Superfine nanometer alumina powder and preparation method and application thereof

Abstract

The invention discloses superfine nano aluminum oxide powder and a preparation method and application thereof, the preparation method comprises the following steps: taking high-purity nano pseudo-boehmite as an aluminum source, and soaking with acid to obtain acidic sol A; adding a grain growth inhibitor, a morphology control agent and a dispersing agent into the sol A, and uniformly mixing to obtain sol B; and freezing and drying the B sol at low temperature to form gel, and then crushing, sieving and calcining to obtain the superfine nano aluminum oxide powder. According to the method for preparing the nano spherical alpha alumina powder by utilizing the pseudo-boehmite, on the basis of ensuring the purity of alumina, the abnormal growth of grains of alumina at high temperature can be effectively inhibited, and the calcination temperature required for converting the alumina into an alpha phase is remarkably reduced, so that the alpha alumina powder is relatively narrow in particle size distribution and relatively high in sphericity degree; the method is simple in process, simple in equipment and suitable for large-scale continuous production.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic powder materials, and specifically relates to ultrafine nano alumina powder and a preparation method and application thereof. Background Art

[0002] α-alumina powder has significant advantages in CMP polishing. Its Mohs hardness is as high as 9, second only to diamond and silicon carbide, which enables it to provide efficient cutting force and high brightness during the polishing process. By controlling the original crystal form and morphology during the phase transition process, α-alumina powder can achieve both cutting force and high brightness, thereby improving polishing efficiency and reducing polishing procedures. In recent years, the new energy vehicle industry has driven the development of sapphire and third-generation semiconductor silicon carbide wafers, and the application of α-alumina in CMP has become more important.

[0003] In the fine polishing of silicon carbide and sapphire wafers for semiconductors, silica sol and alumina are usually used as abrasives to prepare fine polishing liquid. However, due to the relatively low hardness of silica sol, the fine polishing time is long, which reduces production efficiency. Alumina powder has a higher cutting rate than silica sol, but due to the problem of easy agglomeration, sedimentation and large particles, it is easy to cause scratch defects, and the stability of the polishing liquid is not as good as that of silica sol polishing liquid.

[0004] Therefore, it is urgent to prepare a nano-α-alumina powder with a particle size of less than 100nm and very few large particles, so as to reduce defects such as scratches while ensuring a certain cutting rate and improve the stability of the alumina polishing liquid. However, in the preparation process of nano-alumina powder, since alumina powder needs to be calcined at high temperature to transform the crystal phase into a high-hardness α phase, the excessively high calcination temperature causes the alumina grains to grow easily, which makes it extremely difficult to obtain nano-α-alumina below 100nm.

[0005] Patent CN116002737A discloses a method for preparing submicron spherical α-alumina powder using boehmite. The particle size of the obtained alumina powder is too high, reaching 400nm-800nm, which is easy to cause scratches and increase the roughness of the wafer surface.

[0006] Patent CN115893461B discloses a process for preparing nano-alumina polishing powder, and obtains α-alumina powder with a primary particle size of 100nm and a secondary particle size of less than 300nm. However, the preparation process adopts a co-precipitation method of adding ammonia water to adjust the pH. During the precipitation process, abnormal growth and agglomeration of aluminum hydroxide original crystals are prone to occur, which will affect the uniformity and grain control during the subsequent calcination process. In addition, a silane coupling agent is subsequently used to modify the aluminum oxide, and the introduction of Si element can easily reduce the purity of the aluminum oxide powder.

[0007] Patent CN114940886A discloses a process for preparing nano-alumina powder by solution combustion synthesis. The particle size of the prepared alumina is 20-30nm, but the calcination temperature is as high as 1200°C. It is not easy to control the temperature uniformity during the self-propagating combustion process. A lot of nano-dust is also likely to fly during the combustion process. Aluminum salts are flammable and explosive chemicals, which have certain safety risks and are not suitable for industrial production. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a method for preparing nano-spherical α-alumina powder by using pseudo-boehmite. The method can effectively inhibit the abnormal grain growth of alumina at high temperature on the basis of ensuring the purity of alumina, and significantly reduce the calcination temperature required for conversion into α phase, so that the particle size distribution of α-alumina powder is narrow and the sphericity is higher. The method has simple process and simple equipment and is suitable for large-scale continuous production.

[0009] The technical solution adopted by the present invention is: a method for preparing ultrafine nano-alumina powder, comprising the following steps:

[0010] Step 1: Using high-purity nano-pseudo-boehmite as an aluminum source, soaking it in acid to obtain an acidic A sol;

[0011] Step 2: adding a grain growth inhibitor, a morphology control agent, and a dispersant to the A sol, and mixing them evenly to obtain a B sol;

[0012] Step 3: spray-dry the B sol at low temperature, crush it, sieve it, freeze-dry it at low temperature, and then calcine it to obtain ultrafine nano-alumina powder.

[0013] As a preferred embodiment of the above technical solution, the D50 of the pseudo-boehmite is 10-20nm, and the BET is 180-280nm. 2 / g, purity>99.9%.

[0014] As a preferred embodiment of the above technical solution, the acid is any one of dilute nitric acid, dilute sulfuric acid and acetic acid.

[0015] As a preferred embodiment of the above technical solution, the morphology control agent is any one or more of ammonium sulfate, ammonium fluoride, aluminum fluoride, and ammonium carbonate; the grain growth inhibitor is any one or more of nano-boehmite, nano-pseudo-boehmite, nano-aluminum hydroxide, and nano-aluminum oxide; the dispersant is any one or more of hexadecylamine, octadecylamine, and polyoxyethylene alkylamide.

[0016] As a preferred embodiment of the above technical solution, the solid content of the A sol is 20%; the content of the dispersant is 0.1-1%, the content of the morphology control agent is 0.1-1%, and the content of the grain growth inhibitor is 1-5%; the mass ratio of diaspore: water: grain growth inhibitor and morphology control agent is 2-5:10-20:1-5:0.1-1.

[0017] As a preferred embodiment of the above technical solution, the crushing process in step three adopts a ball mill, the sieving mesh number is 80-100 mesh, the calcination temperature is 850-1050°C, and the insulation time is 1-3h; the low-temperature hot air temperature of the low-temperature freeze-drying process is set to 60-100°C, and the drying time is 1-3h.

[0018] The ultrafine nano alumina powder is prepared by the above preparation method.

[0019] As a preferred embodiment of the above technical solution, the α-alumina content in the ultrafine nano alumina powder is greater than 98%, the sphericity of the ultrafine nano alumina powder is greater than 70%, the range of D50 is 50-100nm, the purity of the ultrafine nano alumina powder is greater than 99.9%, the total content of potassium, iron, calcium, magnesium and sodium is less than 50ppm, and the silicon oxide content is less than 100ppm.

[0020] Application of ultrafine nano-aluminum oxide powder, wherein the ultrafine nano-aluminum oxide powder is used for fine chemical mechanical polishing of silicon carbide wafers or LED sapphire substrates.

[0021] The beneficial effects of the present invention are:

[0022] (1) The morphology control agent used in the present invention does not contain metal elements and will volatilize and decompose during the calcination process. The generated gas makes the alumina powder loose and not easy to agglomerate, thereby preventing the further growth of the grains. Ultrafine seed crystals are used as an inhibitor of grain growth. The obtained nano alumina powder is uniform and loose, and the agglomerates are easily broken up.

[0023] (2) The present invention combines low-temperature spray drying technology with low-temperature vacuum freeze drying, so that the pseudo-boehmite gel can be dehydrated faster without the occurrence of primary crystal growth, which consumes less time than traditional low-temperature drying and helps to improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a SEM image of the ultrafine nano-alumina powder obtained in Example 1;

[0025] Figure 2 This is the particle size distribution diagram of the ultrafine nano-alumina powder obtained in Example 1;

[0026] Figure 3 The XRD pattern of the ultrafine nano-alumina powder obtained in Example 1;

[0027] Figure 4 is the SEM image of the alumina powder obtained in the comparative example;

[0028] Figure 5 The particle size distribution diagram of the aluminum oxide powder obtained in the comparative example;

[0029] Figure 6 The XRD pattern of the aluminum oxide powder obtained in the comparative example. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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.

[0031] 《1》Use high-purity nano-pseudo-boehmite as aluminum source and soak it in acid to obtain acidic A sol;

[0032] 《2》Add grain growth inhibitor, morphology control agent and sintering aid to sol A and mix them evenly to obtain sol B;

[0033] 《3》 Dehydrate the B sol by low-temperature spray drying into a gel, remove the water from the gel by freeze drying, and then crush, sieve, and calcine at low temperature to obtain nano-spherical α-alumina powder.

[0034] High-purity pseudo-boehmite, purity of 99.99% or more, D50 = 40nm, Na2O content less than 10ppm, SiO2 content less than 20ppm, peptization index > 95%, there are mature products on the market (ZTL-CAH-0452 or ZTL-CAH-0454 of Yangzhou Zhongtianli New Materials Co., Ltd., purity of 99.995%, Na2O content of 10ppm, SiO2 content of 20ppm, peptization index ≥ 99.5%;);

[0035] The acid is any one of dilute nitric acid, dilute sulfuric acid, and acetic acid. The pH is adjusted to 3-5 and the stirring time is 3-8 hours.

[0036] The solid content of the pseudo-boehmite sol is 20-30%;

[0037] The dispersant is a small molecule dispersant such as hexadecylamine, octadecylamine, polyoxyethylene alkylamide, etc.

[0038] The grain growth inhibitor is any one of nano-boehmite, nano-pseudo-boehmite, nano-aluminum hydroxide, and nano-Al2O3, and the original grain size of the powder is less than 80nm;

[0039] The solid content of the A sol is 20%; the content of the dispersant is 0.1-1%, the content of the morphology control agent is 0.1-0.5%, and the content of the grain growth inhibitor is 0-1%;

[0040] The low-temperature spray drying temperature is 60-100°C, the gel is rapidly dehydrated, and the drying time is 1-2 hours. Then the parameters of the low-temperature vacuum freeze drying gel are as follows: the cold trap temperature is -40°C, the vacuum degree is 10-100Pa, and the drying time is 6-12 hours.

[0041] Embodiment 1:

[0042] Put 1 kg of high-purity 4N pseudo-boehmite powder into a reactor, add 3.5 kg of deionized water, and slowly add high-purity 3N dilute nitric acid solution (the concentration of dilute nitric acid is 20%) during stirring until the pH is below 3 to form a translucent pseudo-boehmite solution. Add 10 g of dispersant hexadecylamine, 10 g of morphology control agent ammonium sulfate, 50 g of nano 4N pseudo-boehmite in sequence, and then gradually add high-purity 3N ammonia water, adjust to pH = 4.5, and continue stirring for 2 hours. The solution was transferred to a low-temperature spray dryer for spray drying, the low-temperature hot air temperature was set to 80°C, the drying time was 2 hours, and most of the free water was removed; the dehydrated gel particles were transferred to a ball mill for ball milling for 2 hours, the ball mill particle size was 5mm, and the ball-milled gel powder was placed in an electromagnetic vibration sieve for 80 mesh screening; the sieved fine powder was placed in a freeze dryer for vacuum freeze drying, the cold trap temperature was set to -40°C, the vacuum degree was set to 50Pa, and the drying time was 12 hours; the dried gel powder was placed in a sintering furnace for calcination, the heating rate was set to 5°C / min, and it was kept at 950°C for 3 hours and cooled naturally.

[0043] Comparative Example:

[0044] Put 1 kg of high-purity 4N pseudo-boehmite powder into a reactor, add 3.5 kg of deionized water, and slowly add high-purity 3N dilute nitric acid solution (the concentration of dilute nitric acid is 20%) during stirring until the pH is below 3 to form a translucent pseudo-boehmite solution. Without adding dispersant and morphology control agent, add 50 g of nano 4N pseudo-boehmite, and then gradually add high-purity 3N ammonia water, adjust to pH = 4.5, and continue stirring for 2 hours. The solution was transferred to a low-temperature spray dryer for spray drying, the low-temperature hot air temperature was set to 80°C, and the drying time was 2h; the dehydrated gel particles were transferred to a ball mill for ball milling for 2h, the ball mill particle size was 5mm, and the ball-milled gel powder was placed in an electromagnetic vibration sieve for 80-mesh screening; the sieved fine powder was placed in a freeze dryer for vacuum freeze drying, the cold trap temperature was set to -40°C, the vacuum degree was set to 50Pa, and the drying time was 12h; the dried gel powder was placed in a sintering furnace for calcination, the heating rate was set to 5°C / min, and it was kept at 950°C for 3h and cooled naturally.

[0045] The SEM image of the ultrafine nano-alumina powder obtained in Example 1 is as follows: Figure 1 As shown, Figure 2 is the particle size distribution diagram of the ultrafine nano-alumina powder. Figure 3 This is the XRD diagram of the ultrafine nano-alumina powder. Figure 4 This is the SEM picture of the aluminum oxide powder obtained in the comparative example. Figure 5 is the particle size distribution diagram of the alumina powder, Figure 6 is the XRD pattern of the alumina powder. Figure 1 It can be seen that the alumina powder particles are fully developed, spherical, and have uniform particle size distribution. Figure 2 From the particle size distribution, it can be seen that the dispersed alumina particle size is concentrated and the average particle size is less than 100nm. Figure 3 From the XRD diagram, it can be seen that the main crystal phase of the calcined alumina powder is α-alumina, and the α-phase content is greater than 95%; Figure 4 , 5, 6 are the performance data of the comparative example, and it can be seen that the grains are relatively more irregular and uneven in size; the alumina particle size is greater than 100nm, the particle size distribution is wide, the main crystal phase is α alumina, and the α phase content is greater than 95%. Analysis: The reason for this phenomenon is that the embodiment adds a dispersant and a morphology control agent, so that the grain morphology can be controlled and the grain size is more uniform.

[0046] The following table compares the product performance of the ultrafine nano alumina powder obtained in Example 1 and the alumina powder obtained in the comparative example, further verifying that the ultrafine nano alumina powder obtained by the preparation method of the present invention has higher performance. The reason for this phenomenon is that the dispersant and morphology control agent are added in the embodiment, so that the grain morphology can be controlled, the grain size is more uniform, and the sphericity is higher.

[0047] D50 average particle size D90 Particle morphology Crystal phase Degree of reunion Sphericity Example 1 84.8nm 124.1nm spherical α＞95％ Slight reunion ＞80％ Comparative Example 120nm 189.6nm Spherical α＞95％ More serious Less than 80%

[0048] The invention adopts a special additive, and during high-temperature calcination, the additive is decomposed into gas to make the powder fluffy and prevent agglomeration; at the same time, the sintering temperature is reasonably controlled to reduce agglomeration as much as possible; the invention controls the production and aggregation of super-large particles through the appropriate amount of seed crystals; the grain growth is uniform by controlling the uniformity of the hydrolysis temperature; the excessively fast grain growth during the aging process is reduced by controlling the steam pressure of hydration and aging; the α phase content of the grains exceeds 98% by controlling the calcining temperature and the heat preservation time, so as to retain sufficient hardness during the polishing process.

[0049] It is worth mentioning that the technical features such as the ball mill involved in the patent application of this invention should be regarded as the prior art. The specific structure, working principle and possible control method and spatial layout method of these technical features can be selected by conventional methods in the field, and should not be regarded as the inventive point of the patent of this invention. The patent of this invention will not be further elaborated.

[0050] The preferred specific embodiments of the present invention are described in detail above. It should be understood that ordinary technicians in this field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in this technical field through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the existing technology should be within the scope of protection determined by the claims.

Claims

1. A method for preparing ultrafine nano-alumina powder, characterized in that: The following steps are included: Step 1: Using high-purity nano-pseudo-boehmite as an aluminum source, soaking it in acid to obtain an acidic A sol; Step 2: adding a grain growth inhibitor, a morphology control agent, and a dispersant to the A sol, and mixing them evenly to obtain a B sol; Step 3: spray-dry the B sol at low temperature, crush it, sieve it, freeze-dry it at low temperature, and then calcine it to obtain ultrafine nano-alumina powder.

2. The method for preparing ultrafine nano-alumina powder according to claim 1, characterized in that: The pseudo-boehmite has a D50 of 10-20 nm and a BET of 180-280 nm. 2 / g, purity>99.9%.

3. The method for preparing ultrafine nano-alumina powder according to claim 1, characterized in that: The acid is any one of dilute nitric acid, dilute sulfuric acid and acetic acid.

4. The method for preparing ultrafine nano-alumina powder according to claim 1, characterized in that: The morphology control agent is any one or more of ammonium sulfate, ammonium fluoride, aluminum fluoride, and ammonium carbonate; the grain growth inhibitor is any one or more of nano-boehmite, nano-pseudo-boehmite, nano-aluminum hydroxide, and nano-aluminum oxide; the dispersant is any one or more of hexadecylamine, octadecylamine, and polyoxyethylene alkylamide.

5. The method for preparing ultrafine nano-alumina powder according to claim 4, characterized in that: The solid content of the A sol is 20%; the content of the dispersant is 0.1-1%, the content of the morphology control agent is 0.1-1%, and the content of the grain growth inhibitor is 1-5%; the mass ratio of diaspore: water: grain growth inhibitor, morphology control agent is 2-5: 10-20: 1-5: 0.1-1.

6. The method for preparing ultrafine nano-alumina powder according to claim 1, characterized in that: In the step 3, a ball mill is used for the crushing process, the sieving mesh number is 80-100 mesh, the calcination temperature is 850-1050°C, and the insulation time is 1-3h; the low-temperature hot air temperature of the low-temperature freeze-drying process is set to 60-100°C, and the drying time is 1-3h.

7. Ultrafine nano alumina powder, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. The ultrafine nano-alumina powder according to claim 7, characterized in that: The α-alumina content of the ultrafine nano-alumina powder is greater than 98%, the sphericity of the ultrafine nano-alumina powder is greater than 70%, the D50 range is 50-100nm, the purity of the ultrafine nano-alumina powder is greater than 99.9%, the total content of potassium, iron, calcium, magnesium and sodium is less than 50ppm, and the silicon oxide content is less than 100ppm.

9. The use of the ultrafine nano-alumina powder as claimed in claim 8, characterized in that: The ultrafine nano aluminum oxide powder is used for fine chemical mechanical polishing of silicon carbide wafers or LED sapphire substrates.

Images