Modified ferromagnetic chromium dioxide composition and method of preparing the same

Claim 2

A MODIFIED FERROMAGNETIC CHROMIUM DIOXIDE COMPOSITION, CONSISTING OF ABOUT 55 TO 62 PERCENT BY WEIGHT OF CHROMIUM, SAID CHROMIUM BEING COMBINED WITH OXYGEN, AND FROM ABOUT 0.005 TO 10 PERCENT BY WEIGHT OF A MODIFIER SELECTED FROM THE GROUP CONSISTING OF LANTHANUM, YTTRIUM, STRONTIUM AND BARIUM, AND MIXTURES THEREOF IN THE FORM OF THE OXIDE(S), THE BALANCE BEING OXYGEN, SAID COMPOSITION BEING IN THE FORM OF ACICULAR PARTICLES HAVING A LENGTH LESS THAN 2U AND AN AXIAL LENGTH TO WIDTH RATIO GREATER THAN 2.1 AND HAVING A TETRAGONAL CYRSTALLINE STRUCTURE OF THE RUTILE TYPE; SAID COMPOSITION HAVING A COERCIVE FORCE GREATER THAN 280 OERSTEDS, A SATURATION MAGNETIZATION GREATER THAN 60 E.M.U./G AND A RESIDUAL MAGNETIZATION GREATER THAN 25 E.M.U./G.

Claim 3

A method of making the modified chromium dioxide of claim 1 comprising intimately admixing a hydrated chromium (III) chromate of the formula Cr2(CrO4)3.nH2O wherein n is from 1 to 8, with a modifier, said modifier being present in an amount of from about 0.005 to 20 percent by weight of the anhydrous salt, Cr2(CrO4)3, said modifier being selected from the group consisting of lanthanum, yttrium, strontium, barium, their oxides, their salts, and mixtures thereof, and heating the foregoing admixture to a temperature of from about 250* to 500*C under a pressure of from about 80 to 1,000 atmospheres of oxygen.

Claim 4

The method of claim 2, wherein the modifier which is admixed is lanthanum, lanthanum oxide, or a lanthanum salt, and wherein the amount of modifier is such as to provide from 0.05 to 3 percent by weight of lanthanum, expressed as metal, based on the anhydrous salt.

Claim 5

The method of claim 2, wherein the modifier which is admixed is strontium, strontium oxide, or a strontium salt, and wherein the amount of modifier is such as to provide from 0.2 to 3 percent by weight of strontium, expressed as metal, based on the anhydrous salt.

Claim 6

THE METHOD OF CLAIM 2, WHEREIN THE MODIFIER WHICH IS ADMIXED IS BARIUM, BARIUM OXIDE, OR ABARIUM SALT, AND WHEREIN THE AMOUNT OF MODIFIER IS SUCH AS TO PROVIDE FROM 0.05 TO 2 PERCENT BY WEIGHT OF BARIUM, EXPRESSED AS METAL, BASED ON THE ANHYDROUS SALT.

Claim 7

The method of claim 2, wherein the modifier which is admixed is yttrium, yttrium oxide, or an yttrium salt, and wherein the amount of modifier is such as to provide from 0.1 to 3 percent by weight of yttrium, expressed as metal, based on the anhydrous salt.

Claim 8

The method of claim 2 wherein said intimate admixing is carried out in the solid state.

Claim 9

The method of claim 2 wherein said intimate admixing is effected by adding the modifier to a solution of the chromium (III) chromate.

Claim 10

An element for magnetic recording comprising a nonmagnetic supporting material carrying bonded to it a magnetic track made of a ferromagnetic composition of modified chromium dioxide as defined in claim 1.

Claim 11

The element of claim 9 wherein the mOdifier is lanthanum.

Claim 12

The element of claim 9 wherein the modifier is yttrium.

Claim 13

The composition of claim 1 wherein the modifier is lanthanum.

Claim 14

The composition of claim 1 wherein the modifier is yttrium.

Claim 15

A chromium dioxide consisting of from about 59.7 to 61.8 percent by weight of chromium, said chromium being combined with oxygen, and from about 0.05 to 1 percent by weight of a modifier selected from the group consisting of lanthanum, yttrium, strontium and barium, and mixtures thereof in the form of the oxide(s), the balance being oxygen, said composition being in the form of acicular particles of a tetragonal crystalline structure of the rutile type, the particle length being less than 0.6 Mu , and the particles having a length/width axial ratio between 3:1 and 30:1; said composition having a coercive force of at least 350 Oersteds, a saturation magnetization greater than 80 e.m.u./g., and a residual magnetization greater than 44 e.m.u./g.

Claim 16

A chromium dioxide consisting of from about 59.7 to 61.8 percent by weight of chromium, said chromium being combined with oxygen, and from about 0.05 to 1 percent by weight of a modifier selected from the group consisting of lanthanum, yttrium, strontium and barium, and mixtures thereof in the form of the oxide(s), the balance being oxygen, said composition being in the form of acicular particles of a tetragonal crystalline structure of the rutile type, the particle length being less than 0.6 Mu , and the particles having a length/width axial ratio between 3:1 and 30:1; said composition having a coercive force of at least 350 Oersteds, a saturation magnetization greater than 80 e.m.u./g., and a residual magnetization greater than 44 e.m.u./g.

Claim 17

The composition of claim 14 wherein the modifier is lanthanum.

Claim 18

The composition of claim 14 wherein the modifier is yttrium.