CN112645703A - Preparation of compact small-grain BaFe by three-step sintering method12O19Preparation method of ferrite ceramic - Google Patents
Preparation of compact small-grain BaFe by three-step sintering method12O19Preparation method of ferrite ceramic Download PDFInfo
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Abstract
The invention discloses a three-step sintering method for preparing compact small-grain BaFe12O19Method for preparing ferrite ceramic, BaFe formed by sol-gel method19O12The powder has small grain diameter and excellent magnetic property, and the used BaFe is realized by granulation and sieving19O12The size uniformity of powder particles; by rapidly increasing the temperature to a large value (T) during sintering1) 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 BaF is inhibited in the processe19O12Grain boundary migration of ceramics while maintaining BaFe19O12The ceramic grain boundary diffusion is active, and compact small crystal grain BaFe is realized19O12And (3) preparing the ceramic. The product synthesized by the method has small grain size and high purity; BaFe thus prepared12O19The ceramic has obviously better compactness, grain size, saturation magnetization and other parameters than BaFe prepared by the traditional method12O19The 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 BaFe12O19A preparation method of ferrite ceramics.
Background
M type barium ferrite (BaFe)19O12) As a magnetoplumbite type ferrite, the magnetoplumbite type ferrite has the characteristics of strong uniaxial magnetocrystalline anisotropy, higher 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 temperature19O12The 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 reduced19O12The 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 BaFe12O19Method for preparing ferrite ceramic capable of obtaining compact small-grain BaFe19O12The ceramic is a mixture of a ceramic and a metal,and the saturation magnetization of the magnetic material is closer to BaFe19O12Theoretical 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 method12O19The 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 BaFe19O12Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe19O12In 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 BaFe19O12Placing 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 size19O12Powder 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 compact in a muffle furnace at 650 ℃ for 3 hours, and removing PVA in the small 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 T1Said temperature T1Rapidly cooling to the temperature T at a cooling rate of 25 ℃/min immediately after 1350-1400 DEG C2Said temperature T2Between 1300 ℃ and 1350 ℃ and at a temperature T2Keeping 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 ℃/min3Carrying out heat preservation at the temperature T3Between 1200 ℃ and 1250 ℃ and at a temperature T3Keeping the temperature for 10 to 20 hours under the condition, then naturally cooling to room temperature to finally obtain compact small-grain BaFe12O19A 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 T1Is 1350 ℃.
Preferably, during said sintering, said T2The temperature is 1300 ℃, and the heat preservation time is 0.5 h.
Preferably, during said sintering, said T3The 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 method19O12The powder has small grain diameter and excellent magnetic property, and the used BaFe is realized by granulation and sieving19O12The size uniformity of powder particles; by rapidly increasing the temperature to a large value (T) during sintering1) 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 process19O12Grain boundary migration of ceramics while maintaining BaFe19O12The ceramic grain boundary diffusion is active, and compact small crystal grain BaFe is realized19O12And (3) preparing the ceramic.
Drawings
FIG. 1 is a compact, small grain BaFe of the present invention19O12The process control curve chart in the preparation method of the ceramic.
FIG. 2 is a compact small grain BaFe of the present invention19O12BaFe prepared in example 1 of the method for preparing ceramics19O12Internal structure of the ceramic, and hysteresis loop.
FIG. 3 is a compact small grain BaFe of the present invention19O12BaFe prepared in comparative example 1 of ceramic preparation method19O12Internal structure of the ceramic, and hysteresis loop.
FIG. 4 is a compact small grain BaFe of the present invention19O12BaFe prepared in comparative example 2 of ceramic preparation method19O12Internal structure of the 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 BaFe12O19The 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 BaFe19O12Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe19O12In 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 BaFe19O12Placing 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 size19O12Powder 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 compact in a muffle furnace at 650 ℃ for 3 hours, and removing PVA in the small 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 T1Said temperature T1Rapidly cooling to the temperature T at a cooling rate of 25 ℃/min immediately after 1350-1400 DEG C2Said temperature T2Between 1300 ℃ and 1350 ℃ and at a temperature T2Keeping 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 ℃/min3Carrying out heat preservation at the temperature T3Between 1200 ℃ and 1250 ℃ and at a temperature T3Keeping the temperature for 10 to 20 hours under the condition, then naturally cooling to room temperature to finally obtain compact small-grain BaFe12O19The ceramic can be specifically referred to the process control graph shown in fig. 1.
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 T1Is 1350 ℃.
Preferably, during said sintering, said T2The temperature is 1300 ℃, and the heat preservation time is 0.5 h.
Preferably, during said sintering, said T3The 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 method19O12The powder has small grain diameter and excellent magnetic property, and the used BaFe is realized by granulation and sieving19O12The size uniformity of powder particles; by rapidly increasing the temperature to a large value (T) during sintering1) 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 process19O12Grain boundary migration of ceramics while maintaining BaFe19O12The ceramic grain boundary diffusion is active, and compact small crystal grain BaFe is realized19O12And (3) preparing the ceramic.
Example 1
Compact small-grain BaFe19O12The 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) 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 BaFe19O12Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe19O12In 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 BaFe19O12Placing 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 size19O12Powder 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 compact in a muffle furnace at 650 ℃ for 3 hours, and removing PVA in 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 ℃/min1The temperature is rapidly reduced after the temperature is reduced (1350 ℃), and in this stage, the density of the sample can be gradually increased along with the temperature rise, and meanwhile, the crystal grains cannot 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 ℃/min2(1300 ℃ C.) and at T2Keeping the temperature for a period of time (0.5h) at the temperature, wherein the grain size is slightly increased, and the compactness of the sample is improved; then continuously and rapidly cooling to a lower temperature T at the speed of 25 ℃/min3(1250 ℃ C.) and at T3Naturally 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 obtained19O12A ceramic.
BaFe finally obtained in example 1 is shown in FIG. 219O12The ceramic has a dense internal structure, an average grain size of about 2.74 μm, and a saturation magnetizationReaching 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) And is subjected to short-time heat preservation and then rapidly cooled to a lower value (T)3) And the compact small crystal grain BaFe is obtained in a long-time heat preservation mode19O12A 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 parameter19O12And (3) preparing the ceramic. Higher temperature (T)1) Used to activate the die; rapidly cooling to a lower temperature (T)2) And the temperature is preserved for a short time, and partial crystal boundary is migrated, so that the crystal grains slightly grow but are not 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 realized19O12And (3) preparing the ceramic.
In the prior art, BaFe is prepared by a traditional sintering mode19O12Ceramic, heating the sample to a higher temperature (1350-1400 ℃) at a heating rate of 4 ℃/min, preserving heat for a period of time, and naturally cooling to obtain BaFe19O12A ceramic. BaFe at 1350-1400 deg.C19O12The density and grain size of the ceramic will increase with increasing temperature, but at the same time BaFe19O12The 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 experiments19O12The ceramic has little change in grain size under the temperature condition of 1200-1250 ℃, that is, under the temperature condition, the grain boundary migration is inhibited, and the grain boundary diffusion is still kept active, so that the temperature can be controlled at 1200-1250 ℃The heat preservation time under the temperature condition ensures that the grain boundary diffusion reaches the equilibrium point, and simultaneously BaFe is caused by the grain boundary diffusion19O12The ceramic is sufficiently compact without increasing the grain size under the temperature condition, thereby obtaining compact small-grain BaFe19O12A ceramic.
Meanwhile, the applicant also finds that BaFe through multiple experiments19O12Under 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 ℃/min1(1350 ℃), then rapidly cooling to T at a speed of 25 ℃/min2(1300 ℃ C.) and at T2Keeping the temperature for 10h, and then naturally cooling to obtain BaFe19O12A ceramic.
BaFe finally obtained in comparative example 1 is shown in FIG. 319O12Internal structure of ceramic, BaFe obtained19O12The grain size of the ceramic is larger and is about 3.81 mu m, and meanwhile, the density of the ceramic still has a space for improving in comparative example 1, which shows that the grain boundary migration still plays a main role in long-time heat preservation at 1300 ℃, the influence of grain boundary diffusion is smaller, the saturation magnetization is reflected on the saturation magnetization, and the saturation magnetization value 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 ℃/min1(1350 ℃ C.) and at T1Keeping the temperature for 3 hours, and then naturally cooling to obtain BaFe19O12A ceramic.
FIG. 4 shows the BaFe finally obtained in comparative example 219O12The 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 (6)
1. Preparation of compact small-grain BaFe by three-step sintering method12O19The preparation method of the ferrite ceramic is characterized by comprising 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 BaFe19O12Primary powder lot;
and (3) granulation and forming: polyvinyl alcohol solution (PVA) with a concentration of 8% as a binder was incorporated into BaFe19O12In 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 BaFe19O12Placing 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 size19O12Powder 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 compact in a muffle furnace at 650 ℃ for 3 hours, and removing PVA in the small 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 T1Said temperature T1Rapidly cooling to the temperature T at a cooling rate of 25 ℃/min immediately after 1350-1400 DEG C2Said temperature T2Between 1300 ℃ and 1350 ℃ and at a temperature T2Keeping 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 ℃/min3Carrying out heat preservation at the temperature T3Between 1200 ℃ and 1250 ℃ and at a temperature T3Keeping the temperature for 10 to 20 hours under the condition, then naturally cooling to room temperature to finally obtain compact small-grain BaFe12O19A ceramic.
2. The method of claim 1, wherein the compact small grain BaFe is prepared by a three-step sintering method12O19The 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 method12O19The preparation method of the ferrite ceramic is characterized in that in the pre-sintering process, the pre-sintering temperature is 1000 ℃.
4. The method of claim 1, wherein the compact small grain BaFe is prepared by a three-step sintering method12O19A method for preparing ferrite ceramic, characterized in that, in the sintering process, the T1Is 1350 ℃.
5. The method of claim 1, wherein the compact small grain BaFe is prepared by a three-step sintering method12O19A method for preparing ferrite ceramic, characterized in that, in the sintering process, the T2The temperature is 1300 ℃, and the heat preservation time is 0.5 h.
6. The method of claim 1, wherein the compact small grain BaFe is prepared by a three-step sintering method12O19A method for preparing ferrite ceramic, characterized in that, in the sintering process, the T3The temperature is 1250 ℃, and the heat preservation time is 10 h.
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