KR102430475B1 - Method for preparing ferrite sintered magnet and ferrite sintered magnet - Google Patents

Abstract

A method of manufacturing a ferrite sintered magnet according to an embodiment of the present invention includes a mixing step of mixing iron oxide, a strontium compound and a dispersing agent to prepare a mixture; and a calcination step of heating the mixture, wherein the dispersant includes polyvinylpyrrolidone (PVP).

Description

The manufacturing method of a ferrite sintered magnet, and a ferrite sintered magnet TECHNICAL FIELD

The present invention relates to a method for manufacturing a ferrite sintered magnet and to a ferrite sintered magnet. More specifically, it relates to a method for manufacturing a ferrite sintered magnet including a calcination step, and a ferrite sintered magnet manufactured by this method.

Ferrite is a composition of AO·nFe ₂ O ₃ (A: divalent metal ion, Sr or Ba) and has a hexagonal magneto-plumbite (M) type crystal structure, and magnetic properties of the material As a material that does not change easily depending on the direction and magnitude of this magnetic field, it is generally used as a material for permanent magnets such as motors for electric vehicles and rotating machines for electric appliances.

Meanwhile, in recent years, miniaturization and high efficiency of motors are required due to environmental problems and various laws and regulations related to energy saving, and high performance is also required for permanent magnets.

The process of manufacturing a ferrite sintered magnet proceeds in the order of mixing, calcining, coarse grinding, fine grinding, forming in a magnetic field, drying, sintering and processing.

Representative magnetic properties of permanent magnets include residual magnetization density (Br), intrinsic coercive force (iHcj), maximum magnetic energy product ((BH) _max )), and squareness ratio (Hkine/iHcj), of which residual magnetization density (Br) is proportional to saturation magnetization ( _MS ), density and degree of orientation, which is the sum of magnetic spin moments of the composition.

Saturation magnetization ( _MS ) is a value that increases according to the degree of ferrite in the calcination step. Generally, ferrite sintered magnets used in motors or rotating machines are strontium ferrite obtained after the calcination process (hereinafter referred to as "Sr ferrite"). ) Sr ferrite crystallinity of the magnet powder is 90% or more, and thus the saturation magnetization (MS ) value is _67emu /g or more.

Conventionally, in order to increase the crystallinity of Sr ferrite, that is, the saturation magnetization ( _MS ) value, a method such as a high calcination temperature, use of high purity iron oxide or addition of cobalt (Co) was used.

However, in the case of a high calcination temperature, the crystallinity of Sr ferrite can be increased by calcining a mixture of iron oxide and strontium carbonate at a high temperature, but there is a disadvantage in that energy consumption is high. There is a problem with the price rising accordingly. In addition, in the case of the addition of the dispersant, the type is limited, and it has been mainly used at or after the grinding step to increase the degree of orientation of the fine powder.

Prior Patent Literature
(Patent Document 1) KR KR10-2015-0013252 A
(Patent Document 1) KR KR10-2012-0120976 A

The problem to be solved by the embodiments of the present invention is to solve the above problems, and even if a low-purity iron oxide is used or a calcination process is performed at a low temperature, a method for manufacturing a ferrite sintered magnet having excellent saturation magnetization ( _MS ) and to provide a sintered magnet manufactured by this method.

A method of manufacturing a ferrite sintered magnet according to an embodiment of the present invention includes a mixing step of mixing iron oxide, a strontium compound and a dispersing agent to prepare a mixture; and a calcination step of heating the mixture, wherein the dispersant includes polyvinylpyrrolidone (PVP).

The dispersant may include PVP having a molecular weight of 50,000 to 200,000.

The PVP may be mixed into the mixture at a weight percent (wt.%) of 0.2 to 1.0.

In the mixing step, boric acid (H ₃ BO ₃ ) may be further added to the mixture.

The pH of the mixture may be 4 to 7.

The mixture may further include at least one of cobalt oxide, lanthanum oxide (La ₂ O ₃ ), and silica (SiO ₂ ), and the cobalt oxide may include at least one of CoO and Co ₃ O ₄ .

The strontium compound may include strontium carbonate (SrCO ₃ ).

Heating in the calcination step may be made at a temperature of 1050 ℃ to 1250 ℃.

According to embodiments of the present invention, a calcination process is performed after adding a dispersing agent containing PVP (Polyvinylpyrrolidone, polyvinylpyrrolidone), and even if low-purity iron oxide is used or the calcination process is performed at a low temperature, saturation magnetization ( Since it is possible to manufacture a ferrite sintered magnet having excellent M _S ), energy consumption and manufacturing cost in the manufacturing process can be lowered.

1 is a scanning electron microscope photograph of the ferrite sintered magnet prepared in Example 1. FIG.
FIG. 2 is a scanning electron microscope photograph of the ferrite sintered magnet prepared in Comparative Example 1. FIG.
3 is a scanning electron microscope photograph of the ferrite sintered magnet prepared in Comparative Example 3. FIG.

Hereinafter, with reference to the accompanying drawings, various embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In addition, throughout the specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated.

A method of manufacturing a ferrite sintered magnet according to an embodiment of the present invention includes a mixing step of mixing iron oxide, a strontium compound and a dispersing agent to prepare a mixture; and a calcination step of heating the mixture, wherein the dispersant includes polyvinylpyrrolidone (PVP).

Hereinafter, each step will be described in detail.

The mixing step is a step of preparing a mixture for calcination. First, raw materials are weighed and mixed in a predetermined ratio. A ball mill, an Attritor-mill, a Turbula mixer, or a Spex mill is used for mixing for about 1 to 20 hours and at the same time performing a grinding treatment. The mixture as a raw material includes an iron compound such as iron oxide and a strontium compound, and may be in the form of a powder or a slurry in which the mixed powder is dispersed in a solvent.

As iron compounds, such as iron oxide, and a strontium compound, compounds, such as an oxide or a carbonate, a hydroxide, or a nitrate, which become an oxide by calcination can be contained. Such iron oxide may include iron (III) oxide (Fe ₂ O ₃ ), and the strontium compound may include strontium carbonate (SrCO ₃ ).

In addition, the mixture contains a dispersing agent including PVP, and PVP will be described in detail later in the calcination step.

In addition, the mixture may further include at least one of cobalt oxide, lanthanum oxide (La ₂ O ₃ ), and silica (SiO ₂ ). Cobalt oxide preferably includes at least one of CoO and Co ₃ O ₄ , and more preferably includes Co ₃ O ₄ .

Cobalt oxide is added to replace a part of the iron element site with cobalt element in an Sr ferrite sintered magnet having a magneto-plumbite (M) type crystal structure, and the saturation magnetization of the Sr ferrite sintered magnet is increased due to the substitution. can be improved In addition to cobalt oxide, an oxide of manganese (Mn) or nickel (Ni) may be added.

On the other hand, if a part of the iron element site is substituted as described above, the balance of ionic valences of the Sr ferrite sintered magnet is broken, and thus magnetic properties may be deteriorated in the Sr ferrite sintered magnet. Lanthanum oxide (La ₂ O ₃ ) is a rare earth oxide added to solve this problem, and the lanthanum element of the added lanthanum oxide (La ₂ O ₃ ) is replaced with a part of the strontium element site of the Sr ferrite sintered magnet through charge compensation. It is possible to solve the problem of deterioration of magnetic properties such as In addition to lanthanum oxide (La ₂ O ₃ ), an oxide of neodymium (Nd) or praseodymium (Pr) may be added.

On the other hand, silica (SiO ₂ ) as a sintering aid may be added to suppress the growth of crystal grains in the subsequent sintering step to improve the coercive force of the Sr ferrite sintered magnet.

The average diameter of the particles of the raw material is not particularly limited, and may be, for example, 0.1 μm to 2.0 μm.

The calcination step is a step of heating the mixture mixed through the mixing step at a temperature of 1050 to 1250° C., thereby promoting the ferrite reaction of the mixture to make a plastic body having a magneto-plumbite (M) type crystal structure. to be. Typically, the calcination step is performed in an oxidizing atmosphere in air.

On the other hand, the calcination time at the calcination temperature is preferably 0.1 to 10 hours, more preferably 1 to 5 hours. In addition, the heating time to the calcination temperature is preferably 4 hours, and the holding time after reaching the calcination temperature is preferably 2 hours to 4 hours.

As mentioned above, it is important to increase the crystallinity of Sr ferrite in the calcination step in which the ferrite reaction is in progress, so that it has a high saturation magnetization ( _MS ) value. Conventionally, in order to increase the crystallinity of Sr ferrite, a method such as a high calcination temperature or use of high purity iron oxide has been used.

However, the method of maintaining a high calcination temperature consumes high energy, and the method of using high-purity iron oxide has a problem in that the price increases as the purity of the iron oxide increases.

On the other hand, in the method for manufacturing a ferrite sintered magnet according to an embodiment of the present invention, since the calcination step is performed after adding a dispersant including PVP to the mixture, calcination is performed at a relatively low temperature using low-purity iron oxide. Even so, it is possible to manufacture an Sr ferrite sintered magnet having excellent saturation magnetization ( _MS ) by maintaining a high degree of crystallinity of Sr ferrite.

Specifically, iron compounds such as iron oxide contain several hundred ppm to several thousand ppm chlorine (Cl) as an impurity, and this chlorine (Cl) reacts with strontium element (Sr) to generate SrCl ₂ , so one of the main phase components It interferes with the formation of strontium element (Sr) into Sr ferrite particles. In other words, it acts as a factor inhibiting the ferrite reaction. When the mixture to which the dispersing agent containing PVP is added is calcined as in this embodiment, Cl ^- ions inside the mixture move toward the N ⁺ charge of the added PVP ^, and metal ions (M ⁺ ), so that SrCl ₂ can be prevented from being generated. By preventing the formation of SrCl ₂ , it helps the ferrite reaction proceed smoothly in the calcination step even when a relatively low temperature and low purity iron oxide are used, which leads to an increase in the saturation magnetization ( _MS ) value.

In addition, the added PVP can be easily removed in the form of CO ₂ in a high temperature environment such as a sintering step.

In addition, unlike the conventional method, since calcination is possible at a relatively low temperature, crystal growth is suppressed accordingly, and it was confirmed that the coercive force (H _Cj ) value is improved. That is, heating for calcination is preferably heated to a temperature of 1050° C. to 1250° C., and more preferably heated to a temperature of 1100° C. to 1200° C. If the calcination temperature is less than 1050 ℃, even if PVP is added, the Sr ferritization reaction is not smooth. If the calcination temperature is 1250 ℃ or less, the ferrite reaction proceeds effectively and the growth of crystals is limited and the coercive force (H _Cj ) value is improved. because it can be done

Meanwhile, the dispersant preferably includes PVP having a molecular weight of 50,000 to 200,000. If the molecular weight of PVP is less than 50,000, it is difficult to prevent the formation of SrCl ₂ , and if the molecular weight of PVP is more than 200,000, it takes a lot of time to remove PVP in the form of CO ₂ due to the molecular weight more than necessary, which increases the production time.

In addition, PVP is preferably mixed into the mixture in a weight percent (wt.%) of 0.2 to 1.0. If it is less than 0.2 wt.%, the amount of PVP added is low, so that the ferrite reaction does not proceed smoothly in the calcination step, and if it exceeds 1.0 wt.%, it takes a lot of time to remove PVP in the form of CO ₂ due to the excessive addition of PVP.

Meanwhile, in the mixing step, boric acid (H ₃ BO ₃ ) may be further added to the mixture. Boric acid (H ₃ BO ₃ ) is added to maintain the pH of the mixture at 4-7. If the pH of the mixture is less than 4 or more than 7, since PVP is difficult to dissolve in the mixture, the crystallinity of ferrite decreases, and it is difficult to obtain a desired saturation magnetization value.

After the calcination step, a grinding step, a molding step, a drying step, and a sintering step may be performed.

The pulverization step is a step of preparing pulverized powder by pulverizing the Sr ferrite particles obtained in the calcination step. In the embodiment of the present invention, the pulverization process is pulverized in two stages: a coarse pulverization step and a fine pulverization step. In addition, in another embodiment, you may implement a grinding|pulverization step in one step.

Since Sr ferrite particles are usually granular or bulky, it is preferable to first perform a coarse grinding step. In the coarse grinding step, dry grinding is performed using a dry vibration mill, a dry ball mill, or the like to obtain a coarsely pulverized powder.

In the fine pulverization step, the coarsely pulverized powder obtained in the coarse pulverization step is wet pulverized using a wet attritor, a ball mill, a jet mill, or the like to obtain a pulverized powder. The fine pulverization time is, for example, preferably 30 minutes to 10 hours when using a wet attritor, and preferably 5 to 50 hours when using a ball mill. It is preferable to adjust these times suitably according to each grinding|pulverization method.

In the coarse grinding process or the fine grinding process, at least one of silica (SiO ₂ ), calcium carbonate (CaCO ₃ ), strontium carbonate (SrCO ₃ ), and barium carbonate (BaCO ₃ ) is added as an additive to improve sinterability and magnetic properties. can In addition, lanthanum oxide (La ₂ O ₃ ), zinc oxide (ZnO), cobalt oxide (CoO, Co ₃ O ₄ ), etc. are added as additives in the pulverization process to promote the substitution effect during sintering and control the growth of particles. can be added.

In addition, since these additives may flow out together with the solvent of the slurry in the case of wet molding, it is preferable to add more than the target content in the Sr ferrite sintered magnet.

Further, in the subsequent molding process, a dispersant may be added in the pulverization process in addition to the above additives in order to improve the fluidity of the slurry, decrease the viscosity, and improve the magnetic orientation of the Sr ferrite sintered magnet. As such a dispersant, an organic compound having a hydroxyl group and a carboxyl group, sorbitol, calcium gluconate, and the like can be used. The dispersant may be added in an amount of 0.1 wt.% to 1.0 wt.% relative to the powder. When the amount of the dispersant added is within the above range, the dehydration property is lowered to prevent the problem of cracks occurring during drying and sintering of the molded body.

The molding step is a process of manufacturing a compact by molding the pulverized powder in a magnetic field. Dry molding or wet molding is possible, but wet molding is preferable from the viewpoint of increasing the magnetic orientation.

When performing wet molding, a slurry can be prepared by performing wet grinding in which the pulverized powder and the dispersion medium are mixed and pulverized, and a molded article can be produced using this. Dehydration and concentration of the slurry can be performed by methods such as centrifugation or filter press.

As a dispersion medium for the slurry, water or a non-aqueous solvent can be used. A surfactant such as gluconic acid, gluconate, or sorbitol may be further added to the slurry along with water. Molding is performed in a magnetic field using such a slurry, and a molded object is produced. The molding pressure may be 0.1 ton/cm 2 to 0.5 ton/cm 2 , and the applied magnetic field may be 5 kOe to 15 kOe.

The drying and sintering step is a process of obtaining a ferrite sintered magnet by continuously drying and sintering the compact in an oxidizing atmosphere in the air. First, dehydration and degreasing may be performed at 50° C. to 100° C. in order to remove moisture and oil remaining in the molded body.

Thereafter, a sintering step is performed. During the sintering process, the magnetic properties of the ferrite sintered magnet can be improved by adjusting sintering conditions such as a temperature increase rate, a maximum temperature, a maximum temperature holding time, and a cooling rate. Specifically, the temperature increase rate is preferably 1 ° C / min to 10 ° C / min, the maximum sintering temperature and the holding time of the maximum temperature are preferably sintering at 1,150 ° C to 1,250 ° C for 30 minutes to 2 hours, cooling time 1 Cooling at a rate of from °C/min to 10 °C/min is preferred.

Hereinafter, a method of manufacturing a ferrite sintered magnet according to the present invention will be described with reference to specific examples and comparative examples.

Example 1

After adding 0.4 wt.% of PVP having a molecular weight of 70,000 together with water to 87 wt.% of iron (III) oxide (Fe ₂ O ₃ ), strontium carbonate (SrCO ₃ ) 13 wt.%, and mixing while pulverizing for 3 hours using a ball mill to prepare a slurry. Silica (SiO ₂ ) and boric acid (H ₃ BO ₃ ) are added to the slurry to prepare a mixture whose pH is adjusted to 5. Thereafter, the mixture was heated at a temperature of 1250° C. for 2 hours to promote a ferrite reaction to prepare a plastic body including Sr ferrite particles.

A coarsely pulverized powder having an average particle diameter of 4 μm was obtained by using a dry vibration mill for the calcined body. Then, water and cobalt oxide (Co ₃ O ₄ ) 1.0wt.%, lanthanum oxide (La ₂ O ₃ ) 2.0wt.%, chromium oxide (Cr ₂ O ₃ ) 0.3wt.%, calcium carbonate ( CaCO ₃ ) 0.8wt.% and silica (SiO ₂ ) were added to complete the fine powder preparation, followed by mixing while pulverizing using a ball mill for 16 hours to obtain a finely pulverized slurry. After the slurry was dehydrated so that the concentration of the pulverized powder was 65 wt.%, a molded body was prepared using a wet magnetic field molding machine in which the magnetic field direction was parallel to the pressing direction. The molding pressure was 0.3 ton/cm ² , and the applied magnetic field was set to 10 kOe.

Thereafter, the sintered body obtained by sintering the green body at 1220° C. for 2 hours was processed using a processing machine to obtain a Sr ferrite sintered magnet.

Example 2

Sr ferrite sintered magnets were manufactured by preparing the same raw material as in Example 1 in the same manner as in Example 1, except that 0.4 wt.% of PVP having a molecular weight of 150,000 was added to the mixture.

Example 3

Sr ferrite sintered magnets were manufactured by preparing the same raw materials as in Example 1 in the same manner as in Example 1, except that the calcination temperature was heated to 1150°C.

Comparative Example 1

Sr ferrite sintered magnets were manufactured by using the same raw materials as in Example 1, except that PVP was not added, in the same manner as in Example 1.

Comparative Example 2

Sr ferrite sintered magnets were manufactured by preparing the same raw materials as in Example 1 in the same manner as in Example 1, except that PVP was not added and the calcination temperature was heated to 1150°C.

Comparative Example 3

Sr ferrite sintered magnets were prepared by preparing the same raw material as in Example 1 in the same manner as in Example 1, except that 2.0 wt.% of PVP having a molecular weight of 70,000 was added to the mixture in excess of 1.0 wt.% .

Comparative Example 4

Sr ferrite sintered magnets were prepared by preparing the same raw material as in Example 1 in the same manner as in Example 1, except that 0.1 wt.% of PVP having a molecular weight of 70,000 was less than 0.2 wt.% and adding 0.1 wt.% to the mixture. .

Comparative Example 5

Sr ferrite sintered magnets were manufactured by preparing the same raw material as in Example 1 in the same manner as in Example 1, except that 0.4 wt.% of PVP having a molecular weight of 10,000 was added to the mixture in the same manner as in Example 1.

Comparative Example 6

Sr ferrite sintered magnets were prepared by preparing the same raw materials as in Example 1 in the same manner as in Example 1, except that 0.4 wt.% of PVP having a molecular weight of 360,000 and exceeding 200,000 was added to the mixture.

Comparative Example 7

Sr ferrite sintered magnets were manufactured by preparing the same raw material as in Example 1 in the same manner as in Example 1, except that the mixture had a pH of 9.

Comparative Example 8

Sr ferrite sintered magnets were manufactured by preparing the same raw materials as in Example 1 in the same manner as in Example 1, except that the mixture had a pH of 2.

Evaluation Example 1: Measurement of magnetic properties

To evaluate the magnetic properties of the Sr ferrite sintered magnets of Examples 1 to 3 and Comparative Examples 1 to 8, the saturation magnetization ( _MS ) and coercive force (H) of each sample using a vibrating sample magnetometer (VSM) _Cj ) was measured and shown in Table 1.

Saturation Magnetization M _S (emu/g) Coercive force H _Cj (Oe) Example 1 78 2,500 Example 2 76 2,500 Example 3 74 3,200 Comparative Example 1 66 2,500 Comparative Example 2 60 3,200 Comparative Example 3 75 1,200 Comparative Example 4 70 2,500 Comparative Example 5 70 2,500 Comparative Example 6 72 1,500 Comparative Example 7 65 2,500 Comparative Example 8 65 2,500

When the saturation magnetization ( _MS ) of the Sr ferrite particles of Examples 1, 2 and Comparative Example 1 is compared, it can be seen that the saturation magnetization ( _MS ) of the Sr ferrite sintered magnet of Comparative Example 1 shows a low value. . This can be confirmed as a result of a decrease in ferrite crystallinity because the calcination process was performed without adding PVP to the mixture, and thus the generation of SrCl ₂ was not prevented and the ferrite reaction was not smoothly performed.

Comparing the saturation magnetization ( _MS ) of the Sr ferrite sintered magnet of Example 3 and Comparative Example 2, the Sr ferrite of Example 3 was calcined at a relatively low calcination temperature (1150° C.) compared to Example 1 It can be seen that the saturation magnetization ( _MS ) of the sintered magnet is not significantly different from that of Example 1, whereas the saturation magnetization ( _MS ) of the Sr ferrite sintered magnet of Comparative Example 2 is significantly lowered compared to that of Example 1. can That is, in the case of the embodiments of the present invention, even when calcining is performed at a low temperature, since the dispersing agent containing PVP is added, it is possible to prepare Sr ferrite particles having a higher ferrite crystallinity than when PVP is not added, In this way, the manufacturing cost can be lowered.

On the other hand, comparing Example 1 and Example 3, in the case of Example 3, despite heating to a relatively low calcination temperature (1100° C.), the ferriticization reaction was smooth and the saturation magnetization ( _MS ) value was large. There is no difference, but due to the low calcination temperature, crystal growth is limited and it can be seen that the coercive force (H _Cj ) has a higher value.

Comparing the coercive force (H _Cj ) of the Sr ferrite sintered magnets of Example 1 and Comparative Example 3, when 2.0 wt.% of PVP is added to the mixture in excess of 1.0 wt.%, PVP is added in excess to increase PVP. It takes a lot of time to remove it in the form of CO ₂ . As a result, crystal grains grow, and it can be seen that in Comparative Example 3, the coercive force (H _Cj ) value of the Sr ferrite sintered magnet is significantly lowered compared to that of Example 1. This can also be confirmed through the scanning electron micrograph in Evaluation Example 2 below.

Comparing the saturation magnetization ( _MS ) of the Sr ferrite sintered magnets of Example 1 and Comparative Example 4, when 0.1 wt.% of PVP is added to the mixture with less than 0.2 wt.% of PVP, the amount of PVP added is low and ferrite in the calcination step. It doesn't help much to keep the reaction going smoothly. Therefore, in the Sr ferrite sintered magnet of Comparative Example 4, it can be confirmed that the saturation magnetization ( _MS ) is decreased.

Comparing the saturation magnetization ( _MS ) of the Sr ferrite sintered magnets of Example 1 and Comparative Example 5, since low molecular weight PVP was added, there is a limitation in preventing the generation of SrCl ₂ in the calcination process, and eventually Comparative Example 5 It can be seen that the saturation magnetization ( _MS ) of the Sr ferrite sintered magnet is decreased.

Comparing the coercive force (H _Cj ) of the Sr ferrite sintered magnets of Example 1 and Comparative Example 6, since high molecular weight PVP was added, it takes a lot of time to remove PVP in the form of CO ₂ . As a result, crystal grains grow, and it can be seen that the coercive force (H _Cj ) value of the Sr ferrite sintered magnet in Comparative Example 6 is significantly lowered compared to that of Example 1.

Comparing the saturation magnetization ( _MS ) of the Sr ferrite sintered magnet of Example 1 and Comparative Example 7, since the pH of the mixture has a high pH value at which PVP is difficult to dissolve, the saturation magnetization of the Sr ferrite sintered magnet of Comparative Example 7 ( M _S ) shows a decreased value compared to that of Example 1, and has a value similar to that of Comparative Example 1.

Comparing the saturation magnetization ( _MS ) of the Sr ferrite sintered magnet of Example 1 and Comparative Example 8, in a similar vein to the case of Comparative Example 8, the pH of the mixture has a low pH value at which PVP is difficult to dissolve. The saturation magnetization ( _MS ) of the Sr ferrite sintered magnet of Example 8 is lower than that of Example 1, and has a value similar to that of Comparative Example 1.

Evaluation Example 2: Scanning Electron Microscopy (SEM) Photograph

Scanning electron micrographs of each of the ferrite sintered magnets of Example 1, Comparative Example 1, and Comparative Example 3 are shown in FIGS. 1 to 3 , respectively.

In the case of Example 1, since 0.4 wt.% of PVP having a molecular weight of 70,000 was added, the ferrite reaction proceeded uniformly, and it can be seen that the particles evenly form a plate shape having a size of about 3 μm.

On the other hand, in the case of Comparative Example 1, it can be confirmed that the size of the particles is smaller than that of Example 1 because PVP is not added, and it can be confirmed that the shape and size of the particles are not uniform because the ferrite reaction is partially progressed. This is consistent with the low saturation magnetization ( _MS ) value of the ferrite sintered magnet of Comparative Example 1, as mentioned in Evaluation Example 1 above.

On the other hand, in the case of Comparative Example 3, it can be confirmed that by adding an excessive amount of PVP more than necessary, the grain particles are enlarged. This is consistent with the low coercive force (H _Cj ) value of the ferrite sintered magnet of Comparative Example 1 as mentioned in Evaluation Example 1 above.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (9)

a blending step of mixing iron oxide, a strontium compound, and a dispersing agent to prepare a mixture; and
a calcination step of heating the mixture;
The dispersant comprises PVP and
Heating for the calcination is heated to a temperature of 1050 ℃ to 1250 ℃,
The dispersant comprises PVP having a molecular weight of 50,000 to 200,000, wherein the PVP is mixed into the mixture in a weight percent of 0.2 to 1.0,
After the calcination step, a grinding step, a molding step, a drying step and a sintering step are performed,
The pulverizing step pulverizes the Sr ferrite particles obtained in the calcination step,
In the forming step, the pulverized powder is molded in a magnetic field to produce a compact,
The drying and sintering step is a method of manufacturing a ferrite sintered magnet in which the compact is continuously dried and sintered in an oxidizing atmosphere in the air, and dehydrated and degreased at 50 to 100 °C to remove moisture and oil remaining in the compact.
delete delete In claim 1,
Method of manufacturing a ferrite sintered magnet further adding boric acid (H ₃ BO ₃ ) to the mixture in the mixing step. In claim 4,
A method of manufacturing a ferrite sintered magnet wherein the pH of the mixture is 4 to 7. In claim 1,
The mixture further comprises at least one of cobalt oxide, lanthanum oxide (La ₂ O ₃ ) and silica (SiO ₂ ),
The cobalt oxide is a method of manufacturing a ferrite sintered magnet comprising at least one of CoO and Co ₃ O ₄ . In claim 1,
The strontium compound is a method of manufacturing a ferrite sintered magnet comprising strontium carbonate (SrCO ₃ ). delete A ferrite sintered magnet manufactured by the method of claim 1 .

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