DE2142110A1 - Anisotropic non-aging permanent magnets - from sintered powdered cobalt and rare earth cpds - Google Patents

Abstract

Powder consisting of one or more cpds. of M and R with hexagonal crystal structure (M is Co opt. combined with Fe, Ni and/or Cu and R is rare earth(s), Y or Th, M5R units) is oriented in a magnetic field, compressed and sintered at temp. above critical sintering temp. for compsn. Pref. M = Co, R = Sm, and sintering temp.

Description

Process for the production of a body with anisotropic permanent magnets Properties.

The invention relates to a method for the division of a Bodies with anisotropic permanent magnetic properties, which are responsible for these properties essential component through one or more connections of M and R with hexagonal Crystal structure is formed, where M is Co or a combination of Co with a or more of the elements Fe, Ni and Cu, and R is one or more of the elements of the rare earths yttrium and thorium is, of which compounds the realm of existence forms a whole with the area of existence of the connection H5R in the system M-R, wherein a powder consisting of one or more of these compounds of M and R, is aligned, compressed and sintered in a magnetic field.

Such a process, but at a sintering temperature (1100 ° C) and a single magnetic material (SuCo5) is restricted from the Dutch Disclosure pen no.

6,917,567 known. Closer studies have shown that too. Obtain high coercive forces, the sintering temperature within a precisely defined temperature range must lie. In particular, it is from an article by F. Westendorp in "Solid State Communications ", neft a, pp. 139-141, '970, it is known that the coercive force IHc heater powder samples from the Sm-Co system as a function of the heating temperature from a certain low heating temperature - 800 ° C - increases rapidly, reaches a maximum value, then decreases again and at a certain high heating temperature - 1250 ° C - assumes a value that differs only slightly from that which occurred before the heating Value differs.

It is therefore obvious to heat at such a temperature that a sintered product with maximum IHc is obtained. But it is found that a magnet made in this way generally has a large Disadvantages: the coercive force and / or the shape of the demagnetization curve, The amount of food on the magnet changes over time by increasing the coercive force of a part or the vast amount of permanent magnetic material from which the Magnetic body is built up, decreases after some time: the so-called aging of the Magnetic body.

This aging of the magnet body causes it to develop two demagnetization curves, which in the same way, but at times t1 and t2 are measured on the same magnetic body, do not cover.

Tests that have led to the invention have shown that the extent of aging that occurs depends on the temperature is, which is sintered. It was also found that above a certain high sintering temperature, no aging occurs. This on the condition; that sintering takes place during a certain minimum period of time.

The method according to the invention is characterized in that the sintering takes place at a temperature which is higher than the critical sintering temperature the chosen composition. Below the critical sintering temperature of a powder with a certain composition the highest temperature is to be understood here, in which it is determined that the sintered powder is still aging.

A magnet body made by the method of the invention has the great advantage9 that aging no longer occurs.

The sintering of M5R powder takes place in a protective coating Atmosphere. In practice, sintering can take place in different ways, E.g. in a room that was sintered with the help of a pump on a certain constant vacuum is maintained, or in a closed vessel that was previously is evacuated.

Try both in a constant vacuum and looking in a sealed one vessel, were carried out. Although it turned out that the critical sintering temperature of the same starting powder was dependent on which of the two processes mentioned above was chosen, and although it turned out that the critical sintering temperature was dependent on the choice of M and R, di. present invention that essential feature that fs each of the relevant M-R connections is such a critical sintering temperature can always be found.

Since, as has already been explained, at higher sintering temperatures the IHo, which can be reached with the help of the relevant M-R connection, from a certain sintering temperature decreases sharply, and only at higher sintering temperatures the desired non-aging is achieved, is generally the final one Magnetic bodies do not age, but for certain applications it is too low Have coercive force.

The above-mentioned disadvantage is completely or partially ameliorated by that an embodiment of the inventive method, after initially the Sintering has taken place at a temperature which is the critical sintering temperature the selected composition exceeds the sintered body obtained a heat treatment is subjected at a temperature which is below the temperature at which it has been sintered.

It has been established that, if by a sintering treatment a non-aging magnetic body is produced at a temperature T, an increase the coercive force can be obtained by being at a temperature below T, e.g. between 800 ° C and T, is re-annealed, while that by sintering advantage obtained at the higher temperature T - namely non-aging - is retained will.

According to a further embodiment of the method according to the invention it is particularly advantageous if the post-annealing temperature is between the sintering temperature and that lower temperature is that in the sintering temperature-cosritive force diagram corresponds to a coercive force equal to the coercive force that the sinter has having kSrper after sintering.

It's been found that even if the after sintering on the temperature T obtained at a temperature for some time is kept that much lower than the example mentioned temperature of 800 ° C, an increase in the coercive force can occur. In particular, a Heat treatment at a temperature between 50 ° C and 300 ° C gives this result.

The invention is described below for some exemplary embodiments Hand of the drawing explained in more detail. They show: FIG. 1 a graphic representation, in which for different magnetic bodies the magnetization M but the one on the outside applied field H is applied; Fig. 2 is a graph in which for a number of magnetic bodies with the same composition the relationship between the coercive force and the sintering temperature is indicated, Fig. 3 is a graph Representation showing a similar relationship between aging and sintering temperature is indicated, Fig. 4 is a graph showing the same relationship as indicated in FIG. 2, but for other sintering conditions, FIG. 5 is a graphical representation Representation, in the same relationship as in Fig. 3, but for the sintering conditions according to FIG. 4, FIG. 6 is a graphic representation in which for a Number of magnetic bodies with the same composition the relationship between the aging and the sintering time is indicated, FIG. 7 is a graphical representation, in which the coercive force a number of patterns over the heating temperature is plotted, and Figures 8 and 9 are graphs showing the increase the coercive force is above the post-treatment temperature.

Embodiment I A powder, which from such a mixture of Sn-Co compounds, the ratio between Sm and Co is 1 X 4.5 was the powder obtained by placing castings in a vibrating mill This composition was ground first under an isostatic Pressure of 20 kb compressed in a magnetic field of 60,000 Oe. Then it became in a closed, evacuated vessel in the presence of an yttrium getter during Periods varying from 10 to 30 minutes at different temperatures between Sintered 1000 ° C and 11500C. The bodies obtained in this way have always been the demagnetization curves and the pore volume were measured. On each of these bodies after the time t, e.g. 1000 hours, the demagnetization curve becomes again measured so that any signs of aging can be detected.

The aging of a magnetic body is reflected 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 as ordinate and the external magnetic field H is plotted as the abscissa. The curve 1 is one for a permanently magnetizable Demagnetization curve characterizing the body. For a field IHo - coercive force - whose direction is opposite to that of magnetication in the body, is the Magnetization H equals zero. The demagnetization curve e is indicative of a magnetic body with a coercive force (IHo) 2 that is lower than the (IHc) 1 belonging to the curve 1. When the two curves are on the same Way have been measured on the same magnetic body, but the second one Would be measured after the first curve, (IHc) 1 - (IHo) 2 is the aging during the period t. In another case, a magnetic body can be used Over a period of time t a demagnetization curve can be measured, which the curve 3 shown corresponds. Such a curve has a "bump" while nevertheless the coercive force (IHc) 1 remains the same. Even in such a case there is it's aging of the magnet.

It turned out that magnetic bodies with the above-mentioned starting composition, which were obtained after sintering at a temperature <1100 ° C, no aging more sufwiesen. It was also found that at higher sintering temperatures the pore volume in the body decreased, creating a non-aging magnet with a higher Saturation magnetization and thus obtained with a higher energy product (EH) max became.

In Table I below are given the magnetic values measured on some of these permanent magnets, which are obtained after sintering at 1120 ° C: TABLE I. Pore volume (%) IHc (Oe) Br (G) (BH) max (106 GOe) 2.0 13,600 7890 14.9 2.0 14,000 7970 15.5 1.5 13,500 8 100 16.0 1.5 14,000 8110 15.75 0.6 14,000 8,300 16.8 In the graph according to Fig. 2, the xoercitive force iHc is given, measured on a number of magnetic bodies from the Sm-Co system sintered at different temperatures in an evacuated and then closed space.

Curve 81 gives the mesa results immediately after sintering, i.e. after the magnetic bodies had been brought back to room temperature. the Curve a2 gives coercive force values measured after a time t.

From the graph it can be seen that at sintering temperatures above 1100 ° C the curves a1 and'a2 coincide, while the curve a2 at sintering temperatures below 1100 ° C lower than curve a1. Magnetic body of the above Composition sintered under the conditions described above, therefore do not show any aging when they are sintered at temperatures above 1100 ° C will. In this case, 1100 ° C is the critical sintering temperature. From the graph further shows that this temperature is much higher than is the sintering temperature at which the maximum coercive force is reached.

In the graph according to FIG. 3, for magnetic bodies sintered under the above-mentioned conditions with the above-mentioned composition, the relative aging is shown Applied above the sintering temperature. H denotes the field that is applied in order to keep a magnetization @ Mg possible (cf. FIG. 1), while Hc (O) represents Hc immediately after sintering and Ho (t) Hc after the lapse of time t.

From this graphical representation l'Kest is also a critical one Derive sintering temperature of 110O0C.

EXAMPLE II A powder of those described in EXAMPLE I. Compressed in a magnetic field in the manner described in this example I, was sintered in a room that - in contrast to Example I - with the help of a Vacuum pump was maintained at a vacuum of about 5 x 10 torr. (A difference with the closed vessel according to example I then that is that during sintering no Sm vapor pressure is built up over the powder). The powder samples were at sintered at different temperatures during 30 minutes and at the in this way obtained magnetic bodies became demagnetization curves immediately after sintering as well as measured after a time t.

In the graph of Fig. 4 are the same as shown in FIG. 2, the measurement results are plotted. The curve d1 was immediately after the Sintering and the curve d2 were measured after a time t. Also in this In this case, the curves fall above a certain temperature - the critical sintering temperature ° together for a material which has the above-mentioned composition and that has been subjected to the above-described sintering treatment is the critical one The sintering temperature is 1065 ° C.

In Fig. 5, in the same way as in Fig. 3, the relative aging is: Applied above the sintering temperature. As from the graphic representation according to FIG. 4, a critical sintered temperature of 1065 ° C. can be derived from this figure.

A difference with the one after aging in a locked one space obtained measurement results is the; that in the case of the "vacuum" sintering process in question the coercive force obtained after sintering somewhat above the critical sintering temperature is only slightly different from the maximum attainable coercive force.

Next is carried out in accordance with the present exemplary embodiment Sintering process has been investigated to what extent the sintering time for manufacture non-aging magnets is important.

As can be seen from the graph according to FIG. 6, the degree to which aging depends. expressed as occurs, also from the sintering time. This graphic representation shows measurements which were carried out on magnets sintered at a sintered temperature of 1070 ° C. A sintering time of at least 30 minutes is found to be a necessary condition for obtaining a non-aging magnet.

Embodiment III A powder which is made from such a mixture of (La-Ce) Co compounds consisted that the atomic ratio (La-Ce): Co is the same 1 s was 4.3, which powder was obtained by casting cast pieces in a vibrating mill zeimahlenwuiden, was first under an isostatic pressure of 20 kb in a Compressed magnetic field of 60,000 0e. Then it was locked in a previously evacuated vessel in the presence of a yittrium getter for 30 minutes sintered at different temperatures between 900 ° C and 1100iC. To the one on this The bodies obtained were always the demagnetization curves and the pore volume both immediately after sintering and after the process a time t measured.

It turned out that in the manner described above on a Temperature above 9600C or above 975 ° C sintered magnetic bodies no aging exhibited.

In Table II values are given that on some of these - non-aging - Permanent magnets are measured. It should be noted that the first example of the table II has a La / Ce ratio that corresponds to the La / Ce ratio in the so-called zer-rich "Mischmetall" is almost the same. Under a "mischmetal" is generally a To understand a mixture of rare earths how this occurs in nature. Such mixed metals are classified as zer-rich or yttrium-rich, depending on the composition designated. Admittedly, there is the advantage of using non-ferrous metal instead pure rare earths in the significantly lower cost of the raw material, while still magnets with acceptable properties can be obtained. the Use of mixed metal in a row is preferable in this context. (One Analysis of the composition shows, for example, the following ratios: Ce 45 - 55% by weight; La 25-35 wt%; Nd - 15 wt%; Pr - 5 wt%; Y - 0.3 wt%; other rare Earths less than 0.1% by weight; other metals less than 0.5% by weight), those with (LaO0.3Ce0.7) Co4.3 The values achieved thus indicate the values that were achieved with a fragmented mischmetal can be achieved when applying the method according to the invention, Aus the last example in the table shows that with a (La0.7Ce0.3) Co4.3 magnet, So with a composition rich in lanthanum, the most favorable values can be achieved. This indicates that using the method according to the invention, for example, magnets from rare Earth and cobalt with one enriched with lanthanum Zer-rich Liischmetallstoffteile can be produced, the cheap magnetic Have properties and in which, in addition, the cost price of the raw material is low.

Embodiment IV A powder that consists of such a gene of (Pr-Sm) Co compounds, the atomic ratio (Pr-Sn) / Co is equal to 1 2 4, was which powder was obtained by making castings in a vibrating mill were ground with this composition, was prepared in the exemplary embodiment III treated way. On the non-aging one obtained after sintering at 1075 ° C The values given in Table III were measured for magnetic bodies.

It is noted that both in Table II and in Table III under "sintering temperature" the temperatures are also given in brackets, above which has been shown to show no aging in sintered powders.

TABLE II Pore volume (erg / gr. Ce) IHc (Ce) Br (G) (BH) max (106.GOe) sintering temperature (° C) (La0.3Ce0.7) Co4.3 5% 73 4,700 6900 10.7 1050 (975) (La0.5Ce0.5) Co4.3 5% 78 6,000 7400 12.6 1000 (960) (La0.7Ce0.3) Co4.3 5% 77 6,500 7,300 12 1050 (975) TABLE III (Pr0.5Sm0.5) Co4.5 9% 83 18,500 7700 14,500 1075 (1060) In the graphic representation of FIG. 7, a curve is drawn which is comparable to the curves a1 of FIGS. 2 and d1 of FIG. 4, but which now also continues on the side of the low temperatures, which curve is the relationship between the coercive force IHc indicates the heater powder pattern and the heating temperature T.

When the samples are heated to temperatures between 8000C and 12500C It turns out that the coercive force increases rapidly at a sintering temperature T1 reaches a maximum (IHc) 1 and then decreases again. Because the critical sintering temperature is generally higher than T1, the coercive force (IHC) 2 is one based on temperature T2 sintered, non-aging magnets generally lower than the coercive force (IHc) 1 of an aging magnet sintered at temperature T1.

As can be seen from the exemplary embodiments below, it is but possible, the - relatively low - coercive force of a non-aging To raise the magnet by heat treatment at a suitable temperature.

Embodiment V A powder in which the atomic ratio Sm: Co n 1 t 4.5 was (a mixture of SmCo5 ur Sm2Co7) was under an icostatisonen Pressure of 20 kb compressed in a magnetic field of 60,000 Ce. Then it became in an evacuated and then closed vessel in the presence of an yttrium getter sintered to 1120 ° C. for 30 minutes. The measured on the obtained sintered body The coercive force was 15,800 Oe. An aging test showed that there was no aging occurred. Then the sintered body was kept at a temperature of for 30 minutes Post-annealed at 1050 ° C, after which a coercive force of 18,100 Ge was measured. A carried out with this post-annealed sintered body Aging attempt showed that no aging occurred in this case either.

The increase in the coercive force caused by the passage of a Heat treatment in an area of relatively high temperature (e.g. from + 800 ° C to 1250 ° C) is illustrated in FIG. 8. In this Figure is the increase # (IHc) 2 reached after sintering at temperature T2 Coercive force (IHc) 2 (see FIG. 7) plotted against the aftertreatment temperature. It turns out that only by a heat treatment in the temperature range between T2 and T a positive result is obtained. It proves to be particularly advantageous 4 to carry out the heat treatment at a temperature T which is higher than the temperature T3 is that of a coercive force in the sintering temperature-coercive force diagram of FIG arises, which is equal to the coercive force that the sintered body after sintering at the temperature T2. The curve shown in Fig. 8 is based on the maximum # (IHc) 2 values that can be achieved at the respective aftertreatment temperatures the heat treatment was always continued until no further increase the coercive force occurred more.

Auoh a heat treatment at a considerably lower level than the aforementioned Temperature range can have a positive effect, as can be seen from the exemplary embodiment below.

Exemplary embodiment VI A powder whose composition is the same as that of of the powder according to Embodiment V was sintered in a room which using a vacuum pump to a vacuum of at least 5.10-5 Torr held became. Under these conditions, the powder was kept at one temperature for 30 minutes sintered by 11250C. The coercive force measured on the obtained body was 19,800 Oe. It turned out that the body after being on for 70 hours exposed to a temperature of 1500C in the air, an increase in the coercive force to 25,100 Oe. Continued heat treatment had no further increase result. This experiment showed that the degree to which the coercive force is due this heat treatment increased, was strongly dependent on the duration of the treatment. Thus, after 10 hours of treatment, there was an increase in the coercive force of 1000 Oe reached.

The increase in coercive force when performing heat treatment in a range of relatively low temperatures (e.g. from 50 ¢ C to 300 ° C) is illustrated in FIG. In this figure, the increment # (IHc) 2 is after Sintering at a temperature T2 reached coercive force (IHc) 2 (see. Fig. 7) applied above the post-treatment temperature. It just turns out that by a heat treatment in the temperature range between T and T7 a positive one Result is achieved. Same as in Fi6. 8 is the basis of the curve shown to the maximum # (IHc) 2 value that can be achieved at the respective aftertreatment temperatures; the heat treatment was always continued until no further increase the coercive force occurred more.

It should also be noted that the temperatures in all of the aforementioned Embodiments with the help of a thermoelectric element as possible on the Place the powder samples were measured. Although they achieve results well together were in agreement, it must nevertheless be taken into account that e.g. in dependence of whether there. Powder sample was packed in molybdenum foil or not, or as a function of whether there was a temperature gradient over the powder pattern or not, the temperatures given are a few cades from the actual heating temperatures may differ.

Claims (12)

P A T E N T A N 5 P R U C H E Method of making a body it is anisotropic permanent magnetic Properties whose essential constituent for these properties is through a or several compounds of M and R formed with a hexagonal crystal structure where M is Co or a combination of Co with one or more of the elements Fe, Ni and Cu and R one or more of the rare earth elements yttrium and Thoriun represents, and the realm of existence of these connections nit the realm of existence the compound M5R in the system M-R forms a whole, being a powder that consists of one or more of these compounds of M and R exists in a magnetic field aligns, compresses and sintered ge, characterized in that the sintering takes place at a temperature which is higher than the critical sintering temperature of the selected Composition is. 2. The method according to claim k, characterized in that the sintering takes place in years after with a constant vacuum. for at least 30 minutes of claim 2, characterized in that 4. Is sintered for at least 30 minutes. 4. The method according to claim 1, characterized in that the sintering takes place in an evacuated and then locked room. 5. The method according to claim 2, characterized in that M - Co, R - Sm, and that the sintering temperature is above 1065 ° C. 6. The method according to claim 4, characterized in .that M a Co, R process and that the sintering temperature reads above 1100 ° C. 7. The method according to claim 4, characterized in that M represents Co, that R represents a combination of essentially lanthanum and cerium, and that the temperature at which sintering takes place is above 975 ° C. experience according to claim 4, characterized in that X represents Co, that R represents a combination of essentially praseodyne and samarium, and that the temperature at which sintering takes place is above 1060 ° C. 9. The method according to claim 1, characterized in that according to dr Sintering at a temperature above the critical sintering temperature the sintered body of a heat treatment at a temperature below the sintering temperature lying temperature is subjected. 10. The method according to claim 9, characterized in that the heat treatment is carried out at a temperature above 800 ° C. ii. The method according to claim 10, characterized in that the heat treatment is carried out at a temperature that is above the temperature in corresponds to the sintering temperature-coercive force diagram of a coercive force which is equal to the coercive force that the sintered body has after sintering. 12. The method according to claim 9, characterized in that the heat treatment is carried out at a temperature between 50 ° C and 300 ° C.