An ultralow dielectric low-temperature silicon aluminum lithium microwave dielectric ceramic material, a preparation method and application thereof
By utilizing the chemical composition of LiBxAl1-xSiO4 and the cold isostatic pressing process, the high-temperature sintering problem of low dielectric constant microwave dielectric ceramic materials was solved, and low-temperature co-fired ceramic materials were prepared. These materials were then applied to microwave devices such as dielectric antennas, microwave substrates, and dielectric resonators, achieving the preparation of microwave dielectric ceramic materials with low dielectric constant and high quality factor.
Patent Information
- Application Number
- CN202410420431.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-09
- Publication Date
- 2025-11-11
- Estimated Expiration
- 2044-04-09
AI Technical Summary
There is a contradiction between the high sintering temperature of existing low dielectric constant microwave dielectric ceramic materials and low cost and low pollution materials. In addition, existing low melting point compounds are prone to moisture absorption and volatilization during the preparation process, which leads to a decrease in dielectric properties and makes it difficult to obtain high-performance ultra-low dielectric low temperature microwave dielectric ceramic materials.
Microwave dielectric ceramic material with the chemical composition of LiBxAl1-xSiO4 was used. Through pre-sintering, cold isostatic pressing and solid-state reaction processes, combined with lithium metaborate (LiBO2) as the boron source, the stoichiometric ratio was controlled, the sintering temperature was reduced and the dielectric properties were improved. Cold isostatic pressing was used instead of granulation to prevent sample contamination.
Lithium aluminum silicate microwave dielectric ceramics with low dielectric constant, low densification temperature and excellent microwave dielectric properties were prepared. They are suitable for low temperature co-fired ceramic technology and can be used in microwave devices such as dielectric antennas, microwave substrates and dielectric resonators. They have good chemical compatibility and low temperature co-fired characteristics.
Smart Images
Figure CN118373675B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ceramic materials technology, and in particular to an ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material, its preparation method, and its application. Background Technology
[0002] Microwave dielectric ceramics (MWDC) are materials that transmit electromagnetic waves in the frequency range of 300MHz to 300GHz and wavelengths between 1m and 0.1mm. Due to their good directionality, strong penetration, and large information capacity, microwave communication systems have become a hot area in modern communication technology development. Currently, the development of advanced wireless communication technologies, represented by 5G, places higher and newer demands on microwave dielectric ceramics, such as lower dielectric constants (ε). r High quality factor (Q×f) and near-zero temperature coefficient of resonant frequency (τ) f ).
[0003] In recent years, with the rapid development of microwave communication technology, a large number of microwave components have been miniaturized, leading to significant advancements in their research. Research has focused on low-dielectric-loss materials. From the perspective of microwave component design, a high quality factor ensures good frequency selectivity of microwave dielectric materials, while a near-zero resonant frequency temperature coefficient guarantees temperature stability. Simultaneously, the use of low-cost, low-pollution materials is a development trend for microwave dielectric ceramics. Furthermore, higher frequencies are also a direction for microwave device development, inevitably pushing the operating frequencies of communication equipment towards millimeter waves, which will highlight the issues of signal delay and signal strength. Therefore, compared to microwave dielectric ceramics with medium to high dielectric constants, low-dielectric-constant microwave dielectric ceramics demonstrate their advantages. Low-dielectric-constant microwave dielectric ceramics can accelerate signal transmission rates and reduce the interactive coupling loss between the substrate and metal electrodes. For microwave components, miniaturization can be achieved through high dielectric constant and LTCC technology. However, the significant increase in operating frequencies will drastically reduce the size of resonant components; therefore, component miniaturization is a natural consequence of millimeter-wave communication. If ε... r High-performance microwave dielectric ceramics present new challenges, such as the difficulty in precisely fabricating resonant components due to their small size. Therefore, ε-coated resonant ceramics are required. r Lower microwave dielectric ceramics.
[0004] Low-Temperature Co-fired Ceramics (LTCC) is a novel material technology developed by Hughes Aircraft Company in 1982. It is used to achieve highly integrated, high-performance electronic packaging, offering significant potential in design flexibility, wiring density, and reliability. Materials used in LTCC should meet the following conditions: 1. A dielectric constant (ε) that meets the requirements. r1. ≤20); 2. High quality factor or low dielectric loss (Q×f>10000GHz); 3. Sintering temperature lower than the electrode melting point (Al melting point is 660℃, Ag melting point is 961℃, Cu melting point is 1084℃); 4. The ceramic material needs to be able to avoid interfacial reaction with the electrode material, and the two should have a high degree of matching in sintering shrinkage. However, the sintering temperatures of currently commercially available microwave dielectric materials are generally higher than the melting points of internal electrode materials such as Ag, Al, and Cu. In general, as low dielectric constant microwave dielectric ceramics gradually develop, the contradiction between high performance and low sintering temperature is a key issue to be resolved. Therefore, how to select suitable low-temperature sintering aids and develop low dielectric constant microwave dielectric ceramic material systems with inherently low sintering temperatures and excellent microwave dielectric properties remains the focus of current research.
[0005] In the microwave or millimeter-wave region, ionic polarizability dominates the contribution of dielectric materials. Therefore, components with low ionic polarizability constitute a large proportion in low-dielectric systems (such as borates, germanates, and silicates). Silicate systems have a tetrahedral [SiO4] framework structure, in which ionic bonds account for 45% and covalent bonds for 55%. Strong Si-O covalent bonds can give the material a low dielectric constant. LiAlSiO4 is a hexagonal crystal structure with space group P6422. Its characteristic feature is a multidimensional layered structure composed of interconnected [AlO4], [SiO4], and [LiO4] tetrahedra, with each layer consisting of alternating [SiO4] / [LiO4] and [AlO4] / [LiO4] tetrahedra. However, the covalent nature of the Al-O and Si-O bonds in LiAlSiO4 leads to a high sintering temperature. Introducing low-melting-point compounds can effectively lower the sintering temperature, but existing low-melting-point compounds are highly hygroscopic and volatile. During the weighing process, they rapidly absorb water, causing the precursor to deviate from stoichiometry or volatilize during sintering, thus failing to obtain the target compound. Furthermore, while existing low-melting-point compounds can effectively lower the sintering temperature, they also lead to a decrease in the dielectric properties of microwave dielectric ceramic materials. Therefore, how to obtain an ultra-low dielectric temperature microwave dielectric ceramic material remains a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention
[0006] The purpose of this invention is to provide an ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material, its preparation method and application, so as to solve the problems existing in the prior art.
[0007] To achieve the above objectives, the present invention provides the following solution:
[0008] One of the technical solutions of this invention: an ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material, with the general chemical formula: LiB x Al 1-x SiO4;
[0009] Where 0.02≤x≤0.1, x represents the molar quantity.
[0010] The second technical solution of the present invention: a method for preparing the above-mentioned ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material, comprising the following steps:
[0011] The raw materials Li2CO3, LiBO2, Al2O3 and SiO2 are mixed evenly by molar amount and pre-fired. Then, they are successively pressed, vacuum treated, cold isostatic pressed and sintered to obtain the ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material.
[0012] Furthermore, the preheating rate is 5°C / min, the temperature is 800–1000°C, and the time is 4–8 hours.
[0013] The parent material LiAlSiO4 can be obtained by pre-firing.
[0014] Furthermore, the pressure for the pressing process is 1 MPa.
[0015] Compression molding is a process that uses low pressure to initially form a green body from a powder sample.
[0016] Furthermore, the vacuum treatment specifically includes: placing the green blank obtained after pressing and molding into a rubber sleeve, venting the air from the rubber sleeve, and sealing it.
[0017] Furthermore, the pressure of the cold isostatic pressing is 250 MPa; the pressure medium used in the cold isostatic pressing is an oil medium.
[0018] Vacuum treatment can isolate the green body from the oil medium during subsequent processing, preventing sample contamination.
[0019] Cold isostatic pressing can make the green body denser, which can better promote sintering and densification.
[0020] Furthermore, the sintering heating rate is 5℃ / min, the temperature is 875~1100℃, and the time is 4~8h.
[0021] This invention uses lithium metaborate (LiBO2) as the boron source and utilizes B... 3+ Replace Al 3+ It can precisely control the stoichiometry and improve the stoichiometry loss caused by water absorption of B2O3 or H3BO3, thereby obtaining high-purity LiB. x Al 1-x SiO4 ceramics. Simultaneously, it can effectively reduce the sintering temperature of LiAlSiO4 ceramics by 200–475℃, and B 3+ Extremely low polarizability This allows the dielectric constant of LiAlSiO4 ceramics to be the lowest among current crystalline ceramics.
[0022] Furthermore, the preparation method of the ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material also includes the steps of wet ball milling (first ball milling) and drying before pre-firing; and the steps of wet ball milling (second ball milling) and drying after pre-firing and before pressing.
[0023] During the wet ball milling process, the mass ratio of raw materials, milling media, and milling aids is 1:2:2.
[0024] Furthermore, the milling media includes zirconia balls;
[0025] The ball milling aid includes water;
[0026] The wet ball milling process is carried out at a speed of 350 r / min for 6–8 h.
[0027] The drying process is carried out at a temperature of 120°C for 1 to 2 hours.
[0028] Furthermore, the purity of Li2CO3, LiBO2, and Al2O3 is 99.99%; the purity of SiO2 is 99%.
[0029] Furthermore, the Li2CO3 is calcined and dried before being weighed in molar amounts; the calcination temperature is 500°C and the time is 2 hours; the drying temperature is 60°C.
[0030] Because Li2CO3 absorbs moisture, it needs to be calcined.
[0031] Furthermore, the zirconia spheres are composed of zirconia spheres with a diameter of 1 mm, zirconia spheres with a diameter of 5 mm, and zirconia spheres with a diameter of 7 mm, in a mass ratio of 3:5:2.
[0032] The first ball milling process is to ensure uniform mixing of the raw materials, while the second ball milling process is to refine the powder of the pre-calcined, agglomerated sample. Using zirconia balls of different diameters allows for more thorough grinding of the agglomerated sample. The drying process is to evaporate the water mixed during ball milling, resulting in a dry sample.
[0033] This invention obtains high-performance microwave dielectric ceramics by combining cold isostatic pressing with solid-state reaction. Solid-state reaction refers to the process of weighing material, primary ball milling, pre-firing, secondary ball milling, PVA addition granulation, pressing, debinding, and sintering. However, because the sample reacts with PVA, cold isostatic pressing (pre-pressing, vacuum treatment, and cold isostatic pressing) is used instead of granulation.
[0034] The third technical solution of the present invention: the application of the above-mentioned ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic material in the fabrication of dielectric antennas, microwave substrates, and dielectric resonators.
[0035] The present invention discloses the following technical effects:
[0036] (1) The ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic material of the present invention has a low dielectric constant, a high quality factor and a considerable temperature coefficient of resonant frequency, and has the potential to be widely used in the manufacture of microwave devices such as dielectric antennas, microwave substrates and dielectric resonators for high-speed signal transmission.
[0037] (2) The metaboric acid (LiBO2) used in this invention can give the prepared ceramic material a low densification temperature of 875-1100℃ and an ultra-low density (2.3 g / cm³). 3 And excellent microwave dielectric properties (ultra-low dielectric constant ε) r =3.34~3.73, high quality factor Q×f=25770~27550GHz and low temperature coefficient of resonant frequency τ f = -22.9 to -16.5 ppm / ℃).
[0038] (3) The ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic material (LiB) of the present invention 0.1 Al 0.9 SiO4 has good chemical compatibility with silver electrodes and has the potential to be applied in low-temperature co-fired ceramics technology.
[0039] (4) The applications of microwave dielectric ceramics in microwave communication are mainly divided into two categories: components based on the principle of microwave dielectric resonators (including dielectric resonators, filters, duplexers, dielectric antennas, etc.) and microwave substrates used for transmitting electromagnetic waves. For the former, the ε of microwave dielectric ceramics... r Q×f and τ f These factors determine the size, frequency selectivity, and temperature stability of the center frequency of the resonant components. For microwave substrates, these correspond to phase delay, attenuation, and the change of phase delay with temperature during microwave transmission. LiB x Al 1-x ε of SiO4 ceramics r Q×f and τ f Both of their performance characteristics are well-suited for applications in microwave communications. Attached Figure Description
[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0041] Figure 1 LiB prepared in Example 1 of this invention 0.02 Al 0.98 XRD and SEM images of SiO4 ceramics, where a is the XRD image and b is the SEM image;
[0042] Figure 2 LiB prepared in Example 2 of this invention 0.04 Al 0.96 XRD and SEM images of SiO4 ceramics, where a is the XRD image and b is the SEM image;
[0043] Figure 3 LiB prepared in Example 3 of this invention 0.05 Al 0.95 XRD and SEM images of SiO4 ceramics, where a is the XRD image and b is the SEM image;
[0044] Figure 4 LiB prepared in Example 4 of this invention 0.06 Al 0.94 XRD and SEM images of SiO4 ceramics, where a is the XRD image and b is the SEM image;
[0045] Figure 5 LiB prepared in Example 5 of this invention 0.08 Al 0.92 XRD and SEM images of SiO4 ceramics, where a is the XRD image and b is the SEM image;
[0046] Figure 6 LiB prepared in Examples 6 and 7 of this invention 0.1 Al 0.9 XRD and SEM images of SiO4 ceramics, where a represents LiB prepared in Example 6. 0.1 Al 0.9 XRD pattern of SiO4 ceramic, b is LiB prepared in Example 6. 0.1 Al 0.9 SEM images of SiO4 ceramics, c is the XRD pattern of Example 7 co-fired with silver, and d is the EDS distribution diagram of Example 7 co-fired with silver.
[0047] Figure 7The image shows the XRD pattern of the LiAlSiO4 ceramic prepared in Comparative Example 1 of this invention.
[0048] Figure 8 LiB prepared as Comparative Example 2 of this invention 0.15 Al 0.85 XRD pattern of SiO4 ceramics;
[0049] Figure 9 LiB prepared as Comparative Example 3 of this invention 0.2 Al 0.8 XRD pattern of SiO4 ceramic. Detailed Implementation
[0050] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.
[0051] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.
[0052] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.
[0053] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.
[0054] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.
[0055] In the following embodiments or comparative examples of the present invention, the Li2CO3 used was subjected to calcination and drying treatment. The calcination temperature was 500°C and the time was 2 hours; the drying temperature was 60°C.
[0056] The zirconia spheres used in the following embodiments or comparative examples of the present invention are composed of zirconia spheres with a diameter of 1 mm, zirconia spheres with a diameter of 5 mm, and zirconia spheres with a diameter of 7 mm, in a mass ratio of 3:5:2.
[0057] Example 1
[0058] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0059] (1) According to LiB 0.02 Al 0.98 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0060] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 1000°C at a heating rate of 5°C / min. It is then pre-calcined at 1000°C for 4 hours to obtain pre-calcined powder.
[0061] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0062] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, cold isostatic pressing is performed at 250 MPa (time 15 min) using vacuum pump oil as the pressure medium. After removing the rubber sleeve, the cylindrical green bodies are sintered at 1100℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.02 Al 0.98 SiO4 ceramics).
[0063] The LiB prepared in this embodiment 0.02 Al 0.98XRD and SEM images of SiO4 ceramics are shown below. Figure 1 , Figure 1 In the image, a is the XRD pattern and b is the SEM pattern.
[0064] from Figure 1 As can be seen from the results, the LiB prepared in this embodiment was calibrated using LiAlSiO4 (#01-073-0252). 0.02 Al 0.98 The X-ray diffraction peaks of SiO4 ceramics sintered at 1100℃ showed no second phase, indicating that a single phase can be formed at this temperature, which also proves that B 3+ Entering the LiAlSiO4 lattice (XRD synthesis of pure phase and peak shift to the right can prove B) 3+ (Entering the crystal lattice). Combined with SEM images, it can be found that when the doping amount is 0.02 mol (accounting for 2 mol% of the total B and Al) and the sintering temperature is 1100℃, the ceramic grain size is relatively large, the grain boundaries are obvious, and the result is relatively dense.
[0065] Example 2
[0066] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0067] (1) According to LiB 0.04 Al 0.96 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0068] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 1000°C at a heating rate of 5°C / min. It is then pre-calcined at 1000°C for 4 hours to obtain pre-calcined powder.
[0069] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0070] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 1075℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.04 Al 0.96 SiO4 ceramics).
[0071] The LiB prepared in this embodiment 0.04 Al 0.96 XRD and SEM images of SiO4 ceramics are shown below. Figure 2 , Figure 2 In the image, a is the XRD pattern and b is the SEM pattern.
[0072] from Figure 2 As can be seen from B 3+ When the doping concentration is 0.04 mol (4 mol% of the total B and Al), no impurity phase is observed in its X-ray diffraction peaks, which matches the standard card of LiAlSiO4 (#01-073-0252). The microstructure (SEM image) shows no pores and distinct grain boundaries, exhibiting a dense state.
[0073] Example 3
[0074] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0075] (1) According to LiB 0.05 Al 0.95 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0076] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 900°C at a heating rate of 5°C / min. It is then pre-calcined at 900°C for 4 hours to obtain pre-calcined powder.
[0077] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0078] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 975℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.05 Al 0.95 SiO4 ceramics).
[0079] The LiB prepared in this embodiment 0.05 Al 0.95 XRD and SEM images of SiO4 ceramics are shown below. Figure 3 , Figure 3 In the image, a is the XRD pattern and b is the SEM pattern.
[0080] from Figure 3 As can be seen from B 3+ When the doping concentration is 0.05 mol (5 mol% of the total B and Al), its X-ray diffraction peaks perfectly match the standard card of LiAlSiO4 (#01-073-0252). Combined with SEM images, it can be observed that the grains are uniform, with clear grain boundaries and no pores.
[0081] Example 4
[0082] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0083] (1) According to LiB 0.06 Al 0.94 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0084] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 900°C at a heating rate of 5°C / min. It is then pre-calcined at 900°C for 4 hours to obtain pre-calcined powder.
[0085] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0086] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 950℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.06 Al 0.94 SiO4 ceramics).
[0087] The LiB prepared in this embodiment 0.06 Al 0.94 XRD and SEM images of SiO4 ceramics are shown below. Figure 4 , Figure 4 In the image, a is the XRD pattern and b is the SEM pattern.
[0088] from Figure 4 As can be seen from B 3+ When the doping concentration is 0.06 mol (6 mol% of the total B and Al), its X-ray diffraction peak energy matches the standard card of LiAlSiO4 (#01-073-0252), and no second phase is formed. The table shows that when the doping concentration is 0.06 mol, B... 3 + It can enter the crystal lattice, thereby lowering the sintering temperature. At the same time, combined with SEM images, it can be seen that grain growth is inhibited, resulting in a reduction in grain size.
[0089] Example 5
[0090] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0091] (1) According to LiB 0.08 Al 0.92The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0092] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 800°C at a heating rate of 5°C / min. It is then pre-calcined at 800°C for 4 hours to obtain pre-calcined powder.
[0093] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0094] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 925℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.08 Al 0.92 SiO4 ceramics).
[0095] The LiB prepared in this embodiment 0.08 Al 0.92 XRD and SEM images of SiO4 ceramics are shown below. Figure 5 , Figure 5 In the image, a is the XRD pattern and b is the SEM pattern.
[0096] from Figure 5 As can be seen from the above, the LiB prepared by sintering at 925℃ in this embodiment... 0.08 Al 0.92 The diffraction peak energies of SiO4 ceramics correspond perfectly to those of LiAlSiO4 (#01-073-0252), and no second phase is observed. Combined with SEM images, it can be seen that the grain size continues to decrease, and the sintering temperature further decreases.
[0097] Example 6
[0098] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0099] (1) According to LiB 0.1 Al 0.9 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0100] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 800°C at a heating rate of 5°C / min. It is then pre-calcined at 800°C for 4 hours to obtain pre-calcined powder.
[0101] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0102] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 875℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.1 Al 0.9 SiO4 ceramics).
[0103] Example 7
[0104] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0105] (1) According to LiB 0.1 Al 0.9The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0106] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 800°C at a heating rate of 5°C / min. It is then pre-calcined at 800°C for 4 hours to obtain pre-calcined powder.
[0107] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0108] (4) Take a small amount of the dried pre-calcined powder prepared in step (3) and mix it thoroughly with 20 wt.% Ag powder (the amount of Ag powder is 20% of the mass of the pre-calcined powder) to obtain mixed powder.
[0109] (5) The mixed powder prepared in step (4) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 875℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.1 Al 0.9 SiO4 ceramics).
[0110] LiB prepared in Examples 6 and 7 0.1 Al 0.9 XRD and SEM images of SiO4 ceramics are shown below. Figure 6 , Figure 6 In the text, 'a' represents the LiB prepared in Example 6. 0.1 Al 0.9 XRD pattern of SiO4 ceramic, b is LiB prepared in Example 6. 0.1 Al 0.9 SEM images of SiO4 ceramics, c is the XRD pattern of Example 7 co-fired with silver, and d is the SEM image and EDS distribution map of Ag element of Example 7 co-fired with silver.
[0111] from Figure 6 As can be seen from the data, the LiB prepared by sintering at 875°C in Example 6... 0.1 Al 0.9 The diffraction peaks of the SiO4 ceramic correspond perfectly to those of LiAlSiO4 (#01-073-0252), and no second phase is observed. Combined with SEM images, it can be seen that the grain size is minimized, and the sintering temperature is reduced to 875℃. The XRD pattern of the co-fired SiO4 ceramic with silver shows LiAlSiO4 as the main phase and Ag as the second phase, with no shift in the main peak. This indicates good chemical compatibility between the two. Clear grain boundaries between LiAlSiO4 and Ag are observed in the SEM and EDS spectra of the co-fired SiO4 ceramic with silver, further confirming the good chemical compatibility between the SiO4 ceramic and the Ag electrode.
[0112] Comparative Example 1
[0113] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0114] (1) Weigh Al2O3 (purity 99.99%), Li2CO3 (purity 99.99%) and SiO2 (purity 99%) according to the stoichiometric ratio (molar ratio) of LiAlSiO4, accurate to 0.0001g, and mix them to obtain a raw material mixture; put the raw material mixture, zirconia balls and deionized water into a nylon can at a mass ratio of 1:2:2, and ball mill at 350r / min for 6h, and dry at 120℃ for 2h to obtain a ball-milled mixture.
[0115] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 1100°C at a heating rate of 5°C / min. It is then pre-calcined at 1100°C for 4 hours to obtain pre-calcined powder.
[0116] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0117] (4) The dried pre-calcined powder prepared in step (3) is pressed into a cylindrical green body (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump and sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 1350℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiAlSiO4 ceramic).
[0118] XRD tests were performed on the LiAlSiO4 ceramics prepared in this comparative example, and the results are shown in the figure. Figure 7 .
[0119] from Figure 7 As can be seen, the diffraction peaks of the LiAlSiO4 ceramic prepared at 1350℃ in this comparative example correspond one-to-one with the standard card (#01-073-0252), and no second phase is generated, indicating that the sample is pure LiAlSiO4 at this time, but its sintering temperature is relatively high.
[0120] Comparative Example 2
[0121] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0122] (1) According to LiB 0.15 Al 0.85 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, zirconia balls, and deionized water were loaded into a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, and then dried at 120℃ for 2h to obtain a ball-milled mixture.
[0123] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 750°C at a heating rate of 5°C / min. It is then pre-calcined at 750°C for 4 hours to obtain pre-calcined powder.
[0124] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0125] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 825℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.15 Al 0.85 SiO4 ceramics).
[0126] The LiB prepared in this comparative example 0.15 Al 0.85 XRD tests were performed on SiO4 ceramics, and the results are shown below. Figure 8 .
[0127] from Figure 8 As can be seen from the data, the LiB prepared in this comparative example at 825℃... 0.15 Al 0.85 Comparison of the diffraction peaks of SiO4 ceramics with the standard card revealed the presence of a second phase in the sample, indicating the addition of B. 3+ A single phase could not be synthesized when the doping amount was 0.15 mol (15 mol% of the total B and Al). The presence of a second phase would deteriorate the dielectric properties of the prepared ceramics, especially the decrease in the quality factor, as shown in Table 1.
[0128] Comparative Example 3
[0129] A method for preparing ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material:
[0130] (1) According to LiB 0.2 Al 0.8 The stoichiometric ratio (molar ratio) of SiO4 was determined by weighing LiBO2 (99.99% purity), Al2O3 (99.99% purity), Li2CO3 (99.99% purity), and SiO2 (99% purity), accurate to 0.0001g, and mixing them to obtain a raw material mixture. The raw material mixture, along with zirconia balls and deionized water, was placed in a nylon container at a mass ratio of 1:2:2 and ball-milled thoroughly at 350r / min for 6h, followed by drying at 120℃ for 2h to obtain the ball-milled mixture.
[0131] (2) The ball milling mixture prepared in step (1) is placed in an alumina crucible and heated to 700°C at a heating rate of 5°C / min. It is then pre-calcined at 700°C for 4 hours to obtain pre-calcined powder.
[0132] (3) Add the pre-calcined powder, zirconia balls and deionized water to a nylon tank in a mass ratio of 1:2:2, and ball mill at 350 r / min for 6 h. Then dry at 120 °C for 2 h to obtain the dried pre-calcined powder.
[0133] (4) The dried pre-calcined powder prepared in step (3) is pressed into cylindrical green bodies (10 mm in diameter and 6-7 mm in height) using a powder press (pressure 1 MPa). The cylindrical green bodies are then neatly arranged and placed in a rubber sleeve. The air in the rubber sleeve is expelled using a vacuum pump, and the sleeve is sealed with a plastic rope. Then, using vacuum pump oil as the pressure medium, cold isostatic pressing is performed at 250 MPa (time 15 min). The cylindrical green bodies are then sintered at 800℃ for 4 h (heating rate 5℃ / min) to obtain ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material (LiB). 0.2 Al 0.8 SiO4 ceramics).
[0134] The LiB prepared in this comparative example 0.2 Al 0.8 XRD tests were performed on SiO4 ceramics, and the results are shown below. Figure 9 .
[0135] from Figure 9 As can be seen from this, the LiB prepared in this comparative example... 0.2 Al 0.8 Comparison of the diffraction peaks of SiO4 ceramics with the standard card revealed the presence of a second phase in the sample, indicating the addition of B. 3+ A single phase could not be synthesized when the doping amount was 0.2 mol (20 mol% of the total B and Al). The presence of a second phase would deteriorate the dielectric properties of the prepared ceramics, especially the quality factor, as shown in Table 1.
[0136] Example 1
[0137] The density, sintering temperature, and microwave dielectric properties of the ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic materials prepared in Examples 1-6 and Comparative Examples 1-3 were measured (evaluation of microwave dielectric properties was performed using the resonant cavity method). The results are shown in Table 1.
[0138] Table 1 Performance of Ultra-Low Dielectric Lithium Aluminosilicate Microwave Dielectric Ceramic Materials
[0139]
[0140]
[0141] As can be seen from Table 1, the density of the ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic material prepared in the embodiments of the present invention is 2.271–2.304 g / cm³. 3 dielectric constant ε r The frequency response time is 3.34–3.73, the quality factor Q×f is 25770–27550 GHz, and the temperature coefficient of resonant frequency τ is [not specified]. fThe dielectric constant is -22.9 to -16.5 ppm / ℃. As can be seen from the above data, the ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic prepared by this invention possesses excellent microwave dielectric properties. Therefore, it can be widely used in the manufacture of microwave communication components such as dielectric antennas, microwave substrates, and dielectric resonators, meeting the technical needs of mobile communication and satellite communication systems.
[0142] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims
1. A method for preparing an ultra-low dielectric low-temperature lithium aluminum silicate microwave dielectric ceramic material, characterized in that, Includes the following steps: The raw materials Li2CO3, LiBO2, Al2O3 and SiO2 are mixed evenly by molar amount and pre-fired. Then, they are successively pressed, vacuum treated, cold isostatic pressed and sintered to obtain the ultra-low dielectric low temperature lithium aluminum silicate microwave dielectric ceramic material. The general chemical formula of the ultra-low dielectric lithium aluminum silicate microwave dielectric ceramic material is: LiB x Al 1-x SiO4; where 0.02≤x≤0.1, and x represents the molar amount.
2. The preparation method according to claim 1, characterized in that, The preheating rate is 5℃ / min, the temperature is 800~1000℃, and the time is 4~8h.
3. The preparation method according to claim 1, characterized in that, The pressing pressure is 1 MPa.
4. The preparation method according to claim 1, characterized in that, The vacuum treatment specifically includes: placing the green blank obtained after pressing and molding into a rubber sleeve, venting the air from the rubber sleeve, and sealing it.
5. The preparation method according to claim 1, characterized in that, The pressure of the cold isostatic pressing is 250 MPa.
6. The preparation method according to claim 1, characterized in that, The sintering process involves a heating rate of 5°C / min, a temperature of 875~1100°C, and a time of 4~8 hours.
7. The preparation method according to claim 1, characterized in that, It also includes the steps of wet ball milling and drying before pre-firing; and the steps of wet ball milling and drying after pre-firing and before pressing. During the wet ball milling process, the mass ratio of raw materials, milling media, and milling aids is 1:2:
2.
8. The preparation method according to claim 7, characterized in that, The ball milling media include zirconium oxide balls; The ball milling aid includes water; The wet ball milling process is carried out at a speed of 350 r / min for 6 to 8 hours. The drying process is carried out at a temperature of 120°C for 1 to 2 hours.