DE2549085A1 - PROCESS FOR PRODUCING A MANGANE-ZINC-FERRO-FERRITE CORE IN PARTICULAR FOR USE IN MAGNETIC HEADS - Google Patents

Description

GUNTETl WAGENER PHY. 7819

fetoatauMKK OEEN / Ff / KOPP

; . - ~ -iii - ν · ■! ■■ '&' 5i .. «!: ti: jen {abr: flk» 20-10-1975

"Process for the production of a Manganese-Zinc-Ferro-Fen \ Lt core especially for use in magnetic heads "

The invention relates to a method for

Manufacture of a manganese-zinc-ferro-ferrite core with a low porosity, especially for use in magnetic pots, In which process the following levels can be distinguished:

the preparation of a mixture with oxides

of iron, manganese and zinc or products which produce these oxides in a subsequent process stage;

preheating this mixture;

grinding the preheated material;

pressing the ground material;

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• the heating of the pressed material to the sintering temperature; and

the sintering of the pressed material.

Recently, ferrites, particularly manganese-zinc-ferrous ferrites, have been widely used in the Magnetic heads used in magnetic recording and reproducing devices such as audio and video tape recorders; these Materials have supplanted alloys like Permalloy and Sendust.

The use of ferrites as magnetic Core material for magnetic heads is aiif reason of good Wear resistance of ferrites, the excellent magnetic properties in terms of saturation magnetization Coercive force and permeability, and also excellent Characteristic curves preferred at high frequencies. In this context, between Manga-Zinc-Ferro-Ferrites, which have the better magnetic properties, and nickel-zinc ferrites, which are more wear-resistant, differentiated will. Good abrasion resistance is particularly important when the ferrite heads are in contact with a high speed Magnetic tape can be used as in video applications. The porosity of ferrites plays a role in this context essential role. For certain applications, for example in video heads, a porosity of the core material is required, which may not exceed a few tenths of a percent. So far it has not been possible using the usual procedure Manganese-zinc-ferro-ferrite cores with such a low Establish porosity. In the German patent application

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1938 31h is mentioned although .a porosity of 0.6 $, but this low porosity was obtained by was performed during heating prior to sintering, a reducing gas containing hydrogen through the ferrite. It should be noted that this process is difficult to control because if the reduction is too extensive, other oxidic phases or even metallic phases can easily form, so that the composition of the material obtained is not well in hand.

"The invention aims to provide a method of

To create the type mentioned at the beginning, with which it is possible to produce manganese-zinc-ferro-ferrite cores with minimal porosity and high resistance to friction.

It has been shown that a manganese-zinc-ferro-ferrite core that meets these conditions is produced can be if according to the invention during one of the steps preceding the sintering to be sintered Material if possible the stoichiometric spinel composition is granted ". By this it is meant that in the formula representing the composition, the ratio of Anions to the cations must be as close as possible to the ratio 3.: ^.

In the usual process for producing manganese-zinc-ferrite cores Ferrο the starting powder in Ivuft or nitrogen at temperatures between 800 and 1000 ⁰ C for a maximum of some ^ Stunden'worgeheizt be. For preheating, the starting powders already contain an excess of oxygen due to the fact that the iron component and sometimes

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the manganese components are also weighed in in the form of the trivalent ion, ie Fe-O., or Mn _{o O} ". Even the preheated powders, even those preheated in nitrogen, still contain a considerable excess of oxygen, in other words they do not have the stoichiometric spinel composition. They are only reduced to this composition during sintering. Underlining carried out by the applicant has shown that this process is an obstacle to obtaining a low porosity. However, if the material already has the stoichiometric spinel composition at the moment of sintering, then low values of the porosity actually show to be realizable.

In the context of the invention it is possible to use a

Preheated powder that does not have the stoichiometric spinel composition to be reduced to this composition when heated to the sintering temperature. A disadvantage with this, however, is that it is difficult to reduce the powder integrally at this stage; Since it is pressed into a desired shape at a significantly high pressure (eg 1000 kg / cm ² ), the oxygen diffuses only slowly from the inside to the outside when it is reduced.

A preferred embodiment of the invented

according to the method is characterized in that the Material when preheating the stoichiometric if possible Spinel composition is granted. Various modes of reduction can be used to achieve this, e.g. before preheating the required ferrous in the form of Fe ^ Oh be added, or a reducing agent can be added to both

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be mixed.

Preheating preferably takes place at

a temperature between I050 to 1250 ⁰ C in an O ₂ -containing gas atmosphere whose partial O "-Oruck the equilibrium 0 corresponds to ₂ -Oruck the material with stoichiometric Spinelzusammensetzung at the used temperature.

Preheating temperatures between 1100 and 1200 ° C provide the best result in this context.

To make sure that on this

Way preheated powders when cooling to room temperature and those made from this powder after the grinding and pressing process blocks obtained when heating to sintering temperature oxidize, these steps must be carried out in a non-oxidizing atmosphere. ■

The invention further relates to a

Manganese-zinc-ferro-ferrite core made using one of the above-mentioned method is obtained, as well as atif a Magnetic head made from such a manganese-zinc-ferro-ferrite core.

The invention is explained in more detail below with the aid of the following examples. Example 1.

As a starting material for the production of an Mn-Zn ferrite product with the composition Mn_ __ ■, Zn .. "_" Fe ^ + _ " _o Fe ^{3 +} 0 ,. , became a .powder mixture of

05 / H VfJP ¹ * Ό, Ό / d d Mr

: 63.58

MnCO ": 25.35 wt .;

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²⁰ I ^ fO 8 5

ZnO: 11.07 wt. $

milled in a ball mill for six hours, h hours in I ^ runs at a temperature of 85O ⁰ C preheated, and subsequently ground again in turn, 'six hours in a ball mill.

The preheated powder contained a considerable excess of oxygen, since the analysis showed that all the Fe ions and some of the Mn ions were present in trivalent form. The powder therefore contained no Fe ² and was therefore not stoichiometric Spinel Composition. ,, -

. . From this powder, blocks were produced by means of isostatic pressing under a pressure of 1000 kg / cm ² , which were sintered in an oven at a temperature of 135O ⁰ C for 2k hours. A gas mixture of nitrogen and oxygen was passed through the furnace both during heating to sintering temperature, during sintering and when cooling to room temperature. The oxygen content was always adjusted to the temperature and was 10 percent by volume at 135O ° C. For this purpose, the partial oxygen pressure p (0 ₂ ) was calculated using the equation log ρ (θ _£ ) =. ~; + B, where T is the temperature in degrees Kelvin, A = -I6.039, and B = 10.822. Example 2. ' ^: '"

For the production of a Mn-Zn-Ferro-Ferrite

Product with the same composition as in Example 1 became a powder mixture of the same composition as this from Example 1 after six hours of grinding in a ball mill in a flowing nitrogen atmosphere

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preheated to a temperature of 85O ⁰ C for 4 hours and then ground again, now 8 hours.

Bie. Composition of the preheated powder

did not yet correspond to the stoichiometric spinel composition; it still contained an excess of oxygen, be it considerably less than in the preheated powder afterwards Example 1.

This powder was made in the same way

as in example 1 blocks pressed. They were subjected to an additional reduction stage for sintering. "This was done

they are placed in an oven in which on one side a mixture of nitrogen and 0.1 $ oxygen is admitted under a slight overpressure (0.01 atm) and on the other side is discharged with heating to a temperature of 1200 ° C. They were kept at this temperature until the discharged gas mixture contained exactly as much oxygen as the admitted gas mixture. When this (equilibrium) state was reached, the furnace was shut off and the temperature was increased to 135O ⁰ C, at which temperature 2k steps were sintered, followed by cooling. The furnace was connected to a buffer vessel, to keep constant the oven pressure during Au'fheizen of 1200 ° C to 135o ° C to the cooling of 1350 ⁰ C to room temperature.
Example 3.

To produce a Mn-Zn-ferro-ferrite product with the composition Mn ^ Zn _ Fe ^ _1Q ^ -Fe ^ O ^ (this composition is also aimed at in the following examples), a powder mixture of

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Fe ₂ O: 6k, 17 wt

MnCO ₃ : 27.35 wt

ZnO: 8.48 wt

after four hours of grinding in a ball mill, it was preheated in Jjuft at a temperature of 835 ° C. for h hours and then ground again for k hours.

This powder was subjected to a reducing agent by preheating it a second time, this time in an oven through which a mixture of nitrogen and 0.1% oxygen was passed. The preheat temperature was now 1,130 ⁰ C and this temperature was maintained as long as that the discharged gas mixture contained the same amount of oxygen as the Inset gas mixture. When this situation was reached (after about five hours) the furnace was filled with pure nitrogen, carefully closed and cooled down at the same time. In order to prevent the powder from oxidizing during preservation, the furnace was connected to a buffer vessel with a variable volume, so that changes in volume could be compensated for and a slight overpressure (0.01 afc) could be maintained during cooling. The powder obtained was pressed into blocks after milling for eight hours. They were heated to 1200 ° C. in a slowly flowing nitrogen atmosphere. The furnace and the buffer vessel were then closed and the temperature was increased to the desired sintering temperature (135O ° C). This temperature was maintained for 2k hours, after which it was cooled to room temperature.

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example H. .

A powder would be produced by wet chemical means

produced from an aqueous solution with the following composition: 76.09% by weight FeSO ^ .7H ₂ O; 13.70 wt. $ MnSO ^ .I ^ O; 10.21 wt. $ ZnSO ^. 7HO. This solution was spray-dried and the sulfate mixture obtained was ^{heated at 1000 °} C. for three hours in I ^ ift for decomposition. Oas resulting powder wtirde five hours preheated for reducing at 1130 ⁰ C in a nitrogen atmosphere with 0.1 $ oxygen. The preheated powder was subjected to the same sintering process as the powder in Example 3 », but the sintering temperature was 1270 ^° C.
Example ^.

A powder mixture of Fe ₂ O ₃ 5 ^, 82 wt. #
Fe ₃ O ₄ 9.23 wt
ZnO 8.51 wt
MnCO ₃ 27, W wt. #

(the required Fe ² wix-d here previously weighed in in the form of Fe 0 ^), after four hours of grinding in a ball mill, it was preheated for Z hours at 1000 ^° C. in a closed oven filled with N2 and cooled to room temperature. The oven remained closed during the entire preheating cycle (heating up, preheating to 1000 ° C and cooling down). The powder obtained was ground for 8 hours and then ^{pressed by isostatic pressing at 1000 kg / cm 2} zxi blocks. The pressed blocks were heated to 1150 ° C in a closed furnace filled with N2

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and then sintered at this temperature for 2k hours and then cooled. The furnace remained closed throughout the sintering cycle.
Example 6.

A powder mixture with the composition of the powder according to Example 3 was prepared and preheated twice in the same way as the powder according to Example 3. The powder obtained was ground for eight hours and pressed into blocks ^{by isostatic pressing at 1000 kg / cm 2.} These blocks were sintered for twenty-four hours in the manner described in Example 5, but at a temperature of 1230 ^° C.

• The porosities of the blocks obtained in the six examples were calculated from Oichtemessungen and are
Example ~ \ 2 3 k 5 6

Porosity (vol. $) 5.6 2.6 1.4 0.5 0.5 0.5

From this it can be concluded that the more

as the powder to be sintered approaches the stoichiometric spinel composition, the lower the porosity of the sintered product. In particular, it shows that it can be reduced from 5t6 to 0.5 i °.

What is remarkable is that the structure

of the sintered blocks according to Examples 4, 5 and 6 are strong that of Ni-Zn ferrite sintered products, with the pores in the Resembles grains, while normally with Mn-Zn ferrite the pores are located on the grain boundaries.

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It also shows that the better the

product of the stoichiometric spinel composition to be sintered the lower the sintering temperature chosen to obtain a sufficiently dense end product can.

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Claims (1)

pirn. 7819 20-10-1975 ■ 7 5 4 9 0 8 5 PATENT CLAIMS: 1.Method of making a manganese-zinc Ferro-ferrite core with low porosity, especially for Use, in magnetic heads, which process follows the steps contains: making a powder mix with Oxides of iron, manganese and zinc or products containing them Generate oxides in a subsequent process stage; preheating this mixture; grinding the preheated material; pressing the ground material; the heating of the pressed material the sintering temperature and the sintering of the pressed material, characterized in that, in order to obtain a core with minimal porosity, the material to be sintered is given the stoichiometric spinel composition as far as possible in one of the stages preceding the sintering. 2. The method according to claim. 1, characterized by the fact that the material is given the stoichiometric spinel composition as far as possible during preheating. 3. The method according to claim 2, characterized in that the preheating takes place at a temperature between 1050 and 1250 ^o C in a gas atmosphere containing 0 ", the partial operating pressure of which corresponds to the equilibrium operating pressure of the material with stoichiometric spinel composition when used Temperature corresponds. k. Verfahr.n according to claim 3 »characterized in that the preheating at a temperature between 609820/1013 PHN. 78 19 20-10-1975 - 1100 and 1200 ° C takes place. Method according to claim 2, characterized in that both the cooling of the material after preheating and the heating to the sintering temperature take place in a non-oxidizing atmosphere. 6. The method according to claim 3 or h, characterized characterized that the sintering at a temperature takes place between 1200 and 1300 ° C. 7. Method according to claim 1, characterized in that that a mixture is produced that contains the required ferrous material in the form of Fe “OL, that this Mixture is preheated at a temperature between 800 and 1250 ° C and the sintering at a temperature takes place between 1050 and 1300 ° C. 8. The method according to claim 7 »characterized in that that preheating takes place in a stationary nitrogen atmosphere. 9. Manganese-zinc-ferro-ferrite core, which is under Application of the method according to any one of claims 1 to was produced. 10. A magnetic head made from a manganese-zinc-ferro-ferrite core according to claim 9. 609820/1013