A preparation method of β"-alumina

Abstract

The invention discloses a method for preparing β″-alumina, and belongs to the technical field of alumina production. The invention utilizes the synergistic effect of modified α-alumina and modified θ-alumina, combined with sodium salt, to promote the transformation of crystal form during sintering, so that the formation of β″-alumina is more stable and has high purity. At the same time, alcohol wet grinding and the use of dispersants and stabilizers are adopted to ensure the uniformity and stability of ball mill slurry, effectively prevent particle agglomeration and precipitation, and improve the preparation efficiency and product quality of β″-alumina. In addition, during calcination, under the protection of nitrogen atmosphere, the preparation process of pre-sintering and main sintering is adopted to ensure the crystalline integrity of the material at high temperature, avoid unnecessary phase change and impurity generation, and obtain β″-alumina with excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of alumina production, and in particular relates to a method for preparing β″-alumina. Background Art

[0002] With the continuous growth of global energy demand and the increasing awareness of environmental protection, efficient and environmentally friendly energy storage technology has become a hot topic of research. Sodium-sulfur batteries, as an electrochemical energy storage technology with superior performance, have attracted much attention due to their high energy conversion efficiency, long life, low cost and environmental protection characteristics. β″-alumina is a key solid electrolyte material in sodium-sulfur batteries, and its performance directly affects the overall performance and service life of the battery. Therefore, it is of great significance to study the preparation method of β″-alumina.

[0003] β″-alumina has become an indispensable ceramic electrolyte material in high-performance energy storage devices such as sodium-sulfur batteries due to its unique crystal structure and excellent physical and chemical properties, especially its stability and conductivity at high temperatures. At present, the preparation methods of β″-alumina mainly include solid-phase synthesis, sol-gel, hydrothermal and the like. Among them, the solid-phase synthesis method has been widely used due to its simple process and low cost. However, this method has difficulties in powder preparation and ceramic tube forming during the preparation process, such as uneven powder particle size distribution, low density, and volatilization of sodium during sintering, which affect the performance and stability of β″-alumina. Therefore, a preparation method of β″-alumina with a short process flow, high product purity and stable product performance is developed to solve the technical problems of complex preparation process of β″-alumina, unstable product purity and performance. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing β"-alumina, so as to solve the technical problems in the prior art of complex preparation process of β"-alumina and unstable product purity and performance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing β″-alumina comprises the following steps:

[0007] (1) Mixing: weighing raw materials in a ratio of 50-80 wt% of modified α-alumina, 10-30 wt% of modified θ-alumina and 10-20 wt% of sodium salt, and mixing them uniformly to obtain modified aluminum sodium salt;

[0008] (2) Ball milling: Place the modified sodium aluminum salt into a ball mill, add the ball milling medium, dispersant and stabilizer respectively, and perform wet milling with alcohol to obtain a ball milling slurry;

[0009] (3) Drying: The ball mill slurry is placed in a spray dryer and the water is completely dried to obtain a dry β″-alumina precursor powder;

[0010] (4) Calcination: The dried β″-alumina precursor powder is placed in an electric furnace, pre-sintered under a nitrogen atmosphere, and then subjected to main sintering. After sintering, it is slowly cooled to room temperature to obtain β″-alumina powder.

[0011] Furthermore, in step (1), when preparing the modified α-alumina, anhydrous ethanol is used to prepare the α-alumina into a solution with a weight volume percentage concentration of 10-12 w / v%, and then γ-aminopropyltriethoxysilane is added to the system, and the mass ratio of γ-aminopropyltriethoxysilane to α-alumina is 1:100-120, so as to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed, the ultrasonic frequency is 100-250 Hz, and the time is 30-50 min, and then stirred for 20-24 hours at a temperature of 20-30°C, and then placed in a drying oven at a temperature of 90-100°C for 12-16 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace, and calcined at a temperature of 600-650°C for 2-3 hours under a nitrogen atmosphere, and cooled to room temperature after the calcination to obtain a modified α-alumina.

[0012] Furthermore, in step (1), the modified θ-alumina is prepared by using anhydrous ethanol to prepare a solution with a weight volume percentage concentration of 10-12 w / v%, and then sodium fluoride is added to the system, the mass ratio of sodium fluoride to θ-alumina is 1:50-100, and the mixture is stirred and mixed manually, and the mixture is allowed to stand for 2-4 hours to obtain a modified θ-alumina reactant; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 2-5°C / min, and the mixture is kept warm in a temperature range of 1000-1200°C for 2-8 hours, and then naturally cooled to room temperature after the end to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 100-120°C to dry to constant weight to obtain a modified θ-alumina.

[0013] Furthermore, the sodium salt is one or both of sodium carbonate and sodium oxalate.

[0014] Furthermore, in step (2), the ball milling medium is deionized water, and the added amount is 20-50% of the mass of the modified sodium aluminum salt; the dispersant is one or two of polyacrylamide and polyethylene glycol, and the added amount is 1-5% of the mass of the modified sodium aluminum salt; the stabilizer is one or more of sodium dodecyl sulfate, polyethylene glycol octylphenyl ether, ethylenediaminetetraacetic acid and glycerol, and the added amount is 0.5-2% of the mass of the modified sodium aluminum salt; the alcohol concentration is 70-75vt%, the alcohol amount is 1-3 times the ball milling medium, and the ball milling time is 4-24 hours.

[0015] Furthermore, in step (3), the hot air inlet temperature of the spray dryer is 100-250°C, the outlet temperature is 80-150°C, and the atomizing disk rotation speed is 8000-12500 r / min.

[0016] Furthermore, in step (4), the pre-sintering temperature is 600-800°C, the calcination time is 2-4 hours, the main sintering temperature is 1200-1400°C, the calcination time is 4-8 hours, and the main sintering temperature is preferably 1200-1300°C.

[0017] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0018] 1. The present invention utilizes the synergistic effect of modified α-alumina and modified θ-alumina, combined with sodium salt, to promote the transformation of the crystal form during the sintering process, so that the formation of β″-alumina is more stable and has high purity. At the same time, the use of alcohol wet grinding and dispersants and stabilizers ensures the uniformity and stability of the ball mill slurry, effectively prevents particle agglomeration and precipitation, and improves the preparation efficiency and product quality of β″-alumina. In addition, during calcination, under the protection of a nitrogen atmosphere, a preparation process of pre-sintering and main sintering is adopted to ensure the crystalline integrity of the material at high temperature, avoid unnecessary phase changes and impurity generation, and thus obtain β″-alumina with excellent performance.

[0019] 2. The present invention successfully introduces organic silicon groups by treating α-alumina with γ-aminopropyltriethoxysilane. These groups can form chemical bonds with the surface of α-alumina, enhance the interaction between particles, and improve its dispersibility in solvents such as water and ethanol. This modification treatment promotes refinement and uniform mixing in the subsequent ball milling process and improves the stability of the slurry. In addition, the introduction of γ-aminopropyltriethoxysilane also promotes the crystal growth of alumina during sintering, which helps the formation and stabilization of β″-alumina phase.

[0020] 3. In the process of preparing modified θ-alumina, the present invention effectively adjusts the surface structure and crystal defects of θ-alumina and increases its active sites by adding sodium fluoride and calcining it at high temperature. These active sites promote the reaction with sodium salts and other alumina phases in the subsequent sintering process, and accelerate the formation rate of β″-alumina phase. At the same time, the heat preservation treatment during the high-temperature calcination process further promotes the rearrangement and optimization of the crystal structure, and improves the stability and reactivity of the modified θ-alumina. Therefore, the use of modified θ-alumina significantly improves the preparation efficiency of β″-alumina. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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 some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 The present invention is a preparation flow chart of a method for preparing β″-alumina. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1

[0025] This embodiment provides a method for preparing β″-alumina, comprising the following steps:

[0026] (1) Mixing: Weigh 600 g of modified α-alumina, 300 g of modified θ-alumina, 60 g of sodium carbonate and 40 g of sodium oxalate, mix them evenly to obtain modified sodium aluminum salt;

[0027] (2) Ball milling: Place the modified sodium aluminum salt in a ball mill, add 200 g of deionized water, 5 g of polyacrylamide, 5 g of polyethylene glycol, and 5 g of sodium dodecyl sulfate, respectively, and add 200 g of 75% alcohol for wet milling. After wet milling for 4 hours, a ball mill slurry is obtained.

[0028] (3) Drying: The ball mill slurry is placed in a spray dryer. The hot air inlet temperature of the spray dryer is 100°C, the outlet temperature is 80°C, and the atomizing disk speed is 8000r / min. After the water is completely dried, a dry β″-alumina precursor powder is obtained.

[0029] (4) Calcination: Place the dried β″-alumina precursor powder into an electric furnace and pre-sinter it in a nitrogen atmosphere at a temperature of 600°C for 2 hours, then perform main sintering at a temperature of 1200°C for 4 hours. After sintering, slowly cool it to room temperature to obtain β″-alumina powder.

[0030] Specifically, in step (1), when preparing the modified α-alumina, 100 g of α-alumina is prepared into a solution with a weight volume percentage concentration of 10 w / v% using 1000 mL of anhydrous ethanol, and then 1 g of γ-aminopropyltriethoxysilane is added to the system to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed at a frequency of 100 Hz for 30 minutes, and then stirred for 20 hours at a temperature of 20°C, and then placed in a drying oven at a temperature of 90°C for 12 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace and calcined at a temperature of 600°C for 2 hours in a nitrogen atmosphere, and then cooled to room temperature after the calcination to obtain a modified α-alumina reactant.

[0031] Specifically, in step (1), when preparing the modified θ-alumina, 100 g of θ-alumina is prepared into a solution with a weight volume percentage concentration of 10 w / v% using 1000 mL of anhydrous ethanol, and then 1 g of sodium fluoride is added to the system, and the mixture is manually stirred and mixed evenly. After standing for 2 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 2°C / min, and the temperature is kept within a temperature range of 1000°C for 2 hours. After the temperature is kept, the mixture is naturally cooled to room temperature to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 100°C to dry to constant weight to obtain a modified θ-alumina.

[0032] Example 2

[0033] This embodiment provides a method for preparing β″-alumina, comprising the following steps:

[0034] (1) Mixing: Weigh 600 g of modified α-alumina, 300 g of modified θ-alumina, 50 g of sodium carbonate and 50 g of sodium oxalate, mix them evenly to obtain modified sodium aluminum salt;

[0035] (2) Ball milling: Place the modified sodium aluminum salt in a ball mill, add 250 g of deionized water, 6 g of polyacrylamide, 6 g of polyethylene glycol and 7 g of polyethylene glycol octylphenyl ether, respectively, and add 300 g of 75% alcohol for wet milling. After wet milling for 10 hours, a ball mill slurry is obtained.

[0036] (3) Drying: The ball mill slurry is placed in a spray dryer. The hot air inlet temperature of the spray dryer is 150°C, the outlet temperature is 110°C, and the atomizing disk speed is 9000r / min. After the water is completely dried, a dry β″-alumina precursor powder is obtained;

[0037] (4) Calcination: Place the dried β″-alumina precursor powder into an electric furnace and pre-sinter it in a nitrogen atmosphere at a temperature of 650°C for 3 hours, then perform main sintering at a temperature of 1300°C for 6 hours. After sintering, slowly cool it to room temperature to obtain β″-alumina powder.

[0038] Specifically, in step (1), when preparing the modified α-alumina, 102g of α-alumina is prepared into a solution with a weight volume percentage concentration of 10.2w / v% using 1000mL of anhydrous ethanol, and then 1.02g of γ-aminopropyltriethoxysilane is added to the system to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed at a frequency of 230Hz for 40min, and then stirred for 22 hours at a temperature of 25°C, and then placed in a drying oven at a temperature of 93°C for 13 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace and calcined at a temperature of 620°C for 2.5 hours in a nitrogen atmosphere, and then cooled to room temperature after the calcination to obtain a modified α-alumina.

[0039] Specifically, in step (1), when preparing the modified θ-alumina, 108g of θ-alumina is prepared with 1000mL of anhydrous ethanol to a weight volume percentage concentration of 10.08w / v%, and then 1.4g of sodium fluoride is added to the system, and the mixture is manually stirred and mixed evenly. After standing for 3 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 4°C / min, and the temperature is kept within a temperature range of 1120°C for 5 hours. After the temperature is kept, the mixture is naturally cooled to room temperature to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 108°C and dried to constant weight to obtain a modified θ-alumina.

[0040] Example 3

[0041] This embodiment provides a method for preparing β″-alumina, comprising the following steps:

[0042] (1) Mixing: Weigh 650 g of modified α-alumina, 250 g of modified θ-alumina, 50 g of sodium carbonate and 50 g of sodium oxalate, mix them evenly to obtain modified sodium aluminum salt;

[0043] (2) Ball milling: Place the modified sodium aluminum salt in a ball mill, add 350 g of deionized water, 25 g of polyethylene glycol, 4 g of polyethylene glycol octylphenyl ether and 4 g of propylene glycol, respectively, and add 500 g of 75% alcohol for wet milling. After wet milling for 18 hours, a ball mill slurry is obtained.

[0044] (3) Drying: The ball mill slurry is placed in a spray dryer. The hot air inlet temperature of the spray dryer is 180°C, the outlet temperature is 90°C, and the atomizing disk speed is 9500r / min. After the water is completely dried, a dry β″-alumina precursor powder is obtained.

[0045] (4) Calcination: Place the dried β″-alumina precursor powder into an electric furnace and pre-sinter it in a nitrogen atmosphere at a temperature of 800°C for 4 hours, then perform main sintering at a temperature of 1350°C for 6 hours. After sintering, slowly cool it to room temperature to obtain β″-alumina powder.

[0046] Specifically, in step (1), when preparing the modified α-alumina, 115g of α-alumina is prepared into a solution with a weight volume percentage concentration of 11.5w / v% using 1000mL of anhydrous ethanol, and then 1.15g of γ-aminopropyltriethoxysilane is added to the system to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed at a frequency of 180Hz for 35min, and then stirred for 22 hours at a temperature of 28°C, and then placed in a drying oven at a temperature of 95°C for 14 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace and calcined at a temperature of 600°C for 2.5 hours in a nitrogen atmosphere, and then cooled to room temperature after the calcination to obtain a modified α-alumina.

[0047] Specifically, in step (1), when preparing the modified θ-alumina, 100 g of θ-alumina is prepared into a solution with a weight volume percentage concentration of 10 w / v% using 1000 mL of anhydrous ethanol, and then 1 g of sodium fluoride is added to the system, and the mixture is manually stirred and mixed evenly. After standing for 4 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 3°C / min, and the temperature is kept within a temperature range of 1050°C for 6 hours. After the temperature is kept, it is naturally cooled to room temperature to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 100°C to dry to constant weight to obtain a modified θ-alumina.

[0048] Example 4

[0049] This embodiment provides a method for preparing β″-alumina, comprising the following steps:

[0050] (1) Mixing: Weigh 750 g of modified α-alumina, 100 g of modified θ-alumina, 100 g of sodium carbonate and 50 g of sodium oxalate, mix them evenly to obtain modified sodium aluminum salt;

[0051] (2) Ball milling: Place the modified sodium aluminum salt in a ball mill, add 400 g of deionized water, 15 g of polyacrylamide, 20 g of polyethylene glycol, 5 g of ethylenediaminetetraacetic acid and 5 g of propylene glycol, and add 600 g of 75% alcohol for wet milling. After wet milling for 20 hours, a ball mill slurry is obtained.

[0052] (3) Drying: The ball mill slurry is placed in a spray dryer. The hot air inlet temperature of the spray dryer is 200°C, the outlet temperature is 130°C, and the atomizing disk speed is 12000r / min. After the water is completely dried, a dry β″-alumina precursor powder is obtained.

[0053] (4) Calcination: Place the dried β″-alumina precursor powder into an electric furnace and pre-sinter it in a nitrogen atmosphere at a temperature of 750°C for 3 hours, then perform main sintering at a temperature of 1400°C for 8 hours. After sintering, slowly cool it to room temperature to obtain β″-alumina powder.

[0054] Specifically, in step (1), when preparing the modified α-alumina, 110g of α-alumina is prepared into a solution with a weight volume percentage concentration of 11w / v% using 1000mL of anhydrous ethanol, and then 1.1g of γ-aminopropyltriethoxysilane is added to the system to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed at a frequency of 250Hz for 50min, and then stirred for 24 hours at a temperature of 30°C, and then placed in a drying oven at a temperature of 100°C for 16 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace, calcined at a temperature of 650°C for 3 hours under a nitrogen atmosphere, and cooled to room temperature after the calcination to obtain a modified α-alumina.

[0055] Specifically, in step (1), when preparing the modified θ-alumina, 100g of θ-alumina is prepared into a solution with a weight volume percentage concentration of 10w / v% using 1000mL of anhydrous ethanol, and then 1.8g of sodium fluoride is added to the system, and the mixture is manually stirred and mixed evenly. After standing for 3 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and the heating rate is controlled at 5°C / min under a nitrogen atmosphere. The temperature is kept within a temperature range of 1200°C for 5 hours, and then naturally cooled to room temperature after the end to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 110°C to dry to constant weight to obtain a modified θ-alumina.

[0056] Example 5

[0057] This embodiment provides a method for preparing β″-alumina, comprising the following steps:

[0058] (1) Mixing: Weigh 700 g of modified α-alumina, 100 g of modified θ-alumina, 100 g of sodium carbonate and 100 g of sodium oxalate, or both, and mix them evenly according to the proportion to obtain modified sodium aluminum salt;

[0059] (2) Ball milling: Place the modified sodium aluminum salt in a ball mill, add 400 g of deionized water, 40 g of polyacrylamide and 10 g of sodium dodecyl sulfate, respectively, and add 500 g of 75% alcohol for wet milling. After wet milling for 22 hours, a ball mill slurry is obtained.

[0060] (3) Drying: The ball mill slurry is placed in a spray dryer. The hot air inlet temperature of the spray dryer is 230°C, the outlet temperature is 120°C, and the atomizing disk speed is 11000r / min. After the water is completely dried, a dry β″-alumina precursor powder is obtained.

[0061] (4) Calcination: Place the dried β″-alumina precursor powder into an electric furnace and pre-sinter it in a nitrogen atmosphere at a temperature of 700°C for 3.5 hours. Then, perform the main sintering at a temperature of 1300°C for 8 hours. After sintering, slowly cool it to room temperature to obtain β″-alumina powder.

[0062] Specifically, in step (1), when preparing the modified α-alumina, 110g of α-alumina is prepared into a solution with a weight volume percentage concentration of 11w / v% using 1000mL of anhydrous ethanol, and then 1.1g of γ-aminopropyltriethoxysilane is added to the system to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed at a frequency of 200Hz for 50min, and then stirred for 24 hours at a temperature of 30°C, and then placed in a drying oven at a temperature of 100°C for 16 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace, calcined at a temperature of 650°C for 3 hours under a nitrogen atmosphere, and cooled to room temperature after the calcination to obtain a modified α-alumina.

[0063] Specifically, in step (1), when preparing the modified θ-alumina, 100g of θ-alumina is prepared into a solution with a weight volume percentage concentration of 10w / v% using 1000mL of anhydrous ethanol, and then 1g of sodium fluoride is added to the system, and the mixture is manually stirred and mixed evenly. After standing for 4 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 4°C / min, and the temperature is kept within a temperature range of 1200°C for 8 hours. After the temperature is kept, it is naturally cooled to room temperature to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 120°C to dry to constant weight to obtain a modified θ-alumina.

[0064] Example 6

[0065] This embodiment provides a method for preparing β″-alumina, comprising the following steps:

[0066] (1) Mixing: Weigh 700 g of modified α-alumina, 100 g of modified θ-alumina, 100 g of sodium carbonate and 100 g of sodium oxalate, mix them evenly to obtain modified sodium aluminum salt;

[0067] (2) Ball milling: Place the modified sodium aluminum salt in a ball mill, add 500 g of deionized water, 25 g of polyacrylamide, 25 g of polyethylene glycol, 10 g of sodium dodecyl sulfate and 10 g of ethylenediaminetetraacetic acid, respectively, and add 500 g of 75% alcohol for wet milling. After wet milling for 24 hours, a ball milling slurry is obtained.

[0068] (3) Drying: The ball mill slurry is placed in a spray dryer. The hot air inlet temperature of the spray dryer is 250°C, the outlet temperature is 150°C, and the atomizing disk speed is 12500r / min. After the water is completely dried, a dry β″-alumina precursor powder is obtained.

[0069] (4) Calcination: Place the dried β″-alumina precursor powder into an electric furnace and pre-sinter it in a nitrogen atmosphere at a temperature of 800°C for 3 hours, then perform main sintering at a temperature of 1250°C for 6 hours. After sintering, slowly cool it to room temperature to obtain β″-alumina powder.

[0070] Specifically, in step (1), when preparing the modified α-alumina, 120g of α-alumina is prepared into a solution with a weight volume percentage concentration of 12w / v% using 1000mL of anhydrous ethanol, and then 1.2g of γ-aminopropyltriethoxysilane is added to the system to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed at a frequency of 250Hz for 50min, and then stirred for 24 hours at a temperature of 30°C, and then placed in a drying oven at a temperature of 100°C for 16 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace, calcined at a temperature of 650°C for 3 hours under a nitrogen atmosphere, and cooled to room temperature after the calcination to obtain a modified α-alumina.

[0071] Specifically, in step (1), when preparing the modified θ-alumina, 120g of θ-alumina is prepared into a solution with a weight volume percentage concentration of 12w / v% using 1000mL of anhydrous ethanol, and then 2g of sodium fluoride is added to the system, and the mixture is manually stirred and mixed evenly. After standing for 4 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 5°C / min, and the temperature is kept within a temperature range of 1200°C for 8 hours. After the temperature is kept, it is naturally cooled to room temperature to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 120°C to dry to constant weight to obtain a modified θ-alumina.

[0072] Comparative Example 1:

[0073] Comparative Example 1 Compared with Example 6, in the preparation process of β″-alumina in Comparative Example 1, α-alumina modification is not performed, and other conditions remain unchanged.

[0074] Comparative Example 2:

[0075] Comparative Example 2 Compared with Example 6, in the preparation process of β″-alumina in Comparative Example 2, θ-alumina is not carried out, and other conditions remain unchanged.

[0076] Comparative Example 3:

[0077] Comparative Example 3 Compared with Example 6, in the preparation process of β″-alumina in Comparative Example 3, no modification of α-alumina and θ-alumina is performed, and other conditions remain unchanged.

[0078] Comparative Example 4:

[0079] Comparative Example 4 Compared with Example 6, in the preparation process of β″-alumina in Comparative Example 4, no dispersant is added, and other conditions remain unchanged.

[0080] Comparative Example 5:

[0081] Comparative Example 5 Compared with Example 6, in the preparation process of β″-alumina in Comparative Example 5, no stabilizer is added, and other conditions remain unchanged.

[0082] Comparative Example 6:

[0083] Comparative Example 6 Compared with Example 6, in the preparation process of β″-alumina in Comparative Example 6, no pre-calcination is performed, and other conditions remain unchanged.

[0084] Experimental example

[0085] The β″-alumina powders prepared in Examples 1-6 and Comparative Examples 1-6 were pressed, and zinc stearate dissolved in alcohol was coated on the mold to facilitate demolding. The pressed tablets were sintered at 1800° C. for 2 hours and cooled in the furnace to obtain β″-alumina ceramic sheets. The β″-alumina powders prepared in Examples 1-6 and Comparative Examples 1-6 were tested for the following properties:

[0086] 1. Particle size analysis of β″-alumina powder

[0087] The particle size of the powder material is detected by an X-ray diffractometer. The detection principle is to measure the particle size based on the phenomenon of light scattering, that is, the smaller the particle size, the larger the scattering angle; the larger the particle size, the smaller the scattering angle. Particles with different particle sizes have different scattered light intensities at different angles, so the intensity signal of the monitored light can show the particle size distribution. The β″-alumina powder prepared in Examples 1-6 and Comparative Examples 1-6 was placed in an X-ray diffractometer, and the test results are shown in Table 1:

[0088]

[0089] According to the test results in Table 1, it can be seen that the average particle size and the maximum particle size of the β″-alumina powder prepared in Examples 1-6 of the present invention are smaller than the particle size of the β″-alumina powder prepared in Comparative Examples 1-6. The experiment shows that when preparing β″-alumina powder, modifying the aluminum source raw materials α-alumina and θ-alumina, adding dispersants and stabilizers to the preparation system, and dividing the calcination process into pre-sintering and main sintering can improve the particle size of the β″-alumina powder.

[0090] Density Analysis of β″-Alumina Ceramic Sheets

[0091] The mold for pressing the ceramic sheet was a cylinder with a diameter of 12.5 mm. The pressing pressures were 99 MPa, 149 MPa, 198 MPa, 247 MPa, 297 MPa, 346 MPa and 396 Pa, respectively. The β″-alumina powders prepared in Examples 1-6 and Comparative Examples 1-6 were used to press the obtained tablets, which had regular shapes. The density of the ceramic sheet was calculated using the following formula:

[0092]

[0093] Among them is m Tablet mass, measured by balance, g; D is the tablet diameter, that is, the mold diameter, mm; h is the tableting height, measured by a vernier caliper, mm. The density calculation results of Examples 1-6 and Comparative Examples 1-6 at different pressing pressures are shown in Table 2:

[0094]

[0095] Small particles can easily fill the gaps between large particles, so the density of β″-alumina powder with larger particle size is higher when pressed.

[0096] According to the calculation results in Table 2, it can be seen that the density of the β″-alumina ceramic sheets prepared in Examples 1-6 of the present invention is smaller than the particle size of the β″-alumina powder prepared in Comparative Examples 1-6. The experiment shows that when preparing β″-alumina powder, modifying the aluminum source raw materials α-alumina and θ-alumina, adding dispersants and stabilizers to the preparation system, and dividing the calcination process into pre-sintering and main sintering can reduce the density of the β″-alumina ceramic sheets, thereby obtaining β″-alumina ceramic sheets with light material.

[0097] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0098] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing β″-alumina, characterized in that: The steps include: (1) Mixing: weighing raw materials in a ratio of 50-80 wt% of modified α-alumina, 10-30 wt% of modified θ-alumina and 10-20 wt% of sodium salt, and mixing them uniformly to obtain modified aluminum sodium salt; (2) Ball milling: Place the modified sodium aluminum salt into a ball mill, add the ball milling medium, dispersant and stabilizer respectively, and perform wet milling with alcohol to obtain a ball milling slurry; (3) Drying: The ball mill slurry is placed in a spray dryer and the water is completely dried to obtain a dry β″-alumina precursor powder; (4) Calcination: The dried β″-alumina precursor powder is placed in an electric furnace, pre-sintered under a nitrogen atmosphere, and then sintered. After sintering, it is slowly cooled to room temperature to obtain β″-alumina powder. When preparing the modified α-alumina, anhydrous ethanol is used to prepare the α-alumina into a solution with a weight volume percentage concentration of 10-12 w / v%, and then γ-aminopropyltriethoxysilane is added, and the mass ratio of γ-aminopropyltriethoxysilane to α-alumina is 1:100-120 to obtain a modified α-alumina reactant; the modified α-alumina reactant is ultrasonically dispersed, the ultrasonic frequency is 100-250 Hz, the time is 30-50 min, and then stirred for 20-24 hours at a temperature of 20-30° C., and then placed in a drying oven at a temperature of 90-100° C. for 12-16 hours to obtain a dried modified α-alumina reactant; the dried modified α-alumina reactant is placed in a tubular furnace, and calcined at a temperature of 600-650° C. for 2-3 hours in a nitrogen atmosphere, and cooled to room temperature after the calcination to obtain a modified α-alumina; When preparing the modified θ-alumina, anhydrous ethanol is used to prepare θ-alumina into a solution with a weight volume percentage concentration of 10-12w / v%, and then sodium fluoride is added, the mass ratio of sodium fluoride to θ-alumina is 1:50-100, and the mixture is manually stirred and mixed evenly. After standing for 2-4 hours, a modified θ-alumina reactant is obtained; the modified θ-alumina reactant is placed in a high-temperature calcining furnace, and in a nitrogen atmosphere, the heating rate is controlled at 2-5°C / min, and the temperature is kept in the temperature range of 1000-1200°C for 2-8 hours, and then naturally cooled to room temperature after the end to obtain a modified θ-alumina preform; the modified θ-alumina preform is washed once with deionized water, and then placed in a drying oven at a temperature of 100-120°C to dry to constant weight to obtain the modified θ-alumina.

2. The method for preparing β″-alumina according to claim 1, characterized in that: The sodium salt is one or both of sodium carbonate and sodium oxalate.

3. The method for preparing β″-alumina according to claim 1, characterized in that: In step (2), the ball milling medium is deionized water, and the added amount is 20-50% of the mass of the modified sodium aluminum salt; the dispersant is one or both of polyacrylamide and polyethylene glycol, and the added amount is 1-5% of the mass of the modified sodium aluminum salt.

4. The method for preparing β″-alumina according to claim 1, characterized in that: In step (2), the stabilizer is one or more of sodium dodecyl sulfate, polyethylene glycol octylphenyl ether, ethylenediaminetetraacetic acid and propylene glycol, and the added amount is 0.5-2% of the mass of the modified sodium aluminum salt; the alcohol concentration is 70-75 vt%, the amount of alcohol used is 1-3 times the ball milling medium, and the ball milling time is 4-24 hours.

5. The method for preparing β″-alumina according to claim 1, characterized in that: In step (3), the hot air inlet temperature of the spray dryer is 100-250°C, the outlet temperature is 80-150°C, and the atomizing disk rotation speed is 8000-12500 r / min.

6. The method for preparing β″-alumina according to claim 1, characterized in that: In step (4), the pre-sintering temperature is 600-800°C, the calcination time is 2-4 hours, and the main sintering temperature is 1200-1400°C, the calcination time is 4-8 hours.

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