DE1767989C - Process for the production of ferromagnetic chromium dioxide - Google Patents

Description

Oxygen, water vapor and NH _a -use & is in the range of 50 to 1000 atmospheres in the actual reaction.

The autoclave that contains the mixture, kana heated by any suitable method, e.g. B. by an electric heater while the temperature of the mixture is measured. After the reaction temperature has been reached, the mixture becomes during a suitable period of time, which depends on the pressure and the reaction temperature, at this Maintained temperature, and then ate «ecooled in the autoclave to room temperature (about 15 to about 35 ° C). After cooling, the mixture is removed from the autoclave, washed with water and dried using a suitable method.

Preferred embodiments of FIG

example 1

A mixture of 20 g of chromium trioxide, 2.5 ml of water and 0.25 ml of ammonia water with 28 percent by weight NH ₃ is placed in a stainless steel autoclave equipped with a thermocouple and a pressure gauge. The internal volume of the autoclave is 40 ml. The autoclave,

S containing the mixture is oxygenated from a gas cylinder up to a pressure of 20 kg / cm * charged and heated by means of an electrical heating device wrapped around the autoclave. The Mix! is under in the autoclave for 2 hours

ίο a pressure of 230 kg / cm ² heated to 380 ° C and cooled to room temperature = r. The cooled product is washed with water and dried. X-ray diffraction analysis as above

has been described, proves that all the products obtained from chromium dioxide in a single Phases consist of a tetragonal crystal structure of the rutile type. An electron microscope Observation also shows that the products are in finely divided powder form Magnetic properties and the mean particle size are shown in Table 1.

table

sample Hc (Oersted) Λ η Im
(Gauss) Br (Gauss) Mean particle size (μ)
Length Width With ammonia water 124
70 4500
4500 1700
600 2.0 to 3.0 0.5 to 1.0
3.0 to 5.0 i 1.0 to 2.0 Without ammonia water

On the other hand, a mixture of 20 g of chromium trioxide with 25 ml of water is the same procedure as it has been described above. The product obtained consists of chromium dioxide in one single phase with a rutile type crystal structure and has the magnetic properties and the mean particle size recorded in TabePe 1.

It is clear from Table 1 that the addition of ammonia water improves the magnetic properties of the chromium dioxide obtained improves.

Example 2

A mixture of 20 g of chromium trioxide, 0.230 g of H ₄ TeO, and 4 ml of water is further mixed with ammonia water, which contains various amounts of ammonium ions according to Table 2. The mixture is placed in a stainless steel autoclave equipped with a thermocouple and a pressure gauge. The internal volume of the autoclave is 40 ml. The autoclave with the mixture is heated by means of an electric heater wound around the autoclave. ^{The mixture is heated to 400 °} C. in the autoclave for 2 hours under a pressure of about 350 atmospheres and cooled to room temperature.

The resulting product is in finely divided powder form and is washed with water. X-ray diffraction analysis as described above proves that all are obtained Chromium dioxide products in a single phase with a rutile-type tetragonal crystal structure exist.

It can be seen from Table 2 that the coercive force increases with an increase in the amount of ammonium ions. The residual magnetization reaches its maximum at about 2.80 percent by weight, based on chromium trioxide, and the maximum magnetization falls as the amount of ammonium ions increases. From the viewpoint of the combination of coercive force, residual magnetization and maximum magnetization leads the addition ₀ 1.40 to 4.20 '/ of ammonium ions to the mixture to an optimum result.

Table 2

Ammonium ions Hc Br 4 π Im sample (NH ₄ ¹⁺ ) (Oersted) (GauQ) (Gauss) No. based on CrO ₁ Weight percent 216 1400 3800 1 0 240 1680 4000 2 0.70 260 1720 ii% 3 1.40 367 2000 3700 4th 2.80 430 1680 3200 5 4.20 512 1200 3000 6th 8.40 518 1200 3000 7th 12.60

Claims (3)

Solution or through the addition of a compound containing ammonium patent claims is achieved even more if the starting material used is 1. Process for the production of ferromagnetic chromium trioxide 0.01 to 20.0 atomic percent table chromium dioxide in the form of a finely divided 5 tellurium. The sum of the atomic percent of tellurium powder by heating chromium trioxide or and chromium should be 100 atomic percent. Chromium trioxide containing 0.01 to 20.0 atomic percent of tellurium, to which 0.01 to 5.0 atomic chromium trioxide has been added under high pressure to a temperature of tellurium, results in a ferroture of 280 to 480 ° C, which is characterized by magnetic properties Chromium dioxide in a single phase I show net that one mixes the chromium trioxide with an aqueous solution containing a tetragonal crystal structure of the rutile ammonium ions type when it is mixed together with the aqueous solution or with an ammonium ion containing solution or the compound at a temperature compound . heated from 280 to 480 ⁰ C under high pressure. This 2. Process for the production of ferromagne- single phase is carried out by a Rön ^ en-DifTraktotischem chromium dioxide according to claim 1, characterized is meter of type D3-F (Rigakudenki Co.) under Vergekenn.'eichnet that ammonium ions are used using copper K x radiation at 35 kV ti ,,. I begins in such an amount that the weight presses 15 niA. Chromium dioxide in a single phase ratio NH ₁ : CrO ₃ in the range of 0.001: 1.0 has a high coercive force and a high level of San ι up to 0.15: 1.0. magnetic magnetization. 3. Process for the production of ferromagne- ao The coercive force {He). Riding magnetization (Hr \ tischem chromium dioxide according to claim 1, characterized and maximum magnetization (AnIm) are derived from the fact that ammonium ions are used in the / - // - hysteresis loop of the ferromagnetic !! in such an amount that the weight · »- material , measured at the maximum field of the ratio NH ₁ ⁴ : CrO ₃ in the range of 0.01: 1.0 2000 oersteds and room temperature. The chromine is up to 0.08: 1.0. 25 oxide, into which tellurium has been incorporated, can be made by: nan chromium trioxide with metallic tellurium or any available part The invention relates to a process for the production of a lurium compound mixed in such an amount that of ferromagnetic chromium dioxide with a desired atomic percentage of tellurium magnetic coercive force and with high salti- 30 is obtained. Advantageously, a Telluri university gmentation. compound with hexavalent THIurium used. The invention particularly relates to a method e.g. B. H ₂ TeO ₄ , H ₆ TeO ₆ or TeO ₃ . For the production of ferromagnetic chromium dioxide Ls it is necessary that the weight ratio in the form of a finely divided powder by heating the NH ₄ ions in the aqueous solution or Vervon chromium trioxide or 0.01 to 20.0 atomic percent 35 bond to the pure chromium trioxide starting material tellurium containing chromium trioxide under high pressure or the chromium trioxide, which is 0.01 to 20.0 atoms at temperatures from 28U to 480 ° C, the percentage of tellurium have been incorporated, in the range that the chromium trioxide with from 0.001: 1.0 to 0 , 15: 1.0. The best results for an aqueous solution containing ammonium ions can be obtained according to the invention if, or with a compound containing ammonium ions, the weight ratio in the range of 0.01: 1.0 is mixed. to 0.08: 1.0. Such a weight ratio In the literature there are already a number of modi- can be achieved by combining a con- ficated chromium dioxide described. In the USA concentration and an added amount of this Patents 2,885,365, 2,923,683 and 2,923,684 aqueous solution. The higher; Requires concentration are ruthenium, antimony and tin as modifiers- 45 a lesser amount of added aqueous middle! zi ^{> r} production of ferromagnetic 1 solution and vice versa. Materials with high coercive force described. Any aqueous solution containing NH ₄ * ions is in Japanese Patent Publication 36-21023 is applicable with: e.g. B. are aqueous solutions of NH ₃ , Tellurium modified chromium dioxide with high coercivity - NH ₄ Cl, NH ₄ F, NH ₁ Br, (NH ₄ J ₂ CrO ₄ or (NH ₄ J ₂ Cr ₈ O ₇ tivkraft described, and in British patent 50 suitable. The chromium trioxide starting material can Document 829 007 are modified with alkali metal with at least one NH ₄ ion-containing composition Chromium dioxide described. bond can be mixed in such an amount. For the development of new magnetic records that the required weight ratio of NH ₄ - voltage bands for recording high resolution ions to chromium trioxide is achieved, are ferromagnetic materials with a high saturation 55 chromium trioxide with or without the addition of the above magnetization and uniform particle size called tellurium compound is with an aqueous needed. In particular, a solution of a suitable concentration compared to the other is required for this purpose known modified chromium _{dioxides improved NH 4} ^f ions according to the usual mixing procedures Coercive force required. mixed. The mixture is placed in an autoclave It has now been found that, starting from brought with 60, that of a corrosion-resistant Maeiner Aqueous solution containing ammonium ions,> vie z. B. stainless steel, made and with or chromium trioxide mixed with an ammonium ion-containing thermocouple to measure the reaction bond, a ferromagnetic temperature and a pressure gauge table chromium dioxide with higher saturation magnetism. It should be ensured that the crowd ization and higher coercive force is obtained 65 of the mixture that is introduced into the autoclave than chromium not containing these additives becomes, with regard to the internal volume of the car trioxide. This surprising effect, which is controlled by the 'klavs, so that the pressure in the autoclave Addition of an aqueous solution containing ammonium ions due to the amount released from the chromium trioxide