A magnetic material and a preparation method thereof

Abstract

The present invention discloses a magnetic material and a preparation method thereof, wherein the material composition is Ni 0.2 Cu 0.1 Co 0.7 Fe 1.97 Al 0.03 O4, with a three-dimensional interconnected porous structure, exhibits a porosity of 45-60%, a saturation magnetization of 28.65-31.22 emu / g, and a coercivity of 625.6-722.4 Oe. This material is prepared using a "template pretreatment-precision introduction-gradient sintering" process: polyvinyl alcohol (PVA-1788) is ultrasonically pretreated with an ethanol-water solution to improve compatibility and then precisely added dropwise at the initial gelation stage. The template is then removed using an alcohol lamp at low temperature and crystallized using a resistance furnace at high temperature, forming a porous structure. This material combines high porosity with excellent magnetic properties, making it suitable for applications in adsorption, catalysis, and other fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic material preparation, and in particular relates to a magnetic material and a preparation method thereof. Background Art

[0002] Nanoferrite materials, with their unique combination of magnetic properties, chemical stability, and tunable surface characteristics, demonstrate irreplaceable potential for application in modern industrial and environmental fields, including magnetic separation, catalytic supports, and microwave absorption. Multi-element doped ferrites (such as Ni-Cu-Co-based ferrites) have become a research hotspot in recent years, as they can effectively optimize key magnetic properties such as saturation magnetization and coercivity through the synergistic effects of metal ions.

[0003] However, the materials prepared by traditional methods have dense structures, porosity less than 10%, and specific surface area usually less than 20m 2 / g, and the pores are isolated and poorly connected, which makes it impossible to achieve efficient material transfer and cannot meet the needs of high-activity interfacial reactions, limiting its application in adsorption, catalysis and other fields that require high-activity surfaces.

[0004] On the other hand, in the existing technology, commonly used pore-forming agents are mostly carbon powder, high molecular polymers, etc., but the carbon powder is large in size, and the pores formed are too large, which affects the strength of the material. In addition, the pores are scattered and disorderly, and it is impossible to construct a regular network interconnected structure, which will also reduce the mechanical strength of the material. When organic polymers (such as polyvinyl alcohol and polyethylene glycol) are selected as templates, due to the inherent conflict between the hydrophobicity of the polymer chain and the hydrophilicity of the metal salt solution, the two have extremely poor compatibility, and the template is prone to agglomeration, stratification or precipitation, resulting in the template being unable to be evenly embedded in the precursor, and ultimately it is difficult to form a network porous structure with uniform distribution and stable structure. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art and provide a magnetic material and a preparation method thereof. By optimizing the template pretreatment and introduction method, compatibility issues are overcome and a magnetic material with a porous network structure rich in pores is finally obtained.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a magnetic material, the steps of the preparation method are as follows:

[0008] Step 1: Prepare the raw materials: Add metal nitrate and citric acid into a beaker, then add distilled water and stir until completely dissolved to obtain a metal salt solution.

[0009] Step 2, gel preparation: add ammonia water dropwise to the metal salt solution to adjust the pH to 6.5-7.5; place the solution on a magnetic stirrer and stir at 80-85°C and 300-500 rpm. After 1 hour of stirring, add pretreated polyvinyl alcohol (model PVA-1788) at a rate of 1-3 drops / second. After the addition is complete, continue stirring for 2 hours.

[0010] Step 3, preliminary sintering: transfer the gel to a ceramic crucible and preheat it with an alcohol burner for 10-15 minutes, 6-10 cm away from the flame, and continue sintering until no smoke is generated. After cooling, grind it into a powder with a particle size of ≤100 μm;

[0011] Step 4, secondary sintering: placing the powder in a resistance furnace, heating it to 900-1000°C at a rate of 5-8°C / min, keeping it at that temperature for 3-4 hours, cooling it naturally to room temperature, and then grinding it again to obtain a magnetic material;

[0012] The pretreatment in step 2 is to dissolve 0.1-0.3 g of polyvinyl alcohol (PVA-1788) in 10 mL of 5%-10% ethanol aqueous solution, and ultrasonically disperse for 40-60 minutes.

[0013] As a further preferred magnetic material.

[0014] Preferably, the metal nitrate in step 1 includes iron nitrate nonahydrate [Fe(NO3)3·9H2O], nickel nitrate hexahydrate [Ni(NO3)2·6H2O], copper nitrate trihydrate [Cu(NO3)2·3H2O], cobalt nitrate hexahydrate [Co(NO3)2·6H2O] and aluminum nitrate hexahydrate [Al(NO3)3·6H2O];

[0015] The added amounts of Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O and Al(NO3)3·6H2O were 1.97 mmol, 0.2 mmol, 0.1 mmol, 0.7 mmol and 0.03 mmol, respectively;

[0016] The molar ratio of citric acid to total metal ions in step 1 is 1.2-1.6:1;

[0017] The distilled water in step 1 is 40-60 mL.

[0018] The present invention also provides a magnetic material prepared according to the method for preparing the magnetic material.

[0019] The chemical composition of the magnetic material is Ni 0.2 Cu 0.1 Co 0.7Fe 1.97 Al 0.03 O4, Al 3+ Doping optimizes the lattice structure; the material is a three-dimensional interconnected porous structure with a porosity of 45~60%, a saturation magnetization of 28.65~31.22emu / g, and a coercive force of 625.6~722.4Oe.

[0020] The core innovation of this invention lies in the collaborative process of "template pretreatment ~ precise introduction ~ gradient sintering", which specifically includes:

[0021] Template pretreatment: Polyvinyl alcohol (PVA-1788) is ultrasonically dispersed in a low-concentration ethanol solution. The amphiphilicity of ethanol (soluble in both water and organic solvents) acts as a bridge to improve the compatibility between the polymer (hydrophobic) and the metal salt solution (hydrophilic). Furthermore, the mechanical force generated by ultrasonic vibrations breaks the forces between the polymer chains, effectively preventing template agglomeration and ensuring uniform dispersion in the solution.

[0022] Precise introduction: The template should be added dropwise at a low speed at the initial stage of gel formation (after stirring for 1 hour). At this time, the solution is in the critical stage of sol-to-gel transformation, the system viscosity is moderate, and the colloidal network is initially formed. The template can be evenly embedded in the colloidal network, avoiding uneven distribution or agglomeration of the template after the subsequent increase in gel viscosity.

[0023] Gradient sintering: Low-temperature (alcohol lamp) sintering can gradually remove the template and form initial pores inside the material; high-temperature (resistance furnace) sintering can promote the development of the crystal phase while inhibiting excessive particle growth, ultimately forming a porous structure.

[0024] The beneficial effects of the present invention compared to the prior art are:

[0025] (1) The prepared magnetic material has a three-dimensional interconnected porous structure with a porosity of 45-60%, which is a qualitative leap compared to traditional methods. The abundant interconnected pores provide efficient channels for material transport. The increased porosity also increases the specific surface area of ​​the material, thereby providing sufficient active sites. It is perfectly suitable for scenarios such as adsorption and catalysis that require highly active interfacial reactions, and overcomes the application limitations of traditional materials caused by their dense structure.

[0026] (2) While maintaining a high porosity, the material still maintains a saturation magnetization of 28.65~31.22emu / g and a coercive force of 625.6~722.4Oe, taking into account excellent magnetic properties and structural characteristics, and can meet the core requirements of magnetic properties in fields such as magnetic separation and microwave absorption.

[0027] (3) The innovative template pretreatment (ethanol-water dispersion + ultrasound) fundamentally solves the compatibility problem between the organic polymer template and the metal salt solution. Combined with the precise dripping at the initial stage of gel formation, it ensures that the template is evenly embedded in the precursor, and ultimately obtains a uniformly distributed and structurally stable porous structure, avoiding the common problems of agglomeration, stratification, and messy pores in traditional template methods.

[0028] (4) The gradient sintering process (low-temperature template removal + high-temperature crystallization phase) is easy to operate and can precisely control pore formation and crystal phase development, which not only ensures the integrity of the pore structure but also promotes the orderly growth of ferrite crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a scanning electron microscope image (SEM) of the magnetic material prepared in Example 1;

[0030] Figure 2 is a SEM image of the magnetic material prepared in Example 2;

[0031] Figure 3 is a SEM image of the magnetic material prepared in Example 3;

[0032] Figure 4 is an SEM image of the magnetic material sample in Comparative Example 1;

[0033] Figure 5 is an energy dispersive X-ray (EDX) spectrum of the magnetic sample in Example 1;

[0034] Figure 6 1 is the hysteresis loop of the magnetic materials in Examples 1 to 3 measured by a vibrating sample magnetometer (VSM). DETAILED DESCRIPTION

[0035] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the following detailed description of the specific embodiments of the present invention is given in conjunction with the following embodiments. The following is merely an example and illustration of the concept of the present invention. Those skilled in the art may make various modifications, additions, or substitute similar methods for the specific embodiments described, and as long as they do not deviate from the concept of the invention, they shall fall within the scope of protection of the present invention.

[0036] The above preparation method of the present invention is described below through specific examples and comparative examples.

[0037] Example 1

[0038] A method for preparing a magnetic material, comprising the following steps:

[0039] Step 1. Raw material preparation: Weigh 1.97 mmol Fe(NO3)3·9H2O, 0.2 mmol Ni(NO3)2·6H2O, 0.1 mmol Cu(NO3)2·3H2O, 0.7 mmol Co(NO3)2·6H2O, 0.03 mmol Al(NO3)3·6H2O, and 0.792 g of citric acid (with a total metal ion molar ratio of 1.2:1) into a beaker, add 40 mL of distilled water, and stir until completely dissolved to obtain a metal salt solution.

[0040] Step 2. Gel preparation: Add ammonia water to the metal salt solution to adjust the pH to 6.5; place the solution on a magnetic stirrer and stir at 80°C and 300 r / min. After 1 hour, add a pretreated polyvinyl alcohol (PVA~1788) template (pretreatment: 0.1g PVA dissolved in 10mL 5% ethanol aqueous solution, ultrasonic dispersion for 40 minutes) at a dropwise addition rate of 1 drop / second. Continue stirring for 2 hours until a viscous gel is formed.

[0041] Step 3: Preliminary sintering: Transfer the gel to a ceramic crucible and preheat it with an alcohol lamp for 10 min (6 cm from the flame). Continue sintering until no smoke is generated. After cooling, grind it into a powder with a particle size of ≤100 μm.

[0042] Step 4: Secondary sintering: Place the powder in a resistance furnace, heat it to 900°C at a rate of 5°C / min, keep it warm for 3 hours, cool it naturally to room temperature, and grind it again to obtain a magnetic material.

[0043] Example 2

[0044] A method for preparing a magnetic material, comprising the following steps:

[0045] Step 1. Raw material preparation: Weigh 1.97 mmol Fe(NO3)3·9H2O, 0.2 mmol Ni(NO3)2·6H2O, 0.1 mmol Cu(NO3)2·3H2O, 0.7 mmol Co(NO3)2·6H2O, 0.03 mmol Al(NO3)3·6H2O, and 0.924 g of citric acid (with a molar ratio of 1.4:1 to total metal ions) into a beaker, add 50 mL of distilled water, and stir until completely dissolved to obtain a metal salt solution.

[0046] Step 2, gel preparation: Add ammonia water dropwise to the metal salt solution to adjust the pH to 7.0; place the solution on a magnetic stirrer and stir at 82°C and 400 r / min. After 1 hour, add the pretreated PVA~1788 template (pretreatment: 0.2g PVA dissolved in 10mL 7% ethanol aqueous solution, ultrasonic dispersion for 50 minutes) dropwise at a drop rate of 2 drops / second. Continue stirring for 2 hours until a viscous gel is formed.

[0047] Step 3: Preliminary sintering: Transfer the gel to a ceramic crucible and preheat it with an alcohol lamp for 12 minutes (8 cm from the flame). Continue sintering until no smoke is generated. After cooling, grind it into a powder with a particle size of ≤100 μm.

[0048] Step 4, secondary sintering: Place the powder in a resistance furnace, heat it to 950°C at a rate of 6°C / min, keep it warm for 3.5 hours, cool it naturally to room temperature, and grind it again to obtain a magnetic material.

[0049] Example 3

[0050] A method for preparing a magnetic material, comprising the following steps:

[0051] Step 1. Raw material preparation: Weigh 1.97 mmol Fe(NO3)3·9H2O, 0.2 mmol Ni(NO3)2·6H2O, 0.1 mmol Cu(NO3)2·3H2O, 0.7 mmol Co(NO3)2·6H2O, 0.03 mmol Al(NO3)3·6H2O, and 1.056 g of citric acid (with a molar ratio of 1.6:1 to total metal ions) into a beaker, add 60 mL of distilled water, and stir until completely dissolved to obtain a metal salt solution.

[0052] Step 2. Gel preparation: Add ammonia water dropwise to the metal salt solution to adjust the pH to 7.5; place the solution on a magnetic stirrer and stir at 85°C and 500 r / min. After 1 hour, add the pretreated PVA~1788 template (pretreatment: 0.3g PVA dissolved in 10mL 10% ethanol aqueous solution, ultrasonic dispersion for 60 minutes) dropwise at a dropwise rate of 3 drops / second. Continue stirring for 2 hours until a viscous gel is formed.

[0053] Step 3: Preliminary sintering: Transfer the gel to a ceramic crucible and preheat it with an alcohol lamp for 15 minutes (10 cm away from the flame). Continue sintering until no smoke is generated. After cooling, grind it into a powder with a particle size of ≤100 μm.

[0054] Step 4: Secondary sintering: Place the powder in a resistance furnace, heat it to 1000°C at a rate of 8°C / min, keep it warm for 4 hours, cool it naturally to room temperature, and grind it again to obtain a magnetic material.

[0055] Comparative Example 1

[0056] The difference from Example 1 is that the pretreated polyvinyl alcohol (PVA-1788) template is added directly all at once.

[0057] Figures 1-3These are scanning electron microscope photos of the magnetic materials of Examples 1 to 3, respectively. It can be seen that the synthesized magnetic materials have a three-dimensional network structure with a large number of pores.

[0058] Figure 4 This is an SEM image of the magnetic material sample from Comparative Example 1. It can be seen that the porosity of the resulting magnetic material is disorganized, with agglomeration and uneven distribution. The porosity is significantly lower than that of Examples 1-3. This indicates that the pretreated polyvinyl alcohol (PVA-1788) template needs to be added slowly to form a three-dimensional network structure.

[0059] Table 1 shows the porosity of the magnetic materials prepared in Examples 1 to 3 and Comparative Example 1.

[0060]

[0061] As can be seen in the table, the porosity reaches 45-60%, a significant improvement compared to traditional methods. The abundant interconnected pores provide efficient channels for material transport. The increased porosity also increases the material's specific surface area, providing ample active sites. This makes it ideal for applications requiring highly active interfacial reactions, such as adsorption and catalysis, and overcomes the application limitations of traditional materials due to their dense structures.

[0062] The innovative template pretreatment (ethanol-water dispersion + ultrasound) fundamentally solves the compatibility problem between the organic polymer template and the metal salt solution. Combined with the precise dripping in the initial stage of gel formation, it ensures that the template is evenly embedded in the precursor, ultimately obtaining a uniformly distributed and structurally stable porous structure, avoiding the problems of agglomeration, stratification, and messy pores common in traditional template methods.

[0063] The gradient sintering process (low-temperature template removal + high-temperature crystal-promoting phase) is easy to operate and can precisely control pore formation and crystal phase development, which not only ensures the integrity of the pore structure but also promotes the orderly growth of ferrite crystals.

[0064] Figure 5 This is the energy dispersive X-ray (EDX) spectrum of the magnetic material sample in Example 1. It can be seen that the synthesized magnetic material contains elements such as Fe, Co, Ni, Cu, O and Al, and the element C is an element in the substrate.

[0065] Figure 6 1 is the hysteresis loop of the magnetic materials in Examples 1 to 3 measured by a vibrating sample magnetometer (VSM). It can be seen from the curve that the prepared materials have ferromagnetic characteristics.

[0066] Table 2 According to Figure 6 The saturation magnetization and coercive force of Examples 1 to 3 are listed.

[0067]

[0068] Table 2 shows that the saturation magnetization of the magnetic samples in Examples 1-3 ranges from 28.65 to 31.22 emu / g, and the coercivity ranges from 625.6 to 722.4 Oe. (2) While maintaining a high porosity, the material still maintains a saturation magnetization of 28.65 to 31.22 emu / g and a coercivity of 625.6 to 722.4 Oe, balancing excellent magnetic performance and structural characteristics, and can meet the core magnetic performance requirements of fields such as magnetic separation and microwave absorption.

Claims

1. A method for preparing a magnetic material, characterized in that: The following steps are involved: Step 1: Prepare the raw materials: Add metal nitrate and citric acid into a beaker, then add distilled water and stir until completely dissolved to obtain a metal salt solution. Step 2, gel preparation: add ammonia water dropwise to the metal salt solution to adjust the pH to 6.5-7.5; place the solution on a magnetic stirrer and stir at 80-85°C and 300-500 rpm. After 1 hour of stirring, add pretreated polyvinyl alcohol (model PVA-1788) at a rate of 1-3 drops / second. After the addition is complete, continue stirring for 2 hours. Step 3, preliminary sintering: transfer the gel to a ceramic crucible and preheat it with an alcohol burner for 10-15 minutes, 6-10 cm away from the flame, and continue sintering until no smoke is generated. After cooling, grind it into a powder with a particle size of ≤100 μm; Step 4, secondary sintering: placing the powder in a resistance furnace, heating it to 900-1000°C at a rate of 5-8°C / min, keeping it at that temperature for 3-4 hours, cooling it naturally to room temperature, and then grinding it again to obtain a magnetic material; The pretreatment in step 2 is to dissolve 0.1-0.3 g of polyvinyl alcohol (PVA-1788) in 10 mL of 5%-10% ethanol aqueous solution, and ultrasonically disperse for 40-60 minutes.

2. The method for preparing a magnetic material according to claim 1, wherein: The metal nitrates in step 1 include Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O and Al(NO3)3·6H2O.

3. The method for preparing a magnetic material according to claim 2, wherein: The added amounts of Fe(NO3)3·9H2O, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O and Al(NO3)3·6H2O were 1.97 mmol, 0.2 mmol, 0.1 mmol, 0.7 mmol and 0.03 mmol respectively.

4. The method for preparing a magnetic material according to claim 1, wherein: The amount of citric acid added in step 1 is 3.6-4.8 mmol; The distilled water in step 1 is 40-60 mL.

5. A magnetic material obtained by the method for preparing a magnetic material according to any one of claims 1 to 4.

6. The magnetic material according to claim 5, characterized in that The chemical composition of the magnetic material is Ni 0.2 Cu 0.1 Co 0.7 Fe 1.97 Al 0.03 O4, Al 3+ Doping optimizes the lattice structure; the material is a three-dimensional interconnected porous structure with a porosity of 45~60%, a saturation magnetization of 28.65~31.22emu / g, and a coercive force of 625.6~722.4Oe.

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