Corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere and preparation method thereof

Abstract

The invention relates to a corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere and a preparation method thereof, and belongs to the technical field of refractory materials. The preparation method comprises the following steps: uniformly mixing a calcium raw material, an aluminum raw material and a magnesium raw material, adding a binding agent, and mixing to obtain a mixed raw material; granulating the mixed raw material to obtain spherical particles; mixing the aluminum raw material and the magnesium raw material; secondly, taking spherical particles as cores, and wrapping the powder mixed in the last step in the rotating process of the pelletizer, so as to form a heterogeneous spherical particle precursor rich in CaCO3; fully drying the obtained precursor spherical particles, calcining in a high-temperature furnace, and cooling along with the furnace to obtain the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere. The corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere prepared by the invention has the characteristics of light weight, good heat insulation property, high use temperature, excellent erosion resistance, high high-temperature strength and good melting point thermal shock resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory materials, and particularly relates to a corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere and a preparation method thereof. Background Art

[0002] With the rapid development of high-temperature industries, the demand for high-performance refractory materials is increasing day by day. Refractory materials not only need to have high strength, erosion resistance and high-temperature resistance, but also need to have low thermal conductivity to achieve efficient heat preservation and insulation effects, thereby reducing energy consumption and carbon emissions. Refractory materials with a hollow sphere structure have become a research hotspot in recent years because of their unique structural design, which can reduce the thermal conductivity of the material while maintaining high mechanical strength and erosion resistance. At present, the main methods for preparing ceramic hollow spheres include the template method and the electrofusion spraying method. The template method involves granulating using organic or inorganic templates (such as polyethylene spheres), and then preparing hollow spheres through processes such as slurry coating, drying, and plastic removal. For example, the invention patent CN116120044A provides a preparation method of an energy-saving and wear-resistant zircon corundum composite hollow sphere casting material. This method granulates using polyethylene spheres as templates, and the process involves slurry filtration and plastic removal of the spheres. Although it can prepare hollow sphere materials with excellent properties, the process is complex and time-consuming, and it is difficult to meet the requirements of large-scale production. On the other hand, the electrofusion spraying method prepares hollow spheres through high-temperature electrofusion and gas spraying, which has the advantages of high production efficiency and high strength of the hollow spheres. For example, Chen Zhening et al. (Chen Zhening, et al. Preparation, structure and properties of lightweight spinel hollow sphere ceramics [J]. Journal of Materials Science and Engineering, 2022, 40(03): 412~417+422) prepared magnesium aluminate spinel hollow sphere ceramics using the electrofusion spraying process. The obtained hollow spheres have high strength and high service temperature, but the electrofusion method has high energy consumption and it is difficult to realize the advantages of a gradient composite structure.

[0003] As an important structural ceramic material, corundum has broad application prospects in the field of high-temperature structural materials due to its high melting point, high hardness, excellent chemical stability and wear resistance. However, the inherent brittleness and poor thermal shock resistance of corundum ceramics limit its further application, especially in an environment of rapid temperature change and thermal shock, where cracking and failure are likely to occur. CMA (calcium magnesium aluminum high-temperature oxide) has the advantage of strong erosion resistance, but the disadvantage is that the preparation process is complex and requires precise control of composition and sintering process. Magnesium aluminate spinel has good thermal shock resistance, high chemical stability and low thermal conductivity, but the disadvantages are lower hardness, worse wear resistance than corundum, limited mechanical strength, lower compressive strength and flexural strength than corundum, and higher preparation cost. The preparation processes such as the electrofusion method have high energy consumption. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres aiming at the deficiencies existing in the above-mentioned prior art. The corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared by the present invention have the characteristics of light weight, good heat insulation, high service temperature, excellent erosion resistance, high high-temperature strength, and good melting point and thermal shock resistance. The process adopted by the present invention is simple and easy to implement, and no harmful gases are generated during the production process, which is beneficial to environmental protection.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method of corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres, comprising the following steps: Step 1, mixing calcium raw materials, aluminum raw materials and magnesium raw materials evenly, and performing homogenization and fine grinding to 325 mesh, adding a binder for kneading to obtain a mixed raw material; Step 2, granulating the mixed raw material in Step 1 to obtain spherical particles; Step 3, mixing aluminum raw materials and magnesium raw materials; Step 4, using the spherical particles obtained in Step 2 as the core, and wrapping the powder mixed in Step 3 during the rotation of the granulator to form a heterogeneous spherical particle precursor rich in CaCO3 inside; Step 5, fully drying the obtained precursor spherical particles, calcining them in a high-temperature furnace, and obtaining the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres after cooling with the furnace.

[0006] Furthermore, the mass percentages of the calcium raw materials, aluminum raw materials, and magnesium raw materials in Step 1 are respectively: 50-60%, 30-40%, 10-20%, and the binder is 4-6 wt% of the sum of the above raw materials.

[0007] Furthermore, the calcium raw materials in Step 1 are taken from one or two of nano calcium carbonate, light calcium carbonate, calcium hydroxide or limestone, and the particle size is ≤0.074 mm.

[0008] Furthermore, the binder in Step 1 is any one of sulfite pulp waste liquor, dextrin, methyl cellulose, polyvinyl alcohol or silica sol.

[0009] Furthermore, the spherical particles in Step 2 are 0.2-0.9 mm.

[0010] Furthermore, the mass percentages of the aluminum raw materials and magnesium raw materials in Step 3 are respectively: 90-100%, 0-10%.

[0011] Further, the aluminum raw materials in the step 1 and step 3 are taken from any one or two of industrial alumina, γ-alumina, α-alumina, and calcined corundum; the magnesium raw materials are taken from one or two of magnesite, light-burned magnesia, high-calcium magnesia sand, or basic magnesium carbonate; the particle sizes of the above raw materials are all ≤ 0.074 mm.

[0012] Further, in the step 5, the calcination is carried out according to the diffusion reaction characteristics of the raw materials to formulate a heating system, that is, it is kept at 1400 - 1450 °C for 1 - 3 hours, and then heated to 1650 - 1700 °C for calcination for 5 - 7 hours.

[0013] Further, the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared by the preparation method have a hollow structure, the composition of the spherical shell is controllable and has a gradient composite structure, that is, the spherical shell is composed of corundum phase, corundum-CMA phase, and CMA-magnesium aluminate spinel phase from the outside to the inside.

[0014] Further, the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres can meet the long-term use in a high-temperature working layer of ≥ 1650 °C.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention adopts a reactive sintering in-situ pore-forming technology process, avoiding the complex process and high energy consumption problems of the traditional template method or electro-fusion spraying method, improving the preparation efficiency of refractory hollow spheres, reducing energy consumption, and meeting the requirements of green manufacturing and sustainable development.

[0016] 2. The present invention combines corundum, CMA, and magnesium aluminate spinel to construct a gradient structure material, which can give full play to the advantages of each material, make up for the deficiencies of single materials, and form a phase gradient composite material with excellent performance.

[0017] 3. The cavity structure inside the hollow spheres prepared by the present invention effectively reduces the thermal conductivity of the material, improves the heat insulation performance, and helps to reduce the energy consumption of high-temperature facilities.

[0018] 4. The corundum phase on the outer layer of the hollow sphere shell prepared by the present invention provides high hardness and excellent wear resistance; the middle layer CMA phase enhances the erosion resistance and chemical stability of the material; the inner layer magnesium aluminate spinel phase provides high strength and thermal shock resistance, enhancing the thermo-mechanical properties of the hollow sphere material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the microstructural and energy spectrum distribution diagrams of Al, Ca, and Mg elements of the cross-section of the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared in Example 1 of the present invention; Figure 2 It is the cross-section and inner side microstructural diagrams of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere shell prepared in Example 2 of the present invention; Figure 3 XRD diffraction pattern of the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared in Example 3 of the present invention. Detailed implementation manners

[0020] The technical solutions and effects of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0021] The raw materials used in the following examples are all commercially available products. Among them, the purity of the light burned magnesite is 98.05%, the purity of the magnesite is 47.28%, the mass ratio of MgO in the high calcium magnesite is 95.12%, the mass ratio of CaO is 3.14%, and the mass ratio of SiO2 is 0.40%. Example 1

[0022] This example provides a method for preparing corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres, including the following steps: Step 1: Mix 54% of light calcium carbonate, 32% of γ-Al2O3, and 14% of light burned magnesite by mass percentage evenly, homogenize and finely grind to 325 mesh, and add 4% of methyl cellulose binder based on the sum of the above raw materials for kneading to obtain a mixed raw material; Step 2: Place the mixed raw material obtained in Step 1 in a disk granulator for granulation to obtain spherical particles with a size of 0.2 - 0.8 mm; Step 3: Mix 90 wt% of γ-Al2O3 raw material and 10 wt% of light burned magnesia raw material; Step 4: Using the spherical particles obtained in Step 2 as the core, during the rotation of the disk granulator, coat the alumina-based raw material and magnesia-based mixed powder in Step 3 to form a heterogeneous spherical particle precursor rich in CaCO3 inside; Step 5: Dry the obtained precursor spherical particles sufficiently, calcine them in a high-temperature furnace at 1400 °C for 2 hours and then raise the temperature to 1700 °C for 5 hours, and cool them with the furnace to obtain the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres.

[0023] The microstructural cross-section and energy spectrum distribution diagrams of Al, Ca, and Mg elements of the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared in this example are as Figure 1 shown. It can be seen from Figure 1 that the spherical particles have a hollow structure, and the element distribution of the hollow spherical shell shows a three-layer distribution structure. The Al element is distributed throughout the spherical shell, the Ca element is mainly enriched in the middle of the spherical shell, the Mg element is mainly enriched on the inner side of the spherical shell, and a small part is distributed in the middle and outer sides of the spherical shell; the refractoriness of the prepared hollow spheres is ≥1850 °C, and the service temperature is ≥1650 °C. Example 2

[0024] This embodiment provides a method for preparing corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres, which includes the following steps: Step 1: Mix 50% calcium hydroxide, 30% γ-Al2O3, and 20% magnesite evenly by mass percentage, homogenize and finely grind them to 325 mesh, and add 5% dextrin binder based on the sum of the above raw materials for kneading to obtain a mixed raw material; Step 2: Place the mixed raw material in Step 1 into a disk granulator for granulation to obtain spherical particles with a size of 0.3 - 0.9 mm; Step 3: Mix 95 wt% α-Al2O3 raw material and 5 wt% light-burned magnesia raw material; Step 4: Using the spherical particles obtained in Step 2 as the core, wrap the alumina-based raw material and magnesia-based mixed powder in Step 3 during the rotation of the disk granulator to form a heterogeneous spherical particle precursor rich in CaCO3 inside; Step 5: Dry the obtained precursor spherical particles sufficiently, calcine them in a high-temperature furnace at 1450 °C for 1 hour and then raise the temperature to 1680 °C for 6 hours of heat preservation, and cool them with the furnace to obtain the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres.

[0025] The cross-section and inner side microstructure diagram of the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared in this embodiment are as shown in Figure 2 shown. The prepared hollow sphere shell has a gradient composite structure, that is, the shell from the outside to the inside is corundum phase, corundum-CMA phase, and CMA-magnesium aluminate spinel phase respectively. The inner side of the shell is mainly rhombic magnesium aluminate spinel, which improves the high-temperature mechanical properties of the material; the middle layer is mainly relatively dense CMA, which can improve the erosion resistance of the material; the outer side is mainly corundum layer, which ensures the high-temperature wear resistance of the material. The prepared hollow spheres have a refractoriness ≥ 1850 °C and a service temperature ≥ 1650 °C. Example 3

[0026] This embodiment provides a method for preparing corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres, which includes the following steps: Step 1: Mix 55% limestone, 35% industrial alumina, and 10% high-calcium magnesia sand evenly by mass percentage, homogenize and finely grind them to 325 mesh, and add 5% dextrin binder based on the sum of the above raw materials for kneading to obtain a mixed raw material; Step 2: Place the mixed raw material in Step 1 into a disk granulator for granulation to obtain spherical particles with a size of 0.2 - 0.7 mm; Step 3: Mix 92 wt% γ-Al2O3 raw material and 8 wt% light-burned magnesia raw material; Step 4: Using the spherical particles obtained in Step 2 as nuclei, during the rotation of the disk granulator, coat them with the alumina-based raw material and magnesia-based mixed powder in Step 3 to form a heterogeneous spherical particle precursor rich in CaCO3 inside; Step 5: Thoroughly dry the obtained precursor spherical particles, calcine them in a high-temperature furnace at 1450 °C for 1 hour and then raise the temperature to 1650 °C and hold for 6 hours, and cool them with the furnace to obtain the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres. The refractory degree of the prepared hollow spheres is ≥1850 °C, and the service temperature is ≥1650 °C.

[0027] The XRD diffraction pattern of the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared in this example is as Figure 3 shown. The main crystal phase of the outer layer of the hollow spheres is corundum, the middle layer is mainly CMA, which is C2M2A 14 , calcium magnesium aluminate-based high-temperature complexes such as CA6 and CA2, and the main crystal phase of the inner layer is magnesium aluminate spinel, which can make up for the deficiencies of a single material phase.

[0028] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres, characterized in that, The preparation method includes the following steps: Step 1: Mix the calcium raw material, aluminum raw material, and magnesium raw material evenly, homogenize and finely grind them to 325 mesh, and add a binder for kneading to obtain a mixed raw material; Step 2: Granulate the mixed raw material obtained in Step 1 to obtain spherical particles; Step 3: Mix the aluminum raw material and the magnesium raw material; Step 4: Using the spherical particles obtained in Step 2 as the core, during the rotation of the granulator, wrap the powder mixture obtained in Step 3 to form a heterogeneous spherical particle precursor rich in CaCO3 inside; Step 5: Thoroughly dry the obtained precursor spherical particles, calcine them in a high-temperature furnace, and cool them with the furnace to obtain the corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres.

2. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1, characterized in that In Step 1, the mass percentages of the calcium raw material, aluminum raw material, and magnesium raw material are respectively: 50-60%, 30-40%, 10-20%, and the binder is 4-6 wt% of the sum of the above raw materials.

3. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1 or 2, characterized in that, In Step 1, the calcium raw material is taken from one or two of nano-calcium carbonate, light calcium carbonate, calcium hydroxide, or limestone, and the particle size is ≤0.074 mm.

4. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1, characterized in that In Step 1, the binder is any one of sulfite pulp waste liquor, dextrin, methyl cellulose, polyvinyl alcohol, or silica sol.

5. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1, characterized in that, The spherical particles in Step 2 are 0.2-0.9 mm.

6. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1, characterized in that, In Step 3, the mass percentages of the aluminum raw material and the magnesium raw material are respectively: 90-100%, 0-10%.

7. The preparation method of the corundum - CMA - magnesium aluminate spinel gradient composite hollow sphere according to claim 1, characterized in that, In Step 1 and Step 3, the aluminum raw material is taken from any one or two of industrial alumina, γ-alumina, α-alumina, or calcined corundum; the magnesium raw material is taken from any one or two of magnesite, light-burned magnesia, high-calcium magnesite, or basic magnesium carbonate; the particle sizes of the above raw materials are all ≤0.074 mm.

8. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1, characterized in that, In Step 5, the calcination is carried out according to the diffusion reaction characteristics of the raw materials to formulate a heating system, that is, keep the temperature at 1400-1450 °C for 1-3 hours, and then raise the temperature to 1650-1700 °C for calcination for 5-7 hours.

9. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 1, wherein, The corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres prepared by the preparation method have a hollow structure, the composition of the spherical shell is controllable and shows a gradient composite structure, that is, the spherical shell is composed of corundum phase, corundum-CMA phase, and CMA-magnesium aluminate spinel phase from the outside to the inside.

10. The preparation method of the corundum-CMA-magnesium aluminate spinel gradient composite hollow sphere according to claim 9, characterized in that, The corundum-CMA-magnesium aluminate spinel gradient composite hollow spheres can meet the long-term use in a high-temperature working layer of ≥1650 °C.

Images