A method for preparing low-temperature sintered high-purity alumina ceramics

Abstract

The present invention discloses a method for preparing low-temperature sintered high-purity alumina ceramics, comprising the following steps: Step 1: mixing aluminum sol, sodium sulfate, aluminum fluoride and water in a mass percentage of 1:1-3:0.08-0.18:1-2 to form a suspension, and obtaining α-Al2O3 powder by heating, stirring, drying, grinding, screening and calcining the suspension; Step 2: grinding, screening, granulating, forming, drying and calcining the α-Al2O3 powder obtained in step 1 to obtain α-Al2O3 ceramics. The temperature of the calcining process in step 1 is 1000-1200°C, the holding time is 1-3h, and the heating rate is 3-5°C / min. The present invention not only greatly reduces the sintering temperature of high-purity alumina, but also the product has low water absorption and shrinkage, the preparation method is simple and convenient, easy to control and large-scale production, and therefore has a large industrialization prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic material preparation, and in particular to a method for preparing low-temperature sintered high-purity alumina ceramics. Background Art

[0002] Alumina ceramics have the characteristics of high mechanical strength, high hardness, good high-temperature insulation performance, and corrosion resistance, and are widely used in mechanical, electronic, and chemical engineering fields. However, for single-phase alumina ceramics, the melting point is as high as 2050°C, the materials are bonded in the form of ionic bonds or covalent bonds, the particle diffusion coefficient is small, the sintering temperature exceeds 1750°C, and the sintering time required is long, the production efficiency is low, and the cost is high. In addition, growth anisotropy and abnormal grains are prone to occur during high-temperature sintering, resulting in uneven structure and even residual pores inside, which reduces the bonding strength between the grains and causes a significant decrease in material performance. Therefore, it is still a huge challenge to prepare high-density alumina ceramics in a simple, reliable, and low-cost manner.

[0003] There are currently three main methods for reducing the sintering temperature of alumina ceramics: (1) Particle size control: By reducing the particle size of alumina powder, such as using nano-ceramic powder to reduce the initial size of the grains, the final sintered product maintains the microcrystalline characteristics, and based on its unique nano-scale effects such as high specific surface area, the sintering activity of the ceramic substrate is significantly improved. However, the use of nano-alumina powder is expensive and the production cost is high; the special process requires complex conditions and low production efficiency, and there are problems such as inability to mass produce and high cost. In particular, in recent years, with the development of ultra-fine raw material particle size, the sintering shrinkage rate of alumina ceramic products has gradually increased from about 17% to about 23%, resulting in a series of problems such as product deformation, cracking, processing allowance and increased difficulty in production; (2) Using other advanced sintering technologies: such as hot isostatic pressing sintering, spark plasma sintering, pulse current sintering or microwave sintering, which can increase the sintering driving force and achieve densification in a shorter time. However, it has high equipment requirements and is expensive. (3) Adding sintering aids: Sintering aids can form solid solutions with alumina, increase lattice distortion, and improve diffusion rate, thereby reducing the sintering temperature of alumina ceramics. Common ones include MnO, TiO2, Fe2O3, etc. They have similar lattice constants to alumina and can form different types of solid solutions with alumina. In addition, the additives themselves or between the additives and the alumina matrix can form a liquid phase at high temperatures, promoting sintering through a dissolution-precipitation mechanism. That is, when the sintering temperature reaches the melting point or eutectic temperature of the additives, the liquid phase begins to appear, promoting the migration and diffusion of particles in the sintered body, and improving the sintering performance of alumina ceramics. Common sintering aids reduce the sintering temperature to 1500-1700℃, but there is still a lot of room for improvement. In addition, the addition of sintering aids such as TiO2 promotes the formation of anisotropic grains with large aspect ratios, significantly affecting the microstructure of alumina ceramics and causing the ceramics themselves to have anisotropy, which has a large limitation on the use method. In summary, these three methods have problems such as complex preparation and high cost. Therefore, it is particularly important to seek a low-cost preparation method. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method of low-temperature sintered high-purity alumina ceramics which has low cost, simple process and is suitable for large-scale production.

[0005] To solve the above technical problems, the technical solution of the present invention is: a method for preparing low-temperature sintered high-purity alumina ceramics, characterized by comprising the following steps:

[0006] Step 1: dissolving aluminum sol, sodium sulfate, and aluminum fluoride in water according to mass percentage to obtain a suspension, and heating, stirring, drying, grinding, screening, and calcining the suspension to obtain α-Al2O3 powder;

[0007] Step 2: Grind, sieve, granulate, shape, dry and calcine the α-Al2O3 powder obtained in step 1 to obtain α-Al2O3 ceramics.

[0008] In the step 1, the mass ratio of aluminum sol, sodium sulfate, aluminum fluoride and water is 1:1-3:0.08-0.18:1-2.

[0009] The aluminum sol comprises the following components by weight: 20.243 wt% Al2O3, 0.012 wt% SiO2, 0.003 wt% Fe2O3, 0.012 wt% Na2O, and 79.73 wt% ethanol organic solvent.

[0010] In the step 1, the temperature of the heating and stirring process is 60-95° C.; the temperature of the drying process is 80-100° C. and the insulation time is 5-8 hours; and the screening process is through a 200-325 mesh sieve.

[0011] The temperature of the calcination process in the step 1 is 1000-1200° C., the holding time is 1-3 hours, and the heating rate is 3-5° C. / min.

[0012] The screening process in step 2 is to pass through a 350-400 mesh sieve; the forming process is dry pressing with a pressure of 18-21 MPa; the temperature of the drying process is 60-100° C. and the holding time is 30-45 minutes.

[0013] In the granulation process in step 2, PVA is added as a binder, with the mass of PVA accounting for 1-3% of the α-Al2O3 powder and the mass concentration being 3-5%.

[0014] The calcination temperature in the calcination process in step 2 is 1350° C., the heating rate is 2-10° C. / min, and the holding time is 30-120 min.

[0015] In the step 1, the particle size of the α-Al2O3 powder is 1 to 5 μm, and the specific surface area is 1 to 5 m 2 / g, the average pore size is 45-60nm, the morphology is hexagonal lamellae, the powders are interlocked, and the diameter-to-thickness ratio is 8-10:1.

[0016] The alumina content of the α-Al2O3 ceramic in step 2 is 98.55-99.25 wt% and the density is 3.59-3.62 g / cm 3 The shrinkage rate is 1-1.2%, and the flexural strength is 204-219 MPa.

[0017] The present invention has the following beneficial effects:

[0018] The present invention successfully prepared alumina ceramics using interlocking hexagonal α-Al2O3 powders prepared by the aluminum sol method. The interlocking hexagonal morphology of the flaky material is utilized, and its porous and micro-nanostructural characteristics are utilized to form an interlaced network structure during the sintering process, which helps to improve the mechanical strength and fracture toughness of the ceramics. Secondly, the flaky structure helps to improve the thermal conductivity of the ceramics, because the flaky particles are arranged in parallel in the sintered body, which can form a better thermal conduction path, thereby reducing the sintering temperature of the alumina ceramics. In addition, the sample has a low water absorption rate and shrinkage rate, which greatly reduces the product's firing deformation and improves the product's processing performance. The preparation process is simple and convenient, has low equipment requirements, is easy to control and scale production, and has great industrial prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The BET and pore size diagrams of the interlocking hexagonal α-Al2O3 powder obtained in Example 1 are shown;

[0020] Figure 2 is a SEM image of the α-Al2O3 alumina ceramic prepared in Example 1;

[0021] Figure 3 is the XRD pattern of α-Al2O3 alumina ceramics prepared in Example 1;

[0022] Figure 4 This is a performance curve comparison of the α-Al2O3 alumina ceramics prepared in Example 1 and the alumina ceramics currently used in industry. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1

[0025] A method for preparing low-temperature sintered high-purity alumina ceramics comprises the following steps:

[0026] Step 1: Add aluminum sol, sodium sulfate, and aluminum fluoride mineralizer to water to obtain a suspension, wherein the mass ratio of aluminum sol: sodium sulfate: aluminum fluoride: water is 1:1:0.16:1. The suspension is heated and stirred at 60°C. After gradually becoming a paste, the suspension is placed in an oven at 80°C for 5 hours. The mixture is ground and passed through a 250-mesh sieve to obtain a precursor. The precursor is placed in a muffle furnace and calcined at 1100°C for 1 hour at a heating rate of 5°C / min to obtain white α-Al2O3 powder.

[0027] Step 2: Grind the powder in step 1 thoroughly and then pass it through a 400 mesh sieve;

[0028] Step 3: After grinding in step 2, select PVA with a mass concentration of 5% as a binder, which is 2% of the mass of α-Al2O3 powder, and add it to the α-Al2O3 powder for granulation;

[0029] Step 4: The powder granulated in step 3 is dry pressed at a pressure of 21 MPa, and the obtained green body is placed in an oven at 60°C for 45 minutes;

[0030] Step 5: calcining the green body after drying in step 4, with a firing temperature of 1350° C., a heating rate of 3° C. / min, and a holding time of 120 min.

[0031] The white α-Al2O3 powder prepared in step 1 has a particle size of 1 μm and a specific surface area of ​​5 m 2 / g, with an average pore size of 45nm. The morphology is all hexagonal and interlocked, with a diameter-to-thickness ratio of about 10:1.

[0032] The alumina content of the α-Al2O3 ceramic prepared in step 5 is 99wt% and the density is 3.60g / cm 3 , shrinkage rate is 1%, and flexural strength is 204MPa.

[0033] Example 2

[0034] A method for preparing low-temperature sintered high-purity alumina ceramics comprises the following steps:

[0035] Step 1: Add aluminum sol, sodium sulfate, and aluminum fluoride mineralizer to water to obtain a suspension, wherein the mass ratio of aluminum sol: sodium sulfate: aluminum fluoride: water is 1:3:0.18:2. The suspension is heated and stirred at 95°C. After gradually becoming a paste, the suspension is placed in an oven at 100°C and kept warm for 8 hours. The resulting precursor is then ground and passed through a 200-mesh sieve and placed in a muffle furnace. The calcination temperature is 1200°C and the temperature is maintained for 1 hour at a heating rate of 3°C / min to obtain white α-Al2O3 powder.

[0036] Step 2: Grind the powder in step 1 thoroughly and then pass it through a 350 mesh sieve;

[0037] Step 3: After grinding in step 2, select PVA with a mass concentration of 3% as a binder, which is 3% of the mass of α-Al2O3 powder, and add it to the α-Al2O3 powder for granulation;

[0038] Step 4: The powder granulated in step 3 is dry pressed at a pressure of 18 MPa, and the obtained green body is placed in an oven at 100°C for 30 minutes;

[0039] Step 5: calcining the green body after drying in step 4, with a sintering temperature of 1350°C, a heating rate of 5°C / min, and a holding time of 100 min.

[0040] The white α-Al2O3 powder prepared in step 1 has a particle size of 5 μm and a specific surface area of ​​1 m 2 / g, with an average pore size of 60nm. The morphology is all hexagonal and interlocked, with a diameter-to-thickness ratio of about 9:1.

[0041] The alumina content of the α-Al2O3 ceramic prepared in step 5 is 99wt% and the density is 3.59g / cm 3 , shrinkage rate is 1.2%, and flexural strength is 215MPa.

[0042] Example 3

[0043] A method for preparing low-temperature sintered high-purity alumina ceramics comprises the following steps:

[0044] Step 1: Add aluminum sol, sodium sulfate, and aluminum fluoride mineralizer to water to obtain a suspension, wherein the mass ratio of aluminum sol: sodium sulfate: aluminum fluoride: water is 1:2:0.1:1.5. The suspension is heated and stirred at 85°C. After the suspension gradually becomes a paste, it is placed in an oven at 90°C for 8 hours. The precursor is ground and passed through a 325-mesh sieve to obtain a precursor. It is placed in a muffle furnace and calcined at 1100°C for 2 hours at a heating rate of 4°C / min to obtain white α-Al2O3 powder.

[0045] Step 2: Grind the powder in step 1 thoroughly and then pass it through a 400 mesh sieve;

[0046] Step 3: After grinding in step 2, select PVA with a mass concentration of 5% as a binder, which is 1% of the mass of α-Al2O3 powder, and add it to the α-Al2O3 powder for granulation;

[0047] Step 4: The powder granulated in step 3 is dry pressed at a pressure of 20 MPa, and the obtained green body is placed in an oven at 100°C for 40 minutes;

[0048] Step 5: calcining the green body after drying in step 4, with a firing temperature of 1350°C, a heating rate of 10°C / min, and a holding time of 70min.

[0049] The white α-Al2O3 powder prepared in step 1 has a particle size of 3 μm and a specific surface area of ​​3 m 2 / g, with an average pore size of 50nm. The morphology is all hexagonal and interlocked, with a diameter-to-thickness ratio of about 8:1.

[0050] The alumina content of the α-Al2O3 ceramic prepared in step 5 is 98.55wt% and the density is 3.59g / cm 3 , shrinkage rate is 1%, and flexural strength is 214MPa.

[0051] Example 4

[0052] A method for preparing low-temperature sintered high-purity alumina ceramics comprises the following steps:

[0053] Step 1: Add aluminum sol, sodium sulfate, and aluminum fluoride mineralizer to water to obtain a suspension, wherein the mass ratio of aluminum sol: sodium sulfate: aluminum fluoride: water is 1:1:0.08:2. The suspension is heated and stirred at 95°C. After gradually becoming a paste, the suspension is placed in an oven at 100°C and kept warm for 5 hours. The resulting precursor is then ground and passed through a 250-mesh sieve and placed in a muffle furnace. The calcination temperature is 1000°C and the temperature is maintained for 3 hours at a heating rate of 3°C / min to obtain white α-Al2O3 powder.

[0054] Step 2: Grind the powder in step 1 thoroughly and then pass it through a 400 mesh sieve;

[0055] Step 3: After grinding in step 2, select PVA with a mass concentration of 4% as a binder, which is 2% of the mass of α-Al2O3 powder, and add it to the α-Al2O3 powder for granulation;

[0056] Step 4: The powder granulated in step 3 is dry pressed at a pressure of 18 MPa, and the obtained green body is placed in an oven at 80°C for 45 minutes;

[0057] Step 5: calcining the green body after drying in step 4, with a firing temperature of 1350°C, a heating rate of 2°C / min, and a holding time of 30 min.

[0058] The white α-Al2O3 powder prepared in step 1 has a particle size of 2 μm and a specific surface area of ​​5 m 2 / g, with an average pore size of 45nm. The morphology is all hexagonal and interlocked, with a diameter-to-thickness ratio of about 10:1.

[0059] The α-Al2O3 ceramic prepared in step 5 has an alumina content of 99.25 wt% and a density of 3.62 g / cm 3 , shrinkage rate is 1.2%, and flexural strength is 219MPa.

[0060] The weight percentage composition of the aluminum sol is: 20.243 wt% Al2O3, 0.012 wt% SiO2, 0.003 wt% Fe2O3, 0.012 wt% Na2O, and 79.73 wt% ethanol organic solvent.

[0061] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some embodiments of its application, and are not intended to limit the present invention. It should be noted that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing low-temperature sintered high-purity alumina ceramics, characterized in that The steps include: Step 1: dissolving aluminum sol, sodium sulfate, and aluminum fluoride in water according to mass percentage to obtain a suspension, and heating, stirring, drying, grinding, screening, and calcining the suspension to obtain α-Al2O3 powder; Step 2: Grinding, screening, granulating, shaping, drying and calcining the α-Al2O3 powder obtained in step 1 to obtain α-Al2O3 ceramics; In the step 1, the mass ratio of aluminum sol, sodium sulfate, aluminum fluoride, and water is 1:1-3:0.08-0.18:1-2; The mass percentage composition of the aluminum sol is: 20.243 wt% Al2O3, 0.012 wt% SiO2, 0.003 wt% Fe2O3, 0.012 wt% Na2O, and 79.73 wt% ethanol organic solvent; The calcination temperature in step 1 is 1000-1200°C, the holding time is 1-3 hours, and the heating rate is 3-5°C / min; The calcination temperature in the step 2 is 1350°C, the heating rate is 2-10°C / min, and the holding time is 30-120min; In the step 1, the particle size of the α-Al2O3 powder is 1 to 5 μm, and the specific surface area is 1 to 5 m 2 / g, the average pore size is 45-60nm, the morphology is hexagonal and the powders are interlocked, with an diameter-to-thickness ratio of 8-10:1; The temperature of the heating and stirring process in step 1 is 60-95°C; the temperature of the drying process is 80-100°C and the holding time is 5-8 hours; the screening process is to pass through a 200-325 mesh sieve; The alumina content of the α-Al2O3 ceramic in step 2 is 98.55-99.25 wt% and the density is 3.59-3.62 g / cm 3 The shrinkage rate is 1-1.2%, and the flexural strength is 204-219 MPa.

2. The preparation method according to claim 1, wherein: The screening process in step 2 is to pass through a 350-400 mesh sieve; the forming process is dry pressing with a pressure of 18-21 MPa; the temperature of the drying process is 60-100° C. and the holding time is 30-45 minutes.

3. The preparation method according to claim 1, wherein: In the granulation process in step 2, PVA is added as a binder, with the mass of PVA accounting for 1-3% of the α-Al2O3 powder and the mass concentration being 3-5%.

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