Patent Grant
11017925
The present invention relates to a soft magnetic powder, a powder magnetic core, a magnetic element, and an electronic device.
Recently, the reduction in the size and weight of mobile devices such as notebook-type personal computers has advanced. However, in order to achieve both a reduction in size and an enhancement of performance at the same time, it is necessary to increase the frequency of a switched-mode power supply. Currently, the driving frequency of a switched-mode power supply has been increased to several hundred kilo hertz or more. However, accompanying this, a magnetic element such as a choke coil or an inductor which is built in a mobile device also needs to be adapted to cope with the increase in the frequency.
For example, JP-A-2004-349585 discloses a powder magnetic core, which is a powder magnetic core containing a magnetic powder having a composition represented by Fe(100-x-Y-z-α-β)BXSiYCuZMαM′β (at %) (wherein M is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti, and Mo, M′ is at least one element selected from the group consisting of V, Cr, Mn, Al, a platinum group element, Sc, Y, Au, Zn, Sn, Re, and Ag, and X, Y, Z, α, and β satisfy the following formulae: 12≤X≤15, 0<Y≤15, 0.1≤Z—3, 0.1≤α≤30, and 0≤β≤10, respectively), wherein the magnetic powder is either a nanocrystalline magnetic powder in which at least 50% or more of the structure is a nanocrystalline structure having a crystalline particle diameter of 100 nm or less or an amorphous magnetic powder having a composition capable of exhibiting the nanocrystalline structure by a heat treatment.
A magnetic powder having such a nanocrystalline structure can be adapted to cope with the increase in the frequency due to excellent soft magnetic properties.
However, in the powder magnetic core described in JP-A-2004-349585, the magnetic permeability of the magnetic powder is slightly low. Therefore, when a green compact such as a powder magnetic core is formed, it has a problem with the magnetic properties.
An advantage of some aspects of the invention is to provide a soft magnetic powder capable of producing a green compact which has a high magnetic permeability, a powder magnetic core and a magnetic element, each of which has favorable magnetic properties, and an electronic device which includes this magnetic element and has high reliability.
The advantage is achieved by the following aspects of the invention.
A soft magnetic powder according to an aspect of the invention has a composition represented by Fe100-a-b-c-d-e-fCuaSibBcMdM′eXf (at %) (wherein M is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, and Mo, M′ is at least one element selected from the group consisting of V, Cr, Mn, a platinum group element, Sc, Y, Au, Zn, Sn, and Re, X is at least one element selected from the group consisting of C, P, Ge, Ga, Sb, In, Be, and As, and a, b, c, d, e, and f are numbers that satisfy the following formulae: 0.1≤a≤3, 0<b≤30, 0<c≤25, 5≤b+c≤30, 0.1≤d≤30, 0≤e≤10, and 0≤f≤10), wherein a crystalline structure having a particle diameter of 1 nm or more and 30 nm or less is contained in an amount of 40 vol % or more, and when the apparent density is assumed to be 100, the tap density is 103 or more and 130 or less.
According to this configuration, a soft magnetic powder which has a high magnetic permeability is obtained, and therefore, by using such a soft magnetic powder, for example, a green compact which has improved magnetic properties can be produced.
In the soft magnetic powder according to the aspect of the invention, it is preferred that the composition is represented by Fe100-a-b-c-d-e-fCuaSibBcMdM′eXfAlgTih (at %), and g and h are numbers that satisfy the following formulae: 0.002≤g≤0.032 and 0≤h≤0.038.
According to this configuration, the magnetic permeability of the soft magnetic powder can be further increased. As a result, a green compact which has reduced iron loss and has a high magnetic permeability is obtained.
In the soft magnetic powder according to the aspect of the invention, it is preferred that the volume resistivity of a green compact in a compacted state is 1 kΩ·cm or more and 500 kΩ·cm or less.
According to this configuration, the particles of the soft magnetic powder are sufficiently insulated from each other, and therefore, the amount of insulating material can be reduced, and thus, the proportion of the soft magnetic powder in a powder magnetic core or the like can be increased by that amount and maximized. As a result, a powder magnetic core which highly achieves both high magnetic properties and low loss at the same time can be realized.
In the soft magnetic powder according to the aspect of the invention, it is preferred that the powder further contains an amorphous structure.
According to this configuration, the crystalline structure and the amorphous structure cancel out magnetostriction, and therefore, the magnetostriction of the soft magnetic powder can be further decreased. As a result, a soft magnetic powder having a particularly high magnetic permeability is obtained. In addition, a soft magnetic powder capable of easily controlling magnetization is obtained.
A powder magnetic core according to an aspect of the invention includes the soft magnetic powder according to the aspect of the invention.
According to this configuration, a powder magnetic core which has improved magnetic permeability is obtained.
A magnetic element according to an aspect of the invention includes the powder magnetic core according to the aspect of the invention.
According to this configuration, a magnetic element which has enhanced performance is obtained.
An electronic device according to an aspect of the invention includes the magnetic element according to the aspect of the invention.
According to this configuration, an electronic device which has high reliability is obtained.
Embodiments of the invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, a soft magnetic powder, a powder magnetic core, a magnetic element, and an electronic device according to the invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
Soft Magnetic Powder
The soft magnetic powder according to the invention is a metal powder having soft magnetism. Such a soft magnetic powder can be applied to any purpose for which soft magnetism is utilized, and is used for, for example, producing a powder magnetic core by binding the particles to one another through a binding material and also by molding the powder into a given shape. Since the magnetic permeability of the soft magnetic powder is high, the thus obtained powder magnetic core has favorable magnetic properties.
The soft magnetic powder according to the invention is a powder having a composition represented by Fe100-a-b-c-d-e-fCuaSibBcMdM′eXf (at %). Here, M is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, and Mo, M′ is at least one element selected from the group consisting of V, Cr, Mn, a platinum group element, Sc, Y, Au, Zn, Sn, and Re, X is at least one element selected from the group consisting of C, P, Ge, Ga, Sb, In, Be, and As, and a, b, c, d, e, and f are numbers that satisfy the following formulae: 0.1≤a≤3, 0<b≤30, 0<c≤25, 5≤b+c≤30, 0.1≤d≤30, 0≤e≤10, and 0≤f≤10.
Further, in the soft magnetic powder according to the invention, a crystalline structure having a particle diameter (crystalline particle diameter) of 1 nm or more and 30 nm or less is contained in an amount of 40 vol % or more, and when the apparent density is assumed to be 100, the tap density is 103 or more and 130 or less.
Such a soft magnetic powder has a high magnetic permeability, and therefore, a powder magnetic core which has improved magnetic properties can be produced.
Hereinafter, the composition of the soft magnetic powder according to the invention will be described in detail.
Fe has a large effect on the basic magnetic properties and mechanical properties of the soft magnetic powder according to the invention.
Cu tends to be separated from Fe when producing the soft magnetic powder according to the invention from a raw material, and therefore causes a fluctuation in the composition, and thus, a region which is easily crystallized is formed partially. As a result, an Fe phase with a body-centered cubic lattice which is relatively easily crystallized is promoted, and thus, Cu can facilitate the formation of the crystalline structure having a small particle diameter as described above.
The content (a) of Cu is set to 0.1 at % or more and 3 at % or less, but is preferably set to 0.3 at % or more and 2 at % or less. When the content (a) of Cu is less than the above lower limit, the micronization of the crystalline structure is impaired, and therefore, there is a fear that the crystalline structure having a particle diameter within the above range cannot be formed. On the other hand, when the content (a) of Cu exceeds the above upper limit, there is a fear that the mechanical properties of the soft magnetic powder may be deteriorated, resulting in embrittlement.
Si promotes amorphization when producing the soft magnetic powder according to the invention from a raw material. Therefore, when producing the soft magnetic powder according to the invention, first, a homogeneous amorphous structure is formed, and thereafter, the amorphous structure is crystallized, whereby a crystalline structure having a more uniform particle diameter is easily formed. Then, the uniform particle diameter contributes to the averaging out of magnetocrystalline anisotropy in each crystalline particle, and therefore, the coercive force can be decreased and also the magnetic permeability can be increased, and thus, the improvement of soft magnetism can be achieved.
The content (b) of Si is set to more than 0 at % and 30 at % or less, but is preferably set to 5 at % or more and 20 at % or less. When the content (b) of Si is less than the above lower limit, amorphization is insufficient, and therefore, there is a fear that it becomes difficult to form a crystalline structure having a small and uniform particle diameter. On the other hand, when the content (b) of Si exceeds the above upper limit, there is a fear that the deterioration of the magnetic properties such as saturation magnetic flux density, maximum magnetic moment, and magnetic permeability or the deterioration of the mechanical properties may be caused.
B promotes amorphization when producing the soft magnetic powder according to the invention from a raw material. Therefore, when producing the soft magnetic powder according to the invention, first, a homogeneous amorphous structure is formed, and thereafter, the amorphous structure is crystallized, whereby a crystalline structure having a more uniform particle diameter is easily formed. Then, the uniform particle diameter contributes to the averaging out of magnetocrystalline anisotropy in each crystalline particle, and therefore, the coercive force can be decreased and also the magnetic permeability can be increased, and thus, the improvement of soft magnetism can be achieved. Further, by using Si and B in combination, based on the difference in atomic radius between Si and B, it is possible to synergistically promote amorphization.
The content (c) of B is set to more than 0 at % and 25 at % or less, but is preferably set to 3 at % or more and 20 at % or less. When the content (c) of B is less than the above lower limit, amorphization is insufficient, and therefore, there is a fear that it becomes difficult to form a crystalline structure having a small and uniform particle diameter. On the other hand, when the content (c) of B exceeds the above upper limit, there is a fear that the deterioration of the magnetic properties such as saturation magnetic flux density, maximum magnetic moment, and magnetic permeability or the deterioration of the mechanical properties may be caused.
Further, the total content of Si and B is defined and set to 5 at % or more and 30 at % or less, but is preferably set to 10 at % or more and 25 at % or less.
M is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, and Mo. When a powder containing an amorphous structure in a large amount is subjected to a heat treatment, M contributes to the micronization of the crystalline structure along with Cu. Therefore, M can facilitate the formation of the crystalline structure having a small particle diameter as described above.
The content (d) of M is set to 0.1 at % or more and 30 at % or less, but is preferably set to 0.5 at % or more and 20 at % or less. Further, in a case where the powder contains a plurality of elements as M, the total content of the plurality of elements is set within the above range. When the content (d) of M is less than the above lower limit, the micronization of the crystalline structure is impaired, and therefore, there is a fear that the crystalline structure having a particle diameter within the above range cannot be formed. On the other hand, when the content (d) of M exceeds the above upper limit, there is a fear that the mechanical properties of the soft magnetic powder may be deteriorated, resulting in embrittlement.
Further, it is particularly preferred that M includes Nb. Nb particularly largely contributes to the micronization of the crystalline structure.
The soft magnetic powder according to the invention may further contain at least one element of M′ and X, each of which is an arbitrary element, and Al and Ti as needed other than the essential elements as described above.
M′ is at least one element selected from the group consisting of V, Cr, Mn, a platinum group element, Sc, Y, Au, Zn, Sn, and Re. Such M′ enhances the magnetic properties of the soft magnetic powder, and also enhances corrosion resistance. The platinum group element refers to any of six elements in periods 5 and 6 and in groups 8, 9, and 10 in the elemental periodic table, and is specifically at least one element of Ru, Rh, Pd, Os, Ir, and Pt.
The content (e) of M′ is set to 0 at % or more and 10 at % or less, but is preferably set to 0.1 at % or more and 5 at % or less. When the content (e) of M′ exceeds the above upper limit, there is a fear that the deterioration of the magnetic properties such as saturation magnetic flux density, maximum magnetic moment, and magnetic permeability or the deterioration of the mechanical properties may be caused.
Further, it is particularly preferred that M′ includes Cr. Cr suppresses the oxidation of the soft magnetic powder, and therefore can particularly suppress the deterioration of the magnetic properties or the deterioration of the mechanical properties accompanying oxidation.
X is at least one element selected from the group consisting of C, P, Ge, Ga, Sb, In, Be, and As. Such X promotes amorphization when producing the soft magnetic powder according to the invention from a raw material in the same manner as B. Therefore, X contributes to the formation of the crystalline structure having a more uniform particle diameter in the soft magnetic powder.
The content (f) of X is set to 0 at % or more and 10 at % or less, but is preferably set to 0.1 at % or more and 5 at % or less. When the content (f) of X exceeds the above upper limit, there is a fear that the deterioration of the magnetic properties such as saturation magnetic flux density, maximum magnetic moment, and magnetic permeability or the deterioration of the mechanical properties may be caused.
Al promotes the formation of the crystalline structure having a uniform particle diameter in the particles of the soft magnetic powder by adding Al in a small amount.
The content (g) of Al is set to preferably 0.002 at % or more and 0.032 at % or less, more preferably 0.004 at % or more and 0.024 at % or less, further more preferably 0.006 at % or more and 0.019 at % or less. If the content (g) of Al exceeds the above upper limit, when the soft magnetic powder according to the invention is produced from a raw material, amorphization is likely to be inhibited. Therefore, when the crystalline structure is finally formed in the particles of the soft magnetic powder, the particle diameter thereof is likely to be non-uniform, and there is a fear that the magnetic properties such as magnetic permeability may be deteriorated. On the other hand, when the content (g) of Al is less than the above lower limit, although amorphization is promoted, it becomes difficult to make the crystallization proceed uniformly in the crystallization treatment. Due to this, the particle diameter of the crystalline structure to be formed is likely to be non-uniform, and therefore, there is a fear that the magnetic properties such as magnetic permeability may be deteriorated.
Ti promotes the formation of the crystalline structure having a uniform particle diameter in the particles of the soft magnetic powder by adding Ti in a small amount.
The content (h) of Ti is set to preferably 0 at % or more and 0.038 at % or less, more preferably 0.002 at % or more and 0.025 at % or less, further more preferably 0.004 at % or more and 0.020 at % or less. If the content (h) of Ti exceeds the above upper limit, when the soft magnetic powder according to the invention is produced from a raw material, amorphization is likely to be inhibited. Therefore, when the crystalline structure is finally formed in the particles of the soft magnetic powder, the particle diameter thereof is likely to be non-uniform, and there is a fear that the magnetic properties such as magnetic permeability may be deteriorated. On the other hand, when the content (h) of Ti is less than the above lower limit, although amorphization is promoted, it becomes difficult to make the crystallization proceed uniformly in the crystallization treatment. Due to this, the particle diameter of the crystalline structure to be formed is likely to be non-uniform, and therefore, there is a fear that the magnetic properties such as magnetic permeability may be deteriorated.
In a case where arbitrary elements Al and Ti as described above are added, Al and Ti are added to the above-mentioned compositional formula, and the composition of the soft magnetic powder according to the invention is represented by Fe100-a-b-c-d-e-fCuaSibBcMdM′eXfAlgTih (at %). At this time, g and h are numbers that satisfy the following formulae: 0.002≤g≤0.032 and 0≤h≤0.038 as described above. In such a soft magnetic powder, by optimizing the balance between amorphization and crystallization in the production, the magnetic properties such as magnetic permeability are enhanced. As a result, a powder magnetic core which has reduced iron loss and a high magnetic permeability can be produced.
The existing ratio of Al to Ti, that is, g/h is not particularly limited, but is preferably about 0.1 or more and 10 or less, more preferably about 0.3 or more and 8 or less, further more preferably about 0.5 or more and 6 or less. When the value of g/h is within the above range, a favorable balance between the probability of irregular shape generation and the frictional resistance on the surface of the particle is achieved, and therefore, the packing factor of the soft magnetic powder when it is compacted is increased. Due to this, a green compact which has particularly high magnetic permeability and saturation magnetic flux density is obtained.
Further, in the soft magnetic powder, O (oxygen) may be intentionally added, however, O may be unintentionally mixed therein as an impurity. In the soft magnetic powder according to this embodiment, the content of O (oxygen) in mass ratio is preferably 50 ppm or more and 700 ppm or less, more preferably 100 ppm or more and 650 ppm or less, further more preferably 200 ppm or more and 600 ppm or less. By controlling the content of O within the above range, the coercive force of the soft magnetic powder can be decreased. Accordingly, the iron loss of a powder magnetic core or a magnetic element can be reduced. Further, also the insulating property between the particles of the soft magnetic powder is easily ensured.
When the content of O is less than the above lower limit, it becomes difficult to stably produce the soft magnetic powder having such a low oxygen concentration, and therefore, there is a fear that problems may occur in the production cost or the production yield. Further, depending on the alloy composition of the soft magnetic powder or the like, the insulating property between the particles is deteriorated, and therefore, there is a fear that the eddy current loss may be increased. On the other hand, when the content of O exceeds the above upper limit, depending on the material composition of the soft magnetic powder or the like, the coercive force is increased, and therefore, there is a fear that the hysteresis loss may be increased.
The content of O is a value measured at a stage before performing a heating treatment such as a crystallization treatment in the below-mentioned method for producing the soft magnetic powder.
In order to set the content of O in the soft magnetic powder within the above range, for example, a material having a low oxygen concentration or a material having a high oxygen concentration may be used as the raw material to be used. That is, by using a material having a low oxygen concentration as the raw material, the content of O in the soft magnetic powder can be decreased, and on the other hand, by using a material having a high oxygen concentration as the raw material, the content of O in the soft magnetic powder can be increased.
Hereinabove, the composition of the soft magnetic powder according to the invention has been described in detail, however, this soft magnetic powder may contain elements (for example, S, N, etc.) other than the above-mentioned elements. In such a case, the total content of such elements other than the above-mentioned elements is preferably less than 0.1 at %. Such elements other than the above-mentioned elements may be contained without regard to whether they are contained inevitably or intentionally as long as the total content thereof is within this range.
The composition of the soft magnetic powder can be determined by, for example, Iron and steel—Atomic absorption spectrometric method specified in JIS G 1257 (2000), Iron and steel—ICP atomic emission spectrometric method specified in JIS G 1258 (2007), Iron and steel—Method for spark discharge atomic emission spectrometric analysis specified in JIS G 1253 (2002), Iron and steel—Method for X-ray fluorescence spectrometric analysis specified in JIS G 1256 (1997), gravimetry, titrimetry, and absorption spectroscopy specified in JIS G1211 to G 1237, or the like. Specifically, for example, an optical emission spectrometer for solids (a spark emission spectrometer, model: Spectrolab, type: LAVMB08A) manufactured by SPECTRO Analytical Instruments GmbH or an ICP device (model: CIROS-120) manufactured by Rigaku Corporation is used.
Further, when C (carbon) and S (sulfur) are determined, particularly, an infrared absorption method after combustion in a stream of oxygen (after combustion in a high-frequency induction heating furnace) specified in JIS G 1211 (2011) is also used. Specifically, a carbon/sulfur analyzer, CS-200 manufactured by LECO Corporation can be used.
Further, when N (nitrogen) and O (oxygen) are determined, particularly, Iron and steel—Method for determination of nitrogen content specified in JIS G 1228 (2006) and Method for determination of oxygen content in metallic materials specified in JIS Z2613 (2006) are also used. Specifically, an oxygen/nitrogen analyzer, TC-300/EF-300 manufactured by LECO Corporation can be used.
The soft magnetic powder according to the invention contains a crystalline structure having a particle diameter (crystalline particle diameter) of 1 nm or more and 30 nm or less in an amount of 40 vol % or more. The crystalline structure having such a particle diameter is small, and therefore, the magnetocrystalline anisotropy in each crystalline particle is easily averaged out. Therefore, the coercive force can be decreased, and a powder which is especially magnetically soft is obtained. In addition, in a case where the crystalline structure having such a particle diameter is contained in a given amount or more, the magnetic permeability of the soft magnetic powder becomes high. As a result, a powder rich in soft magnetism having a low coercive force and a high magnetic permeability is obtained. Then, by containing the crystalline structure having such a particle diameter in an amount not lower than the above lower limit, such an effect is obtained sufficiently.
The content ratio of the crystalline structure having a particle diameter within the above range is set to 40 vol % or more, but is set to preferably 50 vol % or more and 99 vol % or less, more preferably 60 vol % or more and 95 vol % or less. When the content ratio of the crystalline structure having a particle diameter within the above range is less than the above lower limit, the ratio of the crystalline structure having a small particle diameter is decreased, and therefore, the averaging out of magnetocrystalline anisotropy by the exchange interaction of crystalline particles is insufficient, and thus, there is a fear that the magnetic permeability of the soft magnetic powder may be decreased or the coercive force of the soft magnetic powder may be increased. On the other hand, the content ratio of the crystalline structure having a particle diameter within the above range may exceed the above upper limit, however, as described later, there is a fear that the effect of coexistence with an amorphous structure may be insufficient.
Further, the soft magnetic powder according to the invention may contain a crystalline structure having a particle diameter outside the above range (less than 1 nm or more than 30 nm). In such a case, the amount of the crystalline structure having a particle diameter outside the above range is suppressed to preferably 10 vol % or less, more preferably 5 vol % or less. According to this, the decrease in the above-mentioned effect due to the crystalline structure having a particle diameter outside the above range can be suppressed.
The particle diameter of the crystalline structure of the soft magnetic powder according to the invention is obtained by, for example, a method in which the cut surface of the particle of the soft magnetic powder is observed by an electron microscope and a measurement is taken from the observation image, or the like. At this time, a perfect circle having the same area as that of the crystalline structure is assumed, and the diameter of the perfect circle (circle equivalent diameter) can be used as the particle diameter of the crystalline structure.
The content ratio (vol %) is obtained by a method in which an area ratio occupied by crystals having a particle diameter within the above range in the observation image is determined, and the area ratio is defined as the content ratio.
Further, in the soft magnetic powder according to the invention, the average particle diameter of the crystalline structure is preferably 3 nm or more and 30 nm or less, more preferably 5 nm or more and 25 nm or less. According to this, the above-mentioned effect becomes more pronounced, and a powder which is especially magnetically soft is obtained.
The average particle diameter of the crystalline structure of the soft magnetic powder according to the invention can be obtained by, for example, calculation from the width of a diffraction peak in a spectrum obtained by X-ray diffractometry.
On the other hand, the soft magnetic powder according to the invention may further contain an amorphous structure. By the coexistence of the crystalline structure having a particle diameter within the above range and the amorphous structure, the magnetostriction is cancelled out by each other, and therefore, the magnetostriction of the soft magnetic powder can be further decreased. As a result, a soft magnetic powder which has a particularly high magnetic permeability is obtained. In addition, a soft magnetic powder whose magnetization is easily controlled is obtained.
In such a case, the content ratio of the amorphous structure is preferably 2 vol % or more and 500 vol % or less, more preferably 10 vol % or more and 200 vol % or less with respect to the content ratio of the crystalline structure having a particle diameter within the above range. According to this, the balance between the crystalline structure and the amorphous structure is optimized, and thus, the effect of the coexistence of the crystalline structure and the amorphous structure is more pronounced.
Incidentally, it can be confirmed whether or not the structure contained in the soft magnetic powder is amorphous by, for example, examining whether or not a diffraction peak is observed in a spectrum obtained by X-ray diffractometry. It can also be specified by directly confirming the atomic arrangement using a transmission electron microscope or the like.
Further, the soft magnetic powder according to the invention is configured such that the Vickers hardness of the particles is preferably 1000 or more and 3000 or less, more preferably 1200 or more and 2500 or less. The soft magnetic powder having such a hardness can suppress the deformation at a contact point between particles to the minimum when the soft magnetic powder is formed into a powder magnetic core by compression-molding. Therefore, a contact area is suppressed to be small, resulting in increasing the resistivity of a green compact of the soft magnetic powder. As a result, a high insulating property between the particles can be more highly ensured when the powder is compacted.
If the Vickers hardness is less than the above lower limit, when the soft magnetic powder is compression-molded, the particles are likely to be crushed at the contact point between the particles depending on the average particle diameter of the soft magnetic powder. Due to this, the contact area is increased, and the resistivity of a green compact of the soft magnetic powder is decreased, therefore, there is a fear that the insulating property between the particles may be deteriorated. On the other hand, if the Vickers hardness exceeds the above upper limit, the powder compatibility is decreased depending on the average particle diameter of the soft magnetic powder, resulting in decreasing the density when the soft magnetic powder is formed into a powder magnetic core, and therefore, there is a fear that the magnetic properties of the powder magnetic core may be deteriorated.
The Vickers hardness of the particles of the soft magnetic powder is measured by a micro Vickers hardness tester in a central portion of the cross section of the particle. The “central portion of the cross section of the particle” refers to a portion corresponding to the midpoint of a major axis, which is the maximum length of the particle, on a cut surface when the particle is cut along the major axis. Further, the load of pushing an indenter when performing the test is set to 50 mN.
In the soft magnetic powder according to this embodiment, when the apparent density is assumed to be 100, the tap density is 103 or more and 130 or less. Such a soft magnetic powder is a powder in which a difference between the tap density and the apparent density is moderately large. That is, such a soft magnetic powder can be said to be a powder which has a relatively small density (is hardly packed/loose) when it is not tapped (vibrated), but has a relatively large density (is easily packed) when it is tapped. From this, the soft magnetic powder which satisfies the relationship between the apparent density and the tap density as described above can be said to be a powder with few irregular shaped particles and high frictional resistance between the particles.
Such a soft magnetic powder has high adhesion between the particle and an insulating material. Due to this, even if the amount of use of the insulating material is small, a green compact (for example, a powder magnetic core, a magnetic shielding sheet, or the like) having a sufficient mechanical strength can be obtained. Further, since particles having an irregular shape are few, the packing efficiency when the powder is compacted is favorable, and thus, a green compact which has a high packing factor is obtained.
In light of this, by using the soft magnetic powder according to this embodiment, a green compact which has high magnetic properties such as magnetic permeability and saturation magnetic flux density is obtained.
When the apparent density is assumed to be 100, the tap density is preferably 105 or more and 125 or less, more preferably 107 or more and 120 or less.
When the relative value of the tap density is lower than the above lower limit (i.e., 103), when a green compact is obtained by compacting the soft magnetic powder, the packing efficiency of the soft magnetic powder may be deteriorated. Due to this, the magnetic permeability, saturation magnetic flux density, or the like of the green compact may be decreased. On the other hand, when the relative value of the tap density exceeds the above upper limit (i.e., 130), when a green compact is obtained by compacting the soft magnetic powder, the shrinkage ratio may be increased. Due to this, the green compact is likely to be deformed, and the magnetic permeability may be decreased or the dimensional accuracy may be decreased.
The tap density of the soft magnetic powder according to this embodiment slightly varies depending on the particle diameter or the alloy composition, and therefore is not particularly limited, but is preferably 3.6 g/cm3 or more and 5.5 g/cm3 or less, more preferably 3.8 g/cm3 or more and 5.2 g/cm3 or less. Such a soft magnetic powder has high packing efficiency, and therefore, a green compact in which the packing factor of the soft magnetic powder is high can be produced. Therefore, a green compact which has high magnetic properties such as magnetic permeability and saturation magnetic flux density is obtained.
The apparent density of the soft magnetic powder is determined in accordance with Metallic powders—Determination of apparent density specified in JIS Z 2504:2012, and the unit is, for example, g/cm3.
The tap density of the soft magnetic powder is determined in accordance with Metallic powders—Determination of tap density specified in JIS Z 2512:2012, and the unit is, for example, g/cm3.
The relationship between the apparent density and the tap density as described above is particularly affected by the state of the surface of the particle as described above. In this case, it is preferred to add arbitrary elements Al and Ti as described above at the above-mentioned contents. According to this, a powder in which particles having an irregular shape are relatively few, and the frictional resistance between the particles is relatively high is easily obtained. As a result, the packing efficiency of the soft magnetic powder is increased, and also the adhesion between the particle and the insulating material is increased, so that the amount of use of the insulating material is suppressed, and as a result, a powder magnetic core which has high magnetic properties such as magnetic permeability and saturation magnetic flux density can be produced.
When the contents of Al and Ti are low, there is a tendency that particles having an irregular shape are increased, but the frictional resistance between the particles is decreased, and thus, the ratio of the tap density to the apparent density is decreased. On the other hand, when the contents of Al and Ti are high, there is a tendency that particles having an irregular shape are decreased, but the frictional resistance between the particles is increased, and thus, the ratio of the tap density to the apparent density is increased.
The frictional resistance between the particles is sometimes also affected by the oxygen content of the soft magnetic powder. That is, when the oxygen content is high, the frictional resistance between the particles is increased, but the tap density is hardly increased. On the other hand, when the oxygen content is low, there is a tendency that the frictional resistance between the particles is decreased.
The average particle diameter D50 of the soft magnetic powder according to the invention is not particularly limited, but is preferably 1 μm or more and 40 μm or less, more preferably 3 μm or more and 30 μm or less. By using the soft magnetic powder having such an average particle diameter, a path through which an eddy current flows can be shortened, and therefore, a powder magnetic core capable of sufficiently suppressing eddy current loss generated in the particles of the soft magnetic powder can be produced. Further, since the average particle diameter is moderately small, the packing efficiency can be enhanced when the powder is compacted. As a result, the packing density of a powder magnetic core can be increased, and thus, the saturation magnetic flux density and the magnetic permeability of the powder magnetic core can be increased. Incidentally, the average particle diameter D50 of the soft magnetic powder is obtained as a particle diameter when the cumulative frequency from the small diameter side reaches 50% in the mass-based particle size distribution obtained by laser diffractometry.
When the average particle diameter of the soft magnetic powder is less than the above lower limit, the soft magnetic powder is too fine, and therefore, there is a fear that the packing efficiency of the soft magnetic powder are likely to be deteriorated. Due to this, the molding density of the powder magnetic core (one example of the green compact) is decreased, and thus, there is a fear that the saturation magnetic flux density or the magnetic permeability of the powder magnetic core may be decreased depending on the material composition or the mechanical properties of the soft magnetic powder. On the other hand, when the average particle diameter of the soft magnetic powder exceeds the above upper limit, the eddy current loss generated in the particles cannot be sufficiently suppressed depending on the material composition or the mechanical properties of the soft magnetic powder, and therefore, there is a fear that the iron loss of the powder magnetic core may be increased.
In the soft magnetic powder according to the invention, when the particle diameter at which the cumulative frequency from the small diameter side reaches 10% in the mass-based particle size distribution obtained by laser diffractometry is represented by D10 and the particle diameter at which the cumulative frequency from the small diameter side reaches 90% is represented by D90, the value of (D90-D10)/D50 is preferably about 1.0 or more and 2.5 or less, more preferably about 1.2 or more and 2.3 or less. The value of (D90−D10)/D50 is an index which indicates the degree of spreading of the particle size distribution, and when this index is within the above range, the packing efficiency of the soft magnetic powder is favorable. Accordingly, a green compact which has particularly high magnetic properties such as magnetic permeability and saturation magnetic flux density is obtained.
The coercive force of the soft magnetic powder according to the invention is not particularly limited, but is preferably 0.1 Oe or more and 2 Oe or less (7.98 A/m or more and 160 A/m or less), more preferably 0.1 Oe or more and 1.5 Oe or less (39.9 A/m or more and 120 A/m or less). By using the soft magnetic powder having such a low coercive force, a powder magnetic core capable of sufficiently suppressing the hysteresis loss even at a high frequency can be produced.
The coercive force of the soft magnetic powder can be measured using a magnetometer (for example, “TM-VSM 1230-MHHL”, manufactured by Tamakawa Co., Ltd., or the like).
Further, the volume resistivity of the soft magnetic powder according to the invention in a compacted state, that is, when it is formed into a green compact is preferably 1 kΩ·cm or more and 500 kΩ·cm or less, more preferably 5 kΩ·cm or more and 300 kΩ·cm or less, further more preferably 10 kΩ·cm or more and 200 kΩ·cm or less. Such a volume resistivity is achieved without using an insulating material, and therefore is based on the insulating property between the particles of the soft magnetic powder itself. Therefore, by using the soft magnetic powder which achieves such a volume resistivity, particles of the soft magnetic powder are sufficiently insulated from each other, so that the amount of use of the insulating material can be reduced, and thus, the proportion of the soft magnetic powder in a powder magnetic core or the like can be increased to the maximum by that amount. As a result, a powder magnetic core which highly achieves both high magnetic properties and low loss at the same time can be realized.
The volume resistivity described above is a value measured as follows.
First, 0.8 g of the soft magnetic powder to be measured is packed in an alumina cylinder. Then, brass electrodes are disposed on the upper and lower sides of the cylinder.
Then, an electrical resistance between the upper and lower electrodes is measured using a digital multimeter while applying a pressure of 10 MPa between the upper and lower electrodes using a digital force gauge.
Then, the volume resistivity is calculated by substituting the measured electrical resistance, the distance between the electrodes when applying the pressure, and the internal cross-sectional area of the cylinder in the following calculation formula.
Volume resistivity (kΩ·cm)=Electrical resistance (kΩ)×Internal cross-sectional area of cylinder (cm2)/Distance between electrodes (cm)
The internal cross-sectional area of the cylinder can be obtained according to the formula: πr2 (cm2) when the inner diameter of the cylinder is represented by 2r (cm).
The volume resistivity of a green compact as described above is exhibited by enhancing the insulating property between the particles as described above. In this case, as the content of O (oxygen) in the soft magnetic powder is higher, the insulating property is more easily enhanced, however, on the other hand, the magnetic properties such as magnetic permeability are deteriorated. Therefore, by setting the content of O (oxygen) in the soft magnetic powder within the above range, a green compact which has a favorable insulating property so that the volume resistivity is within the above range is obtained without much deteriorating the magnetic properties such as magnetic permeability.
When the soft magnetic powder according to the invention is formed into a green compact, the magnetic permeability of the green compact at a measurement frequency of 100 kHz is preferably 15 or more, more preferably 18 or more and 50 or less. Such a soft magnetic powder contributes to the realization of a powder magnetic core having excellent magnetic properties. Further, the soft magnetic powder has a relatively high magnetic permeability, and therefore also contributes to the miniaturization of a powder magnetic core or a magnetic element.
The magnetic permeability is a relative magnetic permeability (effective magnetic permeability) determined from the self-inductance of a closed magnetic circuit magnetic core coil when a green compact is formed into a toroidal shape. In the measurement of the magnetic permeability, for example, a measurement device such as an impedance analyzer (HEWLETT PACKARD 4194A) is used, and the measurement frequency is set to 100 kHz. Further, the number of turns of a coil wire is set to 7, and the diameter of the coil wire is set to 0.5 mm.
Powder Magnetic Core and Magnetic Element
Next, the powder magnetic core according to the invention and the magnetic element according to the invention will be described.
The magnetic element according to the invention can be applied to a variety of magnetic elements including a magnetic core such as a choke coil, an inductor, a noise filter, a reactor, a transformer, a motor, an actuator, a solenoid valve, and an electrical generator. Further, the powder magnetic core according to the invention can be applied to a magnetic core included in these magnetic elements.
Hereinafter, two types of choke coils will be described as representative examples of the magnetic element.
First, a choke coil to which a first embodiment of the magnetic element according to the invention is applied will be described.
A choke coil 10 (the magnetic element according to this embodiment) shown in
The powder magnetic core 11 (the powder magnetic core according to this embodiment) is obtained by mixing the soft magnetic powder according to the invention, a binding material (binder), and an organic solvent, supplying the obtained mixture in a shaping mold, and press-molding the mixture. That is, the powder magnetic core 11 contains the soft magnetic powder according to the invention. Such a powder magnetic core 11 has a high magnetic permeability, and therefore has improved magnetic properties. Further, the coercive force of the soft magnetic powder is low, and therefore, such a powder magnetic core 11 has reduced iron loss. As a result, when the powder magnetic core 11 is mounted on an electronic device or the like, the power consumption of the electronic device or the like can be reduced or the performance thereof can be increased, and thus, it can contribute to the improvement of the reliability of the electronic device or the like.
Further, as described above, the choke coil 10 which is one example of the magnetic element includes the powder magnetic core 11. Therefore, the choke coil 10 has enhanced performance and reduced iron loss. As a result, when the choke coil 10 is mounted on an electronic device or the like, the power consumption of the electronic device or the like can be reduced or the performance thereof can be increased, and thus, it can contribute to the improvement of the reliability of the electronic device or the like.
Examples of the constituent material of the binding material to be used for producing the powder magnetic core 11 include organic materials such as a silicone-based resin, an epoxy-based resin, a phenolic resin, a polyamide-based resin, a polyimide-based resin, and a polyphenylene sulfide-based resin, and inorganic materials such as phosphates such as magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, and cadmium phosphate, and silicates (liquid glass) such as sodium silicate, and particularly, a thermosetting polyimide-based resin or a thermosetting epoxy-based resin is preferred. These resin materials are easily cured by heating and have excellent heat resistance. Therefore, the ease of production of the powder magnetic core 11 and also the heat resistance thereof can be increased.
The ratio of the binding material to the soft magnetic powder slightly varies depending on the desired saturation magnetic flux density and mechanical properties, the allowable eddy current loss, etc. of the powder magnetic core 11 to be produced, but is preferably about 0.5 mass % or more and 5 mass % or less, more preferably about 1 mass % or more and 3 mass % or less. According to this, the powder magnetic core 11 having excellent magnetic properties such as saturation magnetic flux density and magnetic permeability can be obtained while sufficiently binding the particles of the soft magnetic powder.
The organic solvent is not particularly limited as long as it can dissolve the binding material, but examples thereof include various solvents such as toluene, isopropyl alcohol, acetone, methyl ethyl ketone, chloroform, and ethyl acetate.
To the above-mentioned mixture, any of a variety of additives may be added for an arbitrary purpose as needed.
Examples of the constituent material of the conductive wire 12 include materials having high electrical conductivity, for example, metal materials including Cu, Al, Ag, Au, Ni, and the like.
It is preferred that on the surface of the conductive wire 12, a surface layer having an insulating property is provided. According to this, a short circuit between the powder magnetic core 11 and the conductive wire 12 can be reliably prevented. Examples of the constituent material of such a surface layer include various resin materials.
Next, a method for producing the choke coil 10 will be described.
First, the soft magnetic powder according to the invention, a binding material, any desired additives, and an organic solvent are mixed, whereby a mixture is obtained.
Subsequently, the mixture is dried to obtain a block-shaped dry material. Then, the obtained dry material is pulverized, whereby a granulated powder is formed.
Subsequently, this granulated powder is molded into the shape of a powder magnetic core to be produced, whereby a molded body is obtained.
A molding method in this case is not particularly limited, however, examples thereof include press-molding, extrusion-molding, and injection-molding. The shape and size of this molded body are determined in anticipation of shrinkage when heating the molded body in the subsequent step. Further, the molding pressure in the case of press-molding is set to about 1 t/cm2 (98 MPa) or more and 10 t/cm2 (981 MPa) or less.
Subsequently, by heating the obtained molded body, the binding material is cured, whereby the powder magnetic core 11 is obtained. The heating temperature at this time slightly varies depending on the composition of the binding material and the like, however, in a case where the binding material is composed of an organic material, the heating temperature is set to preferably about 100° C. or higher and 500° C. or lower, more preferably about 120° C. or higher and 250° C. or lower. The heating time varies depending on the heating temperature, but is set to about 0.5 hours or more and 5 hours or less.
According to the above-mentioned method, the choke coil 10 including the powder magnetic core 11 obtained by press-molding the soft magnetic powder according to the invention and the conductive wire 12 wound around the powder magnetic core 11 along the outer peripheral surface thereof is obtained.
The shape of the powder magnetic core 11 is not limited to the ring shape shown in
Further, the powder magnetic core 11 may contain a soft magnetic powder other than the soft magnetic powder according to the above-mentioned embodiment as needed.
Next, a choke coil to which a second embodiment of the magnetic element according to the invention is applied will be described.
Hereinafter, the choke coil according to the second embodiment will be described, however, in the following description, different points from the above-mentioned choke coil according to the first embodiment will be mainly described and the description of the same matter will be omitted.
As shown in
As the choke coil 20 having such a configuration, a relatively small choke coil is easily obtained. In a case where such a small choke coil 20 is produced, by using the powder magnetic core 21 having a high saturation magnetic flux density and a high magnetic permeability, and also having low loss, the choke coil 20 which has low loss and generates low heat so as to be able to cope with a large current although the size is small is obtained.
Further, since the conductive wire 22 is embedded inside the powder magnetic core 21, a void is rarely generated between the conductive wire 22 and the powder magnetic core 21. According to this, vibration of the powder magnetic core 21 due to magnetostriction is suppressed, and thus, it is also possible to suppress the generation of noise accompanying this vibration.
In a case where the choke coil 20 according to this embodiment as described above is produced, first, the conductive wire 22 is disposed in the cavity of a shaping mold, and also the granulated powder containing the soft magnetic powder according to the invention is packed in the cavity. That is, the granulated powder is packed therein so that the conductive wire 22 is included therein.
Subsequently, the granulated powder is compressed together with the conductive wire 22, whereby a molded body is obtained.
Subsequently, in the same manner as in the above-mentioned first embodiment, the obtained molded body is subjected to a heat treatment. By doing this, the binding material is cured, whereby the powder magnetic core 21 and the choke coil 20 (the magnetic element according to the embodiment) are obtained.
Further, the powder magnetic core 21 may contain a soft magnetic powder other than the soft magnetic powder according to the above-mentioned embodiment as needed.
Method for Producing Soft Magnetic Powder
Next, a method for producing the soft magnetic powder according to the invention will be described.
The soft magnetic powder according to the invention may be produced by any production method, and is produced by, for example, any of a variety of powdering methods such as an atomization method (for example, a water atomization method, a gas atomization method, a spinning water atomization method, or the like), a reducing method, a carbonyl method, and a pulverization method.
As the atomization methods, there have been known a water atomization method, a gas atomization method, a spinning water atomization method, and the like, which are divided according to a difference in the type of a cooling medium or the configuration of a device. Among these, the soft magnetic powder according to the invention is preferably produced by an atomization method, more preferably produced by a water atomization method or a spinning water atomization method, and further more preferably produced by a spinning water atomization method. The atomization method is a method in which a molten metal (metal melt) is caused to collide with a fluid (liquid or gas) jetted at a high speed to atomize the molten metal and also cool the atomized metal, whereby a metal powder (soft magnetic powder) is produced. By producing the soft magnetic powder using such an atomization method, an extremely fine powder can be efficiently produced. Further, the shape of the particle of the obtained powder is closer to a spherical shape by the action of surface tension. Due to this, a soft magnetic powder having a high packing factor when producing a powder magnetic core is obtained. That is, a soft magnetic powder capable of producing a powder magnetic core having a high magnetic permeability and a high saturation magnetic flux density can be obtained.
The “water atomization method” as used herein refers to a method in which a liquid such as water or an oil is used as a cooling liquid, and in a state where this liquid is jetted in an inverted conical shape so as to converge on one point, the molten metal is allowed to flow down toward this convergence point and collide with the cooling liquid so as to atomize the molten metal, whereby a metal powder is produced.
On the other hand, by using a spinning water atomization method, the metal melt can be cooled at an extremely high speed. Therefore, the metal melt can be solidified in a state where the chaotic atomic arrangement in the molten metal is highly maintained. Due to this, by performing a crystallization treatment thereafter, a soft magnetic powder having a crystalline structure with a uniform particle diameter can be efficiently produced.
Hereinafter, a method for producing the soft magnetic powder by a spinning water atomization method will be described.
In a spinning water atomization method, a cooling liquid is supplied by ejection along the inner circumferential surface of a cooling cylindrical body, and is spun along the inner circumferential surface of the cooling cylindrical body, whereby a cooling liquid layer is formed on the inner circumferential surface. On the other hand, the raw material of the soft magnetic powder is melted, and while allowing the obtained molten metal to freely fall, a liquid or gas jet is blown to the molten metal. By doing this, the molten metal is scattered, and the scattered molten metal is incorporated in the cooling liquid layer. As a result, the molten metal which is atomized by scattering is solidified by rapid cooling, and therefore, the soft magnetic powder is obtained.
A powder production device 30 shown in
The cooling cylindrical body 1 has a cylindrical shape and is placed so that the axial line of the cylindrical body is along the vertical direction or is tilted at an angle of 300 or less with respect to the vertical direction. Incidentally, the axial line of the cylindrical body is tilted with respect to the vertical direction in
The upper end opening of the cooling cylindrical body 1 is closed by a lid 2, and in the lid 2, an opening section 3 for supplying the flowing down molten metal 25 to the space portion 23 of the cooling cylindrical body 1 is formed.
Further, in an upper portion of the cooling cylindrical body 1, a cooling liquid ejection tube 4 configured to be able to supply the cooling liquid by ejection in the tangential direction on the inner circumferential surface of the cooling cylindrical body 1 is provided. Then, a plurality of ejection ports 5 of the cooling liquid ejection tubes 4 are provided at equal intervals along the circumferential direction of the cooling cylindrical body 1. Further, the tube axial direction of the cooling liquid ejection tube 4 is set so that it is tilted downward at an angle of about 0° or more and 20° or less with respect to a plane orthogonal to the axial line of the cooling cylindrical body 1.
The cooling liquid ejection tube 4 is connected to a tank 8 via the pump 7 through a pipe, and the cooling liquid in the tank 8 sucked by the pump 7 is supplied by ejection into the cooling cylindrical body 1 through the cooling liquid ejection tube 4. By doing this, the cooling liquid gradually flows down while spinning along the inner circumferential surface of the cooling cylindrical body 1, and accompanying this, a layer of the cooling liquid (cooling liquid layer 9) along the inner circumferential surface is formed. Incidentally, a cooler may be interposed as needed in the tank 8 or in the middle of the circulation flow channel. As the cooling liquid, other than water, an oil (a silicone oil or the like) is used, and further, any of a variety of additives may be added thereto. Further, by removing dissolved oxygen in the cooling liquid in advance, oxidation accompanying cooling of the powder to be produced can be suppressed.
Further, in a lower portion of the inner circumferential surface of the cooling cylindrical body 1, a layer thickness adjustment ring 16 for adjusting the layer thickness of the cooling liquid layer 9 is detachably provided. By providing this layer thickness adjustment ring 16, the flowing down speed of the cooling liquid is controlled, and therefore, the layer thickness of the cooling liquid layer 9 is ensured, and also the uniformity of the layer thickness can be achieved. The layer thickness adjustment ring 16 may be provided as needed.
Further, in a lower portion of the cooling cylindrical body 1, a liquid draining net body 17 having a cylindrical shape is continuously provided, and on the lower side of this liquid draining net body 17, a powder recovery container 18 having a funnel shape is provided. Around the liquid draining net body 17, a cooling liquid recovery cover 13 is provided so as to cover the liquid draining net body 17, and a drain port 14 formed in a bottom portion of this cooling liquid recovery cover 13 is connected to the tank 8 through a pipe.
Further, in the space portion 23, the jet nozzle 24 for ejecting a gas such as air or an inert gas is provided. This jet nozzle 24 is attached to the tip end of a gas supply tube 27 inserted through the opening section 3 of the lid 2 and is disposed such that the ejection port thereof is oriented toward the molten metal 25 in a thin stream and further oriented toward the cooling liquid layer 9 beyond the molten metal.
When a soft magnetic powder is produced by such a powder production device 30, first, the pump 7 is operated and the cooling liquid layer 9 is formed on the inner circumferential surface of the cooling cylindrical body 1, and then, the molten metal 25 in the pot 15 is allowed to flow down into the space portion 23. When the gas jet 26 is blown to this molten metal 25, the molten metal 25 is scattered, and the atomized molten metal 25 is incorporated in the cooling liquid layer 9. As a result, the atomized molten metal 25 is cooled and solidified, whereby a soft magnetic powder is obtained.
In the spinning water atomization method, by continuously supplying the cooling liquid, an extremely high cooling rate can be stably maintained, and therefore, the degree of amorphization of a soft magnetic powder to be produced is stabilized. As a result, by performing a crystallization treatment thereafter, a soft magnetic powder having a crystalline structure with a uniform particle diameter can be efficiently produced.
Further, the molten metal 25 atomized to a given size by the gas jet 26 falls by inertia until it is incorporated in the cooling liquid layer 9. Therefore, the liquid droplet is spheroidized at that time. As a result, a soft magnetic powder can be produced.
For example, the flow-down amount of the molten metal 25 which is allowed to flow down from the pot 15 varies depending also on the size of the device and is not particularly limited, but is preferably controlled to be 1 kg or less per minute. According to this, when the molten metal 25 is scattered, it is scattered as liquid droplets with an appropriate size, and therefore, a soft magnetic powder having an average particle diameter as described above is obtained. Further, by controlling the amount of the molten metal 25 to be supplied in a given time to a certain degree, also a sufficient cooling rate is obtained, and therefore, the degree of amorphization is increased, and thus, a soft magnetic powder having a crystalline structure with a uniform particle diameter is obtained. Incidentally, for example, by decreasing the flow-down amount of the molten metal 25 within the above range, it is possible to perform adjustment such that the average particle diameter is reduced.
On the other hand, the outer diameter of the thin stream of the molten metal 25 allowed to flow down from the pot 15, in other words, the inner diameter of the flow-down port of the pot 15 is not particularly limited, but is preferably 1 mm or less. According to this, it becomes easy to make the gas jet 26 uniformly hit the molten metal 25 in a thin stream, and therefore, it becomes easy to uniformly scatter the liquid droplets with an appropriate size. As a result, a soft magnetic powder having an average particle diameter as described above is obtained. Then, also in this case, the amount of the molten metal 25 to be supplied in a given time is controlled, and therefore, a cooling rate is also sufficiently obtained, and thus, sufficient amorphization can be achieved.
Further, the flow rate of the gas jet 26 is not particularly limited, but is preferably set to 100 m/s or more and 1000 m/s or less. According to this, also in this case, the molten metal 25 can be scattered as liquid droplets with an appropriate size, and therefore, a soft magnetic powder having an average particle diameter as described above is obtained. Further, the gas jet 26 has a sufficient speed, and therefore, a sufficient speed is also given to the scattered liquid droplets, and therefore, the liquid droplets become finer, and also the time until the liquid droplets are incorporated in the cooling liquid layer 9 is shortened. As a result, the liquid droplet can be spheroidized in a short time and also cooled in a short time, and thus, further amorphization is achieved. For example, by increasing the flow rate of the gas jet 26 within the above range, it is possible to perform adjustment such that the average particle diameter is reduced.
Further, as other conditions, for example, it is preferred that the pressure when ejecting the cooling liquid to be supplied to the cooling cylindrical body 1 is set to about 50 MPa or more and 200 MPa or less, the liquid temperature is set to about −10° C. or higher and 40° C. or lower. According to this, the flow rate of the cooling liquid layer 9 is optimized, and the atomized molten metal 25 can be cooled appropriately and uniformly.
Further, when the raw material of the soft magnetic powder is melted, the melting temperature is preferably set to about Tm+20° C. or higher and Tm+200° C. or lower, more preferably set to about Tm+50° C. or higher and Tm+150° C. or lower wherein Tm represents the melting point of the raw material. According to this, when the molten metal 25 is atomized by the gas jet 26, the variation in the properties among particles can be suppressed to be particularly small, and also the amorphization of the soft magnetic powder can be more reliably achieved.
The gas jet 26 can also be substituted by a liquid jet as needed.
The cooling rate when cooling the molten metal in the atomization method is preferably 1×104° C./s or more, more preferably 1×105° C./s or more. By the rapid cooling in this manner, a soft magnetic powder having a particularly high degree of amorphization is obtained, and finally, a soft magnetic powder having a crystalline structure with a uniform particle diameter is obtained. In addition, the variation in the compositional ratio among the particles of the soft magnetic powder can be suppressed.
The soft magnetic powder produced as described above is subjected to a crystallization treatment. By doing this, at least part of the amorphous structure is crystallized, whereby a crystalline structure is formed.
The crystallization treatment can be performed by subjecting the soft magnetic powder containing an amorphous structure to a heat treatment. The temperature of the heat treatment is not particularly limited, but is preferably 520° C. or higher and 640° C. or lower, more preferably 560° C. or higher and 630° C. or lower, further more preferably 570° C. or higher and 620° C. or lower. As for the time of the heat treatment, the time to maintain the powder at that temperature is set to preferably 1 minute or more and 180 minutes or less, more preferably 3 minutes or more and 120 minutes or less, further more preferably 5 minutes or more and 60 minutes or less. By setting the temperature and time of the heat treatment within the above ranges, respectively, the crystalline structure having a more uniform particle diameter can be generated more uniformly. As a result, a soft magnetic powder in which a crystalline structure having a particle diameter of 1 nm or more and 30 nm or less is contained in an amount of 40 vol % or more is obtained. This is considered to be because by incorporating a crystalline structure having a small and uniform particle diameter in a relatively large amount (40 vol % or more), an interaction at the interface between the crystalline structure and the amorphous structure is particularly dominant, and accompanying this, the hardness is increased as compared with a case where an amorphous structure is dominant or a case where a crystalline structure having a coarse particle diameter is contained in a large amount.
When the temperature or time of the heat treatment is less than the above lower limit, depending on the material composition of the soft magnetic powder or the like, the crystallization is insufficient, and also the uniformity of the particle diameter is poor, and therefore, the interaction at the interface between the crystalline structure and the amorphous structure cannot be obtained, and thus, there is a fear that the hardness may be insufficient. Due to this, the resistivity in a green compact is decreased, and thus, there is a fear that a high insulating property between the particles cannot be ensured. On the other hand, when the temperature or time of the heat treatment exceeds the above upper limit, depending on the material composition of the soft magnetic powder or the like, crystallization proceeds excessively, and also the uniformity of the particle diameter is poor, and therefore, the interface between the crystalline structure and the amorphous structure is decreased, and also in this case, there is a fear that the hardness may be insufficient. Due to this, the resistivity in a green compact is decreased, and therefore, there is a fear that a high insulating property between the particles cannot be ensured.
The atmosphere of the crystallization treatment is not particularly limited, but is preferably an inert gas atmosphere such as nitrogen or argon, a reducing gas atmosphere such as hydrogen or an ammonia decomposition gas, or a reduced pressure atmosphere thereof. According to this, crystallization can be achieved while suppressing oxidation of the metal, and thus, a soft magnetic powder having excellent magnetic properties is obtained.
In this manner, the soft magnetic powder according to this embodiment can be produced.
The thus obtained soft magnetic powder may be classified as needed. Examples of the classification method include dry classification such as sieve classification, inertial classification, centrifugal classification, and wind power classification, and wet classification such as sedimentation classification.
Further, an insulating film may be formed on the surface of each particle of the thus obtained soft magnetic powder as needed. Examples of the constituent material of this insulating film include inorganic materials such as phosphates such as magnesium phosphate, calcium phosphate, zinc phosphate, manganese phosphate, and cadmium phosphate, and silicates (liquid glass) such as sodium silicate. Further, it may be a material which is appropriately selected from the organic materials listed as the constituent material of the binding material described below.
Electronic Device
Next, an electronic device including the magnetic element according to the invention will be described in detail with reference to
On a back surface of a case (body) 1302 in the digital still camera 1300, a display section 100 is provided, and the display section 100 is configured to display an image taken on the basis of the imaging signal by the CCD. The display section 100 functions as a finder which displays a subject as an electronic image. Further, on a front surface side (on a back surface side in the drawing) of the case 1302, a light receiving unit 1304 including an optical lens (an imaging optical system), a CCD, or the like is provided.
When a person who takes a picture confirms an image of a subject displayed on the display section 100 and pushes a shutter button 1306, an imaging signal of the CCD at that time is transferred to a memory 1308 and stored there. Further, a video signal output terminal 1312 and an input/output terminal 1314 for data communication are provided on a side surface of the case 1302 in this digital still camera 1300. As shown in the drawing, a television monitor 1430 is connected to the video signal output terminal 1312 and a personal computer 1440 is connected to the input/output terminal 1314 for data communication as needed. Moreover, the digital still camera 1300 is configured such that the imaging signal stored in the memory 1308 is output to the television monitor 1430 or the personal computer 1440 by a predetermined operation. Also such a digital still camera 1300 includes a built-in magnetic element 1000, for example, an inductor, a noise filter, or the like.
The electronic device including the magnetic element according to the invention can be applied to, other than the personal computer (mobile-type personal computer) shown in
As described above, such an electronic device includes the magnetic element according to the invention. Therefore, the reliability of the electronic device can be increased.
Hereinabove, the soft magnetic powder, the powder magnetic core, the magnetic element, and the electronic device according to the invention have been described based on the preferred embodiments, but the invention is not limited thereto.
For example, in the above-mentioned embodiments, as the application example of the soft magnetic powder according to the invention, the powder magnetic core is described, however, the application example is not limited thereto, and for example, it may be applied to a magnetic fluid, a magnetic shielding sheet, or a magnetic device such as a magnetic head.
Further, the shapes of the powder magnetic core and the magnetic element are also not limited to those shown in the drawings, and may be any shapes.
Next, specific examples of the invention will be described.
1. Production of Powder Magnetic Core
Sample No. 1
[1] First, the raw material was melted in a high-frequency induction furnace, and also powdered by a spinning water atomization method, whereby a soft magnetic powder was obtained. At this time, the flow-down amount of the molten metal to be allowed to flow down from the pot was set to 0.5 kg/min, the inner diameter of the flow-down port of the pot was set to 1 mm, and the flow rate of the gas jet was set to 900 m/s. Subsequently, classification was performed by a wind power classifier. The alloy composition of the obtained soft magnetic powder is shown in Table 1. Incidentally, in the determination of the alloy composition, an optical emission spectrometer for solids (a spark emission spectrometer), model: Spectrolab, type: LAVMB08A manufactured by SPECTRO Analytical Instruments GmbH was used.
[2] Subsequently, with respect to the obtained soft magnetic powder, a particle size distribution was measured. This measurement was performed using a laser diffraction particle size distribution analyzer (Microtrack HRA9320-X100, manufactured by Nikkiso Co., Ltd.). Then, the D50 (average particle diameter) of the soft magnetic powder was determined based on the particle size distribution, and found to be 20 m.
[3] Subsequently, the obtained soft magnetic powder was heated to 560° C. for 15 minutes in a nitrogen atmosphere. By doing this, the amorphous structure in the particles was crystallized.
[4] Subsequently, the obtained soft magnetic powder was mixed with an epoxy resin (a binding material) and toluene (an organic solvent), whereby a mixture was obtained. The addition amount of the epoxy resin was set to 2 parts by mass with respect to 100 parts by mass of the soft magnetic powder.
[5] Subsequently, the obtained mixture was stirred, and then dried in a short time, whereby a block-shaped dry material was obtained. Then, the thus obtained dry material was sieved through a sieve with a mesh size of 400 μm, and then pulverized, whereby a granulated powder was obtained. The thus obtained granulated powder was dried at 50° C. for 1 hour.
[6] Subsequently, the obtained granulated powder was packed in a shaping mold, and a molded body was obtained under the following molding conditions.
Molding Conditions
[7] Subsequently, the molded body was heated in an air atmosphere at a temperature of 150° C. for 0.75 hours to cure the binding material. By doing this, a powder magnetic core was obtained.
Sample Nos. 2 to 32
Powder magnetic cores were obtained in the same manner as the sample No. 1 except that as the soft magnetic powder, those shown in Table 1 were used, respectively. The average particle diameter D50 of each sample fell within the range of 3 μm or more and 30 μm or less.
Sample Nos. 33 to 44
Powder magnetic cores were obtained in the same manner as the sample No. 1 except that as the soft magnetic powder, those shown in Table 2 were used, respectively. The average particle diameter D50 of each sample fell within the range of 3 μm or more and 30 μm or less.
In Tables 1 and 2, the spinning water atomization method is denoted by “spinning water”, and the water atomization method is denoted by “jet water”.
Further, in Tables 1 and 2, among the soft magnetic powders of the respective sample Nos., those corresponding to the invention are denoted by “Example”, and those not corresponding to the invention are denoted by “Comparative Example”.
Further, the abbreviation “bal.” in Tables 1 and 2 indicates that Fe is the remainder (balance) left over after taking away the other elements in the alloy composition.
2. Evaluation of Soft Magnetic Powder and Powder Magnetic Core
2.1. Measurement of Powder Properties of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the apparent density AD and the tap density TD were measured.
Then, when the apparent density was assumed to be 100, the relative value of the tap density was calculated.
The measurement results and the calculation results are shown in Tables 3 and 4.
2.2. Measurement of Magnetic Properties of Soft Magnetic Powder
2.2.1. Measurement of Coercive Force of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the coercive force was measured under the following measurement conditions.
Measurement Conditions for Coercive Force
Then, the measured coercive force was evaluated according to the following evaluation criteria.
Evaluation Criteria for Coercive Force
A: The coercive force is less than 0.5.
B: The coercive force is 0.5 or more and less than 1.0.
C: The coercive force is 1.0 or more and less than 1.33.
D: The coercive force is 1.33 or more and less than 1.67.
E: The coercive force is 1.67 or more and less than 2.0.
F: The coercive force is 2.0 or more.
The evaluation results are shown in Tables 3 and 4.
2.2.2. Measurement of Magnetic Permeability of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the magnetic permeability was measured under the following measurement conditions.
Measurement Conditions for Magnetic Permeability
The measurement results are shown in Tables 3 and 4.
2.3. Measurement of Contents of Crystalline Structure and Amorphous Structure of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the particle was cut at a plane including the major axis. Then, the cut surface was observed with a transmission electron microscope, and the crystalline structure and the amorphous structure were specified.
Subsequently, the particle diameter of the crystalline structure was measured from the observation image, and the area ratio of the crystalline structure having a particle diameter in a specific range (1 nm or more and 30 nm or less) was determined, and the determined area ratio was regarded as the content (vol %) of the crystalline structure having a predetermined particle diameter.
Subsequently, the area ratio of the amorphous structure was determined, and the determined area ratio was regarded as the content (vol %) of the amorphous structure, and also the ratio of the content of the amorphous structure to the content of the crystalline structure having a predetermined particle diameter (amorphous/crystalline) was determined.
The measurement results are shown in Tables 3 and 4.
2.4. Measurement of Average Crystalline Particle Diameter of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the average particle diameter of the crystalline structure was determined based on the width of a diffraction peak obtained by X-ray diffractometry.
The measurement results are shown in Tables 3 and 4.
2.5. Measurement of Vickers Hardness of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the particle was cut at a plane including the major axis. Then, the Vickers hardness was measured using a micro Vickers hardness tester in a central portion of the cut surface.
The measurement results are shown in Tables 3 and 4.
2.6. Measurement of Volume Resistivity of Soft Magnetic Powder
With respect to each of the soft magnetic powders obtained in the respective Examples and the respective Comparative Examples, the volume resistivity when the soft magnetic powder was formed into a green compact was measured using a digital multimeter.
The measurement results are shown in Tables 3 and 4.
2.7. Measurement of Electrical Breakdown Voltage of Powder Magnetic Core
With respect to each of the powder magnetic cores obtained in the respective Examples and the respective Comparative Examples, the electrical breakdown voltage was measured.
Specifically, after a pair of electrodes were placed in the powder magnetic core, a DC voltage of 50 V was applied between the electrodes, and an electrical resistance between the electrodes was measured using an automatic withstanding voltage insulation resistance tester (TOS9000, Kikusui Electronics Corporation).
Thereafter, while increasing the voltage in increments of 50 V, the measurement of the electrical resistance was repeatedly performed in the same manner as described above. Then, the voltage when the measurement was below the measurement limit of the electrical resistance was recorded as the electrical breakdown voltage.
The measurement results are shown in Tables 3 and 4.
As apparent from Tables 3 and 4, it was confirmed that each of the soft magnetic powders obtained in the respective Examples had a high magnetic permeability.
On the other hand, it was confirmed that each of the soft magnetic powders obtained in the respective Comparative Examples had a relatively low magnetic permeability.
The entire disclosure of Japanese Patent Application No. 2017-081554 filed Apr. 17, 2017 is expressly incorporated herein by reference.
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