Dielectric ceramic material and preparation method therefor

Abstract

The present invention relates to the field of ceramic preparation. A dielectric ceramic material and a preparation method therefor. The preparation method comprises the following steps: S1, preparing an Mg2Al4(Si1-xGex)5O18 powder, where 0＜x≤0.5; and S2, preparing a suspension liquid containing a titanium oxide, adding the suspension liquid containing a titanium oxide and / or a titanium oxide powder into the powder prepared in step S1, and sintering same to obtain a dielectric ceramic material. The method of using germanium to partially replace silicon in traditional cordierite and adding the suspension liquid containing a titanium oxide and / or a titanium oxide powder realizes the targets of a high Qf and a TCF value approximating to zero to a great extent.

Description

Dielectric ceramic material and preparation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 13, 2023, with application number 202311511148.7 and invention name “A dielectric ceramic material and preparation method”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of ceramic preparation, and in particular to a dielectric ceramic material and a preparation method thereof. Background Art

[0004] Cordierite (Mg2Al4Si5O 18 ,MAS) ceramics have a low dielectric constant ε r (4-6) While cordierite has some application value in millimeter-wave communications, its other properties, such as its low quality factor (Qf) (23,000–40,000 GHz), limit its application. Existing research has found that the microwave dielectric properties of dielectric ceramics are influenced by both intrinsic and extrinsic factors. Extrinsic factors include material manufacturing process, raw material type, grain boundaries, secondary phases, porosity, and low density; while intrinsic factors include anharmonic lattice vibrations, compositional order / disorder, and symmetry. This multitude of influencing factors makes the discovery of new cordierite assemblages difficult and prevents the full realization of their high-performance properties.

[0005] Silicate-based microwave dielectrics exhibit ε due to the covalent effect of [SiO4] tetrahedrons. r <10, and its covalent effect is 50% higher than that of Al2O3, but its material density is not conducive to achieving a high quality factor, and to a certain extent, sintering temperatures above 1500°C are required to achieve optimal performance. Cordierite ceramics also have the low quality factor disadvantages of the aforementioned silicate-based microwave dielectrics. In addition, they also have additional challenges, such as a large negative resonant frequency temperature coefficient, polymorphic complexity (highly symmetric hexagonal phase α-cordierite and low-symmetric orthorhombic phase β-cordierite), component order / disorder, and anharmonic lattice vibrations and secondary phase evolution caused by dopants. These shortcomings and challenges have hindered the commercial development of cordierite ceramics in the field of millimeter wave technology.

[0006] In the prior art, microwave dielectric properties are improved by increasing material density and adding sintering aids. The increase in material density will produce low dielectric loss (tanδ) and high Qf value (1 / tanδ). Therefore, the prior art also uses the method of increasing material density to improve microwave dielectric properties, but the sintering temperature required in the preparation process of high-density materials is very high, and the structure will be deformed due to stress, defects, etc. during the preparation process, which will reduce the quality factor. In order to reduce the sintering temperature and increase the density, people have also been seeking to add sintering aids, but almost all sintering aids will have a negative impact on the Qf value of the prepared dielectric ceramic material. For example, BaCu (B2O3) is added as a sintering aid to Mg2Al4Si5O 18 The sintering temperature can be lowered to 900°C, but its Qf value is only about 21,000 GHz.

[0007] In the prior art, the microwave dielectric performance is improved by selecting materials with higher Qf values. r =6.8, Qf=270,000 GHz and TCF=-67 ppm / ℃) to prepare Mg2Al4Si5O 18 For the composite material with +50wt% Mg2SiO4, the sintering temperature was reduced from 1460℃ to 1340℃, and the Qf value increased to 76,374GHz. However, this value is still relatively low and fails to significantly improve the quality factor (Qf value) and temperature coefficient of resonant frequency (TCF value).

[0008] Therefore, the above methods have failed to significantly improve the quality factor of the dielectric properties of cordierite ceramics, and further development of methods is needed to optimize the microwave dielectric properties. Summary of the Invention

[0009] This application addresses the issues of low Qf values ​​and negative TCF values ​​in the microwave dielectric properties of cordierite ceramics in the prior art. By proposing a dielectric ceramic material and preparation method, this application employs a method that partially replaces silicon in conventional cordierite with germanium and adds a titanium oxide suspension and / or titanium oxide powder. This method significantly improves the microwave dielectric quality factor and resonant frequency temperature coefficient of the dielectric ceramic material, enabling broader application in millimeter-wave communications.

[0010] To achieve the above technical objectives, the present application provides a method for preparing a dielectric ceramic material, comprising the following steps:

[0011] S1, preparation of Mg2Al4(Si 1-x Ge x )5O 18 Powder; wherein 0<x≤0.5;

[0012] S2. Prepare a suspension containing titanium oxide; add the suspension containing titanium oxide and / or titanium oxide powder to the powder prepared in step S1, and sinter to obtain a dielectric ceramic material.

[0013] The x is 0.1-0.3; and / or the titanium oxide is selected from at least one of titanium monoxide, titanium dioxide or titanium trioxide; and / or the mass percentage concentration of titanium oxide in the titanium oxide-containing suspension is 3-7 wt%; and / or the volume ratio of the mass of the powder obtained in step S1 to the titanium oxide-containing suspension is 1-3 g:0-1 mL.

[0014] The mass percentage of the titanium oxide powder to the mass percentage of the powder prepared in step S1 is 0-5 wt %; optionally 2.0-4.0 wt %.

[0015] In step S1, the method for preparing the powder includes dispersing a magnesium source, an aluminum source, a silicon source, and a germanium source in a solvent, grinding, drying, and calcining to obtain the powder.

[0016] The magnesium source is selected from at least one of MgO, Mg(OH)2 and MgSO4; and / or, the aluminum source is selected from at least one of Al2O3, Al(OH)3 and Al2(SO4)3; and / or, the silicon source is selected from at least one of SiO2, SiO3 and H2SiO3; and / or, the germanium source is selected from at least one of GeO2, GeCl4 and GeO3; and / or, the molar ratio of the metal elements Mg, Al, Si and Ge in the magnesium source, aluminum source, silicon source and germanium source is 2:4:3.5-4.5:0.5-1.5; and / or, the solvent is ethanol or water; and / or, the volume ratio of the total mass of the magnesium source, aluminum source, silicon source and germanium source to the solvent is 1g:4-5mL.

[0017] In step S1, the drying temperature is 90-100°C and the drying time is 23-26 hours; and / or, the calcination atmosphere is air, the temperature is 1250-1350°C, and the time is 2-8 hours; and / or, after the calcination, the product is screened with a sieve with a specification of 80-120 mesh.

[0018] The grinding method is ball milling, the rotation speed of the ball mill is 250-270 rpm / min, and the time is 22-26 hours.

[0019] In step S2, the method for preparing the titanium oxide-containing suspension includes dispersing the titanium oxide in a solvent; optionally, the solvent is selected from one or more of deionized water and ethanol.

[0020] In step S2, the sintering temperature is 1300-1380°C; optionally 1325-1350°C.

[0021] In step S2, the sintering step also includes the steps of grinding, screening, tableting and sealing and storage; optionally, 80-120 mesh screen is used for screening; optionally, the pressure during tableting is 100-180 MPa; optionally, the sealing and storage time is 20-28 hours; optionally, the sintering time is 2-6 hours.

[0022] After the sintering, the method further includes polishing and / or annealing steps; optionally, the annealing temperature is 1150-1250° C. and the time is 9-12 hours.

[0023] The present application also provides a dielectric ceramic material.

[0024] The technical solution of this application has the following beneficial effects:

[0025] (1) The present application provides a method for preparing a dielectric ceramic material, comprising the following steps: S1, preparing Mg2Al4(Si 1-x Ge x )5O 18 Powder; wherein, 0<x≤0.5; S2, prepare a suspension containing titanium oxide; add the suspension containing titanium oxide and / or titanium oxide powder to the powder prepared in step S1, and sinter to obtain a dielectric ceramic material. In the method of the present application, the method of partially replacing the silicon element in traditional cordierite with germanium element and adding the suspension containing titanium oxide and / or titanium oxide powder achieves the goal of high Qf value and close to zero TCF value to a great extent. The properties of germanium element are closest to those of silicon element, and its ion radius IR is ε r The value is 6.2, the melting point is 1115℃ and the density is 4.25g / cm 3 The above properties far exceed those of other elements of the same valence. Therefore, partial substitution of germanium allows the synthesis of the main phase at a lower temperature, greatly improving the quality factor and temperature coefficient of resonant frequency, and providing low-temperature sintering conditions for the addition of titanium oxide. Adding a suspension containing titanium oxide and / or titanium oxide powder, on the basis of germanium substitution, maintains a low ε r The present invention significantly improves the Qf and TCF values ​​by partially replacing the germanium element with a titanium oxide suspension and / or titanium oxide powder, thereby enhancing the microwave dielectric properties of the dielectric ceramic material. This technical application is superior to conventional cordierite materials and any previous research.

[0026] (2) The present application provides a method for preparing a dielectric ceramic material, which improves the Qf value and TCF value by limiting the mass percentage of the titanium oxide powder to the mass percentage of the ceramic powder prepared in step S1 to 0-5wt%, optionally 2.0-4.0%.

[0027] (3) The present application provides a method for preparing a dielectric ceramic material. In step S2, the sintering temperature is 1300-1380°C, optionally 1325-1350°C, and its Qf value and TCF value are further improved.

[0028] (4) The present application provides a method for preparing a dielectric ceramic material. In step S2, the dielectric ceramic material is obtained by sintering. Optionally, the dielectric ceramic material is obtained by sintering and then annealing, and its Qf and / or TCF value is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] FIG1 is a flow chart of the preparation of Example 1 of the present application. DETAILED DESCRIPTION

[0031] The following examples are provided to further better understand the present application, but are not limited to the best implementation mode described herein, and do not limit the content and protection scope of the present application. Any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior arts shall fall within the scope of protection of the present application.

[0032] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0033] Examples 1-10

[0034] Examples 1-10 provide a series of methods for preparing dielectric ceramic materials. The molar ratios of Mg, Al, Si, and Ge, calcination temperature (°C, step S1), TiO2 powder dosage (wt%, representing the mass percentage of the powder prepared in step S1), and sintering temperature (°C, step S2) involved in the preparation process are shown in Table 1 below. The dielectric ceramic materials of each example were prepared according to the following steps:

[0035] S1. Mg(OH)2 (≥99%), Al2O3 (≥99.99%), SiO2 (≥99.99%) and GeO2 (≥99.9%) were weighed according to the molar ratio of the metal elements Mg, Al, Si and Ge shown in Table 1, placed in a 500 mL ball mill, and ethanol was added, wherein the volume ratio of the total mass of Mg(OH)2, Al2O3, SiO2 and GeO2 to ethanol was 1:5 (g / mL). After ball milling at 260 rpm / min for 24 h, a slurry was obtained. The slurry was dried at 100°C for 24 h, and then calcined in an air atmosphere at the calcination temperature shown in Table 1 for 4 h. Then, it was placed in a ball mill, and the above steps of adding ethanol, ball milling and drying were repeated once. Then, it was sieved with a 100 mesh sieve to obtain a powder.

[0036] S2. Weigh 2 g of TiO2 and disperse it in 40 mL of 25°C water to obtain a suspension. Add 0.5 mL (4 to 5 drops) of the suspension to 1 g of the powder obtained in step S1, then add TiO2 powder. Then grind it manually and sieve it with a 100-mesh sieve. Then, make it into a cylindrical sheet under a pressure of 150 MPa. After sealing and storing for 24 hours, sinter it at the sintering temperature in Table 1 for 4 hours and polish it to obtain a dielectric ceramic material.

[0037] The preparation process is shown in Figure 1. The powder prepared in step S1 of Example 1-10 is Mg2Al4(Si 1-x Ge x )5O 18 , x = 0.2. In Example 1, 0 wt% TiO2 means that only 4-5 drops of titanium oxide suspension were used as a starting point, without additional TiO2 powder. Furthermore, Examples 2-10 all contained 4-5 drops of titanium oxide suspension and additional TiO2 powder.

[0038] Table 1 Preparation conditions of dielectric ceramic material preparation process

[0039] Examples 11-20

[0040] Examples 11-20 provide a series of dielectric ceramic materials. The molar ratios of Mg, Al, Si, and Ge, calcination temperature (°C, step S1), TiO2 powder dosage (wt%, representing the mass percentage of the powder produced in step S1), and sintering temperature (°C, step S2) involved in the preparation of Examples 11-20 correspond to those of Example 1-10. The difference between Examples 11-20 and Example 1-10 is that after polishing in step S2, Example 11-20 also undergoes an annealing step of sintering at 1200°C for 10 hours. The remaining preparation methods are the same as those of Example 1-10.

[0041] Comparative Example 1

[0042] This comparative example provides a dielectric ceramic material. The molar ratios of Mg, Al, and Si involved in its preparation process and the calcination temperature (°C, step S1) are shown in Table 2 below. The difference from Examples 1-10 is that the powder prepared in step S1 is placed in a mortar, and a 5 wt% polyvinyl alcohol solution (PVA solution) is added in an amount of 0.2 mL (2 drops) per 1 gram of powder, ground, and then formed into a cylindrical sheet with a diameter of 12 mm and a thickness of 6 mm under a pressure of 100 MPa. The sheet is then sintered at 600°C for 4 hours (debinding stage), further sintered at 1450°C for 4 hours (densification stage), and polished to obtain the material. GeO2 is not weighed or added in step S1, and step S2 is not performed. The remaining preparation methods are the same as those of Examples 1-10.

[0043] Table 2 Preparation conditions of dielectric ceramic material preparation process

[0044] Comparative Example 2

[0045] This comparative example provides a dielectric ceramic material. The molar ratios of Mg, Al, Si, and Ge involved in its preparation, and the calcination temperature (°C, step S1) are shown in Table 3 below. The difference from Examples 1-10 is that the powder prepared in step S1 is placed in a mortar, and a 5 wt% polyvinyl alcohol solution (PVA solution) is added in an amount of 0.2 mL (2 drops) per gram of powder. The material is ground and then formed into a cylindrical sheet with a diameter of 12 mm and a thickness of 6 mm under a pressure of 100 MPa. The material is then sintered at 600°C for 4 hours (debinding stage), further sintered at 1365°C for 4 hours (densification stage), and polished. Step S2 is not performed. The remaining preparation methods are the same as those of Examples 1-10.

[0046] Table 3 Preparation conditions of dielectric ceramic material preparation process

[0047] Experimental Example 1

[0048] The performance of the dielectric ceramic materials prepared in the examples and comparative examples was tested by using a Keysight E5080B network analyzer to measure the TE 011 Mode dielectric constant ε r , quality factor Qf and temperature stability coefficient. The temperature stability coefficient is calculated as follows:

[0049] Where f1 and f2 are the resonant frequencies at 25°C (T1) and 85°C (T2), respectively.

[0050] The measurement results are shown in Table 4 below.

[0051] Table 4 Performance test results

[0052] It can be seen from Table 4 that, compared with Comparative Example 1, the microwave dielectric properties of the dielectric ceramic materials of Examples 1-20 are all better, not only the Qf value is greatly improved, but also the TCF value is improved.

[0053] Among them, compared with Comparative Example 1, Comparative Example 2 adds the substitution of germanium element, and the microwave dielectric properties of its dielectric ceramic material are improved compared with Comparative Example 1, but the Qf value of Comparative Example 2 is still low and needs to be further improved. Compared with Comparative Example 2, Example 1 adds a titanium oxide suspension on its basis, and the microwave dielectric properties of its dielectric ceramic material are improved; compared with Example 1, Examples 2-10 add titanium oxide powder on its basis, and the TCF value of the microwave dielectric properties of its dielectric ceramic material is significantly improved. In particular, the Qf values ​​of the dielectric ceramic materials of Examples 2-5 and Example 7 are significantly higher than those of Example 1 on the basis of exceeding 10,000 GHz, indicating that the method of performing partial germanium substitution and adding titanium oxide suspension and / or titanium oxide powder in this application can significantly improve the microwave dielectric properties of dielectric ceramic materials.

[0054] Compared with Examples 1-10, Examples 11-20 performed a post-sintering annealing step, wherein the Qf values ​​of Examples 11-20 were greatly improved, and the TCF values ​​of Examples 11, 17-18 were greatly improved.

[0055] In Examples 1-10, the effect of the addition amount of titanium oxide powder is compared. The microwave dielectric properties of the dielectric ceramic materials of Examples 2-8 are better. Therefore, the mass percentage of the titanium oxide powder to the mass percentage of the powder prepared in step S1 can be selected to be 2.0-4.0 wt %.

[0056] Comparing the effects of sintering temperature in Examples 1-10, the microwave dielectric properties of the dielectric ceramic materials of Examples 2-4, Examples 6-8 and Example 10 are better, and therefore, the sintering temperature can be selected to be 1325-1350°C.

[0057] This application realizes a cordierite-based material suitable for millimeter wave applications based on the composition-processing-structure-performance relationship strategy.

[0058] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a dielectric ceramic material, characterized in that: The following steps are involved: S1. Preparation of Mg2Al4(Si 1-x Ge x )5O 18 Powder; wherein 0<x≤0.5; S2, preparing a suspension containing titanium oxide; adding the suspension containing titanium oxide and / or titanium oxide powder to the powder obtained in step S1, and sintering to obtain a dielectric ceramic material.

2. The method for preparing a dielectric ceramic material according to claim 1, characterized in that: The x is 0.1-0.3; and / or, the titanium oxide is selected from at least one of titanium monoxide, titanium dioxide or titanium trioxide; and / or, the mass percentage concentration of titanium oxide in the titanium oxide-containing suspension is 3-7wt%; and / or, the mass ratio of the powder obtained in step S1 to the volume ratio of the titanium oxide-containing suspension is 1-3g:0-1mL.

3. The method for preparing a dielectric ceramic material according to claim 1, characterized in that: The mass percentage of the titanium oxide powder to the mass percentage of the powder obtained in step S1 is 0-5wt%; optionally 2.0-4.0wt%.

4. The method for preparing a dielectric ceramic material according to any one of claims 1 to 3, characterized in that: In step S1, the method for preparing the powder includes dispersing a magnesium source, an aluminum source, a silicon source and a germanium source in a solvent, grinding, drying and calcining to obtain a powder.

5. The method for preparing a dielectric ceramic material according to claim 4, characterized in that: The magnesium source is selected from at least one of MgO, Mg(OH)2 and MgSO4; and / or, the aluminum source is selected from at least one of Al2O3, Al(OH)3 and Al2(SO4)3; and / or, the silicon source is selected from at least one of SiO2, SiO3 and H2SiO3; and / or, the germanium source is selected from at least one of GeO2, GeCl4 and GeO3; and / or, the molar ratio of the metal elements Mg, Al, Si and Ge in the magnesium source, aluminum source, silicon source and germanium source is 2:4:3.5-4.5:0.5-1.5; and / or, the solvent is ethanol or water; and / or, the volume ratio of the total mass of the magnesium source, aluminum source, silicon source and germanium source to the solvent is 1g:4-5mL.

6. The method for preparing a dielectric ceramic material according to claim 4, characterized in that: In step S1, the drying temperature is 90-100°C and the time is 23-26h; and / or, the calcination atmosphere is air, the temperature is 1250-1350°C and the time is 2-8h; and / or, after the calcination, the sieving is performed with a sieve with a specification of 80-120 mesh.

7. The method for preparing a dielectric ceramic material according to claim 1, characterized in that: In step S2, the sintering temperature is 1300-1380°C; optionally 1325-1350°C.

8. The method for preparing a dielectric ceramic material according to claim 1, characterized in that: In step S2, the process before sintering also includes grinding, screening, tableting and sealing and storage steps; optionally, 80-120 mesh sieve is used for screening; optionally, the pressure during tableting is 100-180 MPa; optionally, the sealing and storage time is 20-28 hours; optionally, the sintering time is 2-6 hours.

9. The method for preparing a dielectric ceramic material according to claim 1, characterized in that: In step S2, the sintering further includes polishing and / or annealing steps; optionally, the annealing temperature is 1150-1250° C. and the time is 9-12 hours.

10. A dielectric ceramic material prepared by the method for preparing a dielectric ceramic material according to any one of claims 1 to 9.

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