DE1300861B - Process for the production of ferromagnetic iron oxides - Google Patents

Description

The invention relates to a method for producing strongly ferromagnetic Iron oxide powder, which is excellent as a recording material in magnetogram carriers Ensure qualities of recording and playback as they are to the same extent cannot be achieved by the ferromagnetic iron oxides used up to now.

The known ferromagnetic ones used for magnetogram carriers Iron oxides are ferro-ferric oxide (magnetite) and y-iron (III) oxide. The y-iron (III) oxide can be produced by oxidation of iron (II) salt solutions by either works in the presence of complexing agents, with air and sodium iodate as the oxidizing agent or sodium nitrite, or slowly oxidized with air.

You can produce y-ferric oxide in another way by using magnetite oxidized, obtained by reduction of crystallized «- or γ-iron hydroxides will. In this process, the γ-iron (III) oxide is obtained in fine needles.

Those made using said acicular iron oxides Magnetogram carriers are quite suitable for many purposes. In several ways but do they still have defects. High requirements for recording and playback of picture and sound with very high frequencies they are not sufficient. With recording signals with high frequencies of 10,000 Hz and above there is a sudden drop in the output signal values ascertain.

Accordingly, the aim of the invention is to remedy these disadvantages. the The invention is therefore directed to providing ferromagnetic iron oxides which When recording frequencies up to 10,000 Hz and above, the output values remain the same that almost correspond linearly to the output values and usable output signals deliver over a total frequency range up to about 20,000 Hz.

The invention thus relates to a process in which the precipitates precipitated from an iron (II) salt solution are oxidized with alkali and the y-iron (III) oxide monohydrate thus obtained is then subjected to a reduction or a reduction with subsequent renewed oxidation and that is characterized in that the y-iron (III) oxide monohydrate obtained by the precipitation and subsequent oxidation is initially carried out by an oxidation in the presence of metallic iron and zinc chloride, zinc sulfate, sodium chloride or ammonium chloride as an inhibitor in particles with flake form of a max . Length of 2 [,, a length-to-width ratio of about 5: 1 to 10: 1, a width-to-thickness ratio of about 3: 1 to 5: 1.

Ferro-ferric oxide and that are obtained as products of the process y-ferric oxide in flake form with the dimensions of the particles of the Have starting material that can be compared to the known measures of reduction or Subjects to reduction and oxidation.

Justify the shape and dimensions of the particles of the process products the superiority over the known, previously used oxides, their particles are needle-shaped, as will be explained in detail.

An essential measure of the method of the invention for avoidance needle-shaped modifications is the use of inhibitors, such as zinc chloride, Zinc sulfate, sodium chloride or ammonium chloride. The further measures of felling, Oxidation and reduction are known per se.

It is also noteworthy that what was gained in the course of the proceedings y-iron (III) oxide monohydrate or its anhydride is ferromagnetic from the start. They have a relatively high coercive force, but a low remanence. If a solid sample of dry material is magnetized symmetrically and cyclically a maximum field strength or an Hm value of 1000 Oersted and calculation of the transverse area value of the oxide of the samples to determine the value of the remanence in Gauss, so obtained a value for the coercive force between 250 and 300 oersted and a value for the remanence between about 5 and 20 Gauss.

The iron oxides produced by the process of the invention, however show extraordinarily high values of magnetic induction when you put them in magnetized the same way.

If ferro-ferric oxides are used with the highest field strengths or in terms of measurements applicable Hm values result from varying the reduction conditions Coercive force values ranging from 250 oersted to near 600 oersted, and in their preferred forms, ie those with an FeO content of 25 to 31% the remanence values at 1500 up to 2500 Gauss.

The ratios are similar for y-iron (III) oxide, that of varying of the reduction and reoxidation conditions values of the coercive force from 200 to 450 Oersted and remanence values from 1200 to 2500 Gauss.

The outstanding value of the new oxides is based on performance properties, which are surprising and superior and which they transfer to their magnetogram carriers.

The output values are in an actual linear relationship to the input values in the entire frequency range. All over the frequency up to 20,000 per second and above, this results in usable output values.

In addition, the new magnetogram carriers are characterized by a extremely low noise level and a large dynamic range. Circumstances that make it possible to reproduce signals obtained using conventional; Magnetogram carriers produced by means of known, strongly ferromagnetic iron oxides would be drowned out by the clinging noises.

These excellent performance qualities are due to the special shape and the anisotropy of the small oxide particles, as they are according to the invention for use with magnetogram carriers.

Thanks to this performance, the oxides and magnetogram carriers according to the invention are especially valuable in all those cases where life-like magnetic recordings are required to make and reproduce impulses, the frequency and intensity of which fluctuates, such as B. when recording and playing back television broadcasts from orchestral Music and the like

The following example illustrates the invention. Manufacturing of the lamellar γ-iron (III) oxide monohydrate 28.6 kg of iron (II) chloride become placed in a stirred tank and dissolved in a sufficient amount of water, what gives a volume of 13251. The temperature of the solution is brought to 26.7 ° C. Then a dilute solution of sodium hydroxide is applied for 5 minutes under constant Stirring added to the tank contents. The added sodium hydroxide solution contains 12.7 kg NaOH, at a concentration of 60 to 120 g NaOH per liter. One then lets about 1 hour of air through the tank contents at a speed of 0.57 m3 / min. flow, wherein the initially formed iron (II) precipitate is oxidized. Here it changes its color from dark blue to green, to then a brownish-yellow or take on yellowish brown color. Once the color has turned yellowish brown, diminishes you set the air flow to about 0.28 m3 / min. and then also use the Air supply continued for 1 hour or a little more. Then is the manufacture of the seed material completed.

The seed material obtained and 100 kg of iron (II) chloride in aqueous Solution - concentration about 240 g / 1 - are combined with 16 kg of zinc chloride in aqueous solution Solution - concentration about 360 g / 1-now introduced into a reaction vessel, in which is scrap iron in excess. Then a sufficient amount of water added, bringing the reaction slurry to a volume of about 4731 liters. Then it will be the contents of the reactor are stirred, the suspended solid particles grow and oxidize during a longer reaction time, with about 2.27 M3 / min. Air through the To be blown porridge. The temperature in the reaction space is brought to about 60 ° C and at this level for the duration of this reaction section, which is about 24 to 48 Hours is held.

After the reaction has taken place, the pulp is removed and the finely divided crystallized material washed free of soluble salts, either by decanting or filtering with washing the precipitate. The washed Material is finally dried.

The particles of the product obtained in this way appear under the electron microscope transparent.

Manufacture of flaky ferro-ferric oxide and γ-iron (III) oxide After a starting material has been prepared that has the necessary, flaky Has the shape of the particles, this material becomes through a reduction process or through a reduction and subsequent reoxidation process into strongly ferromagnetic ones Iron oxides transferred with the same particle shape. The procedure is known.

The lamellar particles become through the reduction process of the y-iron (III) oxide monohydrate or its anhydride, converted into ferro-ferric oxide or in a mixture of ferro-ferric oxide and γ-iron (III) oxide, with the help of a reducing agent such as hydrogen or carbon monoxide and with accordingly high temperatures, whereby the originally orthorhombic crystal structure itself converts into a spinel structure. In the case of renewed oxidation (reoxidation) in the particles the ferro-ferric oxide in y-iron (III) oxide under the influence of one Oxidizing agent, e.g. B. air, and transferred at appropriate elevated temperatures. The spinel structure is retained.

Suitable reduction and oxidation processes are described in the literature described. (For example, U.S. Bureau of Mines Bulletin, No. 425 [1941], p. 123 to 136 and 264.) The ferro-ferric oxide according to the invention can, for. B. on the following Ways to be produced: The dried γ-ferric oxide - production as above described - is in a rotary kiln to a temperature between 316 and 538 ° C heated and hydrogen introduced, which with the powdery material, when prevailing a certain temperature, reacts until the iron (II) content is about 23% has increased. The resulting particles of ferro-ferric oxide are made from the Rotary tube discharged by means of a water-cooled screw conveyor and here under Cooled with exclusion of atmospheric oxygen.

The ferro-ferric oxide obtained in this way shows the following values with a magnetization with a maximum field strength or an H "value of 1000 Oersted, as already mentioned above: Coercive force 350 to 450 Oersted; remanence about 1900 Gauss Reduction conditions, the values fluctuate with a coercive force between 250 and 600 Oersteds, the remanence values between 1500 and 2500 Gauss.

The γ-ferric oxide according to the invention can be prepared as follows are: The ferro-ferric oxide obtained as described is in a rotary kiln reheated and oxidized in the process. The brought in goods move through continuously the rotary tube and is in its front part to a temperature of about 174 to 230 ° C, in the rear part from which the reaction product is removed heated to a temperature of about 230 to 285 ° C. Air is used for the oxidation. It is supplied in an amount of about 0.17 m3 / kg treated ferro-ferric oxide. The oxidation product leaves the rotary kiln through a water-cooled screw conveyor tube.

The y-iron (III) oxide obtained in this way shows values of the coercive force from 325 to 375 Oersted and remanence values of about 18,000 Gauss after magnetization under max. field strength or an H "value of 1000 Oersted. If the oxidation conditions are changed, so the values for the coercive force can be between 200 and 450 oersteds and for the remanence fluctuates between 1200 and 2500 Gauss.

Magnetogram carriers of the highest performance are obtained by using y-iron (III) oxide or the ferro-ferric oxide as a magnetically acting powder in the layer coatings or in the bodies of tapes, strips, plates, drums, or other shapes used by magnetic recording media.

Valuable magnetic tapes that contain one of the two oxides can be produced as follows: The following ingredients are mixed and placed in a ball mill: Parts by weight Strongly ferromagnetic iron oxide. . 840 Methyl abietic acid maleic acid glycol ester .... . .. ......... .. ... 60 Vinyl copolymer (13% vinyl acetate-87% vinyl chloride) ...... 120 Plasticizers (a linear, high molecular weight Polyester resin of a dibasic Acid with a divalent ali- phatic alcohol). . . ... . . . . . . 60 Methyl isobutyl ketone ............. 500 Toluene .......................... 300 This mixture is milled in a ball mill for 20 hours or more until the mill mass exhibits a fineness of 6.5 Hegman and a viscosity of approximately 83 Krebs units. This mass is then additionally mixed with 200 parts by weight of toluene and applied by a known method as a thin coating to a cellulose acetate tape in the form of 20 to 30 cm wide strips. The thickness of the coating is, for example, 1.39 mm, but will usually vary between 0.76 and 1.52 mm. The tape, the coating layer of which is still wet, is then passed through a magnetic field by a known method in order to orient the particles. The tape is then dried, pressed and hardened, finally cut into narrow strips and wound onto rolls or spools under slight tension.

Magnetic tapes made in the manner described above using of the products made by the process of the invention were made using a magnetic tape testing machine and all auxiliary testing devices necessary for such testing purposes, subjected to a detailed examination. They were made with other high performance general purpose tapes compared, whose coatings were of the same thickness - 1.39 mm - but which were ferro-ferric oxide or y-iron (III) oxide, the particles of which were needle-shaped. This for comparison known tapes used are hereinafter referred to as "standard" tapes.

The new tapes and the so-called "standard" tapes became one with each other compared, in terms of their frequency response, sharpness, strength and Uniformity of reproduction; furthermore with regard to their ratio of useful to noise level, signal to DC noise and saturated signal to noise, likewise on their greatest bias.

The new tapes were outstanding in the sharpness of their reproduction over an extended frequency range. The same applies to the ratio of the useful level too noise level at high frequencies. In all other exams, the new ones cut Ribbons in comparison to the so-called "standard" ribbons.

The values when comparing the frequency response are listed in the following table: Frequency reproduction Frequency (Hz) 100 I 400 1000 1 5000 f 10000 15000 Output loss (db) New y-ferric oxide ............. -2.5 -2.5 -2.5 -1.6 -3.5 -7.5 "Default" y-ferric oxide ............. -3.5 -3.5 -3.8 -6.0 -10.5 -19.0 New Ferro-ferric oxide ............. -3.5 -3.5 -3.5 -2.5 -4.0 -8.0 "Default" Ferro-ferric oxide ............., 5 -1.8 -2.0 -5.4 -12.0 -20.0 The frequency reproduction of the y-iron (III) oxide tape according to the invention, specifically for the frequency range from 0 to 20,000 Hz, is shown in the diagram (semi-logarithmic scale).

From the diagram and the table above it can be seen that the Signal reproduction curve of the new y-ferric oxide at frequencies up to over 11,000 Hz is essentially linear and that this band extends over the entire frequency range has usable output values up to about 20,000 Hz.

(Deviations in the curve of 1 db upwards or downwards are meaningless.) The reproduction values for tapes with the ferro-ferric oxide according to the invention are very similar, albeit the output values at a frequency of around 10,000 Hz fall off.

The table also shows that each of the "standard" bands the "signal output" begins to drop at 1000 Hz and quite significantly at 5000 Hz has fallen off.

The advantages of the magnetogram carriers, in the manufacture of which the ferromagnetic oxides are used according to the method of the invention, can be summarized as follows: a) The signal reproduction of the magnetogram carriers reaches significantly higher output values at high frequencies. b) Since the magnetogram carriers still provide usable output signals at high frequencies between 10,000 and 20,000 Hz, they can still be used effectively where very high fidelity of the sound is required and where only high frequencies are recorded, as is the case with television recordings the case is.

c) Due to their high output level and other advantages, can the magnetogram carriers operate at lower speeds than before known magnetogram carriers with the same playback performance. A fact that magnetic tapes in special cases, e.g. B. for television programs of particular Meaning is. As a result of low belt speeds, the signs of wear are lower on the recording, playback and erasing heads of the equipment. Likewise are the synchronization errors (pitch fluctuations, the flickering) and distortions, the one Consequences of the mechanical movement of the belt are reduced.

d) The lamellar individual particles of the new oxides are very uniform in their size and free from any tendency to form lumps. It doesn't prepare Difficulty in applying these particles in high concentration in the binder on the tape, to distribute and then to orientate. These properties enlarge the magnetic capacity and increase the quality of the reproduction of the Magnetogram carrier. The greater packing density and increased magnetic induction the magnetogram carrier is obviously due to the layering and sheet position of the thin, lamellar oxide particles.

e) The frequency reproduction of the new oxides is with magnetogram carriers so evenly across the entire frequency range that the Reduced need to compensate for irregularities in playback at various points in the sound spectrum, compensating electronic parts and Having to build circles into the recording and playback devices.

f) The magnetogram carrier with the oxides according to the invention can used in cases where conventional ones fail. Because the Reproduction of the "standard" and other known magnetogram carriers at 10,000 Hz deteriorates significantly, especially at low running speed, so may it when recording signals with a frequency of z. B. 15,000 Hz are added, that there is no perceptible reproduction. The decrease energy of known magnetogram carriers can be so weak at frequencies that are in this range that they are below the noise level of the magnetogram carriers and the playback devices lie. In such cases these magnetogram carriers are worthless. In contrast to show the magnetogram carriers according to the present invention significantly higher acceptance rates, have lower noise levels at frequencies up to at least 20,000 Hz. This results in greater adaptability and a larger area of application the carrier.

g) Magnetic tapes with oxides of the invention can be used without rendering is impaired or suffers, coated with significantly thinner oxide coatings than before. This fact is of particular importance in television programs, where linear belt speeds of 200 to 500 cm / sec. prevail as they are a Makes downsizing of the coils possible. It also makes the production softer Belts with an oxide binder layer possible with very little wear.

Thin coating layers are also cheaper to manufacture, because less material is required for this.

h) Magnetogram carriers according to the invention are in terms of distortion and noise level superior to other magnetogram carriers. The leaflets are shaped Oxide particles that are used are highly uniform in shape and size. They give dispersion coatings that are very uniform, very thin Have a noise level and the magnetogram carriers have softer, even work surfaces make possible. Because the induction of high-frequency signals on the magnetogram carriers by means of skin or surface effects, is achieved through very smooth surfaces a distortion of the signals avoided.

i) The lamellar oxide particles are in the magnetogram carriers stored so favorably that the broad particle sides are exposed to the magnetic fields of the magnetic head are exposed, whereby a high induction is achieved. The coercive force is - under normal working conditions - in these oxides in such a way that those in the material induced magnetization can be satisfactorily quenched.

Claims (1)

Claim: Process for the production of ferromagnetic iron oxides for use in magnetogram carriers, in which the precipitates precipitated from an iron (II) salt solution are oxidized with alkali and the y-iron (III) oxide monohydrate obtained is then subjected to a reduction or reduction is subjected to subsequent renewed oxidation. characterized in that the y-iron (III) oxide monohydrate obtained by the precipitation and subsequent oxidation is initially obtained by oxidation in the presence of metallic iron and zinc chloride, zinc sulfate, sodium chloride or ammonium chloride as an inhibitor in flake-form particles with a maximum length of 2 #t, a length-to-width ratio of about 5: 1 to 10: 1, a width-to-thickness ratio of about 3: 1 to 5: 1.