JPS6131067B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the improvement of anisotropic strontium ferrite magnets having the basic formula of SrO.6Fe ₂ O ₃ . MO・6Fe ₂ O ₃ based oxide permanent magnet (M is Ba,
Sr, Pb) was developed by Philips, and later barium ferrite magnets (BaO,
6Fe ₂ O ₃ ) was the mainstream, but after Cochardt's research report at Westinghouse, strontium ferrite magnets (SrO 6Fe ₂ O ₃ ) with high magnetic anisotropy attracted attention, and various improvements were made. It has been done. In general, in this type of oxide permanent magnet, the residual magnetic flux density Br is a function of the crystal Is, and the density and orientation of the sintered body, and the coercive force Hc depends on the proportion of single domain crystals, and the maximum Energy product (BH)
The squareness of the B-H loop that gives max depends on the degree of orientation and the proportion of single-domain crystals. Therefore, in order to obtain a magnet with high magnetic properties, it was necessary to pay attention to the following points in manufacturing. In other words, during calcination, sufficient ferrite formation (magnetoplumbite formation) is achieved.
Eliminate the residual unreacted substances such as SrO and Fe ₂ O ₃ to increase the σ _s of the powder and increase the degree of orientation during compaction, and in pulverization after calcination, reduce the particle diameter to less than the critical diameter to improve the degree of orientation during compaction. The objective is to increase the density and avoid the inclusion of coarse grains, and to suppress the growth of crystals while increasing the density during sintering. Note that reducing the particle size during pulverization to 0.7μ or less increases the pulverization time and impairs moldability, making it unsuitable for mass production. Furthermore, in sintering, increasing density and suppressing crystal growth are contradictory phenomena. Therefore, increasing Br and increasing Hc are contradictory demands. On the other hand, in order to meet both of these requirements, in addition to the main components, CaO,
Adding PbO, Bi ₂ O ₃ or B ₂ O ₃ (or a compound that can be formed by sintering), or as a crystal growth inhibitor that precipitates at grain boundaries and suppresses crystal growth.
It is known to add SiO ₂ and Al ₂ O ₃ . All of these additives have only one function and are all non-magnetic, so even with these additives, Br, Hc, (BH)max
However, a high-performance magnet with sufficiently improved characteristics has not yet been realized. In view of the above points, the present invention provides a method for producing high-performance strontium ferrite by maximizing the effects of calcination accelerators such as CaO and B ₂ O ₃ and crystal growth inhibitors such as SiO ₂ . The purpose is to provide. The present inventors have developed various additives based on the assumption that the effects of additives should differ depending on the time of addition, and that there must be a time of addition for each additive when it is most effective. As a result of our studies, we have arrived at the present invention. The present invention uses Fe ₂ O ₃ and Sr, which becomes SrO by heating.
The compound has a molar ratio of Fe ₂ O ₃ and SrO of 5.6 to 6.0:1
After mixing, calcining, and wet grinding,
In a method of producing an oxide permanent magnet with a magnetoplumbite crystal structure by forming and sintering in a magnetic field, when mixing raw materials, 0.04 to 0.2% by weight of water-soluble boron compound as boron and 0.6% of silicic anhydride as boron. 1.2% by weight or less (not including 0) of calcium carbonate should be added during the fine pulverization after the above-mentioned calcination, and from the above-mentioned wet pulverization to before compaction in the magnetic field. This method of producing an oxide permanent magnet is characterized in that the boron content is 0.01% by weight or less (not including 0) by eluting the boron. Boron-based additives are effective additives for accelerating the ferritization reaction during calcination and increasing the σ _s of the powder, but if the boron content is less than 0.04 wt%, no effect is observed; If it exceeds 0.2wt%,
After calcination, the crystal grains become coarse. This grain coarsening is not suppressed by the combined addition of SiO ₂ up to 0.6 wt%. If such coarsening of crystal grains occurs, in the subsequent fine pulverization process, when pulverized into powder of 0.7μ or more suitable for mass production, the particle size distribution will expand and coarse grains will be mixed in, resulting in a decrease in Hc. vinegar. Therefore, the appropriate amount of boron to be added is 0.04 to 0.2 wt%. By the way, it has been found that if boron is present in an amount of 0.01wt% or more during sintering that does not involve a ferritization reaction, it not only deteriorates Br but also causes cracks in the sintered body. From this, in order to maximize the effect of boron-based additives, add 0.04 to 0.2 wt% of boron before calcination, and reduce the boron content after calcination and before sintering. It can be seen that it is necessary to adjust it to 0.01% or less. To meet this need, H ₃ BO 3 , H 3 BO ₃ ,
By wet-pulverizing water-soluble compounds such as H ₂ B ₄ O ₆ , K ₂ B ₄ O ₇ , Na ₂ B ₄ O ₇ , and CaB ₄ O ₇ after calcination, boron The compound was allowed to elute. If more than 0.01 wt% of boron remains after wet pulverization, the finely pulverized powder can be adjusted by washing with water. SiO ₂ is an additive that exists at grain boundaries and suppresses crystal growth, and it was confirmed that adding it before calcination contributes more to increasing Hc than adding it during pulverization after calcination. That is, in order to enhance the dispersion of SiO ₂ into the grain boundaries, it is better to add SiO 2 as early as possible in the process. Moreover, by adding SiO ₂ before calcination, it is possible to reduce the coarsening of the crystals after calcination, which reduces the number of coarse particles in the powder after pulverization, which has the effect of suppressing crystal growth during sintering. Combined with this, it exhibits the effect of preventing coarse crystals from being mixed into the sintered body. By the way, if SiO ₂ is added alone to the raw material before calcination, it is not preferable because it not only suppresses crystal growth during calcination but also suppresses the ferritization reaction. However, when it was added in combination with the aforementioned boron compound, ferrite formation progressed sufficiently through calcination, and a powder containing few coarse particles (that is, crystal growth was suppressed) could be obtained. On the other hand, if SiO ₂ is present during sintering, it inhibits crystal growth, resulting in another drawback of lowering density. This is a fine grinding process before sintering.
By adding CaCO ₃ and allowing SiO ₂ and CaO to coexist during sintering, it was possible to suppress crystal growth and increase density at the same time. Note that if SiO ₂ is added in an amount exceeding 0.6 wt%, Br will be degraded even if it is added in combination with boron or CaCO ₃ , so the amount of SiO ₂ added is limited to 0.6 wt%. As mentioned above, CaCO ₃ is added during pulverization before sintering, and SiO ₂ and CaO coexist during sintering.
It has the effect of suppressing crystal growth and improving density at the same time, and was also found to have the effect of preventing the occurrence of cracks after sintering. When CaCO ₃ is added to the raw material before calcination, even if it is added in combination with SiO ₂ , it causes a decrease in Hc,
Although Br improves slightly, (BH)max decreases as Hc decreases. On the other hand, when added at the time of pulverization after calcination, in the case of combined addition with SiO ₂ , Hc could be improved compared to the addition of only SiO ₂ . Although the reason for this is not clear, when CaCO ₃ is heated it turns into CaO and CO ₂
However, in the case of composite addition of CaCO ₃ and SiO ₂ , a part of this CaO enters the grains and increases crystal growth, improving density, but the remaining CaO decomposes at the grain boundaries.
It is thought that it coexists with SiO ₂ and suppresses crystal growth. However, when CaCO ₃ is added before calcination, the CaO that was decomposed during calcination and remained in the grain boundaries is eluted during wet grinding, leaving only CaO that has entered the grains, which acts during sintering and causes the formation of crystals. This is thought to cause coarsening. Note that if the amount of CaCO ₃ added exceeds 1.2 wt%, even if it is added during pulverization, Hc will be significantly lowered, so the amount of CaCO ₃ added is limited to 1.2 wt%. The present invention does not simply select the type and amount of additives, but also specifies the timing of addition, thereby maximizing the effects of the additives, thereby improving density and orientation. A strontium ferrite magnet can be obtained as a sintered body with a high degree of Br≒ and small crystal grains.
4.45KG, _BHC ≒ _3.28KOe , (BH)max is
We were able to achieve a characteristic of 4.55MGOe. In the following experimental examples, examples of the present invention will be explained in detail together with other comparative examples. Experimental Example 1 _Ten samples ₍ No. _{1 to No.} 10) was adjusted. After adding and mixing each additive powder to these samples according to Table 1 before calcination, each sample was heated to 1300
It was calcined at ℃ for 2 hours.

[Table] Next, the calcined product was wet-pulverized. During this pulverization, additives specified in each sample were added according to Table 1. Grinding has a particle size of 0.75~0.8μ
This process was continued until a powder of 100% was obtained. In addition, at the time of crushing
When adding Na ₂ B ₄ O ₇ (sample Nos. 4 to 6),
0.4% in the compact considering elution during wet grinding
I added a large amount so that it remained. Sample No. in which Na ₂ B ₄ O ₇ was added after pulverization and before calcination.
Powders Nos. 7 to 10 were washed with water to adjust the boron content to 0.005 wt% or less. Each of the fine powders of samples No. 1 to 10 obtained in this way was
After molding at a pressure of 0.5t/cm ² under an applied magnetic field of 8KOe, it was burned at 1200°C for 1.5 hours. The occurrence of cracks in the obtained sintered body was observed, and the magnetic properties were measured. The results are shown in Table 1. From the magnet properties in Table 1, sample No. 8 according to the present invention
It can be seen that this sample is significantly superior to any of the other samples Nos. 1-7, 9, and 10. The remaining amount of porosity in the sintered body of sample No. 8 is
It was 0.003wt%. Furthermore, looking at the occurrence of cracks, it can be seen that they occur when Na ₂ B ₄ O ₇ is present in a large amount of 0.4 wt% in the molded article. Experimental Example 2 Fe ₂ O ₃ with a purity of 99% and SrCO ₃ with a purity of 97% were blended at a molar ratio of 5.7, and 0.2% of SiO ₂ was added to this, and 0.15% of Na ₂ B ₄ O ₇ (as boron) was added. 0.03%),
0.03% (0.06% as boron), 0.60% (as boron)
0.12%), 0.90% (0.18% as boron), and 1.2% (0.24% as boron) were added and mixed.
Various samples were prepared and calcined at 1280°C for 2 hours.
After calcining, 0.6 wt% of CaCO ₃ was added during pulverization, and the mixture was wet-pulverized to a particle size of about 0.75 to 0.8 μm. After pulverization, four samples were prepared for each type of sample with boron content of 0.005%, 0.01%, 0.015%, respectively.
Adjusted by washing with water so that 0.03% remained.
It was molded and sintered in the same manner as in Experimental Example 1. The magnetic properties of the sintered body thus obtained were measured, and the results are shown in Table 2 and the figures. In addition, curves a,
b, c, d each have a residual boron content of 0.005%,
The cases of 0.01%, 0.015%, and 0.03% are shown. In addition, _{as a} reference, _SiO2 without using _Na2B4O7
Br = _4150G , _BHC =2970Oe, (BH)
max=3.99M・G・Oe.

[Table] As is clear from Table 2 and the figure, Na ₂ B ₄ O ₇ is
At 0.15%, the effect is hardly exhibited, and
When 1.2% is added, (BH)max decreases _along with _BHC . Furthermore, when the remaining boron content was set to 0.015%, the characteristics deteriorated, and moreover, cracks occurred in about half of the samples. Also, the amount of remaining boron is reduced to 0.03%.
However, the characteristics further deteriorated and cracks occurred in all samples. However, by setting Na ₂ B ₄ O ₇ to 0.3, 0.6, 0.9% and the remaining boron to 0.01% or less, Br can be reduced to 4330~
4510G, 2850~3020Oe _{at BHC} , 4.3 at (BH)max
It showed ~4.56M・G・Oe. As a result, it is found that it is preferable to adjust the amount of boron compound remaining in the sintered body to 0.01 wt% or less in terms of boron. Experimental Example 3 The same raw materials as Experimental Example 2 were mixed at a molar ratio of 5.7,
After adding and mixing 0.2% SiO ₂ and 0.30% Na ₂ B ₄ O ₇
It was calcined at 1280°C for 2 hours. CaCO ₃ 0.2%, 0.6%,
It was wet-pulverized under each addition condition of 1.0% and 1.4%, so that the pulverized particle size was 0.7 to 0.8μ, and the residual boron was adjusted to be about 0.008%. This powder was molded and sintered in the same manner as in Experimental Example 1. Table 3 shows the magnetic properties of each of the obtained sintered bodies.

[Table] When CaCO ₃ was 1.4%, the squareness of the B-H loop decreased along with Hc, leading to a decrease in (BH)max. Therefore, it can be seen that the amount of CaCO ₃ added is preferably 1.2 wt% or less. Experimental example 4 The same raw materials as experimental example 2 were mixed at a molar ratio of 5.8,
0.4% of Na ₂ B ₄ O ₇ and 0.2% and 0.4% of SiO ₂ respectively
%, 0.6%, 0.8% and 1.0% were mixed and calcined at 1300°C for 2 hours.
After calcination, add 0.6% CaCO ₃ during crushing to 0.75~
It was wet-pulverized to a particle size of 0.8μ, washed with water to reduce the boron content to 0.01% or less, and then molded and sintered in the same manner as in Experimental Example 1. Table 4 shows the magnetic properties of each sample at this time.

[Table] Br and (BH)max decreased when SiO ₂ was 0.8%, but high characteristics were exhibited up to 0.6%. As a result
It can be seen that the amount of SiO ₂ added is preferably up to 0.6%. As mentioned above, SiO ₂ is used as an additive before firing.
0.6% or less (not including 0), 0.04 to 0.2% of a water-soluble boron compound as boron, and 1.2% or less (not including 0) of CaCO ₃ during pulverization after calcination to perform wet pulverization. Extremely high Br
A strontium ferrite magnet with _B H _C , (BH)max was obtained.

[Brief explanation of the drawing]

The figure is a graph showing the magnetic properties depending on the amount of Na ₂ B ₄ O ₇ added before calcination and the amount of boron remaining after pulverization under the conditions of 0.2% SiO ₂ added before calcination and 0.6% CaCO ₃ added during pulverization. .

Claims (1)

[Claims] 1 Fe ₂ O ₃ and an Sr compound that becomes SrO when heated are mixed so that the molar ratio of Fe ₂ O ₃ and SrO is 5.6 to 6.0:1, mixed, calcined, wet-pulverized, and then heated in a magnetic field. In the method of manufacturing oxide permanent magnets with a magnetoplumbite crystal structure by molding and sintering, when mixing raw materials, a water-soluble boron compound is converted to boron and 0.04
~0.2% by weight, 0.6% by weight or less (not including 0) of silicic anhydride, adding not more than 1.2% by weight (not including 0) of calcium carbonate during pulverization after the above-mentioned calcination, and the above-mentioned wet method. The boron is eluted from the time of crushing to before molding in a magnetic field to reduce the boron content to 0.01.
A method for producing an oxide permanent magnet, characterized in that the amount is less than or equal to 0% by weight (not including 0).