DD209353A3 - METHOD FOR THE PRODUCTION OF FERRIMAGNETIC NEEDLE-FORMED COBALT MODIFIED BERTHOLLIDIC IRON OXIDE - Google Patents

Abstract

The invention relates to a process for the production of ferrimagnetic needled cobalt-modified berthollidic iron oxides for use in high-coercive and high-energy magnetogram carriers. It is intended by the invention that ferro-magnetic needle-shaped cobalt-modified berthollidic iron oxides can be produced with high coercive force. This is accomplished by dispersing the magnetic iron &&& oxide in water, then adding an aqueous solution of cobalt salt with vigorous stirring, and, optionally with heating, by adding an aqueous alkaline solution whose amount has an OH / Co ratio of 2.0 to 2.5: 1, a heavy soluble cobalt compound is precipitated on the iron &&& oxide. After washing and drying the pigment is partially reduced with an organic reducing agent zurberthollidischen iron oxide.

Description

Field of application of the invention

The invention relates to a method for producing ferrimagnetic needle-shaped cobalt-modified berthollidic iron oxides for use in highly-cooktop and high-energy magnetogram carriers.

Characteristic of the known technical solutions

The continuous improvement of magnetic recording processes places ever higher demands on the magnetic properties of the pigments used. The trimeric ferrimagnetic needle-shaped iron oxides no longer meet the requirements in all fields of application. Modification of such iron oxides with cobalt ions can, in particular, affect the coercive force increase·

In general, two basic processes for cobalt modification are known. The aging process is based on the coprecipitation of the iron (II) and cobalt ions in a strongly alkaline solution with subsequent oxidation to the cobalt-containing goethite, the dehydration, reduction and reoxidation compartment gives a cobalt-containing V "-Fe ₂ O ,. This Yerfahren is characterized in more detail for example in DE OS 2305153, but the advantageous increase of the coercive force is as (. "-. disadvantage of a strong Yerschlechterung the pressure and temperature" ~ "turstabilität the magnetic properties over * This means that fall off by heating the pigment or the magnetic recording medium, for example, 100 ⁰ C, the coercive force and the residual saturation magnetization significantly. with the application of pressure, a similar effect can be observed "Da3 Heist so that Magnetοgrammträger is demagnetized slowly by heating or applying pressure * The second experience d the primary use today is based on the precipitation of cobalt hydroxide on a carrier

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crystallite in an alkaline aqueous dispersion, the cobalt hydroxide can be deposited on goethite, lepidocrocite, hematite, magnetite, berthollide or maghemite · If further processing is necessary, it takes place in the known stages reduction / reoxidation to cobalthaltigen maghemite,

The temperature and pressure stability of the magnetic properties of such cobalt-modified iron oxides is significantly improved compared to those prepared by the co-precipitation process. The achievable coercivity increase is generally dependent on the amount of cobalt used. "As the cobalt content increases, not only is the coercive force but also the temperature stable, and the cobalt content must therefore be kept as low as possible. Berthollides are iron oxides of an unstoichiometric composition. "Generally, they are described by the formula FeO, where χ can be between 1.33 and 1.5. Thus, it corresponds to

Fe, 0th the formula FeO. ,., and -y ** - Fe ₀ O -, 'of the formula FeO ₁ , - · 3 4 1 j33 ~ <> 2 3. 1 ) D

The cobalt modification takes place either on Fe 1 O 2, which is then partially reoxidized (DE OS 2 639 250), or directly on Berthollid (DE OS 2 413 430), another variant. is the cobalt modification of -Jf -Fe ^ O, with subsequent partial reduction (W? 150 190) ·

In the cases mentioned above, the pigment to be treated is slurried in water and admixed with a cobalt saline solution and an aqueous alkali metal hydroxide or ammonia solution. A significant excess of hydroxy ions is used so that OH / Co ratios y are 5: 1, usually It is emphasized in DE OS 2 829 344 that homogeneous cobalt precipitation is only possible if the hydroxyl ion concentration is 2.sup.-3 mol / l, which corresponds to an OH / Co ratio of 25.degree ; 1 »If a lower hydroxyl ion concentration is chosen,

, η λ - ... Γ! ^ R ^ Vi ¹ J '*'

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3o no improvement of the coercive force, based on the deposited amount of Cobauverbindung occur * The achievement of a high coercive force would thus only by increasing.The cobalt content possible. In a further process for cobalt modification, the use of precipitants is completely dispensed with (DE OS 2 022 013) "For this purpose, the pigment is merely moistened with water and treated with a cobalt salt which decomposes into metallic cobalt or cobalt oxide at temperatures below 600 ^° C." Thereafter, the paste is dried and crushed. Finally, the cobalt salt-coated iron oxide is thermally treated to convert it to a cobalt-modified iron oxide. j lead.

Object of the invention

The object of the invention is the preparation of a ferrimagnetic acicular cobalt-modified berthollidic iron oxide having a high coercive force and a reduced cobalt content,

Explanation of the essence of the invention

It is the object of the invention to produce ferrimagnetic acicular cobalt-modified berthollidic iron oxides with high coercive force *

Surprisingly ferromagnetic acicular cobalt-L / modified berthollidische iron oxides are obtained with a high coercive force when the 7 * "-Pe ₉ O dispersed in water, then mixed with an aqueous Cobaltsalzlcsung under intenivem stirring and optionally with heating, alkaline by adding an aqueous Solution whose amount corresponds to an OH / Co ratio of 2.0 to 2.5: 1, a sparingly soluble cobalt compound is precipitated on the ~ f ~ -Pe ₃ O ₃ .

The mixture is then filtered, optionally washed neutral and dried. "The dried and comminuted pigment is charged to a reactor and used to achieve a desired

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Iron II content necessary amount of reducing agent added. The reactor is then purged with oxygen-free nitrogen and heated to a temperature at which the pigment moved by suitable means in the reactor is uniformly coated with the reducing agent. Subsequently, the mixture is heated to the reduction temperature and kept at this temperature for a certain time. After cooling the pigment in a stream of nitrogen, the ferromagnetic acicular cobalt-modified berthollidic iron oxide can be used for the preparation of magnetogram carriers.

Gobalt sulfate or cobalt chloride can be used. The amount of gobalt salt to be used is calculated so that the corresponding ferromagnetic acicular cobalt-modified berthollidic iron oxide contains 0.5 to 7% by weight of cobalt, preferably 1 to 5% by weight.

Hatrium hydroxide or potassium hydroxide can be used as the alkali metal hydroxides. 5 and 2.5 moles of alkali metal hydroxide * per liter, preferably 0.8 to 1.5 moles of alkali metal hydroxide per liter. The pigment concentration in the dispersion is up to 30

The precipitation temperature is between 20 ⁰ C and 100 ⁰ G * varied, the distribution of the reducing agent to the pigment is preferably carried out at temperatures between 50 and 100 C for 20 to 120 minutes.

The amount of reducing agent is calculated so that an iron (II) content of between 1.5 and 20% by weight, based on the amount of iron oxide _3, results. "These are preferably 0.2 to 2.5% by weight of reducing agent, based on the magnetic pigment used The reducing agents used are preferably aliphatic monocarboxylic acids having from 3 to 20 carbon atoms

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290 to 3βΟ ⁰ C, preferably at 300 to 320 ⁰ C performed. This temperature is maintained for 10 to 120 minutes, preferably 20 to 60 minutes. The resulting ferrimagnetic acicular cobalt-modified berthollidic iron oxides of the invention are characterized by high coercive force values at comparatively low cobalt contents. Compared to the known processes with a high OH / Oo ratio or "the process" without precipitant, the values of the coercive force are decidedly higher. Thus, the cobalt content necessary to achieve certain coercive forces can be reduced. This inevitably results in a reduction in the temperature instability of the magnetic properties, since this increases with increasing cobalt content *

Another advantage of the method is due to the fact that the washing process, in which both the alkali and the sulfate or chloride ions are removed, can be significantly shortened. The method according to the invention is explained in more detail in the following exemplary embodiments.

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Embodiment 1

In a stirred tank, 3.4 l of deionized water are introduced, in which 1000 g of T * ~ Fe ₂ O, (particle length 0.35 / μm, length / width ratio 10: 1, coercive force 300 A cm) are distributed by intensive stirring Then a cobalt sulfate solution consisting of 143 g of GoSO, _β 7 HoO and 450 ml of deionized water, slowly mixed with stirring with the dispersion. At a temperature of 25 ⁰ C, an alkaline solution of 44.3 g UaOH and 1300 ml of deionized water is added, wherein the cobalt ions are precipitated as cobalt hydroxide ·

Finally, the pigment is filtered off with suction, washed neutral and dried at 70.degree. C. The dry pigment is ground and added to the reduction reactor. 20 g of stearic acid as reducing agent are added. The rotating reactor is then stirred for 10 minutes with a nitrogen flow of 100 l / h. rinsed, wherein the nitrogen of the residual oxygen has been removed in advance, after the flushing operation, the reactor is heated to 75 ⁰ C and left for 60 minutes at this temperature, in order to distribute the reducing agent on the pigment · Only then the reactor to a product temperature of 310 ⁰ is C heated to perform the partial reduction, after 40 minutes reduction period, the pigment is cooled in a stream of nitrogen. The resulting pigment contains 3.05% by weight of cobalt and 13.74% by weight of iron-II, based on the iron oxide. The adjusted OH / Co ratio was 2.2: 1. The following magnetic values were measured on the sample magnetometer at a measurement field intensity of 4000 A cm: coercive field strength (A cm ^-1 ) 738 saturation magnetization (s10 Ysmg) 1021 remanent saturated magnetization (xiO 7smg) 520

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Embodiment 2

The cobalt modification was carried out in accordance with Example 1, only the amount of reducing agent reduced from 20 g to 5 g. The resulting pigment contains 3.02% by weight of cobalt and 3.92% by weight of iron-IT, based on the iron oxide , The adjusted OH / Co ratio was 2.2: 1, The following magnetic values were measured on the sample vibration magnetometer at a measuring field strength of 4000 A cm: Coercive field strength (A cm) 5βΟ Saturation magnetization (x10 Ysmg) 992 Remanent saturation magnetization (x10 Vsmg) 585

Embodiment 3 (Comparative Example)

In a stirred vessel, 3.4 l of deionized water are introduced, in which 1000 g of γ- Fe ₂ O- (0.15 μm / lane length, length / width ratio 10: 1, coercive force 300 A cm) are obtained by intensive Stirring be distributed. Then, a cobalt sulfate solution consisting of 143 g CoSO ₁ · 7 HPO and 450 ml of deionized water slowly while stirring, with the dispersion.

At a temperature of 25 ^"0 C an alkaline solution of 618 g Haoh and 1300 ml of deionized water is added, the Cobaitionen are precipitated as Cobalthydrosid. Finally, the pigment is filtered off with suction, washed neutral and dried at 70 ⁰ C. The dried pigment is milled and, in the reduction reactor. There are also 20 g of stearic acid as a reducing agent, the rotating reactor is then rinsed for 10 minutes with a nitrogen stream of 100 1 / hour, wherein the nitrogen before the rest deoxygenated * JTach the flushing operation, the reactor 75 ⁰ C. and leave at this temperature for SO minutes to disperse the reductant on the pigment. »Only then does the reactor rise

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a product temperature of 310 ⁰ C heated to perform the partial reduction, Hach 40 minutes reduction period, the pigment is cooled in a nitrogen stream.

The resulting pigment contains 3.11% by weight of cobalt and 13.52% of iron, based on iron oxide. The adjusted OH / Co ratio was 30: 1, whereby an alkali content of 3 mol / l was present in the dispersion,

The following magnetic values were measured on the sample vibration magnetometer at a measuring field strength of 4000 A cm:

Coercive field strength (A cm " ¹ ) 575

-10 -1

Saturation magnetization (z10 Ysmg) 969 remanent saturation magnetization (x10 "7smg") 489

Embodiment 4 (Comparative Example)

1000 g of JT '-ββρΟ, (particle length 0.35 / μm, length / width ratio 10: 1, coercive force 300 A cm ") are mixed with a cobalt nitrate solution consisting of 143 g of Co (ITO ₂ ) 6H ₂ O and 900 ml of deionized water, triturated to a paste. the paste was dried in an oven at 100 ⁰ C. the dried mass is pulverized and for 60 minutes at 350 ⁰ C thermally treated to convert the cobalt nitrate to cobalt oxides *

After cooling, the pigment with 20 g, stearic acid is added as a reducing agent, The rotating reactor is then 10 minutes with a nitrogen flow of 100 1 / hr, purged, with the nitrogen before the residual oxygen was withdrawn, After flushing the reactor to 75 ⁰ C and 60 minutes left at this temperature to distribute the reducing agent on the pigment, Only then the reactor is heated to a product temperature of 310, ⁰ C to perform the partial reduction, compartment 40 minutes reduction period, the pigment is cooled in a nitrogen stream The resulting pigment contains 2.91 g of cobalt and 13.91% by weight of iron-II, based on the iron oxide

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Measure the sample vibration magnetometer at a measurement field strength of 4000 A cm: Coercive field strength (A cm " ¹ ) 562 Saturation magnetization (s1Q Vsing) 1034 Remanent saturation magnetization (SLO" Vsmg "" 485

Claims (4)

239129 7 In trodu ction s 1. "Process" for producing ferrimagnetic acicular cobalt-modified berthollidischer iron oxides from -V ~ -PepO-5 with subsequent partial reduction, characterized in that the precipitation of the cobalt hydroxide on the J ¹ ^ -Fe ₂ O, with a QH / Co ratio from 2.0 to 2.5: 1. 2. A process for the preparation of ferrimagnetic acicular cobalt-modified berthollidischer iron oxides according to item 1, characterized in that the precipitant used is the aqueous solution of the hydroxides of the sodium or potassium ,. 3 «method for producing ferrimagnetic acicular cobalt-modified berthollidischer iron oxides according to item 1, characterized in that the cobalt content of the iron oxide 0.5 to 7% by weight, preferably 1 to 5 GewfS, •, '-. 4 «Process for the preparation of ferrimagnetic acicular cobalt-modified berthollidischer iron oxides according to item 1 and 3, characterized in that are used as cobalt salts Cobaltsu \ Lfat or gobalt chloride.