CA1252995A - Method for the preparation of fine hexagonal ferrite powders, in particular, for magnetic recording - Google Patents
Method for the preparation of fine hexagonal ferrite powders, in particular, for magnetic recordingInfo
- Publication number
- CA1252995A CA1252995A CA000495813A CA495813A CA1252995A CA 1252995 A CA1252995 A CA 1252995A CA 000495813 A CA000495813 A CA 000495813A CA 495813 A CA495813 A CA 495813A CA 1252995 A CA1252995 A CA 1252995A
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- Canada
- Prior art keywords
- solution
- heat
- addition
- application
- titanium
- Prior art date
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- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 25
- 230000005291 magnetic effect Effects 0.000 title claims abstract description 10
- 229910000859 α-Fe Inorganic materials 0.000 title claims abstract description 7
- 238000002360 preparation method Methods 0.000 title claims description 8
- 239000000843 powder Substances 0.000 title claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 35
- 150000001875 compounds Chemical class 0.000 claims abstract description 17
- 239000007795 chemical reaction product Substances 0.000 claims abstract description 15
- 239000010941 cobalt Substances 0.000 claims abstract description 15
- 229910017052 cobalt Inorganic materials 0.000 claims abstract description 15
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000010936 titanium Substances 0.000 claims abstract description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 15
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims abstract description 12
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 12
- 229910052788 barium Inorganic materials 0.000 claims abstract description 8
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052712 strontium Inorganic materials 0.000 claims abstract description 8
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 claims abstract description 8
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims abstract description 7
- 229910052784 alkaline earth metal Inorganic materials 0.000 claims abstract description 6
- 150000001342 alkaline earth metals Chemical class 0.000 claims abstract description 6
- 229960002413 ferric citrate Drugs 0.000 claims abstract description 6
- NPFOYSMITVOQOS-UHFFFAOYSA-K iron(III) citrate Chemical compound [Fe+3].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NPFOYSMITVOQOS-UHFFFAOYSA-K 0.000 claims abstract description 6
- 150000004649 carbonic acid derivatives Chemical class 0.000 claims abstract description 4
- 238000002425 crystallisation Methods 0.000 claims abstract description 4
- 230000008025 crystallization Effects 0.000 claims abstract description 4
- YONPGGFAJWQGJC-UHFFFAOYSA-K titanium(iii) chloride Chemical compound Cl[Ti](Cl)Cl YONPGGFAJWQGJC-UHFFFAOYSA-K 0.000 claims abstract description 4
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 33
- 229910052742 iron Inorganic materials 0.000 claims description 17
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 13
- 230000015572 biosynthetic process Effects 0.000 claims description 12
- 239000000126 substance Substances 0.000 claims description 9
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 8
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 239000002244 precipitate Substances 0.000 claims description 6
- 229920002521 macromolecule Polymers 0.000 claims description 5
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 4
- 125000002091 cationic group Chemical group 0.000 claims description 4
- 230000018044 dehydration Effects 0.000 claims description 4
- 238000006297 dehydration reaction Methods 0.000 claims description 4
- 229910001410 inorganic ion Inorganic materials 0.000 claims description 4
- 229910021506 iron(II) hydroxide Inorganic materials 0.000 claims description 4
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 claims description 4
- 230000007935 neutral effect Effects 0.000 claims description 4
- 229910002651 NO3 Inorganic materials 0.000 claims description 3
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 3
- 239000002253 acid Substances 0.000 claims description 3
- 229910021529 ammonia Inorganic materials 0.000 claims description 3
- 239000006227 byproduct Substances 0.000 claims description 3
- 239000012141 concentrate Substances 0.000 claims description 3
- 238000001556 precipitation Methods 0.000 claims description 3
- 238000000926 separation method Methods 0.000 claims description 3
- 229910052723 transition metal Inorganic materials 0.000 claims description 3
- 150000003624 transition metals Chemical class 0.000 claims description 3
- 239000001569 carbon dioxide Substances 0.000 claims description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 2
- 238000000354 decomposition reaction Methods 0.000 claims description 2
- 239000012153 distilled water Substances 0.000 claims 2
- 230000008030 elimination Effects 0.000 claims 2
- 238000003379 elimination reaction Methods 0.000 claims 2
- 238000005406 washing Methods 0.000 claims 2
- 238000000227 grinding Methods 0.000 claims 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 abstract description 3
- 229910052751 metal Inorganic materials 0.000 abstract description 3
- 239000002184 metal Substances 0.000 abstract description 3
- 239000002245 particle Substances 0.000 abstract description 3
- 239000005416 organic matter Substances 0.000 abstract description 2
- 238000006068 polycondensation reaction Methods 0.000 abstract description 2
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 abstract 1
- 239000005977 Ethylene Substances 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 17
- -1 cobal-t Chemical compound 0.000 description 3
- 239000000306 component Substances 0.000 description 3
- 230000005415 magnetization Effects 0.000 description 3
- 238000006467 substitution reaction Methods 0.000 description 3
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical group [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 238000001033 granulometry Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000006479 redox reaction Methods 0.000 description 2
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- LCKIEQZJEYYRIY-UHFFFAOYSA-N Titanium ion Chemical compound [Ti+4] LCKIEQZJEYYRIY-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910052729 chemical element Inorganic materials 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 150000001860 citric acid derivatives Chemical class 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000005293 ferrimagnetic effect Effects 0.000 description 1
- 239000003302 ferromagnetic material Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 125000004356 hydroxy functional group Chemical group O* 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 235000001055 magnesium Nutrition 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229940091250 magnesium supplement Drugs 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 125000002524 organometallic group Chemical group 0.000 description 1
- 230000005298 paramagnetic effect Effects 0.000 description 1
- 150000002978 peroxides Chemical class 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 150000005846 sugar alcohols Polymers 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Landscapes
- Compounds Of Iron (AREA)
Abstract
Abstract The method disclosed by which to prepare fine hexag-onal ferrites for use in magnetic recording, is one which consists basically in dissolving a) carbonates or other soluble compounds of an aikaline earth metal such as strontium or barium, b) a carbonate or other soluble compound of cobalt, and c) titanium trichlor-ide, all in a solution of ferric citrate and water, whereupon a polycondensation is brought about by ad-dition of ethylene clycol, and heat is applied to eliminate water and organic matter from the compound.
Addition of the alkaline earth metal, the cobalt and the titanium is proportioned precisely on the basis of the stoichimetric properties of the end-product, the formula for which is ReO . (6-x)Fe2O3 . xCoO . xTiO2 where x is the extent to which cobalt and titanium atoms replace iron atoms and Re is the alkaline earth metal. Final application of heat produces crystalliz-ation of the superfine hexaferrite particles.
Addition of the alkaline earth metal, the cobalt and the titanium is proportioned precisely on the basis of the stoichimetric properties of the end-product, the formula for which is ReO . (6-x)Fe2O3 . xCoO . xTiO2 where x is the extent to which cobalt and titanium atoms replace iron atoms and Re is the alkaline earth metal. Final application of heat produces crystalliz-ation of the superfine hexaferrite particles.
Description
~s~9~
Method for the___eparatio __f fi_e hexa~onal ferri_e powders, in _articular, for magnetic recording The invention relates to a method for the preparation of fine hexagonal ferrite powders, destined in part-icular for magnetic recording.
Hexagonal ferrites (hexaferrites) are ferrimagnetic 05 materials having a general chemical formula:
AReO . BMeO . CFe203 where:
A, B and C are stoichiometric indices which vary with the different hexaferrite phases (denoted in general terms by calpital letters M, Y, W, Z ~c.);
Re is usually an alkaline earth metal such as barium or strontium; and Me is a divalent transition metal which, apart from iron, might be zinc, cobal-t, copper, manganese, mag-nesium or niclcel.
The magnetic properties of this particular class of materials render them suitable, either in the normal , ~25299S
state or appropriately doctored, for a great number of applications; one such application of significant interest is that of magnetic recording.
Reference is made throughout the description to a 05 hexaferrite in the M phase, where A=1, 8=0 and C=6, thus producing a chemical formula ReO . 6Fe2C3 It will be observed, nonetheless, that the method as disclosed can be applied with hexagonal ferrites in different phases, that is~ having different stoichio-metric indices.
The object of the method disclosed is to permit of obtaining hexaferrites the physical and the magnetic properties of which -viz, dimensions of the powdered particles, uniformity of the compound, anisotropy, coercivity, magneti~ation &c., can be controlled with ease, thereby making it possible to engineer values for the single properties as near as possible to the optimum values effectively required, these being dependent on the uItimate application of the single hexaferrite product.
An advantage of the method is that it permits of ob-taining a hexaferrite precursor featuring uniformity of atomic structure and anabling formation of the end product (the hexaferrite) at low temperature applied for a relatively short duration, in such a way as to extract finer particles and generally enhance the granulometry of the powder.
~5~29!315 The stated object and the aforesaid advantage, and other advantages besides, are realized with the method disclosed herein, which is characterised in that it envisages the following steps:
05 -preparation of a solution of ferric citrate in water having an excess of citric acid over iron;
-addition of a soluble compound of an alkaline earth metal in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of~a soluble compound of cobalt in stoichi-ometric proportion determined by the stoichiometry of the end-product;
-addition of a soluble compound of titanium in stoi-chiometric proportion determined by the stoichiometry of the end~product;
-a first application of heat at below 100 C by means of which to eliminate unwanted by-products;
-addition of ethylene glycol in a proportion of 10%
by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions;
-a second appllcation of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solu.tion;
-a third application of heat at between 400,..450 C, bringing about total elimi~nation of the organic part of the solidified mass; and -a final application of heat by means of which to in-duce crystallization of the hexaferrite.
"` ~2S~2995 A possible version of the basic method will now bedescribed in detail. Reference is made to the graphs of the accompanying figs 1, 2 and 3, which illustrate the magnetic properties of the end-product in relat-05 ion to its stoichiometric composition and to theduration and temperature of the final application of heat.
The object of the method described herein i8 that of obtaining a hexaferrite in which the iron is partly subst tuted in isoelectronic fashion by cobalt plus titanium, according to the following equation 2Fe ~ (Ti ~ Go thereby obtaining a hexaferrite with the formula ReO . (6-x)Fe203 . xCoO . xTiO2 or in more general terms, where it may be wished to obtain hexaferrites in phases other than M, AReO . BMeO . (C-x)Fe203 . xCoO . x'riO2 where x is the extent to which iron ions are substit-uted by~cobalt and titanium ions.
Unless otherwise stated,~proportions of the various substances utilized in the process are calculated strictly according to the stoichiometry of the end-product.
The first step is preparation of a solution of ferric - ~2S2~9~;
citrate in water, in which the acid moles outnumber the iron by approximately 10 to 1; a solution bf the kind is obtained by dissolving nitrate of iron in distilled wa-ter, and precipitating ferrous hydroxide 05 with an excess of concentrate ammonia; the precipit-ate is separated from the solution and washed in lukewar~ water until neutral pH is obtained, follow-ing which a 1:2mol solution of citric acid in water is added, such that the citric acid out-proportions the iron as aforesaid. This procedure is adopted in view of the fact that the ferrous hydroxide produced is easily dissolved in citric acid, unlike calcined or dried substances generally available through the trade. Likewise, the use of citric acid is preferred, though not obligatory; any other organic ~ hydroxy polyacid may be used.
The solution is pre-heated to a temperature of approx 60...70 C in order to dissolve the precipitate com-pletely, following which a carbonate or an oxide of strontium and/or barium and a carbonate or an oxide or base carbonate of cobalt are added; other soluble compounds of strontium/barium or cobalt may be used, provided that'no anions are introduced which cannot be eliminated by the next application of heat.
Finally, a solution of ~itanium trichloride in water is added.
The trivalent titanium is oxidated directly in solut--ion by a redox reaction in which Ti ~ Fe = Ti + Fe ~L6~52~5 The titanium ion is obtained in solution utilizing titanium trichloride (TiC13) since the oxygen-bearing compounds of tetravalent titanium (TiO2) are not sol-uble in the weak acid environment of a citric acid 05 solution. Likewise, titanium tetrachloride (TiC14) is not suited to the purpose since hydrolysis will occur on contact with the water, producing a hydroxide that is insoluble in citric acid.
As a person skilled in the art will appreciate, if a hexaferrite 'is required in a phase other than M, the soluble compound of a divalent transition metal must be added, and the proportions of the different com-ponents must of course be modified according to the stoichiometric properties of the end-product.
One now has the formation of soluble citrates of the metals introduced, which, besides iron, are strontium and/or barium, cobalt and titanium.
The next step is addition of hydrogen peroxide to the solution in order to oxidate any by-products created as a result of the titanium-and-iron redox reaction;
another oxidating agent may be used as long as no new chemical elements are introduced into the solution.
At this sta~e the solution is heated to a temperature of below 100 ~C in order to eliminate excess hydrogen ; 25 peroxide, and carbon dioxide given off by the decom-position of carbonates.
~thylene glycol (or anoth~er polyalcohol) is now added to the solution in a porportion of 10% by volume, ap-proximately; a typical polycondensation now occurs between the glycol and the citrate, giving rise to ~2,52~95 the formation of long organic macromolecules having chemically-bonded inorganic ions.
The solution is heated once again in order to elimin-ate the water and the azeotropic mixture of H20 and 05 HCl, which evaporates at 110 C. Fol.lowing this heat stage one has the formation, in sequence, of a highly viscous organo-metallic residue having the same cat-ionic composition and the same chemical uniformity of the original solution, and of a solidified mass that possesses the'same properties; the high viscosity of the long organic macromolecules is such as to permit of their total dehydration without any precipitation occurring, hence without any separation of their com-ponents.
A further application o~ heat; a-t a temperature of between 400 and 450 C, burns off and thus eliminates solid organic matter, 10aving an inorganic residue that consists wholly and exclusively of the hexafer-rite components (metals introduced, plus oxygen).
The residue may be ground at this juncture, before a final application of heat takes place to bring about formation of the hexaferrite end-product.
The uniformity of atomic structure possessed by the precursor is not obtainable with traditional ceramics preparation techniques, and it is a property which renders the substance considerably more reactive; the result is that formation of the hexaferrite can occur at lower temperature and in relatively shorter time;
a powder produced by this method is smaller-grained, and has enhanced granulometry.
~L25Z995 The substitution of iron with cobalt and titanium permits of control over the ~agnetic properties of ; the end-product, -thereby matching exactly it to the ultimate application, which in the case of the dis-05 closure is that of magnetic recording. What is more, it will be observed that the Curie point, (the temp-erature at which ferromagnetic materials become para-magnetic) remains sufficiently high even with the substitutions as described implemented in practice.
The graph of fig 1 demonstrates how magnetization (~r) and coercive force (Hc) vary, in a heating cycle of five minutes duration at 1050 C, according to the extent, denoted x, to which iron is substituted by titanium and cobalt. The graph of fig 2 shows how magnetization and coercive force vary, likewise with variation in the extent of substitution x, in a cycle of two minutes at 1150 C.
In the graph of fig 3, it will be seen how in a hexa-ferrite with a substition factor of x = 0.9, assuming heating cycles of 2, 5 and 30 minutes duration res-pectively, magnetization and coercive force vary with variation in the temperature at which the final heat cycle is brought about.
It must be stressed, to the end of interpreting the ~S graphs correctly, that the final heat cycle occurs ~t constant temperature, in theory; also, the graphs relate to a hexaferrite in the M phase wherein a part of the iron is substituted in isoelectronic fashion by cobalt plus titanium, to the extent as denoted by factor x.
Method for the___eparatio __f fi_e hexa~onal ferri_e powders, in _articular, for magnetic recording The invention relates to a method for the preparation of fine hexagonal ferrite powders, destined in part-icular for magnetic recording.
Hexagonal ferrites (hexaferrites) are ferrimagnetic 05 materials having a general chemical formula:
AReO . BMeO . CFe203 where:
A, B and C are stoichiometric indices which vary with the different hexaferrite phases (denoted in general terms by calpital letters M, Y, W, Z ~c.);
Re is usually an alkaline earth metal such as barium or strontium; and Me is a divalent transition metal which, apart from iron, might be zinc, cobal-t, copper, manganese, mag-nesium or niclcel.
The magnetic properties of this particular class of materials render them suitable, either in the normal , ~25299S
state or appropriately doctored, for a great number of applications; one such application of significant interest is that of magnetic recording.
Reference is made throughout the description to a 05 hexaferrite in the M phase, where A=1, 8=0 and C=6, thus producing a chemical formula ReO . 6Fe2C3 It will be observed, nonetheless, that the method as disclosed can be applied with hexagonal ferrites in different phases, that is~ having different stoichio-metric indices.
The object of the method disclosed is to permit of obtaining hexaferrites the physical and the magnetic properties of which -viz, dimensions of the powdered particles, uniformity of the compound, anisotropy, coercivity, magneti~ation &c., can be controlled with ease, thereby making it possible to engineer values for the single properties as near as possible to the optimum values effectively required, these being dependent on the uItimate application of the single hexaferrite product.
An advantage of the method is that it permits of ob-taining a hexaferrite precursor featuring uniformity of atomic structure and anabling formation of the end product (the hexaferrite) at low temperature applied for a relatively short duration, in such a way as to extract finer particles and generally enhance the granulometry of the powder.
~5~29!315 The stated object and the aforesaid advantage, and other advantages besides, are realized with the method disclosed herein, which is characterised in that it envisages the following steps:
05 -preparation of a solution of ferric citrate in water having an excess of citric acid over iron;
-addition of a soluble compound of an alkaline earth metal in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of~a soluble compound of cobalt in stoichi-ometric proportion determined by the stoichiometry of the end-product;
-addition of a soluble compound of titanium in stoi-chiometric proportion determined by the stoichiometry of the end~product;
-a first application of heat at below 100 C by means of which to eliminate unwanted by-products;
-addition of ethylene glycol in a proportion of 10%
by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions;
-a second appllcation of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solu.tion;
-a third application of heat at between 400,..450 C, bringing about total elimi~nation of the organic part of the solidified mass; and -a final application of heat by means of which to in-duce crystallization of the hexaferrite.
"` ~2S~2995 A possible version of the basic method will now bedescribed in detail. Reference is made to the graphs of the accompanying figs 1, 2 and 3, which illustrate the magnetic properties of the end-product in relat-05 ion to its stoichiometric composition and to theduration and temperature of the final application of heat.
The object of the method described herein i8 that of obtaining a hexaferrite in which the iron is partly subst tuted in isoelectronic fashion by cobalt plus titanium, according to the following equation 2Fe ~ (Ti ~ Go thereby obtaining a hexaferrite with the formula ReO . (6-x)Fe203 . xCoO . xTiO2 or in more general terms, where it may be wished to obtain hexaferrites in phases other than M, AReO . BMeO . (C-x)Fe203 . xCoO . x'riO2 where x is the extent to which iron ions are substit-uted by~cobalt and titanium ions.
Unless otherwise stated,~proportions of the various substances utilized in the process are calculated strictly according to the stoichiometry of the end-product.
The first step is preparation of a solution of ferric - ~2S2~9~;
citrate in water, in which the acid moles outnumber the iron by approximately 10 to 1; a solution bf the kind is obtained by dissolving nitrate of iron in distilled wa-ter, and precipitating ferrous hydroxide 05 with an excess of concentrate ammonia; the precipit-ate is separated from the solution and washed in lukewar~ water until neutral pH is obtained, follow-ing which a 1:2mol solution of citric acid in water is added, such that the citric acid out-proportions the iron as aforesaid. This procedure is adopted in view of the fact that the ferrous hydroxide produced is easily dissolved in citric acid, unlike calcined or dried substances generally available through the trade. Likewise, the use of citric acid is preferred, though not obligatory; any other organic ~ hydroxy polyacid may be used.
The solution is pre-heated to a temperature of approx 60...70 C in order to dissolve the precipitate com-pletely, following which a carbonate or an oxide of strontium and/or barium and a carbonate or an oxide or base carbonate of cobalt are added; other soluble compounds of strontium/barium or cobalt may be used, provided that'no anions are introduced which cannot be eliminated by the next application of heat.
Finally, a solution of ~itanium trichloride in water is added.
The trivalent titanium is oxidated directly in solut--ion by a redox reaction in which Ti ~ Fe = Ti + Fe ~L6~52~5 The titanium ion is obtained in solution utilizing titanium trichloride (TiC13) since the oxygen-bearing compounds of tetravalent titanium (TiO2) are not sol-uble in the weak acid environment of a citric acid 05 solution. Likewise, titanium tetrachloride (TiC14) is not suited to the purpose since hydrolysis will occur on contact with the water, producing a hydroxide that is insoluble in citric acid.
As a person skilled in the art will appreciate, if a hexaferrite 'is required in a phase other than M, the soluble compound of a divalent transition metal must be added, and the proportions of the different com-ponents must of course be modified according to the stoichiometric properties of the end-product.
One now has the formation of soluble citrates of the metals introduced, which, besides iron, are strontium and/or barium, cobalt and titanium.
The next step is addition of hydrogen peroxide to the solution in order to oxidate any by-products created as a result of the titanium-and-iron redox reaction;
another oxidating agent may be used as long as no new chemical elements are introduced into the solution.
At this sta~e the solution is heated to a temperature of below 100 ~C in order to eliminate excess hydrogen ; 25 peroxide, and carbon dioxide given off by the decom-position of carbonates.
~thylene glycol (or anoth~er polyalcohol) is now added to the solution in a porportion of 10% by volume, ap-proximately; a typical polycondensation now occurs between the glycol and the citrate, giving rise to ~2,52~95 the formation of long organic macromolecules having chemically-bonded inorganic ions.
The solution is heated once again in order to elimin-ate the water and the azeotropic mixture of H20 and 05 HCl, which evaporates at 110 C. Fol.lowing this heat stage one has the formation, in sequence, of a highly viscous organo-metallic residue having the same cat-ionic composition and the same chemical uniformity of the original solution, and of a solidified mass that possesses the'same properties; the high viscosity of the long organic macromolecules is such as to permit of their total dehydration without any precipitation occurring, hence without any separation of their com-ponents.
A further application o~ heat; a-t a temperature of between 400 and 450 C, burns off and thus eliminates solid organic matter, 10aving an inorganic residue that consists wholly and exclusively of the hexafer-rite components (metals introduced, plus oxygen).
The residue may be ground at this juncture, before a final application of heat takes place to bring about formation of the hexaferrite end-product.
The uniformity of atomic structure possessed by the precursor is not obtainable with traditional ceramics preparation techniques, and it is a property which renders the substance considerably more reactive; the result is that formation of the hexaferrite can occur at lower temperature and in relatively shorter time;
a powder produced by this method is smaller-grained, and has enhanced granulometry.
~L25Z995 The substitution of iron with cobalt and titanium permits of control over the ~agnetic properties of ; the end-product, -thereby matching exactly it to the ultimate application, which in the case of the dis-05 closure is that of magnetic recording. What is more, it will be observed that the Curie point, (the temp-erature at which ferromagnetic materials become para-magnetic) remains sufficiently high even with the substitutions as described implemented in practice.
The graph of fig 1 demonstrates how magnetization (~r) and coercive force (Hc) vary, in a heating cycle of five minutes duration at 1050 C, according to the extent, denoted x, to which iron is substituted by titanium and cobalt. The graph of fig 2 shows how magnetization and coercive force vary, likewise with variation in the extent of substitution x, in a cycle of two minutes at 1150 C.
In the graph of fig 3, it will be seen how in a hexa-ferrite with a substition factor of x = 0.9, assuming heating cycles of 2, 5 and 30 minutes duration res-pectively, magnetization and coercive force vary with variation in the temperature at which the final heat cycle is brought about.
It must be stressed, to the end of interpreting the ~S graphs correctly, that the final heat cycle occurs ~t constant temperature, in theory; also, the graphs relate to a hexaferrite in the M phase wherein a part of the iron is substituted in isoelectronic fashion by cobalt plus titanium, to the extent as denoted by factor x.
Claims (11)
1) A method for the preparation of fine hexagonal fer-rite powders, in particular for magnetic recording, characterised in that it comprises the following steps:
-preparation of a solution of ferric citrate in water having an excess of citric acid over iron;
-addition of a soluble compound of an alkaline earth metal (Re) in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of a soluble compound of cobalt in stoichi-ometric proportion determined by the stoichiometry of the end-product;
-addition of a soluble compound of titanium in stoi-chiometric proportion determined by the stoichiometry of the end-product;
-a first application of heat at below 100 °C by means of which to eliminate unwanted by-products;
-addition of ethylene glycol in a proportion of 10%
by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions;
-a second application of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solution;
-a third application of heat at between 400...450 °C, bringing about total elimination of the organic part of the solidified mass; and -a final application of heat by means of which to in-duce crystallization of the hexaferrite.
-preparation of a solution of ferric citrate in water having an excess of citric acid over iron;
-addition of a soluble compound of an alkaline earth metal (Re) in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of a soluble compound of cobalt in stoichi-ometric proportion determined by the stoichiometry of the end-product;
-addition of a soluble compound of titanium in stoi-chiometric proportion determined by the stoichiometry of the end-product;
-a first application of heat at below 100 °C by means of which to eliminate unwanted by-products;
-addition of ethylene glycol in a proportion of 10%
by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions;
-a second application of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solution;
-a third application of heat at between 400...450 °C, bringing about total elimination of the organic part of the solidified mass; and -a final application of heat by means of which to in-duce crystallization of the hexaferrite.
2) Method as in claim 1 wherein the soluble compound of titanium is titanium trichloride (TiCl3).
3) Method as in claim 1 wherein the alkaline earth metal (Re) is strontium and/or barium and the soluble com-pounds of strontium and/or barium are carbonates and/ or oxides.
4) Method as in claim 1 wherein the soluble compounds of cobalt are neutral or base carbonates and/ or oxides.
5) Method as in claim 1 wherein the excess of citric acid over iron is approximately ten to 1, calculated in moles.
6) Method as in claim 1 wherein preparation of the ferric citrate solution comprises the following steps:
-solution of nitrate of iron in distilled water and precipitation of ferrous hydroxide with an excess of concentrate ammonia;
-separation of the precipitate and washing of same until neutral pH is obtained;
-addition of a 1 : 2mol solution of citric acid in water.
-solution of nitrate of iron in distilled water and precipitation of ferrous hydroxide with an excess of concentrate ammonia;
-separation of the precipitate and washing of same until neutral pH is obtained;
-addition of a 1 : 2mol solution of citric acid in water.
7) Method as in claim 5 wherein the solution of ferric citrate is pre-heated to between 60 and 70 °C approx until the precipitate is totally dissolved.
8) Method as in claim 1 wherein hydrogen peroxide is added to the solution prior to the first application of heat.
9) Method as in claim 1 wherein the soluble compound of a divalent transition metal is added to the solution of ferric citrate in water.
10) Method as in claim 1 wherein the inorganic residue is ground prior to the final application of heat.
11) Method as in claim 1 comprising the following steps:
-solution of nitrate of iron in distilled water and precipitation of ferrous hydroxide with an excess of concentrate ammonia;
-separation of the precipitate and washing of same until neutral pH is obtained;
-addition of a 1 : 2mol solution of citric acid in water such that acid moles outnumber iron moles by approximately 10 to 1;
-preliminary application of heat at 60...70 °C approx until the precipitate is totally dissolved;
-addition of a carbonate of barium and/or strontium in stoichiometric proportion determined by the stoi-chiometry of the end-product;
-addition of carbonate of cobalt in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of titanium trichloride in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of hydrogen peroxide;
-a first application of heat at below 100 °C by means of which to eliminate excess hydrogen peroxide and carbon dioxide produced by decomposition of carbon-ates;
-addition of ethylene glycol in a proportion of 10%
by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions;
-a second application of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solution;
-a third application of heat at between 400...450 °C, bringing about total elimination of the organic part of the solidified mass, so as to leave an inorganic residue;
-grinding of the inorganic residue; and -a final application of heat by means of which to in-duce crystallization of the hexaferrite.
-solution of nitrate of iron in distilled water and precipitation of ferrous hydroxide with an excess of concentrate ammonia;
-separation of the precipitate and washing of same until neutral pH is obtained;
-addition of a 1 : 2mol solution of citric acid in water such that acid moles outnumber iron moles by approximately 10 to 1;
-preliminary application of heat at 60...70 °C approx until the precipitate is totally dissolved;
-addition of a carbonate of barium and/or strontium in stoichiometric proportion determined by the stoi-chiometry of the end-product;
-addition of carbonate of cobalt in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of titanium trichloride in stoichiometric proportion determined by the stoichiometry of the end-product;
-addition of hydrogen peroxide;
-a first application of heat at below 100 °C by means of which to eliminate excess hydrogen peroxide and carbon dioxide produced by decomposition of carbon-ates;
-addition of ethylene glycol in a proportion of 10%
by volume (approx) of the solution with the resultant formation of organic macromolecules having chemically bonded inorganic ions;
-a second application of heat to bring about total dehydration and resultant formation of a solidified mass possessing the same cationic composition and the same chemical uniformity as the original solution;
-a third application of heat at between 400...450 °C, bringing about total elimination of the organic part of the solidified mass, so as to leave an inorganic residue;
-grinding of the inorganic residue; and -a final application of heat by means of which to in-duce crystallization of the hexaferrite.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000495813A CA1252995A (en) | 1985-11-20 | 1985-11-20 | Method for the preparation of fine hexagonal ferrite powders, in particular, for magnetic recording |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000495813A CA1252995A (en) | 1985-11-20 | 1985-11-20 | Method for the preparation of fine hexagonal ferrite powders, in particular, for magnetic recording |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1252995A true CA1252995A (en) | 1989-04-25 |
Family
ID=4131925
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000495813A Expired CA1252995A (en) | 1985-11-20 | 1985-11-20 | Method for the preparation of fine hexagonal ferrite powders, in particular, for magnetic recording |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1252995A (en) |
-
1985
- 1985-11-20 CA CA000495813A patent/CA1252995A/en not_active Expired
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