Preparation method of Ca / Co-Ni doped barium ferrite broadband wave-absorbing ceramic

Abstract

The invention discloses a Ca / Co-Ni doped barium ferrite broadband wave-absorbing ceramic preparation method, which comprises: carrying out wet ball milling on each reaction raw material according to a certain ratio, drying, pre-sintering at a temperature of 950-1000 DEG C to obtain pre-sintered powder, carrying out mixing grinding on the pre-sintered powder and polyvinyl alcohol, carrying out granulation, placing in a mold, and carrying out pressure maintaining for 5 min under a pressure of 16 MPa to prepare a green body; and finally, carrying out heat preservation and glue discharging in a rapid heating furnace at the temperature of 550-650 DEG C, and then continuously heating to 1250-1350 DEG C and sintering to prepare the ceramic. The three-ion-doped ceramic prepared by the method has an M-type phase structure, the ceramic has a soft magnetic characteristic due to doping, the complex dielectric constant of the ceramic is increased, and a formant is generated. And the wave-absorbing bandwidth of the ceramic with the thickness of 1.5 mm, of which the RL is less than-5dB, is 13.5 GHz. The preparation method has the advantages of simple process, rapidness, high practicability and no need of microstructure control, and the prepared ceramic material has the advantages of high temperature resistance, high wave-absorbing property, wide absorption frequency band and the like.

Description

Technical Field

[0001] The invention relates to the technical field of barium ferrite ceramic material modification, and in particular to a method for preparing Ca / Co-Ni doped barium ferrite broadband wave absorbing ceramics. Background Art

[0002] Barium ferrite is a typical hexagonal ferrite with high magnetocrystalline anisotropy, high coercivity and excellent electromagnetic wave absorption properties. Due to its natural resonance characteristics and adjustable magnetic properties, barium ferrite exhibits good wave absorption performance in the microwave frequency band (GHz range).

[0003] However, the electromagnetic wave absorption band of current materials is relatively narrow, and they can only absorb electromagnetic waves in a small frequency band, but cannot achieve broadband absorption, which limits the actual application scope and scenarios. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing Ca / Co-Ni doped barium ferrite broadband absorbing ceramics, adopt a high-temperature solid-phase method to prepare doped barium ferrite powder and ceramic blocks, and improve the absorbing performance of barium ferrite through doping modification, making it an important candidate material for preparing broadband absorbing coatings.

[0005] The present invention provides a method for preparing a Ca / Co-Ni doped barium ferrite broadband wave absorbing ceramic, comprising the following steps:

[0006] (1) Mixing and drying: Weigh the raw materials according to the molar ratio of BaCO3:CaCO3:Co3O4:Fe2O3:Ni2O3=24:6:(6-10x):57:15x, where x=0.1-0.4, add the mixed raw materials into a nylon ball mill, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, then add deionized water according to the ratio of mixed raw materials: water=1000 g:400 ml, place the nylon ball mill on a planetary ball mill and grind at 300 r / min. -1 After ball milling for 5 to 7 hours at a speed of 10000 g / cm2, the mixed powder is poured into a tray and placed in a drying oven for drying until the deionized water evaporates completely to obtain dry powder;

[0007] (2) Pre-sintering: The dry powder obtained in step (1) is ground and sieved, added into an alumina crucible, and placed in a silicon carbon rod resistance furnace at 5°C / min. -1 The temperature is raised to a pre-sintering temperature of 950-1000°C at a rate of 100°C and kept at that temperature for 4-6 hours, and then cooled to room temperature to obtain a doped barium ferrite pre-sintering powder;

[0008] (3) Molding: After grinding and sieving the pre-burned powder obtained in step (2), the pre-burned powder and 5 wt.% of polyvinyl alcohol are weighed in a ratio of pre-burned powder: polyvinyl alcohol = 10: (0.8-1.2), and the pre-burned powder is fully ground and sieved again, and granulated. The granulated powder is then added to a mold and maintained at a pressure of 16 MPa for 5 minutes to obtain a dense green body;

[0009] (4) Sintering: The green body obtained in step (3) is placed on an alumina support plate and placed in a rapid heating furnace at 3°C / min. -1 The temperature was raised to 550-650℃ debinding temperature and kept at this temperature for 1.5-2.5h to debind the green body PVA, and then continued to heat at 5℃·min -1 The temperature is raised to a sintering temperature of 1250-1350°C at a rate and kept at that temperature for 1.5-2.5 hours, and then dropped to room temperature to obtain a ceramic product.

[0010] Preferably, in step (1), the temperature of the drying oven is 70-90° C., the drying and heat preservation time is 20-24 h, and the mass ratio of the ZrO2 grinding balls with diameters of 9 mm and 7 mm used is 1:1.

[0011] Preferably, the pre-firing temperature in step (2) is 1000° C., and the pre-firing insulation time is 4 to 6 hours.

[0012] Preferably, in step (3), the ratio of pre-fired powder to polyvinyl alcohol is 10:1, and the size of the green body is 72.5 l mm×33.82 w mm×2.50 t mm.

[0013] Preferably, in step (4), the binder removal temperature is 600° C., the binder removal insulation time is 2 h, the sintering temperature is 1300° C., and the sintering insulation time is 2 h.

[0014] Beneficial effects of the present invention: The preparation method of the Ca / Co-Ni doped barium ferrite broadband wave absorbing ceramic of the present invention has the following reaction formula: 24BaCO3+6CaCO3+(6-10x)Co3O4+57Fe2O3+15xNi2O3=30Ba 0.8 Ca 0.2 Fe 11.4 Co 0.6-x Ni x O 19+30CO2. The triple-ion-doped ceramics prepared by this method have an M-type phase structure, and doping endows the ceramics with soft magnetic properties, increases their complex permittivity, and the complex permeability first increases and then decreases, generating a resonance peak. The microwave absorption bandwidth with RL less than -5 dB for the prepared 1.5-mm-thick ceramics is 13.5 GHz. This preparation method uses the high-temperature solid-state method to prepare doped barium ferrite powders and ceramic blocks. By doping modification, the microwave absorption performance of barium ferrite is improved, making it an important candidate material for preparing broadband microwave absorption coatings. In addition, this method has the advantages of simple, fast, and practical process, does not require microstructure control, and the prepared ceramic materials have high temperature resistance, strong microwave absorption performance, and wide absorption bandwidth. Description of the Drawings

[0015] Figure 1 XRD pattern of the doped ceramics;

[0016] Figure 2 Fracture morphology of the doped ceramics;

[0017] Figure 3 Curves of electromagnetic parameters of the doped ceramics varying with frequency;

[0018] Figure 4 Reflectivity curves of the doped ceramics with different thicknesses. Detailed Embodiments

[0019] To make the technical solutions of the present invention easier to understand, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings by using specific embodiments.

[0020] Example 1:

[0021] The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorption ceramics in this example includes the following steps:

[0022] (1) Batching and drying: Weigh each reaction raw material according to the molar ratio BaCO3:CaCO3:Co3O4:Fe2O3:Ni2O3 = 24:6:(6 - 10x):57:15x, where x = 0.1. Add the mixed raw materials into a nylon ball milling tank, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, and then add deionized water according to the ratio of mixed raw materials:water = 1000 g:400 ml. Place the nylon ball milling tank on a planetary ball mill and ball mill at a speed of 300 r·min -1 for 5 h. Then pour the mixed powder into a tray and place it in a drying oven at 70 °C for 20 h until the deionized water completely evaporates to obtain dry powder;

[0023] (2) Pre-sintering: The dry powder obtained in step (1) is ground and sieved, added into an alumina crucible, and placed in a silicon carbon rod resistance furnace at 5°C / min. -1 The temperature is raised to a pre-sintering temperature of 950°C at a rate of 10000 ℃ and kept at that temperature for 4 hours, and then cooled to room temperature to obtain a doped barium ferrite pre-sintering powder;

[0024] (3) Molding: After grinding and sieving the pre-burned powder obtained in step (2), the pre-burned powder and 5 wt.% of polyvinyl alcohol are weighed in a ratio of pre-burned powder to polyvinyl alcohol = 10:0.8, and the pre-burned powder is fully ground and sieved again, and granulated. The granulated powder is then added to a mold and maintained at a pressure of 16 MPa for 5 minutes to obtain a dense green body;

[0025] (4) Sintering: The green body obtained in step (3) is placed on an alumina support plate and placed in a rapid heating furnace at 3°C / min. -1 The temperature was raised to 550-650℃ debinding temperature and kept at this temperature for 1.5h to debind the green body PVA, and then continued to heat at 5℃·min -1 The temperature is raised to a sintering temperature of 1250°C at a rate and kept at that temperature for 1.5 hours, and then dropped to room temperature to obtain a ceramic product.

[0026] Embodiment 2:

[0027] The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic of this embodiment comprises the following steps:

[0028] (1) Mixing and drying: Weigh the raw materials according to the molar ratio of BaCO3:CaCO3:Co3O4:Fe2O3:Ni2O3=24:6:(6-10x):57:15x, where x=0.2, add the mixed raw materials into a nylon ball mill, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, then add deionized water according to the ratio of mixed raw materials: water=1000 g:400 ml, place the nylon ball mill on a planetary ball mill and grind at 300 r / min. -1 After ball milling at a speed of 6 h, the mixed powder was poured into a tray, placed in a drying oven at a temperature of 80 ° C, and dried for 22 h until the deionized water evaporated completely to obtain a dry powder;

[0029] (2) Pre-sintering: The dry powder obtained in step (1) is ground and sieved, added into an alumina crucible, and placed in a silicon carbon rod resistance furnace at 5°C / min. -1 The temperature is raised to a pre-sintering temperature of 1000°C at a rate of 1000°C and kept at that temperature for 5 hours, and then cooled to room temperature to obtain a doped barium ferrite pre-sintering powder;

[0030] (3) Molding: After grinding and sieving the pre-burned powder obtained in step (2), the pre-burned powder and 5 wt.% of polyvinyl alcohol are weighed in a ratio of pre-burned powder to polyvinyl alcohol = 10:1, and after fully grinding, the powder is sieved again and granulated. Then, the granulated powder is added to a mold and maintained at a pressure of 16 MPa for 5 minutes to obtain a dense green body;

[0031] (4) Sintering: The green body obtained in step (3) is placed on an alumina support plate and placed in a rapid heating furnace at 3°C / min. -1 The temperature was raised to 600℃ debinding temperature and kept at this temperature for 2h to debind the green body PVA, and then continued to be heated at 5℃·min -1 The temperature is raised to a sintering temperature of 1300°C at a rate and kept at that temperature for 2 hours, and then cooled to room temperature to obtain a ceramic product.

[0032] Embodiment 3:

[0033] The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic of this embodiment comprises the following steps:

[0034] (1) Mixing and drying: Weigh the raw materials according to the molar ratio of BaCO3:CaCO3:Co3O4:Fe2O3:Ni2O3=24:6:(6-10x):57:15x, where x=0.3, add the mixed raw materials into a nylon ball mill, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, then add deionized water according to the ratio of mixed raw materials: water=1000 g:400 ml, place the nylon ball mill on a planetary ball mill and grind at 300 r / min. -1 After ball milling for 7 hours at a speed of , the mixed powder was poured into a tray, placed in a drying oven at a temperature of 90°C, and dried for 24 hours until the deionized water evaporated completely to obtain a dry powder;

[0035] (2) Pre-sintering: The dry powder obtained in step (1) is ground and sieved, added into an alumina crucible, and placed in a silicon carbon rod resistance furnace at 5°C / min. -1 The temperature is raised to a pre-sintering temperature of 9800°C at a rate of 1000°C and kept at that temperature for 6 hours, and then cooled to room temperature to obtain a doped barium ferrite pre-sintering powder;

[0036] (3) Molding: After grinding and sieving the pre-burned powder obtained in step (2), the pre-burned powder and 5 wt.% of polyvinyl alcohol are weighed in a ratio of pre-burned powder to polyvinyl alcohol = 10:1.2, and the pre-burned powder is fully ground and sieved again, and granulated. The granulated powder is then added to a mold and maintained at a pressure of 16 MPa for 5 minutes to obtain a dense green body;

[0037] (4) Sintering: The green body obtained in step (3) is placed on an alumina support plate and placed in a rapid heating furnace at 3°C / min. -1 The temperature was raised to 650℃ debinding temperature and kept at this temperature for 2.5h to debind the green body PVA, and then continued to rise at 5℃·min -1 The temperature is raised to a sintering temperature of 1350°C at a rate and kept at that temperature for 2.5 hours, and then cooled to room temperature to obtain a ceramic product.

[0038] Embodiment 4:

[0039] The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic of this embodiment comprises the following steps:

[0040] (1) Mixing and drying: Weigh the raw materials according to the molar ratio of BaCO3:CaCO3:Co3O4:Fe2O3:Ni2O3=24:6:(6-10x):57:15x, where x=0.4, add the mixed raw materials into a nylon ball mill, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, then add deionized water according to the ratio of mixed raw materials: water=1000 g:400 ml, place the nylon ball mill on a planetary ball mill and grind at 300 r / min. -1 After ball milling at a speed of 6 h, the mixed powder was poured into a tray, placed in a drying oven at a temperature of 80 ° C, and dried for 824 h until the deionized water was completely evaporated to obtain a dry powder;

[0041] (2) Pre-sintering: The dry powder obtained in step (1) is ground and sieved, added into an alumina crucible, and placed in a silicon carbon rod resistance furnace at 5°C / min. -1 The temperature is raised to a pre-sintering temperature of 1000°C at a rate of 1000°C and kept at that temperature for 5 hours, and then cooled to room temperature to obtain a doped barium ferrite pre-sintering powder;

[0042] (3) Molding: After grinding and sieving the pre-burned powder obtained in step (2), the pre-burned powder and 5 wt.% of polyvinyl alcohol are weighed in a ratio of pre-burned powder to polyvinyl alcohol = 10:0.9, and after fully grinding, the powder is sieved again and granulated. The granulated powder is then added to a mold and maintained at a pressure of 16 MPa for 5 minutes to obtain a dense green body;

[0043] (4) Sintering: The green body obtained in step (3) is placed on an alumina support plate and placed in a rapid heating furnace at 3°C / min. -1 The temperature was raised to 650℃ debinding temperature and kept at this temperature for 2h to debind the green body PVA, and then continued to rise at 5℃·min -1 The temperature is raised to a sintering temperature of 1300°C at a rate and kept at that temperature for 2 hours, and then cooled to room temperature to obtain a ceramic product.

[0044] Comparative Example 1:

[0045] The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic of this comparative example comprises the following steps:

[0046] (1) Compounding and drying: Weigh the raw materials according to the molar ratio of BaCO3:CaCO3:Fe2O3=24:6:57, add the mixed raw materials into a nylon ball mill, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, then add deionized water according to the ratio of mixed raw materials: water=1000 g:400 ml, place the nylon ball mill on a planetary ball mill and rotate at 300 r / min. -1 After ball milling at a speed of 6 h, the mixed powder was poured into a tray, placed in a drying oven at a temperature of 80 ° C, and dried for 824 h until the deionized water was completely evaporated to obtain a dry powder;

[0047] (2) Pre-sintering: The dry powder obtained in step (1) is ground and sieved, added into an alumina crucible, and placed in a silicon carbon rod resistance furnace at 5°C / min. -1 The temperature is raised to a pre-sintering temperature of 1000°C at a rate of 1000°C and kept at that temperature for 5 hours, and then cooled to room temperature to obtain a doped barium ferrite pre-sintering powder;

[0048] (3) Molding: After grinding and sieving the pre-burned powder obtained in step (2), the pre-burned powder and 5 wt.% of polyvinyl alcohol are weighed in a ratio of pre-burned powder to polyvinyl alcohol = 10:1, and after fully grinding, the powder is sieved again and granulated. Then, the granulated powder is added to a mold and maintained at a pressure of 16 MPa for 5 minutes to obtain a dense green body;

[0049] (4) Sintering: The green body obtained in step (3) is placed on an alumina support plate and placed in a rapid heating furnace at 3°C / min. -1 The temperature was raised to 650℃ debinding temperature and kept at this temperature for 2h to debind the green body PVA, and then continued to rise at 5℃·min -1 The temperature is raised to a sintering temperature of 1300°C at a rate and kept at that temperature for 2 hours, and then cooled to room temperature to obtain a ceramic product.

[0050] Performance characterization:

[0051] According to the standard sizes of S-band, C1-band, C2-band, X-band and Ku-band, the ceramic samples prepared in the embodiments and comparative examples were cut into dielectric samples using a multifunctional grinder, and performance tests were performed on them.

[0052] Figure 1 is the XRD pattern of doped ceramics. Figure 1It can be seen that the prepared three-ion-doped ceramics have an M-type phase structure. In addition, weak diffraction peaks are found at 32.8°, 37.7°, 41.3°, 43.3° and 57.5°. By comparing with the standard PDF cards (75-0276 and 73-2034), these peaks belong to the phases of X-type and W-type structures. The preparation of hexagonal ferrites is extremely complex, and in different temperature regions, the phase formation temperatures of different types of hexagonal ferrites will overlap.

[0053] Figure 2 (a)-(d) are the fracture morphologies of the doped ceramics. The grain shapes of the ceramics change significantly, and larger irregular blocky grains appear, improving the density of the ceramics.

[0054] Figure 3 are the curves of the electromagnetic parameters of the undoped ceramics varying with frequency. The wave absorption of barium ferrite wave-absorbing materials for electromagnetic waves includes two parts: dielectric loss and magnetic loss. The curves of the dielectric loss and magnetic loss of the ion-doped ceramics varying with frequency are calculated through the measured electromagnetic parameters. As Figure 3 shown. It can be observed from the figure that as the doping amount x of Ni 2+ increases from 0.1 to 0.4, the dielectric loss gradually increases from 0.2 to 0.5; the magnetic loss first increases and then decreases. When x = 0.1, the magnetic loss reaches the maximum value of 1.7, which is about 70% higher than that of the undoped ceramics. Combining the analysis of the results of the electromagnetic parameters, it can be known that the addition of ion doping forms dipoles with the electrons on the oxygen vacancies, and the change in the direction of the dipoles under the action of the electromagnetic field causes the polarization effect to enhance, resulting in an increase in dielectric loss. The addition of Ni 2+ forms dipoles with the electrons on the oxygen vacancies, and the change in the direction of the dipoles under the action of the electromagnetic field causes the polarization effect to enhance, resulting in an increase in dielectric loss. At the same time, an appropriate amount of Ni 2+ doping enhances the magnetic loss and reduces the magnetocrystalline anisotropy, causing the resonance frequency to shift to the low frequency.

[0055] Figure 4 gives the reflectivity curves of the doped ceramics with different thicknesses. It can be observed from the figure that when the ceramic thickness increases from 1.5 mm to 3.5 mm, the frequency of the strongest absorption peak of the RL curve shifts to the low frequency, and the wave-absorbing bandwidth with RL less than -5 dB becomes narrower; as the doping amount x increases, when the ceramic thickness is the same, the frequency of the strongest absorption peak gradually shifts to the high frequency, and the wave-absorbing bandwidth gradually becomes narrower. When x is 0.1 respectively, the wave-absorbing bandwidth with RL less than -5 dB of the 1.5-mm-thick doped ceramics reaches 13.5 GHz, realizing broadband absorption in the 4.5 - 18 GHz frequency band. At this time, the wave-absorbing performance is the best, because the attenuation coefficient of the ceramics with x = 0.1 is relatively large, and the attenuation effect on the electromagnetic waves entering the ceramics is better, obtaining excellent wave-absorbing performance.

[0056] Experimental summary: Doping causes the ceramic to have soft magnetic properties, its complex dielectric constant increases, and its complex permeability first increases and then decreases, generating a resonance peak. The microwave absorption bandwidth with RL less than -5 dB for the 1.5-mm-thick ceramic is 13.5 GHz.

[0057] It should be noted that the embodiments described herein are only partial embodiments of the present invention, rather than all implementation manners of the present invention. The embodiments are only exemplary, and their functions are only to provide a more intuitive and clear way to understand the content of the present invention, rather than a limitation on the technical solutions of the present invention. Without departing from the concept of the present invention, all other implementation manners that can be thought of by those of ordinary skill in the art without creative efforts, as well as other simple substitutions and various changes to the technical solutions of the present invention, all fall within the protection scope of the present invention.

Claims

1. A preparation method of Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramics, characterized in that, It includes the following steps: (1) Ingredients and drying: Weigh each reaction raw material according to the molar ratio of BaCO3:CaCO3:Co3O4:Fe2O3:Ni2O3 = 24:6:(6 - 10x):57:15x, where x = 0.1 - 0.

4. Add the mixed raw materials into a nylon ball milling tank, add ZrO2 grinding balls with diameters of 9 mm and 7 mm according to the ball-to-material ratio of 2:1, and then add deionized water according to the ratio of mixed raw materials:water = 1000 g:400 ml. Place the nylon ball milling tank on a planetary ball mill and ball mill at a speed of 300 r·min -1 for 5 - 7 h. Then pour the mixed powder into a tray and put it into a drying oven to dry until the deionized water completely volatilizes, obtaining dry powder; (2) Pre-sintering: After grinding and sieving the dried powder obtained in step (1), add it into an alumina crucible and place it in a silicon carbide rod resistance furnace. Heat it at a heating rate of 5 °C·min -1 to the pre-sintering temperature of 950 - 1000 °C, hold for 4 - 6 h, and then cool to room temperature to obtain the doped barium ferrite pre-sintered powder; (3) Shaping: After grinding and sieving the pre-sintered powder obtained in step (2), weigh the pre-sintered powder and 5wt.% polyvinyl alcohol according to the ratio of pre-sintered powder: polyvinyl alcohol = 10: (0.8 - 1.2), conduct sufficient grinding, then sieve and granulate again. Then add the granulated powder into a mold, and under a pressure of 16 MPa, hold the pressure for 5 minutes to obtain a dense green body; (4) Sintering: Place the green body obtained in step (3) on an alumina sintering plate and put it in a rapid heating furnace. Heat it at a rate of 3 °C·min -1 to the debinding temperature of 550 - 650 °C and hold for 1.5 - 2.5 h to perform PVA debinding of the green body, then continue to heat it at a rate of 5 °C·min -1 to the sintering temperature of 1250 - 1350 °C and hold for 1.5 - 2.5 h, and then cool it to room temperature to obtain a ceramic product.

2. The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic according to claim 1, characterized in that, In step (1), the temperature of the drying oven is 70 - 90 °C, the drying and heat preservation time is 20 - 24 h, and the mass ratio of the ZrO2 grinding balls with diameters of 9 mm and 7 mm used is 1:

1.

3. The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic according to claim 1, characterized in that, In step (2), the pre-sintering temperature is 1000 °C, and the pre-sintering and heat preservation time is 4 - 6 h.

4. The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic according to claim 1, characterized in that, In the step (3), the pre-burned powder: polyvinyl alcohol = 10:1, and the size of the green body is 72.5 l mm × 33.82 w mm × 2.50 t mm.

5. The preparation method of the Ca / Co-Ni doped barium ferrite broadband microwave absorbing ceramic according to claim 1, characterized in that, In step (4), the debinding temperature is 600 °C, the debinding and heat preservation time is 2 h, the sintering temperature is 1300 °C, and the sintering and heat preservation time is 2 h.

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