DE2215301A1 - Process for the production of a body with anisotropic permanent magnetic shafts - Google Patents

Description

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Registration from i

"Process for the production of a body with anisotropic permanent magnetic properties"

The invention relates to a method for producing a body with anisotropic permanent magnets Properties whose essential component for these properties is represented by an or several compounds of M and R with a hexagonal crystal structure are formed, where M = Co or a combination of Co with one or more of the elements Fe, Ni and Cu and where R is one or more

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of the elements of the rare earths is yttrium and thorium, of which compounds the realm of existence is with that of the connection M, »R in the system M-R a whole forms, which a rough body formed from one or more of these compounds of M and R, to one Powder is crushed, aligned in a magnetic field, compressed and sintered.

It should be noted that the end product, in addition to a main component that only contains compounds that form a whole with the area of existence of the compound MR, can also contain a component that consists of compounds that have a greater content of R than the compound MH itself, for example M ₇ R ₂ included.

A method of the type described is known from Dutch laid-open specification 6907 ^ 99. In addition, it can be concluded from the publication by F. Westendorp in "Solid State Communications", No. 8, pp. 139-141, 1970 that the sinter temperature must be within a precisely defined range in order to obtain high coercive forces, because this publication shows that the coercive force _T H_ of a sintered material

J-C

as a function of the sintering temperature of a certain Temperature on - for SmCo- about 800 ° C - increases rapidly,

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reaches a maximum value (for ShOQ ₅ at about 1Q7 <5 ° C) and then again tendon 11 decreases · It is therefore obvious to sinter at such a temperature that a product with maximum _T H is obtained _;

4- C-

But it turns out that βϊ, η a Magnet made in this way in general has a major disadvantage: the coercive force and / or the shape of the demagnetization curve that the magnet is measured, change with the. Time by the coercive force of a part or the whole amount of permanent magnetic material from which the magnetic body is built up after some time decreases. This phenomenon, which is expressed by that at two different times on a magnetic body If the measured demagnetization curves do not coincide, this is referred to as "aging" of the magnet body.

Tests have shown that the measure in which aging occurs depends on the temperature at which sintering takes place. Besides that it was found that above a certain high sintering temperature, no aging occurs at all. But it is absolutely necessary that during a certain minimum period of time is sintered * To obtain a non-aging magnetic body spll the sintering should therefore take place at a temperature that:

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exceeds the critical sintering temperature of the selected composition. Below the critical sintering temperature of a powder of a certain composition is to be understood here as the highest temperature at which aging of the sintered powder still occurs.

Since, as has already been explained, at higher temperatures the coercive force, which, starting from a certain M-R connection, can maximally be achieved by a certain one The sintering temperature decreases sharply, and because there are no more signs of aging just at higher sintering temperatures, it appears at the first Sight not possible to make a magnetic body that does not age and also has an optimal coercive force having.

As will be explained in more detail below with reference to the drawing, with aging there is a decrease in the coercive force and / or a change in the shape of the demagnetization curve (the "addition"). A change in one or both of these quantities is reflected in the value ·, H. Under j_ _M H

i. _r . r

is to understand the size of the field that is created must be to the remahente magnetization M on reduce by half. As a measure of the combination of the coercive force and the "bulge" is in the following the value ι ,, Η is used.

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The method according to the invention is characterized in that for obtaining a non-aging sintered Magnet body with an optimal combination of coercive force and shape of the demagnetization curve the sintering takes place at a temperature which is the critical sintering temperature of the selected Composition exceeds while both at. the sintering as well as in the preceding manufacturing steps Measures are taken to prevent the oxygen content of the end product from decreasing Hand of a graphical representation of the relationship between coercive force and sintering temperature exceeds the critical value to be determined at different oxygen contents.

Surprisingly, attempts have namely

show that the quantity ± H is not just a function

² r
the sintering temperature, but also the oxygen content of the end product, and this relationship is such that the higher the sintering temperature, the less oxygen is allowed if an optimal combination of coercive force and "buckling" is to be achieved. This has two consequences: On the one hand, at a fixed sintering temperature, which is necessary for the production of a magnet that does not age, a higher _ ^ H and, in particular, a higher one

² r

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Coercive force can be achieved than initially assumed provided that the oxygen content is kept low enough. on the other hand can, provided that the oxygen content is kept sufficiently low, at a higher one Sintered temperature than in the aforementioned case while maintaining an acceptable value of the combination of coercive force and "buckling". So the temperature at which a powder with a given composition is to be sintered is not as critical as one would assume based on the article in "Solid State Communications", for example, if only a sufficiently low oxygen content is ensured.

It also turned out that

the achievable density depends on the oxygen content is. The lower the oxygen content of the to be sintered en material, the more dense it can be sintered at the same temperature.

From the Dutch patent application 69O7.499 it is known that sintering in carry out an inert gas atmosphere in the presence of an oxygen binder. Furthermore, from the Literature e.g. measures known that the admixture of Ca or Sm hybrid to the during sintering

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require sintering powder in order to bind any oxygen present. An exact relationship between oxygen content and sintering temperature on the one hand and density and coercive force or "bulge" on the other hand is not yet known. ^;

It is customary to pre-earn the ground powder at a pressure below 1 kB (eg 0.3 kB) and then compress it isostatically at a high pressure (15 to 20 kB) to a density of> 80% of the theoretical density . According to one embodiment of the method according to the invention, the compression should take place at a pressure of 0 to 15 kB, preferably between 5 and 10 kB. Surprisingly, it was found that if only the oxygen content is below the aforementioned critical value, the density of the sintered end product is always above 90 % of the theoretical density, regardless of the magnitude of the isostatic pressing pressure. In particular, this means. that, with a controlled oxygen content, a considerable saving in terms of the apparatus to be used in the process can be obtained, because instead of a press that can deliver a pressure of 15 to 20 kB, a press that can deliver a pressure of 5 can deliver up to 10 kB.

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The known measures to be taken in particular during sintering lead in special cases to favorable results, but according to a further finding from the invention it is for manufacturing Good magnets absolutely necessary that already during the steps preceding the sintering process and, in particular, during the grinding of the powder, measures are taken to reduce the oxygen content below a critical value, which depends on the requirements to be placed on the end product is.

So far it has been common practice to use grinding devices in the production of Μ, -R powders, those in volatile organic liquids (i.e. with a boiling point below 120 ° C), such as e.g. hexane, CCIk, benzene, acetone or toluene, ground will. In particular, dried toluene is often used because it contains relatively little oxygen contains. In this context it should be noted that the so-called "wet" milling in milling liquids generally to powders with better and more reproducible prospects than that so-called "dry" milling in gases such as argon and hydrogen results.

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According to a further embodiment of the

inventive method should be grinding to a fine powder in the presence of a liquid that wets metal surfaces well.

According to yet another embodiment of the inventive method, it is advantageous if an organic liquid is used having a boiling point below 120 ⁰ C as milling liquid containing a component which has the property that it preferably metal surfaces wetted.

It turned out that through the Use of grinding liquids of the type mentioned above during and after the grinding process is more appropriate Protection of the powder particles from oxidation is obtained in that a skin is formed around the particles forms.

A preferred embodiment of the method according to the invention is characterized in that the liquid which has the property that it wets metal surfaces well or preferentially, a fatty substance such as a mineral, vegetable or animal oil. Below are fatty substances here To understand fats, oils and waxes, i.e. non-volatile, non-water-soluble organic substances. It posed

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it turns out that when using these substances during the grinding process after pressing and sintering of the powder were generally magnetic bodies having a low oxygen content.

Such an application is all the more surprising as it is contradicting itself it seems that during a grinding process a liquid which can be expected to have a more or less lubricating effect. It it turns out that when a grain surface is used, good or preferably wetting Liquid according to the invention, the required grinding time longer than when using the usual grinding liquids is.

The method according to the invention is in particular characterized in that M stands for Co and R stands for Sm and the oxygen content below $ 0.5 and specifically is held below $ 0.45.

The invention further relates to a sintered magnetic body which is produced by one of the above process is prepared.

The invention is explained in more detail below with reference to the drawing. Show it:

Fig. 1 is a graph in which the magnetization M is plotted over the externally applied demagnetizing field H;

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Fig. 2 is a graph showing the relationship between the sintering temperature and the Coercive force;

3 shows a graph of the relative aging as a function of the sintering temperature;

Fig. K is a graph showing the relationship between j_H and the sintering temperature at

² r
different oxygen contents;

Fig. 5 is a graphical representation of the Relationship between the pore volume and the oxygen content bv3i different temperatures of sintered End products, and

6 is a graphic representation of the

Oxygen content of in different milling liquids ground powders as a function of time.

The invention is accomplished with the aid of an Sm-Co magnets the investigations carried out but the present invention is based on the finding that in general for every M-R connection a critical sintering temperature and a critical oxygen content can be found.

A number of Sm-Co powder samples, for example with an atomic ratio of Sm: Co = h, k, which have been obtained by casting pieces in a vibrating mill under various influences which influence the oxygen

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Conditions to a size of 2 to 20 µm were pulverized after precompaction at a pressure of 0.3 kB under an isostatic 15 kB of pressure compressed while aligning in a magnetic field of _ + 8000 Oe. then were at different temperatures for 30 minutes sintered between 1050 and 1150 ° C. It should be noted that sintering can take place under different conditions. It can be done in a room that is kept at a certain vacuum (e.g. between 10 and 10 Torr) with the aid of a pump. It is also possible to sinter in an inert gas atmosphere, either in that a constant gas flow is passed over the pattern, or in that the pattern is placed in a closed room, which is pumped empty before sintering and then with an inert gas, like argon, is filled. The demagnetization curves were obtained on the bodies obtained in this way measured. Each of these bodies was then left in air at a temperature of 150 ° C. for 1000 hours

held, after which again the demagnetization curves. were determined. The temperature of 150 ° C was required in order to be able to determine the occurrence of any signs of aging more quickly.

This aging of the magnet body manifests itself in the demagnetization curve, which is shown on the.

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magnetized magnetic body can be measured. Such a curve is shown in FIG. 1. The magnetization M is plotted as the ordinate and the external magnetic field H as the abscissa. Curve 1 is a demagnetization curve which characterizes a permanently magnetizable body. In the case of a field _T H. (Coercive force), the direction of which is opposite to the direction of magnetization in the body, the magnetization M = O. The demagnetization curve 2 is characteristic of a magnetic body with a coercive force (-pH ") which is lower than that belonging to the curve 1 ( _T H). Wen, the two curves in the same WEI ^se on the same magnetic bodies, but the second time t after the first, have been measured, (j H ") ■ is - (j H"), the aging during the time t.

If, however, not all permanently magnetizable material from which the body is built, ages - for example, when the body is made up of different compounds (either different in M and / or R or different in stoichiometry), of which compounds the one well and the other shows no decrease in _T H - can on one

Ic

Magnetic body after aging during a time t a demagnetization curve of type 3 can be measured. Such a curve has a smaller "bulge", while the coercive force (_H ₁ ) is still the same

_L C I

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remain. In such a case, too, there is talk of aging of the magnet. It is also possible that with aging, both the coercive force and the "bulge" decrease.

In the graph according to FIG. ₁ , the coercive forces are plotted both before (curve a 1) and after a heat treatment at 150 ° C. (curve a 1), measured on Sm — Co magnetic bodies sintered at different temperatures, all of which are almost the same Had oxygen content. The sintering time was always 30 minutes.

From this graph it can be seen that at sintering temperatures below 1100 ° C., the curves a 1 and a 1 do not coincide. Magnets sintered at these temperatures therefore still show signs of aging. At sintering temperatures above 1100 ° C, the curves a ₁ and a ^ coincide: magnets sintered at these temperatures no longer show any aging.

In the graph according to Fig., The relative aging is:

H _c (o) - H _c (t)

rrr-i c X $ 100

Hc (o) ^

applied over the sintering temperature T. Where H

the external field that has to be created in order to achieve a

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To keep magnetization jK , while H / \ 2 i " ^c \ °)

for H measured before and H /, \ for H measured after

■ CC y "C J C

a heat treatment of the magnet body at 150 ° G stands in the air for a time t. The spread of the measurement results is indicated by the aforementioned relationship not as a single line, but as hatched area is shown. Also from this A critical sintering temperature (i.e. a temperature above which must be sintered so that no aging occurs, derived from 1100 ° C.

In the graph according to FIG. K , JLw H is plotted as a function of the sintering temperature at various oxygen contents. It should be noted that in order to be able to show the influence of the oxygen content on the magnetic properties as completely as possible, the graph also shows values that are measured on magnets that are sintered at temperatures such that they can show signs of aging. In order to be able to compare the different values with one another, all measurements are carried out immediately after sintering, before aging has occurred at too low temperatures sintered magnets.

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It should be noted that in order to also include the "bulging" of the demagnetization curves in the comparison, in Fig. K the values of H _m jl

H values (as in Fig. 2) are plotted against the sintering temperature.

From this graph it can be seen that in order to obtain a good combination of coercive force and "buckling" (denoted by i "H)

2 "M c

a certain oxygen content is permissible, which depends on the requirements to be made. For example, if a magnet with j_ H of 10,000 Oe would result

" ^c

it should be produced that sintering is carried out at 1120 ° C., that the oxygen content is not higher than 0.5 i ° (the critical value). In this way it is possible to manufacture sintered MR magnets by conventional techniques. Good magnets can still be produced without working under prepared conditions (for example in a special room with an atmosphere that protects against oxygen and water vapor).

A comparison of the oxygen content and pore volume of various end products resulted Surprisingly, that not only sintered according to expectations at a higher temperature Material has a greater density, but that

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the density to be achieved also depends on the oxygen content. The lower the oxygen content is, the more dense the material can be sintered at the same temperature. This result FIG. 5 shows the pore volume versus the oxygen content is applied. The scatter in the measurement results is indicated by the fact that the mentioned Relationship is shown not as a single line but as a hatched area.

In the context of the present invention, magnetic bodies with different oxygen contents were used manufactured in the following way. Sm-Co castings were made in a vibrating mill using various - influencing the oxygen content of the powder - pulverized grinding fluids. To the To prove the effect of the different milling fluids, the obtained powders were exposed to the air for 100 hours and the oxygen content became measured at regular time intervals. The measurement results are plotted in FIG. 6. It It turns out that when using technical grade toluene as grinding liquid, a high oxygen content (i) with an upper limit of 0.8-0.9 and one lower limit of 0.6 to 0.7 is obtained. When using analytically pure toluene as grinding liquid a significantly better result (2) was achieved.

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same as when applying a mixture Technical toluene and 10 vol. $ mineral oil or oleic acid as grinding liquid (3). A minimum oxygen content was achieved by * only in nimeral oil (e.g. in the under the trade name »Tellus 33» and "Tellus 15" oils available) was ground (4). Since the oil adheres to the powder particles and does not evaporate from these particles, will A satisfactory protective effect even after the grinding process obtain. The superfluous OeI can be stored in a removed (washed away) at the following stage of the manufacturing process. If not all OeI removed the final product may contain Sm carbide. However, this does not affect the magnetic ones Properties.

The effect that the regulation of the oxygen content has on the density of the end product is shown in shown in the table below.

Compr. Density in Sinter Sintering time sintered it 0.8 Pressure (kB) in reference to tempera- (Min.) density 1 theoreti door C ° C) 0.39 sch 0.41 20th 85 1100 15th 89 0.43 15th 83 1100 15th 86.3 o, 4o 15th 84 1100 15th 98 0.42 10 76 1085 15th 96.5 0.34 10 75 1100 15th 96 1.5 4th 62 1085 2O 98 4th 63 1Ο85 15th 97 0 50 1095 1O 97 0 50 1Ο85 15th 64

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The samples were all pre-compressed at a pressure of 0.3 kB. The isostatic compression pressure varied from 0 to 20 kB (column 1). The densities after isostatic compression are given in column 2, the sintering temperatures in column 3 and the sintering times in column h . (The sintering temperatures are the temperatures which are measured at a point as close as possible to the sample to be sintered. The real sintering temperatures can ^{deviate from this by + 1} O ⁰ C). The density (column 5) and the oxygen content (column 6) were measured on the sintered end products. It can be clearly seen that even at a pressure of 15 to 20 kB, the density of the end product is insufficient if the oxygen content is not adequately controlled. On the other hand, it turns out that even without isostatic compression (θ kB) a sufficiently dense end product can be obtained if the oxygen content is controlled. It should also be noted that the sintering took place in a closed room "which had been vented and into which an inert gas (argon) was admitted up to a pressure of at most 0.8 atm. Before sintering.

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Claims (2)

-20- PHN.55 ^ 0 PATENT CLAIMS 1. A method for producing a body with anisotropic permanent magnetic properties, its an essential component for these properties through one or more compounds of M and R with a hexagonal crystal structure, where M = f Co or a combination of Co with an or several of the elements Fe, Ni and Cu and R one or more of the rare earth elements yttrium and Thorium is what compounds the realm of existence with that of the compounds Mt-R in the system M-R forms a whole in which a rough body is made up of one or more of these compounds of M and R formed, crushed into a powder, aligned in a magnetic field, compressed and sintered, characterized in that for obtaining a non-aging sintered magnetic body with optimum Combination of coercive force and shape of the demagnetization curve the sintering takes place at a temperature which is the critical sintering temperature of the selected Composition exceeds during both the sintering and the previous manufacturing stages Measures are taken to prevent the oxygen content of the end product one on the basis of a graphic representation of the 209842/0822 -21- PHN.55 ^ 0 Relationship between the coercive force and the sintering temperature for different oxygen contents the determining critical value. 2. The method according to claim 1, characterized in that the compression under a pressure of 0 to 15 kB, preferably between 5 and 10 kB. 3 »Method according to claim 1 or 2, characterized characterized in that the pulverization of the rough body in a grinding device in the presence of a Liquid takes place, which has the property that it wets metal surfaces well. H. Method according to claim 3j, characterized in that an organic liquid with a boiling point below 120 ° G is used in the grinding device, which contains a component which has the property that it preferably wets metal surfaces. 5. The method according to claim 3 or h, characterized in that the metal surfaces well or preferably wetting liquid is a fatty substance, such as a mineral, vegetable or animal oil. 6. The method according to claim 1 or "2, characterized in that M stands for Co and R for Sm, and the oxygen content is kept below 0.5 % and in particular below 0.45 i ° . 209842/0822 -22- PHN.55 ^ 0 7. Sintered magnet body produced by the method according to one of the preceding claims. 8. Sintered magnetic body made by the method of claim ^, thereby marked as containing Sm carbide. 209842/0822