JP2005045167A - Anisotropic ferrite magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anisotropic ferrite magnet having satisfactory squareness and high coercive force, and to provide a method for manufacturing the anisotropic ferrite magnet. <P>SOLUTION: The magnet has a basic composition expressed by A<SB>1-x</SB>R<SB>x</SB>Fe<SB>2n-y</SB>Co<SB>y</SB>O<SB>α</SB>. In the expression, A denotes at least one of Sr, Ba, and Ca and necessarily includes Sr, and R is at least one kind of La, Nd, and Pr and necessarily includes La. Moreover, y, x, n, and α satisfy the conditions 0.05≤y≤0.5, 1.1≤x/y≤1.6, 5≤n≤6, and α=15-20. Furthermore, in the anisotropic ferrite magnet, a ferrous ion of at least 0.12% in percentage by mass is contained and a squareness ratio Hk/iHc of magnetic characteristic is at least 85%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is extremely useful in a wide range of magnet application fields, and has a high performance anisotropic with a high residual magnetic flux density (Br), coercive force (iHc), and squareness ratio (Hk / iHc). The present invention relates to a conductive ferrite magnet and a manufacturing method thereof.

  Ferrite magnets are used in various applications including rotating machines such as motors and generators. Recently, there has been a demand for ferrite magnets having higher magnetic properties for the purpose of reducing the size and weight in the field of rotating machines for automobiles, and for the purpose of improving efficiency in the field of rotating machines for electrical equipment. In particular, in the field of automotive rotating machines, there is a demand for thin ferrite magnets for miniaturization and weight reduction, and there is a need for ferrite magnets with high coercivity that can withstand demagnetization due to the high demagnetizing field generated by thinning. The current situation is.

Conventionally, high-performance sintered magnets of Sr ferrite or Ba ferrite have been manufactured as follows. That is, after the iron oxide and Sr or Ba carbonate are mixed, the ferritization reaction is terminated by calcination treatment. The calcined clinker is coarsely pulverized. The coarsely pulverized calcined powder is finely pulverized with additives such as SiO ₂ , SrCO ₃ and CaCO ₃ for the purpose of controlling the sintering behavior until the average particle size of the powder becomes 0.5 to 1.0 μm. . The finely pulverized slurry is wet-molded while being oriented in a magnetic field to obtain a molded body. After the molded body is fired, it is processed into a product shape to obtain a product. In this case, it is desirable to add Al ₂ O ₃ or Cr ₂ O ₃ in order to improve the coercive force iHc. The coercive force is improved by adding Al ₂ O ₃ or Cr ₂ O ₃ because Al or Cr dissolves in ferrite and lowers the saturation magnetization of the ferrite, and suppresses grain growth during sintering. It is to do. Therefore, if Al ₂ O ₃ or Cr ₂ O ₃ is added, there is a side effect that the residual magnetic flux density Br proportional to the saturation magnetization inevitably decreases.

In order to solve this problem, the present inventors have intensively studied, and as a result, another metal oxide was added to the composition that can be represented by AO.nFe ₂ O ₃ (where A is one or more of Sr and Ba). It has been found that it is extremely effective to replace a part of the A element of the composition with La or the like and a part of the Fe element with Co element or the like by adding a substance (Patent Document 1). . Magnetism of the magnetoplumbite type ferrite magnet bears the magnetic moment of Fe ions, and has a magnetic structure of a ferrimagnetic material in which this magnetic moment is partially arranged in an antiparallel direction by Fe ion sites. A method for increasing the magnetocrystalline anisotropy constant in this magnetic structure is to replace Fe ions with another element that has a stronger interaction with the crystal lattice. That is, the magnetic moment derived from the orbital angular momentum remains or is replaced with an element such as Co. At the same time, La, Nd, or Pr is added as an element that replaces the Sr or Ba site in consideration of charge compensation.

  With the above in mind, the present inventors have conducted detailed studies aimed at replacing Fe ions with various elements by adding various metal oxides. As a result, Co has remarkable magnet characteristics. It was found that the element improves. However, a sufficient effect cannot be obtained by simply adding the above elements. This is because when the Fe ions are replaced with another kind of element, the balance of the ionic valence is lost and a heterogeneous phase is generated. In order to avoid this phenomenon, the Sr or Ba site may be replaced with an element such as Co. Nd and Pr can be used for this purpose, but it has been found that La is particularly effective.

As a substitute for Al ₂ O ₃ or Cr ₂ O ₃ , a compound addition method of a compound containing La and Co has been found, and a high performance of the ferrite magnet can be realized. A feature of the compound addition method of a compound containing La and Co is that a high coercive force can be achieved without significantly reducing Br. As described above, when Al ₂ O ₃ or Cr ₂ O _{3 is} added, the coercive force is increased by lowering the saturation magnetization, whereas in the case of compound addition of a compound containing La and Co, This is believed to be due to the effect of improving the magnetocrystalline anisotropy constant itself.

Next, another conventional technique will be described.
In Patent Document 2, as a ferrite magnet for performing LaCo substitution, a composition of M _1-x R _x Fe _12-y T _y O _{19 has} a composition of 0.04 <x <0.9, 0.8 <x / y <. It is described that the ratio is 20. As for divalent iron, in the right column on page 8, lines 19 to 25, “The reason why x / y is greater than 1 and the allowable range is large is that Fe ³⁺ → Fe ^This is because the valence is balanced by the reduction of ²⁺ ”. However, the range of addition of divalent iron that contributes to improving the coercive force is not disclosed.

Patent Document 3 is a technique related to an anisotropic ferrite sintered magnet powder having a magnetoplumbite type crystal structure. In Patent Document 3, “To increase iHc, the Fe ²⁺ content is preferably 0.005 to 0.10 wt%, and more preferably 0.01 to 0.07 wt%”. It is described. However, “It is difficult to make the Fe ²⁺ content less than 0.005% by weight in industrial production, and if the Fe ²⁺ content exceeds 0.10% by weight, further improvement in iHc cannot be expected.” is doing. In addition, the structure of patent document 3 is not a sintered magnet but the technique which concerns on a magnetic powder and a bond magnet.
JP-A-8-306072 (page 3) JP-A-11-154604 (pages 7-8) JP 2002-164204 A (pages 3 to 4)

As explained above, the technique of Patent Document 1 in which a compound containing La and Co is added in combination enables a high coercive force while maintaining the Br value. However, as iHc becomes a high coercive force region of approximately 358 kA / m (4500 Oe), there is a problem that the squareness of the MH curve decreases. In addition, there is a limit to the coercive force value that can be obtained only by the combined addition of a compound containing La and Co, and the maximum is approximately 366 kA / m (4600 Oe) under normal production conditions. Therefore, when a coercive force higher than that is required, it is necessary to add Al ₂ O ₃ or Cr ₂ O ₃ to the La—Co additive. In this case, there is a problem that the squareness is further lowered. Squareness is an extremely important magnet characteristic for practical use in anisotropic magnets. If the squareness ratio, which is a quantitative index of squareness, is low, a high energy product value can be obtained even if the residual magnetic flux density Br is high. Absent.
Therefore, an object of the present invention is to provide a high coercivity anisotropic ferrite magnet having good squareness.

(1) The anisotropic ferrite magnet of the present invention has an atomic ratio of A _1-x R _x Fe _{2 n-y} Co _y O _α (where A is at least one of Sr, Ba, and Ca, and Sr must be present). And R is at least one of La, Nd, and Pr and must include La), and y, x, n, and α,
0.05 ≦ y ≦ 0.5,
1.1 ≦ x / y ≦ 1.6,
5 ≦ n ≦ 6,
15 ≦ α ≦ 20
In addition, it is characterized in that it contains 0.12% or more of divalent iron ions by mass percentage, and the squareness ratio Hk / iHc of magnetic properties is 85% or more.

  Here, iHc is a coercive force. Hk is a magnetic field value corresponding to 95% Br in the second quadrant of the MH curve (M is the strength of magnetization, and H is the strength of the applied magnetic field). More preferably, the molar ratio n is set to 5.0 ≦ n ≦ 6.0. The mass percentage (that is, mass%) represents the mass of the element contained per unit mass of the magnet as a percentage.

(2) In the above (1), 0.1 to 3.0% of Cr ₂ O ₃ or Al ₂ O ₃ is contained by mass percentage with respect to the basic composition.

(3) In the above (1) or (2), 0.1 to 1.0% of SiO _{2 is} contained in mass percentage with respect to the basic composition.

  (4) In any one of (1) to (3), the coercive force iHc is 380 KA / m or more. By containing 0.12% or more of divalent iron ions, a coercive force iHc of 380 KA / m or more can be obtained even at a high squareness ratio.

  (5) The method for producing an anisotropic ferrite magnet of the present invention is a method for producing an anisotropic ferrite magnet according to any one of (1) to (4) above, and includes mixing, calcining, coarse pulverization, It comprises pulverization, molding, firing and processing steps, and the basic composition is substantially formed in the calcination stage.

The present inventors detail the relationship between the composition and manufacturing conditions of the La-Co-added ferrite magnet, the magnet characteristics including the squareness ratio obtained at that time, and the amount of divalent iron (Fe ²⁺ amount) contained in the sintered body. As a result, the La / Co ratio was set to 1.1 to 1.6, and all the materials constituting the basic composition were mixed before calcination in order to make the Fe ²⁺ amount 0.12% or more. Thus, the present inventors have found that an anisotropic ferrite magnet with extremely good squareness can be obtained even in a high coercive force region by performing coarse pulverization, molding in a magnetic field, and firing.

There are several methods for defining the squareness ratio of the MH curve in the anisotropic ferrite magnet, but in the present invention, it corresponds to 95% of the residual magnetic flux density Br in the second quadrant of the MH curve. When the magnetic field value to be used is −Hk, the ratio Hk / iHc between Hk and the coercive force iHc is adopted as a quantitative index of the squareness and is called the squareness ratio. When the basic composition of a ferrite magnet containing La and Co is expressed as follows:
A _1-x R _x Fe _2n-y Co _y O _α
(Where A is at least one of Sr, Ba, and Ca and must contain Sr, and R is at least one of La, Nd, and Pr and must contain La). If the atomic ratio x / y is 1.1 or more and 1.6 or less, and the production conditions are appropriately set to control the Fe ²⁺ amount of 0.12% or more by mass percentage to be included in the ferrite magnet, The squareness ratio in the high coercive force region can be improved without accompanying reduction in iHc and Br. When increasing the amount of Fe ^2+, an additive such as a dispersant (alkaline) is added, or R element is added as a hydroxide (for example, La hydroxide) before calcination. The proportion of Sr in A is preferably 80% or more, more preferably 95% or more. If the Ba component increases in A, Br is improved but iHc is decreased. Further, if the Ca component increases, the squareness of the MH curve decreases. The proportion of La in R is preferably 50 atomic percent or more, more preferably 70 atomic percent or more, and particularly preferably 95 atomic percent or more. In order to obtain high Br, it is ideal to use only La as R.

Here, in order to obtain good magnetic properties, the n value must be 5 or more and 6 or less. When the n value exceeds 6, a different phase other than the magnetoplumbite phase (for example, α-Fe ₂ O ₃ ) is generated, and the magnetic characteristics are deteriorated. On the other hand, when the n value is less than 5, a sufficiently good residual magnetic flux density cannot be obtained due to an increase in nonmagnetic components. The y value is set to 0.05 or more and 0.5 or less. If the y value is less than 0.05, a significant effect relating to the present invention is not recognized, and if it exceeds 0.5, the magnetic properties are reduced.

Of particular importance in the basic composition of the magnet in the present invention is the ratio x / y of the R element to Co. The ionic valences of element A and Co are divalent, and the valences of R element and Fe are trivalent. Therefore, if the presence of the grain boundary phase and divalent Fe ions is ignored, it is electrically neutral. In order to satisfy the condition, x / y = 1 must be satisfied. If the x / y value is set to 1 or more in the basic composition and the manufacturing conditions as described later are appropriately selected, an appropriate amount of Fe ²⁺ ions are generated, and the squareness ratio can be improved without reducing the coercive force. . If x / y is less than 1.1, the effect of the present invention is not sufficient, while if it exceeds 1.6, a decrease in coercive force is observed. Further, in order to make the effects related to the present invention effective, it is necessary that 0.12% or more of Fe ²⁺ ions are contained in mass percentage with respect to the fired body. When the amount of Fe ²⁺ ions is less than 0.12%, the effect related to the present invention is not remarkable. If Fe ²⁺ ions are 0.12% or more, the squareness ratio can be improved without causing a reduction in coercive force. Although the mechanism is not necessarily clear, it is presumed that Fe ²⁺ ions play a role of improving the magnetocrystalline anisotropy.

The maximum coercive force obtained with only the basic composition is approximately 366 kA / m (4600 Oe). When a higher coercive force value is required, 0.1 to 3.0% Cr ₂ O ₃ or Al ₂ O ₃ may be added in mass percentage to the basic composition. If it is less than 0.1%, the effect is not remarkable, and if it exceeds 3.0%, the residual magnetic flux density is significantly reduced. Furthermore, adding 0.1 to 1.0% SiO ₂ by mass percentage to the basic composition is effective in realizing a high coercive force value. This is closely related to the fact that SiO ₂ has an effect of suppressing grain growth during sintering. If it is less than 0.1%, the effect is not remarkable, and if it exceeds 1.0%, the effect of suppressing grain growth becomes excessive and the sintered density is lowered.

It is desirable that the above ferrite composition is substantially formed at the calcination stage of the ferrite magnet manufacturing process described below.
For example, in the case of the manufacturing process of the Sr ferrite magnet, the calcining temperature is approximately 1573 K (1300 ° C.). On the other hand, the sintering temperature is about 1473K (1200 ° C.). For example, sintering is performed within a temperature range of 1461 to 1499K. Thus, in the manufacturing process of a ferrite magnet, the calcining temperature is usually higher than the sintering temperature. In order to generate the necessary Fe ²⁺ ions, it is effective to maintain La at an elevated temperature in an excess of Co. By adding the same amount of La and Co ions at the time of calcination and adding excess La at the time of pulverization, the required Fe ²⁺ amount cannot be obtained even when La is excessive with respect to Co only during sintering. The same applies to the case where La and Co are not added at the time of mixing, and all the required amounts of La and Co are added at the time of pulverization. However, it is not always necessary to add all the required amounts of La and Co during mixing. Even if a part of La is excessively added to Co during mixing and the rest is added during pulverization, the effect of the present invention is not substantially impaired.

  Since the anisotropic ferrite magnet according to the present invention has both high coercive force and good squareness, it is suitable for motors for electric parts related to automobiles, particularly motors such as starters, power steering, electric throttles and the like.

  As described above, according to the present invention, the squareness ratio is increased while maintaining the residual magnetic flux density and / or the coercive force larger than the conventional one while being a ferrite magnet substantially having a magnetoplumbite structure. It has the feature that it can be remarkably improved, and can greatly contribute to the development of a wide range of magnet application products as a new ferrite magnet with excellent cost performance.

Hereinafter, details of the present invention will be described by way of examples. However, the present invention is not limited to these examples.
(Example 1)
Sr is selected as the A element, La is selected as the R element, and the oxides of SrCO ₃ , Fe ₂ O ₃ , La ₂ O ₃ and Co element are represented by the ratio represented by Sr _1-x La _x Fe _2ny Co _y , N = 5.80, y = 0.20, and x = 0.20 to 0.30. They were prepared as a plurality of raw materials having different blending ratios as shown in S-7 and S-13 to S-19 in Tables 1 and 2. Next, after wet mixing, the mixture was calcined in air at 1573 K for 1 hour. The calcined powder was dry pulverized with a roller mill to obtain coarsely pulverized powder. Thereafter, wet grinding was performed with an attritor to obtain a slurry. At this time, SiO ₂ , CaCO ₃ and Cr ₂ O ₃ were used as sintering aids in a mass ratio to the pulverized powder of 0.30%, 0.80% (0.45% in terms of CaO), and 0.80%, respectively. Was added at the initial stage of pulverization. The dispersant for ammonium polycarboxylate was added in an amount of 0.3% by mass with respect to the pulverized powder. This slurry was wet-molded in a magnetic field of 10 kOe to obtain a molded body. This molded body was sintered for 2 hours in any temperature range of 1461 to 1499K to obtain a sintered body. That is, as shown in Tables 1 and 2, a plurality of molded bodies were prepared for raw materials having one blending ratio and sintered at different temperatures to obtain a plurality of sintered body samples.

Next, these sintered bodies were processed into a shape of about 10 × 10 × 20 mm, and the magnet properties at room temperature were evaluated by a BH tracer. Tables 1 and 2 also show the results of evaluating the magnet characteristics and the results of evaluating the amount of Fe ²⁺ in the sintered body by the potassium dichromate capacity method. Potassium dichromate is represented by K ₂ Cr ₂ O ₇ . From Tables 1 and 2, the amount of Fe ²⁺ in the sintered body increases with an increase in the x / y ratio, and in the composition range of x / y = 1.1 or more, 0.12% or more of Fe ²⁺ is contained in mass percentage. I understood it. In order to clarify the x / y dependency of the magnet characteristics including the squareness ratio, the results in Tables 1 and 2 are shown in FIGS. In FIG. 2, since Br, iHc and Hk / iHc are dependent on the sintering temperature, the average value of the characteristics of the samples sintered in the temperature range of 1461 to 1499K is adopted as the vertical axis.

The volumetric method (namely, volumetric analysis) is a general term for analytical methods for determining the amount of a certain substance by measuring the volume (volume, etc.). The potassium dichromate capacity method is a measurement method for obtaining the number of Fe ²⁺ ions per unit mass of a sintered ferrite body by a redox titration method using a potassium dichromate solution as a titration solution. Since the masses of the ions and the iron element are substantially the same, the mass of Fe elements equivalent to the obtained number of ^ions is defined as “Fe ²⁺ amount”.

  1 and 2, it can be seen that the squareness ratio Hk / iHc is improved without causing a significant decrease in iHc as the x / y ratio increases. However, when x / y exceeded 1.6, the squareness ratio began to decrease and iHc decreased.

(Example 2)
Sr was selected as the A element, and La was selected as the R element. In this example, La and Co were calcined under the same number of atoms, and La was further added at the initial stage of fine pulverization so that the composition of La was excessive, that is, x / y ≧ 1.0 during sintering. That is, at the time of mixing, the ratio of Sr _{1-x ′} La _{y ′} Fe _{2n′-y ′} Co _{y ′} is set, and La is additionally added at the time of fine pulverization, whereby Sr _1−x La _x Fe _2n−y Co _y. Here, the mixed composition and the amount of La added during pulverization were adjusted so that the composition represented by n = 5.80, y = 0.20, x = 0.20 to 0.30 was obtained. As shown in S-7 to S-12 of Tables 3 and 4, they were prepared as a plurality of raw materials having different blending ratios.

Next, after wet mixing, the mixture was calcined in air at 1573 K for 1 hour. The calcined powder was dry pulverized with a roller mill to obtain coarsely pulverized powder. Thereafter, wet grinding was performed with an attritor to obtain a slurry. At this time, SiO ₂ , CaCO ₃ and Cr ₂ O ₃ were used as sintering aids in a mass ratio with respect to the pulverized powder of 0.30%, 0.80% (0.45% in terms of CaO), and 0.80, respectively. % Was added at the beginning of grinding. This slurry was wet-molded in a magnetic field of 10 kOe to obtain a molded body. This molded body was sintered for 2 hours in any temperature range of 1461 to 1499K to obtain a sintered body. That is, as shown in Tables 3 and 4, a plurality of molded bodies were prepared for raw materials having one blending ratio and sintered at different temperatures to obtain a plurality of sintered body samples.

Next, these sintered bodies were processed into a shape of about 10 × 10 × 20 mm, and the results of evaluating the magnet properties at room temperature with a BH tracer and the results of evaluating the amount of Fe ²⁺ in the sintered body by the potassium dichromate capacity method Are shown in Tables 3 and 4. From Tables 3 and 4, the amount of Fe ²⁺ in the sintered body did not change greatly even when the x / y ratio was increased, and was less than 0.12% by mass percentage. In order to clarify the x / y dependency of the magnet characteristics including the squareness ratio, the results in Tables 3 and 4 are shown in FIGS. In FIG. 4, since Br, iHc, and Hk / iHc are dependent on the sintering temperature, the average value of the characteristics of the samples sintered in the temperature range of 1461 to 1499K is adopted as the vertical axis.

From FIG. 3 and FIG. 4, it was recognized that although the squareness ratio Hk / iHc was improved as the x / y ratio was increased, iHc was significantly reduced. By comparing the results described in Example 1 and Example 2, if the amount of La is excessive with respect to the amount of Co during calcination, Fe ²⁺ can be effectively generated, and as a result It can be seen that the squareness ratio can be remarkably improved without reducing the coercive force.

  INDUSTRIAL APPLICABILITY The present invention is used for a high-performance anisotropic ferrite magnet having a high residual magnetic flux density (Br), coercive force (iHc), and squareness ratio (Hk / iHc) as compared with the prior art, and a manufacturing method thereof. Can do.

It is a figure which shows an example of the magnet characteristic of this invention magnet. It is a figure which shows an example of the magnet characteristic of this invention magnet. It is a figure which shows an example of the magnet characteristic of this invention magnet. It is a figure which shows an example of the magnet characteristic of this invention magnet.

Claims (4)

A _1-x R _x Fe _2n-y Co _y O _α (where A is at least one of Sr, Ba, and Ca, and Sr is necessarily included, and R is La, Nd, or Pr) At least one kind and always includes La), and y, x, n, and α,
0.05 ≦ y ≦ 0.5,
1.1 ≦ x / y ≦ 1.6,
5 ≦ n ≦ 6,
Anisotropy characterized by being 14 ≦ α ≦ 20, containing 0.12% or more of divalent iron ions by mass percentage, and having a squareness ratio Hk / iHc of magnetic properties of 85% or more. Ferrite magnet. _2. The anisotropic ferrite magnet according to claim 1, comprising 0.1 to 3.0% of Cr ₂ O ₃ or Al ₂ O ₃ by mass percentage with respect to the basic composition. The anisotropic ferrite magnet according to claim 1 or _2, which contains 0.1 to 1.0% of SiO ₂ in terms of mass percentage with respect to the basic composition. The anisotropic ferrite magnet according to claim 1, wherein the anisotropic ferrite magnet has a coercive force iHc of 380 kA / m or more.

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