Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/10—Oxidising
  • C23C8/12—Oxidising using elemental oxygen or ozone
  • C23C8/14—Oxidising of ferrous surfaces
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/14—Treatment of metallic powder
  • B22F1/145—Chemical treatment, e.g. passivation or decarburisation
• • 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

Definitions

• the invention relates to a method for stabilizing pyrophoric, needle-shaped metal particles consisting essentially of iron by reaction with oxygen-containing gases at elevated temperature.
• acicular ferromagnetic metal particles with single-region behavior as a magnetizable material for the production of magnetic recording media.
• the high coercive field strengths and high values for the remanent magnetization that can be achieved with such materials prompted the search early on for ways to produce these substances in a simple manner.
• a disadvantage of these materials, which have excellent magnetic properties, is their pyrophoric character.
• the cause of the pyrophoric behavior is the extremely fine grain size of the metal powder with particle sizes of 50 to 2,000 A and the resulting large free surface.
• lattice disorders are also discussed as the cause (cf. Hollemann-Wiberg, Textbook of inorganic chemistry, 1964, page 398).
• the pyrophoric acicular ferromagnetic particles consisting essentially of iron can be stabilized in accordance with the task by reaction with oxygen-containing gases if, in a first stage, at a temperature between 25 and 45 ° C. up to 1/3 of those in the final state Passivation layer formed and then in a second stage at a temperature between 50 and 70 ° C until the formation of the entire passivation layer, the pyrophoric metal particles are treated with an oxygen-containing inert gas, with the proviso that the respective temperature range is set by the oxygen content of the inert gas stream.
• the finely divided, pyrophoric, ferromagnetic and acicular metal particles which consist essentially of iron, are exposed to an oxygen-containing inert gas stream, generally an air / nitrogen stream, in a known manner.
• an oxygen-containing inert gas stream generally an air / nitrogen stream
• the temperature during the stabilization process of the pyrophoric metal particles is adjusted by regulating the oxygen content of the gas stream.
• the difference in the reaction temperatures between the first and the second stage is 15 to 20 ° C. during stabilization.
• Needle-shaped ferromagnetic metal powders are used as starting materials, which consist essentially of iron, but possibly also cobalt and / or L. can contain ickel.
• the pyrophoric metal powder is expediently prepared in a manner known per se by reducing the associated powdery metal oxides by the action of a gaseous reducing agent, preferably hydrogen or a gas containing hydrogen, at temperatures up to 500 ° C., preferably between 250 and 400 ° C.
• the method according to the invention permits effective stabilization of the finely divided ferromagnetic metal particles consisting essentially of iron.
• the two-stage process encloses the finely divided metal particles in a particularly uniform and uniformly oxidic shell, a result that cannot be achieved, for example, by a so-called re-passivation of already passivated material at a higher temperature.
• Stabilized metal particles of this type are therefore outstandingly suitable for the production of magnetic recording media, since they can be processed without special precautionary measures and, above all, can be incorporated excellently into the layer-forming organic binder.
• This particularly good stability when dispersing the stabilized metal particles obtained by the process according to the invention results in magnetic recording layers with a markedly higher remanent magnetization.
• the material produced according to the method according to the invention generally also has a narrower switching field strength distribution, i.e. has a narrower particle size distribution with regard to the remagnetization.
• 392 parts of an iron powder stabilized in this way are mixed with 105 parts of a 20% solution of a polyphenoxy resin with a molecular weight of 30,000 in a mixture of equal parts of tetrahydrofuran and dioxane, 392 parts of a 12.5% solution of a thermoplastic polyester urethane from adipic acid, 1.
• the dispersion is then filtered and applied in a known manner to a 6 / um thick polyethylene terephthalate film in such a thickness that after the alignment of the needle-shaped particles by passing them past a magnetic field and then drying and calendering, a magnetic layer with a layer thickness of 7.1 / um remains.
• the magnetic properties of this layer were determined with a vibration magnetometer at a measuring field of 160 kA / m.
• the coercive field strength Hc [kA / m], the remanent magnetization M [mT], the ratio of remanent magnetization to saturation magnetization M r / M m and the directivity factor RF, ie the ratio of the remanent magnetization in the layer along to across the magnetic, are determined Preferred direction.
• the measured values are given in Table 1.
• Example 1 The procedure is as described in Example 1, but the stabilization process is only carried out at a product temperature of 40 ° C. The drop in reaction temperature occurred after 3.5 hours. The processing of the stabilized iron powder into the magnetic layer was also carried out as indicated in Example 1. The magnetic properties are given in Table 1.
• Example 1 an unstabilized iron powder as used in Example 1 is processed into a magnetic layer in the manner specified there.
• the magnetic properties are given in Table 1.
• a according to Comparative Experiment 1 at a product temperature of 40 0 C stabilized iron powder is then repassivated at 60 ° C. To set this temperature during the post-passivation, however, it is necessary to supply the necessary heat from the outside because of the insufficient heat of reaction. During the post-passivation, the proportion of air in the nitrogen fluidizing gas is 34 percent by volume. After 8 hours, the iron powder is cooled, discharged from the fluidized bed furnace and processed into a magnetic layer as described in Example 1. The magnetic properties are given in Table 1.
• a pyrophoric needle-shaped ferromagnetic iron powder prepared as described in Example 4 of US Pat. No. 4,155,748, is stabilized in the same way as described in Example 1. However, the temperature of 40 ° C is maintained for one hour in the first stage. The stabilized iron powder is further processed into the magnetic layer as described in Example 1. The magnetic properties are given in Table 2.
• Example 2 The procedure is as described in Example 2, but the stabilization process is carried out only at one temperature (40 ° C.). The drop in the reaction temperature occurred after 5.5 hours. Further processing takes place in accordance with Example 2.
• the magnetic values are given in Table 2.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Power Engineering (AREA)
• Hard Magnetic Materials (AREA)
• Magnetic Record Carriers (AREA)
• Paints Or Removers (AREA)
• Powder Metallurgy (AREA)
• Compounds Of Iron (AREA)
• Carbon And Carbon Compounds (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6130824

Family Applications (1)

Country Status (4)

Cited By (3)

Families Citing this family (9)

Family Cites Families (12)

• 1981
  • 1981-04-25 DE DE19813116489 patent/DE3116489A1/de not_active Withdrawn
• 1982
  • 1982-04-08 EP EP82103010A patent/EP0063730A3/fr not_active Withdrawn
  • 1982-04-16 US US06/368,984 patent/US4420330A/en not_active Expired - Fee Related
  • 1982-04-19 JP JP57064086A patent/JPS57181301A/ja active Pending

Also Published As

Similar Documents

Legal Events