US 3663317 A
A method of manufacturing a permanent magnet from compressed M5R powder (M is, for example, Co, R is a rare earth or Th). The powder is obtained by grinding castings in oxygen- and water-free environments in an inert gas or an inert liquid. The resultant magnet exhibits a small ageing effect, while in addition magnets of higher density can be obtained.
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Description (OCR text may contain errors)
Unite States Westendorp et al. [451 May 16, 1972  METHOD OF MAKING A PERMANENT-  References Cited MAGNETISABLE BODY OF UNITED STATES PATENTS COMPRESSED FINE PARTICLES OF A 3 523 836 8/1970 B h 1 148/103 X usc ow eta. COMPOUND OF M AND R 3,540,945 1 1/1970 Stmat et al.  Inventors: Frans Frederik westendorp; Antonius 3,463,678 8/ 1969 Becker ..l48/ 105 Gregorius Riinbeek, both of Emm asingel, Eindhoven, Netherlands Primary Examiner-John F. Campbell Assistant Examiner--Ca.rl E. Hall  Asslgneez U.S. Philips Corporation, New York, NY. Anomey prank R Trifari  Filed: Nov. 18, 1970  ABSTRACT 21 A l.N 90,512 1 pp 0 A method of manufacturing a permanent magnet from compressed M R powder (M is, for example, Co, R is a rare earth  Foreign Application Priority Data or Th). The powder is obtained by grinding castings in oxygenand water-free environments in an inert gas or an inert liquid. Dec. 20, Netherlands The resultant magnet exhibits a Small g g effect, in
addition magnets of higher density can be obtained.  US. Cl ..l48/l03, 29/208,148/105,
264/24, 264/ l l l 1 Claim, 2 Drawing Figures  Int. Cl. ..H0lf 7/06  Field of Search ..29/608; 252/6257, 62.56;
264/24, 111; 335/296; l48/l0l, 103, 105
Pakented May 16, 1972 3,663,317
2 Sheets-Sheet 6 ume) INVliN'l'URfi FRANS F. WESTENDORP ANTONIUS G. RIJNBEEK 1/ (C v k Va Paimt ed ay 16, 1972 3,6331? .2 Sheets-Sheet 2 INVEN'I'ORS FRANS F. WESTENDORP ANTONIUS G. RUNBEEK AG /v 7 METHOD OF MAKING A PERMANENT-MAGNETISABLE BODY OF COMPRESSED FINE PARTICLES OF A COMPOUND OF M AND R The invention relates to a method of manufacturing a permanent-magnetisable body of fine particles of a compound of M and R, the range of existence of which is integral with that of the compound M R having a hexagonal crystal structure, in which M represents Co or a combination of Co with one or more of the elements Fe, Ni and Cu and R represents one or more of the elements of the rare earth metals and/or Th, in which method a casting of the alloy concerned of M and R is ground to a powder of the desired granular size, the powder being pre-densified and orientated simultaneously or subsequently in a magnetic field, after which it is compressed by an isostatic pressure of at least kbar and finally plastically deformed slightly, while said isostatic pressure is maintained.
In this connection the rare earths are to include also the element Y.
The term range of existence is to denote herein a range of concentrations within which for a continuous series of compounds the same crystal structure can be obtained for 100 percent.
Such a method is described in Journal of Applied Physics" Vol. 40, No. l0, pages 4,029 and ff. The resultant magnetic body described therein may have a relative density of 97 percent at the most, which is to be understood to mean that the density of the body is 97 percent of the theoretical density of the M-R compound concerned.
Magnetic bodies thus manufactured have, however, the disadvantageous property that the coercive force decreases with time: there occurs a so-called ageing process. In the aforesaid publication this ageing is referred to and recognized as a disadvantage to practical use of the magnetic bodies. This ageing increases with increasing temperature. However, even at room temperature ageing occurs to an undesirable extent.
In Cobalt 36 (1967), page 40 the cause of ageing is said to be oxidation in air. Since a magnetic body of the kind set forth, having a density of 95 percent or more does not exhibit a porosity such that oxygen or water vapour can penetrate into the body, oxidation is impossible except on the surface. Nevertheless such magnetic bodies are found to age to an appreciable extent.
It was a surprise to find that when the aforesaid known method of manufacturing a magnetic body is carried out on powder obtained, in accordance with the characteristic aspect of the method according to the invention, by grinding and thereafter pressing and orienting it in oxygen and water-free environments in an inert gas or in an inert liquid, magnetic bodies can be obtained, which exhibit ageing to a considerably lesser extent than the bodies hitherto known.
Said advantageous effect of said step during the grinding process on ageing, is the more surprising as, when considering oxidation in air as being the cause of ageing, it cannot be accounted for how any oxidation, which occurs only for a short time i.e. during the grinding process, may be the cause of the ageing effect in a later stage i.e. when the magnetic body has been manufactured.
The method according to the invention will be described more fully with reference to the following example.
Castings of the compound SmCo were ground by means of a coffee mill in a so-called glove box (gas-tight space in which protrude two gloves fastened by the sleeves in holes of the wall and being thus accessible from without) into powder of an average granular size of about 3 pm. The glove box was filled with He gas containing less than 5 ppm of oxygen and/or water vapour. The resultant powder, still in the glove box, was poured into a lead holder, orientated in a magnetic field and pre-densified by an isostatic pressure of 8 kbar. Then the lead holder with the block resulting from the compression, was
taken out of the glove box and subjected to the known compression method: an isostatic pressure of more that l0 kbar during which a slight, plastic deformation was brought about with the block retaining its anisotropic characteristics.
The resultant permanent-magnetisable body was found to have a relative density of 97 percent. The body was then exposed to a temperature of C in air. After 10 minutes the coercive force was found to be 15.900 Oe. After l00, 1,000 and 10,000 minutes the coercive forces were again measured. Graph (a) of FIG. 1 illustrates the variation of the coercive force as a function of time. It should be noted that the ageing effect occurs about 2,000 times more rapidly at a temperature of 100 C than at room temperature. Apart from the time associated with a temperature of 100 C the time associated with a temperature of 27 is therefore plotted on the abscissa.
For illustrating the surprising, favourable effect of the method in accordance with the invention, the graph of FIG. 1 also shows an ageing curve (b) measured on a permanentmagnetisable body having also a density of 97 percent and made from a powder ground by the same method and having the same chemical composition and the same average granular size, however, not being ground under the conditions characteristic of the method according to the invention.
Apart from the aforesaid advantageous effect of the method according to the invention on the ageing process of the final magnetic body a second surprising effect is found to occur: when the castings are ground in accordance with the invention it is found to be possible to manufacture by said known compression method magnetic bodies having a relatively density exceeding the 97 percent, which hitherto was attainable at the most.
Measurements of ageing have shown that such magnetic bodies exhibit an ageing effect decreasing in accordance with an increasing density.
The graph of FIG. 2 illustrates for a few magnetic bodies the relationship between the coercive force at the time t(H (t)) and the coercive force at the time t 10 minutes (H,( 10)) and the time during which the magnetic bodies were exposed to air at 100 C. The magnetic bodies having densities of 98.5 to 99.9 percent were manufactured by the method according to the invention, whereas the bodies having densities of 95.0 and 97.0 percent were manufactured by the method hitherto known.
An additional advantage of permanent magnets manufactured from bodies having such high densities resides in that the energy product (BH),,,,, as compared with that of permanent magnets formed from magnetic bodies differing only in density therefrom, is higher.
The invention relates furthermore to permanent-magnetisable bodies manufactured by the method according to the invention and particularly to such bodies having a relative density of more than 99 percent.
What is claimed is:
A method of manufacturing a permanent-magnetisable body formed from fine. particles of a compound of M and R, the range of existence of which is consistent with that of the compound M R having a hexagonal crystal structure, wherein M represents Co or a combination of Co with one or more of the elements Fe, Ni, and Cu and wherein R represents one or more of the elements of the rare earth metals and/or Th in which a casting of an alloy of M and R is ground to a powder of the desired granular size, said powder being pre-densified and oriented in a magnetic field, after which it is compressed by an isostatic pressure of at least 10 kbar and finally deformed to a slight extent in a plastic manner while retaining its anisotropic characteristics while said isostatic pressure is maintained, characterized in that the grinding and thereafter the predensifying and orienting is performed in an oxygenand water-free environment in an inert fluid.