CS208690B2 - Method of making the magnetic gama of the iron trioxide - Google Patents

Description

The present invention relates to a process for the production of magnetic gamma iron oxide.

Various processes have already been described for the preparation of the magnetic gamma iron oxide used for the production of magnetic tapes and recording members. U.S. Pat. No. 3,015,627 discloses the preparation of magnetic iron oxides from synthetic magnetic gamma monohydrate by reduction and oxidation to give platelet crystalline particles similar to ferric monohydrate particles and preferably having a length to width ratio of up to 10: 1, a width to thickness ratio at least 3: 1 and a length of up to about 5 microns.

Although the recording elements containing these magnetic iron oxides have been satisfactorily proven in many respects, they do not receive various characteristics, which circumstance contributes to their insufficient or limited function in some fields.

The purpose of the invention is to overcome the above disadvantages.

The invention consists in mixing the ferrous chloride with an aqueous solution of the base, wherein the concentration of the ferrous chloride is 29.95 grams to 59.9 grams per liter, the mixture is vigorously stirred while introducing the oxygen-containing gas until the pH of the mixture is between 2.9 and 4.1, and the resulting suspension of synthetic aqueous gamma ferric oxide is maintained at 26.7 to 60.0 ° C and at a pH of between 2.9 and 4.1 while stirring continuously, continuously and continuously. introducing the base and the oxygen-containing gas until 1.2 to 5 parts by weight of synthetic aqueous gamma iron oxide are formed per part by weight of the feed suspension, the aqueous gamma iron oxide is reduced by hydrogen at a temperature of 315.5 to 428 ° C, and the exhaust is reduced with air Oxygen to magnetic gamma oxide jelly208690

According to a preferred embodiment of the invention, metal iron is introduced into the feed suspension before the addition of the base.

According to another embodiment of the invention, the base is selected from the group consisting of sodium hydroxide, ammonium hydroxide or calcium hydroxide.

According to another embodiment of the invention, the aqueous gamma iron oxide particles are coated with at least one hydrophobic aliphatic monocarboxylic acid having 12 to 15 carbon atoms prior to reduction and oxidation.

According to the invention, considerable improvements have been observed in the function of magnetic pulse recording members, in particular in the form of tapes, but these may take the form of strips, discs, cards, cylinders, cinematographic films, electronic computer components and remote measurement accessories.

The unique properties of the synthetic aqueous gamma ferric oxide produced according to the invention result in excellent performance characteristics being achieved with the recording members containing the ferric oxide.

Synthetic aqueous gamma iron oxide, which according to the invention has very fine-grained needle-like crystalline particles, of which at least 70% have a length to width ratio greater than 0: 1 and a length of up to about 2 microns, is prepared according to the invention colloidal feed suspension of aqueous gamma ferric oxide.

It should be noted that a novel process can even produce aqueous gamma iron oxide having a length to width ratio of from 20: 1 to 50: 1. The ferrous chloride is mixed with an aqueous base solution to form precipitated ferrous hydroxide, which is then oxidized with vigorous stirring to form precipitated colloidal hydrated ferric oxide.

Oxygenation is achieved by introducing the oxygen-containing gas into the slurry until the pH is 2.9 to 4.1 (which usually occurs after 1/2 to 2 hours). Although ferrous chloride is used herein, this does not mean that the use of other iron salts (for example, ferrous sulfate or ferrous nitrate) is excluded.

The aqueous base solution used is preferably NaOH, NH 4 OH or Ca (OH) g. The concentration of ferrous chloride should be 30 to 50 grams per liter before the precipitation of ferrous hydroxide. The ferrous chloride may be added to the aqueous base solution or vice versa.

Typically, 90.7 g to 453.6 g NaOH per 3.79 liters, or 24 to 120 g NaOH per liter, or an equivalent amount of other bases may be used. Instead of NH4OH, ammonia gas can be used by contacting the aqueous ferrous chloride solution vigorously with a gaseous mixture containing ammonia and oxygen.

Other bases can also be used, for example KOH, Ba (OH) ₂ , Mg (OH) ₂ , pyridine or aniline. Any oxygen-containing gas may be used for bubbling, which contributes to vigorous mixing of the suspension, preferably air or oxygen.

When the pH of the suspension reaches 2.9 to 4.1, and preferably 3.0 to 3.5, this means that a sufficient hatching suspension has been formed and that the actual step of forming aqueous gamma ferric oxide can be started to produce one part of the hatching the suspension formed from 1.2 to 5 parts and preferably about 2 parts of the total product.

The ratio of product to feed suspension is a critical parameter to be controlled, desirable fine particles with large length to width ratios are obtained using the slow growth ratios listed below. Previous processes have generally used greater than 6: 1 ratios of product to seed suspension resulting in smaller particle length to width ratios.

At the end of the formation of the feed suspension, the temperature generally rises above 26.7 ° C, and at an initial concentration of 30 to 60 g of ferrous chloride per liter, there is usually a sufficient excess of ferrous chloride required to produce the desired synthetic aqueous solution in the next step. gamma iron oxide, which usually takes 5 to 50 hours.

Strict control of pH and temperature conditions is required to obtain the desired product. For example, at a pH of much less than 2.9, the precipitation of the ferric product is imperfect; at a pH well above 4.1, the desired crystalline shape changes.

Similarly, temperatures outside the stated temperature range of 26.7 to 60.0 ° C result in an undesirable product. Metallic iron can also be added in the actual production step, thereby eliminating the need to add a base since iron will create the necessary conditions for a basic reaction.

Formation of the product itself without the use of metallic iron can usually be achieved at a temperature of 26.7 to 48.8 ° C, while using metallic iron requires somewhat higher temperatures.

The amounts of air used and the duration of the reaction are not critical and depend primarily on the design of the reactor. However, vigorous agitation is required to form the seed suspension and the aqueous gamma ferric oxide product itself in order to obtain the desired properties of its particles.

Vigorous mixing ensures sufficient contact with the oxygen-containing gas, thereby promoting precipitation and the shape of the desired product. This can conveniently be accomplished by mechanically stirring and bubbling the oxygen-containing gas through the suspension; this does not preclude the use of other means leading to the same result and known to any person skilled in the art.

From the above-described synthetic aqueous gamma iron oxide Iza, to produce a synthetic magnetic gamma iron oxide exhibiting improved magnetic properties on the recording members.

For magnetic gamma iron particles, length to width ratios of 9: 1 to 20: 1 can be achieved, and the particles themselves can be described as very fine-grained needle-like crystalline particles having a length of up to 2 microns, similar to aqueous gamma iron particles.

The synthetic magnetic gamma iron oxide produced according to the invention has indeed higher particle length to width ratios than would have been possible with prior art processes.

The improved magnetic properties achieved are in direct association with the considerably improved properties of the aqueous gamma iron oxide. Synthetic magnetic gamma ferric oxide can be made from synthetic aqueous gamma ferric oxide by reducing the oxide at high temperature, typically 316 to 427 ° C, with hydrogen to ferric iron oxide, then oxygenating it with air, usually at 233 to 382 ° C. whereupon the product is mechanically thickened, usually in a wheel mixer or in a ball or roller mill, in order to improve its frequency characteristics, in particular the high-frequency characteristics when introduced into the recording members.

The densification is performed to reduce the degree of agglomeration of the particles that may occur during processing while maintaining the same particle size (i.e., virtually no adverse particle change occurs during densification).

An even more preferred method of forming a magnetic gamma ferric oxide from aqueous gamma ferric oxide is to deposit an organic surfactant coating on the aqueous gamma ferric oxide particles prior to reduction and oxidation.

The coating is preferably a monomolecular layer of particles consisting of at least one hydrophobic aliphatic monocarboxylic acid having from 1 to 15 carbon atoms. This coating prevents the particles from being processed in the agglomeration, since it neutralizes the surface active forces and leads to excellent magnetic orientation in the finished product.

The use of such a fatty acid coating makes the use of hydrogen in the treatment unnecessary due to the actual reducing action of the surfactant. The coating may be performed in a variety of ways with a variety of monocarboxylic acids as described in U.S. Pat. No. 3,498,748. Preferably, from about 1.6% to about 10% of coconut oil or lauric acid (alone or in admixture) is used which is rendered water-soluble or dispersible by the addition of 0.15 to 1.5% morpholine wherein the percentages are based on the weight of the aqueous gamma ferric oxide in suspension.

When using the above-described synthetic magnetic gamma ferric oxide in the magnetic pulse recording members, excellent performance characteristics are obtained with these members, in particular with magnetic strips.

The magnetic strip containing the magnetic gamma iron oxide thus produced can be produced by the following process:

The components listed in the table below are mixed in parts by weight and introduced into a ball mill.

magnetic gamma ferric oxide PegOj 840 glycol ester of methyl methacrylate and maleic acid 60 vinyl resin (copolymer, 13% wool acetate and 87% vinyl chloride) 120 plasticizer (linear high molecular weight polyester resin, prepared by reaction of dibasic acid with divalent aliphatic alcohol) 60 methylsulphonyl ketone , 5

This mixture was ground for 20 hours or more until the product had the required fineness and viscosity. The mass is then mixed with another 200 parts of toluene and applied to a cellulose acetate base in the form of a 20.3 to 30.5 cm wide strip according to the known method.

If the applied coating is still wet, it is guided through the magnetic field to orient the particles in a known manner, after which the strip is dried, calendered, compressed and smoothed and finally cut and energized onto rollers or coils with normal coating thickness between 50.8 to 152.4 micrometers, and in the present case is about 114.2 micrometers.

Magnetic tapes, the above-described oxide magnetic gamma železitý® have an orientation ratio of at least 2.4 and maguetické rectangular hysteresis loop having a value of Br / Bm at least 0.84 in an array (10® / 43O.Am ^_1. The magnetic strips have very good frequency characteristics especially high frequency characteristics. ^'J *

However, these values are not to be considered as limitations but as. to illustrate some improvements over the properties of the magnetic gamma-containing tapes of the prior art. ·

These known tapes usually have an orientation ratio of not more than 2.2 and values in Br / Bm around 0.83 in the field (10 ^{6 /} 4n).Am ^-1 , although higher ratios are sometimes reported. However, the magnetic properties of the tapes given to it by the iron oxide contained therein can eventually be altered by changing the particle size of the oxide by changing the working conditions (for example, the ratio of total hydrous gamma iron product to seed suspension, degree of mechanical magnetic gamma iron oxide, etc.).

For example, particles of smaller length lead to smaller Br / Bm values. By carefully controlling the production conditions of the aqueous gamma ferric oxide, the magnetic gamma ferric oxide, and the tape, even more pronounced magnetic performance characteristics can be obtained for the tape, namely Br / Bm values of about 0.91 and approximate ratios of about 5 or higher.

The invention will now be described by way of several exemplary embodiments, which are intended to illustrate and not to limit the invention.

Example,.

A. Preparation of synthetic aqueous gamma iron oxide.

In a 945 liter tank equipped with a mechanical stirrer and an air atomizer in the form of a perforated tube were placed 499 liters of tap water at 26.7 ° C and 87.5 liters of an aqueous solution containing 28.9 kg of ferrous chloride.

The mixture was diluted to 587 liters. With vigorous stirring, 129 liters of aqueous ammonia containing 14 liters of ammonium hydroxide (equivalent to 28.8% ammonia) are pumped in over 15 minutes. Stirring is continued, air is started and oxygenated to pH 3.3 within one hour to form a feed suspension of synthetic aqueous gamma iron oxide. The precipitation of the aqueous gamma ferric oxide is achieved by heating the feed suspension to 37.8 ° C, by adding an additional ammonia solution (197 liters containing 16.1 liters of the above 28.8% ammonium hydroxide) at a rate of 0.416 liters per minute or by injecting 0.01233 to 0.0142 m ³ / min of NH 4 gas while continuing aeration and stirring.

After 7 and 1/2 hours the precipitation was complete, 18.8 liters of ammonia solution or 4.31 kg NH4 was used, the feed volume was 917.5 liters and contained 20.1 kg of hydrous gamma ferric oxide monohydrate.

The final pH was 3.7. This represents a ratio of total aqueous gamma ferric oxide to the feed suspension of about 2: 1, based on the use of a total amount of 29.4 liters of a 28.8% ammonia solution divided by the amount of 28.8% ammonia solution used before heating the feed suspension to 37.8 ° C (15.6 liters).

Examination of the product by X-ray diffraction showed a composition of more than 99% of the ferric oxide gamma monohydrate known as lepidocrokite, and electron microscopy measurement showed needle-like crystals occurring in beams, with an average crystal length of about 2 microns and a length to width ratio of about 2: 1 to 50: 1 (for example, the particles had a length of 1 micron and a width of 0.02 micron). Comparison of the X-ray diffraction of the experimental product prepared by the above procedure with the standard X-ray diffraction pattern on conventional aqueous gamma oxide ferric, according to ASTM 8-96 in the ASTM diffraction label system, gave the following result:

Test product dA ° I / Io

ASTM 8-98 (watery gamma-phase)

6.28 100 ALIGN! 6.26 100 ALIGN! 3.30 92 3.29 90 2.48 75 2.47 80 2.36 15 Dec 2.36 20 May 2.10 20 May 2.09 20 May 1.94 65 1,937 70

Similar results are obtained when using pure gaseous oxygen instead of air and using NaOH or Ca (OH) g instead of NH4OH or NHy gas

B. Synthetic magnetic gamma iron oxide preparation

The surface treatment was carried out by heating the seed suspension of aqueous gamma iron oxide in the tank to 79.5 ° C, then adding a surface-treating mixture of 0.500 kg of coconut fatty acid and 90.8 g of morpholine in 15.14 with stirring. liter of hot water. Heating was continued at 87.8 ° C, the mixture was filtered and the filter cake was washed until the salt was removed.

The product is practically pure aqueous gamma iron oxide coated with approximately 2.5 wt. a fatty acid surfactant.

This material was reduced in either an intermittent furnace or a continuously operating furnace at 400 ° C in a hydrogen atmosphere to ferric oxide and then oxygenated in an air stream at 246 ° C to gamma iron oxide whose magnetic properties were improved by mechanical densification for a period of time. 1/2 hour in a wheel mixer.

The resulting finished oxide, tested magnetically in the field (10/4%) A m ^-1 as a dry powder, showed Hc 365, Br 2,040, Brn 3,470. Hc 362, Br 3,365, Brn 3,760 showed as dispersion in oil. As measured by electron microscopy, the dry iron oxide particles had an average length to width ratio of 9.3 to 1.0 and an average length of up to 2 microns.

A similar iron oxide product is obtained when surface treatment is discarded.

Example 2

In Example IA, the precipitating agent can be replaced with metallic iron to form aqueous gamma ferric oxide. To do this, for example:

Using the procedure described in Example 1, two identical 757 liter synthetic slurry preparations of synthetic aqueous gamma iron oxide are formed from ferrous chloride and ammonia. These batches were combined and fed to a 1,893 liter tank having an inner reservoir containing metallic iron and an aerator positioned below the iron and near the bottom of the tank.

The combined slurries are heated to 60 ° C and maintained at this temperature while oxidizing with air, causing iron to dissolve and precipitate ferric oxide hydrate. This aeration is continued for 36 hours when the aqueous gamma iron oxide in the batch reaches 34.1 kg. The synthetic aqueous gamma ferric oxide thus produced is similar to the product of Example 1A.

As in Example tB, the resulting feed slurry and the contained oxygen were surface treated, filtered, washed, dried, etc. by the procedure of Example 1B to give the final magnetic gamma iron oxide. Also by this process good magnetic properties were obtained.

For dry powder with the test given value of Hc 340, Br 1987, Bm 3500 and an oil dispersion of the received values Hc 363, Br 3365, Bm 3760 in the field of intensity (10V4XA m ^- '.

Example 3

A magnetic gamma ferric oxide was prepared as in Example 1, except that the reduction of the hydrous game of ferric oxide to ferric iron does not use a gaseous reducing agent as hydrogen.

The entire reduction is performed by coating the organic surfactant on the aqueous gamma iron oxide particles at the same oven temperature. This product also has good magnetic properties, as a dry powder of my Hc 303, Br 1 892, Bm 3 388 and as an oil dispersion of my Hc 325, Br 2 841, Bm 3 207.

Example 4

A 893 liter tank equipped with a stirrer and air atomizer is charged with 895 liters of 26.7 ° C warm water and 152 liters of an aqueous solution containing 59.1 kg of ferrous chloride.

With stirring, 303 liters of a solution containing 9.07 kg of NaOH were pumped in over 10 to 15 minutes. While stirring, the oxygenation is carried out by introducing 0.1413 m @ 2 per minute of air until the ferrous precipitate is oxidized to ferric shape. This will take about one hour.

Oxide precipitation is completed by heating the above-mentioned seed suspension to 51.7 ° C, stirring and aerating is continued, and another sodium hydroxide solution is continuously injected until the total product is 40.8 kg of oxide while controlling the addition of the base to the pH was maintained between 3.0 and 3.7. The resulting synthetic aqueous gamma ferric oxide is converted to the magnetic gamma ferric oxide of Example 18 by similar results.

Annex 5

To a 945 liter tank equipped with a stirrer and aerator containing 493 liters of water at 26.7 ° C was added 75.7 liters of an aqueous solution containing 29.03 kg of ferrous chloride.

With constant stirring, 152 liters of lime suspension containing 8.42 kg of Ca (OH) _{2 are} pumped in from 0 to 15 minutes. · Stirring is continued, oxygenation is started and continued for approximately 1 hour until the ferrous precipitate is completely converted to the ferric shape and pH will be about 3.5.

The precipitation of the synthetic aqueous gamma ferric oxide is completed by gradually adding an additional 152 liters of lime slurry over a period of about 8 hours while stirring, aerating at 57.3 ° C and maintaining the pH in the range of 3.0 to 3.7, by controlling the rate of addition of lime. The final flue gas of about 20.4 kg was processed to magnetic gamma iron oxide as described in Example 1 with similar results.

Example 6

A. Preparation of synthetic aqueous gamma iron oxide

Into a 4,550 liter tank equipped with a mechanical stirrer and air atomizer in the form of a perforated tube, 2,170 liters of 4.45 ° C tap water and 299 liters of an aqueous solution containing 117 kg of ferrous chloride are introduced.

With vigorous stirring, 59 liters of aqueous ammonia containing 65.9 liters of ammonium hydroxide (equal to 28.8% ammonia) are pumped in for 15 minutes. Stirring is continued while doing so. The temperature is raised to 30 ° C, the air is turned on and oxygenated to pH 3.8 in one hour and 15 minutes to form a seed suspension of synthetic aqueous gamma ferric oxide.

The precipitation of this oxide was completed by heating the hot seed suspension at 37.9 ° C, adding another ammonia solution (893 liters containing 72.0 liters of the above 28.8% ammonium hydroxide) at a rate of 1.97 liters per minute or otherwise injecting 0. 53808 to 0.67968 mVrain NH 3 while continuing aeration and stirring.

After 7 hours 55 minutes, the precipitation is complete, using 893 liters of ammonia solution or 20.3 kg of NH4, the batch volume being 3,930 liters and containing 102 kg of ferric oxide gamma monohydrate.

The final pH was 4.1. This represents a ratio of total hydrous gamma ferric oxide to an over suspension of approximately 2: 1 based on the total amount of 28.8% ammonia solution used (135.5 liters) divided by the amount of 28.8% ammonia solution used before heating the suspension to 37.9 ° C (63.0 liters).

B. Synthetic magnetic gamma iron oxide preparation

The surface treatment was carried out by heating the aqueous gamma iron oxide product represented by the seed suspension in the tank to 79.5 ° C, then adding a surfactant mixture of 2.59 kg of coconut fatty acid and 0.2268 kg of morpholine while stirring. in 56.8 liters of hot water.

Heating was continued at 87.8 ° C, after which filtration was performed and the filter cake was washed free of salt. The product is practically pure aqueous gamma iron oxide coated with about 3 wt. % fatty acid surfactant.

This material was reduced in a furnace with intermittent or continuous operation at 427 ° C in a reducing atmosphere to ferric iron and then oxygenated in an air stream at 383 ° C to magnetic gamma iron oxide whose magnetic properties were improved by mechanical densification for one hour and 15 minutes in a wheel mixer.

Testing the resulting finished oxide in terms of magnetic field properties (10 ⁶ / 4T) A m -1 showed a dry powder of Hc 335, Br 1 770 and Brn 3 650. The tape showed Hc 310. Electron microscope measurements showed that the particles dry iron oxide had an average length to width ratio of 9.3: 1 and an average length of up to 2 microns.

A similar ferric oxide product is obtained when surface treatment is discarded,

Example 7

Using a magnetic tape testing machine equipped with all the necessary devices for evaluating them, the synthetic gamma ferric oxide of the present invention was introduced into a magnetic tape according to known methods and compared to tapes similarly manufactured and containing magnetic gamma ferric oxides produced by prior methods.

To establish a comparative standard for test tapes to be comparable to each other, tape conveyance was adjusted so that the frequency response was 0 dB at all frequencies including the audible range (approximately 100 to 15,000 Hertz or cycles / sec) using a good audio tape commercially achievable.

The following tapes were compared:

Ribbon # 1: Contains magnetic gamma iron oxide produced by standard methods of reducing and oxidizing the precipitated alpha ferric oxide hydrate, starting from ferrous sulfate (the method for producing alpha ferric oxide hydrate is similar to that described in U.S. Pat. No. 1,327,061 and 1,368,748). No mechanical densification of ferric oxide was performed.

Strip # 2: The magnetic gamma ferric oxide contained therein was prepared similarly to strip # 1, except that the resulting gamma ferric oxide is treated with a surfactant, namely trioxyaluminium tridodecylbenzenesulfonate according to the procedure described in U.S. Pat. No. 3,294,686 and mechanically densified to about 0.85 g / cm @ 2 prior to incorporation into the tape for better frequency response.

Strip # 3: The magnetic game ferric oxide was prepared from precipitated ferric oxide hydrate in a manner similar to that described in U.S. Pat. No. 3,015,627.

Band # 4: The magnetic gamma ferric oxide contained therein was the same as for Band # 3, except that the oxide was mechanically compressed to about 0.85 g / cm 2 prior to incorporation in the band to obtain a better frequency response .

Strip No. 5: The magnetic gamma iron oxide contained therein was prepared according to Example 6.

In another Table 1, a comparison of the magnetic behavior of the above five tapes is made. The tapes were tested on an Ampex 300 tape recording and reproducing apparatus and a tulle tape speed of 19.02 cm / s.

Table 1

Belt number 1 2 3 4 5 grinding time (in hours) 48 48 48 48 48 viscosity after grinding (Kj) coating thickness 79 79 74 75 86 (2.54.10 ^-6 cm) 495 475 450 425 426 peak bias (mA) 6.48 5.68 5.6 5.4 5:

frequency response at 100 Hz (dB)

-1.0

0.8

1.5

2,0

2.1 continued table

Belt number 1 2 3 4 5 at 1 kHz (dB) -0.5 1.3 1,8 2.4 2.6 at 7.5 kHz (dB) 0.1 1.6 1.9 2.7 5.0 at 10 kHz (dB) 0.3 1.6 2,0 2.9 5.8 at 15 kHz (dB) 1,2 2.6 3.0 3.8 8.0 power at 3% THD (dB) 9.8 10.9 11.6 12.0 13.0 AC noise (1-5 kHz) (dB) -69.4 -69.1 -68.8 -68.5 -69.1 DC noise (1-5 kHz) (dB) -61.8 -62.2 -61.8 -59.5 -60.5 saturated power (dB) 500 Hz 16.2 17.4 18.2 18.6 19.3 saturated power (dB) 15 kHz -5.0 -4.5 -4.7 -4.3 0.2 dynamic range (dB) 68.9 70.4 70.6 70.9 71.7 signal / noise (dB) 79.2 80.0 80.4 80.5 82.1 Print Thru 50.4 47.9 43.5 43.5 47.0 Hc belt 319 292 288 283 310 Br pésku 950 1 125 1 287 1 418 1 467 Brn of the bread 1 Br / Bm at I 245 1 420 1 577 1 708 1 683 (10 ⁶ / WA m ' 0.762 0.791 0,816 0.830 0.87 orientation, ratio 1.58 1.78 2.11 2.20 2.90 at 1 000 Oe orientation ratio 2.62 2.97 3.92 4.08 6.35 at field when is the value maximal resistance (10 ⁹ ohms) 100 ALIGN! 175 30 12 1.3

In the above results, the grinding time in hours and the viscosity after grinding in the Kreps stages relate to the conditions for producing each strip as described above. The thickness of the coating refers to the thickness of the magnetic mixture applied to the finished baking.

The frequency response of tape # 5 is by far the best compared to other tapes, especially at higher frequencies. The audible power is in decibels (dB). These units are positive if dB is greater than 0 and are negative if dB is less than 0.

In fact, they mean the ratio and are defined as twenty times the decimal logarithm in the ratio of two numbers. Any units that exist in a 2 to 1 y ratio are, by definition, 20 x log 2 = 20 x. 301 = 6.02 dB of the sentence, or +6 dB is equal to twice the observed quantity, and a1 is any. Similarly +3 dB = 1.41 x observed quantity.

Peak bias refers to the milliamperes of current in the magnetic heads required to produce the maximum output signal at a certain frequency. The bias refers to a high frequency signal connected to the heads, usually about 80,000 Hertz, to provide an undistorted and linear output signal from the magnetic tape.

Performance at 3% THD (Total Harmony Distortion) is important because the highest performance is desirable at this point. The 3% HHD point is more or less arbitrary since an audible signal with more than 3% THD is harmful to the ear.

This power is measured electronically by comparing the pure sine signal to the output signal and increasing the power until 3% THD is reached.

AC noise refers to the Amount level of the AC-stripped tape when the bias is only on the recording heads. Various magnetic oxide formulations using the product and process of the invention have very low alternating current noise, from -71 dB to -67.7 dB (more negative numbers indicate lower noise).

DC noise is determined on a tape that has been erased by a permanent magnet, thereby mimicking erasure, as is done on some cheaper tape recorders. The value obtained is related to the good quality of the magnetic oxide dispersion in the film and to the smoothness of the surface, the better the dispersion and the better the smoothness of the surface, the lower the noise.

The saturated power at 500 Hz is the maximum signal that is obtained from the tape as the input signal increases. This power is directly related to the magnetic properties of the gamma ferric oxide used, the thickness of the coating and the tape, and the density of the coating of the magnetic tape.

Saturated power at 15 kHz is related to the resistance of the magnetic particles in the tape to the field of self-magnetization by generating a 15,000 Hertz encapsulated signal.

Print Thru in dB refers to the echo signal that comes when the tape is unrecorded and the tape is in close proximity. Higher numbers are more favorable. Print Thru signals are commonly found in coil tapes after some time.

The dynamic range is the total dB difference between 1000 Hertz power and AC noise. Signal / noise is the total dB difference between 3% distortion power and AC noise. Higher numbers are most favorable.

The values of Hc, Br, Bm of the tapes are standard magnetic properties and vary with the magnetic properties of the magnetic particles used and also according to the tape making system. All the tapes were made on the same system.

Br / Eto is a measure of the squareness of the magnetic hysteresis loop. The highest number is most favorable, and the No. 5 strip containing the unique magnetic gamma ferric oxide of the invention is completely different in this respect. The measurement was performed in the field (10 ⁶ / 45r) Aa ^-1 in the BH meter for 60 cycles.

The orientation ratio measures the ratio of the Br value (remanent magnetism on the strip after removal of the magnetic field) in a direction parallel to the strip progression to the Br value perpendicular to the strip progression. It was measured both at (10 ^ / 4) T) Am ”^ and at a lower number (usually around 300. (1 000 / 4¾A.m“ ') at which this ratio is maximum. exceptional properties.

The value of 2.90 at (10 / 4lr) A. m -1 is the highest value observed so far for any magnetic gamma iron oxide strip.

The resistance of the tape is the specific electrical resistance of the surface. The lowest value is most welcome.

Example

A. Preparation of a synthetic hydrous gamma ferric oxide and C ³ rybavenMRí yfu

To a tank of 4,550 liters, fitted with 2,170 liters of water at a temperature of 26.7 ferrous chloride solution.

with an air stirrer and air atomizer, to a liter of an aqueous solution containing 147.5 kg

720 l of a solution containing 40 kg of NeOH was pumped under stirring for 10 to 15 minutes. While stirring, oxygenation is carried out by introducing 0.2436 m @ 3 / min of air until the cesium precipitate oxidizes to a ferric shape. This will take about one hour. Oxide precipitation is completed by heating the top seed slurry to 54.4 ° C with agitation and aeration streaks, further injecting additional sodium hydroxide solution until the total flue gas is increased to 92 kg of oxide, while the addition of base is controlled to maintain pH ranging from 3.0 to 3.3. The resulting synthetic aqueous gamma ferric oxide is converted to magnetic gamma ferric oxide.

B. Synthetic magnetic gamma iron oxide preparation

The surface treatment was carried out by heating an inoculum suspension of aqueous gamma iron oxide in a tank to 79.5 ° C, then, with stirring, by adding a surfactant mixture of 0.5 kg of coconut fatty acid and 0.908 kg of morpholine in 15.2 liters of hot water.

Heating was continued at 87.8 ° C, after which filtration was performed and the filter cake was washed free of salt by washing. The product is virtually pure aqueous gamma iron oxide coated with about 2 and 1/2% fatty acid surfactant.

This material was reduced either in an intermittent or continuously operating furnace at 427 ° C in a reducing atmosphere of coconut oil fatty acid to ferric iron oxide and then oxygenated in an air stream at 371 ° C to magnetic gamma iron oxide whose magnetic properties were improved mechanical compacting for 45 minutes in a wheel mixer.

Example 9

A. Preparation of synthetic aqueous gamma iron oxide

A 4,550 liter tank equipped with a mechanical stirrer and an air sprayer in the form of a perforated tube was charged with 2,170 liters of 20 ° C tap water and 286 liters of an aqueous solution containing 147.5 kg of ferrous chloride.

720 liters of sodium hydroxide solution containing 40 kg of sodium hydroxide was pumped under stirring for 15 minutes. Stirring was continued, the air inlet was opened, and complete oxidation was performed to pH 2.9 within one hour and three minutes to form a seed suspension of synthetic aqueous gamma ferric oxide.

The precipitation of this oxide was completed by heating the seed suspension to 38.9 ° C and pumping additional sodium hydroxide solution (796 liters containing 50.0 kg of sodium hydroxide) at a rate of 20.9 liters per minute while maintaining the pH at 2.9-4. And aeration and stirring were continued.

After six hours 45 minutes, the precipitation was complete, 796 liters of sodium hydroxide solution was consumed, the batch volume was 4,170 liters and contained 106.2 kg of ferric oxide gamma hydrate, namely lepidocrocite.

of used sodium hydroxide (90 kg) by dividing the seed suspension to 38.9 ° C

The final pH was 6.7 due to excess sodium hydroxide. This represents a ratio of total ferric oxide gamma flux to feed suspension of approximately 2.2 to 1, based on the total amount of sodium hydroxide used above (40 kg).

B. Synthetic magnetic gamma iron oxide preparation

The surface treatment was performed by heating the seed suspension of the aqueous gamma iron oxide product in a tank to 79.5 ° C, then adding, while stirring, a surfactant mixture of 2.59 kg of coconut fatty acid and 0.227 kg of morpholine in 56.8 liters of hot water.

Heating was continued to 87.8 ° C, filtration was performed and the filter cake was washed free of salt. The product is practically pure aqueous gamma iron oxide coated with about 3 wt. % fatty acid surfactant.

This material was reduced in a continuous or intermittent furnace at 427 ° C in a reducing atmosphere to ferric oxide and then oxygenated in an air stream at 371 ° C to a magnetic gamma ferric oxide whose magnetic properties were improved by mechanical densification for 45 minutes. minutes in a metal mixer.

- 1

The resulting finished oxide, when tested for magnetic field properties (10 ° / 43t), A.m gave Hc 332, Br 2 010, Brn 3 650 as a dry powder, as Hc 311, Br 1 411,

Brno 1 612.

Example 10

Following the procedure of Example 7, the following strips containing magnetic gamma iron oxide were compared:

Strip No. 6: The magnetic gamma iron oxide contained therein is prepared according to Example 8.

Band # 7: The magnetic gamma ferric oxide contained therein is the same as described for Band # 1 in Example 7, except that the oxide was mechanically densified to about 0.85 g / cm 2 before being introduced into the band, to get a better frequency response.

Strip # 8: Magnetic gamma iron oxide was prepared according to Example 9 ·

Table 2 below gives a comparison of the magnetic behavior of the three strips described above. Tapes 6 and 7 were tested on an Ampex 440 tape recorder and tape 8 was tested on an Ampex 300 tape recorder. The tape speed was in all cases 19.02 cm / s.

Table 2

Belt number 6 7 8 grinding time (hours) 48 48 48.7 viscosity after grinding (kJ) 82 86 92 coating thickness (mm.10 ³ ) 10.44 10,033 9,881 peak bias (mA) 5.6 6.3 5.9 frequency response (at 100 Hz) (dB) 1,8 -0.7 1,2 at 1 kHz (dB) 2.8 0.4 2,0 at 7.5 kHz (dB) 5.8 2.8 4.9 at 10 kHz (dB) 6.2 3.0 5.8 at 15 kHz (dB) 5.6 1.6 8.6 power at 3 ® ZHD (dB) 11.3 8.2 11.0

continued table

Belt number 6 7 8 AC noise (1 to 5 kHz) (dB) -69.4 -69.7 -69.4 DC house (1 to 5 kHz) (dB) -65.0 -63.6 -61.3 saturated power (dB 500Hz) saturated power (dB 15 kHz) 17.4 15.3 17.6 0.9 -1.2 1.0 dynamic range (dB) 72.2 70.1 71.4 signal / noise (dB) 80.7 77.9 80.4 Print Thru 46.0 48.0 48.5 Hc tape 286 302 311 Br tape 1 475 1 285 1 411 Brn tape 1 723 1 566 1 612 Br / Bm at (10 ⁶ / 4n) Am ^_1 orientation ratio at (10 ⁶ / 47C) A m ¹ 0,856 0,777 0.875 2.90 1.65 resistance (10 ⁹ ohms) 1.1 > 1 000 0.5

They did

Particle distribution in strips 6 and 7 (described in Example 10) when switching the field is also measured by obtaining the hysteresis loop and its derivative relative to the attached field.

Measurements were made using standard procedures using a hysteresis loop recorder. The peak achieved at coercitidal force is indicated by measuring the width at (1000 / 4L) T m ^- m at 50% of the peak height. Half-width tip to tape no. 6 (particle according to the invention) is 79- (1000 / 4n) Am ^_1 compared to the 131. (1000/47 t) and m ~ ^ for the tape no. 7.

The narrow distribution when switching the field is achieved by the particles being well oriented. Since the field switching pattern is twice as narrow as tape # 7 for tape # 7, there are fewer particles that switch at low fields to give a tape that is less demagnetizing than tape # 7. as a result, the self-degaussing fields generated at high frequencies reduce the power at 15 Hz for tape # 6 less than for tape # 7. Their saturated power at 15,000 Hz is 0.9 dB and -1.2 dB.

Example 12

Thirty tapes containing the magnetic gamma ferrites of the present invention were tested, with the following typical distribution of Br / Bn values and orientation in the field (10 ⁶ / 4n) Am- ':

sample number Br / Bm

0.88-0.89

0.87-0.88

0.86-0.87

0.85-0.86

0.84-0.85

3,2 -3,4

3,0 -3,2

2.8 -3.0

2,6 -2,8

2,4-2,6

Example 13

A. Preparation of synthetic aqueous gamma oxide of ferric oxide

To a 945 liter tank equipped with a mechanical stirrer and air sprayer in the form of a perforated tube was added 485 liters of tap water at 26.7 ° C and 61.3 liters of an aqueous solution containing 29.3 kg of ferrous chloride.

The mixture was diluted to 575 liters. The solution was heated to 30.5 ° C. With vigorous stirring, 129 liters of aqueous ammonia containing 15.25 liters of ammonium hydroxide (28.8% NH 3) were pumped in over 15 minutes.

Stirring was continued, the air inlet was opened, and complete oxidation was performed to pH 3.45 within one hour to form a feed suspension of synthetic aqueous gamma ferric oxide.

Its precipitation was completed by heating the seed suspension to 37.2 ° C by pumping another ammonia solution (204.5 liters) containing 13.2 liters of ammonium hydroxide (about 28.8% · NH 3) at a rate of 0.439 liters per minute.

After 7 hours 28 minutes, the precipitation was complete, the batch volume was 917 liters and contained 18.52 kg of ferric oxide gamma hydrate. The final pH was 3.52.

Micrographs of the above aqueous gamma ferric oxide on an electron microscope were obtained and the following particle size distribution was found assuming each particle was cylindrical in shape, and the distribution was calculated as a percentage of the total particle volume.

Particles having a length / width ratio between: % of all particles by volume 1,0- 5,0 1.49 5,0-10,0 23.34 10,0-15,0 29.04 15,0-20,0 34.03 20.0-25.0 5.80 25,0-30,0 4.30

100 ALIGN!

Example 14

Preparation of synthetic aqueous gamma iron oxide

A 945 liter tank equipped with a mechanical stirrer and an air atomizer in the form of a perforated tube was charged with 625 liters of 29.4 ° C tap water and 61.7 liters of an aqueous solution containing 30.2 kg of ferrous chloride.

The mixture was diluted to 718 liters. With vigorous stirring, 182 liters of aqueous ammonia containing 14.8 liters of ammonium hydroxide (so-called 28.8% NH4) were pumped for 15 minutes.

Stirring was continued, the air was opened, and complete oxidation was performed to pH 3.3 at 52 minutes to form a feed suspension of synthetic aqueous gamma ferric oxide. The precipitation of this oxide was completed by maintaining the seed suspension at 37.9 ° C and injecting 0.4 to 0.01166 m ³ / min of NH ³ gas while continuing aeration and stirring.

After seven hours and twenty minutes, the precipitation was complete, 4.31 kg of NH4 gas was consumed, the feed volume was 917 liters and contained 17.62 kg of ferric oxide gamma hydrate.

The final pH was 3.52. This represents a ratio of total gamma ferric oxide to feed of approximately 2: 1.

Synthetic magnetic gamma iron oxide preparation

The surface treatment was carried out by heating a suspension of the produced aqueous gamma ferric oxide in a tank not at 79.5 ° C, then stirring and simultaneously adding the surfactant mixture of 0.5 kg of coconut fatty acid and 0.0908 kg of morpholine in 15.15 liters of hot water. . Heating was continued at 87.8 ° C, profiled, and the filter cake washed free of salt by washing. The product is practically pure aqueous gamma iron oxide coated with approximately 2 1/2 wt. % fatty acid surfactant.

This material is reduced in a continuously or intermittently operated furnace at 400 ° C in a hydrogen atmosphere to ferric iron oxide and then oxygenated in an air stream at 246 ° C to a magnetic gamma iron oxide whose magnetic properties have been improved by mechanical densification for 45 minutes in wheel mixer.

The resulting final oxide was examined for magnetic properties in the field (10 ^ / FLOA m ^- 'and in the form of a dry powder had a value of 350 Hc, Br 2080, Brno 3690.

Electron microscope measurements were made on the above-produced ferric oxide gamma, and the following particle size distribution results were obtained assuming each particle had a cylindrical shape calculated as a percentage of the total calculated volume of particles.

particles having a length / width ratio between: % of total particles, based on volume 1,0- 4,0 16.63 4.0- 7.0 47,00 7.0-10.0 24.37 10,0-13,0 9.05 13.0-16.0 1.83 16.0-18.6 1.12

100 ALIGN!

Claims (4)

SUBJECT OF THE INVENTION A method for producing a magnetic gamma ferric oxide, characterized in that ferric chloride is mixed with an aqueous base solution, wherein the concentration of ferrous chloride is 29.95 grams to 59.9 grams per liter, the mixture is stirred while introducing the oxygen-containing gas. until the pH of the mixture is between 2.9 and 4.1 and the resulting suspension of synthetic aqueous gamma iron oxide is maintained at a temperature of 26.7 to 60.0 ° C and with stirring at a pH between 2.9 and 4, 1, wherein the base and the oxygen-containing gas are simultaneously and continuously introduced until 1.2 to 5 parts by weight of synthetic aqueous gamma iron oxide are formed per part by weight of the feed suspension; the aqueous gamma iron oxide is reduced by hydrogen at a temperature of 315.5 to 428 ° C and the exhaust gas is oxygenated to magnetic gamma iron oxide at 232 to 382 ° C with air. 17 208690 2. A process according to claim 2, characterized in that metallic iron is introduced into the feed suspension before the base is added. 3. A process according to claim 2, wherein the base is sodium hydroxide, ammonium hydroxide or calcium hydroxide. 4. The process of claim 2 wherein the aqueous gamma iron oxide particles are coated with at least one hydrophobic aliphatic monocarboxylic acid having 12 to 15 carbon atoms prior to reduction and oxidation.