JP5358998B2 - Manufacturing method of sintered ferrite magnet - Google Patents

Description

The present invention relates to an inexpensive method for producing a new and high-performance ferrite sintered magnet having a high residual magnetic flux density Br and a high intrinsic coercive force HcJ that are equal to or higher than those of a La—Co—Sr ferrite sintered magnet.

  Magneto-plumbite type (M-type) sintered ferrite magnets are used in various applications including rotating machines such as motors and generators. Recently, there has been a demand for sintered ferrite magnets with even higher magnetic properties for the purpose of reducing the size and weight of rotating machines for automobiles and for increasing the efficiency of rotating machines for electrical equipment. In particular, from the viewpoint of miniaturization and weight reduction, there is a demand for a sintered ferrite magnet having high HcJ that does not demagnetize due to a demagnetizing field that is generated when it is made thin while maintaining high Br from the viewpoint of miniaturization and weight reduction.

M-type ferrite sintered magnets such as Sr ferrite and Ba ferrite are (a) a step of mixing iron oxide and carbonates of Sr and Ba, (b) a calcination clinker is obtained by performing a ferrite reaction by calcination Process, (c) coarsely pulverizing the calcined clinker, SiO ₂ for controlling the sintering behavior, SrCO ₃ , CaCO ₃ etc. Al ₂ O ₃ or Cr ₂ O ₃ for controlling HcJ if necessary, And a step of wet pulverizing to an average particle size of about 0.5 μm, (d) a step of forming and drying a slurry of ferrite fine particles in a magnetic field, and (e) a step of firing. The sintered body is further processed into a shape according to the purpose of use, and a ferrite sintered magnet is manufactured.

  In the above manufacturing process, if the average particle size of the fine powder particles in the slurry after the wet pulverization is small, the drainage time from the molded body in the molding process in the magnetic field is remarkably increased, so the molding efficiency (per unit time) The number of moldings) greatly decreases, leading to an increase in the cost of sintered ferrite magnets. This is particularly noticeable when the average particle size is less than 0.7 μm. When the average particle size is relatively large, the molding efficiency is improved, but the magnetic properties of the sintered ferrite magnet are conversely lowered. Similarly, in dry molding, since the molding efficiency deteriorates due to the formation of fine particles, a magnetic powder having a somewhat large average particle diameter is required.

Patent Document 1 has hexagonal ferrite as a main phase, and has a general formula: Ca _1-x R _x (Fe _12-y M _y ) _z O ₁₉ (R is at least one selected from rare earth elements including Y and Bi). It is a seed element, which must contain La, M is Co and / or Ni, and x, y and z satisfy the conditions of 0.2 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 1.0, and 0.5 ≦ z ≦ 1.2, respectively. A ferrite sintered magnet having a composition represented by: In paragraph [0018] and Example 6, the sintered ferrite magnet described in Patent Document 1 has about 2% higher saturation magnetization (4πIs) and about 10% higher anisotropic magnetic field (SrM) than Sr ferrite (SrM). H _A ). It is predicted that a sintered ferrite magnet having such a high value will have a high potential that cannot be realized with SrM. In other words, Br of 4.6 kG (460 mT) or more is obtained, and the maximum value of HcJ may increase by about 10%. However, the magnetic properties of sample No. 2 described in Example 2 of Patent Document 1 (when O ₂ = 20% firing) are Br = 4.4 kG (440 mT) and HcJ = 3.93 kOe (313 kA / m). As shown in FIG. 2, this value is lower than expected and there is much room for improvement. In addition, in this ferrite sintered magnet, it is difficult to obtain magnetic properties equivalent to or better than those of La-Co-Sr ferrite sintered magnets, considering the decrease in magnetic properties when mill scale is used as an iron oxide raw material. It is.

Patent Document 2 has hexagonal magnetoplumbite type ferrite as a main phase, R is at least one element selected from rare earth elements (including Y) and Bi, and M is Co or (Co + Zn). When the composition ratio of the total of Ba, R, Fe and M is the following general formula: Ba _1-x R _x (Fe _{12- y My} ) _z O ₁₉ (where 0.04 ≦ x ≦ 0.9, 0.3 ≦ y ≦ 0.8, 0.7 ≦ z ≦ 1.2) is disclosed. The composition of each calcined sample corresponding to the anisotropic sintered magnet shown in Table 1 of Patent Document 2 is particularly out of the range with a small amount of Ca with respect to the specific composition of the sintered ferrite magnet of the present invention. . Further, the magnetic properties (Br and HcJ shown in FIG. 1) of the obtained sintered ferrite are not sufficiently satisfactory for the demand for high performance. Moreover, when the mill scale is used as an iron oxide raw material in Patent Document 2, it is difficult to obtain magnetic characteristics equivalent to or better than those of a La—Co—Sr ferrite sintered magnet.

Patent Document 3 has an M-type ferrite structure, and is composed of at least one element selected from the group consisting of Sr or Sr and Ba, rare earth elements including Y, and R elements that essentially contain La, Ca, Fe, and Co. A ferrite sintered magnet is disclosed which is manufactured by a process of crushing, forming and firing an oxide magnetic material as an element. The oxide magnetic material is represented by the following general formula (1): A _1-xy Ca _x R _y Fe _2n-z Co _z O ₁₉ (atomic ratio), and the sintered ferrite magnet is represented by the following general formula (2): A _{1- x-y + a} Ca _{x + b} R _{y + c} Fe _2n-z Co _{z + d} O ₁₉ (atomic ratio) [In the formulas (1) and (2), x, y, z and n are respectively Ca , Represents the content and molar ratio of R element and Co, a, b, c and d respectively represent the amount of A element, Ca, R element and Co added in the pulverization step, 0.03 ≦ x ≦ 0.4, 0.1 ≦ y ≦ 0.6, 0 ≦ z ≦ 0.4, 4 ≦ n ≦ 10, x + y <1, 0.03 ≦ x + b ≦ 0.4, 0.1 ≦ y + c ≦ 0.6, 0.1 ≦ z + d ≦ 0.4, 0.50 ≦ {( 1-x-y + a) / (1-y + a + b)} ≦ 0.97, 1.1 ≦ (y + c) / (z + d) ≦ 1.8, 1.0 ≦ (y + c) / x ≦ 20, And 0.1 ≦ x / (z + d) ≦ 1.2. ]. This ferrite sintered magnet deviates from the specific composition range of the ferrite sintered magnet of the present invention in that Sr is essential and the Sr or (Sr + Ba) content is higher than the Ca content. Although the ferrite sintered magnet described in Patent Document 3 has high magnetic properties, the demand for higher performance from users has become increasingly severe, and it is not fully satisfactory, and further improvements in magnetic properties are required. ing. Also in this ferrite sintered magnet, it is difficult to obtain magnetic characteristics equivalent to or better than those of a La-Co-Sr ferrite sintered magnet when mill scale is used as an iron oxide raw material.

Patent Document 4 describes the formula: (1-x) CaO. (X / 2) R ₂ O _3. (Ny / 2) Fe ₂ O ₃ .yMO (R is at least one selected from La, Nd, and Pr) Element, which necessarily contains La, M is at least one element selected from Co, Zn, Ni, Mn and necessarily contains Co, x, y, n represent a molar ratio, 0.4 ≦ x ≦ 0.6 0.2 ≦ y ≦ 0.35, 4 ≦ n ≦ 6, and 1.4 ≦ x / y ≦ 2.5.) Oxidation having a hexagonal M-type magnetoplumbite structure as a main phase A magnetic material is disclosed. However, since the oxide magnetic material described in Patent Document 4 does not have Ba, it is out of the specific composition range of the ferrite sintered magnet of the present invention, and the magnetic performance is sufficiently sufficient for today's demand for higher performance. It is not satisfactory. In addition, when mill scale is used as an iron oxide raw material, it is difficult to obtain magnetic characteristics equivalent to or better than La-Co-Sr ferrite sintered magnets.

In Patent Document 5, after milling the mill scale to an average particle size of 20 μm or less, it was temporarily oxidized at 873 to 1173 K in an O ₂ -containing atmosphere or in the air to change the degree of oxidation of the mill scale to 95% or more. After mixing and mixing Sr or Ba oxides or carbonates, after the secondary oxidation treatment to 973K in an inclined rotary furnace with the atmosphere on the raw material inlet side having an O ₂ concentration of 8-10% , A method for producing a ferrite magnet raw material fired at 1548 to 1573 K is disclosed. However, in Patent Document 5, when the composition of the ferrite sintered magnet of the present invention is selected and mill scale powder is used as the iron oxide raw material for the ferrite sintered magnet having such a composition, the decrease in Br and the like is reduced. It is not described that a magnetic property equal to or better than that of a La—Co—Sr ferrite sintered magnet can be obtained by being suppressed. Furthermore, it is not described or suggested that excellent magnetic properties can be obtained even when the mill-scale powder contains a Fe ₃ O ₄ incompletely oxidized state.

Patent No. 3181559 JP-A-11-97225 International Publication No. 05/027153 International Publication No. 06/028185 Patent No.3611872

Accordingly, an object of the present invention is to provide a novel and high-performance ferrite sintered magnet having a magnetic property equivalent to or higher than that of a La-Co-Sr ferrite sintered magnet using an inexpensive mill scale powder as an iron oxide raw material. It is in providing the manufacturing method of.

  As a result of earnest research in view of the above object, the present inventors have an M-type ferrite structure, Ca, R, which is at least one kind of rare earth elements, and which contains La as an essential element, Ba, Fe, and Co as essential elements It has been found that the sintered ferrite magnet has a temperature dependence of high Br, high HcJ and small HcJ (see International Patent Applications PCT / JP2006 / 304805 and PCT / JP2007 / 052525).

By adopting this novel ferrite sintered magnet composition, the present inventors have caused a significant decrease in Br although it is an inexpensive iron oxide raw material. The La-Co-Sr ferrite sintered magnet is a high-performance material even when the mill scale (iron oxide generated and recovered during the hot rolling process of steel ingots and rolling of steel materials) is used. It has been found that magnetic characteristics equivalent to or better than can be obtained. In particular, even when α-Fe ₂ O ₃ obtained without complete oxidation or mill-scale powder composed of α-Fe ₂ O ₃ and Fe ₃ O ₄ is used as an iron oxide raw material, sufficient magnetic properties are obtained. I found that it can be improved.

That is, the method of the present invention for producing a ferrite sintered magnet has an M-type ferrite structure, and is an essential element including R, Ba, Fe, and Co, which are at least one of Ca and rare earth elements and contain La as an essential element. And the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z (atomic ratio)
[(1-xy), x, y and z are the contents of Ca, R element, Ba and Co, respectively, n represents the molar ratio,
0.3 ≦ 1-xy ≦ 0.65,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65,
4 ≦ n ≦ 7, and
1-xy> y
It is a numerical value satisfying. Is a method for producing a sintered ferrite magnet having a composition represented by the following: an iron oxide raw material having a raw material mixing step, a calcining step, a pulverizing step, a molding step, and a firing step, and blended in the raw material mixing step Mill scale powder was used, and the mill scale powder particles were heat-treated at 973-1273 K in the air or in an oxygen-rich atmosphere, and iron oxide (α-Fe ₂ O ₃ or α-Fe ₂ The content of O ₃ and Fe ₃ O ₄ is 97 to 99% by mass, the Al content (Al ₂ O ₃ conversion value) is 0.2% by mass or less, and the Si content (SiO ₂ conversion value) is 0.03 to 0.25. It is characterized by mass%, Ca content (CaO equivalent value) being 0.03 to 0.25 mass% and Cr content (Cr ₂ O ₃ equivalent value) being 0.05 mass% or less .

In the present invention, the sintered ferrite magnet has the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z O _α (atomic ratio)
[(1-xy), x, y and z are the contents of Ca, R element, Ba and Co, n is the molar ratio, α is the content of O,
0.3 ≦ 1-xy ≦ 0.65,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65,
4 ≦ n ≦ 7, and
1-xy> y
It is a numerical value satisfying. However, when the stoichiometric composition ratio is shown when x = z and n = 6, α = 19. It is preferable to have a composition represented by

  The sintered ferrite magnet has a composition satisfying 1 ≦ x / z ≦ 3, the average crystal grain size of the M-type crystal grains along the direction of imparting anisotropy is 0.9 μm or more, and the M-type crystal grains High orientation when the aspect ratio (maximum diameter of c-plane / thickness in the c-axis direction, hereinafter the same meaning) is 30% or more, preferably 50% or more, more preferably 60% or more. Degrees.

  In the sintered ferrite magnet, part of Ba may be replaced with Sr by adding an Sr compound in the mixing step and / or the pulverizing step.

(1) The ferrite sintered magnet of the present invention has high Br and HcJ, and the temperature dependence of HcJ [temperature coefficient (β)] is small. By incorporating this ferrite sintered magnet, low temperature demagnetization is achieved. It can contribute to high performance and miniaturization of small magnet application products (rotary machines, magnet rolls, etc.).
(2) Since the method of the present invention uses an inexpensive mill scale as the iron oxide raw material, the manufacturing cost can be reduced.

[1] Composition
(A) Composition of oxide magnetic material The raw material of the sintered ferrite magnet of the present invention is mainly composed of ferrite having a hexagonal crystal structure, Ca, R, which is at least one of rare earth elements and essentially contains La, Ba , An oxide magnetic material containing Fe and Co as essential elements, having the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z (atomic ratio)
[(1-xy), x, y and z are the contents of Ca, R element, Ba and Co, respectively, n represents the molar ratio,
0.3 ≦ 1-xy ≦ 0.6,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65, and
4 ≦ n ≦ 7
It is a numerical value satisfying. And those having a basic composition represented by The oxide magnetic material is preferably a calcined body.

The Ca content (1-xy) is preferably 0.3 to 0.6, and more preferably 0.35 to 0.55 . If (1-xy) is less than 0.3, the M phase is not generated stably, and ortho-ferrite is generated by the excess R element, so that the magnetic properties are deteriorated. When (1-xy) exceeds 0.6, an undesirable phase such as CaFeO _3-x is formed.

The value of the molar ratio x / z between the R element and Co is preferably 0.31 ≦ x / z ≦ 21.7, more preferably 1 ≦ x / z ≦ 3, and 1.2 ≦ x / z ≦ 2. Is particularly preferred . When x / z is less than 0.31, the occurrence of a heterogeneous phase containing a large amount of Co becomes remarkable, and the squareness ratio (Hk / HcJ) is remarkably deteriorated. When x / z exceeds 21.7, the occurrence of heterogeneous phases such as orthoferrite becomes remarkable, and the magnetic properties are greatly deteriorated.

R is at least one rare earth element composed of La, Ce, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and essentially contains La. In order to impart high magnetic properties, the ratio of La in the R element is preferably 50 atomic% or more, more preferably 70 atomic% or more, and La alone (however, inevitable impurities are allowed) Is particularly preferred. Of the R elements, La is most easily dissolved in the M phase. Therefore, the larger the ratio of La, the greater the effect of improving magnetic properties. The R content (x) is preferably 0.2 to 0.65, more preferably 0.3 to 0.6, still more preferably 0.35 to 0.55, and particularly preferably 0.4 to 0.5. If x is less than 0.2, the substitution amount of Co for the M phase is insufficient, so the M-type ferrite structure becomes unstable, and magnetic phases are generated by generating different phases such as CaO · Fe ₂ O ₃ and CaO · 2Fe ₂ O _3. The characteristics are greatly reduced. When x exceeds 0.65, an unreacted oxide of R element increases, and an undesirable phase such as orthoferrite is generated.

  The Ba content (y) is preferably 0.001 to 0.2, more preferably 0.005 to 0.2, still more preferably 0.01 to 0.2, particularly preferably 0.02 to 0.15, and 0.02 to 0.12. Most preferably. If y is less than 0.001, the effect of improving the magnetic properties by adding Ba cannot be obtained. Conversely, when y exceeds 0.2, the magnetic properties are degraded.

The Co content (z) is preferably 0.03 to 0.65, more preferably 0.1 to 0.55, and particularly preferably 0.2 to 0.4. If z is less than 0.03, the effect of improving magnetic properties by adding Co cannot be obtained. In addition, since unreacted α-Fe ₂ O ₃ remains in the calcined body, slurry leakage occurs from the mold cavity during wet molding. When z exceeds 0.65, a heterogeneous phase containing a large amount of Co is generated and the magnetic properties are greatly deteriorated.

The molar ratio n is a value that reflects the molar ratio of (Ca + R + Ba) and (Fe + Co), and is expressed by 2n = (Fe + Co) / (Ca + R + Ba). The molar ratio n is preferably from 4 to 7, more preferably from 4 to 6, still more preferably from 4.6 to 5.8, and particularly preferably from 4.9 to 5.6. When n is less than 4, the ratio of the nonmagnetic portion increases. When the oxide magnetic material is a calcined body, the shape of the calcined body particles becomes excessively flat and HcJ is greatly reduced. When n exceeds 7, unreacted α-Fe ₂ O ₃ remains in the calcined body, and slurry leakage occurs from the mold cavity during wet molding.

When the oxide magnetic material is a calcined body, it contains 0.05 to 0.2% by mass of B in terms of B ₂ O ₃ or 0.05 to 0.2% by mass of Si in terms of SiO ₂ in order to enhance magnetic properties. Is preferred. If the B or Si content is less than 0.05% by mass, the effect of improving the magnetic properties cannot be obtained, and if it exceeds 0.2% by mass, the magnetic properties are adversely affected.

(B) Composition of sintered ferrite magnet The sintered ferrite magnet obtained by the method of the present invention has an M-type ferrite structure, and is an R element containing at least one of Ca and rare earth elements and containing La as an essential element, Ba Fe, Co are essential elements, and the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z (atomic ratio)
{However, (1-xy), x, y and z are the contents of Ca, R element, Ba and Co, respectively, n represents the molar ratio,
0.3 ≦ 1-xy ≦ 0.65,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65,
4 ≦ n ≦ 7, and
1-xy> y
It is a numerical value satisfying. } Has a basic composition represented by:

The ferrite sintered magnet obtained by the method of the present invention is an improvement of the defect of the conventional Ca—R—Co ferrite sintered magnet that M-type crystal grains are unlikely to be hexagonal plates. That is, when the sintered ferrite magnet of the present invention has anisotropy, it has a microstructure composed of relatively thick (small aspect ratio) M-type crystal grains and a high degree of orientation. Accordingly, it has extremely high Br close to the value predicted from 4πIs, high HcJ corresponding to _HA , and low HcJ temperature dependence [temperature coefficient (β)].

The Ca content (1-xy) is 0.3 to 0.65, preferably 0.4 to 0.55 . If (1-xy) is less than 0.3, the M phase becomes unstable, and ortho-ferrite is generated by excess R element, resulting in a decrease in magnetic properties. When (1-xy) exceeds 0.65, the M phase is not generated, and an undesirable phase such as CaFeO _3-x is generated.

  R is at least one rare earth element composed of La, Ce, Nd, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and essentially contains La. In order to impart high magnetic properties, the ratio of La in the R element is preferably 50 atomic% or more, more preferably 70 atomic% or more, and La alone (however, inevitable impurities are allowed) .) Is particularly preferred. The R content (x) is 0.2 to 0.65, preferably 0.3 to 0.55, and more preferably 0.35 to 0.5. If x is less than 0.2, the substitution amount of Co for the M phase becomes insufficient, and the M-type ferrite structure becomes unstable. When x exceeds 0.65, an unreacted oxide of R element increases and an undesirable phase such as orthoferrite is generated.

  The Ba content (y) is 0.001 to 0.2, preferably 0.005 to 0.2, more preferably 0.01 to 0.2, still more preferably 0.02 to 0.15, and 0.02 to 0.12. Particularly preferred. If y is less than 0.001, the effect of improving the magnetic properties by adding Ba cannot be obtained. If y exceeds 0.2, the magnetic properties deteriorate.

  The Co content (z) is 0.03 to 0.65, preferably 0.1 to 0.55, and more preferably 0.2 to 0.4. If z is less than 0.03, the effect of improving magnetic properties by adding Co cannot be obtained. When z exceeds 0.65, a heterogeneous phase containing a large amount of Co is generated and the magnetic properties are greatly deteriorated.

The molar ratio n has the same meaning as the molar ratio n in the above-described oxide magnetic material, and is 4 to 7, preferably 4 to 6, more preferably 4.5 to 5.5, and further 4.6 to 5.4. preferable. When n is less than 4, the ratio of the non-magnetic portion increases and the magnetic properties are deteriorated. When n exceeds 7, unreacted α-Fe ₂ O ₃ increases and magnetic properties are greatly deteriorated.

The value of the molar ratio x / z between the R element and Co is 0.73 ≦ x / z ≦ 15.62, preferably 1 ≦ x / z ≦ 3, and particularly preferably 1.2 ≦ x / z ≦ 2. Is preferred . By selecting a composition that satisfies these values, the magnetic properties are significantly improved.

  When (R element content)> (Co content)> (Ba content), that is, when x> z> y, the effect of improving magnetic properties is large. Further, when (Ca content)> (Ba content), that is, when 1-x-y> y, high magnetic properties are obtained.

Preferably contains 0.05-0.2 wt% of B in terms of values of B ₂ O _3, more preferably containing 0.08 to 0.15 wt%. By containing these amounts of B, high magnetic properties can be obtained. If it is less than 0.05% by mass, the effect of B content cannot be obtained, and if it exceeds 0.2% by mass, the magnetic properties are deteriorated.

Ferrite sintered magnet obtained by the method of the present invention, 0.1 to 3% by mass of Cr ₂ O ₃ or Al ₂ O ₃ is added in the pulverization step with respect to the total amount of the basic composition, and then molded and fired, Higher HcJ is obtained. If the amount of Cr ₂ O ₃ or Al ₂ O ₃ added is less than 0.1% by mass, the effect of improving HcJ cannot be obtained, and if it exceeds 3% by mass, Br is greatly reduced.

Ferrite sintered magnet has the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z O _α (atomic ratio)
[(1-xy), x, y and z are the contents of Ca, R element, Ba and Co, n is the molar ratio, α is the content of O,
0.3 ≦ 1-xy ≦ 0.65,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65,
4 ≦ n ≦ 7, and
1-xy> y
It is a numerical value satisfying. However, when the stoichiometric composition ratio is shown when x = z and n = 6, α = 19. In order to have high magnetic properties, it is preferable to have a composition represented by
That is, when the relationship between the content x of the R element and the Co content z is x = z and the molar ratio n = 6, the number of moles α of oxygen is 19. The number of moles of oxygen varies depending on the valence of Fe and Co, the n value, the type of R element, the calcination or firing atmosphere. The ratio of oxygen to metal element changes due to oxygen deficiency (vacancy) when firing in a reducing atmosphere, changes in the valence of Fe in the M-type ferrite, changes in the valence of Co, and the like. Therefore, the actual mole number α of oxygen may deviate from 19.

[2] Manufacturing method of sintered ferrite magnet
(A) Manufacture of oxide magnetic materials Oxide magnetic materials (calcined bodies) are liquid phase methods such as solid phase reaction, coprecipitation, hydrothermal synthesis, glass precipitation, spray pyrolysis, It can be produced by the phase method or a combination thereof. Among these, the solid phase reaction method is preferable because of its high practicality. As the oxide magnetic material, two or more calcined bodies having different calcining conditions and / or calcined body compositions may be coarsely pulverized and blended. For example, calcined powder having a composition of n = 4 and n = 7 may be mixed and used as an oxide magnetic material used in the present invention. Further, a recycled material such as a defective product or a sintered product or a processing waste material may be used as the oxide magnetic material.

  In the solid-phase reaction method, an oxide powder, a compound that becomes an oxide by calcining (a Ca compound, an R element compound, a Ba compound, a powder of an iron compound such as a mill scale, and a powder of an Sr compound as necessary) These raw material powders are blended in a predetermined composition, and the resulting mixture is calcined (ferritized) to produce a calcined body (usually granular or clinker).

  It is practical to perform calcination in the atmosphere (substantially equivalent to an oxygen partial pressure of about 0.05 to 0.2 atm), but in an oxygen-excessive atmosphere (for example, an oxygen partial pressure of more than 0.2 atm and 1 atm or less) In particular, it may be performed in an oxygen 100% atmosphere. The calcination temperature is preferably 1373 to 1623 K, and more preferably 1423 to 1573 K. The calcination time is preferably 1 second to 10 hours, more preferably 0.1 to 3 hours. The calcined body is preferably substantially composed of an M phase.

High magnetic properties can be obtained by adding 0.05 to 0.2 parts by mass of a boron compound or SiO ₂ to 100 parts by mass of the mixture before calcination. If the addition amount of the boron compound or SiO ₂ is less than 0.05 parts by mass, the effect of addition cannot be obtained, and if it exceeds 0.2 parts by mass, the magnetic properties are reduced. As the boron compound, H ₃ BO ₃ , B ₂ O ₃ , metaborate [Ca (BO ₂ ) ₂ ] and the like are preferable.

  As the Ca compound, a carbonate, oxide, chloride or the like of Ca is used.

Compounds of R element include oxides such as La ₂ O ₃ , hydroxides such as La (OH) ₃ , carbonates such as La ₂ (CO ₃ ) ₃ / 8H ₂ O, and La (CH ₃ CO ₂ ) Use organic acid salts such as ₃ · 1.5H ₂ O, La ₂ (C ₂ O ₄ ) ₃ · 10H ₂ O. In particular, mixed rare earth (La, Nd, Pr, Ce, etc.) oxides, hydroxides, carbonates, organic acid salts, and the like can be reduced in cost because they are inexpensive.

  As the Ba compound, Ba carbonate, oxide, chloride or the like is used.

The mill-scale powder is ideally oxidized to α-Fe ₂ O ₃ from the surface to the core by heat treatment at 973-1273K in the air or in an oxygen-excess atmosphere, but α-Fe ₂ A mixture of O ₃ and Fe ₃ O ₄ is also acceptable. It is practical to perform the heat treatment in the atmosphere (substantially equivalent to an oxygen partial pressure of about 0.05 to 0.2 atm), but in an oxygen-excess atmosphere (for example, an oxygen partial pressure of more than 0.2 atm and 1 atm or less) In particular, it may be performed in an atmosphere of 100% oxygen. Below 973K, the oxidation effect by heat treatment is hardly obtained. If it exceeds 1273K, the agglomeration and seizure between the powder particles of the mill scale become remarkable, and pulverization described later becomes difficult. The heat treatment time is preferably 0.2 to 10 hours, more preferably 0.5 to 3 hours.

  The average particle size (determined by scanning electron microscope (SEM) observation) of the mill-scale coarse powder subjected to heat treatment is preferably 1 to 15 μm, and preferably 5 to 12 μm in order to promote the oxidation reaction. Is more preferable. It is difficult for industrial production to make it less than 1 μm, and if it exceeds 15 μm, the oxidation effect by heat treatment becomes insufficient.

  In order to promote the calcination reaction (ferritization reaction), it is preferable to finely pulverize the mill-scale coarse powder after heat treatment to an average particle size of 0.5 to 2 μm (determined by SEM observation), 0.7 to 2.0 More preferably, it is μm. If the thickness is less than 0.5 μm, the practicality is poor, and if it exceeds 2 μm, the magnetic properties of the sintered ferrite magnet deteriorate.

The component of the mill scale has a content of iron oxide (total of α-Fe ₂ O ₃ and Fe ₃ O ₄ ) of 97 to 99% by mass, an Al content (Al ₂ O ₃ equivalent value) of 0.2% by mass or less, Si content (SiO ₂ conversion value) is 0.03-0.25 mass%, Ca content (CaO conversion value) is 0.03-0.25 mass%, and Cr content (Cr ₂ O ₃ conversion value) is 0.05 mass% or less. Preferably there is. When the content of iron oxide is lower than the lower limit value, or the content of Al, Si, Ca and Cr exceeds the upper limit value, Br is greatly decreased. The upper limit value of iron oxide and the lower limit value of the contents of Al, Si, Ca, and Cr depend on the composition of the steel ingot, steel material, and the like that are the sources of mill scale. The components of the mill scale powder are iron oxide (total of α-Fe ₂ O ₃ and Fe ₃ O ₄ ) content of 97.5 to 99% by mass, Al content (Al ₂ O ₃ equivalent value) of 0.01 to 0.20. Mass%, Si content (SiO ₂ equivalent value) 0.03 to 0.20 mass%, Ca content (CaO equivalent value) 0.03 to 0.20 mass%, and Cr content (Cr ₂ O ₃ equivalent value) 0.01 to 0.05 mass % Is more preferred.

Examples of the Co compound include oxides such as CoO and Co ₃ O ₄ , and hydroxides such as CoOOH, Co (OH) ₂ and Co ₃ O ₄ · m ₁ H ₂ O (m ₁ is a positive number). , Carbonates such as CoCO ₃ , and basic carbonates such as m ₂ CoCO ₃ · m ₃ Co (OH) ₂ · m ₄ H ₂ O (m ₂ , m ₃ and m ₄ are positive numbers) Is preferably used.

(B) Crushing the calcined body The calcined body is crushed by a jaw crusher, a hammer mill, or the like, and then dry coarsely crushed by a vibration mill, a roller mill, or the like, if necessary. The average particle size of the coarsely pulverized powder is preferably 2 to 5 μm in order to reduce the load of wet or dry fine pulverization in the subsequent step. The average particle diameter can be measured on the basis of a bulk density of 65% by an air permeation method (measuring device: Fischer Sub-Sieve Sizer, hereinafter abbreviated as FSSS). Next, wet pulverization or dry pulverization is performed. When the formed body is pulverized, it is practical and preferable to omit the coarse pulverization and the coarse pulverization and directly perform wet or dry fine pulverization.

Wet fine pulverization is performed by a wet fine pulverizer such as an attritor or ball mill after adding dry coarse pulverization. In order to improve industrial productivity (dehydration characteristics, etc.) and magnetic characteristics, the average particle size of the finely pulverized powder is preferably 0.4 to 1.3 μm (measured based on a bulk density of 65% by FSSS). When the average particle size is pulverized to less than 0.4 μm, HcJ decreases due to abnormal crystal grain growth during firing, and the dehydration characteristics of the molded product during wet molding deteriorate significantly. When the average grain size exceeds 1.3 μm, the ratio of coarse crystal grains in the ferrite sintered body increases, so that HcJ greatly decreases. The average particle size of the finely pulverized powder is more preferably 0.7 to 1.3 μm, and particularly preferably 0.7 to 1.2 μm.

It is preferable to add 0.1 to 1.5% by mass of SiO ₂ and more preferably 0.2 to 1% by mass with respect to the total amount of dry coarsely pulverized powder (calcined powder) charged during wet pulverization. By adding SiO ₂ , high HcJ can be stably obtained. When the addition amount of SiO ₂ is less than 0.1% by mass, the effect of addition cannot be obtained, and when it exceeds 1.5% by mass, the effect of suppressing grain growth becomes excessive and Br decreases.

During wet pulverization, CaCO ₃ is preferably added in an amount of 0.2 to 1.5 mass%, more preferably 0.3 to 1.3 mass%, based on the total amount of calcined powder. By adding CaCO ₃ , the grain growth of M-type ferrite particles during firing is promoted and Br is improved. If the amount of CaCO ₃ added is less than 0.2% by mass, the effect of addition cannot be obtained, and if it exceeds 1.5% by mass, grain growth during firing proceeds excessively and HcJ is greatly reduced.

By adding 0.05 to 10 parts by mass of mill scale powder to 100 parts by mass of calcined powder during wet pulverization , the molar ratio n can be adjusted without deteriorating magnetic properties.

  After the wet pulverization, the obtained slurry is concentrated and molded as necessary. Concentration is performed by centrifugation, filter press or the like.

(C) Molding Molding can be performed dry or wet. When pressure molding is performed without applying a magnetic field, an isotropic sintered ferrite magnet body is obtained. When pressure forming is performed by applying a magnetic field, a molded body for anisotropic ferrite sintered magnet having high magnetic properties is obtained. In order to increase the degree of orientation of the compact, molding in a wet magnetic field is preferable to molding in a dry magnetic field. The applied magnetic field strength is preferably 398 to 1194 kA / m.

  In the case of dry molding, (a) the slurry was dried at room temperature or heated (about 323 to 373 K), crushed with an atomizer, etc., and (b) obtained by molding the slurry in a magnetic field After the compact is crushed with a crusher, etc., the average particle size is classified by sieving to about 100-700μm, and the magnetically oriented granules are obtained in a dry magnetic field. (C) Obtained by dry coarse pulverization and dry fine pulverization. The obtained fine powder is formed by a method of forming in a dry magnetic field or dry non-magnetic forming. The dry molding pressure is preferably about 9.8 to 49 MPa, and when a magnetic field is applied, the applied magnetic field strength is preferably about 398 to 1194 kA / m.

(D) Firing The compact is sintered in ferrite by removing moisture, dispersant, etc. by natural drying in the air or heating (373 to 773 K) in the air or nitrogen atmosphere and then firing. It becomes a magnet. It is practical to perform the firing in the atmosphere (substantially the oxygen partial pressure is about 0.05 to 0.2 atm). Baking may be performed in an oxygen-excess atmosphere (for example, an oxygen partial pressure of more than 0.2 atm and 1 atm or less), particularly in an oxygen 100% atmosphere. Firing is carried out at a temperature of 1423 to 1573 K, preferably 1433 to 1543 K, for 0.5 to 5 hours, preferably 1 to 3 hours. The density of the sintered ferrite magnet of the present invention is preferably 5.05 to 5.10 g / cm ³ .

[3] Characteristics of sintered ferrite magnets The average crystal grain size in the c-axis direction (measured for 50 M-type crystal grains) measured by SEM observation of a cross section parallel to the c-axis of the sintered ferrite magnet was 0.5. more preferably from ～3Myuemu, more preferably from 0.9～2Myuemu, particularly preferably from 1.0～1.6Myuemu. The sintered anisotropic ferrite magnet of the present invention exhibits high HcJ even when the average crystal grain size is 1 μm or more. The c-axis direction of the anisotropic ferrite sintered magnet means an anisotropy imparting direction (a direction that substantially coincides with a magnetic field application direction in forming in a magnetic field).

Since the sintered ferrite magnet has high Br and high HcJ , it preferably contains 30% or more, more preferably 50% or more, and even more preferably 60% or more of M-type crystal grains having an aspect ratio of 3 or less. .

The ferrite sintered magnet obtained by the method of the present invention uses a mill scale as an iron oxide raw material, but in the case of an anisotropic ferrite sintered magnet fired in the atmosphere, 400 to 470 mT at room temperature (293K). Br, 278-478 kA / m HcJ and a squareness ratio (Hk / HcJ) of 80% or more. Furthermore, it has Br of 420 to 470 mT, HcJ of 278 to 478 kA / m and a squareness ratio (Hk / HcJ) of 80% or more. In particular, it has Br of 430 to 470 mT, HcJ of 278 to 478 kA / m and a squareness ratio (Hk / HcJ) of 80% or more. Here, the parameter Hk that is measured to determine the squareness ratio (Hk / HcJ) is the position where 4πI is 0.95Br in the second quadrant of the 4πI (magnetization strength) -H (magnetic field strength) curve. This is the H axis reading.

[4] Magnet Applied Product The sintered ferrite magnet obtained according to the present invention is useful for, for example, a rotating machine, and is suitable for motors or generators such as automobile starters, power steering, electric throttles and the like. It is also suitable for a developing roll magnet roll for a copying machine.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

Example 1
<Mill scale heat treatment and magnetic properties of sintered ferrite magnets>
CaCO ₃ powder (purity 98.8%, including MgO as an impurity), La (OH) ₃ powder (purity 99.9%), BaCO ₃ powder (purity 98.1%, including SrCO ₃ as an impurity 1.45%), mill scale Using powder and Co ₃ O ₄ powder (purity 99%), Ca _1-xy La _x Bay _y Fe _2n-z Co _z O ₁₉ (x = 0.475, y = 0.050, z = 0.30, n = 5.2) It mix | blended so that it might become a composition. The mill-scale powder used was heat-treated in the atmosphere under the heat treatment conditions (heating temperature, holding time) shown in Table 2 in the atmosphere with the ingredients in Table 1 and the average particle size of 1.4 μm (according to SEM observation). After that, the raw iron oxide was wet-pulverized (average particle size 1 μm; observed by SEM). Result of coarse powder mill scale before and after the heat treatment was subjected to X-ray diffraction, X-rays diffraction peaks of the samples before the heat treatment α-Fe ₂ O ₃ + FeO was observed, X-rays of the α-Fe ₂ O ₃ in the samples after the heat treatment Only diffraction peaks were observed. To 100 parts by mass of the blend, 0.1 part by mass of H ₃ BO ₃ powder was added and wet-mixed. After drying, the mixture was calcined at 1473 K for 1 hour in the air.

The calcined body was coarsely crushed and then dry coarsely pulverized with a vibration mill to obtain coarse powder having an average particle size of 5 μm (by FSSS). 45 mass% coarse powder and 55 mass% water are put into a ball mill, 0.28 mass parts SiO ₂ powder (purity 92.1%, the balance is almost water) and 0.50 mass parts CaCO with respect to 100 mass parts of coarse powder. _Three powders were added as a sintering aid and wet pulverization was performed to obtain a slurry containing ferrite fine particles having an average particle size of 0.9 μm (according to FSSS).

  The finely pulverized slurry was compression molded in a parallel magnetic field of 796 kA / m. The obtained compact was fired in the atmosphere at a temperature of 1493 K for 1 hour to obtain an anisotropic ferrite sintered magnet. As a result of measuring the magnetic properties of the obtained sintered body at room temperature (293K) with a B-H tracer, high magnetic properties were obtained (see Table 2).

Examples 2-6
Except for using mill-scale coarse powder (see Table 2, according to SEM observation) before heat treatment having the components of Table 1 and having an average particle size of 3.1 to 30.8 μm, the same as Example 1 An isotropic sintered ferrite magnet was prepared. As a result of measuring the magnetic properties at room temperature, it was found to have high magnetic properties (see Table 2).

The mill-scale coarse powder before and after heat treatment in Examples 2 to 6 was subjected to X-ray diffraction. As a result, an X-ray diffraction peak of α-Fe ₂ O ₃ + FeO was observed in each case before the heat treatment. In all cases, α-Fe ₂ O ₃ (main phase) + Fe ₃ O ₄ (subphase) X-ray diffraction peaks were observed in the samples after heat treatment, and the mill-scale particles were completely α-Fe ₂ O _3. It was found that it was not oxidized. As an example, FIG. 1 shows an SEM photograph of mill scale coarse powder after heat treatment of Example 4, and FIG. 2 shows an SEM photograph of the finely pulverized powder.

Example 7
As the iron oxide raw material, mill-scale fine powder (average particle diameter 1 μm, according to SEM observation) obtained by finely pulverizing mill-scale coarse powder (average particle diameter 12.3 μm) before heat treatment of Example 4 was used. Except for the above, an anisotropic ferrite sintered magnet was produced in the same manner as in Example 1. As a result of measuring the magnetic properties at room temperature, as shown in Table 2, it was found that Br was lower than those of Examples 1-6.

Comparative Example 1
Using the same SrCO ₃ powder as in Example 1 and industrial iron oxide powder (having the components shown in Table 1 and having an average particle size of less than 1 μm), the basic composition of SrO · 5.9Fe ₂ O ₃ is wet. After mixing, it was calcined in air at 1523K for 2 hours. 45% by mass of the calcined coarse powder (average particle size 4 μm (FSSS)) and 55% by mass of water were put into a ball mill, and La (OH) ₃ powder, Co ₃ O ₄ powder and the industrial oxidation were added. A predetermined amount of iron powder was put into a ball mill. Furthermore, as a sintering aid, 0.1% by mass of SrCO ₃ powder, 1.0% by mass of CaCO ₃ powder and 0.3% by mass of SiO ₂ powder are put into a ball mill based on the mass of the coarse powder, and wet pulverization is performed to obtain an average. A slurry in which fine powder having a particle size of 0.9 μm (FSSS) was dispersed was obtained. This slurry was compression molded in a parallel magnetic field of 796 kA / m, and the resulting molded body was fired at 1493 K for 2 hours. The composition of the obtained anisotropic sintered ferrite magnet was (Sr _0.15 La _0.85 ) O · 5.55 [(Fe _0.986 Co _0.014 ) ₂ O ₃ ]. As a result of measuring the magnetic properties at room temperature, as shown in Table 2, high magnetic properties almost equivalent to those of Examples 1 to 7 were obtained.

Comparative Example 2
Under the production conditions of Sample No. 2 of Example 2 of Patent Document 1, fine powder (average particle diameter of 1 μm) obtained by finely pulverizing mill-scale coarse powder (average particle diameter of 12.3 μm) before heat treatment of Example 4 , By SEM observation.) Was carried out in the same manner as Sample No. 2 except that α-Fe ₂ O ₃ powder (for industrial use) was used instead of α-Fe ₂ O ₃ powder (for industrial use). Ca _1-xy La _x Ba _y Fe _2n-z Co _z O ₁₉ (x = 0.500, y = 0, z = 0.43, n = 5.1), 0.4% by mass of SiO ₂ powder was added. A mixture was prepared and calcined in air at 1473K for 3 hours. The obtained calcined body was roughly crushed and coarsely pulverized to obtain a coarse powder of the calcined body. Using a ball mill with water as a medium, 0.6 mass% SiO ₂ and 1.0 mass% CaCO ₃ are added to the coarse powder, wet fine pulverization is performed, and a slurry in which fine pulverization with an average pulverization of 0.9 μm (FSSS) is dispersed is performed. (The fine pulverized average particle size of sample No. 2 in Patent Document 1 is unknown, so the average particle size of the finely pulverized powder of Example 1 was adjusted to 0.9 μm). Thereafter, anisotropic ferrite sintered magnets were produced in the same manner as in Example 1, and the magnetic properties at room temperature were measured. As a result, high magnetic properties similar to those of the above example were obtained (see Table 2).

<Structure of calcined body>
The SEM photograph of the fracture surface of the calcined body of Example 4 (x = 0.475, y = 0.050, z = 0.30, n = 5.2) is shown in FIG. It can be seen that the morphology of the plate-like primary particles (M-type crystal grains) is clear and the growth rate of the M-type crystal grains is high.

  An SEM photograph of the fracture surface of the calcined body of Comparative Example 2 (x = 0.500, y = 0, z = 0.43, n = 5.1) is shown in FIG. The primary particles have an indefinite shape, and no plate-like particles are seen.

  From the comparison between FIG. 3 and FIG. 4, it can be seen that the calcined body of Example 4 to which a predetermined amount of Ba is added has a clear form in which the primary particles are plate-like and thick. In addition, from the SEM observation including FIG. 3, the calcined body of Example 4 has a primary particle aspect ratio (maximum diameter of c-plane / thickness in the c-axis direction) of M type ferrite crystal grains of about 60% or less. It was found to contain.

  As a result of SEM observation of the M-type crystal grains of the ferrite sintered magnet of Example 4 and the ferrite sintered magnet of Comparative Example 2, in the case of Example 4, almost healthy (grown) hexagonal plate-shaped M-type ferrite crystal grains It was found to consist of On the other hand, in the case of Comparative Example 2, it was found that the growth rate of the M-type ferrite crystal grains was lower than that of Example 4, and many M-type ferrite crystal grains not having a hexagonal plate shape were included. It is considered that the difference in magnetic properties between the sintered ferrite magnets of Example 4 and Comparative Example 2 is mainly caused by such a difference in microstructure.

Examples 8-12
<Heat treatment conditions and magnetic properties of sintered ferrite magnets>
For the mill-scale coarse powder (average particle size 12.3 μm) before heat treatment of Example 4, the effect of changing the heat treatment conditions in the atmosphere on the magnetic properties of the sintered ferrite magnet was investigated. An anisotropic ferrite sintered magnet was produced in the same manner as in Example 4 except that the heating conditions of the heat treatment shown in Table 3 were used. Table 3 shows the magnetic properties of the obtained sintered ferrite magnet at room temperature. From Examples 4, 8, 9 and 10, it can be seen that high magnetic properties can be obtained at a heat treatment temperature of 973 to 1273K. Further, from Examples 4, 11 and 12, it can be seen that the heating and holding at the heat treatment temperature of 1173 K is effective in 0.2 hours and is almost saturated in 10 hours.

  From the sintered ferrite magnets obtained in Examples 1 to 5, a sample having a length of 3 mm, a width of 3 mm, and a thickness of 3 mm was cut out and the temperature coefficient (β) of HcJ at 233 to 413 K was measured by VSM. A very small value of about 0.13 (% / K) was obtained. On the other hand, β of the sintered ferrite magnets of Comparative Examples 1 and 2 exceeded 0.15 (% / K), indicating that the low-temperature demagnetization is large.

  In the above embodiment, the case where 100% of the mill scale is used as the iron oxide raw material has been described, but it is not particularly limited. For example, blending conditions of (mill scale powder) :( industrial iron oxide powder; general product) = 5 to 100 parts by mass: 95 to 0 parts by mass are practical and useful effects of the present invention. Can be played.

  Moreover, although the said Example described the case where the wet-pulverized slurry was compression-molded in a magnetic field, it is not particularly limited. The method of the present invention can be applied not only to the case where an orientation magnetic field is applied, but also to other known wet molding methods (such as extrusion molding) in which no orientation magnetic field is applied, and dry molding methods (such as compression molding).

6 is a SEM photograph showing mill scale coarse powder immediately after heat treatment in Example 4. FIG. 6 is a SEM photograph showing milled pulverized fine powder of Example 4 subjected to heat treatment. It is a SEM photograph which shows the fracture surface of the calcined body of Example 4 which concerns on this invention. It is a SEM photograph which shows the fracture surface of the calcined body of the comparative example 2 which has not added Ba.

Claims (2)

It has an M-type ferrite structure, is an R element that is at least one of Ca and rare earth elements and contains La as essential elements, Ba, Fe, and Co as essential elements, and has the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z (atomic ratio)
[(1-xy), x, y and z are the contents of Ca, R element, Ba and Co, respectively, n represents the molar ratio,
0.3 ≦ 1-xy ≦ 0.65,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65,
4 ≦ n ≦ 7, and
1-xy> y
It is a numerical value satisfying. Is a method for producing a sintered ferrite magnet having a composition represented by the following: an iron oxide raw material having a raw material mixing step, a calcining step, a pulverizing step, a molding step, and a firing step, and blended in the raw material mixing step Mill scale powder was used, and the mill scale powder particles were heat-treated at 973-1273 K in the air or in an oxygen-rich atmosphere, and iron oxide (α-Fe ₂ O ₃ or α-Fe ₂ The content of O ₃ and Fe ₃ O ₄ is 97 to 99% by mass, the Al content (Al ₂ O ₃ conversion value) is 0.2% by mass or less, and the Si content (SiO ₂ conversion value) is 0.03 to 0.25. A method for producing a sintered ferrite magnet, characterized in that a mass%, a Ca content (CaO equivalent value) is 0.03 to 0.25 mass%, and a Cr content (Cr ₂ O ₃ equivalent value) is 0.05 mass% or less . The method for producing a sintered ferrite magnet according to claim 1, wherein the sintered ferrite magnet has the following general formula:
Ca _1-xy R _x Ba _y Fe _2n-z Co _z O _α (atomic ratio)
[(1-xy), x, y and z are the contents of Ca, R element, Ba and Co, n is the molar ratio, α is the content of O,
0.3 ≦ 1-xy ≦ 0.65,
0.2 ≦ x ≦ 0.65,
0.001 ≦ y ≦ 0.2,
0.03 ≦ z ≦ 0.65,
4 ≦ n ≦ 7, and
1-xy> y
It is a numerical value satisfying. However, when the stoichiometric composition ratio is shown when x = z and n = 6, α = 19. ] The manufacturing method of the sintered ferrite magnet characterized by the above-mentioned.