CH618537A5 - Permanent-magnetic material containing rare earths and cobalt. - Google Patents

Description

The present invention relates to permanent magnetic rare earth and cobalt containing material and to a method of manufacturing the same using cerium mixed metal.

Permanent magnetic material using

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Cerium mixed metal has already been described many times in the literature. For example, D.V. Ratnam and M.G.H. Wells in AIP Conf. Proc. 18, American Institute of Physics, New York 1974, reported the properties of mixed metal cobalt magnets. Ratnam and Wells report on individual magnets with energy products up to 15 MGOe and coercive fields up to 14 KOe, but these magnets only have demagnetization curves of moderately pronounced squareness.

Cerium mixed metal is understood to mean the light rare earths isolated from ores. For example, E.V. Kleber and B. Love in Technology of Scandium, Yttrium and the Rare Earth Metals, Pergamon Press, New York 1963, p. 10 indicate that bastnasite and monazite have the following percentage of rare earths:

Bastnasite

Monazite

La

30th

38

Ce

50

48.5

Pr

4th

3.6

Nd

14

8.8

Sm

1

0.5

The composition of cerium mixed metal is therefore not constant and varies depending on the starting ore for the most important components cerium, lanthanum, neodymium and praseodymium at least between 45 and 55.20 and 40.5 and 14.0 and 5 atom percent. This is certainly a reason why it is difficult to produce magnets with good properties and reproducible values with cerium metal or cerium metal additives to samarium.

It is therefore an object of the invention to provide a permanent magnetic material to be produced from starting materials containing cerium metal, which not only has energy products of approximately 16 MGOe and coercive field strengths higher than 8 KOe and is characterized by a rectangular demagnetization curve, but is also repeatable and in is economical to manufacture.

According to the invention, the aforementioned object is achieved by a material which is characterized by the following composition:

(Cex, LaX2 NdXJ PrX4) (i-y) Smy Co5to, 2nd

in which

0.27 <xi <0.77 0.15 <X2 <0.65 0.06 <X3 <0.56; X1 + X2 + X3 + X4 = 1 0.02 <X4 <0.52 0 ^ y ^ 0.25

The relatively cheap cerium mixed metal, which is "corrected" by appropriate additions of Ce, La, Nd, Pr, can advantageously be used in the production.

For the production of such materials, it is advisable to proceed in such a way that first of cerium mixed metal, cerium ,. Lanthanum, neodymium, praseodymium, samarium and cobalt are melted in such a way that their final composition corresponds to the chemical formula mentioned above and the cerium mixed metal means an alloy of the composition Cea Lass Nd Y Pr s Sm e with the following parameters:

0.45 <a <0.55

0.20 <β <0.40

0Ì05 <y <0.14

0 <8 <0.05

0 ^ e ^ 0.01

The starting alloy in question is then placed in a roughly comminuted form in a mill, ground to a powder of a few n grain size under protective gas, then the powder formed is aligned in a magnetic field at approx. 50 kOe, compressed isostatically to a compact, between 1035 and 1045 ° C sintered and heat-treated above 300 ° C.

The heat treatment can advantageously be done in two ways. On the one hand, by annealing the permanent magnetic material between 950 and 1020 ° C, preferably 980 ± 10 ° C, for 10 hours, then rapidly cooling it, and then between 300 and 600 ° C, preferably approx. 350 ° C, 30-40 minutes, may also be treated for up to 60 minutes. On the other hand, it is also possible to bring the permanent magnetic material into a lower temperature zone after the tempering, for example of 300 ° C., and to cool it to room temperature after a maximum of 1 hour, but preferably already after 15 minutes. The magnetic materials produced in this way are characterized without exception by high energy products, large coercive field strengths and almost rectangular demagnetization curves. Materials containing cerium-metal-cobalt-cobalt in particular have surprising improvements in the coercive field strength. Materials with an excess proportion of neodymium which is preferably between 0 and 45 atomic percent also have an improved remanence.

The materials can be made from starting alloys in a protective gas atmosphere, e.g. B. sintered under helium or argon. It is recommended to use a sintering additive that is mixed with the starting alloy. A sintering additive is a 60 percent by weight rare earth metal, in particular Ce, La, Nd, Pr or Sm, and an alloy containing 40 percent by weight cobalt, which makes up about 10-14 percent by weight of the total weight of the mixture. It is particularly advantageous to grind the mixture of sintering additive and starting alloy in a comminuted mill in a coarsely comminuted form.

Further details of the invention result from the exemplary embodiments explained with reference to figures.

Here show:

1 shows the demagnetization curves of permanent magnetic material containing alloys of the composition CeMMi.x Cex Cos, 1,2,3 alloys with an excess proportion x of cerium of 0; Denote 0.15 and 0.30.

2 shows the demagnetization curves of permanent magnetic material containing alloys of the composition CeMMj_x Lax Cos, 1,4,5,6 alloys with an excess x in lanthanum of 0; 0.1; Denote 0.2 and 0.3,

3 shows the demagnetization curves of permanent magnetic material containing alloys of the composition CeMMi_x Prx Cos, 1.7.8 alloys with an excess proportion x of praseodymium of 0; Denote 0.05 and 0.1,

4 shows the demagnetization curve of permanent magnetic material containing alloys of the composition CeMMi_x Ndx Cos, 1,9,10,11,12,13 alloys with an excess proportion x of neodymium of 0; 0.25; 0.1; 0.15; Denote 0.3 and 0.5,

5 shows the coercive field strength jHc and the remanence BR of cerium-metal-cobalt-containing, permanent magnetic

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Material depending on the neodymium content of the rare earths,

6 shows the energy product (BH) max of a CeMM-containing alloy as a function of the sintering temperature Ts and

7 shows the demagnetization curves of permanent magnetic material with the composition CeMM0.8 Sm0i2 Cos with an average grain size of approx. 4 x after 20 minutes of annealing at 980 ° C., quenching in liquid nitrogen and tempering at approx. 300.350 and 400 ° C. .

The starting substances for the permanent magnetic material to be produced were cerium mixed metal, the composition of which was determined with the aid of an X-ray fluorescence spectrometer to an accuracy of approximately 1%, and 53.7% by weight cerium, 30.2% by weight lanthanum, 12.0% by weight neodymium and 4.0 weight percent praseodymium, 15 each used 99.9% pure Sm, Ce, La, Nd and Pr and 99.99% pure cobalt. All alloys were melted in batches of 120 g each in a boron nitride crucible under argon as a protective gas in a medium frequency furnace at approx. 1200 ° C. The molten, brittle alloys were then broken up into particles with a diameter of less than 0.5 mm and then ground in a counter-jet mill into powder with a granule size between 2.5 and 4 n. The powders were pressed into cylindrical test specimens at moderate pressure, magnetically aligned in a magnetic field of approx. 50 KOe, pressed isostatically at 600 bar and then sintered between 1035 and 1045 ° C for at least half an hour. Subsequent heat treatment, the sequence of which will be described in detail below, significantly improved the magnetic properties of the materials produced.

Before the sintering, sintered additives consisting of an alloy comprising 60% by weight Sm and 40% by weight cobalt (Sm60-Co 40 sintering additive) were added to the ground starting alloys. The weight of this sintering additive fluctuated between 10 and 14% of the total weight of the compact to be sintered. With suitable starting alloys and with sintering in an oxygen-free atmosphere, however, it is also conceivable to produce magnets without the addition of sintering. In addition to the SmCo alloys, there are also other 40 light rare earths in the form of an SE60-Co40 alloy,

where SE = Ce, La, Pr, Nd is suitable as a sintering additive.

In addition to melting the elements, the pulverized starting alloys were also produced by mixing crushed CeMMCos and SECos alloys and then grinding them together. Correspondingly, comminuted sintering additives were added to the comminuted starting alloys and this mixture was ground to powder in the countercurrent mill.

For a closer examination, the numerous, the main formula

(CeXl LaX! NdX! PrX4) (i-y) Sniy Co5 ~ Fo, 2

corresponding materials 4 alloy series with the following indices selected:

a) 0.56 <xi <0.65 0.23 <X2 <0.29

0.09 <X3 <0, ll; xi + X2 + X3 + X4 = 1

0.03 <X4 <0.04

0 ^ y ^ 0.25

b) 0.27 <xi <0.46 0.41 <X2 <0.65

0.06 <X3 <0.10; xi + X2 + X3 + X4 = 1

0.02 <X4 <0.03

0 ^ y ^ 0.25

c) 0.30 <xi <0.54 0.16 <X2 <0.30

0.12 <X3 <0.51; X1 + X2 + X3 + X4 = 1 0.02 <X4 <0.04 0 ^ y ^ 0.25

d) 0.51 <xi <0.51 0.28 <X2 <0.29

0.11 <X3 <0.12; X1 + X2 + X3 + X4 = 1

0.07 <X4 <0.10 0 ^ y ^ 0.25

In each case, master alloys of the SE Cos type were assumed, the symbol SE containing cerium mixed metal and a further addition of optionally Ce, La, Nd, Pr. The demagnetization curves of the final alloys were recorded with a vibration magnetometer at a maximum field strength of 50 KOe.

The measurement results of a representative selection of the materials corresponding to both the main formula and the compositions claimed in the shortlist are summarized in the table below and in FIGS. 1-5.

Molten alloy composition (atomic percent)

Erschmol- Ce La Nd Pr Br jHc (WxH) max.

zene alloy »(KG) (KOe) (MGOe)

1

53.7

30.2

12.0

4.0

8.1

7.4

15.5

2nd

60.7

25.6

10.2

3.4

8.0

8.1

15.0

3rd

67.6

21.1

8.4

2.8

7.7

6.2

14.3

4th

48.3

37.2

10.8

3.6

8.1

8.3

15.8

5

43.0

44.2

9.6

3.2

8.05

10.0

14.7

6

37.6

51.1

8.4

2.8

7.95

12.7

15.1

7

51.0

28.7

11.4

8.8

8.35

8.2

16.0

8th

48.3

27.2

10.8

13.6

8.1

7.5

15.0

9

51.0

28.7

16.4

3.8

7.85

16.5

14.8

10th

48.3

27.2

20.8

3.6

8.15

16.1

16.1

11

43.0

24.2

29.6

3.2

8.10

13.2

15.8

12

37.6

21.2

38.4

2.8

8.05

12.85

15.2

13

26.9

15.1

56.0

2.0

8.9

4.7

16.2

Table: Composition of the melted alloys as well as the hard magnetic data of the permanent magnetic material made from it using an Sm60-Co40 sintering additive.

On the basis of measurements on permanent magnetic materials which were produced from alloys 1, 2 and 3, it can be seen from the table and FIG. 1 that an increase in the cerium content in the cerium mixed metal (alloy 1, in FIGS. 1-4 is the result thereof) manufactured permanent magnetic material designated 1) initially an enlargement of the coercive field strength has the effect that, with a further increase in the ceran part, the coercive field strength, the remanence and the squareness of the MH curve deteriorate, so that, according to the table, a total proportion of 0. 55 to 0.65 atomic percent cerium has an advantageous effect on the magnetic properties. Permanent magnetic material of this composition thus has surprisingly good magnetic properties.

The table (alloys 1,4,5,6) and FIG. 2 show that an increase in the lanthanum component with an increase in the coercive field strength of jHc = 7.4 KOe in the case of an original cerium mixed metal alloy without additional lanthanum component (alloy 1) on jHc = 12.7 KOe for a total lanthanum content of 51.1 atomic percent (alloy 6). The magnetic remanence BR remains unchanged within the measurement accuracy, as does the perpendicularity of the magnetization curve and the energy product (BH) max. From this it can be determined with certainty that a lanthanum content of 0.40 to 0.50 brings about a considerable improvement in the coercive field strength.

According to the table (alloys 1, 7, 8), increasing the proportion of praseodymium to 5 to 10 atomic percent has a positive effect on the magnetic properties.

As can be seen from the table (alloys 1.9-13) and Fig. 4, an increase in the neodymium content causes the greatest increase in the coercive field strength. The increase from 12 atom percent in cerium mixed metal alloy 1 without additional neodymium content to, for example, 20.8 atom percent in alloy 10 increases both the jHc value from 7.4 KOe to 16.1 KOe and the remanence. When the proportion of neodymium is increased to over 38.4 atomic percent (alloy 12), the coercive field strength jHc deteriorates noticeably and only reaches values of 4.7 KOe at 56.0 atomic percent (alloy 13), but has a remanence of 8 in this composition , 9 KG on. An improvement in the magnetic properties of cerium mixed metal-cobalt alloys therefore occurs - as can also be seen in particular from FIG. 5 - at a neodymium content of 12 to 40 atomic percent.

The materials according to the invention, but also all other permanent magnetic materials containing SEC05, in particular CeMM, can be considerably improved in their magnetic properties by sintering at the appropriate temperature and by subsequent heat treatment.

The optimal sintering temperature was determined on a CeMMCos magnet. The magnet was made using 8-16 weight percent Sm and 40 weight percent Co sintering additive. The CeMMCos and Sm60-Co40 alloys were separated in one

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Counter jet mill ground, mixed v h, aligned in a magnetic field at 50 KOe and pressed isostatically at 100 atm pressure. For the mixtures with 8, 10, 14 and 16 percent by weight, samples were sintered at different temperatures in the range of 1015 ° C <TS <1055 ° C. It was shown that the density p and the remanence BR increase steadily with the sintering temperature. 6, on the other hand, showed a pronounced maximum, which shifts to smaller values as the amount of sintering additive increases and corresponds in a first approximation to the optimal sintering temperature. It emerged from this series of experiments that sintering temperatures between 1035 and 1045 ° C are preferred for all cermic-metal-containing cobalt magnets.

The magnetic materials were first annealed between 950 and 1020 ° C during the subsequent i5 heat treatment. The annealing times were between 20 minutes and 50 hours. After annealing, the sample was rapidly cooled, such as by quenching in liquids such as liquid nitrogen, glycerin or another oil-like organic liquid such as silicone oil. Cooling in a cold protective gas atmosphere, such as under argon or nitrogen, has also proven to be very suitable. In a subsequent tempering treatment at temperatures between 300 and 600 ° C for 10 to 60 minutes, the 25 magnetic properties were further improved.

The improvement in the permanent magnetic properties is explained on the basis of the demagnetization curves shown in FIG. 7 of a magnet with the composition CeMM0.8 Sm0i2 Cos. An improvement in the permanent magnetic properties through the heat treatment described above is of course also conceivable for any other magnet containing cerium-mixed metal cobalt. In Fig. 7, the solid lines represent the demagnetization curves after sintering at Ts = 1040 ° C. The dash-dotted line marks the demagnetization curve after annealing at 980 ° C and quenching in liquid nitrogen, while the dashed lines, the dotted and the roughly dashed demagnetization curves were recorded after tempering at 300.350 and 400 ° C. 40 It can be seen from this that the annealing and quenching increased the coercive field strength by a factor of 2.25, while the subsequent tempering treatment leads to a further increase in; HC by 1 -2 KOe.

In further tests, it was found that a temperature of 980 + 10 ° C is optimal for tempering 45. The increase in the coercive field strength depends on the annealing time. In addition to an increase of jHc up to 2.5 times, an approximation of the demagnetization curve to a rectangular course and an increase in the remanence BR are also found when the annealing time is 6 or more hours. It was also shown that the cooling rate is an extremely critical parameter of the process. Quenching with nitrogen is particularly recommended here, since this leads to a considerable increase in the jHc values and 55 the energy product increases at annealing times> 6 h (in the example in FIG. 7 from 16 to 17 MGOe).

The tempering temperature and time is important for the tempering treatment. Optimal improvements in the magnetic properties are achieved at a tempering temperature of 60 350 ° C and a tempering time between 30 and 40 minutes.

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6 sheets of drawings

Claims (14)

618537 1. Permanent magnetic, rare earth and cobalt-containing material, characterized by the composition: (Cex, LaX2 NdXl PrJ ^ Smy Co5t0.2 in which 0.27 <xt <0.77 0.15 <X2 <0.65 0.06 <X3 <0.56; xi + X2 + X3 + X4 = 1 0.02 <X4 <0.52 0 ^ y ^ 0.25 2. Permanent magnetic material according to claim 1 characterized by the following values of the indices: 0.56 <xi <0.65 0.23 <X2 <0.29 0.09 <X3 <0.1 l; xl + X2 + X2 + X4 = 1 0.03 <X4 <0.04 0 ^ y ^ 0.25 2nd PATENT CLAIMS 3. Permanent magnetic material according to claim 1, characterized by the following values of the indices: 0.27 <xi <0.46 0.41 <X2 <0.65 0.06 <X3 <0.10; X1 + X2 + X3 + X4 = 1 0.02 <X4 <0.03 0 ^ y ^ 0.25 4. Permanent magnetic material according to claim 1, characterized by the following values of the indices: 0.30 <xi <0.54 0.16 <X2 <0.30 0.12 <X3 <0.52; X1 + X2 + X3 + X4 = 1 0.02 <X4 <0.04 0 ^ y ^ 0.25 5. Permanent magnetic material according to claim 1, characterized by the following values of the indices: 0.51 <xt <0.52 0.28 <X2 <0.29 0.11 <X3 <0.12; Xl + X2 + X3 + X4 = l 0.07 <X4 <0.10 0 ^ y ^ 0.25 6. A process for the production of permanent magnetic material according to claim 1, characterized in that initially a starting alloy is melted from cerium mixed metal, cerium, lanthanum, neodymium, praseodymium, samarium and cobalt in such a way that its final composition has the chemical formula (CeXl LaX! Ndx, PrX4) (i_y) Sniy Co5-ìo, 2 corresponds, whereby 0.27 <xi <0.77 0.15 <X2 <0.65 0.06 <X3 <0.56; XI + X2 + X3 + X4 = 1 0.02 <X4 <0.52 0 ^ y ^ 0.25 and the cerium mixed metal means an alloy of the composition Cea LaB NdY Pr5 Sm e with the following parameters: 0.45 <a <0.55 0.20 <ß <0.40 0.05 <y <0.14 0 <5 <0.05 0 ^ e ^ 0.01 that said starting alloy is put into a mill in coarsely comminuted form, ground to a powder of a few p, granule size under protective gas, the powder formed is aligned in a magnetic field at approx. 50 KOe, compressed isostatically to a compact, between 1035 and 1045 ° C sintered and heat treated above 300 ° C. 7. The method according to claim 6, characterized in that the cerium mixed metal of the composition Cea Lap Nd Y Pr 5 Sm E the following parameters a = 0.54 ß = 0.30 y = 0.12 8 = 0.04 and that before the grinding to the starting alloy, a sintering additive is added which makes up 10 to 14 percent by weight of the total material mixture, the sintering additive containing 40% by weight cobalt, balance rare earths, selected from those elements which have the formula of Correspond to final composition. 8. The method according to claim 6, characterized in that the permanent magnetic material is annealed between 950 and 1020 ° C for up to 50 hours. 9. The method according to claim 6, characterized in that the permanent magnetic material is annealed at 980 ± 10 ° C for at least 6 hours. 10. The method according to claim 6, characterized in that the permanent magnetic material is cooled in a liquid, in particular silicone oil, glycerol or liquid nitrogen or in a protective gas atmosphere, in particular argon or nitrogen. 11. The method according to claim 6, characterized in that the alloy is tempered between 300 and 600 ° C for up to 60 minutes, preferably at about 350 ° C for about 30-40 minutes. 12. The method according to claim 6, characterized in that the alloy after tempering in a lower temperature, preferably 300 ° C, brought and after a maximum of 1 hour, preferably 15 minutes, cooled to room temperature. 13. The method according to claim 6, characterized in that the starting alloy is melted from CeMMCos and SECos alloys, CeMM = cerium mixed metal and SE = Ce, La, Nd, Pr. 14. The method according to claim 6, characterized in that the starting alloy consists of mixed and comminuted CeMMCos and SECos alloys, where CeMM = cerium mixed metal and SE = Ce, La, Nd, Pr means.