Vacancy isolation preparation method of monodisperse nano alpha alumina

Abstract

The invention discloses a vacancy isolation preparation method of monodisperse nano alpha alumina, and relates to the technical field of new materials, alpha alumina can be obtained through heat treatment of various activated alumina, but the alpha alumina can be obtained while alumina of other crystal forms is converted into alpha alumina. Generally accompanied by the process of combining and growing other crystal forms of nano-crystalline grains into wormlike alpha-type aluminum oxide crystalline grains, the nano-alpha-type aluminum oxide of less than 100 nanometers is difficult to obtain in a phase inversion manner. According to the preparation method, rho aluminum oxide which can be hydrated to obtain nano-particles is used as a raw material, through adsorption and desorption of lithium chloride, a hydration product is subjected to volume expansion, vacancies left after desorption of lithium ions change a conversion path of phase conversion to alpha aluminum oxide, and combination and growth (hard agglomeration) of crystal grains are prevented; therefore, the monodisperse nano alpha-type aluminum oxide can be efficiently prepared on a large scale.

Description

Technical Field

[0001] The invention relates to the technical field of new materials, and in particular to a vacancy isolation preparation method for monodisperse nano alpha alumina. Background Art

[0002] α-Alumina is the most stable phase among various crystalline forms of alumina. Due to its extremely high hardness, high mechanical strength, excellent wear resistance, high insulation, excellent thermal stability and chemical stability, α-alumina (i.e. corundum phase) has been widely used in structural ceramics, friction materials, refractory materials, electrical insulation materials and other fields. Nano-α-alumina is in urgent need of catalysis, medicine, composite materials, abrasives and high-performance anti-scratch coatings due to its finer particle size, especially in high-tech fields represented by transparent ceramics and nano-ceramics, where nano-α-alumina with uniform and fine particle size must be used. However, the current technology for preparing nano-α-alumina is complex and costly, which seriously restricts the development of the above fields. For example, the price of nano-α-alumina is as high as 300 yuan / kg, which is dozens of times the price of ordinary alumina powder. α-Alumina is the most thermodynamically stable structure of alumina. Since the Bayer process is the mainstream process in the current aluminum industry, the directly obtained aluminum hydroxide will be converted into various transitional aluminas during heating. These transitional aluminas are usually converted into α-alumina above 1200°C. Transitional alumina, also known as transient alumina or activated alumina, usually increases in size during the transformation to α-alumina phase. When transforming to α-alumina, the particle size usually grows to more than 100 nanometers and exhibits a worm-like morphology (Critical factors in the production of sol gel derived porousalumina, Key Engineering Materials Vol. 115 (1996) pp 45-64).

[0003] The phase transition temperature from transition phase alumina to α-alumina is above 1000°C, and even reaches 1200°C. In this case, the generated α-alumina always exists in the form of worm-like sintered bodies with a size of about 100 nm and poor dispersibility. People have obtained α-alumina at 900°C by adding seed crystals or introducing a liquid phase environment, but worm-like sintered bodies of about 100 nm are still unavoidable. When a liquid phase is present, it is easy to form micron-sized lamellae. So far, it is still impossible to prepare fully dispersed α-alumina nanoparticles within 50 nm through high-temperature phase transition, which has also greatly limited its application accordingly.

[0004] Chinese patent application No. 200310114455.8 discloses a method for preparing non-agglomerated nano α-Al2O3 powder, which comprises the following steps: fully dispersing nano carbon black in an inorganic aluminum salt solution having a concentration of 0.5 to 3.0 mol / L, slowly adding a certain concentration of alkali solution in a reaction field having a turbulent effect, controlling the pH value of the final reaction solution to be between 5.0 and 8.0, settling for 7 to 12 hours after the reaction is completed, filtering and washing, treating the filter cake in an inert gas furnace at 1000 to 1200° C. for 1 to 3 hours, and calcining in an air furnace at 600 to 800° C. until the surface coating is completely removed, thereby obtaining a non-agglomerated α-Al2O3 powder having a size of 30 to 60 nm, which does not require grinding, and is evenly distributed.

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

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

[0007] The Chinese patent with application number CN201510000781.9 uses iron oxide and aluminum powder as raw materials, mixes them in a certain proportion and grinds them with a high-energy ball mill. The high-energy ball mill induces an oxidation-reduction reaction to obtain a nano-composite powder mainly composed of α-alumina and α-iron. Hydrochloric acid is then used to remove iron and other impurities in the nano-composite to obtain α-alumina nanoparticles.

[0008] The Chinese patent with application number CN201610364145.9 uses a high-energy ball milling method to grind α-alumina micropowder and then prepare α-alumina nanoparticles through color soaking and high-speed centrifugation.

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

[0010] Therefore, we proposed a vacancy isolation preparation method for monodisperse nano-α-alumina in order to solve the above problems. Summary of the invention

[0011] 1. Technical problem to be solved by the invention: The object of the present invention is to provide a vacancy isolation preparation method for monodisperse nano-α-alumina to solve the problem of low yield and low efficiency existing in the above-mentioned background technology.

[0012] 2. Technical solution: To achieve the above object, the present invention provides the following technical solution: a method for preparing monodisperse nano-α-alumina by vacancy isolation, the method comprising the following steps: Step 1: Weigh 100 g of ρ-type alumina powder and lithium chloride powder with a mass ratio of 1% to 5% of ρ-type alumina powder respectively, mix the two powders and add them into water, stir them thoroughly until they are uniform, so as to cause the ρ-type alumina to react with water to generate a multiphase bulk material composed of bayerite and boehmite, and the nanoparticle size of the nanoparticle is 20 nanometers; Step 2: Soak the treated samples 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.

[0013] Furthermore, the mass of water in the first step is 100 to 400 grams.

[0014] Furthermore, the temperature of the hot water in the second step and the fourth step is 60°C to 80°C.

[0015] Furthermore, the concentration of the lithium chloride aqueous solution in the third step is 6% to 10%.

[0016] Furthermore, the sample is heat treated at a temperature of 1000°C to 1200°C.

[0017] Furthermore, the ball milling dispersion time is 2 hours and the rotation speed is 500 rpm.

[0018] 3. Beneficial effects: By adopting the technical solution provided by the present invention, compared with the prior art, the vacancy isolation preparation method of monodisperse nano α-alumina of the present invention is as follows: The present invention uses cheap and safe ρ alumina as a raw material, lithium chloride is added before hydration of ρ alumina, and after hydration, the lithium-containing hydration product is desorbed from lithium ions in hot water, so that the hydration product produces lithium active sites, and the hydration product (bayerite and boehmite) containing lithium active sites is then immersed in a lithium chloride aqueous solution, so that the hydration product adsorbs lithium chloride, and the hydration product expands in volume by more than twice, changing the path of transient alumina to α-alumina conversion, and the conventional phenomenon of particles converted to α-alumina merging and growing into a worm-like morphology does not occur, and monodisperse nano α-alumina is obtained. The present application can efficiently prepare monodisperse nano α-alumina in large quantities by isolating the merging and growth of grains through the vacancies formed by volume expansion after lithium ion desorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the hydration of ρ alumina and its conversion to α alumina of the present invention; Figure 2 The XRD diagram of the hydrated crystalline form of the rho alumina of the present invention (lithium chloride content is below the detection limit); Figure 3 This is a SEM image of the hydrated p-alumina of the present invention; Figure 4 The XRD diagram of the phase transformation of aluminum oxide during heat treatment of the process of the present invention; Figure 5 For comparison, the XRD pattern of the phase transformation of direct heat treatment of ρ alumina; Figure 6 This is the SEM image of the monodisperse nano-α-alumina obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] 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.

[0021] A method for preparing monodisperse nano-alpha alumina by vacancy isolation comprises the following steps: Step 1: Weigh 100 grams 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 the hydration reaction between the ρ-type alumina and water and solidify them into a complex phase block material composed of bayerite and boehmite, with a nanoparticle size of 20 nanometers and a water mass of 100 to 400 grams.

[0022] Step 2: Soak the solidified sample in hot water for 24 hours to desorb lithium ions and form active sites. The temperature of the hot water is 60°C to 80°C.

[0023] The third step: immerse the Bayerite and Boehmite complex bulk material after lithium ion desorption in a lithium chloride aqueous solution. By adsorbing lithium ions, the volume of the complex bulk material expands more than twice. The concentration of the lithium chloride aqueous solution is 6% to 10%.

[0024] Step 4: Place the above samples in hot water again for 24 hours to desorb lithium ions and form vacancies. The delithiation samples are heat treated for 2 hours. The vacancy effect caused by the adsorption and desorption of lithium ions changes the phase transformation path of α-alumina, converting θ-alumina into α-alumina, and effectively preventing the merging and growth of nanoparticles. The temperature of the hot water is 60℃~80℃, and the temperature of the heat-treated samples is 1000℃~1200℃.

[0025] 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. The ball milling time is 2 hours and the rotation speed is 500 rpm.

[0026] The present invention uses cheap and safe ρ alumina as a raw material. The ρ alumina reacts with water to obtain a hydration product (Bayerite and boehmite) with a particle size of about 20 nm. The hydration product is subjected to heat treatment to obtain transient alumina. The transient alumina is subjected to heat treatment to obtain α alumina. The hydration product of the ρ alumina of the present invention is converted into α-type alumina, and the microscopic morphology such as the particle size of the nanoparticles does not change. In the present invention, lithium chloride is added before hydration of ρ alumina. After hydration, the lithium-containing hydration product is placed in hot water to desorb lithium ions, so that the hydration product produces lithium active sites. In the present invention, the hydration product (Bayerite and Boehmite) containing lithium active sites is immersed in a lithium chloride aqueous solution, so that the hydration product adsorbs lithium chloride, and the hydration product expands in volume by more than two times. The sample after volume expansion is then immersed in hot water to de-lithium to form vacancies. After high-temperature heat treatment, different transient alumina transformation paths occur, directly from θ-type alumina to α-type alumina, while ρ alumina does not undergo a hydration reaction. During heat treatment, the phase transformation path is to directly transform from γ-phase alumina to α-phase alumina. The process of the present invention ensures that during the phase transformation to α-type alumina, nanoparticles do not agglomerate and grow into a conventional worm-like morphology, but monodispersed nano α-type alumina is obtained.

[0027] Embodiment 1: In the first step, 100 grams of ρ-type alumina powder and 1% of lithium chloride powder by weight of ρ-type alumina powder are weighed, added into 200 grams of water and stirred evenly, so that the ρ-type alumina reacts with water and solidifies into a shape. The schematic diagram of the hydration and phase transformation of ρ-type alumina is shown in Figure 1 As shown in Figure 2, the complex bulk material obtained after hydration is mainly composed of bayerite and boehmite, such as Figure 2 Its microstructure is shown in Figure 3 As shown, the particle size of the bayerite and boehmite nanoparticles is 20 nanometers.

[0028] In the second step, the cured sample is immersed in 60°C water for 24 hours to desorb lithium ions.

[0029] In the third step, the bayerite and boehmite bulk materials after lithium ion desorption are immersed in a 6% lithium chloride aqueous solution. After adsorbing lithium ions, the bayerite and boehmite composite bulk materials expand in volume by more than twice.

[0030] The fourth step is to place the above sample in water at 60°C for 24 hours to desorb lithium ions. The de-lithiated sample is heat treated at 1000°C to 1200°C for 2 hours. Figure 4 As shown in Figure 2, the sample is directly transformed from θ alumina to α alumina. Figure 5 As shown in the figure, the sample that has not been adsorbed by lithium ions and has not undergone volume expansion needs to be transformed from γ-alumina to α-alumina.

[0031] The fifth step is to disperse the loose α-alumina by ball milling. The ball milling time is 2 hours and the rotation speed is 500 rpm. Finally, the following is obtained: Figure 6 The monodispersed nano-α-alumina with a particle size of 20 nanometers is shown.

[0032] Embodiment 2: In the first step, 100 grams of ρ-type alumina powder and 2% of lithium chloride powder by mass of the ρ-type alumina powder are weighed respectively, added into 300 grams of water and stirred evenly, so that the ρ-type alumina reacts with water and solidifies into a shape.

[0033] In the second step, the cured sample is immersed in water at 70°C for 24 hours to desorb lithium ions.

[0034] In the third step, the bayerite and boehmite bulk materials after lithium ion desorption are immersed in a 7% lithium chloride aqueous solution. After adsorbing lithium ions, the bayerite and boehmite composite bulk materials expand in volume by more than twice.

[0035] The fourth step is to place the sample in water at 70°C for 24 hours to desorb lithium ions. The sample after delithiation is heat treated at 1000°C to 1200°C for 2 hours to complete the crystal transformation to α-alumina.

[0036] The fifth step is to disperse the loose α-alumina by ball milling. The ball milling time is 2 hours and the rotation speed is 500 rpm, and finally monodispersed nano α-alumina with a particle size of 20 nanometers is obtained.

[0037] Embodiment 3: In the first step, 100 grams of ρ-type alumina powder and 3% of lithium chloride powder by weight of the ρ-type alumina powder are weighed respectively, added into 100 grams of water and stirred evenly, so that the ρ-type alumina reacts with water to undergo hydration and solidify into a shape.

[0038] In the second step, the cured sample is immersed in water at 70°C for 24 hours to desorb lithium ions.

[0039] In the third step, the bayerite and boehmite bulk materials after lithium ion desorption are immersed in an 8% lithium chloride aqueous solution. After adsorbing lithium ions, the bayerite and boehmite complex bulk materials expand in volume by more than twice.

[0040] The fourth step is to place the sample in water at 70°C for 24 hours to desorb lithium ions. The de-lithiated sample is heat treated at 1000°C to 1200°C for 2 hours to complete the crystal transformation to α-alumina.

[0041] The fifth step is to disperse the loose α-alumina by ball milling. The ball milling time is 2 hours and the rotation speed is 500 rpm, and finally monodispersed nano α-alumina with a particle size of 20 nanometers is obtained.

[0042] Embodiment 4: In the first step, 100 grams of ρ-type alumina powder and 4% of lithium chloride powder by weight of the ρ-type alumina powder are weighed respectively, added into 200 grams of water and stirred evenly, so that the ρ-type alumina reacts with water and solidifies into a shape.

[0043] In the second step, the cured sample is immersed in water at 80°C for 24 hours to desorb lithium ions.

[0044] In the third step, the bayerite and boehmite bulk materials after lithium ion desorption are immersed in a 9% lithium chloride aqueous solution. After adsorbing lithium ions, the bayerite and boehmite complex bulk materials expand in volume by more than twice.

[0045] The fourth step is to place the sample in water at 80°C for 24 hours to desorb lithium ions. The de-lithiated sample is heat treated at 1000°C to 1200°C for 2 hours to complete the crystal transformation to α-alumina.

[0046] The fifth step is to disperse the loose α-alumina by ball milling. The ball milling time is 2 hours and the rotation speed is 500 rpm, and finally monodispersed α-alumina with a particle size of 20 nanometers is obtained.

[0047] Embodiment 5: In the first step, 100 grams of ρ-type alumina powder and 5% of lithium chloride powder by weight of the ρ-type alumina powder are weighed respectively, added into 400 grams of water and stirred evenly, so that the ρ-type alumina reacts with water and solidifies into a shape.

[0048] In the second step, the cured sample is immersed in water at 80°C for 24 hours to desorb lithium ions.

[0049] In the third step, the bayerite and boehmite bulk materials after lithium ion desorption are immersed in a 10% lithium chloride aqueous solution. After adsorbing lithium ions, the volume of the bayerite and boehmite composite bulk materials expands by more than twice.

[0050] The fourth step is to place the sample in water at 80°C for 24 hours to desorb lithium ions. The de-lithiated sample is heat treated at 1000°C to 1200°C for 2 hours to complete the crystal transformation to α-alumina.

[0051] The fifth step is to disperse the loose α-alumina by ball milling. The ball milling time is 2 hours and the rotation speed is 500 rpm, and finally monodispersed α-alumina with a particle size of 20 nanometers is obtained.

[0052] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0053] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0054] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" 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 a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in 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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