DE1239606B - Process for the production of ferromagnetic cores with a largely rectangular hysteresis loop - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

PATENT LETTERING

Int. Cl .:

C04b

German class: 80 b -8/092

Number:

File number:

Business day:

1,239,606
S47355VIb / 80b
3rd February 1956
April 27, 1967
June 20, 1968

Display day:
Issue date:
The patent specification differs from the Aüsle script

The invention relates to methods for producing ferromagnetic cores from materials according to Type of ferrite, which have largely rectangular hysteresis loops and in devices for magnetic recording, so-called storage devices, magnetic control organs, magnetic Amplifiers and the like can be used. In these applications they will generally be annular or at least closed cores made of these materials are used.

Materials with a rectangular hysteresis loop are already known, in particular alloys made of iron and nickel or iron and silicon, whose magnetic properties are mostly due to either Have become anisotropic by cold rolling or by heat treatment under a magnetic field. These materials generally have high saturation inductions and low coercive forces

on. ; ·

The main disadvantage of this known metallic Materials with high saturation induction is the generally low value of their specific resistance, which leads to high losses due to eddy currents. These high losses are prolonged Response time as well as a deformation of the hysteresis loop, which their at high frequencies Loses rectangular shape. To avoid these adverse effects, frequencies of several megahertz core sheets made of the mentioned materials with a very small thickness in the order of magnitude of a few microns, so that the manufacturing cost is extremely high will.

It is possible to avoid this disadvantage by using ferromagnetic materials from the ferrite group used, which have a higher resistance and of which a row is largely rectangular Exhibit hysteresis loop. On the other hand, these materials generally have one saturation induction value too low.

Ferrites with an almost rectangular hysteresis loop are mainly used for switching and storage purposes used. You should have as large a rectangular coefficient as possible and as large as possible Have saturation induction, while the coercive force should be as low as possible, so signals higher Voltage can be obtained at relatively low control currents. .

They are already ferrites, ζ. B. Magnesium-Manganese-Ferrites and their production processes are known in which one of these values corresponds to the requirements, but so far there are no ferrites processes for the production of
ferromagnetic cores with largely
rectangular hysteresis loop

Patented for:

Societe Lignes Telegraphiq'ues et Telephoniques, Paris

Representative:

Dipl.-Ing. H. Ciaessen, patent attorney,
Stuttgart 1, Rotebühlstr. 70

Named as inventor:

Andre Pierrot,

Yves Charles Eugene Lescroel,

Bogdan Grabowski, Conflans-Sainte-Honorine;

Charles Louis Guillaud,

Bellevue, Seine-et-Oise (France)

France of February 3, 1955 (684 899),
of May 3, 1955 (55 332)

become known where all these values meet the requirements of practice to a sufficient extent Take into account.

Rectangular ferrites are already known that have a saturation magnetization of over 3000 Gauss, however, these ferrites have a very poor square coefficient. On the other hand are Ferrites with a square coefficient of 0.96 are known, but their saturation magnetization is only are relatively low.

From the magazine "Electronics", April 1953, p. 149, it is known that a ferrite is made from magnesium ferrite was developed with a square ratio of 0.9 and a saturation magnetization of 1780 Gauss.

In the magazine "Tele-Tech" from May 1952 are on pages 50 to 52 and 82 to 84 describe the magnetic properties of some ferrites. There is also a rectangular ferrite is described, which has a saturation magnetization of 2350 Gauss, but only one Has rectangular coefficients of 0.91 and a coercive force of 1.5.

In the journal "Journal of Applied Physics", Vol. 25, No. 2 of February 1954, ferrites are described, which have a square ratio of 0.96. the

«09573/294

However, saturation magnetization is only 1950 Gauss.

Accordingly, according to the method according to the invention, ferrites are obtained which have a square ratio of at least 0.92 have a greater saturation magnetization than the known ferrites and at the same time have a coercive force which is lower than that of the known Ferriten'mit high saturation magnetization.

The method according to the invention produces magnetic cores with a substantially rectangular hysteresis loop obtained, which at the same time have a good rectangular coefficient, a high saturation magnetization and there is a low coercive force. . The method according to the invention comprises on the one hand a certain composition of the starting oxide mixture and, on the other hand, various process steps in the production of these ferrites, which are only sought after in the claimed combination Result.

There are ferrites of the claimed composition and also individual process steps such. B. ¹ the glow in an inert atmosphere and the use of starting materials that are as pure as possible are known per se, but the advantages of the subject matter of the invention are not yet achieved through the composition alone or through individual process features. Simply by combining all measures, ferrites are obtained in which the magnetic properties mentioned are improved overall. The ferrites obtained by the method according to the invention also have a higher specific resistance.

Before explaining the invention, let’s begin with a few definitions of those which determine the hysteresis loops magnetic quantities and their ratio values, to which reference is made below, given:

An approximately rectangular hysteresis loop, which extends from a maximum field strength + H _m to a field strength -H _m , is determined by the following quantities:

Bm = the induction in Gauss corresponding to the field strength H _m;

Brm = the remanent induction in Gauss;
Hcm = the coercive force in Oersted;

Bam = the final value of the induction after a change in the magnetic field strength of

the value ¹ H _1n to the value -—-.

The following coefficients are used to assess the shape of the loop:

ßm = w '"= the" squareness coefficient ";

R _m = - £ - ■ = the "squareness ratio"; as well as the size

"_ Brm + B _m _ 1 '+ ßm

TD D R /?

^ Tm "dm Pm - ** wi

For a largely rectangular hysteresis loop, ß _m and R _m must strive towards 1 and K _{m must be} as large as possible.

The following is always the initial permeability in the demagnetized state for the permeability communicated.

The ferrites according to the invention have a negative coefficient of magnetostriction. _{The linear shrinkage of at least 8 ° / 0} to 30 ° / ₀ that occurs during the sintering and cooling of cores made of these ferrites results in mechanical stresses in the cores which, when a negative magnetostriction coefficient is present, have a favorable effect on the rectangular shape of the "hysteresis loop .

The magnetostrictive effects can through

the value of the coefficient of magnetostriction at saturation X _s , which for the demagnetized state can be characterized by extrapolating the curve of the relative change in the length of the

Sample -γ- is obtained for very high field strengths.

2u The "response time" is defined by considering two windings with negligible time constants, which are arranged on a core made of the relevant magnetic material. This core is subjected to a magnetic field H _m between H _cm and 2 H _cm

and then exposed to the field —.-. Then will

One of the windings receives a current pulse with a very short rise time (for example less than 0.1 microseconds, which brings the magnetic field to the value - H _m . The "response time" τ is the time, expressed in microseconds, in which the voltage generated in the other winding has declined again from zero to 10% of this value after exceeding a maximum value.

The ferrite cores obtained by the method according to the invention have the following properties: The cores according to Examples 1 to 4, which are suitable for communications engineering, have a rectangular coefficient β _m of at least 0.92, an induction5 _TO of more than 3000 Gauss at 20 ⁰ C and a coercive force H _cm of less than 0.6 oersted.

The ferrite cores according to Examples 5 to 8, which are intended for memory devices, have one Rectangular coefficients of at least 0.93, an induction greater than 1850 Gauss, and a coercive force less than 1.2 oersted.

All the cores have a Curie point higher than 12O ⁰ C and an increased resistivity (greater than 10 ³ ohm-cm).

As a result of the higher specific resistance, these cores show negligible eddy current losses on what their use at high frequencies with very short response times (τ <5 microseconds).

The method according to the invention for the production of ferromagnetic cores with a largely rectangular hysteresis loop, in which a homogeneous mixture of fine metal oxide powder, the iron (III) oxide and optionally oxides of the trivalent metals aluminum and chromium and a manganese oxide and optionally oxides of the divalent metals magnesium , Contains zinc and cadmium, pressed and the pressed mixture is heated to a temperature between 1200 and 135O ° C, whereupon a slow cooling takes place in an inert atmosphere, is characterized in that the process steps are combined in such a way that a mixture of χ Molpfozerit Fe ₂ O ₃ , >> mol-

percent Al ₂ O ₃ , ζ mol percent Cr ₂ O ₃ , u mol percent MnO, ν mol percent MgO, s mol percent ZnO and t mol percent CdO in an iron ball mill with steel balls with twice the weight of distilled water for 24 to 48 hours and then with a Pressure between 0.5 and 15 t / cm ^{2 is} pressed into cores, which are then heated for 2 to 6 hours in pure nitrogen, which contains a maximum of 2 percent by volume oxygen, to 1200 to 135O ° C and then cooled in pure nitrogen for about 15 hours The mixture may contain a maximum of 0.5 percent by weight of impurities of silicon dioxide, barium oxide, lead oxide, but not more than 0.05 percent by weight of strontium oxide, and the following conditions must be met for the molar proportions of the starting mixture:. _: . _:

23 < χ + y + ζ <52,

0 < y + ζ <0.25 x,
40 < u + ν <77,

0 <v <20,

0 < s + t < 15, if ν <8,

8 < s. + T < 15, if 8 <ν <20,

d. H. the

duction B _rm = OP,

Induction B _1n = OR, the remanent in-

f-f

which corresponds to the field strength "'"

Talking induction B ^ m = OS as well as the coercive force Hem- From these quantities the coefficients ß _m , R _m and K _{m result} ; one still maintains the size ratio

"m or m .

B _m

one, we get R _1n <1 -

3 Λ

but with the restriction that

50.2 < χ < 52 and 40 < u < 48.8

47 < χ < 52 and 47 < u < 53

to get voted,

25th

3 °

₃₅

sf? = 0 and ν <8 and ν = 1, respectively.

In the following description, the composition before grinding is given in each case. Due to the wear and tear of the iron comminution device during the grinding process, the iron content of the mixture normally increases by about 0.8 molecules Fe ₂ O ₃ per 100 molecules of ground material, so that after grinding a content of Fe ₂ O ₃ increased by this amount is the basis with corrections to be made as the grinder wears slower or faster.

The invention is explained in greater detail below using exemplary embodiments in conjunction with the drawings described. It shows

F i g. 1 a largely rectangular hysteresis loop,

F i g. 2 hysteresis loops for a core according to the invention from a 50 ° / ₀ Fe ₂ O ₃ and 50% MnO-containing material,

Fi g. 3, 4 and 5 for cores made of the same material on which the FIG. _{2 relates, hysteresis loops} for different operating temperatures, the changes in B 7n and H _cm as a function of the operating temperature and the change in R _m as a function of H _m for different operating temperatures,

F i g. 6 to 13 hysteresis loops for examples of cores according to the invention.

In Fig. 1, which represents a rectangular hysteresis loop, which corresponds to a field strength H _m , the quantities defined above are given.As already evident from the limits given above for the sum of the constituents and t , the zinc oxide can be completely or partially replaced by cadmium oxide in all the compositions given be replaced without this practically changing the specified properties for the product obtained.

In the information given in the present description, it should be borne in mind that the molecular percentage of manganese oxide is related in the usual way to the number of manganese atoms, so that in the following the manganese oxide is represented in the usual way by MnO, although different in practice Oxides can be used, such as MnO ₂ , Mn ₃ O ₈ etc.

production method
Composition and type of oxides used

For the mixtures iron (III) oxide Fe ₂ O ₃ , granular manganese oxide Mn ₃ O ₄ or another manganese oxide and optionally zinc oxide ZnO, aluminum oxide Al ₂ O ₃ , chromium oxide Cr ₂ O ₃ , which are obtained from chromic anhydride CrO ₃ , are used can, and magnesia MgO.

These oxides must be pure, and the mixture may contain no more than 0.5 ° / ₀ impurities. Silicon dioxide (SiO ₂ ), barium oxide (BaO), lead oxide (PbO), strontium oxide (SrO) and the like are particularly harmful because these impurities round off the corners of the hysteresis loop. Therefore, the content of each of these oxides must be less than 0.05 percent by weight. .

The optionally magnesium oxide used may consist of more or less hydrated magnesia are obtained, which is converted by baking at 500 ⁰ C in MgO.

The grinding

The oxide mixture is in an iron ball mill with steel balls generally during one Period of 12 to 48 hours with approximately twice its weight in distilled water ground.

The milling, pressing and heat treatment are not changed _{in the presence of Al 2} O ₃ or Cr ₂ O _3.

Since the iron content increases during the grinding process, as already stated above, as a result of iron abrasion from the grinding vessels and from the steel balls, the molar percentages of Fe ₂ O _{3 specified for the compositions prior to grinding must be increased by the amount specified above, by the molar percentages} after grinding.

The pressing

The mixture of oxides is then pressed into the desired core shape.

The influence of the pressing pressure is great. On the one hand, the pressing pressure must be so high that the saturation induction of the end product is sufficiently high and on the other hand still so low that the shrinkage during sintering is great.

With a pressure of about 5 t / cm ² , which gives a linear shrinkage of about 15%, good results have been achieved. However, pressures of 0.5 to 15 t / cm ² can also be used.

The heat treatment

The product obtained in the manner described is subjected to a heat treatment for a period of 2 to 6 hours at a temperature between 1200 and 1350 ⁰ C, in pure nitrogen, to which 0 to 2 percent by volume of oxygen have been added, followed by slow cooling in the Run of about 15 hours in pure nitrogen follows.

For optimal properties, the firing temperature for each composition must be experimental be determined.

In general, the more magnesium oxide MgO the ferrite contains, the higher the temperature must be. For materials with no magnesium oxide MgO very good results at 1250 ⁰ C can be achieved at 10% MgO, it is expedient to burn at 1275 ⁰ C, while with an MgO content of 16% at a temperature of 1300 ° C, satisfactory results delivered.

In one embodiment of the invention, the ground powder can before pressing between 900 and 1100 ⁰ C and then presintered before the pressing and final heat treatment are reground. The temperature of this pre-sintering must be determined in such a way that the final shrinkage of the material is at least greater than 8%, since this shrinkage determines the stresses and thus the properties of the rectangular shape. It has been observed that cores made from a mixture which after normal treatment gave a good rectangular shape of the hysteresis loop, after pre-sintering this mixture at too high a temperature (e.g. 1200 ° C), which results in shrinkage of the order of just 4%. did not have a rectangular hysteresis loop.

For example

F i g. 2 shows hysteresis loops for maximum Field strengths of 2 and 10 oersteds on an annular core of the following dimensions were measured:

Outside diameter 34.1 mm

Inner diameter 26.9 mm

Height 12.2 mm

The initial composition of the substance was:

50 mole percent Fe ₂ O ₃
50 mole percent MnO

The grinding took place for a period of 48 hours in an iron ball mill a capacity of 161 which contains about 3 kg of mixture, about 61 water and about 20 kg of balls contained.

The cores produced therefrom were ^{sintered at 1240 °} C. for a period of 4 hours in pure nitrogen containing 1% oxygen and cooled in pure nitrogen.

The cores showed a shrinkage of 14.8% after sintering and the following properties at a field strength of H _7n = 10 Oersted:

a low coercive force H _cm = 0.5 Oersted, an induction B _7n = 3660 Gauss,

a "squareness coefficient"

Brm _

- - U, y /.

B _7n

The magnetostriction coefficient at magnetic saturation is approximately A ₅ = -4 · 10 ~~ ⁶ The Curie point 0 _C is about 280 ⁰ C. As the analysis showed, the nuclei do not contain any FeO.

F i g. 3 shows the hysteresis loops of cores made from this fabric for 2 oersteds and for different ones Operating temperatures.

F i g. 4 shows the change in B _m and Hcm as a function of the operating temperature.

F i g. 5, which shows the change in the "squareness ratio" R _m as a function of the field strength Hm for different operating temperatures, shows the influence of the temperature on the level of the field strength -Hm- leading to optimal squareness

When used for storage devices for magnetic recording, the ratio Rm to the temperature should change as little as possible, so that suitable operating conditions result within a larger temperature range. The cores forming the subject of the invention have been specially studied for this purpose. The "squareness ratio" R _m changes very little with temperature.

This substance is in the form of rings in magnetic control elements, magnetic commutators, magnetic amplifiers and the like are used.

Example '2

F i g. 6 shows the hysteresis loop measured at H _m = 2 Oersted of a core with the following initial molar composition:

48% Fe ₂ O ₃
45.2% MnO
6.8% ZnO.

55 It follows:

μ = 330

Bm = 3580 Gauss
Hcm = 0.35 oersted

ß _m = 0.94
Brm = 3300 Gauss

0c = 260 ° C

The manufacturing process was the same as that given for Example 1. The addition of zinc results in a reduction in the coercive force H _cm .

B e i s ρ i el 3

F i g. 7 shows the hysteresis loop of a toroidal core measured at H _{7n = 2 Oersted in accordance with FIG}

9 10

given in Example 1, but with the following additions For this substance, there is a field strength

Composition of the starting mixture in mole percent- H _m - 20ersted:

sentences :.

B _m = 2300 Gauss

50 ⁰ Z ₀ Fe ₂ O ₃ 5 5 _m = 2140 Gauss

40 ⁰ Z ₀ MnO Hem = 0.9 Oersted

5% MgO ß *> = ° ^'93

5% ZnO

and for the optimal field strength H _m = 1.4 Oersted:

With the same manufacturing process as for the ίο _ " _mr "

is game 1 one gets the following magnetic properties ο ^

shafts: I.

e de g g

Example 1 gives the following magnetic properties ο

H _cm = 0.8 oersted

B _m = 3260 Gauss ξ ™ Ζ n '? R

B _rm = 3120 Gauss is Z ^m Z i->

Hem = 0.45 Oersted ä _w - iz

pV = 0.96 example 6

F i g. 10 shows for H _7n = 3 Oersted or for the

F i g. 8 shows for H _m = 2 Oersted or: H _m = lOOer- ao optimal field strength H _m = 1.8 Oersted the hysteresis

sted the hysteresis loops of an annular core grind a toroidal core that was used in example 1

of the type specified in Example 1, with the following ascribed type with the following composition of

Composition of the starting mixture in mole percent- starting mixture (in mole percentages):

sentences:

_a5 40 ° / ₀ Fe ₂ O ₃

51.0% Fe ₂ O ₃ . 55% MnO

44.0 ° / ₀ MnO 5 ° / ₀ Al ₂ O ₃

5.0 / o MgO jjj _e grinding and treatment conditions

, correspond to those given in Example 1. The conditions for the grinding and the her- 3 °

position were the same as for example 1. _{The core has the following} magnetic properties: for a field strength H _m = 3 Oersted:

The core has the following magnetic properties - ^H } ¹ * ° | ^rsted stores on: 35

For a field strength H _m = 10 Oersted:. .

H _cm = 0 6 Oersted B _m = 3500 ' Gauss ßrn = 0.92 4 °

and for a field strength H _m == 2 Oersted:

Hem = 0.6 oersted ■

i? _m = 3060 Gauss ". _TT ^, _γ . ". . _π . . , "...

ο _ η OS 45 The hysteresis loops of some examples of ferro-

p », -. u, vd are magnetic substances made of Fe ₂ O ₃ , Al ₂ O ₃ and MnO

in Fig. 13 for various mole percentages of Al ₂ O ₃

The addition of calcium oxide enables this to be demonstrated to the effect of the addition of Al ₂ O ₃

Show burning at a temperature lower than 1300 ° C,

and gives good results at 124O ⁰ C. 50 B '"17

The ^

Magnetic cores are particularly suitable for use in FIG. 11 shows for H _m = 3 Oersted or for the

in magnetic storage. optimal field strength H _m = 2 Oersted the hysteresis

T ₅ ·. ,, grinding of an annular core which in the two

¹ ^ ¹⁶ 55 game 1 described type with the initial co-

F i g. 9 shows for H _m = 2 Oersted and for the settlement of the oxide mixture (in mol percentages):

optimal field strength H _m = 1.4 Oersted die hyste- 45 0 / p _e q

Resis grinding of a toroidal core according to example 1, 50 ° / ° MnO ³

but with the following composition of the statement 50 / Γ Ο

Starting mixture (in mol ^{% additions): 60 T% 3}

The core was made in the same way as for

40 ⁰ Z ₀ Fe ₂ O ₃ ■ Example 1 described prepared.

8 ° / ° ZnO The result for this nucleus is: for a field strength

7% MnO, 65 ^ »= 3 oersteds:

B _m = 2200 Gauss

The manufacturing process was the same as the H _cm = 1 * 40 Oersted

wrote. ß _m = 0.94

809 573/294

Hem = 1.15 oersted 1.8 oersteds: Bm = 2260 Gauss ßm = 0.94 r is the optimal field strength H _1n = H _em = 1.0 oersted Bm = 1960 Gauss ßm = 0.94 Rm = 0.77 JYm = 12

for the optimal field strength H _m = 2 Oersted:

Bm = 1880 Gauss
H _cm = 1.15 oersted

ßm = 0.93

Rm - 0.70

Examples

12 shows the hysteresis loop of a toroidal core with the dimensions given in Example 1 and with the following initial composition of the mixture (in molar percentages) for the optimal field strength H _{m. = 2 Oersted:}

45.0% Fe ₂ O ₃

5.0% Al ₂ O ₃
42.0% MnO

5.0% MgO

3.0% ZnO

20th

The milling and heat treatment conditions were the same as those given in Example 1.

The material has the following magnetic properties for H _m = 2 Oersted:

Hem = 1.2 oersted
Bm = 2320 Gauss

ßm = 0.94

Rm = 0.74

Km = 10

Claims (3)

Patent claims: 1. Process for the production of ferromagnetic cores with a largely rectangular hysteresis loop, in which a homogeneous mixture of fine metal oxide powder, iron (III) oxide and optionally oxides of the trivalent metals aluminum and chromium as well as a manganese oxide and optionally oxides of the divalent metals magnesium, zinc and contains cadmium, pressed and the pressed mixture is heated to a temperature between 1200 and 1350 ° C, followed by slow cooling in an inert atmosphere, characterized in that the process steps are combined in such a way that a mixture of χ mol percent Fe ₂ O ₃ , y mol percent Al ₂ O ₃ , ζ mol percent Cr ₂ O ₃ , u mol percent MnO, ν mol percent MgO, ί mol percent ZnO and t mol percent CdO in an iron ball mill with steel balls with twice the weight of distilled water for 24 to 48 hours and then with a pressure between 0.5 and 15 t / cm ^{2 is} pressed to form cores, which are then 2 to 6 Hours in pure nitrogen, which contains a maximum of 2 percent by volume of oxygen, ^{heated to 1200 to 135O 0} C and then cooled in pure nitrogen for about 15 hours, the mixture at most 0.5 percent by weight impurities, silicon dioxide, barium oxide, lead oxide, however may contain a maximum of 0.05 percent by weight of strontium oxide and the following conditions are met for the molar proportions of the starting mixture: 23 < χ + y + ζ < 52, 0 < y + ζ < 0.25 x,
40 <«+ v <77, 0 <v <20, 0 < s + t < 15, if ν <8, 8 < s + t < 15, if 8 <ν <20, but with the restriction that
50.2 < χ < 52 and 40 < u < 48.8 or. 47 < χ < 52 and 47 < u < 53 to get voted, if y - \ - z - \ - s - \ - t - 0 and ν <8 and ν <1, respectively. 2. Process for the manufacture of ferromagnetic Cores according to Claim 1, in which the starting mixture of the metal oxides is exclusively from oxides of the trivalent metals mentioned, also from manganese oxide and magnesium oxide consists, characterized in that between 50.2 and 52 mole percent of the oxides are trivalent Metals, between 40 and 48.8 mole percent manganese oxide and between 1 and 8 mole percent Magnesium oxide can be used. 3. A method for producing ferromagnetic cores according to claim 1 and 2, characterized in that the oxide mixture used after grinding a first heat treatment for pre-sintering in air at a temperature between 900 and 1100 ⁰ C, then a second grinding, a pressing process and a second heat treatment for a period of 2 to 6 hours at a temperature between 1200 and 1350 ° C in a mixture of pure nitrogen and 0 to 2 percent by volume of oxygen, followed by slow cooling for about 15 hours in pure nitrogen. Considered publications: German patent application ST 4840, (published on July 9, 1953); French Patent Nos. 1051851, 1074864; Belgian Patent No. 525 036; British Patent No. 655,666; U.S. Patent No. 2,640,813; J. applied Physics, 25 (1954), pp. 152 to 154; Physica, June 1936, pp. 463-483; Physically. Zeitschrift, 39 (1938), pp. 208 to 212; Electrotechn. Z., Ed. A, April 1954, pp. 253-256; Philips' Techn. Rundsch., 16 (1954), pp. 124 to 134; Issue 4/5, p. 131, tables; TeIe Tech, May 1952, pp. 50 to 52, 82 to 84: Journal of Appl. Physics, 25 (2), pp. 152-154 (1954); "Electronics" from April 1953, p. 149. Legacy Patents Considered:
German Patent No. 976 406. 35 40 50 55 60 For this purpose 3 sheets of drawings 709 577/321 4.67 © Bundesdruckerei Berlin