DE2142110B2 - PROCESS FOR MAKING A BODY WITH ANISOTROPIC PERMANENT MAGNETIC PROPERTIES FROM A CO DEEP 5 R COMPOUND - Google Patents

Description

Process for the production of a body with anisotropic permanent magnetic properties a C05R connection.

The invention relates to a method for producing a body with anisotropic permanent magnets Properties from one or more compounds with a hexagonal crystal structure of the Type C05R, where Co can be partially replaced by Fe and / or Ni and / or Cu and R can be one or more represents the elements of the rare earths, yttrium and / or thorium, by cooling castings the compound or compounds, aligning the powder in a magnetic field, pressing and sintering.

Such a process, the (C 1100 ⁰⁾ and a single magnetic material (SmCos) but is limited to a single sintering temperature, is known from NL-OS 69 17. 567 More detailed investigations have shown that in order to obtain high coercive forces, the sintering temperature must be kept within a precisely defined temperature range. In particular, it is known from an article by F. W este η d ο r ρ in "Solid State Communications", No. 8, pp. 139 to 141, 1970, that the coercive force iH _{c of} heated powder samples from the Sm-Co system as Function of the heating temperature from a certain low heating temperature - 80O ⁰ C - increases rapidly, reaches a maximum value, then decreases again and at a certain high heating ^{temperature - 1250 0} C - assumes a value that differs only slightly from the value that occurred before the heating distinguishes it lies

it is therefore obvious to sinter at a temperature such that a sintered product with a maximum , H _{c is} obtained. It turns out, however, that a magnet made in this way generally has one major disadvantage: the coercive force and / or

the shape of the demagnetization curve measured on the magnet changes over time by the coercive force of part or all of the permanent magnetic material that makes up the magnetic body is built up decreases after some time; This is

the so-called aging of the magnet body.

The aging of the magnet body manifests itself in the fact that two demagnetization curves which are measured in the same way but at times h and f ₂ on the same magnet body do not coincide.

Experiments that have led to the invention have shown that the extent of aging that occurs depends on the temperature at which it is sintered. It was also found that above one certain high sintering temperature no aging at all

more This occurs on the condition that during

is sintered for a certain minimum period of time.

The method according to the invention is thereby

characterized that the sintering during at least

30 minutes above a temperature at which there is no subsequent aging of the magnetic values of the Sintered body occurs and the sintered body a final heating to a below the Sintering temperature lying temperature is subjected.

A magnet body produced by the method according to the invention has the great advantage on that aging no longer occurs.

The sintering of MsR powder takes place in a pre Oxidation protective atmosphere. In practice it can

the sintering take place in various ways, e.g. B. in a room that during sintering with the help of a Pump is kept at a certain constant vacuum, or in a sealed Vessel that is previously evacuated.

Experiments, both in a constant vacuum and in a sealed vessel, were carried out Although it was found that the sintering temperature of the same starting powder was dependent on which of the above two methods was chosen, and although it was found that the The sintering temperature was also dependent on the choice of M and R, the invention has the essentials Feature on that for each of the M-R connections concerned a favorable sintering temperature can always be found.

Since, as has already been explained, at higher sintering temperatures the / H _a which is maximally achievable with the help of the relevant MR connection,

21 42 HO

of a certain sintering temperature decreases sharply, and since only at higher sintering temperatures the desired non-aging is achieved, in general, the magnetic body finally obtained is not aging, but for certain applications have to ^s low coercive force.

This disadvantage is eliminated by the fact that the sintered body in the method according to the invention subjected to a final heating to a temperature below the sintering temperature will.

It has in fact been found that when by a sintering treatment at a temperature Tein not aging magnetic body is made to increase the coercive force can be obtained by 'is refired at a temperature below T, for example, between 800 ⁰ C and T, while still the advantage obtained by sintering at the higher temperature T - namely non-aging - is retained.

However, it has been found that, even if the magnetic body obtained after sintering to a temperature T is heated for some time to a temperature which is much lower than the mentioned temperature of 800 ° C., an increase in the coercive force may occur. In particular, this may occur a -5 final heating at a temperature between 50 and 300 ⁰ C give this result.

The invention is explained in more detail below for some exemplary embodiments with reference to the drawing. It shows

F i g. 1 is a graphic representation in which the magnetization M is plotted against the field // applied to the outside for various magnetic bodies,

F i g. 2 is a graph showing the relationship between the coercive force and the sintering temperature for a number of magnetic bodies with the same composition,

Fig. 3 is a graph showing a similar relationship between aging and sintering temperature,

F i g. FIG. 4 is a graph showing the same relationship as in FIG. 2, but for other sintering conditions

F i g. 5 is a graph showing the same relationship as in FIG. 3, but for the sintering conditions according to FIG. 4, is specified,

6 is a graphic representation in which for a Number of magnetic bodies with the same composition the relationship between aging and the sintering time is given,

7 is a graph showing the The coercive force of a number of samples is plotted against the heating temperature, and

8 and 9 are graphs in which the Increase in coercive force is plotted over the final heating temperature

Embodiment I.

A Pt'iver which consisted of a mixture of Sm-Co compounds with a ratio between Sm and Co equal to 1 : 4.5 and was thereby obtained. That castings of this composition were ground in a vibrating mill was first compressed under an isostatic pressure of 20 kb in a magnetic field of 6s 60,000 Oe. Then it wunie in a sealed, evacuated vessel in the presence of an yttrium-getter during periods varying from 10 to 30 minutes, sintered at different temperatures between ⁰ C 100G and 1150 ⁰ C. The demagnetization curves and the pore volume were always measured on the bodies obtained in this way. On each of these bodies, after the lapse of time t, e.g. B. 1000 hours, again measured the demagnetization curve so that any signs of aging can be detected.

The aging of a magnetic body is expressed in the demagnetization curve, which can be measured on the magnetized magnetic body. Such a curve is shown in FIG. 1 of the drawing. The magnetization M is plotted as the ordinate and the external magnetic field Wist as the abscissa. Curve 1 is a demagnetization curve characteristic of a permanent magnet. In the case of a field iH _c - coercive force - whose direction is opposite to that of the magnetization in the body, the magnetization M is equal to zero. The demagnetization curve 2 is characteristic of a magnetic body with a coercive force (iH _c ) i which is lower than that (iH _c ) \ . which belongs to curve 1. If the two curves have been measured in the same way on the same magnetic body, but the second was measured a time period ί after the first curve, (ihc) \ - (iHch is the aging during the period t In another case, on a magnetic body after the lapse of a time period t are curve measured a demagnetization corresponding to the curve 3 shown. such a curve has a "bulge", while still providing the coercive force (i H _c) \ remains the same. in such a case, there is aging of the magnet .

It was found that magnetic bodies with the above-mentioned starting composition, which were obtained after sintering at a temperature of> 1100 ^° C., no longer showed any aging. It was also found that the pore volume in the body decreased at higher sintering temperatures , as a result of which a non-aging magnet with a higher saturation magnetization and thus with a higher energy product (BHJmix was obtained.

Below in Table 1, the magnetic values are reported, which are measured in some of these permanent magnets, which have been obtained at 1120 ° C after sintering:

Table Ϊ

Pores iHc (Oe) Br (G) (BHJmn volume (10 ⁶ GOe (O / o) 2.0 13 600 7890 14.9 2.0 14000 7970 15.5 1.5 13 500 8100 16.0 1.5 14000 8110 15.75 0.6 14,000 8300 16.8

In the graph according to FIG. 2 the coercive force iH _{c is} given, measured on a number of sintered magnetic bodies from the Sm-Co system at different temperatures in an evacuated and then closed space.

The curve a _t gives the measurement results immediately after sintering, ie after the magnetic bodies have been brought back to room temperature. The cure vea? gives coercive force values measured after the passage of time.

From the graph it is seen that coincide at sintering temperatures above 1100 ° C, the curves a 'and a ₂ while the curve is located at sintering temperatures below 1100 ⁰ C lower than the curve a \ a _2. Magnetic bodies of the above-mentioned composition which have been sintered under the above-described conditions therefore show no aging when they are sintered at temperatures above 1100 ° C. 1100 ^° C. is the critical sintering temperature in this case. From the graph it appears further that this temperature is much higher than the sintering temperature at which the maximum coercivity is achieved.

In the graph according to FIG. 3 is for sintered under the above-mentioned conditions Magnetic body with the above-mentioned composition the relative aging

A difference with the measurement results obtained after sintering in a closed room is that that in the case of the "vacuum" sintering process in question, the one after sintering is somewhat above the critical one The coercive force obtained at the sintering temperature differs only slightly from the maximum achievable coercive force is.

Furthermore, in the sintering process carried out according to the present exemplary embodiment, it has been investigated to what extent the sintering time is important for the production of unsuitable magnets. As can be seen from the graph of Fig. 6, the degree depends on the aging, expressed as

w, (n

H. [o)

100 " ₍

H _c [o) -

100%

applied above the sintering temperature. Hc denotes the field that must be created in order to obtain a

Magnetization ₃ M _r to keep (see. Fig. 1),

while H ₀ (O) Hc represents immediately after sintering and H '(t) _c H after a lapse of time t.

A critical sintering temperature of 1100 ^° C. can also be derived from this graphic representation.

occurs, also from the sintering time . Measurements which were carried out on magnets sintered at a sintering temperature of 1070 ^° C. are given in this graphic representation. A sintering time of at least 30 minutes is found to be a necessary condition for obtaining a non-aging magnet.

Embodiment III Embodiment II

A powder of the type described in the exemplary embodiment I and compressed in the manner described in this Example I in a magnetic field, sintered in a space which - in deviation from Example I - with the aid of a vacuum pump to a vacuum of about 5 x 10 ^-5 Torr was held. (A difference with the closed vessel according to Example I is then that no Sm vapor pressure is built up over the powder during sintering.) The powder samples were sintered at various temperatures for 30 minutes, and the magnetic bodies obtained in this way were demagnetized --ization curves immediately after sintering as well as after the passage of a time (measured.

G in the graph of F i. 4 , the measurement results are plotted in the same way as in FIG. The curve d \ was measured immediately after sintering and the curve di was measured after a time t. In this case, too, the curves coincide above a certain temperature - the critical sintering temperature. For a material having the above-mentioned composition and the above-described sintering treatment has been subjected, the critical sintering temperature is therefore at 1065 ⁰ G

In Figure 5 is the same as in Figure 3 relative aging:

HAo)

100%

Applied above the sintering temperature, dike as if from the graphic representation according to FIG. 4 shows a critical sintering temperature of 1065 ° C. from this figure

A powder which consisted of such a mixture of (La-Ce) -Co compounds that the atomic ratio (La-Ce): Co was 1: 4.3, which powder was obtained by casting pieces in a vibratory mill ground was first compressed under an isostatic pressure of 20 kb in a magnetic field of 60,000 Oe. Subsequently, it was in a sealed previously evacuated vessel in the presence of a yttrium-getter for 30 minutes at different temperatures between 900 ⁰ C and 1100 ⁰ C sintered in the thus-obtained bodies have been always sierungskurven the demagnetisation and the pore volume, both immediately after Sintering as well as measured after a time t.

It turned out that having the above-described manner at a temperature above 960 ⁰ C and above 975 ° C sintered magnet body no aging.

In table U values are given which are at some of these - non-aging - permanent magnets are measured. It should be noted that the first example of Table II has a La / Ce ratio that corresponds to the La / Ce ratio in the so-called cerium-rich "mischmetal" almost corresponds to A "mischmetal" is generally understood to mean a mixture of rare earths as occurs in nature Such mixed metals are depending on the composition referred to as cerium-rich or yttrium-rich As is well known, there is the advantage of using it Mixed metal instead of pure rare earths in the significantly lower cost of the starting material, true nevertheless magnets with acceptable properties can be obtained. The application of cerium-rich Mixed metal is preferable in this context. (An analysis of the composition results in ζ. Ε the following ratios: 45 to 55 Ce; 25 to 35% La: approx. 15% Nd; about 5% Pr; approx. 03% v; at the

Rare earths less than 0.1%; other metals less than 0.5%.

The values achieved with (LaojCeo.7) Co ₄ J therefore indicate the values that can be achieved with a cerium-rich misch metal when the method according to the invention is used.

The last example in the table shows that with a (LaojCeoj) Co ^ magnet, i.e. with a Lanthanum-rich composition, the most favorable values can be achieved. This indicates that under Use of the method according to the invention, for. B. Magnets made of rare earths and cobalt with a with Lanthanum-enriched cerium-rich mischmetal component can be made that cheap have magnetic properties and in which, in addition, the cost price of the starting material is low

Embodiment IV

A powder composed of such a mixture of (Pr-Sm) Co compounds that the atomic ratio (Pr-Sm) / Co was 1: 4.5, which powder was obtained by placing in a vibrating mill Castings with this composition were ground, was based on the already in the embodiment III treated way. On the - not aging - obtained after sintering at 1075 ° C Magnetic bodies were those in Table II! specified values measured.

It should be noted that both in Table II and in Table III under "Sintering temperature" also the Temperatures are given in brackets above which it has been found that sintered powders do not Show aging.

Table II Pores
volume (erg / gr. Oe) ι H- (Oe) ß- (G) (RHfrm
(10 * GOe) Sinter
temperature
Γ C) 5%
5%
5% 73
78
77 4700
6000
6500 6900
7400
7300 10.7
12.6
12th 1050 (975)
1000 (960)
1050 (975) (Lan.jCeo.7) Co4.i
(Lao.sCen.5) Co4j
(Lao.; Cenj) Co4.3
Table III Pores
volume (erg.gr. Oe) : H- (Oe) Rr (G) (10 * ■ GOe) Simer
temperature
(C) 9% 83 18 500 7700 14 500 1075 (1061 (Prn.5Smo.5) Co.5

In the graph according to FIG. 7 a curve is drawn which is comparable to curves a ₍ of FIG. 2 or d \ of FIG. 4, but which now also continues on the side of the low temperatures, which curve shows the relationship between the coercivity iH _c heaters powder pattern and the heating temperature T indicates. If the samples are heated to temperatures between 800 ° C to 1250 ⁰ C, slellt turned out that the coercive force rapidly increases, temperature at a Sintertem- ^ ₁ 71 a maximum () H ., reached h and then decreases again Since the critical sintering temperature generally higher than Ti is isi the coercive force (jHrh a at the temperature T;. low sintered, non-aging magnets in general than the coercive _S o force (IHCh one on the temperature Γ, sintered, aging magnets. As can be seen from the following exemplary embodiments, it is possible, however, to reduce the - relatively low - coercive force of a non-aging magnet by means of a heat treatment at a r appropriate temperature to increase.

Embodiment V

A powder in which the atomic ratio Sm: CO = 1: 4.5 (a mixture of SmCo-; and Sm * Co7) was under an isostatic pressure of 20 kb compressed in a magnetic field of 60,000 Oe. Then it was evacuated and subsequently in an closed vessel in the presence of an yttrium getter for 30 minutes at 1120 "C. The an The coercive force measured on the obtained sintered body was ½ 300 Oe. An aging test showed that no aging occurred. Then the sintered body was kept at a temperature of 1,050 "C for 30 minutes post-annealed, after which a coercive force of 18,000 Oe was measured. An aging test carried out with this post-annealed sintered body showed that that also in this case no aging occurred.

The increase in the coercive force, the relatively high by conducting a heat treatment in a range of temperatures (eg. B. 8oC of ¹¹ C to 1250 ° C) can be achieved, is in F i g. 8 illustrates. In this figure the increase a (iH _c }: of the coercive force ( _t H _c h (cf. F t g. 7) achieved after sintering at a temperature 7j is plotted over the post-treatment temperature. It turns out that only by a heat treatment A positive result is obtained in the temperature range between T7 and T. It is found to be particularly advantageous to carry out the heat treatment at a temperature which is higher than the temperature Tj as shown in the sintering temperature-coercive force diagram

F i g. 7 corresponds to a coercive force which is equal to the coercive force which the sintered body has after sintering at the temperature T ₂ . The curve shown in Fig. F is based on the maximum dftrt ^ value attainable at the respective post-treatment temperatures: the heat treatment was always continued until no further increase in the coercive force occurred.

Also a heat treatment in a considerably below the aforementioned temperature range He The low temperature range can have a positive effect

have, as can be seen from the following exemplary embodiment.

Embodiment VI

A powder, whose composition was the same as the powder according to the embodiment V, was sintered in a room which was maintained by means of a vacuum pump to a vacuum of at least 5 x 10- ⁵ torr. Under these conditions, the powder was sintered at a temperature of 1125 ° C. for 30 minutes. The coercive force measured on the obtained body was 19,800 Oe. It was found that after the body ^{had been exposed to the air at a temperature of 150 °} C. for 70 hours, the coercive force increased to 25,100 Oe. Continued heat treatment did not result in any further increase. This experiment showed that the extent to which the coercive force increased as a result of this heat treatment was strongly dependent on the length of the treatment. After 10 hours of treatment, an increase in the coercive force of 1000 Oe was achieved.

The increase in the coercive force when performing a heat treatment in a range of relatively low temperatures (e.g. from 50 ° C. to 300 ° C.) is shown in FIG. 9 illustrates. In this figure, the increase A (iH _c ) i in the coercive force (tH _c ) i achieved after sintering at a temperature T ₂ (cf. FIG. 7) is plotted against the post-treatment temperature. It turns out that a positive result is achieved only by a heat treatment in the temperature range between 76 and Τη , ie as in FIG. 8, the curve shown is based on the maximum Af / Hck-Wen achievable at the relevant post-treatment temperature: the heat treatment was always continued until no further increase in the coercive force occurred.

It should also be noted that the temperatures in all of the aforementioned embodiments with the aid of a thermoelectric element were measured as possible at the point of the powder sample. Although the The results obtained were in good agreement with each other, it must nevertheless be taken into account that z. B. depending on whether the powder sample was packaged in molybdenum or not, or in Depending on whether there was a temperature gradient over the powder sample or not, the specified ones Temperatures can deviate by a few degrees from the real heating temperatures.

For this 4 sheets of drawing auneon

Claims (9)

Claims -. 1. Process for the production of a body with anisotropic permanent magnetic properties one or more compounds with a hexagonal crystal structure of the type C05R, where Co partially can be replaced by Fe and / or Ni and / or Cu and R can be one or more of the elements of Represents rare earths, yttrium and / or thorium, by grinding castings from the compound or compounds, aligning the powder in one Magnetic field, pressing and sintering, characterized in that the sintering during takes place at least 30 minutes above a temperature at which no later aging of the magnetic values of the sintered body occurs, and the sintered body is subsequently heated to a temperature below the sintering temperature Temperature is subjected. 2. The method according to claim 1, characterized in that in a space with a constant Vacuum is sintered. 3. The method according to claim 2, characterized in that in the case of R = samarium at a temperature above 1065 ⁰ C is sintered. 4. The method according to claim 1, characterized in that in an evacuated and then sealed space is sintered. 5. The method according to claim 4, characterized in that in the case of R = samarium at a temperature above 1100 ⁰ C is sintered. 6. The method according to claim 4, characterized in that that sintering is carried out at a temperature above 975 ° C. when R is a combination of is essentially lanthanum and cerium 7. The method according to claim 4, characterized in that ^{sintering is carried out at a temperature of above 1060 0} C if R is a combination of essentially praseodymium and samarium 8. The method according to any one of claims 1 to 7, characterized in that the final Heating at a temperature above 800 ° C is carried out. 9. The method according to any one of claims 1 to 7, characterized in that the final heating at a temperature between 50 and 300 ⁰ C is carried out.