- Email: [email protected]
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials With High Magnetic Properties
Available online at www.sciencedirect.com
.-" ....; II
ScienceDirect
JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2009, 16(2): 84-88
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials With High Magnetic Properties CHANG Ying",
WANG Da-peng",
LI Wei 3 ,
PAN WeF,
YU Xiao-jun",
QI Min 2
0. School of Automotive Engineering, Dalian University of Technology, Dalian 116024, Liaoning, China; 2. School of Material Science and Technology, Dalian University of Technology, Dalian 116024, Liaoning, China; 3. Functional Materials Research Institute, China Iron and Steel Research Institute Group, Beijing 100081, China) Abstract: Rare earth permanent magnetic materials are typical electrical conductor, and their magnetic properties will decrease because of the eddy current effect, so it is difficult to keep them stable for a long enough time under a high frequency AC field. In the present study, as far as rare earth permanent magnets are concerned, for the first time, rare earth permanent magnets with strong electrical insulation and high magnetic performance have been obtained through experiments, and their properties are as follows: (1) Sm, TM17 : B, =0.62 T, j H, =803.7 kA/m, (BH)m = 58.97 kJ/m', p=7 n· m, (2) NdFeB: B,=O. 485 T, ;R=766. 33 kA/m, (BH)m=37. 96 kJ/m' , p=9 n· m. The magnetic properties of Sm2TM 17 and NdFeB are obviously higher than those of ferrite permanent magnet, and the electric insulating characteristics of Sm2TM17 and NdFeB applied have in fact been approximately the same as those of ferrite. Therefore, Sm2TM17 and NdFeB will possess the ability to take the place of ferrite under a certain high frequency AC electric field. Key words: Sm2TM 17 ; NdFeB; electrical insulation; eddy current
During the last decade, following the swift development of high-tech equiprnents , the permanent magnetic parts of an apparatus applied in the equipment, such as, microwave, atomic energy, and MRI, are required to work steadily under higher frequency AC (alternating current) electric field[I-3]. As far as rare earth magnetic alloys with metallic conductance are concerned, due to the strong exothermic phenomenon of eddy current occurring in magnets under AC electric field, the magnetic energy will be exhausted. According to stronger magnetism-temperature relevancy, rare earth permanent magnets will be induced to obvious demagnetization, owing to serious wastage of eddy current. Fig. 1 (a) shows that the rare earth magnet formerly had a certain ordered orientation of Pi' when it was put under a high frequency AC electric field. An eddy current would occur, as Fig. 1 (b) shows, and the magnet would convert into the heat demagnetization state without accordant orientation.
At present, permanent magnetic ferrites with excellent electric insulation are still applied in the domain of high-tech equipments , thus it is difficult for these equipments to develop into "high quality, micromation , economizing resources" because of ferrite's own lower magnetic properties and a greater useful volume[4-6]. Ferrites substituted by rare earth permanent magnets with high magnetic properties are a tendency, but in this case, the improvement in the insulating characteristic of rare earth permanent magnets is crucial. Up to now, with regard to the insulating characteristic of rare earth permanent magnetic alloys, the reports have not been referred to yet. According to theoretic analyses in this study, for the first time, the experiments for producing rare earth permanent magnetic materials with electric insulating characteristic are carried out. The way, which is roundly an electrical insulating measure from tiny magnetic powders to the whole magnets'
Foundation Item: Item Sponsored by Liaoning Provincial Natural Science Foundation (20071090) Biography: CHANG Ying(l977-) , Female, Post Doctor; E-mail: [email protected]. en; Revised Date: September 17,2007
Issue 2
(a) Magnet with tropism;
Fig. 1
(b) Magnet without tropism
Result of eddy current acting on rare earth magnetic material in AC electric field
exterior, to holding back the effect of eddy current occurring in magnets is designed.
,.....,
1
"§ a
Experimental Process
Magnetic powders, including anisotropic/ isotropic SmzTM17(TM=Co, Fe, c«. z» or NdFeB, were soaked in organic impregnant , in which powders could be wrapped by electrically insulating macromolecule polymers [epoxies resin (ER), silane (SC), epoxy polyester resin (EPD and poly vinglbutyral (PVB) J. By selecting and confecting macromolecule organic matters with multifold components, the optimal components were discovered. Subsequently, the magnetic powders were compressed (anisotropic/isotropic) to take the shape of 8 mm X 10 mm cylinders with a single-pillar rectifying the hydraulic presser, and were isothermally heat-treated at 145 ·C for 30 min. Finally, the PrH curves (magnetization curve) were measured with the help of the 2000- H Hysteretic Loops Instrument, and the value of electric resistivity p was also measured.
2
• 85 •
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials
Discussion
2. 1 Confirming optimal macromolecule component and corresponding content By examination, the components of the organic matter were selected as follows, SC (1 %), ER (2 %), EPI (l %- 9 %), PVB (0 - 8 %) (in mass percent), and industrial pure acetone was chosen as the organic impregnant. After the magnetic particles SmZCo17 and NdFeB were pretreated with SC, they were put into the impregnant without PVB and ERI, and adequately mixed. In Fig. 2, the curves of electric resistivities versus organic components are seen.
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Curves of electric-resistivity versus content of ER and SC for NdFeB and 8ml TM 17
11 ERI% 1 SCI%
Usually, the electric resistivities of sinter Sm, C0 17 and sinter NdFeB are 8. 6X10- 3 n- cmz/m and 1. 5X ro" n . ern! /m, respectively (International unit system are 8. 6 X 10- 5 n . em and 1. 5 X 10- 4 n . cm , respectively) . In Fig. 2, it is seen that Sm, TM 17 and NdFeB magnets are still the common bonded rare earth permanent magnets as the contents of ER and SC are respectively 3 % and 1 % (in mass percent), and accordingly, the electric resistivities of Sm, TM 17 and NdFeB are 6 X 10- 4 n . m and 1 X 10- 3 n . m , respectively. Moreover, the value of electric resistivies p will gradually increase with an increase in the content of ER. Therefore, owing to the magnetic powders wrapped with electric insulating ER and SC, the electric insulation of rare earth permanent bonded magnets is better than that of sinter magnets. However, by depending on ER and SC alone, the magnets cannot possess enough electric insulation to work stably in a high frequency AC electric
Vol. 16
Journal of Iron and Steel Research, International
• 86 •
field, so it is necessary to append other stronger electric insulating organic components again. In Fig. 3. for NdFeB and Sm, TM I 7 • the curves of electric resistivities p versus the total contents of ER. SC. EPI, and PVB are shown. The developmental trend of curves in Fig. 3 is similar to the one in Fig. 2. but the value of p with 20% (in mass percent) organic matter in Fig. 2 is very close to the value of 16 % organic matter in Fig. 3. The content of organic matter directly influences the improvement in magnetic properties. thus it indicates that the organic matter in Fig. 3 possesses components that are better suited than those in the organic matter shown in Fig. 2. and they are more beneficial to produce rare earth permanent magnets with both high magnetic properties and better electric insulation. In addition, in Fig. 3. it shows that both the curves ascend rapidly before the content of organic matter reaches 12 %. that is to say. the value of p increases easily during that time, and after the content exceeds 12 %. the curves ascend rather more slowly, so it is considered that 12 % (in mass percent) is the optimal content of organic matter. and correspondingly. the electric resistivities of Sm, TM 17 and N dFeB are respectively 7 n . m and 4 X 10 1 n • m , at the same time. the components of the organic matter are EPI (5 %) • PVB (4%). ER (2%). and SC 0%); Moreover in Fig. 3, the "12 %" point is also a turning point of ascending curves, as only including ER 01%) and SC 0%). the values of pare O. 5 -1 n . m, Therefore. by this experiment, it is seen that selecting appropriate organic components would benefit to produce
rare earth permanent magnets with high magnetic properties in an AC electric field. Deciphering the optimal soaking time in impregnant Taking Sm, TMI1 and NdFeB particles as examples, in which granularities were from 40 Ilm to 100 Ilm. the particles were soaked in organic imp regnant with insulated organic matter. For the sake of allowing the magnetic particles to complete even dispersion in the impregnant , it was necessary to find the optimal soaking time; hence. the magnetic particles were all wrapped adequately so as to improve the magnets' own electrical insulation. In Fig. 4 and Fig. 5, for Sm, TMI1 and NdFeB. the curves of p versus soaking time are shown in the range of 10-160 min. From both Fig. 4 and Fig. 5. it can be seen that the curves of p ascend very rapidly for 40 min, after that. the curves ascend gradually to a fixed value. Consequently. it was explained that the magnetic particles had not been completely wrapped by organic matter as the soaking time was less than 40 min in this article, but time was prolonged. organic matters would wrap the magnetic particles completely. 2. 2
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Fig. 3 Curves of p versus content of EPI, PVB, ER, and SC C%, in mass percent) for NdFeB and SmzTM 17
til
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Fig. S Curve of p versus soaking time for NdFeB
Issue 2
• 87 •
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials
After the soaking time exceeded 40 min, the values of p increased more difficultly, even though the time was prolonged. The result obtained was that 40 min was the suitable soaking time in this experiment. Besides, comparing the values of the point at a certain abscissa between Fig. 4 and Fig. 5, it showed that the value of every point in Fig. 5 was always higher than the value of its corresponding point in Fig. 4, for example, the values of points (at 40 min) were about 7 n . m and 9 n . m. The reason was that the electric insulating characteristics of different rare earth magnets were decided by their own p (permeability), p (electric resistivity), and L (inductor) if they were wrapped by the same components and contents of organic matter. Sm2TM I7 alloy in Fig. 4 had metallic Cu (its electric resistivity p was very little) as an important component part, but every metallic component in the NdFeB alloy had a higher resistivity p than metallic Cu.
2. 3 Analyzing the combining ability of interface between metallic magnetic particle and organic matter As for improving the electrical insulation of rare earth magnets, it is very important that the interface between metallic magnetic particles and organic matters have a strong combining ability and no interspaces. In order to identify the combining ability in this article, taking Sm2TM 17 as an example, in Fig. 6, it can be seen under SEM that the magnetic particles appear wrapped by 12 % organic matter (40 min soaking time). Fig. 7 shows them partly enlarged to 100 multiples, the white light area A shows organic matters, and the black area B shows a small uncovered part of magnetic particles. From Fig. 6, it is obvious that Sm2TM I7 magnetic particles are mostly wrapped by organic matter, and uncovered magnetic particles could hardly be seen. In Fig. 7, it also shows that the uncovered part of 40 pm -1 00 pm particles is less than about 5 pm. Thereby, organic matters wrapping Sm2 TM I7 magnetic particles are able to hold back eddy current penetrating interfaces so as to avoid forming a closed whole eddy current loop. It benefits to improve electric insulation of rare earth magnets. Fig. 8 showed the SEM combining appearance between surfaces of magnetic particles and organic matters (area A: organic matters, area B: magnetic particles). In Fig. 8, it can be seen that no interspaces exist in the interfaces between organic matter and magnetic particles, that is to say, magnetic particles are
Fig. 6
SEM micrograph of magnetic particles
A-Organic matters;
B-Uncovered
Fig. 7 SEM appearance partly enlarged to 100 multiples of magnetic particles
Fig. 8
SEM micrograph of magnetic particle combined with organic matter
not only wrapped entirely, but their combining ability to organic matters is sufficiently solid, accordingly, they further prevent the eddy current field from occurring again. At the same time, it has been identified that the chosen components of organic matter are very effective for the electric insulation of magnets.
Journal of Iron and Steel Research, International
• 88 •
2. 4 Comparing the properties of rare earth permanent magnetic 8m2TN and NdFeB to permanent magnetic ferrite After they were wrapped by organic matter in the organic impregnant , Sm2TM I 7 and NdFeB magnetic particles took the shape of 8 mm X 10 mm cylinders, and finally the whole surface of every magnet was sprayed with PVB. In Table 1, the performances of Sm2TM 17 and NdFeB magnets used in this article are shown. At present, so far as ferrite is concerned, the highest value of (BH)Ol is also less than 39.8 kJ/m3 in the experiment, but in general, its values of (BH)m are 15.92 - 31. 83 kJ/m3 , and even the values of j He are much lower than those of the rare earth permanent magnets' and its p is 10 1 -10 2 0 • m in practice. From Table 1, it can be seen that the magnetic performances of Sm2TMI 7 and NdFeB are obviously better than that of ferrite. So far as electric insulation is concerned, the electric insulations of both the Sm2TM 17 and NdFeB magnets are approximately equal to the one of ferrite, and they are able to work stably in a 500 kHz AC electric field for a long time. In other words, Sm2 TM 17 and NdFeB possess the ability to take the place of ferrite under a certain high frequency AC electric field.
3
manent magnetic materials are decided only by the materials' p (permeability), p (electric resistivity) , and L (inductor). As metallic Cu with very low electric insulation is one main component of Sm2 TM 17 , the electric insulation of Sm2TM 17 IS worse than that of NdFeB under the same conditions. (2) By this experiment, the chosen components and contents (5 % EPI, 4 % PVB, 2 % ER, and 1 % SC) of organic matter are very effective and the soaking time (40 min) is also valid. All these are beneficial for producing excellent electric insulating rare earth permanent magnets with good properties. (3) In this study, high magnetic property rare earth magnets with electric insulation have been obtained, and their properties are as follows: Sm2 TM17 : B,=0.62 T, jHe=803.7 kA/m, (BH)m=58.97 kJl m", p=7 n- m; NdFeB: B,=O. 485 T, iHe=766. 33 kA/m, (BH)m =37.96 kJ/m3 , and p=9 o· m. Magnetic properties of Sm2 TM I 7 and NdFeB are obviously higher than those of permanent magnetic fer": rite, and the electric insulations of Sm2TM 17 and NdFeB applied are in fact approximately equal to those of ferrite. References : [lJ
Conclusions (l) The electric insulations of rare earth per-
Table 1
Properties of Sm, TM 17 and NdFeB magnets Performance parameters
)
(EH)m/(k]' m- 3 )
NdFeB
pl(O' m)
B,/T j
[3J
[4J
0.62
B,/T jHc/(kA'm- l
[2J
Values of properties
7
pl(O'm)
He/(kA • m- 1 )
(BH)m/(k] • m- 3 )
803.7 58.97
[5J
9
0.485 766.33 37.96
Vol. 16
[6J
TANG Ren-yuan. Research and Development of Rare Earth Permanent Magnet Machines [n. Journal of Shenyang University of Technology, 2005, 27(2): 162 (in Chinese). CHANG Ying , YU Xiao-jun, LI Wei, et al. Microstructure and Magnetic Properties of Double-Phase Nanocomposite NdFeB [J]. Journal of Rare Earths, 2005, 23(Supplement): 270. DONG Zheng-zhu. Current Status and Plan of Hard Ferrite Materials Industry in China [n. J Magri Mater Devices, 2001, 32(2): 22 (in Chinese). ZHANG Chang-wen, LI Hua, DONG Iian-min, et al. Electronic Structure and Magnetic Properties of SmCo7 - xZrx [n. Chinese Physics Letters, 2006, 23(6): 1581. LI Jun. Preparation, Structure and Properties of Two Types of Magnetic Composite Materials Used for Motors [OJ. Chengdu , Sichuan University, 2006 (in Chinese). PAN Wei, LI Wei. Rare Earth Cobalt Base Permanent Magnets With Special Application [n. Metallic Functional Materials. 1999, 6(4): 161.
.-" ....; II
ScienceDirect
JOURNAL OF IRON AND STEEL RESEARCH, INTERNATIONAL. 2009, 16(2): 84-88
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials With High Magnetic Properties CHANG Ying",
WANG Da-peng",
LI Wei 3 ,
PAN WeF,
YU Xiao-jun",
QI Min 2
0. School of Automotive Engineering, Dalian University of Technology, Dalian 116024, Liaoning, China; 2. School of Material Science and Technology, Dalian University of Technology, Dalian 116024, Liaoning, China; 3. Functional Materials Research Institute, China Iron and Steel Research Institute Group, Beijing 100081, China) Abstract: Rare earth permanent magnetic materials are typical electrical conductor, and their magnetic properties will decrease because of the eddy current effect, so it is difficult to keep them stable for a long enough time under a high frequency AC field. In the present study, as far as rare earth permanent magnets are concerned, for the first time, rare earth permanent magnets with strong electrical insulation and high magnetic performance have been obtained through experiments, and their properties are as follows: (1) Sm, TM17 : B, =0.62 T, j H, =803.7 kA/m, (BH)m = 58.97 kJ/m', p=7 n· m, (2) NdFeB: B,=O. 485 T, ;R=766. 33 kA/m, (BH)m=37. 96 kJ/m' , p=9 n· m. The magnetic properties of Sm2TM 17 and NdFeB are obviously higher than those of ferrite permanent magnet, and the electric insulating characteristics of Sm2TM17 and NdFeB applied have in fact been approximately the same as those of ferrite. Therefore, Sm2TM17 and NdFeB will possess the ability to take the place of ferrite under a certain high frequency AC electric field. Key words: Sm2TM 17 ; NdFeB; electrical insulation; eddy current
During the last decade, following the swift development of high-tech equiprnents , the permanent magnetic parts of an apparatus applied in the equipment, such as, microwave, atomic energy, and MRI, are required to work steadily under higher frequency AC (alternating current) electric field[I-3]. As far as rare earth magnetic alloys with metallic conductance are concerned, due to the strong exothermic phenomenon of eddy current occurring in magnets under AC electric field, the magnetic energy will be exhausted. According to stronger magnetism-temperature relevancy, rare earth permanent magnets will be induced to obvious demagnetization, owing to serious wastage of eddy current. Fig. 1 (a) shows that the rare earth magnet formerly had a certain ordered orientation of Pi' when it was put under a high frequency AC electric field. An eddy current would occur, as Fig. 1 (b) shows, and the magnet would convert into the heat demagnetization state without accordant orientation.
At present, permanent magnetic ferrites with excellent electric insulation are still applied in the domain of high-tech equipments , thus it is difficult for these equipments to develop into "high quality, micromation , economizing resources" because of ferrite's own lower magnetic properties and a greater useful volume[4-6]. Ferrites substituted by rare earth permanent magnets with high magnetic properties are a tendency, but in this case, the improvement in the insulating characteristic of rare earth permanent magnets is crucial. Up to now, with regard to the insulating characteristic of rare earth permanent magnetic alloys, the reports have not been referred to yet. According to theoretic analyses in this study, for the first time, the experiments for producing rare earth permanent magnetic materials with electric insulating characteristic are carried out. The way, which is roundly an electrical insulating measure from tiny magnetic powders to the whole magnets'
Foundation Item: Item Sponsored by Liaoning Provincial Natural Science Foundation (20071090) Biography: CHANG Ying(l977-) , Female, Post Doctor; E-mail: [email protected]. en; Revised Date: September 17,2007
Issue 2
(a) Magnet with tropism;
Fig. 1
(b) Magnet without tropism
Result of eddy current acting on rare earth magnetic material in AC electric field
exterior, to holding back the effect of eddy current occurring in magnets is designed.
,.....,
1
"§ a
Experimental Process
Magnetic powders, including anisotropic/ isotropic SmzTM17(TM=Co, Fe, c«. z» or NdFeB, were soaked in organic impregnant , in which powders could be wrapped by electrically insulating macromolecule polymers [epoxies resin (ER), silane (SC), epoxy polyester resin (EPD and poly vinglbutyral (PVB) J. By selecting and confecting macromolecule organic matters with multifold components, the optimal components were discovered. Subsequently, the magnetic powders were compressed (anisotropic/isotropic) to take the shape of 8 mm X 10 mm cylinders with a single-pillar rectifying the hydraulic presser, and were isothermally heat-treated at 145 ·C for 30 min. Finally, the PrH curves (magnetization curve) were measured with the help of the 2000- H Hysteretic Loops Instrument, and the value of electric resistivity p was also measured.
2
• 85 •
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials
Discussion
2. 1 Confirming optimal macromolecule component and corresponding content By examination, the components of the organic matter were selected as follows, SC (1 %), ER (2 %), EPI (l %- 9 %), PVB (0 - 8 %) (in mass percent), and industrial pure acetone was chosen as the organic impregnant. After the magnetic particles SmZCo17 and NdFeB were pretreated with SC, they were put into the impregnant without PVB and ERI, and adequately mixed. In Fig. 2, the curves of electric resistivities versus organic components are seen.
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~ 4l
4
8
12
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3
7
1
1
Fig. 2
Curves of electric-resistivity versus content of ER and SC for NdFeB and 8ml TM 17
11 ERI% 1 SCI%
Usually, the electric resistivities of sinter Sm, C0 17 and sinter NdFeB are 8. 6X10- 3 n- cmz/m and 1. 5X ro" n . ern! /m, respectively (International unit system are 8. 6 X 10- 5 n . em and 1. 5 X 10- 4 n . cm , respectively) . In Fig. 2, it is seen that Sm, TM 17 and NdFeB magnets are still the common bonded rare earth permanent magnets as the contents of ER and SC are respectively 3 % and 1 % (in mass percent), and accordingly, the electric resistivities of Sm, TM 17 and NdFeB are 6 X 10- 4 n . m and 1 X 10- 3 n . m , respectively. Moreover, the value of electric resistivies p will gradually increase with an increase in the content of ER. Therefore, owing to the magnetic powders wrapped with electric insulating ER and SC, the electric insulation of rare earth permanent bonded magnets is better than that of sinter magnets. However, by depending on ER and SC alone, the magnets cannot possess enough electric insulation to work stably in a high frequency AC electric
Vol. 16
Journal of Iron and Steel Research, International
• 86 •
field, so it is necessary to append other stronger electric insulating organic components again. In Fig. 3. for NdFeB and Sm, TM I 7 • the curves of electric resistivities p versus the total contents of ER. SC. EPI, and PVB are shown. The developmental trend of curves in Fig. 3 is similar to the one in Fig. 2. but the value of p with 20% (in mass percent) organic matter in Fig. 2 is very close to the value of 16 % organic matter in Fig. 3. The content of organic matter directly influences the improvement in magnetic properties. thus it indicates that the organic matter in Fig. 3 possesses components that are better suited than those in the organic matter shown in Fig. 2. and they are more beneficial to produce rare earth permanent magnets with both high magnetic properties and better electric insulation. In addition, in Fig. 3. it shows that both the curves ascend rapidly before the content of organic matter reaches 12 %. that is to say. the value of p increases easily during that time, and after the content exceeds 12 %. the curves ascend rather more slowly, so it is considered that 12 % (in mass percent) is the optimal content of organic matter. and correspondingly. the electric resistivities of Sm, TM 17 and N dFeB are respectively 7 n . m and 4 X 10 1 n • m , at the same time. the components of the organic matter are EPI (5 %) • PVB (4%). ER (2%). and SC 0%); Moreover in Fig. 3, the "12 %" point is also a turning point of ascending curves, as only including ER 01%) and SC 0%). the values of pare O. 5 -1 n . m, Therefore. by this experiment, it is seen that selecting appropriate organic components would benefit to produce
rare earth permanent magnets with high magnetic properties in an AC electric field. Deciphering the optimal soaking time in impregnant Taking Sm, TMI1 and NdFeB particles as examples, in which granularities were from 40 Ilm to 100 Ilm. the particles were soaked in organic imp regnant with insulated organic matter. For the sake of allowing the magnetic particles to complete even dispersion in the impregnant , it was necessary to find the optimal soaking time; hence. the magnetic particles were all wrapped adequately so as to improve the magnets' own electrical insulation. In Fig. 4 and Fig. 5, for Sm, TMI1 and NdFeB. the curves of p versus soaking time are shown in the range of 10-160 min. From both Fig. 4 and Fig. 5. it can be seen that the curves of p ascend very rapidly for 40 min, after that. the curves ascend gradually to a fixed value. Consequently. it was explained that the magnetic particles had not been completely wrapped by organic matter as the soaking time was less than 40 min in this article, but time was prolonged. organic matters would wrap the magnetic particles completely. 2. 2
40
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a
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Curve of p versus soaking time for SmzTM. 7
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Fig. 3 Curves of p versus content of EPI, PVB, ER, and SC C%, in mass percent) for NdFeB and SmzTM 17
til
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102 01...-..:...--.........- -........---o._--....1 40 80 120 160 Soaking time/min
Fig. S Curve of p versus soaking time for NdFeB
Issue 2
• 87 •
Improved Electrical Insulation of Rare Earth Permanent Magnetic Materials
After the soaking time exceeded 40 min, the values of p increased more difficultly, even though the time was prolonged. The result obtained was that 40 min was the suitable soaking time in this experiment. Besides, comparing the values of the point at a certain abscissa between Fig. 4 and Fig. 5, it showed that the value of every point in Fig. 5 was always higher than the value of its corresponding point in Fig. 4, for example, the values of points (at 40 min) were about 7 n . m and 9 n . m. The reason was that the electric insulating characteristics of different rare earth magnets were decided by their own p (permeability), p (electric resistivity), and L (inductor) if they were wrapped by the same components and contents of organic matter. Sm2TM I7 alloy in Fig. 4 had metallic Cu (its electric resistivity p was very little) as an important component part, but every metallic component in the NdFeB alloy had a higher resistivity p than metallic Cu.
2. 3 Analyzing the combining ability of interface between metallic magnetic particle and organic matter As for improving the electrical insulation of rare earth magnets, it is very important that the interface between metallic magnetic particles and organic matters have a strong combining ability and no interspaces. In order to identify the combining ability in this article, taking Sm2TM 17 as an example, in Fig. 6, it can be seen under SEM that the magnetic particles appear wrapped by 12 % organic matter (40 min soaking time). Fig. 7 shows them partly enlarged to 100 multiples, the white light area A shows organic matters, and the black area B shows a small uncovered part of magnetic particles. From Fig. 6, it is obvious that Sm2TM I7 magnetic particles are mostly wrapped by organic matter, and uncovered magnetic particles could hardly be seen. In Fig. 7, it also shows that the uncovered part of 40 pm -1 00 pm particles is less than about 5 pm. Thereby, organic matters wrapping Sm2 TM I7 magnetic particles are able to hold back eddy current penetrating interfaces so as to avoid forming a closed whole eddy current loop. It benefits to improve electric insulation of rare earth magnets. Fig. 8 showed the SEM combining appearance between surfaces of magnetic particles and organic matters (area A: organic matters, area B: magnetic particles). In Fig. 8, it can be seen that no interspaces exist in the interfaces between organic matter and magnetic particles, that is to say, magnetic particles are
Fig. 6
SEM micrograph of magnetic particles
A-Organic matters;
B-Uncovered
Fig. 7 SEM appearance partly enlarged to 100 multiples of magnetic particles
Fig. 8
SEM micrograph of magnetic particle combined with organic matter
not only wrapped entirely, but their combining ability to organic matters is sufficiently solid, accordingly, they further prevent the eddy current field from occurring again. At the same time, it has been identified that the chosen components of organic matter are very effective for the electric insulation of magnets.
Journal of Iron and Steel Research, International
• 88 •
2. 4 Comparing the properties of rare earth permanent magnetic 8m2TN and NdFeB to permanent magnetic ferrite After they were wrapped by organic matter in the organic impregnant , Sm2TM I 7 and NdFeB magnetic particles took the shape of 8 mm X 10 mm cylinders, and finally the whole surface of every magnet was sprayed with PVB. In Table 1, the performances of Sm2TM 17 and NdFeB magnets used in this article are shown. At present, so far as ferrite is concerned, the highest value of (BH)Ol is also less than 39.8 kJ/m3 in the experiment, but in general, its values of (BH)m are 15.92 - 31. 83 kJ/m3 , and even the values of j He are much lower than those of the rare earth permanent magnets' and its p is 10 1 -10 2 0 • m in practice. From Table 1, it can be seen that the magnetic performances of Sm2TMI 7 and NdFeB are obviously better than that of ferrite. So far as electric insulation is concerned, the electric insulations of both the Sm2TM 17 and NdFeB magnets are approximately equal to the one of ferrite, and they are able to work stably in a 500 kHz AC electric field for a long time. In other words, Sm2 TM 17 and NdFeB possess the ability to take the place of ferrite under a certain high frequency AC electric field.
3
manent magnetic materials are decided only by the materials' p (permeability), p (electric resistivity) , and L (inductor). As metallic Cu with very low electric insulation is one main component of Sm2 TM 17 , the electric insulation of Sm2TM 17 IS worse than that of NdFeB under the same conditions. (2) By this experiment, the chosen components and contents (5 % EPI, 4 % PVB, 2 % ER, and 1 % SC) of organic matter are very effective and the soaking time (40 min) is also valid. All these are beneficial for producing excellent electric insulating rare earth permanent magnets with good properties. (3) In this study, high magnetic property rare earth magnets with electric insulation have been obtained, and their properties are as follows: Sm2 TM17 : B,=0.62 T, jHe=803.7 kA/m, (BH)m=58.97 kJl m", p=7 n- m; NdFeB: B,=O. 485 T, iHe=766. 33 kA/m, (BH)m =37.96 kJ/m3 , and p=9 o· m. Magnetic properties of Sm2 TM I 7 and NdFeB are obviously higher than those of permanent magnetic fer": rite, and the electric insulations of Sm2TM 17 and NdFeB applied are in fact approximately equal to those of ferrite. References : [lJ
Conclusions (l) The electric insulations of rare earth per-
Table 1
Properties of Sm, TM 17 and NdFeB magnets Performance parameters
)
(EH)m/(k]' m- 3 )
NdFeB
pl(O' m)
B,/T j
[3J
[4J
0.62
B,/T jHc/(kA'm- l
[2J
Values of properties
7
pl(O'm)
He/(kA • m- 1 )
(BH)m/(k] • m- 3 )
803.7 58.97
[5J
9
0.485 766.33 37.96
Vol. 16
[6J
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