High bulk density yttria ceramic and method of making same

Abstract

The application relates to the field of ceramic sintering, in particular to high-packing-density yttrium oxide ceramic and a preparation method thereof, and provides a yttrium oxide ceramic sintering method which can be operated under non-pressurized conditions, utilizes a trace amount of fluxing agent for doping, simultaneously utilizes zirconium tetrachloride to form a uniform zirconium doping system in a grinding process, and through a special temperature rising and falling sintering process, can realize the ceramic sintering effect with high transparency and high density without additional pressure.

Description

Technical Field

[0001] This application relates to the field of ceramic sintering, and in particular to a high packing density yttrium oxide ceramic and its preparation method. Background Technology

[0002] Yttrium oxide sintered ceramics are advanced ceramic materials made by sintering high-purity yttrium oxide powder through a specific process. They have excellent high-temperature stability, corrosion resistance, light transmittance, and high mechanical properties, and play an important role in many scientific and technological fields.

[0003] The key process in preparing yttrium oxide sintered ceramics is the sintering step. Due to the high melting point of yttrium oxide, conventional sintering processes easily lead to insufficient internal sintering, making atomic migration difficult and resulting in a low overall density after sintering. Currently, the main sintering methods for yttrium oxide include the following: 1. High-pressure sintering: By applying pressure of more than 150MPa during the sintering process to press the ceramic, a higher density can be obtained during the sintering process.

[0004] 2. Ultra-high temperature sintering: In some schemes, sintering is carried out at a temperature of about 1700℃ or higher under vacuum or oxygen-free environment. At the same time, the oxide impurities, residual carbon or other components in the system are removed by hydrogen reduction, thereby obtaining a high-density yttrium oxide system.

[0005] Both methods mentioned above have a certain industrial application basis, but they also have some problems. High-pressure sintering is relatively simple, but for blanks with complex properties and certain cavities and channels, high pressure can easily cause problems such as channel exploration and structural deformation. The second method, however, has more stringent conditions, and even under ultra-high temperature environments, the density of the system can still be low. Furthermore, the demanding reaction conditions introduce more unpredictability into the construction process. In addition, sintering at 1700℃ in this system also has a negative impact on the transparency of yttrium oxide. To achieve a high-transparency ceramic system, additional methods such as vacuum sintering or hydrogen sintering are usually required, which also increases equipment costs.

[0006] Based on the above, some schemes add fluxes to the system. Lanthanum oxide and yttrium fluoride have been reported as fluxes for the above systems. However, adding sintering aids usually leads to a decrease in the transparency of the system, which has a certain impact on the preparation of high-transmittance yttrium oxide ceramics. Summary of the Invention

[0007] Based on the above problems, the purpose of this application is to provide a sintered yttrium oxide ceramic system, the main purpose of which is to maximize the packing density of yttrium oxide under relatively mild conditions while maintaining high transparency.

[0008] First, this application provides a method for preparing high-density yttrium oxide ceramics, comprising the following steps: S1. Prepare the green body powder according to the following mass proportions. 100 parts of yttrium oxide powder 2-5 parts organic binder Alumina 0.1-0.3 parts 0.1 to 0.3 parts of niobium oxide Other metal oxide fluxes: 0.1–0.3 parts Other adjuvants: 0-3 parts The other additives include any number of dispersants, defoamers, lubricants, grinding aids, and flocculants; The other metal oxide fluxes include any number of sodium oxide, potassium oxide, and magnesium oxide. S2. After mixing the above powders, add solvent and ball mill until D50 is 0.1-1μm, then spray granulate and press into a green body; S3. Sinter the green body at a temperature not exceeding 800℃ to remove the binder; S4. Further heat to 1700-2000℃ for sintering to obtain yttrium oxide ceramic.

[0009] In the sintering of yttrium oxide crystals, the main factors affecting transparency are as follows: 1. During the reaction process, residual pores cannot be discharged, which leads to a decrease in the density of the system, and the pores will affect the transparency of the system.

[0010] 2. Even trace amounts of impurities can significantly affect the transparency of the system.

[0011] 3. If the grain size in the system is too large, it will cause more obvious scattering, which will also lead to a decrease in the transparency of the system.

[0012] In the above scheme, firstly, the overall doping content is low, with the total mass fraction of alumina, niobium oxide, and other metal oxide fluxes not exceeding 1 part. This prevents the formation of independent crystalline phases and thus avoids adverse effects on the system's transparency. Simultaneously, the synergistic doping of alumina and niobium oxide in this system effectively suppresses abnormal yttrium oxide grain growth during sintering, allowing for submicron-level grain size control under non-high-pressure sintering conditions and reducing scattering at grain boundaries. Furthermore, niobium oxide in this system also inhibits defect formation. The combined effect of these two factors significantly improves the ceramic's densification rate and sintering uniformity, providing high packing density and high transparency without additional external pressure.

[0013] Preferably, in step S2, zirconium tetrachloride is also added, wherein the mass fraction of zirconium tetrachloride is 1 to 2 parts; The solvent is water. In step S2, after the other components are mixed with water, zirconium tetrachloride is slowly added in batches.

[0014] In the above scheme, zirconium tetrachloride is hydrolyzed using an aqueous solvent during the ball milling stage, thereby depositing a certain amount of zirconium on the surface of yttrium oxide particles. Compared to directly introducing zirconium oxide into the system, this scheme allows zirconium to exhibit higher sintering activity and more uniform distribution, more effectively suppressing grain growth. Furthermore, the slow addition method prevents excessively vigorous hydrolysis or localized crystallization of zirconium tetrachloride, and also avoids equipment corrosion. After hydrolysis, the system forms a more uniform zirconium distribution, significantly improving the system's uniformity and density.

[0015] Preferably, the other metal oxide flux is a combination of calcium oxide and boron oxide, wherein the mass ratio of calcium oxide to boron oxide is 1:1 to 9.

[0016] In the above scheme, the composite system of calcium oxide and boron oxide can utilize the low melting point of boron oxide to form a low-viscosity liquid phase at high temperature, which has a significant effect on reducing the sintering temperature. Calcium oxide can not only form a liquid phase with boron oxide, but also provide oxygen vacancies to accelerate the diffusion rate of ions. The two can work together to achieve sintering at low temperature. At the same time, calcium oxide can also prevent excessive volatilization of boron oxide at low temperature, thereby improving the sustainability of the fluxing effect.

[0017] Preferably, in step S4, during the heating process, the temperature is first raised to 1300-1500℃ and sintered for 10-30 minutes, and then the temperature is further raised to 1700-2000℃ to obtain yttrium oxide ceramic.

[0018] In the above scheme, a two-step sintering method is adopted. In the first sintering process, a low-temperature pre-sintering method is used. During this process, the yttrium oxide blank is significantly densified, the pores gradually close, and the grains begin to grow but have not yet coarsened. At this time, there are several large thermal stresses and structural stresses inside. Staying in this process helps to release the stress. After the stress is released, the atoms can be reactivated by heating during the next heating process. Since the pores have been closed during this process, a pure internal environment can be better created for the subsequent high-temperature sintering, which helps to improve the transparency of the system overall.

[0019] Preferably, after calcination at 1300℃~1500℃, the sample is first annealed, then cooled to 500~800℃ and held for 10~20 minutes, before being heated to 1700~2000℃ for a second calcination.

[0020] In the above scheme, an annealing treatment is performed between the two calcinations. Within the temperature range of 500-800℃, the yttrium atoms in yttrium oxide have a certain degree of activity and mobility, which can fully induce grain boundary relaxation and also help to expel pores. At the same time, the temperature is relatively low, and staying in this temperature range can ensure the full release of stress while avoiding pore merging, coarsening, and continued grain growth in the ceramic crystal within the temperature range of 500-800℃. This maintains a finer overall grain structure and improves the overall strength, transparency, and density of the system.

[0021] Preferably, during the calcination process at 1700–2000°C, the temperature is first increased to 1000–1200°C at a rate of 5–10°C / min, and then increased to the target temperature at a rate of 1–3°C / min for calcination.

[0022] In the above scheme, a segmented heating method is adopted to ensure uniform temperature inside and outside the billet, avoid additional thermal stress caused by excessive heating, and provide sufficient time for air to be discharged, thereby improving the overall density and transparency of the system.

[0023] Preferably, when calcining at 1300–1500°C, the heating rate is no higher than 6°C / min.

[0024] In the first heating step, the temperature is controlled to be relatively low. The main purpose is to ensure that the billet is heated evenly when it is close to the temperature at which the liquid phase forms, so as to avoid uneven distribution of the liquid phase and deformation of the billet caused by sudden local temperature rise. At the same time, it also avoids carbonization of internal residual binders and other components, which would have an adverse effect on the strength and transparency of the system.

[0025] Preferably, after sintering in step S4, the temperature is first lowered to 700-1000°C at a rate not exceeding 10°C / min, held for 10-30 minutes, and then lowered to room temperature.

[0026] In the above scheme, a heat preservation interval of 10 to 30 minutes is set in the range of 700 to 1000℃. The main purpose is to further eliminate the residual stress generated during the cooling process of high-temperature sintered ceramics, avoid internal cracking or the formation of microcracks caused by rapid cooling, help maintain the integrity of the crystal structure, improve the uniformity of grain boundary distribution, avoid the generation of more cracks in the grain boundary area caused by cooling, and improve the integrity and mechanical properties.

[0027] Preferably, in step S1, lanthanum oxide is also added, wherein the mass fraction of lanthanum oxide is 0.1 to 0.5 parts per 100 parts by mass of yttrium oxide.

[0028] In the above scheme, lanthanum atoms in lanthanum oxide can be dissolved in the lattice of yttrium oxide, which increases the grain boundary diffusion coefficient and further promotes the densification of the system. At the same time, it reduces the accumulation of impurities in the grain boundary region, improves the strength and purity of the grain boundary, and can also form a synergistic effect with niobium oxide to further optimize the sintering temperature and suppress grain growth while appropriately reducing the temperature.

[0029] In addition, this application also relates to high packing density yttrium oxide ceramics prepared by the above preparation method, which have a high relative density, extremely low porosity, and due to the uniform and dense overall grain size, can achieve very high branch transmittance in the visible to near-infrared band, have good overall mechanical strength, and have excellent chemical stability and thermal shock resistance.

[0030] In summary, this application provides a yttrium oxide ceramic sintering method that can be operated under non-pressurized conditions. By using a trace amount of flux doping and zirconium tetrachloride to form a uniform zirconium doping system during the grinding process, and through a special heating and cooling sintering process, high transparency and high density ceramic sintering effect can be achieved without applying additional pressure. Detailed Implementation

[0031] The technical solutions in this application will be further described through the following specific embodiments.

[0032] Example 1: In this example, a transparent yttrium oxide ceramic was designed and sintered. The specific preparation steps are as follows: S1. Prepare the powder raw materials according to the following proportions by weight: 100 parts of yttrium oxide powder (purity ≥99.99%, D50=0.3μm); Alumina (α-alumina, purity ≥99.99%, D50=0.1μm) 0.2 parts; Niobium oxide (purity ≥ 99.99%) 0.2 parts; Calcium oxide (purity ≥99.99%) 0.05 parts; Boron oxide (purity ≥ 99.99%) 0.15 parts; Based on the above-mentioned powder, for every 100 parts by weight of yttrium oxide powder, the following auxiliary materials are also prepared: Organic binder (polyvinyl alcohol, degree of polymerization 1750±50) 3 parts; Lubricant (PEG-4000) 1 part; Dispersant (ammonium citrate) 0.3 parts; Defoamer (n-butanol) 0.3 parts.

[0033] S2. After mixing the powder raw materials prepared in step S1, deionized water is added to control the solid content to 40 wt%. Then, the mixture is added to a ball mill for ball milling. The ball milling media is zirconia balls, and the ball-to-material ratio is controlled at 4:1. Ball milling is performed for 10 hours. During the ball milling process, for every 100 parts by mass of yttrium oxide powder, 2 parts by mass of zirconium tetrachloride are added. Zirconia tetrachloride is first dispersed in anhydrous ethanol at a mass ratio of 1:5, and added in five batches, one batch every 1 hour from the start of ball milling, until the addition is complete after 5 hours. After the above ball milling step is completed, the auxiliary materials are dispersed in deionized water at a mass ratio of 1:5 and added to the ball mill. Ball milling continues for 2 hours, followed by spray granulation. The inlet air temperature for spray granulation is 220℃, the outlet air temperature is 110℃, and the atomization pressure is controlled at 0.55 MPa. In this embodiment, the powder particle size D50 is measured to be 60 ± 10 μm. After spraying, the powder is pressed into a circular green body with a diameter of 20mm in a stainless steel mold at a pressure of 150MPa.

[0034] S3. The green compact is heated to 300℃ at a heating rate of 1℃ / min and held for 120min. Then, it is heated to 600℃ at a heating rate of 0.5℃ / min and held for 120min to complete the glue removal step. This step is carried out entirely in an air atmosphere.

[0035] S4. Increase the temperature to 1000℃ at a rate of 5℃ / min, then increase it to 1400℃ at a rate of 3℃ / min, hold for 20 min, then decrease it to 600℃ at a rate of 10℃ / min for the first annealing, hold for 15 min, then increase it to 1100℃ at a rate of 8℃ / min, and finally increase it to 1800℃ at a rate of 2℃ / min, hold for 4 h. After sintering, decrease the temperature to 800℃ at a rate of 10℃ / min, hold for 20 min, and then allow it to cool naturally to 20℃ to complete the sintering step. This step is carried out entirely under nitrogen atmosphere at atmospheric pressure. It should be noted that while vacuum sintering could further improve the system's density, nitrogen sintering better balances the economics of the production process and the product performance.

[0036] After the above preparation is completed, the surface is polished on both sides until the surface roughness Ra < 5 nm, and then ultrasonically cleaned with deionized water for 10 min for later use.

[0037] For Example 1, step S4 is adjusted to obtain the following specific example: Example 1-1: In step S4, the first pre-sintering is not performed. After the binder is removed, the temperature is directly increased to 1100℃ at a heating rate of 5℃ / min, and finally increased to 1800℃ at a heating rate of 2℃ / min, and held at that temperature for 4 hours. After sintering, the temperature is decreased to 800℃ at a rate of 10℃ / min, held for 20 minutes, and then naturally cooled to 20℃ to complete the sintering step.

[0038] In Examples 1-2, in step S4, after the first pre-sintering is completed, no annealing is performed. The temperature is directly increased to 1800°C at a heating rate of 2°C / min and held for 4 hours. After sintering, the temperature is decreased to 800°C at a rate of 10°C / min, held for 20 minutes, and then naturally cooled to 20°C to complete the sintering step.

[0039] In Examples 1-3, in step S4, after the second sintering is completed, the temperature is directly reduced to 20°C at a rate of 10°C / min, instead of remaining at 800°C.

[0040] Examples 1-4 differ from Example 1 in that, during the first sintering, the temperature is increased to 1000°C at a rate of 5°C, and then increased to 1500°C at a rate of 3°C / min, and held for 20 minutes.

[0041] Examples 1-5 differ from Example 1 in that, during the first sintering, the temperature is increased to 1000°C at a rate of 5°C, and then increased to 1300°C at a rate of 3°C / min, and held for 20 minutes.

[0042] Examples 1-6 differ from Example 1 in that, during the first sintering, the temperature is increased to 1000°C at a rate of 5°C, and then increased to 1200°C at a rate of 3°C / min, and held for 20 minutes.

[0043] Examples 1-7 differ from Example 1 in that, after the second sintering, the temperature is reduced to 1000°C at a rate of 10°C / min, held for 20 minutes, and then naturally cooled to 20°C.

[0044] Examples 1-8 differ from Example 1 in that, after the second sintering, the temperature is reduced to 600°C at a rate of 10°C / min, held for 20 minutes, and then naturally cooled to 20°C.

[0045] Examples 1-9 differ from Example 1 in that zirconium tetrachloride is added to the ball milling system all at the beginning of the ball milling process.

[0046] Example 2 differs from Example 1 in that zirconium tetrachloride is not added in step S2, while zirconium oxide is added in step S1 according to the same zirconium mass. That is, in step S1, 1.06 parts by mass of zirconium oxide powder (content > 99.99%) is added during powder preparation.

[0047] Based on Example 2, the sintering conditions in step S4 were adjusted to obtain Examples 2-1 to 2-3. Specifically, Example 2-1 has the same sintering conditions as Example 1-1, Example 2-2 has the same sintering conditions as Example 1-2, and Example 2-3 has the same sintering conditions as Example 1-3.

[0048] In Examples 3-1 to 3-8, the dosage was adjusted based on Example 1, as shown in Table 1.

[0049] The above embodiments were verified by the following experiments: 1. Determine the measured density and calculate the relative density according to Archimedes' method.

[0050] 2. Transmittance: Using a UV-Vis spectrophotometer, the linear transmittance of light at a wavelength of 600 nm was measured for a 2 mm thick sample.

[0051] For each set of embodiments, 10 samples were fired for each embodiment. The experimental results of the above embodiments are shown in Table 2.

[0052] In the above scheme, a comparison between Example 1 and Example 2 shows that in this scheme, zirconium tetrachloride is used for dispersion during ball milling. Compared to directly adding zirconium oxide in Example 2, this significantly improves the overall relative density and transmittance of the system. The system dispersed by zirconium tetrachloride during ball milling significantly enhances the fluxing and grain growth inhibition effects of zirconium, while directly adding zirconium dioxide requires a larger amount of zirconium. At the same addition amount, this significantly improves the transparency and density of the system during atmospheric pressure sintering. In Examples 1-9, adding all of the zirconium tetrachloride to the system at once easily leads to rapid hydrolysis of the zirconium tetrachloride, resulting in a significant decrease in the uniformity of dispersion in the system; its effect is even weaker than the scheme of directly adding zirconium oxide.

[0053] In Examples 1-2 to 1-9, the sintering steps were adjusted. It can be seen that in Example 1-1, no pre-sintering was performed, resulting in only one sintering, leading to more pores in the system and a certain loss in relative density and transparency. In Example 1-2, directly raising the temperature to the subsequent sintering temperature after the first pre-sintering resulted in more defects in the system, thus reducing transparency. In Example 1-3, directly cooling to room temperature after sintering made it difficult to fully release internal stress, resulting in a certain decrease in overall system transparency. Furthermore, in Examples 1-5 to 1-8, the parameters for the two cooling cycles were adjusted. It can be seen that controlling the pre-sintering temperature within the range of 1300–1500℃ resulted in better overall transparency.

[0054] In Examples 3-1 to 3-9, it can be seen that the addition of lanthanum oxide, which was further added in Examples 3-5 to 3-7, has a certain effect on improving the transparency of the system, but the cost will also increase slightly. The addition can be selected according to actual needs. In Examples 3-1 to 3-3, the ratio of calcium oxide and boron oxide was adjusted. It can be seen that when the ratio of calcium oxide to boron oxide in the system is controlled within the range of 1:1 to 9, the overall transparency and packing density are good, and the sintering process of the system is improved to a certain extent. In Examples 3-8 to 3-11, it can be seen that both alumina and niobium oxide have a positive effect on the transparency of the system, and the absence of niobium oxide will lead to a certain decrease in the packing density of 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 high packing density yttrium oxide ceramics, characterized in that, Includes the following steps: S1. Prepare the green body powder according to the following mass proportions. 100 parts of yttrium oxide powder 2-5 parts organic binder Alumina 0.1-0.3 parts 0.1 to 0.3 parts of niobium oxide Other metal oxide fluxes: 0.1–0.3 parts Other adjuvants: 0-3 parts The other additives include any number of dispersants, defoamers, lubricants, grinding aids, and flocculants; The other metal oxide fluxes include any number of sodium oxide, potassium oxide, and magnesium oxide. S2. After mixing the above powders, add solvent and ball mill until D50 is 0.1-1μm, then spray granulate and press into a green body; S3. Sinter the green body at a temperature not exceeding 800℃ to remove the binder; S4. Further heat to 1700-2000℃ for sintering to obtain yttrium oxide ceramic.

2. The method for preparing high packing density yttrium oxide ceramics according to claim 1, characterized in that, In step S2, zirconium tetrachloride is also added, with a mass fraction of 1 to 2 parts. The solvent is water. In step S2, after the other components are mixed with water, zirconium tetrachloride is added in batches.

3. The method for preparing high packing density yttrium oxide ceramics according to claim 1, characterized in that, The other metal oxide flux is a combination of calcium oxide and boron oxide, wherein the mass ratio of calcium oxide to boron oxide is 1:1 to 9.

4. The method for preparing high packing density yttrium oxide ceramics according to claim 1, characterized in that, In step S4, during the heating process, the temperature is first raised to 1300-1500℃ and sintered for 10-30 minutes, and then the temperature is further raised to 1700-2000℃ to obtain yttrium oxide ceramic.

5. The method for preparing high packing density yttrium oxide ceramics according to claim 4, characterized in that, After calcination at 1300℃~1500℃, the furnace undergoes an annealing process, cooling to 500~800℃ and holding for 10~20 minutes. Then, it is heated to 1700~2000℃ for a second calcination.

6. The method for preparing high packing density yttrium oxide ceramics according to claim 5, characterized in that, During the calcination process, the temperature is first increased to 1000-1200℃ at a rate of 5-10℃ / min, and then increased to the target temperature at a rate of 1-3℃ / min for calcination.

7. The method for preparing high packing density yttrium oxide ceramics according to claim 5, characterized in that, When calcining at 1300–1500℃, the heating rate should not exceed 6℃ / min.

8. The method for preparing high packing density yttrium oxide ceramics according to claim 1, characterized in that, After sintering in step S4, the temperature is first lowered to 700-1000℃ at a rate not exceeding 10℃ / min, held for 10-30 minutes, and then lowered to room temperature.

9. The method for preparing high packing density yttrium oxide ceramics according to claim 1, characterized in that, In step S1, lanthanum oxide is also added, with the lanthanum oxide comprising 0.1 to 0.5 parts by mass per 100 parts by mass of yttrium oxide.

10. High packing density yttrium oxide ceramics prepared by the preparation method according to any one of claims 1 to 9.

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