An eggshell-type magnesium aluminate spinel hollow sphere and a preparation method thereof

Abstract

The present invention discloses an eggshell-type magnesia-aluminum spinel hollow sphere and a preparation method thereof; after electrofused magnesia, activated alumina powder and an additive are ball-milled and premixed, using polystyrene spheres as spherical supports, phenolic resin solution is added, and according to the concentration of the phenolic resin solution and the stirring speed, the thickness of the resin layer on the surface of the polystyrene spheres is jointly controlled. By controlling the particle size of the ball-milled premix, the thickness of the shell layer is controlled; it is formed and sieved in a granulator, and then through steps such as drying and heat treatment, magnesia-aluminum spinel hollow spheres are synthesized at low temperature. The present invention uses inexpensive and easily obtainable raw materials, has the characteristics of low cost and simple preparation process, and the prepared magnesia-aluminum spinel hollow spheres have excellent high-temperature resistance.

Description

Technical Field

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

[0002] With the continuous increase in the demand for energy efficiency in the high-temperature industrial field, the research and development of refractory materials that can be directly applied to working linings and have high mechanical strength, high corrosion resistance, and low heat conduction performance have received extensive attention. Insulating refractory materials used near high-temperature regions will have better energy-saving effects. Therefore, on the premise of ensuring that their performance meets the requirements, introducing lightweight aggregates into refractory materials helps to reduce the bulk density of lining refractory materials and improve the energy-saving efficiency of thermal equipment.

[0003] Magnesium aluminate spinel has excellent properties such as high melting point, low thermal conductivity, low thermal expansion coefficient, good thermal shock stability, and alkali erosion resistance. Magnesium aluminate spinel hollow aggregates will become a new hot spot for improving the high-temperature serviceability of materials. At present, there is less research and development on the preparation of hollow spinel materials, and mainly processes such as in-situ decomposition for pore formation, foam method, and electrofusion spraying are used.

[0004] Among them, for the patented technology of "Preparation method of ferrous aluminate spinel hollow spheres" (CN102910922A), the preparation method of ferrous aluminate spinel hollow spheres. Iron-containing compounds and aluminum-containing compounds are proportioned according to a molar ratio of Fe n+ :Al 3+ of 1:2, and additives are introduced at the same time, and then smelted. The melt is blown into spheres, and then screened to obtain ferrous aluminate spinel hollow spheres. This method requires processes such as smelting and blowing, and has the disadvantage of complex operating processes. "Preparation, structure and properties of lightweight spinel hollow sphere ceramics" (Chen Zhening, Chen Huizi, Wang Jiabang. Preparation, structure and properties of lightweight spinel hollow sphere ceramics [J]. Journal of Materials Science and Engineering, 20,40(03):412-417+422.) uses ρ-Al2O3 and light-burned magnesia to prepare lightweight spinel hollow spheres through solid-phase reaction. This method requires a relatively high synthesis temperature and complex control of the sphere-forming process. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides an eggshell-type magnesium aluminate spinel hollow sphere and a preparation method thereof: after ball-milling and premixing fused magnesia, activated alumina powder and additives, using polystyrene spheres as spherical supports, adding phenolic resin solution, forming and sieving in a granulator, and then through steps such as drying and heat treatment, magnesium aluminate spinel hollow spheres are synthesized at low temperature; it uses fewer raw materials, the process is relatively simple, the preparation cost is low, the preparation process is relatively simple, and the prepared hollow spheres have excellent high-temperature resistance.

[0006] The technical solution adopted by the present invention is as follows: an eggshell-type magnesia-alumina spinel hollow sphere, and the added weight parts of the raw materials are: 29-55 parts of fused magnesite powder, 45-69 parts of activated alumina powder, and 1-5 parts of polystyrene spheres; the addition amount of the additive is 1-5% of the total weight of the raw materials.

[0007] The purity of the fused magnesite is >97%, and the particle size is ≤1μm.

[0008] The purity of the activated alumina powder is >98%, and the particle size is ≤5μm.

[0009] The additive is one or more of rare earth lanthanum oxide, organic iron, and ferric oxide, and the purity is >99.9%.

[0010] The phenolic resin is a thermosetting phenolic resin, and the solid content is ≤40%.

[0011] The purity of the polystyrene spheres is >99.9%, and the particle size is 0.5-2mm.

[0012] A preparation method of an eggshell-type magnesia-alumina spinel hollow sphere includes the following steps:

[0013] Step 1: Prepare a resin solution by mixing phenolic resin and alcohol in a mass ratio of 5-9:1-5 to form a resin solution;

[0014] Step 2: Put the fused magnesite, activated alumina powder and additive into a ball mill for dry ball milling for 2-10h at a rotation speed of 400-800r / min to grind into fine powder to obtain a premix;

[0015] Step 3: Add the polystyrene spheres to a spherical granulator and rotate at a speed of 60-120r / min. During the rotation process, spray the resin solution until it evenly covers the surface of the polystyrene spheres, and then add the premix until a uniform spherical precursor is formed. Dry and cure the obtained precursor at 80-200°C for 4-20h, and finally calcine it at 1300°C to 1500°C in an oxidizing atmosphere for 1-5h to obtain the eggshell-type magnesia-alumina spinel hollow sphere.

[0016] The particle size of the premix obtained in Step 2 is 1-7μm.

[0017] The present invention is mainly used for the preparation of hollow aggregates in the field of heat-insulating refractory materials. The present invention uses polystyrene spheres as a spherical support body, and jointly controls the thickness of the resin layer on the surface of the polystyrene spheres according to the concentration of the phenolic resin solution and the stirring speed; by controlling the particle size of the ball-milled premix, the thickness of the shell layer is controlled.

[0018]

[0019] In the present invention, the magnesium aluminate spinel phase is formed in-situ at low temperature, which not only maintains the good physical and chemical properties of magnesium aluminate spinel itself, has high mechanical strength and chemical stability at high temperature, but also reduces the cost of producing lightweight aggregates, and at the same time increases the strength of single balls. During subsequent application, it can play a very good supporting role.

[0020] The additives of the present invention are one or more of rare earth lanthanum oxide, organic iron, and ferric oxide. The introduction of rare earth and iron ions promotes the production and growth of magnesium aluminate spinel crystals formed in-situ. After the crystal growth is completed, these transition ions will inhibit the abnormal growth of grains and improve the mechanical properties of the spherical shell.

[0021] In addition, these transition ions can promote the formation of secondary carbon from phenolic resin and polystyrene balls, which has high carbon activity and can volatilize relatively quickly under the action of an air atmosphere.

[0022] After the drying and curing process of the polystyrene balls of the present invention, they will shrink sharply to form a polycondensate, forming pores, which in turn provides a more sufficient contact area with oxygen for the phenolic resin on the inner wall of the ball, contributing to the volatilization of the phenolic resin.

[0023] In step one, by putting fused magnesia, activated alumina powder and additives into a ball mill for dry ball milling, not only the purpose of uniform mixing of materials is achieved, but during the grinding process, the particle size of the powder is further reduced, the specific surface area of the powder is increased to a certain extent, and the surface activation energy of the particles is reduced.

[0024] The beneficial effects of the present invention are as follows: The present invention prepares a shell-type magnesium aluminate spinel hollow ball by making a premix from fused magnesia, activated alumina powder and additives, and then pelletizing the premix, polystyrene balls and phenolic resin solution. The prior ball milling of fused magnesia, activated alumina powder and additives increases the specific surface area of the powder, reduces the surface activation energy of the particles, and effectively reduces the synthesis temperature of magnesium aluminate spinel crystals; the present invention uses cheap and easily available raw materials, has the characteristics of low cost and simple preparation process, and the prepared shell-type magnesium aluminate spinel hollow balls have excellent high-temperature resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD pattern of the shell-type magnesium aluminate spinel hollow ball prepared by the present invention after heat treatment at 1400 °C;

[0026] Figure 2 is Figure 1 a photograph of the shell-type magnesium aluminate spinel hollow ball shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The present invention will be further described in detail below in conjunction with specific embodiments. A kind of eggshell - type magnesium - aluminum spinel hollow sphere provided by the embodiments of the present invention and its preparation method, wherein the purity of fused magnesia is > 97%, and the particle size is ≤ 1μm; the purity of activated alumina powder is > 98%, and the particle size is ≤ 5μm; the phenolic resin is thermosetting phenolic resin, and the solid content is ≤ 40%; the purity of polystyrene spheres is > 99.9%, and the particle size is 0.5 - 2mm.

[0028] Example 1

[0029] Take 29 parts of fused magnesia powder, 69 parts of activated alumina powder, and the additive dosage accounts for 1% of the weight of the original materials. Ball - mill the above - mentioned raw materials in a planetary ball mill for 8 - 10h at a rotation speed of 400 - 500r / min to obtain a premixed material with a particle size of 1 - 3μm; prepare a resin solution from phenolic resin and alcohol; then add 2 parts of polystyrene spheres to a spherical granulator and rotate it at a speed of 60 - 75r / min. During the rotation process, spray the resin solution on the surface of the polystyrene spheres until the resin layer thickness on the surface of the polystyrene spheres reaches 0.7 - 0.9mm, and then add the premixed material until a spherical precursor is formed. Dry and cure the obtained precursor at 80 - 120°C for 16 - 20h, and finally calcine it at 1450°C - 1500°C for 1 - 2h in an oxidizing atmosphere to obtain the eggshell - type magnesium - aluminum spinel hollow sphere, and the shell layer thickness is 0.5 - 1mm.

[0030] The additive used in this example is rare - earth lanthanum oxide, and the phenolic resin and alcohol are configured into a phenolic resin solution according to a mass ratio of 5 - 6:1 - 2.

[0031] Example 2

[0032] Take 45 parts of fused magnesia powder, 52 parts of activated alumina powder, and the additive dosage accounts for 3% of the weight of the original materials. Ball - mill the above - mentioned raw materials in a planetary ball mill for 6 - 8h at a rotation speed of 500 - 600r / min to obtain a premixed material with a particle size of 3 - 5μm; prepare a resin solution from phenolic resin and alcohol; then add 3 parts of polystyrene spheres to a spherical granulator and rotate it at a speed of 75 - 90r / min. During the rotation process, spray the resin solution on the surface of the polystyrene spheres until the resin layer thickness on the surface of the polystyrene spheres reaches 0.6 - 0.8mm, and then add the premixed material until a spherical precursor is formed. Dry and cure the obtained precursor at 110 - 140°C for 12 - 16h, and finally calcine it at 1400°C - 1450°C for 2 - 3h in an oxidizing atmosphere to obtain the eggshell - type magnesium - aluminum spinel hollow sphere, and the shell layer thickness is 1 - 2mm.

[0033] The additive used in this example is organic iron, and the phenolic resin and alcohol are configured into a phenolic resin solution according to a mass ratio of 6 - 7:2 - 3.

[0034] Example 3

[0035] Mix 50 parts of fused magnesia powder, 45 parts of activated alumina powder, and the additive is added in an amount of 2% of the weight of the raw materials. Ball mill the above raw materials in a planetary ball mill for 4 - 6 h at a rotation speed of 600 - 700 r / min to obtain a premix with a particle size of 5 - 7 μm; Prepare a resin solution from phenolic resin and alcohol; Then add 5 parts of polystyrene balls to a spherical granulator and rotate it at a speed of 90 - 105 r / min. During the rotation process, spray the resin solution on the surface of the polystyrene balls until the thickness of the resin layer on the surface of the polystyrene balls reaches 0.5 - 0.7 mm, and then add the premix until a spherical precursor is formed. Dry and cure the obtained precursor at 140 - 170 °C for 8 - 12 h, and finally calcine it at 1350 - 1400 °C in an oxidizing atmosphere for 3 - 4 h to obtain eggshell - type magnesium aluminate spinel hollow balls with a shell thickness of 2 - 3 mm.

[0036] The additives used in this example are lanthanum oxide and iron trioxide (molar ratio 1:1), and the phenolic resin and alcohol are prepared into a phenolic resin solution according to a mass ratio of 7 - 8:3 - 4.

[0037] Example 4

[0038] Mix 55 parts of fused magnesia powder, 40 parts of activated alumina powder, and the additive is added in an amount of 5% of the weight of the raw materials. Ball mill the above raw materials in a planetary ball mill for 2 - 4 h at a rotation speed of 700 - 800 r / min to obtain a premix with a particle size of 1 - 3 μm; Prepare a resin solution from phenolic resin and alcohol; Then add 5 parts of polystyrene balls to a spherical granulator and rotate it at a speed of 105 - 120 r / min. During the rotation process, spray the resin solution on the surface of the polystyrene balls until the thickness of the resin layer on the surface of the polystyrene balls reaches 0.4 - 0.6 mm, and then add the premix until a spherical precursor is formed. Dry and cure the obtained precursor at 170 - 200 °C for 4 - 8 h, and finally calcine it at 1300 - 1350 °C in an oxidizing atmosphere for 4 - 5 h to obtain eggshell - type magnesium aluminate spinel hollow balls with a shell thickness of 0.5 - 1 mm.

[0039] The additives used in this example are lanthanum oxide and organic iron (molar ratio 1:1), and the phenolic resin and alcohol are prepared into a phenolic resin solution according to a mass ratio of 8 - 9:4 - 5.

[0040] This preparation method has the following advantages: The raw materials are non - toxic, harmless, and easy to obtain, so the production cost is relatively low; This preparation process only requires ball milling, granulation, drying, and firing processes, so the process is simple.

[0041] The eggshell - type magnesium aluminate spinel hollow balls prepared in Example 2 were tested by XRD. Figure 1 It is the X - ray diffraction pattern of the eggshell - type magnesium aluminate spinel hollow balls prepared in Example 2 after heat treatment at 1400 °C.Figure 2 The Figure 1 photo of the eggshell-shaped magnesia-aluminum spinel hollow sphere shown in the figure.

[0042] The parts not detailed in this invention are prior art. The above embodiments will help those skilled in the art to further understand this invention, but do not limit this invention in any form. Within the scope of this invention defined by the appended claims, various changes in form, details or equivalents made using this invention manual are within the protection scope of this invention.

Claims

1. An eggshell type magnesia alumina spinel hollow ball, characterized by: The shell thickness of the magnesia-alumina spinel hollow sphere is 0.5-3 mm; the weight proportions of the raw materials added are: 29-55 parts of fused magnesia powder, 45-69 parts of activated alumina powder, and 1-5 parts of polystyrene balls; the amount of additives added is 1-5% of the total weight of the raw materials; the additives are one or more of rare earth lanthanum oxide, organic iron, and ferric oxide, and the purity is greater than 99.9%. The preparation method comprises the following steps: Step 1: Prepare a resin solution by mixing phenolic resin and alcohol in a mass ratio of 5-9:1-5; Step 2: Place the fused magnesia, activated alumina powder and additives into a ball mill and dry-mill for 2-10 hours at a speed of 400-800 r / min to grind them into fine powder to prepare a premix; Step 3: Add polystyrene balls into a spherical granulator and rotate at a speed of 60~120r / min. During the rotation, spray the resin solution until it is evenly covered on the surface of the polystyrene balls. Then add the premix until a uniform spherical precursor is formed. The resulting precursor is dried and cured at 80~200℃ for 4~20h, and finally calcined at 1300℃~1500℃ in an oxidizing atmosphere for 1~5h; a magnesium-aluminum spinel phase is formed in situ at low temperature; and eggshell-type magnesium-aluminum spinel hollow balls are obtained.

2. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 1, characterized in that: The purity of fused magnesia is greater than 97% and the particle size is ≤1μm.

3. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 1, characterized in that: The purity of activated alumina powder is greater than 98% and the particle size is ≤5μm.

4. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 1, characterized in that: Phenolic resin is a thermosetting phenolic resin with a solid content of ≤40%.

5. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 1, characterized in that: The purity of polystyrene balls is >99.9% and the particle size is 0.5~2mm.

6. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 1, characterized in that: The particle size of the premix prepared in step 2 is 1-7 μm.

7. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 1, characterized in that: The mass ratio of phenolic resin to alcohol is 5-9:1-5, the stirring speed is 60-120 r / min, and the thickness of the resin layer on the surface of the polystyrene ball is 0.4-0.9 mm.

8. The eggshell-type magnesium-aluminum spinel hollow sphere according to claim 7, characterized in that: The mass ratio of phenolic resin to alcohol is 6-7:2-3, the stirring speed is 75-90 r / min, the thickness of the resin layer on the surface of the polystyrene ball is 0.6-0.8 mm, and the particle size of the premix is 3-5 μm.

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