A microwave dielectric material with high bending strength and high Q value and its preparation method

Abstract

The present invention relates to a microwave dielectric material with high flexural strength and high Q value and a preparation method thereof. The microwave dielectric material chemically comprises a magnesium niobate matrix and a flaky oxide as a second phase dispersed in the magnesium niobate matrix; the flaky oxide phase is at least one of flaky aluminum oxide, flaky tin oxide, flaky silicon oxide, flaky zirconium oxide, flaky titanium oxide, and flaky tungsten oxide, with 0.1≤x≤5.

Description

Technical Field

[0001] The present invention relates to a microwave dielectric material with high bending strength and high Q value and a preparation method thereof, and belongs to the field of ceramic materials. Background Art

[0002] Microwave dielectric ceramics refer to a type of functional ceramic used as the core component of dielectric filters in the microwave frequency band (300MHz~300GHz). With the advantages of high dielectric constant, low dielectric loss and a resonant frequency coefficient close to 0, it can be widely used not only as an insulating substrate material in microwave circuits, but also as a key material for making microwave functional devices such as dielectric resonators and filters. It has been widely used in microwave communications such as satellites and mobile communications.

[0003] With the development of mobile 5G communications and information and communication technologies, communication frequencies and bandwidths are gradually increasing. Traditional devices such as cavity filters no longer meet the performance requirements of microwave communication equipment. These devices are now placing higher demands on dielectric materials: high Qf values, moderate dielectric constants, near-zero resonant frequency coefficients, and good operational reliability. Depending on device design requirements, a suitable dielectric constant can meet the device size and frequency requirements, a high Q value can enhance the device's frequency selectivity, a near-zero frequency temperature coefficient can improve the device's adaptability, and good mechanical properties can ensure its operational reliability. MgNb2O6 dielectric ceramics, due to their excellent microwave dielectric properties (Qf ≈ 100,000 GHz), have been considered a key candidate for fifth-generation communication technology. However, this material system suffers from poor mechanical properties and a low flexural strength (98 MPa). These issues, including material failure and poor operational reliability, have limited its mass production. Summary of the Invention

[0004] In response to the above problems, the present invention provides a microwave dielectric material with high bending strength and high Q value and a preparation method thereof.

[0005] On the one hand, the present invention provides a microwave dielectric material with high flexural strength and high Q value. The chemical composition of the microwave dielectric material includes: a magnesium niobate matrix, and a flaky oxide dispersed in the magnesium niobate matrix as a second phase (referred to as the G component); the flaky oxide phase is at least one of flaky aluminum oxide, flaky tin oxide, flaky silicon oxide, flaky zirconium oxide, flaky titanium oxide, and flaky tungsten oxide, and 0.1≤x≤5.

[0006] In the present invention, a specific content of flaky oxide is selected as a toughening secondary phase. The flaky oxides hinder grain growth in the magnesium niobate ceramic matrix, reducing the size of the ceramic crystals and contributing to grain refinement and strengthening. Furthermore, the flaky oxides act as pinning agents, deflecting cracks to a certain extent near the flaky aluminum oxide, effectively dissipating fracture energy. Furthermore, to minimize dielectric loss in the microwave dielectric material and enhance the pinning effect of the flaky oxides, flaky aluminum oxide is preferably used as the flaky oxide.

[0007] Preferably, the molar ratio of Mg element to Nb element in the magnesium niobate matrix is ​​(1.0-1.05):2, preferably 1.03:2.

[0008] Preferably, the length of the flaky oxide is 10-18 μm, the aspect ratio is (6-9):1, and the thickness is 800 nm-3 μm; more preferably, the length of the flaky oxide is 15 μm, the aspect ratio is (6-9):1, and the thickness is 1-2 μm.

[0009] Preferably, the microwave dielectric material has a dielectric constant of 19.4 to 20.6, a Qf value of 79100 to 114600 GHz, and a bending strength of 122.5 to 155 MPa.

[0010] Preferably, considering that for the MgNb2O6 system, a Qf value decrease of no more than 10% has good application prospects, the xwt% value is preferably 0.1 to 1wt%.

[0011] Preferably, when 0.1≤x<1, the dielectric constant of the microwave dielectric material is 20.1-20.6, the Qf value is 109100-114600 GHz, and the bending strength is 122.5-153 MPa.

[0012] On the other hand, the present invention provides a method for preparing a microwave dielectric material with an ultra-high Q value. Magnesium niobate powder and flaky oxide powder are weighed and mixed according to the chemical composition of the microwave dielectric material, and then granulated and formed to obtain a green billet; the obtained green billet is first heated to 1250-1300°C and kept warm for 4-6 hours, and then cooled to 1000-1100°C and kept warm for 4-6 hours to obtain the microwave dielectric material with high flexural strength and high Q value.

[0013] In the present invention, a method for preparing high-performance MgNb2O6 ceramics with simple process and good controllability is developed by adding a toughening second phase based on the solid phase reaction method. Specifically, the present invention first adopts a non-stoichiometric ratio to synthesize MgNb2O6 powder during the synthesis process, thereby preventing the MgNb2O6 powder from being stoichiometrically synthesized in the traditional solid phase reaction method. 0.66 Nb 11.33 O 29The production of a high-loss second phase improves the microwave dielectric properties of the material. Then, a flaky oxide of a specific component (for example, flaky aluminum oxide, with a size of about 15 μm, an aspect ratio of 6:1 to 9:1, preferably 7:1, and a thickness of 1 to 2 μm) is used as a toughening agent with a lamellar morphology as an elemental component solid-dissolved in the matrix phase. The toughening agent has good chemical stability and does not react with the ceramic matrix. It can significantly enhance the flexural strength of the ceramic, which helps to improve the application reliability of MgNb2O6 ceramics and expand the application market. The material system used in the present invention has a higher Qf value and higher flexural strength than those reported in the literature. It is preferred that the toughening agent with flaky aluminum oxide as the main component has a good toughening effect on the MgO-Nb2O5 binary system. Therefore, the present invention uses flaky oxides such as flaky aluminum oxide as a toughening agent so that it can better play a mechanical toughening effect.

[0014] Preferably, the preparation method of the magnesium niobate powder includes: weighing and mixing a Mg source and a Nb source according to Mg:Nb=(1.0~1.05):2, and then keeping warm at 900~1000℃ (for example, 950℃) for at least 4 hours to obtain the magnesium niobate powder; preferably, the Mg source is MgO and / or basic MgCO3, and the Nb source is Nb2O5.

[0015] Preferably, the particle size D of the magnesium niobate powder is 90 <3μm.

[0016] Preferably, the heating rate is 5-10°C / min.

[0017] Preferably, the cooling rate is 1-5°C / min.

[0018] Beneficial effects:

[0019] In the present invention, the prepared microwave dielectric ceramic material has a dielectric constant of 20.05, a resonance temperature coefficient of -69ppm / ℃, a high Q·f value of 109100GHz and a high bending strength of 153MPa. It can be used as a key core material for electronic components such as antennas and substrates for microwave mobile communications, and is widely used in the fifth-generation mobile communications industry.

[0020] Compared with the prior art, the method for preparing MgNb2O6-based microwave dielectric ceramics of the present invention has the characteristics of simple process, can significantly improve the material yield while ensuring material properties, is suitable for large-scale industrial production, and has important application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The XRD patterns of the microwave dielectric material before and after doping with the G additive in the present invention;

[0022] Figure 2 is a curve diagram showing the relationship between the amount of microwave dielectric material G added and the flexural strength of the ceramic in the present invention;

[0023] Figure 3 The graph is a relationship graph between the amount of microwave dielectric material G added and the sum of the ceramic quality factors in the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0025] In the present invention, the microwave dielectric material with high flexural strength and high Qf is composed of an MN-xwt%G system, where MN is a microwave dielectric material containing Mg, Nb, and O, and G is a flaky oxide. The mass fraction of G, xwt%, ranges from 0 to 5wt%. While excessive amounts of toughening agent (>1wt%) can easily deteriorate material properties, an addition of 1wt% or less can significantly improve the material's flexural strength while maintaining a high Qf value.

[0026] In the present invention, a small amount of a second phase toughening agent component G is added to a magnesium niobate matrix (MN, a microwave dielectric material containing Mg, Nb and O elements), which can mechanically enhance the ceramic matrix.

[0027] Optionally, the raw material composition of the microwave dielectric material MN can be MgO+Nb2O5, wherein the molar ratio of MgO+Nb2O5 can be (1.0-1.05):1, preferably 1.03:1.

[0028] The following is an exemplary description of the method for preparing the microwave dielectric material with high bending strength and high Q value provided by the present invention.

[0029] Preparation of MN powder. Mg source and Nb source are mixed according to the composition of MN, and then kept at 950°C for at least 4 hours to obtain MN powder. The Mg source can be MgO or basic MgCO3. The Nb source can be Nb2O5. As an example, the raw materials of MN microwave dielectric material are weighed according to a molar ratio, and then water is added. The mixture is ground into a slurry using zirconium balls on a planetary ball mill, and then dried and calcined to obtain MN powder. The ball mill slurry particle size D50 is less than 2, and the synthesis temperature is kept at 950°C for not less than 4 hours.

[0030] The G powder is flaky aluminum oxide with a size of about 15 μm, an aspect ratio of 6:1 to 9:1 (preferably 7:1), and a thickness of 1-2 μm.

[0031] MN powder and G powder are mixed in a certain proportion, ball-milled, granulated and formed, and sintered under a specific sintering system to form the microwave dielectric material with ultra-high Q value. Specifically, the total mass of MN powder and G powder is calculated as 100wt%, and the mass percentage of the G powder is between 0 and 5wt%. The above-mentioned specific sintering system can be to first increase the temperature to 1250-1300℃ at 5-10℃ / min, keep it warm for 4-6 hours, then reduce the temperature to 1100-1200℃ at 1℃ / min, and keep it warm for another 4-6 hours. The subsequent cooling and sintering process, compared with the previous high-temperature sintering process, controls the slower cooling rate and cooling temperature, which is conducive to uniform growth of the material, elimination of internal stress, and improvement of comprehensive performance, especially dielectric and mechanical properties.

[0032] In the present invention, a vector network analyzer is used to test the dielectric constant of a microwave dielectric material having high flexural strength and high Q value. A vector network analyzer is used to test the Qf value of a microwave dielectric material having high flexural strength and high Q value. A universal mechanical testing machine is used to test the flexural strength of a microwave dielectric material having high flexural strength and high Q value.

[0033] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below.

[0034] Example 1

[0035] (1) Accurately weigh 1.0 mol of Nb2O5 and 1.03 mol of basic MgCO3 with a purity greater than 99.9%, add them to a nylon ball mill, and pour in deionized water with 10 mm diameter zirconium oxide balls in a weight ratio of material: ball: water = 1:1.5:2; the ball milling time is 2 h, and the ball milling slurry particle size D 50 The particle size is 2 μm. After ball milling, the slurry is dried in an oven at 130°C. The dried powder is placed in a sagger, calcined at 950°C for 4 hours, and then cooled in the furnace to obtain MN synthetic powder.

[0036] (2) G is a flaky aluminum oxide with a size of about 15 μm, an aspect ratio of (6 to 9):1, and a thickness of 1 to 2 μm;

[0037] (3) Weigh 100g MN synthetic powder and 0.1g G powder toughening agent, add them into a nylon ball mill, pour in deionized water and 10mm diameter zirconia balls, the weight ratio of which is material: ball: water = 1:1.2:2; ball milling time is 2h, and the ball milling slurry particle size D 50 The particle size is 2μm. After the ball milling, the slurry is poured into an enamel dish, placed in an oven, and dried at 130°C. PVA aqueous solution is used for granulation to prepare samples of two sizes. Sample 1 is placed in a mold with a diameter of 6mm and molded under a pressure of 100MPa. The molded sample height is 4mm. It is placed in a muffle furnace and heated to 1300°C at 6°C / min, kept warm for 4h, and then reduced to 1000°C at 1°C / min, and kept warm for 5h to obtain a microwave dielectric material. The properties are shown in Table 1. Sample 2 is placed in a 45×45mm mold and molded under a pressure of 100MPa. The molded sample height is 40mm. It is placed in a muffle furnace and heated to 1300°C at 6°C / min, kept warm for 4h, and then reduced to 1000°C at 1°C / min, and kept warm for 5h to obtain a microwave dielectric material. Processed into a standard national standard flexural strength test specimen (3×4×36mm) Test results are shown in Figure 2 .

[0038] Example 2

[0039] The preparation of the microwave dielectric material in Example 2 refers to Example 1, with the only difference being that 0.3 g of flaky aluminum oxide is added.

[0040] Example 3

[0041] The preparation of the microwave dielectric material in Example 3 refers to that in Example 1, except that 0.5 g of flaky aluminum oxide is added.

[0042] Example 4

[0043] The preparation of the microwave dielectric material in Example 4 refers to that in Example 1, except that 1 g of flaky aluminum oxide is added.

[0044] Example 5

[0045] The preparation of the microwave dielectric material in Example 5 refers to that in Example 1, except that 2 g of flaky aluminum oxide is added.

[0046] Example 6

[0047] The preparation of the microwave dielectric material in Example 6 refers to that in Example 1, with the only difference being that 3 g of flaky aluminum oxide is added.

[0048] Example 7

[0049] The preparation of the microwave dielectric material in this Example 7 refers to that in Example 1, with the only difference being that 4 g of flaky aluminum oxide is added.

[0050] Example 8

[0051] The preparation of the microwave dielectric material in Example 8 refers to Example 1, with the only difference being that 5 g of flaky aluminum oxide is added.

[0052] Example 9

[0053] The preparation of the microwave dielectric material in Example 9 refers to Example 1, with the only difference being that 0.2 g of flaky aluminum oxide is added.

[0054] Example 10

[0055] The preparation of the microwave dielectric material in this Example 10 refers to that in Example 1, with the only difference being that 0.4 g of flaky aluminum oxide is added.

[0056] Example 11

[0057] The preparation of the microwave dielectric material in this Example 11 refers to that in Example 1, with the only difference being that 0.6 g of flaky aluminum oxide is added.

[0058] Example 12

[0059] The preparation of the microwave dielectric material in this Example 12 refers to that in Example 1, with the only difference being that 0.8 g of flaky aluminum oxide is added.

[0060] Comparative Example 1

[0061] The preparation of the microwave dielectric material in this comparative example 1 refers to that in Example 1, except that 0 g of flaky aluminum oxide is added.

[0062] Comparative Example 2

[0063] The preparation of the microwave dielectric material in Comparative Example 2 refers to Example 1, with the only difference being that 6 g of flaky aluminum oxide was added.

[0064] Comparative Example 3

[0065] The preparation of the microwave dielectric material in Comparative Example 3 refers to Example 1, with the only difference being that 0.5 g of alumina powder with no special morphology and an average particle size of 18 μm was added.

[0066] Table 1 shows the performance parameters of the microwave dielectric materials prepared in Examples 1-8 and Comparative Examples 1-2 of the present invention:

[0067] MN powder / g G powder / g Dielectric constant Q·f / GHz Bending strength / Mpa Example 1 100 0.1 20.6 113000 122.5 Example 2 100 0.3 20.3 114600 132.5 Example 3 100 0.5 20.2 113400 145 Example 4 100 1 20.1 109100 153 Example 5 100 2 19.9 89400 155 Example 6 100 3 19.8 85300 151.5 Example 7 100 4 19.6 81000 153 Example 8 100 5 19.4 79100 148 Example 9 100 0.2 20.5 113000 127.5 Example 10 100 0.4 20.2 113900 142.5 Example 11 100 0.6 20.2 112400 150 Example 12 100 0.8 20.1 110300 151 Comparative Example 1 100 0 20.7 113000 94 Comparative Example 2 100 6 19.4 70100 150 Comparative Example 3 100 0.5 20.6 91700 96 .

[0068] Figure 1The XRD patterns of microwave dielectric materials prepared in Comparative Example 1, Example 1, Example 3, Example 4, and Comparative Example 8 before and after glass doping are shown. The ceramics still have MgNb2O6 as the primary crystalline phase, but due to the low doping content of flaky alumina, the corresponding phase is absent. When the flaky alumina content is greater than or equal to 5 wt%, the presence of flaky oxides as a toughening secondary phase can be detected.

[0069] Figure 2 and Figure 3 This is a curve showing the effect of doping the toughening agent of the present invention on the quality factor and flexural strength of ceramics in Example 1, wherein the G powder doping amounts of 0.1wt%, 0.3wt%, 0.5wt%, 1.0wt%, 5.0wt% and 6.0wt% correspond to Comparative Example 1, Example 2, Example 3, Example 4, Example 8 and Comparative Example 2 in the present invention, respectively. It can be seen that a certain doping amount can improve the flexural strength of the material while maintaining a relatively high quality factor, but when the doping amount is too high, the flexural strength of the material is not significantly improved, and the quality factor will be reduced.

Claims

1. A method for preparing a microwave dielectric material with high flexural strength and high Q value, characterized in that: The microwave dielectric material comprises a magnesium niobate matrix and a flaky oxide as a second phase dispersed in the magnesium niobate matrix; the flaky oxide phase is flaky aluminum oxide, the mass fraction of the flaky aluminum oxide is xwt%, and the value of x ranges from 0.1≤x<1; the flaky aluminum oxide has a length of 10 to 18 μm, an aspect ratio of (6 to 9):1, and a thickness of 800 nm to 3 μm; and the molar ratio of Mg to Nb in the magnesium niobate matrix is ​​(1.03 to 1.05):

2. The preparation method of the microwave dielectric material with high flexural strength and high Q value comprises: weighing magnesium niobate powder and flaky aluminum oxide powder according to the chemical composition of the microwave dielectric material and mixing them, and then granulating and molding them to obtain a green billet; heating the obtained green billet to 1250-1300° C. at a heating rate of 5-10° C. / min and keeping the temperature for 4-6 hours, and then cooling the temperature to 1000-1100° C. at a cooling rate of 1-5° C. / min and keeping the temperature for 4-6 hours, thereby obtaining the microwave dielectric material with high flexural strength and high Q value.

2. The method for preparing a microwave dielectric material with high flexural strength and high Q value according to claim 1, characterized in that: The flaky aluminum oxide has a length of 15 μm, an aspect ratio of (6-9):1, and a thickness of 1-2 μm.

3. The method for preparing a microwave dielectric material with high flexural strength and high Q value according to claim 1, characterized in that: The preparation method of the magnesium niobate powder comprises: weighing and mixing a Mg source and a Nb source according to the ratio of Mg:Nb=(1.03-1.05):2, and then keeping the mixture at 900-1000°C for at least 4 hours to obtain the magnesium niobate powder.

4. The method for preparing a microwave dielectric material with high flexural strength and high Q value according to claim 3, characterized in that: The Mg source is MgO and / or basic MgCO3, and the Nb source is Nb2O5.

5. The method for preparing a microwave dielectric material with high flexural strength and high Q value according to claim 3, characterized in that: The particle size D of the magnesium niobate powder 90 <3μm.

6. The microwave dielectric material with high flexural strength and high Q value prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The microwave dielectric material has a dielectric constant of 20.1 to 20.6, a Qf value of 109100 to 114600 GHz, and a bending strength of 122.5 to 153 MPa.

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