Graphene-containing rare earth permanent magnet material and preparation method thereof

Abstract

The present invention involves a graphene-containing rare earth permanent magnet material and preparation method thereof. The graphene-containing rare earth permanent magnet material, comprising: 20.6 to 23.4 weight percent of neodymium, 6.6 to 7.5 weight percent of praseodymium, 0.95 to 1.20 weight percent of boron, 0.4 to 0.6 weight percent of cobalt, 0.11 to 0.15 weight percent of copper, 2.0 to 2.4 weight percent of lanthanum, 1.7 to 2.1 weight percent of cerium, 1 to 5 weight percent of graphene, a remainder being iron. The graphene-containing rare earth permanent magnet material exhibits excellent temperature resistance, good conductivity and magnet properties even without any heavy rare earth elements like terbium or dysprosium, which dramatically reduces the cost, promotes the efficient utilization of rare earth resources and improves product quality. The preparation method within this invention is simple to realize, easy to control, cost-effective and has high production efficiency and stable product performances.

Claims

1. A preparation method of a graphene-containing rare earth permanent magnet material comprising the following steps: S1. proportionally mixing a graphene powder with a magnet alloy powder to obtain a graphene-containing rare earth permanent magnet powder, the magnet alloy powder containing neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron in proportion; orientating the graphene-containing rare earth permanent magnet powder under a magnet field with a protection of an inert gas, and pressing the oriented graphene-containing rare earth permanent magnet powder to form a green body; S2. isostatic pressing the green body obtained from S1; sintering the isostatic pressed green body in a sintering furnace; and tempering the sintered green body to obtain a graphene-containing rare earth permanent magnet material.

2. The preparation method of claim 1, wherein in the Step S1, the magnet alloy powder is prepared by the following steps: mixing neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron powder in proportion to form a magnet alloy; then smelting the magnet alloy to form a magnet alloy ingot; the magnet alloy ingot is made into thin magnet alloy sheets by a rapid solidification process; the thin magnet alloy sheets are then treated by hydrogen decrepitation to form a magnet alloy fragments; the magnet alloy fragments are then processed into magnet alloy powders by jet milling.

3. The preparation method of claim 2, wherein in the rapid solidification process, the processed molten state magnet alloy is poured onto a rotating water-cooled copper rolls for rapid quenching, with a rotation speed of 2.5_m/s to 3_m/s.

4. The preparation method of claim 1, wherein in the Step S1, the magnet alloy powder has a diameter of 0.5 μm to 1.5 μm.

5. The preparation method of claim 1, wherein in the Step S1, the graphene-containing rare earth permanent magnet powder is orientated under a magnet field with a magnet field strength of 1.6 T to 2.5 T.

6. The preparation method of claim 1, wherein in the Step S2, a pressure of the isostatic pressing is 230_MPa to 280_MPa, a pressing time is 90s to 150s.

7. The preparation method of claim 1, wherein in the Step S2, the green body is treated by isostatic pressing, and then placed in a vacuum sintering furnace for sintering, followed by a two-stage tempering treatment to obtain the graphene rare earth permanent magnet material.

8. The preparation method of claim 1, wherein in the Step S2, a temperature of a first tempering treatment is 860° C. to 940° C., and the temperature is maintained for 120_mins to 180_mins, while a temperature of a second tempering heat treatment is 550° C. to 600° C., and the temperature is maintained for 120_mins to 180 mins.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) To facilitate the understanding of those skilled in the art, the present invention will be further explained in combination with the following specific embodiments, but the protection is not limited thereto.

(2) [The First Embodiment]

(3) The graphene-containing rare earth permanent magnet material in the first embodiment comprises 21.5 weight percent of neodymium, 6.9 weight percent of praseodymium, 1.1 weight percent of boron, 0.5 weight percent of cobalt, 0.12 weight percent of copper, 2.2 weight percent of lanthanum, 1.9 weight percent of cerium, 3 weight percent of graphene, a remainder being iron.

(4) The preparation method of the graphene-containing rare earth permanent magnet material in the first embodiment includes the following steps:

(5) S1: proportionally mixing a graphene powder with a magnet alloy powder to obtain a graphene-containing rare earth permanent magnet powder; the magnet alloy powder contains neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron in proportion; orientating the graphene-containing rare earth permanent magnet powder under a magnet field with the protection of an inert gas, and pressing the oriented graphene-containing rare earth permanent magnet powder to form a green body;

(6) S2: isostatic pressing the green body obtained from the preparation S1; sintering the isostatic pressed green body in a sintering furnace; tempering the sintered green body to obtain a graphene-containing rare earth permanent magnet material.

(7) In accordance with the preparation step S1, the magnet alloy powder is prepared by the following steps: mixing neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron powder in proportion to form a magnet alloy; then smelting the magnet alloy to form a magnet alloy ingot; the magnet alloy ingot is then made into thin magnet alloy sheets by a rapid solidification process; the thin magnet alloy sheets are then treated by hydrogen decrepitation to form magnet alloy fragments; the magnet alloy fragments are then processed into magnet alloy powders by jet milling.

(8) In accordance with the preparation step S1, in the rapid solidification process, the processed molten state magnet alloy is poured onto a rotating water-cooled copper rolls for rapid quenching, with a rotation speed of 2.7 m/s. Thickness of the obtained thin magnet alloy sheets is 0.3 mm.

(9) In accordance with the preparation step S1, the diameter of the magnet alloy powder is 0.5 μm-1.5 nm.

(10) In accordance with the preparation step S1, the graphene-containing rare earth permanent magnet powder is orientated under a magnet field with a magnet field strength of 2 T.

(11) In accordance with the preparation step S2, the isostatic pressing of the green body is conducted at a pressure of 250 MPa and a pressing time of 120 s.

(12) In accordance with the preparation step S2, the sintering process comprises of the following steps:

(13) A: placing the isostatic pressing treated green body in a sintering furnace, closing the furnace lid and evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa;

(14) B: feeding the sintering furnace with argon until pressure inside the sintering furnace reaches 80 Pa and keeping at this pressure; increasing temperature of the sintering furnace to 270° C. at a heating rate of 3° C./min and keeping at this temperature. The heating and holding time is 180 mins;

(15) C: continuing to feed the sintering furnace with argon until the pressure in the sintering furnace reaches 230 Pa and maintaining at this pressure; increasing temperature of the sintering furnace to 800° C. at a heating rate of 3.5° C./min;

(16) D: stop feeding argon and then evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa; increasing temperature of the sintering furnace to 1100° C. at a heating rate of 2.5° C./min and keeping at this temperature. The heating holding time is 270 mins.

(17) In accordance with the preparation step S2, the graphene-containing rare earth permanent magnet material is obtained via first isostatic pressing of the green body obtained from the preparation step S1, sintering the isostatic pressing treated green body in a vacuum sintering furnace, and then tempering the sintered green body following a two-stage tempering process.

(18) In accordance with the preparation step S2, the two-stage tempering process is conducted at 900° C. for 150 mins of the first stage and 580° C. for 150 mins of the second stage.

(19) [The Second Embodiment]

(20) The graphene-containing rare earth permanent magnet material in the second embodiment comprises 20.6 weight percent of neodymium, 7.5 weight percent of praseodymium, 0.95 weight percent of boron, 0.4 weight percent of cobalt, 0.11 weight percent of copper, 2.4 weight percent of lanthanum, 1.7 weight percent of cerium, 1 weight percent of graphene, a remainder being iron.

(21) The preparation method of the graphene-containing rare earth permanent magnet material in the second embodiment is as follows:

(22) S1: proportionally mixing a graphene powder with a magnet alloy powder to obtain the graphene-containing rare earth permanent magnet powder; the magnet alloy powder contains neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron powder in proportion; orientating the graphene-containing rare earth permanent magnet powder under a magnet field with the protection of an inert gas, and pressing the oriented graphene-containing rare earth permanent magnet powder to form a green body;

(23) S2: isostatic pressing of the green body obtained from S1; sintering the isostatic pressing treated green body in a sintering furnace; tempering the sintered green body to obtain the graphene-containing rare earth permanent magnet material.

(24) In accordance with the preparation step S1, preferably, the magnet alloy powder is prepared by the following steps: mixing neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron powder in proportion to form a magnet alloy; then smelting the magnet alloy to form a magnet alloy ingot; the magnet alloy ingot is made into thin magnet alloy sheets by a rapid solidification process; the thin magnet alloy sheets are then treated by hydrogen decrepitation to form magnet alloy fragments; the magnet alloy fragments are then processed into magnet alloy powders by jet milling.

(25) In accordance with the preparation step S1, in the rapid solidification process, the processed molten state magnet alloy is poured onto a rotating water-cooled copper rolls for rapid quenching, with a rotation speed of 2.5 m/s. The thickness of the obtained thin magnet alloy sheets is 0.35 mm.

(26) In accordance with the preparation step S1, the diameter of the magnet alloy powder is 0.5 nm-1.5 nm.

(27) In accordance with the preparation step S1, the graphene-containing rare earth permanent magnet powder is orientated under a magnet field with a magnet field strength of 1.6 T.

(28) In accordance with the preparation step S2, the isostatic pressing of the green body is conducted at a pressure of 230 MPa and a pressing time of 150 s.

(29) In accordance with the preparation step S2, the sintering process comprises of the follow steps:

(30) A: placing the isostatic pressing treated green body in a sintering furnace, closing the furnace lid and evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa;

(31) B: feeding the sintering furnace with argon until pressure in the sintering furnace reaches 60 Pa and keeping at this pressure; increasing temperature of the sintering furnace to 260° C. at a heating rate of 2.5° C./min and keeping at this temperature. The heating and holding time is 210 mins;

(32) C: continuing to feed the sintering furnace with argon until the pressure in the sintering furnace reaches 200 Pa and maintaining at this pressure; increasing temperature of the sintering furnace to 760° C. at a heating rate of 3° C./min;

(33) D: stop feeding argon and then evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa; increasing temperature of the sintering furnace to 1050° C. at a heating rate of 2° C./min and keeping at this temperature. The heating and holding time is 300 mins.

(34) In accordance with the preparation step S2, the graphene-containing rare earth permanent magnet material is obtained via first isostatic pressing of the green body obtained from the preparation step S1, sintering the isostatic pressing treated green body in a vacuum sintering furnace, and then tempering the sintered green body following a two-stage tempering process.

(35) In accordance with the preparation step S2, the two-stage tempering process is conducted at 860° C. for 180 mins of a first stage and 550° C. for 180 mins of a second stage.

(36) [The Third Embodiment]

(37) The graphene-containing rare earth permanent magnet material in the third embodiment comprises 23.4 weight percent of neodymium, 6.6 weight percent of praseodymium, 1.2 weight percent of boron, 0.6 weight percent of cobalt, 0.15 weight percent of copper, 2.0 weight percent of lanthanum, 2.1 weight percent of cerium, 5 weight percent of graphene, a remainder being iron.

(38) The preparation method of the graphene-containing rare earth permanent magnet material in the third embodiment is as follows:

(39) S1: proportionally mixing a graphene powder with a magnet alloy powder to obtain a graphene-containing rare earth permanent magnet powder; the magnet alloy powder contains neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron in proportion; orientating the graphene-containing rare earth permanent magnet powder under a magnet field with the protection of an inert gas, and pressing the oriented graphene-containing rare earth permanent magnet powder to form a green body;

(40) S2: isostatic pressing of the green body obtained in preparation step S1; sintering the isostatic pressed green body in a sintering furnace; tempering the sintered green body to obtain a graphene-containing rare earth permanent magnet material.

(41) In accordance with the preparation step S1, the magnet alloy powder is prepared by the following steps: mixing neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron powder in proportion to form a magnet alloy; then smelting the magnet alloy to form a magnet alloy ingot; the magnet alloy ingot is made into thin magnet alloy sheets by a rapid solidification process; the thin magnet alloy sheets are then treated by hydrogen decrepitation to form magnet alloy fragments; the magnet alloy fragments are then processed into magnet alloy powders by jet milling.

(42) In accordance with the preparation step S1, in the rapid solidification process, the processed molten state magnet alloy is poured onto a rotating water-cooled copper rolls for rapid quenching, with a rotation speed of 3 m/s. The thickness of the obtained thin magnet alloy sheets is 0.33 mm.

(43) In accordance with the preparation step S1, the diameter of the magnet alloy powder is 0.5 nm-1.5 μm.

(44) In accordance with the preparation step S1, the graphene-containing rare earth permanent magnet powder is orientated under a magnet field with a magnet field strength of 2.5 T.

(45) In accordance with the preparation step S2, the isostatic pressing of the green body is conducted at a pressure of 280 MPa and a pressing time of 90 s.

(46) In accordance with the preparation step S2, the sintering process comprises of the follow steps:

(47) A: placing the isostatic pressing treated green body in a sintering furnace, closing the furnace lid and evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa;

(48) B: feeding the sintering furnace with argon until pressure in the sintering furnace reaches 100 Pa and keeping at this pressure; increasing temperature of the sintering furnace to 310° C. at a heating rate of 3.5° C./min and keeping at this temperature. The heating and holding time is 150 mins;

(49) C: continuing to feed the sintering furnace with argon until the pressure in the sintering furnace reaches 250 Pa and maintaining at this pressure; increasing temperature of the sintering furnace to 820° C. at a heating rate of 4° C./min;

(50) D: stop feeding argon and then evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa; increasing temperature of the sintering furnace to 1140° C. at a heating rate of 3° C./min and keeping at this temperature. The heating and holding time is 240 mins.

(51) In accordance with the preparation step S2, the graphene-containing rare earth permanent magnet material is obtained via first isostatic pressing of the green body obtained from the preparation step of S1, sintering the isostatic pressing treated green body in a vacuum sintering furnace, and then tempering the sintered green body following a two-stage tempering process.

(52) In accordance with the preparation step S2, the two-stage tempering process is conducted at 940° C. for 120 mins of the first stage and 550° C. for 120 mins of the second stage.

(53) [The Fourth Embodiment]

(54) The graphene-containing rare earth permanent magnet material in the fourth embodiment comprises 22 weight percent of neodymium, 7.2 weight percent of praseodymium, 1.0 weight percent of boron, 0.45 weight percent of cobalt, 0.14 weight percent of copper, 2.2 weight percent of lanthanum, 1.8 weight percent of cerium, 4 weight percent of graphene, a remainder being iron.

(55) The preparation method of the graphene-containing rare earth permanent magnet material in embodiment 4 is as follows:

(56) S1: proportionally mixing a graphene powder with a magnet alloy powder to obtain a graphene-containing rare earth permanent magnet powder; the magnet alloy powder contains neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron in proportion; orientating the graphene-containing rare earth permanent magnet powder under a magnet field with the protection of an inert gas, and pressing the oriented graphene-containing rare earth permanent magnet powder to form a green body;

(57) S2: isostatic pressing the green body obtained in preparation step S1; sintering the isostatic pressed green body in a sintering furnace; tempering the sintered green body to obtain a graphene-containing rare earth permanent magnet material.

(58) In accordance with the preparation step S1, the magnet alloy powder is prepared by the following steps: mixing neodymium, praseodymium, boron, cobalt, copper, lanthanum, cerium and iron powder in proportion to form a magnet alloy; then smelting the magnet alloy to form a magnet alloy ingot; the magnet alloy ingot is made into thin magnet alloy sheets by a rapid solidification process; the thin magnet alloy sheets are then treated by hydrogen decrepitation to form magnet alloy fragments; the magnet alloy fragments are then processed into magnet alloy powders by jet milling.

(59) In accordance with the preparation step S1, in the rapid solidification process, the processed molten state magnet alloy is poured onto a rotating water-cooled copper rolls for rapid quenching, with a rotation speed of 2.8 m/s. The thickness of the obtained thin magnet alloy sheets is 0.3 mm.

(60) In accordance with the preparation step S1, the diameter of the magnet alloy powder is 0.5 nm-1.5 nm.

(61) In accordance with the preparation step S1, the graphene-containing rare earth permanent magnet powder is orientated under a magnet field with a magnet field strength of 2.2 T.

(62) In accordance with the preparation step S2, the isostatic pressing of the green body is conducted at a pressure of 260 MPa and a pressing time of 100 s.

(63) In accordance with the preparation step S2, the sintering process comprises of the follow steps:

(64) A: placing the isostatic pressing treated green body in a sintering furnace, closing the furnace lid and evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa;

(65) B: feeding the sintering furnace with argon until pressure in the sintering furnace reaches 90 Pa and keeping at this pressure; increasing temperature of the sintering furnace to 280° C. at a heating rate of 3° C./min and keeping at this temperature. The heating and holding time is 180 mins;

(66) C: continuing to feed the sintering furnace with argon until the pressure in the sintering furnace reaches 220 Pa and maintaining at this pressure; increasing temperature of the sintering furnace to 790° C. at a heating rate of 3.5° C./min;

(67) D: stop feeding argon and then evacuating the furnace until the absolute vacuum degree in the furnace is below 0.1 Pa; increasing temperature of the sintering furnace to 1120° C. at a heating rate of 2.5° C./min and keeping at this temperature. The heating and holding time is 280 mins.

(68) In accordance with the preparation step S2, the graphene-containing rare earth permanent magnet material is obtained via first isostatic pressing of the green body obtained from the preparation step of S1, sintering the isostatic pressing treated green body in a vacuum sintering furnace, and then tempering the sintered green body following a two-stage tempering process.

(69) In accordance with the preparation step S2, the two-stage tempering process is conducted at 920° C. for 160 mins of the first stage and 580° C. for 150 mins of the second stage.

(70) Contents of the rest embodiments of the present invention are similar to that of the first embodiment and for simplicity, they will not be repeated here.

(71) [Comparative example 1]

(72) The differences between the comparative example 1 and the first embodiment of the present invention lies in the different compositions of the magnet alloy. The permanent magnet material of the comparative example 1 has a composition of 21.5 weight percent of neodymium, 6.9 weight percent of praseodymium, 1.1 weight percent of boron, 0.5 weight percent of cobalt, 0.12 weight percent of copper, 2.2 weight percent of lanthanum, 1.9 weight percent of cerium, a remainder being iron.

(73) The sintered rare earth permanent magnet materials obtained from comparative example 1 and the embodiments 1-4 of the present invention are then processed in to a Φ 10 mm×7 mm cylinder respectively and tested according to GB/T 13560-2017. The performances are shown in the following table:

(74) TABLE-US-00001 Item Remanence B.sub.r Remanence B.sub.r Intrinsic coercive (20° C.) (450° C.) force H.sub.cj Unit T T KA/m Embodiment 1 1.41 1.17 1494 Embodiment 2 1.37 1.08 1340 Embodiment 3 1.44 1.13 1395 Embodiment 4 1.43 1.11 1432 Comparative 1.34 0.92 1288 example 1

(75) There are no defects like cracks, voids, impurities or exfoliations on the surface of the Nd—Fe—B magnets obtained from comparative example 1 and embodiments 1-4 of the present invention. The electrical resistivity of the magnet in the first embodiment is 1.1×10.sup.−4 Ω.Math.m. By means of incorporating graphene into Nd—Fe—B alloy powders and compounding it with components like neodymium, praseodymium, boron, cobalt, copper, lanthanum and cerium, and then adjusting the ratios of each component, the graphene-containing rare earth permanent magnet material with good temperature resistance, conductivity and magnet properties is obtained. The graphene-containing rare earth permanent magnet material of the present invention exhibits excellent properties even without any heavy rare earth elements like terbium or dysprosium, which dramatically reduces the cost, promotes the effective utilization of rare earth resources and improves product quality.

(76) The present invention is not limited by the implementation schemes mentioned in the above embodiments, although they do show the preferred implementation schemes. All variations, modifications and replacements to the disclosed embodiments which are apparent to those skilled in the art and do not depart from the concept of the present invention fall in the scope of the present invention.