DE1592492C - Process for the production of ferromagnetic chromium dioxide - Google Patents

Description

1 2

The invention relates to the production of ferro models and Lorentz microscopy can be magnetic, flexible, fibrous chromium dioxide. be assumed that they are magnetic individual fields

In engineering, magnetic substances are used to represent.

especially those with high saturation magnetization. Die for the transfer. in ferromagnetic tion, to a considerable extent and for many applications, temperatures and areas of application, such as magnetic recordings, nuclei, pressures are interrelated, generally used by magnetic coils and permanent magnets. The rule applies that the higher the temperature in the an-chromium dioxide has a high saturation magnetization range, the higher the pressure required for optimalization, and newer methods must be selected to produce it. position has become known, in which chromium oxides io Although pressures of 4000 kg / cm ² or more can be used with an average chromium valence of over, one works preferentially with half past four hydrothermally treated. These lower pressures, as they become more useful, deliver ferromagnetic chromium dioxide in simpler, less costly apparatuses that allow finely divided forms, the individual particles of which are highly borrowed. High pressures and temperatures result in at least about 10 microns in size. It is also known, in general, to form chromium dioxide with chromium dioxide in dense form by thermal larger particles. Usually one works with the decomposition of chromyl chloride. to manufacture. Pressures in the range of 517 to 1033 kg / cm ² . at

The invention is based on known processes, these pressures come primarily from reaction

for the production of ferromagnetic chromium dioxide temperatures between 350 and 450 ° C in question,

at increased pressure and temperature in 20 Mostly, the pressure and temperature conditions

Presence of water. for 1 to 24 hours or more.

It is characteristic that chromium oxide or In many cases a conversion time of

a mixture of chromium oxides with a through- about 10 hours.

average value of chromium of at least The production of ferromagnetic chromium

4 in the presence of 0.25 to 10 parts by weight of alkali 35 dioxide takes place in the presence of slightly melted

dichromate, based on the weight of the chromium alkali metal dichromate and limited amounts of than

oxyds, and water present in an amount of min- reaction medium. Usually

at least 2 to a maximum of 5 moles of water per mole of dichromate is dichromate in amounts of 0.25 to 10 weight

chromate to 350 to 500 ° C under a pressure of parts per part of the higher-quality chromium oxide

at least 258 kg / cm ^{2 is} heated. As a reaction 30 turns. Larger proportionate amounts of dichromate

participants can also use chromium (ITI) oxide, Cr ₂ O ₃ , but the productivity

lie. did the apparatus then reduced it. Preferably

By suitable selection of the process conditions, about 2.5 parts of dichromate are used per part of

As in detail below, higher-valued chromium oxide can be used. All alkali dichro

explains, extract chromium dioxide from the over- 35 mate, ζ. B. Lithium dichromate, sodium dichromate,

weighing single particles longer than 10 microns, potassium dichromate, rubidium dichromate, cesium dichromate

can be obtained in a new fibrous form. chromate or mixtures thereof can be used

In the process of the invention, dichromates of lithium, potassium and higher-valent chromium oxides must be assumed, ie sodium are preferred. At least 2 moles of chromium oxide or a mixture of chromium oxide, but not more than 5 moles, of water oxides in which the average chromium valence per mole of dichromate is used should preferably be at least 4. The starting material is preferably 4 moles per mole of dichromate. If you increase the water content of chromium (VI) oxide, CrO ₃ , but you can also content in the reaction mixture, so the part of other oxides, such as Cr ₂ O ₅ and Cr ₃ O ₈ and the size of the chromium dioxide generated, are mixtures with other oxides and with CrO ₃ 45, however, if excessive amounts of water are used, so apply. If the conversion to chromium dioxide is incomplete, the required higher-value oxide can also be generated on site, for example, if a temperature of 350 ° C is maintained, an acid, e.g. B. nitric acid, at least 3 moles of water per mole of dichromate are used with that present in the reaction mixture. When calculating the dichromate reacts as specified. The amount of water to be used is in the form of

Only water present in chromium hydration water is included as the starting material.

(Vl) oxide applied, then the chromium dioxide falls min- Various per se known modification

at least partially in the form of long, thin, fibrous, mediums can be used for the method of the invention

flexible, highly magnetic strips or threads can be applied. Examples of these are in the

that are 20 to 200 microns or longer. For inorganic 55 U.S. Patents 2,885,365, 2,923,683, 2,923,684,

In niche, fibrous materials, these particles are unspecified 2,923,685, 3,034,988, and 3,068,176. Loading

Usually uniformly dimensioned, they have a preferred addition of antimony that is used

Axis ratio, i.e. a ratio of longitudinal can be used to reduce the particle size

axis to the transverse axis, of at least 10: 1 and and to increase the coercive force. Has proven itself

usually from 50: 1 to 200: 1 or even higher. 60 also the addition of iron, which is the Curie temperature

They also have a high saturation magnetization. and affects the coercive force; also can tellurium

One can apply products of much smaller particle size. The mentioned patents

size and higher coercive force by providing information about the proportion of modification

one of the reaction mixture a reactive form means that of 0.008 percent by weight, based on

of chromium (III) oxide mixed in. Both types of particles, 65 the higher-quality chromium oxide reactants,

i.e. the long-fiber strips or the smaller ones for ruthenium up to 25% in the case of antimony,

Particles can be viewed as single crystals. can make out. In general, the proportion

Based on the investigation with the help of the bitter modifier below 14% and preferably

3 4

are below 5%. It stands to reason that one should separate on the basis of their length,

not only connections of the-mentioned elements, the sieve numbers 100 (149 micron mesh size),

but also the elements themselves as modifiers- 140 (105 micron mesh size) and 400 (37 micron

can add funds. Tellurium, for example, in mesh size) can serve to do this. CrO ₂ fibers

Form of the oxide TeO ₂ or telluric acid H ₈ TeO ₆ 5 of various lengths of products accordingly

admitted. Example 12 below. (The

Chromium (III) oxide is generally in the quantities specified sieve numbers correspond to the US

up to 1.5 parts or more per part by weight of the higher standard sieve.) '

valuable chromium oxide. If one applies more than Regardless of the chosen separation method

1.5 parts of chromium (III) oxide per part of the higher-quality io, the separation can be carried out particularly easily.

Chromium oxide, the reaction can lead to chromium, if the CrO ₂ particles in non-magnetic

dioxide become incomplete. A condition exist for the procedure. The individual particles can

of the invention suitable reactive form of the chromium can be magnetized by converting them into known

(III) -oxyds is made by taking off a mode of action of a fast magnetic

aqueous, chromium (III) nitrate or chromium (III) chloride 15 exposed to an alternating field. If you turn it when it is damp

solution containing the hydroxide with ammonium state to be carried out separation methods, so is

hydroxyd precipitates. The precipitation of chromium (III) - it is often advantageous to have the separation at a temperature

Hydroxyd is carefully washed with water to maintain temperature near or above

To remove nitrate or chloride anions, and then the Curie point lies to the possible effect

essentially heated at atmospheric pressure or bypassing 20 false magnetic fields. Is working

annealed, d. H. at a pressure in the region of 0.5, at such temperatures, one uses

to 5.2 kg / cm ² and a temperature of 200 to a high-boiling, non-reactive liquid than

1000 ⁰ C. This heating is preferably carried out in a suspending medium, for example a seeded

in an oxidizing atmosphere, d. H. in counterpart petroleum fraction or an organic acid

wait for air or oxygen to give a product a suitable boiling point.

obtained, which in certain cases contains chromium with a value above 3 for the particularly important intrinsic magnetic properties, but below 4 for the substances of the invention. For heating or annealing, a wide range of possible uses is generally sufficient _{, including the coercive field, // ci} , the saturation per g, for example, 10 minutes, up to several hours, 30 or the sigma value <τ, and the rernanence ratio, for example up to 24 hours. nis u _r / (T _s , ie the ratio of the coercive force

The method of the invention can be used in any appa or remanence, based on the saturation per g.

temperature that the desired temperature coercive force and saturation are in Bozorth's »Ferro-

perätur- und Druckbedingungen and magnetism «, D. van Nostrand & Com., New York

against the chemical attack of the reaction 35 (1951), pp. 5 to 8, explained. The following

mixture is resistant. At an appropriate sigma values kept in a field of

Embodiment of the method of the invention performs 4400 gauss with an apparatus similar to that determined by

the desired reaction mixture is poured into a tray. B a r d e 11 on pp. 226 to 228 of his book

flexible platinum tube, seals the tube and »Magnetic Materials in the Electrical Industry,

subjects it to the desired temperature and 40 Phylosophical Library, New York (1955), described

Printing conditions. At the end of the reaction time, benen is equivalent. The definition of the coercive field

the closed tube is cooled, preferably off- {H _e t) is the »Special Technical Publication No. 85

frightened, opened, the contents taken out and of the American Society for Testing Materials «,

the ferromagnetic chromium dioxide by washing entitled "Symposium of Magnetic Testing" (1948),

insulated with water and drying. The product can be found in 45 pp. 191 to 198. The values for the

from deep gray to black in color and represents a coercive field were with a DC ballistic

strongly magnetic chromium dioxide in the form of a measuring device that has a modified execution

uniform, small particles, stripes or threads shaped like that of Davis and Hartenheim

of the well-known tetragonal crystal structure. in the journal "Review of Scientific Instruments",

The separation of the longer chromium dioxide fibers 5 ° 7, p. 147 (1936), described device represents,
of the simultaneously produced, non-fibrous material The chromium dioxide produced according to the invention, which plays a role in the method of the invention as a magnetic component of carriers for, can in known ways, for example magnetic recordings, for. B. magnetic tapes by hand. The longer fibers of the non-fibrous material, usable as they are used in television recordings, can, however, also be separated by other methods from the 55 and for information storage, for example, for the production of such carriers dispersed wise by sieving in the wet state. This one the chromium dioxide in an organic poly-working method is carried out with facilities, meren binders, where it is magnetically oriented as they are common in the paper industry. In doing so, while the binder is sufficiently sifted out in the wet state, one can leave a 60 remaining liquid to allow the movement of the magnetic sludge of the material to be separated in a particle. The chromium dioxide flowing, suspending medium can flow through a series of rotating sieve drums, also for magnetic inks, as a developer ία, which use ferromagnetography and in compressed form with meshes in the desired separation for the formation of permanent magnets. The degree corresponding size are equipped. The 65 fibrous chromium dioxide can be used as a reinforcing fiber

otation of the screen drums leads to the fact that they are built into composite structures, too

'little little bit with the long dimension, it has been more or less interesting to use decorative

be oriented parallel to the screen surface, so that relative effects in plastics are proven; these effects

5 6

are washed by magnetic orientation of the fibers to become water-soluble components

Remove during the formation of the plastic articles. The water-insoluble portion consisted of

called. In tangled form, the fibers produce small, strongly magnetic CrO ₂ particles (2.2 g),

Practical filters that are specially designed to be up to 2.5 microns long and up to 0.5 microns

suitable for holding back magnetic dust. 5 were wide. Below are their magnetic properties

The following examples illustrate the shafts:

Invention. Unless otherwise stated, ^ ' -45 are Oersted

all quantities are to be regarded as weight specifications. Os ........ 90 3 Gauss [cm ³ / g]

or 39 ', 8 Gauss [cm ³ / g]

B is ρ ie 1 1 ¹⁰ a _r la _s 0.44

iiine made of chromium trioxide, CrO ₃ (2 g), chromium oxide, the product obtained showed an X-ray image of Cr ₂ Oj (I g) and sodium dichromate dihydrate, Na ₂ Cr ₂ O ₇ - with a typical tetragonal crystal structure, as it is for 2 H ₂ O (5 g) Existing mixture has been thoroughly chromium dioxide is characteristic. In a microscopic examination by hand under nitrogen, it was found that the kenen container was ground and, in a platinum tube, the product consisted of single crystals. Under use which was then hermetically sealed. The small tube was placed in a larger pressure vessel - the »Lorentz technique« resulted in another underside and a pressure of 878 kg / cm ² . To the melting and the implementation of the crystals 20 constitute individual magnetic fields. Einzu ₇ nits, the temperature was then per minute

increased by 2 ° C to 265 ° C. and this latter Tem- Examples 2 to 10 Maintain temperature for 4 hours. Subsequently

the temperature continued to increase by 2 ° C per minute. These examples illustrate the use

increased up to 400 ⁰ C, at which temperature the 35 of sodium dichromate in the process of the invention

Pressure was 1033 kg / cm ² . After 6 hours of grounding. The raw material used, the

heating to 400 ° C, the pressure vessel was cooled, settlement conditions and the magnetic charac-

the platinum tube removed and opened. The lag ristic data of the products are given in Table 1

a black solid before, 'which is listed thoroughly with water.

Table 1

example

Use in g

Na.Cr, O ,! CrO ₃ , Cr ₂ O ₃ :. £ H, O

water Art
the
Her
position 0 D. 0 B. 0 F. 0 F. 1 E. 2 B. 0 B. 0 B. 1 B.

Magnetic properties

(Oe)

(GauD cm '/ g)

(Gaußi a _r / a _s cm '/ g) i

Particle size and shape

3 2 3 6 2 2 2 2 4

1*

1*

1*

2 *

3 *

2 *

7.5 10 15

7.5

38 282

37

44

479 283 336 350

237

92.1 87.4 90.6 91.1

19.4 \ 0.21

39.0 '0.45

18.1 j 0.20

15.5: 0.17

84.4. 39.6 j 0.47

84.9 88.5

36.8 41.3

79.3 I 38.0

88.0

35.6, 0.41

Length: 38 to 200 microns Width: 1.6 to 6 microns 10 microns or less, 0.5 microns or less 8 to 137 microns long, 0.8 to 6.4 microns wide, 11.2 to 51 microns long, 0.8 to 1.6 microns wide to 3.5 microns long, 0.4 microns wide usually to 2 microns long and b:

0.3 microns wide to 20 microns long, to 0.5 microns wide

mostly 3 microns or less, 0.3 microns or less

Explanations for table 1:

*) Made by heating Cr, O, 9 H, O to 150 ° C for 4 hours and then at 450 ° C for 2 hours.

B = 850 atm without heating, then temperature increase by 2 ° C / min. to 265 ° C, 4 hours 265 ⁰ C, increase of 2 ° C / min to 400 ⁰ C, 6 Hours 400 ⁰ C atm at 1000th

D = 2600 atm without heating, then temperature increase by 2 ° C / min. to 265 ° C, 4 hours 265 ° C, increase by 2 ⁰ CVMiE to 40O ⁰ C for 6 hours 40O ⁰ C atm at 3000th

E = 875 atm without heating, temperature increase to 265 ° C, 4 hours at 265 ° C, increase by 1 ° C / min. to 35O ⁰ C, 6 hours

35O ° C at 1000atm.
F = 2600 atm without heating, rapid heating to 180 ° C, then increase by 10 ° C / 15 minutes to 450 ° C 6 hours tx

450 ⁰ C and 3000 atm. - ¹

Example 11

A. A mixture of 6.0 g CrO ₃ , 15 g K ₂ Cr ₂ O _7, and 1.2 g H ₂ O was placed in a platinum tube and the tube was then hermetically sealed. It was then placed in a larger pressure vessel and a pressure of 2893 kg / cm ^{2 was} applied. The temperature was raised within one hour to 22O ⁰ C and then further increased by 16 ° C per hour, until reaching 450 ⁰ C. At this temperature the pressure was 3099 kg / cm ² . 450 ° C and 3099 kg / cm ² were maintained for 24 hours, after which the container was cooled and relaxed. The platinum tube was removed and opened, it contained a black solid which was washed thoroughly with water. The water-insoluble portion consisted of ferromagnetic chromium dioxide, which was in the form of small individual particles, 14 to 128 microns long and 0.8 to 3.2 microns wide. The magnetic properties are as follows:

Coercive Field 27 Oersted

Saturation induction. 91.8 Gauss [cm ³ / g]

Remanence 14.7 Gauss [cm ³ / g]

Remanence ratio 0.16

B. A fiber or thread was picked from the product according to A and considered tested its flexibility. To do this, one end of the fiber was attached to the tip of a fine one Tungsten rod cemented, which is then horizontally over the lens carrier with a camera device equipped microscope was clamped so that the fiber was in the field of view of the microscope. A very fine chisel edge (a section of a razor blade) was then placed in a micro-flipper attached and the edge interlocking with the free end of the crystal moved, causing the crystal to flex. The length of the fibrous crystal between its breakpoint and the chisel edge was about 120 microns. The crystal was 2 to 3 microns wide, the third dimension was also roughly 2 to 3 microns. The crystal went without it Difficulty turning to an angle of about 30 "and, upon release, returned to its starting position back.

B e i s ρ i e 1 e 12 to

These examples illustrate the use of various alkali dichromates in the process the invention. Starting materials, conversion conditions and magnetic data of the products are in Table 2 compiled. ■

Table 2

CrO ₃ , Use in g Tuesday
chromate i water
I. Art Magnetic (Gauss
cm ³ / g) properties OrlOs ■ Particle size and shape at
game 2 Cr ₂ O ₃ ■ 5 + · 0.6 the
Her
position H"
(Oe) 88.5 Cr '.
(Gauss
cmVg)! 0.46 up to 6 microns long, 12th 1* B. 341 i
40.7! up to 0.25 microns wide 2 ·! 5 + - \ 0 87.8 ¹ 0.43 up to 12 microns long. 13th 1* B. 285 38.0 , up to 0.5 microns wide 2 I. 5 + - 1 0.5 87.0 0.46 up to 12 microns long. 14th 1* B. 285 39.6 y up to 0.5 microns wide 2 ■ i 5 ++ j O 86.5 0.47 up to 10 microns long 15th 2 * B. 366 40.5 y up to 0.5 microns wide 4.5! 11.25 ++ ! ° 89.3 I.
'j 0.28 up to 51 microns long. 16 j 0 L. 42 25.4; up to 3.2 microns wide !

* Produced by heating C ₂ O ₃ · 9 H ₂ O at 150 ^° C. for 4 hours and at 450 ³ C. for 2 hours.
⁺ K ₂ Cr ₂ O ₇
⁺⁺ Li ₂ Cr ₂ O ₇ · 2 H ₂ O

B = 850atm without heating, temperature increase by 2 ° C min. To 265 ° C, 4 hours at 265 ° C, increase by 2 ° C / min. to 400 ⁰ C, 6 hours at 1000 atm to 400 ⁰ C.

L = without heating to 850 atm, Tcmperatursteigerung in 70 minutes to 400 ⁰ C, 16 hours at 1000 atm 400''C.

' ^: · Examples 17 to 24 ■ ^:

These examples illustrate various embodiments of the method of the invention. Raw materials, Conversion conditions and magnetic data of the products are summarized in Table 3.

109 646 151

ίο

Plate 3

CrO ₃ Cr ₂ O ₃ Use ir ig additions Art Magnetic ! σ,
(Gauss
cm '/ g) properties 0.41 Particle size and shape at
game 2 1** Na-Cr.O,
-2H ₂ O water O the
Her
position Ha
(Oe) 89.5 a _r \
! (Gauss! A _T \ a _s
cm '/ g) i 30 microns or less 17th 5 O B. 206 37.0 ger / 1 micron or 0.28 fewer 2 1 ^V O 88.6 up to 15 microns long, 18th 5 O B. 68 25.1 0.47 to 2 microns wide 2 2 + 1- O 85.5 up to 5 microns long, 19th 5 O B. 394 39.8 0.47 up to 0.15 microns wide 2 1* Sb ₂ O ₃ 84.0 up to 10 microns long, 20th 5 O (0.02) B. 440 39.0 0.49 to 0.4 microns wide 2 1* Fe ₂ O ₃ x 2.5 82.3 up to 3 microns long, 21 5 1 H ₂ O (0.065) B. 444 39.9 0.49 up to 0.2 microns wide 2 1* Fe ₂ O ₃ x 2.5 82.0 3.5 microns or less 22nd 5 1 H ₂ O (0.065) E. 542 40.0 ger / 0.2 micron or 0.34 fewer 0 1*. 1.9 cm ³ 89.9 up to 12 microns long, 23 10 *** O water ENT ₃ B. 142 30.1 up to 1 micron wide (70%) 0.20 3 0 CrO ₂ (0.38) 92.8 8 to 168 microns long, 24 7.5 O F. 37 18.5 0.8 to 8 microns wide

Explanations for table 3:

* Made by heating Cr ₂ O ₃ · 9H ₂ O to 150 ° C for 4 hours, then to 450 ° C for 2 hours. ♦ * Made by heating Cr _a O ₃ to 470 ° C for 3 hours.
*** Anhydrous Na ₂ Cr ₂ O ₇ .

+ Uncalcined Cr ₂ O ₃ ■ 9 H ₂ O.
++ Cr ₂ O ₃ ■ 9 H ₂ O, annealed for 2 hours at 525 ° C.
B = - ■ Without heating to 850 atm, temperature increase by 2 ° C / min. to 265 ° C, 4 hours at 265 ⁰ C, increase of 2 ° C / min.

atm to 400 ° C, 6 hours at 400 ⁰ C up to 1000.
E = without heating to 895 atm, temperature increase by 2 ° C / min. to 265 ° C, 4 hours 265 ⁰ C, increase l ° C / min.

to 350 ° C, 6 hours at 350 ° C and 1000 atm.

F = Without heating to 2640atm, temperature rise rapidly to 180 ° C for ₁ additional increase of 10 ⁰ C for 15 min. At 450 ° C, for 6 hours at 450 ⁰ C and 3000 atm.

Example 25

A mixture of 4.5 g of CrO ₃ and 11.25 g of sodium dichromate dihydrate was exposed to a pressure of 878 kg / cm ² in the cold and heated ^{to 400 °} C. as quickly as possible. At 400 ^° C. the pressure was 1033 kg / cm ² . 400 ° C and 1033 kg / cm ^a were maintained for 12 hours, after which the mixture was cooled to room temperature and let down. The chromium dioxide obtained had the following magnetic properties:

Hd 39 Oersted

a " 92.8 Gauss [cm ³ / g]

Ur 16.0 Gauss [erring]

tJr / Ua 0.17

Claims (8)

Patent claims: 1. A process for the production of ferromagnetic chromium dioxide at elevated pressure and elevated temperature in the presence of water, characterized in that chromium oxide or a mixture of chromium oxides with an average value of chromium of at least 4 in the presence of 0.25 to 10 parts by weight of alkali metal dichromate, based to the weight of the chromium oxide, and water in an amount of at least 2 to at most 5 moles of water per mole of dichromate is heated ^{to 350 to 500 ° C under a pressure of at least 258 kg / cm 2.} 2. The method according to claim 1, characterized in that that in the reaction mixture there are iron, antimony, ruthenium, tellurium and compounds these metals are present, which act as modifiers for the chromium dioxide. 3. The method according to claim 1 and 2, characterized in that the alkali metal dichromate lithium, Sodium or potassium dichromate and that the dichromates are mixed with one another. 4. The method according to claim 1 to 3, characterized in that the chromium oxide used is CrO ₃ , Cr ₂ O ₅ or Cr ₃ O ₈ and that mixtures of these oxides can be present. 5. The method according to claim 1 to 4, characterized in that together with CrO ₃ and chromium (III) oxide, Cr ₂ O ₃ , is used. 6. The method according to claim 5, characterized in that a mixture of Cr ₂ O ₃ , CrO ₃ and Na ₂ Cr ₂ O ₇ · 2 H ₈ O is used as the starting material. 7. The method according to claim 1, characterized in that it is _{assumed that a CrO 3} , which was formed on the spot during the reaction of alkali metal dichromate with acid. 8. The method according to claim 1, characterized in that the chromium oxide present is CrO ₃ .