Bimodal activated alumina fines and method for making same

Abstract

The application discloses a bimodal active alumina micropowder and a preparation method thereof, and relates to the field of refractory materials. The bimodal active alumina micropowder is obtained by mixing and ball milling first calcined alumina and second calcined alumina according to a weight ratio. The first calcined alumina is prepared by calcining first alumina blanks at 1000-1300 DEG C, and the first alumina blanks comprise industrial alumina powder, a first particle size stabilizer and an organic binder; the first particle size stabilizer comprises magnesium oxide, magnesium sulfate, hexacarbonylmolybdenum and chromium trioxide. The second calcined alumina is prepared by calcining second alumina blanks at 1400-1800 DEG C, and the second alumina blanks comprise industrial alumina powder, a second particle size stabilizer and an organic binder; the second particle size stabilizer comprises silicon dioxide, aluminum fluoride and calcium fluoride. The bimodal active alumina micropowder has the advantages of stable particle size distribution, good and stable dispersibility in refractory castable, and is beneficial to improving the product stability of the refractory castable.

Description

Technical Field

[0001] This invention relates to the field of refractory materials, and in particular to a bimodal active alumina micro powder and its preparation method. Background Technology

[0002] Bimodal activated alumina micro powder is an α-alumina micro powder with high alumina content and low sodium content, exhibiting a bimodal particle size distribution. It possesses excellent physical properties and is suitable for castables in low-cement or ultra-low-cement systems such as corundum, alumina-magnesium, corundum-spinel, high-alumina, and high-alumina-mullite. Compared with traditional alumina powder, it can effectively improve the workability, sintering properties, and high-temperature resistance of refractory products. Therefore, bimodal activated alumina micro powder has a wide range of application prospects.

[0003] One related technology discloses a bimodal activated alumina micro powder, which is obtained by calcining industrial alumina powder at different temperatures to obtain calcined alumina precursors with two different primary crystal sizes. These precursors are then ball-milled. However, the primary crystal size of the calcined alumina precursors is significantly affected by the calcination temperature, calcination time, heating rate, and cooling rate. When obtaining calcined alumina precursors with relatively uniform and stable particle size, it is necessary to strictly control the calcination temperature, calcination time, heating rate, and cooling rate. Otherwise, the particle size of the calcined alumina precursors will have poor stability, easily affecting the particle size distribution stability of the bimodal activated alumina, and consequently affecting the dispersion stability of the bimodal activated alumina in refractory castables. Summary of the Invention

[0004] In order to improve the problem that the particle size distribution stability of calcined alumina primary crystals is poor in related technologies, which easily affects the particle size distribution stability of bimodal activated alumina and thus affects the dispersion stability of bimodal activated alumina in refractory castables, this application provides a bimodal activated alumina micro powder and its preparation method.

[0005] Firstly, the bimodal activated alumina micro powder provided in this application adopts the following technical solution:

[0006] A bimodal activated alumina micro powder, comprising the following raw materials by weight:

[0007] First calcined alumina: 40-60 parts

[0008] Second calcined alumina: 40-60 parts

[0009] The first calcined alumina is obtained by calcining a first alumina billet at 1000-1300℃, and the second calcined alumina is obtained by calcining a second alumina billet at 1400-1800℃;

[0010] Based on raw materials, the first alumina billet includes industrial alumina powder, a first particle size stabilizer, and an organic binder, wherein the weight ratio of the industrial alumina powder, the first particle size stabilizer, and the organic binder is 100:(3-6):(4-10).

[0011] The first particle size stabilizer comprises magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, and chromium trioxide, wherein the weight ratio of magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, and chromium trioxide is (0.1-0.5):1:(0.2-0.4):(0.3-0.5).

[0012] The second alumina blank comprises industrial alumina powder, a second particle size stabilizer, and an organic binder, wherein the weight ratio of the industrial alumina powder, the second particle size stabilizer, and the organic binder is 100:(5-9):(8-12).

[0013] The second particle size stabilizer includes silicon dioxide, aluminum fluoride, and calcium fluoride, wherein the weight ratio of silicon dioxide, aluminum fluoride, and calcium fluoride is 1:(0.4-0.8):(0.2-0.6).

[0014] Magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, chromium trioxide, and an organic binder are added to industrial alumina powder to prepare a first alumina billet. Calcination of this first alumina billet at 1000-1300℃ yields first calcined alumina with a particle size concentrated in the range of 0.5-1.0 μm. During calcination, magnesium oxide inhibits the growth of α-alumina crystals, and magnesium sulfate reduces the agglomeration of α-alumina crystals at 1000-1300℃, which is beneficial for obtaining α-alumina crystals with a particle size concentrated in the range of 0.5-1.0 μm, thus mitigating the problems of large particle size dispersion and poor stability of α-alumina crystals in second calcined alumina. Molybdenum hexacarbonyl and chromium trioxide can, on the one hand, increase the proportion of first-calcined alumina with a particle size in the range of 0.5-1.0 μm. On the other hand, the atmosphere generated during the high-temperature decomposition of molybdenum hexacarbonyl and chromium trioxide is conducive to changing the growth orientation of alumina crystals, promoting the transformation of other alumina crystal forms into α-alumina, and further increasing the α-alumina content in the bimodal activated alumina micropowder, which is beneficial to improving the heat resistance of the bimodal activated alumina micropowder. The main function of the organic binder is to uniformly and stably disperse magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, and chromium trioxide into the industrial alumina powder, which is beneficial to further improve the particle size stability of the first-calcined alumina.

[0015] A second alumina blank is prepared by adding silica, aluminum fluoride, calcium fluoride, and an organic binder to industrial alumina powder. Calcination of this second alumina blank at 1400-1800℃ yields a second calcined alumina with a particle size concentrated in the range of 3.0-3.5 μm. When the calcination temperature is within the 1400-1800℃ range, other alumina crystal forms can essentially transform into α-alumina. Therefore, molybdenum hexacarbonyl and chromium trioxide are not required to promote the transformation of other alumina crystal forms into α-alumina in the second alumina blank. In this application, silica promotes the growth of α-alumina crystals to the 3.0-3.5 μm range, while aluminum fluoride and calcium fluoride reduce the agglomeration of α-alumina crystals in the 1400-1800℃ environment, which is beneficial for obtaining α-alumina crystals with a particle size concentrated in the 3.0-3.5 μm range and reduces the problems of large particle size dispersion and poor stability of α-alumina crystals in the second calcined alumina. In addition, the main function of the organic binder is to uniformly and stably disperse silicon dioxide, aluminum fluoride and calcium fluoride into the industrial alumina powder, which is beneficial to further improve the particle size stability of the second calcined alumina.

[0016] Furthermore, the particle size distribution of the calcined alumina primary crystals produced by calcining the first and second alumina billets in this application is minimally affected by the heating and cooling rates of the calcination temperature. Therefore, there is no need to strictly control the heating and cooling rates of the calcination temperature during the production process.

[0017] Since the first calcined alumina in this application is mostly concentrated in the range of 0.5-1.0 μm, and the second calcined alumina is mostly concentrated in the range of 3-3.5 μm, it can effectively improve the particle size distribution stability of the bimodal active alumina micro powder, which is beneficial to improving the dispersion stability of the bimodal active alumina micro powder in refractory castables.

[0018] Optionally, in the first alumina blank, the weight ratio of the industrial alumina powder, the first particle size stabilizer, and the organic binder is 100:(5-6):(8-10).

[0019] When the weight ratio of industrial alumina powder, first particle size stabilizer and organic binder is within this range, the proportion of first calcined alumina with a particle size in the range of 0.5-1.0μm can be increased, that is, the particle size distribution stability of first calcined alumina can be further improved.

[0020] Optionally, in the first particle size stabilizer, the weight ratio of magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide is (0.2-0.3):1:(0.2-0.3):0.5.

[0021] When the weight ratio of magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide is within this range, it can not only further improve the particle size distribution stability of the first calcined alumina, but also effectively improve the compressive strength of the bimodal active alumina micro powder.

[0022] Optionally, in the second alumina blank, the weight ratio of the industrial alumina powder, the second particle size stabilizer, and the organic binder is 100:(7-9):(10-12).

[0023] When the weight ratio of industrial alumina powder, second particle size stabilizer, and organic binder is within this range, the proportion of first calcined alumina with a particle size in the range of 3.0-3.5μm can be increased, which can further improve the particle size distribution stability of second calcined alumina.

[0024] Optionally, in the second particle size stabilizer, the weight ratio of silicon dioxide, aluminum fluoride, and calcium fluoride is 1:(0.5-0.6):(0.4-0.5).

[0025] When the weight ratio of silicon dioxide, aluminum fluoride, and calcium fluoride is within this range, it can not only further improve the particle size distribution stability of the second calcined alumina, but also effectively improve the compressive strength of the bimodal active alumina micro powder.

[0026] Optionally, the organic binder is selected from at least one of carboxymethyl chitosan and polyvinyl alcohol.

[0027] Carboxymethyl chitosan and polyvinyl alcohol have advantages such as wide availability of raw materials and low cost, which can reduce the production cost of bimodal active alumina micro powder.

[0028] Preferably, the viscosity of the carboxymethyl chitosan is 100 mPa·s to 200 mPa·s.

[0029] Secondly, the preparation method of bimodal activated alumina micro powder provided in this application adopts the following technical solution: A preparation method of bimodal activated alumina includes the following steps:

[0030] After uniformly mixing industrial alumina powder and the first particle size stabilizer, an organic binder is added, the mixture is stirred evenly, and then pressed into blocks to obtain the first alumina billet.

[0031] After uniformly mixing industrial alumina powder and a second particle size stabilizer, an organic binder is added, the mixture is stirred evenly, and then pressed into blocks to obtain a second alumina billet.

[0032] The first alumina billet is calcined at a temperature of 1000-1300℃ to obtain the first calcined alumina.

[0033] The second alumina billet is calcined at a temperature of 1400-1800℃ to obtain the second calcined alumina.

[0034] The first calcined alumina and the second calcined alumina were mixed in a certain proportion and then ball-milled to obtain bimodal active alumina micro powder.

[0035] The first alumina billet is calcined at a lower temperature to obtain first calcined alumina with a particle size concentrated in the range of 0.5-1.0 μm. The second alumina billet is calcined at a higher temperature to obtain second calcined alumina with a particle size concentrated in the range of 3.0-3.5 μm. Then, the two calcined alumina precursors with different particle size ranges are mixed and ball-milled to improve the flowability of bimodal active alumina micro powder, which has a promoting effect on improving the flowability of refractory castables.

[0036] Optionally, the calcination temperature of the first alumina billet is 1150-1250℃.

[0037] When the calcination temperature of the first calcined alumina billet is in the range of 1150-1250℃, the proportion of first calcined alumina with a particle size in the range of 0.5-1.0μm can be further increased, which further promotes the improvement of the particle size stability of the first calcined alumina. At the same time, it can also further promote the conversion of other crystal forms of alumina into α-alumina, which further promotes the improvement of the compressive strength of bimodal active alumina micro powder.

[0038] Optionally, the calcination temperature of the second alumina billet is 1450-1550℃.

[0039] When the calcination temperature of the second calcined alumina billet is in the range of 1450-1550℃, the proportion of second calcined alumina with a particle size in the range of 3.0-3.5μm can be further increased, which further promotes the improvement of the particle size stability of the second calcined alumina. At the same time, it can also further promote the conversion of other crystal forms of alumina into α-alumina, which further promotes the improvement of the compressive strength and heat resistance of bimodal active alumina micro powder.

[0040] Optionally, the holding time during calcination of the first alumina billet and the second alumina billet is 5-6 hours.

[0041] When the holding time of the first alumina billet and the second alumina billet is within the above range, it can further promote the conversion of other crystal forms of alumina into α-alumina, which can further promote the improvement of the compressive strength and heat resistance of bimodal active alumina micro powder, while not causing energy waste.

[0042] In summary, the technical solution of this application has at least the following beneficial effects:

[0043] The first and second calcined alumina have good particle size distribution stability, which is beneficial to improving the particle size distribution stability of bimodal active alumina micro powder. This can improve the distribution stability of bimodal active alumina micro powder in refractory castables and promote the improvement of the compressive strength of refractory castables. Detailed Implementation

[0044] The following specific experiments provide further details of this application.

[0045] The composition of the industrial alumina powder in the following examples and comparative examples is as follows:

[0046] The mass fractions of each component in industrial alumina powder are as follows: Al2O3 accounts for 99.83%, Fe2O3 accounts for 0.03%, SiO2 accounts for 0.04%, R2O accounts for 0.1%, and moisture accounts for 0.32%.

[0047] Example

[0048] Example 1

[0049] A bimodal activated alumina micro powder, based on raw materials, comprises 60 kg of first calcined alumina and 40 kg of second calcined alumina.

[0050] The first calcined alumina is obtained by calcining a first alumina billet at a specific temperature, and the second calcined alumina is obtained by calcining a second alumina billet at a specific temperature.

[0051] Based on raw materials, the first alumina billet includes 100 kg of industrial alumina powder, 0.75 kg of magnesium oxide, 1.5 kg of magnesium sulfate, 0.3 kg of molybdenum hexacarbonyl, 0.45 kg of chromium trioxide, and 10 kg of carboxymethyl chitosan with a viscosity of 100 mPa·s.

[0052] The second alumina billet consists of 100 kg of industrial alumina powder, 4.5 kg of silicon dioxide, 3.6 kg of aluminum fluoride, 0.9 kg of calcium fluoride, and 8 kg of carboxymethyl chitosan.

[0053] In addition, the preparation method of bimodal activated alumina micro powder in this embodiment includes the following steps:

[0054] Industrial alumina powder, magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide are mixed evenly according to the formula, carboxymethyl chitosan is added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the first alumina billet.

[0055] Industrial alumina powder, silicon dioxide, aluminum fluoride, and calcium fluoride are mixed evenly according to the formula. Carboxymethyl chitosan is then added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the second alumina blank.

[0056] The first alumina billet was calcined at a temperature of 1000℃, with a heating rate of 5℃ / min. After heating to 1000℃, the holding time was 3h. After holding, the cooling rate was 20℃ / min to obtain the first calcined alumina.

[0057] The second alumina billet was calcined at a temperature of 1400℃, with a heating rate of 5℃ / min. After heating to 1000℃, the holding time was 3h. After holding, the cooling rate was 20℃ / min to obtain the second calcined alumina.

[0058] The first calcined alumina and the second calcined alumina were mixed in a certain ratio and then ball-milled at a ball-to-material ratio of 3:1 for 1 hour to obtain bimodal active alumina micro powder.

[0059] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.7 μm and the second peak is at 3.2 μm.

[0060] Example 2

[0061] A bimodal activated alumina micro powder differs from Example 1 in that the raw material ratios of the first and second calcined alumina are different.

[0062] In this embodiment, the amount of the first calcined alumina added is 50 kg, and the amount of the second calcined alumina added is also 50 kg.

[0063] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.6 μm and the second peak is at 3.4 μm.

[0064] Example 3

[0065] A bimodal activated alumina micro powder differs from Example 1 in that the raw material ratios of the first and second calcined alumina are different.

[0066] In this embodiment, the amount of the first calcined alumina added is 40 kg, and the amount of the second calcined alumina added is also 60 kg.

[0067] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.7 μm and the second peak is at 3.1 μm.

[0068] Example 4

[0069] A bimodal activated alumina micro powder, based on raw materials, comprises 50 kg of first calcined alumina and 50 kg of second calcined alumina.

[0070] The first calcined alumina is obtained by calcining a first alumina billet at a specific temperature, and the second calcined alumina is obtained by calcining a second alumina billet at a specific temperature.

[0071] Based on raw materials, the first alumina billet includes 100 kg of industrial alumina powder, 1.25 kg of magnesium oxide, 2.5 kg of magnesium sulfate, 0.5 kg of molybdenum hexacarbonyl, 0.75 kg of chromium trioxide, and 4 kg of carboxymethyl chitosan with a viscosity of 100 mPa·s.

[0072] The second alumina billet consists of 100 kg of industrial alumina powder, 2.5 kg of silicon dioxide, 2 kg of aluminum fluoride, 0.5 kg of calcium fluoride, and 10 kg of carboxymethyl chitosan.

[0073] In addition, the preparation method of the bimodal active alumina micro powder in this embodiment is the same as that in Example 1.

[0074] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.7 μm and the second peak is at 3.3 μm.

[0075] Example 5

[0076] A bimodal activated alumina micro powder, based on raw materials, comprises 50 kg of first calcined alumina and 50 kg of second calcined alumina.

[0077] The first calcined alumina is obtained by calcining a first alumina billet at a specific temperature, and the second calcined alumina is obtained by calcining a second alumina billet at a specific temperature.

[0078] Based on raw materials, the first alumina billet includes 100 kg of industrial alumina powder, 1.25 kg of magnesium oxide, 2.5 kg of magnesium sulfate, 0.5 kg of molybdenum hexacarbonyl, 0.75 kg of chromium trioxide, and 8 kg of carboxymethyl chitosan with a viscosity of 100 mPa·s.

[0079] The second alumina billet consists of 100 kg of industrial alumina powder, 3.5 kg of silicon dioxide, 2.8 kg of aluminum fluoride, 0.7 kg of calcium fluoride, and 10 kg of carboxymethyl chitosan.

[0080] In addition, the preparation method of the bimodal active alumina micro powder in this embodiment is the same as that in Example 1.

[0081] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.6 μm and the second peak is at 3.2 μm.

[0082] Example 6

[0083] A bimodal activated alumina micro powder, based on raw materials, comprises 50 kg of first calcined alumina and 50 kg of second calcined alumina.

[0084] The first calcined alumina is obtained by calcining a first alumina billet at a specific temperature, and the second calcined alumina is obtained by calcining a second alumina billet at a specific temperature.

[0085] Based on raw materials, the first alumina billet includes 100 kg of industrial alumina powder, 1.5 kg of magnesium oxide, 3 kg of magnesium sulfate, 0.6 kg of molybdenum hexacarbonyl, 0.9 kg of chromium trioxide, and 10 kg of carboxymethyl chitosan with a viscosity of 100 mPa·s.

[0086] The second alumina billet consists of 100 kg of industrial alumina powder, 4.5 kg of silicon dioxide, 3.6 kg of aluminum fluoride, 0.9 kg of calcium fluoride, and 12 kg of carboxymethyl chitosan.

[0087] In addition, the preparation method of the bimodal active alumina micro powder in this embodiment is the same as that in Example 1.

[0088] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.6 μm and the second peak is at 3.4 μm.

[0089] Example 7

[0090] A bimodal activated alumina micro powder, based on raw materials, comprises 50 kg of first calcined alumina and 50 kg of second calcined alumina.

[0091] The first calcined alumina is obtained by calcining a first alumina billet at a specific temperature, and the second calcined alumina is obtained by calcining a second alumina billet at a specific temperature.

[0092] Based on raw materials, the first alumina billet includes 100 kg of industrial alumina powder, 0.6 kg of magnesium oxide, 3 kg of magnesium sulfate, 0.9 kg of molybdenum hexacarbonyl, 1.5 kg of chromium trioxide, and 10 kg of carboxymethyl chitosan with a viscosity of 100 mPa·s.

[0093] The second alumina billet consists of 100 kg of industrial alumina powder, 4.5 kg of silicon dioxide, 2.7 kg of aluminum fluoride, 1.8 kg of calcium fluoride, and 12 kg of carboxymethyl chitosan.

[0094] In addition, the preparation method of the bimodal active alumina micro powder in this embodiment is the same as that in Example 1.

[0095] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.7 μm and the second peak is at 3.1 μm.

[0096] Example 8

[0097] The difference between this bimodal activated alumina micro powder and Example 7 is that the preparation method of the bimodal activated alumina micro powder is different.

[0098] In this embodiment, the preparation method of bimodal activated alumina micro powder includes the following steps:

[0099] Industrial alumina powder, magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide are mixed evenly according to the formula, carboxymethyl chitosan is added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the first alumina billet.

[0100] Industrial alumina powder, silicon dioxide, aluminum fluoride, and calcium fluoride are mixed evenly according to the formula. Carboxymethyl chitosan is then added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the second alumina blank.

[0101] The first alumina billet was calcined at a temperature of 1250℃, with a heating rate of 5℃ / min. After heating to 1250℃, the holding time was 3h. After holding, the cooling rate was 20℃ / min to obtain the first calcined alumina.

[0102] The second alumina billet was calcined at a temperature of 1550℃, with a heating rate of 5℃ / min. After heating to 1550℃, the holding time was 3h. After holding, the cooling rate was 20℃ / min to obtain the second calcined alumina.

[0103] The first calcined alumina and the second calcined alumina were mixed in a certain ratio and then ball-milled at a ball-to-material ratio of 3:1 for 1 hour to obtain bimodal active alumina micro powder.

[0104] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.6 μm and the second peak is at 3.3 μm.

[0105] Example 9

[0106] The difference between this bimodal activated alumina micro powder and Example 8 is that the preparation method of the bimodal activated alumina micro powder is different.

[0107] In this embodiment, the preparation method of bimodal activated alumina micro powder includes the following steps:

[0108] Industrial alumina powder, magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide are mixed evenly according to the formula, carboxymethyl chitosan is added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the first alumina billet.

[0109] Industrial alumina powder, silicon dioxide, aluminum fluoride, and calcium fluoride are mixed evenly according to the formula. Carboxymethyl chitosan is then added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the second alumina blank.

[0110] The first alumina billet was calcined at a temperature of 1250℃, with a heating rate of 20℃ / min. After heating to 1250℃, the holding time was 3h. After holding, the cooling rate was 50℃ / min to obtain the first calcined alumina.

[0111] The second alumina billet was calcined at a temperature of 1550℃, with a heating rate of 20℃ / min. After heating to 1550℃, the holding time was 3h. After holding, the cooling rate was 50℃ / min to obtain the second calcined alumina.

[0112] The first calcined alumina and the second calcined alumina were mixed in a certain ratio and then ball-milled at a ball-to-material ratio of 3:1 for 1 hour to obtain bimodal active alumina micro powder.

[0113] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.7 μm and the second peak is at 3.4 μm.

[0114] Example 10

[0115] The difference between this bimodal activated alumina micro powder and Example 8 is that the preparation method of the bimodal activated alumina micro powder is different.

[0116] In this embodiment, the preparation method of bimodal activated alumina micro powder includes the following steps:

[0117] Industrial alumina powder, magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide are mixed evenly according to the formula, carboxymethyl chitosan is added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the first alumina billet.

[0118] Industrial alumina powder, silicon dioxide, aluminum fluoride, and calcium fluoride are mixed evenly according to the formula. Carboxymethyl chitosan is then added, stirred evenly, and pressed into a rectangular block of 10cm*10cm*5cm to obtain the second alumina blank.

[0119] The first alumina billet was calcined at a temperature of 1250℃, with a heating rate of 5℃ / min. After heating to 1250℃, the holding time was 5.5h. After holding, the cooling rate was 20℃ / min, and the first calcined alumina was obtained.

[0120] The second alumina billet was calcined at a temperature of 1550℃, with a heating rate of 5℃ / min. After heating to 1550℃, the holding time was 5.5h. After holding, the cooling rate was 20℃ / min to obtain the second calcined alumina.

[0121] The first calcined alumina and the second calcined alumina were mixed in a certain ratio and then ball-milled at a ball-to-material ratio of 3:1 for 1 hour to obtain bimodal active alumina micro powder.

[0122] Tests showed that the particle size distribution of the bimodal activated alumina micropowder in this embodiment has two peaks: the first peak is at 0.7 μm and the second peak is at 3.1 μm.

[0123] Comparative Example

[0124] Comparative Example 1

[0125] An activated alumina micro powder differs from that in Example 2 in that:

[0126] The magnesium oxide in the first alumina billet is replaced by an equal amount of magnesium sulfate.

[0127] Comparative Example 2

[0128] An activated alumina micro powder differs from that in Example 2 in that:

[0129] The magnesium sulfate in the first alumina billet is replaced by an equal amount of magnesium oxide.

[0130] Comparative Example 3

[0131] An activated alumina micro powder differs from that in Example 2 in that:

[0132] The hexacarbonyl molybdenum in the first alumina billet is replaced by an equal amount of chromium trioxide.

[0133] Comparative Example 4

[0134] An activated alumina micro powder differs from that in Example 2 in that:

[0135] In the first alumina billet, chromium trioxide is replaced by an equal amount of molybdenum hexacarbonyl.

[0136] Comparative Example 5

[0137] An activated alumina micro powder differs from that in Example 2 in that:

[0138] In the second alumina billet, aluminum fluoride is replaced by an equal amount of calcium fluoride.

[0139] Comparative Example 6

[0140] An activated alumina micro powder differs from that in Example 2 in that:

[0141] The calcium fluoride in the second alumina billet is replaced by an equal amount of aluminum fluoride.

[0142] Performance test data

[0143] (1) Experiment 1: Take 10 kg of the first calcined alumina from each of Examples 1, Examples 4-10 and Comparative Examples 1-4, and take 10 kg of the second calcined alumina from each of Examples 1, Examples 4-10 and Comparative Examples 5-6. Test the particle size distribution of the first calcined alumina and the second calcined alumina, and record it in Table 1 and Table 2 below.

[0144] (2) Experiment 2: Refractory castables were prepared according to the following formula: 55 kg mullite M70, 5 kg mullite M60, 15 kg andalusite, 5 kg silane powder, 7 kg calcium aluminate cement, 3 kg bimodal activated alumina powder, 5 kg silica fume, and 5 kg water. The bimodal activated alumina powder used in refractory castables 1-10 corresponded to the bimodal activated alumina powders in Examples 1-10, respectively; the bimodal activated alumina powder used in refractory castables 11-16 corresponded to the activated alumina powders in Examples 1-6, respectively. The compressive strength of refractory castables 1-10 was tested and recorded in Table 3 below.

[0145] Table 1

[0146]

[0147] Based on the data from Examples 2 and Comparative Examples 1-4, and in conjunction with the data in Table 1, it can be seen that magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, and chromium trioxide have a synergistic effect on improving the particle size distribution stability of the first calcined alumina. The absence of any one of them will affect the particle size distribution stability of the first calcined alumina.

[0148] Based on Examples 2 and 4-6 and the data in Table 1, it can be seen that when the weight ratio of industrial alumina powder, first particle size stabilizer and organic binder is in the range of 100:(5-6):(8-10), the proportion of first calcined alumina with a particle size in the range of 0.5-1.0μm can be increased, that is, the particle size distribution stability of first calcined alumina can be further improved.

[0149] Based on Examples 6 and 7 and the data in Table 1, it can be seen that when the weight ratio of magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide is in the range of (0.2-0.3):1:(0.2-0.3):0.5, the particle size distribution stability of the first calcined alumina can be further improved, which has a promoting effect on improving the particle size distribution stability of bimodal active alumina micro powder and is beneficial to improving the particle size distribution stability of bimodal active alumina.

[0150] Based on Examples 8 and 9 and the data in Table 1, it can be seen that the particle size distribution of the first calcined alumina is less affected by the heating and cooling rates of the calcination temperature. Therefore, there is no need to precisely control the heating and cooling rates during the production process.

[0151] Table 2

[0152]

[0153] Based on Example 2 and Comparative Examples 5-6, and combined with the data in Table 2, it can be seen that the combination of aluminum fluoride and calcium fluoride is more conducive to improving the particle size distribution stability of the second calcined alumina.

[0154] Based on Examples 2 and 4-6 and the data in Table 2, it can be seen that when the weight ratio of industrial alumina powder, second particle size stabilizer and organic binder is in the range of 100:(7-9):(10-12), the proportion of first calcined alumina with a particle size in the range of 3.0-3.5μm can be increased, that is, the particle size distribution stability of second calcined alumina can be further improved.

[0155] Based on Examples 6 and 7 and the data in Table 2, it can be seen that when the weight ratio of silicon dioxide, aluminum fluoride, and calcium fluoride is 1:(0.5-0.6):(0.4-0.5), the particle size distribution stability of the second calcined alumina can be further improved.

[0156] Based on Examples 8 and 9 and the data in Table 2, it can be seen that the particle size distribution of the second calcined alumina is less affected by the heating and cooling rates of the calcination temperature. Therefore, there is no need to precisely control the heating and cooling rates during the production process.

[0157] Table 3

[0158]

[0159]

[0160] Based on the data from Example 2 and Comparative Examples 1-6, and in conjunction with Table 3, it can be seen that the size distribution of the first calcined alumina and the second calcined alumina affects the dispersion performance of bimodal active alumina micropowder in refractory castables. When the dispersibility of bimodal active alumina micropowder is poor, it can easily have an adverse effect on the compressive strength of refractory castables.

[0161] Combining Examples 7 and 8 with the data in Table 3, it can be seen that when the calcination temperature of the first alumina billet is in the range of 1150-1250℃ and the calcination temperature of the second alumina billet is in the range of 1450-1550℃, it has a further promoting effect on improving the compressive strength and heat resistance of the refractory castable. The reason may be that when the calcination temperature is in the range of 1150-1250℃, it can further promote the conversion of other crystal forms of alumina into α-alumina.

[0162] Combining Examples 8 and 10 with the data in Table 3, it can be seen that a holding time of 5-6 hours between the first and second alumina billets further promotes the improvement of the compressive strength and heat resistance of the refractory castable. This may be because a holding time of 5-6 hours between the first and second alumina billets can further promote the conversion of other alumina crystals into α-alumina.

[0163] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing bimodal activated alumina micro powder, characterized in that: The process includes the following steps: First, industrial alumina powder and a first particle size stabilizer are uniformly mixed, then an organic binder is added, and the mixture is stirred until homogeneous. The mixture is then pressed into a 10cm x 10cm x 5cm rectangular block to obtain a first alumina ingot. Second, industrial alumina powder and a second particle size stabilizer are uniformly mixed, then an organic binder is added, and the mixture is stirred until homogeneous. The mixture is then pressed into a 10cm x 10cm x 5cm rectangular block to obtain a second alumina ingot. Third, the first alumina ingot is calcined at a temperature of 1000-1300℃ to obtain first calcined alumina. The second alumina billet is calcined at a temperature of 1400-1800℃ to obtain the second calcined alumina. After mixing 40-60 parts by weight of the first calcined alumina and 40-60 parts by weight of the second calcined alumina according to the specified ratio, the mixture is ball-milled to obtain bimodal active alumina micro powder. Based on raw materials, in the first alumina billet, the weight ratio of the industrial alumina powder, the first particle size stabilizer, and the organic binder is 100:(3-6):(4-10); the first particle size stabilizer includes magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, and chromium trioxide, and the weight ratio of the magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl, and chromium trioxide is (0.1-0.5):1:(0.2-0.4):(0.3-0.5); in the second alumina billet, the weight ratio of the industrial alumina powder, the second particle size stabilizer, and the organic binder is 100:(5-9):(8-12); the second particle size stabilizer includes silicon dioxide, aluminum fluoride, and calcium fluoride, and the weight ratio of the silicon dioxide, aluminum fluoride, and calcium fluoride is 1:(0.4-0.8):(0.2-0.6).

2. The method for preparing bimodal activated alumina micro powder according to claim 1, characterized in that: In the first alumina blank, the weight ratio of the industrial alumina powder, the first particle size stabilizer and the organic binder is 100:(5-6):(8-10).

3. The method for preparing bimodal activated alumina micro powder according to claim 1 or 2, characterized in that: In the first particle size stabilizer, the weight ratio of magnesium oxide, magnesium sulfate, molybdenum hexacarbonyl and chromium trioxide is (0.2-0.3):1:(0.2-0.3):0.

5.

4. The method for preparing bimodal activated alumina micro powder according to claim 3, characterized in that: In the second alumina blank, the weight ratio of the industrial alumina powder, the second particle size stabilizer and the organic binder is 100:(7-9):(10-12).

5. The method for preparing bimodal activated alumina micro powder according to claim 4, characterized in that: In the second particle size stabilizer, the weight ratio of silicon dioxide, aluminum fluoride and calcium fluoride is 1:(0.5-0.6):(0.4-0.5).

6. The method for preparing bimodal activated alumina micro powder according to claim 1, characterized in that: The organic binder is selected from at least one of carboxymethyl chitosan and polyvinyl alcohol.

7. The method for preparing bimodal activated alumina micro powder according to claim 1, characterized in that: The calcination temperature of the first alumina billet is 1150-1250℃.

8. The method for preparing bimodal activated alumina micro powder according to claim 1, characterized in that: The calcination temperature of the second alumina billet is 1450-1550℃.

9. The method for preparing bimodal activated alumina micro powder according to claim 1, characterized in that: The holding time for calcining the first alumina billet and the second alumina billet is 5-6 hours.

10. A bimodal activated alumina micro powder, characterized in that: It is prepared by the method for preparing bimodal active alumina micro powder according to any one of claims 1-9.

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