JP2019172509A - Ferrite sintered magnet - Google Patents

Abstract

To provide a ferrite sintered magnet having excellent Br and HcJ in good balance.SOLUTION: There is provided a ferrite sintered magnet having a main phase particle containing ferrite having a hexagonal structure, two particle boundaries formed between two main phase particles, and a multiparticle boundary surrounded by three or more main phase particles. The ferrite sintered magnet contains Ca, R, Sr, Fe and Co, where R is at least one kind of element selected from a group consisting of rare earth elements and Bi, and contains at least La. In a cross section containing an easy magnetization axial direction of the ferrite sintered magnet, a total area Am of the main phase particle and a total area Ag of the multiparticle boundary satisfy the following formula (1): 85%≤Am/(Am+Ag)≤98% (1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sintered ferrite magnet.

  As a material for a permanent magnet made of an oxide, hexagonal M-type (Magnet Plumbite) Sr ferrite or Ba ferrite is known. Ferrite magnets made of these ferrites are provided as permanent magnets in the form of sintered ferrite magnets or bonded magnets. In recent years, along with miniaturization and high performance of electronic components, ferrite magnets are also required to have high magnetic properties while being small.

  Generally, residual magnetic flux density (Br) and coercive force (HcJ) are used as indicators of the magnetic characteristics of the permanent magnet, and it is evaluated that the higher these are, the higher the magnetic characteristics are. Conventionally, from the viewpoint of improving Br and HcJ of a permanent magnet, studies have been made by changing the composition, such as adding a predetermined element to a ferrite magnet.

  For example, Patent Document 1 discloses an oxide magnetic material and a sintered magnet that can improve Br and HcJ by containing at least La and Co in M-type Ca ferrite.

JP 2006-104050 A

  As described above, in order to obtain both Br and HcJ satisfactorily, attempts have been made to change the combination of elements added to the main composition in various ways. What kind of combination of additive elements gives high characteristics? It is not clear yet. In addition, the structural design of a sintered ferrite magnet that takes into account conditions other than the constituent elements such as the main composition and additive elements has not been sufficiently studied.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a sintered ferrite magnet having excellent Br and HcJ in a balanced manner.

The present invention comprises a main phase particle containing ferrite having a hexagonal crystal structure, a two-particle grain boundary formed between the two main phase particles, and a multi-grain grain boundary surrounded by three or more main phase particles. The ferrite sintered magnet includes Ca, R, Sr, Fe, and Co, wherein R is at least one element selected from the group consisting of rare earth elements and Bi. In a cross section including at least La and including the easy axis direction of magnetization of the ferrite sintered magnet, the total area Am of the main phase particles and the total area Ag of the multi-grain boundary satisfy the following formula (1): A ferrite sintered magnet is provided.
85% ≦ Am / (Am + Ag) ≦ 98% (1)

  In the ferrite sintered magnet, when Am and Ag satisfy the above formula (1), the orientation and particle size of the main phase particles become uniform, and a ferrite sintered magnet having excellent Br and HcJ in a balanced manner can be obtained. it can.

The sintered ferrite magnet preferably further contains 0.03 to 0.3% by mass of Al in terms of Al ₂ O ₃ . It is also preferred to include from 0.037 to 0.181% by weight of the ferrite sintered magnet further B in _H 3 BO ₃ terms. When the ferrite sintered magnet contains Al or B within the above range, the magnetic properties can be further improved in a balanced manner.

  According to the present invention, it is possible to provide a sintered ferrite magnet having excellent Br and HcJ in a balanced manner.

FIG. 1 is a diagram showing a cross section including a magnetization easy axis direction of a sintered ferrite magnet according to an embodiment of the present invention, (a) is a schematic diagram of the cross section, and (b) is a schematic diagram of (a). It is a TEM photograph of the section of the ferrite sintered magnet obtained in Example 4 corresponding to the figure. FIG. 2 is a TEM photograph of a cross section including the easy axis direction of the sintered ferrite magnets obtained in the examples and comparative examples. (A), (b), and (c) are Example 4 and Example, respectively. 2 and a cross section of the sintered ferrite magnet of Comparative Example 1 are shown.

  Hereinafter, preferred embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

(Sintered ferrite magnet)
FIG. 1 is a diagram showing a cross section of a ferrite sintered magnet according to an embodiment of the present invention, (a) is a schematic diagram of the cross section, and is obtained in Example 4 described later described in (b). It is a figure based on a TEM photograph. The cross section of the ferrite sintered magnet shown in FIG. 1 includes an easy axis (c-axis) direction Y and a hard axis direction X perpendicular thereto. In FIG. 1, the main phase particle 4 has a plate-like shape extending (orientated) in the hard axis direction X. In FIG. 1, a sintered ferrite magnet 10 includes a main phase particle 4 containing ferrite having a hexagonal crystal structure, a two-grain boundary 1 formed between the two main phase particles 4, and three or more main phases. It has a multi-grain grain boundary 2 surrounded by particles 4. The ferrite having the hexagonal crystal structure is preferably magnetoplumbite type ferrite (M type ferrite).

In the ferrite sintered magnet 10 according to the present embodiment, the total area Am of the main phase particles 4 and the total area Ag of the multi-grain grain boundaries 2 in the cross section including the easy magnetization axis direction Y satisfy the following formula (1). Hereinafter, the value of Am / (Am + Ag) may be referred to as a main phase area ratio (%). Am and Ag can be counted, for example, within a range of 4.7 μm × 7.6 μm.
85% ≦ Am / (Am + Ag) ≦ 98% (1)

  According to the ferrite sintered magnet according to the present embodiment, the balance between Br and HcJ is excellent. The reason for this is not clear, but can be considered as follows. 85% ≦ Am / (Am + Ag) ≦ 98% means that the area ratio of the main phase particles is higher than a certain level than the area of the multi-grain boundaries, and there are more than a certain number of multi-grain boundaries, This is considered to correspond to the fact that phase particles are growing properly. Thereby, it is considered that the orientation and particle size of the main phase particles 4 become uniform, and the magnetic properties can be improved in a balanced manner. Thereby, it is considered that the orientation and particle size of the main phase particles 4 become uniform, and the magnetic properties can be improved in a balanced manner. In the case of 85%> Am / (Am + Ag), it means that the area of the main phase particles is not so large, which is considered to correspond to the increase of the area of the nonmagnetic component. On the other hand, when Am / (Am + Ag)> 98%, this indicates that the area ratio of the main phase particles is considerably increased, which is considered to correspond to the fact that the main phase particles are growing too much.

  In the present embodiment, when the main phase area ratio is 85% or more, the area ratio of the nonmagnetic component is reduced, and the magnetic properties of the ferrite sintered magnet can be improved in a balanced manner. In the present embodiment, when the main phase area ratio is 98% or less, the growth of the main phase particles 4 is moderately promoted, and a well-balanced magnetic characteristic is easily obtained.

  From the same viewpoint, the main phase area ratio is preferably 86% or more, more preferably 88% or more, and further preferably 89% or more. From the same viewpoint, the main phase area ratio is preferably 97% or less, more preferably 96% or less, and further preferably 95% or less.

  In the ferrite sintered magnet 10, the main phase particles 4 are crystal particles, whereas the multi-grain grain boundary 2 includes a glass phase, and the glass phase occupies most of the glass phase. The glass phase can suppress the contact between the main phase particles 4 in the calcination step, the firing step, and the like, and can suppress the growth of the main phase particles 4. On the other hand, the glass phase becomes a liquid phase in the firing step and can promote the movement of elements and the growth of the main phase particles 4. Therefore, in the ferrite sintered magnet 10, when the above formula (1) is satisfied and a glass phase is appropriately generated, the growth of the main phase particles 4 can be controlled, and the orientation and the particle size of the main phase particles 4 are uniform. It is thought that it can be made. As a result, a ferrite sintered magnet having a good balance of magnetic properties can be obtained.

Moreover, in the ferrite sintered magnet 10 according to the present embodiment, the number Nm of the main phase particles 4 and the number Ng of the multi-grain grain boundaries 2 in the cross section including the easy magnetization axis direction Y satisfy the following formula (2). preferable. Hereinafter, the value of Nm / (Nm + Ng) may be referred to as the main phase number ratio (%). Nm and Ng can be counted, for example, within a range of 4.7 μm × 7.6 μm.
50% ≦ Nm / (Nm + Ng) ≦ 65% (2)

  50% ≦ Nm / (Nm + Ng) means that the number of main phase particles is equal to or greater than the number of multi-grain grain boundaries, and excessive grain growth is suppressed while main phase particles are growing properly. It is thought that it corresponds to. Thereby, it is considered that the orientation and particle size of the main phase particles 4 become uniform, and the magnetic properties can be improved in a balanced manner. In the case of 50%> Nm / (Nm + Ng), it means that the number of main phase particles is less than the number of multi-grain grain boundaries, and this is considered to correspond to non-uniform orientation and particle size. On the other hand, when Nm / (Nm + Ng)> 65%, it means that the number of main phase particles is considerably larger than the number of multiparticle grain boundaries, and the number of multiparticle grain boundaries is too small. This is thought to correspond to growth being promoted too much.

  From the same viewpoint, the main phase number ratio is preferably 51% or more, more preferably 52% or more, and further preferably 53% or more. From the same viewpoint, the main phase number ratio is preferably 63% or less, more preferably 60% or less, and still more preferably 58% or less.

  The sintered ferrite magnet 10 according to the present embodiment is an oxide containing Ca, R, Sr, Fe, and Co as metal elements. R is at least one element selected from the group consisting of rare earth elements and Bi, and contains at least La.

The sintered ferrite magnet 10 according to this embodiment preferably includes a metal element in an atomic ratio represented by the following formula (3).
_{Ca 1-w-x R w} Sr x Fe z Co m ··· (3)
In formula (3), w, x, z, and m satisfy the following formulas (4) to (7). When w, x, z, and m satisfy the following formulas (4) to (7), the ferrite sintered magnet tends to obtain a better residual magnetic flux density Br and coercive force HcJ.
0.360 ≦ w ≦ 0.420 (4)
0.110 ≦ x ≦ 0.173 (5)
8.51 ≦ z ≦ 9.71 (6)
0.208 ≦ m ≦ 0.269 (7)

The Ca coefficient (1-wx) in the atomic ratio of the metal elements in the sintered ferrite magnet 10 according to the present embodiment is preferably more than 0.435 and less than 0.500. If the Ca coefficient (1-w-x) exceeds 0.435, the main phase particles 4 are likely to be M-type ferrite. In addition to reducing the proportion of non-magnetic phases such as α-Fe ₂ O _3, it is possible to suppress the generation of non-magnetic hetero phases such as orthoferrite due to excessive R, and magnetic properties (particularly Br or HcJ ). From the same viewpoint, the Ca coefficient (1-w-x) is more preferably 0.436 or more, and further preferably more than 0.445. On the other hand, when the Ca coefficient (1-w-x) is less than 0.500, the main phase particles 4 are easily converted to M-type ferrite, and the nonmagnetic phase such as CaFeO _3-x is reduced, resulting in excellent magnetic properties. Characteristics are easily obtained. From the same viewpoint, the Ca coefficient (1-w-x) is more preferably 0.491 or less.

  R in the atomic ratio of the metal element in the sintered ferrite magnet according to the present embodiment is at least one element selected from the group consisting of rare earth elements and Bi, and includes at least La. Examples of rare earth elements include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. R is preferably La. When R is La, the anisotropic magnetic field can be improved.

  The coefficient (w) of R in the atomic ratio of the metal elements in the sintered ferrite magnet according to the present embodiment is preferably 0.360 or more and 0.420 or less. When the coefficient (w) of R is within the above range, good Br, HcJ and squareness ratio Hk / HcJ tend to be obtained. When the coefficient (w) of R is 0.360 or more, the amount of Co solid solution in the ferrite sintered magnet becomes sufficient, and it becomes easy to suppress the decrease in Br and HcJ. From the same viewpoint, the coefficient (w) of R is more preferably more than 0.370, and further preferably 0.380 or more. On the other hand, if the coefficient (w) of R is 0.420 or less, non-magnetic heterogeneous phase such as orthoferrite is suppressed, and the sintered ferrite magnet has a higher Hk / HcJ and is more practical. be able to. From the same viewpoint, the R coefficient (w) is more preferably less than 0.410.

  The coefficient (x) of Sr in the atomic ratio of metal elements in the sintered ferrite magnet according to this embodiment is preferably 0.110 or more and 0.173 or less. When the coefficient (x) of Sr is within the above range, better Br, HcJ and Hk / HcJ can be obtained. When the coefficient (x) of Sr is 0.110 or more, the ratio of Ca and / or La becomes small, and it becomes easy to suppress a decrease in HcJ. On the other hand, when the coefficient (x) of Sr is 0.173 or less, sufficient Br and HcJ are easily obtained. From the same viewpoint, the coefficient (x) of Sr is more preferably less than 0.170, and further preferably less than 0.165.

  The Fe coefficient (z) in the atomic ratio of the metal elements in the sintered ferrite magnet according to the present embodiment is preferably 8.51 or more and 9.71 or less. When the coefficient (z) of Fe is within the above range, better Br, HcJ and Hk / HcJ can be obtained. The coefficient (z) of Fe is more preferably more than 8.70 and less than 9.40 from the viewpoint of obtaining better HcJ. Further, the Fe coefficient (z) is more preferably more than 8.90 and less than 9.20 from the viewpoint of obtaining better Hk / HcJ.

  The Co coefficient (m) in the atomic ratio of metal elements in the sintered ferrite magnet according to the present embodiment is preferably 0.208 or more and 0.269 or less. When the Co coefficient (m) is 0.208 or more, more excellent HcJ can be obtained. From the same viewpoint, the Co coefficient (m) is more preferably more than 0.210, still more preferably more than 0.220, and particularly preferably 0.250 or more. On the other hand, if the Co coefficient (m) is 0.269 or less, more excellent Br can be obtained. From the same viewpoint, the Co coefficient (m) is more preferably 0.250 or less. Moreover, an anisotropic magnetic field can be improved more because a ferrite sintered magnet contains Co.

The ferrite sintered magnet 10 according to the present embodiment preferably includes B (boron). The content of B in the sintered ferrite magnet 10 is preferably 0.037% by mass or more and 0.181% by mass or less in terms of H ₃ BO ₃ . When the sintered ferrite magnet 10 contains 0.037% by mass or more in terms of H ₃ BO ₃ , stable HcJ can be easily obtained even when the calcining temperature changes, and the main phase area ratio and main Since the phase number ratio is improved, Br and HcJ are easily improved in a balanced manner. From the same viewpoint, the B content is more preferably 0.050% by mass or more, and even more preferably 0.070% by mass or more in terms of H ₃ BO ₃ . On the other hand, when the content of B in the sintered ferrite magnet 10 is 0.181% by mass or less in terms of H ₃ BO ₃ , high HcJ is easily maintained. From the same viewpoint, the content of B is more preferably 0.165% by mass or less, and further preferably 0.150% by mass or less in terms of H ₃ BO ₃ .

The sintered ferrite magnet 10 according to this embodiment preferably further contains Al (aluminum). The content of Al in the ferrite sintered magnet 10 is preferably 0.03% by mass or more and 0.3% by mass or less in terms of Al ₂ O ₃ . When ferrite sintered magnet 10 contains 0.03% by mass or more of Al in terms of Al ₂ O ₃ , grain growth during calcination tends to be suppressed, and the main phase area ratio and main phase number ratio tend to be improved. As a result, Br and HcJ of the obtained sintered ferrite magnet 10 are easily improved in a balanced manner. From the same viewpoint, the content of Al is more preferably 0.10% by mass or more in terms of Al ₂ O ₃ . On the other hand, when the content of Al in the ferrite sintered magnet 10 is 0.3% by mass or less in terms of Al ₂ O ₃ , excellent Br and HcJ can be obtained.

The sintered ferrite magnet 10 according to the present embodiment can further include Si (silicon). The content of Si in the ferrite sintered magnet 10 can be 0.1 to 3% by mass in terms of SiO ₂ . When the ferrite sintered magnet 10 contains Si within the above range, high HcJ is easily obtained. From the same viewpoint, the content of Si may be 0.5 to 1.0 mass% in terms of SiO _2.

  The sintered ferrite magnet 10 according to the present embodiment may further include Ba (barium). When the ferrite sintered magnet 10 contains Ba, the content of Ba in the ferrite sintered magnet can be 0.001 to 1.0% by mass in terms of BaO, and 0.001 to 0.068% by mass. There may be. Even if the ferrite sintered magnet contains Ba in the above range, the HcJ of the ferrite sintered magnet can be maintained at a high value. However, when Ba is contained in an amount exceeding 1.0 mass% in terms of BaO, the dependency on the sintering temperature is lowered and the coercive force tends to be lowered.

  The sintered ferrite magnet 10 according to the present embodiment further includes Cr, Ga, Mg, Cu, Mn, Ni, Zn, In, Li, Ti, Zr, Ge, Sn, V, Nb, Ta, Sb, As, W, Mo, etc. may be included. The content of each element is preferably 3% by mass or less, more preferably 1% by mass or less in terms of oxide. Further, from the viewpoint of avoiding deterioration of magnetic properties, the total content of these elements is preferably 2% by mass or less.

  The sintered ferrite magnet 10 according to the present embodiment preferably does not contain an alkali metal element (Na, K, Rb, etc.). Alkali metal elements tend to reduce the saturation magnetization of the ferrite sintered magnet 10. However, the alkali metal element may be included in the raw material for obtaining the ferrite sintered magnet 10, for example, and if included in such a case, the alkali metal element is included in the ferrite sintered magnet 10. It may be. The content of the alkali metal element that does not greatly affect the magnetic identification is 3% by mass or less.

  The composition of the sintered ferrite magnet 10 can be measured by fluorescent X-ray quantitative analysis. The presence of the main phase can be confirmed by X-ray diffraction or electron beam diffraction.

  The average particle diameter of the main phase particles 4 in the ferrite sintered magnet 10 according to the present embodiment is preferably 1.5 μm or less, more preferably 1.0 μm or less, and further preferably 0.5 to 1.0 μm. It is. By having such an average crystal grain size, high HcJ is easily obtained. The average particle diameter of the main phase particles 4 of the ferrite sintered magnet 10 can be, for example, the Feret diameter (n = 10 particles) in the cross section including the easy axis direction of magnetization.

(Manufacturing method of ferrite sintered magnet)
Below, an example of the manufacturing method of the ferrite sintered magnet 10 which concerns on this embodiment is shown. The manufacturing method includes a raw material powder preparation step, a calcination step, a pulverization step, a forming step, and a baking step. Moreover, the said manufacturing method may be provided with the drying process of the fine grinding | pulverization slurry, and the kneading | mixing process between the said grinding | pulverization process and the said shaping | molding process, and a degreasing process is carried out between the said shaping | molding process and the said baking process. You may have. Each step will be described below.

<Raw material powder preparation process>
In the raw material powder preparation step, the raw material powder is obtained by mixing the raw materials of the sintered ferrite magnet to obtain a raw material mixture and, if necessary, pulverizing it. First, as a raw material of a ferrite sintered magnet, a compound (raw material compound) containing one or two or more of elements constituting the ferrite magnet is exemplified. The raw material compound is preferably, for example, in powder form. Examples of the raw material compound include oxides of each element or compounds (carbonates, hydroxides, nitrates, etc.) that become oxides upon firing. For example, SrCO ₃ , La ₂ O ₃ , Fe ₂ O ₃ , BaCO ₃ , CaCO ₃ , Co ₃ O ₄ , H ₃ BO ₃ , Al ₂ O ₃ , and SiO ₂ can be exemplified.

  For example, each raw material is weighed and mixed so as to obtain a desired ferrite sintered magnet composition, and then mixed and pulverized for about 0.1 to 20 hours using a wet attritor, a ball mill, or the like. The average particle diameter of the raw material compound powder is preferably about 0.1 to 2.0 μm from the viewpoint of enabling uniform blending, for example. The raw material powder contains at least Ca, R, Sr, Fe, Co, and B. In particular, when the raw material powder contains B, stable HcJ is easily obtained even when the calcining temperature is changed, and the main phase area ratio and main phase number ratio are improved, so that Br and HcJ are balanced. It becomes easy to improve well. When the ferrite sintered magnet contains Al, the raw material powder further contains Al. Thereby, the grain growth at the time of calcination tends to be suppressed, and the main phase area ratio and the main phase number ratio tend to be improved.

  Part of the raw material can also be added in the pulverization step described later. However, in this embodiment, it is preferable not to add a part of the raw material in the pulverization step. That is, it is preferable that all of Ca, R, Sr, Fe, Co and B (excluding elements inevitably mixed) constituting the sintered ferrite magnet to be obtained are supplied from the raw material powder in the raw material powder preparation step. . In particular, it is preferable that all of B constituting the ferrite sintered magnet is supplied from the raw material powder in the raw material powder preparation step. Moreover, it is preferable that all of the Al constituting the ferrite sintered magnet is supplied from the raw material powder in the raw material powder preparation step. Thereby, the above-described effects due to the raw material powder containing B or Al are further easily obtained.

<Calcination process>
In the calcining step, the raw material powder obtained in the raw material powder preparation step is calcined. The calcination is preferably performed in an oxidizing atmosphere such as air (atmosphere). The calcination temperature is preferably in the temperature range of 1100 to 1400 ° C, more preferably 1100 to 1300 ° C, and even more preferably 1150 to 1300 ° C. The calcination time (the time for holding at the calcination temperature) can be 1 second to 10 hours, and preferably 1 second to 5 hours. The calcined body obtained by calcining contains 70% or more of the main phase (M phase) as described above. The primary particle size of the calcined body is preferably 5 μm or less.

<Crushing process>
In the pulverization step, the calcined body that has been granulated or agglomerated in the calcination step is pulverized and again powdered. Thereby, shaping | molding in the shaping | molding process mentioned later becomes easy. In this pulverization step, raw materials not mixed in the raw material powder preparation step may be further added. However, from the viewpoint of improving the main phase area ratio and the main phase number ratio, it is preferable that all raw materials are mixed in the raw material powder preparation step. The pulverization step may be a two-step process in which, for example, the calcined body is pulverized (coarse pulverization) into a coarse powder, and then finely pulverized (fine pulverization).

The coarse pulverization is performed using, for example, a vibration mill or the like until the average particle size becomes 0.5 to 5.0 μm. In the fine pulverization, the coarsely pulverized material obtained by the coarse pulverization is further pulverized by a wet attritor, a ball mill, a jet mill or the like. In the fine pulverization, the average particle size of the obtained fine pulverized material is preferably 0.08 to 2.0 μm, more preferably 0.1 to 1.0 μm, and still more preferably about 0.1 to 0.5 μm. As such, fine grinding is performed. The specific surface area of the finely pulverized material (for example, determined by the BET method) is preferably about 4 to 12 m ² / g. The suitable pulverization time varies depending on the pulverization method. For example, in the case of a wet attritor, it is preferably about 30 minutes to 20 hours, and in the case of wet pulverization with a ball mill, it is preferably about 10 to 50 hours.

  In the fine pulverization step, in the case of the wet method, as the dispersion medium, non-aqueous dispersion media such as toluene and xylene can be used in addition to water. When a non-aqueous dispersion medium is used, high orientation tends to be obtained during wet molding described later. On the other hand, the use of an aqueous dispersion medium is advantageous from the viewpoint of productivity.

In the fine pulverization step, for example, a polyhydric alcohol represented by the general formula C _n (OH) _n H _{n + 2} may be added as a dispersant in order to increase the degree of orientation of the sintered body obtained after firing. Here, as a polyhydric alcohol, in general formula, it is preferable that n is 4-100, It is more preferable that it is 4-30, It is more preferable that it is 4-20, It is 4-12 Is particularly preferred. Examples of the polyhydric alcohol include sorbitol. Two or more polyhydric alcohols may be used in combination. Furthermore, other known dispersants may be used in combination with the polyhydric alcohol.

  When adding a polyhydric alcohol, it is preferable that the addition amount is 0.05-5.0 mass% with respect to an addition target object (for example, coarsely pulverized material), and 0.1-3.0 mass. % Is more preferable, and 0.2 to 2.0% by mass is even more preferable. The polyhydric alcohol added in the fine pulverization step is thermally decomposed and removed in a baking step described later.

<Molding process>
In the molding step, the pulverized material (preferably finely pulverized material) obtained after the pulverization step is molded in a magnetic field to obtain a molded body. Molding can be performed by either dry molding or wet molding. From the viewpoint of increasing the degree of magnetic orientation, it is preferably performed by wet molding.

  In the case of molding by wet molding, for example, after obtaining the slurry by performing the above-described fine grinding process in a wet manner, the slurry is concentrated to a predetermined concentration to obtain a slurry for wet molding, and this is used. It is preferable to perform molding. Concentration of the slurry can be performed by centrifugation or a filter press. It is preferable that the finely pulverized material accounts for about 30 to 80% by mass in the total amount of the slurry for wet molding. In this case, a surfactant such as gluconic acid, gluconate and sorbitol may be added to the slurry. A non-aqueous dispersion medium may be used as the dispersion medium. As the non-aqueous dispersion medium, an organic dispersion medium such as toluene and xylene can be used. In this case, it is preferable to add a surfactant such as oleic acid. In addition, you may prepare the slurry for wet shaping | molding by adding a dispersion medium etc. to the fine ground material of the dry state after fine grinding.

In the wet molding, the wet molding slurry is then molded in a magnetic field. In that case, the molding pressure is preferably about 9.8 to 49 MPa (0.1 to 0.5 ton / cm ² ), and the applied magnetic field is preferably about 398 to 1194 kA / m (5 to 15 kOe). .

<Baking process>
In the firing step, the molded body obtained in the molding step is fired to obtain a sintered body. Thereby, the sintered body of a ferrite magnet as described above, that is, a sintered ferrite magnet is obtained. Firing can be performed in an oxidizing atmosphere such as the air. The firing temperature is preferably 1050 to 1270 ° C, more preferably 1080 to 1240 ° C. Moreover, it is preferable that baking time is about 0.5 to 3 hours.

  When a molded body is obtained by wet molding as described above, if the molded body is not sufficiently dried and heated rapidly in the firing process, volatilization of the dispersion medium or the like may occur violently and cracks may occur in the molded body. There is. Therefore, from the viewpoint of avoiding such inconvenience, before reaching the above sintering temperature, the molded body is sufficiently dried by heating from room temperature to about 100 ° C., for example, at a low temperature rising rate of about 1 ° C./min. It is preferable to suppress the generation of cracks. Further, when a surfactant (dispersing agent) or the like is added, for example, by heating at a rate of temperature increase of about 3 ° C./min in a temperature range of about 100 to 500 ° C., these are sufficiently removed. (Degreasing treatment) is preferable. In addition, these processes may be performed at the beginning of a baking process, and may be performed separately before a baking process.

  Furthermore, the rate of temperature rise when heating to the firing temperature is preferably 5 ° C./min or less, more preferably 3 ° C./min or less, still more preferably 1 ° C./min or less, and It is particularly preferably 5 ° C./min or less. When the temperature increase rate is within the above range, the main phase area ratio and the main phase number ratio of the obtained sintered ferrite magnet tend to be improved. On the other hand, the cooling rate when cooling from the firing temperature is preferably 5 ° C./min or more, and more preferably 10 ° C./min or more. When the temperature decreasing rate is within the above range, a sintered ferrite magnet having excellent Br and HcJ in a well-balanced state can be easily obtained.

  Through the above steps, the main phase particles 4, the two grain boundaries 1 located between the two main phase particles 4, and the multi-grain grain boundaries 2 surrounded by three or more main phase particles 4, The ferrite sintered magnet 10 having the main phase area ratio of 85% or more is manufactured.

  As mentioned above, although the suitable manufacturing method of the ferrite sintered magnet was demonstrated, as long as the ferrite sintered magnet of this invention is manufactured, the manufacturing method is not limited to the manufacturing method demonstrated above, Conditions etc. are changed suitably. be able to.

  The shape of the ferrite sintered magnet is not particularly limited. The ferrite sintered magnet may have a plate shape such as a disk, may have a column shape such as a cylinder or a square column, may have a shape such as a C shape, an arc shape, an arch shape, or the like, or a ring shape. It may be.

  The sintered ferrite magnet according to the present embodiment can be used for, for example, rotating machines such as motors and generators, and various sensors.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example.

(Preparation of sintered ferrite magnet)
[Example 1]
<Raw material powder preparation process>
Calcium carbonate (CaCO ₃ ), lanthanum oxide (La ₂ O ₃ ), strontium carbonate (SrCO ₃ ), iron oxide, and cobalt oxide (Co ₃ O ₄ ) are prepared as raw materials for metal elements constituting the sintered ferrite magnet. did. In a ferrite sintered magnet containing these raw materials at an atomic ratio represented by the following formula (3a), w = 0.39, x = 0.14, z = 9.1, m = 0.25. Weighed and mixed. Next, boric acid (H ₃ BO ₃ ), silicon oxide (SiO ₂ ), and aluminum oxide (Al ₂ O ₃ ) were further prepared as raw materials for the sintered ferrite magnet. The boron content is 0.16% by mass in terms of H ₃ BO ₃ , the silicon content is 0.72% by mass in terms of SiO ₂ , and the aluminum content is 0% with respect to the entire ferrite sintered magnet obtained. Boric acid, silicon oxide, and aluminum oxide were weighed and added to the above mixture so as to be 0.05 mass%. The obtained raw material mixture was mixed with a wet attritor, pulverized, and dried to obtain a raw material powder.
_{Ca 1-w-x La w} Sr x Fe z Co m ··· (3a)

<Calcination and grinding process>
The raw material powder was calcined in the atmosphere at 1200 ° C. for 2 hours to obtain a calcined body. The obtained calcined body was coarsely pulverized by a small rod vibration mill so that the specific surface area determined by the BET method was 0.5 to 2.5 m ² / g. The obtained coarsely pulverized material was finely pulverized for 32 hours using a wet ball mill to obtain a wet molding slurry having finely pulverized particles having a specific surface area determined by the BET method of 7.0 to 10 m ² / g. The finely pulverized slurry was dehydrated with a centrifuge and the solid content concentration was adjusted to 70 to 80% by mass to obtain a slurry for wet molding.

<Molding and firing process>
The wet molding slurry is applied to the wet molding slurry from above and below the cylindrical cavity by using a wet magnetic field molding machine including a mold having a cylindrical cavity, and the direction parallel to the pressure direction (applied magnetic field) Direction) and an applied magnetic field of 10 kOe to obtain a cylindrical molded body having a diameter of 30 mm and a thickness of 15 mm. The obtained molded body was sufficiently dried at room temperature in the air. The dried compact was fired in the air at a rate of 1.0 ° C./min, held at 1205 ° C. for 1 hour, and then cooled down at 10.0 ° C./min. A magnet was obtained.

[Example 2]
In the firing step, the dried compact was heated at 5.0 ° C./min in the atmosphere, held at 1215 ° C. for 1 hour, and then calcined at a temperature of 5.0 ° C./min. Obtained the sintered ferrite magnet of Example 2 in the same manner as Example 1.

[Example 3]
In the firing step, the dried molded body was heated at 1.0 ° C./min in the atmosphere, held at 1190 ° C. for 4 hours, and then lowered at 10.0 ° C./min. Obtained a sintered ferrite magnet of Example 3 in the same manner as Example 1.

[Example 4]
In the firing step, the dried molded body was heated at 0.5 ° C./min in the atmosphere, held at 1205 ° C. for 1 hour, and then lowered at 10.0 ° C./min. Obtained the sintered ferrite magnet of Example 4 in the same manner as Example 1.

[Comparative Example 1]
A ferrite sintered magnet of Comparative Example 1 was obtained in the same manner as in Example 2 except that boric acid and aluminum oxide were not added in the raw material powder preparation step.

(Evaluation methods)
[Main phase area ratio and main phase number ratio in the cross section including the easy axis direction]
The upper and lower surfaces of the cylindrical ferrite sintered magnets obtained in the examples and comparative examples were polished. Thereafter, the ferrite sintered magnet was cut along a plane including the direction of the easy axis of magnetization (applied magnetic field in molding), and the cut surface was observed with a transmission electron microscope (TEM). In the TEM image, 10 ranges of 4.7 μm × 7.6 μm were selected, and the area Am occupied by the main phase particles existing in each range and the area Ag occupied by the multi-grain grain boundaries were determined, and the main phase area ratio was determined Calculated. The average value was calculated | required from the area ratio in 10 selected ranges. The main phase particles, the two-particle grain boundaries, and the multi-grain grain boundaries in the TEM image were discriminated visually from the color density of the TEM image.

  Further, in the TEM image, 10 ranges of 4.7 μm × 7.6 μm were selected, and the number Nm of particulate main phase particles existing in each range and the number Ng of multi-grain grain boundaries were counted, and the number of main phases The percentage was determined. In addition, when even a part of the main phase particles or the like is included in the range, it is assumed that it exists in the range. The average value was determined from the number ratio in the selected 10 ranges. Table 1 shows the calculation results of the main phase area ratio and the main phase number ratio (average value).

[Magnetic properties]
After processing the upper and lower surfaces of each cylindrical sintered ferrite magnet obtained in the examples and comparative examples, using a B-H tracer with a maximum applied magnetic field of 25 kOe, these residual magnetic flux densities Br (mT) and coercive force HcJ (KA / m) was determined. The value of Br + HcJ / 10 was calculated from the obtained values of Br and HcJ. Br + HcJ / 10 is an index indicating the overall magnetic properties of the sintered ferrite magnet, and it has recently been demanded that the balance between Br and HcJ is maintained such that the value of Br + HcJ / 10 is increased. That is, a high Br + HcJ / 10 means that the sintered ferrite magnet has excellent Br and HcJ in a balanced manner. Table 1 shows the values of Br, HcJ, and Br + HcJ / 10.

  FIG. 1B is a TEM photograph showing a cross section including the easy magnetization axis direction of the sintered ferrite magnet obtained in Example 4. The black part in FIG. 1B is the multi-particle grain boundary 2, and the other white or gray part is the main phase particle 4. In FIG. 1B, the ferrite sintered magnet 10 is surrounded by a plurality of main phase particles 4, a two-particle grain boundary 1 located between the two main phase particles 4, and three or more main phase particles 4. As a result of the analysis, it was confirmed that the main phase area ratio was 85% or more and the main phase number ratio was 50% or more.

  Further, FIG. 2 shows TEM photographs of cross sections including the easy axis direction of the sintered ferrite magnets obtained in the examples and comparative examples. 2, (a) shows the cross section of the ferrite sintered magnet of Example 4 (same as (b) of FIG. 1), (b) shows the cross section of the ferrite sintered magnet of Example 2, and (c ) Shows a cross section of the sintered ferrite magnet of Comparative Example 1. FIG. 2 shows that the main phase particles are dense in the order of (c), (b), and (a), and both the main phase area ratio and the main phase number ratio increase.

  As is clear from Table 1, the ferrite sintered magnet of the example whose main phase area ratio is 85% or more has a high value of Br + HcJ / 10, and has excellent Br and HcJ in a well-balanced manner, so that it is generally high. It was confirmed to have magnetic properties.

DESCRIPTION OF SYMBOLS 1 ... 2 grain boundary, 2 ... Multi grain boundary, 4 ... Main phase particle, 10 ... Ferrite sintered magnet.

Claims (3)

Ferrite sintering having a main phase particle containing ferrite having a hexagonal crystal structure, a two-particle grain boundary formed between the two main phase particles, and a multi-grain grain boundary surrounded by three or more main phase particles A magnet,
The sintered ferrite magnet includes Ca, R, Sr, Fe and Co,
R is at least one element selected from the group consisting of rare earth elements and Bi and contains at least La;
A ferrite sintered magnet in which the total area Am of the main phase particles and the total area Ag of the multi-grain grain boundaries satisfy the following formula (1) in a cross section including the easy axis of magnetization of the sintered ferrite magnet.
85% ≦ Am / (Am + Ag) ≦ 98% (1) The ferrite sintered magnet further contains Al,
The ferrite sintered magnet according to claim 1, wherein the content of Al is 0.03 to 0.3% by mass in terms of Al ₂ O ₃ . The ferrite sintered magnet further includes B,
The content of B is 0.037 to 0.181 wt% in _H 3 BO ₃ terms ferrite sintered magnet according to claim 1 or 2.