Classifications

• • 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
• • 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
  • H01F1/061—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 with a protective layer
• • 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

Definitions

• the invention relates to a process for the production of acicular ferromagnetic iron particles by reducing iron (III) oxide provided with a shape-stabilizing surface coating, which is obtained by annealing acicular iron (III) oxide hydroxide, with hydrogen at 275 to 425 ° C. and the use thereof Iron particles for the production of magnetic recording media.
• ferromagnetic metal powders and metal thin layers are of particular interest for the production of magnetic recording media, since in this way the energy product and the information density can be increased considerably and such recording media result in narrower signal widths and better signal amplitudes compared to the current standard .
• the corresponding metal particles must show magnetic single-range behavior; moreover, the anisotropy that is present or can additionally be achieved by the magnetic alignment in the strip should be only slightly impaired by external influences, such as temperature or mechanical stress, that is, the small particles should preferably be shape-anisotropic Case should be acicular and generally should be between 10 2 and 10 4 ⁇ in size.
• the object of the invention was therefore to provide a method for producing acicular ferromagnetic iron particles, with which pronounced shape-anisotropic particles with high values for coercive field strength, remanence and relative remanence can be obtained in a simple manner.
• acicular ferromagnetic iron particles are acicular, with a dimensionally stable
• Ironing surface coating provided with ferric oxide with the required properties by reduction with hydrogen at 275 to 425 ° C if the acicular iron (III) oxide used from acicular iron (III) oxide hydroxide by annealing for 10 minutes to 10 Hours at 250 to 390 ° C in a water vapor atmosphere with a water vapor partial pressure (pH 2 0) of at least 30 mbar is obtained.
• iron (III) oxide hydroxide in the form of lepidocrocite-FeOOH) or a mixture of goethite ( ⁇ -FeOOH) and lepidocrocite, but with a minimum lepidocrocite content of 20% by weight, is used as the starting material for this process, and this material Annealed for 10 minutes to 10 hours at 250 to 390 ° C. in an atmosphere containing water vapor with a water vapor partial pressure of 30 to 1013 mbar based on normal conditions.
• the iron (III) oxide hydroxides mentioned have a BET specific surface area of 20 to 75 m 2 / g, an average particle length between 0.2 and 1.5 and preferably between 0.3 and 1.2 / ⁇ m and a length-increase -Thickness ratio of at least 10, advantageously 10 to 40 characterized. They can be prepared from iron (II) salt solutions with alkalis with simultaneous oxidation, such as in DE-AS 10 61 760. For this purpose, iron (III) oxide hydrate nuclei up to an amount of 25-60 mol% are made from an aqueous iron (II) chloride solution using alkalis, such as alkali hydroxide or ammonia, at temperatures between 10 and 36 ° C. with vigorous stirring to produce fine air bubbles.
• alkalis such as alkali hydroxide or ammonia
• the solids content of iron (III) oxide hydroxide in the aqueous suspension should be between 10 and 70 g / l, preferably 15-65 g / l. After filtering off and washing out the precipitate, the iron (III) oxide hydrates thus obtained are dried at 60 to 200 ° C.
• iron (III) oxide hydroxides required for the process according to the invention are now provided in a known manner with a shape-stabilizing surface coating which participates in maintaining the outer shape during the further processing steps. Suitable for this is e.g. the treatment of ferric oxide hydroxides 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 iron (III) oxide hydroxides on their surface with hydrolysis-resistant oxygen acids of phosphorus, their salts or esters and aliphatic mono- or polybasic carboxylic 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, where one or more hydrogen atoms of the aliphatic chain can be substituted by hydroxyl or amino radicals.
• Oxidic and oxitricarboxylic acids such as oxalic acid, tartaric acid and citric acid are particularly suitable.
• the iron (III) oxide hydroxides which have been given a shape-stabilizing effect in the manner described are then annealed for 10 minutes to 10 hours at temperatures between 250 to 390 ° C. in a water vapor-containing atmosphere with a water vapor partial pressure of at least 30 mbar.
• the end product is acicular iron (III) oxide provided with the surface coating formed according to the previous equipment.
• This tempering can be carried out discontinuously or continuously.
• Reactors such as muffle furnaces, rotary tube furnaces or swirl furnaces are suitable for batch drainage.
• air, inert gases or air / inert gas mixtures can be passed over or through the resting or moving iron oxide, with these gases being loaded beforehand with the appropriate amount of water vapor.
• the gases or gas mixtures are expediently saturated with water vapor at temperatures between 40 ° C. and the boiling point of the water, in particular between 50 ° C. and the boiling point of the water, and introduced into the reactors in this state.
• the water can of course also be mixed directly in the form of steam or the other gases.
• the tempering can be carried out particularly advantageously in continuous reactors, for example in a continuous rotary tube furnace, since here, in addition to the water vapor in the gas passed through, water vapor from the dehydration reaction of the iron (III) oxide hydroxide is always supplied in the same amount ⁇ . This can therefore be done without or with little ⁇ gas flows can be worked. After a short setting time, the corresponding required water vapor partial pressure of preferably 70 to 1013 mbar in the reaction space is reached.
• the iron (III) oxide hydroxide of the specified composition is subjected directly to this tempering and only then - as described - provided with a surface finish.
• the iron (III) oxide provided with a shape-stabilizing surface coating is reduced in a manner known per se with hydrogen at 275 to 425, preferably at 300 to 400 ° C. It is recommended that the finely divided iron powder obtained in this way be passed over an air or Passivating the oxygen-inert gas mixture, since this enables the pyrophoric character of the needle-shaped iron particles with a length between 0.1 to 0.8 ⁇ m and a length-to-thickness ratio of 5 to 25: 1 to be controlled.
• the method according to the invention it is possible to produce acicular ferromagnetic iron particles which are distinguished by a pronounced shape anisotropy. This is achieved in that the starting products are both largely free of dendrites and treated to maintain the outer shape and, in addition, result in a well-crystallized iron (III) oxide for the subsequent reduction reaction due to the inventive tempering.
• the resulting iron particles are characterized by markedly improved values for coercive field strength, specific remanence and relative remanence. If the iron particles L J obtained according to the invention ⁇ Used in the usual way for the production of magnetogram carriers, the needle-shaped particles can be magnetically oriented particularly easily, and important electroacoustic values, such as depth and height controllability, are also improved.
• the nitrogen surface SN2 determined according to BET was primarily used to characterize the acicular iron (III) oxide hydroxides used, such as lepidocrocite and goethite-lepidocrocite mixture.
• the appearance and the dimensions (L / D ratio) of the iron oxide hydroxide particles provide information from electron micrographs.
• the goethite-lepidocrocite ratio was determined by X-ray analysis.
• the magnetic values of the iron powder were measured with a vibration magnetometer at a magnetic field of 160 or 800 kA / m.
• the values of the coercive field strength, H c , measured in kA / m, were related to a stuffing density of ⁇ 1.6 g / cm 3 in the powder measurements.
• Specific remanence (M r / ⁇ ) and saturation (M m / ⁇ ) are given in nTm 3 / g.
• remanent coercive field strength H R is an important assessment variable.
• H R in the case of constant field demagnetization, half of the particles are remagnetized at the field strength H R in terms of volume. It thus represents a characteristic quantity for recording processes, which in particular determines the operating point in magnetic recording. The more inconsistent the retentive ⁇ ititive field strength of the individual magnetic particles in the recording layer, the wider
• h 5 for the total width of the remanence curve and h 25 for the steepness of the remanence curve is determined from the constant field demagnetization curve. The values are determined according to The number index at the letter H indicates how many of the particles are magnetized in percent.
• an iron (III) oxide hydroxide (sample A) with a specific surface area SN2 of 37.6 m 2 / g, which consists of a mixture of 9 5 % FeOOH and 5% ⁇ -FeOOH, produced.
• sample A 70 parts were annealed in a tube furnace at 350 ° C. at a pressure of 25 mbar. The test lasted one hour. In order to keep the pressure constant, air is metered in via a vacuum valve, which has previously been dried over silica gel.
• the resulting iron (III) oxide (sample B) has a surface area of 51.3 m 2 / g.
• sample A ⁇ Another 70 parts of sample A are annealed in the same tube furnace at 350 ° C. The test lasted one hour. In this case, however, a mixture of 100 Nl / h air and water vapor (P H2O 845 mbar) is passed over the pigment.
• the resulting iron (III) oxide (sample C) has a surface area of 34.9 m 2 / g.
• sample D produced from sample B has a surface area of 42.1 m 2 / g, a phosphate content of 1.1% by weight and a carbon content of 0.06% by weight.
• sample E produced from sample C are: surface area 36.3 m 2 / g, phosphate content 1.2% by weight and carbon content 0.04% by weight.
• Samples D and E are reduced to iron pigments 4 and 5a as described in comparative experiment 1. Part of the sample 5a is passivated in an air-nitrogen mixture at a temperature below 50 ° C. (sample 5b). The measurement results are shown in Table 1.
• sample A from comparative experiment 1 50 parts of sample A from comparative experiment 1 are stirred into 400 parts by volume of water. After a dispersion time of 10 minutes, a solution of 4.5 parts by volume of water, 0.35 parts by volume of H 3 PO 4 (85% strength) and 0.5 part of H 2 C 2 O 4 .2H 2 O is added. After the dispersion has ended, this becomes Filtered off water and the filter cake was dried in air at 170 C (sample F). Sample F has a surface area of 37 m 2 / g, a phosphate content of 1.4% by weight and a carbon content of 0.14% by weight.
• sample F A further 70 parts of the sample F were prepared as in United g leichsver- described seeking 1, oxide sample to the iron (III) H with a surface area of 47.9 m 2 / g in water vapor-containing air stream annealed. The reduction of sample H to iron pigment 7 also takes place as described in comparative experiment 1. The measurement results are shown in Table 1. ⁇ Comparison 3 ⁇
• An iron (III) oxide hydroxide produced according to DE-AS 10 61 760 consists of 97% ⁇ -FeOOH and 3% ⁇ -FeOOH and has a surface area of 32.7 m 2 / g (sample J).
• 70 parts of sample J are, as described in comparative experiment 1, annealed in a vacuum to pigment Kl with a surface area of 44.8 m 2 / h within one hour and a further 70 parts in the same way within 3 hours to sample K2 with a surface area of 40 , 8 m 2 / g.
• 70 parts of sample J are annealed to samples L1 and L2 in 1 or 3 hours, as also described in comparative test 1, in an atmosphere containing water vapor. II has a surface area of 33.0 m 2 / g and L2, such a 30, 4 m 2 / g ⁇
• Example 2 50 parts of this sample M are, as described in Example 1, equipped with 1% H 3 PO 4 and 1% H 2 C 2 O 4 .2H 2 0 (data in% by weight, based on -FeOOH), filtered and dried.
• the resulting product M1 has a phosphate content of 1.4% by weight, a carbon content of 0.06% by weight and a surface area of 36.8 m 2 / g.
• sample M 50 parts are annealed in a continuous rotary tube at 350 C and an average residence time of 45 minutes in a steam containing nitrogen.
• the resulting iron (III) oxide is finished as described in Example 1, the phosphate content is 1.2% by weight, the Konlenstoff content 0.06% by weight and the surface is 23.4 m 2 / g (sample M2).
• This sample M2 is reduced in the same way as the sample M1 from comparative experiment 5.
• the iron (III) oxide hydroxide sample N ( ⁇ -FeOOH with an ⁇ -FeOOH content of 30% and a surface area of 26.1 m 2 / g) and sample ⁇ ( ⁇ - FeOOH with an ⁇ -FeOOH content of 68% and a surface area of 39.0 m 2 / g).
• a ferric oxide hydroxide prepared in the customary manner with a proportion of 6% ⁇ -FeOOH and 94% ⁇ -FeOOH and a surface area of 29.4 m 2 / g are, as described in Example 4, in a rotary tube at 350 ° C and a p H 0 of 88 mbar with an average residence time of 30 minutes and then equipped as described in comparative experiment 2.
• the resulting sample R1 has a surface area of 32.8 m 2 / g, a phosphate content of 1.0% by weight and a carbon content of 0.03% by weight.
• the resulting iron pigment 23 shows the measurement results given in Table 7.
• the material is then passivated by passing an air / nitrogen mixture at temperatures below 50 ° C.
• Example 6 The sample R given in Example 6 is provided with a surface coating, also reduced (iron pigment 24) and passivated, without tempering, as also described. The measurement results are shown in Table 7.
• Each 800 parts of the passivated iron particles No. 23 and 24 produced according to Example 6 and Comparative Experiment 7 are in a 600-volume steel cylinder mill, which contains 9000 parts of steel balls with a diameter between 4 and 6 mm, with 456 parts of a 13 percent solution of a thermoplastic Polyester urethane from adipic acid, 1,4-butanediol and 4,4'-diisocyanatodiphenylmethane in a solvent mixture of equal parts of tetrahydrofuran and dioxane, 296 parts of a 10 percent solution of a polyvinylformal binder containing 82 percent vinyl formal, 12 percent vinyl acetate and 6 percent vinyl alcohol units , in the solution Oil mixture, 20 parts of butylocarate and a further 492 parts of the solvent mixture mentioned and mixed for 4 days.
• the magnetic properties of the magnetic layer are listed in Table 8.

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

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• 1979
  • 1979-09-01 DE DE19792935357 patent/DE2935357A1/de not_active Withdrawn
• 1980
  • 1980-07-31 US US06/174,240 patent/US4295879A/en not_active Expired - Lifetime
  • 1980-08-21 EP EP80104974A patent/EP0024692B1/fr not_active Expired
  • 1980-08-21 DE DE8080104974T patent/DE3067268D1/de not_active Expired
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