CN112645703B - Preparation of compact small-grain BaFe by three-step sintering method 12 O 19 Preparation method of ferrite ceramic - Google Patents
Preparation of compact small-grain BaFe by three-step sintering method 12 O 19 Preparation method of ferrite ceramic Download PDFInfo
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Abstract
The invention discloses a three-step sintering method for preparing compact small-grain BaFe 12 O 19 Method for preparing ferrite ceramic, BaFe formed by sol-gel method 19 O 12 The powder has small grain diameter and excellent magnetic property, and the used BaFe is realized by granulation and sieving 19 O 12 The size uniformity of powder particles; by rapidly increasing the temperature to a large value (T) during sintering 1 ) Then rapidly cooling to a lower value (T) 2 ) Keeping the temperature for a short time, and then continuously and rapidly cooling to a lower value (T) 3 ) And the heat preservation is carried out for a longer time, and the BaFe is inhibited in the process 19 O 12 Grain boundary migration of ceramics while maintaining BaFe 19 O 12 The ceramic grain boundary diffusion is active, and compact small crystal grain BaFe is realized 19 O 12 And (3) preparing the ceramic. The product synthesized by the method has small grain size and high purity; BaFe thus prepared 12 O 19 The ceramic has obviously better compactness, grain size, saturation magnetization and other parameters than BaFe prepared by the traditional method 12 O 19 The ceramic can meet higher application requirements.
Description
Technical Field
The invention relates to the technical field of magnetoplumbite type ferrite materials, in particular to a three-step sintering method for preparing compact small-grain BaFe 12 O 19 A preparation method of ferrite ceramics.
Background
M type barium ferrite (BaFe) 12 O 19 ) As a magnetoplumbite-type ferrite, has a strong uniaxial magnetocrystalline anisotropyThe material has the characteristics of high performance, high saturation magnetization, excellent chemical stability and the like, and is widely applied to microwave devices such as circulators and the like. With the continuous development of society, the requirements for the electronic industry are higher and higher, and no matter whether electronic devices or materials are used, the performance needs to be further improved to meet the requirements of the social development. The conventional sintering method improves BaFe only by increasing the calcination temperature 12 O 19 The densification of ceramics, but this method has limited contribution to densification. The high calcination temperature can lead the crystal grain to grow very quickly, and more air holes in the ceramic cannot be discharged in time, so the compactness is not high, the saturation magnetization of the sample is further lower than the theoretical value, and the BaFe is greatly reduced 12 O 19 The properties of the ceramic.
Therefore, it is necessary to provide a solution to the above-mentioned drawbacks in the prior art.
Disclosure of Invention
In view of the above, it is necessary to provide a three-step sintering method for preparing compact small-grain BaFe 12 O 19 Method for preparing ferrite ceramic capable of obtaining compact small-grain BaFe 12 O 19 Ceramic with saturation magnetization closer to BaFe 12 O 19 Theoretical value of the ceramic.
In order to overcome the defects in the prior art, the invention provides the following technical scheme:
preparation of compact small-grain BaFe by three-step sintering method 12 O 19 The preparation method of the ferrite ceramic comprises the following steps:
preparing a precursor solution: mixing ferric nitrate (Fe (NO) 3 ) 3 ) And barium nitrate (Ba (NO) 3 ) 2 ) The powder is prepared from the following components in a molar ratio of 12 : 1 Weighing, dissolving in deionized water to obtain a clear solution, adding citric acid with the same amount of substances as nitrate ions in ferric nitrate and barium nitrate, and fully stirring to completely dissolve the citric acid to obtain a precursor solution;
adjusting the pH value: continuously stirring, and slowly dropwise adding ammonia water into the precursor solution until the pH value of the solution is 6-7 to form light green transparent sol;
gel formation: putting the sol into a water bath kettle, heating in a water bath to form wet gel, putting the wet gel into an electrothermal blowing drying box, and preserving heat for 36 hours to obtain loose dry gel;
pre-burning: grinding the dry gel into powder, presintering the powder in a muffle furnace at the presintering temperature of 1000-1100 ℃, and preserving heat for 3 hours to obtain BaFe 12 O 19 Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe 12 O 19 In the primary powder, the mass of PVA doped in the primary powder is 5-10% of that of the pre-sintered primary powder, and the PVA is ground in a mortar to be uniformly mixed; mixing the BaFe 12 O 19 Placing the powder in a mould to be pressed into a large green body; grinding the large green body into powder again in a mortar, sieving the powder through 80-mesh and 120-mesh sieves, and taking the powder in the middle layers of the 80-mesh and 120-mesh sieves to obtain BaFe with proper particle size 12 O 19 Powder material; placing the powder in a mould, and pressing into a small green compact under the pressure of 5 MPa;
rubber discharging: calcining the small green bodies in a muffle furnace at 650 ℃ for 3 hours to remove PVA in the small green bodies;
and (3) sintering: placing the green body after the rubber discharge in a muffle furnace, setting the temperature rise speed to be 4 ℃/min, and heating the sample to the temperature T 1 Said temperature T 1 Rapidly cooling to the temperature T at a cooling rate of 25 ℃/min immediately after 1350-1400 DEG C 2 Said temperature T 2 Between 1300 ℃ and 1350 ℃ and at a temperature T 2 Keeping the temperature for 0.5 to 1 hour under the condition, and then rapidly cooling to the temperature T at the cooling speed of 25 ℃/min 3 Keeping the temperature T 3 Between 1200 ℃ and 1250 ℃ and at a temperature T 3 Keeping the temperature for 10 to 20 hours under the condition, then naturally cooling the mixture to room temperature to finally obtain compact small-grain BaFe 12 O 19 A ceramic.
Preferably, in the adjusting the pH, the pH is 7.
Preferably, in the pre-firing process, the pre-firing temperature is 1000 ℃.
Preferably, during said sintering, said T 1 Is 1350 ℃.
Preferably, during said sintering, said T 2 The temperature is 1300 ℃, and the heat preservation time is 0.5 h.
Preferably, during said sintering, said T 3 1250 ℃ and the heat preservation time is 10 h.
Compared with the prior art, the technical scheme of the invention is that BaFe is formed by a sol-gel method 12 O 19 The powder has small particle size and excellent magnetic property, and the BaFe is realized by granulation and sieving 12 O 19 The size uniformity of powder particles; by rapidly increasing the temperature to a large value (T) during sintering 1 ) Then rapidly cooling to a lower value (T) 2 ) Keeping the temperature for a short time, and then continuously and rapidly cooling to a lower value (T) 3 ) And the heat preservation is carried out for a longer time, and the BaFe is inhibited in the process 12 O 19 Grain boundary migration of ceramics while maintaining BaFe 12 O 19 The ceramic grain boundary diffusion is active, and compact small crystal grain BaFe is realized 12 O 19 And (3) preparing the ceramic.
Drawings
FIG. 1 is a compact, small grain BaFe of the present invention 12 O 19 The process control curve chart in the preparation method of the ceramic.
FIG. 2 is a compact small grain BaFe of the present invention 12 O 19 BaFe prepared in example 1 of the method for preparing ceramics 12 O 19 Internal structure diagram of ceramic, and hysteresis loop.
FIG. 3 is a compact small grain BaFe of the present invention 12 O 19 BaFe prepared in comparative example 1 of ceramic preparation method 12 O 19 Internal structure diagram of ceramic, and hysteresis loop.
FIG. 4 is a compact, small grain BaFe of the present invention 12 O 19 Method for preparing ceramicBaFe prepared in comparative example 2 12 O 19 Internal structure diagram of ceramic, and hysteresis loop.
The following specific embodiments will further illustrate the invention in conjunction with the above-described figures.
Detailed Description
The invention will be further explained with reference to the drawings and examples.
The invention discloses a three-step sintering method for preparing compact small-grain BaFe 12 O 19 The preparation method of the ferrite ceramic comprises the following steps:
preparing a precursor solution: mixing ferric nitrate (Fe (NO) 3 ) 3 ) And barium nitrate (Ba (NO) 3 ) 2 ) Weighing the powder according to a molar ratio of 12:1, dissolving the powder in deionized water to obtain a clear solution, adding citric acid with the same amount of substances as nitrate ions in ferric nitrate and barium nitrate, and fully stirring to completely dissolve the citric acid to obtain a precursor solution;
adjusting the pH value: continuously stirring, and slowly dropwise adding ammonia water into the precursor solution until the pH value of the solution is 6-7 to form light green transparent sol;
gel formation: putting the sol into a water bath kettle, heating in a water bath to form wet gel, putting the wet gel into an electrothermal blowing drying box, and preserving heat for 36 hours to obtain loose dry gel;
pre-burning: grinding the xerogel into powder, placing the powder in a muffle furnace for presintering at the presintering temperature of 1000-1100 ℃, and preserving heat for 3 hours to obtain BaFe 12 O 19 Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe 12 O 19 In the primary powder, the mass of PVA doped in the primary powder is 5-10% of that of the pre-sintered primary powder, and the PVA is ground in a mortar to be uniformly mixed; mixing the BaFe 12 O 19 Placing the powder in a mould to be pressed into a large green body; grinding the large green body into powder again in a mortar, sieving the powder through 80-mesh and 120-mesh sieves, and taking the powder in the middle layers of the 80-mesh and 120-mesh sieves to obtain BaFe with proper particle size 12 O 19 Powder material; placing the powder in a mould, and pressing into a small green compact under the pressure of 5 MPa;
rubber discharging: calcining the small green bodies in a muffle furnace at 650 ℃ for 3 hours to remove PVA in the small green bodies;
and (3) sintering: placing the green body after the rubber discharge in a muffle furnace, setting the temperature rise speed to be 4 ℃/min, and heating the sample to the temperature T 1 Said temperature T 1 Rapidly cooling to the temperature T at a cooling rate of 25 ℃/min immediately after 1350-1400 DEG C 2 Said temperature T 2 Between 1300 ℃ and 1350 ℃ and at a temperature T 2 Keeping the temperature for 0.5 to 1 hour under the condition, and then rapidly cooling to the temperature T at the cooling speed of 25 ℃/min 3 Keeping the temperature T 3 Between 1200 ℃ and 1250 ℃ and at a temperature T 3 Keeping the temperature for 10 to 20 hours under the condition, then naturally cooling to room temperature to finally obtain compact small-grain BaFe 12 O 19 Ceramics, particularly as can be seen in the figures 1 The process control graph is shown.
Preferably, in the adjusting the pH, the pH is 7.
Preferably, in the pre-firing process, the pre-firing temperature is 1000 ℃.
Preferably, during said sintering, said T 1 Is 1350 ℃.
Preferably, during said sintering, said T 2 The temperature is 1300 ℃, and the heat preservation time is 0.5 h.
Preferably, during said sintering, said T 3 The temperature is 1250 ℃, and the heat preservation time is 10 h.
Compared with the prior art, the technical scheme of the invention is that BaFe is formed by a sol-gel method 12 O 19 The powder has small grain diameter and excellent magnetic property, and the used BaFe is realized by granulation and sieving 12 O 19 The size uniformity of powder particles; by rapidly increasing the temperature to a large value (T) during sintering 1 ) Then rapidly cooling to a lower value (T) 2 ) Keeping the temperature for a short time, and then continuously and rapidly cooling to a lower temperatureValue of (T) 3 ) And the heat preservation is carried out for a longer time, and the BaFe is inhibited in the process 12 O 19 Grain boundary migration of ceramics while maintaining BaFe 12 O 19 The ceramic grain boundary diffusion is active, and compact small crystal grain BaFe is realized 12 O 19 And (3) preparing the ceramic.
Examples 1
Compact small-grain BaFe 12 O 19 The preparation method of the ceramic comprises the following steps:
preparing a precursor solution: mixing ferric nitrate (Fe (NO) 3 ) 3 ) And barium nitrate (Ba (NO) 3 ) 2 ) The powder is prepared from the following components in a molar ratio of 12 : 1 Weighing, dissolving in deionized water to obtain a clear solution, adding citric acid with the same amount of substances as nitrate ions in ferric nitrate and barium nitrate, and fully stirring to completely dissolve the citric acid to obtain a precursor solution;
adjusting the pH value: continuously stirring, and slowly dropwise adding ammonia water into the precursor solution until the pH value of the solution is 6-7 to form light green transparent sol;
gel formation: putting the sol in a water bath kettle, heating in a water bath to form wet gel, putting the wet gel in an electrothermal blowing drying box, and preserving heat for 36 hours to obtain loose dried gel;
pre-burning: grinding the xerogel into powder, placing the powder in a muffle furnace for presintering at the presintering temperature of 1000-1100 ℃, and preserving heat for 3 hours to obtain BaFe 12 O 19 Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe 12 O 19 In the primary powder, the mass of PVA doped in the primary powder is 5-10% of that of the pre-sintered primary powder, and the PVA is ground in a mortar to be uniformly mixed; mixing the BaFe 12 O 19 Placing the powder in a mould to be pressed into a large green body; grinding the large green compact into powder again in a mortar, sieving the powder through 80-mesh and 120-mesh sieves, and taking the powder in the middle layer of the 80-mesh and 120-mesh sieves to obtain BaFe with proper particle size 12 O 19 Powder material; placing the powder in a mold, and pressing under a pressure of 5MPaPreparing a small green body;
rubber discharging: calcining the small blocks in a muffle furnace at 650 deg.C 3 H, removing PVA from the small green compact;
and (3) sintering: placing the small green compact after the rubber discharge into a muffle furnace, and heating the sample to a higher temperature T at the heating rate of 4 ℃/min 1 The temperature is rapidly reduced after (1350 ℃), and in this stage, the density of the sample can be gradually increased along with the rise of the temperature, and meanwhile, the crystal grains can not grow to be extremely large due to the rapid temperature reduction; then the temperature is reduced to a lower value T at the cooling speed of 25 ℃/min 2 (1300 ℃ C.) and is at T 2 Keeping the temperature for a period of time (0.5h), wherein the grain size is slightly increased at the stage, and the density of the sample is improved; then continuously and rapidly cooling to a lower temperature T at the speed of 25 ℃/min 3 (1250 ℃ C.) and at T 3 Naturally cooling after keeping the temperature for a period of time (10h), wherein the grain size is unchanged, the compactness is obviously improved due to long-time heat preservation, and finally the compact small-grain BaFe is obtained 12 O 19 A ceramic.
BaFe finally obtained in example 1 is shown in FIG. 2 12 O 19 The ceramic has a compact internal structure, the average grain size is about 2.74 mu m, and the saturation magnetization reaches 67.8 emu/g.
The preparation method can rapidly raise the temperature to a very high value (T) 1 ) Then rapidly cooled to a lower value (T) 2 ) Performing short-time heat preservation, and rapidly cooling to a lower value (T) 3 ) And the compact small-grain BaFe is obtained in a long-time heat preservation mode 12 O 19 A ceramic. Theoretical analysis and experiments prove that the growth of crystal grains is mainly determined by grain boundary migration, and the compactness is mainly determined by grain boundary diffusion. The preparation method is based on the principle and realizes compact small-grain BaFe by adjusting the sintering temperature parameter 12 O 19 And (3) preparing the ceramic. Higher temperature (T) 1 ) Used to activate the die; rapidly cooling to a lower temperature (T) 2 ) And keeping the temperature for a short time, and transferring partial crystal boundary to make the crystalThe grains grow slightly without being too small; again rapidly cooling to a lower temperature (T) 3 ) And the heat preservation is carried out for a long time to inhibit the migration of the grain boundary, the growth of the crystal grain is almost stopped at the moment to form small crystal grains, and simultaneously, the diffusion activity of the grain boundary can be kept, so that more crystal grains can be contained in unit volume, and the compact small crystal grain BaFe is realized 12 O 19 And (3) preparing the ceramic.
The prior art generally prepares BaFe by a traditional sintering mode 12 O 19 Ceramics, mixing the sample with 4 Heating to a higher temperature (1350-1400 ℃) at a heating rate of/min, preserving heat for a period of time, and naturally cooling to obtain BaFe 12 O 19 And (3) ceramic. BaFe at 1350-1400 deg.C 12 O 19 The density and grain size of the ceramic will increase with increasing temperature, but at the same time BaFe 12 O 19 The crystal grains of the ceramic can grow to be large, so that the internal structure of the ceramic has a plurality of pores, the compactness of the ceramic is not high enough, and the saturation magnetization is small.
The applicant finds that BaFe through multiple experiments 12 O 19 Under the temperature condition of 1200-1250 ℃, the grain size of the ceramic hardly changes, namely under the temperature condition, the grain boundary migration is inhibited, and the grain boundary diffusion still keeps active, therefore, the holding time under the temperature condition of 1200-1250 ℃ can be controlled, the grain boundary diffusion reaches the equilibrium point, and BaFe is enabled to be simultaneously diffused through the grain boundary 12 O 19 The ceramic is sufficiently compact without increasing the grain size under the temperature condition, thereby obtaining compact small-grain BaFe 12 O 19 A ceramic.
Meanwhile, the applicant also finds that BaFe through multiple experiments 12 O 19 Under the temperature condition of 1300-1350 ℃, the densification process and the growth process of the crystal grains exist at the same time, namely under the temperature condition, the crystal boundary migration and the crystal boundary diffusion can both occur, so the holding time under the temperature condition of 1300 ℃ can be controlled, the crystal grains grow, and the compactness is improved. Meanwhile, in order to prevent the crystal grains from growing too much, the heat preservation time is properly set to be 0.5-1 h.
In order to further illustrate the technical effects of the present invention, the following two comparative examples are used for comparison.
Comparative example 1
Same as example 1, except that in the final sintering process, the sample was heated to T at a temperature rise rate of 4 ℃/min 1 (1350 ℃), then rapidly cooling to T at a speed of 25 ℃/min 2 (1300 ℃ C.) and at T 2 Heat preservation 10 h, then naturally cooling to obtain BaFe 12 O 19 A ceramic.
As shown in the figure 3 In which are shown comparative examples 1 Finally obtaining BaFe 12 O 19 Internal structure of ceramic, BaFe obtained 12 O 19 The grain size of the ceramic was large, about 3.81 μm, and the density thereof was comparative example 1 There is still room for improvement, which indicates that the crystal boundary migration still plays a main role when the temperature is kept at 1300 ℃ for a long time, the influence of the crystal boundary diffusion is small, and the saturation magnetization is only 60.6 emu/g.
Comparative example 2
Same as example 1, except that in the final sintering process, the sample was heated to T at a temperature rise rate of 4 ℃/min 1 (1350 deg.C) and at T 1 Keeping the temperature for 3 hours, and then naturally cooling to obtain BaFe 12 O 19 A ceramic.
FIG. 4 shows a comparative example 2 Finally obtaining BaFe 12 O 19 The internal structure of the ceramic, as is evident from the figure, is already large, about 4.56 μm in average grain size. Meanwhile, the saturation magnetization is 64.1 emu/g. It is shown that under the temperature condition of 1350 ℃, the grain boundary migration mainly occurs, the grain boundary diffusion is inhibited, and therefore, the grain size rapidly grows up but is not dense.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (3)
1. Preparation of compact small-grain BaFe by three-step sintering method 12 O 19 The preparation method of the ferrite ceramic is characterized by comprising the following steps:
preparing a precursor solution: weighing ferric nitrate and barium nitrate powder according to a molar ratio of 12:1, dissolving in deionized water to obtain a clear solution, adding citric acid with the same amount of substances as nitrate ions in ferric nitrate and barium nitrate, and fully stirring to completely dissolve the citric acid to obtain a precursor solution;
adjusting the pH value: continuously stirring, and slowly dropwise adding ammonia water into the precursor solution until the pH value of the solution is 6-7 to form light green transparent sol;
gel formation: putting the sol in a water bath kettle, heating in a water bath to form wet gel, putting the wet gel in an electrothermal blowing drying box, and preserving heat for 36 hours to obtain loose dried gel;
pre-burning: grinding the xerogel into powder, placing the powder in a muffle furnace for presintering at the presintering temperature of 1000-1100 ℃, and preserving heat for 3 hours to obtain BaFe 12 O 19 Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution with the concentration of 8 percent is used as a binding agent to be mixed with BaFe 12 O 19 In the primary powder, the mass of the doped polyvinyl alcohol solution is 5-10% of that of the pre-sintered primary powder, and the primary powder is ground in a mortar to be uniformly mixed; mixing the BaFe 12 O 19 Placing the powder in a mould to be pressed into a large green body; putting the large green body in a mortarGrinding again to obtain powder, sieving with 80 mesh and 120 mesh sieves, collecting powder in the middle layer of 80 mesh and 120 mesh sieves to obtain BaFe with suitable particle size 12 O 19 Powder material; placing the powder in a mould, and pressing into a small green compact under the pressure of 5 MPa;
rubber discharging: calcining the small block green compact in a muffle furnace at 650 ℃ for 3 hours, and removing the polyvinyl alcohol solution in the small block green compact;
and (3) sintering: placing the green body after the rubber discharge in a muffle furnace, setting the temperature rise speed to be 4 ℃/min, and heating the sample to the temperature T 1 Said temperature T 1 Is 1350 ℃, and then is immediately and rapidly cooled to the temperature T at the cooling rate of 25 ℃/min 2 Said temperature T 2 Is 1300 ℃ and is at a temperature T 2 Keeping the temperature for 0.5 hour under the condition, and rapidly cooling to the temperature T at the cooling speed of 25 ℃/min 3 Keeping the temperature T 3 Is 1250 ℃ and at a temperature T 3 Keeping the temperature for 10 hours under the condition, then naturally cooling to room temperature to finally obtain compact small-grain BaFe 12 O 19 And (3) ceramic.
2. The method of claim 1, wherein the compact small grain BaFe is prepared by a three-step sintering method 12 O 19 The preparation method of the ferrite ceramic is characterized in that in the process of adjusting the pH value, the pH value is 7.
3. The method of claim 1, wherein the compact small grain BaFe is prepared by a three-step sintering method 12 O 19 The preparation method of the ferrite ceramic is characterized in that in the pre-sintering process, the pre-sintering temperature is 1000 ℃.
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| CN104250097A (en) * | 2013-06-27 | 2014-12-31 | 广东江粉磁材股份有限公司 | Hexagonal ferrite used for preparing noise inhibition sheet and preparation method thereof |
| CN105669181A (en) * | 2016-01-13 | 2016-06-15 | 杭州电子科技大学 | Preparation method of compact small-grain YIG ceramic |
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| CN103030406A (en) * | 2013-01-02 | 2013-04-10 | 桂林理工大学 | Ptc ceramic sintering method |
| CN104250097A (en) * | 2013-06-27 | 2014-12-31 | 广东江粉磁材股份有限公司 | Hexagonal ferrite used for preparing noise inhibition sheet and preparation method thereof |
| CN105669181A (en) * | 2016-01-13 | 2016-06-15 | 杭州电子科技大学 | Preparation method of compact small-grain YIG ceramic |
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| Synthesis of dense, fine-grained hexagonal barium ferrite ceramics by two-step sintering process;Enmin Zhou等;《INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY》;20180111;第14卷(第4期);第1023-1029页 * |
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