CN111848153A - Microwave dielectric ceramic, preparation method of microwave dielectric ceramic and communication device - Google Patents
Microwave dielectric ceramic, preparation method of microwave dielectric ceramic and communication device Download PDFInfo
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Abstract
The invention discloses a microwave dielectric ceramic, a preparation method of the microwave dielectric ceramic and a communication device, wherein the chemical composition expression of the microwave dielectric ceramic is as follows: mg (magnesium)(1‑x)CaxTiO4-yMO, where x is 0.004-0.05 and M is Nb(2/5)、Ce、Sm(2/3)And one or more of Zn and Mn, wherein y is 0.005-0.015. The Qf value of the microwave dielectric ceramic provided by the invention is more than 60000; temperature coefficient: plus or minus 3.5ppm at 150 ℃ and plus or minus 8.5ppm at minus 40 ℃; the dielectric constant is 20.5 +/-1, and the dielectric material meets the relevant requirements of being applied to a 5G base station as a dielectric material.
Description
Technical Field
The invention relates to the technical field of electronic ceramic materials, in particular to a microwave dielectric ceramic, a preparation method of the microwave dielectric ceramic and a communication device.
Background
The microwave dielectric ceramic is a novel functional electronic ceramic material which is developed in the last 30 years, is used as a dielectric material in microwave frequency band (mainly UHF and SHF frequency band) circuits and can complete one or more functions.
Wherein MCT-based ceramic (MgCaTiO)4MCT) has a composite perovskite structure, and is a microwave dielectric ceramic with high quality factor (Qf value) in an X wave band. Specifically, the MCT-based ceramic is a ceramic material with magnesium, calcium and titanium as main metal elements, wherein the MCT-based ceramic material has low density and large lattice vibration amplitude at different temperatures, which causes large temperature drift of the MCT-based material, for example, the conventional MCT-based ceramic material can only reach the temperature drift of 3ppm at a high temperature of 105 ℃ and negative 8ppm at a low temperature of negative 10 ℃ (6 ppm at a temperature of 150 ℃ and 13ppm at a temperature of negative 40 ℃))。
The MCT-based ceramic can be used as a dielectric material to be applied to a communication base station, for example, a communication base station filter made of the existing MCT-based ceramic is utilized, the temperature of the filter can be changed by heat generated when the communication base station works, if the temperature drift of the MCT-based ceramic is large, the electrical stability of a device can be seriously influenced, a rear-end device needs to be further optimized integrally, and the 5G cost is high. Therefore, the MCT-based ceramic material in the prior art has the problem that the temperature drift is large, so that the 5G base station needs to perform overall optimization on a rear-end device, and the cost of the 5G base station is high.
It can be seen that the prior art is still in need of improvement and development.
Disclosure of Invention
In view of the above disadvantages of the prior art, the present invention aims to provide a microwave dielectric ceramic, a method for preparing the microwave dielectric ceramic, and a communication device, and aims to solve the problem of large temperature drift of the microwave dielectric ceramic in the prior art.
The technical scheme of the invention is as follows:
the microwave dielectric ceramic comprises the following chemical composition expression: mg (magnesium)(1-x)CaxTiO4-yMO, where x is 0.004-0.05 and M is Nb2/5、Ce、Sm2/3And one or more of Zn and Mn, wherein y is 0.005-0.015.
The effect of above-mentioned scheme lies in: the microwave dielectric ceramic has a perovskite structure, wherein rare earth metal elements Nb, Ce, Sm, Zn and Mn can enter crystal lattices for pinning, so that the amplitude of crystal lattice vibration is reduced, and the intrinsic performance of the microwave dielectric ceramic can be improved. Specifically, the microwave dielectric ceramic can realize a Qf value of more than 60000; temperature coefficient (also called temperature drift, temperature drift): plus or minus 3.5ppm at 150 ℃ and plus or minus 8.5ppm at minus 40 ℃; the dielectric constant is 20.5 +/-1, and the dielectric material meets the relevant requirements of being applied to a 5G base station as a dielectric material.
A preparation method of a microwave dielectric ceramic comprises the following steps:
dissolving magnesium salt, calcium salt, organic titanate and organic acid in water to obtain a mixed solution;
adjusting the pH of the mixed solution to form a sol;
drying the sol to obtain xerogel;
pre-sintering the xerogel to obtain precursor powder;
and pressing and molding the precursor powder, and then performing microwave sintering to obtain the microwave dielectric ceramic.
The effect of above-mentioned scheme lies in: magnesium salt, calcium salt, organic titanate and organic acid are used as raw materials, a sol-gel process is adopted to prepare microwave dielectric ceramic nano powder (precursor powder) with very uniform chemical components and particle size distribution, and a microwave sintering technology is utilized to realize the sintering of high-density microwave dielectric nano ceramic (the theoretical density is more than 98%) with high Qf value (60000-80000 GHz) and temperature drift of nearly 0ppm (the temperature drift at 150 ℃ is-1 ppm to +1ppm) within the sintering temperature range of 900-1200 ℃.
In a further preferred embodiment, after the obtaining of the mixed solution, the method further includes: and adding at least one of niobium salt, cerium salt, samarium salt and manganese salt into the mixed solution.
The effect of above-mentioned scheme lies in: the niobium salt, the cerium salt, the samarium salt and the manganese salt are metal salts and can be mixed with other components in a solution mode, so that a small amount of rare earth metal elements can be uniformly introduced into the microwave medium nano-ceramics, and the effect of improving the intrinsic performance of the microwave medium nano-ceramics through the small amount of rare earth metal elements is achieved.
In a further preferred embodiment, the magnesium salt is magnesium nitrate, the calcium salt is calcium nitrate, and the organic titanate is butyl titanate.
The effect of above-mentioned scheme lies in: the magnesium nitrate, the calcium nitrate and the butyl titanate are beneficial to the formation of sol, and can be reacted at a lower pre-sintering temperature to form precursor powder.
In a further preferable scheme, the organic acid is citric acid, wherein the organic acid is citric acid, and the molar ratio of the citric acid to the organic titanate is 1-3: 1.
The effect of above-mentioned scheme lies in: the organic acid can improve the dissolving effect of the magnesium salt, the calcium salt and the organic titanate, so that a mixed solution can be quickly obtained; the citric acid is polybasic organic carboxylic acid, so that sol is formed; by controlling the molar ratio of the citric acid to the organic titanate, namely, controlling the ratio of the molar ratio of the citric acid to the sum of the molar ratios of calcium ions and magnesium ions in the mixed solution, metal ions such as calcium ions and magnesium ions can be uniformly dispersed in the sol.
In a further preferred embodiment, the adjusting the pH of the mixed solution includes: adding ammonia water into the mixed solution, and adjusting the pH value of the mixed solution.
The effect of above-mentioned scheme lies in: the ammonia water is weak base, and can ensure the stability of the pH value of a sol system.
In a further preferable scheme, the pre-sintering temperature is 750-850 ℃.
The effect of above-mentioned scheme lies in: in the pre-sintering temperature, the lower limit temperature is the temperature for starting reaction synthesis, and the upper limit temperature is the minimum temperature under the premise of ensuring sufficient reaction, so that the high activity of the pre-sintered precursor powder is ensured.
In a further preferred aspect, the press forming includes: and mixing the precursor powder with a binder, and then pressing and molding.
The effect of above-mentioned scheme lies in: the precursor powder is more easily press-molded by adding the binder.
In a further preferable scheme, the sintering temperature of the microwave sintering is 1000-1150 ℃.
The effect of above-mentioned scheme lies in: the sintering temperature is not higher than 1200 ℃, so that the internal thermal stress of the microwave dielectric ceramic can be minimized, and the high-densification microwave dielectric ceramic can be prepared.
A communication device is made of the microwave dielectric ceramic.
The effect of above-mentioned scheme lies in: the microwave dielectric ceramic has high Qf (60000-80000 GHz) and temperature drift of nearly 0 (the temperature drift at 150 ℃ is-1 ppm to +1ppm), and the performance of a 5G base station can be improved by taking the microwave dielectric ceramic as a dielectric material of the 5G base station.
Compared with the prior art, the microwave dielectric ceramic provided by the invention has the chemical composition expression as follows: mg (magnesium)(1-x)CaxTiO4-yMO, where x is 0.004-0.05 and M is Nb2/5、Ce、Sm2/3And one or more of Zn and Mn, wherein y is 0.005-0.015. The rare earth metal elements Nb, Ce, Sm, Zn and Mn can improve the intrinsic performance of the microwave dielectric ceramic, and the Qf value of the microwave dielectric ceramic is more than 60000; the temperature coefficient is less than +/-3.5 ppm at 150 ℃ and less than +/-8.5 ppm at minus 40 ℃; the dielectric constant is 20.5 +/-1, and the dielectric material meets the relevant requirements of being applied to a 5G base station as a dielectric material.
Drawings
FIG. 1 is a flow chart of the present invention for preparing the microwave dielectric ceramic.
Fig. 2 is a schematic structural view of the microwave sintering furnace according to the present invention.
FIG. 3 is a schematic structural diagram of a sample stage in the microwave sintering furnace according to the present invention
In the figure: the device comprises a glass fiber heat insulation shell-1, a zirconia lining-2, a sample table-3, a silicon carbide rod-4, a thermocouple port-5, a pyrometer-6, a digital display-7, a data recorder-8, a capacitor-301 and a rheostat-302.
Detailed Description
The invention provides a microwave dielectric ceramic, a preparation method of the microwave dielectric ceramic and a communication device, and in order to make the purpose, technical scheme and effect of the invention clearer and clearer, the invention is further described in detail by referring to the attached drawings and taking examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The dielectric ceramic is widely used in components such as resonators, filters, dielectric substrates, dielectric guided wave loops and the like in modern communications such as mobile communication, satellite communication, military radars, global positioning systems, Bluetooth technology, wireless local area networks and the like, and is a key basic material of the modern communication technology.
The dielectric ceramic applied to the microwave circuit has high mechanical strength, good chemical stability and good stability over time, and also needs to meet the following dielectric property requirements: (1) the microwave dielectric material has relatively high dielectric constant r under microwave frequency, and r is generally required to be more than 20 so as to facilitate miniaturization and integration of microwave devices; (2) the dielectric loss is extremely low under the microwave resonance frequency, namely the quality internal number (Q) is very high, so that the excellent frequency selection characteristic is ensured, the insertion loss of the device under high frequency is reduced, and the Qf is generally required to be more than 30000; (3) a temperature coefficient (τ f) of the resonant frequency close to zero to ensure a high stability of the resonant frequency of the device in a temperature variation environment.
The invention provides a microwave dielectric ceramic, which has a chemical composition expression as follows: mg (magnesium)(1-x)CaxTiO4Wherein x is 0.004-0.05.
Therefore, the microwave dielectric ceramic of the invention is MCT-based dielectric ceramic (also called MCT system dielectric ceramic). Specifically, in the chemical composition expression of the microwave dielectric ceramic, Mg, Ca and Ti are (1-x): x: 1, wherein x is 0.004-0.05. In other words, the molar ratio of Mg, Ca and Ti is Mg: Ca: Ti (0.95 to 0.996): (0.004-0.05): 1, and Mg + Ca Ti 1: 1.
the microwave dielectric ceramic also contains rare earth metal elements, so that the aim of improving the intrinsic performance of the microwave dielectric ceramic can be fulfilled. The microwave dielectric ceramic material is composed of a crystal structure, in particular ABO3The reason of temperature drift caused by the perovskite structure is that B site atoms vibrate, and the effect obtained by adding proper rare earth metal elements is two reasons: firstly, B-site atoms are replaced, so that the vibration of crystal lattices is more disordered, and the amplitude of B-site vibration is reduced; the second is to achieve a pinning effect between the AO atoms (similar to a rivet pinning two things together, so called pinning effect) to reduce the overall lattice vibration. Experiments show that the content of the rare earth metal element is different, so that the performance of the final microwave dielectric ceramic is influenced, and the intrinsic performance of the microwave dielectric ceramic can be effectively improved by controlling the content of the rare earth metal element in the microwave dielectric ceramic. Optionally, the chemical composition expression of the microwave dielectric ceramic is as follows: mg (magnesium)(1-x)CaxTiO4-yMO, where x is 0.004-0.05 and M is Nb2/5、Ce、Sm2/3And one or more of Zn and Mn, wherein y is 0.005-0.015. That is, M is a rare earth metal element and MO is a rare earth metal oxide, that is, MO is Nb2O5、Sm2O3At least one of CeO, ZnO and MnO.
For example, the chemical composition expression of the microwave dielectric ceramic is as follows: mg (magnesium)(1-x)CaxTiO4—yNb2/5O、Mg(1-x)CaxTiO4—yCeO、Mg(1-x)CaxTiO4—ySm2/3O、Mg(1-x)CaxTiO4—yZnO、Mg(1-x)CaxTiO4—yMnO、Mg(1-x)CaxTiO4—yMn1/2Ce1/2O。
Experiments show that the microwave dielectric ceramic can realize the Qf value of more than 60000 and the temperature coefficient: 150℃ < + > 3.5ppm, minus 40℃ < + > 8.5ppm and a dielectric constant of 20.5 +/-1, and meets the relevant requirements applied to a 5G base station.
At present, the MCT-based dielectric ceramic is generally prepared by a conventional solid phase method. Specifically, the conventional solid phase method is to select high-purity oxide or carbonate, prepare materials according to a formula proportion, perform ball milling, calcination and grinding, add a certain amount of binder, perform granulation and compression molding, and perform sintering. The conventional solid phase method has simple process and low requirement on equipment, and is the most important preparation method of modern ceramic powder at present. However, the MCT-based precursor powder prepared by the conventional solid phase method has the following disadvantages: firstly, the mechanical means of mixing can not eliminate the uneven micro distribution of the raw materials, so that the diffusion process is difficult to smoothly carry out, and the raw materials are difficult to fully react to obtain a high-purity target phase; secondly, as the thinning process mainly adopts a mechanical crushing means, some impurities are easily introduced, thereby damaging the dielectric property of the material; thirdly, the mechanical refining can not ensure the microscopic uniformity of the component distribution of the powder, the granularity is difficult to reach below 1 mu m, and the activity of the prepared powder is poor, so that the sintering temperature of the ceramic is high.
In addition, in the solid phase synthesis method, during the sintering process of MCT-based ceramic precursor powder by adopting low-temperature co-firing, a large amount of low-melting-point glass phase (for example, 2 mol% of B) is added2O3And 10 mol% CuO) to lower the sintering temperature. Because the glass phase usually greatly damages the material performance, the low-temperature co-fired ceramic element has low performance and poor quality.
The nano ceramic refers to a ceramic material with a nano-scale phase in a microstructure, namely the grain size, the grain boundary width, the second phase distribution, the defect size and the like of the ceramic are all on the nano-scale level. Because the crystal grain, the crystal boundary and the combination of the crystal grain and the crystal boundary of the nano-ceramics are all in the nano level, the quantity of the refined crystal boundary can be greatly increased, the strength, the toughness and the superplasticity of the ceramic material are greatly improved, and the electrical property, the thermal property, the optical property, the magnetic property and other properties of the ceramic material are greatly influenced. The nanoceramic has unique properties different from the traditional ceramic due to its volume percentage of interface occupancy comparable to that of particles, high surface activity, small size effect and disorder of interface. The nano ceramic has the characteristics of mechanical properties including hardness, fracture toughness, low-temperature ductility and the like. The mechanical property of the nano-scale ceramic composite material, especially the hardness and the strength are greatly improved at high temperature.
However, the existing ceramic sintering method is difficult to make the nano-ceramic compact, and abnormal growth of crystal grains occurs, which seriously affects the performance of the nano-ceramic.
Tests show that the nano ceramic has the advantage that high densification can be achieved by sintering at a lower temperature, and the nano ceramic is beneficial to solving the problems of strengthening and toughening of the ceramic.
The sintering temperature of the existing MCT-based dielectric ceramic is usually more than 1350 ℃, which seriously restricts the dielectric property of the MCT-based dielectric ceramic and further limits the application range of the MCT-based dielectric ceramic.
Based on this, as shown in fig. 1, the present invention provides a method for preparing the microwave dielectric ceramic, which is characterized by comprising:
s100, dissolving magnesium salt, calcium salt, organic titanate and organic acid in water to obtain a mixed solution;
s200, adjusting the pH value of the mixed solution to form sol;
s300, drying the sol to obtain dry gel;
s400, pre-sintering the xerogel to obtain precursor powder;
and S500, pressing and forming the precursor powder, and then performing microwave sintering to obtain the microwave dielectric ceramic.
The preparation method of the microwave dielectric ceramic is a preparation method of nano ceramic, realizes nano-crystallization of the dielectric ceramic, reduces microwave sintering temperature, and improves dielectric property of the microwave dielectric ceramic. The preparation method specifically comprises the steps of preparing microwave dielectric ceramic nano powder (precursor powder) with very uniform chemical components and particle size distribution by using magnesium salt, calcium salt, organic titanate and organic acid as raw materials and adopting a sol-gel process, compacting the sintered dielectric ceramic by using a microwave sintering technology, avoiding the problem of abnormal growth of crystal grains, and sintering the high-compactness microwave dielectric nano ceramic (with the theoretical density of more than 98%) with high Qf value (60000-80000 GHz) and temperature drift of near 0 (the temperature drift of 150 ℃ is-1 ppm to +1ppm) at the sintering temperature of 900-1200 ℃.
In S100, magnesium salt, calcium salt and organic titanate can provide magnesium element, calcium element and titanium element for the microwave dielectric ceramic. The magnesium salt, the calcium salt and the organic titanate can be dissolved in an acid solution to form a mixed solution.
Alternatively, the magnesium salt is magnesium nitrate, the calcium salt is calcium nitrate, and the organic titanate is butyl titanate. Compared with other magnesium salts and calcium salts, the magnesium nitrate and the calcium nitrate are hydrolyzed and then are subjected to pre-sintering, so that the magnesium nitrate and the calcium nitrate are more easily heated and decomposed to release nitrogen dioxide, and acid radical ions are prevented from remaining in the microwave dielectric ceramic. The butyl titanate (n-butyl titanate) can be directly hydrolyzed to generate amorphous metatitanic acid and CH3(CH2)3Further formation of OH, metatitanic acidTitanium dioxide, and CH3(CH2)3OH is volatilized or decomposed after being heated.
In alkaline environment, magnesium salt and calcium salt have hydrolysis to a certain degree. Further, the organic acid can provide an acidic environment for the mixed solution, which is beneficial to the rapid dissolution of magnesium salt, calcium salt and the like. Moreover, compared with inorganic acid, the organic acid is easier to volatilize or decompose under high temperature condition, and can not remain in the microwave dielectric ceramic. Optionally, the organic acid is an organic polycarboxylic acid, such as citric acid. Citric acid is also known as citric acid and has the chemical name of 2-hydroxypropane-1, 2, 3-tricarboxylic acid. The citric acid is tribasic acid, and three carboxylic acids can respectively form coordination polymers with different metal ions; and spaces formed between the citric acid and the carboxylic acid are used for limiting the solvent and other ions which are not complexed; in this case, when the relative molecular mass increases, the fluidity of the system decreases, and a sol is formed.
In one embodiment of the present invention, after dissolving the magnesium salt, the calcium salt, the organic titanate, and the organic acid in water, the method further comprises: and adding at least one of niobium salt, cerium salt, samarium salt and manganese salt into the mixed solution.
The niobium salt, the cerium salt, the samarium salt and the manganese salt are metal salts, and can be mixed with other components in a solution mode, so that a small amount of rare earth metal elements are uniformly introduced into the microwave medium nano-ceramic, and the effect of improving the intrinsic performance of the microwave medium nano-ceramic through the small amount of rare earth metal elements is achieved. Optionally, the niobium salt, the cerium salt, the samarium salt and the manganese salt are respectively niobium nitrate, cerium nitrate, samarium nitrate and manganese nitrate.
In one embodiment of the invention, the organic acid is citric acid, wherein the organic acid is citric acid, and the molar ratio of the citric acid to the organic titanate is 1-3: 1. The organic acid can improve the dissolving effect of the magnesium salt, the calcium salt and the organic titanate, so that a mixed solution can be quickly obtained; the citric acid is polybasic organic carboxylic acid, so that sol is formed; by controlling the molar ratio of the citric acid to the organic titanate, namely, controlling the ratio of the molar ratio of the citric acid to the sum of the molar ratios of calcium ions and magnesium ions in the mixed solution, metal ions such as calcium ions and magnesium ions can be uniformly dispersed in the sol.
The S100 specifically includes:
s101, providing starting raw materials of magnesium nitrate, calcium nitrate, butyl titanate, niobium nitrate, cerium nitrate, samarium nitrate, manganese nitrate and the like with the purity of more than 99%;
s102, according to chemical expression Mg(1-x)CaxTiO4yMO, dissolving barium nitrate, butyl titanate and citric acid in a certain amount of deionized water to form a mixed solution, wherein x is 0.004-0.01, and y is 0.005-0.015, and citric acid and metal ions (Mg) are added into the mixed solution2+And Ca2+) Is 2: 1.
S103, adding at least one of niobium nitrate, cerium nitrate, samarium nitrate, manganese nitrate and the like according to a chemical expression Mg(1-x)CaxTiO4yMO, wherein x is 0.004-0.01, and y is 0.005-0.015.
In the S200, sol is formed by adjusting the pH of the solution. Specifically, the pH of the solution is adjusted by adding an alkaline solution to the mixed solution.
Optionally, the alkaline solution is an aqueous solution of a weak base. In one embodiment of the present invention, the adjusting the pH of the mixed solution includes: adding ammonia water into the mixed solution, and adjusting the pH value of the mixed solution. Wherein, the ammonia water is weak base, and can ensure the stability of the pH value of the sol system. And the ammonia water can volatilize in the heating process and also can not remain in the microwave dielectric ceramic.
The pH adjustment is used for realizing the formation of stable sol, the addition amount of the alkaline solution can be determined according to the actual sol formation condition, and in one embodiment of the invention, the pH of the solution is adjusted to 8-9 to form stable sol. When the pH value is too high, the magnesium salt and the calcium salt are hydrolyzed to a certain degree, and the organic titanate is also hydrolyzed, so that the uniformity of metal ions in the sol is influenced to a certain degree. From another perspective, in addition, when the mixed solution is adjusted to an alkaline environment, there is a certain degree of hydrolysis of magnesium salt, calcium salt, and organic titanate, which also undergoes hydrolysis, thereby facilitating the formation of sol. Therefore, the adjustment of pH can be determined in accordance with practical circumstances.
Specifically, the S200 includes: and slowly adding ammonia water into the mixed solution until the pH value reaches 8-9, and continuously stirring at the temperature of 50-80 ℃ to form transparent sol. The sol effect can be improved at the above pH and temperature.
In the step S300, a xerogel is obtained by drying the sol. Alternatively, the sol is dried in an oven at 150 ℃ until a xerogel is formed. Experiments show that in the process of drying the sol, the drying temperature is increased, so that water can be quickly evaporated, the efficiency is improved, and the gel is easy to agglomerate when the drying temperature is too high. Therefore, the xerogel is prepared at a lower temperature, and then the presintering is carried out, so that the uniformity of the particle size of the precursor powder obtained after the presintering is favorably ensured.
The invention adopts a solution method to obtain MCT transparent sol with high microscopic uniformity on at least molecular level. Meanwhile, a small amount of modifier is added into the mixed solution in a solution mode, so that the MCT-based dielectric ceramic nano powder with uniform particle size distribution and high performance (high Qf and near 0 temperature drift) is prepared.
And in S400, pre-burning the xerogel to obtain precursor powder, wherein the particle size of the precursor powder is 200-400 nanometers. As can be seen, the precursor powder is MCT-based dielectric ceramic precursor powder with the particle size of 200-400 nanometers. Because the precursor powder is finer and the microwave sintering temperature is lower, the precursor powder with the target particle size can be formed by combining a sol process and a pre-sintering process without further crushing treatment, thereby achieving the purpose of reducing the microwave sintering temperature.
In one embodiment of the present invention, the pre-firing temperature is 750 to 850 ℃. In the experimental process, the following results are found: in the pre-sintering temperature, the lower limit temperature is the temperature for starting reaction synthesis, and the upper limit temperature is the minimum temperature under the premise of ensuring full reaction, so that high activity of the pre-sintered precursor powder is realized.
The specific pre-sintering time can be determined according to the specific conditions of pre-sintering, and in one embodiment of the invention, the pre-sintering time is 1-2 hours, so that the powder is ensured to react fully.
And S500, performing microwave sintering on the pressed precursor powder to obtain the microwave dielectric ceramic. The microwave dielectric ceramic has a fast heating speed, specifically, the heating speed of the traditional sintering method is 10 ℃/min as fast as possible, and the heating speed of the microwave sintering can reach 200 ℃/min; and the microwave sintering is more uniform.
The microwave sintering is to heat the whole material to the sintering temperature by using the dielectric loss of precursor powder (ceramic material) in a microwave electromagnetic field so as to realize sintering and densification. The microwave is a high-frequency electromagnetic wave, and the frequency range of the microwave is 0.5-300 GHz; the frequency used in microwave sintering is mainly 2.45 GHz. Under the action of a microwave electromagnetic field, the ceramic material generates a series of dielectric polarizations, such as electron polarization, atom polarization, dipole-turn polarization, interface polarization and the like. The types of microscopic particles participating in polarization are different, and the time period for establishing or eliminating polarization is different. Because the frequency of the microwave electromagnetic field is very high, the dielectric polarization process in the ceramic material cannot follow the change of the external electric field, and the polarization intensity vector P always lags behind the electric field E, so that current in the same phase as the electric field is generated, and dissipation in the ceramic material is formed. In the microwave band, absorption current generated by mainly dipole polarization and interface polarization constitutes dielectric dissipation of the ceramic material, i.e. the interaction of the ceramic material with microwaves causes the ceramic material to absorb microwave energy and be heated.
The microwave sintering process is essentially different from the conventional sintering process: while the heat is diffused from the surface to the inside in the conventional sintering, the microwave sintering utilizes the heating characteristic of microwaves, namely the microwave energy absorbed by the ceramic material is converted into the kinetic energy and the potential energy of partial molecules in the material, so that the whole material is uniformly heated at the same time, and the heating and sintering speed is very high.
Moreover, when microwave sintering is carried out, because the ceramic material is heated uniformly inside and outside simultaneously, the ceramic is made to be ceramicThe temperature gradient in the ceramic material is small, so that the thermal stress in the material can be minimized, which is very beneficial to preparing high-densification dielectric ceramic material. For example, for TiO2Microwave sintering of nano ceramic at 950 deg.c to make TiO2Achieving the density of 98 percent of theoretical density.
The rapid microwave sintering method can also prevent the crystal grains from growing in the sintering process. For example, ZrO containing yttrium2And (3) sintering a nano powder (10-20 nm) blank, if the temperature is increased, the cooling rate is kept at 500 ℃/min, the temperature is kept at 1200 ℃ for 2 min, the density of a sintered body can reach more than 95% of the theoretical density, the whole sintering process only needs 7 min, and the grain size in the sintered body can be controlled below 200 nm.
In one embodiment of the present invention, the press forming includes: and mixing the precursor powder with a binder and then pressing and molding. And a binder is added into the precursor powder, so that the precursor powder is easier to mold. Optionally, the binder is a glue, such as polyvinyl alcohol (PVA).
The binder can be burnt off under the high-temperature condition in the subsequent sintering process, and the finally sintered microwave dielectric ceramic does not contain the binder such as PVA and the like. Optionally, before microwave sintering, the precursor after press forming is subjected to binder removal and primary sintering. Namely, glue such as PVA is removed before microwave sintering, and the microwave sintering effect is improved.
In one embodiment of the invention, the sintering temperature of the microwave sintering is 1000-1150 ℃. The sintering temperature of the invention is not higher than 1200 ℃, so that the internal thermal stress of the ceramic material can be minimized, and the high-densification microwave dielectric ceramic material can be prepared.
As shown in fig. 2 and 3, the microwave sintering furnace of the present invention includes: the glass fiber heat insulation device comprises a glass fiber heat insulation shell 1, a zirconia lining 2 arranged on the bottom surface of the glass fiber heat insulation shell 1, a sample table 3 arranged on the zirconia lining 2, a plurality of silicon carbide rods 4 arranged on the inner side of the glass fiber heat insulation shell 1 and located beside the sample table 3, a thermocouple port 5 arranged on the glass fiber heat insulation shell 1, a pyrometer 6 arranged above the glass fiber heat insulation shell 1, a digital display 7 connected with the pyrometer 6, and a data recorder 8 connected with the digital display 7, wherein the sample table 3 comprises a capacitor 301 and a rheostat 302 connected with the capacitor 301.
Specifically, the S500 specifically includes:
s501, adding PVA (polyvinyl alcohol) binder into the precursor powder, uniformly mixing and stirring, and performing powder granulation and compression molding;
s502, performing binder removal and primary sintering on the pressed and molded precursor powder in a muffle furnace, and then sintering the precursor powder into microwave dielectric ceramic in a microwave sintering furnace, wherein the parameters of the microwave sintering comprise: the microwave frequency is 3GHz, the power is 3.5KW, the sintering temperature is 1000-1150 ℃, and the sintering time is 0.5-2 hours.
The invention provides a preparation method of MCT-based microwave dielectric ceramic, which has the microwave sintering temperature below 1200 ℃ and can have a high quality factor. Specifically, magnesium nitrate, calcium nitrate and butyl titanate are used as raw materials, and Mg-Ca-Ti transparent sol with microscopic uniformity above a molecular level is obtained in a solution mode. Meanwhile, a small amount of modifier (rare earth metal nitrate, etc.) is added into the mixed solution in a solution mode, so that (MgCaTiO) with uniform chemical composition and particle size distribution is prepared4MCT) based dielectric ceramic nano-powder, and a microwave sintering technology is utilized, so that high-density MCT based microwave dielectric nano-ceramic with high Q x f (60000-80000 GHz) and temperature drift close to 0(150 ℃ resonance frequency temperature coefficient tau f-1 to +1 ppm/DEG C) can be sintered at the sintering temperature of 900-1200 ℃, and the industrial energy consumption and the production cost of the material system are effectively reduced.
The invention provides a communication device which is manufactured by using the microwave dielectric ceramic. Specifically, the communication device may be a filter, a GPS antenna, or the like. Further, the communication device is applied in a 5G base station. The microwave dielectric ceramic has high Q multiplied by f (60000-80000 GHz) and temperature drift of nearly 0 (the temperature drift at 150 ℃ is-1 ppm to +1ppm), and can ensure the electrical stability of a communication device at different temperatures.
Lower pairPreparation of Mg by the invention(1-x)CaxTiO4The overall flow of-yMO is described.
1) Magnesium nitrate, calcium nitrate and butyl titanate with the purity of more than 99 percent are taken as initial raw materials; according to the chemical expression Mg(1-x)CaxTiO4-yMO, in which M represents Nb2/5、Ce、Sm2/3Dissolving magnesium nitrate, calcium nitrate, butyl titanate and citric acid into a certain amount of deionized water according to a stoichiometric ratio of a stoichiometric composition to form a mixed solution, wherein the total molar ratio of the added citric acid to the metal ion nitrate is 2: 1; then, adding at least one of niobium nitrate, cerium nitrate, samarium nitrate, manganese nitrate and the like into the mixed solution according to a certain proportion;
2) slowly adding ammonia water into the mixed solution prepared in the step 1) at 70 ℃ until the pH value reaches 8-9, and continuously stirring to form transparent sol;
3) drying the transparent sol prepared in the step 2) in an oven at 150 ℃ until dry gel is formed;
4) pre-sintering the xerogel obtained in the step 3), wherein the pre-sintering temperature is 750-850 ℃, the pre-sintering time is 1-2 hours, and precursor powder of the MCT-based dielectric ceramic is obtained, and the particle size of the precursor powder is 200-400 nanometers;
5) adding PVA into the MCT-based ceramic precursor powder synthesized in the step 4), uniformly stirring and mixing, and performing powder granulation and blank pressing molding by using a traditional process;
6) and (3) carrying out binder removal and primary sintering on the precursor powder molded in the step 5) in a traditional muffle furnace, and then sintering the precursor powder into MCT-based microwave dielectric ceramic in a microwave sintering furnace, wherein the microwave frequency is 3GHz, the power is 3.5KW, the sintering temperature is 1000-1150 ℃, and the overall sintering time is 0.5-2 hours.
The chemical expression of the prepared MCT microwave dielectric ceramic is as follows: mg (magnesium)(1-x)CaxTiO4-yMO. x is 0.004-0.01, y is 0.005-0.015, MO is niobium pentoxide, cerium oxide, samarium oxide and manganese oxide, and the MCT microwave dielectric ceramic can be prepared byThe high-density microwave dielectric nano ceramic is sintered at the temperature of below 1200 ℃, and has adjustable dielectric constant r (19.6-21), extremely high quality factor (Qxf value is 60000-8000 GHz) and near-zero resonant frequency temperature coefficient tau f (-1 ppm/DEG C) at the temperature of 150 ℃.
The technical solution of the present invention will be described below by specific examples.
Example 1
The chemical composition expression of the microwave dielectric ceramic prepared in the embodiment is as follows: is Mg0.96Ca0.04TiO4—0.005La2/ 3The O is prepared by taking magnesium nitrate, calcium nitrate, butyl titanate and lanthanum nitrate with the purity of 99% as starting raw materials through the following process steps:
1) magnesium nitrate (Mg (NO) with a purity of 99%3)2) Calcium nitrate (Ca (NO)3)2) Butyl titanate, lanthanum nitrate (La (NO)3)3·6H2O) and citric acid (C)6H8O7·H2O) is used as a starting material. Dissolving magnesium nitrate, calcium nitrate, butyl titanate, lanthanum nitrate, citric acid and citric acid in deionized water according to the stoichiometric ratio of chemical compositions to form a mixed solution, wherein the total molar ratio of the added citric acid to the metal ion nitrate is 2:1, and then adding lanthanum nitrate into the mixed solution according to a certain proportion to dissolve the lanthanum nitrate to form the mixed solution;
2) slowly adding ammonia water into the mixed solution prepared in the step 1) until the pH value reaches 8, and continuously stirring at 70 ℃ to form transparent sol;
3) drying the transparent sol prepared in the step 2) in an oven at 150 ℃ until dry gel is formed;
4) pre-sintering the xerogel obtained in the step 3), wherein the pre-sintering temperature is 850 ℃, and the pre-sintering time is 1.5 hours, so as to obtain precursor powder (D50 ═ 300nm) of the MCT-based dielectric ceramic;
5) adding 3 wt% of PVA into the MCT-based ceramic precursor powder synthesized in the step 4), uniformly mixing and stirring, and performing powder granulation and blank pressing molding by using a traditional process;
6) and (3) carrying out glue removal and primary sintering on the MCT-based ceramic precursor powder subjected to press forming in the step 5) in a traditional muffle furnace, and then sintering the MCT-based microwave dielectric ceramic in a microwave sintering furnace, wherein the microwave frequency is 3GHz, the power is 3.5KW, the sintering temperature is 1180 ℃, and the overall sintering time is 1 hour.
7) The microwave dielectric ceramic has the relative dielectric constant r of 20.65, the quality factor Qf of 73500GHz and the temperature coefficient tau f of resonance frequency of 1.2 ppm/DEG C.
Example 2
In this embodiment, the chemical composition expression of the microwave dielectric ceramic is Mg0.97Ca0.03TiO4—0.005CeO2—0.005MnO2The preparation method comprises the following steps of taking magnesium nitrate, calcium nitrate, cerium nitrate, manganese nitrate, butyl titanate and citric acid with the purity of 99% as initial raw materials:
1) magnesium nitrate (Mg (NO) with a purity of 99%3)2) Calcium nitrate (Ca (NO)3)2) Cerium nitrate (Ce (NO)3)2) Manganese nitrate (Mn (NO)3)2) Butyl titanate, and citric acid (C)6H8O7·H2O) is used as a starting material. Dissolving magnesium nitrate, calcium nitrate, cerium nitrate, manganese nitrate, butyl titanate and citric acid in a certain amount of deionized water according to the stoichiometric ratio of the chemical compositions to form a mixed solution, wherein the total molar ratio of the added citric acid to the metal ion nitrate is 2: 1. Then, adding cerium nitrate and manganese nitrate according to a certain proportion, and dissolving to form a mixed solution;
2) slowly adding ammonia water into the mixed solution prepared in the step 1) until the pH value reaches 9, and continuously stirring at 70 ℃ to form transparent sol;
3) drying the sol prepared in the step 2) in a drying oven at 150 ℃ until dry gel is formed;
4) pre-sintering the xerogel obtained in the step 3), wherein the pre-sintering temperature is 850 ℃, and the pre-sintering time is 2 hours, so as to obtain MCT-based dielectric ceramic precursor powder (D50 is 420 nm);
5) adding 3 wt% of PVA into the MCT-based ceramic precursor powder synthesized in the step 4), uniformly mixing and stirring, and performing powder granulation and blank compression molding by using a traditional process;
6) and (3) carrying out glue removal and primary sintering on the MCT-based ceramic precursor powder subjected to press forming in the step 5) in a traditional muffle furnace, and then sintering the MCT-based microwave dielectric ceramic in a microwave sintering furnace, wherein the microwave frequency is 3GHz, the power is 3.5KW, the sintering temperature is 1050 ℃, and the overall sintering time is 1 hour.
7) The microwave dielectric ceramic has the relative dielectric constant r of 20.72, the quality factor Qf of 77900GHz and the temperature coefficient tau f of resonance frequency of 0.5 ppm/DEG C.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (10)
1. The microwave dielectric ceramic is characterized in that the chemical composition expression of the microwave dielectric ceramic is as follows: mg (magnesium)(1-x)CaxTiO4-yMO, where x is 0.004-0.05 and M is Nb(2/5)、Ce、Sm(2/3)And one or more of Zn and Mn, wherein y is 0.005-0.015.
2. A preparation method of microwave dielectric ceramic is characterized by comprising the following steps:
dissolving magnesium salt, calcium salt, organic titanate and organic acid in water to obtain a mixed solution;
adjusting the pH of the mixed solution to form a sol;
drying the sol to obtain xerogel;
pre-sintering the xerogel to obtain precursor powder;
and pressing and molding the precursor powder, and then performing microwave sintering to obtain the microwave dielectric ceramic.
3. A method for preparing a microwave dielectric ceramic according to claim 2, wherein after obtaining the mixed solution, the method further comprises: and adding at least one of niobium salt, cerium salt, samarium salt and manganese salt into the mixed solution.
4. The method for preparing microwave dielectric ceramic according to claim 2, wherein the magnesium salt is magnesium nitrate, the calcium salt is calcium nitrate, and the organic titanate is butyl titanate.
5. The preparation method of microwave dielectric ceramic according to claim 2, wherein the organic acid is citric acid, and the molar ratio of the citric acid to the organic titanate is 1-3: 1.
6. A method for preparing a microwave dielectric ceramic according to claim 2, wherein the adjusting the pH of the mixed solution comprises: adding ammonia water into the mixed solution, and adjusting the pH value of the mixed solution.
7. The preparation method of microwave dielectric ceramic according to claim 2, wherein the pre-sintering temperature is 750-850 ℃.
8. A method of making a microwave dielectric ceramic according to claim 2, wherein the press forming comprises: and mixing the precursor powder with a binder, and then pressing and molding.
9. The method for preparing microwave dielectric ceramic according to claim 2, wherein the sintering temperature of the microwave sintering is 1000-1150 ℃.
10. A communication device, wherein the communication device is fabricated using the microwave dielectric ceramic of claim 1.
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Application publication date: 20201030 |