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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/18—Non-metallic particles coated with metal
• • 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
  • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
  • B22F9/26—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions using gaseous reductors

Definitions

• This invention relates to fine particles of ferromagnetic metal and a process for producing the same. More particularly it relates to fine particles of ferromagnetic metal obtained by adding a compound such as a salt of a metal which is different from iron and exclusive of alkali metal (which metal will hereinafter be referred to as a "different kind metal") to an aqueous suspension of iron ⁇ -oxyhydroxide, to adhere the different kind metal onto the iron 2-oxyhydroxide, followed by reduction, and such a process for producing the fine particles.
• a compound such as a salt of a metal which is different from iron and exclusive of alkali metal
• Fine particles of ferromagnetic metal iron having a high coercive force and a high magnetic flux density have recently been noted for elevating the performance of cassette tapes for audio and for developing video tapes for compact YTR (video tape recorders).
• magnetic powder is made finer, such a tendency is observed that the coercive force is enhanced, but the dispersibility, weather resistance, orientativity, etc. of magnetic powder become inferior.
• the starting iron a-oxyhydroxide is made finer, the resulting particles are liable to collapse at the time of being reduced on heating.
• a process of adding a different kind metal to iron a-oxyhydroxide has been developed.
• the resulting iron a-oxyhydroxide has greatly varied particulate forms, depending on the kind, quantity and addition manner of the metal compound added., and all the characteristics of fine particles of metal obtained by heating and reduction are also much different from those in the case where no different kind metal is added. Further, depending on the quantity of the additive, branched particles may be formed or the acicularity of particles of iron a-oxyhydroxide may be lost, although this varies depending on the kind of the compound of the different kind metal added.
• the dope process is promising as a proces for improving the characteristics of the fine particles of metal, but the adhesion process is rather preferable for improving the objective characteristics of the fine particles.
• the adhesion process includes a process of suspending in water, powder or a wet cake of iron a-oxyhydroxide and then adding an aqueous solution of a salt or the like of a different kind metal, to effect the adhesion; and a process of adding an acid or an alkali to the above aqueous suspension to once sufficiently disperse the agglomerate of iron a-oxyhydroxide, followed by adding an aqueous solution of a salt or the like of a different kind metal, and adding an alkali or an acid for neutralization to adhere the compound of the different kind metal, and thereafter filtering the resulting material.
• the coexistent anions can be removed to a certain extent by water-washing after the heat treatment, but several tens-% of their amount prior to the water-washing remain in iron a-oxyhydroxide, hence it is impossible to entirely remove the effect of anions.
• water-washing is carried out without the heat treatment, it is inevitable that a portion of the metal compound to be adhered flows away. Further, according to these processes, only limited metals such as Ni, Co, Ca, Mn, Mg, etc. can be adhered.
• the present invention provides a process for producing fine particles of ferromagnetic metal by adding an aqueous solution of a compound of a metal which is different from iron and exclusive of alkali metal (this metal hereinafter being referred to as a "different kind metal”), to an aqueous suspension of iron a-oxyhydroxide, to adhere said compound of a different kind metal onto particles of iron a -oxyhydroxide, followed by reduction, characterised in that the method comprises adding a ferrous salt together with said compound of a different kind metal to said aqueous suspension of iron a-oxyhydroxide to effect the adhesion.
• the present invention further provides fine particles of ferromagnetic metal obtained by adding an aqueous solution of a compound of a metal which is different from iron and exclusive of alkali metal (this metal hereinafter being referred to as a "different kind metal”), to an aqueous suspension of iron a-oxyhydroxide, to adhere said compound of a different kind metal onto particles of iron a-oxyhydroxide, followed by reduction, characterised in that the fine particles of ferromagnetic metal, are obtained by adding a ferrous salt together with said compound of a different kind metal to said aqueous suspension of iron a-oxyhydroxide to effect the adhesion.
• the present invention provides a process for producing fine particles of ferromagnetic metal, which comprises adding to an aqueous suspension of iron a-oxyhydroxide, an aqeous solution of a compound such as salt, metal acid salt, oxide, of a different kind metal from iron (including an acidic or alkaline aqueous solution) and an aqueous solution of a ferrous salt, followed by oxidation reaction, filtration, water-washing, drying and reduction, and the thus produced fine particles of ferromagnetic metal.
• a process for producing fine particles of ferromagnetic metal which comprises adding to an aqueous suspension of iron a-oxyhydroxide, an aqeous solution of a compound such as salt, metal acid salt, oxide, of a different kind metal from iron (including an acidic or alkaline aqueous solution) and an aqueous solution of a ferrous salt, followed by oxidation reaction, filtration, water-washing, drying and reduction, and the thus produced fine particles of ferromagne
• the above aqueous suspension of iron a-oxyhydroxide may include a slurry formed by preparation of iron a-oxyhydroxide, or a suspension obtained by suspending in water, a wet cake or dried powder of iron a-oxyhydroxide obtained from the above slurry.
• This aqueous suspension may be acidic, alkaline or neutral.
• the present invention has a merit that even the slurry formed by preparation or iron a-oxyhydroxide can be used as it is.
• Examples of the above different kind metai are Ni, Co, Mg, Ca, Sr, Ba, Ti, Cr, Mo, Mn, Cu, Ag, Zn, Cd, Al, Si, Sn, Pb, Bi, Nb and Sm.
• One or more kinds of the metals can be used.
• alkali metals are excluded, because they dissolve in an aqueous solvent in large quantities and hardly deposit on iron a-oxyhydroxide.
• the above aqueous solution of a compound such as salt of a different kind metal added may be used in the form of a neutral, acidic or alkaline aqueous solution.
• a neutral, acidic and alkaline aqueous solutions which is choiced among the neutral, acidic and alkaline aqueous solutions, can be decided taking into account the solubility of the salt or the like of a different kind metal in the aqueous solutions, as well as whether or not a uniform adhesion occurs to a desired extent when the solutions are added to the aqueous suspension of iron a-oxyhydroxide.
• These regulations of the solutions can be achieved by dissolving an acidic or alkaline substance in the solutions.
• the atom/molecule ratio i.e. a ratio of the number of atoms to that of molecules; this applies to the ratio hereinafter mentioned
• the ratio is preferably in the range of about 0.005 to 0.4, more preferably 0.01 to 0.2. If the ratio is too large, the resulting iron a-oxyhydroxide having the metal adhered thereon is liable to agglomerate.
• the atom/ molecule ratio of "Fe(II)/ ⁇ /FeOOH" relative to iron a-oxyhy- aroxide, based on the amount of the metal adhered is preferably in the range of about 0.0025 to 0.3.
• the ratio is not limited to the above range, but if the ratio is too small, the adhesion strength of the added different kind metal onto iron. a-oxyhydroxide is insufficient depending on the amount ratio of Fe(II) to the different kind metal added at the same time, as mentioned later. If the ratio is too large, the iron a-oxyhydroxide resulting from the adhesion is liable to agglomerate.
• the amount ratio of the compound such as salt of the different kind metal and the ferrous salt to be added is preferably 0.5 or higher in terms of the atom ratio of "Fe(II)/ different kind metal (M)" (i.e. the ratio of the respective numbers of the atoms; this applies to those hereinafter mentioned), based on the amount of the metalsadhered.
• This ratio is not limited to the above range, but if the ratio is too small, the adhesion strength of the compound of the different kind metal onto iron a-oxyhydroxide is insufficient.
• the reaction mixture may, if necessary, be adjusted to an appropriate pH, whereby a part or most part of the different kind metal precipitates or gels around iron a-oxyhydroxide .or singly in the form of a compound such as hydroxide, its hydrate, oxide, etc. together with ferrous ions.
• the precipitate or the like at this stage is not yet adhered onto iron a-oxyhydroxide, or even if adhered, it has a low adhesion strength; hence the particles are liable to collapse at the time of reduction step.
• the oxidation process by air or an oxidizing agent is carried out.
• the precipitated Fe(II) is oxidized through the oxidation reaction and deposited or epitaxialized onto the surface of iron a-oxyhydroxide in the form of iron a-oxyhydroxide, and at that time, involves the different kind metal therein to effect a strong adhesion of the different kind metal onto iron a-oxyhydroxide. And the particles thus obtained hardly collapse at the time of reduction step.
• Iron a-oxyhydroxide prepared according to conventional processes is observed to contain very fine particles which are much smaller than average size particles and cause degradation of transfer characteristics and extension of Hc(coercive force) distribution i.e. SFD(switching field distribution).
• very fine particles are combined with larger particles and disappear; hence particles of iron a-oxyhydroxide having the metal compound adhered thereon after oxidation reaction has a uniform particle size.
• the thus combined very fine particles do not separate from the larger particles even in the reduction reaction, to give fine particles of metal well retaining the particulate form of iron a-oxyhydroxide after adhesion.
• iron ⁇ -oxyhydroxide which was then filtered and washed with water to obtain a wet cake (2,500g) (1,000g, as dry weight of iron ⁇ -oxyhydroxide), followed by adding water (24l), stirring for one hour, adding acetic acid so as to give a pH of 3.5, stirring for 30.minutes, adding an aqueous solution of NiSO 4 (0.5 mol/l) (1,124 ml) and then an aqueous solution of FeSO 4 (0.5 mol/l)(1,124 ml), stirring for 15 minutes, adding an aqueous solution.
• the Ni-adhered iron a-oxyhydroxide (500g) was reduced by hydrogen at a flow amount of 20l/min., at a reduction temperature of 500°C for 5 hours to obtain fine particles of ferromagnetic metal retaining a good particulate form of the Ni-adhered iron a-oxyhydroxide.
• the magnetic characteristic values of the thus prepared magnetic powder were as follows: Hc:l,5880e, ⁇ s:159 emu/g, and ⁇ r/ ⁇ s:0.53
• the characteristic values of an oriented sheet obtained by using this magnetic powder were as follows: Hc:1,463Oe, Br:2,984 gauss, Br/Bm:0.846, and SFD:0.432.
• He was higher by about 1000e as compared with fine particles of metal bbtained according to a process of Comparative examples mentioned later, and also SFD was improved.
• Magnetic powder was prepared in the same manner as in Example 1 except that the kind and amount of the salt of the different kind metal added and the atomic ratio of the different kind metal to Fe(II) were varied. As in the case of Example 1, nearly 100% of the added metal was retained on the iron a-oxyhydroxide, and anions and Na + were scarcely observed; thus, fine particles of ferromagnetic metal well retaining the particulate form of the adhered iron a-oxyhydroxide were obtained.
• An aqueous solution of NiSO 4 (0.5 mol/l)(1,290 ml) was added at a flow rate of 20 ml/min. to a reaction slurry of iron a-oxyhydroxide prepared as in Example 1, followed by adding an aqueous solution of FeSO 4 (0.5 mol/l) (1,290 ml) at a flow rate of 20 mi/min., stirring for 30 minutes, and carrying out oxidation reaction for 6 hours, while passing air at a low amount of 0.2 l/min. to obtain a Ni-adhered iron a-oxyhydroxide as in the case of Example 1. Reduction was carried out as in Example 1 to obtain fine particles of ferromagnetic metal well retaining the particulate form of the Ni-adhered iron oxyhydroxide.
• Example 11 was repeated except that the kind and amount of the salt of the different kind metal and the reduction temperature were varied. Metal-adhered iron a-oxyhydroxides similar to that of Example 11 were formed, and fine particles of ferromagnetic metal well retaining their particulate form.
• the resulting Ni-adhered iron a-oxyhydroxide contained 0.32% of SO 4 2- , and collapse of particles due to reduction was observed.
• the characteristic properties of the magnetic powder were as follows: Hc:1,4650e, ⁇ s:155 emu/g and ⁇ r/ ⁇ s:0.51. Further, SFD of the oriented sheet was 0.612, i.e. notably inferior to those of Examples.
• Ni was adhered as in Comparative example 1, followed by filtering, washing with water (60l), drying and reducing under the same conditions as in Example 1.
• Comparative example 1 was repeated except that the added salt of the different kind metal was changed to Al 2 (SO 4 ) 3 .

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

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Citations (5)

• 1983
  • 1983-02-22 JP JP58028149A patent/JPS59153810A/ja active Granted
• 1984
  • 1984-02-22 DE DE8484301141T patent/DE3461871D1/de not_active Expired
  • 1984-02-22 EP EP84301141A patent/EP0118253B1/de not_active Expired

Patent Citations (5)

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