CN106145917A - A kind of coercitive secondary of permanently magnetic strontium ferrite that improves is combined adding method - Google Patents

Abstract

The invention discloses a low-cost secondary composite addition method, which can increase the intrinsic coercive force of materials without reducing the remanence. Its specific steps: ① Ingredients: on the basis of strontium ferrite calcined material, carry out secondary compound addition, ② ball milling, adding dispersant during ball milling, wherein dispersant includes C ₆ H ₁₄ O ₆ , HCOOH, Ca(C One or more substances in ₆ H ₁₁ O ₇ ) ₂ , C ₆ H ₇ NaO ₆ ; ③Dehydration; ④Shaping; ⑤Sintering; ⑥Grinding and performance testing. The additives involved in the secondary composite addition disclosed by the present invention are cheap, without the addition of expensive rare earth or noble metal oxides, and the intrinsic coercive force can be increased by about 136 ~ 144kA/m or so, reaching 336 ~ 344kA/m.

Description

A secondary composite addition method for improving the coercive force of permanent magnet strontium ferrite

technical field

The invention belongs to the field of preparation of permanent magnet ferrite in functional materials, and in particular relates to a secondary compound addition method for improving the coercive force of permanent magnet strontium ferrite.

Background technique

At present, the global demand for permanent ferrite is increasing year by year, and China, as a major user of permanent ferrite, maintains a faster growth in demand. The M-type permanent magnet ferrite industry has developed rapidly in recent decades, and China's output has risen to the forefront of the world, but the problem is that the permanent magnet ferrite produced by most domestic enterprises is still at a low level for a long time. Moreover, the utilization rate of raw materials is low, and the production technology is far behind other countries. Therefore, improving the performance of the product and improving the production process have always been the focus of research in the field of permanent ferrite materials.

Permanent ferrite mainly refers to hexagonal M-type strontium ferrite or barium ferrite, and its magnetic performance indicators mainly include remanence (B _r ), coercive force (H _cb , H _cj ), magnetic energy product (BH ) _max , where the remanence B _r and intrinsic coercive force H _cj , the larger the value, the better the magnetic energy of the magnet.

The remanence (B _r ) of a magnet depends on the density, degree of orientation, and saturation magnetization (4πIs) determined by the lattice, expressed by:

B _r =4πIs×degree of orientation×density

M-type strontium ferrite and barium ferrite have a 4πIs value of about 4.65 kG. Density and orientation are at most 98% of theoretical values, even for wet-pressed sintered magnets with the highest density and orientation values.

H _cj is proportional to the product of the anisotropic magnetic field ( _HA = 2K ₁ /Is) and the ratio of single-domain grains (f _c ), ( _HA × fc), where K ₁ represents the individual magnetic crystals determined by the crystal structure. Anisotropy constant. It is known that M-type strontium ferrite has the largest K ₁ value, and it is difficult to increase it. Whereas if the ferrite grain is in a single domain state, then H _cj can be expected to be a maximum, since the magnetization must be rotated against the anisotropic field, thereby reversing the magnetization.

According to the above theory, if the product performance is to be improved, the microstructure of the pre-sintered material can be improved by ion doping instead, or the secondary addition process can be carried out on the basis of the existing pre-sintered material. For the secondary addition process, additives such as CaCO ₃ , CaO and some rare earth oxides increase the remanence, while the coercive force and intrinsic coercive force of the material also decrease; Al ₂ O ₃ , SiO ₂ , Cr ₂ O _3. While SrCO ₃ , H ₃ BO ₃ and other additives increase the coercive force and intrinsic coercive force of the material, the remanence also decreases sharply. This is also the main problem facing the current secondary addition process. The Chinese invention patent (publication number CN102408229A) discloses a method for increasing the coercive force of permanent magnet ferrite, which has a certain effect on the improvement of the magnetic properties of the magnet, but the additive R _x Al _y Fe _z O _m preparation process developed by it It is complicated, time-consuming and labor-intensive, and the additives added at the same time contain rare earth elements such as cobalt and praseodymium, which greatly increases the cost.

Contents of the invention

Aiming at the above existing problems, the present invention develops a secondary composite addition method to increase the coercive force of the material under the premise of keeping the remanence unchanged through the selection of additives, the exploration of the addition ratio and the optimization of the addition method.

To achieve the above object, the present invention adopts the following technical solutions:

A secondary composite addition method for improving the coercive force of permanent magnet strontium ferrite, comprising the following steps:

Ingredients: on the basis of strontium ferrite calcined material, carry out secondary composite addition, the secondary composite additive is pretreated first, and the mass percentage of the total weight is 1% to 6%, and the secondary composite addition The substance is one or a mixture of substances of type A, type B and type C, the type A substance is CaCO ₃ , SiO ₂ ·nH ₂ O, H ₃ BO ₃ , and the type B substance is Al ₂ O ₃ , Cr ₂ O ₃ , MgO, Mn ₂ O ₃ , C-type substances are NaCl, KCl;

Ball milling: add dispersant, and carry out secondary ball milling in the ball mill. The steel balls used are bearing steel balls with a diameter of 5.50-7.50 mm. The ball milling time is ≥18 hours; the mass percentage of material, balls and water is 1: (13-16 ): (1.6～1.9), the particle size of the slurry after the second ball milling is ≤0.9μm;

Dehydration: Transfer the slurry from the second ball mill to a dehydrator for dehydration. The dehydration time is 5-12 hours, so that the moisture content of the slurry reaches 34-45%;

Molding: Use a wet press molding machine to press the dehydrated slurry under a magnetic field. The size of the pressed sample is: diameter 25mm, height 10mm, density ≥ 5.20g/cm ³ ;

Sintering: Sintering the sample forming blank in a tube furnace;

Grinding and performance test: After the sintered sample is cooled, grind the upper and lower surfaces to meet the product requirements, and use the MATS-2010 permanent magnet measuring device to test the magnetic properties of the prepared sample.

Further, the mass percentages of the total weight of the pretreated secondary composite additives are: 0.2%-1.4% CaCO ₃ , 0.15%-0.4% Al ₂ O ₃ , 0.5%-1.3% Cr ₂ O ₃ , 0.1% to 0.9% H ₃ BO ₃ , 0.05% to 0.45% SiO ₂ nH ₂ O, 0.3% to 0.9% MgO, 0.25% to 1.2% Mn ₂ O ₃ , 0.1% to 0.8% NaCl, 0.05% to 0.65% KCl.

Further, the pretreatment method of the secondary composite additive is: weighing according to the formula → ball milling → sintering → crushing → fine grinding → sieving, and finally dissolving the sieved secondary additive powder in an organic solvent to obtain Secondary compound additive, wherein the organic solvent is two or more organic substances in (CH ₂ OH) ₂ , CH ₃ COCH ₃ , CH ₃ CH ₂ OH or polyethylene glycol.

Further, the dispersant added in the ball milling process in step (2) is one or more of C ₆ H ₁₄ O ₆ , HCOOH, Ca(C ₆ H ₁₁ O ₇ ) ₂ , C ₆ H ₇ NaO ₆ Substances, wherein the weight percentage of the dispersant is 0.6% to 1.3%.

Furthermore, the pressing pressure in step (4) is 0.35-0.5 tons/cm ² , the magnetizing current is 15.0A, the applied magnetic field is about 5-15KOe, the pressure is kept for 3.5s, and the demagnetization is 4s. The forming slurry is oriented and formed under a magnetic field.

The method according to claim 1, characterized in that step (5) is firstly sintered at a temperature of 300-360°C in the sintering process, and the sintering time is 2h. This stage is mainly drainage and dispersant decomposition, and then The heating rate is 5°C/min to 1185-1205°C for sintering, the sintering time is 4h, and the heat preservation is 2h.

Beneficial effect:

1. Class A substances have the effect of raising remanence, and class B substances have the effect of raising intrinsic coercive force. NaCl and KCl have certain improvements to these two properties, and the second compound addition is carried out according to the formula ingredients of the present invention Finally, under the premise that the remanence of the material can be maintained, its intrinsic coercive force has been greatly improved (about 136-144kA/m), and it has no effect on the molding and sintering of the product.

2. The formula does not require the addition of some precious metal oxides or rare earth elements, and the price is lower. The performance improvement is equivalent to the effect of secondary addition of some precious metal oxides or rare earth elements, which is more in line with the requirements of mass production.

3. After the pretreatment of the additives added twice, the distribution of the additives is more uniform and the loss of the additives is effectively suppressed.

Description of drawings

The demagnetization curve figure of Fig. 1 embodiment 2;

Fig. 2 is the cross-sectional scanning electron micrograph of the sample prepared in Example 2 of the present invention;

Figure 3 is a cross-sectional scanning electron microscope image of a sample prepared in a comparative example.

detailed description

Example 1

A secondary composite addition method for improving the coercive force of permanent magnet strontium ferrite, the specific steps are as follows: on the basis of the primary calcined material of strontium ferrite, perform secondary composite addition, and the secondary composite additive is first pretreated , the mass percentage of the total weight is 1%, and the pretreated secondary composite additives include 0.2% CaCO ₃ , 0.15% Al ₂ O ₃ , 0.5% Cr ₂ O ₃ , 0.1% H ₃ BO ₃ , 0.05% SiO ₂ ·nH ₂ O. The weight percentage of the mixture of C ₆ H ₁₄ O ₆ , HCOOH and Ca(C ₆ H ₁₁ O ₇ ) ₂ added was 7%. Secondary ball milling is carried out in the ball mill, the steel balls used are bearing steel balls with a diameter of 5.50-7.50mm, and the ball milling time is ≥18h; the mass percentage of material, ball and water is 1:(13-16):(1.6-1.9 ), the slurry particle size after secondary ball milling is ≤0.9μm. Transfer the slurry from the second ball mill to a dehydrator for dehydration. The dehydration time is 5-12 hours. Use a wet press molding machine to press the dehydrated slurry under a magnetic field. The molding pressure is 0.35-0.5 tons/cm ² , The magnetizing current is 15.0A, the external magnetic field is about 5-15KOe, the holding pressure is 3.5s, and the demagnetization is 4s. The size of the pressed sample is: diameter 25mm, height 10mm, density ≥ 5.20g/cm ³ . The sample molding blank was sintered in a tube furnace at a temperature of 300-360°C for 2 hours, and then sintered at a heating rate of 5°C/min to 1185-1205°C for 4 hours and held for 2 hours. After the sintered sample is cooled, the upper and lower surfaces are ground to meet the product requirements, and the magnetic properties of the prepared sample are tested using the MATS-2010 permanent magnet measuring device.

The magnetic properties of Example 1 are: B _r =401.5mT, H _cb =301.6kA/m, H _cj =328.2kA/m, (BH) _max =31.7kJ/m ³ . Example 2

Compared with Example 1, the weight percentage of the secondary composite additive is 3%, and the pretreated secondary composite additive includes 1.0% CaCO ₃ , 0.15% Al ₂ O ₃ , 0.6% Cr ₂ O ₃ , 0.25 %H ₃ BO ₃ , 0.2% SiO ₂ ·nH ₂ O, 0.3% MgO, 0.2% Mn ₂ O ₃ , 0.3% NaCl.

Fig. 1 is the demagnetization curve figure of this embodiment, it can be seen from this figure that the magnetic properties of embodiment 2 are: B _r =412.7mT, H _cb =310.6kA/m, H _cj =338.6kA/m, (BH ) _max = 33.9 kJ/m ³ .

Example 3

Compared with Example 1, the percentage of the secondary composite additive is 5%, and the pretreated secondary composite additive includes 1.0% CaCO ₃ , 0.4% Al ₂ O ₃ , 1.0% Cr ₂ O ₃ , 0.6% H ₃ BO ₃ , 0.6% SiO ₂ ·nH ₂ O, 0.4% MgO, 0.5% Mn ₂ O ₃ , 0.5% KCl. The magnetic properties of Example 3 are: B _r =390.8mT, H _cb =300.3kA/m, H _cj =319.2kA/m, (BH) _max =30.4kJ/m ³ .

comparative example

On the basis of the primary calcined material of strontium ferrite, without any addition, the mixture of dispersant C ₆ H ₁₄ O ₆ , HCOOH, Ca(C ₆ H ₁₁ O ₇ ) ₂ accounted for 7% by weight, and the ball mill Zhonglai conducts secondary ball milling, the steel balls used are bearing steel balls with a diameter of 5.50-7.50mm, and the ball milling time is ≥18h; the mass percentage of material, balls and water is 1:(13-16):(1.6-1.9), After the second ball milling, the particle size of the slurry is ≤0.9μm. Transfer the slurry from the second ball mill to a dehydrator for dehydration. The dehydration time is 5-12 hours. Use a wet press molding machine to press the dehydrated slurry under a magnetic field. The molding pressure is 0.35-0.5 tons/cm ² , The magnetizing current is 15.0A, the external magnetic field is about 5-15KOe, the holding pressure is 3.5s, and the demagnetization is 4s. The size of the pressed sample is: the diameter is 25mm, and the height is 10mm. The sample molding blank was sintered in a tube furnace at a temperature of 300-360°C for 2 hours, and then sintered at a heating rate of 5°C/min to 1185-1205°C for 4 hours and held for 2 hours. After the sintered sample is cooled, the upper and lower surfaces are ground to meet the product requirements, and the magnetic properties of the prepared sample are tested using the MATS-2010 permanent magnet measuring device.

The magnetic properties of the comparative example are: B _r =420.6mT, H _cb =168.9kA/m, H _cj =178.0kA/m, (BH) _max =34.1kJ/m ³ .

By comparison, the remanence of the strontium ferrite samples prepared in the examples is comparable and the coercive force is obviously higher than that of the comparative examples. Comparing Fig. 2 with Fig. 3, the particle distribution of the embodiment is more uniform, finer and denser than that of the comparative example.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (6)

1. the raising coercitive secondary of permanently magnetic strontium ferrite is combined adding method, it is characterised in that comprise the following steps:

1) dispensing: on the basis of Strontium ferrite powder, carries out the compound interpolation of secondary, and secondary Compound Supplement first carries out pre-place Reason, the mass percent of shared gross weight are 1%～6%, and described secondary Compound Supplement is in A class, B class and C class material The mixture of one or more, described A class material is CaCO₃、SiO₂·nH₂O、H₃BO₃, B class material is Al₂O₃、Cr₂O₃、 MgO、Mn₂O₃, C class material is NaCl, KCl；

2) ball milling: adding dispersant, carrying out secondary ball milling in ball mill, steel ball used is the axle of diameter 5.50～7.50mm Holding steel ball, Ball-milling Time is >=18h；Material, ball, the mass percent of water are 1:(13～16): (1.6～1.9), after secondary ball milling Slurry Granularity≤0.9 μm；

3) it is dehydrated: the slip of secondary ball milling being transferred to dewaterer and being dehydrated, dewatering time is 5～12h, makes the aqueous of slip Rate reaches 34～45%；

4) being molded: use Wet-pressing molding machine to be pressed the slip after dehydration under magnetic field, the size of compacting sample is: A diameter of 25mm, high 10mm, density >=5.20g/cm³；

5) sinter: in tube furnace, sample formation blank is sintered；

6) grinding and performance test: after the sample cooling after to be sintered, polish upper and lower surface, meet product requirement, use MATS- 2010 permanent magnetism measurement apparatus carry out magnetism testing to prepared sample.

2. method according to claim 1, it is characterised in that gross weight shared by secondary Compound Supplement after pretreatment Mass percent be respectively as follows: 0.2%～1.4%CaCO₃, 0.15%～0.4%Al₂O₃, 0.5%～1.3%Cr₂O₃, 0.1% ～0.9%H₃BO₃, 0.05%～0.45%SiO₂·nH₂O, 0.3%～0.9%MgO, 0.25%～1.2%Mn₂O₃, 0.1% ～0.8%NaCl, 0.05%～0.65%KCl.

3. method according to claim 1, it is characterised in that the preprocess method of secondary Compound Supplement is: by formula Weighing → ball milling → sintering → broken → fine grinding → sieve, the secondary additive powder after finally sieving is dissolved in organic solvent In, prepare secondary Compound Supplement, wherein organic solvent is (CH₂OH)₂、CH₃COCH₃、CH₃CH₂In OH or polyethylene glycol two kinds Or two or more organic matter.

4. method according to claim 1, is characterized in that, the dispersant that step (2) is added in mechanical milling process is C₆H₁₄O₆、HCOOH、Ca(C₆H₁₁O₇)₂、C₆H₇NaO₆In one or more materials, the wherein percentage by weight shared by dispersant It is respectively 0.6%～1.3%.

5. method according to claim 1, is characterized in that, the compressing pressure described in step (4) is 0.35～0.5 Ton/cm², the electric current that magnetizes is 15.0A, and externally-applied magnetic field is approximately 5～15KOe, pressurize 3.5s, and demagnetize 4s.

6. method according to claim 1, is characterized in that, step (5), in sintering process, is first at 300～360 DEG C At a temperature of be sintered, sintering time 2h, this stage is mainly draining and dispersant and decomposes, after with the intensification speed of 5 DEG C/min Degree is sintered to 1185～1205 DEG C, and sintering time is 4h, is incubated 2h.