Cobalt modified acicular γ ferric oxide and process for preparing the same

Claim 2

Synthetic cobalt modified acicular gamma ferric oxide wherein the cobalt is present in an amount of at least about 1/4 atomic percent cobalt, based on the iron content, which when incorporated with vinyl copolymer recording binder at a level of 75% by weight provides a polyethylene terephthalate based magnetic recording member which exhibits a magnetic stability coefficient of from about 4,000 to about 10,000.

Claim 3

The product of claim 1 wherein the atomic percent cobalt is about 2 to 5, based on the iron content.

Claim 4

A process for the manufacture of synthetic acicular gamma ferric oxide containing at least about 1/4 atomic percent cobalt, based on the iron content, which when incorporated with recording binder at a level of 75% by weight provides a magnetic recording member which exhibits a magnetic stability coefficient of from about 4000 to about 10,000 comprising the steps of: (a) introducing aqueous alkali into aqueous ferrous chloride containing from about 0.25 to 0.7 pound ferrous chloride per gallon, said alkali being added at the rate of from about 0.03 to 0.2 equivalents per minute per mole dissolved ferrous chloride while maintaining the temperature at about 60°-90° F.; continuing said addition until sufficient alkali has been added to precipitate from about 20 to 85% of the iron as ferrous hydroxide; (b) introducing oxygen-containing gas into said aqueous mixture until the pH is between about 2.6 and 4.1 and the ferrous hydroxide precipitate is oxidized to the lepidocrocite form; (c) adding water-soluble cobalt salt to the resulting lepidocrocite seed slurry in an amount equivalent to at least about 0.25 atomic percent cobalt based on the total iron introduced; (d) maintaining said slurry at about 80°-160° F. and a pH between about 2.6 and 4.1 while simultaneously and continuously introducing alkali and oxygen-containing gas until the iron content is substantially completely precipitated in the form of lepidocrocite; (e) and adding aqueous alkali while introducing oxygen-containing gas into said aqueous mixture at about 80°-160° F. to a pH between about 7 and 9.5 until substantially all of the cobalt ion has precipitated on the surface of said lepidocrocite; (f) reducing in a reducing atmosphere said cobalt modified lepidocrocite to cobalt modified ferroso-ferric oxide at a temperature of from about 650° to 800° F., and subsequently oxidizing in an oxidizing atmosphere to cobalt modified acicular gamma ferric oxide.

Claim 5

A process for the manufacture of synthetic acicular gamma ferric oxide containing at least about 1/4 atomic percent cobalt, based on the iron content, which when incorporated with recording binder at a level of 75% by weight provides a magnetic recording member which exhibits a magnetic stability coefficient of from about 4000 to about 10,000 comprising the steps of: (a) introducing aqueous alkali into aqueous ferrous chloride containing from about 0.25 to 0.7 pound ferrous chloride per gallon, said alkali being added at the rate of from about 0.03 to 0.2 equivalents per minute per mole dissolved ferrous chloride while maintaining the temperature at about 60°-90° F.; continuing said addition until sufficient alkali has been added to precipitate from about 20 to 85% of the iron as ferrous hydroxide; (b) introducing oxygen-containing gas into said aqueous mixture until the pH is between about 2.6 and 4.1 and the ferrous hydroxide precipitate is oxidized to the lepidocrocite form; (c) adding water-soluble cobalt salt to the resulting lepidocrocite seed slurry in an amount equivalent to at least about 0.25 atomic percent cobalt based on the total iron introduced; (d) maintaining said slurry at about 80°-160° F. and a pH between about 2.6 and 4.1 while simultaneously and continuously introducing alkali and oxygen-containing gas until the iron content is substantially completely precipitated in the form of lepidocrocite; (e) and adding aqueous alkali while introducing oxygen-containing gas into said aqueous mixture at about 80°-160° F. to a pH between about 7 and 9.5 until substantially all of the cobalt ion has precipitated on the surface of said lepidocrocite; (f) reducing in a reducing atmosphere said cobalt modified lepidocrocite to cobalt modified ferroso-ferric oxide at a temperature of from about 650° to 800° F., and subsequently oxidizing in an oxidizing atmosphere to cobalt modified acicular gamma ferric oxide.

Claim 6

The process of claim 3 wherein the cobalt modified lepidocrocite produced in step "e" is coated with at least one hydrophobic aliphatic monocarboxylic acid having from about 8 to about 24 carbon atoms prior to the reduction and oxidation of step "f".

Claim 7

The process of claim 3 wherein the final product is mechanically densified.

Claim 8

The process of claim 3 wherein said alkali is selected from sodium hydroxide, potassium hydroxide, or calcium hydroxide.

Claim 9

The process of claim 2 wherein said cobalt salt is added in an amount equivalent to from about 2 to 5 atomic percent cobalt based on the total iron introduced.

Claim 10

The process of claim 3 wherein said oxidation in step f) is performed in a current of air.