Method of producing cobalt-modified magnetic particles

Claim 1

A method of producing cobalt-modified magnetic particles which comprises: (a) heating an aqueous suspension of amorphous ferric hydroxide at an elevated temperature from 100° C. to 250° C. at an alkaline pH in the presence of an effective amount of at least one growth regulating agent dissolved in the suspension, in the presence or in the absence of α-ferric oxide seed crystals of minor axes not more than 0.4 microns in average in amounts of 0.1-25 mole % in terms of Fe content in relation to the ferric hydroxide in the suspension, the growth regulating agent being selected from the group consisting of an organic phosphoric acid, a hydroxycarboxylic acid, a polybasic acid, an aminocarboxylic acid, an aminosulfonic acid, an aromatic sulfonic acid, a thiocarboxylic acid, a water soluble salt of any one of the acids, a water soluble ester of any one of the acids, a polyamine, a thioalcohol, a polyhydric alcohol and a β-dicarbonyl compound, for a length of time sufficient to convert the amorphous ferric hydroxide into acicular α-ferric oxide, (b) converting the α-ferric oxide into γ-ferric oxide by reduction thereof followed by oxidation, and (c) forming an aqueous suspension of the γ-ferric oxide and ferrous hydroxide and cobaltous hydroxide in amounts of 0.5-50 mole %, respectively in relation to the Fe content of the γ-ferric oxide in the suspension, said suspension having an alkaline pH and maintaining the suspension at a temperature from 30° C. to 50° C. for a time sufficient to form a cobalt modified γ-ferric oxide; said cobalt modified γ-ferric oxide when incorporated into a tape effecting a magnetic recording tape having an improved squareness ratio.

Claim 2

A method of producing cobalt-modified magnetic particles which comprises: (a) heating an aqueous suspension of amorphous ferric hydroxide at an elevated temperature from 100° C. to 250° C. at an alkaline pH in the presence of an effective amount of at least one growth regulating agent dissolved in the suspension, in the presence or in the absence of α-ferric oxide seed crystals of minor axes not more than 0.4 microns in average in amounts of 0.1-25 mole % in terms of Fe content in relation to the ferric hydroxide in the suspension, the growth regulating agent being selected from the group consisting of an organic phosphoric acid, a hydroxycarboxylic acid, a polybasic acid, an aminocarboxylic acid, an aminosulfonic acid, an aromatic sulfonic acid, a thiocarboxylic acid, a water soluble salt of any one of the acids, a water soluble ester of any one of the acids, a polyamine, a thioalcohol, a polyhydric alcohol and a β-dicarbonyl compound, for a length of time sufficient to convert the amorphous ferric hydroxide into acicular α-ferric oxide, (b) converting the α-ferric oxide into γ-ferric oxide by reduction thereof followed by oxidation, and (c) forming an aqueous suspension of the γ-ferric oxide and ferrous hydroxide and cobaltous hydroxide in amounts of 0.5-50 mole %, respectively in relation to the Fe content of the γ-ferric oxide in the suspension, said suspension having an alkaline pH and maintaining the suspension at a temperature from 30° C. to 50° C. for a time sufficient to form a cobalt modified γ-ferric oxide; said cobalt modified γ-ferric oxide when incorporated into a tape effecting a magnetic recording tape having an improved squareness ratio.

Claim 17

The method as claimed in any one of claims 1 to 15, wherein step (a) is performed in the presence of α-ferric oxide seed crystals.