Garnet ferrite with high dielectric constant and high flexural strength and preparation method thereof

Abstract

The application belongs to the field of microwave ferrite materials, and provides a garnet ferrite with high dielectric constant and high bending strength and a preparation method thereof, so as to solve the problems of abnormal grain growth and high porosity caused by excessive liquid phase in the sintering process of the existing high dielectric constant bismuth-substituted garnet ferrite, and the problem of low bending strength caused thereby. In the main phase system of the bismuth-containing microwave garnet ferrite, a proper amount of nano-SiO2 is introduced as a grain boundary regulator, which is conducive to forming a dense and uniform fine-grained microstructure and optimizing the ferromagnetic resonance line width; while maintaining the high dielectric constant endowed by the high polarization rate of bismuth ions, the fracture toughness and intrinsic strength of the ferrite are significantly improved by means of fine-grained strengthening mechanism, so that the bending strength of the ferrite is increased, thereby effectively solving the problems of micro-cracks and edge collapse easily occurring in the processing steps such as slicing, grinding and polishing of the high dielectric microwave substrate, and meeting the application requirements of miniaturization and high yield production of the microwave circulator and isolator.

Description

Technical Field

[0001] This invention belongs to the field of microwave ferrite materials, specifically providing a garnet ferrite material with high dielectric constant and high bending strength and its preparation method, which can be applied to microwave circulators / isolators. Background Technology

[0002] With the rapid development of microwave communication technology towards higher frequencies and miniaturization, the miniaturization of circulators and isolators in microwave systems has become an inevitable trend in the industry. In the design of microwave ferrite devices, the substrate size is inversely proportional to the square root of the dielectric constant of the gyromagnetic material used; therefore, developing microwave ferrite materials with high dielectric constants is a key approach to achieving device miniaturization. Currently, the dielectric constant of garnet ferrite can be significantly improved by introducing bismuth ions with high polarizability to replace some yttrium ions at the dodecahedral sites. However, due to the low melting point of bismuth oxides, a large amount of liquid phase is easily formed during sintering. Excessive liquid phase can lead to abnormal grain growth, resulting in an uneven microstructure and high porosity, making the material prone to cracking during subsequent processing. Furthermore, research on microwave garnet ferrite mainly focuses on improving single properties, making it difficult to simultaneously meet the requirements of device miniaturization and the mechanical properties required for precision machining, while industry applications generally require a flexural strength of not less than 50 MPa.

[0003] For example, patent document CN113896521A discloses a garnet ferrite prepared by solid-state reaction method, with the chemical formula Bi. 1.3 Y 1.6 Gd 0.083 Ca 0.577 Fe 4.09 V 0.002 Al 0.2 Nb 0.2 Zr 0.005 In 0.003 Sn 0.14 Mn 0.56 O 12 Dielectric constant ε′=25.16, ferromagnetic resonance linewidth ΔH=16.8Oe, saturation magnetization 4πM s =1040 Gs. For example, Chinese patent CN112456998A discloses a high dielectric constant garnet ferrite material with the chemical formula Bi. 1.4 Ca a+2b Zr a V b Fe 5.03-a-b O 11.97 The material exhibits a moderate saturation magnetization of 4πM. s=1071 Gs and a relatively large dielectric constant ε′=25.3. Although the above materials achieved a saturation magnetization of around 1000 Gs and a relatively high dielectric constant by introducing a high concentration of bismuth plasma, meeting the electromagnetic design requirements for miniaturization of some devices, their mechanical properties were not investigated. Furthermore, patent document CN114890779A discloses a formulation of Y... 2.48 Gd 0.5 Dy 0.02 In 0.3 Fe 4.49 O 11.69 Garnet ferrite, this material has a high density of 5.41 g / cm³. 3 It has a porosity of 1.96%, a flexural strength of 118.84 MPa, and specific high-power magnetic properties, with a spin wave linewidth of 23.5 Oe and a ferromagnetic resonance linewidth of 169 Oe. However, the dielectric constant of this material is at a conventional level, which cannot meet the core requirements of the current microwave communication devices to evolve towards miniaturization and high integration. Summary of the Invention

[0004] The purpose of this invention is to provide a garnet ferrite with high dielectric constant and high flexural strength and its preparation method, so as to solve the problems of abnormal grain growth and increased porosity caused by excessive liquid phase during the sintering process of existing bismuth-substituted garnet ferrite with high dielectric constant, and the resulting low flexural strength.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A garnet ferrite with high dielectric constant and high flexural strength, characterized in that the chemical formula of the garnet ferrite material is: Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12 , 1.5≤a≤2.0, 0 <b≤0.8,0.3≤c≤0.7,0<d≤0.3。

[0007] Furthermore, the preparation method of the garnet ferrite with high dielectric constant and high flexural strength includes the following steps:

[0008] Step 1, Ingredients: According to the chemical formula Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12, 1.5 ≤ a ≤ 2.0, 0 < b ≤ 0.8, 0.3 ≤ c ≤ 0.7, 0 < d ≤ 0.3, calculate and weigh the raw materials, which are Bi2O3, CaCO3, Y2O3, ZrO2, V2O5, Fe2O3;

[0009] Step 2, primary ball milling: Ball mill and mix the raw materials, dry and screen them after ball milling to obtain the primary ball mill powder;

[0010] Step 3, pre-sintering: Pre-sinter the primary ball mill powder at 800 - 900 °C, with a holding time of 1 - 5 h. After pre-sintering, crush and screen it to obtain the pre-sintered material;

[0011] Step 4, secondary ball milling: Based on the mass of the pre-sintered material, add 0.1 - 0.3 wt% of SiO2 to the pre-sintered material and conduct secondary ball milling. After ball milling, dry and screen it to obtain the secondary ball mill powder;

[0012] Step 5, granulation: Add an aqueous solution of polyvinyl alcohol (PVA) to the secondary ball mill powder for granulation to obtain the granulated material;

[0013] Step 6, forming: Place the granulated material into a mold for pressing to form a green body;

[0014] Step 7, sintering: Place the green body in a sintering furnace under an oxygen atmosphere, continuously introduce oxygen at a flow rate of 0.3 - 0.8 L / min, with a sintering temperature of 900 - 950 °C and a holding time of 18 - 20 h.

[0015] Further, the process of primary ball milling is as follows: Place the raw materials, zirconia balls, and deionized water in a planetary ball mill for ball milling. The mass ratio of balls:materials:water is 4:1:1.5, and the ball milling time is 5 - 8 hours.

[0016] Further, the process of secondary ball milling is as follows: Place the raw materials, zirconia balls, and deionized water in a planetary ball mill for ball milling. The mass ratio of balls:materials:water is 4:1:1.5, and the ball milling time is 6 - 10 hours.

[0017] Further, during the granulation process, the usage amount of the aqueous solution of polyvinyl alcohol (PVA) is 8 - 12 wt% of the mass of the secondary ball mill powder.

[0018] Further, the pressure for pressing and forming is 150 - 200 Mpa.

[0019] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0020] This invention provides a microwave garnet ferrite with both high dielectric constant and high mechanical strength, and its preparation method. An appropriate amount of nano-SiO2 is introduced as a grain boundary regulator into the bismuth-containing microwave garnet ferrite main phase system. During sintering, the nano-SiO2 precipitates and segregates at the grain boundaries, forming a physical barrier layer and generating a grain boundary pinning effect. This suppresses secondary recrystallization induced by the bismuth-rich liquid phase, avoiding abnormal grain coarsening and its encapsulation of pores, ultimately forming a dense and uniform fine-grained microstructure. Simultaneously, it optimizes the ferromagnetic resonance linewidth. Furthermore, while maintaining the high dielectric constant imparted by the high polarizability of bismuth ions, the fine-grained strengthening mechanism significantly improves the fracture toughness and intrinsic strength of the ferrite, increasing its bending strength. This effectively solves the microcrack and edge chipping problems that easily occur in the slicing, grinding, and polishing processes of high-dielectric microwave substrates, meeting the application requirements of miniaturization and high-yield mass production of microwave circulators and isolators.

[0021] In summary, this invention provides a garnet ferrite material with high dielectric constant and high flexural strength, and its preparation method. Compared with the prior art, the advantages of the garnet ferrite material of this invention are: the dielectric constant ε' ≥ 31, and it also has a moderate saturation magnetization (4πM). s With a linewidth ΔH≤100Oe and a bending strength σ≥126 MPa, it promotes device miniaturization while possessing high bending strength, which is beneficial for processing. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the garnet ferrite material in Embodiment 1 of the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the garnet ferrite material in Embodiment 2 of the present invention.

[0024] Figure 3 This is a scanning electron microscope image of the garnet ferrite material in Embodiment 3 of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] Example 1

[0027] This embodiment provides a garnet ferrite with high dielectric constant and high flexural strength, which is prepared by the following steps:

[0028] Ingredients: Based on the chemical formula Bi a Ca b Y 3-a-b Zr c V d Fe5-c-d O 12 a=1.58, b=1.2, c=0.6, d=0.3; calculate and weigh the raw materials, which are Bi2O3, CaCO3, Y2O3, ZrO2, V2O5, and Fe2O3, with analytical purity;

[0029] One-time ball milling: Load the raw materials into the ball mill jar, and add zirconia balls and deionized water in a ratio of material:ball:water = 1:4:1.5. Discharge the material after one-time ball milling for 6 hours.

[0030] Pre-firing: The corundum crucible containing the powder is placed in a box furnace with an air atmosphere for pre-firing at a temperature of 850°C for 4 hours.

[0031] Secondary ball milling: The pre-calcined material and SiO2 additive are ball milled twice in a planetary ball mill. The SiO2 additive accounts for 0.3 wt% of the main formulation. The ball:material:water mass ratio is 4:1:1.5. The ball milling is carried out for 6 hours, and then dried and passed through an 80-mesh sieve.

[0032] Granulation: After drying the secondary material obtained from the secondary ball milling, 10wt% PVA solution is added by weight percentage and then granulated and sieved.

[0033] Molding: The granulated fine powder is placed into a mold and pressed under a pressure of 200 MPa;

[0034] Sintering: The formed green parts are placed in an oxygen atmosphere sintering furnace and sintered using a multi-step sintering method. Oxygen is continuously introduced at a flow rate of 0.5 L / min, the sintering temperature is 910℃, and the holding time is 20 h.

[0035] Example 2

[0036] This embodiment provides a garnet ferrite with high dielectric constant and high flexural strength, which is prepared by the following steps:

[0037] Ingredients: Based on the chemical formula Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12 a=1.59, b=1.2, c=0.6, d=0.3; calculate and weigh the raw materials, which are Bi2O3, CaCO3, Y2O3, ZrO2, V2O5, and Fe2O3, with analytical purity;

[0038] One-time ball milling: Load the raw materials into the ball mill jar, and add zirconia balls and deionized water in a ratio of material:ball:water = 1:4:1.5. Discharge the material after one-time ball milling for 6 hours.

[0039] Pre-firing: The corundum crucible containing the powder is placed in a box furnace with an air atmosphere for pre-firing at a temperature of 830℃ for 4 hours.

[0040] Secondary ball milling: The pre-calcined material and SiO2 additive are ball milled twice in a planetary ball mill. The SiO2 additive accounts for 0.3 wt% of the main formulation. The ball:material:water mass ratio is 4:1:1.5. The ball milling is carried out for 6 hours, and then dried and passed through an 80-mesh sieve.

[0041] Granulation: After drying the secondary material obtained from the secondary ball milling, 10wt% PVA solution is added by weight percentage and then granulated and sieved.

[0042] Molding: The granulated fine powder is placed into a mold and pressed under a pressure of 200 MPa;

[0043] Sintering: The formed green body is placed in a sintering furnace with an oxygen atmosphere, and oxygen is continuously introduced at a flow rate of 0.5 L / min. The sintering temperature is 910℃, and the holding time is 20 h.

[0044] Example 3

[0045] This embodiment provides a garnet ferrite with high dielectric constant and high flexural strength, which is prepared by the following steps:

[0046] Ingredients: Based on the chemical formula Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12 a=1.6, b=1.2, c=0.6, d=0.3. Calculate and weigh the raw materials, which are Bi2O3, CaCO3, Y2O3, ZrO2, V2O5, and Fe2O3, with analytical purity.

[0047] One-time ball milling: Load the raw materials into the ball mill jar, and add zirconia balls and deionized water in a ratio of material:ball:water = 1:4:1.5. Discharge the material after one-time ball milling for 6 hours.

[0048] Pre-firing: The corundum crucible containing the powder is placed in a box furnace with an air atmosphere for pre-firing at a temperature of 845℃ for 4 hours.

[0049] Secondary ball milling: The pre-calcined material and SiO2 additive are ball milled twice in a planetary ball mill. The SiO2 additive accounts for 0.3 wt% of the main formulation. The ball:material:water mass ratio is 4:1:1.5. The ball milling is carried out for 6 hours, and then dried and passed through an 80-mesh sieve.

[0050] Granulation: After drying the secondary material obtained from the secondary ball milling, 10wt% PVA solution is added by weight percentage and then granulated and sieved.

[0051] Molding: The granulated fine powder is placed into a mold and pressed under a pressure of 200 MPa;

[0052] Sintering: The formed green body is placed in a sintering furnace with an oxygen atmosphere, and oxygen is continuously introduced at a flow rate of 0.5 L / min. The sintering temperature is 910℃, and the holding time is 20 h.

[0053] Comparative Example 1

[0054] This comparative example provides a garnet ferrite, prepared by the following steps:

[0055] Ingredients: Based on the chemical formula Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12 Given a=1.6, b=1.2, c=0.6, d=0.3, calculate and weigh the raw materials, which are Bi2O3, CaCO3, Y2O3, ZrO2, V2O5, and Fe2O3, with analytical purity.

[0056] One-time ball milling: Load the raw materials into the ball mill jar, and add zirconia balls and deionized water in a ratio of material:ball:water = 1:4:1.5. Discharge the material after one-time ball milling for 6 hours.

[0057] Pre-firing: The corundum crucible containing the powder is placed in a box furnace with an air atmosphere for pre-firing at a temperature of 850°C for 4 hours.

[0058] Secondary ball milling: The pre-calcined material is ball-milled twice in a planetary ball mill with a ball:material:water mass ratio of 4:1:1.5 for 6 hours, then dried and passed through an 80-mesh sieve;

[0059] Granulation: After drying the secondary material obtained from the secondary ball milling, 10wt% PVA solution is added by weight percentage and then granulated and sieved.

[0060] Molding: The granulated fine powder is placed into a mold and pressed under a pressure of 200 MPa;

[0061] Sintering: The formed green parts are placed in an oxygen atmosphere sintering furnace and sintered using a multi-step sintering method. The sintering temperature is 910℃ and the holding time is 20h.

[0062] The basic performance of the garnet ferrite materials prepared in Examples 1-3 and Comparative Example 1 were tested, and the test results are shown in Table 1.

[0063] Table 1 Basic Performance Table

[0064]

[0065] As can be seen from the table, the density d of the garnet ferrite materials prepared in Examples 1 to 3 of this invention is higher than that of the comparative example, and the porosity P is lower than that of the comparative example, thus resulting in higher flexural strength than the comparative example. Therefore, the garnet ferrite material provided by this invention can achieve both high dielectric constant and high flexural strength.

[0066] Furthermore, such as Figure 1 , Figure 2 , Figure 3 The images shown are scanning electron microscope (SEM) images of the garnet ferrite materials prepared in Examples 1, 2, and 3, respectively. As can be seen from the images, the grain size distribution is uniform, the grains are full, and the grain boundaries are clear.

[0067] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A garnet ferrite with high dielectric constant and high flexural strength, characterized in that, The chemical formula of the garnet ferrite material is: Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12 , 1.5≤a≤2.0, 0 <b≤0.8,0.3≤c≤0.7,0<d≤0.3。 2. The method for preparing garnet ferrite with high dielectric constant and high flexural strength according to claim 1, characterized in that, Includes the following steps: Step 1.配料: According to the chemical formula Bi a Ca b Y 3-a-b Zr c V d Fe 5-c-d O 12 , where 1.5 ≤ a ≤ 2.0, 0 < b ≤ 0.8, 0.3 ≤ c ≤ 0.7, 0 < d ≤ 0.3, calculate and weigh the raw materials, and the raw materials are Bi2O3, CaCO3, Y2O3, ZrO2, V2O5, Fe2O3; Step 2, primary ball milling: The raw materials are ball milled and mixed, then dried and sieved to obtain primary ball milled powder; Step 3, Pre-calcination: The ball-milled powder is pre-calcined at 800~900℃ for 1~5 hours. After pre-calcination, it is crushed and sieved to obtain pre-calcined material. Step 4, Secondary ball milling: Based on the mass of the pre-fired material, add 0.1~0.3wt% of SiO2 to the pre-fired material and perform secondary ball milling. After ball milling, dry and sieve to obtain secondary ball milled powder. Step 5: Granulation: Add polyvinyl alcohol (PVA) aqueous solution to the secondary ball milling powder for granulation to obtain granulated material; Step 6: Molding: The granulated material is placed into a mold and pressed to form a green body; Step 7, Sintering: Place the green blank in a sintering furnace with an oxygen atmosphere, and continuously introduce oxygen at a flow rate of 0.3~0.8L / min. The sintering temperature is 900~950℃, and the holding time is 18~20h.

3. The method for preparing garnet ferrite with high dielectric constant and high flexural strength according to claim 2, characterized in that, The ball milling process is as follows: the raw material, zirconia balls, and deionized water are placed in a planetary ball mill for ball milling. The mass ratio of balls:material:water is 4:1:1.5, and the ball milling time is 5 to 8 hours.

4. The method for preparing garnet ferrite with high dielectric constant and high flexural strength according to claim 2, characterized in that, The secondary ball milling process is as follows: the raw material, zirconia balls, and deionized water are placed in a planetary ball mill for ball milling. The mass ratio of balls:material:water is 4:1:1.5, and the ball milling time is 6 to 10 hours.

5. The method for preparing garnet ferrite with high dielectric constant and high flexural strength according to claim 2, characterized in that, During the granulation process, the amount of polyvinyl alcohol (PVA) aqueous solution used is 8-12 wt% of the mass of the secondary ball milled powder.

6. The method for preparing garnet ferrite with high dielectric constant and high flexural strength according to claim 2, characterized in that, The pressure for compression molding is 150~200 MPa.

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