Method for sintering a piezoelectric ceramic hemisphere of large dimensions

Abstract

The application discloses a sintering method for super-large-size piezoelectric ceramic hemispheres, and belongs to the technical field of ceramics. The method comprises the following steps: 3D printing a supporting hemispherical component, sintering the supporting hemispherical component, and preparing a piezoelectric ceramic hollow hemisphere. The method for 3D printing the supporting hemispherical component is as follows: TiO2, SiO2, MgO and alumina powder are mixed, dispersed in photosensitive resin, and sucrose and ammonium citrate are added to control the solid content of the slurry to 68-72 wt%. After mixing, the slurry is ball milled for 23-25 h, then stirred at a speed of 900-1100 r / min for 0.8-1.2 h, and then vacuum stirred at a speed of 180-220 r / min for 8-12 min to obtain mixed slurry. The mixed slurry is subjected to ultraviolet irradiation and curing after 3D printing to obtain a cured component. The sintering method for super-large-size piezoelectric ceramic hemispheres provided by the application solves the problems of irreversible creep and geometric collapse of super-large-size piezoelectric ceramic, improves the sintering geometric precision, reduces the density difference, and improves the piezoelectric performance and dielectric performance.

Description

Technical Field

[0001] This invention belongs to the field of ceramic technology, specifically relating to a method for sintering ultra-large size piezoelectric ceramic hemispheres. Background Technology

[0002] Piezoelectric ceramic hemispheres, with their excellent axisymmetric acoustic directivity, high electromechanical coupling coefficient, and stable energy conversion efficiency, occupy a core position in high-end fields such as underwater acoustic detection and communication, medical ultrasound focused therapy, large-structure health monitoring, and high-power ultrasonic transducers. The electro-acoustic conversion performance of these components is highly dependent on the geometric accuracy and material consistency of the sintered ceramic hemisphere.

[0003] For small piezoelectric ceramic hemispheres with diameters ranging from a few millimeters to tens of millimeters, the low self-weight and low thermal mass of the green body result in extremely low risks of gravity-induced creep and collapse during sintering. Furthermore, the uniform distribution of the internal temperature and atmosphere fields effectively suppresses warping, cracking, and uneven densification caused by thermal stress. Simultaneously, small-sized green bodies can be prepared using conventional processes such as bulk turning / grinding, cold isostatic pressing + finishing, and molding + subsequent shaping. These processes minimize material removal, waste, and offer a wide processing window, consistently meeting geometric accuracy and performance requirements.

[0004] However, as high-end equipment upgrades towards higher power, longer distance, and higher precision, the demand for ultra-large piezoelectric ceramic hemispheres with an inner diameter ≥250mm is becoming increasingly urgent. However, their fabrication faces multiple bottlenecks that are difficult to overcome with existing technologies. Specifically, for ultra-large hemispheres with an inner diameter ≥250mm, the hemisphere blank is heavy, and during the sintering heating-holding stage, the cap and equatorial regions are prone to irreversible creep and geometric collapse due to the difference in gravity. Simultaneously, the large-sized blank exhibits temperature and atmosphere gradients, which easily induce differential shrinkage, asynchronous phase transformation, and migration of volatile component Pb, ultimately resulting in uneven thickness, roundness deviation, cracking, and density gradients. These defects directly deteriorate the electrode consistency and polarization uniformity of the device, limiting the application of large-sized hemispheres in high-power ultrasonic scenarios.

[0005] Therefore, developing a new sintering technology that can overcome the above-mentioned multiple bottlenecks and achieve high-precision molding and high-performance consistency of ultra-large piezoelectric ceramic hemispheres has become a key challenge that urgently needs to be overcome in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for sintering ultra-large piezoelectric ceramic hemispheres, which solves the problems of irreversible creep and geometric collapse in ultra-large piezoelectric ceramics, improves sintering geometric accuracy, reduces density differences, and enhances piezoelectric and dielectric properties.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for sintering ultra-large piezoelectric ceramic hemispheres includes the following steps: 3D printing of a sintering hemisphere component, sintering of the sintering hemisphere, and preparation of a hollow piezoelectric ceramic hemisphere.

[0009] The method for 3D printing the sintered hemispherical component is as follows: TiO2, SiO2, MgO and alumina powder are mixed and dispersed in a photosensitive resin, and sucrose and ammonium citrate are added to adjust the solid content of the slurry to 68-72 wt%. After mixing, the mixture is ball-milled for 23-25 ​​hours, then stirred at a rate of 900-1100 r / min for 0.8-1.2 hours, and then vacuum stirred at a rate of 180-220 r / min for 8-12 minutes to obtain a mixed slurry. After 3D printing, the mixed slurry is cured by ultraviolet irradiation to obtain a cured component.

[0010] The alumina powder has a purity of ≥99.9% and a particle size of ≤1μm;

[0011] The mass ratio of alumina powder, TiO2, SiO2, MgO, sucrose, and ammonium citrate is 100:9-11:4-5:2-2.5:2.5-3:1-1.5.

[0012] The photosensitive resin contains 1-3 wt% photoinitiator;

[0013] The ball-to-material ratio of the ball mill is 4-5:1, and the ball mill temperature is controlled at 10-15℃.

[0014] The ultraviolet irradiation time is 15-20 seconds.

[0015] The method for sintering the hemispherical bearing is as follows: the solidified component is degreased at 940-960℃, held at that temperature for 4.5-5.5 hours, then cooled to room temperature. The degreased component is then sintered at 1050-1150℃ in an air atmosphere for 1.4-1.6 hours, then heated to 1390-1400℃, switched to an argon atmosphere, and held for 2.4-2.6 hours. After cooling, the sintered component is polished to obtain the hemispherical bearing component.

[0016] The defatting process involves a heating rate of 0.08-0.12℃ / min and a cooling rate of 2.8-3.2℃ / min to room temperature.

[0017] The heating rate during the sintering process is 0.8-1.2℃ / min, and the cooling rate is 1.8-2.2℃ / min to room temperature;

[0018] The degreasing atmosphere is a mixture of argon and oxygen, with an oxygen content of 1.5-2 vol.

[0019] The fire-bearing hemispherical component consists of an inner hemispherical shell, an outer hemispherical shell, and a base. The inner hemispherical shell, the outer hemispherical shell, and the base are all uniformly provided with through-hole structures, with a porosity of 65-75%.

[0020] The thickness of the inner hemisphere, outer hemisphere, and base is 18-22mm.

[0021] The inner diameter of the outer hemisphere of the sintering hemisphere is 8-12 mm larger than the outer diameter of the piezoelectric ceramic hemisphere blank, and the outer diameter of the inner hemisphere of the sintering hemisphere is 10-14 mm smaller than the inner diameter of the piezoelectric ceramic hemisphere blank.

[0022] A schematic diagram of the hemispherical support structure is shown in the attached figure. Figure 1 As shown.

[0023] The method for preparing the piezoelectric ceramic hollow hemisphere is as follows: piezoelectric ceramic powder is ball-milled to a particle size ≤1 μm, dried, and then cold isostatically pressed to obtain a piezoelectric ceramic hemisphere blank; the ceramic hemisphere is assembled with a firing support hemisphere component, the piezoelectric ceramic hemisphere blank is placed between the inner and outer hemisphere shells, then placed on a base, and the whole is placed in an alumina crucible. The alumina crucible is placed in a kiln for sintering, heated to 1280-1300 ℃ and held for 2.4-2.6 h, then cooled to room temperature, and the sample is taken out to obtain the piezoelectric ceramic hollow hemisphere.

[0024] The pressure of the cold isostatic pressing is 180-220 MPa, and the holding time is 9-11 min;

[0025] The heating rate during the sintering process is 1-2℃ / min, and the cooling rate is 1.8-2.2℃ / min;

[0026] The thickness of the piezoelectric ceramic hollow hemisphere is 8-12 mm;

[0027] The inner diameter of the piezoelectric ceramic hollow hemisphere is 250-350 mm. Attached image description:

[0028] Figure 1 This is a schematic diagram of the structure of the fire-bearing hemispherical component.

[0029] Figure 2 This is a schematic diagram of the use of the hemispherical support structure.

[0030] Figure 3 This is a schematic diagram of the hemispherical structure of the firing support in Examples 1-7.

[0031] Figure 3 In the diagram, 1 is the crucible, 2 is the outer hemisphere, 3 is the inner hemisphere, 4 is the base, 5 is the crucible lid, and 6 is the piezoelectric ceramic.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. This invention achieves the sintering of ultra-large piezoelectric hemispheres by preparing a sintering body that matches the piezoelectric ceramic, thereby obtaining ultra-large piezoelectric ceramic hemispheres with a diameter greater than 250 mm. This method is applicable to the sintering of ultra-large piezoelectric ceramic hemispheres, reducing problems such as cracking, collapse, low density, adhesion, and temperature difference during the sintering process.

[0034] 2. Traditional pure alumina sintered bodies undergo a solid-phase reaction with PbO in PZT ceramics at high temperatures, generating a continuous low-melting-point glass phase. This results in a tight adhesion between the two after cooling, causing severe peeling of the ceramic surface upon separation. This invention introduces TiO2, SiO2, and MgO into the alumina matrix. After two-step sintering, these additives may react in situ with some Al2O3 to generate a composite phase mainly composed of magnesium aluminum spinel (MgAl2O4), aluminum titanate (Al2TiO5), and a small amount of high-viscosity glass phase. This composite phase has high chemical stability and can effectively isolate the direct contact between PZT and active Al2O3, significantly alleviating the adhesion and peeling problems at the interface between the sintered body and the piezoelectric ceramic, thereby inhibiting the formation of harmful glass reaction layers from the source.

[0035] 3. During the sintering and cooling process of ultra-large ceramic blanks, the mismatch in the coefficient of thermal expansion (CTE) between the sintering substrate and the ceramic generates huge interfacial thermal stress, which is the main cause of internal microcracks. This invention introduces TiO2, SiO2 and MgO into the alumina matrix. The composite phase generated after sintering can reduce the coefficient of thermal expansion of the sintering substrate, improve the matching degree with PZT ceramics, alleviate thermal stress, and further optimize the piezoelectric and dielectric properties of piezoelectric ceramics.

[0036] 4. The method provided by this invention can stably prepare high-performance, highly consistent ultra-large-sized piezoelectric ceramic hemispheres. The ceramic hemispheres prepared using this invention have an inner diameter of 255-355 mm, and the equatorial cross-sectional roundness of the hollow piezoelectric ceramic hemispheres is measured to be 1.8-2.6 mm, with a thickness deviation of 0.23-0.29 mm. They possess the following excellent properties: the total adhesion area with the substrate is controlled at 1.6%-2.2%; and the ceramic density is stable at 7.45-7.55 g / cm³. 3 piezoelectric constant d 33 The piezoelectric constant is 294-324 pC / N. 33The relative standard deviation is 2.17%-2.68%; the dielectric constant is 1190-1320, and the relative standard deviation of the dielectric constant is 2.45%-2.69%; the dielectric loss tanδ is 0.3%-0.5%, and the dielectric loss fluctuation is only ±0.1%. The uniformity of various performance indicators is excellent, which fully meets the practical application requirements of ultra-large size piezoelectric ceramic hemispheres. Detailed Implementation

[0037] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0038] Example 1

[0039] A method for sintering ultra-large piezoelectric ceramic hemispheres is as follows:

[0040] (1) 3D printed hemispherical components

[0041] 2 kg of TiO2, 900 g of SiO2, 440 g of MgO, and 20 kg of alumina powder were mixed and dispersed in photosensitive resin. 560 g of sucrose and 240 g of ammonium citrate were added to control the solid content of the slurry to 70 wt%. After mixing, the mixture was ball-milled for 24 h, then stirred at 1000 r / min for 1 h, and then vacuum stirred at 200 r / min for 10 min to obtain a mixed slurry. The mixed slurry was used for 3D printing, and after printing, it was cured by ultraviolet irradiation to obtain a cured component.

[0042] The alumina powder has a purity of ≥99.9% and a particle size of 0.8μm;

[0043] The photosensitive resin contains 2 wt% photoinitiator;

[0044] The ball-to-material ratio of the ball mill is 4:1, and the ball mill temperature is controlled at 12℃.

[0045] The ultraviolet irradiation time was 18 seconds.

[0046] (2) Sintering of the hemispherical bearing:

[0047] The solidified component was degreased at 950℃, kept at that temperature for 5 hours, and then cooled to room temperature. The degreased component was then sintered at 1100℃ in an air atmosphere for 1.5 hours, then heated to 1395℃, switched to an argon atmosphere, and kept at that temperature for 2.5 hours. After cooling, the sintered component was polished to obtain a sintered hemispherical component.

[0048] The defatting process involves a heating rate of 0.1℃ / min and a cooling rate of 3℃ / min to room temperature.

[0049] The heating rate during the sintering process is 1℃ / min, and the cooling rate is 2℃ / min until the temperature drops to room temperature.

[0050] The degreasing atmosphere is a mixture of argon and oxygen, with an oxygen content of 1.8 vol.

[0051] The fire-bearing hemispherical component consists of an inner hemispherical shell, an outer hemispherical shell, and a base. The inner hemispherical shell, the outer hemispherical shell, and the base are all uniformly set as square through-hole structures with a side length of 3mm and a porosity of 70%. The thickness of the inner hemispherical shell, the outer hemispherical shell, and the base is 20mm.

[0052] The inner diameter of the outer hemisphere of the sintering hemisphere is 8 mm larger than the outer diameter of the piezoelectric ceramic hemisphere blank, and the outer diameter of the inner hemisphere of the sintering hemisphere is 10 mm smaller than the inner diameter of the piezoelectric ceramic hemisphere blank.

[0053] A schematic diagram of the hemispherical support structure is shown in the attached figure. Figure 2 As shown.

[0054] (3) Preparation of piezoelectric ceramic hollow hemispheres

[0055] Piezoelectric ceramic powder was ball-milled to a particle size of 0.7 μm, dried, and then cold isostatically pressed to obtain a piezoelectric ceramic hemispherical blank. The ceramic hemispherical blank was assembled with a sintering hemispherical component, with the piezoelectric ceramic hemispherical blank placed between the inner and outer hemispherical shells, and then placed on a base. The whole assembly was placed in an alumina crucible, and the alumina crucible was placed in a kiln for sintering. The temperature was raised to 1290 °C and held for 2.5 h, then cooled to room temperature, and the sample was taken out to obtain a piezoelectric ceramic hollow hemispherical.

[0056] The pressure of the cold isostatic pressing is 200 MPa, and the holding time is 10 min;

[0057] The heating rate during the sintering process is 1.5℃ / min, and the cooling rate is 2℃ / min.

[0058] The thickness of the piezoelectric ceramic hollow hemisphere is 8 mm;

[0059] The inner diameter of the piezoelectric ceramic hollow hemisphere is 255 mm.

[0060] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 1.8 mm, and the thickness deviation was 0.23 mm.

[0061] After sintering and cooling, the piezoelectric ceramic hemispheres and the sintered body did not form a continuous reaction layer and no continuous adhesion occurred. Only sporadic, discontinuous point adhesions existed on the ceramic surface, with the total adhesion area accounting for 1.6%.

[0062] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss tanδ parameters were tested. The density was measured using the Archimedes displacement method, the piezoelectric properties were measured using a piezoelectric testing instrument, and the dielectric properties and dielectric loss were measured using an impedance analyzer. The calculated values ​​of the piezoelectric coefficient fluctuation and dielectric constant fluctuation are relative standard deviations, and the dielectric loss fluctuation is the absolute fluctuation range.

[0063] The sampling method involved selecting four points at 90° intervals along the meridian direction of the ceramic hemisphere (from the apex to the equator), in two annular regions: the middle (50% of the height) and the upper (75% of the height), for a total of eight points. Samples conforming to the corresponding testing standards were then cut and processed near each sampling point. The test results are shown in Table 1.

[0064] Table 1. Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 1

[0065]

[0066] Example 2

[0067] A method for sintering ultra-large piezoelectric ceramic hemispheres is as follows:

[0068] (1) 3D printed hemispherical components

[0069] 2.25 kg of TiO2, 1 kg of SiO2, 500 g of MgO, and 25 kg of alumina powder were mixed and dispersed in photosensitive resin. 625 g of sucrose and 250 g of ammonium citrate were added to control the solid content of the slurry to 68 wt%. After mixing, the mixture was ball-milled for 23 h, then stirred at 900 r / min for 1.2 h, and then vacuum stirred at 180 r / min for 12 min to obtain a mixed slurry. The mixed slurry was used for 3D printing, and after printing, it was cured by ultraviolet irradiation to obtain a cured component.

[0070] The alumina powder has a purity of ≥99.9% and a particle size of 1μm;

[0071] The photosensitive resin contains 1 wt% photoinitiator;

[0072] The ball-to-material ratio of the ball mill is 4:1, and the ball mill temperature is controlled at 10℃.

[0073] The ultraviolet irradiation time is 20 seconds.

[0074] (2) Sintering of the hemispherical bearing:

[0075] The cured component was degreased at 940℃, held for 5.5 hours, and then cooled to room temperature. The degreased component was then sintered at 1050℃ in an air atmosphere for 1.6 hours, then heated to 1390℃, switched to an argon atmosphere, and held for 2.6 hours. After cooling, the sintered component was polished to obtain a sintered hemispherical component.

[0076] The degreasing process involves a heating rate of 0.08℃ / min and a cooling rate of 2.8℃ / min to room temperature.

[0077] The heating rate during the sintering process is 0.8℃ / min, and the cooling rate is 1.8℃ / min until the temperature drops to room temperature.

[0078] The degreasing atmosphere is a mixture of argon and oxygen, with an oxygen content of 1.5 vol.

[0079] The fire-bearing hemispherical component consists of an inner hemispherical shell, an outer hemispherical shell, and a base. The inner hemispherical shell, the outer hemispherical shell, and the base are all uniformly set as square through-hole structures with a side length of 4mm and a porosity of 65%. The thickness of the inner hemispherical shell, the outer hemispherical shell, and the base is 18mm.

[0080] The inner diameter of the outer hemisphere of the sintering hemisphere is 10 mm larger than the outer diameter of the piezoelectric ceramic hemisphere blank, and the outer diameter of the inner hemisphere of the sintering hemisphere is 12 mm smaller than the inner diameter of the piezoelectric ceramic hemisphere blank.

[0081] A schematic diagram of the hemispherical support structure is shown in the attached figure. Figure 2 As shown.

[0082] (3) Preparation of piezoelectric ceramic hollow hemispheres

[0083] Piezoelectric ceramic powder was ball-milled to a particle size of 0.5 μm, dried, and then cold isostatically pressed to obtain a piezoelectric ceramic hemispherical blank. The ceramic hemispherical blank was assembled with a sintering hemispherical component, with the piezoelectric ceramic hemispherical blank placed between the inner and outer hemispherical shells, and then placed on a base. The whole assembly was placed in an alumina crucible, and the alumina crucible was placed in a kiln for sintering. The temperature was raised to 1280 ℃ and held for 2.6 h, then cooled to room temperature, and the sample was taken out to obtain a piezoelectric ceramic hollow hemispherical.

[0084] The pressure of the cold isostatic pressing is 180 MPa, and the holding time is 11 min;

[0085] The heating rate during the sintering process is 1℃ / min, and the cooling rate is 1.8℃ / min.

[0086] The thickness of the piezoelectric ceramic hollow hemisphere is 10 mm;

[0087] The inner diameter of the piezoelectric ceramic hollow hemisphere is 305 mm.

[0088] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 2.1 mm, and the thickness deviation was 0.26 mm.

[0089] After sintering and cooling, the piezoelectric ceramic hemisphere and the sintered body did not form a continuous reaction layer and no continuous adhesion occurred. Only sporadic, discontinuous point adhesions existed on the ceramic surface, with the total adhesion area accounting for 2.1%.

[0090] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss parameters were tested; the testing methods and sampling were the same as in Example 1, and the test results are shown in Table 2.

[0091] Table 2 Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 2

[0092]

[0093] Example 3

[0094] A method for sintering ultra-large piezoelectric ceramic hemispheres is as follows:

[0095] (1) 3D printed hemispherical components

[0096] 3.3 kg of TiO2, 1.5 kg of SiO2, 750 g of MgO, and 30 kg of alumina powder were mixed and dispersed in photosensitive resin. 900 g of sucrose and 450 g of ammonium citrate were added to control the solid content of the slurry to 72 wt%. After mixing, the mixture was ball-milled for 25 h, then stirred at 1100 r / min for 0.8 h, and then vacuum stirred at 220 r / min for 8 min to obtain a mixed slurry. The mixed slurry was used for 3D printing, and after printing, it was cured by ultraviolet irradiation to obtain a cured component.

[0097] The alumina powder has a purity of ≥99.9% and a particle size of 0.8μm;

[0098] The photosensitive resin contains 3 wt% photoinitiator;

[0099] The ball-to-material ratio of the ball mill is 5:1, and the ball mill temperature is controlled at 15℃.

[0100] The ultraviolet irradiation time is 15 seconds.

[0101] (2) Sintering of the hemispherical bearing:

[0102] The cured component was degreased at 960℃, held for 4.5 hours, and then cooled to room temperature. The degreased component was then sintered at 1150℃ in an air atmosphere for 1.4 hours, then heated to 1400℃, switched to an argon atmosphere, and held for 2.4 hours. After cooling, the sintered component was polished to obtain a sintered hemispherical component.

[0103] The degreasing process involves a heating rate of 0.12℃ / min and a cooling rate of 3.2℃ / min to room temperature.

[0104] The heating rate during the sintering process is 1.2℃ / min, and the cooling rate is 2.2℃ / min until the temperature drops to room temperature.

[0105] The degreasing atmosphere is a mixture of argon and oxygen, with an oxygen content of 2 vol.

[0106] The fire-bearing hemispherical component consists of an inner hemispherical shell, an outer hemispherical shell, and a base. The inner hemispherical shell, the outer hemispherical shell, and the base are all uniformly set as square through-hole structures with a side length of 5mm and a porosity of 75%. The thickness of the inner hemispherical shell, the outer hemispherical shell, and the base is 22mm.

[0107] The inner diameter of the outer hemisphere of the sintering hemisphere is 12 mm larger than the outer diameter of the piezoelectric ceramic hemisphere blank, and the outer diameter of the inner hemisphere of the sintering hemisphere is 14 mm smaller than the inner diameter of the piezoelectric ceramic hemisphere blank.

[0108] A schematic diagram of the hemispherical support structure is shown in the attached figure. Figure 2 As shown.

[0109] (3) Preparation of piezoelectric ceramic hollow hemispheres

[0110] Piezoelectric ceramic powder was ball-milled to a particle size of 1 μm, dried, and then cold isostatically pressed to obtain a piezoelectric ceramic hemispherical blank. The ceramic hemispherical blank was assembled with the firing support hemispherical component. The piezoelectric ceramic hemispherical blank was placed between the inner and outer hemispherical shells, and then placed on the base. The whole assembly was placed in an alumina crucible, and the alumina crucible was placed in a kiln for sintering. The temperature was raised to 1300 °C and held for 2.4 h, then cooled to room temperature, and the sample was taken out to obtain a piezoelectric ceramic hollow hemispherical.

[0111] The pressure of the cold isostatic pressing is 220 MPa, and the holding time is 9 minutes.

[0112] The heating rate during the sintering process is 2℃ / min, and the cooling rate is 2.2℃ / min;

[0113] The thickness of the piezoelectric ceramic hollow hemisphere is 12 mm;

[0114] The inner diameter of the piezoelectric ceramic hollow hemisphere is 355 mm.

[0115] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 2.6 mm, and the thickness deviation was 0.29 mm.

[0116] After sintering and cooling, the piezoelectric ceramic hemispheres and the sintered body did not form a continuous reaction layer and no continuous adhesion occurred. Only sporadic, discontinuous point adhesions existed on the ceramic surface, with the total adhesion area accounting for 2.2%.

[0117] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss parameters were tested; the testing methods and sampling were the same as in Example 1, and the test results are shown in Table 3.

[0118] Table 3 Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 3

[0119]

[0120] Example 4

[0121] Example 4 uses the ultra-large size piezoelectric ceramic hemisphere sintering method described in Example 1. The difference is that in the step of 3D printing the sintered hemisphere component, alumina powder is used instead of the addition of TiO2, SiO2 and MgO. That is, only alumina powder is used to disperse in the photosensitive resin. The other steps are the same.

[0122] The specific preparation method for the 3D printing of the fired hemispherical component is as follows:

[0123] 23.34 kg of alumina powder was dispersed in photosensitive resin, and 560 g of sucrose and 240 g of ammonium citrate were added to control the solid content of the slurry to 70 wt%. After mixing, the mixture was ball-milled for 24 h, then stirred at 1000 r / min for 1 h, and then vacuum stirred at 200 r / min for 10 min to obtain a mixed slurry. The mixed slurry was used for 3D printing, and after printing, it was cured by ultraviolet irradiation to obtain a cured component.

[0124] The alumina powder has a purity of ≥99.9% and a particle size of 0.8μm;

[0125] The photosensitive resin contains 2 wt% photoinitiator;

[0126] The ball-to-material ratio of the ball mill is 4:1, and the ball mill temperature is controlled at 12℃.

[0127] The ultraviolet irradiation time was 18 seconds.

[0128] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 4.5 mm, and the thickness deviation was 0.42 mm.

[0129] After sintering and cooling, the interface between the piezoelectric ceramic hemisphere and the substrate became blurred, and continuous adhesion occurred, with the total adhesion area accounting for 16.8%. The ceramic surface peeled off severely during demolding.

[0130] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss parameters were tested. The testing methods and sampling were the same as in Example 1, and the test results are shown in Table 4.

[0131] Table 4 Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 4

[0132]

[0133] Example 5

[0134] Example 5 uses the ultra-large piezoelectric ceramic hemisphere sintering method of Example 1. The difference is that in the step of 3D printing the sintered hemisphere component, the addition of MgO is omitted in the sintered hemisphere formula, while the other steps are the same.

[0135] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 2.4 mm, and the thickness deviation was 0.28 mm.

[0136] After sintering and cooling, localized sheet-like adhesions appeared at the interface between the piezoelectric ceramic hemisphere and the sintering substrate, with the total adhesion area accounting for 8.3%.

[0137] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss parameters were tested; the testing methods and sampling were the same as in Example 1, and the test results are shown in Table 5.

[0138] Table 5 Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 5

[0139]

[0140] Example 6

[0141] Example 6 uses the ultra-large size piezoelectric ceramic hemisphere sintering method of Example 1. The difference is that in the step of 3D printing the sintered hemisphere component, the addition of SiO2 is omitted in the sintered hemisphere formula, while the other steps are the same.

[0142] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 2.8 mm, and the thickness deviation was 0.31 mm.

[0143] After sintering and cooling, the interface between the piezoelectric ceramic hemisphere and the sintering body became blurred, with dot-like and localized sheet-like adhesions appearing, accounting for 11.6% of the total adhesion area.

[0144] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss parameters were tested; the testing methods and sampling were the same as in Example 1, and the test results are shown in Table 6.

[0145] Table 6 Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 6

[0146]

[0147] Example 7

[0148] Example 7 adopts the ultra-large size piezoelectric ceramic hemispherical sintering method of Example 1. The difference is that, in the sintering of the sintering body, the two-step method is eliminated and the sintering is carried out directly in argon gas at 1395℃ in one step. The other steps are the same.

[0149] The specific sintering method for the hemispherical bearing is as follows:

[0150] The cured component was degreased at 950℃, kept at that temperature for 5 hours, and then cooled to room temperature. The degreased component was then sintered by heating to 1395℃, switching to an argon atmosphere, and holding for 2.5 hours. After cooling, the sintered component was polished to obtain a sintered hemispherical component.

[0151] The defatting process involves a heating rate of 0.1℃ / min and a cooling rate of 3℃ / min to room temperature.

[0152] The heating rate during the sintering process is 1℃ / min, and the cooling rate is 2℃ / min until the temperature drops to room temperature.

[0153] The degreasing atmosphere is a mixture of argon and oxygen, with an oxygen content of 1.8 vol.

[0154] The fire-bearing hemispherical component consists of an inner hemispherical shell, an outer hemispherical shell, and a base. The inner hemispherical shell, the outer hemispherical shell, and the base are all uniformly set as square through-hole structures with a side length of 3mm and a porosity of 70%. The thickness of the inner hemispherical shell, the outer hemispherical shell, and the base is 20mm.

[0155] The roundness of the equatorial section of the piezoelectric ceramic hollow hemisphere was measured to be 2.5 mm, and the thickness deviation was 0.22 mm.

[0156] After sintering and cooling, the piezoelectric ceramic hemispheres and the sintered body did not form a continuous reaction layer, but there were many point-like adhesions, with the total adhesion area accounting for 4.6%.

[0157] For the prepared piezoelectric ceramic hollow hemispheres, their density, piezoelectric properties, dielectric properties, and dielectric loss parameters were tested; the testing methods and sampling were the same as in Example 1, and the test results are shown in Table 7.

[0158] Table 7 Performance test results of the piezoelectric ceramic hollow hemispheres prepared in Example 7

[0159]

[0160] The ceramic hemispheres prepared in Examples 1-3 exhibited an adhesion area with the sintered substrate that was controlled to an extremely low level of less than 5%, and consisted of easily removable dot-like adhesions. In contrast, when using a pure alumina sintered substrate in Example 4, the adhesion area reached as high as 16.8%, forming a continuous reaction layer that was difficult to separate. This demonstrates that the composite phase sintered substrate of the present invention can effectively isolate the contact between PZT and active Al2O3, thereby inhibiting the formation of a low-melting-point glass phase from the source.

[0161] The ceramics prepared in Examples 1-3 exhibited an average dielectric loss (tanδ) of less than 0.5% and good uniformity. In contrast, Examples 4-7, especially groups 4, 5, and 6 which lacked MgO or SiO2, showed an average tanδ exceeding 0.66% and poor uniformity. Tanδ is a sensitive indicator of internal defects in materials; its significant increase directly confirms that the comparative examples showed an increase in internal microcracks due to CTE mismatch or interfacial reactions, thus indirectly demonstrating the superior effect of the present invention in reducing thermal stress and preventing microcracks.

[0162] The piezoelectric constants (d) of the ceramics prepared in Examples 1-3 33 The relative standard deviations were all below 3%, indicating a high degree of consistency in performance from the dome to the equator. Meanwhile, the d values ​​of Examples 4-7... 33 The relative standard deviation is generally greater than 4%, reaching a maximum of 7.25%. This proves that the porous sintering body structure, the matched CTE and the stepwise sintering process of the present invention synergistically ensure the uniformity of the temperature field and stress field of the ultra-large size green body during the sintering process, and overcome the size effect.

[0163] The piezoelectric constants of the ceramics obtained in Examples 5-7 indicate that the absence of TiO2, SiO2, and MgO (Examples 5 and 6) or the simplification of key processes (Example 7), while partially alleviating adhesion, leads to a surge in dielectric loss and deterioration of uniformity. This demonstrates that the combined addition of TiO2, SiO2, and MgO, along with the specific two-step sintering process, forms a synergistic and indispensable organic whole, jointly achieving the dual goals of inhibiting interfacial reactions and managing thermal stress.

[0164] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for sintering ultra-large piezoelectric ceramic hemispheres, characterized in that, The method includes the following steps: 3D printing of a sintered hemispherical component, sintering of the sintered hemispherical component, and preparation of a piezoelectric ceramic hollow hemispherical. The method for 3D printing the sintered hemispherical component is as follows: TiO2, SiO2, MgO and alumina powder are mixed and dispersed in a photosensitive resin, and sucrose and ammonium citrate are added to adjust the solid content of the slurry to 68-72 wt%. After mixing, the mixture is ball-milled for 23-25 ​​hours, then stirred at a rate of 900-1100 r / min for 0.8-1.2 hours, and then vacuum stirred at a rate of 180-220 r / min for 8-12 minutes to obtain a mixed slurry. After 3D printing, the mixed slurry is cured by ultraviolet irradiation to obtain a cured component. The mass ratio of alumina powder, TiO2, SiO2, MgO, sucrose, and ammonium citrate is 100:9-11:4-5:2-2.5:2.5-3:1-1.

5. The method for sintering the hemispherical bearing is as follows: the solidified component is degreased at 940-960℃, held at that temperature for 4.5-5.5 hours, then cooled to room temperature. The degreased component is then sintered at 1050-1150℃ in an air atmosphere for 1.4-1.6 hours, then heated to 1390-1400℃, switched to an argon atmosphere, and held for 2.4-2.6 hours. After cooling, the sintered component is polished to obtain the hemispherical bearing component. The fire-bearing hemispherical component consists of an inner hemispherical shell, an outer hemispherical shell, and a base. The inner hemispherical shell, the outer hemispherical shell, and the base are all uniformly provided with through-hole structures, with a porosity of 65-75%. The method for preparing the piezoelectric ceramic hollow hemisphere is as follows: piezoelectric ceramic powder is ball-milled to a particle size ≤1 μm, dried, and then cold isostatically pressed to obtain a piezoelectric ceramic hemisphere blank; the ceramic hemisphere is assembled with a firing support hemisphere component, the piezoelectric ceramic hemisphere blank is placed between the inner and outer hemisphere shells, then placed on a base, and the whole is placed in an alumina crucible. The alumina crucible is placed in a kiln for sintering, heated to 1280-1300 ℃ and held for 2.4-2.6 h, then cooled to room temperature, and the sample is taken out to obtain the piezoelectric ceramic hollow hemisphere. The thickness of the piezoelectric ceramic hollow hemisphere is 8-12 mm; The inner diameter of the piezoelectric ceramic hollow hemisphere is 250-350 mm.

2. The method for sintering ultra-large piezoelectric ceramic hemispheres according to claim 1, characterized in that, The alumina powder has a purity of ≥99.9% and a particle size of ≤1μm; The photosensitive resin contains 1-3 wt% photoinitiator; The ultraviolet irradiation time is 15-20 seconds.

3. The method for sintering ultra-large piezoelectric ceramic hemispheres according to claim 1, characterized in that, In the sintering step of the hemispherical bearing, The defatting process involves a heating rate of 0.08-0.12℃ / min and a cooling rate of 2.8-3.2℃ / min to room temperature. The heating rate during the sintering process is 0.8-1.2℃ / min, and the cooling rate is 1.8-2.2℃ / min to room temperature; The degreasing atmosphere is a mixture of argon and oxygen, with an oxygen content of 1.5-2 vol.

4. The method for sintering ultra-large piezoelectric ceramic hemispheres according to claim 1, characterized in that, In the preparation steps of the piezoelectric ceramic hollow hemisphere, The pressure of the cold isostatic pressing is 180-220 MPa, and the holding time is 9-11 min; The heating rate during the sintering process is 1-2℃ / min, and the cooling rate is 1.8-2.2℃ / min.

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