Submicron high-thermal-conductivity aluminum oxide and preparation process thereof

Abstract

The invention belongs to the technical field of inorganic non-metallic material preparation, and particularly relates to submicron high-thermal-conductivity aluminum oxide and a preparation process thereof.The preparation process comprises the steps that industrial aluminum oxide serves as a raw material, wet modification is conducted, grinding is conducted through a grinding machine, slurry is subjected to spray drying, and low-temperature calcination is conducted to obtain the submicron high-thermal-conductivity aluminum oxide; the wet modification method comprises the following steps: adding the industrial alumina and the composite modification liquid into a reaction kettle according to a mass ratio of (0.3-0.5): 1, carrying out gradient temperature control reaction for 3.5-6 hours in a stirring state, stopping stirring, and filtering to obtain filter residues, namely the alumina subjected to wet modification. The submicron aluminum oxide prepared by the preparation process disclosed by the invention is uniform in particle size distribution, low in impurity sodium content and good in thermal conductivity, and can be applied to the field of 5G communication and other high-performance computers.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic non-metallic material preparation, and in particular relates to a submicron high thermal conductivity aluminum oxide and a preparation process thereof. Background Art

[0002] Alumina, due to its exceptional physical properties and chemical stability, has shown broad application prospects in a variety of high-tech fields. Submicron alumina, typically with a particle size ranging from 0.1 to 1 micron, exhibits excellent insulation properties, high-temperature resistance, thermal conductivity, and high heat dissipation efficiency, making it widely used in various electronic products. With the development of 5G communications and other high-performance computing fields, electronic devices are trending towards miniaturization and higher performance, placing higher demands on heat dissipation materials.

[0003] Currently, the main methods for preparing submicron alumina include ammonium aluminum carbonate thermal decomposition, aluminum alcohol salt hydrolysis, spark discharge, spray pyrolysis, and sol-gel methods. While these processes can produce submicron alumina with low sodium content, they are complex, costly, and environmentally polluting. To reduce production costs, research is increasingly underway to produce submicron alumina using industrial alumina as the primary raw material. These methods primarily employ high-temperature calcination followed by crushing (dry or wet crushing). While this method can produce submicron alumina, its particle size distribution is too broad, and the newly formed interfaces have high surface energy, leading to electrostatic agglomeration of particles and poor dispersibility. Furthermore, these processes consume a lot of energy and have limited impurity removal, making them unable to meet the demands of today's 5G communications and other high-performance computing fields. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a submicron high thermal conductivity alumina and its preparation process. The submicron high thermal conductivity alumina not only has a D50 of 0.4-0.6μm, good dispersibility and strong thermal conductivity, but also has a sodium content of less than 200ppm, and can be effectively applied to the 5G communication field and other high-performance computer fields.

[0005] The present invention provides a preparation process of submicron high thermal conductivity alumina, which uses industrial alumina as raw material, performs wet modification, grinds it in a grinder, spray-dries the slurry, and calcines it at low temperature to obtain submicron high thermal conductivity alumina. The wet modification method is as follows: industrial alumina and composite modification liquid are added into a reactor in a mass ratio of 0.3-0.5:1, and the reaction is carried out under gradient temperature control for 3.5-6 hours under stirring. Stirring is stopped, and the filter is filtered. The filter residue is the wet-modified alumina.

[0006] Industrial alumina is obtained by calcining aluminum salts at high temperatures. It has a relatively high impurity content, irregular crystal structure, and is prone to agglomeration. The present invention first uses a wet process to modify it, forming an active coating on the alumina surface, which effectively inhibits agglomeration caused by new interfacial surface energy. It is then crushed and refined using a grinder to reduce the alumina particle size while also preventing secondary agglomeration. Spray drying is then used to form fine particles, and finally, low-temperature calcination is performed. The resulting alumina not only has a submicron particle size, but also exhibits improved compactness, low sodium impurity content, and excellent thermal conductivity.

[0007] Preferably, in the above technical solution, the particle size of the industrial alumina is less than 3 μm and the purity is greater than 99%.

[0008] Preferably, in the above technical solution, the preparation method of the composite modified liquid is: ethanol and deionized water are mixed in a volume ratio of 1:1 to obtain a solvent, and then 1.5-2% of the solvent mass of the modifier and 0.3-0.5% of the solvent mass of the additive are added, and the pH is adjusted to 3-4 with oxalic acid to obtain the result.

[0009] Preferably, in the above technical solution, the modifier is a composition of a polysiloxane coupling agent and a phosphate coupling agent in a mass ratio of 1:0.5-1.5; and the additive is triammonium citrate. The polysiloxane coupling agent and the phosphate coupling agent of the present invention serve as modifiers, wherein the polysiloxane coupling agent can coat the surface of the alumina to form an active layer, suppressing the surface energy of the new interface and improving the dispersion performance, while the phosphate coupling agent can form a water-soluble complex with sodium ions and be discharged with the solution; and the additive triammonium citrate can complex with other impurities in the alumina, such as iron ions and titanium ions, thereby improving its whiteness and suppressing the re-adsorption of sodium ions.

[0010] Preferably, in the above technical solution, the gradient temperature control reaction procedure is as follows: first, the temperature is raised to 35-45°C for 0.5-1.5 hours, and then the temperature is further raised to 60-70°C for 1-3 hours. In this technical solution, by controlling the different reaction temperatures, the sodium phosphate chelates at a lower temperature in the first stage, and the polysiloxane film is formed and coated on the alumina surface at a higher temperature in the second stage, thereby improving its dispersion performance.

[0011] Preferably, in the above technical solution, the grinding method is: adding the wet-modified alumina into a grinder equipped with grinding media, first grinding at 700-800 rpm for 20-30 min, then grinding at 1400-1600 rpm for 50-60 min, and then grinding at 900-1000 rpm for 20-30 min to complete the grinding. In this technical solution, low-speed grinding and dispersion are first adopted, and then medium-high speed crushing is adopted, and then the speed is reduced to refine and relax the interface energy, which effectively avoids the accumulation of new interface energy during crushing, prevents the phenomenon of re-agglomeration, and has good dispersibility.

[0012] Preferably, in the above technical solution, the grinding medium is a mixture of zirconia microspheres and alumina microspheres in a mass ratio of 1-3:1, wherein the zirconia microspheres have a particle size of 0.1-0.3 mm and the alumina microspheres have a particle size of 0.5-1 mm. The present invention uses zirconia and alumina microspheres as a composite grinding medium, which not only acts as a buffer to reduce local stress cracking, but also the fine alumina removed from the grinding can serve as seed crystals for subsequent calcination.

[0013] Preferably, in the above technical solution, before spray drying, the ground alumina is added to deionized water to prepare a slurry with a solid content of 35-45%, an inlet temperature of 200-220°C, and an outlet temperature of 100-120°C; the spray drying part is connected to the calcination tail gas emission pipeline.

[0014] Preferably, in the above technical solution, the low-temperature calcination temperature is 1100-1250°C for 3-4 hours, and nitrogen containing 5-10% water vapor is introduced during the calcination. The introduction of a nitrogen atmosphere containing water vapor during calcination causes sodium ions to react with the water vapor and volatilize from the crystal lattice, further achieving the purpose of removing sodium ions. The tail gas can be condensed to recover the sodium hydroxide solution.

[0015] The present invention also provides submicron high thermal conductivity aluminum oxide prepared by the above preparation process.

[0016] Advantages compared to existing technologies: The present invention uses process alumina as raw material and can be modified through wet method.

[0017] The present invention combines wet modification with sand mill crushing, which can effectively solve the phenomenon of particle re-agglomeration caused by the rapid increase in the surface energy of the new interface during the aluminum oxide crushing process, thereby improving the dispersibility and stability of the aluminum oxide; at the same time, in the wet modification process, the use of composite modifiers and additives can also remove part of the sodium ions and other impurities, thereby improving the thermal conductivity of the aluminum oxide and its whiteness; the use of composite grinding media and stepped speed for grinding can further refine the aluminum oxide into a submicron level, while preventing it from re-agglomerating and avoiding the generation of cracks, thereby ensuring its high thermal conductivity.

[0018] The present invention adopts spray drying after grinding to quickly form fine particles, and then adopts low-temperature calcination, which can not only ensure the conversion rate of the aluminum oxide α phase, but also make the particle surface smoother and tighter, and further improve the thermal conductivity. At the same time, during the low-temperature calcination, an atmosphere containing water vapor is introduced to further reduce the sodium content in the aluminum oxide.

[0019] The aluminum oxide obtained by the present invention has an average particle size of 0.4-0.6 μm, a maximum particle size D97 of less than 2 μm, a whiteness of more than 95%, a sodium content of less than 200 ppm, and a high α-alumina conversion rate. It is a high-performance, high-thermal-conductivity aluminum oxide that can be used in the 5G communication field and other high-performance computer fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of aluminum oxide prepared by the process of Example 1 of the present invention; Figure 2 This is the particle size distribution diagram of aluminum oxide prepared by the process of Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form new or preferred technical solutions, but the present invention is not limited to these embodiments, and these embodiments do not limit the present invention in any way.

[0022] The aluminum oxide used in the present invention is industrial aluminum oxide with a particle size of less than 3 μm and a purity of more than 99%. Polysiloxane coupling agent (Z-6173) and phosphate coupling agent (FX-1) are also used.

[0023] The present invention is described in further detail below in conjunction with specific embodiments: Example 1 A preparation process of submicron high thermal conductivity aluminum oxide specifically comprises the following steps: (1) Wet modification: First prepare the composite modification liquid, mix ethanol and deionized water in a volume ratio of 1:1 to obtain a solvent, then add 2% of the solvent mass of the modifier (the mass ratio of siloxane coupling agent and phosphate coupling agent is 1:0.5) and 0.3% of the solvent mass of triamine citrate, and adjust the pH to 3-4 with oxalic acid to obtain the product; then add industrial alumina and the composite modification liquid in a mass ratio of 0.3:1 into the reactor, under stirring (400 rpm), first raise the temperature to 35 ° C for reaction for 1.5 hours, then continue to raise the temperature to 60 ° C for reaction for 3 hours, stop stirring, filter, and the filter residue is the wet-modified alumina; the filtrate is sent to the sewage treatment pool; (2) Mill grinding: Add the wet-modified alumina into a mill containing a grinding medium with a mass ratio of 1:1 of zirconia microspheres (0.1-0.3 mm) and alumina microspheres (0.5-1 mm). Grind at 700 rpm for 30 min, then at 1400 rpm for 60 min, and then at 900 rpm for 30 min to complete the grinding. (3) Spray drying: The ground alumina is added to deionized water to prepare a slurry with a solid content of 35% and spray dried. The inlet temperature is 200-220°C and the outlet temperature is 100-120°C. The spray drying area is connected to the calcination tail gas emission pipeline. (4) Low-temperature calcination: The spray-dried material is transferred into a calcining furnace and introduced into a N2 + 10% water vapor atmosphere. It is calcined at 1100°C for 4 hours. After cooling, submicron high thermal conductivity alumina is obtained.

[0024] Example 2 A preparation process of submicron high thermal conductivity aluminum oxide specifically comprises the following steps: (1) Wet modification: First prepare the composite modification liquid, mix ethanol and deionized water in a volume ratio of 1:1 to obtain a solvent, then add 1.8% of the solvent mass of the modifier (the mass ratio of siloxane coupling agent and phosphate coupling agent is 1:1) and 0.4% of the solvent mass of triamine citrate, and adjust the pH to 3-4 with oxalic acid to obtain the product; then add industrial alumina and the composite modification liquid in a mass ratio of 0.4:1 into the reactor, under stirring (400 rpm), first raise the temperature to 40℃ for reaction for 1h, then continue to raise the temperature to 65℃ for reaction for 2h, stop stirring, filter, and the filter residue is the wet-modified alumina; the filtrate is sent to the sewage treatment pool; (2) Mill grinding: Add the wet-modified alumina into a mill containing a grinding medium with a mass ratio of 2:1 of zirconia microspheres (0.1-0.3 mm) and alumina microspheres (0.5-1 mm). Grind at 750 rpm for 25 min, then at 1500 rpm for 55 min, and then at 950 rpm for 25 min to complete the grinding. (3) Spray drying: The ground alumina is added to deionized water to prepare a slurry with a solid content of 40% for spray drying. The inlet temperature is 200-220°C and the outlet temperature is 100-120°C. The spray drying area is connected to the calcination tail gas emission pipeline. (4) Low-temperature calcination: The spray-dried material is transferred into a calcining furnace and introduced into a N2 + 7% water vapor atmosphere. It is calcined at 1150 ° C for 4 hours. After cooling, submicron high thermal conductivity alumina is obtained.

[0025] Example 3 A preparation process of submicron high thermal conductivity aluminum oxide specifically comprises the following steps: (1) Wet modification: First prepare the composite modification liquid, mix ethanol and deionized water in a volume ratio of 1:1 to obtain a solvent, then add 1.5% of the solvent mass of the modifier (the mass ratio of siloxane coupling agent and phosphate coupling agent is 1:1.5) and 0.5% of the solvent mass of triamine citrate, and adjust the pH to 3-4 with oxalic acid to obtain the product; then add industrial alumina and the composite modification liquid in a mass ratio of 0.5:1 into the reactor, under stirring (400 rpm), first raise the temperature to 45 ° C for reaction for 0.5 h, then continue to raise the temperature to 70 ° C for reaction for 1 h, stop stirring, filter, and the filter residue is the wet-modified alumina; the filtrate is sent to the sewage treatment pool; (2) Mill grinding: Add the wet-modified alumina into a mill containing a grinding medium with a mass ratio of 3:1 of zirconia microspheres (0.1-0.3 mm) and alumina microspheres (0.5-1 mm). Grind at 800 rpm for 20 min, then at 1600 rpm for 50 min, and then at 1000 rpm for 20 min to complete the grinding. (3) Spray drying: The ground alumina is added to deionized water to prepare a slurry with a solid content of 45% and spray dried. The inlet temperature is 200-220°C and the outlet temperature is 100-120°C. The spray drying area is connected to the calcination tail gas emission pipeline. (4) Low-temperature calcination: The spray-dried material is transferred into a calcining furnace and introduced into a N2 + 10% water vapor atmosphere. It is calcined at 1250 ° C for 3 hours. After cooling, submicron high thermal conductivity alumina is obtained.

[0026] Comparative Example 1 A preparation process of submicron high thermal conductivity alumina, which differs from Example 1 in that, in step (1), the modifier is only a siloxane coupling agent.

[0027] Comparative Example 2 A preparation process of submicron high thermal conductivity aluminum oxide is different from that of Example 1 in that, in step (1), the additive triammine citrate is not added.

[0028] Comparative Example 3 A preparation process of submicron high thermal conductivity alumina, which differs from Example 1 in that, in step (1), the wet modification reaction temperature is 60°C for 4.5 hours.

[0029] Comparative Example 4 A preparation process of submicron high thermal conductivity aluminum oxide, which differs from Example 1 in that step (1) is omitted and specifically comprises the following steps: (1) Mill grinding: Add the wetted alumina into a mill containing a grinding medium with a mass ratio of 1:1 of zirconium oxide microspheres (0.1-0.3 mm) and aluminum oxide microspheres (0.5-1 mm). Grind at 700 rpm for 30 min, then at 1400 rpm for 60 min, and then at 900 rpm for 30 min to complete the grinding. (2) Spray drying: The ground alumina is added to deionized water to prepare a slurry with a solid content of 35% for spray drying. The inlet temperature is 200-220°C and the outlet temperature is 100-120°C. The spray drying area is connected to the calcination tail gas emission pipeline. (3) Low-temperature calcination: The spray-dried material is transferred into a calcining furnace and introduced into a N2 + 10% water vapor atmosphere. It is calcined at 1100°C for 4 hours. After cooling, submicron high thermal conductivity alumina is obtained.

[0030] Comparative Example 5 A preparation process of submicron high thermal conductivity alumina, which differs from Example 1 in that, in step (2), the grinding condition is grinding at 1400 rpm for 120 min.

[0031] Comparative Example 6 A preparation process of submicron high thermal conductivity alumina, which differs from Example 1 in that in step (2), the grinding medium is zirconium oxide microspheres (0.1-0.3 mm).

[0032] Comparative Example 7 A preparation process for submicron high thermal conductivity alumina, which differs from Example 1 in that no water vapor atmosphere is added during calcination in step (4).

[0033] Comparative Example 8 A preparation process of submicron high thermal conductivity alumina, which differs from Example 1 in that, in step (4), a high temperature calcination of 1450°C is adopted.

[0034] Test example 1. The submicron high thermal conductivity alumina prepared in Example 1 was observed under a high magnification electron microscope (×10000 times), and its particle size was tested and statistically analyzed. The results were as follows: Figure 1 and Figure 2 shown.

[0035] As can be seen from the figure, the surface of the aluminum oxide prepared by the present invention is relatively smooth and dispersed, and its particle size distribution is mainly between 0.1-1 μm, reaching the submicron level.

[0036] 2. The average particle size, whiteness, sodium content, α-phase conversion rate, and thermal conductivity of the submicron-grade high thermal conductivity alumina prepared by the methods of Examples 1-3 and Comparative Examples 1-8 were tested, and the results are shown in Table 1. The particle size was tested using an OMEC POP (9) laser particle size distribution analyzer; the whiteness was tested using a whiteness meter according to the GB / T5950-2008 whiteness measurement method; the sodium content was tested using an ICP-MS method; the α-phase conversion rate was semi-quantitatively analyzed using XRD; and the thermal conductivity was tested using a heat flow method thermal conductivity analyzer according to the ASTM E1530-19 standard.

[0037] Table 1

[0038] From the results of Examples 1-3, it can be seen that the alumina prepared by the preparation process of the present invention has a D50 particle size of 0.5±0.1 μm, reaching the submicron level, and a narrow particle size distribution. The sodium content is less than 200 ppm, the whiteness is high, the impurity content is low, the α-phase conversion rate is high, and the thermal conductivity is above 2 W / mK. It is a submicron high thermal conductivity alumina. From the results of Comparative Examples 1-8, it can be seen that the modifier in Comparative Example 1 is only a siloxane coupling agent, without a phosphate coupling agent, which cannot complex and remove sodium in the raw material, and the sodium content is relatively high; in Comparative Example 2, triammonium citrate is not used to remove metal impurities such as iron and titanium, and the whiteness is relatively poor; in Comparative Example 3, the reaction is directly carried out at 60°C, and the complexing effect on sodium is relatively poor; in Comparative Example 4, the alumina is not wet-modified, which not only directly affects the dispersibility of the alumina and is easy to agglomerate, but also has a relatively high sodium content and poor whiteness; in Comparative Example 5, the high-speed crushing body is directly used during grinding, which affects its particle size distribution and is prone to re-agglomeration; in Comparative Example 6, only zirconium oxide is used as the grinding medium, although it can also reach the submicron level, but there is no seed in the subsequent calcination process, and the α-phase conversion rate is relatively low; in Comparative Example 7, water vapor is not introduced during the low-temperature calcination process, and although the overall effect is not significant, it cannot further remove sodium; in Comparative Example 8, high-temperature calcination is directly used, and it will agglomerate and directly affect the particle size.

[0039] In summary, the preparation process of the present invention combines wet modification with wet grinding, which can not only solve the phenomenon of particle re-agglomeration caused by the increase in surface energy of the new interface during the crushing of alumina, but also remove impurities such as sodium. At the same time, by combining spray drying with low-temperature calcination, the obtained alumina particles are dense and uniform. Using the calcination tail gas for spray drying heat can also save energy consumption, and is suitable for industrial production. The obtained submicron alumina has uniform particle size distribution, low sodium content, and good thermal conductivity, and can be used in 5G communication fields and other high-performance computer fields.

[0040] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing submicron high thermal conductivity alumina, characterized in that: Using industrial alumina as raw material, after wet modification, grinding in a grinder, spray drying the slurry, and low-temperature calcination, submicron high thermal conductivity alumina can be obtained; The wet modification method is as follows: industrial alumina and composite modification liquid are added into a reactor in a mass ratio of 0.3-0.5:1, and the reaction is carried out under gradient temperature control for 3.5-6 hours under stirring. Stirring is stopped, and the filter is filtered. The filter residue is the wet-modified alumina.

2. The process for preparing submicron high thermal conductivity alumina according to claim 1, characterized in that: The particle size of the industrial alumina is less than 3 μm and the purity is greater than 99%.

3. The process for preparing submicron high thermal conductivity alumina according to claim 1, characterized in that: The preparation method of the composite modified liquid is as follows: ethanol and deionized water are mixed in a volume ratio of 1:1 to obtain a solvent, then 1.5-2% of the solvent mass of a modifier and 0.3-0.5% of the solvent mass of an additive are added, and the pH is adjusted to 3-4 with oxalic acid to obtain the composite modified liquid.

4. The process for preparing submicron high thermal conductivity alumina according to claim 3, characterized in that: The modifier is a composition of a polysiloxane coupling agent and a phosphate coupling agent in a mass ratio of 1:0.5-1.5; and the additive is triamine citrate.

5. The process for preparing submicron high thermal conductivity alumina according to claim 1, characterized in that: The procedure of the gradient temperature control reaction is: first increase the temperature to 35-45°C for reaction for 0.5-1.5 hours, and then continue to increase the temperature to 60-70°C for reaction for 1-3 hours.

6. The process for preparing submicron high thermal conductivity alumina according to claim 1, characterized in that: The grinding method comprises the following steps: adding the wet-modified alumina into a grinder equipped with grinding media, grinding at 700-800 rpm for 20-30 min, then grinding at 1400-1600 rpm for 50-60 min, and then grinding at 900-1000 rpm for 20-30 min to complete the grinding.

7. The process for preparing submicron high thermal conductivity aluminum oxide according to claim 6, characterized in that: The grinding medium is a mixture of zirconium oxide microspheres and aluminum oxide microspheres in a mass ratio of 1-3:1, wherein the particle size of the zirconium oxide microspheres is 0.1-0.3 mm, and the particle size of the aluminum oxide microspheres is 0.5-1 mm.

8. The process for preparing submicron high thermal conductivity alumina according to claim 1, characterized in that: Before spray drying, the ground alumina is added to deionized water to prepare a slurry with a solid content of 35-45%, an inlet temperature of 200-220°C, and an outlet temperature of 100-120°C; the spray drying part is connected to the calcination tail gas emission pipeline.

9. The process for preparing submicron high thermal conductivity aluminum oxide according to claim 1, characterized in that: The temperature of low-temperature calcination is 1100-1250°C, the time is 3-4 hours, and N2 containing 5-10% water vapor is introduced during calcination.

10. Submicron high thermal conductivity alumina prepared by the preparation process according to any one of claims 1 to 9.

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