A method for rapidly annealing shaped dielectric ceramic using microwaves
By using microwave rapid annealing, high-power microwaves are used to repair defects in dielectric ceramics, solving the problems of thermal damage and high energy consumption caused by traditional thermal annealing. This method achieves non-destructive and rapid repair of dielectric ceramics, improves dielectric performance, and is suitable for high-frequency communication devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIHUA UNIV
- Filing Date
- 2026-04-29
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies for preparing dielectric ceramics by high-temperature sintering have residual defects such as oxygen vacancies and grain boundary micropores, which lead to deterioration of dielectric loss. Furthermore, traditional hot annealing processes result in thermal damage, high energy consumption, and poor uniformity, making it difficult to meet the performance requirements of high-frequency communication devices.
The microwave rapid annealing method utilizes the transient bulk heating effect of high-power microwaves and the vector effect of strong electromagnetic fields to repair intrinsic and extrinsic defects in dielectric ceramics within seconds, avoiding grain growth and volatilization of low-melting-point components, thus achieving non-destructive and uniform repair.
It significantly reduces dielectric loss, improves quality factor, meets the performance requirements of high-frequency communication devices, shortens process time to the second level, has low energy consumption, and is suitable for mass production of multiple series of oxide dielectric ceramics.
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Figure CN122102690A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electronic information functional ceramic materials and electronic devices, specifically to a method for forming dielectric ceramics using microwave rapid annealing. Background Technology
[0002] Dielectric ceramics are core materials for 5G / 6G high-frequency communication, aerospace exploration technology, and communication devices such as high-frequency filters, samplers, and antennas. As 6G technology expands into millimeter-wave and terahertz bands, electronic devices place stringent demands on the dielectric loss and quality factor of dielectric ceramics. However, during the high-temperature sintering process, residual defects such as oxygen vacancies and grain boundary micropores are inevitably generated in dielectric ceramics. These residual defects can cause problems such as polarization relaxation, electromagnetic wave scattering, and increased leakage current in high-frequency circuits, leading to a deterioration in dielectric loss.
[0003] Currently, the mainstream method for treating residual defects in formed ceramics in the industry is high-temperature hot annealing, which relies on heat conduction to drive the repair of defects within the ceramic body through thermal energy. However, this process causes irreversible thermal damage to the ceramic material under prolonged high-temperature conditions: to achieve effective repair, high-temperature long-term holding (usually several hours) is required, which can easily lead to problems such as abnormal grain growth, volatilization of low-melting-point components (Pb, Bi, Li, P, etc.), and segregation of grain boundary ions. This introduces new loss factors, resulting in high energy consumption, poor uniformity, and unsatisfactory treatment effects.
[0004] The application of microwave technology in the ceramics field is currently limited to the densification stage of green body sintering. Existing methods all focus on using the microwave heating effect to achieve rapid sintering of ceramic green bodies. However, the rapid heating / cooling characteristics of microwave sintering can actually lock in a large number of residual defects during the ceramic forming process, and existing technologies completely ignore the potential of microwaves in the post-processing and repair of formed bulk ceramics.
[0005] In summary, developing a process that enables low-power, rapid, non-destructive, and uniform repair of defects in molded dielectric ceramics, and solving the long-standing pain points of traditional thermal annealing, is a key technical challenge that urgently needs to be overcome in the field of high-frequency dielectric ceramics. Summary of the Invention
[0006] The purpose of this invention is to address the shortcomings of existing technologies and provide a method for rapidly annealing molded dielectric ceramics using microwaves. This method solves the industry pain points of traditional high-temperature annealing, such as thermal damage, uneven repair, long cycle time, and high energy consumption. It enables second-level non-destructive post-processing of molded dielectric ceramic materials, significantly reducing the dielectric loss of ceramics in the microwave and terahertz frequency bands, and meeting the application requirements of next-generation communication devices.
[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:
[0008] A method for rapidly annealing molded dielectric ceramics using microwaves includes the following steps:
[0009] (1) Sample pretreatment: The sintered and dense molded dielectric ceramic block is cleaned and dried;
[0010] (2) Microwave annealing: The treated molded dielectric ceramic block is placed in the sample cavity of the microwave annealing system. Under atmospheric conditions, the ceramic block is subjected to continuous pulse annealing treatment for 1 to 10 seconds using microwaves of 2.45 GHz ± 50 MHz and an output power of 0.5 to 2 kW.
[0011] (3) Cooling and unloading: After the annealing is completed, microwave radiation is stopped, and the ceramic block is naturally cooled to room temperature along with the sample chamber. The ceramic sample processing is completed when it is taken out.
[0012] As a preferred approach, the core of this method is to achieve rapid defect repair through the synergistic effect of two unique microwave effects:
[0013] ① Transient heating effect: High-power microwaves of 0.5~2 kW directly couple with polar groups inside the ceramic, achieving synchronous and uniform heating inside and outside the ceramic. It provides sufficient heat within seconds to dissolve micropores and microcracks between grains inside the ceramic and repair non-intrinsic defects. At the same time, the processing time of 1~10 s completely avoids grain growth and volatilization of low-melting-point components.
[0014] ② Strong electromagnetic field vector effect: The strong electric field of high-power microwaves can directly act on charged point defects in ceramic crystals, reduce the activation energy of defect migration, drive point defect migration and accelerate recombination, reduce the intrinsic defect concentration, and at the same time, for distributed segregated ions, the strong electric field also accelerates their migration, realizes the homogenization of ion distribution, and suppresses the polarization loss caused by charged ions in the microwave, millimeter wave and terahertz frequency bands.
[0015] As a preferred approach, the microwave annealing system employs a rectangular waveguide transmission series structure: the annealing system includes a sample cavity, a rectangular waveguide, a microwave input port, and a cooling system; microwaves are input from the left microwave input port and transmitted to the sample cavity via the rectangular waveguide; an openable sample cavity cover is provided on the upper surface of the sample cavity, and the molded dielectric ceramic block to be processed is placed horizontally inside the sample cavity; the cooling system is installed on the far right of the system and is directly connected to the waveguide cavity, achieving system heat dissipation and continuous operation through air cooling. The system is compatible with the 2.45 GHz industrial microwave frequency band, and the sample cavity is located at the position of the maximum field strength at 1 / 4 wavelength of the rectangular waveguide. The system is compatible with 0.5~2 kW high-power pulsed microwaves and molded dielectric ceramic blocks with a thickness of 0.5~10 mm, and operates entirely in an atmospheric environment.
[0016] As a preferred embodiment, in step (1), the formed dielectric ceramic block is any one of MgTa2O6 ceramic, BaZnP2O7 ceramic, or microwave dielectric ceramic k20 with a dielectric constant of 20, and the thickness of the ceramic block is 0.5~10 mm.
[0017] As a preferred embodiment, when the molded dielectric ceramic block is MgTa2O6 ceramic, in step (2), the microwave output power is 1~2 kW and the annealing time is 3~6 s.
[0018] As a preferred embodiment, when the formed dielectric ceramic block is BaZnP2O7 ceramic, in step (2), the microwave output power is 1~1.5 kW and the annealing time is 2~4 s.
[0019] As a preferred embodiment, when the molded dielectric ceramic block is a microwave dielectric ceramic with a dielectric constant of 20, in step (2), the microwave output power is 1~2 kW and the annealing time is 3~6 s.
[0020] As a preferred method, in step (2), the annealing process is carried out without an inert or reducing protective atmosphere, without programmed heating or holding stages, and the annealing process is completed by a single microwave pulse.
[0021] As a preferred method, in step (1), the cleaning and drying process specifically involves: ultrasonically cleaning the ceramic block with anhydrous ethanol, and then drying it in a 60 °C forced-air drying oven for 2 h.
[0022] As a preferred method, after treatment, the dielectric loss of dielectric ceramics in the terahertz band is reduced by 30% to 100% compared with that before treatment, and the quality factor Q×f in the microwave band is increased by 30% to 60%. Moreover, the ceramic grain size, crystal structure, and phase composition remain unchanged from those before annealing, and there is no component volatilization.
[0023] As a preferred method, sample pretreatment is as follows:
[0024] MgTa2O6 ceramic green bodies were prepared by solid-state reaction method and sintered at 1400 °C for 4 h to obtain densified MgTa2O6 ceramic blocks with thicknesses of 0.6 mm and 6 mm. The blocks were ultrasonically cleaned with anhydrous ethanol for 10 min and then dried in a drying oven at 60 °C for 2 h for later use.
[0025] Alternatively, a solid-state reaction method can be used to prepare BaZnP2O7 ceramic green bodies, which are then sintered in air at 825 °C for 4 h to obtain densely formed BaZnP2O7 ceramic blocks with thicknesses of approximately 0.6 mm and 6 mm. These blocks are ultrasonically cleaned with anhydrous ethanol for 10 min and then dried in a drying oven at 60 °C for 2 h for later use.
[0026] Alternatively, K20 ceramic powder with a dielectric constant of 20 can be used. After sintering in air at 1300 °C for 4 h, a fully densified K20 ceramic block with a thickness of about 0.6 mm is obtained. This block is then ultrasonically cleaned with anhydrous ethanol for 10 min and dried at 60 °C for 2 h for later use.
[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0028] ① Achieve non-destructive repair of molded dielectric ceramics. This invention overcomes the limitations of traditional processes that cause thermal damage. Through high-power microwave transient annealing, it simultaneously repairs both intrinsic defects (micropores, ion segregation) and intrinsic defects (charged oxygen vacancies, ions, etc.) within the ceramic body while completely maintaining the original grain size, crystal structure, and phase composition. This fundamentally avoids the problems of abnormal grain growth and volatilization of low-melting-point components, achieving non-destructive and rapid repair of defects in molded dielectric ceramics.
[0029] ② Significant improvement in efficiency and energy consumption. This invention shortens the traditional annealing process cycle, which can take several hours, to 1-10 seconds, greatly reducing the process time and improving efficiency. The annealing process is completed using only a momentary pulse, consuming less than 1% of the energy of traditional hot annealing. It is green and low-carbon, making it suitable for industrial mass production needs.
[0030] ③ Microwave annealing significantly improves performance. This invention achieves ceramic defect repair through high-power microwave annealing. The treated dielectric ceramics exhibit a 30%~100% reduction in dielectric loss in the terahertz band and a 30%~60% increase in the microwave band quality factor Q×f, solving the core bottleneck in high-frequency performance breakthroughs of dielectric ceramics and meeting the stringent requirements of terahertz communication devices.
[0031] ④ The process is highly versatile and simple to operate. The process of this invention does not require a protective atmosphere, a precise temperature control system, or complex post-processing. It can be completed in an atmospheric environment and is suitable for a variety of oxide dielectric ceramics sintered at high, medium, and low temperatures. Attached Figure Description
[0032] Figure 1 A schematic diagram of the microwave annealing system used in the embodiments of the present invention.
[0033] Among them, 1-rectangular waveguide, 2-sample cavity, 3-sample cavity cover plate, 4-cooling system, 5-formed dielectric ceramic block.
[0034] Figure 2 SEM and XPS images of the dielectric properties and microstructure of MgTa2O6 ceramics before and after microwave annealing in the terahertz and microwave bands (approximately 7.5 GHz).
[0035] (a) shows the changes in dielectric constant and dielectric loss of MgTa2O6 ceramics in the 0.5-1.1 THz frequency band after different microwave annealing conditions; (b) shows the changes in dielectric properties of MgTa2O6 ceramics in the microwave frequency band (approximately 7.4 GHz) before and after microwave annealing; (c) shows the cross-sectional microstructure of MgTa2O6 ceramic samples before and after microwave treatment at 2 kW / 6 s; and (d) shows the XPS energy spectrum of oxygen atoms in MgTa2O6 ceramics under different microwave treatment conditions.
[0036] Figure 3 Terahertz dielectric properties and microstructure of BaZnP2O7 ceramics before and after microwave annealing.
[0037] (a) shows the changes in dielectric constant, dielectric loss, and quality factor of BaZnP2O7 ceramics with frequency in the 0.5-1.1THz frequency band after different microwave annealing conditions; (b) shows the cross-sectional microstructure of BaZnP2O7 ceramic samples before and after microwave treatment at 1 kW / 4s.
[0038] Figure 4 Terahertz dielectric properties and microstructure of K20 ceramics before and after microwave annealing.
[0039] (a) shows the changes in dielectric constant, dielectric loss, and quality factor of K20 ceramics with frequency in the 0.5-1.1 THz frequency band after different microwave annealing conditions; (b) shows the cross-sectional microstructure of K20 ceramic samples before and after microwave treatment at 1.5 kW / 6s. Detailed Implementation
[0040] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.
[0041] The testing methods used in all embodiments and comparative examples of this invention are as follows:
[0042] Microscopic morphology characterization: Field emission scanning electron microscopy (SEM) was used to observe the cross-sectional morphology of the ceramic and to statistically analyze the changes in grain size and porosity before and after microwave treatment;
[0043] Oxygen vacancy characterization: X-ray photoelectron spectroscopy (XPS) was used to quantitatively determine the changes in oxygen vacancy concentration in ceramics;
[0044] Dielectric performance testing: The dielectric constant and quality factor Q×f in the microwave band were tested using a vector network analyzer, and the dielectric performance in the 0.2~1.2 THz band was tested using a terahertz time-domain spectrometer (THz-TDS).
[0045] An embodiment provides a method for rapidly annealing molded dielectric ceramics using microwaves, comprising the following steps:
[0046] (1) Sample pretreatment: The sintered and dense molded dielectric ceramic block is cleaned and dried;
[0047] (2) Microwave annealing: The treated molded dielectric ceramic block is placed in the sample cavity of the microwave annealing system. Under atmospheric conditions, the ceramic block is subjected to continuous pulse annealing treatment for 1 to 10 seconds using microwaves of 2.45 GHz ± 50 MHz and an output power of 0.5 to 2 kW.
[0048] (3) Cooling and unloading: After the annealing is completed, microwave radiation is stopped, and the ceramic block is naturally cooled to room temperature along with the sample chamber. The ceramic sample processing is completed when it is taken out.
[0049] The core of this method is to achieve rapid defect repair through the synergistic effect of two unique microwave effects:
[0050] ① Transient heating effect: High-power microwaves of 0.5~2 kW directly couple with polar groups inside the ceramic, achieving synchronous and uniform heating inside and outside the ceramic. It provides sufficient heat within seconds to dissolve micropores and microcracks between grains inside the ceramic and repair non-intrinsic defects. At the same time, the processing time of 1~10 s avoids grain growth and volatilization of low-melting-point components.
[0051] ② Strong electromagnetic field vector effect: The strong electric field of high-power microwaves directly acts on charged point defects inside ceramic crystals, reducing the activation energy of defect migration, driving point defect migration and accelerating recombination, reducing the intrinsic defect concentration. At the same time, for distributed segregated ions, the strong electric field can accelerate their migration, achieve uniform ion distribution, and suppress polarization loss caused by charged ions in microwave, millimeter wave and terahertz frequency bands.
[0052] like Figure 1As shown in the embodiment, the microwave annealing system adopts a rectangular waveguide transmission series structure: the annealing system includes a sample cavity 2, a rectangular waveguide 1, a microwave input port, and a cooling system 4; microwaves are input from the left microwave input port and transmitted to the sample cavity 2 via the rectangular waveguide; an openable sample cavity cover 3 is provided on the upper surface of the sample cavity; the molded dielectric ceramic block 5 to be processed is placed horizontally inside the sample cavity; the cooling system 4 is installed on the far right of the system and is directly connected to the rectangular waveguide cavity; the system heats up and ensures continuous operation through air cooling; the system is compatible with the 2.45 GHz industrial microwave frequency band; the sample cavity is located at the position of the maximum field strength of 1 / 4 wavelength of the rectangular waveguide; the system is compatible with 0.5~2 kW high-power pulsed microwaves and 0.5~10 mm thick molded dielectric ceramic blocks 5; and operates entirely in an atmospheric environment.
[0053] In some embodiments, in step (1), the formed dielectric ceramic block is any one of MgTa2O6 ceramic, BaZnP2O7 ceramic, or K20 microwave dielectric ceramic (commercial ceramic with a dielectric constant of about 20), and the thickness of the ceramic block is 0.5~10 mm.
[0054] In some embodiments, when the molded dielectric ceramic block is MgTa2O6 ceramic, in step (2), the microwave output power is 1~2 kW and the annealing time is 3~6 s.
[0055] In some embodiments, when the molded dielectric ceramic block is BaZnP2O7 ceramic, in step (2), the microwave output power is 1~1.5 kW and the annealing time is 2~4 s.
[0056] In some embodiments, when the molded dielectric ceramic block is a K20 microwave dielectric ceramic, in step (2), the microwave output power is 1~2 kW and the annealing time is 3~6 s.
[0057] In some embodiments, in step (2), the annealing process is carried out without an inert or reducing protective atmosphere, without programmed heating or holding stages, and the annealing process is completed by a single microwave pulse.
[0058] In some embodiments, the cleaning and drying process in step (1) specifically involves ultrasonically cleaning the ceramic block with anhydrous ethanol and then drying it in a 60 °C forced-air drying oven for 2 h.
[0059] In some embodiments, after treatment, the dielectric loss of the dielectric ceramic in the microwave and terahertz frequency bands is reduced by more than 30% and the quality factor Q×f is increased by more than 50% compared with that before treatment, and the ceramic grain size and crystal structure remain unchanged.
[0060] Figure 2Dielectric properties of MgTa2O6 ceramics in the microwave and terahertz bands before and after microwave annealing. Figure 2 The dielectric properties of MgTa2O6 dielectric ceramics before and after microwave treatment are shown in the microwave and terahertz frequency bands. In the microwave band (approximately 7.4 GHz), the quality factor Q×f of the ceramic sample significantly improved after microwave annealing (2 kW / 6 s), increasing dramatically from 62958 GHz to 87312 GHz, while the dielectric constant also showed a slight increase. In the higher terahertz band (approximately 0.8 THz), after 2 kW / 6 s treatment, the dielectric loss significantly decreased from 0.017 in the untreated sample to 0.01, and the dielectric constant slightly increased from 22.34 to 22.9. Cross-sectional SEM images revealed numerous obvious micropores between the grains in the untreated control group sample, while the number of micropores inside the ceramic treated with 2 kW / 6 s microwave was significantly reduced. XPS energy dispersive spectroscopy (EDS) at 1 s showed that after 2 kW / 6 s microwave treatment, the relative content of oxygen vacancies decreased from 15.38% to 13.28%.
[0061] Figure 3 Terahertz dielectric properties and microstructure of BaZnP2O7 ceramics before and after microwave annealing. Figure 3 It can be seen that under the condition of 1 kW / 4s, the terahertz dielectric loss of BaZnP2O7 ceramics is effectively suppressed, and its peak quality factor Q×f is significantly improved from 70195 GHz (@0.68 THz) in the untreated sample to 81324 GHz (@0.79 THz). However, the dielectric constant decreases to some extent (from 7.25 to 6.3). The cross-sectional SEM images show that the untreated sample exhibits certain gaps between grains, indicating relatively loose bonding. In contrast, the microwave-treated sample shows a more compact cross-section, suggesting that high-power microwaves can effectively promote the repair of internal pores in the material.
[0062] Figure 4 Terahertz dielectric properties and microstructure of K20 ceramics before and after microwave annealing. Figure 4The changes in dielectric loss of K20 ceramic before and after microwave treatment reveal that after 2 kW / 6 s microwave treatment, its terahertz dielectric loss decreased significantly (from 0.013 to 0.0075), and its quality factor Q×f value increased substantially, with the peak value increasing from 53,350 GHz (@0.7 THz) in the untreated sample to 110,840 GHz (@0.9 THz), an increase of over 100%. Simultaneously, the dielectric constant of the material also achieved a stable increase of approximately 2%. Comparison of cross-sectional SEM images reveals that the untreated sample exhibits significant porosity and looseness at grain boundaries, while after 2 kW / 6 s microwave treatment, the internal grain arrangement of the ceramic becomes more compact. XPS testing results show that the relative content of oxygen vacancies decreased from 23.98% before treatment to 22.65%.
[0063] Example 1
[0064] This embodiment provides a method for high-power microwave rapid annealing to form MgTa2O6 ceramics, the steps of which are as follows:
[0065] Sample pretreatment: MgTa2O6 ceramic green bodies were prepared by solid-state reaction method and sintered at 1400 °C for 4 h to obtain densified MgTa2O6 ceramic blocks with thicknesses of 0.6 mm and 6 mm. The blocks were ultrasonically cleaned with anhydrous ethanol for 10 min and then dried in a drying oven at 60 °C for 2 h for later use.
[0066] High-power microwave transient annealing: The dried ceramic block is placed in the sample cavity of the high-power microwave annealing system under atmospheric conditions. The microwave frequency is set to 2.45 GHz, the output power is 1~2 kW, and continuous pulse annealing is performed for 3~6 s.
[0067] Cooling and unloading: After annealing, stop microwave radiation and allow the sample to cool naturally to room temperature in the cavity before removing the sample.
[0068] Performance test results:
[0069] Microstructure: Observation of the microstructure of the sample cross-section revealed no significant change in ceramic grain size before and after annealing, a significant reduction in intergranular micropores, and no abnormal grain growth. Figure 3 As shown;
[0070] Oxygen vacancy concentration: The relative oxygen vacancy content was 15.38% before annealing, and decreased to 13.28% after microwave annealing at 1.5kW / 6s.
[0071] Dielectric properties: In the microwave band (approximately 7.4 GHz), the quality factor Q×f increased from 62958 GHz to 87312 GHz, an improvement of 38.7%; in the terahertz band (approximately 0.8 THz), the dielectric loss decreased from 0.017 to 0.01, a reduction of 41.2%, and the quality factor Q×f increased from 47350 GHz to 79016 GHz. Figure 2 As shown.
[0072] Example 2
[0073] This embodiment provides a method for rapidly annealing BaZnP2O7 ceramics using high-power microwaves, the steps of which are as follows:
[0074] Sample pretreatment: BaZnP2O7 ceramic green bodies were prepared by solid-state reaction method and sintered in air at 825 °C for 4 h to obtain densified BaZnP2O7 ceramic blocks with thicknesses of approximately 0.6 mm and 6 mm. The blocks were ultrasonically cleaned with anhydrous ethanol for 10 min and then dried in a drying oven at 60 °C for 2 h for later use.
[0075] Microwave annealing: The dried ceramic block is placed in the sample chamber of a high-power microwave annealing system under atmospheric conditions. The microwave frequency is set to 2.45 GHz, the output power is 1~1.5 kW, and continuous pulse annealing is performed for 2~4 s.
[0076] Cooling and unloading: After annealing, microwave radiation is stopped, and the sample is allowed to cool naturally to room temperature in the cavity before being removed to complete the defect repair.
[0077] Performance test results:
[0078] Microstructure: The ceramic grain size did not change significantly before and after annealing, the grain boundary gaps were significantly reduced, the density was increased, and no P or Zn components volatilized.
[0079] Dielectric properties: In the 0.68 THz terahertz band, the quality factor Q×f improved from 70195 GHz to 81324 GHz, an increase of 15.9%, while dielectric loss was significantly reduced, such as... Figure 4 As shown.
[0080] Example 3
[0081] This embodiment provides a method for repairing defects in K20 ceramics using high-power microwave transient annealing, the steps of which are as follows:
[0082] Sample pretreatment: Commercially standardized K20 ceramic powder was sintered in air at 1300 °C for 4 h to obtain fully densified K20 ceramic blocks with a thickness of about 0.6 mm. The blocks were ultrasonically cleaned with anhydrous ethanol for 10 min and dried at 60 °C for 2 h for later use.
[0083] High-power microwave annealing: The dried ceramic block is placed in the sample chamber of the high-power microwave annealing system under atmospheric conditions. The microwave frequency is set to 2.45 GHz, the output power is 1.5 kW, and the continuous pulse annealing is performed for 6 s.
[0084] Cooling and unloading: After annealing, microwave radiation is stopped, and the sample is allowed to cool naturally to room temperature in the cavity before being removed to complete the defect repair.
[0085] Performance test results:
[0086] Microstructure: The size of ceramic grains did not change significantly before and after annealing, but grain boundary pores were largely eliminated, resulting in a significant increase in density.
[0087] Oxygen vacancy concentration: The relative content of oxygen vacancy before annealing was 23.98%, which decreased to 22.65% after annealing;
[0088] Dielectric properties: In the 0.7 THz terahertz band, the dielectric loss decreased from 0.013 to 0.0075, a reduction of 42.3%, the quality factor Q×f increased from 53350 GHz to 110840 GHz, an increase of 107.8%, and the dielectric constant steadily increased by about 2%.
[0089] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A method for rapidly annealing molded dielectric ceramics using microwaves, characterized in that, Includes the following steps: (1) Sample pretreatment: The sintered and dense molded dielectric ceramic block is cleaned and dried; (2) Microwave annealing: The treated molded dielectric ceramic block is placed in the sample cavity of the microwave annealing system. Under atmospheric conditions, the ceramic block is subjected to continuous pulse annealing treatment for 1 to 10 seconds using microwaves of 2.45 GHz ± 50 MHz and an output power of 0.5 to 2 kW. (3) Cooling and unloading: After the annealing is completed, microwave radiation is stopped, and the ceramic block is naturally cooled to room temperature along with the sample chamber. The ceramic sample processing is completed when it is taken out.
2. The method for forming dielectric ceramics using microwave rapid annealing according to claim 1, characterized in that, The core of this method is to achieve rapid defect repair through the synergistic effect of two unique microwave effects: ① Transient heating effect: High-power microwaves of 0.5~2 kW directly couple with polar groups inside the ceramic, achieving synchronous and uniform heating inside and outside the ceramic. It provides sufficient heat within seconds to dissolve micropores and microcracks between grains inside the ceramic and repair non-intrinsic defects. At the same time, the processing time of 1~10 s completely avoids grain growth and volatilization of low-melting-point components. ② Strong electromagnetic field vector effect: The strong electric field of high-power microwaves can directly act on charged point defects inside ceramic crystals, reduce the activation energy of defect migration, drive point defect migration and accelerate recombination, reduce the intrinsic defect concentration, and at the same time, for distributed segregated ions, the strong electric field also accelerates their migration, realizes the homogenization of ion distribution, and suppresses the polarization loss of ions in microwave, millimeter wave and terahertz frequency bands.
3. The method for forming dielectric ceramics using microwave rapid annealing according to claim 1, characterized in that, The annealing system comprises a sample cavity, a rectangular waveguide, a microwave input port, and a cooling system. Microwaves are input from the left microwave input port and transmitted to the sample cavity via the rectangular waveguide. The sample cavity has an openable and closable cover plate on its upper surface, and the molded dielectric ceramic block to be processed is placed horizontally inside the sample cavity. The cooling system is installed on the far right of the system and is directly connected to the waveguide cavity. Air cooling is used to achieve system heat dissipation and ensure continuous operation. The system is compatible with the 2.45 GHz industrial microwave band. The sample cavity is located at the position of the maximum field strength at 1 / 4 wavelength of the rectangular waveguide. The system is compatible with 0.5~2 kW high-power pulsed microwaves and molded dielectric ceramic blocks with a thickness of 0.5~10 mm, and operates entirely in an atmospheric environment.
4. The method for forming dielectric ceramics using microwave rapid annealing according to claim 1, characterized in that, In step (1), the formed dielectric ceramic block is any one of MgTa2O6 ceramic, BaZnP2O7 ceramic, and microwave dielectric ceramic k20 with a dielectric constant of 20, and the thickness of the ceramic block is 0.5~10 mm.
5. The method for forming dielectric ceramics using microwave rapid annealing according to claim 4, characterized in that, When the shaped dielectric ceramic block is MgTa2O6 ceramic, in step (2), the microwave output power is 1~2 kW and the annealing time is 3~6 s.
6. The method for forming dielectric ceramics using microwave rapid annealing according to claim 4, characterized in that, When the molded dielectric ceramic block is BaZnP2O7 ceramic, in step (2), the microwave output power is 1~2 kW and the annealing time is 2~4 s.
7. The method for forming dielectric ceramics using microwave rapid annealing according to claim 4, characterized in that, When the molded dielectric ceramic block is a K20 microwave dielectric ceramic, in step (2), the microwave output power is 1~2 kW and the annealing time is 3~6 s.
8. The method for forming dielectric ceramics using microwave rapid annealing according to claim 1, characterized in that, In step (2), the annealing process is carried out without an inert or reducing protective atmosphere, without programmed heating or holding stages, and the annealing process is completed by a single microwave pulse. And / or in step (1), the cleaning and drying process specifically involves: ultrasonically cleaning the ceramic block with anhydrous ethanol, and then drying it in a 60 °C forced-air drying oven for 2 h.
9. The method for forming dielectric ceramics using microwave rapid annealing according to claim 1, characterized in that, Compared with the untreated state, the dielectric loss of dielectric ceramics in the terahertz band is reduced by 30% to 100%, and the quality factor Q×f in the microwave band is improved by 30% to 60%.
10. The method for forming dielectric ceramics using microwave rapid annealing according to claim 1, characterized in that, Step (1) Sample pretreatment is as follows: MgTa2O6 ceramic green bodies were prepared by solid-state reaction method and sintered at 1400 °C for 4 h to obtain densified MgTa2O6 ceramic blocks with thicknesses of 0.6 mm and 6 mm. The blocks were ultrasonically cleaned with anhydrous ethanol for 10 min and then dried in a drying oven at 60 °C for 2 h for later use. Alternatively, a solid-state reaction method can be used to prepare BaZnP2O7 ceramic green bodies, which are then sintered in air at 825 °C for 4 h to obtain densified BaZnP2O7 ceramic blocks with thicknesses of 0.6 mm and 6 mm. These blocks are ultrasonically cleaned with anhydrous ethanol for 10 min and then dried in a drying oven at 60 °C for 2 h for later use. Alternatively, microwave dielectric ceramic K20 with a dielectric constant of 20 can be used. After sintering in air at 1300 °C for 4 h, a fully densified K20 ceramic block with a thickness of 0.6 mm is obtained. This block is then ultrasonically cleaned with anhydrous ethanol for 10 min and dried at 60 °C for 2 h for later use.