Aluminothermic reaction sintered alumina hollow sphere heat-insulating refractory material and preparation method thereof

Abstract

The invention belongs to the technical field of refractory materials, and discloses an aluminothermic reaction sintered alumina hollow sphere heat-insulating refractory material and a preparation method thereof. The aluminothermic reaction sintered aluminum oxide hollow sphere heat-insulating refractory material comprises the following raw materials in percentage by mass: 20-30% of aluminum oxide hollow spheres with the particle size of 3-5mm, 10-20% of aluminum oxide hollow spheres with the particle size of 1-3mm, 5-15% of aluminum oxide hollow spheres with the particle size of 0.1-1mm, 2-10% of light-burned magnesia, 20-30% of activated aluminum oxide powder, 15-25% of magnesium peroxide powder and 4-7% of metal aluminum powder, a binding agent accounting for 2-4% of the total mass of the raw materials is added. According to the refractory material, aluminum and magnesium peroxide are subjected to aluminothermic reaction and self-reaction sintering, a continuous spinel structure is formed on the surfaces of the matrix and the aluminum oxide hollow spheres, high strength is achieved through sintering at low temperature, and low thermal conductivity and high thermal shock stability are both considered.

Description

Technical Field

[0001] The invention belongs to the technical field of refractory materials, and in particular relates to an aluminothermic reaction sintered alumina hollow ball heat-insulating refractory material and a preparation method thereof. Background Art

[0002] Alumina hollow ball products have excellent thermal insulation properties and are used as insulation materials in high-temperature kilns to reduce heat loss, thereby reducing energy consumption and saving production costs. Because of their good refractory properties, they are often used as non-contact melt working linings in high-temperature kilns, and the operating temperature can reach 1800°C. However, alumina hollow ball products have the disadvantage of poor thermal shock resistance. They are prone to cracking and peeling when used in an environment with large temperature fluctuations, making it difficult to meet the requirements of long-term use in intermittent kilns. In addition, due to the high sintering temperature, the production cost remains high.

[0003] Patent CN101429044A discloses an alumina hollow ball product containing magnesium oxide. Magnesium oxide is introduced into the matrix of the alumina hollow ball product or into the matrix and aggregate to form an in-situ generated or pre-synthesized magnesium-aluminum spinel phase at high temperature to improve the thermal shock stability of the preparation. However, the product needs to be sintered at a high temperature of 1700°C, which consumes a lot of energy.

[0004] Patent CN1554616A discloses a method for preparing lightweight and high-strength hollow alumina sphere ceramics. Insulating bricks are prepared using hollow alumina spheres and α-Al2O3 powder as raw materials and phosphoric acid solution as a binder. However, the bricks also need to be fired at a high temperature of 1700°C. If they are sintered at 900°C, they can be used for masonry, but high-temperature secondary sintering is still required after masonry to make the strength meet the use requirements. In addition, the matrix phase of the brick is a dense corundum phase, which leads to its high thermal conductivity and poor thermal shock resistance.

[0005] In summary, how to obtain high strength of alumina hollow sphere materials under low temperature sintering while taking into account low thermal conductivity and high thermal shock stability is the current technical difficulty. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an aluminothermic reaction sintered alumina hollow ball insulating refractory material and a preparation method thereof in view of the shortcomings of the prior art. The refractory material utilizes aluminum and magnesium peroxide to undergo aluminothermic reaction self-reaction sintering to form a continuous spinel structure on the surface of the matrix and the alumina hollow ball. It is sintered at a low temperature to achieve higher strength while taking into account low thermal conductivity and high thermal shock stability.

[0007] In order to solve the technical problem proposed by the present invention, the present invention provides an aluminothermic reaction sintered alumina hollow ball insulating refractory material, comprising the following raw materials in percentage by weight: 20-30% of alumina hollow balls with a particle size of 3-5 mm, 10-20% of alumina hollow balls with a particle size of 1-3 mm, 5-15% of alumina hollow balls with a particle size of 0.1-1 mm, 2-10% of light-burned magnesia, 20-30% of activated alumina powder, 15-25% of magnesium peroxide powder, 4-7% of metallic aluminum powder, and 2-4% of a binder in an amount of the total weight of the above raw materials.

[0008] In the above scheme, the Al2O3 content of the hollow alumina spheres is greater than 99%.

[0009] In the above scheme, the MgO content of the light-burned magnesia is greater than 92%, and the particle size is 180-325 meshes.

[0010] In the above scheme, the Al2O3 content of the activated alumina powder is greater than 99%, and the particle size is less than 325 meshes.

[0011] In the above scheme, the MgO2 content of the magnesium peroxide powder is ≥99.9%, the particle size is <10 μm, and the median particle size D 50 0.5~1.5μm.

[0012] In the above scheme, the Al content of the metal aluminum powder is ≥99% and the particle size is <50 μm.

[0013] In the above scheme, the binder is a viscous liquid organic substance.

[0014] Preferably, the binder is one or more of tung oil, phenolic resin, maltose, honey and the like.

[0015] Furthermore, when the binder is a phenolic resin, a resin curing agent needs to be added, and the added amount of the resin curing agent is 1 to 4% of the mass of the phenolic resin.

[0016] In the above scheme, the mass ratio of the magnesium peroxide powder to the metallic aluminum powder is (3.12-3.5):1.

[0017] Preferably, the sum of the mass of the magnesium peroxide powder and the metal aluminum powder accounts for 20-32% of the total mass of the raw materials excluding the binder.

[0018] The present invention also provides a method for preparing a heat-insulating refractory material of aluminothermic reaction-sintered hollow alumina balls, comprising the following steps:

[0019] 1) ball-milling and mixing magnesium peroxide powder, metallic aluminum powder and a portion of a binder to prepare a thermite;

[0020] 2) adding activated alumina powder to the thermite, and continuing to ball-mill and mix to obtain a diluted thermite;

[0021] 3) mixing and stirring the hollow alumina balls of various particle sizes, light-burned magnesia and the remaining binder to obtain hollow alumina balls coated with light-burned magnesia;

[0022] 4) mixing and stirring the light-burned magnesia-coated alumina hollow balls and the diluted thermite to obtain a mixture;

[0023] 5) Fill the mixture into the mold, vibrate it to make it dense and pressurize the surface to level it, demould it after shaping, dry it naturally, and heat it to 600-700℃ to induce thermite reaction of magnesium peroxide powder and metallic aluminum powder, so that the hollow alumina sphere insulating refractory material is sintered as a whole.

[0024] In the above scheme, the ball milling mixing is carried out under vacuum or inert atmosphere, the ball milling speed is 16-50r / min, the ball milling time in step 1) is 2-4h, the ball milling time in step 2) is 1-2h, and the material temperature during the ball milling process is ≤60°C.

[0025] In the above scheme, the amount of the binder used in step 1) is 50-70% of the total amount of the binder.

[0026] In the above scheme, the stirring rate in step 3) is 45 to 90 r / min, and the stirring time is 10 to 30 min.

[0027] In the above scheme, the stirring rate in step 4) is 60 to 120 r / min, and the stirring time is 10 to 30 min.

[0028] In the above scheme, the pressure of the pressurized leveling is 0.4-0.6MPa.

[0029] In the above scheme, the natural drying time is 24 to 48 hours.

[0030] In the above scheme, the heating time is 20 to 30 minutes.

[0031] In the above scheme, the bulk density of the aluminothermic reaction sintered alumina hollow sphere insulating refractory material is 1.20-1.40 g / cm 3 The room temperature compressive strength is 16-25MPa, the thermal conductivity is 0.55-0.65W / m·K when the hot surface temperature is 1000℃, 1100℃ air cooling and heat cycle 15-20 times, and the 0.1MPa load softening temperature is greater than 1700℃.

[0032] The technical principles of the present invention are as follows:

[0033] Magnesium peroxide reacts with aluminum powder to generate spinel and magnesium oxide (reaction formula 1), and the theoretical consumption ratio of magnesium peroxide and aluminum powder is 3.11:1; excess magnesium peroxide decomposes into oxygen and magnesium oxide at 300-500°C (reaction formula 2), and a large number of bubbles are evenly dispersed in the matrix, reducing the volume density and thermal conductivity of the material, so that the thermal insulation effect is better; the generated magnesium oxide reacts with activated alumina, and Al2O3 on the surface of the hollow alumina sphere reacts with the active magnesium sand to form a continuous spinel structure on the matrix and the surface of the hollow alumina sphere (reaction formula 3), so that the hollow alumina sphere particles are more tightly connected, thereby improving the strength and thermal shock resistance of the material.

[0034] Reaction formula 1: 3MgO2+2Al=2MgO+MgAl2O4;

[0035] Reaction 2: 2MgO2=2MgO+O2↑;

[0036] Reaction equation 3: MgO+Al2O3=MgAl2O4.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) The present invention uses magnesium peroxide as an oxygen source to react with metallic aluminum to generate spinel, while releasing a large amount of heat, so that the material self-sinters, significantly reducing the sintering energy consumption; excess magnesium peroxide decomposes to generate oxygen, which evenly disperses small bubbles in the matrix, reduces the volume density and thermal conductivity of the material, and improves the thermal insulation effect.

[0039] 2) The present invention mixes activated alumina powder with thermite to dilute and disperse the thermite, reduce the reaction intensity of thermite, and avoid material cracking caused by excessive local temperature. At the same time, magnesium oxide generated by the reaction of activated alumina powder with thermite and magnesium oxide generated by the decomposition of excess magnesium oxide fully contact and react to form evenly distributed spinel in situ in the matrix, and a certain volume expansion occurs to compensate for the shrinkage caused by the melting and sintering of the powder at high temperature, so that the hollow alumina balls and the matrix are more closely combined, and the material strength is improved. MgO on the surface of the active magnesia reacts with the hollow alumina balls and the activated alumina powder to generate spinel, so that the spinel in the matrix and the hollow alumina balls are connected into a network structure, thereby improving the strength and thermal shock stability of the material. DETAILED DESCRIPTION

[0040] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0041] In the following examples, the Al2O3 content of the alumina hollow spheres used is greater than 99%; the MgO content of the light-burned magnesia is greater than 92%, and the particle size is 180-325 mesh; the Al2O3 content of the activated alumina powder is greater than 99%, and the particle size is less than 325 mesh; the MgO2 content of the magnesium peroxide powder is ≥99.9%, and the particle size is less than 10 μm, and the median particle size D 50 The Al content of the metal aluminum powder is ≥99%, and the particle size is <50μm.

[0042] Example 1

[0043] The aluminothermic reaction sintered alumina hollow ball insulating refractory material in this embodiment includes the following raw materials in percentage by weight: 20% alumina hollow balls with a particle size of 3-5 mm (excluding 5 mm), 15% alumina hollow balls with a particle size of 1-3 mm (excluding 3 mm), 10% alumina hollow balls with a particle size of 0.1-1 mm (excluding 1 mm), 5% light-burned magnesia, 24% activated alumina powder, 20% magnesium peroxide powder, 6% metallic aluminum powder, and 2% tung oil of the total weight of the above raw materials.

[0044] The preparation method of the aluminothermic reaction sintered alumina hollow sphere insulating refractory material in this embodiment comprises the following steps:

[0045] 1) Magnesium peroxide powder and metallic aluminum powder are placed in a ball mill equipped with an atmosphere protection device and a cooling device, a portion of tung oil (70% of the total amount of tung oil) is added, argon gas is filled for protection, the ball mill is started, the speed is 25r / min, and the ball milling and mixing are performed for 4 hours. The material temperature during the ball milling process is ≤60°C, and the thermite is obtained;

[0046] 2) Adding activated alumina powder to the thermite, continuing ball milling for 1 hour, with the material temperature being ≤60°C during the ball milling process, to obtain a diluted thermite;

[0047] 3) placing the hollow alumina balls of various particle sizes and light-burned magnesia in a mixer, adding the remaining tung oil, and stirring at a rate of 90 r / min for 30 min to obtain hollow alumina balls coated with light-burned magnesia;

[0048] 4) Add the diluted thermite into a mixer, and stir and mix with the hollow alumina balls wrapped in light-burned magnesia at a stirring rate of 90 r / min for 30 min to obtain a mixture;

[0049] 5) Fill the mixture into a mold of 500mm×500mm×100mm, compact it by vibration and pressurize the surface with 0.4MPa to make it flat. After shaping, demould it and place it naturally for 24 hours to dry. After further drying at 100℃±10℃ for 48 hours, place it on a kiln car covered with magnesia sand particles, put it into a medium-temperature heating furnace at 650℃ and heat it for 30 minutes to induce thermite reaction of magnesium peroxide powder and metallic aluminum powder, so that the hollow alumina sphere insulating refractory material is sintered as a whole.

[0050] Example 2

[0051] The aluminothermic reaction sintered alumina hollow ball insulating refractory material in this embodiment includes the following raw materials in percentage by mass: 25% alumina hollow balls with a particle size of 3-5 mm (excluding 5 mm), 10% alumina hollow balls with a particle size of 1-3 mm (excluding 3 mm), 8% alumina hollow balls with a particle size of 0.1-1 mm (excluding 1 mm), 6% light-burned magnesia, 22% activated alumina powder, 22% magnesium peroxide powder, 7% metallic aluminum powder, and 4% maltose of the total mass of the above raw materials.

[0052] The preparation method of the aluminothermic reaction sintered alumina hollow sphere insulating refractory material in this embodiment comprises the following steps:

[0053] 1) Magnesium peroxide powder and metallic aluminum powder are placed in a ball mill equipped with an atmosphere protection device and a cooling device, a portion of maltose (50% of the total amount of maltose) is added, argon gas is filled for protection, the ball mill is started, the speed is 20r / min, and the ball milling and mixing are performed for 3h. The material temperature during the ball milling process is ≤50°C, and the thermite is obtained;

[0054] 2) Adding activated alumina powder to the thermite, continuing ball milling for 2 hours, with the material temperature being ≤50°C during the ball milling process, to obtain a diluted thermite;

[0055] 3) placing the hollow alumina balls of various particle sizes and light-burned magnesia in a mixer, adding the remaining maltose, and stirring at a rate of 60 r / min for 30 min to obtain hollow alumina balls coated with light-burned magnesia;

[0056] 4) Add the diluted thermite into a mixer, and stir and mix with the hollow alumina balls wrapped in light-burned magnesia at a stirring rate of 120 r / min for 20 min to obtain a mixture;

[0057] 5) Fill the mixture into a 500mm×500mm×100mm mold, compact it by vibration and pressurize the surface with 0.6MPa to level it. After shaping, demould it and let it stand naturally for 24 hours to dry. Place it on bauxite fine sand and heat the material to 600-700℃ with a flame spray gun for 20 minutes to induce thermite reaction of magnesium peroxide powder and metallic aluminum powder, so that the hollow alumina sphere insulating refractory material is sintered as a whole.

[0058] Example 3

[0059] The aluminothermic reaction sintered alumina hollow ball insulating refractory material in this embodiment includes the following raw materials in percentage by weight: 22% of alumina hollow balls with a particle size of 3-5 mm (excluding 5 mm), 10% of alumina hollow balls with a particle size of 1-3 mm (excluding 3 mm), 7% of alumina hollow balls with a particle size of 0.1-1 mm (excluding 1 mm), 8% of light-burned magnesia, 22% of activated alumina powder, 24% of magnesium peroxide powder, 7% of metallic aluminum powder, and 3% of the total weight of the above raw materials, and 1% of urotropine by weight of the phenolic resin.

[0060] The preparation method of the aluminothermic reaction sintered alumina hollow sphere insulating refractory material in this embodiment comprises the following steps:

[0061] 1) Magnesium peroxide powder and metallic aluminum powder are placed in a ball mill equipped with an atmosphere protection device and a cooling device, a portion of phenolic resin (2% of the total mass of the raw materials) is added, argon gas is filled for protection, the ball mill is started, the speed is 30r / min, and the ball milling and mixing are performed for 4h. The material temperature during the ball milling process is ≤60°C, and the thermite is obtained;

[0062] 2) Adding activated alumina powder to the thermite, continuing ball milling for 1 hour, with the material temperature being ≤60°C during the ball milling process, to obtain a diluted thermite;

[0063] 3) placing hollow alumina balls of various particle sizes and light-burned magnesia in a mixer, adding the remaining phenolic resin (1% of the total mass of the raw materials), and stirring at a speed of 45 r / min for 30 min to obtain hollow alumina balls coated with light-burned magnesia;

[0064] 4) Add the diluted thermite into a mixer, stir and mix with the light-burned magnesia-wrapped alumina hollow balls at a rate of 90 r / min for 20 min, then add hexamethylenetetramine and stir for 5 min to obtain a mixture;

[0065] 5) Fill the mixture into a 500mm×500mm×100mm mold, compact it by vibration and pressurize the surface with 0.5MPa to make it flat. After shaping, demould it, leave it naturally for 24 hours to dry, place it on a kiln car covered with corundum fine sand, put it into a medium-temperature kiln at 700℃, and bake it for 25 minutes to induce thermite reaction of magnesium peroxide powder and metallic aluminum powder, so that the hollow alumina sphere insulating refractory material is sintered as a whole.

[0066] Comparative Example 1

[0067] The difference between Comparative Example 1 and Example 1 is that the content of magnesium peroxide is 18% and the content of metallic aluminum powder is 8%.

[0068] Comparative Example 2

[0069] The only difference between Comparative Example 2 and Example 1 is that the ball mill is filled with air.

[0070] Comparative Example 3

[0071] The difference between Comparative Example 3 and Example 2 is that the magnesium peroxide is 24% and the metal aluminum powder is 5%.

[0072] Comparative Example 4

[0073] The only difference between Comparative Example 4 and Example 2 is that the heating temperature is 500-600°C.

[0074] Comparative Example 5

[0075] The only difference between Comparative Example 5 and Example 3 is that: no ball mill and step-by-step mixing process are used, all raw materials are stirred at once using a stirrer, and the phenolic resin and hexamethylenetetramine are added at the end.

[0076] Comparative Example 6

[0077] The only difference between Comparative Example 6 and Example 3 is that, with other components remaining unchanged, 3% of magnesium peroxide powder and 1% of metal aluminum powder are additionally added to the total original components.

[0078] The bulk density, room temperature compressive strength, thermal conductivity and thermal shock stability of the alumina hollow sphere insulating refractory materials of each embodiment and comparative example were tested with reference to GB / T 4513.6-2017.

[0079] The comparison of the test data of each embodiment and the current domestic industry standard technical indicators is shown in the following table:

[0080]

[0081] The test data of each comparative ratio are as follows:

[0082]

[0083] Through the data of the alumina hollow ball insulating refractory materials in the various embodiments and comparative examples and the conventional alumina hollow ball bricks in the industry standards, it can be known that the alumina hollow ball insulating refractory material provided by the present invention forms a spinel network skeleton in the matrix and between the alumina hollow balls due to self-reaction overall sintering, which significantly improves the room temperature pressure resistance and thermal shock stability of the material, and produces uniformly dispersed small bubbles due to the decomposition of magnesium peroxide, further reducing the bulk density and thermal conductivity. There is no need to spend time and energy to high-temperature sinter the products, which saves energy lost in the firing of alumina hollow ball bricks and can greatly improve production efficiency. The raw material purity is high and the high-temperature performance is good.

[0084] The above embodiments are merely examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above descriptions. It is not necessary and impossible to list all the implementation methods here, and the obvious changes or modifications derived therefrom are still within the protection scope of the invention.

Claims

1. A thermally sintered alumina hollow sphere heat-insulating refractory material, characterized in that: The invention comprises the following raw materials in percentage by weight: 20-30% of hollow alumina balls with a particle size of 3-5mm, 10-20% of hollow alumina balls with a particle size of 1-3mm, 5-15% of hollow alumina balls with a particle size of 0.1-1mm, 2-10% of light-burned magnesia, 20-30% of activated alumina powder, 15-25% of magnesium peroxide powder, 4-7% of metallic aluminum powder, and 2-4% of a binder in proportion to the total weight of the above raw materials.

2. The aluminothermic reaction sintered alumina hollow sphere insulating refractory material according to claim 1, characterized in that: The sum of the masses of the magnesium peroxide powder and the metal aluminum powder accounts for 20-32% of the total mass of the raw materials excluding the binder; the mass ratio of the magnesium peroxide powder to the metal aluminum powder is (3.12-3.5):

1.

3. The aluminothermic reaction sintered alumina hollow sphere insulating refractory material according to claim 1, characterized in that: The binder is one or more of tung oil, phenolic resin, maltose and honey. When the binder is phenolic resin, a resin curing agent needs to be added, and the amount of the resin curing agent added is 1-4% of the mass of the phenolic resin.

4. The aluminothermic reaction sintered alumina hollow sphere insulating refractory material according to claim 1, characterized in that: The magnesium peroxide powder has a MgO2 content of ≥99.9%, a particle size of <10 μm, and a median particle size D 50 The Al content of the metal aluminum powder is ≥99%, and the particle size is <50μm; the Al2O3 content of the activated alumina powder is >99%, and the particle size is <325 mesh.

5. The aluminothermic reaction sintered alumina hollow sphere insulating refractory material according to claim 1, characterized in that: The Al2O3 content of the alumina hollow sphere is greater than 99%; the MgO content of the light-burned magnesia is greater than 92%, and the particle size is 180-325 meshes.

6. The aluminothermic reaction sintered alumina hollow sphere insulating refractory material according to claim 1, characterized in that: The bulk density of the aluminothermic reaction sintered alumina hollow sphere insulating refractory material is 1.20 to 1.40 g / cm 3 The room temperature compressive strength is 16-25MPa, the thermal conductivity is 0.55-0.65W / m·K when the hot surface temperature is 1000℃, 1100℃ air cooling and heat cycle 15-20 times, and the 0.1MPa load softening temperature is greater than 1700℃.

7. A method for preparing the thermal reaction sintered alumina hollow sphere insulating refractory material according to any one of claims 1 to 6, characterized in that: The following steps are involved: 1) ball-milling and mixing magnesium peroxide powder, metallic aluminum powder and a portion of a binder to prepare a thermite; 2) adding activated alumina powder to the thermite, and continuing to ball-mill and mix to obtain a diluted thermite; 3) mixing and stirring the hollow alumina balls of various particle sizes, light-burned magnesia and the remaining binder to obtain hollow alumina balls coated with light-burned magnesia; 4) mixing and stirring the light-burned magnesia-coated alumina hollow balls and the diluted thermite to obtain a mixture; 5) Fill the mixture into the mold, vibrate it to make it dense and pressurize the surface to level it, demould it after shaping, dry it naturally, and heat it to 600-700℃ to induce thermite reaction of magnesium peroxide powder and metallic aluminum powder, so that the hollow alumina sphere insulating refractory material is sintered as a whole.

8. The method for preparing the thermal reaction sintered alumina hollow sphere insulating refractory material according to claim 7, characterized in that: The ball milling mixing is carried out under vacuum or inert atmosphere, the ball milling speed is 16-50 r / min, the ball milling time in step 1) is 2-4 h, the ball milling time in step 2) is 1-2 h, and the material temperature during the ball milling process is ≤60°C.

9. The method for preparing the thermal reaction sintered alumina hollow sphere insulating refractory material according to claim 7, characterized in that: The amount of the binder in step 1) is 50-70% of the total amount of the binder; the stirring rate in step 3) is 45-90 r / min, and the stirring time is 10-30 min; the stirring rate in step 4) is 60-120 r / min, and the stirring time is 10-30 min.

10. The method for preparing the thermal reaction sintered alumina hollow sphere insulating refractory material according to claim 7, characterized in that: The pressure of the pressurized leveling is 0.4-0.6 MPa; the time of the natural drying is 24-48 hours; and the time of the heating is 20-30 minutes.

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