CN104528787A - Method for preparing small-particle-size aluminium oxide powder - Google Patents

Abstract

The invention provides a method for preparing alumina powder with fine particle diameter, which belongs to the technical field of powder preparation and particle diameter control. The process flow is: use industrial aluminum hydroxide or transition phase alumina powder as raw material, add crystal seed, dispersant, particle size control component and gas phase source to the raw material powder, mix the raw material powder evenly and press it into a green body. The green body is calcined at high temperature in an atmosphere containing hydrogen halide and particle size control components, the calcined green body is broken into powder, and after secondary molding, it is calcined at a low temperature in an atmosphere containing a higher concentration of hydrogen halide to obtain a particle size of less than 0.14 μm, the content of α-Al ₂ O ₃ is 100% sub-micron or nano-sized alumina powder. The invention has low reaction temperature, short reaction time, simple process and good dispersibility of the obtained alumina powder.

Description

A method for preparing fine-grained alumina powder

technical field

The invention belongs to the technical field of powder preparation and particle size control, and particularly provides a method for preparing alumina powder with fine particle size.

Background technique

Fine particle size alumina powder (submicron and nanoscale alumina powder) not only has the characteristics of high melting point, high hardness, high strength and corrosion resistance, but also has significant surface effect, small size effect, quantum effect, and macroscopic quantum tunneling effect. As well as high sintering activity, it exhibits a series of excellent electrical, magnetic, optical, mechanical and chemical macroscopic properties, and has broad application prospects in abrasives, cutting tools, composite materials, microelectronics, chemicals, aerospace industry, fine ceramics and other fields. The preparation of fine particle size alumina powder mainly includes solid phase synthesis method, chemical pyrolysis method, amorphous crystallization method, sol-gel method, liquid phase precipitation method and other methods. The solid-phase method is to grind and calcinate aluminum or aluminum salt, and obtain fine-grained alumina powder directly after a solid-phase reaction occurs. The gas-phase method uses metal element, halide, hydride or organometallic compound as raw material, and synthesizes fine-grained alumina through gas-phase thermal decomposition and chemical reaction. The liquid-phase precipitation method is to precipitate the active ingredients in the raw materials through a chemical reaction in a solution state, and then filter, wash, dry, and thermally decompose to prepare fine-grained alumina. The preparation of fine particle size has problems such as difficult control of particle size and shape, complicated process, and high cost.

Chinese patent CN1095360A discloses a kind of α-alumina powder and its production method. It is calcined in a protective atmosphere containing hydrogen chloride or halogen under the condition of containing seed crystals and/or shape control agents to obtain fine particle size and special structure. Aluminum oxide powder. The particle size of the fine-grained alumina powder obtained is 0.6-3.7 μm, and it is difficult to prepare a powder with a finer particle size (<0.6 μm). Chinese patent CN1386705A discloses a fine powder of α-alumina and its preparation method. The mixture of α-Al ₂ O ₃ precursor, seed crystal and grain growth inhibitor is heated at 600-1000°C in an atmosphere containing HCl Calcined directly to obtain fine-grained alumina powder, in which the content of α-Al ₂ O ₃ is greater than 90%. In this method, the calcination temperature is lower, and the content of α-Al ₂ O ₃ is not high. Chinese patent CN102009993A discloses a two-stage calcination method (low-temperature calcination + high-temperature calcination) to prepare submicron-sized alumina. Activated alumina is first calcined at a low temperature of 400-900°C, and then calcined at a high temperature of 1100-1400°C to obtain Submicron alumina powder, the particle size of alumina powder is 0.4-0.8μm. When calcined at low temperature (<900°C), alumina still exists in the form of transition phase alumina, and the phase transition between transition phase alumina is a displacement phase transition, which does not destroy chemical bonds. There are few defects in the crystal and the activation effect is not significant. . When calcined at high temperature, alumina tends to grow and it is difficult to obtain nano-sized alumina powder. The present invention comprehensively utilizes the addition of seed crystals and/or shape control agents, adopts a specially designed sintering atmosphere containing hydrogen halide and/or fluoride (aluminum fluoride), and performs two rounds of compacting and two calcinations on the powder (high-temperature calcination + low temperature calcination). When calcined at high temperature, the particles undergo a reconstruction phase transition, the particles shrink locally, and a large number of small cracks and other defects are formed on the surface. During low-temperature calcination, the particles are further broken up in an atmosphere containing hydrogen halide. The high-temperature calcination + low-temperature calcination method has a better crushing effect under the action of the above mechanism and other mechanisms whose principles are still unclear, so that submicron or nanoscale alumina powder with a particle size of less than 0.14 μm can be prepared.

Contents of the invention

The object of the present invention is to provide a kind of method for preparing fine-grained aluminum oxide powder, specifically comprises the following steps:

1. Raw material mixing: use industrial aluminum hydroxide or transition phase alumina powder as raw material, add 0.5~4.5wt.% seed crystal, 0.1~1.5wt.% dispersant, 0.01~1.2wt.% crystal grain to the raw material powder Growth inhibitor, 0-0.5wt.% gas phase source, mixed uniformly by stirring or ball milling, and then dried at 50-80°C for 3-5 hours to obtain a mixture;

The transition phase alumina is γ-Al ₂ O ₃ , δ-Al ₂ O ₃ , ζ-Al ₂ O ₃ , η-Al 2 O ₃ , θ- _{Al 2 O 3} , κ-Al ₂ O ₃ and One or more of χ-Al ₂ O ₃ .

The seed crystals are oxides, nitrides, carbides or carbonitrides of aluminum, titanium, zirconium and vanadium with an average particle size of less than 30 nm.

The grain growth inhibitor is used in the preparation of fine-grained alumina powder, including compounds and mixtures of metals such as magnesium, yttrium, zirconium, and niobium, such as YCl ₃ , Nb ₂ O ₃ , ZrO ₂ , Mg(OH ) One or more of Cl, MgO and MgCl ₂ .

The dispersant is an acid or lipid with a molecular weight in the range of 120-600, containing methyl and benzene rings, such as phenyl acetate, benzoic acid, methyl benzoate, n-butyl benzoate and the like.

2. Primary billet making: add 2.5-5wt.% dextrin or polyvinyl alcohol to the dried mixture, and shape it under a pressure of 560-800MPa to obtain a primary billet;

3. Primary calcination: the primary body is calcined at a high temperature in an atmosphere containing hydrogen halide and particle size control components, the calcination temperature is 1160-1300°C, and the calcination time is 2-3 hours to obtain a primary calcined body; The diameter control component is an aluminum halide;

The atmosphere containing hydrogen halides and particle size control components is a mixed gas phase of hydrogen halides, ammonia, aluminum halides, hydrogen, nitrogen and air, the concentration of hydrogen halides in the gas phase is 0.1 to 1.0%, and the concentration of ammonia is 1.1-1.5%, the concentration of aluminum halide is 1-2%, the concentration of hydrogen is 3-5%, the concentration of nitrogen is 6-10%, and the balance is air.

During primary calcination, ammonia halide and halogen compound can also be pre-added to the mixture, and decomposed at high temperature to obtain hydrogen halide, ammonia, nitrogen, chlorine or aluminum halide. The halogen compound is ammonium perchlorate, ammonium hypochlorite, hexafluoroaluminate and the like.

For industrial production, calcination (including primary green body calcination and secondary green body calcination) can be carried out in a continuous manner with tunnel kiln, rotary kiln or pusher furnace.

4. Secondary billet making: crush the primary calcined green body into powder, add 2.5-5wt.% dextrin or polyvinyl alcohol to the crushed powder, and shape it under a pressure of 560-800 MPa to obtain a secondary green body;

5. Secondary calcination: The secondary green body is calcined at a low temperature, the calcination temperature is 510-900°C, and the calcination time is 2-5 hours. After the secondary calcination, the secondary calcined green body is obtained. After the secondary calcined green body is broken, the alumina powder with a particle size of less than 0.14 μm and a content of α-Al ₂ O ₃ of 100% is obtained. The appearance of the fine particle size alumina is as follows: Figure 2 shows.

During the secondary calcination, an atmosphere containing a relatively high concentration of hydrogen halide gas is used, wherein the concentration of hydrogen halide is 1.6-2.0%, the concentration of ammonia gas is 2.3-3%, the concentration of hydrogen gas is 8-10%, and the concentration of nitrogen gas is 11%. ~13%, the balance is air.

During the secondary calcination, the ammonium halide, ammonium perchlorate or ammonium hypochlorite can also be pre-added to the mixture and decomposed at high temperature to obtain hydrogen halide, ammonia, nitrogen or chlorine.

In the present invention, aluminum hydroxide or transition alumina powder is calcined in two stages of high temperature and low temperature in an atmosphere containing halogen and halogen compound gas. During high-temperature calcination, halide molecules destroy the regular arrangement of atoms in the original alumina crystal, forming Al ³⁺ ion vacancies, which accelerate the diffusion rate of Al ³⁺ ions and the crystal phase transition of Al ₂ O ₃ . During the phase transition process, the morphology control agent participates in the phase transition reaction, and the generated gas-phase compound intermediate product promotes atom migration, which is beneficial to crystal phase transition and crystal growth. During the low-temperature calcination process, the alumina powder with higher activity and more defects will be further refined after being calcined in an atmosphere containing a higher concentration of halide gas phase to obtain fine-grained alumina powder with better dispersibility. The billet making process controls the compactness of the powder particles by changing the pressing pressure, which plays a vital role in increasing the concentration of reactants and increasing the rate of chemical reactions. Introducing the halide in the atmosphere prolongs the reaction time between the halide and the raw material powder, and improves the uniformity of the reaction. The introduction of halogen reduces the calcination temperature, promotes the crystal transformation of alumina, and can realize the refinement of alumina powder at a lower temperature. The invention has the advantages of controllable crystal form, particle size and shape of the alumina powder, high powder uniformity, easy control of the reaction process, less side reactions, simple process, and easy industrial production.

Description of drawings

Fig. 1 is a process flow diagram of the present invention

Figure 2 shows the morphology of fine-grained alumina

Detailed ways

Example 1: Preparation of fine-grained alumina powder with aluminum hydroxide as raw material

Using industrial aluminum hydroxide powder as raw material, add 0.5wt.% seed crystal (20nm α-TiNC), 0.1wt.% dispersant (benzoic acid), 0.015wt.% grain growth inhibitor ( Mg(OH)Cl), mixed uniformly by means of stirring or ball milling, and then dried at 50° C. for 8 hours to obtain a mixture. Add 1wt.% dextrin or polyvinyl alcohol to the dried mixture, and shape it under a pressure of 600 MPa to obtain a primary green body; the primary green body is calcined at a high temperature at 1160° C. for 8 hours. The concentration of hydrogen fluoride in the primary calcination atmosphere is 0.1%, the concentration of ammonia is 1.1%, the concentration of aluminum fluoride is 1%, the concentration of hydrogen is 4%, the concentration of nitrogen is 6%, and the balance is air. After the primary calcination, the primary calcined green body is obtained; the primary calcined green body is broken into powder, and 0.5wt.% dextrin or polyvinyl alcohol is added to the crushed powder, and it is formed under a pressure of 560MPa to obtain a secondary green body; the two The secondary green body is calcined at a low temperature, the calcining temperature is 510° C., and the calcining time is 2 hours. The concentration of hydrogen fluoride in the secondary calcination atmosphere is 1.6%, the concentration of ammonia gas is 2.3%, the concentration of hydrogen gas is 9%, the concentration of nitrogen gas is 11%, and the balance is air. A secondary calcined body is obtained after the secondary calcination, and fine-grained alumina powder is obtained after the secondary calcined body is crushed. The average particle diameter of the obtained alumina powder was 0.09 μm, and the content of α-Al ₂ O ₃ was 100%.

Example 2: Preparation of fine-grained alumina powder using γ-Al ₂ O ₃ as raw material

Using γ-Al ₂ O ₃ as raw material, add 1wt.% seed crystal (15nm V ₂ O ₅ ), 0.6wt.% dispersant (phenyl acetate), 1.2wt.% grain growth inhibitor to the raw material powder Agent (MgO) and 0.4wt.% gas phase source (ammonium hypochlorite), mixed uniformly by stirring or ball milling, and then dried at 80°C for 3 hours to obtain a mixture. Add 2.6wt.% dextrin or polyvinyl alcohol to the dried mixture and shape it under a pressure of 700MPa to obtain a primary green body; the primary green body is calcined at a high temperature at 1300°C for 3 hours . The concentration of hydrogen chloride in the primary calcination atmosphere is 1.0%, the concentration of ammonia is 1.5%, the concentration of aluminum fluoride is 2%, the concentration of hydrogen is 5%, the concentration of nitrogen is 10%, and the balance is air. After the primary calcination, the primary calcined green body is obtained; the primary calcined green body is broken into powder, and 2wt.% dextrin or polyvinyl alcohol is added to the broken powder, and it is shaped under a pressure of 700MPa to obtain the secondary green body; the secondary The green body is calcined at a low temperature, the calcining temperature is 700° C., and the calcining time is 3 hours. The concentration of hydrogen chloride in the secondary calcination atmosphere is 2%, the concentration of ammonia gas is 2.5%, the concentration of hydrogen gas is 8%, the concentration of nitrogen gas is 12%, and the balance is air. A secondary calcined body is obtained after the secondary calcination, and fine-grained alumina powder is obtained after the secondary calcined body is crushed. The average particle diameter of the obtained alumina powder was 0.13 μm, and the content of α-Al ₂ O ₃ was 100%.

Example 3: Preparation of fine-grained alumina powder with aluminum hydroxide and NH ₄ F as raw materials

Using θ-Al ₂ O ₃ powder as raw material, add 0.8wt.% seed crystal (15nm α-TiO ₂ ), 1.0wt.% dispersant (methyl benzoate), 0.06wt.% grain Growth inhibitor (MgCl ₂ ), 0.5wt.% gas phase source (NH ₄ Cl), mixed uniformly by means of stirring or ball milling, and then dried at 60° C. for 4 hours to obtain a mixture. Add 3wt.% dextrin or polyvinyl alcohol to the dried mixture, and shape it under a pressure of 580 MPa to obtain a primary green body; the primary green body is calcined at a high temperature at 1200° C. for 6 hours. The concentration of hydrogen bromide in the primary calcination atmosphere is 0.5%, the concentration of ammonia is 1.2%, the concentration of aluminum fluoride is 2%, the concentration of hydrogen is 3%, the concentration of nitrogen is 8%, and the balance is air. After the primary calcination, the primary calcined green body is obtained; the primary calcined green body is broken into powder, and 3wt.% dextrin or polyvinyl alcohol is added to the broken powder, and it is formed under a pressure of 600MPa to obtain the secondary green body; the secondary The green body is calcined at a low temperature, the calcining temperature is 900° C., and the calcining time is 12 hours. The concentration of hydrogen bromide in the secondary calcination atmosphere is 1.8%, the concentration of ammonia gas is 3%, the concentration of hydrogen gas is 10%, the concentration of nitrogen gas is 13%, and the balance is air. A secondary calcined body is obtained after the secondary calcination, and fine-grained alumina powder is obtained after the secondary calcined body is crushed. The average particle diameter of the obtained alumina powder was 0.14 μm, and the content of α-Al ₂ O ₃ was 100%.

Example 4: Using aluminum hydroxide and NH ₄ Cl as raw materials, 700MPa was formed to prepare fine-grained alumina powder

Using industrial aluminum hydroxide powder as raw material, add 4.5wt.% seed crystal (30nm α-Al ₂ O ₃ ), 1.5wt.% dispersant (benzoic acid), and 0.08wt.% grain growth to the raw material powder Inhibitor (Nb ₂ O ₃ ), 0.15wt.% gas phase source (ammonium perchlorate), mixed uniformly by means of stirring or ball milling, and then dried at 70° C. for 5 hours to obtain a mixture. Add 2.9wt.% dextrin or polyvinyl alcohol to the dried mixture, and shape it under a pressure of 800MPa to obtain a primary green body; the primary green body is calcined at a high temperature at 1200°C for 2 hours . The concentration of hydrogen chloride in the primary calcination atmosphere is 0.8%, the concentration of ammonia is 1.3%, the concentration of aluminum fluoride is 1.5%, the concentration of hydrogen is 4.5%, the concentration of nitrogen is 9.0%, and the balance is air. After the primary calcination, the primary calcined green body is obtained; the primary calcined green body is broken into powder, and 1wt.% dextrin or polyvinyl alcohol is added to the crushed powder, and it is formed under a pressure of 800 MPa to obtain the secondary green body; the secondary The green body is calcined at a low temperature, the calcining temperature is 600° C., and the calcining time is 10 hours. The concentration of hydrogen chloride in the secondary calcination atmosphere is 1.7%, the concentration of ammonia gas is 2.3%, the concentration of hydrogen gas is 9%, the concentration of nitrogen gas is 12%, and the balance is air. A secondary calcined body is obtained after the secondary calcination, and fine-grained alumina powder is obtained after the secondary calcined body is crushed. The average particle diameter of the obtained alumina powder was 0.03 μm, and the content of α-Al ₂ O ₃ was 100%.

Example 5: Aluminum hydroxide and NH ₄ Cl are used as raw materials, and 500 MPa is formed to prepare fine-grained alumina powder

Except that the pressing pressure in the primary billet making process is 650MPa, and the pressing pressure in the secondary billet making process is 650MPa, the fine-grained alumina powder is prepared according to the same method as in Example 4, and the average particle diameter of the gained alumina powder is 0.08 μm, the content of α-Al ₂ O ₃ is 100%.

Example 6: Using aluminum hydroxide and NH ₄ Cl as raw materials, 300MPa molding to prepare fine-grained alumina powder

Except that the pressing pressure in the primary billet making process is 560MPa, and the pressing pressure in the secondary billet making process is 560MPa, the fine-grained alumina powder is prepared according to the same method as in Example 4, and the average particle diameter of the gained alumina powder is 0.10 μm, the content of α-Al ₂ O ₃ is 100%.

Comparative Example 1: Preparation of fine-grained alumina powder by non-press forming process

Except that there is no primary billet making and secondary billet making process, fine-grained alumina powder is prepared according to the same method as in Example 4. The average particle diameter of the obtained alumina powder is 0.82 μm, and the content of α-Al ₂ O ₃ is 100%.

Comparative Example 2: Preparation of fine-grained alumina powder by low-temperature calcination + high-temperature calcination process

Except changing the temperature of the primary calcination to 480°C and the temperature of the secondary calcination to 1180°C, the fine-grained alumina powder was prepared according to the same method as in Example 4, and the average particle diameter of the obtained alumina powder was 37 μm, α - The content of Al ₂ O ₃ is 99%.

Comparative Example 3: Preparation of fine particle size alumina powder by air calcination process

Except that both the primary calcination and the secondary calcination are carried out in an air atmosphere, the fine particle size alumina powder is prepared according to the same method as in Example 4. The average particle size of the obtained alumina powder is 2.5 μm, and α-Al ₂ O ₃ The content is 98%.

The following table is the data comparison table of embodiment 1-6 and comparative example 1-3:

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (11)

1. prepare a method for fine grain size alumina powder, it is characterized in that:

Step one, with industrial aluminium hydroxide or transition aluminas powder for raw material, in raw material powder, add a certain amount of batching, adopt stir or the mode of ball milling mix after dry 3 ~ 5 hours at 50 ~ 80 DEG C, obtain compound;

Step 2, compound after the drying obtain a base substrate after press forming;

Step 3, a base substrate are carrying out high-temperature calcination, and calcining temperature is 1000 ~ 1150 DEG C, and calcination time is 3.5 ~ 8 hours, is once calcined base substrate after high-temperature calcination;

Step 4, will once calcine base substrate and be broken into powder, after press forming, obtain secondary base substrate;

Step 5, secondary base substrate is carried out low temperature calcination, calcining temperature is 510 ~ 900 DEG C, and calcination time is 2 ~ 5 hours, obtains secondary clacining base substrate after low temperature calcination, obtains fine grain size alumina powder after the fragmentation of secondary clacining base substrate.

2. a kind of method preparing fine grain size alumina powder as claimed in claim 1, is characterized in that: described batching comprises 0.5 ~ 4.5wt.% crystal seed, 0.1 ~ 1.5wt.% dispersion agent, 0.01 ~ 1.2wt.% grain growth inhibitor, 0 ~ 0.5wt.% gaseous sources; Described idiosome calcining carries out in the atmosphere containing hydrogen halide and size controlling constituent element, and described size controlling constituent element is aluminum halide; Described secondary base substrate calcining carries out in containing the atmosphere of hydrogen halide.

3. a kind of method preparing fine grain size alumina powder as claimed in claim 1, is characterized in that: described transition aluminas is γ-Al ₂o ₃, δ-Al ₂o ₃, ζ-Al ₂o ₃, η-Al ₂o ₃, θ-Al ₂o ₃, κ-Al ₂o ₃with χ-Al ₂o ₃in one or more.

4. a kind of method preparing fine grain size alumina powder as claimed in claim 2, is characterized in that: described crystal seed is that median size is less than the aluminium of 30nm, titanium, zirconium, the oxide compound of vanadium, nitride, carbide or carbonitride; Described grain growth inhibitor is one or more in magnesium, yttrium, zirconium, the compound of niobium and mixture.

5. a kind of method preparing fine grain size alumina powder as claimed in claim 2, it is characterized in that: described dispersion agent is that molecular weight is in 120 ~ 600 scopes, acids containing methyl and phenyl ring or lipid, such as phenylacetate, phenylformic acid, methyl benzoate, n-butylbenzoate etc.

6. a kind of method preparing fine grain size alumina powder as claimed in claim 1, it is characterized in that: the compound after oven dry and the powder that once calcining base is broken into all once will be calcined and secondary clacining after press forming again, the binder dextrin added or the content of polyvinyl alcohol are 2.5 ~ 5wt.%, and compacting pressure is 560 ~ 800MPa.

7. a kind of method preparing fine grain size alumina powder as claimed in claim 1, it is characterized in that: once adopt during calcining containing the atmosphere of low concentration hydrogen halide, wherein the concentration of hydrogen halide is 0.1 ~ 1.0%, the concentration of ammonia is 1.1 ~ 1.5%, the concentration of aluminum halide is 1 ~ 2%, the concentration of hydrogen is 3 ~ 5%, the concentration of nitrogen is 6-10%, surplus is air.

8. a kind of method preparing fine grain size alumina powder as claimed in claim 1, it is characterized in that: adopt containing the atmosphere of higher concentration hydrogen halide during secondary clacining, wherein the concentration of hydrogen halide is 1.6 ~ 2.0%, the concentration of ammonia is 2.3 ~ 3%, the concentration of hydrogen is 8 ~ 10%, the concentration of nitrogen is 11 ~ 13%, surplus is air.

9. a kind of method preparing fine grain size alumina powder as claimed in claim 1, it is characterized in that: when once calcining, halogenation ammonia and halogen compounds can be added in compound in advance, at high temperature decompose and obtain hydrogen halide, ammonia, chlorine and aluminum halide, halogen compounds is ammoniumper chlorate, hypochlorous acid ammonium, hexafluoro aluminate;

During secondary clacining, halogenation ammonia can be added in compound in advance, at high temperature decompose and obtain hydrogen halide and ammonia.

10. a kind of method preparing fine grain size alumina powder as claimed in claim 1, is characterized in that: for suitability for industrialized production, calcines available tunnel furnace, rotary kiln or pusher type furnace and carry out in a continuous manner.

11. a kind of methods preparing fine grain size alumina powder as claimed in claim 1, is characterized in that: the particle diameter of fine grain size alumina powder is less than 0.14 μm, α-Al ₂o ₃content be 100%.