A liquid doping method for preparing a hexagonal M-type strontium ferrite block

Abstract

The application discloses a liquid doping preparation method of a hexagonal system M-type strontium ferrite block, relates to the technical field of permanent ferrite preparation, and aims at solving the problems of uneven distribution of dopants, formation of impurities and high energy consumption of sintering complexity caused by solid-state direct doping. The application comprises the following steps: taking Fe(NO3)9H2O, Sr(NO3)2 and NaOH as raw materials, and preparing strontium ferrite powder by a hydrothermal method; adding C8H20O4Si-anhydrous ethanol dispersion liquid into the nano strontium ferrite powder, grinding uniformly, completing doping, pressing into shape, sintering, cooling and obtaining a strontium ferrite block product; the application adopts liquid C8H 20 O4Si doping, the amount of which is less than that of directly doped solid-state silicon dioxide, so that the cost can be reduced; the strontium ferrite powder is prepared by the hydrothermal method, the crystal grains are small, uniform and active, and the sintering can be completed at a lower temperature; and the product prepared by the application is free of impurities, has good grain dispersity and excellent magnetic performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of preparation of permanent magnets, in particular to a liquid doping preparation method of hexagonal crystal system M-type strontium ferrite blocks. BACKGROUND

[0002] As a kind of permanent magnet material, strontium ferrite has a stable hexagonal magnetoplumbite structure, high coercivity, excellent chemical stability, high Curie temperature and high resistivity. At the same time, the raw materials are cheap and abundant, and strontium ferrite has been widely used in various fields such as communication technology, medical devices, automobile industry and energy development. With the rapid development of the electronic information era and the advent of the new energy era, the performance of strontium ferrite must be improved to meet the needs of production and life. At present, the industry usually adopts ion doping or changes the synthesis method to seek the improvement of the performance of strontium ferrite, but the current two methods have encountered a bottleneck in the improvement of magnetic properties, and a new method is urgently needed to improve the performance of strontium ferrite.

[0003] Traditional strontium ferrite doping generally directly adds solid compounds (such as SiO2, Al2O3 or kaolin, etc.) to SrM, and then directly sintering. But this method generally brings problems such as uneven distribution of dopants and formation of impurities to the strontium ferrite, and the magnetic properties of the obtained sample often cannot meet the expectation. In the paper J.Alloy.Compd.860 (2021) 157890, the grain growth inhibition process of strontium ferrite powder doped with SiO2 after sintering is studied, and it is found that SiO2 can effectively inhibit the excessive growth of grains and reduce the growth rate of grains, thereby enhancing the coercivity of the ceramic dense sample, but with the increase of the amount of SiO2 doping, obvious alpha-Fe2O3 impurities will appear in the strontium ferrite, which will greatly affect the magnetic properties of the sample; In the invention patent with the publication number CN105060870B and the name of a preparation method of high coercivity hexagonal strontium ferrite, Dechang Ceng et al. added Al2O3 to the primary pre-sintering material of strontium ferrite, and the research showed that the more the amount of Al ion doping, the greater the coercivity of the sample, but the more serious the lattice distortion of the sample; In the invention patent application with the publication number CN112500148A and the name of a preparation method of high coercivity strontium ferrite magnetic material, Delin Qu et al. used modified kaolin to prepare strontium ferrite, and the strontium ferrite prepared by this method had high coercivity and high remanence performance, but the sintering process was complex and the sintering temperature was high, reaching 1320℃, which had high energy consumption.

[0004] In summary, a liquid doping preparation method of hexagonal crystal system M-type strontium ferrite blocks is urgently needed to solve these problems. SUMMARY

[0005] The application aims to provide a liquid doping preparation method of a hexagonal crystal system M-type strontium ferrite block, so as to solve the problems of uneven distribution of dopants, formation of impurities and high energy consumption of sintering caused by solid-state direct doping.

[0006] To achieve the above object, the application provides the following technical scheme: a liquid doping preparation method of a hexagonal crystal system M-type strontium ferrite block, comprising the following specific steps:

[0007] Step one: pure Fe(NO3)9H2O and Sr(NO3)2 are dissolved in deionized water to prepare a mixed nitrate solution, and pure NaOH solution is added dropwise into the mixed nitrate solution while stirring, and the stirring is continued until the reaction is completed after the dropwise addition is completed;

[0008] Step two: the slurry obtained in step one is moved into the inner container of a reaction kettle for heating, and the temperature is raised to the set temperature and kept for a sufficient time, and then the furnace is cooled to room temperature;

[0009] Step three: after the solution obtained in step two is poured out, the remaining part is moved into a centrifuge, and is washed with dilute hydrochloric acid by centrifugation for multiple times, and then is washed with distilled water by centrifugation for multiple times, and then is washed with anhydrous ethanol until the pH value is neutral, the supernatant is poured out after each centrifugation, and finally the strontium ferrite powder is obtained by drying;

[0010] Step four: the dried strontium ferrite powder is put into a mortar for grinding to obtain dispersed SrM ferrite nanopowder;

[0011] Step five: a certain amount of SrM ferrite nanopowder is taken, C8H 20 O4Si is dispersed with anhydrous ethanol, and then a to-be-doped amount is added to the SrM ferrite nanopowder, and is fully ground to be uniform;

[0012] Step six: the powder mixture after grinding in step five is placed in a mold for compression molding;

[0013] Step seven: after the sample compressed in step six is sintered at a set temperature in a muffle furnace, the strontium ferrite block product is obtained by furnace cooling.

[0014] Preferably, in step one, the molar ratio of Fe 3+ / Sr 2+ is 4, the molar ratio of OH - / NO3 - is 3.

[0015] In the above preferred scheme, preferably, the stirring is continued for 10-30 min after the dropwise addition of the NaOH solution is completed.

[0016] Preferably, in step two, the reaction kettle containing the slurry is heated to 220 DEG C in a forced air drying oven and kept for 6 h.

[0017] Preferably, in the step three, the dilute hydrochloric acid is a dilute hydrochloric acid solution prepared by mixing 25ml of hydrochloric acid into 475ml of deionized water.

[0018] Preferably, in the step three, the centrifugal washing is performed by using a high-speed centrifuge at 6000r / min for 5min each time, and the dilute hydrochloric acid, distilled water, and anhydrous ethanol are each centrifugally washed for 4 times. After the pH value is neutralized, the anhydrous ethanol is dried in a drying oven at 80℃ for 24h.

[0019] Preferably, in the step five, the C8H 20 O4Si is used for dispersing the product grains and improving the magnetic properties. 20 Preferably, the addition amount of C8H

[0020] Preferably, in the step six, the pressing pressure is 6MPa, and the pressing time is 5min.

[0021] Preferably, in the step seven, the heating rate is 5℃ / min, the sintering temperature is 1100-1200℃, and the calcination time is 2h.

[0022] Preferably, the strontium ferrite bulk product is a single-phase SrM ferrite without impurities, and the grains are hexagonal clusters, and the saturation magnetization is greater than 66emu / g.

[0023] Compared with the prior art, the method has the following beneficial effects:

[0024] 1. The liquid-state doping preparation method of the hexagonal crystal system M-type strontium ferrite bulk product uses anhydrous ethanol for dispersion, so that the doping amount is greatly reduced, which is beneficial to cost reduction and batch production. 20 O4Si is used for dispersion, and the distribution is more uniform, so that the product is a single-phase SrM ferrite without impurities, the grain dispersion is good, the magnetic properties are excellent, and the coercive force is relatively high.

[0025] 2. The liquid-state doping preparation method of the hexagonal crystal system M-type strontium ferrite bulk product uses the strontium ferrite nano-powder prepared by the hydrothermal method to prepare the bulk material, so that the grains are more fine and uniform, the particle purity is high, the dispersion is good, the reaction activity is higher, the sintering into a dense bulk can be performed at a lower temperature, and the sintering at a lower temperature is beneficial to the doping of the liquid-phase C8H 20 O4Si to obtain a product with better coercive force and saturation magnetization, which is beneficial to the further in-depth research and exploration of the liquid-phase doping. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Example 1: C8H20 XRD pattern of SrM ferrite sample of O4Si.

[0027] Figure 2 Example 1 with C8H 20 Room temperature hysteresis loop plot of SrM ferrite sample of O4Si.

[0028] Figure 3 Example 1 with C8H 20 Typical SEM morphology plot of SrM ferrite of O4Si.

[0029] Figure 4 Example 1 without C8H 20 XRD pattern of SrM ferrite comparative sample of O4Si.

[0030] Figure 5 Example 1 without C8H 20 Room temperature hysteresis loop plot of SrM ferrite comparative sample of O4Si.

[0031] Figure 6 Example 1 without C8H 20 Typical SEM morphology plot of SrM ferrite of O4Si.

[0032] Figure 7 Example 2 with C8H 20 XRD pattern of SrM ferrite sample of O4Si.

[0033] Figure 8 Example 2 with C8H 20 Room temperature hysteresis loop plot of SrM ferrite sample of O4Si.

[0034] Figure 9 Example 2 with C8H 20 Typical SEM morphology plot of SrM ferrite sample of O4Si.

[0035] Figure 10 XRD pattern of SrM ferrite comparative sample of Example 3 with varying sintering temperature.

[0036] Figure 11 Room temperature hysteresis loop plot of SrM ferrite comparative sample of Example 3 with varying sintering temperature.

[0037] Figure 12 Typical SEM morphology plot of SrM ferrite of Example 3 with varying sintering temperature. DETAILED DESCRIPTION

[0038] The present invention proposes the use of tetraethyl orthosilicate (C8H 20O4Si) instead of solid phase compound. Tetraethyl orthosilicate is a liquid substance which can be decomposed into SiO2, CO2 and H2O at high temperature. Since CO2 and H2O can be volatilized at high temperature, C8H 20 O4Si can be used as an additive of ferrite material instead of SiO2 to adjust the coercivity and other magnetic properties. Since liquid doping has good fluidity, C8H 20 O4Si can improve the non-uniformity of solid phase doping, thus playing a role in refining grains, pinning domain walls and modifying SrM ferrite. Based on long-term research and practice, the inventor has made important progress in the technology of liquid C8H 20 O4Si doping. The inventor uses the method of anhydrous ethanol dispersion to greatly reduce the doping amount, and uses SrM ferrite nano-powder prepared by hydrothermal method, which is beneficial to improve the magnetic properties of sintered magnets. The following embodiments further describe the technical solutions of the present application. The following embodiments are only a part of the examples of the present application.

[0039] Example 1

[0040] According to the requirements of strontium ferrite preparation by hydrothermal method, according to the foregoing steps, step one Fe 3+ / Sr 2+ atomic ratio of 4, OH - / NO3 -Molar ratio of 3, respectively, 3.23 g (8 mmol) Fe (NO3) 3·9H2O, 0.42 g (2 mmol) Sr (NO3) 2 and 3.36 g (84 mmol) NaOH. Fe (NO3) 3·9H2O and Sr (NO3) 2 were placed in 20 ml of deionized water, magnetic stirring for 20 min to completely dissolved. NaOH was dissolved in 30 ml of distilled water, and placed in an ultrasonic cleaner to completely dissolved. Then the NaOH solution was added dropwise to the nitrate solution under magnetic stirring, after the end of the dropwise, continue magnetic stirring for 20 min to complete the reaction. The above liquid was moved into the reactor inner and locked into the reactor, tighten the reactor, put into the air drying oven at 220 ℃ for 6 h, and then naturally cooled to room temperature. 25 ml of hydrochloric acid was measured and dissolved in 475 ml of deionized water to prepare a dilute hydrochloric acid solution. Carefully pour the supernatant in the reactor inner, and then pour the remaining mixture into a centrifuge tube, inject an appropriate amount of dilute hydrochloric acid solution, shake evenly. The solution in the centrifuge tube after shaking was centrifuged in a high speed centrifuge at 6000 r / min for 5 min, carefully pour the supernatant, pour into an appropriate amount of dilute hydrochloric acid and centrifuge again, repeat the centrifugation and pour the supernatant four times. Replace deionized water as the centrifugal liquid, repeat the centrifugation and pour the supernatant four times again. Replace anhydrous ethanol as the centrifugal liquid, centrifugal cleaning to pH neutral. Finally, after pouring the supernatant, the centrifuge tube with strontium ferrite attached to the wall was put into the drying oven, and the strontium ferrite powder was obtained by drying at 80 ℃ for 24 h. 1 g of the above obtained powder was weighed, and 0.2 wt% of C8H 20 O4Si was added. The specific adding process was: 2 g of C8H 20 O4Si (2.141 ml) was placed in a beaker, anhydrous ethanol was added to 20 ml to obtain a dilution solution, and 0.02 ml was added dropwise to the strontium ferrite powder, and grinded for 15 min. 0.2 g of the mixture after adding C8H 20 O4Si was weighed, and was pressed into a flat cylindrical sample with a diameter of 6 mm under a pressure of 6 MPa for 5 min. The sample was placed in a muffle furnace and heated to 1100 ℃ at a heating rate of 5 ℃ / min for 2 h, and then cooled to room temperature after sintering. The obtained was SrM ferrite sample. In addition, the SrM ferrite prepared by the above method without adding C8H 20 O4Si was used as a comparative sample, and other preparation conditions were unchanged.

[0041] The Figure 1 XRD pattern of the obtained SrM ferrite was attached, and compared with the XRD diffraction pattern of the pure M-type SrM ferrite standard card, no other impurity peak was found, indicating that the prepared sample was single-phase SrM ferrite. The Figure 2 room temperature hysteresis loop diagram of the obtained SrM ferrite showed that the sample exhibited typical hard magnetic characteristics, Hc 249.84 kA / m, saturation magnetization M s 66.70 emu / g. Fig. 2 Figure 3 is a typical SEM morphology diagram of the obtained SrM ferrite, from which it can be seen that the sample grain size is uneven at 0.8 pm, the grain boundary is clear, and the grains are hexagonal clusters.

[0042] Fig. 2 Figure 4 is a typical SEM morphology diagram of the obtained SrM ferrite, from which it can be seen that the sample grain size is uneven at 0.8 pm, the grain boundary is clear, and the grains are hexagonal clusters. 20 Fig. 3 is an XRD diffraction diagram of the SrM ferrite without adding C8H Figure 1 Fig. 3 is an XRD diffraction diagram of the SrM ferrite without adding C8H 20 O4Si does not introduce impurities. Compared with the paper J. Alloy. Compd. 860 (2021) 157890, direct addition of SiO2 is obviously improved. From Fig. 3 Figure 5 Fig. 4 is a room temperature hysteresis loop diagram of the sample, from which it can be seen that the coercive force H c 237.26 kA / m, which is 5.3% lower than that of the C8H 20 O4Si doped SrM ferrite. From Fig. 4 Figure 6 Fig. 5 is a SEM morphology diagram of the sample, from which it can be seen that the sample grain size is concentrated at about 1.2 pm, and the grains present a large number of agglomerations. Compared with Fig. 2 Figure 3 and Fig. 3, it is proved that C8H Figure 6 O4Si can well disperse the grains. 20 O4Si can well disperse the grains.

[0043] Example 2

[0044] In this example, the sample with C8H 20 O4Si is prepared in the same way as in Example 1, and the variable parameter is the amount of C8H 20 O4Si added, which is 0.4 wt%, specifically: take 0.04 ml of the C8H 20 O4Si-ethanol diluent prepared in Example 1 above, and uniformly drop it into the strontium ferrite powder, and grind for 15 min.

[0045] Fig. 6 Figure 7 is an XRD spectrum of the product obtained in this example, and there are no impurity diffraction peaks other than the SrM ferrite in the figure, indicating that a single-phase hexagonal M-type SrM ferrite is prepared. Fig. 3 Figure 8 Fig. 7 is a room temperature hysteresis loop diagram of the obtained sample, in which the saturation magnetization M s is basically unchanged (66.72 emu / g), and the coercive force H c increases to 258.03 kA / m. Fig. 4 Figure 9The image shows a typical SEM morphology of the obtained sample. The grains are fine and uniformly distributed. Compared to Example 1, this improvement is due to the increased addition of C8H... 20 The amount of O4Si resulted in smaller grain sizes compared to SrM ferrite prepared with 0.2 wt% tetraethyl orthosilicate, maintaining a size of approximately 0.9 μm, which is near the single-domain critical size of SrM ferrite. This is due to its H... c The main reason for the significant increase.

[0046] Example 3

[0047] In this embodiment, C8H is added. 20 The O4Si sample was prepared using the same method as in Example 2, except that the sintering temperature was changed to 1200℃.

[0048] Appendix Figure 10 The XRD pattern of the product obtained in this embodiment shows clear SrM ferrite characteristic peaks in the sample, compared with the attached... Figure 7 This also indicates the addition of C8H. 20 O4Si can suppress the formation of impurity phases. (See attached image) Figure 11 The obtained SrM ferrite has a room temperature hysteresis loop, and its coercivity H is shown. c and saturation magnetization M s The values ​​are 117.22 kA / m and 73.20 emu / g, respectively. (See attached table for comparison.) Figure 8 It can be seen that the coercivity H of the sample sintered at 1200℃ is greater than that of the sample sintered at 1100℃. c Significantly reduced, while saturation magnetization M s There was also a significant increase. (From the attached...) Figure 12 The SEM morphology images show that the sample grains are significantly larger and multiple grains are fused together, with the grain size concentrated at around 1.9 μm.

[0049] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0050] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A liquid doping method for preparing a hexagonal M-type strontium ferrite bulk, characterized by, The method comprises the following specific steps: Step 1: pure Fe(NO3)·9H2O and Sr(NO3)2 are dissolved in deionized water in proportion to prepare a mixed nitrate solution, and pure NaOH solution is added dropwise into the mixed nitrate solution while stirring, and the stirring is continued until the reaction is completed after the dropping is completed; Step 2: the slurry obtained in step 1 is moved into the inner container of a reaction kettle for heating, and the temperature is raised to the set temperature and kept for a sufficient time, and then the furnace is cooled to room temperature; Step 3: after the solution obtained in step 2 is poured out, the remaining part is moved into a centrifuge, and is cleaned by centrifugation with dilute hydrochloric acid for multiple times, and then is cleaned by centrifugation with distilled water for multiple times, and then is cleaned with anhydrous ethanol until the pH value is neutral, the upper clear liquid is poured out after each centrifugation, and finally the strontium ferrite powder is obtained by drying; Step 4: the dried strontium ferrite powder is put into a mortar for grinding to obtain dispersed SrM ferrite nano powder; Step five: take a certain amount of SrM ferrite nanopowder, disperse C8H 20 O4Si with anhydrous ethanol, and add the amount to be doped to the SrM ferrite nanopowder and grind thoroughly to uniformity; C8H 20 O4Si is used to disperse product grains and improve magnetic properties, C8H 20 O4Si in the SrM ferrite nanopowder is added in an amount of 0.2-0.4wt%. Step 6: the powder mixture after grinding in step 5 is placed in a mold for compression molding; Step 7: the sample after compression molding in step 6 is taken out and sintered in a muffle furnace at a set temperature, and then the furnace is cooled to obtain a strontium ferrite bulk product.

2. The method according to claim 1, wherein the method is characterized by: The step one, Fe 3+ / Sr 2+ Atomic ratio is 4, OH - / NO3 - Molar ratio is 3.

3. The method according to claim 2, wherein the liquid doping method for preparing a bulk hexagonal M-type strontium ferrite is characterized in that: In step 1, the stirring is continued for 10-30 min after the dropping of the NaOH solution is completed.

4. The method according to claim 1, wherein the method is characterized by: In step 2, the reaction kettle containing the slurry is heated to 220℃ and kept for 6 h in a forced air drying oven.

5. The method according to claim 1, wherein the method is characterized by: In step 3, the dilute hydrochloric acid is a dilute hydrochloric acid solution prepared by taking 25 ml of hydrochloric acid and dissolving in 475 ml of deionized water.

6. The method according to claim 1, wherein the method is characterized by: In step 3, the centrifugal cleaning is performed by using a high-speed centrifuge at 6000 r / min for 5 min each time, the dilute hydrochloric acid and the distilled water are each cleaned by centrifugation for 4 times, the anhydrous ethanol is cleaned by centrifugation until the pH value is neutral, and then the sample is dried in a drying oven at 80℃ for 24 h.

7. The method according to claim 1, wherein the method is characterized by: In step 6, the compression pressure is 6 MPa, and the compression time is 5 min.

8. The method according to claim 1, wherein the method is characterized by: In step 7, the temperature rising speed is 5℃ / min, the sintering temperature is 1100-1200℃, and the calcination time is 2 h.

9. The method according to claim 1, wherein the method is characterized by: The strontium ferrite bulk product is a single-phase SrM ferrite without impurities, the crystal grains of which are in the form of hexagonal groups, and the saturation magnetization thereof is greater than 66 emu / g.

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