JP7468009B2 - Ferrite calcined body, sintered ferrite magnet and method for producing same - Google Patents

Description

The present invention relates to a ferrite calcined body, a ferrite sintered magnet, and a method for producing the same.

Although the maximum energy product of ferrite sintered magnets is only one-tenth that of rare-earth sintered magnets (e.g., NdFeB sintered magnets), they offer excellent cost performance because their main raw material is inexpensive iron oxide, and they are characterized by being extremely chemically stable. For this reason, they are used for a variety of purposes, including various motors and speakers, and are still the largest magnet material in terms of global production volume.

A typical sintered ferrite magnet is Sr ferrite with a magnetoplumbite structure, and its basic composition is _SrFe12O19 . In the second half of the _1990s , Sr-La-Co sintered ferrite magnets, in which part of the Sr2 ⁺ in _SrFe12O19 was replaced with ^La3+ and part of the Fe3 ⁺ was replaced with Co2 ⁺ , were put into practical use _{, greatly} improving the magnetic properties of ferrite magnets. In 2007, Ca-La-Co sintered ferrite magnets with even better magnetic properties were put into practical use.

In both the Sr-La-Co ferrite sintered magnets and the Ca-La-Co ferrite sintered magnets, Co is essential to obtain high magnetic properties. Sr-La-Co ferrite sintered magnets contain about 0.2 atomic Co, while Ca-La-Co ferrite sintered magnets contain about 0.3 atomic Co. The price of Co (cobalt oxide) is ten to several tens of times that of iron oxide, the main raw material of ferrite sintered magnets. Therefore, the raw material cost of Ca-La-Co ferrite sintered magnets is inevitably higher than that of Sr-La-Co ferrite sintered magnets. The greatest feature of ferrite sintered magnets is that they are inexpensive, so even if they have high magnetic properties, they are difficult to accept in the market if they are expensive. Therefore, there is still a high demand for Sr-La-Co ferrite sintered magnets worldwide.

In recent years, the price of Co has soared due to the growing demand for Li-ion batteries caused by the increased supply of electric vehicles. As a result, it has become difficult to maintain product prices even for Sr-La-Co sintered ferrite magnets, which offer excellent cost performance. Against this background, the issue of how to reduce the amount of Co used while maintaining magnetic properties has become an urgent issue.

Although it is not intended to reduce the amount of Co, it is known that, for example, in Sr-La-Co based ferrite sintered magnets, the residual magnetic flux density (hereinafter referred to as "B _r ") is improved by replacing part of the Co with Zn (Patent Document 1, etc.).

It has also been proposed to replace part of the Co in Ca-La-Co ferrite sintered magnets with Zn (Patent Documents 2 and 3, etc.).

Japanese Patent Application Laid-Open No. 11-154604 Korean Patent Publication No. 10-2017-0044875 JP 2009-246243 A

However, when part of the Co in a Sr-La-Co based sintered ferrite magnet is replaced with Zn as in Patent Document 1, the improvement in B _r is not that great, while the coercive force (hereinafter referred to as "H _cJ ") decreases significantly, and this has not yet led to practical application.

Patent Document 2 discloses a Ca-Sr-La-Fe-Co-Zn ferrite sintered magnet, and although it lists the magnetic properties such as saturation magnetization (4πIs), anisotropic magnetic field (H _A ), and maximum energy product, it does not list the values of B _r and H _cJ .

Patent Document 3 discloses a Ca-A(Sr,Ba)-La-Fe-Co-Zn ferrite sintered magnet, but in the examples, a grinding process (hereinafter referred to as the "heat treatment re-grinding process") consisting of a first fine grinding process, a process of heat treating the powder obtained by the first fine grinding process, and a second fine grinding process of grinding the heat-treated powder again is essential. The heat treatment re-grinding process is an unconventional grinding process that requires a long period (88 hours) of the first fine grinding process and heat treatment (1 hour at 800°C), so there is no description of what level of magnetic properties can be obtained from a typical grinding process on a mass production scale (only one grinding, about 10 hours).

An object of the present invention is to provide a sintered ferrite magnet which has high B _r , little decrease in H _cJ , and uses less Co than conventional sintered ferrite magnets.
A more specific object of the present invention is to provide a sintered ferrite magnet which has a higher HcJ than a Sr-La-Co sintered ferrite magnet in which part of the Co is replaced with Zn, when the atomic ratio y (Co content) is 0.15≦y<0.2, and which uses less _Co than a general Sr-La-Co sintered ferrite magnet (containing Co in an atomic ratio of about 0.2); and to provide a sintered ferrite magnet which has magnetic properties substantially equivalent to a general Ca-La-Co sintered ferrite magnet, and which uses less Co than a general Ca-La-Co sintered ferrite magnet (containing Co in an atomic ratio of about 0.3), when the atomic ratio y (Co content) is 0.2≦y≦0.25.

That is, the ferrite calcined body of the present invention is
The general formula Ca1 _{-xRxFe2n-y-zCoyZnz} shows the atomic ratio of the metal elements Ca, R, Fe, Co and Zn (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.4＜x≦0.5,
0.2 ≦y≦0.25,
0 < z < 0.11, and
9.0≦2n≦11.0 ,
Satisfy.

In the ferrite calcined body of the present invention, the 2n preferably satisfies 9.0≦2n≦10.31.

In the ferrite calcined body of the present invention, it is preferable that z satisfies 0.02≦z≦0.1.

The sintered ferrite magnet of the present invention is
The general formula Ca1 _{-xRxFe2n-y-zCoyZnz} shows the atomic ratio of the metal elements Ca, R, Fe, Co and Zn (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.3＜x≦0.5,
0.2 ≦y≦0.25,
0 < z < 0.11, and
6.8≦2n≦11.0 ,
Satisfy.

In the sintered ferrite magnet of the present invention, the 2n preferably satisfies 6.8≦2n≦10.31.

In the sintered ferrite magnet of the present invention, it is preferable that z satisfies 0.02≦z≦0.1.

The sintered ferrite magnet of the present invention preferably further contains up to 1.5 mass % of Si , calculated as _SiO2 .

The method for producing a sintered ferrite magnet of the present invention comprises the steps of:
The general formula Ca1 _{-xRxFe2n-y-zCoyZnz} shows the atomic ratio of the metal elements Ca, R, Fe, Co and Zn (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.4＜x≦0.5,
0.2 ≦y≦0.25,
0 < z < 0.11, and
9.0≦2n≦11.0 ,
A raw material powder mixing process for mixing raw material powders satisfying the above to obtain a mixed raw material powder;
a calcination step of calcining the mixed raw material powder to obtain a calcined body;
A grinding step of grinding the calcined body to obtain a powder of the calcined body;
a molding step of molding the powder of the calcined body to obtain a molded body, and a firing step of firing the molded body to obtain a sintered body;
including.

In the method for producing a sintered ferrite magnet of the present invention, the 2n preferably satisfies 9.0≦2n≦10.31.

In the manufacturing method of the sintered ferrite magnet of the present invention, it is preferable that z satisfies 0.02≦z≦0.1.

In the method for producing a sintered ferrite magnet of the present invention, it is preferable to further include a step of adding 1.5 mass % or less of _SiO2 to 100 mass % of the calcined body or the powder of the calcined body after the calcining step and before the molding step.

In the method for producing a sintered ferrite magnet of the present invention, it is preferable to further include a step of adding 1.5 mass% or less of _CaCO3 , calculated as CaO, to 100 mass% of the calcined body or the powder of the calcined body after the calcination step and before the molding step.

In the method for producing a sintered ferrite magnet of the present invention, it is preferable that the average heating rate in the temperature range from 800°C to the sintering temperature in the sintering step is 600°C/hour or more and 1000°C/hour or less.

In the method for producing a sintered ferrite magnet of the present invention, it is preferable that the average temperature drop rate in the temperature range from the sintering temperature to 800°C in the sintering step is 1000°C/hour or more.

According to the present invention, it is possible to provide a sintered ferrite magnet that has high B _r , little decrease in H _cJ , and uses less Co than conventional sintered ferrite magnets.
Specifically, when the atomic ratio y (Co content) is 0.15≦y<0.2, it is possible to provide a ferrite sintered magnet that has a higher _HcJ than a Sr-La-Co sintered ferrite magnet in which part of the Co is replaced with Zn, and that uses less Co than a typical Sr-La-Co sintered ferrite magnet (containing Co in an atomic ratio of about 0.2); and when the atomic ratio y (Co content) is 0.2≦y≦0.25, it is possible to provide a ferrite sintered magnet that has magnetic properties roughly equivalent to a typical Ca-La-Co sintered ferrite magnet, and that uses less Co than a typical Ca-La-Co sintered ferrite magnet (containing Co in an atomic ratio of about 0.3).

1. Ferrite calcined body The ferrite calcined body of the present invention is
In the general formula Ca1 _{- xRxFe2n -yzCoyZnz} , which shows the atomic ratio of the metal elements Ca, R, Fe, Co _{and Zn} (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.4＜x≦0.5,
0.15≦y≦0.25,
0 < z < 0.11, and
4.5≦n≦5.5,
Satisfy.

In the ferrite calcined body of the present invention, the atomic ratio x (R content) is 0.4<x≦0.5. If x is 0.4 or less or exceeds 0.5, a high B _r cannot be obtained. R is at least one rare earth element, and is an element essentially containing La. The content of rare earth elements other than La is preferably 50% or less of the total amount of R in terms of molar ratio.

The atomic ratio y (Co content) is 0.15≦y≦0.25. If y exceeds 0.25, the effect of reducing the amount of Co used cannot be obtained. If y is less than 0.15, the decrease in _HcJ is large, which is not preferable. If the atomic ratio y is in the range of 0.15≦y<0.2, the _HcJ is higher than when a part of Co in an Sr-La-Co ferrite sintered magnet is replaced with Zn, and a ferrite sintered magnet is obtained in which the amount of Co used is reduced compared to a general Sr-La-Co ferrite sintered magnet (containing Co at about 0.2 atomic ratio). If the atomic ratio y (Co content) is in the range of 0.2≦y≦0.25, a ferrite sintered magnet is obtained that has magnetic properties almost equivalent to those of a general Ca-La-Co ferrite sintered magnet, and contains less Co than a general Ca-La-Co ferrite sintered magnet (containing Co at about 0.3 atomic ratio).

The atomic ratio z (Zn content) is 0<z<0.11. When z is 0 (not contained), high B _r cannot be obtained, and when z is 0.11 or more, the decrease in H _cJ is large, which is not preferable. The atomic ratio z is preferably 0.02≦z≦0.1.

In the above general formula, 2n is a molar ratio and is expressed as 2n = (Fe + Co + Zn) / (Ca + R). n is 4.5 ≤ n ≤ 5.5. If n is less than 4.5 or more than 5.5, a high _Br cannot be obtained.

The general formula is expressed by the atomic ratio of metal elements, but the composition containing oxygen (O) is expressed by the general formula: Ca1 _{- xRxFe2n -yzCoyZnzOα .} The number of moles of _oxygen α is basically _α =19, but it varies depending on the valences of Fe and Co, and the values of x, y, z, and n. In addition, the ratio of oxygen to metal elements changes due to oxygen vacancies (vacancies) when fired in a reducing atmosphere, changes in the valence of Fe in the ferrite phase, changes in the valence of Co, etc. Therefore, the actual number of moles of oxygen α may deviate from 19. Therefore, in the present invention, the composition is expressed by the atomic ratio of metal elements that are the easiest to specify.

The main phase constituting the ferrite calcined body of the present invention is a compound phase (ferrite phase) having a hexagonal magnetoplumbite (M-type) structure. In general, magnetic materials, particularly sintered magnets, are composed of multiple compounds, and the compound that determines the characteristics of the magnetic material (physical properties, magnetic properties, etc.) is defined as the "main phase."

"Having a hexagonal magnetoplumbite (M-type) structure" means that when X-ray diffraction of the calcined ferrite body is measured under typical conditions, the X-ray diffraction pattern observed is primarily that of a hexagonal magnetoplumbite (M-type) structure.

An example of a method for producing a sintered ferrite magnet of the present invention, including the method for producing the ferrite calcined body of the present invention described above, is described below.

2. Method for manufacturing sintered ferrite magnets As the raw material powder, compounds such as oxides, carbonates, hydroxides, nitrates, and chlorides of each metal can be used regardless of the valence. _{A solution in which the raw material powder is dissolved may also be used. Examples of Ca compounds include carbonates, oxides, and chlorides of Ca. Examples of La compounds include oxides such as La2O3 , hydroxides} such as La(OH) ₃ , and carbonates such as _La2 ( _CO3 ) _3.8H2O . Examples of Fe compounds include iron oxide, iron _{hydroxide, iron chloride, and mill scale. Examples of Co compounds include oxides such as CoO and Co3O4 ,} hydroxides such as _CoOOH and Co(OH) ₂ , carbonates such as _CoCO3 , and basic carbonates such as _m2CoCO3.m3Co (OH) _2.m4H2O ( _{m2 , m3} , and _m4 are positive numbers). Examples of _Zn compounds include _ZnO .

In order to promote the reaction during calcination, compounds containing B ( _boron ), such as _B2O3 and _{H3BO3 ,} may be added up to _about 1 mass% as necessary. The addition of _H3BO3 is particularly effective in improving the magnetic properties. The amount of _{H3BO3 added} is preferably 0.3 mass% or less, and most preferably about 0.1 mass%. _H3BO3 also has the effect of controlling the shape and size of crystal grains during sintering, so _it may be added after calcination (before pulverization or sintering) or both before and after calcination.

Raw material powders that satisfy the components and composition of the ferrite calcined body of the present invention described above are mixed to obtain a mixed raw material powder. The raw material powders may be blended and mixed in either a wet or dry manner. The raw material powders can be mixed more uniformly by stirring with a medium such as steel balls. In the case of a wet method, it is preferable to use water as the dispersion medium. In order to increase the dispersibility of the raw material powder, a known dispersant such as ammonium polycarboxylate or calcium gluconate may be used. The mixed raw material slurry may be calcined as it is, or the raw material slurry may be dehydrated and then calcined.

The mixed raw material powder obtained by dry mixing or wet mixing is heated in an electric furnace, gas furnace, etc., and a solid-phase reaction forms a ferrite compound with a hexagonal magnetoplumbite (M-type) structure. This process is called "calcination," and the resulting compound is called the "calcined body."

In the calcination process, a solid-phase reaction occurs in which the ferrite phase is formed as the temperature rises. If the calcination temperature is less than 1100°C, unreacted hematite (iron oxide) remains, resulting in poor magnetic properties. On the other hand, if the calcination temperature exceeds 1450°C, the crystal grains grow too much, and the crushing process may take a long time. Therefore, the calcination temperature is preferably 1100°C to 1450°C. The calcination time is preferably 0.5 to 5 hours. The calcined body after calcination is preferably coarsely crushed using a hammer mill or the like.

By going through the above steps, the ferrite calcined body of the present invention can be obtained. Next, we will explain the manufacturing method of the sintered ferrite magnet of the present invention.

After the calcined body is coarsely pulverized, it is pulverized (finely pulverized) by a vibration mill, a jet mill, a ball mill, an attritor, or the like to obtain a powder of the calcined body (finely pulverized powder). The average particle size of the powder of the calcined body is preferably about 0.4 μm to 0.8 μm. In the present invention, the value measured by the air permeability method using a powder specific surface area measuring device (for example, SS-100 manufactured by Shimadzu Corporation) or the like is referred to as the average particle size (average particle size) of the powder. The pulverization process may be either dry pulverization or wet pulverization, or both may be combined. In the case of wet pulverization, water and/or a non-aqueous solvent (organic solvent such as acetone, ethanol, xylene, etc.) is used as a dispersion medium. Typically, a slurry containing water (dispersion medium) and the calcined body is produced. A known dispersant and/or surfactant may be added to the slurry at a solid content ratio of 0.2 to 2 mass %. After wet pulverization, the slurry may be concentrated.

In the molding process, the slurry after the grinding process is press molded in a magnetic field or without a magnetic field while removing the dispersion medium. Press molding in a magnetic field allows the crystal orientation of the powder particles to be aligned (oriented), dramatically improving the magnetic properties. Furthermore, to improve the orientation, 0.1 to 1 mass% of a dispersant and lubricant may be added to the slurry before molding. The slurry may also be concentrated as necessary before molding. Concentration is preferably performed by centrifugation, a filter press, etc.

After the calcination step and before the molding step, a sintering aid may be added to the calcined body or the powder of the calcined body (coarsely pulverized powder or finely pulverized powder). As the sintering aid, it is preferable to add only SiO ₂ or both SiO ₂ and CaCO _3. The ferrite sintered magnet of the present invention belongs to the Ca-La-Co ferrite sintered magnet as is clear from its composition. In the Ca-La-Co ferrite sintered magnet, Ca is contained as a main phase component, so that a liquid phase is generated and sintering can be performed without adding sintering aids such as SiO ₂ and CaCO ₃ as in the conventional Sr-La-Co ferrite sintered magnet. In other words, the ferrite sintered magnet of the present invention can be manufactured without adding SiO ₂ and CaCO ₃ , which mainly form the grain boundary phase in the ferrite sintered magnet. However, in order to suppress the decrease in H _cJ , the following amounts of SiO ₂ and CaCO ₃ may be added.

The amount of SiO ₂ added is preferably 1.5% by mass or less relative to 100% by mass of the calcined body or powder of the calcined body to which it is added. The amount of CaCO ₃ added is preferably 1.5% by mass or less in terms of CaO relative to 100% by mass of the calcined body or powder of the calcined body to which it is added. The sintering aid can be added, for example, by adding it to the calcined body obtained by the calcination process and then performing the pulverization process, adding it during the pulverization process, or adding it to the powder of the calcined body (finely pulverized powder) after the pulverization process, mixing it, and then performing the molding process. In addition to SiO ₂ and CaCO ₃ , Cr ₂ O ₃ , Al ₂ O ₃ , etc. may be added as a sintering aid. The amount of each of these added may be 1% by mass or less.

In the present invention, the amount of _CaCO3 added is expressed in terms of CaO. The amount of _CaCO3 added based on the amount added in terms of CaO is as follows:
It can be calculated by the formula: (molecular weight of _CaCO3 × amount added in CaO equivalent) / molecular weight of CaO. For example, when adding 0.5 mass% of _CaCO3 in CaO equivalent,
{(40.08 [atomic weight of Ca] + 12.01 [atomic weight of C] + 48.00 [atomic weight of O × 3] = 100.09 [molecular weight of _CaCO3 ]) × 0.5 mass% [amount added in CaO equivalent]} / (40.08 [atomic weight of Ca] + 16.00 [atomic weight of O] = 56.08 [molecular weight of CaO]) = 0.892 mass% [amount added of _CaCO3 ].

The compact obtained by press molding is degreased as necessary and then fired (sintered). Firing is carried out using an electric furnace, gas furnace, etc. Firing is preferably carried out in an atmosphere with an oxygen concentration of 10% by volume or more, more preferably 20% by volume or more, and most preferably 100% by volume. The firing temperature is preferably 1150°C to 1250°C. The firing time is preferably 0 hours (not held at the firing temperature) to 2 hours.

During the temperature rise in the sintering process, the average temperature rise rate in the temperature range from 800°C to the sintering temperature is set to between 600°C/hour and 1000°C/hour, and further, during the temperature drop after the sintering time is kept (including the case where no holding is performed) in the sintering process, the average temperature drop rate in the temperature range from the sintering temperature to 800°C is set to 1000°C/hour or more, which is preferable because it shortens the lead time and improves the magnetic properties. Note that these effects can be obtained by adopting only the above-mentioned temperature drop rate, but it is more preferable to adopt both the above-mentioned temperature rise rate and temperature drop rate.

When the temperature is increased, if the average heating rate in the temperature range from 800°C to the firing temperature is less than 600°C/hour, the effect of shortening the lead time and improving the magnetic properties cannot be sufficiently obtained. Even if the average heating rate exceeds 1000°C/hour, it is possible to shorten the lead time and improve the magnetic properties, but depending on the structure and size of the firing furnace, it may be difficult for the temperature of the object to be fired (molded body) to follow the temperature inside the furnace (or the set temperature of the firing furnace). Therefore, the upper limit of the average heating rate is set to 1000°C/hour. In the embodiment of the present invention, all temperatures mentioned refer to the temperature of the object to be heat-treated. The temperature is measured by contacting an R thermocouple with the object to be heat-treated in the firing furnace.

There is no particular restriction on the heating rate up to 800°C, but in consideration of shortening the lead time, it is desirable to have a heating rate similar to that in the temperature range from 800°C to the firing temperature, that is, an average heating rate of 600°C/hour to 1000°C/hour over the entire temperature range from room temperature or furnace temperature (preheating temperature, etc.) to the firing temperature.

When cooling after keeping the firing temperature for a specified time (including cases where no holding is performed), if the average cooling rate in the temperature range from the firing temperature to 800°C is less than 1000°C/hour, the effect of shortening the lead time and improving the magnetic properties cannot be fully achieved. There is no particular restriction on the cooling rate below 800°C, but considering the shortening of the lead time, it is preferable to cool to near room temperature at a cooling rate similar to or close to that in the temperature range from the firing temperature to 800°C.

After the firing process, the material goes through known manufacturing processes such as machining, cleaning, and inspection to finally produce a sintered ferrite magnet.

3. Sintered Ferrite Magnet As described above, the ferrite calcined body of the present invention can be sintered by forming a liquid phase without adding sintering aids such as _SiO2 or _CaCO3 , and the sintered ferrite magnet of the present invention can be obtained. In this case, the components and composition of the ferrite calcined body are basically the same as those of the sintered ferrite magnet (not taking into account the inclusion of impurities during the manufacturing process).

On the other hand, when a sintering aid is added, particularly when Ca (e.g., _CaCO3 ), which is also the main component of the ferrite calcined body, is added as a sintering aid, the Ca component increases in the ferrite sintered magnet as a whole, and the other elements decrease relatively. For example, when 1.5 mass% of _CaCO3 , calculated as CaO, is added as a sintering aid to the ferrite calcined body of the present invention, the maximum fluctuation occurs, from 0.4<x≦0.5 (calcined body) to 0.3<x≦0.5 (sintered magnet), and from 4.5≦n≦5.5 (calcined body) to 3.4≦n≦5.5 (sintered magnet).

Therefore, the sintered ferrite magnet of the present invention has the following properties:
In the general formula Ca1 _{- xRxFe2n -yzCoyZnz} , which shows the atomic ratio of the metal elements Ca, R, Fe, Co _{and Zn} (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.3＜x≦0.5,
0.15≦y≦0.25,
0 < z < 0.11, and
3.4≦n≦5.5,
It will satisfy the above.

The composition of the sintered ferrite magnet of the present invention, including oxygen (O), the main phase constituting the sintered ferrite magnet, and the definition of the hexagonal magnetoplumbite (M-type) structure are the same as those of the sintered ferrite magnet of the present invention. As described above, the ranges of x and n vary from those of the sintered ferrite magnet, but the reasons for limiting the atomic ratios x, y, and z, and the reason for limiting n are the same as those of the sintered ferrite magnet, and therefore will not be explained here.

As described above, in the manufacturing method of the ferrite sintered magnet of the present invention, _SiO2 may be added as a sintering aid in an amount of 1.5 mass% or less relative to 100 mass% of the calcined body or powder of the calcined body. The _SiO2 added as a sintering aid becomes a liquid phase component during firing (sintering) and exists as one component of the grain boundary phase in the ferrite sintered magnet. Therefore, when the above-mentioned amount of _SiO2 is added as a sintering aid, the obtained _ferrite sintered magnet contains 1.5 mass% or less of Si in terms of SiO2 . In this case, the content of each element represented by the general formula: Ca1 _{- xRxFe2n - yzCoyZnz} is relatively reduced by the inclusion of Si , but the _ranges of x, y, z, n, etc. in the general formula do not fundamentally change. The Si content is calculated by converting the respective compositions (mass%) of CaCO3, La(OH) ₃ , Fe2O3 _{, Co3O4} , _ZnO and _SiO2 from the composition (mass%) of Ca, R, Fe, Co, Zn and Si in the component analysis results of the sintered _ferrite magnet (e.g., results from an ICP optical _{emission spectrometer} ) and expressing the content ratio (mass%) relative to the total of 100% by mass.

The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Experimental Example 1
As an experimental example based on the present invention, CaCO3 powder _, La _{(OH)3 powder} , SrCO3 powder, _Fe2O3 powder, Co3O4 powder _and ZnO _powder were weighed out in a predetermined composition so that the atomic ratios of the general formula _Ca1 -x-x'LaxSrx'Fe2n-yzCoyZnz were 1-x-x', x _, x', y, z and 2n as shown in samples No. _{1 to} 15 and ₁₈ in Table _1. 0.1 mass% of _H3BO3 powder was added to 100 mass% of the weighed powders. The powders were then mixed in a wet _ball mill _for 4 hours, dried and sized to obtain 16 types of mixed raw material powders.

As a comparative example, _{SrCO3 powder,} La _{(OH)3 powder, Fe2O3 powder, Co3O4 powder and ZnO powder} were weighed out to a predetermined composition so that the atomic ratios of Sr, La, Co, Zn and n in the general formula _{Srx'LaxFe2n - yzCoyZnz} were the atomic ratios shown in samples No. ₁₆ and ₁₇ in Table 1, and 0.1 mass% of _H3BO3 powder was added to 100 mass% of the weighed powders _. The powders were then mixed in a wet ball mill for 4 hours, dried and sized to obtain _two types of mixed raw material powders.

The 18 types of mixed raw material powders obtained were each calcined in air for 3 hours at the calcination temperatures shown in Table 1, yielding 18 types of calcined bodies.

The calcined bodies were coarsely pulverized in a small mill to obtain 18 types of coarsely pulverized powders of the calcined bodies. _CaCO3 (addition amount converted to CaO) and _SiO2 shown in Table 1 were added to 100% by mass of the coarsely pulverized powders of the calcined bodies obtained, and the powders were finely pulverized in a wet ball mill using water as a dispersion medium until the average particle size shown in Table 1 was obtained (measured by air permeability method using a powder specific surface area measuring device (SS-100 manufactured by Shimadzu Corporation)), to obtain 18 types of finely pulverized slurries.

While removing the dispersion medium, each finely ground slurry obtained from the grinding process was molded using a parallel magnetic field molding machine (vertical magnetic field molding machine) in which the pressure direction and magnetic field direction are parallel, applying a magnetic field of approximately 1 T and a pressure of approximately 2.4 MPa, obtaining 18 types of molded bodies.

The resulting molded bodies were inserted into a firing furnace, and samples No. 1 to 14 were heated from room temperature to the firing temperature at an average rate of 1000°C/hour while air was flowing at a flow rate of 10 L/min, and fired for one hour at the firing temperature shown in Table 1. After firing, the heater of the firing furnace was turned off, the air flow rate was changed from 10 L/min to 40 L/min, and the temperature was lowered from the firing temperature to 800°C at an average rate of 1140°C/hour, and the samples were cooled to room temperature in the furnace. Samples No. 15 to 17 were heated from room temperature to the firing temperature at an average rate of 400°C/hour while air was flowing at a flow rate of 10 L/min, and fired for one hour at the firing temperature shown in Table 1. After firing, the heater of the firing furnace was turned off, and while the air flow rate was kept at 10 L/min, the temperature was lowered from the firing temperature to 800°C at an average rate of 300°C/hour, and then cooled to room temperature in the furnace. Sample No. 18 was heated from room temperature to 1100°C at an average rate of 400°C/hour while air was flowing at a flow rate of 10 L/min, and then heated from 1100°C to the firing temperature at an average rate of 1°C/minute, and fired for 1 hour at the firing temperature shown in Table 1. After firing, the heater of the firing furnace was turned off, and while the air flow rate was kept at 10 L/min, the temperature was lowered from the firing temperature to 800°C at an average rate of 300°C/hour, and then cooled to room temperature in the furnace (see Patent No. 6217640).

The measurement results of B _r , H _cJ and H _k /H _cJ of the obtained 18 types of sintered ferrite magnets are shown in Table 1. In Table 1, samples Nos. 1 to 4 and 7 to 11 without an * next to the sample No. are experimental examples based on the present invention. Samples Nos. 5, 6, and 12 to 18 marked with an * are experimental examples (comparative examples) that do not satisfy the present invention. Samples Nos. 13 and 14 marked with an * are experimental examples reproducing the Ca-Sr-La-Fe-Co-Zn sintered ferrite magnet described in Patent Document 2. Sample No. 15 marked with an * is experimental examples reproducing the Ca-A(Sr)-La-Fe-Co-Zn sintered ferrite magnet described in Patent Document 3. Samples Nos. 16 and 17 marked with an * are experimental examples (comparative examples) in which part of the Co in a conventional Sr-La-Co sintered ferrite magnet was replaced with Zn. Sample No. 18 marked with an asterisk is an experimental example of a typical Ca-La-Co sintered ferrite magnet (containing 0.3 atomic ratio of Co). Note that _Hk in Table 1 is the value of H at the position in the second quadrant of the J (magnetization magnitude)-H (magnetic field strength) curve where J is 0.95× _Jr ( _Jr is remanent magnetization, _Jr ＝ _Br ).

The atomic ratios in Table 1 indicate the atomic ratios (composition) of the raw material powders when they were mixed. The atomic ratios (composition of the sintered magnet) in the sintered body (sintered ferrite magnet) after sintering can be calculated based on the atomic ratios when mixed, taking into account the amounts of additives ( _H3BO3 , _etc. ) added before the calcination process and the amounts of sintering aids ( _CaCO3 and _SiO2 ) added after the calcination process and before the shaping process, and these calculated values are basically the same as the results of analyzing the sintered ferrite magnet with an ICP optical emission spectrometer (for example, Shimadzu ICPV-1017).

When the atomic ratio y (Co content) is 0.15≦y<0.2 as in samples 3 and 4, both B _r and H _cJ are higher than those of samples 16 and 17, which are experimental examples (comparative examples) in which part of the Co in conventional Sr-La-Co based sintered magnets has been replaced with Zn, despite having roughly the same Co content. In addition, it is possible to reduce the amount of Co used (from 0.2 to 0.15) compared to general Sr-La-Co based sintered magnets (containing a Co atomic ratio of about 0.2).

When the atomic ratio y (Co content) is 0.2≦y≦0.25, as in samples No. 1, 2, and 7 to 11, they have magnetic properties roughly equivalent to those of sample No. 18, an experimental example of a typical Ca-La-Co sintered ferrite magnet (containing 0.3 Co in atomic ratio), and the amount of Co used can be reduced (from 0.3 to 0.25 or less) compared to a typical Ca-La-Co sintered ferrite magnet (containing about 0.3 Co in atomic ratio).

Moreover, as is clear from a comparison of Samples 1 and 2, which are experimental examples based on the present invention, with Samples 5 and 6 (which do not contain Zn), which are experimental examples (comparative examples) that do not satisfy the present invention, the sintered ferrite magnets of the present invention have excellent B _r and H _cJ . Moreover, as is clear from a comparison of Sample 10, which is an experimental example based on the present invention, with Sample 12 (which has a low Ca content), which is an experimental example (comparative example) that does not satisfy the present invention, the sintered ferrite magnets of the present invention have high H _cJ .

Furthermore, it can be seen that Samples 1, 2, and 7 to 11, which are experimental examples based on the present invention and have an atomic ratio y (Co content) of 0.2≦y≦0.25, have superior B r and H cJ compared to Samples 13 and 14, which are reproduction experiments of the Ca-Sr-La-Fe-Co-Zn sintered ferrite magnet described in Patent Document 2, and Sample No. 15, which is a reproduction experiment of the Ca-A(Sr)-La-Fe-Co- _Zn sintered _ferrite magnet described in Patent Document 3.

For samples No. 13 and No. 14, which are reproduction experiments of the Ca-Sr-La-Fe-Co-Zn ferrite sintered magnet described in Patent Document 2, the experiments were performed using the additive conditions described in Patent Document 2 ( _CaCO3 = 1.70 mass%, _SiO2 = 0.45 mass%, _Fe2O3 = 10 mass%, _La2O3 = 1.5 mass%). However, since the magnetic properties were extremely low ( _Br = 0.44T, _{HcJ =} about 180kA/m), the experiments were performed under almost the same additive (sintering aid) conditions as in the experimental example based on the present invention. As a result, _Br and _{HcJ were} as shown in Table 1, and the maximum energy product ((BH) _max ) was 4.89MGOe (sample No. 13) and 4.69MGOe (sample No. 14), and the 5.64MGOe and 5.65MGOe described in Patent Document 2 were not obtained.

Furthermore, for sample No. 15, which is a reproduction experiment of the Ca-A(Sr)-La-Fe-Co-Zn ferrite sintered magnet described in Patent Document 3, the heat treatment and re-grinding process described in Patent Document 3 was not carried out, and grinding was carried out under the same conditions (grinding was carried out only once) as in the experimental example based on the present invention. Also, for the additives (sintering aids), the experiment was carried out with almost the same amounts added as in the experimental example based on the present invention ( _CaCO3 = 0.4 mass% and _SiO2 = 0.4 mass% in terms of CaO). As a result, the B _r and H _cJ were as shown in Table 1.

Experimental Example 2
As an experimental example based on the present invention, CaCO3 powder, La( _{OH)3 powder, Fe2O3 powder , Co3O4} powder _and ZnO _{powder were} weighed out in a predetermined composition so that the atomic ratios of 1- _x -x', x, x', y, z and 2n in the general formula Ca1-x-x'LaxSrx'Fe2n-yzCoyZnz were as shown in Sample No. _19-27 in Table ₂ , and 0.1 mass% of _{H3BO3 powder} was added to the total of 100 mass% of _the weighed powders. _After that, they were mixed in a wet ball mill for 4 hours, and then dried and sized to obtain 9 types of mixed raw material powders. All 9 types of mixed raw material powders obtained were calcined in air at the calcination temperatures shown in Table 2 for 3 hours, and 9 types of calcined bodies were obtained.

The calcined bodies were coarsely pulverized in a small mill to obtain nine types of coarsely pulverized powders of the calcined bodies. _CaCO3 (addition amount converted to CaO) and _SiO2 shown in Table 2 were added to 100% by mass of the coarsely pulverized powders of the calcined bodies obtained, and the powders were finely pulverized in a wet ball mill using water as a dispersion medium until the average particle size shown in Table 2 was obtained (measured by air permeability method using a powder specific surface area measuring device (SS-100 manufactured by Shimadzu Corporation)). Nine types of finely pulverized slurries were obtained.

While removing the dispersion medium, each finely ground slurry obtained from the grinding process was molded using a parallel magnetic field molding machine (vertical magnetic field molding machine) in which the pressure direction and magnetic field direction are parallel, applying a magnetic field of approximately 1 T and a pressure of approximately 2.4 MPa, obtaining nine types of molded bodies.

Each of the resulting molded bodies was inserted into a firing furnace, and while air was flowing at a flow rate of 10 L/min, the temperature was raised from room temperature to the firing temperature at an average rate of 1000°C/hour, and the bodies were fired for 1 hour at the firing temperature shown in Table 2. After firing, the heater of the firing furnace was turned off, the air flow rate was changed from 10 L/min to 40 L/min, and the temperature was lowered at an average rate of 1140°C/hour from the firing temperature to 800°C, and the bodies were cooled to room temperature in the furnace.

The measurement results of B _r , H _cJ and H _k /H _cJ for the nine types of sintered ferrite magnets obtained are shown in Table 2. Samples No. 19 to 27 in Table 2 are all experimental examples based on the present invention. _Hk in Table 2 is the value of H at the position in the second quadrant of the J (magnitude of magnetization) -H (magnetic field strength) curve where J is 0.95 × J _r (J _r is remanent magnetization, J _r = B _r ).

The atomic ratios in Table 2 indicate the atomic ratios (composition) of the raw material powders when they were mixed. The atomic ratios (composition of the sintered magnet) in the sintered body (sintered ferrite magnet) after sintering can be calculated based on the atomic ratios when mixed, taking into account the amounts of additives ( _H3BO3 , _etc. ) added before the calcination process and the amounts of sintering aids ( _CaCO3 and _SiO2 ) added after the calcination process and before the shaping process, and these calculated values are basically the same as the results of analyzing the sintered ferrite magnet with an ICP optical emission spectrometer (for example, Shimadzu ICPV-1017).

Samples No. 19 to 27, with an atomic ratio y (Co content) of 0.2≦y≦0.25, have magnetic properties roughly equivalent to those of sample No. 18, an example of a typical Ca-La-Co sintered ferrite magnet (containing 0.3 atomic Co) in Experimental Example 1, and can use less Co (from 0.3 to 0.25 or less) than a typical Ca-La-Co sintered ferrite magnet (containing about 0.3 atomic Co).

Moreover, as is clear from a comparison of Samples 19 to 27 with Nos. 5 and 6 (containing no Zn), which are experimental examples (comparative examples) in Experimental Example 1 that do not satisfy the requirements of the present invention, the sintered ferrite magnets of the present invention have excellent B _r and H _cJ . Moreover, as is clear from a comparison of Samples 19 to 27 with No. 12 (containing a low Ca content), which is an experimental example (comparative example) in Experimental Example 1 that does not satisfy the requirements of the present invention, the sintered ferrite magnets of the present invention have high H _cJ .

Furthermore, it is seen that samples Nos. 19 to 27 have superior B r and H cJ compared to samples Nos. 13 and 14, which are reproduction experiments of the Ca-Sr-La-Fe-Co-Zn sintered ferrite magnet described in Patent Document 2, and sample No. 15, which is a reproduction experiment of the Ca-A(Sr)-La-Fe-Co- _Zn sintered _ferrite magnet described in Patent Document 3.

According to the present invention, it is possible to provide a sintered ferrite magnet that has high B _r , little decrease in H _cJ , and uses less Co than conventional sintered ferrite magnets, and therefore the magnet can be suitably used in various motors, etc.

Claims (14)

The general formula Ca1 _{-xRxFe2n-y-zCoyZnz} shows the atomic ratio of the metal elements Ca, R, Fe, Co and Zn (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.4＜x≦0.5,
0.2 ≦y≦0.25,
0 < z < 0.11, and
9.0≦2n≦11.0 ,
A ferrite calcined body that satisfies the above requirements. In the ferrite calcined body according to claim 1,
A ferrite calcined body, wherein the 2n satisfies 9.0≦2n≦10.31. The ferrite calcined body according to claim 1 or 2,
The ferrite calcined body, wherein z satisfies 0.02≦z≦0.1. The general formula Ca1 _{-xRxFe2n-y-zCoyZnz} shows the atomic ratio of the metal elements Ca, R, Fe, Co and Zn (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.3＜x≦0.5,
0.2 ≦y≦0.25,
0 < z < 0.11, and
6.8≦2n≦11.0 ,
A sintered ferrite magnet that satisfies the above requirements. The sintered ferrite magnet according to claim 4,
A sintered ferrite magnet, wherein 2n satisfies 6.8≦2n≦10.31. The sintered ferrite magnet according to claim 4 or 5,
A sintered ferrite magnet, wherein z satisfies 0.02≦z≦0.1. The sintered ferrite magnet according to any one of claims 4 to 6,
A sintered ferrite magnet further containing 1.5 mass% or less of Si calculated as _SiO2 . The general formula Ca1 _{-xRxFe2n-y-zCoyZnz} shows the atomic ratio of the metal elements Ca, R, Fe, Co and Zn (wherein R is at least one rare earth element and essentially contains La),
The x, y, z, and n (wherein 2n is a molar ratio expressed as 2n=(Fe+Co+Zn)/(Ca+R)) are
0.4＜x≦0.5,
0.2 ≦y≦0.25,
0 < z < 0.11, and
9.0≦2n≦11.0 ,
A raw material powder mixing process for mixing raw material powders satisfying the above to obtain a mixed raw material powder;
a calcination step of calcining the mixed raw material powder to obtain a calcined body;
A grinding step of grinding the calcined body to obtain a powder of the calcined body;
a molding step of molding the powder of the calcined body to obtain a molded body, and a firing step of firing the molded body to obtain a sintered body;
A method for producing a sintered ferrite magnet comprising the steps of: The method for producing a sintered ferrite magnet according to claim 8,
A method for producing a sintered ferrite magnet, wherein 2n satisfies 9.0≦2n≦10.31. The method for producing a sintered ferrite magnet according to claim 8 or 9,
A method for producing a sintered ferrite magnet, wherein z satisfies 0.02≦z≦0.1. The method for producing a sintered ferrite magnet according to any one of claims 8 to 10,
A method for producing a ferrite sintered magnet, further comprising the step of adding 1.5 mass% or less of _SiO2 to 100 mass% of the calcined body or powder of the calcined body after the calcination step and before the molding step. The method for producing a sintered ferrite magnet according to any one of claims 8 to 11,
A method for producing a ferrite sintered magnet, further comprising the step of adding 1.5 mass% or less of _CaCO3 , calculated as CaO, to 100 mass% of the calcined body or powder of the calcined body after the calcination step and before the molding step. The method for producing a sintered ferrite magnet according to any one of claims 8 to 12,
A method for producing a sintered ferrite magnet, wherein the average heating rate in the temperature range from 800°C to the firing temperature in the firing step is 600°C/hour or more and 1000°C/hour or less. The method for producing a sintered ferrite magnet according to claim 13,
A method for producing a sintered ferrite magnet, wherein the average temperature drop rate in the temperature range from the sintering temperature to 800°C in the sintering step is 1000°C/hour or more.