DE1696412B1 - Process for the production of ferrite cores with a rectangular hysteresis loop and spinel structure - Google Patents

Description

ί 696412

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The invention relates to a method for producing sintering and after-annealing to 0.5 to 3 volume

is set by ferrite cores with a rectangular hysteresis percentage.

loop and spinel structure by sintering in air Any type of ferrite is suitable for such a process,

at 1100 to 1500 ⁰ C and afterglow below with the oxygen harmless during the afterglow

of 1000 ⁰ C. 5 is absorbed. The temperature for afterglow

With British Patent 760 035, a is heavily dependent on the ferrite composition

Process has become known in which the after- and is accordingly to a value between

annealing set at temperatures above 1000 ⁰ C and 600 and 1000 ° C.

Performed in water vapor as a neutral atmosphere- When using this relatively low afterglow will. The use of the neutral atmospheric temperature values has now shown that on the one hand In this manufacturing process, the sphere should be guaranteed to be afterglow in a pure water vapor atmosphere put that in the oxidation in the sintering to ferrite cores with completely inadequate legal process remaining oxygen residue is eliminated leads to angularity ratio and, on the other hand, at atmo- and that during afterglow there is no oxygen in the spherical conditions relative to the above Ferrite material can penetrate again. 15 leads to a high reject rate, whereas with the inven-

According to this method, it is possible to adjust the water vapor content of the magnet according to the produce cores with a high squareness ratio, afterglow optimal results are to be achieved, but the endeavor in technology is further when it is taken into account that is already above gone there to achieve a lower of about 5 volume percent water vapor no magnet rejection rate the manufacturing process for magnetic cores 20 more with useful squareness cores to simplify significantly. nis have revealed.

For example, US Pat. No. 2,994,522 has made known an optimal result of the other process achieved with the invention, in which the nits are shown in the fact that both the mean sintering does not take place in a protective gas atmosphere by about 10 ° / ₀ (from about 30 to about 20 ° / ₀ ), but at certain oxygen contents. 25 has been reduced, as well as the daily spread. While it is not considered harmful to achieve satisfactory results of the rejects feature values of a maximum of nisse if the 40% has decreased to a maximum of 15%. The sintering takes place with the admission of oxygen, so reject is here as before on the value of the but expressly emphasized that the afterglow is related to the squareness ratio,
under the influence of a neutral protective gas atmosphere, the must be drawn. With this knowledge, however, the thermal reaction that concludes the process is at least an arrangement required for the first described and crystallization, which consists of a smtering process followed by a device that is simpler to use than the afterglow process. During sintering, the sintering takes place at least in an open vessel at a temperature, in the present case between 1100 and 1500 ^° C., at which the spinel phase is stable and measures must be taken to ensure that the at which the crystal grain size increases, so that the protective gas atmosphere alone is effective during the afterglow - the cations and anions involved should remain accordingly. the distribution and thus the spinel

It has now been shown that a surprising 4 ° form structure. For afterglow according to the invention

Way technically and economically useful results both the sintering temperature for a short time

under certain conditions it is also lowered to a temperature value, which, however

are to be achieved if, in further simplification, the is still so high that the oxygen absorption and

Manufacturing facilities also do the afterglow not the course of the corresponding chemical reaction

in a neutral atmosphere, but rather below 45, as well as, since this is the most effective

Atmospheric conditions is carried out. samst, water vapor in the above specified

Even if the limits of using this procedure are in effect.

produced magnetic cores overall, while it turned out to be at a rejection rate to be regarded as satisfactory is not at all critical, below which have shown, it has been shown that the process takes place under the influence of gas, if only none Extent of both the fluctuation of the daily memory-reducing atmosphere is applied, so is Paint values over a longer period of time as well as this in the afterglow phase in so far as different than once the daily spread of the respective characteristic values, an oxidizing atmosphere and, on the other hand, a the rejection rate of the magnetic cores produced must be present in temperature during the oxidation and With regard to their squareness ratio as a disadvantage 55 the course of the chemical reaction is guaranteed. is to be seen, however, when it is remedied, the tech- This means, however, that during the afterglow, oxygen niche Benefit and the importance of the last absorption by the ferrite is promoted by called process can be significantly increased a correspondingly small amount of water vapor in could. the acting air atmosphere is adjusted.

The object of the invention is therefore to provide a few examples

explained in more detail when using a production that is as simple as possible.

Iungsververfahren magnetic cores with satisfactory Before the sintering treatment, the metal oxide squareness ratio converted into ferrites with a relatively short, longer period of time via raw materials using known ceramic processes. Almost form the basis To manufacture scrap rate with as little scatter as possible. 65 pure oxide raw materials, the finest in the trade

According to the invention, this object will thereby have attainable granule sizes. These oxides are

solved that the afterglow is carried out in air and then with a mixing agent, usually water,

and the water vapor content of the air when mixed and in a steel ball mill, colloid

mill or attritor ground. After grinding, the homogeneous oxide mixture is dried in the oven, and this cake is presintered after pulverization, for what purpose the oxide mixture is exposed to a temperature slightly below the final sintering temperature. The pre-sintering Under certain conditions it can be for part of the oxide mixture or it can be omitted entirely will. After pre-sintering or, if this is not used, after annealing the oxide mixture is crushed to a particle size that can be processed ceramically, and it becomes organic Added binders, which are also effective as particle lubricants. Then through conventional equipment pressed the oxide mixture into the desired shape. The one so shaped Metal oxide is then ready for the processing according to the invention.

In the case of an offset that contains a trivalent cation and a divalent cation, such as 40 ° / ₀ Fe ₂ O ₃ , 55 ° / ₀ MnCO ₃ and 5% CuO, the pre-sintering takes place at a temperature between 600 and 1000 ⁰ C for one Duration between 30 and 180 minutes instead. As the binder 3 ° / ₀ and polyvinyl alcohol as a lubricant 0.25 weight percent dibutyl phthalate is used here. The pressing takes place until a specific weight of between about 2.5 and 4.0 g / cm ^{3 is reached} .

According to the conventional ceramic method, the Cu-Mn ferrite is at for about 10 minutes Sintered at 1250 ° C. Time and temperature are a function of composition; for periods of

The temperature can be between 1100 and 1500 ° C for 2 minutes to 4 hours. After sintering the ferrite is post-annealed in an environment which, in addition to air, contains water vapor in amounts of about 0.5 contains up to 3 percent by volume. During the afterglow process, the ferrite is raised to a temperature of around 900 ° C cooled, which can be achieved with Cu-Mn ferrite in about 10 to 15 minutes.

The amount of water vapor in the air-water vapor mixture varies between about 0.5 and

3 percent by volume of the total atmosphere surrounding the ferrite. As already mentioned, the upper limit of the added water vapor is extremely critical in that the rectangular shape of the hysteresis loop of the ferrite can no longer be achieved if more than 5% water vapor is used. The beneficial effects of water vapor are illustrated by the information in the table below for an air-water vapor mixture. In this table, F _{1 is} the undisturbed jL signal, F ₁ 'is the read-disturbed L signal, V _{0 is} the write- disturbed 0 signal, T _{s is} the switching time, and F ₁ YF ₀ is the L / 0 ratio, which is generally rectangular of a signal is defined.

T fH water H ₂ O Sintering 7e> it Afterglow V ₁ Operating values Vx V ₀ T ₁ V ₁ '/ V ₀ JUIU.
No. temperature Volume temperature Z4CIL temperature (mv) (mv) (mv) μ8βϋ 4.1 ⁰ C percent ⁰ C Minutes ⁰ C 40 38 9.2 1.00 4.5 1 1200 8th 920 44 41.5 9.9 1.02 0.55 2 25th 3.0 1200 8th 920 56 22nd 48 0.96 0.25 3 37 6.0 1200 8th 920 60 13th 54 0.8 0.25 4th 47 10.5 1200 6V2 920 56 12th 50 0.75 0.31 5 62 21.5 1200 6V2 920 54 15th 47 - 1.2 6th 82 50.0 1200 6V2 920 18th 12th 10 ■ - · 0.23 7th 100 100.0 1200 6V ₂ 920 59 13th 50 0.75 0.62 8th 62 21.5 1200 6V ₂ 920 72 31 50 - 9 62 21.5 1170 6th 900

The table shows that in the case of sintered products which have been produced with an addition of more than 5% water vapor, the Ζ, / 0 ratio is severely impaired, if not unusable. At 3% water vapor, the ratio V ₁ JV _{0 is} equal to 4.5, while at 6% water vapor it is equal to 0.55.

Up to an upper critical value of the water vapor content during the afterglow is so to speak a catalytic effect, which ensures that the hysteresis loop has an optimal rectangular shape achieved. Furthermore, the yield of the useful ferrite material is also increased. As already mentioned, the nature of this catalytic effect of water vapor has not yet been precisely determined so that various explanations for it are possible. So z. B. the water vapor Cause surface migration of the ions and promote the solid-state reactions that occur during manufacture a ferrite with a rectangular hysteresis loop are required; on the other hand, the water vapor could also facilitate the formation of crystallization nuclei, promote surface diffusion and the number of the reaction centers.

The invention can be applied to any ferrite system in which oxygen is used during the annealing phase can be absorbed. There are several typical examples of three-cation-by-two-cation ferrite systems, such as B. Mn-Zn-Fe; Ni-Zn-Fe; Mg-Mn-Fe; Mn-Fe; Ni-Fe; Zn-Fe; Cu-Fe and Mg-Fe.

With all these ferrites, the sintering takes place at temperatures between 1100 and 1500 ° C, while the afterglow temperature of these ferrites necessarily depends on the particular ferrite composition depends and is generally above 600 ° C.

Claims (1)

Claim: Process for the production of ferrite cores with a rectangular hysteresis loop and spinel structure by sintering in air at 1100 to 1500 ° C and afterglow below 1000 ° C, characterized in that the afterglow is carried out in air and the Water vapor content of the air both during sintering and afterglow to 0.5 to 3 percent by volume is set.