DE1667854C - Process for the production of ferromagnetic chromium dioxide - Google Patents

Description

ι 2

The production of ferromagnetic chromium from 0.01 to 0.1 atm and continuously the Reakoxyd by various methods is fed from the tion chamber, the temperature of which in the literature, z. B. from the USA patents 2 9S6 9SS range from 250 to 375 ° C and their pressure at and 3 034 988. known. The literature describes the synthesis of chromium dioxide, its modification by 5 particularly important mangetic properties, which is kept at most 1 atm. The use of various additives and which make the products according to the invention valuable for processing it as a magnetic material in a wide variety of applications are toggle tapes and devices. The induction coercive force (Hh). the saturation per the various methods for preparing the ferro- or grams of σ-value (σ i) and the modified Remanenzmagnetischen oxide and oxide loading, 0 _verhältnjs 1M _{ie the} ratio de "remanence / g written. Most diesel Vei drives require »« ■ «·» "» \ „j ·

however, the use of high pressure equipment. for saturation / g. The terms "remanence" and

j: - i ^ k ta, rir, vu hu otu / 9 snn atmospheres eienen. "Saturation" are in "Ferromagnetism" ·· > n Bo-

The preferred pressures for these processes are zorth, ä. 3 dis od -vu .. m «.—« j ο—, ~ - ₅ .

are required in the range of about 200 to 500 at- 15 New York, 1951. The ones mentioned here

atmospheres. The most commonly used σ values are in a field of 4400 Gauss with

The procedure described for these cases is intended to be an apparatus similar to the apparatus

the decomposition of chromium trioxide in aqueous media is discussed in Magnetic Materials in the Electricial

at pressures from 200 to 300 atmospheres and temperature industry "by T. R. Bardell. 3. 226 to 228

Temperatures of 200 to 500 C required. 20 (Philosophical Library. New York. 1955). described

Another method for the production of ferro- will. The term "induction coercive force" (// *) is in magnetic CrO, described in U.S. Patent "Special Technical Publication" No. A-5 of American Papers 3,074,778 and 3,078,147. Here Society for Testin Materials with the title "Symposium Will Cbromyl Chloride On Substrates From Inorganic On Magnetic Testing". 1948, pp. 191 to 198. Fibers or impure chromium dioxide at 35. The values mentioned here for the induction coercive force in an oxygen atmosphere at a temperature of 300 to 500 ^° C. are decomposed in a ballistic direct current apparatus. Another determined which is a modified form of apparatus for the manufacture of ferromagnetic apparatus. that of Davis and H arti η in "The Review Chromdioxyd ist in der USA.-Patent 3 117 093 of Scientific Instruments", 7, p. 147 (1936). described. In this procedure, the higher 30 is written.

Oxides of chromium of the general formula Cr _x O ₁ ,, For the production of high-quality recordings

should wherein the ratio of 2 to _y .y 4-6 is, voltage materials, the magnetic material

in an aqueous acidic medium at pressures im preferably a saturation / g or a σ value σ «

Range from 50 to 3000 atmospheres to temperatures of at least 60 electromagnetic units / g

Doors heated from 250 to 500 ^a C. 35 have. Materials with a saturation / g of more

With the discovery of a ferromagnetic chromium as 65, especially those with a saturation via dioxyds with suitable magnetic properties 75, particularly good products result,
and uniformly small particle size, which will preferably be a desired amount of certain applications in the manufacture of magnetic higher chromium oxide, usually chromium trioxide, table recording tapes, magnetic data valency above 4, and certain amounts and information storage or data processing - Modifying metals in the form of their oxides or processing systems, making generator parts usable, resulted in useful compounds such as antimony oxides, in itself the need for another, cheaper corrosion and heat-resistant vessel, for example a process for its manufacture. The oxides of chromium, made of ceramic material, stainless steel, with magnetic properties are given in all or in platinum boats and placed in a generally uniform, small particle with a tetra-suitable furnace. The temperature of the furnace will have a gonal crystal structure, the average length of which will gradually increase to the range from 250 to 375 ° C, not greater than 10 μ, with a maximum of 10% of the Once heating is started, a particle will be longer than 10 μ . These particles contain a mixture of nitrogen oxide and oxygen, nitrogen 58.9 to 61.9% chromium and have an X-ray 50 or an inert gas such as argon continuously 30 diffraction pattern, the analysis of which shows that it is in its utes up to about 10 hours Normal pressures passed over the entirety of a tetragonal crystal structure with the chromium mixture. The black crystalline cell constant of a ₀ = 4.41 ± 0.10 Λ and c ₀ = 2.90 product is easily equivalent to suitable ± 0.10 Λ after cooling. These particles are ground in the apparatus described in water and acetone, U.S. Patent 2,956,955. 55 washed and then dried in the air.

The invention is based on the object. It is then suitable for testing the magnetic

simple and cheap way to achieve the above properties.

Requirements corresponding ferromagnetic chrome die for the production of the ferromagnetic

Dioxide, the chemicals used for high-quality record- Chromium oxides are common

tion materials is useful. fio lent chemically pure, d. i.e., their purity is little-

The invention is based on a process for st; ns 99.0 ° / ₀ · Normally, chromium trioxide is CrO ₃

Production of ferromagnetic chromium dioxide of this purity and powdery, finely ground ones

used by heating a chromium compound with a consistency. However, it is also possible

Use chromium valence above 4 in a gas or other oxides such as Cr ₂ O ₆ and Cr ₃ O ₈ .

Gas mixture in a reaction chamber at elevated 65 denier higher oxides can be an inoculum that consists of

Temperature. It is characteristic that the gas consists of pure chromium dioxide and has good ferromagnetic

or the gas mixture can be added on entry into the reaction table properties Lat. Except

chamber NO under a pressure or partial pressure CrO _a inoculum can also be modified

3 4

Agents included in the reaction mixture are particularly important. However, it has been shown that with

will. The starting substances are heated at a relatively low rate of

Given mixing device and before the introduction rend of the passage of temperature through the

mixed well in the reactor. Area in which the melting point of CrO,

Modifying agents are located, for example, in the S (about 20OC), there is a greater porosity USA patents 2 923 683, 2 923 684. 2 923 685 sets in the material and ferro-

and 2,885,365. Obtained as suitable connecting magnetic crystals in better yield

For example, antimony trioxide can be used as fertilizer.

pentoxide. Tin or tellurium metal or oxide and the method according to the invention can be used with stick-suitable compounds of titanium, magnesium, iron, > Oxide is practically the only gas that is released during the Cobalt, nickel, ruthenium and alkali metals for reaction is present to be performed. the to be etched. It has been shown that this materia reaction takes place by the pressure in the Reaklien the magnetic properties of the Oxyds tion chamber to remove a substantial part increase. the ambient air is lowered and then about 1 to

if \ _ iiruiuiriKAyu uci ixuiiiintuiui.K in r.uri v "j"-> -j to M "K .... _K. " t "... tj" _r L "ft j_" ι, t! ": »» -_ "yy." .-.

Oxygen is heated, decomposed / t it is to be lower.

Oxides of chromium below the positive tetravalent if mixtures of nitric oxide with another

State. It is very difficult to use the gas conditions in the method according to the invention

To control this decomposition in such a way that the reduction is achieved, nitrogen oxide is of decisive importance

tion ends in the positive tetravalent state. There 20 component, while the other gas primarily

however, this was found to be a reduction or a diluent. Any gas can

Decomposition in the presence of a mild reducing agent can be used as a diluent if it has the

by means, namely nitrogen, can be steered in this way, does not affect the reducing effect of the nitrogen oxide

that large amounts of chromium dioxide occur at low levels and no further reduction of the ferro-

Press are available. As the following examples show, the decomposition of chromium trioxide is caused by _{magnetic CrO 2 after its formation}

other higher chromium oxides to form Example 1
ferromagnetic chromium dioxide in good yield

catalyzed when this decomposition is carried out in the presence of 3 g of CrO ₃ in a platinum boat of ½ cm oxygen and nitrogen oxide, being 30 length weighed. The boat was initially placed in a Pyrex nitrogen oxide in an amount of 2 to a pipe of 31 mm diameter and 90 cm length 9 percent by volume, preferably 2.5 to 4.5 volume. The boat was placed in a tube furnace percent, there is. Preferably placed for the reaction that it was in the middle, whereupon according to the invention a gas mixture in which was started, a gas ^ s-nisch at normal pressure the volume ratio of NO / O ₂ in the range of 35 over the boat to direct. The gas mixture is 2:98 to 9:91. Other gas mixtures containing 3.5 percent by volume of NO and 96.5 percent by volume of nitrogen oxide have also been used, and percent O ₂ . The flow rate of the gas mixture led to the formation of ferromagnetic chromium was set to 200 ml / minute. The temperature dioxide. These other suitable gas mixtures in the furnace were made up of nitrogen oxide and nitrogen in proportions from room temperature to 175 ° C within 10 minutes and then slowly within 1 to 10% nitrogen oxide, the remainder nitrogen and nitrogen oxide, half of 1 hour over the Melting point of CrO ₂ rest inert gas, ζ. B. argon, in similar proportions. increased to 225 ° C. The furnace was then faster. These gas mixtures are heated to 325 ° C within 20 minutes for the purpose of this. Suitable for the invention, but the above temperature was maintained for 2 hours, said mixtures of NO and O _{2 are} preferred. In 45 while the gas mixture continues in the above general amount, a total pressure of 1 atmosphere is applied passed through the tube furnace. Strongly reducing gas mixtures, e.g. B. was. At the end of the heating time of 2 hours of carbon dioxide-carbon dioxide mixtures and hydrogen, the platinum boat was taken out of the furnace. The weight loss of this sample became or, in the latter case, to sulfates, e.g. B. Chromium sulfate. determined with 18.5%. The product obtained v / ar a

Because chromium trioxide is used as the starting material, black crystalline material. This product has melted material at about 200 ° C and, when its crushed in a mortar, begins to decompose in water and acetone, it becomes solid, it is washed under the and air dried before its atmospheres used according to the invention at temperature 55 magnetic Properties were measured. The temperatures between about 250 and 375 ⁰ C, whereby a following magnetic properties were ge range of 275 to 35O ⁰ C is preferred chromium found in: H _c i = 31 Oersteds; σ, = 84.9 electromagnetic converted. The reaction takes place at the table units / g; a _T = 4.3 electromagnetic in-preferred temperatures faster than outside / g.

half of this range. It is sufficient to keep the reaction mixture 60 For pure CrO ₂ , a saturation magnet of 0.5 to 10 hours below the above-mentioned sation value of about 90 electromagnetic single-atmosphere conditions was found to be good units / g. Because the saturation magnetization achieves results, while most often a reaction time of 1 to 2 hours is applied as approximately proportional to the amount of the reaction time present. CrO ₂ can be viewed, the purity can be

Easily calculate when performing the method according to Figure 65 of the ferromagnetic product. in the

Invention is the speed with which the present example was the existing CrO ₃ -

Participants calculated on the final temperature amount on this basis at 94%. Through

are heated at which they are held, not X-ray analysis has also been found that the

I 667 854

CrO _{1 was present} in the tetiagonal rutile structure. Furthermore v ;. n in the Rönlgenbeugungsbildern weak Lh..en present, _t a Cr O, content of about 5 ° / ₀ corresponded.

Example 2

This example illustrates the preparation of an antimony modified ferromagnetic chromium oxide with good ferromagnetic properties.

2.7 g CrO, un <? 0.3 g of St ₃ O ₁ were placed in a platinum boat, which was placed in the middle of the Pyrex tube of 31 mm diameter described in Example 1, whereupon this was started The easiest mixture of NO and O ₁ in Example 1

named composition oei i-sormaiuiui-κ uutui to direct the Pyrex pipe. Here, too, the furnace was baked to a temperature of 300 ° C. according to the heating program mentioned in Example 1, which was maintained for 2 hours. During this time the gas mixture continued to flow through the tube furnace. At the end of the heating period of 2 hours, the platinum boat with the sample contained therein was removed from the furnace and cooled in the air. The weight loss of this sample was found to be 2.2% of the original CrO ₃ weight. The black crystalline product obtained in this experiment was ground in a mortar, washed in water and acetone, and air dried before its magnetic properties were measured. The following magnetic properties were determined for this sample: H _ei = 114 Oersted; a _s = - 65.9 electromagnetic units / g; a _r = 13.6 electromagnetic units / g.

The CrOj content of this sample was determined in the manner described in Example 1 to be 73%. X-ray analysis showed strong lines for _{rutile-type CiO 2} and weak lines for Sb ₂ O ₃ . Since there was a slight shift in the position of the CrOj lines, a certain solubility of the Sb ₂ O ₃ in the CrO ₂ -Ki istall lattice can be assumed.

Example 3

This example describes the preparation of modif with ^tellurium: .- ith ferromagnetic Chromoxydkristallen?.

1.8 g of CrO _{3 was} mixed with 0.1 oO g of crystalline elemental tellurium. The mixture was crushed and passed through a sieve with a mesh size of 74 μ. The crystalline mixture was placed in a platinum boat 5 cm long, which was placed in an oven in the form of a Pyrex tube 31 mm in diameter and 90 cm in length. Then a start was made to pass a mixture of oxygen and nitrogen oxide in the proportions mentioned in Example 1 at normal pressure through the tube over the boat which contained the CrOj-Te mixture. The oven was heated according to the heating program described in Example 1 to a temperature of 300 ° C., which was maintained for 1 hour; During this time, the gas mixture continued to be passed through the pipe ίο. At the end of this heating period, the platinum boat was removed from the furnace and left to cool in the air. The weight loss was 17.4 ⁰ Z ₀ , based on the original weight of the CrO _{1 placed} in the platinum boat.

* 3 Duj Uw; j; ^ «D * ii« nJt%. _ne «ΛιιΐιαΑβ c /» tiuiar7p crystalline material was crushed in a Möiser, washed in water and acetone _fc and dried in the air before the magnetic properties were measured. The following magnetic properties

ao shafts were determined: H et = 49 Oersted; σ, - 84.5 electromagnetic units / g; a _T --- 10.4 electromagnetic units / g.

The X-ray diagram of this crystalline product showed only strong lines for CrO ₂ in the rutile crystal

»5 structure. Since in this case there was no significant shift of the lines compared to the normal CrO ₂ image, no significant solubility of the Te in the CrO ₂ crystal lattice can be assumed.

B e i s ρ i e I e 4 to 9

In order to determine the influence of a change in the amount ratio of NO to O ₂ in the atmosphere in which the ferromagnetic crystals are formed, Examples 4 to 9 were carried out in

in the same manner as described in the previous examples, with the difference that the ratio of NO to O ₂ in the gas mixture which was introduced into the pipe was changed.

In the manner described in Example 1, six additional samples of ferromagnetic CrO ₂ were prepared. The proportion of NO in the gas mixture in these tests varied between 1.5 and 33 percent by volume. In each case the sample was heated to a temperature of 275 ° C for a period of 8 to 20 hours. These samples were not washed with water and acetone after the synthesis, but this washing would have resulted in a slight improvement in the magnetic properties. The results obtained with the ferromagnetic oxide samples prepared under these conditions are shown in Table I below.

Table I CrOv reactions at 275 ° C as a function of the NO / Oj ratio

Introduced NO, measured at normal pressure, volume percent (ReM oxygen)

Heating time at:> 75 ^Ü C, hours

Weight loss,%

Induction cocvulsive force (// _c <). Oersted

Saturation, σ ,,
electromagnetic units / g

Remanence, a _r ,
electromagnetic F.inhciicn / g

CrO ₂ , weight percent

⁵ I. Ice pie ' ⁷ I. 8th ⁴ I. 9 ⁶ I. 3.5 2.5 33 20th 5 10 9 8th 20.7 12th 18.1 19.7 23.8 28 19.9 28 31 - 24.2 31 60.5 59.6 O 0.67 54.9 1.84 1.96 27 1.61 67 66 O 61

18.2
0

10.3

0
11th

Example 10 to 13

In order to determine the influence of changes in temperature in the production of ferromagnetic CrO ₂ according to the invention, four additional samples _{were prepared using a gas mixture of 3.5 ° / 0} NO and 96.5 ° / ₀ O, the samples were heated to temperatures of 275 to 350 "C for different lengths of time. These samples were not washed with water and acetone after the synthesis, but this washing would have resulted in a slight improvement in the magnetic properties. The ferromagnetic properties that were determined for the products in these examples , are listed in Table II below.

Tables

CrOj reaction in an atmosphere of 3.5 ° / ₀ NO and 96.5% O ₂ depending on the temperature _ao (heating rates as in example 1)

10 rice P i c I 13th 17.5 11th 12th 1 Heating time, hours 275 2 2 350 Temperature, ⁰ C 20.4 300 325 19.2 Weight loss, ° / ₀ 18.9 19.2 induction coercive force 31 33 (HΉ). Oersted 38 37 Saturation, he », electro 45.8 72.3 magnetic units / g 80.4 75.0 Remanence, σ _Γ , electro 1.2 3.4 magnetic units / g 51 3.3 3.5 80 CrO ₂ . Weight percent ... 89 83

Example 14

3 g of CrO ₃ were weighed into a platinum boat and. as indicated in Example 1, placed in a tube furnace. One end of the tube furnace was connected via a needle valve to a source of NO gas which was set to a pressure of about 1 atm. The other end of the tube furnace was connected to a water jet pump via a mercury manometer. After the platinum boat was introduced into the tube furnace, it was closed and a water jet pump turned on. After evacuating the tube furnace to a negative pressure of about 18 mm / Hg (0.02 Atm) according to the Mcnometer display. the needle valve was opened to allow the introduction of NO gas into the tube furnace. The gas flow was regulated with the aid of the needle valve until a constant pressure of about 50 mm / Hg (0.065 atm) could be read on the manometer. The tube furnace was then started to heat up, the procedure being as in Example 1, with the exception that a maximum temperature of 300 ° C. instead of 325 ° C. was set. The platinum boat was then taken out of the tube furnace and allowed to cool in air at room temperature. The black crystalline product demonstrated a weight loss vrr. 19.5 ° / ,. based on the weight of the starting material applied CrO ₁ . After crushing. Washing after drying according to Example 1 was determined. d; eat the product / u 59 percent by weight from IrO. existed and had the following magnetic properties: Het ■ - 80 to 100 Oc, et, - 54 electromagnetic units / g. n _r --- 11.0 electromagnetic units / g.

Example 15

There was prepared a different C ₃ O "sample durcli heating of CrO ₃ in a muffle furnace (3 hours at 300 ⁰ C). There was a weight loss of about 7%. and the X-ray diffraction pattern only showed the characteristic applicable _{to Cr 3} O _8. The sample was then ground up and 3 g, as described in Example 1, placed in a platinum boat and introduced into a tube furnace. It was then heated to 275 ° C. (about 8 hours), during which time a mixture of 5.2 percent by volume NO and 94.8 percent by volume O _{2 was passed} into the tube furnace. The product obtained consisted of 49 percent by weight CrO ₂ and had the following magnetic properties: // <· <-28 Oersted, σ »= 39.4 electromagnetic units / g. σ _Γ = 0.91 electromagnetic units / g.

Example 16

By spreading a thin layer of CrO ₃ in an aluminum dish and heating it to 360 ³ C in an oxygen atmosphere (16 hours) at normal pressure, a Cr ₁ O ₅ -PrObC was produced.

Example 1 was repeated with the exception that instead of CrO _{3, Cr 1} O _{5 was} now used as the starting material. The black crystalline final product had tetogen on the weight of Cr ₁ O ₆ used as the starting material has a weight loss of 12.2 ° / _O and contained 62.4 percent by weight of CrO. ₁ The magnetic properties are as follows: / Y ₁ - * = 100 Oersted, σ, = 57.4 clectromagnetic units / g, (T ₁ - = 11.5 electromagnetic units / g.

40 Examples 17 to 25

In each of these examples, 3 g of CrO _{3 were} weighed into a platinum boat and. as described in Example 1, introduced into a tube furnace. In each case the oven was quickly heated to the temperature given in Table III and held at that temperature for the time also given in the table. During the heating season, a mixture of NO + argon in the composition shown in Table Ml in percentage by volume was introduced into the furnace. After washing and drying, the products obtained showed the data shown in Table III.

SS Examples 26 to 30

In each of these examples, 3 g of CrO _{3 were} weighed into a small platinum pouch and. as in the example 'bf. ^ chricben, introduced into a tube furnace. In each «i

6. ' In this case, the oven was quickly heated to the temperature given in Table IV and kept at this temperature for the temperature also given in Table IV. During the hot spell wunle ciu mixture of NO I N. in the Tabetic IV in Voitim pronrnt wicHcrgcgcbcnencn composition «ι» Ι ·· ι furnace introduced. After W-een un «j IrtHknr ^1, the products obtained showed the data shown in TaUlIe IY .ml.

209635/16

(ο

10

Table III CrOj reaction in an atmosphere of NO - \ - argon

17th 18th 19th B e i s ρ
20 21 2.5
300 el
22nd 23 24 25th 5.5
275 1.5
300 1.0
325 1.5
300 4.0
96.0
20.4
40 0.75
325 0.5
350 1.0 0.5
350 325 2.2
97.8
18.18
25th 2.2
97.8
19.19
37 2.2
97.8
19.48
37 4.0
96.0
20.2
37 57.7 4.0
96.0
18.75
37 4.0
96.0
20.08
44 4.4 ι 11.1
95.6 88.9
21.28 I 20.81
51! 44 23.3 64.2 70.1 61.9 3.0
64 72.8 53.2 36.7 j 38.2
] 0.7
26th 3.7
71 4.0
78 3.5
69 4.1
81 2.9
59 2.0 1.7
41 42

Heating time, hours Temperature 'C

Gas mixture, volume percentage at normal pressure

NO

argon

Weight loss, ° / ₀

Induction coercive force Hd, Oersted ... saturation, σ ,, electromagnetic

Units / g Remanence, a _r , electromagnetic

'Units / g

CrO ₁ , weight percent

Table IV CrOj reaction in an atmosphere of NO f N ₁

example

26 '27 I 28 j 29

Heating time, hours Temperature ⁰ C Gas mixture, volume percent, measured at normal pressure

NO

N _s

Weight loss, ° / ₀ Induction coercive force Heu Oersted Saturation, »τ ,, electromagnetic units / g Remanence, oy, electromagnetic units / g CrO ₂ . Weight percent

7th
275

98

20.18 32 28.4

1.0 32

300

1.9
98.1
20.24
37
49.4

2.2 55

0.5 1.5 325 300 2.0 4.2 98.0 95.8 19.19 20.46 40 37 • 69.3 44.1 4.0 1.7 77 49

0.25 325

4.2 95.8 18.49 35 69.2

3.4 77

Claims (6)

Patent claims: 1. Process for the production of ferromagnetic chromium dioxide by heating a chromium compound with a chromium valence above 45 4 in a gas or a gas mixture in a reaction chamber at elevated temperature, characterized in that the gas or the gas mixture when entering the reaction chamber NO under a pressure or partial 50 contains pressure of 0.01 to 0.1 atm and is continuously supplied to the reaction chamber, the Temperature in the range of 250 to 375 ° C and the pressure of which is kept at 1 atm or less. 2. The method according to claim 1, characterized in that the gas mixture is at least 1 to 10 percent by volume of NO and 99 to 90 percent by volume a gaseous, in particular nitrogen. Contains argon or oxygen existing diluent. 3. The method according to claim 1 and 2, characterized in that the chromium compound Heated for 0.5 to 10 hours. 4. The method according to claim 1 to 3, characterized in that the temperature in the Maintains reaction chamber at 275 to 350 ° C 5. The method according to claim 1 to 4, characterized in that one is used as the chromium compound Chromium trioxide is used. 6. The method according to claim 1 to 5, characterized in that the temperature is slowly increased to the desired temperature range.