DE1802469A1 - Process for the production of ferromagnetic chromium dioxide - Google Patents

Description

FARBENFABRIKENBAYERAG 1802469

LEVERKUSEN-Beyenwk .. .. HteBt-Abbey »« GB / HM ^U " ^Λί ·« **

Process for the production of ferromagnetic chromium dioxide

The present invention relates to a process for the production of ferromagnetic chromium dioxide.

Since a work by R.S. Schwartz and co-workers (Am. Chem. Soc. 24, I676 (1952) it is known that during the decomposition chromic acid under increased oxygen pressure ferromagnetic, Chromium dioxide crystallizing in the rutile lattice can be obtained relatively pure. According to U.S. patent 2,956,955, when chromic acid decomposes under hydrothermal conditions, only coarse products are produced obtained with a low coercive force below 100 {_ OeJ. Such Products are not useful for many uses, such as magnetic recording processes.

In a number of patents (e.g. British Patent 859 957, British Patent 1 006-610, U.S. Patent 3,571 0 ^ 3) it is shown that the addition of suitable modifiers influences the particle size and shape and thus also the Coercive force can be controlled.

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Wit- "set forth in U.S. Patents 3,117,993 and 3,37,1,043, However, the addition of the modifying substances to the C -romic acid before the pressure treatment does not yet lead to the desired particle size or the necessary narrow particle size distribution.

The US Patent 3,278,263 relates to a process for the preparation of ferromagnetic chromium dioxide, wherein the chromium (III) oxide or Ch'rom (IIl) oxide hydrates at temperatures up to 500 ⁰ C and under elevated pressure is heated with an oxidizing agent .

It has been suggested in U.S. Patent 3,117,093 that not chromic acid but chromium oxide phases with an average chromium oxidation level between 4 and 6 with or without To subject modifier to pressure treatment. This process has the disadvantage that all of the chromic acid to be used are first converted into the mentioned oxide phases of lower oxidation level in an upstream process must, which are then exposed to hydrothermal conditions in a second stage.

Another possibility of effectively introducing the modifying substances is described in the U.S. Patent 3 371 043 been. In a first stage, under hydrothermal conditions, the modifier is in proportion ferromagnetic chromium dioxide nuclei containing large quantities produced, which then in a second pressure stage with

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further chromic acid is implemented. This process has the disadvantage that a high pressure process is already used in the first stage is needed.

A process has now been found for the production of ferromagnetic chromium dioxide by hydrothermal treatment of chromic acid at temperatures from 200 to 40O ⁰ C and pressures of 1 to 500 kg / qcm in the presence of nucleating substances, which is characterized in that the nucleating substance is a chromium oxide in which the chromium has an average oxidation level between 4 and 6.

Surprisingly, it has been found that the disadvantages of the previously known processes can be avoided if a chromium oxide phase with an average value of chromium between 4 and 6 is first produced in a first stage and then the product of the first stage in a second stage with a large one Excess, of chromic acid, subjecting it to hydrothermal conditions. Since the product of the first L ·. tufe can be obtained very easily by heating chromic acid under normal pressure, only a single pressure stage is necessary with the new process. Furthermore, since the predominant part of the reaction mixture in the second stage consists of chromic acid, only a little of the product of the first stage is required.

In a known way, the properties of the ferromagnetic Chromium dioxide varies by adding modifiers will. These modifiers are already used in the first stage of the production of the nucleating phase with the

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medium valence of chromium between 4 and 6 added. The modifiers known from the literature cited above can be used as modifiers, in particular Oxides and / or fluorides of manganese, cobalt, iron, niobium, kuthenium, arsenic, antimony, vanadium, etc., as described in British Patents 859,937 and 1,073,483, respectively will. The oxide-forming compounds of tellurium and / or antimony are preferably used. The tellurium can too can be used in elemental form or in the form of its alloy with antimony.

It was known that chromium oxide phases with an average chromium oxidation number between 4 and 6 result in a hydrothermal Let treatment be converted into magnetic clock chromium dioxide. Under no circumstances could it have been foreseen, however Small amounts of these watchomic oxide phases mixed with chromic acid are sufficient to produce a high quality under hydrothermal conditions ferromagnetic ^ to generate chromium dioxide.

In detail, the process can be carried out as follows:

The product of the first stage is prepared by preferably adding a mixture of chromic acid and a substance serving as a modifier, eg TeOv, or bb ^ O ,, in air or in an acidic atmosphere under normal pressure to temperatures in the range 200-j80 ° G is heated. The heating time can be a few hours to a few days. The modifier-containing chromium oxides shown in this way contain, as can be determined by X-ray, that of US Schwartz and

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Staff ^ Am.uhem.Soc. 74 »167 (1952) described phases" Gr, Ug "or Cr ₂ O ₁ -" or a mixture of the phases mentioned. The product of the first stage is not ferromagnetic. The amount of modifier can be varied within a wide range 1-30%, preferably 3-20%, based on chromic acid, of, for example, TeOp or bbpü-, can be used.

The intensively ground product of the 1st stage is mixed with chromic acid and water. The amount of the product from the 1st stage depends on the target particle size and the amount of modifier retained in the product from the 1st stage; Amounts of 1-40 i ° relative to the employed in the second stage chromic acid are possible, preferably amounts of from 5-20 $ applied. The amount of water is not very critical; enough water should be added to produce a stiff paste. Amounts of 50-150 # based on the product of the first stage are favorable.

The mixture of the product of the 1st stage, chromic acid and water in a suitable container, eg a stainless steel beaker in an autoclave at temperatures of 200-400 ⁰ C, preferably 280-350 ⁰ C., whereby pressures of 1-500, preferably 150-350

kg / cm can be set. The reaction time is not critical it can be 1-8 hours and more.

The product is washed free of chromate with water and at 11u-120 ° C dried in a drying cabinet.

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I ... watch chromium dioxide produced in the manner described has values for the remanent magnetization of 4UO-500 / Sauss.cm .g " ¹ _7 and coercive forces of 200-500 / Öe_J7.

The products consist of needle-shaped particles of uniform shape and size in a size range of 0.1-2 / u needle length and U, 02-0.1 .u needle width.

The good magnetic values and the favorable dimensions of the single particles make the product obtained by the process described particularly suitable for the production of magnetic recording media.

By varying the amount of the product of the 1st otufe and through Change in the type and content of the modifier in the product In the first stage, the particle size and coercive force can be changed and the product can be optimally adapted to a specific application will.

Example 1t

. a) 1st stage: 2000 g Gro, and 120 g Teop were well mixed, heated in the course of 5 hours at 25O ° O and held for 5 days under normal pressure at 25O ⁰ G. The very hard product, which mainly consisted of "Cr ^ Og", was broken up and dry-ground in an oil mill filled with steel balls.

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b.) 60 g of the product of the 1st stage were mixed with 405 g of OrO and stirred into 5u ml HpO with a high-speed stirrer. The mixture was placed in a stainless steel jar and that Place the vessel in an autoclave lined with Hasteiloy U

brought. The autoclave was subjected to an oxygen pressure of 60 kg / cm and heated ^{to 340-35O 0 O in the course of 3-4 hours.} This temperature was kept for 8 hours

Pressure was adjusted to 225 kg / cm, flat cooling was pulverized substance, chromate washed with water and with TIO ⁰ C dried. The yield was 387 g, the following magnetic values were determined: Br //: 4 68 / Gauss.cm ⁵ .g ~ ¹ - 7 Jtj _p ^! 356 / Oe _- /.

Example 2;

The product from the 1st stage was the same as in Example 1. 20 g of the product from the 1st stage were mixed with .452 g OrO and stirred into 50 ml HpO using a high-speed stirrer. The mixture was placed in a hemanite jar and the jar placed in a Hastelloy U-lined autoclave. The mixture was heated ⁰ C in the course of 3-4 hours and held at 340-35O this i'emperatur 8 hours; the result was a pressure of 235 kg / cm. The product was worked up as described in Example 1. The yield was 394 g; The following magnetic values were determined: Br / P: '432 / Gauss.cm ³ .g ~ ¹ _7J _Hc 250 / Üe_ /.

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a, j 1st stage; 2000 g CrO ₃ and 240 g l e O ^ were well mixed, heated Ιιί over 5 hours at 25O ⁰ C and held for 5 days under Nqrroaldruck at 25O ⁰ O "which consisted mainly of" Gr, Og "The very hard product, , was broken and ground dry in a ußhwingmühle filled with steel balls.

b.) 2, stage; 60 g of the product of the 1st stage, 405 g of UrO * and 50 ml of UnO were subjected to the treatment described in Example 1. The yield of uhromdipxide was 386 g, the following magnetic values were determined; Br / £; 429 / Iauss, cB ³ .g ~ ¹ J7j _Hc 388 / ßej,

Example 4:

aj 1, stage; The product of the 1st stage prepared according to Example 1a was tempered for 2 hours in a rotary kiln at> 0O ° ß, then contained a mixture of the Pijaaen "Or, O ₀ " and "

b.) Z, ötufe? 60 g of the friaduct d§r 1, stage, 405 g

and 50 ml I ₂ O were dsr in iJeispieX 2 öegiehriebnn wj treatment untewz®% en, pie yield of ^ hromdi # 5cid was 382 gj, the fpjLende magnetic values were determined s s 474 ßmnz.mt?,% ** JJ _m ; 185

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Example 5:

a,) 1st stage: 2000 g of GrO and 240 g of Sb ₃ O ₅ were mixed well and tempered at 250 ° for 5 days. The very hard product, which consisted mainly of "Cr ^ Og", was broken up and dry-ground in a vibrating mill filled with steel balls.

b.) 2nd stage: 40 g of the product from the 1st stage, 428 g of CrO ₅ and 50 ml of HpO were subjected to the pressure treatment described in Example 2. A pressure of 257 kg / cm was obtained. The yield of clockoma dioxide was 391 g. tia the following iviagnet values were determined: Br / f: 457 / Gauss.cm ³ g ~ ¹ - 7J _Hc

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Claims (1)

Pa t entansprüche "j 802469 1) Process for the production of ferromagnetic chromium dioxide by hydrothermal treatment of chromic acid at temperatures from 200 to 400 ° C and pressures from 1 to 500 kg / qcm in the presence of nucleating substances, characterized in that a chromium oxide is used as the nucleating substance in which the chromium has an average oxidation level between 4 and 6. 2) The method according to claim 1, characterized in that the a modifier is added to the nucleating substance. 5) Method according to claim 2, characterized in that as Modifier tellurium or compounds of tellurium are used. 4) Method according to claim 2, characterized in that compounds of antimony are used as a modifier. 5) Method according to one of claims 1 to 4, characterized in that that the nucleating substance is used in amounts of 1 to 40 percent by weight, based on chromic acid. 6) Method according to one of claims 1 to 5 *, characterized in that the modifiers are used in amounts of 1 to JO percent by weight, based on the nucleating chromium oxide phase. 7) Method according to one of claims 1 to 6, characterized in that that the hydrothermal conversion takes place at pressures of 150 to 350 kg / qcm. 109844/1424 Le A 11 744 - 10 -