A method for producing a permanent magnet ferrite

Abstract

The application discloses a preparation method of permanent magnet ferrite, and belongs to the technical field of magnetic material preparation. The method uses iron concentrate powder as an iron source raw material, converts the iron concentrate powder into iron oxide through drying and multi-stage oxidation treatment in a rotary kiln, and obtains the permanent magnet ferrite material through the steps of batching, secondary grinding, pre-sintering, secondary continuous ball milling, pressing forming and sintering. The preparation method provided by the application uses the low-cost and high-yield iron concentrate powder to replace red iron oxide to prepare the high-performance ferrite material, widens the selection range of the high-performance permanent magnet ferrite raw material, reduces the raw material cost, improves the use value of the iron concentrate powder, keeps the silicon content in the iron concentrate powder consistent through multi-stage grinding and homogenization, avoids the fluctuation of the silicon content, and improves the stability of the performance of the high-performance magnetic material; and the pre-sintering process and the raw material ratio are optimized, so that the remanence of the permanent magnet ferrite is greater than or equal to 4350Gs, and the intrinsic coercive force is greater than or equal to 5400Oe.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnetic material preparation, and particularly relates to a preparation method of permanent magnetic ferrite. BACKGROUND

[0002] China is a big country in the production of magnetic materials, and permanent magnetic ferrite as a kind of magnetic material is the most widely used magnetic material at present, which is widely used in the driving or starting motor of motorcycles, automobiles, office automation, audio, sound and video recorders, and the like; in addition, it is also widely used in household appliances such as washing machines, microwave ovens, variable frequency air conditioners, refrigerators and electric tools. With the development trend of miniaturization and lightness of various electronic and electrical products, the demand for high-performance permanent magnetic ferrite materials is increasing, and the iron source of the high-performance permanent magnetic ferrite material basically cannot be separated from red iron oxide as a raw material for production.

[0003] The patent application file with the publication number CN101786869B discloses a calcium permanent magnetic ferrite material and a preparation method thereof, which can make the value of residual magnetization Br reach 4200-4700Gs and the value of intrinsic coercivity Hcj reach 4500-6200KOe at a sintering temperature of 1150℃ or lower, but the iron source thereof is Fe2O3, and red iron oxide as an auxiliary product of a steel plant has limited sources, large price fluctuations, and contains acidic chlorine or sulfide corrosion, and high-end red iron oxide is in short supply and has a high cost.

[0004] In order to reduce the cost, researchers use other iron source materials such as iron scale or iron powder to replace carbonized red iron, but the magnetic performance obtained by this method is low, and the magnetic performance is difficult to meet the requirements of high-performance permanent magnetic ferrite materials. The patent application file with the publication number CN114163226A discloses a method for preparing strontium permanent magnetic ferrite pre-fired material using super iron powder, which proposes to use super iron powder with the same particle size as strontium carbonate as raw material, to use the hot flue gas in the rotary kiln to exchange heat with the ball material, to oxidize the magnetite in the ball material into hematite to prepare the ferrite pre-fired material, and although this method proposes to use super iron powder instead of red iron oxide for production, because the oxygen content of the hot flue gas in the rotary kiln is much lower than that of air, the oxidation degree of FeO in the iron powder is low, and the intrinsic coercivity Hcj value of the obtained magnetic performance is only 3000-3200Oe, and the performance is low.

[0005] Therefore, based on the iron source defects of high-performance permanent magnetic ferrite materials, the development of high-performance permanent magnetic ferrite materials is seriously restricted. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of permanent magnetic ferrite, which uses low-cost and high-yield raw materials to manufacture high-performance permanent magnetic ferrite materials.

[0007] The object of the present application can be achieved by the following technical solutions.

[0008] The present application provides a preparation method of permanent magnet ferrite, comprising the following steps:

[0009] Step one, the iron powder is placed in an externally heated segmented rotary kiln, and is dried and multi-stage oxidized under negative pressure. After cooling and discharging, the iron powder is ground and mixed to obtain oxidized iron powder. The Fe2O3 conversion rate of the oxidized iron powder is ≥96%, the mass content of FeO is ≤1.2wt%, and the particle size is ≤5μm. The Fe2O3 conversion rate is calculated as (mass content of FeO before oxidation-mass content of FeO after oxidation) / mass content of FeO before oxidation×100%.

[0010] Step two, the oxidized iron powder, strontium carbonate, calcium carbonate, lanthanum oxide, cobalt oxide, sodium carbonate and boric acid are mixed uniformly to obtain a mixture. After mixing with water, the mixture is ground to obtain a slurry;

[0011] Step three, the slurry is dehydrated and concentrated to obtain a concentrated slurry with a solid content of 65-85%. The concentrated slurry is pre-burned in a rotary kiln to obtain dense granular material with a loose bulk density of 2.5-3.0g / cm 3 After being ground by a dry ball mill, the pre-burned material is crushed to obtain a pre-burned material with a particle size of 4-6μm. The pre-burned material is mixed with water in a mass ratio of 1:1-2.3, and additives are added for secondary continuous ball milling to obtain a fine slurry with an average particle size of 0.8-1.1μm;

[0012] Step four, the fine slurry is concentrated to a solid content of 65-75% and then pressed into a shape under a magnetic field. The shaped body is sintered in air at a sintering temperature of 1190-1240℃ for 2-4h to obtain a permanent magnet ferrite material.

[0013] Further, the iron powder is a 200-mesh undersize material, and the composition contains 70-72wt% of Fe, 28-31wt% of FeO, ≤0.35wt% of SiO2, and 0-12wt% of water.

[0014] Further, the externally heated segmented rotary kiln can be heated by electricity or gas. An induced draft fan is arranged at the feeding end, and an air inlet adjusting valve and a negative pressure gauge are arranged at the discharging end.

[0015] Further, in step one, the parameters of the iron powder in the externally heated segmented rotary kiln are as follows:

[0016] The first heating section is at 250-350℃, the second heating section is at 350-550℃, the third heating section is at 550-650℃, the fourth heating section is at 650-750℃, and the fifth heating section is at 750-850℃.

[0017] The iron concentrate powder stays in the first heating section and the third heating section for 0.5-1 h, stays in the fifth heating section for 1-3 h, and stays in the second heating section and the fourth heating section for less than 0.5 h.

[0018] The iron concentrate powder is subjected to multi-stage oxidation in the externally heated multi-section rotary kiln. By controlling the staying time of the iron concentrate powder at different temperatures, the reaction free energy difference of the iron concentrate powder at different temperatures is utilized to change the organization form and internal structure of the iron concentrate powder, so that most of the FeO in the iron concentrate powder is converted into Fe2O3. From the microstructure, the particle form is changed into flocculent form, the pore in the structure is enlarged, and the particle activity is enhanced, which is beneficial to the subsequent solid-phase reaction and ion substitution with strontium, calcium, lanthanum and cobalt at high temperature, and high-performance ferrite material can be prepared.

[0019] Further, in step one, the negative pressure is -30 to -5 Pa.

[0020] The oxidation of the iron concentrate powder in the negative pressure environment can make the oxygen content in the rotary kiln sufficient to meet the demand for oxygen during the oxidation of FeO, thereby ensuring the oxidation effect.

[0021] Further, the first grinding adopts a through-type ball mill with a rotation speed of 28-34 r / min and a processing capacity of 1.5-3 t / h, and the grinding medium is a grinding ball.

[0022] Further, in step two, the mass fractions of the components of the mixture are as follows:

[0023] 80-84 parts of the iron oxide concentrate, 0.5-3 parts of strontium carbonate, 4-5 parts of calcium carbonate, 7-9 parts of lanthanum oxide, 1.5-3 parts of cobalt oxide, 0-0.3 parts of sodium carbonate, and 0-0.3 parts of boric acid.

[0024] The value of (molar mass of the iron oxide concentrate + 3 / 2 times the molar mass of the cobalt oxide) / (molar mass of the strontium carbonate + molar mass of the calcium carbonate + 2 times the molar mass of the lanthanum oxide) is 4.9-5.5.

[0025] Further, the second grinding adopts a jar mill or a sand mill with a grinding time of 5-10 h, and the grinding medium is a grinding ball.

[0026] Further, in step two, the particle size of the slurry is tested by the air permeation method, and the particle size is ≤1.5 μm, and the amount of the oversize of the 200-mesh standard sieve is ≤0.5%.

[0027] Further, the settings of the pre-burning of the thick slurry in the rotary kiln are as follows:

[0028] The thick slurry stays in the temperature section of 600-900 °C for 2-3 h and stays in the temperature section of 1100-1250 °C for 0.5-2 h.​​

[0029] Further, the rotary kiln pre-burning is increased combustion fan air volume, so that the residual oxygen content in the tail gas is greater than or equal to 8%.

[0030] Further, in step three, the additives include calcium carbonate, calcium gluconate and silicon powder, which are added in the secondary continuous ball mill slurry in the mass fraction, and the mass fraction is as follows:

[0031] Calcium carbonate 0.4-1.0%, calcium gluconate 0.05-0.4%, and silicon powder 0-0.35%.

[0032] Further, in step four, the magnetic field strength of the magnetic field is greater than or equal to 7000 Oe.

[0033] Further, the silicon content of the permanent magnet ferrite material is less than or equal to 0.4wt%, which is detected by using a fluorescence analyzer of Japan.

[0034] By limiting the silicon content contained in the additives to control the silicon content of the permanent magnet ferrite material to be less than or equal to 0.4wt%, the excessive silicon in the ferrite material can be prevented, and the production of silicates can be avoided. The silicates will combine with calcium and strontium in the ferrite material, resulting in performance deterioration.

[0035] The beneficial effects of the present application are:

[0036] (1) The ferrite preparation method provided by the present application uses iron concentrate powder which is low in cost and high in yield to completely replace iron oxide red to prepare high-performance ferrite material, which widens the selection range of high-performance permanent magnet ferrite raw materials, reduces the cost of raw materials, and can produce greater economic benefits; the use of iron concentrate powder in the oxidation route is expanded from the production of low-grade magnetic materials to the production of high-performance magnetic materials, thereby improving its value.

[0037] (2) The ferrite preparation method provided by the present application performs multi-stage grinding and homogenization on the iron concentrate powder, that is, first, a dry method is used to pass through a ball mill to coarsely grind by filling larger grinding media, and then a wet method is used to fill small grinding media for fine grinding. The hierarchical grinding can effectively improve the grinding efficiency and reduce the power cost; the homogenization after the first-stage grinding can keep the silicon content in the iron concentrate powder consistent, and the intrinsic coercive force of the high-performance magnetic material is sensitive to silicon elements, so that the fluctuation of silicon content is avoided, and the stability of the performance of the high-performance magnetic material is improved.

[0038] (3) In the pre-burning stage of the ferrite preparation method provided by the present application, the residence time is extended at 600-900℃, CO2 released during the decomposition of the added raw materials calcium carbonate and strontium carbonate is used to make the material structure more loose, gaps are generated between the materials, and the combustion air volume is increased to increase the residual oxygen content in the tail gas, so that the iron concentrate powder is completely oxidized and converted into Fe2O3, and Fe 2+Risk of residual leading to magnetic performance decline.

[0039] (4) The ferrite preparation method provided by the application uses iron concentrate powder as an iron source, and reasonable molar ratio is selected to prepare the ferrite material, so that the permanent magnet ferrite residual magnetism is greater than or equal to 4350Gs, and the intrinsic coercive force is greater than or equal to 5400Oe. BRIEF DESCRIPTION OF DRAWINGS

[0040] The application will be further described below with reference to the drawings.

[0041] Figure 1 is an SEM image of the iron oxide concentrate powder prepared in Example 6 of the application;

[0042] Figure 2 is an SEM image of the iron oxide concentrate powder prepared in Comparative Example 2 of the application. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the application.

[0044] Example 1

[0045] The embodiment provides a preparation method of a permanent magnet ferrite, and the specific steps are as follows:

[0046] Step one, the iron concentrate powder is placed in an externally heated segmented rotary kiln provided with an induced draft fan at the feeding end and an air inlet adjusting valve and a negative pressure gauge at the discharging end. The iron concentrate powder is dried and subjected to multi-stage oxidation under a negative pressure environment of-30 to-5Pa. After the material in the rotary kiln is cooled and discharged, it is subjected to primary grinding by a through-type ball mill, and then is homogenized by a mixer to obtain iron oxide concentrate powder with a particle size of less than or equal to 5μm.

[0047] The iron concentrate powder is a 200-mesh undersize product, and the content of Fe element in the composition is 71wt%, the content of FeO is 30wt%, the content of SiO2 is 0.32wt%, and the water content is 2wt%.

[0048] The parameters of the iron concentrate powder in the externally heated segmented rotary kiln are as follows:

[0049] The first heating section is at 250 to 350℃, the second heating section is at 350 to 550℃, the third heating section is at 550 to 650℃, the fourth heating section is at 650 to 750℃, and the fifth heating section is at 750 to 850℃.

[0050] The iron concentrate powder stays in the first heating section and the third heating section for 1 hour, stays in the fifth heating section for 2 hours, and stays in the second heating section and the fourth heating section for 0.4 hour.

[0051] The rotating speed of the ball mill is 30 r / min, and the grinding medium is the grinding ball.

[0052] The Fe2O3 conversion rate of the iron oxide concentrate powder is 96.6%, the FeO mass content is 1.0%, and the particle size is ≤5 μm. The Fe2O3 conversion rate is calculated in the following manner: (the mass content of FeO before oxidation - the mass content of FeO after oxidation) / the mass content of FeO before oxidation x 100%.

[0053] In step two, the iron oxide concentrate powder, strontium carbonate, calcium carbonate, lanthanum oxide, cobalt oxide, sodium carbonate and boric acid are mixed uniformly to obtain a mixture. After mixing with water, the mixture is subjected to secondary grinding to obtain a slurry. The particle size of the slurry is tested by the air permeation method, and the particle size is ≤1.5 μm, and the content of the oversize of the 200 mesh standard sieve is ≤0.5%.

[0054] In the mixture, the mass fractions of the components are as follows:

[0055] The iron oxide concentrate powder is 84 parts, the strontium carbonate is 2.8 parts, the calcium carbonate is 4.1 parts, the lanthanum oxide is 8 parts, the cobalt oxide is 2.0 parts, the sodium carbonate is 0.3 parts, and the boric acid is 0.1 part.

[0056] The value of (the molar amount of the iron oxide concentrate powder + the molar amount of the cobalt oxide x 3 / 2) / (the molar amount of the strontium carbonate + the molar amount of the calcium carbonate + the molar amount of the lanthanum oxide x 2) is 5.19 (wherein the molar amount of the iron oxide concentrate powder is calculated according to the mass of the iron oxide concentrate powder / the relative molecular weight of the iron oxide).

[0057] The device for the secondary grinding is a sand mill, and the grinding time is 8 hours. The grinding medium is the grinding ball.

[0058] In step three, the slurry is dewatered and concentrated to obtain a concentrated slurry with a solid content of 70%. The concentrated slurry is pre-fired in a rotary kiln to obtain dense granular material with a loose bulk density of 2.7 g / cm 3 The air flow of the combustion fan is increased during the pre-firing of the rotary kiln, so that the residual oxygen content in the tail gas is ≥8%. The pre-fired material is crushed by a dry ball mill to obtain a pre-fired material with a particle size of 4-6 μm. The pre-fired material is mixed with water at a mass ratio of 1:1, and an additive is added for secondary continuous ball milling. The additive includes calcium carbonate, calcium gluconate and silicon powder. The mass fractions of the additive in the secondary continuous ball milling slurry are as follows: the calcium carbonate content is 0.8 wt%, the calcium gluconate content is 0.1 wt%, and the silicon powder content is 0.35 wt%. A fine slurry with an average particle size of 1.0 μm is obtained.

[0059] In the pre-firing of the concentrated slurry in the rotary kiln, the following settings are made:

[0060] The thick slurry is kept at 600-900℃ for 3h and at 1100-1250℃ for 1h.

[0061] Step four, the fine slurry is concentrated to 75% solid content and then is pressed into a shape under a magnetic field with a strength of 7000 Oe. The shaped body is sintered in air at a temperature of 1190-1240℃ for 4h to obtain a permanent magnet ferrite material. The silicon content of the permanent magnet ferrite material is less than or equal to 0.4wt% as determined by a fluorescence analyzer made by Rigaku.

[0062] Example 2

[0063] The difference between this example and Example 1 is that the mass fractions of the components of the mixture in Step two are different. The value of (molar amount of iron oxide fine powder + 3 / 2 times molar amount of cobalt oxide) / (molar amount of strontium carbonate + molar amount of calcium carbonate + 2 times molar amount of lanthanum oxide) is controlled to be 5.23. The other conditions and steps are the same as in Example 1. The mass fractions of the components of the mixture are as follows:

[0064] Iron oxide fine powder 84 parts, strontium carbonate 2.8 parts, calcium carbonate 4.1 parts, lanthanum oxide 8 parts, cobalt oxide 2.2 parts, sodium carbonate 0.2 parts, boric acid 0.2 parts.

[0065] Example 3

[0066] The difference between this example and Example 1 is that the mass fractions of the components of the mixture in Step two are different. The value of (molar amount of iron oxide fine powder + 3 / 2 times molar amount of cobalt oxide) / (molar amount of strontium carbonate + molar amount of calcium carbonate + 2 times molar amount of lanthanum oxide) is controlled to be 4.94. The other conditions and steps are the same as in Example 1. The mass fractions of the components of the mixture are as follows:

[0067] Iron oxide fine powder 83 parts, strontium carbonate 0.9 parts, calcium carbonate 5 parts, lanthanum oxide 9 parts, cobalt oxide 1.5 parts, sodium carbonate 0.1 parts, boric acid 0.3 parts.

[0068] Example 4

[0069] The difference between this example and Example 1 is that the mass fractions of the components of the mixture in Step two are different. The value of (molar amount of iron oxide fine powder + 3 / 2 times molar amount of cobalt oxide) / (molar amount of strontium carbonate + molar amount of calcium carbonate + 2 times molar amount of lanthanum oxide) is controlled to be 4.98. The other conditions and steps are the same as in Example 1. The mass fractions of the components of the mixture are as follows:

[0070] Iron oxide fine powder 80 parts, strontium carbonate 1.1 parts, calcium carbonate 5 parts, lanthanum oxide 9 parts, cobalt oxide 3 parts, sodium carbonate 0.1 parts, boric acid 0.3 parts.

[0071] Example 5

[0072] The difference between this example and example 1 is that the mass ratio of each component of the mixture in step two is different, the value of (molar quantity of iron oxide powder + 3 / 2 molar quantity of cobalt oxide) / (molar quantity of strontium carbonate + molar quantity of calcium carbonate + 2 molar quantity of lanthanum oxide) is 5.45, and other conditions and steps are the same as in example 1. The mass ratio of each component of the mixture is as follows:

[0073] Iron oxide powder 84 parts, strontium carbonate 2 parts, calcium carbonate 4.0 parts, lanthanum oxide 8.8 parts, cobalt oxide 3 parts, sodium carbonate 0.1 part, boric acid 0.3 part.

[0074] Example 6

[0075] The difference between this example and example 1 is that the mass ratio of each component of the mixture in step two is different, the value of (molar quantity of iron oxide powder + 3 / 2 molar quantity of cobalt oxide) / (molar quantity of strontium carbonate + molar quantity of calcium carbonate + 2 molar quantity of lanthanum oxide) is 5.09, and other conditions and steps are the same as in example 1. The mass ratio of each component of the mixture is as follows:

[0076] Iron oxide powder 84 parts, strontium carbonate 2.8 parts, calcium carbonate 5.0 parts, lanthanum oxide 7.5 parts, cobalt oxide 3 parts, sodium carbonate 0.1 part, boric acid 0.3 part.

[0077] The electron microscope image of the iron oxide powder prepared in this example is shown in Figure 1 .

[0078] Comparative Example 1

[0079] Compared with example 4, in step one of this comparative example, the induced draft fan is not arranged at the feeding end of the externally heated sectional rotary kiln, and the natural exhaust mode is adopted, and other conditions and steps are the same as in example 4.

[0080] At this time, the conversion rate of Fe2O3 of the iron oxide powder is 81.3%, the mass content of FeO is 5.6%, and the particle size is ≤5 μm. The calculation method of the conversion rate of Fe2O3 is (mass content of FeO before oxidation - mass content of FeO after oxidation) / mass content of FeO before oxidation x 100%.

[0081] Comparative Example 2

[0082] Compared with example 6, in step one of this comparative example, the iron powder is not subjected to multi-stage oxidation in the externally heated sectional rotary kiln, but is directly oxidized by heating, and other conditions and steps are the same as in example 4.

[0083] The parameter settings of the iron powder in the externally heated sectional rotary kiln are as follows:

[0084] The heating temperature is 750-850°C, and the residence time is 3h.

[0085] The Fe203 conversion rate of the fine iron oxide powder at this time is 89.3%, the FeO mass content is 3.2%, the particle size is less than or equal to 5 μm, and the Fe203 conversion rate is calculated as (mass content of FeO before oxidation - mass content of FeO after oxidation) / mass content of FeO before oxidation x 100%.

[0086] The electron microscope image of the fine iron oxide powder prepared in the present comparative example is shown in Figure 2. Figure 2 .

[0087] Comparative Example 3

[0088] Compared with Example 1, the residence time of the pre-burning in the rotary kiln in Step 3 of the present comparative example is 1 h at 600-900 °C, the combustion-supporting air volume is not increased, and the residual oxygen content in the tail gas is 6%. At this time, the loose bulk density of the dense granular material is 2.4 g / cm 3 , and the other conditions and steps are the same as in Example 1.

[0089] Comparative Example 4

[0090] Compared with Example 6, the input amount of the additive in Step 3 of the present comparative example is different, and the other conditions and steps are the same as in Example 1.

[0091] At this time, the additive includes calcium carbonate, calcium gluconate, and silicon powder, and the mass fractions of calcium carbonate, calcium gluconate, and silicon powder in the secondary continuous ball mill slurry are 0.8 wt%, 0.1 wt%, and 0.4 wt%, respectively.

[0092] The silicon content of the permanent magnet ferrite material prepared in the present comparative example is 0.45 wt% as detected by a fluorescence analyzer of Rigaku, Japan.

[0093] Comparative Example 5

[0094] Compared with Example 1, the mass fractions of the components of the mixture in Step 2 of the present comparative example are different, and the value of (molar amount of fine iron oxide powder + molar amount of cobalt oxide x 3 / 2) / (molar amount of strontium carbonate + molar amount of calcium carbonate + molar amount of lanthanum oxide x 2) is 5.59, and the other conditions and steps are the same as in Example 1. The mass fractions of the components of the mixture are as follows:

[0095] Fine iron oxide powder 86 parts, strontium carbonate 2.0 parts, calcium carbonate 3.5 parts, lanthanum oxide 9.5 parts, cobalt oxide 3.0 parts, sodium carbonate 0.2 parts, and boric acid 0.2 parts.

[0096] Comparative Example 6

[0097] Compared with Example 1, the mass fractions of the components of the mixture in Step 2 of the present comparative example are different, the value of (molar amount of iron oxide fine powder + 3 / 2 molar amount of cobalt oxide) / (molar amount of strontium carbonate + molar amount of calcium carbonate + 2 molar amount of lanthanum oxide) is 4.82, and other conditions and steps are the same as those of Example 1. The mass fractions of the components of the mixture are as follows:

[0098] Iron oxide fine powder 76 parts, strontium carbonate 2.3 parts, calcium carbonate 4.5 parts, lanthanum oxide 7 parts, cobalt oxide 1.2 parts, sodium carbonate 0.2 parts, and boric acid 0.2 parts.

[0099] Comparative Example 7

[0100] Compared with Example 1, the mass fractions of the components of the mixture in Step 2 of the present comparative example are different, the value of (molar amount of iron oxide fine powder + 3 / 2 molar amount of cobalt oxide) / (molar amount of strontium carbonate + molar amount of calcium carbonate + 2 molar amount of lanthanum oxide) is 5.55, and other conditions and steps are the same as those of Example 1. The mass fractions of the components of the mixture are as follows:

[0101] Iron oxide fine powder 76 parts, strontium carbonate 1.8 parts, calcium carbonate 3.6 parts, lanthanum oxide 6.8 parts, cobalt oxide 1.2 parts, sodium carbonate 0.2 parts, and boric acid 0.2 parts.

[0102] The permanent magnet ferrite materials prepared in Examples 1-6 and Comparative Examples 1-7 were detected, and the results are shown in Table 1:

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from Table 1, in the examples, by adjusting the molar ratio value in the mixture and optimizing the formula proportion, the residual magnetism of the permanent magnet ferrite is ≥4350Gs, and the intrinsic coercive force is ≥5400Oe. In Comparative Example 1, the iron fine powder is not naturally oxidized under negative pressure environment, and the FeO content in the oxidized iron fine powder is 5.6% detected by chemical titration method, which is too high, and the subsequent process cannot completely oxidize it, thereby reducing the performance; in Comparative Example 2, the iron fine powder is not subjected to multi-stage oxidation in the rotary kiln, and the FeO content in the oxidized iron fine powder is 5.6% detected by chemical titration method, which is too high, and the subsequent process cannot completely oxidize it, thereby reducing the performance; in Comparative Example 3, the iron fine powder is not subjected to multi-stage oxidation in the rotary kiln, and the FeO content in the oxidized iron fine powder is 5.6% detected by chemical titration method, which is too high, and the subsequent process cannot completely oxidize it, thereby reducing the performance; in Comparative Example 4, the iron fine powder is not subjected to multi-stage oxidation in the rotary kiln, and the FeO content in the oxidized iron fine powder is 5.6% detected by chemical titration method, which is too high, and the subsequent process cannot completely oxidize it, thereby reducing the performance; in Comparative Example 5, the iron fine powder is not subjected to multi-stage oxidation in the rotary kiln, and the FeO content in the oxidized iron fine powder is 5.6% detected by chemical titration method, which is too high, and the subsequent process cannot completely oxidize it, thereby reducing the performance; and in Comparative Example 6, the iron fine powder is not subjected to multi-stage oxidation in the rotary kiln, and the FeO content in the oxidized iron fine powder is 5.6% detected by chemical titration method, which is too high, and the subsequent process cannot completely oxidize it, thereby reducing the performance. Figure 1 and Figure 2The SEM images of the iron oxide fine powder obtained by the multi-stage oxidation show that the microstructure of the iron oxide fine powder is flocculent and the activity is good, while the microstructure of the iron oxide fine powder not obtained by the multi-stage oxidation is granular and the activity is poor, resulting in the performance reduction; in the Comparative Example 3, the residence time is not prolonged and the combustion air volume is not increased at 600-900℃ in the pre-burning stage, and the residual oxygen content in the tail gas is too low (6%), resulting in that the residual FeO cannot be completely oxidized, thereby resulting in the performance reduction; in the Comparative Example 4, the silicon content in the prepared permanent magnet ferrite material is 0.45% detected by the fluorescence analyzer of Japan Risheng, which exceeds 0.4%, and the excess silicon leads to the generation of silicates, which will combine with calcium and strontium in the ferrite material to precipitate, resulting in the performance deterioration; in the Comparative Examples 5-7, the molar ratio is out of the range of 4.9-5.5 during the batching, resulting in the deviation of the composition structure of the ferrite material and the performance reduction.

[0107] It should be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, 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 only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0108] Although the embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to the 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 method of producing a permanent ferrite magnet, characterized by, The method comprises the following steps: Step one, the iron powder is placed in an externally heated segmented rotary kiln, and is dried and subjected to multi-stage oxidation under negative pressure. After cooling and discharging, the iron powder is subjected to one-stage grinding and mixing to obtain an oxidized iron powder, the conversion rate of Fe2O3 in the oxidized iron powder is ≥96%, the mass content of FeO is ≤1.2%, and the particle size is ≤5 μm; Step two, the oxidized iron powder, strontium carbonate, calcium carbonate, lanthanum oxide, cobalt oxide, sodium carbonate and boric acid are uniformly mixed to obtain a mixture, and the mixture is mixed with water, and then subjected to two-stage grinding to obtain a slurry; Step three, the slurry is dewatered and concentrated to obtain a concentrated slurry with a solid content of 65-85%, the concentrated slurry is pre-burned in a rotary kiln to obtain dense granular material with a loose bulk density of 2.5-3.0 g / cm 3 After dry ball milling, 4-6 μm pre-burned material is obtained, which is mixed with water at a mass ratio of 1:1-2.3, additives are added for secondary continuous ball milling to obtain fine slurry with an average particle size of 0.8-1.1 μm; Step four, the fine slurry is concentrated to a solid content of 65-75%, and then is formed into a shaped body under a magnetic field. The shaped body is sintered in air, the sintering temperature is 1190-1240 ℃, and the sintering is performed for 2-4 h to obtain a permanent magnet ferrite material; In step one, the parameters of the iron powder in the externally heated segmented rotary kiln are as follows: The first heating stage: 250-350 ℃, the second heating stage: 350-550 ℃, the third heating stage: 550-650 ℃, the fourth heating stage: 650-750 ℃, and the fifth heating stage: 750-850 ℃; The iron powder stays in the first heating stage and the third heating stage for 0.5-1 h, stays in the fifth heating stage for 1-3 h, and stays in the second heating stage and the fourth heating stage for less than 0.5 h each; In step two, the mass fractions of the components of the mixture are as follows: Oxidized iron powder: 80-84 parts, strontium carbonate: 0.5-3 parts, calcium carbonate: 4-5 parts, lanthanum oxide: 7-9 parts, cobalt oxide: 1.5-3 parts, sodium carbonate: 0-0.3 parts, and boric acid: 0-0.3 parts; The value of (molar amount of oxidized iron powder + molar amount of cobalt oxide × 3 / 2) / (molar amount of strontium carbonate + molar amount of calcium carbonate + molar amount of lanthanum oxide × 2) is 4.9-5.

5.

2. A method of making a permanent ferrite magnet according to claim 1, wherein, The iron powder is a 200-mesh undersize product, the content of Fe element in the composition is 70-72 wt%, the content of FeO is 28-31 wt%, the content of SiO2 is ≤0.35 wt%, and the water content is 0-12 wt%.

3. The method for preparing a permanent magnet ferrite according to claim 1, characterized in that, In step one, the negative pressure is -30 to -5 Pa.

4. The method for preparing a permanent magnet ferrite according to claim 1, characterized in that, In step two, the particle size of the slurry is tested by the air permeation method, the particle size is ≤1.5 μm, and the 200-mesh standard sieve oversize is ≤0.5%.

5. The method for preparing a permanent magnet ferrite according to claim 1, characterized in that, The settings of the pre-sintering of the concentrated slurry in the rotary kiln are as follows: The concentrated slurry stays in the temperature stage of 600-900 ℃ for 2-3 h, and stays in the temperature stage of 1100-1250 ℃ for 0.5-2 h.

6. The method of claim 1, wherein the permanent ferrite is prepared by the steps of: In step three, the additives include calcium carbonate, calcium gluconate and silicon powder, and the mass fractions of the three in the two-stage continuous ball milling slurry are as follows: ​ Calcium carbonate: 0.4-1.0%, calcium gluconate: 0.05-0.4%, and silicon powder: 0-0.35%.

7. The method of claim 1, wherein the permanent ferrite is prepared by the steps of: In step four, the magnetic field strength of the magnetic field is ≥7000 Oe. ​ 8. The method of claim 1, wherein the permanent ferrite is prepared by the steps of: The silicon content of the permanent magnet ferrite material is ≤0.4 wt%. ​

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