A method for preparing aluminum sol for preparing alumina polycrystalline fiber

Abstract

The invention provides a method for preparing aluminum sol for preparing alumina polycrystalline fibers. The invention prepares the aluminum sol by a two-step method. Firstly, hydrochloric acid is reacted with aluminum element to obtain a clear and transparent precursor solution and then the solution is aged. Aluminum powders of different specifications are mixed in a certain proportion and kept for later use. Aluminum powders of different particle sizes react in different degrees and generate different amounts of heat, thereby controlling the temperature of the reaction environment in the container to fluctuate within a small range. Then, part of the precursor solution is added into a reaction container, and after being heated to a certain temperature, aluminum powder is added through the container mouth for multiple times, and part of the precursor solution is supplemented, thereby effectively reducing the intensity of the reaction between the aluminum powder and the precursor solution in the reaction process, achieving uniformity of the quality of the aluminum sol and stability of the solid content, and providing a raw material with stable performance that improves the product quality of alumina polycrystalline fibers.

Description

Technical Field

[0001] The invention belongs to the field of material technology, and in particular relates to a method for preparing aluminum sol for preparing aluminum oxide polycrystalline fibers. Background Art

[0002] Alumina polycrystalline fiber is a new type of high-performance inorganic fiber with high tensile strength and elastic modulus, good electrical insulation and oxidation resistance, good corrosion resistance in acidic environments, and the ability to maintain good chemical stability in oxidizing or reducing atmospheres. It also has the advantages of low thermal conductivity, low thermal expansion coefficient, and good thermal shock resistance. It is currently widely used in refractory materials, structural reinforcement materials, and environmentally friendly recycling.

[0003] Alumina polycrystalline fibers are mainly prepared by the sol-gel method, and the performance of the precursor aluminum sol directly determines the quality of the alumina polycrystalline fibers. In the production process, the precursor aluminum sol used in the production of alumina polycrystalline fibers is mainly prepared by reacting acid or strong acid and weak alkaline aluminum salts with metallic aluminum. When preparing aluminum sol in the laboratory and in small batches, the problem of this method is not obvious, but in the process of industrial production of aluminum sol, the reaction process is more violent and uncontrollable, resulting in unstable solid content of the prepared aluminum sol, large quality fluctuations, easy precipitation or transparent gel insoluble in water. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing aluminum sol for preparing alumina polycrystalline fibers. The aluminum sol prepared by the present invention has high clarity, good fluidity, uniform quality, and stable solid content, thereby providing a raw material with stable performance for improving the quality of alumina polycrystalline fiber products.

[0005] The present invention provides a method for preparing aluminum sol for preparing aluminum oxide polycrystalline fiber, comprising the following steps:

[0006] A) mixing elemental aluminum with hydrochloric acid to react and obtain a reaction solution;

[0007] B) aging the reaction solution to obtain a precursor solution;

[0008] C) Take part of the precursor solution, heat it, and add the graded aluminum powder and the remaining precursor solution alternately in the following manner:

[0009] The graded aluminum powder is divided into n parts, and the remaining precursor solution is divided into m parts. The graded aluminum powder and the remaining precursor solution are added alternately in sequence in such a manner that one part of the remaining precursor solution is added for every 3 to 8 parts of the graded aluminum powder, until all parts are added, and then stirred at a constant temperature to obtain an aluminum sol;

[0010] The graded aluminum powder includes a first aluminum powder of 300-400 mesh, a second aluminum powder of 600-1000 mesh, and a third aluminum powder of 2000-3500 mesh; the mass ratio of the first aluminum powder, the second aluminum powder, and the third aluminum powder is (2-3): (4-6): (2-3).

[0011] Preferably, 10≤n≤50, 2≤m≤15.

[0012] Preferably, the elemental aluminum includes one or more of aluminum ingot, aluminum block and aluminum powder;

[0013] The molar ratio of the elemental aluminum to the hydrochloric acid is 1:(1-3).

[0014] Preferably, the aging temperature in step B) is 20-35° C., and the aging time in step B) is 2-5 days; after the aging, solid-liquid separation is performed to obtain a precursor solution.

[0015] Preferably, the mass concentration of the precursor solution is 10-25%;

[0016] The mass ratio of the graded aluminum powder to the precursor solution is 1:(7-18).

[0017] Preferably, the heating temperature in step C) is 80-100°C.

[0018] Preferably, the mass of the part of the precursor in step C) is 70-80% of the mass of the precursor solution in step B).

[0019] Preferably, the mixed gas generated during the reaction in step C) is condensed and refluxed.

[0020] Preferably, the time interval between any two adjacent additions of graded aluminum powder is 20 to 40 minutes.

[0021] Preferably, the temperature of the constant temperature stirring in step C) is 60-90° C.; and the time of the constant temperature stirring in step C) is 5-20 hours.

[0022] The invention provides a method for preparing aluminum sol for preparing alumina polycrystalline fiber, comprising the following steps: A) mixing elemental aluminum with hydrochloric acid, reacting to obtain a reaction solution; B) aging the reaction solution to obtain a precursor solution; C) taking part of the precursor solution, heating it, and alternately adding graded aluminum powder and the remaining precursor solution in the following manner: dividing the graded aluminum powder into n parts, dividing the remaining precursor solution into m parts, and adding one part of the remaining precursor solution in turn in a manner of adding 3-8 parts of the graded aluminum powder and supplementing one part of the remaining precursor solution, and adding the graded aluminum powder and the remaining precursor solution alternately in sequence until all parts are added, stirring at a constant temperature to obtain the aluminum sol; the graded aluminum powder comprises a first aluminum powder of 300-400 meshes, a second aluminum powder of 600-1000 meshes, and a third aluminum powder of 2000-3500 meshes; the mass ratio of the first aluminum powder, the second aluminum powder, and the third aluminum powder is (2-3):(4-6):(2-3). The invention prepares aluminum sol by a two-step method. First, hydrochloric acid is reacted with aluminum element to obtain a clear and transparent precursor solution and then the solution is aged. Aluminum powders of different specifications are mixed in a certain proportion and kept for later use. Aluminum powders of different particle sizes react in different degrees and generate different amounts of heat, thereby controlling the temperature of the reaction environment in the container to fluctuate within a small range. Then, part of the precursor solution is added to the reaction container, and after heating to a certain temperature, aluminum powder is added through the container mouth for multiple times, and part of the precursor solution is supplemented, thereby effectively reducing the intensity of the reaction between the aluminum powder and the precursor solution in the reaction process, achieving uniformity of the quality of the aluminum sol and stability of the solid content, and providing a raw material with stable performance that improves the quality of alumina polycrystalline fiber products.

[0023] Compared with the one-step method commonly used in the prior art, the two-step method adopted by the present invention uses hydrochloric acid and aluminum powder to directly react to prepare aluminum sol. The aluminum powder with smaller particle size reacts violently with hydrochloric acid and the reaction process cannot be controlled, and there is a risk of material overflow. At the same time, the violent reaction generates a large amount of heat, which accelerates the loss of water in the material and easily causes the aluminum sol to produce gel due to the volatilization of a large amount of water. Compared with the one-step method, the two-step method for preparing aluminum sol first uses aluminum powder with larger particle size to react with hydrochloric acid, which slows down the intensity of the reaction and releases part of the heat generated by the reaction. The reaction speed of the prepared precursor and the aluminum powder with smaller particle size is controlled, which is more conducive to increasing the proportion of effective ingredients in the aluminum sol and enhancing the stability of subsequent alumina polycrystalline fiber production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 is an autocorrelation function diagram of the aluminum sol in Example 1 of the present invention;

[0026] Figure 2 This is a graph showing the light intensity variation of the aluminum sol in Example 1 of the present invention over time. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing aluminum sol for preparing aluminum oxide polycrystalline fiber, comprising the following steps:

[0028] A) mixing elemental aluminum with hydrochloric acid to react and obtain a reaction solution;

[0029] B) aging the reaction solution to obtain a precursor solution;

[0030] C) Take part of the precursor solution, heat it, and add the graded aluminum powder and the remaining precursor solution alternately in the following manner:

[0031] The graded aluminum powder is divided into n parts, and the remaining precursor solution is divided into m parts. The graded aluminum powder and the remaining precursor solution are added alternately in sequence in the manner of adding 3 to 8 parts of the graded aluminum powder and adding one part of the remaining precursor solution. After all the additions are completed, the graded aluminum powder and the remaining precursor are stirred at a constant temperature to obtain an aluminum sol;

[0032] The graded aluminum powder includes a first aluminum powder of 300-400 mesh, a second aluminum powder of 600-1000 mesh, and a third aluminum powder of 2000-3500 mesh; the mass ratio of the first aluminum powder, the second aluminum powder, and the third aluminum powder is (2-3): (4-6): (2-3).

[0033] In the present invention, the elemental aluminum preferably includes one or more of aluminum ingots, aluminum blocks and aluminum powder; the hydrochloric acid preferably uses a hydrochloric acid solution with a concentration of 35~37%, and the molar ratio of the elemental aluminum to the hydrochloric acid is preferably 1:(1~3), more preferably 1:(1~2), such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, preferably a range value with any of the above values ​​as the upper or lower limit.

[0034] In the present invention, the reaction is preferably carried out at room temperature, the reaction is an exothermic reaction, the reaction time is related to the amount of precursor solution prepared, the preparation time in the present invention is preferably 4 to 5 hours, the pH of the obtained reaction solution is less than 1, and the reaction solution includes aluminum chloride, a small amount of hydrochloric acid and a small amount of insoluble impurities.

[0035] After the above reaction is completed, the present invention cools the obtained reaction solution to room temperature for aging, and then removes the bottom precipitate by solid-liquid separation to obtain a clear and transparent precursor solution, wherein the precursor solution includes aluminum chloride and hydrochloric acid.

[0036] In the present invention, the aging temperature is preferably room temperature, such as 20-35° C., more preferably 25-30° C.; the aging time is preferably 2-5 days, more preferably 3-4 days.

[0037] After completing the solid-liquid separation, the present invention preferably adds water to the filtrate to prepare the concentration of the filtrate to 10-20%, more preferably 15-16%. The present invention controls the concentration of the precursor solution within the above range, which is beneficial to control the reaction rate of the precursor solution and the aluminum powder, and ensure the proportion of the effective ingredients in the preparation of the aluminum sol.

[0038] After obtaining the precursor solution, the present invention takes a portion of the precursor solution and heats it to a certain temperature, then adds graded aluminum powder through the container mouth in multiple times, and adds the remaining precursor solution in multiple times to react. After the reaction is completed, it is stirred at a constant temperature for a certain period of time to obtain a light blue clear and transparent aluminum sol.

[0039] In the present invention, the graded aluminum powder is a mixed aluminum powder containing aluminum powders of different particle sizes. In the present invention, the graded aluminum powder includes at least three kinds of aluminum powders of particle sizes. The particle size of the first aluminum powder is preferably 300-400 mesh, 300-400 mesh, such as 300 mesh, 310 mesh, 320 mesh, 330 mesh, 340 mesh, 350 mesh, 360 mesh, 370 mesh, 380 mesh, 390 mesh, 400 mesh, preferably a range value with the above arbitrary numerical values ​​as the upper limit or lower limit. The particle size of the second aluminum powder is preferably 600-1000 mesh, more preferably 700-900 mesh, such as 600 mesh, 650 mesh, 700 mesh, 750 mesh, 800 mesh, 850 mesh, 900 mesh, 950 mesh, 1000 mesh, preferably a range value with the above arbitrary numerical value as the upper limit or lower limit, the particle size of the third aluminum powder is preferably 2000~3500 mesh, more preferably 2500~3500 mesh, such as 2000 mesh, 2100 mesh, 2200 mesh, 2300 mesh, 2400 mesh, 2500 mesh, 2600 mesh, 2700 mesh, 2800 mesh, 2900 mesh, 3000 mesh, 3100 mesh, 3200 mesh, 3300 mesh, 3400 mesh, 3500 mesh, preferably a range value with the above arbitrary numerical value as the upper limit or lower limit.

[0040] In the present invention, the mass ratio of the first aluminum powder, the second aluminum powder and the third aluminum powder is preferably (2-3): (4-6): (2-3), more preferably (2-3): (4-5): (2-3), such as 2:5:3, 2:6:2, 3:4:3 or 3:5:2. The mixed aluminum powder with particle size distribution in the present invention is used as the reaction raw material, which can avoid the problems of abnormal color of aluminum sol, abnormal degree of polymerization, abnormal reaction, unstable solid content, easy precipitation or formation of water-insoluble transparent gel caused by using single particle size aluminum powder as raw material in the prior art.

[0041] In the present invention, the mass ratio of the graded aluminum powder to the precursor solution is preferably 1: (7-18), more preferably 1: (12-15), such as 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, preferably a range value with any of the above values ​​as the upper or lower limit; the mass of the part of the precursor solution taken is preferably 70-80% of the total mass of the precursor solution, more preferably 73-78%, such as 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, preferably a range value with any of the above values ​​as the upper or lower limit; the mass of the remaining precursor solution is preferably 20-30% of the total mass of the precursor solution, more preferably 22-27%, such as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0042] In the present invention, the part of the precursor is heated to 80-100°C, more preferably 85-90°C.

[0043] In the present invention, the graded aluminum powder and the remaining precursor solution are preferably added alternately in multiple times. Specifically, the graded aluminum powder is divided into n parts, and the remaining precursor solution is divided into m parts. For every 3 to 8 parts of graded aluminum powder added, one part of the remaining precursor solution is added. The graded aluminum powder and the remaining precursor solution are added alternately in sequence until all are added. The mixture is then stirred at a constant temperature for a certain period of time to obtain a light blue, clear and transparent aluminum sol.

[0044] In the present invention, the graded aluminum powder can be divided into n parts uniformly or unevenly, preferably uniformly, and the remaining precursor solution can be divided into m parts uniformly or unevenly, preferably uniformly, for easy operation and stable quality.

[0045] In the present invention, 10≤n≤50, 2≤m≤15, preferably, n is 20 or 30, and m is 3, 4, 5 or 6.

[0046] During the reaction of aluminum powder and precursor solution, as the reaction proceeds, the precursor solution is gradually consumed, the intensity of the reaction slows down, and the reaction temperature decreases, which is not conducive to the formation of effective ingredients in the aluminum sol; the present invention preferably adds one part of precursor solution for every n parts of graded aluminum powder added, which is beneficial to maintaining the stability and controllability of the reaction, and is also beneficial to the formation of effective ingredients in the aluminum sol.

[0047] In the present invention, preferably, for every 3 to 8 parts of graded aluminum powder added, one part of the remaining precursor solution is added, more preferably, for every 4 to 7 parts of graded aluminum powder added, one part of the remaining precursor solution is added, and most preferably, for every 5 to 6 parts of graded aluminum powder added, one part of the remaining precursor solution is added.

[0048] In the present invention, any two adjacent added portions of graded aluminum powder have a certain time interval to ensure sufficient reaction, and the time interval is preferably 20-40 min, more preferably 25-35 min, such as 20 min, 25 min, 30 min, 35 min, 40 min, preferably a range value with the above arbitrary numerical values ​​as the upper or lower limit. The present invention divides the graded aluminum powder into n portions, and there are n-1 time intervals, which may be equal or unequal. On the premise that the graded aluminum powder is evenly divided into n portions, it is preferred to set the same n-1 time intervals. Furthermore, based on this premise and on the premise that the remaining precursor solution is evenly divided into m portions, the number of additions of the graded aluminum powder separated by the m portions of the remaining precursor solution is also preferably equal.

[0049] During the entire process of the reaction of the graded aluminum powder and the precursor solution, the generated gas is condensed and refluxed. During the condensation process, the temperature of the condensed water does not exceed 25°C, the condensation area of ​​a single device is not less than 3 square meters, and the condensation time accompanies the entire reaction process. The present invention sets a condensation reflux treatment for the generated gas (a large amount of water vapor, hydrogen and part of the hydrogen chloride gas) during the reaction process. The reflux water with a lower temperature has a cooling effect on the mixed liquid in the container. At the same time, a large amount of hydrogen chloride gas is dissolved in the reflux water after condensation to form a hydrogen chloride solution, which reduces the escape of hydrogen chloride gas and ensures that the aluminum-chlorine ratio in the prepared aluminum sol meets the quality requirements of the aluminum sol.

[0050] After the reaction is completed, the present invention stirs the obtained reaction solution at a constant temperature for a certain period of time to obtain a light blue clear and transparent aluminum sol.

[0051] In the present invention, the constant temperature is preferably 60-90° C., more preferably 70-85° C., most preferably 75-80° C., and the stirring time is preferably 5-20 hours, more preferably 5-10 hours.

[0052] The invention provides a method for preparing aluminum sol for preparing alumina polycrystalline fiber, comprising the following steps: A) mixing elemental aluminum with hydrochloric acid, reacting to obtain a reaction solution; B) aging the reaction solution to obtain a precursor solution; C) taking a part of the precursor solution, heating it, and alternately adding graded aluminum powder and the remaining precursor solution in the following manner: dividing the graded aluminum powder into n parts, dividing the remaining precursor solution into m parts, and adding one part of the remaining precursor solution in turn in a manner of adding 3-8 parts of the graded aluminum powder and supplementing it with one part of the remaining precursor solution, and adding the graded aluminum powder and the remaining precursor alternately in sequence until all the parts are added, stirring at a constant temperature to obtain the aluminum sol; the graded aluminum powder comprises a first aluminum powder of 300-400 meshes, a second aluminum powder of 600-1000 meshes, and a third aluminum powder of 2000-3500 meshes; the mass ratio of the first aluminum powder, the second aluminum powder, and the third aluminum powder is (2-3):(4-6):(2-3). The invention prepares aluminum sol by a two-step method. First, hydrochloric acid is reacted with aluminum element to obtain a clear and transparent precursor solution and then the solution is aged. Aluminum powders of different specifications are mixed in a certain proportion and kept aside. Aluminum powders of different particle sizes react in different degrees and generate different amounts of heat, thereby controlling the temperature of the reaction environment in the container to fluctuate within a small range. Then, part of the precursor is added to the reaction container, and after heating to a certain temperature, aluminum powder is added through the container mouth for multiple times, and part of the precursor solution is supplemented, thereby effectively reducing the intensity of the reaction process between the aluminum powder and the precursor solution, achieving uniformity of the quality of the aluminum sol and stability of the solid content, and providing a raw material with stable performance that improves the quality of alumina polycrystalline fiber products.

[0053] In order to further illustrate the present invention, a method for preparing aluminum sol for preparing alumina polycrystalline fibers provided by the present invention is described in detail below in combination with examples, but it should not be understood as limiting the scope of protection of the present invention.

[0054] Example 1

[0055] (1) Weighing a certain mass of elemental aluminum and 36% hydrochloric acid, the molar ratio of elemental aluminum to hydrochloric acid being 1:3, after sufficient reaction, leaving the obtained mixed solution to stand for 3 days and then filtering, adding a certain mass of water to the filtrate to prepare the filtrate into a solution with a concentration of 15%, thereby obtaining a precursor solution;

[0056] (2) Weigh 600 kg of the precursor solution, add it into the reaction vessel, and heat it to 90 °C;

[0057] (3) Weigh 12 kg of 400-mesh aluminum powder, 30 kg of 800-mesh aluminum powder, and 18 kg of 2500-mesh aluminum powder, mix them evenly, and divide them into 30 equal portions; after adding the first portion of aluminum powder, turn on the condenser, keep the cooling water temperature of the condenser at 25 ± 1 ° C, and the cooling area of ​​the condenser is 4 square meters. The mixed gas produced by the reaction is condensed and refluxed through the condenser. 30 minutes after adding the first portion of aluminum powder, add the second portion of aluminum powder, 30 minutes after adding the second portion of aluminum powder, and add the third portion of aluminum powder, and so on until the fifth portion of aluminum powder is added;

[0058] (4) Before adding the sixth portion of aluminum powder, add 40 kg of precursor solution to the reaction vessel, and then add the sixth portion of aluminum powder; 30 minutes after adding the sixth portion of aluminum powder, add the seventh portion of aluminum powder, and 30 minutes after adding the seventh portion of aluminum powder, add the eighth portion of aluminum powder, and so on until the tenth portion of aluminum powder is added;

[0059] (5) Before adding the eleventh portion of aluminum powder, add 40 kg of precursor solution to the reaction vessel, and then add the eleventh portion of aluminum powder; 30 minutes after adding the eleventh portion of aluminum powder, add the twelfth portion of aluminum powder, and 30 minutes after adding the twelfth portion of aluminum powder, add the thirteenth portion of aluminum powder, and so on until the fifteenth portion of aluminum powder is added;

[0060] (6) Before adding the aluminum powder for the sixteenth time, add another 40 kg of the precursor solution to the reaction vessel, and then add the sixteenth portion of aluminum powder; 30 minutes after adding the sixteenth portion of aluminum powder, add the seventeenth portion of aluminum powder, and 30 minutes after adding the seventeenth portion of aluminum powder, add the eighteenth portion of aluminum powder, and so on until the twentieth portion of aluminum powder is added;

[0061] (7) Before adding the aluminum powder for the 21st time, add 40 kg of the precursor solution to the reaction vessel, and then add the 21st portion of aluminum powder; 30 minutes after adding the 21st portion of aluminum powder, add the 22nd portion of aluminum powder, and 30 minutes after adding the 22nd portion of aluminum powder, add the 23rd portion of aluminum powder, and so on until the 25th portion of aluminum powder is added;

[0062] (8) Before adding the aluminum powder for the 26th time, add 40 kg of the precursor solution to the reaction container, and then add the 26th portion of aluminum powder; 30 minutes after adding the 26th portion of aluminum powder, add the 27th portion of aluminum powder, and 30 minutes after adding the 27th portion of aluminum powder, add the 28th portion of aluminum powder, and so on until the 30th portion of aluminum powder is added;

[0063] (9) During the entire reaction process, the condenser is kept open to continuously condense and reflux the mixed gas;

[0064] (10) After the 30th portion of aluminum powder is added, the mixture is kept warm for 8 hours to obtain aluminum sol;

[0065] (11) The aluminum sol prepared in this embodiment has high clarity, no impurities remaining and good fluidity;

[0066] (12) The average particle size of the aluminum sol prepared in this embodiment is 603.2 nm.

[0067] (13) The solid content of the aluminum sol prepared in this embodiment is 24%.

[0068] (14) Figure 1 It is an autocorrelation function diagram of the aluminum sol in Example 1 of the present invention, which represents a function curve of refracted light changing with time. The number of scattered points in the diagram represents the ion concentration in the solution. The fewer the scattered points, the lower the concentration of the solute in the solution. Figure 1 The scattered points in the solution represent the Brownian motion of particles. Figure 1 It can be seen that the scattered points gradually return to stability, which means that the test results are correct, but there are a small number of larger particles distributed in the aluminum sol.

[0069] (15) Figure 2 The light intensity of the aluminum sol in Example 1 of the present invention changes with time. Figure 2 The horizontal axis represents the intensity of the refracted light of the particles. The narrower the distribution range of each point, the better the uniformity of the particle size in the solution. The wider the distribution, the larger the distribution range of the particle size in the solution, and the more uneven the solution. Figure 2 It can be seen that the aluminum sol solution prepared in Example 1 has good uniformity overall.

[0070] Example 2

[0071] Aluminum sol was prepared according to the method in Example 1, except that, in Example 2, before adding aluminum powder for the eighth time, 40 kg of precursor solution was added to the reaction container, before adding aluminum powder for the sixteenth time, 40 kg of precursor solution was added to the reaction container, before adding aluminum powder for the twenty-fourth time, 40 kg of precursor solution was added to the reaction container, before adding aluminum powder for the thirty-second time, 40 kg of precursor solution was added to the reaction container, and before adding aluminum powder for the fortieth time, 40 kg of precursor solution was added to the reaction container instead of "before adding aluminum powder for the sixth time, 40 kg of precursor solution was added to the reaction container" in Example 1. 40kg of precursor solution is added to the reaction vessel before the eleventh addition of aluminum powder, 40kg of precursor solution is added to the reaction vessel before the sixteenth addition of aluminum powder, 40kg of precursor solution is added to the reaction vessel before the twenty-first addition of aluminum powder, and 40kg of precursor solution is added to the reaction vessel before the twenty-sixth addition of aluminum powder. In Example 2, after the forty-fifth portion of aluminum powder is added, the aluminum sol is obtained after being kept warm for 8h, instead of "after the thirtieth portion of aluminum powder is added, the aluminum sol is obtained after being kept warm for 8h" in Example 1;

[0072] In the process of preparing aluminum sol in Example 2, the reaction is relatively slow, and the prepared aluminum sol has good clarity and is colorless;

[0073] The solid content of the aluminum sol prepared in Example 2 is 15.6%.

[0074] Comparative Example 1

[0075] Aluminum sol was prepared according to the method in Example 1, except that 60 kg of 2500 mesh aluminum powder was used in Comparative Example 1 to replace the mixed aluminum powder consisting of "12 kg 400 mesh aluminum powder, 30 kg 800 mesh aluminum powder, and 18 kg 2500 mesh aluminum powder" in Example 1.

[0076] The aluminum sol prepared in Comparative Example 1 had a large viscosity and poor fluidity, and could not be tested. It formed a gel after being left for a period of time.

[0077] The solid content of the aluminum sol prepared in Comparative Example 1 is 28%.

[0078] Comparative Example 2

[0079] (1) Weighing a certain mass of elemental aluminum and 36% hydrochloric acid, the molar ratio of elemental aluminum to hydrochloric acid being 1:3, after sufficient reaction, leaving the obtained mixed solution to stand for 3 days and then filtering, adding a certain mass of water to the filtrate to prepare the filtrate into a solution with a concentration of 15%, thereby obtaining a precursor solution;

[0080] (2) Weigh 800 kg of the precursor solution, add it into the reaction vessel, and heat it to 90 °C;

[0081] (3) Weigh 60 kg of 2500 mesh aluminum powder and divide it into 30 equal portions; add the first portion of aluminum powder, then open the condenser, keep the cooling water temperature of the condenser at 25±1°C, and the cooling area of ​​the condenser is 4 square meters. The mixed gas produced by the reaction is condensed and refluxed through the condenser. Add the second portion of aluminum powder 30 minutes after adding the first portion of aluminum powder, and add the third portion of aluminum powder 30 minutes after adding the second portion of aluminum powder, and so on until the thirtieth portion of aluminum powder is added;

[0082] (4) During the entire reaction process, the condenser is kept open to continuously condense and reflux the mixed gas;

[0083] (5) After the 30th portion of aluminum powder is added, the temperature is kept at room temperature for 8 hours to obtain aluminum sol;

[0084] (6) The aluminum sol prepared in Comparative Example 2 was white and had poor clarity;

[0085] (7) The solid content of the aluminum sol prepared in the comparative example is 23.5%.

[0086] Comparative Example 3

[0087] Aluminum sol was prepared according to the method in Example 1, except that 60 kg of 400-mesh aluminum powder was used in Comparative Example 3 to replace the mixed aluminum powder consisting of "12 kg of 400-mesh aluminum powder, 30 kg of 800-mesh aluminum powder, and 18 kg of 2500-mesh aluminum powder" in Example 1.

[0088] The aluminum sol prepared in Comparative Example 3 contained more suspended matter and more impurities remained at the bottom;

[0089] The solid content of the aluminum sol prepared in Comparative Example 3 is 20.8%.

[0090] Comparative Example 4

[0091] Aluminum sol was prepared according to the method in Example 1, except that 30 kg of aluminum powder with a mesh number of 100 mesh, 15 kg of aluminum powder with a mesh number of 500 mesh, and 15 kg of aluminum powder with a mesh number of 1000 mesh were used in Comparative Example 4 to replace the mixed aluminum powder consisting of "12 kg of aluminum powder with a mesh number of 400 mesh, 30 kg of aluminum powder with a mesh number of 800 mesh, and 18 kg of aluminum powder with a mesh number of 2500 mesh" in Example 1;

[0092] In the process of preparing aluminum sol in Comparative Example 4, the reaction process stability is poor. The reaction is relatively slow in the first 4 to 5 additions of aluminum powder. The reaction is extremely violent in 1 to 2 additions of aluminum powder in the 6 to 10 additions. As the number of aluminum powder additions increases, the intensity of the reaction gradually stabilizes. A small amount of incompletely reacted aluminum powder is present in the prepared aluminum sol, and the aluminum sol is colorless.

[0093] The solid content of the aluminum sol prepared in Comparative Example 4 is 20.6%.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing aluminum sol for preparing alumina polycrystalline fibers, comprising the following steps: A) mixing elemental aluminum with hydrochloric acid to react and obtain a reaction solution; B) aging the reaction solution to obtain a precursor solution; C) Take part of the precursor solution, heat it, and add the graded aluminum powder and the remaining precursor solution alternately in the following manner: The graded aluminum powder is divided into n parts, and the remaining precursor solution is divided into m parts. The graded aluminum powder and the remaining precursor solution are added alternately in sequence in such a manner that one part of the remaining precursor solution is added for every 3 to 8 parts of the graded aluminum powder, until all parts are added, and then stirred at a constant temperature to obtain an aluminum sol; The graded aluminum powder includes a first aluminum powder of 300 mesh, a second aluminum powder of 800 mesh, and a third aluminum powder of 2500 mesh; the mass ratio of the first aluminum powder, the second aluminum powder, and the third aluminum powder is 2:5:3; 10≤n≤50, 2≤m≤15; The mass concentration of the precursor solution is 10-25%; the mass ratio of the graded aluminum powder to the precursor solution is 1:(7-18); The mass of the part of the precursor in step C) is 70-80% of the mass of the precursor solution in step B).

2. The preparation method according to claim 1, characterized in that: The elemental aluminum includes one or more of aluminum ingot, aluminum block and aluminum powder; The molar ratio of the elemental aluminum to the hydrochloric acid is 1:(1-3).

3. The preparation method according to claim 1, characterized in that: The aging temperature in step B) is 20-35° C., and the aging time in step B) is 2-5 days. After the aging is completed, solid-liquid separation is performed to obtain a precursor solution.

4. The preparation method according to claim 1, characterized in that: The heating temperature in the step C) is 80-100°C.

5. The preparation method according to claim 1, characterized in that: The mixed gas generated during the reaction in step C) is condensed and refluxed.

6. The preparation method according to claim 1, characterized in that: The time interval between any two adjacent additions of graded aluminum powder is 20 to 40 minutes.

7. The preparation method according to claim 1, characterized in that: The temperature of the constant temperature stirring in the step C) is 60-90° C.; the time of the constant temperature stirring in the step C) is 5-20 hours.

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