Niobate-based microwave dielectric ceramic as well as preparation method and application thereof

Abstract

The invention discloses niobate-based microwave dielectric ceramic and a preparation method and application thereof, and belongs to the technical field of microwave dielectrics.MgO, Nb2O5, CaCO3 and TiO2 are mixed according to a certain proportion through a solid-phase reaction method, ball milling, drying, sieving, presintering, secondary ball milling, granulation, sieving and blank making are conducted, and blocky niobate-based microwave dielectric ceramic is obtained; a composite substrate is prepared based on the dielectric ceramic and ferrite, and the problems that an existing single ferrite substrate is low in dielectric constant and large in magnetic loss and cannot meet the miniaturization process requirement of a microstrip circulator are solved. The circulator can be widely applied to broadband and miniaturized circulators.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave dielectrics, and in particular relates to a niobate-based microwave dielectric ceramic and a preparation method and application thereof. Background Art

[0002] Microwave dielectric ceramics, as dielectric materials, are widely used in the preparation of microwave components such as dielectric substrates, resonators, filters, antennas, etc. Microwave dielectric ceramic components have the characteristics of small size, light weight, good temperature stability, and low price. They are widely used in mobile communications, global satellite positioning systems, repeaters, and military radar systems.

[0003] In recent years, with the increasing demand for electronic information technology and equipment, ferrite circulators are developing in the direction of miniaturization, high power capacity, and broadband. Circulators based on traditional single ferrite substrate designs are subject to technical problems such as low dielectric constant, large magnetic loss, and second harmonic interference. The miniaturization, high power, and broadband functions of circulators have reached their limits and cannot meet the needs of the development of new equipment technology. The new ferrite-dielectric ceramic composite substrate is one of the key materials for circulators. The microstrip circulator designed based on this composite substrate inherits the technical characteristics of dielectric ceramics such as high dielectric constant, low loss, and adjustable performance, and can realize the miniaturization, high power, and ultra-wideband design of circulators. Therefore, it is crucial to develop a dielectric ceramic that matches the ferrite composite substrate. Summary of the invention

[0004] The purpose of the present invention is to meet the new demand for dielectric ceramics in the new ferrite-dielectric ceramic composite substrate, and to prepare a niobate-based microwave dielectric ceramic that matches the dielectric constant and thermal expansion coefficient of ferrite by a solid phase reaction method. The ceramic also has a high quality factor. Finally, by nesting the ceramic with garnet ferrite, a high-reliability ferrite-dielectric ceramic composite substrate is prepared.

[0005] The present invention is achieved through the following technical solutions.

[0006] A niobate-based microwave dielectric ceramic has a chemical composition expression of Mg4Nb2O9-CaTiO3, wherein the molar ratio of Mg4Nb2O9 to CaTiO3 is 4:1.

[0007] A method for preparing niobate-based microwave dielectric ceramics comprises the following steps: Nb2O5 and MgO were mixed according to the stoichiometric formula for synthesizing Mg4Nb2O9 to obtain powder 1; CaCO3 and TiO2 were mixed according to the stoichiometric formula for synthesizing CaTiO3 to obtain powder 2; powder 1 and powder 2 were mixed according to a molar ratio of 4:1, put into a nylon ball mill, added with distilled water and zirconium oxide balls, and ball milled for 12-24 hours to obtain powder 3; Powder 3 is placed in an oven, maintained at 100-120° C. for drying, and passed through a 40-mesh sieve to obtain powder 4; Powder 4 is placed in a bell furnace, maintained at 1000-1200° C. for pre-calcination for 6-8 hours to obtain powder 5; Powder 5 is placed in a nylon ball mill, distilled water and zirconium oxide balls are added, and ball milled for 12-24 hours to obtain powder 6; Powder 6 is placed in a spray granulator, 8wt.%-16wt.% of PVA is added for granulation, and passed through a 40-mesh sieve to obtain powder 7; The powder material is pressed into a green body by a hydraulic press, and sintered at 1300-1350° C. for 4-6 hours to obtain Mg4Nb2O9-CaTiO3 microwave dielectric ceramics.

[0008] The present invention uses MgO, Nb2O5, CaCO3 and TiO2 as raw materials to prepare niobate-based microwave dielectric ceramics, adopts a spray granulation process, and has a simple preparation process. The prepared Mg4Nb2O9-CaTiO3 microwave dielectric ceramics have excellent performance, wherein the dielectric constant ε r It is 15.27-15.43, the quality factor Q×f is 58812-77274GHz, the coefficient of thermal expansion CTE is 10.79-10.87ppm / ℃, and the three-point bending strength is 160-187Mpa.

[0009] An application of niobate-based microwave dielectric ceramics for ferrite circulator composite substrates; The ferrite circulator composite substrate is prepared by a nested molding method; The nested molding method comprises: nesting the processed ferrite disc into the hole of the dielectric ceramic substrate, spreading the adhesive evenly on the substrate with a scraper, vacuum adsorbing for 30 minutes, scraping off the excess adhesive on the surface of the substrate after completion, placing the embedded composite substrate in a muffle furnace for sintering, the sintering temperature is 600° C. to 800° C., the time is 10 minutes to 30 minutes, and after sintering, the substrate is ground and polished with a high-precision grinding and polishing machine.

[0010] The beneficial effects of the present invention are as follows: the prepared Mg4Nb2O9-CaTiO3 microwave dielectric ceramic not only has excellent dielectric properties, but also has high three-point bending strength, and has a thermal expansion coefficient similar to that of ferrite, which ensures the high reliability of the ferrite circulator composite substrate, can achieve the stabilization of the structure and performance of the ferrite circulator, and has great application prospects and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a metallographic diagram. DETAILED DESCRIPTION

[0012] The technical solution of the present invention is described in detail below.

[0013] The chemical raw materials Nb2O5 and MgO were mixed according to the stoichiometric formula Mg4Nb2O9, and the raw material ratio was: 498g Nb2O5, 302g MgO. CaCO3 and TiO2 were mixed according to the stoichiometric formula CaTiO3, and the raw material ratio was: 46.83g CaCO3, 37.4g TiO2. 884.23g of the mixed powder was put into a nylon ball mill, 1326g of distilled water was added, 1768g of zirconia balls were added, and the mixture was ball milled on a planetary ball mill for 24 hours; The ball-milled raw materials were placed in an oven and dried at 110°C, and then passed through a 40-mesh sieve; The dried and sieved powder is placed in a bell furnace and pre-fired at 1000°C for 4 hours; The pre-sintered powder was placed in a nylon ball mill, 884 g of distilled water and 1768 g of zirconium oxide balls were added, and then ball milled on a planetary ball mill for 24 hours; The raw materials after secondary ball milling were added with 10wt.% PVA, and put into a spray granulator with a centrifugal atomizer speed of 220 rpm and an outlet temperature of 180°C for granulation, and then passed through a 40-mesh sieve and pressed into a green body with a pressure of 3MPa using an oil press. The green body was 69mm long and 69mm wide. The green body was sintered at a temperature of 1°C / min to 1300-1350°C and kept at that temperature for 4 hours to obtain niobate-based microwave dielectric ceramics.

[0014] Preparation of circulator composite substrate: embed the processed ferrite disc into the hole of the dielectric ceramic substrate, spread the adhesive evenly on the substrate with a scraper, and vacuum adsorb for 30 minutes. After that, scrape off the excess adhesive on the surface of the substrate, place the embedded composite substrate in a muffle furnace for sintering at a temperature of 600℃~800℃ and a time of 10min~30min. After sintering, use a high-precision grinding and polishing machine to grind and polish the substrate.

[0015] The present invention is not limited to the above-described embodiments, and many variations of details are possible without thereby departing from the scope and spirit of the present invention.

Claims

1. A niobate-based microwave dielectric ceramic, characterized in that: Its chemical composition expression is Mg4Nb2O9-CaTiO3, where the molar ratio of Mg4Nb2O9 and CaTiO3 is 4:

1.

2. A process for preparing niobate-based microwave dielectric ceramics, characterized in that: include: MgO and Nb2O5 are mixed according to the stoichiometric formula for synthesizing Mg4Nb2O9 to obtain powder 1; CaCO3 and TiO2 are mixed according to the stoichiometric formula for synthesizing CaTiO3 to obtain powder material 2; Powder 1 and powder 2 were mixed in a molar ratio of 4:1, distilled water was added, and the mixture was ball-milled to obtain powder 3; Dry the powder 3, sieve it, and obtain the powder 4; Heat the powder material 4, maintain the temperature at 1000-1200°C for 4-6 hours, and obtain the powder material 5; Add powder 5 into distilled water and ball-mill to obtain powder 6; Add 8wt.%-16wt.% of PVA to powder 6, granulate, and sieve to obtain powder 7; The powder material is pressed into a green body, and sintered at 1300-1400° C. for 6-8 hours to obtain a niobate-based microwave dielectric ceramic.

3. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The heating is carried out in a bell furnace at a temperature of 100-120°C.

4. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The mesh number of the sieving is 40 meshes.

5. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The ball milling equipment adopts a planetary ball mill with a rotation speed of 60-80 rpm, and the balls in contact with the material are nylon and zirconia balls.

6. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The ball milling time is 12-24 hours.

7. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The granulation adopts a spray granulator, the rotation speed of the centrifugal atomizer is 200-240 rpm, and the outlet temperature is 160-180°C.

8. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The pressing is performed by a hydraulic press at a pressure of 3 MPa, and the green compact is in a block shape with a length of 69 mm and a width of 69 mm.

9. The process for preparing the niobate-based microwave dielectric ceramic according to claim 2, characterized in that: The heating rate of the sintering is 1°C / min.

10. A method for preparing a niobate-based microwave dielectric ceramic composite substrate, characterized in that: The processed ferrite disc is embedded in the hole of any one of the dielectric ceramic substrates of claim 1 to claim 9, the adhesive is spread on the substrate, and the embedded composite substrate is sintered at a sintering temperature of 600°C to 800°C for 10 minutes to 30 minutes. After sintering, the substrate is ground and polished.

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