A method for preparing monodisperse nano α-aluminum oxide by vacancy isolation

Abstract

The present invention discloses a method for preparing vacancy-isolated monodisperse nano-α-aluminum oxide, which relates to the field of new material technologies. α-aluminum oxide can be obtained by heat-treating various activated aluminas. However, when other crystal forms of alumina are transformed into the α-aluminum oxide phase, generally, a process in which nano-crystals of other crystal forms merge and grow into worm-like α-aluminum oxide grains occurs. Therefore, it is very difficult to obtain nano-α-aluminum oxide with a size below 100 nm by means of phase transformation. In this application, ρ-aluminum oxide, which can be hydrated to obtain nano-particles, is used as the raw material. Through the adsorption and desorption of lithium chloride, the volume of the hydrated product expands, and the vacancies left after the desorption of lithium ions change the transformation path to the α-aluminum oxide phase, preventing the merging and growth of grains (hard agglomeration), so that monodisperse nano-α-aluminum oxide can be efficiently prepared in large quantities.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and particularly to a method for preparing vacancy-isolated monodisperse nano α-aluminum oxide. Background Art

[0002] α-aluminum oxide is the most stable phase among various crystal forms of aluminum oxide. Due to its extremely high hardness, relatively high mechanical strength, excellent wear resistance, high insulation, outstanding thermal stability and chemical stability, α-aluminum oxide (i.e., corundum phase) has been widely used in the fields of structural ceramics, friction materials, refractory materials, electrical insulating materials, etc. Nano α-aluminum oxide is in urgent demand in the fields of catalysis, medicine, composite materials, abrasives and high-performance scratch-resistant coatings due to its finer particle size. Especially in the high-tech fields represented by transparent ceramics and nano-ceramics, nano α-aluminum oxide with uniform and small particle size must be used. However, the current technology for preparing nano α-aluminum oxide has a complex process and high cost, which severely restricts the development of the above fields. For example, the price of nano α-aluminum oxide is as high as 300 yuan / kg, which is dozens of times the price of ordinary alumina powder. α-aluminum oxide is the most stable structure of aluminum oxide thermodynamically. Since the Bayer process is the mainstream process in the current aluminum industry, the directly obtained aluminum hydroxide will transform into various transition-state aluminum oxides during the heating process. These transition-state aluminum oxides usually transform into α-aluminum oxide above 1200°C. Transition-state aluminum oxides, also known as transient aluminum oxides or activated aluminum oxides, usually increase in particle size during the transformation to the α-aluminum oxide phase. When transformed into α-aluminum oxide, the particle size usually also grows to more than 100 nanometers, showing a worm-like morphology (Critical factors in the production of sol gel derived porous alumina, Key Engineering Materials Vol. 115 (1996) pp 45-64).

[0003] The phase transition temperature from transition-phase aluminum oxide to α-aluminum oxide is above 1000°C, even reaching 1200°C. In this case, the generated α-aluminum oxide always exists in the form of worm-like sintered bodies with a size of about 100 nm and poor dispersibility. People have obtained α-aluminum oxide at 900°C by adding crystal seeds or introducing a liquid-phase environment, but the worm-like sintered bodies of about 100 nm still cannot be avoided, and micron-scale platelets are easily formed when there is a liquid phase. So far, through high-temperature phase transition, it is still impossible to prepare completely dispersed α-aluminum oxide nanoparticles within 50 nm, which also greatly limits its application.

[0004] Chinese Patent with application number 200310114455.8 discloses a non-agglomerated nano α-Al 2O 3 A method for preparing powder, which comprises fully dispersing nano carbon black in an inorganic aluminum salt solution with a concentration of 0.5 - 3.0 mol / L, then slowly adding an alkali solution with a certain concentration in a reaction field with a turbulent effect, controlling the pH value of the final reaction solution to be 5.0 - 8.0, aging for 7 - 12 hours after the reaction is completed, then filtering and washing, treating the filter cake in an inert gas furnace tank at 1000 - 1200 °C for 1 - 3 hours, and calcining in an air furnace tank at 600 - 800 °C until the surface coating is completely removed, to obtain α - Al 2 O 3 powder with a size of 30 - 60 nm, uniform distribution and no agglomeration without grinding.

[0005] The Chinese patent with the application number CN200610104871.3 uses aluminum salt as the raw material, sodium chloride and potassium chloride as the isolation agents, and adds α - alumina seeds to prepare nano - α - alumina.

[0006] The Chinese patent with the application number CN201310556198.7 uses aluminum nitrate and iron nitrate as the raw materials, uses α - iron oxide as both the seed and the isolation phase, and uses the chemical precipitation method to prepare α - alumina nanoparticles.

[0007] The Chinese patent with the application number CN201510000781.9 uses iron oxide and aluminum powder as the raw materials, proportionally mixes them and grinds them with a high - energy ball mill, induces a redox reaction through high - energy ball milling to obtain a nano - composite powder mainly composed of α - alumina and α - iron, and then uses hydrochloric acid to remove iron and other impurities in the nano - composite to obtain α - alumina nanoparticles.

[0008] The Chinese patent with the application number CN201610364145.9 uses the high - energy ball milling method to grind α - alumina fine powder and then prepares α - alumina nanoparticles through color immersion and high - speed centrifugation.

[0009] The above - mentioned methods for preparing monodisperse nano - α - alumina generally have problems such as complex processes, the use of strong acids, strong bases, low output or low efficiency. For example, the ball - milling method requires continuous ball - milling for dozens of hours, with high energy consumption and low output. Therefore, even though the above - mentioned methods for preparing nano - α - alumina have been developed, the price of nano - α - alumina is still as high as 300 yuan / kg.

[0010] Therefore, we propose a vacancy - isolation preparation method for monodisperse nano - α - alumina to solve the problems mentioned above. Summary of the Invention

[0011] 1. Technical problems to be solved by the invention:

[0012] The object of the present invention is to provide a method for preparing monodisperse nano α-aluminum oxide by vacancy isolation, so as to solve the problems of low yield and low efficiency existing in the above-mentioned background technology.

[0013] 2. Technical solution:

[0014] To achieve the above object, the present invention provides the following technical solution: A method for preparing monodisperse nano α-aluminum oxide by vacancy isolation, the method comprising the following steps:

[0015] First step: Weigh 100 grams of ρ-type alumina powder and lithium chloride powder with a mass ratio of 1% - 5% of the ρ-type alumina powder respectively. After mixing the two powders, add them to water and stir well until uniform to promote the reaction of ρ-type alumina with water to form a composite bulk material composed of bayerite and boehmite, and the particle size of its nanoparticles is 20 nanometers;

[0016] Second step: Immerse the sample treated above in hot water and keep it for 24 hours to desorb lithium ions and form active sites;

[0017] Third step: Immerse the bayerite and boehmite composite bulk material after lithium ion desorption in an aqueous lithium chloride solution, and through the adsorption of lithium ions, the composite bulk material expands by more than twice its volume;

[0018] Fourth step: Place the above sample in hot water again and keep it for 24 hours to desorb lithium ions and form vacancies. The vacancy effect caused by the adsorption and desorption process of lithium ions changes the phase transformation path of α-type alumina, converts θ-type alumina into α-type alumina, and effectively prevents the aggregation and growth of nanoparticles;

[0019] Fifth step: Disperse the loose α-type alumina by ball milling to finally obtain monodisperse nano α-type alumina with a particle size of 20 nanometers.

[0020] Further, the mass of water in the first step is 100 - 400 grams.

[0021] Further, the temperature of the hot water in the second step and the fourth step is 60°C - 80°C.

[0022] Further, the concentration of the aqueous lithium chloride solution in the third step is 6% - 10%.

[0023] Further, the temperature of the heat treatment of the sample is 1000°C - 1200°C.

[0024] Further, the time of ball milling dispersion is 2h and the rotation speed is 500 revolutions per minute.

[0025] 3. Beneficial effects:

[0026] Adopting the technical solution provided by the present invention, compared with the prior art, the method for preparing monodisperse nano-α-aluminum oxide by vacancy isolation of the present invention:

[0027] The present invention uses inexpensive and safe ρ-aluminum oxide as a raw material. Lithium chloride is added before the hydration of ρ-aluminum oxide. After hydration, the lithium-containing hydrated product is desorbed of lithium ions in hot water, so that the hydrated product generates lithium active sites. The hydrated product containing lithium active sites (bayerite and boehmite) is then immersed in an aqueous lithium chloride solution, so that the hydrated product adsorbs lithium chloride, and the hydrated product swells by more than twice its volume, changing the path of the transformation of transient alumina to α-alumina. There is no phenomenon that the particles in the conventional transformation to α-alumina merge and grow into a worm-like morphology, and monodisperse nano-α-aluminum oxide is obtained. In this application, the volume expansion after lithium ion desorption forms vacancies to isolate the grain growth by merging, and monodisperse nano-α-aluminum oxide can be prepared efficiently and in large quantities. Description of the Drawings

[0028] Figure 1 Schematic diagram of the hydration of ρ-aluminum oxide of the present invention and its transformation to α-aluminum oxide;

[0029] Figure 2 XRD pattern of the crystal form after the hydration of ρ-aluminum oxide of the present invention (lithium chloride content is below the detection limit);

[0030] Figure 3 SEM image of ρ-aluminum oxide after hydration of the present invention;

[0031] Figure 4 XRD pattern of the phase transformation of alumina during the process heat treatment of the present invention;

[0032] Figure 5 XRD pattern of the phase transformation of directly heat-treating ρ-aluminum oxide for comparison;

[0033] Figure 6 SEM image of the monodisperse nano-α-aluminum oxide obtained in Example 1 of the present invention. Detailed Embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0035] A method for preparing monodisperse nano-α-aluminum oxide by vacancy isolation, comprising the following steps:

[0036] Step 1: Weigh 100 grams of ρ-aluminum oxide powder and lithium chloride powder accounting for 1% - 5% of the ρ-aluminum oxide powder respectively. After mixing the two powders, add them to water and stir well until uniform, promoting the hydration reaction between ρ-aluminum oxide and water and solidifying into a shape, generating a composite bulk material composed of bayerite and boehmite, with its nanoparticle size being 20 nanometers, and the mass of water being 100 - 400 grams.

[0037] Step 2: Immerse the sample after the above-mentioned solidification and shaping in hot water and keep it for 24 hours to desorb lithium ions and form active sites, with the temperature of the hot water being 60°C - 80°C.

[0038] Step 3: Immerse the bayerite and boehmite composite bulk material after lithium ion desorption in an aqueous lithium chloride solution. By adsorbing lithium ions, the composite bulk material undergoes a volume expansion of more than twice, with the concentration of the aqueous lithium chloride solution being 6% - 10%.

[0039] Step 4: Place the above sample in hot water again and keep it for 24 hours to desorb lithium ions and form vacancies. After the sample after lithium deintercalation undergoes heat treatment for 2 hours, the vacancy effect caused by the lithium ion adsorption and desorption process changes the phase transformation path of α-aluminum oxide, converting θ-aluminum oxide into α-aluminum oxide and effectively preventing the coalescence and growth of nanoparticles. The temperature of the hot water is 60°C - 80°C, and the temperature for the heat treatment of the sample is 1000°C - 1200°C.

[0040] Step 5: Conduct ball milling and dispersion on the porous α-aluminum oxide to finally obtain monodisperse nano-α-aluminum oxide with a particle size of 20 nanometers. The time for ball milling and dispersion is 2h, and the rotation speed is 500 revolutions per minute.

[0041] The present invention uses inexpensive and safe ρ-aluminum oxide as the raw material. The ρ-aluminum oxide reacts with water to obtain a hydrated product (bayerite and boehmite) with a particle size of about 20 nm. The hydrated product undergoes heat treatment to obtain transient alumina, and the transient alumina undergoes heat treatment to obtain α-alumina. In the present invention, the hydrated product of ρ-aluminum oxide is transformed into α-aluminum oxide, and the microscopic morphology such as the nanoparticle size does not change.

[0042] Before the hydration of ρ-aluminum oxide, lithium chloride is added. After hydration, the lithium-containing hydrated product is desorbed of lithium ions in hot water, enabling the hydrated product to generate active sites of lithium. In this invention, the hydrated product containing lithium active sites (bayerite and boehmite) is immersed in an aqueous lithium chloride solution again, allowing the hydrated product to adsorb lithium chloride, and the hydrated product undergoes a volume expansion of more than twice. For the sample after volume expansion, it is immersed in hot water to remove lithium and form vacancies, and through high-temperature heat treatment, different transient alumina transformation paths occur. It directly transforms from θ-aluminum oxide to α-aluminum oxide, while ρ-aluminum oxide does not undergo a hydration reaction. During heat treatment, the phase transformation path is to directly transform from γ-phase aluminum oxide to α-phase aluminum oxide. The process of this invention enables the transformation to α-aluminum oxide phase without the aggregation and growth of nanoparticles into the conventional worm-like morphology, but instead obtains monodisperse nano-α-aluminum oxide.

[0043] Example 1:

[0044] In the first step, 100 grams of ρ-aluminum oxide powder and 1% (by mass of the ρ-aluminum oxide powder) of lithium chloride powder are weighed respectively, and 200 grams of water is added and stirred evenly to cause the hydration reaction of ρ-aluminum oxide with water and solidify it into a mold. The schematic diagram of the hydration and phase transformation of ρ-aluminum oxide is as Figure 1 shown. The composite bulk material obtained after hydration mainly consists of bayerite and boehmite, as Figure 2 shown, and its microstructure is as Figure 3 shown. The particle size of bayerite and boehmite nanoparticles is 20 nanometers.

[0045] In the second step, the solidified sample is immersed in water at 60 °C for 24 hours to desorb lithium ions.

[0046] In the third step, the bayerite and boehmite bulk materials after lithium ion desorption are immersed in a 6% aqueous lithium chloride solution. After adsorbing lithium ions, the bayerite and boehmite composite bulk material undergoes a volume expansion of more than twice.

[0047] In the fourth step, the above sample is placed in water at 60 °C for 24 hours to desorb lithium ions. The sample after lithium removal is heat-treated at 1000 °C - 1200 °C for 2 hours. From the XRD crystal form evolution (as Figure 4 shown), the sample directly transforms from θ-aluminum oxide to α-aluminum oxide. For comparison (as Figure 5 shown), the sample that has not adsorbed lithium ions and has not undergone volume expansion needs to transform from γ-aluminum oxide to α-aluminum oxide.

[0048] In the fifth step, the loose α-aluminum oxide is ball-milled and dispersed for 2 hours at a rotation speed of 500 revolutions per minute, and finally, monodisperse nano-α-aluminum oxide with a particle size of 20 nanometers as Figure 6 shown is obtained.

[0049] Example 2:

[0050] In the first step, 100 grams of ρ-aluminum oxide powder and lithium chloride powder accounting for 2% of the mass of the ρ-aluminum oxide powder were weighed respectively, added to 300 grams of water and stirred evenly to cause the ρ-aluminum oxide to undergo a hydration reaction with water and solidify into a mold.

[0051] In the second step, the solidified sample was immersed in water at 70 °C for 24 hours to desorb lithium ions.

[0052] In the third step, the boehmite and diaspore bulk materials after lithium ion desorption were immersed in a 7% aqueous lithium chloride solution. After adsorbing lithium ions, the boehmite and diaspore composite bulk material underwent a volume expansion of more than twice.

[0053] In the fourth step, the above sample was placed in water at 70 °C for 24 hours to desorb lithium ions. The sample after lithium removal was heat-treated at 1000 °C to 1200 °C for 2 hours to complete the crystal form transformation into α-aluminum oxide.

[0054] In the fifth step, the loose α-aluminum oxide was ball-milled and dispersed for 2 hours at a rotation speed of 500 revolutions per minute, and finally monodisperse nano-α-aluminum oxide with a particle size of 20 nanometers was obtained.

[0055] Example 3:

[0056] In the first step, 100 grams of ρ-aluminum oxide powder and lithium chloride powder accounting for 3% of the mass of the ρ-aluminum oxide powder were weighed respectively, added to 100 grams of water and stirred evenly to cause the ρ-aluminum oxide to undergo a hydration reaction with water and solidify into a mold.

[0057] In the second step, the solidified sample was immersed in water at 70 °C for 24 hours to desorb lithium ions.

[0058] In the third step, the boehmite and diaspore bulk materials after lithium ion desorption were immersed in an 8% aqueous lithium chloride solution. After adsorbing lithium ions, the boehmite and diaspore composite bulk material underwent a volume expansion of more than twice.

[0059] In the fourth step, the above sample was placed in water at 70 °C for 24 hours to desorb lithium ions. The sample after lithium removal was heat-treated at 1000 °C to 1200 °C for 2 hours to complete the crystal form transformation into α-aluminum oxide.

[0060] In the fifth step, the loose α-aluminum oxide was ball-milled and dispersed for 2 hours at a rotation speed of 500 revolutions per minute, and finally monodisperse nano-α-aluminum oxide with a particle size of 20 nanometers was obtained.

[0061] Example 4:

[0062] In the first step, 100 g of ρ-aluminum oxide powder and lithium chloride powder accounting for 4% of the mass of the ρ-aluminum oxide powder are weighed respectively, added to 200 g of water and stirred evenly to cause the ρ-aluminum oxide to undergo a hydration reaction with water and solidify into a mold.

[0063] In the second step, the solidified sample is immersed in water at 80 °C for 24 hours to desorb lithium ions.

[0064] In the third step, the boehmite and böhmite bulk materials after lithium ion desorption are immersed in a 9% aqueous lithium chloride solution. After adsorbing lithium ions, the boehmite and böhmite composite bulk material undergoes a volume expansion of more than twice.

[0065] In the fourth step, the above sample is placed in water at 80 °C for 24 hours to desorb lithium ions. The sample after lithium removal is heat-treated at 1000 °C to 1200 °C for 2 hours to complete the crystal form transformation to α-aluminum oxide.

[0066] In the fifth step, the porous α-aluminum oxide is ball-milled and dispersed for 2 hours at a rotation speed of 500 revolutions per minute, and finally monodisperse α-aluminum oxide with a particle size of 20 nm is obtained.

[0067] Example 5:

[0068] In the first step, 100 g of ρ-aluminum oxide powder and lithium chloride powder accounting for 5% of the mass of the ρ-aluminum oxide powder are weighed respectively, added to 400 g of water and stirred evenly to cause the ρ-aluminum oxide to undergo a hydration reaction with water and solidify into a mold.

[0069] In the second step, the solidified sample is immersed in water at 80 °C for 24 hours to desorb lithium ions.

[0070] In the third step, the boehmite and böhmite bulk materials after lithium ion desorption are immersed in a 10% aqueous lithium chloride solution. After adsorbing lithium ions, the boehmite and böhmite composite bulk material undergoes a volume expansion of more than twice.

[0071] In the fourth step, the above sample is placed in water at 80 °C for 24 hours to desorb lithium ions. The sample after lithium removal is heat-treated at 1000 °C to 1200 °C for 2 hours to complete the crystal form transformation to α-aluminum oxide.

[0072] In the fifth step, the porous α-aluminum oxide is ball-milled and dispersed for 2 hours at a rotation speed of 500 revolutions per minute, and finally monodisperse α-aluminum oxide with a particle size of 20 nm is obtained.

[0073] Content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0074] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0075] In the description of the present invention, it should be noted that, unless otherwise clearly specified and defined, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0076] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing monodisperse nano-α-alumina by vacancy isolation, characterized in that: The method comprises the following steps: Step 1: Weigh 100 g of ρ-type alumina powder and 1% to 5% of lithium chloride powder respectively, mix the two powders and add them into water, stir them thoroughly until they are uniform, so as to promote hydration reaction between the ρ-type alumina and water and solidify them into a composite bulk material composed of bayerite and boehmite, and the nanoparticle size of the nanoparticle is 20 nanometers; Step 2: Soak the solidified sample in hot water for 24 hours to desorb lithium ions and form active sites; Step 3: Immerse the Bayerite and Boehmite composite bulk material after lithium ion desorption in a lithium chloride aqueous solution, and adsorb lithium ions to cause the composite bulk material to expand in volume by more than two times; Step 4: The above samples were placed in hot water again for 24 hours to desorb lithium ions and form vacancies. The de-lithiated samples were heat treated for 2 hours. The vacancy effect caused by the adsorption and desorption of lithium ions changed the phase transformation path of α-alumina, converting θ-alumina into α-alumina, and effectively preventing the merging and growth of nanoparticles. Step 5: The loose α-alumina is dispersed by ball milling to finally obtain monodisperse nano α-alumina with a particle size of 20 nanometers.

2. The vacancy isolation preparation method of monodisperse nano-α-alumina according to claim 1, characterized in that: The mass of water in the first step is 100 to 400 grams.

3. The vacancy isolation preparation method of monodisperse nano-α-alumina according to claim 1, characterized in that: The temperature of the hot water in the second step and the fourth step is 60°C to 80°C.

4. The vacancy isolation preparation method of monodisperse nano-α-alumina according to claim 1, characterized in that: The concentration of the lithium chloride aqueous solution in the third step is 6% to 10%.

5. The vacancy isolation preparation method of monodisperse nano-α-alumina according to claim 1, characterized in that: The sample is heat treated at a temperature of 1000°C to 1200°C.

6. The vacancy isolation preparation method of monodisperse nano-α-alumina according to claim 1, characterized in that: The ball milling dispersion time is 2 hours, and the rotation speed is 500 rpm.

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