AU2021107330A4 - Rare earth free permanent magnet of sintered ferrite and procedure thereof - Google Patents

Abstract

The embodiments of the present disclosure provide a rare-earth free sintered ferrite magnet. The sintered ferrite magnet provided in the present disclosure have the chemical formula Sro.9. Bao.iCaxAlyCozFei2-y-Oi9. The optimized quaontofa of Ca, Al and Co wre substituted in pure Sro.9Bao.1Fe12O9 to enhance the performance of ferrite magnet. A synthesis method to prepare Sro.9.xBao.iCaxAlyCozFe12-y-zOi9 hexaferrite magnet in bulk form is provided. The sintered ferrite magnet exhibit a substantial maximum energy product of 12.73 MGOe. (a) 7.5 7.0 0 6.5 6.0 5.5 0.0 0.1 0.2 0.3 0.4 Substitution of x =Ca (b)10.0 9.5 -- O 0 9.0 8.5 8.0 0.0 0.1 0.2 0.3 0.4 Substitution of y = Al (C) 13.0 12.5 12.0 0 11.5 m 11.0 10.5 6' 10.0 0.0 0.1 0.2 Substitution of z =Co FIGURE 1(a, b and c)

Description

(a) 7.5

7.0

6.5

6.0

5.5

0.0 0.1 0.2 0.3 0.4 Substitution of x =Ca

(b)10.0 9.5 -- O

9.0

8.5

8.0 0.0 0.1 0.2 0.3 0.4 Substitution of y = Al

(C) 13.0 12.5

12.0

11.5

m 11.0

10.5 6' 10.0 0.0 0.1 0.2 Substitution of z =Co

FIGURE 1(a, b and c)

Rare earth free permanent magnet of sintered ferrite and procedure thereof

TECHNOLOGY

[0001] Embodiments of the present invention relates to an inexpensive ferrite sintered

magnetic material which is rare-earth free and have good energy product.

BACKGROUND

[0002] Permanent magnets (PMs) have great importance in our daily life because of their

applicability in number of devices ranging from toys to sophisticated scientific instruments

such as data storage, motors, mobile communications, generators, transformers, sensors and

actuators, aerospace and defence, to focus electron beams, medical diagnostic devices etc.

[0003] Most widely used hard magnetic materials i.e. PMs are comprise rare-earth and metallic

elements (e.g. Nd2Fe1 4B or SmCo 5 and Sm2Coi 7 ) or noble metals (e.g. L1O-FePt and CoPt).

[0004] Due to growing shortage, and more or less a solitary source of manufacturing, the cost

of rare earth magnets has increased immensely, and will remain to rise. Thus, there is a pressing

need to develop a rare-earth free PMs.

[0005] PMs prepared by utilizing hard ferrites is a candidate for rare-earth free magnet and as

an alternative for metallic magnets since they are very cost-effect and easy to manufacture.

[0006] PMs made from hard ferrites are not as good as alloys, but they are far cheaper and

easier to make.

[0000] Permanent ferrite magnets are usually made as either sintered magnets (a pressed

ceramic powder) or bonded magnets (made as a composite by extrusion or moulding). Bonded

dust magnets, made of hexaferrite in an elastic or plastic binder to make a plastoferrite which

is easily workable and can be cut into any shape, are familiar to all of us as fridge magnets,

both on and inside the door. Magnetic materials for good PMs need to be hard magnetically,

and resistant to demagnetisation. Therefore, they need to have stable domains, and must have

a large remanence and coercivity. A large, square loop with a high energy product is also

preferable, so more energy is needed to demagnetise the material. The M-type ferrites are

ideally suited to such applications.

[0000] Even though they are much less expensive that neodymium magnets, especially with

the large recent increases in cost and production of Nd magnets, ferrites are still extremely

valuable PMs because of the huge volumes produced, accounting for 34% of the global sales

of $11 billion in 2010.

[0000] The global PMs market is expected to grow from USD 34.4 billion in 2021 to USD 54.1

billion by 2026, at a CAGR of 9.5% during the forecast period. The PM industry is growing

due to the rise in demand for PMs from various applications, globally.

[0000] Today the most common uses for hard hexaferrites are still as PMs in refrigerator seal

gaskets, microphones and loud speakers, small motors for cordless appliances and in

automobile applications (a modem car may contain over 100 small hexaferrite-based motors

and sensors). For this reason, M-type hexaferrites account for over 90% of the total permanent magnetic materials manufactured globally, with 50 g of hexaferrite alone produced for every man, woman and child on the planet each year.

[0000] Two increasingly important markets globally for PMs are in motors for electric

powered cars, and generators in wind turbines. As the scarcity and cost of neodymium magnets

increases, hard ferrites will become economically more attractive as magnets for these

applications, despite their inferior properties, especially for smaller wind turbines.

[0000] The application of PMs in hybrid electric vehicles in the automotive industry is growing.

High-performance hybrid electric vehicles require about 2 - 3 kg of rare earth magnets. Hybrid

electric vehicles use both an electric motor and an internal combustion engine to propel the

vehicle. The use of hybrid electric vehicles is expected to increase in regions experiencing high

pollution. Governments are implementing more environmentally friendly electric drive

systems in various regions. In addition, high gasoline prices will also drive the demand for

electric vehicles soon. This would create a huge demand for permanent magnets during the

forecast period.

[0000] In the consumer electronics segment, PMs are used in magnetic heads of Hard Disk

Drives (HDD), CDs, as well as in motors of peripheral devices such as printers, fax machines,

scanners, and photocopies. The increasing usage of cloud computing and related development

resulted in the growing demand for data centers to store enormous amount of data. The growing

demand from data centers for HDD pushes the demand for permanent magnets. These magnets

are also used in air conditioners, washing machines, dryers, cooling fan motors in computers,

fans, microwaves, loudspeakers, and VCR tape drive motors, among others. PMs help enhance

the efficiency of such appliances.

[0000] The ferrite PMs is also known as a sintered ceramic magnet and even as hard ferrite

sintered magnet. They are known as ceramic magnets because they are electrically insulating.

Ferrite permanent magnets exist in two forms - Strontium Ferrite (SrFe12Oi9) magnets and

Barium Ferrite (BaFe12019) Magnets.

[0000] Ferrite PMs are technically known as hard ferrite materials (when exposed to a brief

external magnetic field, the material retains magnetism due to having high coercivity, He).

They are not the same as soft ferrite materials as used in transformer cores (which do not retain

magnetism after exposure to a brief magnetic field because soft ferrite materials have low

coercivity). The high coercive force of ferrite magnets means they are classified as hard

materials, like all the other PMs.

[0000] Ferrite magnets are extremely popular due to their characteristics. Ferrite magnets are

corrosion free - for long term performance they are superb; if looked after they are capable of

exceeding most products lifecycles. Ferrite magnets can be used up to +250 °C (and in some

cases up to +300 °C). Ferrite magnets are also low cost, particularly in high volume production

runs.

[0011] Magnetoplumbite also known as M-type hexaferrite (MFe12Oi9, M = Ba, Sr, Pb) with a

centrosymmetric structure, which is built from four building blocks viz. S, S*, R and R* with

alternately stacking along the easy magnetization c-axis. This hexaferrite belongs to the space

group of P63/mmc, in which the 24 Fe3+ ions distributed in one bipyramidal (2b) sites, one

tetrahedral (4ff) and three octahedral (12k, 4f2 and 2a). Out of the five sublattices, 12k, 2a and

2b have eight Fe3+ ions with the spin in upward while 4fj and 4f2 sites have four Fe3+ ions with the spin in downward, thus the remaining four upward spins possess a net magnetic moment of 20 B at OK. The coupling amongst antiparallel (4fi and 4f2) and parallel (12k, 2a, 2b) sub lattices by super-exchange interactions via 02- ions emerges as ferrimagnetic arrangement. 12k sublattice of M-type hexaferrites is substance to a robust exchange interaction for the account of the linkage amongst R (R*) and S (S*) blocks, and Fe4/2-0-Fe2b, Fe4f1-O-Fe2a,

Fe 3*12k-O-Fe 3*4j2, and Fe 3*12k-O-Fe 3*4 1 triads validate the relatively healthy exchange

coupling.

[0000] The representative magnetic properties of a PM include; saturation magnetization (Ms),

residual magnetization (Mr), residual magnetic flux density (Br), coercivity (He), maximum

energy product ((BH)max), and squareness ratio (Mr/Ms).

[0000] In magnetics, the maximum energy product is an important figure-of-merit for the

strength of a permanent magnet material.

[0000] The maximum energy product is defined based on the magnetic hysteresis saturation

loop (B-H curve), in the demagnetizing portion where the B and H fields are in opposition. It

is defined as the maximal value of the product of B and H along this curve (actually, the

maximum of the negative of the product, -BH, since they have opposing signs):

(BH)max = max(-B - H).

[0000] Equivalently, it can be graphically defined as the area of the largest rectangle that can

be drawn between the origin and the saturation demagnetization B-H curve

[0000] Beside, the M-type PMs are inexpensive and have many other advantages over rare

earth containing neodymium magnets, the lower value of (BH)max of M-type PMs are

remained a challenge for researchers.

SUMMARY

[0000] The embodiments of the present disclosure provide a ferrite material comprising

substituted hexaferrites as a permanent magnet.

[00001 In one embodiment, there is provided a chemical formula of hexaferrite. The hexaferrite

provided in the present disclosure have the chemical formula Sro.f-xBao.iCaxAlyCoFel2-y-zO19

(where, x = 0.0, 0.1, 0.2, 0.3 and 0.4, y = 0.0, 0.1, 0.2, 0.3 and 0.4 and z = 0.0, 0.05, 0.1,

0.15 and 0.20).

[0000] In another embodiment, there is provided a synthesis method to prepare Sro.9

xBao.CaAlyCozFe2-y-zO9 (hereinafter referred to as SBCACFO) hexaferritemate rial in

powder form synthesized by a combination of two synthesis routes; namely sol-gel auto

combustion route followed by conventional high temperature solid-state route.

[0000] According to a further aspect, SBCACFO hexaferrite attains a saturation magnetization

and a higher value of saturation magnetization and coercivity.

[0000] According to a further aspect, SBCACFO hexaferrite attains a maximum energy product

of 12.73 MGOe.

[0000] The foregoing is a non-limiting summary of the invention, which is defined by the

attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0000] Through the following detailed description with reference to the accompanying

drawings, the above and other objectives, features, and advantages of example embodiments

of the present disclosure will become more apparent. Several example embodiments of the

present disclosure will be illustrated by way of example but not limitation in the drawings in

which:

[0000] Fig. 1 schematically illustrates a curve graph of the relation between the magnetization

and applied magnetic field of a SBCACFO hexaferrite material according to the embodiments

of the present disclosure.

[0000] Fig. 2 schematically illustrates a graph showing the change in the maximum energy

product of SBCACFO hexaferrite material according to the embodiments of the present

disclosure and frequency.

DETAILED DESCRIPTION

[0000] Principles and spirits of the present disclosure will now be described with reference to

various example embodiments illustrated in the drawings. It should be appreciated that

description of those embodiments is merely to enable those skilled in the art to better

understand and further implement the present disclosure and is not intended for limiting the

scope disclosed herein in any manner.

[0000] The hexaferrite material of the present invention comprises a primary phase of a

hexagonal structure, wherein the elements constituting the primary phase comprise a

composition represented by the following formula:

Sro.9.xBao.iCaxAlyCozFe12-y-zO9.

x<! 0.4,

! y O0.4

and

O! z ! 0.2.

[0000] It is possible to obtain a high maximum energy product when the content of Ca (calcium,

x) is in the range of 0.0 to 0.4. More preferably, the content of Ca is at x = 0.3. If the content

of Ca is within the above range, it is possible to prevent the problem that the maximum energy

product is reduced since the phase becomes unstable at certain sintering temperatures; or that

the maximum energy product is reduced since the content of substitutional solid solution of Ca

isreduced.

[00001 It is possible to obtain a high saturation magnetization, anisotropic magnetic field and

maximum energy product when the content of Al (Aluminium, y) is in the range of 0.0 to 0.4.

More preferably, the content of Al is at x = 0.3.

[0000] It is possible to obtain a high magnetocrystalline anisotropy and maximum energy

product when the content of Co (cobalt, z) is in the range of 0.0 to 0.2. If the content of Co (z)

is within the above range, it is possible to prevent an increase in the costs and to prevent the

problem that the maximum energy product is reduced since the saturation magnetization and

the anisotropic magnetic field are reduced at the same time due to a decrease in the content of substitutional solid solution of Co or the phase becomes unstable at certain sintering temperatures.

[0000] Properties of the materials, magnetic in particularly, are heavily depend upon the

particle size. The magnetic properties of the hexaferrite is different in 'nano' form as compared

to their bulk counterpart.

[0000] Preparation techniques plays a vital role while governing the size of the particle.

Chemical methods known to produce material in nano-dimension. Among the many chemical

methods, sol-gel auto-combustion method is known to be easy and inexpensive. Importantly,

it has proven faster way to prepare the hexa-ferrite in nano-meter dimension.

[0000] The process for preparing a Sro.9xBao.iCaxAlyCozFe12-y-zOi9ferrite magnetic material

and a sintered magnet according to an embodiment of the present invention is as follows.

[0000] High purity strontium nitrate Sr(N03)2, barium nitrate Ba(N03)2, calcium nitrate

tetrahydrate Ca(N03)2-4H 2 0, aluminium nitrate nanohydrate Al(NO 3) 3 -9H20, cobalt nitrate

hexahydrate Co(NO3)2-6H20 and ferric nitrate (Fe(N03)3.9H20) purchased from Sigma

Aldrich was used as starting materials.

[0000] Citric acid (C 6H 80 7 .H2 0) was used as a chelating agent.

[0000] The weighing of the starting materials were calculated based on their molecular weights.

[0000] The nitrates to citric acid ratio was kept at 1:3, where the amount of citric acid was

obtained from the molecular weight of ferrite compound and citric acid.

[0000] All the starting materials were mixed thoroughly in double distilled water with their

desired stoichiometric proportion.

[0000] The whole mixture was kept on hot plate with magnetic stirrer. The mixture was

continually stirred at a constant temperature of 90 °C.

[0000] Liquid ammonia was slowly poured in order to maintain the pH a constant value 7.

[0000] After continuously stirring and heating for 2-3 hours the mixture become viscous and

sol was formed and after some time it converts into dried gel. By the process of self-combustion

the dried gel was burnt and converted into a fine ash with dark brown in colour.

[0000] The as-obtained material was ground thoroughly using agate mortar and pestle.

[0000] The as-obtained ground material was first annealed at 1100 °C for 6 hours.

[0000] Annealed powder was then ground and was pressed with 5000 kg/cm2 pressure to form

disc shaped pellet of a diameter 10 mm and a thickness of 5 mm.

[0000] The disc shaped pellet was finally sintered at 1300 °C for 12 hours.

[0000] It is possible to use these SBCACFO sintered ferrite pellet as a permanent magnet.

[0000] The process to obtain the structural and magnetic properties of SBCACFO ferrite

magnetic material and a sintered magnet according to an embodiment of the present invention

is as follows.

[0000] It is possible to confirmed the crystallographic structure of SBCACFO by X-ray

diffraction pattern (XRD).

[0000] XRD data confirmed the hexagonal crystallographic structure of sol-gel synthesized

SBCACFO ferrite material. Polycrystalline nature of the particle is evidenced without the

signature of any impurity or secondary phases.

[0000] It is possible to obtain the bulk density 'p' of the SBCACFO sintered magnets by the

Archimedes's principal:

where p is the density of the sample, Wa and W. are the weights of the SBCACFO sintered

magnets in air and in water, respectively.

[0000] The bulk density values of different composition of SBCACFO sintered magnets are

given in Table 1-3.

[0000] In embodiments, it is possible to investigate the magnetic properties of the SBCACFO

sintered magnets by vibrating sample magnetometry.

[0000] The variation in magnetization (M) with applied magnetic field (H), M-H hysteresis

loops, were obtained by applying magnetic field up to ±2.5 T at room temperature.

[0000] Magnetization attains the saturation and exhibit a saturation magnetization (Ms) value.

The values of Ms are presented in Table 1-3.

[0000] SBCACFO sintered magnets possessed hard magnetic structure having coercivity (He)

well-above 5000 Oe. The values of He are presented in Table 1-3.

[0000] Residual magnetization (Mr) of SBCACFO sintered magnets was obtained from the M

H plots and are given in Table 1-3.

[0000] Maximum flux density of SBCACFO sintered magnets was obtained from the M-H

plots and are given in Table 1-3.

Table 1

Example Sample formula p 4xiMs Mr He (BH)Max no. (0 ! x ! 0.4) (g/cm 3) (kG) (emu/g) (kOe) (MGOe) 1 Sro.9Bao.1Fe12O19 5.07 3.98 42.5 6.2 5.58 2 Sro.8Cao.iBao.1Fe12Oi9 5.09 4.11 44.2 6.6 6.10 3 Sro.7Cao.2Bao.1Fe12Oi9 5.12 4.36 48.5 6.8 7.03 4 Sro.6Cao.3Bao.1Fe12O19 5.12 4.45 52.3 6.9 7.53 Sro.5Cao.4Bao.1Fe12Oi9 5.13 4.41 48.2 7.0 7.15

Table 2

Example Sample formula p 4xiMs Mr He (BH)Max no. (0 ! y ! 0.4) (g/cm 3 ) (kG) (emu/g) (kOe) (MGOe) 6 Sro. 6 Cao.3Bao.iAlo.1Feii.9019 5.14 4.67 54.2 7.2 8.20 7 Sro.6 Cao.3Bao.iAlo.2Feii.809 5.15 4.81 57.2 7.3 9.01 8 Sro.6Cao.3Bao.iAlo.3Fell. 7 0 1 9 5.14 4.95 59.4 7.5 9.55 9 Sro.6 Cao.3Bao.iAlo. 4Feii. 60 1 9 5.13 4.87 59.1 7.6 9.50

Table 2

Example Sample formula p 4xiMs Mr He (BH)Max no. (0 ! z ! 0.2) (g/cm3 ) (kG) (emu/g) (kOe) (MGOe) 10 Sro.6Cao.3Bao.iAlo.3Coo.o 5Feii. 65 0 19 5.15 5.03 60.4 7.9 10.29 11 Sro.6Cao.3Bao.iAlo.3Coo.1Feii. 60 19 5.13 5.13 62.5 8.4 11.28 12 Sro.6Cao.3Bao.iAlo.3Coo.i 5Fell.5 5 0 19 5.14 5.19 65.5 9.1 12.73 13 Sro.6Cao.3Bao.iAlo.3Coo.2Fell. 5 0 1 9 5.12 5.15 64.1 9.2 12.64

[0000] Variation of calculated maximum flux density of SBCACFO sintered magnets with

calcium, aluminium and cobalt substitution in SBCACFO is shown in Fig. 1 (a-c).

[0000] SBCACFO sintered magnets can be fabricated in any shape and dimension, for e.g.

circular disc or in rectangular pieces, Fig. 2 (a and b).

[0000] Although, the present disclosure has been described with reference to various

embodiments, it should be understood that the present disclosure is not limited to the disclosed

embodiments. Particularly, the present disclosure is intended to cover various modifications

and equivalent arrangements included in the spirit and scope of the appended claims.

[00001 The reference to any prior art in this specification is not, and should not be taken as, an

acknowledgement or any form of suggestion that such prior art forms part of the common

general knowledge.

EDITORIAL NOTE 2021107330

There are 2 pages of claims only.

Claims (1)

1. A sintered hexaferrite for permanent magnet application comprising:

a material of a stoichiometric chemical formula,

the hexaferrite material is prepared by sol-gel auto-combustion route, followed by solid

state sintering process,

the sintered hexaferrite magnet having the magnetization changes with applied

magnetic field.

2. The sintered SBCACFO hexaferrite magnet according to Claim 1, a stoichiometric

chemical formula for hexaferrite material comprising, strontium (Sr), barium (Ba),

calcium (Ca), aluminium (Al), cobalt (Co) and iron (Fe) elements represented by the

formula;

Sro.9-xBao.iCaxAlyCozFe12-y-zOi9.

wherein,

0 ! x ! 0.4,

0O! y ! 0.4

and

0O! z ! 0.2.

where x = 0.0, 0.1, 0.2, 0.3 and 0.4, y = 0.0, 0.1, 0.2, 0.3 and 0.4 and z = 0.0, 0.05,

0.1, 0.15 and 0.20

3. The prepared sintered SBCACFO hexaferrite magnet do not comprises any rare-earth

element.

4. The sintered SBCACFO hexaferrite magnet according to Claim 1 and 2, a sintered

hexaferrite magnet, has a maximum energy product ((BH)max) of 12.73 MGOe or

more, while the saturation magnetization (4xMs) is 5.19 kG or more and the coercivity

is 9.2 kOe or more.

5. The sintered SBCACFO hexaferrite magnet according to Claim 1, higher value of

maximum energy product is beneficial for prepared sintered hexaferrite for permanent

magnet application.

6. The sintered SBCACFO hexaferrite magnet according to Claim 1 and 2, a sintered

hexaferrite magnet exhibit a higher magnetization, residual magnetization, coercivity

and maximum energy product for calcium substitution of x = 0.3.

7. The sintered SBCACFO hexaferrite magnet according to Claim 1 and 2, a sintered

hexaferrite magnet exhibit a higher magnetization, residual magnetization, coercivity

and maximum energy product for aluminium substitution of x = 0.3.

8. The sintered SBCACFO hexaferrite magnet according to Claim 1 and 2, a sintered

hexaferrite magnet exhibit a higher magnetization, residual magnetization, coercivity

and maximum energy product for cobalt substitution of x = 0.15 to 0.2.

(a) 7.5

7.0

(BH)Max (MGOe) 6.5

6.0 2021107330

5.5

0.0 0.1 0.2 0.3 0.4 Substitution of x = Ca

10.0 (b) 9.5 (BH)Max (MGOe)

9.0

8.5

8.0 0.0 0.1 0.2 0.3 0.4 Substitution of y = Al

(c) 13.0 12.5 (BH)Max (MGOe)

12.0

11.5

11.0

10.5

10.0 0.0 0.1 0.2 Substitution of z = Co

FIGURE 1 (a, b and c)

20 mm 2021107330

(a) 10 mm

10 mm

(b) 5 mm

FIGURE 2 (a and b)