Flat Soft Magnetic Powder and Production Method Therefor

Abstract

Provided is a flaky soft magnetic powder including an FeSiAl alloy having an oxygen content of 0.6 mass % or less, a manganese content of 0.1 mass % to 1.0 mass %, and the balance incidental impurities. The flaky soft magnetic powder has an average particle size of 43 to 60 m and exhibits a coercive force Hc of 106 A/m or less as measured under application of a magnetic field in an in-plane direction of the flaky soft magnetic powder. The ratio of the tap density to the true density of the flaky soft magnetic powder is 0.17 or less. Also provided is a method of producing the flaky soft magnetic powder. The use of the flaky soft magnetic powder can produce a magnetic sheet having particularly high magnetic permeability.

Claims

1. A flaky soft magnetic powder comprising an FeSiAl alloy having an oxygen content of 0.6 mass % or less, a manganese content of 0.1 mass % to 1.0 mass %, and the balance incidental impurities, wherein the flaky soft magnetic powder has an average particle size of 43 to 60 m and exhibits a coercive force Hc of 106 A/m or less as measured under application of a magnetic field in an in-plane direction of the flaky soft magnetic powder, and the ratio of the tap density to the true density of the flaky soft magnetic powder is 0.17 or less.

2. The flaky soft magnetic powder according to claim 1, wherein the average particle size is 50 to 60 m.

3. The flaky soft magnetic powder according to claim 1, wherein the coercive force Hc is 90 A/m or less.

4. The flaky soft magnetic powder according to any claim 1, wherein the ratio of the tap density to the true density of the flaky soft magnetic powder is 0.11 or less.

5. The flaky soft magnetic powder according to claim 1, wherein the oxygen content is 0.3 mass % or less.

6. The flaky soft magnetic powder according to claim 1, wherein the manganese content is 0.3 mass % to 0.7 mass %.

7. A method of producing the flaky soft magnetic powder according to claim 1, the method comprising the steps of: preparing a raw material powder by gas atomization or disk atomization technique; flattening the raw material powder; and heat-treating the flattened powder at 700 to 900 C. under vacuum or in an argon atmosphere.

8. The method according to claim 7, wherein the flattening step involves wet flattening with an organic solvent, and the organic solvent is added in an amount of 100 parts by mass or more relative to 100 parts by mass of the raw material powder.

9. The method according to claim 7, wherein the flattening step involves the use of a flattening aid in an amount of 5 parts by mass or less relative to 100 parts by mass of the raw material powder.

Description

EXAMPLES

[0038] The present invention will now be described in more detail by way of examples.

[0039] Nos. 1 to 21 (Examples)

[0040] <Preparation of Flaky Powder>

[0041] Powder having a predetermined composition was prepared by a gas atomization or disk atomization process, and then subjected to classification, to prepare raw material powder having a particle size of 150 m or less. In the gas atomization process, an alloy was molten in an alumina crucible, the molten alloy was discharged through a nozzle (diameter: 5 mm) disposed below the crucible, and high-pressure argon gas was sprayed to the molten alloy. The resultant raw material powder was then flattened with an attritor. In the flattening process with an attritor, SUJ2 balls (diameter: 4.8 mm) were placed in an agitation vessel, the raw material powder and industrial ethanol were added to the agitation vessel, and an agitation blade was rotated at 300 rpm. The industrial ethanol was added in an amount of 200 to 500 parts by mass relative to 100 parts by mass of the raw material powder. No flattening aid was used, or a flattening aid was added in an amount of 1 to 5 parts by mass relative to 100 parts by mass of the raw material powder. The flattened powder and the industrial ethanol were removed from the agitation vessel and transferred to a stainless steel dish, followed by drying at 80 C. for 24 hours. The flattened powder was heat-treated under vacuum or in an argon atmosphere at 700 to 900 C. for two hours, to produce a flaky soft magnetic powder. The flaky soft magnetic powder was evaluated for the properties described below. Table 1 illustrates detailed conditions for preparation of the flaky powder.

[0042] <Evaluation of Flaky Powder>

[0043] The resultant flaky powder was evaluated for average particle size, true density, tap density, oxygen content, nitrogen content, and coercive force. The average particle size and the true density were determined by laser diffractometry and the gas replacement method, respectively. For evaluation of the tap density, the flaky powder (about 20 g) was placed in a cylinder (volume: 100 cm.sup.3), and the filling density was determined under the following conditions (drop height: 10 mm, tapping: 200 times). For determination of the coercive force, the flaky powder was placed in a cylindrical resin container having a diameter of 6 mm and a height of 8 mm, and was subjected to the measurement under magnetization in a height direction and a diametrical direction of the container. Since the thickness direction of the flaky powder corresponds to the height direction of the cylindrical container, the coercive force of the flaky powder in a thickness direction is determined under magnetization in the height direction of the container, and the coercive force of the flaky powder in an in-plane direction is determined under magnetization in the diametrical direction of the container. The coercive force was determined under application of a magnetic field of 144 kA/m.

[0044] <Preparation and Evaluation of Magnetic Sheet>

[0045] Chlorinated polyethylene was dissolved in toluene, and the flaky powder was dispersed in the solution. The resultant dispersion was applied to a polyester resin (coating thickness: about 100 m) and dried at ambient temperature and humidity, followed by pressing at 130 C. and 15 MPa, to prepare a magnetic sheet having dimensions of 150 mm by 150 mm by 50 m (thickness). The volume filling ratio of the flaky powder in the magnetic sheet was about 50%. The magnetic sheet was then cut into a toroidal piece having an outer diameter of 7 mm and an inner diameter of 3 mm. The impedance characteristics of the piece were measured with an impedance meter at room temperature and 1 MHz. The magnetic permeability (real part of complex magnetic permeability: ) was calculated on the basis of the measured impedance characteristics. The resultant magnetic sheet was embedded in a resin, and a cross section of the sheet was polished. An image of the cross section was captured with an optical microscope. The lengths of the in plane-direction and thicknesses of 50 particles randomly selected from the microscopic image were measured, and the aspect ratio was determined by averaging the measured length/thickness ratios.

[0046] Nos. 22 to 40 (Comparative Examples)

[0047] A flaky powder was prepared and evaluated and a magnetic sheet was prepared and evaluated as in Nos. 1 to 21, except that the flaky powder was prepared under the conditions illustrated in Table 2.

[0048] The present invention should not be limited to the above-described examples. The results of evaluation are illustrated in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Coer- Coer- Real Amount cive cive part of raw force force of Prepar- mate- Heat- Aver- in in com- Raw ation rial Flat- treat- Heat- age Ratio in- thick- plex material of raw powder/ tening ment treat- part- of tap Oxygen Mn plane ness mag- powder mate- amount aid temper- ment icle density content content direc- direc- netic composition rial of (mass ature atmo- size to true (mass (mass tion tion of No (mass %) powder solvent %) ( C.) sphere (m) density %) %) (A/m) (A/m) sheet Note 1 Fe-9.5Si-.5Al GA 0.25 0 800 Vacuum 55 0.17 0.42 0.91 82 201 170 Examples 2 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 44 0.15 0.51 0.90 93 203 168 of the 3 Fe-8.0Si-7.0Al GA 0.25 0 850 Vacuum 43 0.13 0.45 0.10 88 180 165 present 4 Fe-8.0Si-7.0Al GA 0.25 0 800 Vacuum 55 0.15 0.35 0.23 65 163 180 invention 5 Fe-8.0Si-7.0Al DA 0.25 0 800 Vacuum 55 0.15 0.40 0.35 61 151 179 6 Fe-9.0Si-6.0Al GA 0.30 0 800 Vacuum 46 0.15 0.59 0.13 98 220 166 7 Fe-9.0Si-6.0Al GA 0.50 0 800 Vacuum 46 0.16 0.38 0.45 58 118 180 8 Fe-9.0Si-6.0Al GA 0.50 0 800 Vacuum 46 0.14 0.55 0.70 77 155 175 9 Fe-9.0Si-6.0Al GA 0.50 0 800 Vacuum 43 0.15 0.24 0.96 71 171 173 10 Fe-9.0Si-6.0Al GA 0.25 2 800 Vacuum 48 0.16 0.53 0.25 80 203 171 11 Fe-9.0Si-6.0Al GA 0.25 5 800 Vacuum 49 0.14 0.34 0.31 61 151 179 12 Fe-9.0Si-6.0Al GA 0.25 0 700 Vacuum 55 0.17 0.56 0.31 79 143 175 13 Fe-9.0Si-6.0Al GA 0.25 0 740 Vacuum 55 0.14 0.35 0.77 71 144 177 14 Fe-9.0Si-6.0Al GA 0.25 0 900 Vacuum 55 0.16 0.49 0.55 60 132 184 15 Fe-9.0Si-6.0Al GA 0.25 0 800 Ar 51 0.16 0.59 0.85 102 225 168 16 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 52 0.14 0.47 0.40 55 127 183 17 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 54 0.11 0.28 0.93 73 168 185 18 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 54 0.13 0.43 0.63 65 150 185 19 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 55 0.16 0.53 0.20 88 202 169 20 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 57 0.13 0.43 0.61 60 138 183 21 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 59 0.14 0.35 0.81 73 168 180 Note GA: gas atomization Note DA: disk atomization

TABLE-US-00002 TABLE 2 Real part Coer- Coer- of Amount cive cive com- of raw force force plex mate- Heat- Aver- in in mag- Raw Prepar- rial Flat- treat- Heat- age Ratio in- thick- netic material ation powder/ tening ment treat- part- of tap Oxygen Mn plane ness perme- powder of raw amount aid temper- ment icle density content content direc- direc- ability composition material of (mass ature atmo- size to true (mass (mass tion tion of No (mass %) powder solvent %) ( C.) sphere (m) density %) %) (A/m) (A/m) sheet Note 22 Fe-9.5Si-5.5Al WA 0.25 0 800 Vacuum 47 0.16 1.30 0.31 106 200 160 Compar- 23 Fe-8.0Si-7.0Al GA 0.25 10 800 Vacuum 60 0.15 1.50 0.30 115 268 163 ative 24 Fe-9.0Si-6.0Al GA 0.25 0 800 Air 55 0.15 2.60 0.90 272 630 130 Examples 25 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 55 0.15 1.40 0.10 179 350 153 26 Fe-9.5Si-5.5Al GA 0.60 0 800 Vacuum 40 0.16 0.51 0.20 83 201 159 27 Fe-8.0Si-7.0Al GA 0.70 0 800 Vacuum 35 0.14 0.55 0.45 58 110 159 28 Fe-8.0Si-7.0Al GA 1.00 0 800 Vacuum 30 0.15 0.58 0.55 54 132 160 29 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 40 0.09 1.63 0.60 110 233 163 30 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 35 0.15 0.49 0.50 65 132 161 31 Fe-9.0Si-6.0Al GA 0.25 0 No No 53 0.15 0.26 0.30 731 1830 110 thermal thermal treatment treatment 32 Fe-9.0Si-6.0Al GA 0.25 0 500 Vacuum 53 0.15 0.45 0.20 339 655 151 33 Fe-9.0Si-6.0Al GA 0.25 0 600 Vacuum 53 0.15 0.51 0.45 223 481 154 34 Fe-9.0Si-6.0Al GA 0.25 0 950 Vacuum 53 0.18 0.55 0.31 185 493 155 35 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 49 0.18 0.56 0.70 78 131 160 36 Fe-9.0Si-6.0Al GA 0.25 0 800 Nitrogen 53 0.15 0.34 0.80 203 490 153 37 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 48 0.14 0.47 0.01 137 301 159 38 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 56 0.13 0.28 1.50 221 503 158 39 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 52 0.11 0.53 0.60 210 480 155 40 Fe-9.0Si-6.0Al GA 0.25 0 800 Vacuum 65 0.11 0.53 0.60 78 140 150 Note Underlined numerals and terms fall outside the scope of the present invention Note GA: gas atomization Note WA: water atomization

[0049] In Comparative Example No. 22 illustrated in Table 2, the raw material powder is prepared by water atomization. Thus, the flaky powder has a high oxygen content, resulting in no improvement in magnetic permeability. In Comparative Example No. 23, the addition of an excess amount of the flattening aid leads to prolonged flattening time and thus an increase in oxygen content, resulting in no improvement in magnetic permeability. In Comparative Example No. 24, the heat-treatment in an air atmosphere leads to an increase in oxygen content, resulting in no improvement in magnetic permeability. In Comparative Example No. 25, a high oxygen content results in no improvement in magnetic permeability.

[0050] In Comparative Example Nos. 26 to 28, the ratio of the amount of the raw material powder to that of the solvent is higher than that in the Examples. This leads to no increase in average particle size, resulting in no improvement in magnetic permeability. In Comparative Example No. 29, the long-term flattening leads to a decrease in average particle size and an increase in oxygen content, resulting in no improvement in magnetic permeability. In Comparative Example No. 30, no increase in average particle size results in no improvement in magnetic permeability. In Comparative Example No. 31, no heat-treatment leads to no reduction in coercive force, resulting in no improvement in magnetic permeability.

[0051] In Comparative Example Nos. 32 and 33, a heat-treatment temperature lower than that in the Examples leads to no reduction in coercive force, resulting in no improvement in magnetic permeability. In Comparative Example No. 34, a heat-treatment temperature higher than that in the Examples leads to an increase in tap density/true density ratio and an increase in coercive force caused by agglomeration of powder, resulting in no improvement in magnetic permeability. In Comparative Example No. 35, a flattening period shorter than that in the Examples leads to insufficient flattening of the powder, resulting in no improvement in magnetic permeability. In Comparative Example No. 36, the heat-treatment in a nitrogen atmosphere leads to an increase in coercive force, resulting in no improvement in magnetic permeability.

[0052] In Comparative Example No. 37, a manganese content lower than that in the Examples leads to no reduction in coercive force, resulting in no improvement in magnetic permeability. In Comparative Example No. 38, a manganese content higher than that in the Examples leads to no reduction in coercive force, resulting in no improvement in magnetic permeability. In Comparative Example No. 39, a coercive force higher than that in the Examples results in no improvement in magnetic permeability.

[0053] In Comparative Example No. 40, an average particle size D.sub.50 larger than that in the Examples leads to difficulty in forming the sheet. Thus, the flaky powder exhibits poor orientation, resulting in low magnetic permeability. In contrast, the flaky soft magnetic powders of Example Nos. 1 to 21 (i.e., the flaky soft magnetic powders satisfying the conditions according to the present invention) exhibit significantly advantageous effects. That is, the results demonstrate that the use of each of the flaky soft magnetic powders can produce a magnetic sheet for an electromagnetic wave absorber having sufficiently high magnetic permeability.