Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
  • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
  • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
  • H01F1/065—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder obtained by a reduction
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
  • B22F9/22—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds using gaseous reductors

Definitions

• the invention relates to a process for the production of acicular ferromagnetic metal particles consisting essentially of iron by reducing acicular iron (III) oxide hydroxide provided with a shape-stabilizing surface coating or the iron (III) oxide obtained therefrom by dewatering by means of decomposable organic compounds and hydrogen.
• Acicular ferromagnetic metal particles are of particular interest for the production of magnetic recording media because of their high saturation retentivity and high coercive force.
• the object of the invention was therefore to provide a method for producing acicular ferromagnetic metal particles consisting essentially of iron, with which it is possible in a simple manner to obtain pronounced shape-anisotropic particles which are distinguished by a high degree of fineness, a narrow particle size distribution and a high coercive field strength.
• acicular ferromagnetic metal particles consisting essentially of iron can be produced by reducing acicular iron (III) oxide hydroxide provided with a shape-stabilizing surface coating or the iron (III) oxide obtained therefrom by dewatering according to the task, if the reduction is carried out using decomposable organic compounds and hydrogen at a temperature between 270 and 450 ° C.
• iron (III) oxide hydroxide or iron (III) oxide provided with a surface coating in a first stage by means of decomposable organic compounds in an inert gas atmosphere at a temperature between 270 and 650 ° C. to FeO x , with values for x from 1.33 to 1.44, and in a second stage by means of hydrogen at a temperature between 270 and 450 ° to the metal.
• the starting material for the process according to the invention is iron (III) oxide hydroxide in the form of ⁇ -FeOOH and -FeOOH in a mixture of 80 to 100% ⁇ -FeOOH and 0 to 20% -FeOOH or 70 to 100% -FeOOH and 0 to 30% ⁇ -FeOOH suitable.
• the corresponding iron (III) oxide hydroxides expediently have a BET surface area of at least 20 and up to 120 m 2 / g, the average particle length is between 0.10 and 1.5 / ⁇ m with a length-to-thickness ratio of at least 5, expediently 8 to 40.
• iron (III) oxides obtained from the iron (III) oxide hydroxides mentioned by dewatering at more than 250 ° C. can also be used.
• Correspondingly modified iron oxides are used in a known manner as starting materials for producing metal particles which contain further alloy constituents, such as cobalt, nickel and / or chromium, in addition to iron.
• iron (III) oxide hydroxides or iron (III) oxides are now provided in a known manner with a shape-stabilizing surface coating, which helps to maintain the outer shape during the further processing steps. Suitable for this is e.g. the treatment of iron (III) oxide hydroxides or oxides with an alkaline earth metalation and a carboxylic acid or another organic compound which has at least two groups capable of chelating with the alkaline earth metalation. These processes are described in DE-OSes 24 34 058 and 24 34 096.
• Also known and described in DE-OS 26 46 348 is the shape-stabilizing treatment of the iron (III) oxide hydroxides or oxides on their surface with hydrolysis-resistant oxygen acids of phosphorus, their salts or esters and aliphatic mono- or polybasic car- Bon acids.
• hydrolysis-resistant substances are phosphoric acid, soluble mono-, di- or triphosphates such as potassium, ammonium dihydrogen phosphate, disodium or dilithium orthophosphate, trisodium phosphate, sodium pyrophosphate and metaphosphates such as sodium metaphosphate.
• the compounds can be used alone or as a mixture with one another.
• esters of phosphoric acid with aliphatic monoalcohols having 1 to 6 carbon atoms can advantageously be used.
• Carboxylic acids in the process are saturated or unsaturated aliphatic carboxylic acids with up to 6 carbon atoms and up to 3 acid groups, it being possible for one or more hydrogen atoms in the aliphatic chain to be substituted by hydroxyl or amino radicals.
• Oxidic and oxitricarboxylic acids such as oxalic acid, tartaric acid and citric acid are particularly suitable.
• shape-stabilizing equipment suitable in the process according to the invention are the known surface coatings with tin compounds (DE-PS 19 07 691) or with silicates or Si0 2 (JP-OS 121 799/77 and JP-OS 153 198/77).
• the iron (III) oxide hydroxides or oxides thus equipped are reduced to metal by means of decomposable organic compounds and hydrogen.
• Suitable organic compounds are all organic substances which are decomposable in the temperature range between 270 and 650 ° C. in the presence of the iron oxide hydroxides or iron oxides.
• longer-chain carboxylic acids and their salts, amides of long-chain carboxylic acids, long-chain alcohols, starches, oils, polyalcohols, waxes, paraffins and polymeric substances such as polyethylene are suitable for this.
• There is a high boiling point or sublimation point advantageous to avoid losses of organic matter before the reduction effect begins.
• the iron (III) oxide hydroxides or oxides are mechanically mixed with the solid or liquid organic substances or coated with them in a suitable solution or suspension of the substance. Shape stabilization and application of the organic substance can also take place simultaneously or immediately one after the other, for example in an aqueous suspension of the particles.
• the organic compounds can also be present during or before the crystal growth of the iron (III) oxide hydroxides.
• the organic substance is added at the beginning of the FeOOH synthesis, for example before the precipitation of Fe (OH) 2 . The addition after nucleation has ended or during or after the growth stage is also suitable.
• the shape-stabilizing surface coating is subsequently formed in the aqueous suspension of the particles or after the filter cake has been freed from inorganic salts in water.
• carbon contents 0.5 to 20% by weight, based on FeOOH or Fe 2 0 3, are sufficient.
• the iron (III) oxide hydroxide or oxide provided with the surface coating and with the organic compound is then reduced at 270 to 450 ° C. with simultaneous transfer of hydrogen.
• the duration of the reduction depends on the batch size and reactor type and is therefore between 30 minutes and 30 hours.
• the process according to the invention can be carried out in such a way that, in a first step, the iron (III) oxide hydroxide or oxide provided with a surface coating by means of the organic decomposable compound under inert gas, usually nitrogen, is reduced at temperatures between 270 and 650 ° C to FeO x with values for x from-1.33 to 1.44. In a second stage immediately following, the FeO x is then reduced to hydrogen at 270 to 450 ° C. to the metal.
• the reductions and, if appropriate, the dewatering of FeOOH to Fe 2 O 3 before and at the start of the reduction can be carried out both batchwise and continuously, for example in a separate reactor.
• a separate reactor e.g. rotary tube or fluidized bed technology
• the type of product used, e.g. FeOOH or Fe203, and the reduction process co-current or counter-current mode of operation of solids and gas or steam flows can be used.
• the organic reduction to FeO x can be carried out simultaneously with the dewatering of FeOOH and at the same point in the reactor or, in the case of a continuous procedure, the dewatering to Fe 2 0 3 and the organic reduction to FeO x in a reactor by addition of the organic matter take place locally at the appropriate location of the reactor.
• the acicular ferromagnetic metal particles obtainable by the process according to the invention still largely have the shape stemming from the starting materials and, despite the preceding conversion reaction, they are uniform and particularly fine-particle according to the starting material. As a result, they are characterized by high values with regard to their magnetic properties, such as the coercive force and above all the remanence.
• the high squareness of the hysteresis loop shows a narrow switching field strength distribution due to the uniform shape.
• Such metal particles are outstandingly suitable as magnetic materials for the production of magnetic recording media.
• these substances are expediently passivated before further processing. This means encasing the metal particles with an oxide layer by controlled oxidation in order to eliminate the pyrophoricity caused by the large free surface area of the small particles. For example, this is achieved by passing an air / nitrogen mixture over the metal powder.
• the passivation can also be carried out by wetting the pigments with organic solvents in the presence of oxygen or with other known oxidation and / or coating processes.
• the metal particles obtainable by the process according to the invention can be oriented magnetically particularly easily.
• important electroacoustic values, such as depth and height modulation, and especially the noise due to the fine nature of the material are improved.
• the present invention is explained by way of example using the following experiments.
• the magnetic values of the samples were measured with a vibration magnetometer at a magnetic field of 160 kA / m or after premagnetization in a pulse magnetizer in a vibration magnetometer.
• samples 1 and 2 were each reduced to a pyrophoric metal pigment (py) in a hydrogen stream of 30 Nl / h. After measuring the magnetic powder values, the rest was passivated in an air-nitrogen stream of 2 N1 air / h and 30 N1 nitrogen / h at temperatures below 60 ° C (pa). The measurement results are shown in Table 2.
• Example 2 100 parts of the FeOOH starting material used in Example 2 were mixed directly with 2.5 (sample 1) and 5 (sample 2)% by weight of stearic acid and processed further in accordance with example 2. The measurement results are shown in Table 2.
• Example 3 A ⁇ -FeOOH which had been treated with oxalic acid / phosphoric acid in accordance with Example 3 was reduced directly with hydrogen as indicated in Example 3.
• the coercive field strength of the pyrophoric material was 63.1 kA / m.
• a ⁇ -FeOOH with a specific surface area of 30 m 2 / g was provided with a tin oxide coating according to the information in DE-AS 19 07 697 by neutralizing the acidic SnCl 2 -containing aqueous suspension of the particles.
• the amount of tin was 1% by weight based on FeOOH.
• a coating of 3% by weight of olive oil was produced in the same dispersion by adding olive oil.
• the FeOOH thus equipped was reduced to metal in a hydrogen stream (30 Nl / h) at 370 ° C. for 7 hours.
• the results of the measurements of the pyrophoric material (py) and of a material (pa) passivated with acetone in the presence of air are given in Table 3.
• Example 4 The procedure is as described in Example 4, but the equipped with tin oxide / olive oil material is passivated first within 30 minutes in a nitrogen stream at 520 ° C to FeO 1.33 and then reduced as in Example 4 with hydrogen to the metal and.
• the measurement results are shown in Table 3.
• Example 7 The procedure is as described in Example 7, but the material finished with phosphoric acid / olive oil is first reduced to FeO 1.33 in a stream of nitrogen at 470 ° C. in 30 minutes and then to metal as indicated. The measurement results are shown in Table 5.
• the specific surface area of the metal particles is 26.6 m 2 / g.
• Example 10 The procedure was as described in Example 10, but instead of adding phosphoric acid / olive oil, a mixture of 761 g of SnCl 2 was used . 2 H 2 0 and 1.2 kg of olive oil are added to the suspension and air is passed through after the addition for 2 hours. The first stage of the reduction led to FeO 1.34 (1.2% Sn, 0.13% C) and the reduction to the metal was carried out at 310 ° C in a fluidized bed furnace. The measurement results on the sample stabilized with a nitrogen / air mixture at 40 ° C. are given in Table 6.
• the powder obtained showed an H c of 87.3 [kA / m] and an M r / g of 61 [nTm 3 / g] in the pulse magnetometer.
• sample A 80 g were dewatered in air at different temperatures. The conditions and results are summarized in the table. 40 g of the dewatered products B 1, B 2 and B 3 were mixed with 3% by weight of stearic acid, then kept in an oven at 100 ° C. for 1 hour. The samples were then reduced to Fe01.35 at 360 ° C. in a nitrogen stream of 10 Nl / h within 30 minutes and then, without isolating the FeO 1.35 , directly reduced to iron at 360 ° C. The results are shown in Table 7.
• Magnetic layer has a layer thickness of 4 / um.
• the magnetic foils produced in this way were cut into 3.81 mm wide magnetic tapes and then tested.
• the measurement of the magnetic properties was carried out in a measuring field of 160 kA / m, the coercive force H c in [kA / m], remanent magnetization M and saturation magnetization M in [mT] as well as the guideline factor Rf, the remanence along / across.
• the noise-to-noise ratio RG A was determined against the reference band IEC IV and the copy loss K o . The results are shown in Table 8.
• Example 8 The procedure was as described in Example 15, but the metal particles obtained in Example 10 were used. The results are shown in Table 8.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Hard Magnetic Materials (AREA)
• Compounds Of Iron (AREA)
• Paints Or Removers (AREA)
• Magnetic Record Carriers (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=6169825

Family Applications (1)

Country Status (4)

Cited By (1)

Families Citing this family (8)

Citations (4)

Family Cites Families (12)

• 1982
  • 1982-07-31 DE DE19823228669 patent/DE3228669A1/de not_active Withdrawn
• 1983
  • 1983-07-23 DE DE8383107240T patent/DE3374480D1/de not_active Expired
  • 1983-07-23 EP EP83107240A patent/EP0105110B1/fr not_active Expired
  • 1983-07-28 US US06/518,000 patent/US4439231A/en not_active Expired - Lifetime
  • 1983-08-01 JP JP58139512A patent/JPS5944809A/ja active Granted

Patent Citations (4)

Also Published As

Similar Documents

Legal Events