WO2022038531A1

WO2022038531A1 - A permanent magnetic material and a method for its preparation

Info

Publication number: WO2022038531A1
Application number: PCT/IB2021/057588
Authority: WO
Inventors: Mahesh Kallyadan Veettil; Satya Narayan Malik
Original assignee: Mahindra Cie Automotive Ltd.
Priority date: 2020-08-19
Filing date: 2021-08-18
Publication date: 2022-02-24

Abstract

The present disclosure provides a permanent magnetic material and a method for its preparation. The permanent magnetic material of the present disclosure has a hexagonal magnetoplumbitic crystal structure. The method for preparing the permanent magnetic material is efficient and economical. The method provides strontium ferrite based magnetic material having properties in-line with the commercially available high-grade ferrite magnets and that requires fewer amounts of rare earth metals.

Description

A PERMANENT MAGNETIC MATERIAL AND A METHOD FOR ITS

PREPARATION

FIELD

The present disclosure relates to a permanent magnetic material and a method for its preparation.

DEFINITIONS

As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.

Coercivity (He): The term “coercivity”, also known as the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Coercivity is usually measured in oersted or ampere/meter units and is denoted by He.

Intrinsic coercivity (iHc): The term “intrinsic coercivity” refers to the resistance of a magnetic material to changes in magnetization, equivalent to the field intensity necessary to demagnetize (to make the magnetic polarization to zero) the fully magnetized material. Units of Intrinsic coercivity are A/m (in SI units) and Oersteds, Oe (in cgs units).

Residual magnetic flux density (Br): The term “residual magnetic flux density” also known as residual induction is the magnetic induction corresponding to the zero magnetizing force in a magnetic material after saturation in a closed circuit. Units of Br are tesla, T (SI units) and gauss, G (cgs units).

Magnetic remanence (Mr): The term “magnetic remanence” refers to the magnetization left behind in a ferromagnetic material after an external magnetic field (enough to achieve saturation) is removed.

Saturation magnetization (Ms): The term “saturation magnetization” is a measure of the maximum amount of magnetic field that can be generated by a material. Magnetic saturation is the state reached in a sample when an increase in applied external magnetic field H cannot further increase the magnetization of the material. BACKGROUND

The background information herein below relates to the present disclosure but is not necessarily prior art.

In the field of permanent magnets, the challenge lies in delivering the high magnetic performance with relatively low volume of magnet body for the purpose of miniaturization motors in automobiles and thereby reducing the weight and increasing their efficiency. Rare earth (RE) metals based permanent magnets can meet this requirement in terms of magnetic performance with a low volume. However, due to the geographical constraints, availability and higher cost of the rare earth metal together with the stringent processing methods make the production of these magnets complicated. The RE metal based permanent magnets are very prone to oxidation and therefore always required a protective anti-corrosion coating. All these factors caused high product cost and that fails meeting the expectation of the market. The ferrite magnets are very cheaper due to abundant and low-cost raw materials and relatively simple processing steps. The ferrite magnets are chemically inert and resist demagnetization even at high operating temperature whereas RE magnets are very prone to demagnetization at higher operating temperatures. The cheaper raw materials and process cost, chemical inertness and high operating temperature are the main advantages of ferrite magnets over RE magnets. However, there are constrains in terms of achievable magnetic properties.

Conventionally, the process of preparation of anisotropic ferrite magnets involves the use of ball mill, pulverizer and sintering. In another method, the surfactants are used in the ball milled samples to increase the orientation degree of the crystal grains which in turn improve remanence value of the sintered magnet. The most practical way to achieve maximum remanence value is to achieve sintered density close to the theoretical value of 5.15 g/cc. These are the widely used methods. However, the mass production of the ferrite magnets having a main phase expressed by SrO.nFe2C>3 is difficult for the reasons of lower productivity.

Mn, Co, Ni and Zn are being used for remarkable improvement of the magnetic properties of the ferrite magnets. However, mere addition of these elements destroyed the balance in ion valency and caused formation of undesirable phases. To overcome this, Sr or Ba sites can simultaneously be replaced by different elements for meeting the charge compensation. It has been found that La is also effective in keeping the ion valency balanced, so La, Nd, and Pr may be used. However, for a desired improvement of the magnetic properties of the ferrite magnets a high amount of LaiCL is required during the milling process and the cost of using La2C>3 as raw material is also high.

There is, therefore, felt a need for a permanent magnetic material and a method for its preparation that mitigates the drawbacks mentioned hereinabove.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are as follows.

An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

Another object of the present disclosure is to provide a permanent magnetic material.

Yet another object of the present disclosure is to provide an economical and cost effective method for preparing a permanent magnetic material.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure provides a permanent magnetic material which comprises a hexagonal magnetoplumbitic structure having a chemical formula,

A(i__X’__X”)R_X’M_X”Fe_n-zN_zOi9 wherein, A is essentially Sr, and optionally Ba; R is a rare earth element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu); M is at least one selected from the group consisting of Ca and Mg; N is at least one selected from the group consisting of Co and Zn; n is a mole ratio of Fe to A; and x’, x” and z are number of moles of the respective elements. The present disclosure further provides a method for preparing a permanent magnetic material. The method (100) comprises the following steps: Initially a predetermined amount of a raw material (102) is obtained. The raw material is then homogenized (104) in a milling attritor to obtain a homogenized raw material having a first predetermined particle size. The homogenized raw material is then calcined (106) at a first predetermined temperature for a first predetermined time period to form a pellet having a hexagonal magnetoplumbitic crystal structure. The pellet is then pulverized (108) to obtain a pulverized powder having a second predetermined particle size. A predetermined amount of an additive is added to the pulverized powder to obtain a mixture. The mixture is then subjected to a wet comminution (110) to obtain a slurry having a third predetermined particles size and a predetermined solid content. The slurry is then compacted by pressing in a predetermined magnetic field to orient the magnetic particles in a magnetization direction to obtain a compacted material. The compacted material then undergoes sintering (114) at a second predetermined temperature for a second predetermined time period under air atmosphere to obtain the permanent magnetic material.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present disclosure will now be described with the help of the accompanying drawing, in which:

Figure 1 illustrates a schematic representation for the flow-path of the method in accordance with the present disclosure;

Figure 2 illustrates a graph showing the relations between the amount (wt%) of Cerium oxide added and the magnetic properties- residual magnetic flux density (Br) and intrinsic coercivity (iHc) in Example 1 ;

Figure 3 illustrates a graph showing the relations between the calcination temperature and the final magnetic properties- residual magnetic flux density (Br) and intrinsic coercivity (iHc) in Example 2;

Figure 4 illustrates a graph showing the relations between the amount (wt%) of Cobalt oxide added and the magnetic properties- residual magnetic flux density (Br) and intrinsic coercivity (iHc) in Example 3; Figure 5 illustrates a graph showing the relations between the amount (wt%) of Cerium oxide added and the magnetic properties- residual magnetic flux density (Br) and intrinsic coercivity (iHc) in Example 4; and

Figure 6 illustrates the XRD pattern of the samples of the present disclosure, (a) Sr-Ferrite: Strontium ferrite comparative sample with no Co and Ce, (b) Ce-Sr-Ferrite: Strontium ferrite with Ce addition, and (c) Ce-Co-Sr-Ferrite: Strontium ferrite with Ce and Co addition.

List of Reference Numerals

DETAILED DESCRIPTION

Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.

In a conventional production process of ferrite magnets, it is disclosed that the elements Mn, Co, Ni and Zn are being used for a remarkable improvement in the magnetic properties of the ferrite magnets. However, the mere addition of these elements destroyed the balance in ion valency and caused the formation of undesirable phases. To overcome this, Sr or Ba sites are simultaneously replaced by different elements for meeting the charge compensation. La, Nd, and Pr may be used as it has been found that La is particularly effective. However, for a desired improvement of the magnetic properties of the ferrite magnets a high amount of La2C>3 is required during the milling process and the cost of using LaiCL as raw material is also high.

The present disclosure provides a permanent magnetic material and a method for its preparation.

In an aspect, the present disclosure provides a permanent magnetic material. The permanent magnetic material comprises a hexagonal magnetoplumbitic crystal structure having a chemical formula,

A(i._X’._X”)R_X’M_X”Fe_n-zN_zOi9 wherein n is a mole ratio of Fe to A; and x’, x” and z are number of moles of respective elements.

In accordance with an embodiment of the present disclosure, A is essentially strontium (Sr), and optionally barium (Ba). In an exemplary embodiment, A is Sr.

In accordance with the present disclosure, R is rare earth element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). In an exemplary embodiment, R is cerium (Ce).

In accordance with the present disclosure, M is at least one selected from the group consisting of Ca and Mg. In an exemplary embodiment, M is Ca.

In accordance with the present disclosure, N is at least one selected from the group consisting of Co and Zn. In an exemplary embodiment, N is Co.

In accordance with the present disclosure, n is in the range of 10 to 12. In an exemplary embodiment, n is 11.6.

In accordance with the present disclosure, x’ is in the range of 0.05 to 0.50. In an exemplary embodiment, x’ is 0.125.

In accordance with the present disclosure, x” is in the range of 0 to 0.10. In an exemplary embodiment, x” is 0.027.

In accordance with the present disclosure, z is in the range of 0 to 0.25. In an exemplary embodiment, z is 0.037.

In accordance with the present disclosure, the magnetic material has a residual magnetic flux density (Br) in the range of 4000 G to 4700 G, and intrinsic coercivity (iHc) in the range of 3600 Oe to 5000 Oe. In an embodiment, the Br achieved is 4400 G, and maximum intrinsic coercivity (iHc) is 4900 Oe.

In another aspect, the present disclosure provides a method (100) for preparing a permanent magnetic material.

Initially, a predetermined amount of a raw material (102) is obtained. In accordance with the present disclosure, the raw material is selected from the group consisting of metal precursor and rare earth metal precursor.

The metal precursor is selected from the group consisting of iron oxide, iron chloride, iron carbonate, iron sulphate, strontium carbonate, strontium oxide, strontium sulphate, strontium nitrate, strontium hydroxide, barium oxide, barium carbonate, calcium carbonate, calcium oxide, calcium phosphate, calcium chloride, calcium hydroxide, silica, cobalt oxide, cobalt carbonate, cobalt chloride, cobalt nitrate, cobalt sulphate, cobalt acetate, zinc oxide, zinc carbonate and zinc nitrate. In an exemplary embodiment, the metal precursors for preparing a permanent magnetic material are iron oxide (Fe2Oa), strontium carbonate (SrCCL), calcium carbonate (CaCCh), and cobalt oxide (CO3O4).

The rare earth metal precursor is a metal salt of a rare earth element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). In an embodiment of the present disclosure, the rare earth metal precursor is selected from cerium oxide (CcCL). neodymium oxide (Nd2Oa), niobium oxide (Nl^Ch).

The cerium precursor (rare earth metal precursor) is selected from the group consisting of cerium oxide, cerium carbonate, cerium acetate, cerium nitrate, cerium hydroxide, cerium sulphate. In an exemplary embodiment, the rare earth metal precursor is cerium oxide (CcCL).

In accordance with the present disclosure, the predetermined amount of the raw material is in the range of 90 to 100 wt% with respect to the total weight of the permanent magnetic material. In an exemplary embodiment, the predetermined amount of raw material is 98.5 wt%.

In accordance with the present disclosure, the amount of iron oxide (iron precursor) is in the range of 70 to 90 wt%. In an exemplary embodiment, the amount of iron oxide is 86 wt%.

In accordance with the present disclosure, the amount of strontium carbonate or strontium oxide (strontium precursor) is in the range of 5 to 20 wt%. In an embodiment of the present disclosure, the amount of strontium oxide is 10 wt%. In an exemplary embodiment, the amount of strontium carbonate is 14 wt%. In accordance with the present disclosure, the amount of cerium oxide, cerium carbonate, cerium acetate, cerium nitrate, cerium hydroxide, or cerium sulphate (cerium precursor) is in the range of 0.1 to 10 wt%. In an exemplary embodiment, the amount of cerium oxide is 3 wt%.

In accordance with an embodiment of the present disclosure, the amount of cobalt oxide, cobalt carbonate, cobalt chloride, cobalt nitrate, cobalt sulphate or cobalt acetate (cobalt precursor) is in the range of 0 to 0.5 wt%. In an exemplary embodiment, the amount of cobalt oxide is 0.3 wt%.

In accordance with the present disclosure, the amount of zinc oxide, zinc carbonate and zinc nitrate (zinc precursor) is in the range of 0 to 0.4 wt%. In an exemplary embodiment, the amount of zinc oxide is 0.25 wt%.

In accordance with the present disclosure, the amount of calcium carbonate, calcium oxide, calcium phosphate, calcium chloride or calcium hydroxide (calcium precursor) is in the range of 0.1 to 0.5 wt%. In an embodiment of the present disclosure, the amount of calcium oxide is 0.25 wt%. In an exemplary embodiment, the amount of calcium carbonate is 0.25 wt%.

In accordance with the present disclosure, the amount of silica is in the range of 0.1 to 0.5 wt%. In an exemplary embodiment, the amount of silica is 0.25 wt%.

All the amounts are with respect to the total weight of the permanent magnetic material.

In accordance with the present disclosure, a mole ratio of Fe and A is in the range of 10 to 12. In an exemplary embodiment, the mole ratio of Fe and A (Sr) is 11.6.

In accordance with the present disclosure, a mole ratio of Co to Ce is in the range of 0 to 1.0. In an exemplary embodiment, the mole ratio of Co to Ce is 0.3.

The raw material is then homogenized (104) in a milling attritor to obtain a homogenized raw material having a first predetermined particle size.

The milling attritor is selected from the group consisting of attrition milling, wet ball milling and planetary ball milling.

The first predetermined particle size is an important parameter and has an impact on the effective doping of Ce atom in the magnetic material. In accordance with the present disclosure, the first predetermined particle size is in the range of 0.3 to 0.9 microns. In an exemplary embodiment, the first predetermined particle size is maintained as low as 0.5 pm.

The homogenized raw material is then calcined (106) at a first predetermined temperature for a first predetermined time period to form a pellet having a hexagonal magnetoplumbitic crystal structure.

In accordance with the present disclosure, the first predetermined temperature is in the range of 1100 °C to 1300 °C. In an exemplary embodiment, the first predetermined temperature is 1190 °C.

In accordance with the present disclosure, the first predetermined time period is in the range of 30 minutes to 180 minutes. In an exemplary embodiment, the first predetermined time period is 150 minutes.

The pellet is then pulverized (108) to obtain a pulverized powder having a second predetermined particle size.

The pulverization is performed using vibratory mill or Hardinge mill.

In accordance with the present disclosure, the second predetermined particle size is in the range of 2 to 4 microns. In an exemplary embodiment, the second predetermined particle size is less than 3 microns.

A predetermined amount of an additive is added to the pulverized powder to obtain a mixture.

In accordance with the present disclosure, the additive is selected from the group consisting of vanadium pentoxide, chromium oxide, aluminium oxide, silica, boric acid, cobalt oxide, cobalt carbonate, zinc oxide and zinc carbonate. In an embodiment of the present disclosure, the additive is selected from vanadium pentoxide, chromium oxide, and aluminum oxide. In an exemplary embodiment, the additive is selected from boric acid, vanadium pentoxide, chromium oxide, and silica.

The additives are optionally added to improve the coercivity as well as physical properties of the magnetic material. These additives improve the sintering process, control the grain growth, and enhance the physical strength and magnetic properties of the permanent magnetic material. The predetermined amount of the additive is in the range of 0 to 10 wt% with respect to the total weight of the magnetic material. In an exemplary embodiment, the amount of boric acid is 0.02 wt%, the amount of C^Ch is 0.2 wt%, the amount of V2O5 is 0.1 wt% and the amount of SiCh is 0.35 wt%.

The mixture is then subjected to a wet comminution (110) to obtain a slurry having a third predetermined particle size and a predetermined solid content.

In accordance with the present disclosure, the third predetermined particle size is in the range of 0.5 to 0.9 microns. In an exemplary embodiment, the third predetermined particle size is 0.7 microns.

In accordance with the present disclosure, the predetermined solid content is in the range of 30 to 50%. In an exemplary embodiment, the solid content is 35%.

The slurry is then compacted by pressing in a predetermined magnetic field to orient the magnetic particles in a magnetization direction to obtain a compacted material.

In accordance with the present disclosure, the predetermined magnetic field is in the range of 2 to 12 kG. In an exemplary embodiment, the magnetic field is 5 kG.

The compacted slurry then undergoes sintering (114) at a second predetermined temperature for a second predetermined time period under air atmosphere to obtain the permanent magnetic material.

In accordance with the present disclosure, the second predetermined temperature is in the range of 1100 °C to 1300 °C. In an exemplary embodiment, the second predetermined temperature is 1220 °C.

In accordance with the present disclosure, the second predetermined time period is in the range of 15 minutes to 180 minutes. In an exemplary embodiment, the second predetermined time period is 120 minutes.

The present disclosure provides an improved and low-cost method for producing high grade permanent magnetic material having high residual magnetic flux density (Br) and intrinsic coercivity (iHc). This permanent magnets are extremely suitable for wide varieties of magnet applications wherein high performance and miniature magnet is demanded. Even though the properties of the permanent magnetic material achieved in the present disclosure is in-line with the commercially available high-grade ferrite magnets only, the major advantages of the present disclosure are: i) use of comparatively cheaper rare earth oxide, CcCL (ca. Rs. 240/kg) than the currently used rare earth additive La2C>3 (ca. Rs. 350/kg); ii) the percentage addition of CeC>2 required to achieve similar properties with that of La2C>3 is much lower than the later one; and iii) the magnetic properties matching with one of the starting grades of high-grade series (in which cobalt oxide is used as an active additive) are achieved without the use of costlier cobalt oxide (ca. Rs. 3500/kg).

The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

EXPERIMENTAL DETAILS:

EXPERIMENT 1: Method for the preparation of permanent magnetic material in accordance with the present disclosure (see figure 1)

EXAMPLE 1

Step (i): obtaining raw material (102)

In the present disclosure, the permanent magnetic material was produced by using the raw materials- iron oxide, strontium carbonate, cerium oxide, calcium carbonate, silica, cobalt oxide. In this example effect of cerium at different wt. % on magnetic properties was studied.

Step (ii): Homogenizing step (104)

In this step, iron oxide and strontium carbonate were selected in such a way that Fe to Sr mole ratio was 11.6. Cerium oxide was added at various wt % as shown in the table 1 (figure 2). 0.25 wt % calcium carbonate, 0.25 wt % silica and 0.2 wt % boric acid were also added. T1 provides a comparative conventional material where no cerium was used. Homogenization of all these raw materials was done by attrition in a milling attritor until the particle size was achieved ~0.5 microns (milled powder) as tested by Fisher sub sieve sizer.

Step (iii): Calcination (106)

The so obtained milled powder (homogenized raw material) was calcined in a temperature- controlled furnace at 1190 °C for 150 minutes in air atmosphere to form a pellet.

Step (iv): Coarse crushing/pulverization (108)

The pellets formed in the calcination step was made into coarse crushed powder (pulverized powder) having particles size <4 microns with the help of a pulverizer or vibratory ball mill.

Step (v) and (vi): Fine milling/wet comminution (110)

Other fine additives such as 0.02 wt% of boric acid, 0.2 wt% of CnOs. 0.10 wt% of vanadium pentoxide, and 0.35 wt% SiO2 were added to the coarse crushed powder (pulverized powder) to obtain a mixture. Fine milling of the mixture was done by attrition milling with water as dispersion medium. The particle size of the fine milled slurry was maintained at less than 0.70 microns.

Step (vii): Pressing (112)

Fine milled slurry with 35 to 40 % solid content (after settling and decantation of excess water) was subjected to anisotropic pressing to form a solid cylinder shape test pieces (-12 mm height and 40 mm diameter) in the presence of magnetic field >5 k G and to orient ferrite particles in the easy magnetization direction to obtain a compacted material.

Step (viii): Sintering (114)

The compacted material was then dried enough at room temperature and then fired (sintered) at 1220 °C for 120 minutes in air atmosphere to obtain the permanent magnetic material.

The sintered test piece (the permanent magnetic material) was subjected to surface grinding and polishing to make both the flat surface parallel and the magnetic properties was checked using magnetic properties analyzer (Permagraph instrument).

Table- 1 Trial % CeO₂ % Fe₂O₃ % SrCO₃ % CaCO₃ Br (G) iHc (Oe)

T-l 0.0 86.03 13.72 0.25 4200 3600

T-2 1.0 86.03 13.72 0.25 4240 4070

T-3 1.5 86.03 13.72 0.25 4250 4254

T-4 2.0 86.03 13.72 0.25 4400 4325

T-5 2.5 86.03 13.72 0.25 4140 4090

T-6 3.0 86.03 13.72 0.25 4050 4159

T-7 4.0 86.03 13.72 0.25 4060 4032

It was observed from table 1 that better combination magnetic properties were obtained when the magnetic material contained 2 wt% of CeO₂ (T-4).

EXAMPLE 2 The effect of calcination temperature on the magnetic properties was studied (see figure 3). The best trial material in example 1 (T-4) was selected. Trials were conducted with varying temperatures as mentioned in Table-2.

Table-2

Trial Temp (°C) Br (G) iHc (Oe)

T-8 1150 4280 3825

T-4 1190 4400 4325

T-9 1230 4240 4184

T-10 1270 4370 3853 It was observed from Table 2 that useful combination Br and iHc values were obtained with calcination at a temperature of 1190 ° C. The different combination of magnetic properties can be achieved by increasing or decreasing the calcination temperature.

EXAMPLE-3 The effect of cobalt addition in homogenization step was studied. Various amount of cobalt oxide were added in the homogenization step of the best trial material as described in Example- 1 and the sample preparation was done according to the steps described in example- 1 with T4 trial with different Cobalt oxide % as mention in Table- 3 (figure 4).

Table-3

Trial % Co₃O₄ % CeO₂ % Fe₂O₃ % SrCO₃ Br (G) iHc (Oe)

T-4 0 2 86.03 13.72 4400 4325

T-l l 0.275 2 86.03 13.72 4200 4849

T-12 0.3 2 86.03 13.72 4270 4433

T-13 0.4 2 86.03 13.72 4100 4700

T-14 0.45 2 86.03 13.72 4100 4494

It can be observed that the addition of Co helped to achieve higher iHc values without causing drastic decrease in Br values. It was further observed that the highest iHc values were obtained when CO3O4 wt % was about 0.275 wt%.

EXAMPLE-4 The effect of different wt% of Ce with a fixed amount of Co has been studied. Various amount of Ce were added in the homogenization step of the best trial material as described in Example-3 and sample preparation was done according to the steps described in example- 1. The details are as mention in Table- 4 (see figure 5).

Table-4 Trial % Co₃O₄ % CeO₂ % Fe₂O₃ % SrCO₃ Br (G) iHc (Oe)

T-15 0.275 1 86.03 13.72 4090 4384

T-16 0.275 1.5 86.03 13.72 4250 4307

T-l l 0.275 2 86.03 13.72 4200 4849

T-17 0.275 3 86.03 13.72 4150 4443

It was observed from table 4 that better combination of magnetic properties were achieved when CeO₂ was 2 wt% and CO3O4 was 0.275 wt% (T-l l).

EXAMPLE-5 Magnetic properties with respect to various additives and addition stages are as shown in table 5.

Table 5: Magnetic properties with respect to various additives and addition stages

Conventional

Table 5 shows that the addition of only cerium oxide during red mixing process and with no cobalt oxide either in red milling or later in fine milling process resulted in the final magnetic property with intrinsic coercivity (iHc) greater than 4150 Oe with the residual magnetic flux density (Br) greater than 4300 G. This was further improved to Br greater than 4400 G and iHc of 4325 Oe with cobalt oxide addition along with the above composition later in the fine milling stage. In another experiment, with the addition of cobalt oxide along with cerium oxide in red milling, the coercivity, iHc achieved is greater than 4900 Oe keeping the residual magnetic flux density, Br value above 4050 G. The same composition can be modified to get a combination of Br of 4150 G and iHc greater than 4650 Oe by fine tuning the process parameters and additives composition.

The coarse-crushed calcined powders of comparative sample (Sr-Ferrite), Ce added sample (Ce-Sr-Ferrite), and Co and Ce added (Ce-Co-Sr-Ferrite) were measured with respect to magnetic properties by a vibrating sample magnetometer. The maximum intensity of a magnetic field in which the measurement was carried out was 6T. The values of saturation magnetization (Ms), magnetic remanence (Mr) and coercivity (He) were determined. Also, formed phases were identified by X-ray diffraction and confirmed the formation of strontium ferrite structure (see figure 6). The measurement results are shown in Table-6.

Table-6

Sample ID Ms (emu/g) Mr (emu/g) He (kOe) Formed phase

Sr-Ferrite 76.82 32.70 0.9 M phase

Ce-Sr-Ferrite 70.83 35.05 3.3 M phase

Co-Ce-Sr Ferrite 79.15 37.86 3.5 M phase

It was clear from the results of table 6 that the addition of Ce resulted in the substantial improvement in coercive force (He) and Mr values with no extreme lowering of Ms when compared with the undoped comparative samples. With further addition of Co along with Ce all the magnetic parameters remarkably increased. This can be made into bulk sintered magnets having higher performance than that of comparative example.

TECHNICAL ADVANCEMENTS AND ECONOMICAL SIGNIFICANCE

The present disclosure described herein above has several technical advantages including, but not limited to, the realization of the method for preparing a strontium ferrite based magnetic material that:

- is efficient and economical;

- provides strontium ferrite based magnetic material having properties in-line with the commercially available high-grade ferrite magnets; and

- requires less amount of rare earth metals.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.

The numerical values given for various physical parameters, dimensions, and quantities are only approximate values, and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions, and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.

While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

One of the objects of the Patent Law is to provide protection to new technologies in all fields and domain of technologies. The new technologies shall or may contribute in the country economy growth by way of involvement of new efficient and quality method or product manufacturing in India. To provide the protection of new technologies by patenting the product or process will contribute significant for innovation development in the country. Further by granting patent the patentee can contribute in manufacturing the new product or new process of manufacturing by himself or by technology collaboration or through the licensing.

The applicant submits that the present disclosure will contribute in country economy, which is one of the purposes to enact the Patents Act, 1970. The product in accordance with present invention will be in great demand in country and worldwide due to novel technical features of a present invention is a technical advancement in the magnetic material. The technology in accordance with present disclosure will provide product cheaper, saving in time of total process of manufacturing. The saving in production time will improve the productivity, and cost cutting of the product, which will directly contribute to economy of the country.

The product will contribute new concept in the magnetic material wherein patented process/product will be used. The present disclosure will replace the whole concept of magnetic material being used in this area from decades. The product is developed in the national interest and will contribute to country economy.

The economy significance details requirement may be called during the examination. Only after filing of this Patent application, the applicant can work publically related to present disclosure product/process/method. The applicant will disclose all the details related to the economic significance contribution after the protection of invention.

Claims

CLAIMS:

1. A permanent magnetic material comprises: a hexagonal magnetoplumbitic structure having a chemical formula,

A(i__X’__X”)R_X’M_X”Fe_n-zN_zOi9 wherein,

A is essentially Sr, and optionally Ba;

R is a rare earth element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu);

M is at least one selected from the group consisting of Ca and Mg;

N is at least one selected from the group consisting of Co and Zn; n is a mole ratio of Fe to A; and x’, x” and z are number of moles.

2. The magnetic material as claimed in claim 1, wherein the n is in the range of 10 to 12; the x’ is in the range of 0.05 to 0.50; the x” is in the range of 0 to 0.10; and the z is in the range of 0 to 0.25.

3. The magnetic material as claimed in claim 1, wherein said magnetic material is characterized by a residual magnetic flux density (Br) in the range of 4000 G to 4700 G, and said intrinsic coercivity (iHc) is in the range of 3600 Oe to 5000 Oe.

4. A method for preparing a permanent magnetic material, said method (100) comprises the following steps:

(i) obtaining (102) a predetermined amount of a raw material;

(ii) homogenizing (104) said raw material in a milling attritor to obtain a homogenized raw material having a first predetermined particle size; (iii) calcining (106) said homogenized raw material at a first predetermined temperature for a first predetermined time period to form a pellet having a hexagonal magnetoplumbitic crystal structure;

(iv) pulverizing (108) said pellet to obtain a pulverized powder having a second predetermined particle size;

(v) adding a predetermined amount of an additive to said pulverized powder to obtain a mixture;

(vi) subjecting said mixture to a wet comminution (110) to obtain a slurry having a third predetermined particles size and a predetermined solid content;

(vii) compacting (112) said slurry by pressing in a predetermined magnetic field to orient the magnetic particles in a magnetization direction to obtain a compacted material; and

(viii) sintering (114) the compacted material at a second predetermined temperature for a second predetermined time period under air atmosphere to obtain the permanent magnetic material. The method as claimed in claim 4, wherein said raw material is selected from a metal precursor and a rare earth metal precursor. The method as claimed in claim 4, wherein said raw material is selected from the group consisting of iron oxide, iron chloride, iron carbonate, iron sulphate, strontium carbonate, strontium oxide, strontium sulphate, strontium nitrate, strontium hydroxide, barium oxide, barium carbonate, cerium oxide, cerium carbonate, cerium acetate, cerium nitrate, cerium hydroxide, cerium sulphate, calcium carbonate, calcium oxide, silica, cobalt oxide, cobalt carbonate, cobalt chloride, cobalt nitrate, cobalt sulphate, cobalt acetate, zinc oxide, zinc carbonate and zinc nitrate. The method as claimed in claim 4, wherein a mole ratio of Fe to A is in the range of 10.0 to 12.0; and a mole ratio of Co to Ce is in the range of 0 to 1.0. The method as claimed in claim 4, wherein said additive is selected from the group consisting of vanadium pentoxide, chromium oxide, aluminium oxide, silica, boric acid, cobalt oxide, cobalt carbonate, zinc oxide and zinc carbonate. The method as claimed in claim 4, wherein said predetermined amount of the raw material is in the range of 90 to 100 wt%, and said predetermined amount of the additive is in the range of 0 to 10 wt% with respect to the total weight of the permanent magnetic material.

10. The method as claimed in claim 4, wherein said first predetermined particle size is in the range of 0.3 to 0.9 microns. 11. The method as claimed in claim 4, wherein said first predetermined temperature is in the range of 1100 °C to 1300 °C; and said first predetermined time period is in the range of 30 minutes to 180 minutes.

12. The method as claimed in claim 4, wherein said second predetermined particle size is in the range of 2 to 4 microns. 13. The method as claimed in claim 4, wherein said third predetermined particles size is in the range of 0.5 to 0.9 microns, and said predetermined solid content is in the range of 30 to 50 wt%.

14. The method as claimed in claim 4, wherein said predetermined magnetic field is in the range of 2 to 12 kG. 15. The method as claimed in claim 4, wherein said second predetermined temperature is in the range of 1100 °C to 1300 °C, and said second predetermined time period is in the range of 15 minutes to 180 minutes.