DE1955611A1 - Process for making a hard magnetic ferrite - Google Patents

Description

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D ^ i.üng. Egon Prince ^! βοοο Mun.hn 6o. November 4, 1969

Dr. Gertrud HaUSer Ern «berg« r »» breed 19

Dipi.-ing. Gottfried Leiser

Patent attorney * 1955611

Telegrams ι Labyrinth Munich

Telephone: 83 15 10 Postal check account ι Manchen 117078

THE PLESSEY COMPANY LIMITED ■

2 / έΡ Vicarage Lane
Ilford, Essex, Great Britain

Our sign; P 2058

Process for making a hard magnetic ferrite

The invention "relates to hard magnetic ferrites, and more particularly the production of hard ferrites of the general formula:

^Me x ^Sr (lx) ° * ^{n Fe} 2 ° 3- ' ^where x ^a 0 - 1, aa 4.0 - 7.0 and Me = barium, calcium or lead

These ferrites are of the mixture at temperatures between ⁰ 9QO C and 1300 ° C generally prepared by mixing the carbonates of strontium and / or barium / calcium / lead with iron oxide in the required proportions and burning. The ferrite obtained is finely ground in the presence of water to form a slurry,. which is then pressed into compact shapes in the presence of a magnetic field. After sintering and the

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Magnetization ", these briquettes form ceramic magnets with improved magnetic properties in a preferred direction; these magnets will hereinafter be called" special type "magnets. The present invention aims to provide hard magnetic ferrites with improved maximum BH values. According to the invention, this becomes thereby reached, that prior to the Kaizinierungsstufe necessary for Eildung of such a ferrite component a specific one. amount, preferably between 0.1 and 4.0 wt. #, adding metal borates. borate amounts between 0.5 and 0.75 wt.% have The invention has been applied to strontium ferrites with particular advantages, and among the metal borates, the borates of alkali metals or alkaline earth metals are the most suitable.

In this way, maximum BH values can be achieved which are higher than what was available with additives previously suggested. It is believed that the effects of the known additives can be divided into two groups. In the first of these groups, it is assumed that the additive forms a non-ferromagnetic layer which surrounds the individual strontium ferrite crystals or separates them from one another, which the Bloch ¹ sees resistance to wall displacement. In the second group, the additive is believed to have a flux effect by melting at a temperature slightly lower than that at which sintering and crystal growth occurs. Some substances falling into this second group can preferentially promote the growth of smaller crystals and therefore tend to form uniformly large crystals throughout the ferrite.

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The addition should of course not have a disturbing side effect; exercise on the finished ferrite or, for example, his Decrease density.

It is believed that the addition of borates stimulates growth of ferrite crystals during sintering, without to cause a noticeable dilution of the metal ion content, which .to the magnetic properties contribute to the finished ferrite. The borates can be a j "Reduction of crystal growth" cause so that. = the crystals obtained are relatively small and have a uniform size and a critical size. Examples of suitable borates, in particular for use with strontium ferrite, are barium metaborate, strontium metaborate, sodium metaborate and Sodium perborate and lead metaborate and calcium metaborate are also believed to have beneficial results in Regarding the maximum BH values you can deliver.

A hard magnetic ferrite, especially a hard one magnetic strontium ferrite, which according to the invention Method obtained also falls within (| the scope of the invention and the reason for the after Addition of the borate achieved a substantial improvement in the Ferrite can be seen in the fact that both the flux effect and the influence on crystal growth and the controlled separation of individual crystals occur during the formation of the ferrite, without the effective Ions in the ferrite are diluted in number. Experiments were carried out with strontium ferrite; one can assume, however, that others are tough

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Ferrites, especially barium ferrite and lead ferrite, also due to the addition of metal borates before calcination be improved.

Examples

Experiments with a view to determining the optimal prosentic content of borate to be added were carried out with strontium ferrite SrO 5.8 Fe ₂ O- at 1250 ° C
was fired and sintered at 1260 ° C, using different amounts of barium metaborate according to Table I.
contained.

^B rem. ^{(G) Bra} max. preserved magnets Table I. ■ 3700 2.6 3800 3.2 (MG0) H ₀ (0) $ added properties of 3900 3.6 2400 Barium metaborate 3900 3.6 2500 3700 3.2 2800 0 3700 3.3 2600 0.25 3700 3.2 2500 0.50 3600 3.0 2550 0.75 st. that under this Bedii 2500 1.00 2200 2.00 ize the OOti- 3.00 4.00 abelle I zei,

times amount of addition in terms of improvement
of B___ and the BH values approximately between 0.5 and 0.75

J. Cdi

and in relation to the Koerzitlvlcraft H at or near
is $ 0.50 barium metaborate.

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Comparative tests were also carried out in which the results obtained with strontium metaborate or sodium inetaborate or sodium perborate were compared with those obtained with barium metaborate; 0.5% of the additive was used in each pail and the perite was again SrO 5.8 ^ ^e 2 ° 3 ', ^the calcination was carried out at 1275 ° C and the sintering at 1240 ° C. The results are given in Table II.

Table II "

Addition ^B rem. ^{(G) BH} max. ^{(MG0) H} c ⁽ⁱ²ⁱ >

none (for comparison) 3800 2.5 1800

0.5% barium metaborate 4000 3.65 2450

0.5% strontium metaborate 4000 3.55 2500

0.5% sodium metaborate 3900 3.5 2800

0.5% sodium perborate 4000 3.6 2600

In every pail there was quite a considerable improvement both in relation to H and in particular in relation to.

^{on BI} W. «« * «" ·

Finally two perrites containing the same basic components were produced, one with an addition of 1.0% barium metaborate and the other in a manner previously proposed with an addition of 1% lead monosilicate. The results are given in Table III.

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Tabel additive III ■> ^Bra max (MG0) 4th
9 H _c (0) Lead monosilicate
Bar iunrae tab or at ^B rem. ^ ^G 3,
3, 2350
3250 3950
3960

Table IL clearly shows that the use of a metal ^{borate gives} a substantial improvement in both the value and the H ₀ values of the product.

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Claims (9)

Patent claims! Process for the production of a hard magnetic ferrite, wherein a substance mixture becomes a ferrite of the desired molecular composition is fired, characterized in that the mixture before calcination a metal borate is added. .... ■■ 2. 'The method according to claim 1 * characterized in that the borate is added to a mixture of substances which, after calcination, results in a "special kind" of ferrite. 3. The method according to claim 1 or 2, characterized in that the borate is added in an amount between 0.1 and 4 i> . 4. The method according to claim 1 or 2, characterized in that that the metal borate in an amount between 0.25 and 1 # is added. "-, 5 »Method according to claim 1 or 2, characterized in that the borate is added in an amount between 0.50 and 0.75 % . 6. The method according to any one of the preceding claims, there-: characterized in that an alkali or alkaline earth borate is added as the metal borate. '{ ■ ■ - "I 7. The method according to any one of the preceding claims, characterized in that barium metaborate, strontium 009824/1323 -Q- metaborate, sodium metaborate and / or sodium perborate is added. 8. The method according to any one of the preceding claims, characterized in that the borate one according to the Calcination strontium ferrite is added to the resulting mixture. 9. The method according to any one of the preceding claims, characterized in that the borate according to one of the Calcination of a. Strontiuin ferrite of the formula SrO 5.8 ΡθαΟ resulting mixture is added. 0 0 9 8 2 4/1323