CS207373B2 - Method of making the modified ferromagnetic chromium dioxide - Google Patents

Abstract

Process for producing modified ferromagnetic chromium dioxide by thermal decomposition of chromium(III) chromate hydrate under high pressures, characterised in that a mixture of Cr2(CrO4)3.nH2O, in which n is a number from 8 to 12, with small quantities of ruthenium or tellurium or a compound thereof is prepared and the mixture is heated at temperatures of between 250 DEG C and 500 DEG C under a pressure of at least 80 atmospheres. Such a procedure makes it possible to obtain, in a simple and economical manner, a modified chromium dioxide which is characterised by a good coercive force, without significantly depressing the saturation magnetisation, with optimum granulometric properties in the form of small acicular and uniform particles. This product is used in various magnetic recording sectors (audio and video and electronic calculators).

Description

The present invention relates to a process for the production of modified ferromagnetic chromium dioxide under pressures in the range of 19.6 to 49 MPa.

As is known, this product is used in various fields of magnetic recording, for example for magnetic tapes for audio or video recording and for electronic computers.

As a result of these applications, ferromagnetic chromium dioxide must have a magnetization δ at saturation as high as possible, in addition, the product must have good coercive strength as well as good particle size properties, i.e. it must be in the form of small acicular and uniform particles .

However, it is not easy to put such different requirements into mutual consent.

Ferromagnetic chromium dioxide can be produced by thermal decomposition of CrO 2 at high temperatures and high pressures. The product thus obtained is pure, i.e., free of all other chromium oxides, but its magnetic and granulometric properties are insufficient for its use in the above mentioned fields. While the magnetization at saturation (which is a property of the product itself) is high, the coercive force, which lies below 15.9 kA / m, is too low. In addition, the granulometric properties of the product are unsatisfactory or large inhomogeneous and small elongated particles are obtained.

On the other hand, chromium trioxide, characterized by higher coercive strength values and smaller and more needle-like particles, is obtained when the chromium oxide is heated under pressure in the presence of certain modifying elements and / or compounds thereof, particularly ruthenium, tellurium, antimony and tin. These elements are deposited in the crystal lattice of chromium trioxide. However, the products thus obtained appear to be magnetized at saturation which is considerably lower than that of unmodified chromium oxide.

In Italian Pat. Pat. No. 922,283 describes the preparation of chromium dioxide, based on the hydrated chromium chromate of the formula Cr íCrO ^ ^) ^. nH ₂ 0, and n is 1 to 8 chromene This hydrated chromium at temperatures between 250 and 500 ° C and decomposes to CrO 2 at pressures between 7.8 and 98 MPa.

The resulting product shows good magnetic properties as well as good particle size properties. The coercive force can reach 27.8 кА / m, the particles being small, elongated and of uniform size. Best results are obtained when n lies between 2 and 4.

If n has a value greater than 4, the coercive force deteriorates with increasing value of n. If n exceeds 8, the flue gas is impure due to the presence of CrOOK. In addition, under these conditions the magnetization at saturation decreases considerably.

From Italian Pat. No. 956,230, which relates to CrO ₉ -based ferromagnetic compounds modified with lanthanum, yttrium, barium or strontium, shows that the addition of these elements or compounds according to the same procedure will allow products having a higher coercive strength (up to about 34.9 kА / m) and a saturation magnetization that is somewhat less than that of unmodified chromium oxide.

Again, the best value of n is between 2 and 4, and if n is greater than 8, the product is impure due to the presence of CrOOH.

Hydrated chromium chromate is produced by starting from an aqueous chromium chromium solution which must be evaporated until a paste is obtained which is then dehydrated until a desired value of n, which generally lies between 2 and 4, is reached. expensive.

Accordingly, the present invention is based on the object of providing a simple and economical process for producing modified chromium dioxide which can achieve good coercive strength without substantially reducing the saturation magnetization of the product and which further allows to obtain a product with good granulometric properties, i.e. narrow acicular and uniform particles.

The above drawbacks are eliminated by the process according to the invention, which consists in the preparation of a mixture of CrrCrD ^ J JnHpO, where n is from 8 to 12, and from such a mass amount of ruthenium or tellurium or a compound thereof, calculated as an element, is 0.05 to 1%, based on anhydrous SiO2, and the mixture is heated to 250-500 ° C.

Indeed, it has been found that using δ values between 8 and 12, in the presence of ruthenium or tellurium, not only produces no CrOOH, but produces fumes having excellent magnetic properties, with good coercive strength and a particularly high saturation magnetization, which it is only slightly lower than that of unmodified chromium oxide.

It has further been found that in the process according to the invention, particularly small amounts of ruthenium or tellurium are sufficient to obtain excellent products, for example 0.2 wt. % calculated as explained below.

Tellurium or its compounds are particularly preferred. The amount by weight of ruthenium or tellurium or compounds thereof, calculated as an element relative to the anhydrous Cr (CrO4), is 0.05 to 1%, preferably about 0.1 to about 0.8% and particularly preferably 0.1 to 0%. , 5

In the case of tellurium, the best results are generally obtained with a mass range of 0.1 to 0.1

0.2%.

In addition to metallic ruthenium, various ruthenium compounds may be used, preferably RuOg, Ru (OH) 1, Rudi 1, RuCl 2, RuF 2, RuBry 4 Ru 4, RuS ^{8 8} (AlHCl 4, Ru 4).

In addition to metallic tellurium, various tellurium compounds can be used, such as the compounds - TeO ₂ , TeO 1, TiO ₆ , TeCl ₄ , TeBr ₄ and TeS 2 TeSg.

According to a further embodiment of the invention, CpgCrO4-ynHgO is used wherein n is between 9 and 12

The degree of hydration of chromium chromite, i.e., the number of moles of HgO per mole of lr ₂ (IrO? P, is 8 to 12, corresponding to 24.2 and 32.2% H ₂ O, calculated on anhydrous chromium chromate.

Since hydrated chromium chromate is produced by evaporating the chromium chromate solution and then drying the paste until a certain residual content of hydration water is reached, the number of moles of HgO for each mole of Cr 1 Cr 2 is naturally a mean value which can be and cannot be an integer. Thus, values between 8 and 12 mean both integers -8, 9, 10, 11 and 12, as well as any intermediate values between these integers.

In general, degrees of hydration between 0.1 and 12 are used, with preferred values being between 9 and 12. In the case of tellurium, practically the best results are obtained with values of 10 to 11. The temperature to which the starting mixture is heated is 250 to 500 ° C. , with benefit . 320-400 ° C.

The above heating time, which is used to bring the starting mixture to the above reaction temperature, is not critical. The same applies to the cooling of CrO2 at the end of the reaction. The time required for these workflows is generally set as a function of the features of the available instruments.

The minimum residence time of the mixture at the above reaction temperatures, which is required for the reaction itself to complete, decreases with increasing temperature. However, further heating beyond this minimum time does not cause any problems. In general, residence times at reaction temperatures are from 30 minutes to 2 hours.

The pressure at which the reaction is carried out is the pressure,. which is in the reaction medium at the completion of the reaction. It should also be noted that when chromium chromate decomposes into CrOg, 0g develops, which, if not provided with a discharge device, causes an increase in the pressure in the autoclave in which the reaction takes place. These final reaction pressures generally lie between 7.84 and 98%. Equally good results are obtained with pressures above 98 but their use is too costly. It is advantageous to operate at pressures between 1.9.6 and 49 M < a >.

If the autoclave is brought under pressure before heating, in order to achieve the desired final pressure in the hot state, not only the thermal expansion of the pressurized gas, but also the 0g which is released during the reaction and itself the higher the ratio between the volume of the reaction mixture and the total volume of the autoclave, the higher the pressure is. In addition, the pressure generated by the heat evaporation of the water in the autoclave must also be taken into account, the water coming from the reaction mixture where it was introduced through the hydrating water of chromium chromate.

The pressurization in the cold state may be effected by means of a gas, for example oxygen, air or nitrogen.

In addition, water may be introduced into the cavity between the flask or chamber containing the feed mixture and the autoclave at which point the pressure of the hot water obtained is essentially from the evaporation of the H2O so added instead of the chromium chromate hydration water evaporation. This procedure does not change the course of the reaction or the results obtained.

In addition to tellurium or ruthenium, other elements known as chromium trioxide modifiers, such as iron in the case of ruthenium and iron, yttruum and copper in the case of tellurium, can be added to the starting mixture. Iron is preferably used. These additional moodficitors can be introduced in the form of elements or in the form of their compounds. For example, their mono-quantitative number may be between 0.1 and 1%, calculated as an element based on anhydrous CrgCCrO ^^. '

The hydrated chromium chromene to be used as the starting material according to the invention is a salt type compound. It is soluble in water and appears anorphic under X-rays.

This compound can be obtained by simple chemical reactions, which have long been described in the literature (for a complete calculation of these compounds, see, for example, the book Chemische Handbuch der Inorganischen Chemie, Verlag Chemie (1962), 8. Auuflage-Chrom, Vol. B, p. 104). - 105). .

A preferred method of manufacture is to reduce the CrO 2 dissolved in water with methanol in an atomic meander according to the following reaction formula:

5CrO ₃ + CH ₃ OH -> C 2 (Cr 2 O ₄ ) ₃ + _{2H 2} O + CO ₂ .

The solution was evaporated and the paste formed was dried until the desired degree of hydration was achieved. The drying is carried out, for example, at a temperature of 110 to 16 ° C under vacuum.

By ruthenium or tellur, or possibly other urine, chromium chromene can be added to the chromium chrome using conventional mixing techniques.

For example, the hydrated chromite chromate may be spread together with the oolicate in an agate medium. It has been found that it is particularly advantageous to add the chromate to the aqueous chromium chromene solution with stirring until solid chromium chromite is obtained therefrom. In addition, this procedure makes it possible to obtain exhaust gases which are higher. coorective forces.

The apparatus suitable for carrying out the reaction will now be described. Seen from the stainless steel or other suitable material, the autoclave is scalded with a first vent that allows it to generate a certain initial pressure before starting the reaction. With the help of the second valve, the pressure can be released until the reaction is complete and after the autoclave has cooled.

The autoclave contains a pressure gauge for measuring the pressure. With the aid of a thermocouple placed in the reaction mass, the recording device can monitor the evolution of the internal temperature as a function of time. The autoclave is heated in an electric oven of suitable dimensions or in a chamber in which the hot gas is circulated or with similar systems.

The determination of the properties of the obtained product can be carried out in various ways, for example:

X with the aid of an X-ray diffractionometer, since CrO ₂ has a known spectrum-diffraction spectrum;

a releon microscope, for example at 50,000 times magnification, to determine the size, shape and granulomeeric distribution of the particles obtained;

by detecting the following magnetic properties: msonetzzation. (S _Q) when the residual saturation magmtismus _(β ρ) or custom kooecitivní ·· force (Hci), said first · OBT 'values ^are expressed in electromagnetic jednotách on grgm and third ^class is expressed in A / m. The electromechanical unit per ^gram is equal to 20 µm.

The products obtained by the process according to the invention have the same X-ray diffraction pattern as the non-thanked CrO2 and are composed of needle-like and stent-like shells whose length is smaller. than 1 / um.

Maanetizact products obtained when saturation is only very slightly smaller than maagneizace ^{'p RI} 3ycení nepoděkované ^ u ^ tai proofed with chromium. · · Výrtaky detects vjýctozí Sotai 2 which contains or ruthenUum telluc in hmoonootních mtnossvích stopped-UP 0.5%, based on ^b EFTA ^d ý chromium chromate, ooaí _8g, generally kteM ^t] OF ^and above 17 ^{203Ϊτ. í 0—} a ° iže Exceed or exceed i 176 ⁰ ° £ Τ · 10 ”\

The collective strength of the product obtained is good. For te-Hur, it can reach or exceed 39.7 kA / m and the addition of another mooifier can further increase these values, for example up to 40.7 kA / m.

The main advantage! The invention can be summarized as follows:

. it is possible to produce a modernized chromium trioxide with good coefficient of force and good non-radiological properties without appreciably disturbing its saturation manneisation;

these results are obtained with very slight moodficator added, while the properties of chromium oxide only slightly increase;

^p from ^p Úsobí ccording to the invention is inexpensive and jetaotachý. Compared with the ^p rocedure productions ^{would CrOg b} u3 neat or with the addition of La, T, Sr or Ba, as described vi teskných Pat. Nos. 922 283 and 256 230, a considerable advantage is achieved in that the chromium chromate must be dehydrated to a degree of hydration of about 10 (i.e., up to mass, water content of approx. Ont 5 (ie by mass, water content approximately 10.67%) · Dehydration process · This is considerably simplified.

Some examples of embodiments will now be given to explain the invention.

Peak ice 1

The chromium chromate to be used as the starting material was prepared as follows:

000 g of CrO) was dissolved in destioované water přčeemž volume of the solution was placed on 4 · tulle ^first solution introduced into the tanks ^Th ^ which yřoi development ^and had pocket ^ u · 10 · cast and was equipped míchačlem, reflux condenser and thermometer.

Was fed dropwise 12β g · CHjOH and the whole was heated up to the boiling point · then boiling was continued for 15 hours until complete conversion of the alcohol which is to zoOíOI COG Remove from playlist search ^ o ^ -cm ³ solution and · in that patterns of ^{P b} defined yl ooér ^C r ^"+ / ^{Cr) +} jodomeerickou titration hexavalent chromium, and chromium determined total oioožsví oxidation with NagCOg Pomerania thus determined was 1.5. In addition, the concentration of chronic anhydrous chromene was determined in solution. This concentration was 47β g / l Cr ^ CiO ^)}.

4, ⁶ . cm. ³ roztota what ^made answer ^{50 g} of anhydrous C ^ Cr ^ y ^ t was introduced into a vessel and talrněné vigorous stirring with soíseno mnnoetvío 0, admixed 1416 g RuOg omo ^ v! was 0.2% Ru, based on anhydrous chromium chromate.

The vessel, which was continuously stirred, was then heated in a water bath to allow excess water to evaporate and to obtain sufficient thick paste, which was then dried in an oven at 160 ° C under vacuum until it was obtained. Anhydrous chromium chromene with 10 molecules of hydration water. Λ

After carefully spreading in an agate mortar, the solid was introduced into a 130 ml titanium flask, which was placed in an autoclave of the above-described stainless steel type and 200 ml internal volume. · 20 cm ^ of distilled water was introduced into the cavity between the flask and the autoclave wall · The autoclave was heated in a hot gas circulation chamber. · A pressure of 11.38 MPa was created inside the autoclave with the aid of an oxygen cylinder at the start of the test. · The pressure inside the potoin autoclave increased during heating due to oxygen formation, evaporating water and heat expansion. After three hours, the temperature inside the autoclave reached 340 ° C and was held at this temperature for 15 hours. 120 minutes · The end pressure was 34.4 MPa · After cooling, the pressure was discharged and the autoclave opened. A black powder was formed in the vessel, which was then ground in a ball mill, washed with water until the wash water was clean, and dried in an oven. The diffraction diagram of the obtained product under X-rays showed that the product is CrOg.

The product coercive strength and ^δ Γ / ^β ratio were determined using an alternating current hysteresis plot, operating at a field strength of approximately 7.95 kPa / m. The coercive force was 32.2 кА / m, while the ratio ^β _ρ / & ₃ was 0.52. Magnetization at saturation was determined using a Foner vibrating magnetometer, which was able to produce a maximum intensity of 1.43 MA / m. was 1750W. The 10% of unmodified chromium oxide, measured by the same apparatus, totaled 1 76.0 to 1 * 7707Й. 1

Examples 2 to 5

The test of Example 1 was repeated, with the amount of RuOg added to the chromium chromene solution being modified to give different percentages of ruthenium in the starting mixture based on the anhydrous chromium chromium. The results are given in Table I below.

Table : ¹ ' Test number Number of moles of hydration water % ruthenium _; based on the anhydrous Cr ₂ iCrO _{4) 3} у Hei (kA / m) • V * p 2 ¹⁰ 0.1 27.4 0 * 40 3 10 0.3 29.8 0.43 4 10 .. 0,5 26.3 0.39 5 10 0.8 23.1 0.37

Examples 6 to 9,

The procedure of Example 1 was followed, but with the following difference.

The oven drying was not carried out until the hydrated chromium chromite hydrate had a degree of hydration of 10, but up to grades 8, 9 and 12.

In Test 9, the amount of RuOg added to the chromium chromene solution was such that 0.5% of ruthenium relative to anhydrous chromium chromium was obtained in the starting mixture.

The results obtained are shown in Table II below.

Ί

Table II Number Number of moles % ru ^ rula, Hci ' δ _Γ A _s Γ s tests moisturizing based on anhydrous (where·) water C.rVCrO ₄ ) ₃ 6 8 0.2 24.7 0.37 Ί 9 0.2 .29.5 0.44 8 12 0.2 22.6 0.38 9 12 0.5 25.5 0.40.

Example 10

The procedure of Example 1 was followed except that:

ruthenium was added in the form of RuCr) to such an extent that the added ruthenium, based on Сг ₂ (СгОд) р was 0.2 drying, was carried out in the oven until the hydrate of chromate chromate reached 9.

The product obtained had a coefficient force of 23.9 kA / m.

Ex-lk la. 11 _d:. -. -. ·. ... . у. . . .

The procedure of Example 1 was followed, except that the chromium chromate solution as an additive, in addition to RuO _2, also had alpha-F 2 O 3 .alpha.-ego O 3 produced as follows:

The FeCO3 solution was hydrolyzed by NH3 to. pH-value 9.7. After filtration, the cake was washed with water until all of the Cl ions were removed. The cake was dispersed in the cooker and the dispersion was boiled for one hour. It was then filtered again and dried. The solid product was ground in wet form. a rotating container containing porcelain beads for 15 hours. Then · was. again, and the resulting cake was fed to a solution of chromium chromate in a mass such that the additive, calculated as iron, was equal to 0.5% based on the anhydrous chromium chromate. The product obtained had a coefficient of strength of 38.2 kA / m.

For example, 12 to 26,

In these examples, the compound was used instead of the compound Chromium chromate solution prepared according to Example 1 was mixed with various mixtures of TeOg so that the tellurium additives resulting therefrom had a size of 0.1, 0.2, 0.3 according to the test. 0.4, 0.5 or 0.8%, based on anhydrous (C C í íccc); .

The test was continued according to the conditions of Example 1 to achieve a degree of hydration of 8 and 8, respectively. 9, respectively. 10, respectively. 11, respectively. 12, according to the respective test.

The results are found in the following table - IIIy,

Table III

Test number number of moles moisturizer % tellurium on anhydrous Hci (kA / m) ^6/6 ₈ water «Wj.

12 10 0.1 40.6 0.59 13 11 0.1 39.4 - 14 9 0.2 38.2 - 15 Dec 10 0.2 42.6 0.58 16 11 0.2 42.6 - 17 12 0.2 41.4 - 18 10 0.3 38.2 0.55 19 Dec 12 0.3 40.6 - 20 May 9 0.4 33.0 - 21 10 0.4 38.2 0.55 22nd 11 0.4 36.2 - 23 8 0.5 29.4 0.44 24 10 0.5 33.4 0.51 25 12 0.5 31.8 0.48 26 10 0.8 28.6 0.42

Sample No. 15 has an average particle length of 0.22 µm and a mean distance to width ratio of 12: 1. 70% of the particles have a length between 0.15 and 0.32 / m and a length to width ratio of 8: 1 to 19: 1.

Test # 15 was repeated twice, changing both end temperature and pressure. In a second test used rearward ^CE temperature ^{of 380} ° C and 33.32 MPa, and tlat third ^CE test temperature of 320 ° ^C and a pressure of ² ^ and 7.44. All had výrobty ^yp ro Hci _⁸ and 8 _p / 8 _g of the same value.

Tellnium content of samples 15 and 18 tulle. analyzed by mass spectrometry; sample 15 showed 0.25% Te based on CrO 2, while sample 18 showed 0.33%.

EXAMPLE 27

In this example, a tulle chromium chromium solution prepared according to the instructions of the example and tulle was added to the metal tellurium at 0.5 wt. %, based on anhydrous CrCCrOoJ ·

Next, the procedure was carried out according to Example 1 until it reached a degree of hydration of 10.

The product obtained had a coefficient force of 26.2 kA / m.

Example 28 to 30

The procedure of Example 15 was followed, except that other mooifiers were added to the chromium chromium tulle solution in addition to TeO.

In Test 28, the alpha-F? Op produced according to Example 11 was added at a mass equivalent to the addition of 0.75% Fe based on anhydrous chromium chromate. The resulting product had the following property:

Hci '41 ^, 7 kA' ^m , δβ »1 684ИГ.10 ⁴ } δρ / δ ₈ - 0 ^, 57.

In test 29, this added YgO 2 in hmoo. %, which corresponds to an additive of 0.50% Ί based on anhydrous chromium chromene.

The exhaust thus obtained had the following characteristics:

Hci = 44.2 kA / m, δ ^s = 17241 ^ 10 ^-4 , ^ ^{/ δ} ₈ = 0.59.

In test 30, CuO.nHgO in such mass was added. %, which corresponded to an addition of 0.50% Cu, based on anhydrous chromium chromate. · The product obtained has the following characteristics:

Hci = 44, δ. kA / m, = 1 '85a3t ^ .10' ⁴ , δ ^ δ ₈ = 0.59.

Claims (13)

Process for producing a modified ferromagnetic chromium trioxide by thermal decomposition of hydrated chromium chromium at a pressure of 19, δ to 49 M * a, characterized in that a mixture is prepared from CrgCrO ^ yHOO, where n is from 8 to 12, ^ ^ rs of the quantity of ruthenium or tellurium, or a compound which, calculated as the element is between 0.05 and 1%, based on anhydrous Сг ₂ (СгОд) р and the mixture was heated at 250-500 ° C. 2. The process of claim 1, wherein tellurium or a compound thereof is used. 3. The method of claim 1, you nčuUící ^marks in the pouUžje rutheoia or tellurium or a compound hmoonostním mnoožtví 0.1 to 0.5% · 4. The process of claim 3, wherein tellurium or a compound thereof is used in a molar amount of 0.1 to 0.2%. 5. Method according to any of the preceding claims, you nčuUící ^marks in · that a Cr-CCrO.) ,. nH "0, where n is between 9 and 12. δ. 5. The process of claim 5, wherein the tellurium or tellurium compound used is Crg (CrO4) nHgO, wherein n is between 10 and 11. 7. A process according to any one of Claims 1, 3 or 5, characterized in that ruthenium dioxide is used as the rutherium compound. 8. A process according to any one of Claims 1 to 8, characterized in that tellurium dioxide is used as the tellurium compound. 9. A method according to any one of předcl-ház eících points you ^marks oauUící in that the heating temperature of the mixture is in the range from 320 to 400 ° C. 10. A process as claimed in any one of the foregoing points, characterized ⁱⁿ that ruthenium or tellurium or a compound thereof is added to an aqueous chromium chromium solution and the starting mixture is formed by evaporating the solution and subsequently drying the paste thus obtained. ” 11. A method according to any one of přjicházeeících points you oauUící ^marks in that added to the mixture further modTil ^ i ^ Ujica element or compound thereof. 12. The method of claim 11, wherein the mono-mono-amount of the further pollutant or compound thereof, calculated as the element, is between 0.1 and 1.0% based on the anhydrous chromium chromite. 13. A method according to claim 11 or 12, characterized in that iron is added as an additional modifying element.