Preparation method of cold-sintering-assisted low-temperature densified KTaO3 ceramic material

Abstract

The invention belongs to the technical field of microwave dielectric ceramic preparation, and particularly relates to a preparation method of a cold-sintering-assisted low-temperature densified KTaO3 ceramic material. The preparation method comprises the following steps: mixing KTaO3 powder with K2CO3 aqueous solutions with different concentrations and addition amounts, and combining specific uniaxial pressure, sintering temperature and heat preservation time to realize preliminary densification of the ceramic material; and then, the densification of the KTaO3 ceramic is further realized through annealing treatment at different temperatures. Compared with a traditional cold sintering method, the K2CO3 aqueous solution is used as a liquid phase medium, the solubility of the KTaO3 powder can be effectively improved, and the initial compactness degree is improved; compared with a traditional solid-phase sintering method, the densification temperature of the ceramic material can be remarkably reduced, volatilization of the K element can be reduced, and therefore generation of a second phase is avoided, the obtained ceramic material is excellent in dielectric property, the preparation technology is simple, energy consumption is reduced, and the good application prospect is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave dielectric ceramic preparation, and specifically relates to a preparation method of cold sintering-assisted low-temperature densification KTaO 3 ceramic material. Background Art

[0002] The rapid progress of 5G communication technology has greatly promoted the development of the microwave communication field. The significant reduction in the size and weight of handheld communication devices fully demonstrates the urgent market demand for device miniaturization. For microwave dielectric ceramics, a high dielectric constant can significantly reduce the volume of electronic components and promote the miniaturization of devices, while a high quality factor can reduce energy loss and improve frequency selectivity. Therefore, the research and preparation of microwave dielectric ceramics with high dielectric constant and high quality factor are of great significance for the development of integrated circuits and wireless communication.

[0003] KTaO 3 is an early ferroelectric crystal that exhibits excellent dielectric properties at room temperature, which gives it great application potential in fields such as high-capacity integrated circuits and low-frequency communication devices. However, the sintering temperature of KTaO 3 microwave dielectric ceramics synthesized by conventional solid-phase methods is usually greater than 1350°C. This high-temperature sintering process not only consumes a large amount of energy but also causes problems such as potassium element evaporation and a too narrow sintering window, thereby having an adverse impact on the ceramic properties.

[0004] The cold sintering process (CSP) is an economical and practical new sintering technology that can effectively reduce the sintering temperature and show significant advantages in the preparation of dense ceramics, composites, etc. In recent years, due to its low temperature and short time characteristics, the cold sintering technology has been widely used in the preparation of various materials. However, the related applications of cold sintering mostly focus on water-soluble materials. For low-solubility compounds, research shows that changing the type of liquid phase and adding subsequent annealing treatment can effectively promote the densification of ceramic materials. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method of cold sintering-assisted low-temperature densification KTaO 3 ceramic material. By changing the cold sintering conditions and subsequent annealing temperature, KTaO with high density and excellent performance can be prepared at low temperature 3 microwave dielectric ceramics, with a simple process, energy saving, and good application prospects.

[0007] To achieve the above purpose, the technical solution of the present invention is as follows:

[0008] The preparation method of the KTaO 3 powder includes the following steps:

[0009] Step 1: Add anhydrous potassium carbonate K 2 CO 3 , Tantalum pentoxide Ta 2 O 5 The original powder is according to the chemical formula KTaO 3 Weighing is performed.

[0010] Step 2: Pour the powder prepared in step 1 into a ball mill, and perform the first ball milling according to the mass ratio of powder, zirconium oxide balls and anhydrous ethanol solution of 1:5:2. The ball mill speed is 280r / min, and the ball milling time is 4h. The slurry after the first ball milling is dried at 65°C, and the dried powder is sieved with an 80-mesh sieve.

[0011] Step 3: Pre-calculate the sieved powder obtained in step 2 in an atmosphere at 900°C for 4 hours.

[0012] Step 4: The powder pre-sintered in step 3 was subjected to a second ball milling according to the mass ratio of powder, zirconium oxide ball and anhydrous ethanol solution of 1:5:1. The ball mill speed was 280 r / min and the ball milling time was 4 h. The slurry after the second ball milling was dried at 65 ° C. The dried powder was sieved with a 100 mesh screen to obtain KTaO 3 Single phase powder.

[0013] A cold sintering assisted low temperature densification KTaO 3 The method for preparing a ceramic material comprises the following steps:

[0014] Step 5: Use deionized water and K 2 CO 3 Configuration 0-6 mol% K 2 CO 3 Solution, specific K 2 CO 3 The concentrations are 0 mol%, 2 mol%, 4 mol%, and 6 mol%.

[0015] Step 6: KTaO 3 Powder and K 2 CO 3 The solution is uniformly mixed, where K 2 CO 3 The amount of KTaO added to the solution is 3 3wt%-7wt% of powder, specific K 2 CO 3 The amount of solution added is KTaO 3 3wt%, 5wt%, 7wt% of powder.

[0016] Step 7: Put the mixture obtained in Step 6 into a steel mold, apply a pressure of 250 - 350 MPa and a temperature of 90°C - 150°C, and keep the temperature and pressure for 20 - 60 min to obtain preliminarily densified KTaO 3 ceramics; this step is cold sintering, the cold sintering temperatures are 90°C, 120°C, 150°C, the pressures are 250 MPa, 300 MPa, 350 MPa, and the holding time of temperature and pressure is 20 min, 40 min, 60 min.

[0017] Step 8: Put the KTaO 3 ceramics obtained in Step 7 into a high-temperature furnace, set the annealing temperature at 1150°C - 1300°C, and keep the temperature for 4 h to obtain densified KTaO 3 ceramics. The annealing temperatures are 1150°C, 1200°C, 1250°C, 1300°C.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] (1) The preparation method of the cold-sintering assisted low-temperature densification KTaO 3 ceramic material can prepare KTaO 3 microwave dielectric ceramics with high density and excellent performance under low-temperature conditions. The process is simple, energy consumption is saved, and it has good application prospects.

[0020] (2) In the cold sintering process of the present invention, a K 2 CO 3 solution with a specific concentration is used as the liquid-phase medium, which can effectively improve the solubility of KTaO 3 powder, promote the preliminary densification of KTaO 3 ceramics, and make its relative density reach 79%.

[0021] (3) Under the annealing conditions 150°C lower than the traditional sintering temperature, the present invention realizes the densification of KTaO 3 ceramics, with a relative density as high as 97%, and avoids the generation of K 6 Ta 10.8 O 30 phase caused by the volatilization of potassium element, thus improving the dielectric properties. Description of the Drawings

[0022] Figure 1 (a) to (d) correspond to the SEM surface morphology diagrams of Examples 1, 2, 3, and 4 after annealing at 1200°C in sequence;

[0023] Figure 2 are the XRD diffraction patterns of Examples 1, 5, 6, 7, and 16. Detailed Embodiments

[0024] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0025] The KTaO used in the present invention 3 The raw material powder is prepared by a solid-phase method, and the specific steps are the same as those described above.

[0026] Example 1: A method for preparing a cold sintering-assisted low-temperature densification KTaO 3 ceramic material, in which KTaO 3 powder is mixed with a 7 wt% K solution with a concentration of 4 mol% 2 CO 3 solution. Subsequently, the mixture is placed in a steel mold, a pressure of 300 MPa is applied, and cold sintering is carried out at 120 °C, and heat preservation and pressure holding are carried out for 40 min to achieve preliminary densification of the ceramic; finally, the ceramic sample is annealed at a temperature of 1200 °C for 4 h to obtain Specimen 1.

[0027] The differences in Examples 2-15 are only in the cold sintering and annealing conditions, as shown in Table 1

[0028] Table 1

[0029]

[0030] Example 16: Preparation of KTaO 3 ceramics by the traditional high-temperature solid-phase method. An aqueous acrylic acid solution is added to the pre-sintered powder as a binder for granulation, and it is pressed into a shape and sintered in an air atmosphere at 1350 °C for 4 hours to obtain Specimen 16.

[0031] Relative density after cold sintering of some examples in Table 2

[0032] Sample number Relative density after cold sintering (%) 1 78.26％ 2 74.62％ 3 76.78％ 4 79.14％ 8 70.66％ 9 74.46％ 10 77.18％ 11 78.03％ 12 72.58％ 13 77.81％ 14 71.15％ 15 77.31％

[0033] Dielectric properties after annealing of some examples in Table 3

[0034] Sample number Relative density (%) Dielectric constant Q×f (GHz) 1 97.58％ 235.65 3305 2 92.28％ 183.02 725 3 95.49％ 202.96 1742 4 96.62％ 213.48 2613 5 93.81％ 191.07 1109 6 96.22％ 208.77 2496 7 89.52％ 153.45 254 16 94.73％ 196.23 1526

[0035] As can be seen from Table 2, conditions such as uniaxial pressure, temperature, heat preservation time, concentration and addition amount of the K 2 CO 3 solution during the cold sintering process will all affect the preliminary densification degree of the sample. The relative density of the sample after cold sintering increases with the increase of the concentration and addition amount of the K 2 CO 3 solution, but for uniaxial pressure, temperature, and heat preservation time, it shows a trend of first increasing and then decreasing. When K 2 CO 3When the solution concentration is increased from 0 mol% to 6 mol%, the relative density of the sample is increased from 74.62% to 79.14%, indicating that K 2 CO 3 solution can effectively promote the dissolution of KTaO 3 powder. In Example 4, that is, when the concentration of K 2 CO 3 solution is 6 mol%, the content is 7 wt%, the uniaxial pressure is 300 MPa, the temperature is 120 °C, and the time is 40 min, the preliminary densification degree of KTaO 3 ceramics is the best, and the relative density reaches 79.14%.

[0036] As can be seen from Table 3, with the increase of the concentration of K 2 CO 3 solution and the annealing temperature, the relative density and dielectric properties of the annealed samples first increase and then decrease. Generally speaking, Example 1 has the highest densification degree, the relative density is as high as 97.58%, and the dielectric properties are the best ε r = 235.65, Q×f = 3305 GHz, and both are better than Example 16 prepared by the traditional high-temperature solid-phase method.

[0037] Figure 1 (a) to (d) correspond to the SEM images of the surface morphologies of Examples 1, 2, 3, and 4 after annealing at 1200 °C in sequence. The results show that the introduction of K 2 CO 3 solution can not only increase the solubility of KTaO 3 during the cold sintering process, improve its preliminary densification degree, but also promote grain growth during the subsequent annealing process. However, when the potassium element concentration in the solution is too high, abnormal growth of individual grains will occur, making the microstructure uneven, and ultimately leading to a decrease in the densification and properties of the ceramics.

[0038] Figure 2 The XRD diffraction patterns of Examples 1, 5, 6, 7, and 16 are shown. The diffraction peaks of Examples 1, 5, and 6 are all matched with the characteristic peaks of KTaO 3 (PDF#70-4802), and its space group is Pm-3m(221). This indicates that the K 2 CO 3 solution introduced during the cold sintering process will not produce a second phase, and within the range of 1150 °C - 1250 °C, the annealing temperature has little effect on the structural parameters of the sample. When the sintering temperature is greater than 1300 °C, K appears in the XRD diffraction patterns of Examples 7 and 16 6 Ta 10.8 O 30Phase (triangle symbol in the figure), and with the increase of temperature, the content of this phase also increases. This shows that too high a sintering temperature will cause the volatilization of potassium element, thus generating K 6 Ta 10.8 O 30 phase, which is not conducive to the improvement of the density of KTaO 3 ceramics, and has an adverse effect on its dielectric properties.

[0039] In summary, the preparation method of the cold sintering-assisted low-temperature densification KTaO 3 ceramic material used in the present invention introduces K 2 CO 3 solution as the liquid phase medium, effectively improving the initial densification degree of KTaO 3 ceramics, and high-density and excellent-performance KTaO 3 microwave dielectric ceramics can be prepared under low-temperature annealing conditions, reducing the volatilization of potassium element and avoiding the generation of K 6 Ta 10.8 O 30 phase. The process is simple, energy-saving, and has good application prospects.

Claims

1. A method for preparing a cold sintering-assisted low-temperature densification KTaO3 ceramic material, characterized in that: KTaO3 powder was mixed with K2CO3 aqueous solution of different concentrations and addition amounts, and the initial densification of the ceramic material was achieved through cold sintering, combined with specific uniaxial pressure, sintering temperature and holding time. Subsequently, the densification of KTaO3 ceramics was further achieved through annealing treatment at different temperatures.

2. The method for preparing a cold sintering-assisted low-temperature densification KTaO3 ceramic material according to claim 1, characterized in that: The preparation method of the KTaO3 powder comprises the following steps: Step 1: weigh the original powders of anhydrous potassium carbonate K2CO3 and tantalum pentoxide Ta2O5 according to the chemical formula KTaO3; Step 2: Pour the powder prepared in step 1 into a ball mill, and perform the first ball milling according to the mass ratio of powder, zirconium oxide balls and anhydrous ethanol solution of 1:5:

2. The ball mill speed is 280r / min, and the ball milling time is 4h. The slurry after the first ball milling is dried at 65°C, and the dried powder is sieved with an 80-mesh sieve; Step 3: pre-calculate the sieved powder in step 2 in an atmosphere at 900°C for 4 hours; Step 4: The powder pre-sintered in step 3 is subjected to a second ball milling according to the mass ratio of powder, zirconium oxide balls and anhydrous ethanol solution of 1:5:

1. The ball mill speed is 280 r / min and the ball milling time is 4 h. The slurry after the second ball milling is dried at 65°C. The dried powder is sieved with a 100-mesh sieve to obtain KTaO3 single-phase powder.

3. The method for preparing a cold sintering assisted low temperature densification KTaO3 ceramic material according to claim 1, characterized in that: The following steps are involved: Step 5: Prepare a 0-6 mol% K2CO3 solution with deionized water and K2CO3; Step 6: uniformly mix the KTaO3 powder and the K2CO3 solution, wherein the amount of the K2CO3 solution added is 3wt%-7wt% of the KTaO3 powder; Step 7: Put the mixture obtained in step 6 into a steel mold, apply a pressure of 250-350 MPa and a temperature of 90°C-150°C, and keep the temperature and pressure for 20-60 minutes to obtain a preliminary densified KTaO3 ceramic; Step 8: Place the KTaO3 ceramic obtained in step 7 into a high temperature furnace, set the temperature to 1150°C-1300°C for annealing, and obtain a dense KTaO3 ceramic after keeping the temperature for 4 hours.

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