CA1037294A

CA1037294A - Cobalt-rare earth metal permanent magnetic material

Info

Publication number: CA1037294A
Application number: CA240,519A
Authority: CA
Inventors: Hans-Peter Klein; Hartmut Nagel
Original assignee: BBC Brown Boveri AG Switzerland
Current assignee: BBC Brown Boveri AG Switzerland
Priority date: 1975-01-14
Filing date: 1975-11-26
Publication date: 1978-08-29
Also published as: DE2504838C2; JPS6012416B2; JPS5196726A; NL7600238A; GB1479871A; FR2297926B1; CH599661A5; NL177536B; NL177536C; DE2504838A1; FR2297926A1

Abstract

ABSTRACT OF THE DISCLOSURE

Title of the Invention COBALT-RARE EARTH METAL
PERMANENT MAGNETIC MATERIAL

A permanent magnetic material for use under variable temperatures such as in electric motors, which has the composition (MM1-xNdx)1-ySmyCo5, in which 0.38 ? x ? 0.65, 0 ? y ? 0.25, and MM is a mischmetal of the composition Ce .alpha. La .beta. Pr ? wherein the parameters .alpha. , .beta., ? , satisfy the conditions 0.50< .alpha. < 0.70 0.22< .beta. < 0.45 0.00< ? < 0.06, and .alpha. + .beta. + ? = 1.

Description

` 103q29~
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention relates to a permanent magnetic material which contains rare earth metals, especially neodymium, and cobalt, to a process for its production and to a use for same.
Copending Canadian Application No. 233,251, filed August 11, 1975, discloses related subject matter.
Description of Prior Art:
- 10 Material of the above-mentioned type is known, for example, from the article by W.A.A.~. Velge and K.H.J. Buschow ; in Proc. IEE Conf. on Magn. Mat., pages 45-50, London 1967.
According to Figure 4 of this publication, the (La, Nd)Co5 alloys mentioned there possess, according to the proportion of neodymium at room temperature, only a slight dependence of - the coercitive field strength of IHC on the temperature. Such an independence of the coercitive field strength from ; temperature variations is very desirable when one uses j ~ permanent magnets, for example in electric motors. In addition i~ 20 to this, however, high values of the remanence Br and of the Coercitive field strength IHc are also frequently neceSSarY

prerequisites which the permanent magnetic material has to fulfill. (La, Nd)Co5 alloys, however, even at room temperature, where the coercitive field strength is generally greater than . -.
at higher temperatures, only reach coercitive field strengths of at most 3kOe. In addition, the coercitive field strength ;~ of (La, Nd)Co5 alloys decreases monotonically as the temperature ` rises, to an extent dependent upon their composition, even at temperatures which are only slightly above room . 1, '

-2- ~
.

"~ .
',` ~''"' .. :, lQ3q2~
tem~erature, so that a u~e of theae alloys as pexmanent ~agnets at elevated temperatures, sa~ at 300 C is wlthout interest.
SUMMA~Y OF THE IN~ENTION
Accordingly, it ;`5 an o~ject of the present invention to proviae a permanent-magnet~c material which contains rare earth metals, especially neodymium, and cobalt, whose coercitive field strength IHC above room te~perature decreases only fairly ; . slowly as the temperature rises, but which ~ven at temperatures of . up to 300C still shows values of the coercitive field strength , . 10 which permit use of the material in special fields of application, such as in places where coercitive field strengths of more that . 2kOe are required at temperatures around 300C, and which further-. more, can also be produced in an economical manner by a simple process.
Briefly, this and other objects of this invention as . will hereinafter become clear from the ensuing discussion have been attained by pro~iding a material having the composition ~ :
.~ (MMl XNdX)l ySmyCo5, in which 0.38~ x~ 0.65, 0 y~ 0.25 and MM
.`~ represents mischmetal of the composition Ce~ La~ Pr~ , and the ~:~ 20 parameters a, ~ and ~ fulfill the conditions :; 0 50 ~ ~c 0 70 0.22 < ~< 0 45 - .
0.00 < y ~ 0.06 and a + ~ + y = 1.
Such a material can be used for the production of . 25 permanent magnets with a more or less temperature-independent coerci~ive field strength between room temperature and 300C.

~
.

.... ~
" .
'' ' :
., .
:
' ' :
.:. . .

Since such a material in addition po~sesses a coercitive field ' strength of over 2kOe even at tempe~ature~ around 300C, it is ; eminentl~ sui,table as a permanent ~agnetic-~aterial in the con-struction of electric ~otors. The coercitive of permanent mag-nets prepared from the ab~ve magnetic-material has a temperature depending ~ IHC kOe , of less than 0.02 in the range of ~ T C 0C ~ T ~ 300 C.
A particular advantage is also the favourable price of this ~, material, since it can be produced solely from the cheap cerium , mischmetal of neodymium and co~alt without the use of expensive lQ samarium or ~ith only a small addition thereof.
The process of this invention for the production of ,~ such a material comprises ~elting together (l-x') ~l-y) moles of cerium mischmetal of the composition Ce~ La~ Pr~ Nd~ , in which 0.45 ~ ~ ~ 0.65 ; 15 0.20 ~ ~ ~ 0.40 ~' ' ~ ~ ~ 0'05 0.05 < ~ ~ 0.15 and a + ~ + y + ~
,' with x'(1-y) moles of neodymium, 5 moles of cobalt and possibly , y moles of samarium, in which 0.20 <x' ~ 0.85 and 0~ y ~ 0.25.
! '-BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily attained as the same becomes better understood by reference to the follow- ' ing detailed description when considered in connection with the " 25 accompanying drawings, wherein:
` . FIGURE 1 shows the coercitive field strength IHC (kOe) of permanent magnetic materials of the composition (MMl XNdX) ,'- 0 85SmO 15Co5, in which x passes through the values 0; 0.13;
.. ~.~: ' ~:

4_ : :' " .

;.
~,;. ~ ' ,,.

~037Z94 0.25j Q.38 and 0.65, dependi~ng upon th~ te~perature T (C), and FIGURE 2 sho~s the coerciti~e field strength IHC (kOe) of permanent-magnetic mater~al of the ~3~osition Sml n Ndn C5~
in which n passes thr~ugh the values 0; 0.25; and 0.45, depending . 5 upon the temperature T ( C~.
-DESCRIPTION OF THE PREFE~RED EMBODIMENTS
The materials of Figure 1 in which x = 0 and 0.13, and also the materials of ~igure 2 are used only for comparison with the materials according to this invention, which are repre-10 sented in Figure 1 by the materials with x = 0.25; 0,38 and 0.65.
- Having generally described the invention, a more complete understanding can be obtained by reference to certain :
: specific examples, which are included for purposes of illustra-' tion only and are not intended to be limiting unless otherwise ~-- 15 specified.
~:~ EXAMPLE 1 Permanent magnetic materials of the alloy series : (MMl X NdX) Co5, with 0 ~ x ~ 0.65, were produced as follows:

( eO.61 Lao,34 PrO 05) Co5 = MM Co5 (x = 0) 2. (MMo 87 Ndo,l3) Co5 (x = 0.13)

3, (MMo 75 Ndo.25) C5 (x = O.25) , " , .'''.'' ''', '.,':
:,, ~::.

-":
.' :

. . .
.'' .

~` ` 1037294 'I
' Z I :

`~ ,1

4. (MMo 62 NdO.38) C5 (x = 0.38) .
,` 5. (MMo 35 Ndo.65) Co5 (x = 0.65) . tj ` I In the alloys 1 - 5, the mixed metal, MM is CeO 61 LaO 34 PrO 05 Materials according to this invention are represented by the alloys 3 - 5.
1, These alloys serve as initial alloys for further processing to form hard mag- Z
Zl netic test bodies and still have no content of samarium, so that y = O. I
., I . . I .
The alloy 1 was made by melting the elements cerium, lanthanum, praseodymium and cobalt weighed out in stoichiometrical proportions and possess~!! ~
' I! ing a purity of 99.9o/.
: IZ
`i ` Zl The alloys 2 - 5, on the other hand, were made by melting the ele- Z
I ments neodymium and cobalt weighed out in stoichiometrical proportions (pùrity in each case 99.9%) and from cerium mischmetal whose composition had ::' I', been determined to within 1% by means of an X-ray fluorescence spectrometer, and whichshowed 53 atom per cent of cerium, 30 atom per cent of lanthanium, ' ~`
¦l 13 atom per cent of neodymium and 4 atom per cent of praseodymium, All the initial alloys 1 - 5 were made molten in batches of 120 9 ., 1 1 .
each in a boron nitride crucible under an argon protective gas atmosphere with a medium frequency furnace at about 1200C. The fused brittle initial ! alloys, after they had solidified and cooled to room temperature, were then , ~ I
1 20 I ground into particles with diameters of less than 0.5 mm and then ground to ¦ -a powder with a particle size between 2.5 and 4 ~m in a counter jet mill. ¦ `

, ;. il I :
I; ! :::
,, ,;,.~
: ~1 -6-, ` I!
., ,, Z
;. ~Z

; 1037Z9~
To these ~round initi.al alloys there were then added powdered sinter additives consisting of an alloy containin~ 60 per cent by weight of Sm and 40 per cent by weight of cobalt (.~m 40 Co 60 alloy~. The weight of th~s sinter adaitive varied between 10 and 14% of the total weight of the end product consisting of : the initial alloy and the sinter additive. The initial alloy and the sinter additive were mixed and pressed at moderate pres-.. sure to form cylindrical test bodies, magnetically aligned in a magnetic fi~d at about 50 kOe, isostatically pressed at 600 atmospheres and then sintered for at least 30 minutes at about 1040C. After this, the test bodies were heat treated at 980C
for about 6 hours, rapidly cooled in argon or liquid nitrogen and then annealed at about 350C for about 30 to 40 minutes.
- In this way, test bodies were obtained of the follow-as ing compositions:
.- 1 Ce LaO 29 PrO 04 SmO lsCos = MMo 85 SmO.15 Co5 2 (MM Nd ) Sm Co . 5 5 ~ .
4. (MMo 62 Ndo.38) 0.85 0.15 5 ~; 205. (MMo 35 Ndo.65) 0.85 0.15 5 ; once again with MM = CeO 61 LaO 34 PrO 05 ... : The demagnetisation curves of these test bodies -- were then recorded after being subjected to pulses in an approx-imately 60 kOe magnetic DC field with a vibration magnetometer C 25 at a maximum field strength of 50 kOe.
.~ In Figure 1, the coercitive field strength IHC of , . . .
test bodies, which as described above, had been obtained : by the addition of an Sm 40 Co 60 sinter .

~' . --7--~ ' 1037Z94 additive to the powdered initial alloys 1 - 5 is plotted against the temperatur T. From these curves one can see the marked dependence of the coercitive ¦I field strength IHC at room temperature on the neodymium content. Thus the Il coercitive field strength of materials of the composition (MMl x ~dx) ,` 0 85SmO 15 Co5, above a neodymium proportion of x = 0.25 falls it is true continuously at room temperature. However, test bodies with a neodymium proportion x =0.38 or x = 0.65 (numbers 4 and 5 of Figure 1) have higher coerci tive field strengths than other test bodies with a lower neodymium content at '' between 90 and 300C or 150 and 300C, respectively, and in addition, show 'I the lowest dependence of the coercitive field strength on the temperature.
.
ji The coercitive field strength IHC = 5 kOe of the test body with the neodymium proportion of x = 0.65 varied, between O and 170C, for example, only by . !, approximately + 10%. A further advantage of the materials according to this ', invention with a neodymium proportion greater than 0.25 is that the remanence 1~ 15 , Br is higher and also less dependent on temperature, as compared with the Ce MM
~ ! Cos alloy. From the demagnetisation curve of the test body with a neodymium ; 'I proportion of x = 0.65 a remanence Br f 8.9 kg was recorded, which was approx-~ Il imately 10% higher than that of the test body of the alloy 2. 1 ~
:., Ij I ~.
- I Instead of preparing the test bodies as described above, it is also ` 20 1¦ possible to proceed as follows.
1 :: ' 1 , .
¦ 1 For example, it is also possible to mix size-reduced Ce MM Co5, 'I Nd Co5 and Sm 40 Co 60 alloys followed by grinding them together in order 1.. , 1 , ~.
' l i ' , I! - I ::

1` .

.. 'j l : .
~.

. . ~ : . - . .

~37Z94 to o~tain the po~der ~or the pressed ~odies. In this case, as sinter additives one can use, as in the preYiously mentioned process, ~n addi~t~on to the Sm 40 Co 60 alloy other alloys such as Ce 40 Co 60, La 40 Co 60 or Wd 40 Co 60 alloys.
~` 5 A further possibility of producing test bodies con-sists in first of all homogenislng, with heat treatment at tem-peratures between 1150 and 1250C, the alloys (MMl x NdX) 1 y SmyCo5, in which 0.25 ~ x ~ 1 and o c y ~ 0.25, made by melting the components samarium, ne~aymi~m, cerium mischmetal and cobalt weighed.~ out in stiochiometrical proportions. From these homo-genised alloys it is then possible in a grinding device to pro-duce spherical monocrystalline samples having a diameter of a few millimeters, which after pulses in a strong magnetic field ~; can be tested for their magnetic properties in a magnetometer.

The superiority of the MMl-X NdX Co5 alloys, in which x ~ 0.25, in regard to the independence of the coercitive ; field strength on variations in temperatures above room tempera-ture, and the highly advantageous nature of the choice of the alloys from the plurality of RE Co5 alloys, in which RE repre-,. . ..
~ sents one or more of the rare earth metals, can be seen from ; Example 2.
In this Example permanent magnets were produced from ..: -,~ the following alloys:
:, .
6. Sm Co5 , .",;, SmO 75 Ndo 25 C5 8. S~lo 55 Ndo 45 Co5 - ~;
', ' .~ . , : ` l . ~
' ! I

From these alloys, test bodies were produced in a manner completely analogous to the first example and were tested for their magnetic properties in ¦ a magnetometer.

1 In Figure 2, the coercitive field strength IHC of these test ll bodies is plotted against the temperature T. From these curves, it is possiblel :
I to see, in complete analogy to the curves of Figure 1, a considerable decreasein the coercitive field strength at room temperature for a neodymium content x greater than 0.25. Nevertheless, with all the alloys the coercitive field ,' strengths IHC still depend very strongly on the temperature, because even in - 10 ~~ the case of the alloy 8 with a neodymium proportion of x = 0.45, the coercitive¦
1 field strengths between room temperature and 170 or 300C varied by 60 and i ', 400% respectively, while in the case of the alloy 5 of the cerium mischmetal : 1l neodymium alloys (Figure 1) the corresponding variations are only 10 and I i -~ 200% respectively. I
~ -,; 15 ll The advantages of the material (MMl X NdX)l y SmyCo5, wherein " 0.25 < x < 1 described above are obtained with an MM of the composition 'I `;:
Ce~ La~ Pr~ , in which . o 50 < ~ < 0 70 .:' '' l ..
0.22 < ~ < 0.45 ~¦ 0.00 < ~ < 0.06 and ~ + ~ + ~ = 1, and for - 20 l¦ a samarium proportion, y, of between 0 and 0.25.
:.
Having now fully described the invention, it will be apparent il to one of ordinary skill in the art that many changes and modifications can be I made thereto wlthout departing from the spirit or scope of the invention as set forth herein.
~ .

;". . -10- :' 1 l .
''' ; I '~. ~'

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A permanent magnetic material of the formula (MM1-xNdx)1-ySmyCo5, in which 0.38 ? x ? 0.65, 0 ? y ? 0.25, and MM is mischmetal of the composition Ce.alpha. La.beta. Pr? wherein the parameters .alpha. , .beta. ,? satisfy the conditions 0.50 < .alpha. < 0.70 0.22 < .beta. < 0.45 0.00 < ? < 0.06, and .alpha. + .beta. + ? = 1.

2. The material of Claim 1, wherein .alpha. , .beta. and ?
possess the approximate values 0.61; 0.34 and 0.05, respectively.

3. The material of Claim 1 having the composition (MN1-xNdx) 0.85Sm0.15Co5, in which 0.38 ? x ? 0.65.

4. A process for the production of the permanent magnetic material of Claim 1 which comprises melting together (1-x') (1-y) moles of cerium mischmetal of the composition Ce .alpha. La .beta. Pr ? Nd .delta. , wherein 0.45< .alpha. < 0.65 0.20< .beta. < 0.40 0.00< ? < 0.05 0.05< .delta. < 0.15 and .alpha. + .beta. + ? + .delta. = 1, x'(1-y) moles of neodymium, 5 moles of cobalt and up to y moles of samarium, wherein 0.33 ? x'? 0.50 and 0 ? y ? 0.25.

5. A permanent magnet made of the permanent magnetic material of Claim 1 whose dependence of the coercitive field on the temperature , in the range 0 ? T ? 300°C

is less than 0.02.

6. The permanent magnet of Claim 5 having a coercitive field strength greater than 2 kOe at temperatures of up to 300°C.

7. A permanent magnetic material, of the formula:
(MM1-xNdx)1-ySmyCo5, wherein 0.38 ? x ? 0.65; 0 ? y ? 0.25; and MM is a mischmetal of the composition Ce .alpha. La .beta. Pr ? , wherein 0.50< .alpha. < 0.70 0.22< .beta. < 0.45 0.00< ? < 0.06 and .alpha. + .beta. + ? = 1.0 wherein the coercivity of permanent magnets prepared from said permanent magnetic material has a temperature dependency, , of less than 0.02 in the range of 0°C ? T ? 300°C

8. A permanent magnet characterized by a coercive field having a temperature dependency, , of less than 0.02 in the range of 0°C ? T ? 300°C, and prepared from the permanent magnetic material of Claim 7.

9. A process for the production of the permanent magnetic material of Claim 7, which comprises melting together (1-x') (1-y) moles of cerium mischmetal of the composition Ce .alpha. La .beta. Pr ? Nd .delta. , wherein 0.45 < .alpha. < 0.65 0.20 < .beta. < 0.40 0.00 < ? < 0.05 0.05 < .delta. < 0.15 and .alpha. + .beta.+ ? + .delta. = 1;
x'(1-y) moles of neodymium, 5 moles of cobalt and y moles of Sm, wherein 0.33 ? x' ? 0.50 and 0 ? y ? 0.25;
wherein the resulting permanent magnetic material has magnetic properties such that the coercive field of permanent magnets prepared from said permanent magnetic materials has a temperature dependency, , of less than 0.02 in the range of 0°C ? T ? 300°C.