DE2030327C3 - Process for the production of a ferromagnetic chromium dioxide - Google Patents

Description

3. The method according to claim 1, characterized in that the mineral acid and nitric acid acetone can be used as the organic solvent.

The invention relates to a process for producing a ferromagnetic chromium dioxide with a crystalline structure of the rutile type by calcining a mixture of an oxide of chromium, the average valency of which is greater than 4, and a metal nitrate at temperatures of 250 to 50O ⁰ C and washing the calcined product.

The previously known manufacturing processes for ferromagnetic chromium dioxide include, for example, a process for the thermal decomposition of chromium trioxide (CrO ₃ ) under a higher oxygen pressure, a process using the self- _{decomposition pressure of chromium trioxide (CrO 3} ).

The French patent specification 12 24 486 gives a process for the production of chromium dioxide in one completely closed vessel with heating using self-decomposition pressure (oxygen pressure) of chromium trioxide, which is also carried out under overpressure.

However, the above-described methods work under excessively high pressure conditions carried out significantly above 500 at, which with regard to the risk of explosion and difficulties are, and continue to be, undesirable in the industry in terms of handling, apparatus, and materials these processes are unsatisfactory in terms of the yield of the desired product even if the

product obtained excellent magnetic properties

^{Α ίί} teWCT ^S Zrit was also provides a method for preparing magnetic chromium dioxide unto relatively low pressure developed, but here is the Yield of the desired product is low and its magnetic properties s.nd n.cht zufneden- ^Ste Äufeabe The invention therefore the provision of a process for the production of a ferromagnetic chromium dioxide which can be carried out relatively simply and independently of pressure conditions, the chromium dioxide being obtained in high yield

^W1 This object is achieved according to the invention by a method of the type indicated at the beginning, which is characterized in that at least 0.01 mol of barium nitrate, calcium nitrate, strontium nitrate and / or bleed nitrate is used per mole of chromium oxide and the calcined product is initially mixed with a mineral acid , then washed with water and then with an organic solvent

^W 'a1s mineral acid is nitric acid and advantageously used as the organic solvent is acetone. In the context of the invention, a chromium oxide with an average valence of greater than 4 is _{understood to mean mainly chromium trioxide (CrO 3} ), but decomposed intermediate products, for example trichromoctoxide (Cr ₃ O ₈ ), chromium hemipentoxide (Cr ₂ O ₅ ) and mixtures of CrO can also be used ₃ , Cr ₃ O ₈ , Cr ₂ O ₅ and CrO ₂ .

The nitrates used in the method according to the invention have melting points or Zersetzunespunkte of above 15O ⁰ C and may be applicable also in the form of anhydrides or hydrates. When using calcium, strontium, barium or lead nitrate, excellent results are achieved in terms of the yield of the desired product.

According to the invention, the presence of the above The above-mentioned nitrates together with the above chromium compounds are absolutely necessary; However, it is also possible to use compounds which are practically these two starting materials form. This represents a preferred embodiment according to the invention.

For example, especially when nitric acid becomes a chromate or bichromate of calcium, Barium, strontium or lead is added, chromium trioxide and the corresponding nitrate to a large extent Extent formed. The ratio of chromate or bichromate to nitric acid can be stoichiometric, to form chromium trioxide, but an excess, for example up to 4 times, can also be used.

The ratio can be increased by adding a chromium compound with an average valence can be controlled from above 4. In this case too, the concentration of nitric acid is preferable about 5 percent by weight, although this is not critical.

The mixing ratio of chromium oxide and calcium, strontium, barium and / or lead nitrate is, as stated above, at least 0.01 mol of nitrate per 1 mol of chromium oxide, the ratio according to the types of chromium oxide and nitrate and the treatment conditions, such as pressure, can be varied

If a M ^ chungverhaltn.s below the above- Mixing can, if desired, in the presence of a

According to the limit specified, the small amount of water used depends on the

Adding the nitrate is practically ineffective and other types of ingredients can be carried out. the

On the other hand, mixing in excessive nitrate results in the order of addition of each ingredient is not

No particular 5 critical to the chromium compound. Then the mass is dried and

Effect. The mixing ratio is heated under prak-, with the ferromagnetic chromium dioxide

table from the point of view of viewpoints, with a pre- independent of the pressure being obtained. The heating

added ratio is in the range from 0.05 to 1 mole. is preferably at 400 to 440 ⁰ C in the absence

If only chromium oxide is thermally decomposed, an improver and in the presence of one

the stable state of chromium dioxide is hardly i ₀ improver at 370 to 410 ⁰ C in the atmosphere

reached, but the Tnoxvd is carried out in chrome sesqui sphere. Even when executing the heating

oxide transferred. Therefore, it is advantageous to use the pressurized or reduced pressure miners

Settlement of chromium oxide under a high partial temperature in the range from 250 to 500 ⁰ C _{1 in} particular

to control the pressure of oxygen to the range of special 300 to 500 ⁰ C.

To achieve the formation of chromium dioxide. One of the- i ₅ The application of high pressures by tech-like control has often been extremely difficult. Determined from a niche point of view. For example, the invention is surprisingly the range of pressures from 500 to 1000 atm applied to the stable state of chromium dioxide can be achieved. Taking into account the reaction components, a nitrate of calcium, strontium, barium duck, the devices and similar factors and / or lead as an essential component of the chromium ao can be used satisfactorily up to about 2000 atm anoxyd in the mixture specified above -, / . An extremely reduced pressure ratio is added. not recommended, as this favors the decomposition

Even the presence of a very small proportion increases, as a result of which a decrease in the yield of chromium

this metal nitrate shows an effect on the dioxide and a deterioration in its quality

Training this stable area. Therefore, as can occur. A reduced pressure up to about 400 mmHg

according to the invention the chromium dioxide practically can be put to practical use. At increase

regardless of the pressure of the oxygen or a rise in temperature, the rate of increase can

Inert gases such as nitrogen or argon are formed. durance can be increased relatively up to about 150 to 21O ⁰ C,

Experiments have shown that the desired pro - but at higher temperatures the tempe-

Surprisingly, the ductility is preferably gradually increased even at a reduced temperature. Therefore

Pressure can be formed and thus the time required for heating can be varied in

Making the product far easier to perform than depending on the conditions; usually is

a period of 0.5 to 50 hours is sufficient under the pressure conditions listed above,

with gas according to the prior art. Oxygen gas or an inert gas such as nitrogen gas

It is appropriate to use enhancing agents, i. H. Auxiliary or argon can be introduced if desired

medium, to improve the magnetic quality or the self-decomposition pressure can also be used.

of the material. be used.

In a particular embodiment of the process, the process according to the invention is carried out according to the invention, before calcination, tene calcinierU; Product still contains some impurities Mixture uniformly with one of a first 40 grades that can be removed by cleaning. The Raw chromium dioxide obtained may contain a component and a second component if necessary Improving agents are mixed, being the first to be broken and then with a mineral component Chromates, bichromates, nitrates, oxides, halo acids such as nitric acid, hydrochloric acid, phosphoric acid, genide, halogenates or perhalogenates of lithium, then with water and finally with a Potassium, sodium, rubidium, cesium and, secondly, suitable organic solvents such as acetone Constituent antimony, tellurium, nickel, chromium, manganese, washed and dried, being a ferromagne iron, Obtained cobalt, thallium, titanium, vanadium, bismuth, table chromium dioxide of high purity Cadmium, germanium, tin and molybdenum or will. Of the mineral acids especially the their oxides, the fluorides of iron, cobalt, zinc, and nitric acid are preferred. Your focus is not Nickel or magnesium or the sulphates of manganese, 5 ° critical, although a higher concentration is preferred Cobalt, chrome or nickel can be used. will. A nitric acid with a concentration of

Examples of alkali halides are their chlorides; more than 5 percent by weight is satisfactory.

Bromides and iodides. The invention is described below with reference to the examples

Chromates, bichromates and nitrates of the alkali metals. play explained in more detail.

As a second component of the improver 55 The magnetic properties of chromium dioxide are particularly the metals antimony, tin, tellurium were preferred by means of an automatic recording and their oxides. It is also possible to use two or more devices for direct current magnetization properties in combination. The principle was as follows:
be turned. The automatic recording device for the same

The amount is depending on the current magnetization properties is used with a intended purpose of the desired product. A magnetic flux integral circuit in conjunction with Excess of the additive is hardly detrimental as it acts as Brockman and Miller integral circuits and ei pollution equipped with the magnetizer described below. The excitation coil is Cleaning process is removed. However, those on the primary side of the sample are wound and the both components of the enhancement agent in quantities «5 search coil is wound on the secondary side, and above about 0.001 moles, preferably 0.05 to, the device is arranged so that the in the 0.5 mol per 1 mol of chromium oxide effective. The on this secondary coil by magnetizing the primary way formed mass is mixed homogeneously. The coil generated voltage by the direct current

I ·

is more strongly integrated with high gain and the RC integrating circuit.

The magnetic flux obtained from the output of the integrator and ds; Magnesiation currents of the primary coil are automatically recorded by the XY recorder.

example 1 Parts by weight

Chromium trioxide CrO ₃ 100

Calcium nitrate Ca (NO ₃ ), · 4 H ₂ O. 25th

The above materials were uniformly mixed water with a large amount and then dried, and the mixture was heated min at atmospheric pressure initially at a temperature increase of 7.5 ° C / and ^ nn maintained at 440 ⁰ C for 1.5. The crude product obtained in this way was broken up and then washed with 30% strength nitric acid, then washed with water ao and then with acetone and finally dried, the purified magnetic chromium dioxide ¹ ) being obtained.

This product was found by X-ray diffraction to be a magnetic chromium dioxide of »5 was a rutile type crystal structure.

Magnetic properties:

Saturation (as) 1300 gauss / g

Remanence (ar) 110 gauss / g

Coercive force (Hc) 44 öe

Example 2 Parts by weight

35

Magnetic properties

Saturation (as) 1120 gauss / g

Remanence (or) 110 gauss / g

Coercive force (Hc) 46 öe

Example 4 Parts by weight

Chromium trioxide CiO ₃ 100

Barium nitrate Ba (NOj) ₂ 16

These materials were uniformly mixed with a small amount of water, dried, heated at a rate of 5 ° C / min, and then kept at about 410 ° C for 2 hours at atmospheric pressure, and then purified in the same manner as in Example 1, whereby a magnetic chromium dioxide ¹ ) of high purity was obtained.

Magnetic properties:

Saturation (as) 750 gauss / g

Remanence (or) 80 gauss / g

Coercive force (Hc) 30 öe

Example 5

Parts by weight

Chromium trioxide CrO ₃ 100

Barium Nitrate Ba (NO ₃ ), 13

Strontium nitrate Sr (NO ₃ ) U 10.5

Chromium trioxide CrO ₃ 100

Strontium Nitrate Sr (NO ₃ ) ₂ 21

These materials were uniformly mixed and then mixed at one rate at atmospheric pressure heated at 7.5 ° C / min and then held at 440 ° C for 1.5 h. The thereby obtained Crude product was broken up and washed with concentrated nitric acid, then with sufficient Water and then washed with acetone and finally dried, the purified being magnetic Chromium dioxide *) was obtained.

According to X-ray diffraction, this product had a rutile type crystal structure.

Magnetic properties

Saturation (as) 980 gauss / g

Remanence (ar) 100 gauss / g

Coercive force (Hc) 50 oe

Example 3

Parts by weight

Chromium trioxide CrO ₃ 100

Lead nitrate Pb (NO ₃ )., 33

These materials were uniformly mixed with a small amount of water, and then dried and calcined under the same conditions as in Example I and then purified to ^{obtain a magnetic chromium dioxide 3} ) of high purity.

¹ l in an amount of 75 parts by weight

² ) in an amount of 73 parts by weight

³ ) in an amount of 74 parts by weight

₅₀

55 These materials were uniformly mixed with a small amount of water, dried, at a rate of 7 ° C / min to 210 ° C and then at a rate of l ° C / min to 450 ⁰ C at atmospheric pressure and heated at this temperature for Held for 30 min. The crude product was purified in the same manner as in Example 1, and a magnetic chromium dioxide ¹ ) of high purity was obtained.

Magnetic properties

Saturation (as) 1108 gauss / g

Remanence (ar) 93 gauss / g

Coercive Force (Hc) 51e

Example 6 Parts by weight

Chromium trioxide CrO ₃ 100

Strontium nitrate SnNOj) ₁ 11

Lead nitrate Pb (NO ₃ ), 17

The mixture was treated and purified under the same conditions as in Example 5, and a magnetic chromium dioxide ³ ) of high purity was obtained.

Magnetic properties

Saturation (as) 1041 gauss / g

Remanence (ar) 106 gauss / g

Coercive force (Hc) 47 öe

Example 7 Parts by weight

Chromium trioxide CrO ₃ 100

Barium Nitrate Ba (NO ₃ ^ 15

Calcium nitrate Ca (NO ₃ J ₂ -4 H ₁ O .. 8

1) in an amount of 80 parts by weight

2) in an amount of 72 parts by weight

³ ) in an amount of 71 parts by weight

The mixture was treated and purified under the same conditions as in Example 5, and a magnetic chromium dioxide ¹ ) of high purity was obtained.

Magnetic properties

Saturation (as) 1276 gauss / g

Remanence (ar) 150 gauss / g

Coercive force (Hc) 47 öe

Example 8

Chromium trioxide CrO ₃ 9 mol

Lead chromate PbCrO ₄ I MoI

Concentrated nitric acid HNO ₃ 2.3 mol

Water 1 mole

The mixture was uniformly mixed and gradually heated and dried, and then heated at a rate of 3 ° C / min to 400 ⁰ C and maintained at atmospheric pressure at this temperature for about. 1 The obtained product was purified in the same manner as in Example 1 to ^{obtain a magnetic chromium dioxide of high purity 2} ) which had a rutile type crystal structure based on X-ray diffraction.

Magnetic properties

Saturation (as) 1130 gauss / g

Remanence (ar) 98 gauss / g

Coercive force (Hc) 39 öe

Example 9

Chromium trioxide CrO ₃ 6 MoI

Barium dichromate Ba ₂ Cr ₂ O ₇ 1 mol

Calcium chromate CaCrO ₄ 1 mol

Strontium chromate SrCrO ₄ 1 mol

Concentrated nitric acid HNO ₃ 6.5 mol

Water 3 moles

The mixture was treated and purified in the same manner as in Example 1, and a magnetic chromium dioxide ³ ) of high purity was obtained.

Magnetic properties

Saturation (as) 987 gauss / g

Remanence (or) 101 gauss / g

Coercive force (Hc) 45 öe

Example 10

Weight styles

Chromium trioxide CrO ₃ 20

Barium nitrate Ba (NO ₃ ) ₂ 5.3

Antimony Oxide Sb ₂ O ₃ I.

Magnetic properties

Saturation (as) 960 gauss / g

Remanence (ar) 210 gauss / g

Coercive force (Hc) 120 öe

Example II

Chromium trioxide CrO ₃ 1,000 moles

Barium Nitrate Ba (NO ₃ J ₂ 0.100 Mol

Potassium Nitrate KNO ₃ 0.050 Mol

Antimony oxide Sb ₂ O ₃ 0.017 mol

Tellurium metal Te 0.040 mol

The materials were mixed uniformly and at atmospheric pressure at a rate of

• 5 3 ° C / min to 310 ⁰ C, then heated at a rate of 0.3 ° C / min to 390 ° C and held at this temperature for 35 min. The product thus obtained was purified in the same manner as in Example 1, and a magnetic chromium dioxide ¹ ) of high purity was obtained.

Magnetic properties

Saturation (as) 960 gauss / g

Remanence (ar) 400 gauss / g

Coercive force (Hc) 200 oe

y ₂
Potassium dichromate K ₂ Cr ₂ O ₇ 0.5

Potassium Nitrate KNO ₃
Tin metal Sn

0.5
1

1) in an amount of 74 parts by weight

² ) in an amount of 8.1 moles

³ ) in an amount of 5.5 moles

4) in an amount of 15 parts by weight

Particle shape

Short axis 0.2 μ

Long axis I μ

Axis ratio 5: 1

purity
More than 96%

Example 12

Chromium trioxide CrO ₃ 1,000 mol

Barium Nitrate Ba (NO ₃ )., 0.100 mol

Rubidium Nitrate RbNO ₃ 0.034 MoI

Antimony oxide Sb ₂ O ₃ 0.017 mol

₄ "tellurium metal Te 0.040 mol

The mixture was hydrogenated at atmospheric pressure at a rate of 3 C / min ^c to about 210 ⁰ C and then heated at a rate of 0.3 ° C / min to 380 ° C and the calcined product withdrawn immediately after the temperature of 380 ⁰ C. had achieved. The product was purified in the same manner as in Example 1, and a chromium dioxide ² ) of high purity was obtained.

Magnetic properties

Saturation (as) 953 gauss / g

Remanence (ar) 415 gauss / g

Coercive force (Hc) 250 öe

The materials were uniformly mixed with a small amount of water and dried, and then heated to 420 ° C. at atmospheric pressure at a rate of 3 ° C./min and held at that temperature for 3 minutes. The product thus obtained was purified in the same manner as in Example 1, and a magnetic chromium dioxide ⁴ ) of high purity was obtained.

Particle shape

Short axis 0.2 μ

Long axis 1 μ

Axis ratio 5: I

Example 13

Chromium trioxide CrO ₃ 1,000 moles

Lead nitrate Pb (NO ₃ ) ₂ 0.150 mol

Rubidium Nitrate RbNO ₃ 0.034 MoI

Antimony oxide Sb ₂ O ₃ 0.017 mol

Tellurium metal Te 0.040 mol

1) in an amount of 0.8 mol

2) in an amount of 0.72 moles

709 616/127

The materials were uniformly mixed with a small amount of water and at a rate of 3 'C / min to 2I0 ° C at ordinary pressure, then / min to 38O ⁰ C heated at a rate of 0.3 ° C and after at 38O ⁰ C for about 5 minutes, the calcined product was removed. The obtained product was broken and then _{washed with 30% HNO 3} and sufficiently washed with water and then with acetone. After washing, the product was dried and a magnetic chromium dioxide ¹ ) of high purity was obtained.

Magnetic properties

Saturation (as) 930 gauss / g

Remanence (ar) 405 gauss / g

Coercive force (Hc) 230 öe

In the following examples only the operating conditions are listed, since the ferromagnetic Chromium dioxide was obtained under the same experimental conditions.

Example 14
composition

Chromium trioxide CrO ₃ 1,000 moles

Calcium nitrate Ca (NO ₃ ) ₂ 0.150 mol

Potassium Nitrate KNO ₃ 0.025 Mol

Antimony oxide Sb ₂ O ₃ 0.017 mol

Tin metal Sn 0.040 mole

Treatment conditions

Pressure atmospheric pressure

Heating rate. 3 ° C / min to 42O ⁰ C holding time at 420 ° C for 5 min

cleaning

15% HNO ₃ solution, water and acetone.

High purity chromium dioxide 0.74 mole Magnetic properties

Saturation (as) 954 gauss / g

Remanence (στ) 196 gauss / g

Coercive Force (Hc) 111 öe

Example 15
composition

Chromium trioxide CrO ₃ 1,000 mol

Strontium Nitrate Sr (NO ₃ ) ₂ 0.100 Mol

Sodium dichromate Na ₂ Cr ₂ O, ·

2 H ₂ O 0.050 mol

Antimony oxide Sb, O ₃ 0.017 mol

Tellurium metal Te. "0.040 mol

Treatment conditions

Pressure atmospheric pressure

Rate of increase 3 ° C / min to 310 ⁰ C

the temperature 0.3 ° C / min to 390 ° C

Holding time 35 min at 39O ° C

cleaning

Washed with 40% HNO ₃ solution, water and acetone in that order.

Chromium dioxide of high purity. 0.87 moles Magnetic properties
Saturation (ers) 980 jauss / g

1) in an amount equal to 0.7 mol

Remanence (ar) 415 gauss / g

Coercive Force (Hc) 210 öe

Example 16 Composition

Chromium trioxide CrO ₃ 1.0 mol

Calcium chromate CaCrO ₄ 0.1 mol

Nitric acid HNO ₃ 0.4 mol

Treatment conditions

Pressure atmospheric pressure

Rate of increase in the temperature ... 7.5 ° C / inin holding time 90 min at 44O ⁰ C

cleaning

Washed with 60% HNO ₃ solution, water and acetone in this order.

Chromium dioxide of high purity. 0.85 moles Magnetic properties

Saturation (as) 1320 gauss / g

Remanence (ar) 112 gauss / g

Coercive force (Hc) 48 öe

Example 17 J ₀ composition

Chromium trioxide CrO ₃ 1.0 mol

Strontium chromate SrCrO ₁ 0.1 mol

Nitric acid 0.4 mol

treatment

Pressure atmospheric pressure

Rate of temperature increase 7.5 ° C / min

Hold time 90 minutes at 44O ⁰ C

cleaning

Washed with 30% HNO ₃ , water and acetone in that order

Chromium dioxide of high purity. 0.83 moles Magnetic properties

Saturation (as) 930 gauss / g

Remanence (ar) 116 gauss / g

Coercive force (Hc) 43 öe

Example 18 Composition

Barium dichromate Ba ₂ Cr ₂ O, 1 mol

Lead chromate PbCrO ₄ 1 mol

Nitric acid HNO ₄ (40%) 4 mol

treatment

Pressure atmospheric pressure

Speed of temperature increase 7.5 ° C / min

Hold time 90 min at 440 ^° C

cleaning

Washed with 15% HNO ₃ , water and acetone in that order

Chromium dioxide of high purity. 0.75 moles

Magnetic properties

Saturation (as) 1200 gauss / g

Remanence (ar) 85 gauss / g

Coercive force (Hc) 40 eyelets

Example 19 Composition

Chromium trioxide CrO ₃ 1,000 moles

Lead nitrate Pb (NO ₃ J ₂ 0.100 mol

Potassium Nitrate KNO ₃ 0.050 Mol

Antimony oxide Sb ₂ O ₃ 0.017 mol

Tellurium metal Te 0.040 mol

treatment

Pressure to 450 mmHg

regulated speed of tem- 3 ° C / min to 31O ⁰ C

peraturerhöhung 0.3 ° C / min to 390 ⁰ C

Hold time 35 min at 390 ° C

cleaning

Wash with 15% HNO ₃ , water and acetone in this order

Chromium dioxide of high purity. 0.74 moles

Magnetic properties

Saturation (as) 928 gauss / g

Remanence (ar) 366 gauss / g

Coercive Force (Hc) 157 öe

Example 20 Composition

Chromium trioxide CrO ₃ 1,000 moles

Strontium Nitrate Sr (NO ₃ J ₂ 0.200 Mol

Rubidium nitrate RbNO ₃ 0.034 mol

Antimony oxide Sb ₄ O ₃ 0.017 mol

Tellurium metal Te 0.040 mol

treatment

Pressure regulation on

400 mmHg speed of the tem- 3 ° C / min to 210 ⁰ C

temperature increase 0.3 ° C / min up to 380 ° C

Hold for 50 min at 380 ° C

cleaning

Wash with 15% HNO _S , water and acetone in this order

Chromium dioxide of high purity. 0.75 moles Magnetic properties

Saturation (as) 903 gauss / g

Remanence (cm) 385 gauss / g

Coercive force (Hc) 180 öe

Example 21 Composition

Chromium trioxide CrO ₃ 1,000 moles

Lead nitrate Pb (NOs) ₂ 0.100 mol

Sodium nitrate NaNO ₃ 0.025 mol

Antimony trioxide Sb-O, 0.017 mole

Tin metal Sn 0.040 mole

Rate of temperature increase 3 ° C / min to 420 ⁰ C

Hold for 5 minutes at 420 ^° C

cleaning

Wash with 30% HNO ₃ , water and acetone in this order

Chromium dioxide of high purity. 0.84 moles ίο Magnetic properties

Saturation (as) 955 gauss / g

Remanence (ar) 202 gauss / g

Coercive force (Hc) 109 öe

Example 22

composition

Chromium trioxide CrO ₃ 1,000 moles

Calcium nitrate Ca (NO ₃ ) ₂ · 4 H ₂ O. .0.100 mol

ao rubidium nitrate RbNO ₃ 0.050 mol

Antimony oxide Sb ₂ O ₃ 0.017 mol

Tellurium metal Te 0.040 mol

treatment

»5 pressure regulation to 2 atm

in a pressure vessel speed of temperature increase 3 ° C / min to 310 ° C

0.3 ° C / min to 390 ° C hold time 35 min at 39O ⁰ C

cleaning

Wash with 15% HNO ₃ , water and acetone in this order

Chromium dioxide of high purity. 0.83 Mo! Magnetic properties

Saturation (as) 946 gauss / g

_4U remanence (ar) 388 gauss / g

Coercive force (Hc) 186 öe

treatment
Pressure ...

Regulation to 20 atm in a pressure vessel Example 23 Composition

Chromium trioxide CrO ₃ 1,000 moles

Calcium nitrate Ca (NO ₃ ) ₂ · 4 H ₂ O .. 0.100 mol

Rubidium nitrate RbNO ₃ 0.034 mol

Antimony oxide Sb ₂ O ₃ 0.017 mol

Tellurium metal Te 0.040 mol

treatment

Pressure regulation to 20 atm

in a DruckgefäO speed of the tem- 3 ° C / min to 21O ⁰ C

temperature increase 0.3 ° C / min up to 380 ° C

Hold for 5 min at 380 ° C

cleaning

Wash with 20% HNO ₃ , water and acetone in this order

Chromium dioxide of high purity. 0.85 moles Magnetic properties

Saturation (as) 950 gauss / g

Remanence (στ) 420 gauss / g

Coercive Force (Hc) 307 öe

Claims (2)

20 30 327 claims: 1. A process for the production of a ferromagnetic chromium dioxide by calcining a mixture of an oxide of chromium, the average valency of which is greater than 4, and a metal nitrate at temperatures of 250 to 500 ⁰ C and washing the calcined product, characterized in that ic per mole of the chromium oxide, at least 0.01 mol of barium nitrate, calcium nitrate, strontium nitrate and / or lead nitrate is used and the calcined product is washed first with a mineral acid, then with water and then with an organic solvent. 2. The method according to claim 1, characterized in that the mixture prior to calcination uniformly with a ver ao consisting of a first component and a second component improvers are mixed, the first component being chromates, bichromates, nitrates, oxides, Halides, halogenates or perhalates of lithium, potassium, sodium, rubidium, and cesium as a second component antimony, tellurium, nickel, »5 chromium, manganese, iron, cobalt, thallium, titanium, Vanadium, bismuth, cadmium, germanium, tin and molybdenum or their oxides, the fluorides of Iron, cobalt, zinc, nickel or magnesium or the sulphates of manganese, cobalt, or chromium Nickel can be used.