CN114988886A - Preparation method of high-purity alpha-alumina powder capable of being sintered at low temperature - Google Patents
Preparation method of high-purity alpha-alumina powder capable of being sintered at low temperature Download PDFInfo
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Abstract
The invention discloses a preparation method of high-purity alpha-alumina powder capable of being sintered at low temperature, which is characterized by taking industrial aluminum hydroxide or industrial aluminum oxide as a raw material, carrying out primary calcination at 950-1150 ℃ and heat preservation for 1-6 hours to obtain easily-ground transition phase aluminum oxide, carrying out ball milling refinement, acid washing to remove sodium, filter pressing and drying, then mixing with a composite mineralizer, a grain growth inhibitor and a sodium absorbent, carrying out secondary calcination at 1200-1350 ℃ and heat preservation for 4-16 hours to obtain the high-purity alpha-alumina powder capable of being sintered at low temperature. The average particle size D50 of the high-purity alpha-alumina powder which can be sintered at low temperature and is prepared by the method is less than or equal to 0.5 mu m, and the alpha phase containsThe content is more than or equal to 97 percent, the sodium content is less than 100ppm, and Al 2 O 3 The content is more than or equal to 99.9 percent, the ceramic can be sintered into porcelain after being subjected to wet ball milling, spray granulation and compression molding and then being kept at 1500-1600 ℃ for 2-8 hours, and the density of the product is more than or equal to 3.92g/cm 3 . The method realizes the low-temperature phase inversion of the alumina, is suitable for industrial production, and the obtained powder has the characteristics of high alpha phase conversion rate, fine crystal grains and the like, so that the ceramic green body has high density, low sintering temperature, small sintering shrinkage, high ceramic density and good physical properties of products.
Description
Technical Field
The invention belongs to the technical field of powder preparation, and particularly relates to a preparation method of high-purity alpha-alumina powder capable of being sintered at low temperature.
Background
The alumina ceramic has the advantages of high melting point, wear resistance, corrosion resistance, high hardness, good electrical insulation and the like, and is widely applied to industries such as metallurgy, aviation, machinery, building materials, electronic devices and the like. However, the sintering temperature of alumina ceramics is generally high. The firing temperature of 85 alumina porcelain is 1500-1550 ℃, the firing temperature of 90 alumina porcelain is 1550-1600 ℃, the firing temperature of 95 alumina porcelain is 1600-1650 ℃, the firing temperature of 99 alumina porcelain reaches more than 1750 ℃, a large amount of energy is consumed, and meanwhile, the method provides a severe challenge for sintering equipment.
At present, methods for reducing the sintering temperature of alumina ceramics are summarized into three types: (1) the special sintering process is adopted, the sintering atmosphere or the sintering pressure is mainly changed, and the methods need advanced kiln equipment and are not suitable for production and operation of common enterprises; (2) the additive is introduced, although the method can realize the purpose of reducing the temperature at lower cost, the introduction amount of the common sintering aid is more than 5 percent, and the product requirement of alumina porcelain with the content of more than or equal to 99 percent cannot be met; (3) the alpha-alumina powder with small granularity and high activity is generally obtained by hydrolyzing aluminum isopropoxide or chemically synthesizing aluminum ammonium sulfate and the like, but the method is not suitable for large-scale industrial production due to high raw material cost and inevitable environmental pollution. In addition, fine alumina powder is obtained by mechanical pulverization, but the method still has problems in actual production, if the calcination temperature is too high, although the alpha phase conversion rate is high, the powder has high particle hardness due to large primary grain size, and is difficult to pulverize into fine powder, and impurities are introduced in the pulverizing process to reduce the alumina content; if the calcining temperature is reduced, although the fine powder is obtained by easy pulverization, the defects of the ceramic product are increased due to insufficient alpha phase conversion rate, and the performance requirements of the ceramic product cannot be met.
CN111205070A discloses a preparation method of easily sintered high-purity alumina. The method prepares high-purity pseudo-boehmite by hydrolyzing aluminum isopropoxide, and obtains the specific surface area of 10-20m by multiple times of calcination 2 The density of the high-purity alumina powder sintered at 1400 ℃ is 3.88g/cm 3 . The prepared alumina powder has low alpha conversion rate, large specific surface area and low apparent density, so that the ceramic green body has low density, phase change still exists in the sintering process, the volume shrinkage is large, the product has many defects and the performance is poor; meanwhile, the preparation method has the advantages of high raw material cost, low intermediate bulk density, small kiln loading amount, high calcination cost and incapability of realizing batch industrial production.
CN103145164A discloses a method for preparing alumina powder for low-temperature sintering of fine ceramics. The method adopts industrial gamma-alumina and industrial fine-grain alpha-alumina as raw materials, after powder with D50 less than 5 mu m is obtained by ball milling, 0.2-5% of mineralizer is mixed to calcine for 2-10 h at 850-1300 ℃, and non-high-purity alpha-alumina ceramic powder with primary crystal less than 0.8 mu m is obtained after jet milling, ball milling and sand milling and spray granulation, and can be sintered into porcelain at 1500-1550 ℃. The method adopts gamma-alumina with high specific surface area as a raw material, and has the advantages of low apparent density, less kiln loading, high single weight energy consumption, low yield and high cost; meanwhile, a high-content mineralizer is introduced, so that the mineralizer is easy to remain after low-temperature calcination, the purity of powder is reduced, the impurity content of alkali metal oxides is high, the density of ceramic is reduced, and the high-content mineralizer affects kiln equipment and the environment; the calcined powder is subjected to air flow, ball milling and sanding to obtain refined powder, so that the method has the advantages of multiple devices, long working procedures and high energy consumption.
Disclosure of Invention
The invention aims to solve the problems of high raw material cost, complex process, environmental pollution, large primary crystal size, low alpha phase conversion rate, high sodium oxide content, low alumina purity, high ceramic sintering temperature, multiple product defects, poor performance and the like in the production of the prior art, and provides a preparation method of high-purity alpha-alumina powder which is suitable for industrial production and can be sintered at low temperature.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows
A preparation method of high-purity alumina powder capable of being sintered at low temperature comprises the following steps of firstly, calcining industrial aluminum hydroxide or industrial aluminum oxide for the first time at 950-1150 ℃ for heat preservation for 1-6 hours to obtain transition phase aluminum oxide powder with less gamma phase; preparing transition phase alumina powder, deionized water, a dispersant and a sodium removing agent into slurry, ball-milling until the particle size D50 is less than or equal to 0.3 mu m, and then carrying out filter pressing, washing, drying and crushing to obtain second powder; mixing a composite mineralizer, a grain growth inhibitor and a sodium absorbent into the second powder to obtain third powder; and (3) carrying out secondary calcination on the third powder, keeping the temperature at 1200-1350 ℃ for 4-16 h, cooling, crushing, screening and grinding to obtain the high-purity alpha-alumina powder capable of being sintered at low temperature, wherein the alpha phase is more than or equal to 97%. The high-purity alpha-alumina powder is subjected to wet ball milling, spray granulation and compression molding, is subjected to heat preservation at 1500-1600 ℃ for 2-6h, and is sintered into porcelain, wherein the density is more than or equal to 3.92g/cm 3 。
In the invention, industrial aluminum hydroxide or industrial aluminum oxide is used as a raw material, and is subjected to primary low-temperature calcination at 950-1150 ℃ and heat preservation for 1-6 h; preferably the first calcination is carried out at a temperature of 1050 ℃ to 1150 ℃ for 2 to 4 hours to obtain transition phase alumina, wherein alpha-alumina is less than 40%, particularly less than 25%, and the balance is transition phase alumina, including gamma phase, kappa phase, theta phase, etc., wherein gamma phase alumina is usually not more than 10%, preferably not more than 5%.
Further, the dispersant in the step is one or more of polyethylene glycol, ammonium polyacrylate, ammonium polymethacrylate and ammonium citrate, the addition amount of the dispersant is 0.2-1.5 wt% of the mass of the added alumina powder, and the dispersant has two functions: firstly, grinding is assisted and the solid content is improved; secondly, the powder is calcined, oxidized, volatilized, loosened and refined.
Furthermore, the sodium removing agent is one of boric acid, citric acid, acetic acid and dilute hydrochloric acid, the addition amount of the acid is 0.1-1% of the content of the transition phase alumina, and the sodium content is effectively reduced through acid washing and water washing.
Further, the drying mode is microwave drying, warm air drying and spray drying.
Further, the composite mineralizer is a mixture of boric acid, ammonium chloride and magnesium oxide or magnesium nitrate, magnesium chloride and other magnesium salts, the introduction amount of the magnesium salts accounts for 0.02-0.1% of the transition phase alumina powder, and the total introduction amount of the boric acid and the ammonium chloride accounts for 0.2-0.5% of the transition phase alumina powder. According to the invention, through the compounding of the three mineralizers, the sodium can be further removed, the appearance of an alumina product can be improved, the calcination temperature can be reduced, the primary crystal size of the alumina powder can be inhibited, the alpha phase conversion rate can be improved, and the like.
Further, the sodium absorbent is quartz sand, preferably the particle size is 0.8-8 mm, and accounts for 5-15% of the specific weight of the mixed alumina powder. The sodium content in the product can be further reduced to below 100ppm by the quartz sand reacting with sodium oxide at the calcination temperature and adsorbing on the quartz sand.
Furthermore, the industrial kilns are shuttle kilns, tunnel kilns and roller kilns. Preferably, a roller kiln which can realize continuous production and has a uniform temperature field is selected.
The average grain diameter D50 of the high-purity alpha-alumina powder which can be sintered at low temperature and is prepared by the method is less than or equal to 0.5 mu m, the alpha phase content is more than or equal to 97 percent, the sodium content is less than 0.01 percent, the purity is more than or equal to 99.9 percent, and the density of the ceramic product is more than or equal to 3.92g/cm 3 。
The invention has the following advantages:
(1) the raw material is industrial aluminum hydroxide or industrial aluminum oxide, the raw material is easy to obtain, and the cost is low.
(2) The two times of calcination are low-temperature calcination, and a roller kiln which can continuously run and has a uniform temperature field can be selected; the first low-temperature calcination is mainly to obtain less gamma-phase transition alumina, the transition phase alumina has small specific surface area, is easy to break, has high apparent density and is easy to obtain refined intermediate phase powder; the second low-temperature calcination can realize the complete conversion of the alpha phase at a lower temperature, and primary crystals do not grow obviously. The two-time low-temperature calcination phase inversion technology solves the contradiction between the traditional high alpha phase conversion rate and the growth of original crystal grains.
(3) Removing impurities such as sodium, iron and the like in the raw materials by acid pickling and water washing of an acidic sodium removing agent, and removing impurities for many times in a manner of introducing a sodium absorbing agent and a mineralizing agent during mixing to obtain ultra-low-sodium high-purity alumina powder with the sodium content of less than 0.01%;
(4) the powder has low impurity content, small primary crystal and high alpha phase conversion rate, and when the powder is used for preparing ceramics, the green compact has high density, low sintering temperature, small sintering shrinkage, high density and good mechanical property, and can be widely applied to the product fields of various precise alumina ceramics, refractory materials, grinding and polishing and the like.
Drawings
FIG. 1 is an XRD spectrum of the powder obtained by the first low-temperature calcination and the second low-temperature calcination of the raw powder in example 1.
FIG. 2 is an SEM photograph of a low-temperature sinterable high-purity alumina powder of example 1.
FIG. 3 is a graph showing the particle size distribution of the high purity alumina powder and commercial alumina powder of the same type prepared in the examples.
FIG. 4 is a graph of the density of ceramics prepared from the high purity alumina powder prepared in the examples and commercial alumina powders of the same type as a function of sintering temperature.
FIG. 5 is an SEM photograph of a cross section of a ceramic made from the high purity alumina powder prepared in the examples and a commercial alumina powder of the same type.
Detailed Description
The invention is further illustrated by the following examples:
the present invention will be described in further detail with reference to the following examples.
Example 1
Preparing transition-phase alumina powder: putting industrial aluminum hydroxide into a sagger, carrying out primary calcination in a roller kiln, keeping the temperature at 1050 ℃ for 4h to obtain transition phase aluminum oxide powder, adding 1 wt% of ammonium polymethacrylate, 0.5 wt% of boric acid and a certain amount of deionized water into the powder, carrying out ball milling for 7 hours until the solid content of slurry is 60%, and carrying out filter pressing, washing, filter pressing and warm air drying on the slurry to obtain the low-sodium transition phase aluminum oxide powder.
Rietveld refinement fitting was performed on the transition phase alumina, and the content of each transition phase was calculated, the results of which are shown in Table 1.
TABLE 1 Rietveld refinement results for transition phase alumina powders
| Composition of phase | α-Al 2 O 3 | κ-Al 2 O 3 | θ-Al 2 O 3 | γ-Al 2 O 3 |
| Phase content (wt%) | 9.6 | 53.9 | 35.9 | 0.6 |
Preparing the alumina powder capable of being sintered at low temperature: and (2) mixing the low-sodium transition-phase alumina powder with 0.2 wt% of ammonium chloride, 0.1 wt% of boric acid, 0.05 wt% of magnesium oxide and 10 wt% of quartz sand with the particle size of 2-4 mm, loading the mixture into a sagger, calcining the sagger in a roller kiln for the second time, and preserving the heat at 1200 ℃ for 4 hours to obtain single-crystal alpha-alumina powder. The powder is detected after being crushed and screened to remove the sodium absorbent quartz sand, and the result is as follows: BET 7.4m 2 (g) apparent density of 0.96g/cm 3 ，Al 2 O 3 High purity alpha-alumina powder with the percent more than 99.9wt percent.
ICP analysis of the α -alumina powder obtained in this example was performed, and the results are shown in table 2.
TABLE 2 composition and content of each component of the alpha-alumina powder obtained in example 1
The powder test XRD, SEM and particle size distribution results are shown in figure 1, figure 2 and figure 3, and the analysis shows that the alpha phase conversion rate reaches 99%, the primary crystal size is about 0.4 μm, and the average particle size is 0.52 μm.
Preparing alumina ceramics: the obtained powder is subjected to ball milling, granulation and 40MPa press forming, and is sintered for 4 hours at 1520 ℃, and the product density is 3.92g/cm 3 (the density is 98%), the size is shrunk by 16.3%, and the three-point bending strength is 350 MPa.
In addition, the sintering density of the powder of this example and the commercial powder from different sources was compared with the temperature, as shown in FIG. 4. As can be seen, the examples were compared at the same sintering temperature.
Example 2
Preparing transition-phase alumina powder: putting industrial aluminum hydroxide into a sagger, carrying out primary calcination in a roller kiln, keeping the temperature at 1150 ℃ for 2 hours to obtain transition phase aluminum oxide powder, adding 1 wt% of ammonium polymethacrylate, 0.5 wt% of boric acid and a certain amount of deionized water into the powder, carrying out ball milling for 7 hours until the solid content of slurry is 80%, and carrying out filter pressing, washing, filter pressing and warm air drying on the slurry to obtain the low-sodium transition phase aluminum oxide powder.
Preparing the alumina powder capable of being sintered at low temperature: and mixing the low-sodium transition-phase alumina powder with 0.3 wt% of ammonium chloride, 0.1 wt% of boric acid, 0.05 wt% of magnesium oxide and 13 wt% of quartz sand with the particle size of 4-6 mm, loading the mixture into a sagger, calcining the sagger in a roller kiln for the second time, and preserving the temperature at 1250 ℃ for 6 hours to obtain single-crystal alpha-alumina powder. The powder is detected after being ground, and the result is as follows: BET ═ 7.1m 2 (g) apparent density of 0.98g/cm 3 ，Al 2 O 3 High purity alpha-alumina powder with the weight percent more than 99.9 percent.
Preparing alumina ceramics: ball milling, spray granulating, pressing at 40MPa, sintering at 1500 deg.C for 6 hr to obtain ceramic with density of 3.92g/cm 3 (the density is 98%), the size is shrunk by 15.4%, and the three-point bending strength is 315 MPa.
Example 3
Preparing transition-phase alumina powder: putting industrial aluminum hydroxide into a sagger, calcining in a roller kiln, keeping the temperature at 1000 ℃ for 2 hours to obtain transition phase aluminum oxide powder, adding 1 wt% of ammonium polymethacrylate, 0.5 wt% of boric acid and a certain amount of deionized water into the powder, ball-milling for 5 hours to obtain slurry containing 70% of solid, and carrying out filter pressing, washing, filter pressing and warm air drying on the slurry to obtain the low-sodium transition phase aluminum oxide powder.
Preparing the alumina powder capable of being sintered at low temperature: and mixing the low-sodium transition phase alumina powder with 0.2 wt% of ammonium chloride, 0.1 wt% of boric acid, 0.03 wt% of magnesium oxide and 10 wt% of quartz sand with the particle size of 2-6 mm, loading the mixture into a sagger, calcining the sagger in a roller kiln for the second time, and preserving the temperature at 1300 ℃ for 10 hours to obtain single-crystal alpha-alumina powder. The powder is detected after being ground, and the result is as follows: BET ═ 6.8m 2 (g) apparent density of 0.98g/cm 3 ，Al 2 O 3 High purity alpha-alumina powder with the percent more than 99.9wt percent.
Preparing alumina ceramics: the powder is ball-milled, granulated by spraying, pressed and formed under 40MPa, sintered for 2 hours at 600 ℃ and has the ceramic density of 3.94g/cm 3 (density 98.5%), size shrinkage 15.4% and three-point bending strength 325 MPa.
A comparison of the parameters of the finished ceramic fired from the powders prepared in the examples with those of other powders is shown in Table 3.
TABLE 3 comparison table of parameters of ceramic products obtained by firing the powders prepared in examples and other powders
Claims (7)
1. A preparation method of high-purity alpha-alumina powder capable of being sintered at low temperature is characterized by comprising the following steps:
1) carrying out primary calcination on industrial aluminum hydroxide or industrial alumina in an industrial kiln, and keeping the temperature at 950-1150 ℃ for 1-6h to obtain transition phase alumina powder with gamma-phase alumina not more than 10%;
2) adding deionized water, a dispersing agent and a sodium removing agent into the transition-phase alumina powder to prepare slurry, ball-milling until the particle size D50 is less than or equal to 0.3 mu m, and carrying out filter pressing, washing, drying and crushing to obtain second powder;
3) adding a composite mineralizer, a grain growth inhibitor and a sodium absorbent into the second powder, and uniformly mixing to obtain third powder;
4) and (3) carrying out secondary calcination on the third powder in an industrial kiln, keeping the temperature at 1200-1350 ℃ for 4-16 h, cooling and crushing, and screening out a sodium absorbent to obtain the high-purity alpha-alumina powder capable of being sintered at a low temperature.
2. The production method according to claim 1, characterized in that: the first calcination temperature is 1050-1150 ℃, and the temperature is kept for 2-4 h; the temperature of the second calcination is 1250-1350 ℃, and the heat preservation is carried out for 8-12 h.
3. The method of claim 1, wherein: in the step 2), the dispersant is one or more of polyethylene glycol, ammonium polyacrylate, ammonium polymethacrylate and ammonium citrate, and the addition amount of the dispersant is 0.2-1.5 wt% of the weight of the added alumina powder.
4. The method of claim 1, wherein: in the step 2), the sodium removing agent is one of boric acid, citric acid, acetic acid and dilute hydrochloric acid, and the addition amount of the sodium removing agent is 0.1-1% of the content of the transition phase alumina.
5. The method of claim 1, wherein: in the step 3), the composite mineralizer comprises boric acid and ammonium chloride, and the introduction amount of the boric acid and the ammonium chloride accounts for 0.2-0.5% of the transition-phase alumina powder; the grain growth inhibitor is one of magnesium oxide, magnesium hydroxide or magnesium salt, and the introduced amount of the magnesium oxide, the magnesium hydroxide or the magnesium salt accounts for 0.02-0.1% of the transition-phase alumina powder.
6. The preparation method according to claim 5, wherein the magnesium salt in the grain growth inhibitor is one or more of magnesium nitrate, magnesium chloride and magnesium carbonate.
7. The method of claim 1, wherein: in the step 3), the sodium absorbent is quartz sand, the particle size is 0.8-8 mm, and the sodium absorbent accounts for 5-15 wt% of the second powder.
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| CN115974112A (en) * | 2022-12-15 | 2023-04-18 | 西北工业大学 | Low-sodium submicron alpha-alumina powder and preparation method and application thereof |
| CN116462490A (en) * | 2023-04-27 | 2023-07-21 | 无锡成旸科技股份有限公司 | High-hardness alumina grinding powder and preparation method thereof |
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