Magnetic material and a method of synthesising the same

Abstract

A process for producing Co, Al alloyed NdFeB nanoparticles, by a microwave assisted combustion process, followed by a reduction diffusion process, includes the steps of: preparing a first solution of boric acid dissolved in 4 N HNO.sub.3, dissolving iron nitrate nonahydrate, neodymium nitrate hexahydrate, cobalt nitrate hexahydrate, aluminium nitrate, the first solution in deionized water to form a second solution, adding glycine to the second solution in a molar ratio of 1:1 to form a third solution, subjecting the third solution to microwave radiation, thereby forming an first powder of NdFeCoAlB oxides, mixing the first powder with calcium hydride in a mass ratio of 1:1.1 (NdFeCoAlB oxides:CaH.sub.2) to form a second powder, compacted into a powder block, annealing the second powder in a vacuum furnace, washing the annealed second powder with a solution of ethylenediaminetetraacetic acid; and vacuum drying the second powder.

Claims

1. A process for producing Co, Al alloyed NdFeB nanoparticles, by a microwave assisted combustion process, followed by a reduction diffusion process, the process comprising the steps of: preparing a first solution of boric acid dissolved in 4 N Nitric Acid (HNO.sub.3); dissolving iron nitrate nonahydrate, neodymium nitrate hexahydrate, cobalt nitrate hexahydrate, aluminium nitrate, and the first solution in deionized water to form a second solution; adding glycine to the second solution in a molar ratio of 1:1 to form a third solution; subjecting the third solution to microwave radiation, thereby forming a first powder of NdFeCoAlB oxides; mixing the first powder with calcium hydride in a mass ratio of 1:1.1 (NdFeCoAlB oxides:CaH.sub.2) to form a second powder, compacted into a powder block; annealing the second powder in a vacuum furnace; washing the annealed second powder with a solution of ethylenediaminetetraacetic acid; and vacuum drying the second powder, wherein the solution of ethylenediaminetetraacetic acid is a solution of ethylenediaminetetraacetic acid in methanol and triethanolamine.

2. The process as claimed in claim 1, wherein the step of subjecting the third solution to microwave radiation comprises the step of: subjecting the third solution to microwave radiation of approximately 330 W for a duration of approximately 10 minutes.

3. The process as claimed in claim 1, wherein the step of annealing the second powder in a vacuum furnace, comprises the step of: annealing the second powder in a vacuum furnace at a temperature of 800 C. for 2 hours.

4. The process as claimed in claim 1, wherein the step of washing the annealed second powder with a solution of ethylenediaminetetraacetic acid, comprises the step of: further washing the annealed second powder with methanol.

5. A process for producing Co, Al alloyed NdFeB nanoparticles, by a microwave assisted combustion process, followed by a reduction diffusion process, the process comprising the steps of: preparing a first solution of boric acid dissolved in 4 N Nitric Acid (HNO.sub.3); dissolving iron nitrate nonahydrate, neodymium nitrate hexahydrate, cobalt nitrate hexahydrate, aluminium nitrate, and the first solution in deionized water to form a second solution; adding glycine to the second solution in a molar ratio of 1:1 to form a third solution; subjecting the third solution to microwave radiation, thereby forming a first powder of NdFeCoAlB oxides; mixing the first powder with calcium hydride in a mass ratio of 1:1.1 (NdFeCoAlB oxides:CaH.sub.2) to form a second powder, compacted into a powder block; forming the second powder into a compacted powder block; providing an inert gas atmosphere; and subjecting the compacted powder block to microwave radiation, within the inert gas atmosphere, to form an annealed second powder; washing the annealed second powder; and vacuum drying the second powder.

6. The process as claimed in claim 5, wherein the step of subjecting the compacted powder block to microwave radiation, within the inert gas atmosphere, comprises the preceding step of: positioning the compacted powder block in a silicon carbide (SiC) powder bath.

7. The process as claimed in claim 5, wherein the step of washing the annealed second powder comprises: dissolving ammonium chloride in methanol to form a fourth solution; and washing the annealed second powder in the fourth solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:

(2) FIG. 1 shows the chemical compound of ethylenediaminetetraacetic acid (EDTA);

(3) FIG. 2 shows a schematic representation of the complexants after the reactions of CaO, EDTA and triethanolamine;

(4) FIG. 3 shows a schematic flowchart for a process for producing Co, Al alloyed NdFeB nanoparticles according to a first embodiment of the disclosure;

(5) FIG. 4 shows a schematic flowchart for a process for producing Co, Al alloyed NdFeB nanoparticles according to a second embodiment of the disclosure;

(6) FIG. 5 shows a typical X-ray diffraction pattern for the NdFeCoAlB powder produced by the process of FIG. 3

(7) FIG. 6 shows a typical X-ray diffraction pattern for the NdFeCoAlB powder of FIG. 5 after removal of the CaO by-product;

(8) FIG. 7 shows typical hysteresis loops for NdFeCoAlB powder produced by the process of FIG. 3;

(9) FIG. 8 shows a Transmission Electron Microcopy micrograph of NdFeCoAlB powder produced by the process of FIG. 3; and

(10) FIG. 9 shows a Rietveld refinement of NdFeCoAlB powder produced by the process of FIG. 3.

(11) It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

(12) FIG. 3 illustrates schematically a process for the production of Co, Al alloyed NdFeB nanoparticles according to a first embodiment of the disclosure.

(13) A first solution is prepared by dissolving boric acid in 4N Nitric Acid (HNO.sub.3).

(14) This first solution is then combined with calculated amounts of iron nitrate nonahydrate (Fe(NO.sub.3).sub.3), neodymium nitrate hexahydrate (Nd(NO.sub.3).sub.3), cobalt nitrate hexahydrate (Co(NO.sub.3).sub.2), aluminium nitrate (Al(NO.sub.3).sub.3), and dissolved in deionized water to form a second solution.

(15) Glycine (C.sub.2H.sub.5NO.sub.2) is added to the second solution in a molar ratio of 1:1 (second solution:glycine) to obtain a stable third solution.

(16) The third solution is then subjected to microwave irradiation at a low microwave power of 330 W for 10 minutes. In one example of the process, a Sharp Model R-899R household microwave oven was used to generate the microwave irradiation.

(17) Microwave heating of the third solution results in evaporation of water and other volatiles from the third solution. Due to the exothermic reaction of nitrate salts and glycine the third solution is spontaneously converted to a first powder, being an ultra-fine NdFeCoAlB oxide powder.

(18) The desired Nd.sub.15Fe.sub.59Co.sub.15Al.sub.3B.sub.8 nanoparticles are then synthesized by mixing the first powder (the NdFeCoAlB oxide powder) with calcium hydride (CaH.sub.2) in a mass ratio of 1:1.1 (NdFeCoAlB oxides:CaH.sub.2) to form a second powder, compacted into a block. The second powder is then annealed in a vacuum furnace.

(19) Reduction is then carried out at 800 C. for 2 hours to form a powder containing the desired hard magnetic phase Nd.sub.15Fe.sub.59Co.sub.15Al.sub.3B.sub.8 together with a soft magnetic phase -Fe, with a non-magnetic calcium oxide (CaO) by product, as shown in the x-ray diffraction pattern of FIG. 5.

(20) The annealed second powder is then washed to remove the calcium oxide (CaO) by-product. The annealed second powder is washed with an ethylenediaminetetraacetic acid (EDTA) solution (a solution of ethylenediaminetetraacetic acid in methanol and triethanolamine) to remove the non-magnetic calcium oxide by-product.

(21) The washed annealed second powder is then further washed in methanol. This second washing step is followed by vacuum drying to obtain the dried second powder. FIG. 6 illustrates the x-ray diffraction pattern of the washed second powder after the removal of the CaO by-product.

(22) FIG. 4 illustrates schematically a process for the production of Co, Al alloyed NdFeB nanoparticles according to a second embodiment of the disclosure. The process according to the second embodiment is substantially identical to the process of the first embodiment as described above.

(23) A first solution is prepared by dissolving boric acid in 4N Nitric Acid (HNO.sub.3).

(24) This first solution is then combined with calculated amounts of iron nitrate nonahydrate (Fe(NO.sub.3).sub.3), neodymium nitrate hexahydrate (Nd(NO.sub.3).sub.3), cobalt nitrate hexahydrate (Co(NO.sub.3).sub.2), aluminium nitrate (Al(NO.sub.3).sub.3), and dissolved in deionized water to form a second solution.

(25) Glycine (C.sub.2H.sub.5NO.sub.2) is added to the second solution in a molar ratio of 1:1 (second solution:glycine) to obtain a stable third solution.

(26) The third solution is then subjected to microwave irradiation (for example, using Dawnyx Technologies Pte Ltd, Model HTVF-3) at a low microwave power of 1200 W for 10 minutes.

(27) The first powder (the NdFeCoAlB oxide powder) is then mixed with calcium hydride (CaH.sub.2) in a mass ratio of 1:1.1 (NdFeCoAlB oxides:CaH.sub.2) to form a second powder.

(28) In contrast to the first embodiment, the annealing of the second powder involves the use of microwave radiation to perform the annealing step.

(29) The second powder is formed into a compacted powder block. The compacted powder block is then placed into a powder bed of silicon carbide (SiC). The SiC powder bed is then provided with an insulating sleeve. The SiC powder bed is provided with a stirrer mechanism to agitate the powder bed during the microwave annealing process step.

(30) The SiC powder bed with the compacted powder block of the second powder is placed inside a microwave enclosure. In this arrangement, the microwave irradiation is carried out in an Ar atmosphere. In other arrangements the reduction diffusion may be carried out using a different inert gas.

(31) In this arrangement, the microwave power was controlled to achieve a heating rate of 3 C./minute and an 800 C. temperature. The compacted powder block was held at the 800 C. temperature for a duration of two hours to complete the annealing reaction.

(32) The annealed second powder is then washed to remove the calcium oxide (CaO) by-product. The annealed second powder is washed using a solution of ammonium chloride NH.sub.4Cl in methanol (CH.sub.3OH) to remove the non-magnetic calcium oxide by-product. The washing step is followed by vacuum drying to obtain the dried second powder. FIG. 6 illustrates the x-ray diffraction pattern of the washed second powder after the removal of the CaO by-product.

(33) The magnetic properties at room temperature of the second powder are represented in FIG. 7 for both the as-synthesised material and for the material after the further removal of the CaO by-product.

(34) As illustrated in FIG. 7, after the removal of the calcium oxide by-product, the resultant magnetic properties have been increased by 25% over those of the prior art. The magnetization (Ms) remanence magnetization (Mr) and coercivity (Hc) before and after calcium oxide removal are Ms=37 emu/gm, Mr=23 emu/gm, Hc=12 kOe and Ms=105 emu/gm, Mr=71 emu/gm, Hc=9.2 kOe respectively.

(35) The ratio Mr/Ms is termed reduced remanence and is 0.5 for isotropic magnets. In the present example, the reduced magnetization for the final product of the process of the disclosure is 0.67. Since this value is greater than 0.5 it indicates that the magnetic phases are exchange coupled.

(36) A morphological analysis of the powder material shows the particles are nano sized, as illustrated in the sample micrograph of FIG. 8. The nanoparticles are faceted, with their size varying between 7 nm to 45 nm. The Rietveld refinement of the X-ray diffraction data for the NdFeCoAlB powder (after removal of the CaO by-product) indicates a composition made up of 94% NdFeCOAlB hard magnetic phase and 6% of alpha-Fe soft magnetic phase, as illustrated in FIG. 9.

(37) The average crystallite size calculated from Rietveld refinement of X-ray diffraction pattern was .sup.40 nm for NdFeCoAlB hard magnetic phase and .sup.30 nm for -Fe soft magnetic phase.

(38) Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

(39) The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the disclosure as defined by the accompanying claims.