Production process of high-performance permanent ferrite

Abstract

The application discloses a production process of high-performance permanent ferrite, and belongs to the technical field of permanent ferrite preparation. The raw materials are prepared according to weight parts, wherein the iron oxide is 80-88 parts, the strontium carbonate is 0.5-5 parts, the calcium carbonate is 3-10 parts, the lanthanum oxide is 4-10 parts, and the cobalt sesquioxide is 1-3 parts. After mixing, pre-sintering, primary grinding, secondary ball milling, magnetic field forming and sintering, the sintered body is obtained. In the sintering process, the temperature rising rate in the temperature interval of 900 DEG C-1200 DEG C is strictly controlled to be 1.5-3 DEG C / min, the uniform diffusion reaction of the doped elements in the green body is ensured, the temperature rising rate and the holding time are simultaneously adjusted according to the adding proportion of different elements in the high-performance permanent ferrite, the uniformity of the grain size of the ferrite is improved, the squareness is improved, and the demagnetization resistance of the high-performance permanent ferrite is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of permanent magnet ferrite preparation, and particularly relates to a production process of high-performance permanent magnet ferrite. BACKGROUND

[0002] Ferrite is a kind of metal oxide with ferromagnetism, which is prepared by sintering of iron trioxide and one or more other metal oxides (for example, nickel oxide, zinc oxide, manganese oxide, magnesium oxide, barium oxide, strontium oxide, etc.). The resistivity of ferrite is much larger than that of metal and alloy magnetic materials, and ferrite also has high dielectric performance. The magnetic performance of ferrite has high permeability at high frequency, so ferrite has become a non-metallic magnetic material widely used in the field of high-frequency weak current.

[0003] At present, the performance research of permanent magnet ferrite mostly focuses on residual magnetism, intrinsic coercive force and magnetic energy product, and less on squareness. The squareness will affect the product quality of permanent magnet ferrite, represents the demagnetization resistance of the product, and the better the squareness, the closer to 1, the better the demagnetization resistance; the worse the squareness, the easier the demagnetization.

[0004] The patent application file with the publication number CN114956801B discloses a kind of high squareness permanent magnet strontium ferrite magnetic material and preparation method thereof, by using subsection gradient temperature setting sintering at sintering, using different heating rates at sintering initial stage, sintering intermediate stage and high temperature sintering stage, control grain morphology and diameter / thickness ratio, make sample have good comprehensive performance. But the permanent magnet strontium ferrite magnetic material prepared in the embodiment of the technical solution has high squareness, but its intrinsic coercive force is only 2500-3000 Oe, and even under the same sintering conditions, the squareness of high-performance permanent magnet strontium ferrite magnetic material is lower after adjusting the raw material input mode in the comparative example. It cannot have high performance and high squareness at the same time, and the prepared material has defects. SUMMARY

[0005] The purpose of the present application is to provide a production process of high-performance permanent magnet ferrite to solve the problem of poor squareness of high-performance permanent magnet ferrite prepared by the prior art.

[0006] The purpose of the present application can be achieved by the following technical solution:

[0007] The present application provides a production process of high-performance permanent magnet ferrite, comprising the following steps:

[0008] Step one, prepare raw materials according to weight parts, iron oxide: 80-88 parts, strontium carbonate: 0.5-5 parts, calcium carbonate: 3-10 parts, lanthanum oxide: 4-10 parts, cobalt sesquioxide: 1-3 parts, uniformly mix the raw materials to obtain a mixture;

[0009] Step two, the mixture is mixed with water to obtain a first slurry, and the first slurry is dried and pre-sintered to obtain a first pre-sintered material, and the first pre-sintered material is ground to obtain a first pre-sintered material powder;

[0010] Step three, the first pre-sintered material powder is added with composite auxiliary materials and water for secondary ball milling to obtain a second slurry;

[0011] Step four, the second slurry is formed into a green body in a magnetic field, and the green body is placed in a sintering kiln, heated to 900°C, and then heated to 1200°C at a heating rate of 1.5-3°C / min, and held for 60-120 min to obtain a sintered body, and the squareness of the sintered body is >0.92.

[0012] Further, the purity of the iron oxide is >99.0%, the purity of the strontium carbonate is >98.5%, the purity of the calcium carbonate is >98.5%, the purity of the lanthanum oxide is >99%, and the mass fraction of cobalt in the cobalt sesquioxide is >72%. Controlling the purity of the raw materials can reduce the introduction of impurity elements and avoid affecting the performance of the ferrite.

[0013] Further, in step two, the pre-sintering temperature is 1250-1350°C, and the holding time is 0.5-4h. Pre-sintering can promote solid-phase reactions between the raw materials, generate part of the ferrite phase, reduce the sintering shrinkage of the finished product, and improve the completeness of the reaction.

[0014] Further, in step two, the first grinding device is a Raymond mill, and the particle size of the first pre-sintered material powder is 1.5-3μm. The first grinding refines the pre-sintered material, making the subsequent addition of composite auxiliary materials more uniform.

[0015] Further, in step three, the mass ratio of the secondary ball milling is as follows:

[0016] Material: ball: water = 1: (5-15): (1-3).

[0017] Secondary ball milling can further refine the particles, increase the contact area between ions, promote the progress of solid-phase reactions, and improve the densification and grain growth of the product.

[0018] Further, the composite auxiliary materials include, calculated as a percentage of the mass of the first pre-sintered material powder:

[0019] CaCO3: 0.1-1%, SiO2: 0.05-0.4%, dispersant: 0.1-0.5%, and borate: 0.1-0.5%.

[0020] The composite auxiliary materials have the effects of promoting densification and growth, reducing loss, and improving dispersibility in the preparation of ferrite, and together improve the magnetic properties and frequency characteristics of the ferrite material.

[0021] Further, the dispersant is at least one of calcium gluconate and sorbitol.

[0022] Further, the borate is a calcium borate.

[0023] Further, the particle size of the secondary slurry is 0.6-1.0 μm.

[0024] Further, in step four, the magnetic field strength of the magnetic field forming is 800-1000 kA / m; and the density of the green body is 3.3-3.45 g / cm 3 The green body density affects the densification process of sintering.

[0025] Advantages of the present application:

[0026] (1) Since high-performance permanent ferrite needs to be doped with metal ions and rare earth elements, and the diffusion reaction of metal ions and rare earth elements in the material mainly occurs in the high-temperature heating stage, the present application controls the heating rate of the sintering heating stage (900-1200℃) to be 1.5-3℃ / min, realizes uniform diffusion reaction of the doping elements in the green body, avoids partial concentration leading to uneven particle size in the sintered body, and thus ensures the magnetic properties of high-performance permanent ferrite while improving the squareness. Only the heating rate of the high-temperature heating stage needs to be controlled in the entire production process, and the process is simple.

[0027] (2) The production process provided by the present application adjusts the heating rate and holding time (900-1200℃ temperature section) according to the addition proportion of different elements in the high-performance permanent ferrite at the same time, improves the uniformity of the grain size of the ferrite, and improves the squareness. As a rare earth element, lanthanum has a larger ionic radius and will replace trivalent iron ions into the lattice. The solubility of lanthanum ions is limited, and a secondary phase LaFeO3 will be formed. The secondary phase gathers at the grain boundary and affects the diffusion reaction of other ions, reducing the uniformity of the grain size of the ferrite. When the lanthanum proportion is high, the heating rate needs to be increased to promote the rapid diffusion of lanthanum ions and shorten the holding time to avoid the precipitation of lanthanum during the reaction, thereby reducing the secondary phase and uniform diffusion reaction. The ionic radius of cobalt element is smaller than that of lanthanum, and its diffusion is easier. The embedding will change the stress distribution in the lattice, thereby hindering the normal growth of the crystal grains and promoting the refinement of the crystal grains. The heating rate needs to be reduced and the holding time needs to be extended to realize sufficient diffusion reaction and inhibit the growth of the crystal grains. BRIEF DESCRIPTION OF DRAWINGS

[0028] The present application will be further described below in conjunction with the drawings.

[0029] Figure 1 is the demagnetization curve diagram of the sintered body prepared in Example 1 of the present application;

[0030] Figure 2is an electron microscope image of the sintered body prepared in Example 1 of the present application;

[0031] Figure 3 is an electron microscope image of the sintered body prepared in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0033] Example 1

[0034] Step one, prepare raw materials according to weight fraction, iron oxide: 85 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 5 parts, cobalt sesquioxide: 2 parts, uniformly mix the raw materials to obtain a mixture;

[0035] The purity of the iron oxide is >99%, the mass fraction of SiO2 is ≤0.01%, the mass fraction of chloride is ≤0.05%, and the average particle size is 0.90 μm; the purity of the strontium carbonate is >98.5%, and the average particle size is 1.5 μm; the purity of the calcium carbonate is >98.5%, and the average particle size is 3 μm; the purity of the lanthanum oxide is >99%, and the average particle size is 3 μm; the mass fraction of cobalt in the cobalt sesquioxide is >72%, and the average particle size is 2.5 μm.

[0036] Step two, mix the mixture with water for 2 h to obtain a first slurry, dry the first slurry, and then pre-sinter at a temperature of 1260°C for 2 h to obtain a first pre-sintered material, which is put into a Raymond mill for first grinding to obtain a first pre-sintered material powder with a particle size of 2 μm;

[0037] Step three, take 500 g of the first pre-sintered material powder, and add 2.5 g of CaCO3, 1.8 g of SiO2, 1 g of Ca3(BO3)2, and 1.5 g of sorbitol according to the percentage of the mass of the first pre-sintered material powder, and put the materials (the sum of the first pre-sintered material powder, CaCO3, SiO2, Ca3(BO3)2, and sorbitol), steel balls (for ball milling), and water into a ball mill in a mass ratio of 1:8:1.5 to perform second ball milling to obtain a second slurry, and the average particle size of the second slurry is 0.83 μm measured by a WLP-216;

[0038] Step four, control the water content of the second slurry at 35%, and form a green body under the action of a magnetic field, and the magnetic field strength during forming is 900 kA / m, and the density of the green body is 3.34 g / cm​3 The diameter of the green body is 15mm The height of the sintered body is 15mm, the water content of the green body is 13%, the green body is placed in a sintering kiln, heated to 900℃, and then heated to 1200℃ at a heating rate of 2℃ / min, and kept for 90min to obtain the sintered body. The demagnetization curve of the sintered body prepared in this example is shown in Figure 1 , and the electron microscope image is shown in Figure 2 .

[0039] Example 2

[0040] The difference from Example 1 is that the heating rate of 2℃ / min in step four is adjusted to 1.8℃ / min, and the other conditions and steps are the same as those in Example 1.

[0041] Example 3

[0042] The difference from Example 1 is that the heating rate of 2℃ / min in step four is adjusted to 2.2℃ / min, and the other conditions and steps are the same as those in Example 1.

[0043] Example 4

[0044] The difference from Example 1 is that the composite auxiliary material dosage is increased and the secondary ball milling process parameters are adjusted, and the other steps and conditions are the same as those in Example 1.

[0045] The specific steps are as follows:

[0046] Step one, prepare raw materials according to weight ratio, iron oxide: 85 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 5 parts, cobalt sesquioxide: 2 parts, uniformly mix the raw materials to obtain a mixture;

[0047] Among them, the purity of iron oxide is >99%, the mass fraction of SiO2 is ≤0.01%, the mass fraction of chloride is ≤0.05%, and the average particle size is 0.90μm; the purity of strontium carbonate is >98.5%, and the average particle size is 1.5μm; the purity of calcium carbonate is >98.5%, and the average particle size is 3μm; the purity of lanthanum oxide is >99%, and the average particle size is 3μm; the mass fraction of cobalt in cobalt sesquioxide is >72%, and the average particle size is 2.5μm.

[0048] Step two, mix the mixture with water for 2h to obtain a first slurry, dry the first slurry and pre-sinter, the pre-sintering temperature is 1250℃, and the holding time is 4h, to obtain a first pre-sintered material, which is put into a Raymond mill for first grinding to obtain a first pre-sintered material powder with a particle size of 3μm;

[0049] Step three, take 500g of the first pre-sintering material powder, add 5g of CaCO3, 2.0g of SiO2, 0.5g of Ca3(BO3)2 and 2.5g of sorbitol according to the percentage of the mass of the first pre-sintering material powder, put the material (the sum of the first pre-sintering material powder, CaCO3, SiO2, Ca3(BO3)2 and sorbitol), steel balls (cleaned) and water into a ball mill in a mass ratio of 1:15:3, and then carry out secondary ball milling to obtain a secondary material slurry, and the average particle size of the secondary material slurry is 0.80μm measured by WLP-216;

[0050] Step four, control the water content of the secondary material slurry at 35%, and then shape the secondary material slurry under the action of a magnetic field to obtain a green body, the magnetic field strength during shaping is 900kA / m, the density of the green body is 3.35g / cm 3 , the diameter of the green body is 15mm, and the water content of the green body is 13%, the green body is placed in a sintering kiln, heated to 900℃, then heated to 1200℃ at a heating rate of 2℃ / min, and kept for 90min to obtain a sintered body.

[0051] Example 5

[0052] The difference between example 1 and example 5 is that the adding amount of the composite auxiliary material is reduced and the secondary ball milling process parameters are adjusted, and the other steps and conditions are the same as those of example 1.

[0053] The specific steps are as follows:

[0054] Step one, prepare raw materials according to weight parts, iron oxide: 85 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 5 parts, cobalt sesquioxide: 2 parts, and mix the raw materials uniformly to obtain a mixed material;

[0055] The purity of the iron oxide is >99%, the mass fraction of SiO2 is ≤0.01%, the mass fraction of chloride is ≤0.05%, and the average particle size is 0.90μm; the purity of the strontium carbonate is >98.5%, and the average particle size is 1.5μm; the purity of the calcium carbonate is >98.5%, and the average particle size is 3μm; the purity of the lanthanum oxide is >99%, and the average particle size is 3μm; the mass fraction of cobalt in the cobalt sesquioxide is >72%, and the average particle size is 2.5μm.

[0056] Step two, mix the mixed material with water for 2h to obtain a first material slurry, and then dry the first material slurry and carry out pre-sintering, the pre-sintering temperature is 1350℃, and the holding time is 0.5h, to obtain a first pre-sintering material, which is put into a Raymond mill for primary grinding to obtain a first pre-sintering material powder with a particle size of 1.6μm;

[0057] ​Step three, take 500g of the primary calcined material, add 0.5g of CaCO3, 0.25g of SiO2, 2.5g of Ca3(BO3)2 and 0.5g of sorbitol, according to the percentage of the mass of the primary calcined material, put the material (the sum of the primary calcined material, CaCO3, SiO2, Ca3(BO3)2 and sorbitol), steel balls (cleaned) and water into a ball mill in a mass ratio of 1:5:1, and then perform secondary ball milling to obtain a secondary slurry, and the average particle size of the secondary slurry is 0.89μm measured by a WLP-216;

[0058] Step four, control the water content of the secondary slurry at 35%, and then perform molding under the action of a magnetic field to obtain a green body, the magnetic field strength during molding is 900kA / m, the density of the green body is 3.35g / cm 3 , the diameter of the green body is , the height of the green body is 15mm, and the water content of the green body is 13%, then place the green body in a sintering kiln, heat to 900℃, then heat to 1200℃ at a heating rate of 2℃ / min, and keep the temperature for 90min to obtain a sintered body.

[0059] Example 6

[0060] The difference between Example 1 and Example 6 is that the weight fractions of the raw materials in Step one are different, and the heating rate in Step four is adjusted from 2℃ / min to 3℃ / min, and other conditions and steps are the same as those in Example 1. The weight fractions of the raw materials are as follows:

[0061] Iron oxide: 80 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 10 parts, and cobalt sesquioxide: 2 parts.

[0062] Example 7

[0063] The difference between Example 1 and Example 7 is that the weight fractions of the raw materials in Step one are different, and the heating rate in Step four is adjusted from 2℃ / min to 3℃ / min, and the holding time is adjusted from 90min to 60min, and other conditions and steps are the same as those in Example 1. The weight fractions of the raw materials are as follows:

[0064] Iron oxide: 86 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 10 parts, and cobalt sesquioxide: 2 parts.

[0065] Example 8

[0066] The difference between Example 1 and Example 8 is that the weight fractions of the raw materials in Step one are different, and the heating rate in Step four is adjusted from 2℃ / min to 1.5℃ / min, and other conditions and steps are the same as those in Example 1. The weight fractions of the raw materials are as follows:

[0067] ​Iron oxide: 85 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 4 parts, cobalt trioxide: 3 parts.

[0068] Example 9

[0069] The difference between Example 1 is that the weight parts of raw materials in step one is different, and the heating rate in step four is adjusted from 2℃ / min to 1.5℃ / min, and the holding time is adjusted from 90min to 120min. Other conditions and steps are the same as Example 1. The weight parts of raw materials are as follows:

[0070] Iron oxide: 85 parts, strontium carbonate: 1 part, calcium carbonate: 5 parts, lanthanum oxide: 4 parts, cobalt trioxide: 3 parts.

[0071] Comparative Example 1

[0072] Compared with Example 1, the heating rate in step four of this comparative example is adjusted from 2℃ / min to 1.3℃ / min, and other steps and conditions are the same as Example 1.

[0073] Comparative Example 2

[0074] Compared with Example 1, the heating rate in step four of this comparative example is adjusted from 2℃ / min to 3.2℃ / min, and other steps and conditions are the same as Example 1. The electron microscope image of the sintered body prepared in this comparative example is shown in Figure 3 .

[0075] The sintered bodies prepared in Examples 1-9 and Comparative Examples 1-2 were tested for performance, and the results are shown in Table 1.

[0076] After the upper and lower surfaces of the sintered body were ground flat and finely ground with a 140 mesh grinding wheel, it was tested under the NIM-2000 permanent magnet material magnetic performance detection system manufactured by Beijing Measurement Institute.

[0077] Table 1

[0078]

[0079]

[0080] As can be seen from Table 1, under the same raw material formula in Examples 1-3, both the increase and decrease of the heating rate will affect the squareness of the ferrite, and under the formula and heating rate of Example 1, the ferrite prepared has high remanence and intrinsic coercive force, and the squareness reaches 0.952. The microstructure of the magnet of Example 1 is shown in Figure 2As shown, the magnet section SEM analysis shows that the crystal structure is closely arranged, the grain size is relatively uniform, the porosity in the magnet is 0.8%, and no abnormal growth of grains (such as larger grains engulfing surrounding small grains or pores and rapidly growing, etc.) is observed. In the raw material formula of Example 6 and Example 7, the proportion of lanthanum is increased compared with Example 1, and by increasing the heating rate and shortening the holding time, the prepared ferrite material can have excellent comprehensive performance. Compared with Example 1, Example 8 and Example 9 increase the proportion of cobalt, and in Example 9, the heating rate is increased and the holding time is prolonged, and the prepared ferrite material has excellent performance, in which the squareness reaches 0.971, and has excellent demagnetization resistance. Compared with Example 1, the heating rate in the comparative examples is too low or too high, which leads to a low value of the squareness of the ferrite, and the magnetic material is easy to demagnetize. The electron micrograph of Comparative Example 2 is shown in FIG. 8, in which the grain size deviation is large, the uniformity is poor, and there are abnormal growth of grains. Figure 3 As shown, the magnet section SEM analysis shows that the crystal structure is closely arranged, the grain size is relatively uniform, the porosity in the magnet is 0.8%, and no abnormal growth of grains (such as larger grains engulfing surrounding small grains or pores and rapidly growing, etc.) is observed. In the raw material formula of Example 6 and Example 7, the proportion of lanthanum is increased compared with Example 1, and by increasing the heating rate and shortening the holding time, the prepared ferrite material can have excellent comprehensive performance. Compared with Example 1, Example 8 and Example 9 increase the proportion of cobalt, and in Example 9, the heating rate is increased and the holding time is prolonged, and the prepared ferrite material has excellent performance, in which the squareness reaches 0.971, and has excellent demagnetization resistance. Compared with Example 1, the heating rate in the comparative examples is too low or too high, which leads to a low value of the squareness of the ferrite, and the magnetic material is easy to demagnetize. The electron micrograph of Comparative Example 2 is shown in FIG. 8, in which the grain size deviation is large, the uniformity is poor, and there are abnormal growth of grains.

[0081] It should be noted that, in the present document, the relational terms such as first and second and the like can only be used to differentiate one entity or action from another entity or action, and do not necessarily require or imply that there is any such actual relationship or order between these entities or actions. Moreover, the terms "comprising", "including", or any other variant are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include those elements only, but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0082] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A production process for high-performance permanent magnet ferrite, characterized in that, Includes the following steps: Step 1: Prepare the raw materials according to the following weight proportions: iron oxide: 80-88 parts, strontium carbonate: 0.5-5 parts, calcium carbonate: 3-10 parts, lanthanum oxide: 4-10 parts, cobalt trioxide: 1-3 parts. Mix the raw materials evenly to obtain a mixture. Step 2: Mix the raw materials with water to obtain a primary slurry. After drying the primary slurry, pre-sinter it to obtain a primary pre-fired material. After grinding it once, obtain the primary pre-fired material powder. Step 3: Add composite additives and water to the pre-calcined powder and perform secondary ball milling to obtain secondary slurry; Step 4: The secondary slurry is magnetically shaped to obtain a green body. The green body is placed in a sintering kiln and heated to 900℃. Then, the temperature is increased to 1200℃ at a rate of 1.5-3℃ / min and held for 60-120min to obtain a sintered body. The squareness of the sintered body is >0.

92. In step three, the composite auxiliary materials, calculated as a percentage of the mass of the pre-fired powder, include: CaCO3: 0.1-1%, SiO2: 0.05-0.4%, dispersant: 0.1-0.5%, borate: 0.1-0.5%; The particle size of the secondary slurry is 0.6-1.0 μm.

2. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, The purity of the iron oxide is >99.0%, the purity of the strontium carbonate is >98.5%, the purity of the calcium carbonate is >98.5%, the purity of the lanthanum oxide is >99%, and the mass fraction of cobalt in cobalt trioxide is >72%.

3. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, In step two, the pre-sintering temperature is 1250-1350℃, and the holding time is 0.5-4h.

4. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, In step two, the equipment for the first grinding is a Raymond mill, and the particle size of the pre-burned powder is 1.5-3μm.

5. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, In step three, the quality of the secondary ball milling is as follows: Material: Ball: Water = 1: (5-15): (1-3).

6. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, The dispersant is at least one of calcium gluconate and sorbitol.

7. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, The borate is a calcium borate.

8. The production process of a high-performance permanent magnet ferrite according to claim 1, characterized in that, In step four, the magnetic field strength for magnetic field forming is 800-1000 kA / m; the density of the green blank is 3.3-3.45 g / cm³. 3 .

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