JP7247467B2 - Method for producing sintered ferrite magnet and sintered ferrite magnet - Google Patents

Description

The present invention relates to a method for producing a sintered ferrite magnet and a sintered ferrite magnet.

Although the maximum energy product of ferrite sintered magnets is only 1/10 that of rare earth sintered magnets (e.g. NdFeB sintered magnets), their main raw material is cheap iron oxide, which makes them excellent in terms of cost performance. It has the characteristic of being extremely stable over time. Therefore, the world production weight is still the largest among magnetic materials.

Among the various applications where ferrite sintered magnets are used, such as motors and speakers, there is a strong demand for high-performance materials for automobile electrical equipment motors and home appliance motors. In recent years, against the background of soaring prices of rare earth raw materials and the emergence of procurement risks, industrial motors and drive motors and generators for electric vehicles (EV, HV, PHV, etc.), which used to use only rare earth sintered magnets, Applications of sintered ferrite magnets are also being considered.

A typical sintered ferrite magnet is Sr ferrite having a magnetoplumbite (M-type) structure, and its basic composition is represented by SrFe ₁₂ O ₁₉ . In the latter half of the 1990s, Sr—La—Co system ferrite sintered magnets in which part of Sr ²⁺ in SrFe ₁₂ O ₁₉ was replaced with La ³⁺ and part of Fe ³⁺ was replaced with Co ²⁺ were put into practical use. The magnetic properties of the magnet are greatly improved. In 2007, a Ca--La--Co ferrite sintered magnet with further improved magnetic properties was developed and is currently in practical use. Ferrite sintered magnets are also required to have higher performance.

The research group of the present inventors has previously optimized the atomic ratio of each constituent element and the value of n in order to improve the magnetic properties of a Ca-La-Co ferrite sintered magnet, and has specified La and Co. A Ca--La--Co ferrite sintered magnet was proposed (Patent Document 1).

In addition, the research group of the present inventors has previously attempted to improve the performance by improving the manufacturing method, and in the firing process of a Ca-La-Co ferrite sintered magnet, in the temperature range from 1100 ° C. to the firing temperature A high residual magnetic flux density (hereinafter referred to as “B _r ”) and a high It was proposed to improve the coercive force (hereinafter referred to as "H _cJ ") while maintaining the squareness ratio (hereinafter referred to as "H _k /H _cJ ") (Patent Document 2).

WO2006/028185 WO2014/021149

The proposals of Patent Documents 1 and 2 are extremely excellent in that they can improve the magnetic properties of Ca--La--Co ferrite sintered magnets. However, the Co content must be about 0.3 in terms of atomic ratio (Co/Fe=0.03, that is, about 3% of the Fe content), and Sr--La--Co ferrite sintered magnets (where the Co content is The atomic ratio is about 0.2, Co/Fe=0.017, that is, about 1.7% of the Fe content). Also, a Ca--La--Co ferrite sintered magnet must contain La in an atomic ratio equal to or greater than the amount of Ca in order to develop good magnetic properties. The price of Co (Co oxide) is ten to several ten times that of iron oxide, which is the main component of sintered ferrite magnets, and La (La oxide and La hydroxide) is also more expensive than iron oxide. Therefore, there is a problem that the cost of raw materials is inevitably increased, and the price of the sintered ferrite magnet is increased. In addition, in Patent Document 2, since the rate of temperature increase in the firing process is very low (1 to 4° C./min), it is unavoidable to increase the cost due to the long lead time, and the cost of raw materials and process costs. There is a problem of double cost increase.

The embodiments of the present disclosure make it possible to provide low-cost ferrite sintered magnets having magnetic properties comparable to those of conventional Ca—La—Co based ferrite sintered magnets.

A non-limiting exemplary method of manufacturing a ferrite sintered magnet of the present disclosure includes:
In the general formula showing the atomic ratio of the metal elements Ca, La, Fe and Co: Ca _1-x La _x Fe _2n-y Co _y , the 1-x and y, and n (2n is the molar ratio, 2n = (Fe + Co) / (Ca + La)) is
0.5<1−x<0.6,
0.15≦y<0.25 and 4≦n≦6
A raw material powder mixing step for obtaining a mixed raw material powder by mixing raw material powders satisfying
a calcining step of calcining the mixed raw material powder to obtain a calcined body;
a pulverizing step of pulverizing the calcined body to obtain a powder;
A molding step of molding the powder to obtain a molded body;
A firing step of firing the compact to obtain a sintered body,
In the firing step, the temperature rise rate in the temperature range from 800° C. to the firing temperature is 600° C./hour or more and 1000° C./hour or less.

According to the embodiment of the present disclosure, since the atomic ratio y (Co content) is 0.15 ≤ y < 0.25, the conventional Ca-La-Co ferrite sintered magnet (where the Co content is atomic ratio of about 0.3), the Co content can be reduced, and the raw material cost can be reduced. In addition, since the atomic ratio 1-x (content of Ca) is 0.5<1-x<0.6, the atomic ratio x (content of La) can be reduced. As a result, the content of La, which is more expensive than iron oxide, can be reduced, and raw material costs can be reduced. Furthermore, since the temperature rise 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 conventional method for producing a Ca—La—Co ferrite sintered magnet (for example, The lead time can be shortened and the process cost can be reduced compared to Patent Document 2, etc.).

In one embodiment, the calcination temperature in the calcination step is 1200° C. or more and 1250° C. or less.

According to the embodiment of the present disclosure, the calcination temperature in the calcination step is 1200° C. or more and 1250° C. or less, so the calcination temperature is compared with the conventional method for producing a Ca—La—Co ferrite sintered magnet. can be lowered. Thereby, the process cost can be reduced.

In one embodiment, the firing temperature in the firing step is 1170°C or higher and 1190°C or lower.

According to the embodiment of the present disclosure, since the firing temperature in the firing step is 1170° C. or higher and 1190° C. or lower, the firing temperature is relatively low compared to the conventional method for producing a Ca—La—Co ferrite sintered magnet. be able to. Thereby, the process cost can be reduced.

In one embodiment, after the calcination step and before the molding step, the step of adding a sintering aid is further included, wherein the sintering aid includes at least one of _CaCO3 and _SiO2 , and the amount of _CaCO3 added is 0.5% by mass or less in terms of CaO with respect to 100% by mass of the calcined body or powder to be added, and the amount of _SiO2 added is 100% by mass of the calcined body or powder to be added. is 0.6% by mass or less with respect to

According to embodiments of the present disclosure, magnetic properties can be improved.

In one embodiment, the sintering aid contains at least CaCO ₃ and SiO ₂ , and the amount of CaCO ₃ added is 0.3 mass in terms of CaO with respect to 100 mass% of the calcined body or powder to be added. % or more and 0.5 mass % or less, and the amount of SiO ₂ added is 0.4 mass % or more and 0.6 mass % or less with respect to 100 mass % of the calcined body or powder to be added, When the amount of _CaCO3 added is 0.4% by mass or less in terms of CaO, the ratio of the amount of _CaCO3 added to the amount of _SiO2 added [ _CaCO3 addition amount (CaO conversion)/ _SiO2 addition amount] is 0.6 is less than 1.0, and the amount of CaCO ₃ added exceeds 0.4% by mass in terms of CaO, the ratio of the amount of CaCO ₃ added to the amount of SiO ₂ added [CaCO ₃ added amount (CaO equivalent) / SiO ₂ addition amount] is more than 0.83 and less than 1.25.

According to the embodiments of the present disclosure, the magnetic properties can be further improved.

In one embodiment, in the firing step, the temperature drop rate in the temperature range from the firing temperature to 800°C is 300°C/hour or more.

According to embodiments of the present disclosure, magnetic properties can be further improved.

A non-limiting exemplary sintered ferrite magnet of the present disclosure comprises a main phase composed of ferrite having a hexagonal magnetoplumbite (M-type) structure and a second phase existing between the two main phases. The results of composition analysis by spherical aberration correction transmission electron microscope (Cs-TEM) and EDS (energy dispersive X-ray spectroscopy) analysis using it in the vicinity of the interface between the main phase and the second phase are as follows. (1) and (2) are satisfied.
(1) In the main phase, Ca (atomic %)/Fe (atomic %) increases in a range within 2 nm from the interface compared to a range exceeding 2 nm from the interface.
(2) In the interface, Ca (atomic %)/Fe (atomic %) is 0.14 or less.

According to the embodiments of the present disclosure, it is possible to provide low-cost ferrite sintered magnets having magnetic properties comparable to those of conventional Ca—La—Co based ferrite sintered magnets.

4 is a graph showing the relationship between the sintering temperature and the phase ratio of a ferrite sintered magnet according to an embodiment of the present disclosure and a conventional Ca—La—Co based ferrite sintered magnet. 4 is a graph showing composition analysis results of a ferrite sintered magnet according to an embodiment of the present disclosure by spherical aberration correction transmission electron microscope (Cs-TEM) and EDS (energy dispersive X-ray spectroscopy) analysis using the same. 4 is a photograph showing an STEM-BSE image of a ferrite sintered magnet of Comparative Example.

1. Method for Manufacturing Sintered Ferrite Magnet Hereinafter, a method for manufacturing a sintered ferrite magnet according to an embodiment of the present disclosure will be described in detail.

[1] Raw material powder mixing step In the general formula showing the atomic ratio of the metal elements Ca, La, Fe and Co: Ca _1-x La _x Fe _2n-y Co _y , the 1-x and y and n are A raw material powder satisfying 0.5<1−x<0.6, 0.15≦y<0.25, and 4≦n≦6 is prepared.

The atomic ratio 1-x (Ca content) is 0.5<1-x<0.6. If 1-x is 0.5 or less or 0.6 or more, it is not possible to obtain magnetic properties equivalent to those of conventional Ca--La--Co ferrite sintered magnets.

The atomic ratio x (La content) is 0.4<x<0.5 in relation to 1−x. La may be partially substituted with at least one rare earth element other than La. The substitution amount is preferably 50% or less of La in terms of molar ratio.

1-x and x have a relationship of 1<(1-x)/x<1.5. If (1-x)/x is 1 or less or 1.5 or more, it is not possible to obtain magnetic properties equivalent to those of conventional Ca--La--Co ferrite sintered magnets.

In the conventional Ca-La-Co ferrite sintered magnet, the atomic ratio of the La content in the calcined body before Ca (CaCO ₃ ) is added as a sintering aid is the same as the atomic ratio of the Ca content. Alternatively, it is known that the magnetic properties are improved by setting Ca≦La (for example, International Publication No. 2012/090935). One of the features of the embodiments of the present disclosure is that the atomic ratio of the Ca content is higher than the atomic ratio of the La content. As a result, the material cost can be reduced by reducing the La content.

The atomic ratio y (content of Co) satisfies 0.15≦y<0.25. If y is less than 0.15 or greater than 0.25, it is not possible to obtain magnetic properties equivalent to those of conventional Ca--La--Co ferrite sintered magnets. The atomic ratio y (content of Co) is preferably 0.18<y≦0.24, more preferably 0.20<y≦0.24. The content of Co in conventional Ca--La--Co ferrite sintered magnets was required to be about 0.3 in terms of atomic ratio. One of the features of the embodiments of the present disclosure is that the Co content is less than 0.25 in terms of atomic ratio. As a result, the material cost can be reduced by reducing the Co content.

In the above general formula, 2n is a molar ratio expressed by 2n=(Fe+Co)/(Ca+La). n is 4≤n≤6. If n is less than 4 or more than 6, it is not possible to obtain magnetic properties equivalent to those of conventional Ca--La--Co ferrite sintered magnets.

Although the above compositions are indicated by atomic ratios of metal elements, compositions containing oxygen (O) are represented by the general formula: Ca _1-x La _x Fe _2n-y Co _y O _α . The number of moles α of oxygen is α=19 when the stoichiometric composition ratio when La and Fe are trivalent and Co is divalent, and x=y and n=6, but Fe and the valence of Co, x and y, n values, and the like. In addition, the ratio of oxygen to the metal element changes due to oxygen vacancies (vacancy) when firing in a reducing atmosphere, changes in the valence of Fe in the ferrite phase, changes in the valence of Co, and the like. Therefore, the actual number of moles α of oxygen may deviate from 19 in some cases. Therefore, in the embodiments of the present disclosure, the composition is represented by the atomic ratio of the metal elements, which makes it most easy to identify the composition.

As raw material powders, oxides, carbonates, hydroxides, nitrates, chlorides, etc. of respective metals can be used regardless of valence. A solution obtained by dissolving the raw material powder may 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, mill scale, and the like. Co compounds include oxides such as CoO and Co ₃ O ₄ , and hydroxides such as CoOOH, Co(OH) ₂ , Co ₃ O ₄ ·m ₁ H ₂ O (where m ₁ is a positive number). , _{CoCO3 , and basic carbonates such as m2CoCO3.m3Co(OH)2.m4H2O, where m2 , m3 , m4 are positive numbers .} mentioned.

A compound containing B (boron), such as B ₂ O ₃ and H ₃ BO ₃ , may be added up to about 1% by mass in order to promote the reaction during calcination. Addition of H ₃ BO ₃ is particularly effective in improving magnetic properties. The amount of H ₃ BO ₃ added is preferably 0.3% by mass or less, most preferably about 0.1% by mass. Since H ₃ BO ₃ also has the effect of controlling the shape and size of crystal grains during firing, it may be added after calcination (before pulverization or before calcination). may be added.

Each of the prepared raw material powders is mixed to obtain a mixed raw material powder. Blending and mixing of raw material powders may be carried out by either a wet method or a dry method. Stirring with a medium such as a steel ball allows the raw material powder to be mixed more uniformly. In the wet method, it is preferable to use water as a dispersion medium. A known dispersant such as ammonium polycarboxylate and calcium gluconate may be used for the purpose of enhancing the dispersibility of the raw material powder. The mixed raw material slurry may be calcined as it is, or may be calcined after dewatering the raw material slurry.

[2] Calcination process The mixed raw material powder obtained by dry mixing or wet mixing is heated using an electric furnace, a gas furnace, etc., and a hexagonal magnetoplumbite (M type ) to form a ferrite compound of the structure This process is called "calcination", and the resulting compound is called "calcined body".

The main phase constituting the sintered ferrite magnet obtained by the method for producing a sintered ferrite magnet according to the embodiment of the present disclosure is a 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 properties (physical properties, magnetic properties, etc.) of the magnetic material is defined as the "main phase."

The phrase “having a hexagonal magnetoplumbite (M type) structure” means that X It means that a line diffraction pattern is mainly observed.

The calcination step is preferably performed in an atmosphere with an oxygen concentration of 5% by volume or more. If the oxygen concentration is less than 5% by volume, abnormal grain growth, generation of heterogeneous phases, and the like are caused. A more preferable oxygen concentration is 20% by volume or more.

In the calcining step, a solid phase reaction that forms a ferrite phase progresses as the temperature rises. If the calcining temperature is less than 1100° C., unreacted hematite (iron oxide) remains, resulting in poor magnetic properties. On the other hand, if the calcining temperature exceeds 1450° C., the crystal grains grow too much, which may require a long time for pulverization in the pulverization step. Therefore, the calcination temperature is preferably 1100°C to 1450°C, and the conventional method for producing a Ca-La-Co ferrite sintered magnet is generally carried out at 1200°C to 1300°C. However, in the embodiment of the present disclosure, calcination is possible even at a relatively low temperature of 1200° C. or higher and 1250° C. or lower. This is also one of the features of the embodiments of the present disclosure. Thereby, the process cost can be reduced. The calcination time is preferably 0.5 to 5 hours. It is preferable to coarsely pulverize the calcined body after calcination with a hammer mill or the like.

[3] Pulverization step The calcined body is pulverized (pulverized) by a vibration mill, jet mill, ball mill, attritor, or the like to obtain a powder (finely pulverized powder). The average particle size of the powder is preferably about 0.4 μm to 0.8 μm. In the present disclosure, the value measured by the air permeation method using a powder specific surface area measuring device (eg SS-100 manufactured by Shimadzu Corporation) is referred to as the average particle size of the powder (average particle size). The same applies to the following description. The pulverization step 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 a 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% by mass. After wet grinding, the slurry may be concentrated.

[4] Forming step In the forming step, the slurry after the pulverization step is press-molded in a magnetic field or in a non-magnetic field while removing the dispersion medium. By press-molding in a magnetic field, the crystal orientation of the powder particles can be aligned (orientated), and the magnetic properties can be dramatically improved. Furthermore, in order to improve orientation, 0.1% to 1% by mass of a dispersant and a lubricant may be added to the slurry before molding. Also, the slurry may be concentrated before molding, if necessary. Concentration is preferably carried out by centrifugation, filter press or the like.

[5] Firing Step The compact obtained by press molding is degreased as necessary and then fired (sintered).
The embodiment of the present disclosure is characterized in that in the firing step, the rate of temperature increase (amount of temperature increase per unit time) in the temperature range from 800 ° C. to the firing temperature is 600 ° C./h or more and 1000 ° C./h or less. is one. In the following, the explanation presumed by the present inventors for this feature will be described, but this explanation is presumed from the knowledge obtained at the present time, and is intended to limit the technical scope of the present disclosure. isn't it.

FIG. 1 is used in the following description. FIG. 1 shows Ca with a Co content less than 0.3 in atomic ratio (0.18 in atomic ratio) when the heating rate in the temperature range from 800° C. to the firing temperature is 450° C./hour. - It is a graph showing the relationship between the firing temperature and the phase ratio of a La-Co ferrite sintered magnet and a conventional Ca-La-Co ferrite sintered magnet (with a Co content of about 0.3 in atomic ratio). . In FIG. 1, the horizontal axis is the firing temperature (° C.) and the vertical axis is the phase ratio (%). In FIG. 1, black plots indicate Ca—La—Co ferrite sintered magnets with an atomic ratio of Co content of less than 0.3, and white plots indicate conventional Ca—La—Co ferrite magnets. The sintered magnets are shown, in which round plots indicate the main phase (ferrite phase having a hexagonal magnetoplumbite (M type) structure), square plots indicate the hematite phase, and triangle plots indicate the phase ratio of the La orthoferrite phase ( %).

As shown in FIG. 1, in the Ca—La—Co based ferrite sintered magnet, in the temperature range from about 700° C. to the firing temperature during the heating process of the firing process, one of the ferrite compounds formed by the calcination process (for example, 30% to 50%) decomposes (white circle plot in FIG. 1), hematite phase (white square plot), La orthoferrite phase (white triangle plot) and Co Heterogeneous phases such as spinel phases are produced. The heterogeneous phase generated by decomposition changes again to a ferrite compound by the time firing is completed, and in the sintered body after firing, almost 100% (excluding the grain boundary phase) is a ferrite compound (hexagonal magnetoplumbite ( The present inventors' research has revealed that a ferrite phase having an M-type structure) is formed.

In conventional Ca—La—Co ferrite sintered magnets with a Co content of about 0.3 in atomic ratio, the decomposition initiation temperature of the ferrite compound is as low as about 700° C., and the decomposed heterogeneous phase is regenerated into a ferrite compound. Since the temperature (about 1100° C.) at which the change to the final temperature is slightly lower than the sintering temperature, almost no heterogeneous phase remained in the sintered body after sintering, and the magnetic properties were hardly affected.

However, when the Co content is less than 0.3 in atomic ratio (the black plot in FIG. 1 is when the Co content is 0.18 in atomic ratio), the ferrite compound (black round plot in FIG. 1) As the decomposition start temperature shifts to the high temperature side (about 800 ° C. to about 900 ° C.), different phases such as the decomposed hematite phase (same black square plot) and La orthoferrite phase (same black triangle plot) become ferrite again. A phenomenon occurs in which the temperature at which the change to the compound ends also shifts to a higher temperature side (near the firing temperature or above the firing temperature), and a heterogeneous phase remains in the sintered body after firing, which adversely affects the magnetic properties. has been clarified by the research of the present inventors.

The inventors of the present invention have tried methods such as increasing the firing temperature or lengthening the firing time in order to eliminate the heterogeneous phase. has declined significantly. Therefore, the present inventors focused on the rate of temperature rise in the firing process, and suppressed the decomposition of the ferrite compound by increasing the rate of temperature rise in the temperature range from the decomposition start temperature of around 800°C to the firing temperature as fast as possible. Furthermore, the inventors have found that grain growth of the ferrite compound can be suppressed by setting the firing temperature slightly lower than the conventional one. Furthermore, it was found that decomposition of the ferrite compound can be further suppressed by making the atomic ratio of the Ca content larger than the atomic ratio of the La content in the general formula for mixing the raw material powders.

If the temperature rise rate in the temperature range from 800° C. to the firing temperature is less than 600° C./hour, the decomposition of the ferrite compound cannot be suppressed, and is about the same as the conventional Ca—La—Co ferrite sintered magnet. magnet properties cannot be obtained. Even if the heating rate exceeds 1000° C./hour, it is possible to achieve the same effect as the embodiment of the present disclosure, but depending on the structure and size of the firing furnace, the temperature of the object to be fired (formed body) may increase. It may be difficult to follow the temperature inside the furnace (or the set temperature of the firing furnace). Therefore, the upper limit of the temperature increase rate was set to 1000° C./hour. In addition, in the embodiments of the present disclosure, when the temperature is described, it refers to the temperature of the object to be heat-treated.

The rate of temperature rise up to 800°C is not particularly limited, but considering the shortening of the lead time, the rate of temperature rise similar to the temperature range from 800°C to the firing temperature, that is, the room temperature or the furnace temperature (preheating temperature, etc.) to the firing temperature, it is desirable that the heating rate is 600° C./hour or more and 1000° C./hour or less.

Firing is performed using an electric furnace, a gas furnace, or the like. Firing is preferably performed in an atmosphere having an oxygen concentration of 10% by volume or more. More preferably 20% by volume or more, most preferably 100% by volume. In the conventional method for producing a Ca--La--Co ferrite sintered magnet, firing is generally carried out at a temperature of 1190.degree. C. to 1250.degree. However, in the embodiment of the present disclosure, firing is possible even at a relatively low temperature of 1170° C. or higher and 1190° C. or lower. This is also one of the features of the embodiments of the present disclosure. Thereby, the process cost can be reduced. The firing time is preferably 0 hour (no holding at the firing temperature) to 2 hours.

It is desirable that the temperature drop rate after firing is 300°C/hour or more in the temperature range from the firing temperature to 800°C. As a result, the sintered ferrite magnet according to the embodiment of the present disclosure having the features described below is obtained, and the magnetic properties are further improved.

After the firing process, a sintered ferrite magnet is finally manufactured through known manufacturing processes such as a working process, a cleaning process, and an inspection process.

[6] Step of adding sintering aid A sintering aid may be added to the calcined body or powder (coarsely pulverized powder or finely pulverized powder) after the calcining step and before the molding step. The sintering aid contains at least one of CaCO ₃ and SiO ₂ . The amount of CaCO ₃ added is 0.5% by mass or less in terms of CaO with respect to 100% by mass of the calcined body or powder to be added. The amount of SiO ₂ added is 0.6% by mass or less with respect to 100% by mass of the calcined body or powder to which it is added. Magnetic properties can be improved by adding a sintering aid.

More preferably, the sintering aid contains both CaCO ₃ and SiO ₂ , and the amount of CaCO ₃ added is 0.3% by mass in terms of CaO with respect to 100% by mass of the calcined body or powder to be added. It is more than 0.5 mass % or less. The amount of SiO ₂ added is 0.4% by mass or more and 0.6% by mass or less with respect to 100% by mass of the calcined body or powder to be added. Furthermore, when the amount of CaCO ₃ added is 0.4% by mass or less in terms of CaO, the ratio of the amount of CaCO ₃ added to the amount of SiO ₂ added [amount of CaCO ₃ added (calculated as CaO)/amount of SiO ₂ added] is 0 .6 and less than 1.0, and when the amount of _CaCO3 added exceeds 0.4% by mass in terms of CaO, the ratio of the amount of _CaCO3 added to the amount of _SiO2 added [ _CaCO3 added amount (CaO equivalent )/SiO ₂ added amount] is more than 0.83 and less than 1.25. This can further improve the magnetic properties.

The sintering aid is added, for example, by adding it to the calcined body obtained by the calcining step and then performing the pulverizing step, adding it during the pulverizing step, or adding it to the powder after the pulverizing step (fine pulverized powder). It is possible to adopt a method such as adding to and mixing and then carrying out the molding step. As a sintering aid, in addition to CaCO ₃ and SiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ and the like may be added. The amount of each of these added may be 5% by mass or less.

2. Sintered Ferrite Magnet The sintered ferrite magnet of the embodiment of the present disclosure includes a main phase made of ferrite having a hexagonal magnetoplumbite (M-type) structure and a second phase existing between the two main phases. The results of composition analysis by spherical aberration correction transmission electron microscope (Cs-TEM) and EDS (energy dispersive X-ray spectroscopy) analysis using it in the vicinity of the interface between the main phase and the second phase are as follows. It is characterized by satisfying (1) and (2).
(1) In the main phase, Ca (atomic %)/Fe (atomic %) increases in a range within 2 nm from the interface compared to a range exceeding 2 nm from the interface.
(2) In the interface, Ca (atomic %)/Fe (atomic %) is 0.14 or less.
This feature improves the magnetic properties, especially the _HcJ .

Furthermore, in addition to the above (1) and (2), the sintered ferrite magnet of the embodiment of the present disclosure has
(3) In the Ca-enriched region, except for periodic peaks, compared with a sintered magnet fired at a normal heating rate (slower than the heating rate of the embodiment of the present disclosure) Therefore, the value of Ca (atomic %)/Fe (atomic %) is small.
(4) The slope of the straight line connecting the position where Ca begins to concentrate and the value of Ca (atomic %)/Fe (atomic %) at the interface is 0.064 or more.
It has the characteristics of

The overall composition of the sintered ferrite magnet of the embodiment of the present disclosure is the composition described in the method for manufacturing the sintered ferrite magnet of the embodiment of the present disclosure, that is, the atoms of the metallic elements Ca, La, Fe and Co In the general formula showing the ratio: Ca _1-x La _x Fe _2n-y Co _y , the 1-x and y, and n (2n is a molar ratio, expressed as 2n = (Fe + Co) / (Ca + La) ) satisfies 0.5<1−x<0.6, 0.15≦y<0.25, and 4≦n≦6. The sintered ferrite magnet of the embodiment of the present disclosure having the above-mentioned characteristics is notably obtained when it has a high _HcJ as shown in Experimental Example 2 described later.

The embodiments of the present disclosure will be described in more detail by examples, but the embodiments of the present disclosure are not limited thereto.

Experimental example 1
In the general formula Ca _1-x La _x Fe _2n-y Co _y , sample No. 1 in Table 1 has an atomic ratio. CaCO ₃ powder, La(OH) ₃ powder, Fe ₂ O ₃ powder and Co ₃ O ₄ powder were blended and mixed so that 1-x, x, y and n shown in 1 to 14 were obtained, and six types (( 1-x, y, n) is (0.55, 0.24, 5.20), (0.55, 0.20, 5.20), (0.55, 0.18, 5.20) , (0.50, 0.24, 5.20), (0.60, 0.24, 5.20), (0.55, 0.13, 5.23)) mixed raw material powders were obtained . 0.1% by mass of H ₃ BO ₃ powder was added and mixed with respect to 100% by mass of each mixed raw material powder. Based on the six types of mixed raw material powder obtained, the calcining temperature, sintering aid, temperature increase rate, and sintering temperature shown in Table 1 are applied, and the calcining process, crushing process, molding process, and firing process are performed. 14 types of sintered ferrite magnets shown in Table 1 were obtained. Details of each step are as follows.

In the pulverization step, each mixed raw material powder was mixed with a wet ball mill for 4 hours. After mixing, the mixture was dried and granulated. In the calcination step, calcination was performed at the calcination temperature shown in Table 1 for 3 hours. In the pulverization step, each calcined body is coarsely pulverized with a hammer mill to obtain a coarsely pulverized powder, and CaCO ₃ (CaO conversion) and SiO ₂ shown in Table 1 are added to 100% by mass of the coarsely pulverized powder of each calcined body. and pulverized with a wet ball mill using water as a dispersion medium until the average particle size reaches 0.6 μm (measured by the air permeation method using a powder specific surface area measuring device (SS-100 manufactured by Shimadzu Corporation)). . In the molding step, each finely pulverized slurry obtained in the pulverization step is subjected to about 1 T using a parallel magnetic field molding machine (vertical magnetic field molding machine) in which the direction of pressure and the direction of the magnetic field are parallel while removing the dispersion medium. Molding was performed at a pressure of about 50 MPa while applying a magnetic field. In the sintering step, each molded body was heated at the rate of temperature increase shown in Table 1, and fired at the firing temperature shown in Table 1 in the atmosphere for 1 hour. During firing, air was flowed into the firing furnace at a flow rate of 10 L/min.

In Table 1, the rate of temperature increase of "60° C./hour" (1° C./min) is a representative example of the example of Patent Document 2 (International Publication No. 2014/021149), from room temperature to 1100° C. is 450° C./hour (7.5° C./min), and the temperature rise rate from 1100° C. to the firing temperature (1170° C.) is 60° C./hour (1° C./min). In addition, the temperature increase rate of "600 ° C./h" means that both the temperature increase rate from room temperature to 800 ° C. and the temperature increase rate from 800 ° C. to the firing temperature (1170 ° C. or 1190 ° C.) are 600 ° C./h. (10°C/min). Furthermore, the temperature increase rate of "1000°C/hour" means that both the temperature increase rate from room temperature to 800°C and the temperature increase rate from 800°C to the firing temperature (1170°C) are 1000°C/hour (16. 7/min). The temperature drop from the firing temperature to 800° C. was performed at 360° C./hour (6° C./min) for all samples.

Table 1 shows the measurement results of B _r , H _cJ and H _k /H _cJ of the obtained sintered ferrite magnet. In Table 1, sample no. (Sample Nos. 1 to 5) are experimental examples based on the embodiments of the present disclosure, and those marked with * are conventional examples (Sample Nos. 6 and 7, the above It is an experimental example showing an example in which the temperature is increased at a temperature increase rate described in a representative example of the example of Patent Document 2) and comparative examples (Sample Nos. 8 to 14). Note that H _k of H _k /H _cJ in Table 1 is such that J is 0.95×J _r (J _r is residual is the value of H at the location where the magnetization, J _r =B _r ).

The atomic ratios in Table 1 and Table 2 below indicate the atomic ratios (blending composition) when the raw material powders are blended. The atomic ratio (composition of the sintered magnet) in the sintered body (ferrite sintered magnet) after firing is based on the atomic ratio at the time of blending, and the additives (H ₃ BO ₃ , etc.) added before the calcination process and the amount of sintering aids (CaCO ₃ and SiO ₂ ) added after the calcining process and before the forming process. is basically the same as the result of analysis by an ICP emission spectrometer (eg ICPV-1017 manufactured by Shimadzu Corporation).

As shown in Table 1, sample Nos. obtained by the method for manufacturing a sintered ferrite magnet that satisfies all the embodiments of the present disclosure. The ferrite sintered magnets of 1 to 5 have the magnetic properties (B _r =about 0.460 T, H _cJ = 350 kA/m). Above all, when the atomic ratio y (content of Co) exceeds 0.20 (0.24), the best magnetic properties are obtained. In addition, since the atomic ratio y (the content of Co) is 0.15≦y<0.25, the conventional Ca—La—Co ferrite sintered magnet (the Co content is about 0.3 in atomic ratio) The Co content can be reduced compared to , and the raw material cost can be reduced. In addition, since the atomic ratio 1-x (content of Ca) is 0.5 < 1-x < 0.6 (atomic ratio 1-x (content of Ca) and atomic ratio x (content of La) is 1<(1−x)/x<1.5), the atomic ratio x (La content) can be reduced. As a result, the content of La, which is more expensive than iron oxide, can be reduced, and raw material costs can be reduced.

Sample no. The ferrite sintered magnet No. 2 was subjected to X-ray diffraction using an X-ray diffractometer (D8 ADVANSED/TXS manufactured by Bruler AX), and the obtained X-ray diffraction pattern was subjected to Rietveld analysis to quantitatively evaluate the constituent phases. rice field. As a result, the sample No. In the ferrite sintered magnet No. 2, the phase ratio of the main phase (ferrite phase having a hexagonal magnetoplumbite (M type) structure) was 100%, and the phase ratios of the hematite phase and the La orthoferrite phase were 0%. . It is believed that this is because the embodiment of the present disclosure suppresses decomposition of the ferrite compound.

Furthermore, in the embodiment of the present disclosure, the calcining temperature in the calcining step can be set to 1200° C. or more and 1250° C. or less. can be relatively low. In addition, in the embodiment of the present disclosure, since the firing temperature in the firing step can be set to 1170° C. or more and 1190° C. or less, the firing temperature is relatively low compared to the conventional method for producing a Ca—La—Co ferrite sintered magnet. be able to. Therefore, the process cost can be reduced by these.

On the other hand, as in the conventional examples (samples No. 6 and 7), even if the embodiment of the present disclosure is satisfied except for the temperature increase rate, the temperature increase rate described in the representative example of the example of Patent Document 2 When the temperature is raised, it is not possible to obtain magnetic properties equivalent to those of conventional Ca--La--Co ferrite sintered magnets (where the Co content is about 0.3 in terms of atomic ratio). Sample No. of the conventional example. 7, the sample No. Quantitative evaluation of the constituent phases was performed in the same manner as in case 2. As a result, sample no. In the ferrite sintered magnet No. 7, the phase ratio of the main phase (ferrite phase having a hexagonal magnetoplumbite (M-type) structure) was 97.2%, and the phase ratio of the hematite phase was 2.8%. This is because the rate of temperature increase is slower than in the embodiments of the present disclosure, so the heterophase generated by the decomposition of the ferrite compound cannot completely change back into the ferrite compound, and the heterophase (hematite phase in this case) remains. This is thought to be because

In the conventional examples (Sample Nos. 6 and 7), it took about 233 minutes to reach the firing temperature from room temperature. On the other hand, according to the embodiment of the present disclosure, it has magnetic properties equivalent to those of conventional Ca—La—Co ferrite sintered magnets (with a Co content of about 0.3 in terms of atomic ratio), and , The time required to reach the firing temperature after raising the temperature from room temperature is about 115 minutes at 600°C/hour and about 69 minutes at 1000°C/hour, which is less than half that of the conventional example. . That is, the lead time can be significantly shortened and the process cost can be reduced compared to the conventional method of manufacturing a Ca--La--Co ferrite sintered magnet (for example, Patent Document 2).

Moreover, as shown in the comparative example, sample No. 8 to 10, when the atomic ratio 1-x (Ca content) does not satisfy 0.5 < 1-x < 0.6 (atomic ratio 1-x (Ca content) and atomic ratio x (When the content of La does not satisfy 1<(1−x)/x<1.5), sample No. 11, if the atomic ratio y (the Co content) does not satisfy 0.15≦y<0.25, a conventional Ca—La—Co ferrite sintered magnet (where the Co content is the atomic ratio 0.3) cannot be obtained. Moreover, sample no. As in 12 and 13, the amount of SiO ₂ added as a sintering aid is 0.30% by mass, and the preferred range of the embodiment of the present disclosure (0.4% by mass or more and 0.6% by mass or less) If less, even sample no. 14, the amount of _CaCO3 added (0.5% by mass) and the amount of _SiO2 added (0.4% by mass) are within the preferred range of the embodiment of the present disclosure (the amount of _CaCO3 added is 0 in terms of CaO .3% by mass or more and 0.5% by mass or less, and the amount of _SiO2 added is 0.4% by mass or more and 0.6% by mass or less), but the amount of _CaCO3 added is 0.4% by mass in terms of CaO %, the ratio of the amount of _CaCO3 added to the amount of _SiO2 added [amount of _CaCO3 added (calculated as CaO)/amount of _SiO2 added] is more than 0.83 and less than 1.25. If not ([CaCO ₃ addition amount (CaO conversion) / SiO ₂ addition amount] is 1.25), the conventional Ca-La-Co ferrite sintered magnet (Co content is about 0.3 in atomic ratio) It may be difficult to obtain magnetic properties equivalent to those of

Experimental Example 2 The atomic ratio, n, calcining temperature, addition amounts of SiO ₂ and CaCO ₃ (addition amounts are converted to CaO), heating rate, and sintering temperature of each sample were set to the values shown in Table 2. Sample Nos. 15 and 16 had a temperature drop rate of 11100° C./hour from the firing temperature to 800° C. (185° C./minute, after firing, the bottom of the firing furnace was lowered to expose the sample to the atmosphere for cooling). For 17 and 18 , the temperature decrease rate from the firing temperature to 800 ° C. is 1140 ° C./hour (19 ° C./min. After firing, the heater of the firing furnace is turned off, and the air flow rate is 10 L / min to 40 L / min to cool in the furnace. ), samples of experimental examples (samples Nos. 15 to 1 8 ) based on the embodiment of the present disclosure were produced in the same manner as in Experimental Example 1. Table 2 shows the measurement results of B _r , H _cJ and H _k /H _cJ . As shown in Table 2, sample no. Ferrite sintered magnets of 15-18 have excellent H _cJ .

Experimental Example 3 Sample No. of Experimental Example 2; 16 sintered bodies (ferrite sintered magnets after firing and before magnetization), the rate of temperature increase from 800°C to the firing temperature is 60°C/hour, and the rate of temperature decrease from the firing temperature to 800°C is 300°C/hour. Sample no. A sintered body of a comparative example was prepared in the same manner as in No. 16 . Each sintered body is processed by ion milling, and a spherical aberration correction transmission electron microscope (Cs-TEM) is used to analyze the composition by EDS from the interface of the main phase in contact with the second phase toward the inside of the main phase. gone. FIG. 2 shows the relationship between Ca (atomic %)/Fe (atomic %) obtained from the EDS analysis results and the distance from the interface. In FIG. 2 , the thick solid line indicates the sintered ferrite magnet (Sample No. 16) of the embodiment of the present disclosure, and the thin solid line indicates the sintered ferrite magnet of the comparative example.

As shown in FIG. 2, in the main phase, in the range exceeding 2 nm from the interface of the main phase in contact with the second phase to the inner direction of the main phase, Ca (atomic %) / Fe (atomic %) including peaks that appear periodically is almost constant (Ca (atomic %)/Fe (atomic %) in the portion other than the periodic peaks is about 0.04), whereas from the interface of the main phase in contact with the second phase to the main phase Ca (atomic %)/Fe (atomic %) increases remarkably in the range within 2 nm in the inward direction, particularly within the range within 1.5 nm. This is because the Ca concentration is high within a range of 2 nm (preferably within 1.5 nm) from the interface. In addition, in the vicinity of the interface of the main phase in contact with the second phase where Ca (atomic %)/Fe (atomic %) is highest (the Ca concentration is highest), Ca (atomic %)/Fe (atomic %) is 0. 14 or less. Furthermore, in the Ca-enriched region, except for periodic peaks, compared to a sintered magnet fired at a normal heating rate (slower than the heating rate of the embodiment of the present disclosure) , the value of Ca (atomic %)/Fe (atomic %) is small. In addition, the point on FIG. 2 where Ca (atomic %)/Fe (atomic %) starts to increase (the Ca concentration starts to increase) and the point of Ca (atomic %)/Fe (atomic %) at the interface are connected. The absolute value of the slope of the straight line is 0.064 or more. It is believed that the _HcJ is improved by having these features.

On the other hand, in the ferrite sintered magnet of the comparative example, Ca (atomic %)/Fe (atomic %) gradually increases from around 4 nm from the interface of the main phase in contact with the second phase toward the inside of the main phase. In addition, in the vicinity of the interface of the main phase in contact with the second phase where Ca (atomic %)/Fe (atomic %) is highest (the Ca concentration is highest), Ca (atomic %)/Fe (atomic %) is 0. 17 or more. Furthermore, in the region where Ca is concentrated, except for the periodically appearing peaks, compared with the ferrite sintered magnet (sample No. 17) of the embodiment of the present disclosure, Ca (atomic %) / Fe ( atomic %) values are large. In addition, the point on FIG. 2 where Ca (atomic %)/Fe (atomic %) starts to increase (the Ca concentration starts to increase) and the point of Ca (atomic %)/Fe (atomic %) at the interface are connected. The absolute value of the slope of the straight line is 0.035.

Experimental example 4
Comparative example used in Experimental example 3 (Sample No. 2 of Experimental example 2 except that the temperature increase rate from 800 ° C. to the firing temperature is 60 ° C./hour and the temperature decrease rate from the firing temperature to 800 ° C. is less than 300 ° C./hour .16) is shown in FIG. Table 3 shows the EDX analysis values (atomic %) of analysis points 1 to 3 shown in FIG.

In a Ca--La--Co ferrite sintered magnet, there are variations in composition within the grains of the main phase (ferrite phase having a hexagonal magnetoplumbite (M-type) structure=M phase). As shown in Table 3 , in the portion where Ca (atomic %) / La (atomic %) is large, Co (atomic %) / Fe (atomic %) is small (analysis point 3), Ca (atomic %) / La (atomic %) is small, Co (atomic %)/Fe (atomic %) is large (analysis points 1 and 2). Co is an element that _has a large magnetocrystalline anisotropy and contributes to the improvement of _HcJ . do.

Based on these findings, the explanation presumed by the present inventors regarding the mechanism by which H _cJ is improved in the ferrite sintered magnet of the embodiment of the present disclosure will be described below. It is an estimate and is not intended to limit the scope of this disclosure.

As in the comparative example in FIG. 2 of Experimental Example 3, Ca (at atomic %)/Fe (atomic %) is 0.17 or more, that is, when the Ca concentration is high near the interface of the main phase, it is considered that Co is in a poor state. Since Co is an element that positively contributes to the magnetocrystalline anisotropy of the sintered ferrite magnet, it is considered that the magnetocrystalline anisotropy deteriorates at the main phase interface where Co is in a poor state. On the other hand, in the ferrite sintered magnet of the embodiment of the present disclosure, Ca (atomic %)/Fe (atomic %) is 0.14 or less, and the concentration of Ca is lower than that of the comparative example. Therefore, it is considered that the fact that Co is prevented from being in a poor state and the deterioration of magnetocrystalline anisotropy is reduced contributes to the improvement of _HcJ .

According to the embodiments of the present disclosure, it is possible to provide low-cost ferrite sintered magnets having magnetic properties equivalent to those of conventional Ca—La—Co based ferrite sintered magnets. It can be suitably used for industrial motors and electric vehicle (EV, HV, PHV, etc.) drive motors and generators.

Claims (3)

General formula showing the atomic ratio of the metallic elements of Ca, La, Fe and Co: Ca _1-x La _x Fe ₂
In _ny Co _y , the 1-x and y, and n (2n is a molar ratio, expressed as 2n (Fe + Co) / (Ca + La)) are
0.5<1−x<0.6,
0.2< y<0.25 and 4≤n≤6
A raw material powder mixing step for obtaining a mixed raw material powder by mixing raw material powders satisfying
a calcining step of calcining the mixed raw material powder to obtain a calcined body;
a pulverizing step of pulverizing the calcined body to obtain a powder;
A molding step of molding the powder to obtain a molded body;
A firing step of firing the compact to obtain a sintered body,
The calcining temperature in the calcining step is 1200° C. or more and 1250° C. or less,
In the firing step, the temperature rise rate in the temperature range from 800 ° C. to the firing temperature is 600 ° C./hour or more and 1000 ° C./hour or less,
The firing temperature in the firing step is 1170° C. or higher and 1190° C. or lower,
After the calcination step and before the molding step, the step of adding a sintering aid is further included, wherein the sintering aid contains at least CaCO 3 and SiO 2, and the amount of CaCO ₃ added _{is the} amount to be added. It is 0.3% by mass or more and 0.5% by mass or less in terms of CaO with respect to 100% by mass of the calcined body or powder, and the amount of SiO 2 added is 100% by mass of the calcined body or powder to be added _. % to 0.4% by mass or more and 0.6% by mass or less, and when the amount of CaCO3 added is 0.4% by mass or less in terms of CaO, the ratio of the amount of CaCO3 _added to _the amount of _SiO2 added [CaCO ₃ addition amount (CaO conversion) / SiO ₂ addition amount] is more than 0.6 and less than 1.0, and when the addition amount of CaCO ₃ exceeds 0.4% by mass in terms of CaO, CaCO ₃ addition A method for producing a sintered ferrite magnet, wherein the ratio of the amount to the SiO2 _addition amount [CaCO3 _addition amount (CaO conversion) / SiO2 _addition amount] is more than 0.83 and less than 1.25 . 2. The method for producing a sintered ferrite magnet according to claim 1 , wherein in the firing step, the temperature drop rate in the temperature range from the firing temperature to 800° C. is 300° C./hour or more. General formula showing the atomic ratio of the metallic elements of Ca, La, Fe and Co: Ca _1-x La _x Fe ₂
In _ny Co _y , the 1-x and y, and n (2n is a molar ratio, expressed as 2n (Fe + Co) / (Ca + La)) are
0.5<1−x<0.6,
0.2<y<0.25, and
satisfying 4 ≤ n ≤ 6,
A ferrite sintered magnet containing at least one of 0.5% by mass or less of CaCO3 and 0.6% by mass or less of _SiO2 as _a sintering aid in terms of CaO ,
It contains a main phase made of ferrite having a hexagonal magnetoplumbite (M-type) structure and a second phase existing between the two main phases, and in the vicinity of the interface between the main phase and the second phase A ferrite sintered magnet that satisfies the following (1) and (2) as a result of composition analysis by spherical aberration correction transmission electron microscope (Cs-TEM) and EDS (energy dispersive X-ray spectroscopy) analysis using the same .
(1) In the main phase, Ca (atomic %)/Fe (atomic %) increases in a range within 2 nm from the interface compared to a range exceeding 2 nm from the interface.
(2) In the interface, Ca (atomic %)/Fe (atomic %) is 0.14 or less.

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