CN114933468B - Cold sintering assisted low temperature densification of Zn 3 B 2 O 6 Preparation method of microwave ceramic material - Google Patents

Cold sintering assisted low temperature densification of Zn 3 B 2 O 6 Preparation method of microwave ceramic material Download PDF

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CN114933468B
CN114933468B CN202210534519.2A CN202210534519A CN114933468B CN 114933468 B CN114933468 B CN 114933468B CN 202210534519 A CN202210534519 A CN 202210534519A CN 114933468 B CN114933468 B CN 114933468B
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李郴
刘亚晗
姜宇
毛敏敏
宋开新
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Hangzhou Dianzi University
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Abstract

The invention belongs to the technical field of microwave dielectric ceramic material preparation, and relates to cold sinteringJunction assisted low temperature densification of Zn 3 B 2 O 6 Preparation method of microwave ceramic material, zn is added 3 B 2 O 6 Mixing with 20wt.% glacial acetic acid aqueous solution with different concentrations to form a solid-liquid mixture, adopting a hot pressing method, realizing densification by adjusting sintering temperature, sintering time and uniaxial pressure, and further realizing densification by different annealing temperatures. Compared with the traditional high-temperature solid-phase reaction, the method can realize densification in a lower temperature range, has the advantages of simple preparation process, lower sintering temperature, shorter time and energy consumption saving, and the obtained microwave dielectric ceramic material has excellent performance and good application prospect.

Description

Cold sintering assisted low temperature densification of Zn 3 B 2 O 6 Preparation method of microwave ceramic material
Technical Field
The invention relates to cold sintering assisted low temperature densification of Zn 3 B 2 O 6 A preparation method of microwave ceramic material. Belongs to the technical field of microwave dielectric ceramic material preparation.
Background
The microwave dielectric ceramic is a novel multifunctional ceramic material, and is generally used as a dielectric material for microwave components such as dielectric resonators, dielectric filters, dielectric antennas and the like. In recent years, with the rapid development of multipath communication technologies such as the internet of things, the internet +, 5G communication, the beidou global positioning system, the wireless mobile base station, the VR virtual technology and the like, the microwave technology is gradually developing in two directions of higher frequency and wider frequency band, so that resources in the limited microwave frequency band are reasonably and efficiently used, and a higher standard is provided for the microwave dielectric ceramic material. The low dielectric constant can improve the transmission rate of radio signals, the high quality factor can improve the circuit gain to a certain extent, and reduce the energy loss to maintain the stability of operation, therefore, the low dielectric constant (e) is sought r <15 Microwave dielectric materials with low loss (high Q x f) are becoming the focus of academic interest.
Under the background of the peak of the current carbon neutralization carbon, the sintering temperature of the high-temperature solid phase sintering (TSP) is high, the sintering time is long, and the energy is consumed; and at high temperature, the ceramic cannot be co-fired with a metal wire with low melting point and low resistivity, so that the integrated packaging of the microwave dielectric ceramic as a substrate is hindered, and certain materials are easy to generate additional phases in the high-temperature sintering process to generate additional chemical reactions, so that the performance of the materials is influenced. The cold sintering technology (CSP) greatly reduces the sintering temperature and the sintering time, can realize densification only by a certain liquid phase and pressure, has simple process flow, less energy consumption and lower manufacturing cost, and reduces the emission of carbon dioxide. In addition, the technology can highly integrate and prepare ceramic dielectric, metal and base plates with low processing temperature and low loss, and overcomes the chemical incompatibility of ceramic, metal electrodes and PCB plates at high temperature.
Disclosure of Invention
The invention provides cold sintering assisted low-temperature densification Zn 3 B 2 O 6 The preparation method of the microwave ceramic material realizes that the densified ceramic with uniform crystal grains and relative density of more than or equal to 90% is prepared under the condition of low temperature, compared with the traditional high-temperature solid-phase sintering reaction method, the method can realize densification within a lower temperature range, the preparation process is simple, and the obtained microwave dielectric ceramic material has excellent performance and good application prospect.
In order to achieve the purpose, the technical scheme of the invention is as follows:
cold sintering assisted low-temperature densification Zn 3 B 2 O 6 Method for preparing microwave ceramic material, zn 3 B 2 O 6 Mixing with 20wt.% glacial acetic acid aqueous solutions with different concentrations (C) to form a solid-liquid mixture, then carrying out densification by adjusting the Sintering Temperature (ST), the sintering time (T) and the uniaxial pressure (P) by a hot pressing method, and finally further carrying out densification by different Annealing Temperatures (AT). Wherein: c =0.5mol/L, 1mol/L, 2mol/L, 4mol/L, 6mol/L, 8mol/L; ST =120 ℃, 140 ℃, 160 ℃, 180 ℃, 200 ℃; t =30min, 60min, 90min, 120min, 150min; p =100MPa, 200MPa, 300MPa, 400MPa, 500MPa; AT =400 ℃,450 ℃, 500 ℃, 550 ℃, 700 ℃; zn prepared by the method 3 B 2 O 6 Microwave ceramics of dielectric constant (e) r ) The range is 5.0 to 5.95, the range of the quality factor Qxf is 6000 to 20620GHz, and the range of the resonant frequency temperature coefficient (tau f) is-70ppm/℃~-66.4ppm/℃。
Cold sintering assisted low-temperature densification Zn 3 B 2 O 6 The preparation method of the microwave ceramic material comprises the following steps:
the method comprises the following steps: weighing and proportioning: according to the formula Zn 3 B 2 O 6 Weighing raw materials ZnO and H 3 BO 3 (ii) a Experimental errors are avoided, a precision electronic scale is used for weighing the required raw materials, the weighing error is allowed to be +/-0.0005 g, and the pollution of other powder materials is avoided in the whole process, so that the accuracy of the experiment is ensured;
step two: primary ball milling: pouring the raw materials into a ball milling tank, drying the slurry to constant weight after ball milling to obtain a first ball grinding material;
step three: pre-burning: sieving the primary ball-milled material, and presintering to obtain dry powder;
step four: secondary ball milling: ball-milling the dry powder obtained by pre-sintering for the second time, drying the dry powder to constant weight after ball-milling, grinding and sieving to obtain Zn 3 B 2 O 6 And (3) powder.
Step five: mixing materials: weighing Zn 3 B 2 O 6 Adding 20wt.% glacial acetic acid aqueous solution with different molar concentrations into the powder, and uniformly mixing to form a dough-like aqueous mixture;
step six: and (3) low-temperature sintering: putting the water-containing mixture obtained in the fifth step into a die, putting the die on a tablet press for pressure maintaining, then moving the die into a hot press, heating the sintering temperature to 160-200 ℃, sintering for 60-150min, and applying 300-500MPa pressure to the die to obtain densified ceramic;
step seven: and (3) drying: drying the densified ceramic obtained in the sixth step in a drying oven at the temperature of 120 ℃ for 24 hours to remove residual moisture to obtain Zn 3 B 2 O 6 A ceramic sample;
step eight: cold sintering auxiliary annealing treatment: zn obtained in the step seven 3 B 2 O 6 And placing the ceramic sample on the pre-sintered powder, and then placing the ceramic sample into a high-temperature furnace for annealing treatment, wherein the annealing temperature is 400-700 ℃.
The first stepNeutral ZnO and H 3 BO 3 The purity of (A) is 99.99%; before weighing, znO and H 3 BO 3 Drying in a high-temperature oven at 120 deg.C. Before weighing, znO and H 3 BO 3 The pretreatment is carried out by the following method: adding ZnO and H 3 BO 3 And (3) drying the mixture in a high-temperature box at 120 ℃ for at least 6 hours to remove extra moisture in the raw materials, so that the influence of the raw materials which are easy to absorb water on the accuracy of the experiment is prevented. Due to B in the calcination process 2 O 3 Volatilization leads to the loss of boron, so when weighing, 12wt.% more H is weighed 3 BO 3 As a compensation.
The specific steps of the primary ball milling in the second step are as follows: pouring the raw materials into a ball milling tank, taking zirconia beads as a ball milling medium, and mixing the raw materials according to the proportion of 1:4, adding absolute ethyl alcohol, adding the amount of the absolute ethyl alcohol to 3/4 of the ball milling tank, putting the ball milling tank into a ball mill, ball milling the mixed slurry for 6 hours at 200r/min, pouring the mixed slurry into a drying box filled with a plastic film, and placing the drying box in a constant-temperature oven at 80 ℃ to dry the absolute ethyl alcohol.
In the third step, the pre-burning comprises the following specific steps: and grinding the powder subjected to primary ball milling and drying, sieving the powder with a 100-mesh sieve, pouring the powder into a crucible, putting the crucible into a high-temperature furnace, pre-burning the powder for 3 hours at 825 ℃, and naturally cooling the powder to obtain dry powder.
In the fourth step, the second ball milling comprises the following specific steps: pouring the dry powder obtained by pre-sintering into a ball milling tank, and taking zirconia beads as ball milling media according to the proportion of 1:4, adding absolute ethyl alcohol, adding the amount of the absolute ethyl alcohol to 3/4 of the ball milling tank, then putting the ball milling tank into a ball mill, ball milling the mixed slurry for 6 hours at 200r/min, pouring the mixed slurry into a drying box filled with a plastic film, placing the drying box in a constant-temperature oven at 80 ℃ to dry the absolute ethyl alcohol, and grinding the dried powder to pass through a 200-mesh sieve.
The concrete steps of mixing in the fifth step are as follows: zn obtained after secondary ball milling 3 B 2 O 6 Pouring the powder and 20wt.% glacial acetic acid aqueous solution with different concentrations into an agate mortar, manually grinding and mixing for 2-5min to uniformly mix solid and liquid, wherein the concentration is 0.5-8 mol/L. Wherein C =0.5mol/L, 1mol/L, 2mol/L, 4mol/L, 6mol/L, 8mol/L.
The low-temperature sintering in the sixth step comprises the following specific steps: pouring the mixture into a stainless steel mold with the diameter of 12.7mm, then placing the stainless steel mold into a hot press, applying uniaxial pressure of 4MPa at room temperature, keeping the pressure for 5min, then performing cold sintering treatment by using the hot press, wherein the uniaxial pressure of the hot press is 300-500MPa, the temperature of the hot press is increased to the sintering temperature at the heating rate of 5 ℃/min, the sintering temperature is 160-200 ℃, the sintering time is 60-150min, then cooling to the room temperature at the same rate, and taking out the mold. The uniaxial pressure of the hot press is 100MPa, 200MPa, 300MPa, 400MPa and 500MPa; the sintering temperature is 120 ℃, 140 ℃, 160 ℃, 180 ℃ and 200 ℃; the sintering time is 30min, 60min, 90min, 120min and 150min.
The drying in the seventh step comprises the following specific steps: and (3) demolding and taking out the sample in the mold, putting the sample into a constant-temperature drying oven at the temperature of 120 ℃ for drying for 24 hours, and removing the residual liquid phase in the sample.
And step eight, placing the sample with the optimal sintering characteristic obtained by cold sintering on the pre-sintered powder which is sieved by a 100-mesh sieve, then placing the pre-sintered powder into a high-temperature furnace, setting the temperature to be 4 ℃/min, heating to a required annealing temperature point (AT), preserving heat for 3h, naturally cooling, and taking out the sample. The annealing temperature is 400 ℃,450 ℃, 500 ℃, 550 ℃ and 700 ℃.
The invention adopts cold sintering and subsequent low-temperature annealing treatment technology to prepare densified Zn 3 B 2 O 6 Compared with the traditional high-temperature solid-phase reaction, the method can realize densification at a lower temperature range, has the advantages of simple preparation process, lower sintering temperature, shorter time and energy consumption saving, and the obtained microwave dielectric ceramic material has excellent performance and good application prospect.
The invention adopts annealing treatment, and atomic cluster [ ZnO ] formed by combining in a cold sintering stage under the action of heat 4 ]And [ BO ] 3 ]Will precipitate in Zn with lower chemical potential 3 B 2 O 6 On the crystal grains, the crystal grains are bonded with atomic group bonds on the interface to finally form compact Zn 3 B 2 O 6 Overall, and therefore further optimize its performance.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 shows Zn prepared in examples 1, 5 and 6 of the present invention 3 B 2 O 6 Microwave ceramic material and primary Zn 3 B 2 O 6 XRD pattern of the powder;
FIG. 2 shows Zn prepared in example 1 of the present invention and in comparative examples 1 to 6 3 B 2 O 6 The relation graph of the bulk density and the relative density of the microwave ceramic material and the concentration of glacial acetic acid;
FIG. 3 shows Zn prepared in examples 1 to 2 of the present invention and in comparative examples 7 to 9 3 B 2 O 6 The density and relative density of the microwave ceramic material block are plotted against the sintering time;
FIG. 4 shows Zn prepared in examples 1 and 3 of the present invention and comparative examples 10 to 12 3 B 2 O 6 The density and relative density of the microwave ceramic material block are plotted against the cold sintering temperature;
FIG. 5 shows Zn prepared in examples 3 and 4 of the present invention and comparative examples 13 to 15 3 B 2 O 6 Plot of bulk density and relative density of microwave ceramic material versus uniaxial pressure;
FIG. 6 shows Zn prepared in examples 1 and 3 of the present invention and comparative examples 10 to 12 3 B 2 O 6 Microwave dielectric property diagrams of the microwave ceramic material at different sintering temperatures;
FIG. 7 shows Zn prepared in examples 1 and 5 to 6 of the present invention and in comparative examples 16 to 19 3 B 2 O 6 Relative density graphs of the microwave ceramic material at different sintering temperatures;
FIG. 8 shows Zn prepared in examples 3 and 5 to 6 of the present invention and comparative examples 16 to 19 3 B 2 O 6 Microwave ceramic material at different sintering temperaturesA graph of the relationship between the lower dielectric constant and the porosity-corrected dielectric constant;
FIG. 9 shows Zn prepared in examples 3 and 5 to 6 of the present invention and comparative examples 16 to 19 3 B 2 O 6 The relationship between the quality factor and the grain size of the microwave ceramic material at different sintering temperatures is shown;
FIG. 10 shows Zn prepared in examples 3 and 5 to 6 of the present invention and in comparative examples 16 to 19 3 B 2 O 6 And (3) a resonant frequency temperature coefficient graph of the microwave ceramic material at different sintering temperatures.
Detailed Description
The following description of the embodiments of the present invention will be made with reference to the accompanying drawings. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1:
the invention provides a method for preparing Zn by cold sintering and subsequent low-temperature annealing treatment 3 B 2 O 6 The preparation method of the microwave ceramic material is specifically shown in the following examples.
Zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-60min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
The method comprises the following steps: weighing and proportioning: according to the formula Zn 3 B 2 O 6 Weighing raw materials: znO, H 3 BO 3 . Adding ZnO and H 3 BO 3 Drying in a high temperature oven at 120 deg.C for at least 6h to remove additional water from the raw materials. Due to B in the calcination process 2 O 3 Volatilization leads to the loss of boron, so when weighing in the first step, an additional 12wt.% (i.e. 0.24 g) of H is weighed 3 BO 3 As a compensation;
step two: primary ball milling: pouring the raw materials into a ball milling tank, taking zirconia beads as a ball milling medium, adding absolute ethyl alcohol according to the proportion of 1. Then pouring the mixed slurry into a drying box filled with a plastic film, and placing the drying box in a constant-temperature drying oven at 80 ℃ to dry the absolute ethyl alcohol to obtain a first ball grinding material;
step three: pre-burning: grinding the powder subjected to primary ball milling and drying, sieving the powder by a 100-mesh sieve, pouring the sieved powder into a crucible, and putting the crucible into a high-temperature furnace, wherein the temperature regulating program of the high-temperature furnace is set as follows: heating to 825 deg.C at a rate of 5 deg.C/min, maintaining for 3 hr, and naturally cooling to obtain dry powder;
step four: secondary ball milling: pouring dry powder obtained by pre-sintering into a ball milling tank, taking zirconia beads as ball milling media, and mixing the dry powder with the dry powder according to the proportion of 1:4, adding absolute ethyl alcohol, wherein the amount of the absolute ethyl alcohol is approximately 3/4 of that of the ball milling tank, then putting the ball milling tank into a ball mill, and ball milling the mixed powder slurry for 6 hours at 200 r/min. Then pouring the mixed powder slurry into a drying box filled with a plastic film, placing the drying box in a constant-temperature oven at 80 ℃ to dry the absolute ethyl alcohol, and then grinding the dried powder and sieving the ground powder with a 200-mesh sieve to obtain Zn 3 B 2 O 6 A powder;
step five: mixing materials: 2g of Zn obtained after secondary ball milling are weighed 3 B 2 O 6 Adding 20 wt% (0.4 ml) of 4.0mol/L glacial acetic acid aqueous solution into the powder, pouring into an agate mortar, and manually grinding and mixing for 2min to 5min to uniformly mix solid and liquid to form a dough-shaped aqueous mixture;
step six: and (3) low-temperature sintering: the mixture was poured into a 12.7mm diameter stainless steel mold and then placed in a hot press, first under 4MPa uniaxial pressure at room temperature for 5min. Then, carrying out cold sintering treatment by using a hot press, setting the uniaxial pressure of the hot press to be 300MPa, raising the temperature to 180 ℃ by using the hot press at the temperature rise rate of 5 ℃/min, sintering at the temperature for 60min, then reducing the temperature to room temperature at the same rate, and taking out the die to obtain the densified ceramic;
step seven: and (3) drying: drying the densified ceramic sample obtained in the last step in a drying oven at 120 ℃ for 24 hours to remove residual moisture and residual liquid phase in the sample to obtain Zn 3 B 2 O 6 Ceramic samples.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.89g/cm 3 The relative density was 91.71%, the dielectric constant (er) was 5.05, the quality factor Qxf was 6,320GHz, and the temperature coefficient of resonance frequency (. Tau.f) was-70.67 ppm/deg.C.
Comparative example 1: zn for preparing 180-300 MPa-60min deionized water solution 3 B 2 O 6 Microwave ceramic material
This comparative example is compared to example 1 except that 20.wt% (i.e., 0.4 ml) of deionized water was added in the mixing process in step five and the process was the same as in example 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.25g/cm 3 The relative density was 76.47%.
Comparative example 2:
zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-60min-0.5mol/L 3 B 2 O 6 Microwave ceramic material
This comparative example is compared with example 1, except that 20.wt% (i.e., 0.4 ml) of 0.5mol/L glacial acetic acid aqueous solution is added in the mixing process of the fifth step, and the process is the same as that of example 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.55g/cm 3 The relative density was 83.73%.
Comparative example 3:
zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-60min-1.0mol/L 3 B 2 O 6 Microwave ceramic material
This comparative example is compared with example 1 except that 20.wt% (i.e., 0.4 ml) of 1.0mol/L glacial acetic acid aqueous solution is added in the mixing process of the fifth step, and the process is the same as that of example 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.81g/cm 3 The relative density was 89.96%.
Comparative example 4: preparing glacial acetic acid water solution of 180-300 MPa-60min-2.0mol/LZn 3 B 2 O 6 Microwave ceramic material
This comparative example is compared with example 1, except that 20.0 mol/L glacial acetic acid aqueous solution (i.e., 0.4 ml) is added in the mixing process of step five, and the process of the other steps is the same as that of example 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.86g/cm 3 The relative density was 91.59%.
Comparative example 5: zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-60min-6.0mol/L 3 B 2 O 6 Microwave ceramic material
This comparative example is compared with example 1 except that 20.0 mol/L glacial acetic acid aqueous solution (i.e., 0.4 ml) was added in the mixing process of step five, and the process of the other steps is the same as that of example 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.84g/cm 3 The relative density was 91.15%.
Comparative example 6: zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-60min-8.0mol/L 3 B 2 O 6 Microwave ceramic material
This comparative example is compared with example 1, except that 20.0 mol/L glacial acetic acid aqueous solution (i.e., 0.4 ml) is added in the mixing process of step five, and the process of the other steps is the same as that of example 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.82g/cm 3 The relative density was 90.55%.
Example 2: zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-30min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
Compared with the embodiment 1, the difference of this embodiment is that the sintering time in the low temperature sintering process of the step six is changed to 30min, and the rest steps are the same as the embodiment 1.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.68g/cm 3 Photo ofThe para-density was 87.05%.
Comparative example 7: zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-90min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
Compared with the embodiment 2, the difference of the comparative example is that the sintering time in the low-temperature sintering process of the step six is changed to 90min, and the rest steps are the same as the embodiment 2.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.87g/cm 3 The relative density was 91.68%.
Comparative example 8: zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-120min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
Compared with the embodiment 2, the difference of the comparative example is that the sintering time in the low-temperature sintering process of the step six is changed to 120min, and the rest steps are the same as the embodiment 2.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.85g/cm 3 The relative density was 91.62%.
Comparative example 9: zn for preparing glacial acetic acid aqueous solution of 180-300 MPa-150min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
Compared with the embodiment 2, the difference of the comparative example is that the sintering time in the low temperature sintering process of the sixth step is changed to 150min, and the rest steps are the same as the embodiment 2.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.88g/cm 3 The relative density was 91.67%.
Example 3: zn for preparing 200-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material
Compared with the embodiment 1, the difference of the embodiment is that the sintering temperature in the low-temperature sintering process of the step six is changed to 200 ℃, and the processes of the other steps are the same as the embodiment 1.
Obtained Zn 3 B 2 O 6 Block of microwave ceramic materialThe density was 3.91g/cm 3 The relative density was 92.18%, the dielectric constant (er) was 4.95, the quality factor Qxf was 6,210GHz, and the temperature coefficient of resonance frequency (. Tau.f) was-69.5 ppm/deg.C.
Comparative example 10: zn for preparing 120-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material
The comparative example is compared with example 3, except that the sintering temperature in the low temperature sintering process of step six is changed to 120 ℃, and the processes of the other steps are the same as those of example 3.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.59g/cm 3 The relative density was 84.64%, the dielectric constant (er) was 3.92, the quality factor Qxf was 4,086GHz, and the temperature coefficient of resonance frequency (. Tau.f) was-71.5 ppm/deg.C.
Comparative example 11: zn for preparing 140-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material
Compared with example 3, the difference of this comparative example is that the sintering temperature in the low-temperature sintering process of step six is changed to 140 ℃, and the processes of the other steps are the same as those of example 3.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.72g/cm 3 The relative density was 87.48%, the dielectric constant (er) was 4.91, the quality factor Qxf was 5,300GHz, and the temperature coefficient of resonance frequency (. Tau.f) was-70.9 ppm/deg.C.
Comparative example 12: zn for preparing 160-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material
The comparative example is different from example 3 in that the sintering temperature in the low-temperature sintering process of the sixth step is changed to 160 ℃, and the processes of the other steps are the same as those of example 3.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.84g/cm 3 The relative density was 90.68%, the dielectric constant (er) was 4.9, the quality factor Qxf was 5,720GHz, and the temperature coefficient of resonance frequency (. Tau.f) was-71.4 ppm/. Degree.C.
Example 4: zn for preparing glacial acetic acid aqueous solution of 200-100 MPa-60min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
Compared with the embodiment 3, the difference of this embodiment is that the uniaxial pressure in the low-temperature sintering process of the step six is changed to 100MPa, and the rest of the process is the same as that of the embodiment 3.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.55g/cm 3 The relative density was 83.21%.
Comparative example 13: zn for preparing 200-200 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material
The comparative example is different from example 4 in that the uniaxial pressure in the low-temperature sintering process of the sixth step is changed to 200MPa, and the processes of the other steps are the same as those of example 4.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.77g/cm 3 The relative density was 89.54%.
Comparative example 14: zn for preparing glacial acetic acid aqueous solution of 200-400 MPa-60min-4.0mol/L 3 B 2 O 6 Microwave ceramic material
The comparative example is different from example 4 in that the uniaxial pressure in the low-temperature sintering process of the step six is 400MPa, and the processes of the other steps are the same as those of example 4.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.88g/cm 3 The relative density was 92.09%.
Comparative example 15: zn for preparing 200-500 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material
The comparative example is different from example 4 in that the uniaxial pressure in the low-temperature sintering process of step six is changed to 500MPa, and the processes of the other steps are the same as those of example 4.
Obtained Zn 3 B 2 O 6 The bulk density of the microwave ceramic material is 3.86g/cm 3 The relative density was 92.01%.
Example 5: zn for preparing 200-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material and annealing treatment at 500 deg.c
This example compares with example 3, except that eight cold sintering assisted annealing treatments were added: and (3) placing the cold sintering characteristic sample obtained in the comparative example 12 on the pre-sintered powder which is sieved by a 100-mesh sieve, then placing the pre-sintered powder into a high-temperature furnace, setting the high-temperature furnace to heat to 500 ℃ at the heating rate of 4 ℃/min, preserving the heat for 3h, and taking out the sample after natural cooling. The rest of the procedure was the same as in example 3.
Obtained Zn 3 B 2 O 6 The microwave ceramic material has a relative density of 94.78%, a dielectric constant (er) of 5.83, a quality factor Qxf of 20,036GHz, and a temperature coefficient of resonance frequency (. Tau.f) of-67.5 ppm/deg.C.
Comparative example 16: zn for preparing 200-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material and annealing treatment at 400 deg.c
Compared with the embodiment 5, the difference of the comparative example is that in the step eight cold sintering auxiliary annealing treatment, the temperature of the high-temperature furnace is raised to 400 ℃, and the rest steps are the same as the embodiment 5.
Obtained Zn 3 B 2 O 6 The microwave ceramic material has a relative density of 93.8%, a dielectric constant (er) of 5.38, a quality factor Qxf of 9,102GHz, and a temperature coefficient of resonance frequency (. Tau.f) of-68.9 ppm/deg.C.
Comparative example 17: zn for preparing 200-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material and annealing treatment at 450 deg.c
Compared with the embodiment 5, the difference of the comparative example is that in the step eight cold sintering auxiliary annealing treatment, the temperature of the high-temperature furnace is raised to 450 ℃, and the rest steps are the same as the embodiment 5.
Obtained Zn 3 B 2 O 6 The microwave ceramic material has a relative density of 94.56% and a dielectric constant (er)5.54, the quality factor Q multiplied by f is 16,046GHz, and the temperature coefficient (tau f) of the resonant frequency is-68.2 ppm/DEG C.
Comparative example 18: zn for preparing 200-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material and annealing treatment at 550 deg.c
The comparative example is compared with example 5, except that in the eight-step cold sintering auxiliary annealing treatment, the temperature of the high-temperature furnace is raised to 550 ℃, and the processes of the other steps are the same as those of example 5.
Obtained Zn 3 B 2 O 6 The microwave ceramic material has a relative density of 94.59%, a dielectric constant (er) of 5.95, a quality factor Qxf of 20.620GHz, and a temperature coefficient of resonance frequency (. Tau.f) of-67.2 ppm/deg.C.
Comparative example 19: zn for preparing 200-300 MPa-60min-4.0mol/L glacial acetic acid aqueous solution 3 B 2 O 6 Microwave ceramic material and annealing treatment at 700 deg.c
Compared with the embodiment 5, the difference of the comparative example is that in the step eight cold sintering auxiliary annealing treatment, the temperature of the high-temperature furnace is raised to 700 ℃, and the rest steps are the same as the embodiment 5.
Obtained Zn 3 B 2 O 6 The microwave ceramic material has a relative density of 94.24%, a dielectric constant (er) of 5.71, a quality factor Qxf of 19,420GHz, and a temperature coefficient of resonance frequency (. Tau.f) of-66.7 ppm/deg.C.
Example 6: preparation of Zn by traditional high-temperature solid-phase method 3 B 2 O 6 Microwave ceramics
Adding 5wt.% of PVA as a binder into the pre-sintered powder, grinding the pre-sintered powder uniformly, sieving one part of the pre-sintered powder with a 100-mesh sieve, sieving the other part of the pre-sintered powder with a 60-mesh sieve, weighing 1.6g of powder sieved with the 60-mesh sieve, tabletting the powder to prepare a ceramic blank, taking the powder sieved with the 100-mesh sieve as a sintering padding, and sintering the ceramic blank in a high-temperature furnace to obtain Zn 3 B 2 O 6 Microwave ceramics, the parameters of the high-temperature furnace are set as follows: 4 min/DEG C (heating rate) — 650 ℃ (degumming temperature) -4 h (degumming time) -875 ℃ to 975 ℃ (sintering temperature) -4 h (heat preservation time) -4 min/DEG C (cooling rate) -800 ℃ (cooling to the temperature and natural cooling). The sintering temperatures are respectively as follows: 875 deg.C, 900 deg.C, 925 deg.C, 950 deg.C, 975 deg.C.
Obtained Zn 3 B 2 O 6 The microwave ceramic material has relative densities of 91.45%, 92.88%, 95.03%, 96.89%, and 96.38%, respectively, wherein the dielectric constant (er) is 6.04, the quality factor Qxf is 54,450GHz, and the temperature coefficient of resonance frequency (τ f) is-65.8 ppm/deg.C when the sintering temperature is 925 deg.C.
Zn prepared in examples 1, 5 and 6 3 B 2 O 6 Microwave ceramic material and primary Zn 3 B 2 O 6 The XRD pattern of the powder is shown in figure 1.
It can be seen from FIG. 1 that all diffraction peaks are associated with monoclinic Zn 3 (BO 3 ) 2 (PDF # 71-2063) the characteristic peaks match, with a space group of I12/c1. This indicates that the liquid phase introduced during cold sintering and the uniaxial pressure applied do not alter Zn 3 (BO 3 ) 2 No second phase is produced. The diffraction peak intensity increases with increasing sintering temperature, since the cold sintering temperature is very low, zn 3 B 2 O 6 The crystallinity of the ceramic is lower in the cold sintering process, and the crystallization capability of the ceramic is enhanced along with the increase of the sintering treatment temperature, which is shown in an XRD (X-ray diffraction) pattern that the intensity of diffraction peaks is enhanced along with the increase of the crystallinity.
Example 1 Zn prepared in comparative examples 1 to 6 3 B 2 O 6 The bulk density and relative density of the microwave ceramic material are related to the concentration of glacial acetic acid as shown in figure 2.
It can be seen from FIG. 2 that Zn is present when deionized water is used as a solvent 3 B 2 O 6 The relative density of the ceramic sample was low, only 76.47%. And when glacial acetic acid is used as solvent, zn 3 B 2 O 6 The density of the ceramic is rapidly increased, and when the concentration of the glacial acetic acid is 4mol/L, the maximum density reaches 3.89g/cm 3 The relative density was 91.71%, indicating that glacial acetic acid contributes to increase Zn 3 B 2 O 6 When the density of the ceramic is more than 4mol/L, the density of the sample does not increase any more and even tends to decrease.
Zn prepared in examples 1 to 2 and comparative examples 7 to 9 3 B 2 O 6 The bulk density and relative density of the microwave ceramic material as a function of sintering time are shown in FIG. 3.
From FIG. 3 it can be seen that cold sintering produces densified Zn 3 B 2 O 6 The microwave ceramic can be finished within 60min, the sintering time is continuously increased, and the bulk density and the relative density are basically unchanged. This may be the case in a cold sintering system, where the liquid phase is depleted and dissolution of the particles no longer proceeds as the sintering time increases.
Zn prepared in examples 1 and 3 and comparative examples 10 to 12 3 B 2 O 6 The bulk density and relative density of the microwave ceramic material as a function of cold sintering temperature are shown in FIG. 4.
It can be seen from fig. 4 that increasing the sintering temperature shows a monotonically increasing trend in density. At 120 ℃ the density was 3.59g/cm 3 The relative density reaches 84.64 percent; at 200 ℃ the density was 3.91g/cm 3 The relative density was 92.18%.
Examples 3 and 4, comparative examples 13 to 15 3 B 2 O 6 The bulk density and relative density of microwave ceramic material as a function of uniaxial pressure is shown in figure 5.
It can be seen from FIG. 5 that Zn is increased with the uniaxial pressure 3 B 2 O 6 The compactness of the microwave ceramic is obviously improved, the relative density of 92 percent is already achieved under 300MPa, and when the applied uniaxial pressure is increased continuously, the die is easy to lock, so that the demoulding of a sample is difficult, and the surface of the ceramic sample is easy to crack.
Zn prepared in examples 1 and 3 and comparative examples 10 to 12 3 B 2 O 6 The microwave dielectric properties of the microwave ceramic material at different sintering temperatures are shown in fig. 6.
From fig. 6, it can be seen that the dielectric constant (er) and the quality factor (Q × f) are increased with the increase of the cold sintering temperature, and the trend is the same as the variation trend of the relative density (ρ r), which indicates that the increase of the density is helpful to improve Zn 3 B 2 O 6 Microwave dielectric properties of microwave ceramics. Q x f although showing monotonic increaseThe increase range of the temperature coefficient (tau f) of the resonance frequency is not very large, the temperature coefficient (tau f) of the resonance frequency is firstly increased and then decreased on the whole, and the temperature coefficient (tau f) of the resonance frequency is gradually increased after the cold sintering temperature is more than 160 ℃, and the tau f is not greatly fluctuated on the whole and is in the range of +/-2 ppm/DEG C when the cold sintering temperature is 200 ℃.
Zn prepared in examples 1, 5 to 6 and comparative examples 16 to 19 3 B 2 O 6 The relative densities of the microwave ceramic material at different sintering temperatures are shown in fig. 7.
It can be seen from FIG. 7 that the relative density of the cold-sintered sample increased from 92% to 95% with the increase of the annealing temperature, and the relative density decreased with the increase of the annealing temperature, which is probably due to abnormal grain growth at the higher annealing temperature, resulting in Zn 3 B 2 O 6 Pores are generated among the microwave ceramic grains. To obtain Zn with a relative density higher than 95% 3 B 2 O 6 Microwave ceramics, the sintering temperature needs to be higher than 925 ℃, and Zn prepared by cold sintering auxiliary annealing process 3 B 2 O 6 The microwave ceramic can be obtained only at 500 ℃. Therefore, the cold sintering and the subsequent low-temperature annealing process can greatly reduce the densification sintering temperature of the ceramic.
Zn prepared in examples 3, 5 to 6 and comparative examples 16 to 19 3 B 2 O 6 The relationship between the dielectric constant of the microwave ceramic material at different sintering temperatures and the dielectric constant after porosity correction is shown in fig. 8.
From FIG. 8, it can be seen that Zn is prepared by cold sintering at 200 deg.C 3 B 2 O 6 After microwave ceramic annealing, er increases with the increase of annealing temperature, and has the same tendency as er (cor) change. When annealed at 700 ℃, there is a tendency for er to decrease, which may be related to Zn at this annealing temperature 3 B 2 O 6 The abnormal growth of the microwave ceramics is related. The er is 5.95 after annealing at 550 ℃, and Zn prepared by a conventional solid-phase sintering method at 925 DEG C 3 B 2 O 6 The er (6.04) of the microwave ceramics is similar.
Zn prepared in examples 3, 5 to 6 and comparative examples 16 to 19 3 B 2 O 6 The relationship between the quality factor and the grain size of the microwave ceramic material at different sintering temperatures is shown in fig. 9.
From FIG. 9, it can be seen that Zn is prepared by cold sintering at 200 deg.C 3 B 2 O 6 The microwave ceramics have a poor Q x f value, and with further annealing treatment, the Q x f increases significantly, reaching a maximum Q x f value of 20620.21GHz at an annealing temperature of 550 ℃. Also of note is Zn prepared by conventional solid phase sintering 3 B 2 O 6 The Q multiplied by f value of the microwave ceramic is 54450.36GHz and is higher than that of the sample subjected to annealing treatment, which shows that high-temperature sintering is still an effective means for inhibiting dielectric loss and obtaining the best ceramic performance. The cold sintering and post annealing processes, although having certain limitations, can also suppress dielectric loss to some extent. Furthermore, it can be seen from the variation of the grain size that Zn is formed after the cold sintering and annealing treatment 3 B 2 O 6 The average grain sizes of the microwave ceramics are all very small and are all smaller than 1 mu m, which shows that the cold sintering process effectively controls the grain growth and obtains a ceramic microstructure with fine grains.
Zn prepared in examples 3, 5 to 6 and comparative examples 16 to 19 3 B 2 O 6 The resonant frequency temperature coefficients of the microwave ceramic material at different sintering temperatures are shown in fig. 10.
From FIG. 10, it can be seen that Zn is prepared by cold sintering at 200 deg.C 3 B 2 O 6 The error of the tau value of the microwave ceramic is large, which is mainly due to the weak resonance response of the cold-sintered sample. For Zn after annealing 3 B 2 O 6 The tau f value of the microwave ceramic is increased along with the increase of the annealing temperature, and is increased from nearly-70 ppm/DEG C at 200 ℃ to-66.7 ppm/DEG C at 700 ℃.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in the embodiments without departing from the principles and spirit of the invention, and these embodiments are still within the scope of the invention.

Claims (8)

1. Cold sintering assisted low-temperature densification Zn 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: weighing and proportioning: according to the formula Zn 3 B 2 O 6 Weighing raw materials ZnO and H 3 BO 3 ；
Step two: primary ball milling: pouring the raw materials into a ball milling tank, drying the slurry to constant weight after ball milling to obtain a first ball grinding material;
step three: pre-burning: sieving the primary ball-milled material, and presintering to obtain dry powder;
step four: secondary ball milling: ball-milling the dry powder obtained by pre-sintering for the second time, drying the dry powder to constant weight after ball-milling, grinding and sieving to obtain Zn 3 B 2 O 6 Powder;
step five: mixing materials: weighing Zn 3 B 2 O 6 Adding 20wt.% of 2-8 molar glacial acetic acid aqueous solution into the powder, and uniformly mixing to obtain a dough-like aqueous mixture;
step six: and (3) low-temperature sintering: putting the water-containing mixture obtained in the fifth step into a die, putting the die on a tablet press for pressure maintaining, then moving the die into a hot press, heating the sintering temperature to 160-200 ℃, sintering for 60-150min, and applying 300-500MPa pressure to the die to obtain densified ceramic;
step seven: and (3) drying: drying the densified ceramic obtained in the sixth step in a drying oven at the temperature of 120 ℃ for 24 hours to remove residual moisture, and obtaining Zn 3 B 2 O 6 A ceramic sample;
step eight: cold sintering auxiliary annealing treatment: zn obtained in the seventh step 3 B 2 O 6 And placing the ceramic sample on the pre-sintered powder, and then placing the ceramic sample into a high-temperature furnace for annealing treatment, wherein the annealing temperature is 400-700 ℃.
2. Cold sintering assisted low temperature densification Zn according to claim 1 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: the above-mentionedZnO and H in the first step 3 BO 3 The purity of the product is 99.99%; before weighing, znO and H are added 3 BO 3 Drying at 120 deg.C in a high-temperature oven.
3. Cold sintering assisted low temperature densification Zn in accordance with claim 1 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: the step two is a specific step of primary ball milling: pouring the raw materials into a ball milling tank, using zirconia beads as ball milling media, and mixing the raw materials according to the proportion of 1:4, adding absolute ethyl alcohol, adding the amount of the absolute ethyl alcohol to 3/4 of the ball milling tank, putting the ball milling tank into a ball mill, ball milling the mixed slurry for 6 hours at 200r/min, pouring the mixed slurry into a drying box filled with a plastic film, and placing the drying box in a constant-temperature oven at 80 ℃ to dry the absolute ethyl alcohol.
4. Cold sintering assisted low temperature densification Zn according to claim 1 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: in the third step, the pre-burning comprises the following specific steps: and grinding the powder subjected to primary ball milling and drying, sieving the powder with a 100-mesh sieve, pouring the powder into a crucible, putting the crucible into a high-temperature furnace, presintering the powder for 3 hours at 825 ℃, and naturally cooling the powder to obtain dry powder.
5. Cold sintering assisted low temperature densification Zn in accordance with claim 1 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: in the fourth step, the second ball milling comprises the following specific steps: pouring the dry powder obtained by pre-sintering into a ball milling tank, taking zirconia beads as ball milling media, and mixing the dry powder with the zirconia beads according to the proportion of 1:4, adding absolute ethyl alcohol, adding the amount of the absolute ethyl alcohol to 3/4 of the ball milling tank, then putting the ball milling tank into a ball mill, ball milling the mixed slurry for 6 hours at 200r/min, pouring the mixed slurry into a drying box filled with a plastic film, placing the drying box in a constant-temperature oven at 80 ℃ to dry the absolute ethyl alcohol, and grinding the dried powder to pass through a 200-mesh sieve.
6. The cold sintering aid of claim 1Zn for assisting low-temperature densification 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: the concrete steps of mixing in the fifth step are as follows: zn obtained after secondary ball milling 3 B 2 O 6 Pouring the powder and 20wt.% glacial acetic acid aqueous solution with different concentrations into an agate mortar, manually grinding and mixing for 2-5min to uniformly mix solid and liquid, wherein the concentration is 2-8 mol/L.
7. Cold sintering assisted low temperature densification Zn according to claim 1 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: the low-temperature sintering in the sixth step comprises the following specific steps: pouring the mixture into a stainless steel mold with the diameter of 12.7mm, then placing the stainless steel mold into a hot press, applying uniaxial pressure of 4MPa at room temperature, keeping the pressure for 5min, then performing cold sintering treatment by using the hot press, wherein the uniaxial pressure of the hot press is 300-500MPa, the temperature of the hot press is increased to the sintering temperature at the heating rate of 5 ℃/min, the sintering temperature is 160-200 ℃, the sintering time is 60-150min, then cooling to the room temperature at the same rate, and taking out the mold.
8. Cold sintering assisted low temperature densification Zn according to claim 1 3 B 2 O 6 The preparation method of the microwave ceramic material is characterized by comprising the following steps: the drying in the seventh step comprises the following specific steps: demoulding and taking out a sample in the mould, putting the sample into a constant-temperature drying oven with the temperature of 120 ℃ for drying for 24 hours, and removing a residual liquid phase in the sample; the eight cold sintering auxiliary annealing treatment specifically comprises the following steps: placing the sample with the optimal sintering characteristic obtained by cold sintering on pre-sintered powder which is sieved by a 100-mesh sieve, then placing the pre-sintered powder into a high-temperature furnace, setting the temperature to be 4 ℃/min, heating to the required annealing temperature, keeping the annealing temperature at 400-700 ℃, preserving the heat for 3h, and naturally cooling and then taking out the sample.
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