Nano-porous alloys with strong permanent magnetism and preparation method therefor

Abstract

A kind of nano-porous FePt alloys with strong permanent magnetism and a preparation method therefor. The nano-porous FePt alloys have the composition of Fe.sub.wCo.sub.xPt.sub.yPd.sub.z and are composed of an ordered hard magnetic L1.sub.0-FePt phase, and have an integrated doubly-connected nano-porous structure with pore sizes of 10-50 nm, and ligament thicknesses of 20-80 nm. Under an applied magnetic field of 50 kOe, the coercivity, magnetization intensity and remanence of the alloys are 13.4-18.5 kOe, 40.4-56.3 emu/g and 28.3-37.4 emu/g, respectively. The master alloy ingots are prepared using electric arc melting or induction melting; the alloy ribbons are prepared using the single-roller melt-spinning equipment; the precursors mainly containing nano-composite phases of hard magnetic L1.sub.0-FePt and soft magnetic Fe.sub.2B are obtained directly by the melt-spinning or obtained by conducting vacuum annealing on the melt-spun ribbons; and the nano-porous FePt alloys with a single L1.sub.0-FePt phase are obtained by the electrochemical dealloying technique, thereby filling in the technical blank of nano-porous metal materials with permanent magnetism.

Claims

1. A preparation method for nano-porous FePt alloys with strong permanent magnetism comprising: (1) precursor alloys ingots are prepared using electric arc melting or high-frequency induction melting under an Ar atmosphere; (2) amorphous or amorphous+nanocrystalline alloy ribbons are prepared using a single-roller melt-spinning technology, and a thickness and phase structure of the ribbons are controlled by a rotational speed of a copper roller; (3) precursors containing uniformly distributed nano-composite phases of hard magnetic L1.sub.0-FePt and soft magnetic Fe.sub.2B are directly obtained by melt-spinning or obtained by conducting vacuum annealing on the melt-spun ribbon samples; (4) by taking the precursor as a working electrode, Ag/AgCl as a reference electrode, and an acid solution with a H.sup.+concentration of 0.02-1.0 mol/L as an electrolytic solution, dealloying is conducted using electrochemical technique under constant voltages of 0.28-1.5 V, phases mainly including soft magnetic Fe.sub.2B except hard magnetic L1.sub.0-FePt are selectively dissolved, and nano-porous FePt alloys with permanent magnetism containing a single L1.sub.0-FePt phase are prepared; the nano-porous FePt alloys with strong permanent magnetism, wherein the nano-porous alloys are composed of ordered hard magnetic of L1.sub.0-Fe-Pt phase and have a chemical composition of Fe.sub.wCo.sub.xPt.sub.yPd.sub.z, w, x, y and z respectively representing atomic percent of each corresponding element in the expression, where 25w55, 0x25, 45w+x55, 45y55, 0z10, 45y+z55, and w+x+y+z=100; the nano-porous alloys are prepared from the precursor alloys through a dealloying technique, and have an integrated doubly-connected nano-porous structure with pore sizes of 10-50 nm, and ligament thicknesses of 20-80 nm; an expression of the composition of the precursors for preparing the nano-porous alloys is Fe.sub.aCo.sub.bPt.sub.cPd.sub.dB.sub.eC.sub.fP.sub.gSi.sub.h, a, b c, d, e, f, g and h respectively representing atomic percent of each corresponding element in the expression, where 30a70, 0b30, 40a+b70, 8c40, 0d5, 8c+d40, 10e35, 0f5, 0g5, 0h3, 10e+f+g+h35, and a+b+c+d+e+f+g+h=100, and the nano-porous FePt alloys with strong permanent magnetism has strong permanent magnetism: under an applied magnetic field of 50 kOe, a coercivity is 13.4-18.5 kOe, a magnetization is 40.4-56.3 emu/g, and a remanence is 28.3-37.4 emu/g.

2. A preparation method for nano-porous FePt alloys with strong permanent magnetism, comprising: (1) raw materials including Fe, Co, Pt, Pd, B, C, Fe.sub.3P, and Si with a purity of 99 wt. % are weighed and mixed according to a nominal composition of Fe.sub.aC o.sub.bPt.sub.cP d.sub.dB.sub.eC.sub.fP.sub.g Si .sub.h; (2) the alloys containing P and/or C element(s) are prepared into master alloy ingots using high-frequency induction melting under an Ar atmosphere, and P- and C-free alloys are prepared into master alloy ingots using a nonconsumable electric-arc furnace under an Ar atmosphere; the alloys are repeatedly melted for four times to guarantee chemical homogeneity; the master alloy ingots are spun into continuous ribbon samples with a width of about 2 mm and thicknesses of about 10-50 m using a single-roller melt-spinning equipment under an Ar atmosphere, and a ribbon thickness is controlled by a rotational speed of a copper roller; (3) structure and thermal properties of the alloy ribbon samples prepared at different rotational speeds of the copper roller are examined; an annealing temperature of the alloy ribbons is determined in combination of structure and thermal analysis; and if the alloy ribbons contain a nano-composite phase structure of hard magnetic L1.sub.0-FePt and soft magnetic Fe.sub.2B, step (5) is directly performed; otherwise, step (4) is performed; (4) the alloy ribbons are annealed using vacuum heat treatment to obtain ribbon precursors containing a nano-composite phase structure of hard magnetic L1.sub.0-FePt and soft magnetic Fe.sub.2B; (5) nanocrystalline ribbon precursors are dealloyed by an electrochemical workstation, phases mainly including soft magnetic Fe.sub.2B except hard magnetic L1.sub.0-FePt are selectively dissolved, and the nano-porous FePt alloys with permanent magnetism containing a single L1.sub.0-FePt phase are prepared; and (6) structure characterization, morphology observation and magnetic property tests are conducted on the obtained nano-porous alloy; a structure of each of the ribbon samples, the precursor alloys and the dealloyed nano-porous metals is characterized by an X-ray diffractometer and a high-resolution transmission electron microscope; a morphology of the nano-porous metals is observed through a scanning electron microscope; a ligament composition of the nano-porous metals is determined by energy spectrum analysis; thermal properties of the ribbon samples are evaluated by a differential scanning calorimeter; electrochemical properties of the precursor alloys are evaluated by the electrochemical workstation; and magnetic properties of the alloy ribbons and the nano-porous metals are tested using a superconducting quantum interference device; the nano-porous FePt alloys with strong permanent magnetism, wherein the nano-porous alloys are composed of ordered hard magnetic of L1.sub.0-FePt phase and have the chemical composition of Fe.sub.wCo.sub.xPt.sub.yPd.sub.z, w, x, y and z respectively representing atomic percent of each corresponding element in the expression, where 25w55, 0x25, 45w+x55, 45y55, 0z10, 45y+z55, and w+x+y+z=100; the nano-porous alloys are prepared from precursor alloys through a dealloying technique, and have an integrated doubly-connected nano-porous structure with pore sizes of 10-50 nm, and ligament thicknesses of 20-80 nm; an expression of the composition of the precursors for preparing the nano-porous alloys is Fe.sub.aCo.sub.bPt.sub.cPd.sub.dB.sub.eC.sub.fP.sub.gSi.sub.h, a, b c, d, e, f, g and h respectively representing atomic percent of each corresponding element in the expression, where 30a70, 0b30, 40a+b70, 8c40, 0d5, 8c+d40, 10e35, 0f5, 0g5, 0h3, 10e+f+g+h35, and a+b+c+d+e+f+g+h=100; and the nano-porous FePt alloys with strong permanent magnetism, having strong permanent magnetism: under an applied magnetic field of 50 kOe, a coercivity is 13.4-18.5 kOe, a magnetization is 40.4-56.3 emu/g, and a remanence is 28.3-37.4 emu/g.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows an X-ray diffraction (XRD) pattern of a nano-porous FePt alloy obtained by dealloying a Fe.sub.60Pt.sub.10B.sub.30 alloy ribbon after annealing at 823 K for 900 s.

(2) FIG. 2 shows a secondary electron image of a scanning electron microscope (SEM) of a nano-porous FePt alloy obtained by dealloying a Fe.sub.60Pt.sub.10B.sub.30 alloy ribbon after annealing at 823 K for 900 s.

(3) FIG. 3 shows an Energy Dispersive X-Ray (EDX) spectrum composition analysis result of a nano-porous FePt alloy obtained by dealloying a Fe.sub.60Pt.sub.10B.sub.30 alloy ribbon after annealing at 823 K for 900 s.

(4) FIG. 4 shows a hysteresis loop of a nano-porous FePt alloy obtained by dealloying a Fe.sub.60Pt.sub.10B.sub.30 alloy ribbon after annealing at 823 K for 900 s.

DETAILED DESCRIPTION

(5) The specific embodiments of the present invention are further described below in conjunction with the technical solution and the accompanying drawings.

Embodiment 1: Precursor Alloy Composition Fe.SUB.60.Pt.SUB.10.B.SUB.30

(6) Step 1: Material Mixing

(7) Raw materials including Fe, Pt and B with the purity of greater than 99 wt. % are weighed and mixed according to the nominal composition of Fe.sub.60Pt.sub.10B.sub.30.

(8) Step 2: Melting of Master Alloy Ingot and Preparation of Melt-Spun Ribbon

(9) The weighed raw materials are mixed and then put in a water-cooled copper hearth of a non-consumable electric arc melting furnace, and repeatedly melted for four times under an Ar atmosphere to obtain an alloy ingot with homogeneous chemical composition. The master alloy ingot is crushed and then put in a quartz tube with a nozzle diameter of about 0.5 mm, and heated to a molten state through induction melting under an Ar atmosphere. The alloy melt is sprayed onto a copper roller rotating at high speed under a pressure difference, melt-spun at the linear speed of about 25-50 m/s, and a continuous alloy ribbon with a width of about 2 mm and a thickness of about 10-50 m is obtained.

(10) Step 3: Structure Characterization and Thermal Property Evaluation of Melt-Spun Alloy Ribbon

(11) The XRD (Cu-K radiation, =0.15406 nm) and HRTEM results confirm that the structure of the all alloy ribbons obtained at different melt-spinning speeds is amorphous phase. The DSC is used to evaluate the thermal properties of the ribbon. It is determined that the appropriate annealing temperature for the ribbon sample is 823 K in combination with structure analysis result.

(12) Step 4: Preparation of Precursor Alloy

(13) The melt-spun ribbon is put in the quartz tube, vacuumed to less than 210.sup.3 Pa and subsequently sealed. The ribbon sealed within the tube is put in the annealing furnace and annealed at the temperature of 783-863K for 900s, and then taken out and subsequently put in the cool water for quenching. The structure of the annealed alloy ribbon is detected by the XRD and the HRTEM, and the magnetic properties are tested using the SQUID under the maximum applied magnetic field of 50 kOe. In combination with structure and magnetic property analysis results, the alloy ribbon with nano-composite phases of hard magnetic L1.sub.0-FePt and soft magnetic Fe.sub.2B and exhibiting optimum permanent magnetism as obtained by annealing at 823 K is selected as the precursor alloy.

(14) Step 5: Electrochemical Property Test and Dealloying

(15) The room-temperature electrochemical properties of the precursor alloy are evaluated by an electrochemical workstation at a scanning rate of 1 mV/s in a 0.1 mol/L H.sub.2SO.sub.4 solution, thereby measuring that the critical potential of the alloy is about 280 mV (vs Ag/AgCl reference electrode), and the corresponding operating voltage is in the range of 180-45 mV when the current density is 20-50 m A/cm.sup.2. A constant potential mode with a potential of 170 mV is selected to dealloy the precursor alloy, so as to prepare a nano-porous FePt alloy.

(16) Step 6: Structure and Morphology Characterization and Magnetic Property Test of Nano-Porous Alloy

(17) As shown in FIG. 1, the XRD pattern reveals that the prepared nano-porous alloy has a single L1.sub.0-FePt phase. The SEM image shown in FIG. 2 confirms that the alloy has a doubly-connected nano-porous structure, and is integrated in structure and uniform in pore size and ligament thickness, and both the pore size and the ligament thickness are about 20 nm. As shown in FIG. 3, the EDX spectrum analysis indicates that the alloy ligament only contains two elements of Fe and Pt with the chemical composition of Fe.sub.48.2Pt.sub.51.8, and is consistent with the result of the XRD. The magnetic properties of the alloy are tested using the SQUID under an applied magnetic field of 50 kOe. FIG. 4 shows a hysteresis loop of the prepared nano-porous alloy, indicating that the alloy has strong permanent magnetism: the coercivity (.sub.iH.sub.c), magnetization (M.sub.50) and remanence (M.sub.r) under the applied magnetic field of 50 kOe are 18.5 kOe, 52.6 emu/g and 34.0 emu/g, respectively.

Embodiment 2: Precursor Alloy Composition Fe.SUB.52.Pt.SUB.29.B.SUB.19

(18) Steps of material mixing, melting of master alloy ingot, melt-spinning of ribbon sample and characterization of sample structure are the same as steps 1-3 in embodiment 1. The results of the XRD and HRTEM indicate that the ribbon prepared at the melt-spinning speed of 20-37 m/s has a nano-composite phase structure of L1.sub.0-FePt and Fe.sub.2B, and can be used as a precursor alloy for dealloying without heat treatment. Steps of electrochemical property test, dealloying and structure, morphology characterization and magnetic property test of the nano-porous alloy are the same as steps 5 and 6 in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.50.1Pt.sub.49.9, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 16.2 kOe, 51.9 emu/g, and 36.2 emu/g, respectively.

(19) The present embodiment has the advantage that the heat treatment process can be selectively omitted, and the alloy ribbon can be directly dealloyed, so that the technique for preparing the nano-porous FePt alloy is more simple and efficient.

Embodiment 3: Precursor Alloy Composition Fe.SUB.50.Pt.SUB.20.B.SUB.30

(20) The implementation step is the same as that in embodiment 2. The alloy ribbon prepared at the melt-spinning speed of 25-35 m/s has nano-composite phases of L1.sub.0-FePt, Fe.sub.2B and FeB, and does not need the annealing process. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.47.7Pt.sub.52.3, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 16.6 kOe, 47.8 emu/g and 32.8 emu/g, respectively.

Embodiment 4: Precursor Alloy Composition Fe.SUB.45.Pt.SUB.25.B.SUB.30

(21) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.46.5N.sub.53.5, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 14.7 kOe, 43.3 emu/g and 29.6 emu/g, respectively.

Embodiment 5: Precursor Alloy Composition Fe.SUB.60.Pt.SUB.15.B.SUB.25

(22) The implementation step is the same as that in embodiment 1. The nano-porous FePt alloy finally obtained after annealing at 783 K for 900 s contains nano-composite phases of L.sub.10-FePt and Fe.sub.2B, and contains a certain proportion of amorphous phase at the same time. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.49.2N.sub.50.8, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 18.1 kOe, 50.9 emu/g and 35.3 emu/g, respectively.

Embodiment 6: Precursor Alloy Composition Fe.SUB.60.Pt.SUB.20.B.SUB.20

(23) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.52.2N.sub.47.8, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 17.8 kOe, 53.9 emu/g and 37.2 emu/g, respectively.

Embodiment 7: Precursor Alloy Composition Fe.SUB.55.Pt.SUB.25.B.SUB.20

(24) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.52.5N.sub.47.5, and .sub.iH.sub.c, M.sub.50 and M.sub.r are 16.9 kOe, 52.4 emu/g and 33.6 emu/g, respectively.

Embodiment 8: Precursor Alloy Composition Fe.SUB.50.Pt.SUB.30.B.SUB.20

(25) The implementation step is the same as that in embodiment 2. The structure of the alloy ribbon prepared at 35 m/s contains nano-composite phases of L.sub.10-FePt and Fe.sub.2B, and contains a certain proportion of amorphous phase at the same time. The alloy ribbon can be directly dealloyed as a precursor alloy without the annealing process. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.45.3N.sub.54.7, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 15.9 kOe, 50.8 emu/g and 35.6 emu/g, respectively.

Embodiment 9: Precursor Alloy Composition Fe.SUB.40.Pt.SUB.25.B.SUB.35

(26) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.47.2N.sub.52.8, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 14.2 kOe, 40.4 emu/g and 28.3 emu/g, respectively.

Embodiment 10: Precursor Alloy Composition Fe.SUB.70.Pt.SUB.10.B.SUB.20

(27) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.54.5N.sub.45.5, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 13.4 kOe, 56.3 emu/g and 36.2 emu/g, respectively.

Embodiment 11: Precursor Alloy Composition Fe.SUB.30.Co.SUB.30.Pt.SUB.20.B.SUB.20

(28) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.25.6Co.sub.24.8Pt.sub.49.6, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 18.4 kOe, 42.1 emu/g and 30.3 emu/g, respectively.

Embodiment 12: Precursor Alloy Composition Fe.SUB.55.Pt.SUB.20.Pd.SUB.5.B.SUB.20

(29) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.50.8N.sub.39.8Pd.sub.9.4, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 17.0 kOe, 52.9 emu/g and 36.5 emu/g, respectively.

Embodiment 13: Precursor Alloy Composition Fe.SUB.55.Pt.SUB.25.B.SUB.15.C.SUB.5

(30) A master alloy ingot is obtained by high-frequency induction melting under an Ar atmosphere. The remaining implementation steps are the same as those in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.49.4N.sub.50.6, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 17.3 kOe, 51.1 emu/g and 36.4 emu/g, respectively.

Embodiment 14: Precursor Alloy Composition Fe.SUB.55.Pt.SUB.25.B.SUB.15.P.SUB.5

(31) A master alloy ingot is obtained by high-frequency induction melting under an Ar atmosphere. The remaining implementation steps are the same as those in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.46.3N.sub.53.7, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 17.9 kOe, 50.9 emu/g and 35.8 emu/g, respectively.

Embodiment 15: Precursor Alloy Composition Fe.SUB.55.Pt.SUB.25.B.SUB.17.Si.SUB.3

(32) The implementation step is the same as that in embodiment 1. The finally obtained nano-porous FePt alloy has the chemical composition of Fe.sub.45.9N.sub.54.1, and the .sub.iH.sub.c, M.sub.50 and M.sub.r are 15.5 kOe, 53.8 emu/g and 37.4 emu/g, respectively.

(33) Comparison example 1 (Fe.sub.53Pt.sub.44C.sub.3) is selected from the literature [Gopalan et al, J Magn Magn Mater, 322(2010): 3423], and the alloy is a bulk material formed by spark plasma sintering the as-milled powder. The coercivity of the alloy is 11.1 kOe.

(34) Comparison example 2 (Fe.sub.50Pt.sub.50) is selected from the literature [Chen et al, J Magn Magn Mater, 239(2002): 471], and the alloy is a film sample formed by sputtering. The coercivity is 6.5 kOe.

(35) Comparison example 3 (Fe.sub.56Pt.sub.44) is selected from the literature [Sun et al, IEEE T Magn, 37(2001): 1239], and the alloy is in form of nano-particles obtained by chemical deposition. The coercivity is 9.0 kOe.

(36) Compared with the above-mentioned comparison examples, the nano-porous FePt permanent magnets disclosed in the present invention show higher coercivity.

(37) Annexed table: Nano-Porous FePt Alloys with Strong Permanent Magnetism and Precursor Compositions and Magnetic Properties thereof, where .sub.iH.sub.c, M.sub.50 and M.sub.r respectively represent the coercivity, magnetization and remanence under an applied magnetic field of 50 kOe.

(38) TABLE-US-00001 Porous alloy Precursor alloy .sub.iH.sub.c M.sub.50 M.sub.r (at. %) (at. %) (kOe) (emu/g) (emu/g) Remarks Embodiment 1 Fe.sub.48.2Pt.sub.51.8 Fe.sub.60Pt.sub.10B.sub.30 18.5 52.6 34.0 Embodiment 2 Fe.sub.50.1Pt.sub.49.9 Fe.sub.52Pt.sub.29B.sub.19 16.2 51.9 36.2 No need of heat treatment Embodiment 3 Fe.sub.47.7Pt.sub.52.3 Fe.sub.50Pt.sub.20B.sub.30 16.6 47.8 32.8 No need of heat treatment Embodiment 4 Fe.sub.46.5Pt.sub.53.5 Fe.sub.45Pt.sub.25B.sub.30 14.7 43.3 29.6 Embodiment 5 Fe.sub.49.2Pt.sub.50.8 Fe.sub.60Pt.sub.15B.sub.25 18.1 50.9 35.3 Embodiment 6 Fe.sub.52.2Pt.sub.47.8 Fe.sub.60Pt.sub.20B.sub.20 17.8 53.9 37.2 Embodiment 7 Fe.sub.52.5Pt.sub.47.5 Fe.sub.55Pt.sub.25B.sub.20 16.9 52.4 36.6 Embodiment 8 Fe.sub.45.3Pt.sub.54.7 Fe.sub.50Pt.sub.30B.sub.20 15.9 50.8 35.6 No need of heat treatment Embodiment 9 Fe.sub.47.2Pt.sub.52.8 Fe.sub.40Pt.sub.25B.sub.35 14.2 40.4 28.3 Embodiment 10 Fe.sub.54.5Pt.sub.45.5 Fe.sub.70Pt.sub.10B.sub.20 13.4 56.3 36.2 Embodiment 11 Fe.sub.25.6Co.sub.24.8Pt.sub.49.6 Fe.sub.30Co.sub.30Pt.sub.20B.sub.20 18.4 42.1 30.3 Embodiment 12 Fe.sub.50.8Pt.sub.39.8Pd.sub.9.4 Fe.sub.55Pt.sub.20Pd.sub.5B.sub.20 17.0 52.9 36.5 Embodiment 13 Fe.sub.49.4Pt.sub.50.6 Fe.sub.55Pt.sub.25B.sub.15C.sub.5 17.3 51.1 36.4 Embodiment 14 Fe.sub.46.3Pt.sub.53.7 Fe.sub.55Pt.sub.25B.sub.15P.sub.5 17.9 50.9 35.8 Embodiment 15 Fe.sub.45.9Pt.sub.54.1 Fe.sub.55Pt.sub.25B.sub.17Si.sub.3 15.5 53.8 37.4 Comparison Fe.sub.53Pt.sub.44C.sub.3 11.1 Bulk sample example 1 Comparison Fe.sub.50Pt.sub.50 6.5 Film sample example 2 Comparison Fe.sub.56Pt.sub.44 9.0 Nano particles example 3