method for metal oxide particles according to  claim 1 ,
 wherein the metal oxide particles are hexagonal ferrite particles selected from the group consisting of barium ferrite, strontium ferrite, and a mixed crystal of barium ferrite and strontium ferrite.   
     
     
         11 . The production method for metal oxide particles according to  claim 1 ,
 wherein the organic compound is selected from the group consisting of a carboxylic acid, a carboxylate, an anionic surfactant, and a water-soluble polymer.   
     
     
         12 . A metal oxide powder which is obtained by the production method according to  claim 1 . 
     
     
         13 . The metal oxide powder according to  claim 12 , which is a ferromagnetic hexagonal ferrite powder. 
     
     
         14 . The metal oxide powder according to  claim 12 , which is a magnetic powder for magnetic recording. 
     
     
         15 . The metal oxide powder according to  claim 12 ,
 wherein an average sphere equivalent diameter is 5 nm to 30 nm.   
     
     
         16 . The metal oxide powder according to  claim 12 ,
 wherein a coefficient of variation in the sphere equivalent diameter is 5% to 40%.   
     
     
         17 . A magnetic recording medium comprising
 a magnetic layer that contains a ferromagnetic powder and a binder on a nonmagnetic support,   wherein the ferromagnetic powder is the metal oxide powder according to  claim 12 .