DE2148554A1 - Process for the production of a polycrystalline ferrite body - Google Patents

Description

PHN 5190 C KOPP / HG

Dipl.-Ing. HORST AUER

PC; ¹ OrJtOFiWcJt

Applicant: NV FII.LIrS ' GLGEiUMPtNFABRIEKEH File: PHN- 5190

Registration vow »

Sep 28, 1971

Process for producing a polycrystalline

Ferrite body

The invention relates to

a method for producing a polycrystalline ferrite body in which a finely divided ferrite-forming Starting mixture is formed, which is ground, pressed into a body of the desired shape and is sintered. (Under "ferrite" here is a crystalline reaction product of the oxides of iron and one or more other divalent metals or divalent metallic complexes. A "ferrite-forming mixture" here is a mixture of oxides of the desired metals and / or

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of compounds which produce oxides of the desired metals when heated).

One such procedure is

from the American patent specification 3,472,780 known.

As is well known, bodies find out

a sintered, oxidic ferromagnetic Material, which material is commonly referred to as "ferrite", including use as cores for electromagnetic transducers for converting changes in electrical signals into changes magnetic induction, or vice versa.

Since electromagnetic transducers or magnetic heads with a magnetic recording medium that touches it and moves quickly, such as a magnetic tape, should work together, are the mechanical Properties, and in particular the abrasion resistance, really important. A distinction should be made between two types of abrasion. The first kind that is related to the hardness of the material used, is expressed in a uniform "total" decrease the thickness of the material of the contact surface of the transducer. The characteristic of the transducer itself is not affected by this attrition. The second type, that of the polycrystalline structure of the is inherent in the material used, is expressed by the crumbling of ferrite crystals from the

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Contact area of the transducer under the influence of the abrasive action of the recording medium. if Break out crystals at the edge of the useful gap, the straightness of this gap is lost, whereby under certain circumstances the gap length, i.e. the dimension of the useful gap in the direction in which the recording medium moves with respect to the transducer can be enlarged such that the write / read quality of the transducer is impaired. Namely, it was found that with the known regular crystal structures, a crystal can break out relatively easily along the grain boundary. If with such a crystal structure once a crystal has broken out, the surrounding crystals are less supported and it is very likely that more and more crystals will break out. The second type of attrition can therefore affect the characteristic of the transducer.

In the German patent specification

No. 1.09 ^ · 955 attention was drawn to this problem which, according to this patent, thereby that was solved as a core for a transductor that has a high resistance to crumbling must have, a ferrite body made of the largest possible, irregularly shaped crystals is used became. With such a crystal structure, the MJgUch-

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The ability of a crystal to break out is much lower because the irregularly shaped and consequently interlocking crystals "hold" each other. In particular, in the cited patent proposed to use a ferrite single crystal as a core for a transducer. The production is sufficient large ferrite single crystals is particularly expensive. There is also the disadvantage that the Resistance to abrasion of the first type of single crystals turns out to be less than the polycrystalline ones Materials has proven.

The invention aims to be a

To create polycrystalline ferrite material which has such favorable abrasion properties that it in particular is suitable for use in magnetic heads.

The method according to the invention

is characterized in that before the sintering treatment is carried out, a grain growth promoting Substance or a combination of such substances is added, which substance or which combination of substances is chosen from the group consisting of: BaF,

₂ ; the oxides of B, Bi, Pb, Si, Ca, Cu, Mg and V; and Fe (PO.), while, depending on the composition of the ferrite-forming mixture, the amount added and the sintering temperature are chosen such that interdigitated crystals with an average grain size of more than 50 μm are obtained.

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insane

To a in relation to the

According to a preferred embodiment, obtaining the crystal structure as homogeneous as possible is the final product of the process according to the invention, the substance which promotes grain growth or the combination such substances are added to the starting mixture to be ground. It should be noted that in this case the The scatter in the mean grain size can be very small, i.e. so-called duplex structures are not appear. To obtain an end product that is beneficial when used as a core for a magnetic head Has magnetic and electrical properties, the ferrite-forming starting mixture is preferred After the grinding process, it is first pre-sintered and ground again, after which it is compressed into the desired shape and is sintered; in other words: a pre-sintered powder is used.

To get an end product with if possible

favorable magnetic and electrical properties To obtain, the method according to the invention can be modified so that the desired abrasion-resistant crystal structure occurs only on the surface or on part of the surface and that the inside has a fine-grain structure, which leads to favorable electrical and magnetic properties Properties is required.

Another preferred embodiment of the method according to the invention is characterized in that the ferrite-forming component

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initial mixture is pressed and, if necessary, presintered; that the substance promoting grain growth or the combination of such substances locally on the outside of the after pressing and the eventual Presintering obtained body is attached, and that this body is then sintered.

In addition, the procedure

can also be modified according to the invention in such a way that the end product itself is a fine-grained one

W has structure, but has tracks or patterns consisting of interlocking crystals with an average grain size of more than 50 μm.

Another preferred embodiment of the method according to the invention is characterized in that the substance promoting grain growth or the combination of such substances is added to the starting mixture; that this mixture is ground, pressed and presintered, and that

fc the body obtained after pressing and pre-sintering locally to such a sintering temperature during sintering is brought about that the desired crystal structure occurs only at this point. A local Heating to the sintering temperature can be done e.g. with the help of a laser beam or with the help of a Pt wire can be achieved through which current is passed.

Determined the grain growth

promoting substances have proven to be particularly effective within the scope of the invention _} provided that the correct Kosafciii-i tion -of added menp and

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Sintering temperature was found.

According to a preferred

Embodiment of the inventive process is in the manufacture of Ni-Zn ferrite an amount from 0.01 to 1% by weight of the particular composition by its molekulaire mixture.

xB 0 + ySiO + zCaO

added, where 1 ^. χ ^ f 10; 0 ^ y ^ 10; 0 ^ ζ ^ 5 is, while the sintering temperature is between 1180 ° C and 1275 ° C.

It turns out that on

in this way, with the aid of the above-mentioned addition, a ferrite body with interlocking crystals a mean grain size of more than 50 / µm can be. It should be noted that the scatter in the mean grain size is particularly small, and that the magnetic and electrical properties of the ferrite bodies obtained in this way are particularly special are cheap.

Although by the aforementioned

In addition to obtaining the desired crystal structure, attention should also be paid to other properties will. The crystal interfaces should be clean and not contain any large pores. this is achieved by having an amount of 0.00? - 0.25% by weight of the starting mixture is added.

According to a preferred embodiment of the process according to the invention, the additive

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by the following molecular composition marked:

2B ₂ O ^ + SiO ₂ ,

while the. Sintering temperature between 118O ° C and 124o ° C.

It turns out that then

in particular after sintering the pressed powder at a temperature between 1220 ^° C. and 1230 ^° C., a product with a maximum mean grain size (J \ 500 / μm) W can be obtained.

According to another preferred

Embodiment of the inventive method is the additive characterized by the following molecular composition:

BO + 2SiO + CaO.

d j (L

It turns out that then, after sintering the pressed powder, a product can be obtained, in which the mean grain size does not depend, or only to a small extent, on the sintering temperature used

is dependent. In particular, it turns out that changes in the sintering temperature between 118O ° C and 1275 ° C hardly affect the mean grain size, whereby however, this grain size is probably below the values found in the first preferred embodiment.

According to another preferred

In the embodiment of the process according to the invention, the additive is characterized by the following molecular composition:
B ₂ O _{3 +} 2SiO ₂ ,

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while the sintering temperature is between 1240 ° C and 1300 ° C. It turns out that after the Sintering of the ground and pressed powder a product is obtained which has a high initial permeability / U. as well as having a high density.

In the production of Ni-Zn

-Ferrite bodies also has the addition of CaO + BO. Proven to be particularly effective. According to a preferred embodiment of the inventive method of a Ni-Zn ferrite, an amount of 0.01 in the preparation of - added 0.2 weight ^ o CaO + BO during the sintering at a temperature between 1175 ° C and 125O ° C. and preferably takes place between 1200 ^0C and 1250 ° C.

Another preferred embodiment of the method according to the invention is characterized in that in the production of a Ni-Zn ferrite body an amount of 0.05-0 »5 wt. ^ BaF and / or SrF is added during sintering takes place at a temperature between 1200 ° C and 125O ° C .

A further preferred embodiment of the inventive method is characterized in that a Ni-Zn ferrite in the production of an amount of 0.05 -. 0> 5 wt% of Bi 0 is added during the sintering at a temperature between 1175 ° C and 1275 ° C takes place.

Surprisingly, it was found that the addition of CaO + Β _? 0_ at the

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position of Mn-Zn ferrite bodies even more effective than in the production of Ni-Zn ferrite bodies provided that the correct sintering conditions were chosen.

A preferred embodiment

form of the inventive method is thus characterized in that a Mn-Zn ferrite an amount of 0.005 in the preparation of -. is added 0.06 wt $ CaO + B ₂ ⁰ O, and that the sintering in an oxygen containing atmosphere at a temperature takes place between 135O ° C and 14OO ° C.

Another preferred embodiment of the method according to the invention is characterized in that in the production of an Mn-Zn ferrite body an amount of 0.005-1 wt. $ of the mixture determined by its molecular composition:

XB ₂ O ₃ + ySiO ₂ + ZFe ₃ (PO ^) ₂ ,

where 0 _y f χ ^ 1; 0 <ζ y <1; 0 <ζ ζ ^ - 1 is added, and that sintering takes place in an oxygen-containing atmosphere at a temperature between 135O ° C and 14OO ° C.

Another preferred embodiment of the method according to the invention is characterized in that in the production of an Mn-Zn ferrite body an amount of 0.005-0.5 Wt. $ BaF is added and that sintering

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in an oxygen-containing atmosphere at a Temperature between 135O ° C and 14OO ° C takes place.

Another preferred one

Embodiment of the inventive method is characterized in that a Mn-Zn ferrite an amount of 0.005 in the preparation of -. Is added 0.05 $ Vp ⁰ C, and that the sintering in an oxygen containing atmosphere at a temperature between 1375 ° C and 14OO ° C takes place.

The invention relates to

further to a polycrystalline ferrite body, which is obtained by using one or more of the above Process is established.

The invention is described below

explained in more detail with reference to the drawing and the following exemplary embodiments; however, the invention is not restricted to these examples. Embodiment 1

Ferrite-forming systems of the composition:

49.50 - 49.99 mol. # Fe ₂ O j NiO and ZnO in the ratio 18:32

a series (0.01 wt. $, 0.1 wt. $ and 1 wt. $) Of additives added.

Any of the mixtures obtained

was pre-ground for 6 hours in a ball mill, which also contained a grinding liquid and then for 3 hours at one temperature

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preheated from 850 ⁰ C in oxygen. This was followed by regrinding for 16 hours. The powders obtained in this way (grain size 0.1 μm up to a few microns) were pre-pressed into blocks at a pressure of 10 kg / cm and then re-pressed in an icecatical pressure vessel at a pressure of 1000 kg / cm. The pressed product was for hours at maximum temperatures of: 1180 ⁰ C, 1200 ° C, 1225 ° C, 1250 ^o C respectively. 1275 ⁰ C in an oxygen-containing atmosphere (for example air, or a relatively more oxygen-containing gas mixture) sintered. The heating-up time was 16 hours and the cooling time was 24 hours.

The obtained in this way

Products have been polished and etched on one of their surfaces to verify their crystal structure. An average crystal size was determined on the basis of photomicrographs by dividing the number of crystal boundaries passed when passing through a certain distance to this distance, whereby the magnification should naturally be taken into account.
If A = distance in cm on the photograph,

S = enlargement scale (1 cm = -. Um),

N = number of crystal boundaries counted, O = mean cross-section of a crystal in, um,
so 6 = - ^ z (, um).

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Those found this way

Average grain sizes are given in Table I as a function of the additive and the sintering temperature for a sintering time of 2k hours.

With the help of this table

a professional can adapt a certain material to his particular needs.

By way of comparison, it should be mentioned that

the mean grain size of the one produced in the usual way Ni-Zn ferrite is 10-20 μm, while this material also has a particularly regular crystal structure. The middle Grain size of the material produced by the method according to the invention is, as it has been found has, at least a factor of 10 higher, while the crystals are particularly irregular in shape and are interlocked.

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TABLE I. 1 180 - Sintering temperature ( ^c
1200 1225 1250 120 164 1275 154 - 256 246 113 256 molecular
Together
setting of the
Addition Weight $ 1 11 - 272 - 62 62 0.01 55 - 53 679 104 65 B ₂ O ₃ 0.1 271 76 230 153 119 37 1 85 27 124 22nd 25th 124 0.01 16 45 19th 136 129 30th 2B ₂ O ₃ + SiO ₂ 0.1 124 .45 365 100 95 176 1 76 19th 82 14th 24 95 0.01 9 14th 23 165 34 B ₂ O ₃ + SiO ₂ 0.1 19th 18th 102 119 250 1 85 95 21 18th 160 0.01 14th 16 26th 28 19th B ₂ O _{3 +} 2SiO ₂ 0.1 17th 21 130
11 131
13th 4o 1 144
10 127
10 22nd 29 137
21 0.01 13th 20th 71 68 35 BO + 2SiO
^J + CaO 0.1
1 70 76 1 12 153 54 0.01 2 34 83 95 161 SiO ₂ 0.1 23 1 10 154 75 + CaO 1 1 10 33 36 84 0.01 23 15th 19th 17th B ₂ O ₃ + CaO 0.1 12th 64 58 43 1 4o 21 26th 55 0.01 25th 29 43 29 Fe (P0 ₄ ) ₂ 0.1 31 68 77 47 1 5.2 15th 17th 54 0.01 17th 25th B ₂ O ₃ + SiO ₂ 0.1 ^{+ Fe} 3 ^(PO 4 ^ 1

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• Continuation of table I.

molecular
Together
setting of the
Addition Weight $ 1180 Sintering temperature ( ^c
1200 1225 1250 17th 21 1275 0.01 15th 16 111 73 26th BaF ₂ 0.1 3 121 15th 16 86 1 7th 13th 18th 2k 14th 0.01 13th 16 161 58 28 SrF ₂ 0.1 3 68 16 21 k5 1 11 13th 20th 28 32 O 01 25th 20th 17th 2k 35 CuF ₂ O, 1 13th 16 15th 20th 29 1 17th 13th 19th 30th 19th 0.01 - 26th 50 ko 32 PbO 0.1 61 57 23 20th 59 1 17th 12th 19th 22nd 23 0.01 15th 17th 81 100 19th Bi ₂ O ₃ 0.1 93 92 30th 26th 90 1 36 kl 50

It should be noted that the below

Application of the sintered products obtained according to the invention for the intended purpose Purpose have particularly favorable magnetic and electrical values. (The following Example proves this:

An addition of 0.01 wt. # ( ^B ₂ ° 3 ^{+ Si0} ₂ ) »sintering temperature 118O ° C, results in a product with a density of 5.305 g / cnT and a, u. = II6O;

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and an addition of 0.01 wt. $ ( ^B 2 ° T ⁺ p sxntertemperature 125O ° C, gives a product with a density of 51310 g / cm and a / U. = 1700. (The X-ray density for this composition is 5.336 g / cm ³ )).

A number of more thorough investigations have been carried out on ferrite-forming systems.

ψ led to which CaO + B _? 0 was added. Which he

The results of these investigations are shown in the figure, the mean grain size (in / um) as a function of the added amount in wt. ^ and the Sxntertemperature T shows. It can be clearly seen that a maximum mean crystal size (25Ο, um) is achieved with a precisely defined combination of lower temperature and added amount.

It should be noted that this is here

^ cited result for the behavior of this

Application mentioned the grain growth promoting substances is characteristic.

It should also be noted that,

depending on the reactivity of the ferrite-forming mixture concerned (which is determined by the type and the Quality of the raw materials is determined) The system shown in the figure of lines of the same mean grain size as a whole still somewhat with respect to can move the axes.

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Embodiment II

A same set of

Investigations as in embodiment I were carried out on ferrite-forming systems with the following composition:

52.75 moles. # Fe ₂ O ₃

22 moles. # ZnO

25.25 moles. $> Mno

carried out. The starting mixture was treated in the same way as in embodiment I. This means that any mixture for 6 hours pre-ground in a ball mill and then h hours long was preheated at a temperature of 85O ⁰ C in air. Then 6 hours afterground long. The powders obtained in this way were pre-pressed into blocks at a pressure of 10 kg / cm and placed in an isostatic pressure vessel at a

Pressure of 1000 kg / cm re-pressed.

The pressed blocks were

then sintered, with the range of sintering temperatures, however, was higher than in Example I, namely, selected from 1200 and ⁰ C and 1JfOO ⁰ C.

The mean grain sizes measured on the end products are shown in Table II given as a function of the type and amount of additive and the sintering conditions.

Condition A means that at

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a temperature of 1300 ° C for 2 hours in air was sintered.

Condition B means that

was sintered at a temperature of 137O ⁰ C for 5 hours in 100 $ oxygen in order to obtain the desired crystal structure.

Condition C means that ^ at a temperature of 139O ⁰ C for 5 hours in

100 ^ o oxygen was sintered to obtain the desired crystal structure.

In cases B and C can

then at a lower temperature (e.g. 1290 ° C) for a few hours (e.g. 3 hours) in one 0.1 $ oxygen-containing atmosphere are post-heated in order to set the ferro-ferric equilibrium, according to which, for example, cooling can be carried out in a nitrogen atmosphere under very white conditions.

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TABEL II 785 22nd 287 23 (molecular)
Together
setting of the
Addition Weight 50 69-9IO 0.01 828 I6-5OO ^B 2 ° 3 0.1 16 56 1 Sintering condition
ABC 26th 24 0.01 81 16 CaO + BO 0.1 180 24-300 24 0.01 828 16 SiO + CaO 0.1 169 14th 1 44 211 0.01 648 710 B ₂ O ₃ + SiO ₂ 0.1 90 240 481 1 61 339 0.01 764 931 B ₂ O ₃ + 2SiO ₂ 0.1 12- 130 153 219 1 37 48 0.01 2B ₂ O _{3 +} SiO ₂ 0.1 130 282 373 1 22nd 0.01 481 784 B ₂ O _{3 +} 2SiO ₂ 0.1 255 23 + CaO 1 68 117 0.01 s 1000 23 B ₂ O ₃ + SiO ₂ 0.1 90 166 226 + Fe ₃ (PO ^) ₂ 1 17th 89 BO ₊ 2SiO 0.01 1 ρ « f pQ] 0.1 1

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Continuation of table I.

(molecular)
Together
setting of the
Addition Weight Sintering condition
AB C- , 1,000 2BO ₊ SiO 0.01 994 355 0.1 368 144 ^e 3 4 2 1 114 21 0.01 311 105 Fe ₃ (P (V ₂ 0.1 40-1000 321 1 22-450 1240 0.01 96 269 BaF ₂ 0.1 710 68 1 269 620 0.01 17th 211 SrF ₂ 0.1 14th 47 1 304 23 0.01 24 66 CaF ₂ 0.1 17th 48 1 35 23-180 0.01 18th 22-450 ^Bi 2 ° 3 0.1 225 281 22-500 1 382 26th 0.01 17th 21 PbO 0.1 347 24 1 261 19th 0.01 23 174 CuO 0.1 27 271 1 22nd

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Continuation of table I.

(molecular)
Assemble
and des
Addition Weight
* Sintering condition
AWAY C. 18th 0.01 18th 19th MgO 0.1 22nd 207 1 172 9 7 ^ 5 0.01 25th 331 ^V 2 ° 5 0.1 27 29 1 56 2k 0 18th 22nd 0 21 18th 0 22nd

Embodiment III

A number of investigations have been carried out on ferrite samples, on the surface of which a thin layer of the substances that promote grain growth mentioned in the above exemplary embodiments was applied (by vapor deposition or brushing), after which the samples were kept at temperatures between 1200 ° C. and 125O ° C. and for periods were sintered between 2 hours and 2k hours.

Half of the examined

A number of samples were made by grinding a Ni-Zn ferrite-forming mixture for 6 hours, For 3 hours at a temperature of

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- eCc * -

850 ⁰ C pre-sintered in an oxygen-containing atmosphere, regrind for Λ6 hours, pre-pressed and isostatically re-pressed at a pressure of 100 kg / cm, after which a layer of a substance that promotes grain growth was applied, which mixture was then placed in oxygen at one temperature for 24 hours was sintered from 1240 ° C. It turned out that samples produced in this way did not produce a useful result.

The other half of the pattern

was made by using a Ni-Zn ferrite-forming Mixture ground for 6 hours, presintered for 3 hours, regrind, pre-pressed and isostatically re-pressed at a pressure of 1000 kg / cm, after which a layer of the Grain growth promoting substance was attached to the surface. If the agent to be attached is in powder is present, it can be immediate be attached to the pressed body. If it is present in a liquid state, recommends It is advisable to pre-sinter the pressed body for a short time first, so that a denser structure is obtained. Without exception, each of the above-mentioned grain growth promoting substances became after application and then sintering the desired crystal

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get structure. When using the substances CuO, CaO + SiO, SrF, BaF it turned out that

£ w l £ ^ v

the desired crystal structure was most restricted to the surface, while besides the deformation of the surface was the least.

Embodiment IV

A number of attempts at wear and tear

was carried out on magnetic heads made of conventional Ni-Zn ferrite with regularly shaped crystals and with an average grain size of 10 to 20 µm as well as on magnetic heads made of Ni-Zn ferrite produced by the method according to the invention (i.e. with interlocking crystals with an average grain size of more than 50 μm).

For these attempts were

Commercially available magnetic sound tapes (Kodak P 300 M; BASF PES 18) are used, which run at an increased tape speed 38 cm / sec along the heads. This was done at certain times the frequency characteristic was determined and became the product recorded with the aid of the relevant head subject to a quality assessment.

It turned out that

the service life of heads made of the material produced by the method according to the invention in the relevant Fall twice longer and when mooring

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the same reject criteria was even longer by a factor of 3.

Material life head

regularly for 1500 hours stalt

= 10-20 / µm

irregularly designed 4500 hours 50 to

2 0 9 8 1 R / 1 3 5

Claims (3)

Patent claims : (Ι ·) Method of manufacture a polycrystalline ferrite body in which a finely divided ferrite-forming starting mixture is formed, ground, pressed and sintered, characterized in that before the sintering treatment a substance which promotes grain growth or a combination of such substances is added selected from the group consisting of: BaF; SrF; the oxides of B, Bi, Ca, Cu, Mg, Pb, Si, V; and Fe "(PO.), while such Combination of amount added and sintering temperature, depending on the composition of the ferrite-forming mixture, is chosen that interlocking crystals with a middle Grain size of more than 50 / µm can be obtained. 2. Method according to claim 1, characterized in that the substance promoting grain growth or the combination of such substances is added to the starting mixture to be ground. 3 · Method according to claim 1, characterized characterized in that the ferrite-forming starting mixture is pressed and, if necessary, pre-sintered; that the one that promotes grain growth Substance or the combination of such substances on the outside of the after pressing and, if necessary, pre-sintering obtained body is attached, and that 20981/1 354 2H8554 then the body is sintered. k. Method according to claim 1, characterized in that the substance which promotes grain growth or a combination thereof Substances are added to the starting mixture; that this mixture is ground, pressed and presintered; and that after pressing and pre-sintering obtained body is brought locally to such a sintering temperature during sintering, that the desired crystal structure only occurs at this point. 5 method according to claim 1, characterized in that in the production of a Ni-Zn ferrite body an amount of 0.001-1 Wt. $, Preferably 0.007-0.25 wt. $, Of the through its molecular composition is determined by the mixture: ₂ 0 + ySiO + zCaO, where 1 χ · .10; 0 .vy Ό; 0 / z'5 is added, and that sintering takes place at a temperature between 1180 ° C and 1275 ° C. 6. The method according to claim 5 » characterized in that χ = 2, y = 1 and ζ =, and that the sintering takes place at a temperature between 1180 ⁰ C and 1240 ° C. 7. Method according to claim 5 »characterized in that χ = 1, y = 2 and ζ = 1. 209816/1354 8. The method according to claim 5> characterized in that χ = 1, y = 2 and z = 0, and that the sintering at a temperature between 124o ° C and 1300 ⁰ C. 9. The method according to claim 1, characterized in that an amount of 0.01-0.2 wt. $> CaO + BO is added during the production of a Ni-Zn ferrite body, and that the sintering takes place at a temperature between 1175 ° C and 1250 ° C and preferably between 1200 ° C and 1250 ⁰ C takes place. 10. The method according to claim 1, characterized in that an amount of 0.05-0.5 wt.% _{BaF p} and / or SrF _{p is} added in the production of a Ni-Zn ferrite body, and that the sintering takes place at one temperature is carried out between 1200 ° C to 1250 ^o C. 11. The method according to claim 1, characterized in that in the production of a Ni-Zn ferrite body, an amount of 0.05-0> 5 wt. $ Bi 0 is added, and that the sintering takes place at a temperature between 1175 ^° C and 1275 ° C takes place. 12. The method according to claim 1, characterized in that in the production of a Mn-Zn ferrite body an amount of 0.005-0.06 wt. CaO + Bp ^ o is added, and that sintering in an oxygen-containing atmosphere on a 20981 B / 13 5 4 2H855A Temperature between 135O ° C and 1 ^ 0O ⁰ C takes place. 13 · The method of claim 1, characterized in that in the preparation of a Mn-Zn ferrite a lot of 0,0Q5 - 1 wt ^ o of its molecular composition given mixture. O ₃ + ySiO () _{3 2} + ₃ where O χ Ij 0 y ■ 1; 0 r ζ · 1 is added, and that the sintering takes place in an oxygen-containing atmosphere at a temperature between 135O ° C and 1400 ^o C. I ^. Procedure after opening 1, characterized in that a Mn-Zn ferrite an amount of 0.005 in the preparation of -. 0.5 "£ BaF ₀ is added, and that the sintering in a säuerstoffhaltigen atmosphere at a temperature between 135o ° C and iii00 ^c C takes place . 15 · The method according to claim 1, characterized in that in the production of an Mn-Zn ferrite body, an amount of 0.05-0.05 wt Temperature between 1375 ° C and 1 ^ OO ° C takes place. i6. Polycrystalline ferrite body, which is produced by one or more of the processes according to claims 1-16. 209816/1354