A rapid sintering formed alumina ceramic and a method for manufacturing the same

Abstract

This application relates to the field of ceramic sintering, and in particular to a rapid sintering method for forming alumina ceramics and its preparation method. By adding a small amount of calcium phosphate powder to the system, the flux can be protected through ion containment properties, and the carbon removal effect can be improved. At the same time, PMMA is used to form channels during heating, and PVA is used to provide the viscosity of the green body. Overall, the hot working performance of the system can be improved, the processing time can be shortened, and the overall mechanical properties can be improved.

Description

Technical Field

[0001] This application relates to the field of ceramic sintering, and in particular to a rapid sintering method for forming alumina ceramics and its preparation method. Background Technology

[0002] Alumina ceramics are a widely used material, and the alumina ceramic powder sintering process is a key technology that forms a dense ceramic body by treating alumina powder at high temperature. By sintering alumina powder in solid conditions at a high temperature of over 1500℃, the powder particles are connected, and the green body is formed into a ceramic workpiece.

[0003] In the ceramic sintering process, adding sintering aids can lower the sintering temperature and increase the sintering rate. The mechanism lies in altering the pathways of mass migration or reducing the energy required for atomic diffusion. For example, sintering aids such as calcium oxide and magnesium oxide can form a low-melting-point liquid phase at high temperatures. Through a dissolution-precipitation effect, solid particles partially dissolve into the liquid phase and rapidly migrate to adhere to pores or precipitate at other locations, thus rapidly densifying the green body. Meanwhile, iron oxide, copper oxide, and manganese oxide can form solid solutions with alumina. The flux ions enter the crystal lattice, causing lattice distortion in alumina, which facilitates diffusion and can achieve densification at lower temperatures or in a shorter time.

[0004] During sintering, additional binders such as PVB are needed to form a preliminary bond between the powder particles, imparting plasticity to the alumina powder, improving the strength of the green body, and reducing defects within the green body. During sintering, the binder must completely volatilize during the debinding process; any carbon residue is unacceptable as it would hinder sintering and negatively impact the forming of alumina ceramic workpieces. However, the binder also influences the flux in the system. For example, copper oxide and iron oxide flux systems are easily reduced in an oxygen-free environment during debinding, thus losing their fluxing effect. Magnesium oxide, calcium oxide, and other fluxes containing boron or bismuth with lower melting points are more prone to softening and liquefaction in the later stages of debinding, causing them to encapsulate the not-yet-debinded binder within the sintering system, forming internal carbon residue that severely affects the color and properties of the ceramic system. Summary of the Invention

[0005] To achieve the above objectives, this application aims to provide a novel fluxing and binding system that can meet the requirements of rapid sintering at high sintering rates. First, this application provides a method for preparing rapidly sintered alumina ceramics, specifically including the following steps: S1. Prepare the powder according to the following mass proportions: 100 parts of alumina powder; 0.5 to 2 parts of calcium phosphate powder; Flux 0.1 to 3 parts; 2-5 parts organic binder; 0.2 to 1 part polyethylene glycol; Other auxiliary agents: 0-3 parts; The other additives include any number of dispersants, defoamers, lubricants, grinding aids, and flocculants; The organic binder comprises the following components by mass percentage: PMMA 10-20%; PVA margin; S2. The mixed powder from step S1 is added to a solvent and ground until D50 is 0.5-2μm, and then pressed into a blank; S3. Sinter to 300-600℃ and then perform debinding treatment; S4. Alumina ceramics are obtained by high-temperature sintering at 1400-1600℃.

[0006] In the above scheme, calcium phosphate is first added. Calcium phosphate has good ion-accommodating capacity, absorbing some ions that easily undergo chemical valence changes and reducing their sensitivity to reduction by residual carbon, thus indirectly protecting the flux and allowing it to perform its function. Simultaneously, calcium phosphate powder also assists in grinding, effectively improving powder gradation and maintaining stability during sintering and binder removal, preventing residual carbon buildup. Furthermore, during sintering, the introduction of calcium phosphate decomposes to produce active CaO and P2O5. CaO forms a eutectic liquid phase with Al2O3, lowering the sintering temperature and overall achieving rapid sintering.

[0007] Based on the above, the adhesive adopts a compound system of PMMA and PVA. PMMA refers to polymethyl methacrylate, which can decompose rapidly under heat, providing pores for PVA to be discharged. PVA refers to polyvinyl alcohol, which can provide viscosity in the system and has good flowability. With the assistance of calcium phosphate for interfacial lubrication and PMMA providing pores, PVA can have the performance of rapid discharge, effectively reducing the discharge time of the system.

[0008] Meanwhile, based on the above, polyethylene glycol can improve the processability of the slurry mixture in step S2 and promote particle dispersion. On the other hand, it can also improve the lubrication properties of the powder, so that calcium phosphate powder can better achieve the ash-forming effect.

[0009] In summary, this scheme utilizes calcium phosphate to achieve rapid sintering and rapid binder removal. At the same time, a small amount of PMMA is used to form channels during the binder removal process. Ultimately, while ensuring the strength of the system, the sintering temperature is reduced, the sintering rate is increased, and the ash residue is reduced.

[0010] Preferably, the calcium phosphate powder is β-tricalcium phosphate.

[0011] β-Tricalcium phosphate (β-Ca3(PO4)2) exhibits better stability at high temperatures and typically does not undergo phase transformation within the alumina sintering temperature range, thus avoiding microcracks caused by volume effects. Simultaneously, at the grain boundaries of alumina, it can assist fluxes such as magnesium oxide in forming a composite structure, helping to prevent excessive grain growth in alumina, ensuring the overall uniformity of the ceramic, reducing internal stress, and further improving the strength of the alumina ceramic system.

[0012] Preferably, the flux specifically comprises the following components in parts by weight: 0.2 to 0.5 parts magnesium oxide 0.1 to 0.3 parts of titanium dioxide Manganese oxide 0.05-0.1 parts Yttrium oxide 0.05 to 0.1 parts.

[0013] In the above system, yttrium oxide is added to the magnesium oxide-titanium oxide-manganese oxide base. Yttrium oxide has a strong interfacial segregation effect, which can continuously coarsen the grains and improve the uniformity of the alumina composition. On the other hand, it also has stronger chemical stability. At the same time, the overall amount of flux added is relatively small, which also helps to maintain the stability of alumina ceramics at high temperatures and improves the performance of the final product. Overall, it is a solution that balances rapid sintering and low flux addition.

[0014] Preferably, the organic binder further includes 5-10% PBMA.

[0015] PBMA (n-butyl methacrylate) can improve the cold working performance and demolding toughness of the preform, and reduce edge defects during demolding. On the other hand, it can also soften and flow in advance at 150-250℃, providing an escape channel for the pyrolysis gases of PMMA and PVA, reducing the internal pressure of the pores, reducing bubbling and cracking defects, and helping to improve the overall density uniformity and dimensional precision.

[0016] Preferably, in step S3, before sintering, the green body is soaked in hot water at 60-90°C for 10-20 minutes.

[0017] The main purpose of this step is to achieve a partial pre-removal of the binder before sintering, thereby increasing the rate of binder removal and reducing the time required for binder removal and sintering in step S3.

[0018] Preferably, in step S4, the heating rate is controlled as follows: first, the temperature is increased to 1000-1200°C at a rate of 5-10°C / min, and then increased to the target sintering temperature at a rate of 1-3°C / min.

[0019] In the above scheme, a faster heating rate is used at low temperature. The main purpose is to avoid excessive time before the grains grow significantly, which could lead to entanglement within the system. Then, the heating rate is controlled during the second-stage densification process. The main purpose is to ensure that the pores have sufficient time to escape and to prevent the pores from being trapped inside the grains. At the same time, yttrium oxide can provide a better grain boundary pinning effect during this process, which can better control the final grains and also help to eliminate internal stress.

[0020] Preferably, the other additives include a dispersant, wherein the dispersant has a mass fraction of 0.5 to 1.5 parts, and the dispersant is any one of ammonium polyacrylate, sodium polyacrylate, and polyethylene glycol fatty acid ester, and / or; The other additives include defoamers, wherein the defoamers are present in parts by weight of 0.1 to 0.5 parts, and the defoamers are any one of polydimethylsiloxane, polyether-modified silicone oil, and / or; The other additives include a lubricant, wherein the lubricant has a mass fraction of 0.2 to 0.8 parts, and the lubricant is any one of stearic acid, zinc stearate, and paraffin wax.

[0021] Overall, the main purpose of dispersants is to promote the stable dispersion of alumina particles in water and reduce the viscosity of the slurry to provide better grinding results. The purpose of defoamers is to reduce the generation of gas during ball milling and avoid gas defects in the green body. The purpose of lubrication is to improve the demolding performance of the green body.

[0022] Preferably, in step S2, the solvent is one or more of water, ethanol, and isopropanol, and the mass of the solvent is 30-50% of the mass of the powder in step S1.

[0023] Overall, the solvents mentioned above are within the ideal range for spray granulation, which can produce granulated powder with good sphericity and flowability, and the grinding process is also relatively smooth. Introducing a small amount of ethanol and isopropanol can improve volatility and reduce the energy consumption of spray drying, but there are certain additional requirements for the treatment of subsequent organic wastewater.

[0024] Furthermore, this application also provides alumina ceramics prepared by the above-described method. In this approach, the prepared alumina ceramics exhibit high flexural strength and fracture toughness, while requiring a shorter sintering time and lower sintering temperature, achieving rapid sintering and effectively reducing the production cost of the system.

[0025] In summary, this application provides a rapidly sinterable ceramic by adding a small amount of calcium phosphate powder to the system. On the one hand, the ion-accommodating properties can protect the flux, and on the other hand, the carbon removal effect is improved. At the same time, PMMA is used to form channels during heating, and PVA is used to provide the viscosity of the green body. Overall, the hot working performance of the system can be improved, the processing time can be shortened, and the overall mechanical properties can be improved. Detailed Implementation

[0026] The technical solutions in this application will be further described through the following specific embodiments.

[0027] Example 1 series refers to a series of alumina ceramic workpieces prepared by different sintering methods. Except for the sintering temperature and time, and the binder removal temperature and time, all other conditions are the same. Specifically, Example 1-1 is prepared using the following method: Example 1-1: In this example, a method for rapidly prototyping alumina ceramic workpieces is provided, specifically including the following steps: S1. Prepare the following components according to mass fraction: 100 parts of alumina powder (α-alumina, with dual particle size distribution, coarse material D50=5μm, accounting for 60% by mass, and fine material D50=0.8μm, accounting for 40% by mass); 1.2 parts of β-tricalcium phosphate powder (D50=1.5μm); 0.6 parts of flux, specifically including magnesium oxide, titanium dioxide, manganese oxide and yttrium oxide, with the following mass parts of the four components: Magnesium oxide (D50=1μm) 0.3 parts, 0.15 parts of titanium dioxide (D50=1μm) Manganese oxide (D50=1μm) 0.07 parts, Yttrium oxide (D50=1μm) 0.08 parts; Four parts of organic binder, specifically including PVA, PMMA, and PBMA, with the following mass fractions of the four components: 3.2 parts of PVA (degree of polymerization 1750, degree of alcoholysis 88%) PMMA (number average molecular weight 80K) 0.4 parts, PMBA (number average molecular weight 120K) 0.4 parts; 0.5 parts of polyethylene glycol (PEG-500); Dispersant (ammonium polyacrylate, molecular weight 3K) 1 part; 0.2 parts of defoamer (BASF FoamStar® SI 2299); Lubricant (zinc stearate) 0.3 parts.

[0028] S2. Prepare a mixed solvent of water and anhydrous ethanol (mass ratio 7:3). Mix the above powder with the mixed solvent at a solid-liquid ratio of 1:0.4. Then grind until D50 is 0.8μm. After spray granulation, press the powder isostatically at 300MPa for 120s to obtain the green body.

[0029] S3. The green body is immersed in 80℃ hot water for 15 minutes, and then sintered and debinded. During the debinding process, the gas atmosphere is air. First, the temperature is raised to 150℃ at a rate of 3℃ / min and held for 20 minutes. Then, the temperature is raised to 300℃ at a rate of 3℃ / min and held for 45 minutes. Then, the temperature is raised to 480℃ at a rate of 1.5℃ / min and held for 60 minutes. Finally, the temperature is raised to 550℃ at a rate of 3℃ / min and held for 30 minutes to remove residual carbon.

[0030] S4. After the debinding in step S3 is completed, the system is subjected to high-temperature sintering. First, the temperature is increased from room temperature to 1100℃ at a rate of 8℃ / min, and then increased from 1100℃ to 1470℃ at a rate of 2℃ / min. The temperature is held for 3.5 hours in an air atmosphere. After sintering, the system is cooled to room temperature in the furnace to obtain ceramic products.

[0031] Examples 1-2, based on Example 1-1, extend the glue discharge time, as follows: During the glue removal process, the temperature is first increased to 150℃ at a rate of 3℃ / min and held for 30min, then increased to 300℃ at a rate of 3℃ / min and held for 60min, then increased to 480℃ at a rate of 1.5℃ / min and held for 90min, and finally increased to 550℃ at a rate of 3℃ / min and held for 45min to remove residual carbon.

[0032] Examples 1-3 differ from Example 1-1 in that the sintering time is extended and the sintering temperature is increased, as detailed below: During the sintering process, the sintering temperature was 1570℃ and the sintering time was 4.5h.

[0033] Examples 1-4 differ from Examples 1-1 in that they simultaneously extend the debinding time and sintering time, and increase the sintering temperature, as detailed below: During the glue removal process, the temperature is first increased to 150℃ at a rate of 3℃ / min and held for 30min, then increased to 300℃ at a rate of 3℃ / min and held for 60min, then increased to 480℃ at a rate of 1.5℃ / min and held for 90min, and finally increased to 550℃ at a rate of 3℃ / min and held for 45min to remove residual carbon.

[0034] During the sintering process, the sintering temperature was 1570℃ and the sintering time was 4.5h.

[0035] The difference between Example 2 and Example 1 lies in the adjustment of the flux, as detailed below: 0.3 parts magnesium oxide, 0.15 parts of titanium dioxide, 0.1 parts manganese oxide, 0.05 parts of yttrium oxide; The difference between Example 3 and Example 1 lies in the adjustment of the flux, as detailed below: 0.3 parts magnesium oxide, 0.15 parts of titanium dioxide, 0.05 parts of manganese oxide, 0.1 parts of yttrium oxide; The difference between Example 4 and Example 1 lies in the adjustment of the flux, as detailed below: 0.3 parts magnesium oxide, 0.15 parts of titanium dioxide, 0.15 parts manganese oxide, The difference between Example 5 and Example 1 is that the mass fraction of β-tricalcium phosphate powder is 0.5 parts.

[0036] The difference between Example 6 and Example 1 is that the mass fraction of β-tricalcium phosphate powder is 2 parts.

[0037] The difference between Example 7 and Example 1 is that β-tricalcium phosphate powder is not added.

[0038] The difference between the Example 8 series and the Example 1 series is that the β-tricalcium phosphate powder is replaced by an equal mass of hydroxyapatite (HA) powder (D50=1.0μm).

[0039] The difference between the Example 9 series and the Example 1 series lies in the specific components of the organic binder as follows: 2.8 parts PVA PMMA 0.4 parts, PMBA 0.8 copies.

[0040] The difference between the Example 10 series and the Example 1 series lies in the specific components of the organic binder as follows: 2.8 parts PVA PMMA 0.8 parts, 0.4 copies of PMBA.

[0041] The difference between the Example 11 series and the Example 1 series lies in the specific components of the organic binder as follows: 3.4 parts PVA PMMA 0.4 parts, 0.2 copies of PMBA.

[0042] The difference between the Example 12 series and the Example 1 series lies in the specific components of the organic binder as follows: 3.2 parts PVA PMMA 0.8 parts, The difference between the Example 13 series and the Example 1 series lies in the specific components of the organic binder as follows: PVA 3.0 parts, PMMA 0.8 parts, 0.2 copies of PMBA.

[0043] The difference between the Example 14 series and the Example 1 series lies in the specific components of the organic binder as follows: PVA 3.6 parts, 0.4 copies of PMBA.

[0044] The difference between the Example 15 series and the Example 1 series is that polyethylene glycol is not added.

[0045] The difference between the Example 16 series and the Example 1 series is that polyethylene glycol is replaced by PEG-200 by an equal mass.

[0046] The difference between the Example 17 series and the Example 1 series is that polyethylene glycol is replaced by PEG-400 by an equal mass.

[0047] The difference between the Example 18 series and the Example 1 series is that polyethylene glycol is replaced by PEG-1000 by an equal mass.

[0048] The difference between the Example 19 series and the Example 1 series is that polyethylene glycol is replaced by PEG-2000 by an equal amount.

[0049] For the above series of embodiments, each series adopts four different preparation methods similar to the series of embodiments 1. Taking the series of embodiments 2 as an example, embodiment 2-1 adopts the same debinding and sintering steps as embodiment 1-1, embodiment 2-2 adopts the same debinding and sintering steps as embodiment 1-2, and so on.

[0050] For the ceramic materials prepared by the above methods, the flexural and compressive strengths of the system were determined using a universal testing machine with a span of 30 mm and a loading rate of 0.5 mm / min, in accordance with GB / T 4740-1999 "Test Method for Compressive Strength of Ceramic Materials" and GB / T 4741-1999 "Test Method for Flexural Strength of Ceramic Materials". The specific experimental results are shown in the table below.

[0051] Based on the experimental data above, it can be seen that, overall, Examples 1-1 achieve similar experimental results to Examples 1-4 with shorter debinding times, lower sintering temperatures, and shorter sintering times. This indicates that the method can effectively reduce the sintering temperature and time of the system to achieve better sintering results. As a control, in Examples 5-7, the amount of β-tricalcium phosphate powder added was adjusted. It can be seen that in Example 7, the absence of β-tricalcium phosphate leads to a significant loss of strength at low debinding times, and also results in a decrease in overall mechanical properties. In Example 8, replacing β-tricalcium phosphate powder with hydroxyapatite (HA) powder has some effect, but has a slight impact on overall mechanical strength. This may be because hydroxyapatite has a significant impact on the alumina lattice, easily leading to a decrease in internal crystal uniformity. Furthermore, the higher the sintering temperature, the greater its impact on mechanical strength.

[0052] Furthermore, in Examples 2-4, the amount of yttrium oxide was mainly adjusted. It can be seen that yttrium oxide improves the overall mechanical strength of the system, and the strength improvement performance is higher in the experimental group with lower sintering temperature. It can improve the overall stability of flux at low sintering temperature, and can also promote grain coarsening and improve the overall uniformity of alumina ceramics.

[0053] In Examples 9-14, the binder was adjusted overall. It can be seen that under short debinding times, the debinding effect of Examples 12 and 14 under -1 condition was significantly weaker than that under -2 condition, indicating that the composition ratio of the organic binder has a significant impact on the debinding process. In Example 12, it can be seen that the lack of PMBA affects the debinding performance of the system, resulting in significantly weaker mechanical properties under -1 condition compared to -2. A similar phenomenon occurs in Example 14 when PMMA is lacking, and the effect of lacking PMMA is more pronounced than that of lacking PMBA. In Example 9, the excessive addition of PMBA while the amount of PMMA remained unchanged not only affected the overall preform forming performance, leading to weakened mechanical strength, but also easily caused excessive dispersion, thus adversely affecting the overall strength during debinding. This not only affects mechanical strength but also negatively impacts the density and dimensional uniformity of the system.

[0054] In Examples 15-19, it can be seen that polyethylene glycol also affects the overall mechanical strength. In Example 15, without the addition of polyethylene glycol, a significant loss of strength occurs when the sintering temperature or the debinding time is reduced. In Examples 16-19, different polyethylene glycols are added. It can be seen that the use of PEG-200 has a slight adverse effect on the overall strength. When the molecular weight of PEG is too large, the change in the conditions during the debinding stage will have a more significant impact on the system. It is possible that large PEG molecules are more likely to generate carbon residue in the system.

[0055] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing rapidly sintered alumina ceramics, characterized in that, Includes the following steps: S1. Prepare the powder according to the following mass proportions: 100 parts of alumina powder; 0.5 to 2 parts of calcium phosphate powder; Flux 0.1 to 3 parts; 2-5 parts organic binder; 0.2 to 1 part polyethylene glycol; Other auxiliary agents: 0-3 parts; The other additives include any number of dispersants, defoamers, lubricants, grinding aids, and flocculants; The organic binder comprises the following components by mass percentage: PMMA 10-20%; PVA margin; S2. The mixed powder from step S1 is added to a solvent and ground until D50 is 0.5-2μm, and then pressed into a blank; S3. Sinter to 300-600℃ and then perform debinding treatment; S4. Alumina ceramics are obtained by high-temperature sintering at 1400-1600℃.

2. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, The calcium phosphate powder is β-tricalcium phosphate.

3. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, The flux specifically comprises the following components in parts by weight: 0.2 to 0.5 parts magnesium oxide 0.1 to 0.3 parts of titanium dioxide Manganese oxide 0.05-0.1 parts Yttrium oxide 0.05 to 0.1 parts.

4. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, The organic binder also includes 5-10% PBMA by mass.

5. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, In step S3, before sintering, the green body is soaked in hot water at 60-90°C for 10-20 minutes.

6. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, The number-average molecular weight of the polyethylene glycol is 400 to 1000.

7. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, In step S4, the heating rate is controlled as follows: first, the temperature is increased to 1000-1200°C at a rate of 5-10°C / min, and then increased to the target sintering temperature at a rate of 1-3°C / min.

8. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, The other additives include dispersants, the dispersants being 0.5 to 1.5 parts by weight, and the dispersants being any one of ammonium polyacrylate, sodium polyacrylate, and polyethylene glycol fatty acid esters, and / or; The other additives include defoamers, wherein the defoamers are present in parts by weight of 0.1 to 0.5 parts, and the defoamers are any one of polydimethylsiloxane, polyether-modified silicone oil, and / or; The other additives include a lubricant, wherein the lubricant has a mass fraction of 0.2 to 0.8 parts, and the lubricant is any one of stearic acid, zinc stearate, and paraffin wax.

9. The method for preparing rapidly sintered alumina ceramics according to claim 1, characterized in that, In step S2, the solvent is one or more of water, ethanol, and isopropanol, and the mass of the solvent is 30-50% of the mass of the powder in step S1.

10. The alumina ceramic prepared by the preparation method according to any one of claims 1 to 9.

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