Zinc oxide ceramic with controllable nonlinearity coefficient and preparation method and application thereof

Abstract

This invention discloses a zinc oxide ceramic with tunable nonlinear coefficient, its preparation method, and its applications, belonging to the field of functional ceramics and their preparation technology. This invention solves the problem that existing ZnO-based varistor ceramics cannot achieve tunable nonlinear coefficients. This invention uses AlN as an additive to dope and modify ZnO, utilizing the significant difference in conductivity between AlN and ZnO to construct a Schottky barrier within the ZnO grains, inducing the varistor properties of the ZnO ceramic; and AlN and ZnO have the same crystal structure, Al... 3+ Ions can easily enter the ZnO lattice, achieving the purpose of improving nonlinear characteristics through doping. This allows AlN to simultaneously act as a varistor and a doping modifier for ZnO, resulting in doped zinc oxide ceramics that possess both a single-phase cubic zinc sphalerite-type zinc oxide structure and varistor properties. By changing the doping content of AlN, the nonlinear coefficient and varistor potential gradient can be controlled, thus broadening the application range of zinc oxide ceramics.

Description

Technical Field

[0001] This invention relates to a zinc oxide ceramic with adjustable nonlinear coefficient, its preparation method and application, belonging to the field of functional ceramics and their preparation technology. Background Technology

[0002] A varistor is a resistive device with nonlinear current-voltage characteristics. When a circuit experiences overvoltage, the varistor clamps the voltage, absorbing excess current to protect sensitive components. Pure ZnO ceramics do not possess varistor properties; they are typically prepared by adding other oxides. Currently, the most common method is to use ZnO as the main component, adding small amounts of metal oxides as varistor forming agents, such as Bi₂O₃, MnO₂, Sb₂O₃, Co₃O₄, and Cr₂O₃, to construct a Schottky barrier at the ZnO grain interfaces, thus achieving the varistor properties of ZnO-based ceramics. In recent years, to improve the potential gradient and nonlinear characteristics of ZnO-based varistors, researchers have further added Al₂O₃, CeO₂, and rare earth oxides (Y₂O₃, La₂O₃) to ZnO-based ceramics. However, because the ZnO-based ceramics prepared by these methods have a multi-component structure, it is difficult to control the varistor potential gradient and nonlinear coefficient simply by adjusting the amount of a single oxide added. Therefore, it is essential to provide a zinc oxide ceramic with adjustable nonlinear coefficients and its preparation method. Summary of the Invention

[0003] To address the problem that existing ZnO-based varistors cannot achieve adjustable nonlinear coefficients, this invention provides a zinc oxide ceramic with adjustable nonlinear coefficients, its preparation method, and its applications.

[0004] The technical solution of the present invention:

[0005] One objective of this invention is to provide a method for preparing zinc oxide ceramics with adjustable nonlinear coefficients, the method comprising the following steps:

[0006] (1) Zinc oxide and modified raw materials are added to ethanol, mixed evenly by ball milling, dried into mixed powder, and then subjected to high-temperature sintering to obtain pre-sintered powder; the modified raw material is AlN powder;

[0007] (2) The pre-fired powder and binder are mixed, pressed into pre-made blocks, and then sintered at high temperature again to obtain zinc oxide ceramic.

[0008] Further specified, the molar ratio of the modified raw material to zinc oxide in (1) is (0.5-2):100.

[0009] Further specified, (1) the drying temperature is 60-80℃ and the heat preservation time is 4-6h.

[0010] Further restrictions are imposed: (1) the medium-high temperature sintering temperature is 200-800℃, the holding time is 2h, and the heating rate is 10℃ / min.

[0011] Further specifying, in (2), the adhesive is a PVA aqueous solution with a volume fraction of 5 wt% and a PVA molecular weight of 10000.

[0012] Further specified, the mass ratio of pre-calcined powder to PVA is 1:0.5.

[0013] Further, in (2), the pressing temperature is room temperature, the pressure is 10-12 MPa, and the holding time is 10 min.

[0014] Further specified, (2) the high temperature sintering process is as follows: heat up to 1100℃ at a rate of 10℃ / min and hold for 1h, then heat up to 1250-1450℃ and hold for 3h.

[0015] The second objective of this invention is to provide a zinc oxide ceramic obtained by the above preparation method, which has the characteristic of adjustable nonlinear coefficient.

[0016] A third objective of this invention is to provide an application of the aforementioned zinc oxide ceramic, specifically for the preparation of energy storage devices, lightning protection devices, and grounding devices.

[0017] Beneficial effects:

[0018] This invention uses AlN as an additive to dope and modify ZnO. Taking advantage of the significant difference in conductivity between AlN and ZnO, the addition of AlN can construct a Schottky barrier within the ZnO grains, inducing the varistor properties of the ZnO ceramic. Furthermore, AlN and ZnO have the same crystal structure. 3+ Ions can easily enter the ZnO lattice, achieving the purpose of improving nonlinear characteristics through doping. This allows AlN to simultaneously act as a varistor and a doping modifier for ZnO, resulting in doped zinc oxide ceramics that possess both a single-phase hexagonal wurtzite zinc oxide structure and varistor properties. By changing the AlN doping content, the nonlinear coefficient and varistor potential gradient can be controlled, thus broadening the application range of zinc oxide ceramics. Attached Figure Description

[0019] Figure 1 Comparison diagrams of crystal phase analysis of the doped zinc oxide ceramics prepared in Examples 1-6;

[0020] Figure 2 SEM images of the doped zinc oxide ceramic prepared in Example 1, and elemental distribution maps of Zn and Al.

[0021] Figure 3SEM images of the doped zinc oxide ceramics prepared in Examples 2-6, where d represents Example 2, e represents Example 3, f represents Example 4, g represents Example 5, and h represents Example 6;

[0022] Figure 4 Impedance analysis results of the doped zinc oxide ceramics prepared in Examples 1, 4, 5 and 6 are shown; where a is Example 1, b is Example 4, c is Example 5 and d is Example 6. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0027] Example 1:

[0028] The specific steps for preparing zinc oxide ceramics with adjustable nonlinear coefficients in this embodiment are as follows:

[0029] (1) Disperse 19.9496g of zinc oxide and 0.0504g of AlN in 110mL of ethanol solvent (AlN accounts for 0.5mol% of zinc oxide), and mix them evenly by ball milling at 300rad / min for 12h at room temperature. Then keep warm at 80℃ for 6h and dry the mixed powder.

[0030] (2) The dried mixed powder is pre-fired. The pre-fired process is as follows: the temperature is raised from room temperature to 200℃ at a heating rate of 10℃ / min, and held for 2 hours. After the holding period, the powder is cooled to room temperature in the furnace to obtain the pre-fired powder.

[0031] (3) 9.7g of binder was added to 19.5g of pre-fired powder, wherein the binder was a 5 wt% PVA aqueous solution with a molecular weight of 10,000. The mixture was spray-dried and mixed evenly. Then, it was pressed at 10 MPa for 10 min at room temperature to obtain a preform. Finally, the preform was placed in a high-temperature furnace and heated from room temperature to 1100℃, held for 1 h, then heated to 1250℃ and held for 3 h, with a heating rate of 10℃ / min. After the holding period, it was cooled to room temperature with the furnace to obtain zinc oxide ceramic. The surface of the sintered ceramic was coated with silver paste and annealed at 600℃ for 40 min with a heating rate of 10℃ / min to obtain zinc oxide ceramic capacitors.

[0032] The crystal structure of the doped zinc oxide ceramic obtained in this embodiment was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown. Referring to PCPDF card #79-0206, the diffraction peaks of the doped ceramic are the same as the standard diffraction peaks of hexagonal wurtzite zinc oxide. No other diffraction peaks were observed besides the standard peak positions, indicating that the doped ceramic is a single phase, Al. 3+ Ions enter the ZnO lattice and partially substitute Zn sites. Scanning electron microscopy images of the doped ceramics are shown below. Figure 2 As shown in Figure (a), the doped ceramic exhibits a dense grain boundary structure without obvious pores. Further surface scan elemental distribution analysis of Al and Zn was performed, as shown in... Figure 2 As shown in (b) and (c), Zn is uniformly distributed at grains and grain boundaries, while Al is mainly distributed within the grains. This indicates that some AlN grains are embedded within ZnO grains. However, since the AlN crystal structure is the same as ZnO, Al can partially dissolve in the ZnO lattice, so diffraction peaks of other crystalline phases are not visible in the XRD.

[0033] The volt-ampere characteristics of the doped zinc oxide ceramic obtained in this embodiment were tested, and its nonlinearity coefficient was 13.21, with a voltage gradient of 15.98 V / mm. To further analyze the source of the varistor characteristics of the doped ceramic, impedance analysis was performed on the doped ceramic, and the test results were fitted. The results are as follows: Figure 4 As shown in (a), the presence of two regions with a large difference in conductivity in the doped ceramic indicates that the varistor properties of this doped ceramic are caused by the Schottky barrier formed between the ZnO grains and the embedded AlN grains.

[0034] Example 2:

[0035] The difference between this embodiment and embodiment 1 is as follows: In step (3): the precast block is placed in a high-temperature furnace, heated from room temperature to 1100℃, kept at that temperature for 1 hour, then heated to 1450℃, kept at that temperature for 3 hours, and the heating rate is 10℃ / min. The remaining process steps and parameter settings are the same as in embodiment 1.

[0036] The crystal structure of the doped zinc oxide ceramic obtained in this embodiment was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown in the figure, the diffraction peaks of the doped ceramic are the same as the standard diffraction peaks of hexagonal wurtzite zinc oxide. Apart from the standard peaks, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase.

[0037] The scanning electron microscope image of the doped zinc oxide ceramic surface obtained in this embodiment is as follows: Figure 3 As shown in (d), the zinc oxide-doped ceramic forms a dense grain boundary structure, and compared with... Figure 2 As shown in (a), the grain size increases significantly with increasing sintering temperature, but no obvious pores are formed in the ceramic.

[0038] The current-voltage characteristics of the zinc oxide doped ceramic obtained in this embodiment were tested, and its nonlinear coefficient was 23.41, and its voltage gradient was 19.80 V / mm.

[0039] Example 3:

[0040] The difference between this embodiment and embodiment 1 is that the pre-firing process in step (2) is as follows: the temperature is increased from room temperature to 800℃ at a heating rate of 10℃ / min and kept at that temperature for 2 hours. The remaining process steps and parameter settings are the same as in embodiment 1.

[0041] The crystal structure of the doped zinc oxide ceramic obtained in this embodiment was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown in the figure, the diffraction peaks of the doped ceramic are the same as the standard diffraction peaks of hexagonal wurtzite zinc oxide. Apart from the standard peaks, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase.

[0042] The scanning electron microscope image of the doped zinc oxide ceramic surface obtained in this embodiment is as follows: Figure 3 As shown in (e), the doped ceramic has obvious pores, is not dense, has uneven grain size, and obvious grain boundaries, which indicates that the pre-sintering temperature has a significant impact on the grain size.

[0043] The current-voltage characteristics of the doped ceramic were tested, and its nonlinear coefficient was 22, with a voltage gradient of 18.09 V / mm.

[0044] Example 4:

[0045] The difference between this embodiment and embodiment 1 is that in step (1), AlN accounts for 1 mol% of zinc oxide. The remaining process steps and parameter settings are the same as in embodiment 1.

[0046] The crystal structure of the obtained doped zinc oxide ceramic was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the diffraction peaks of the doped zinc oxide ceramic are the same as the standard diffraction peaks of hexagonal wurtzite zinc oxide. Apart from the standard peak positions, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase.

[0047] The scanning electron microscope image of the doped zinc oxide ceramic surface obtained in this embodiment is as follows: Figure 3 As shown in (f), the ceramic forms a dense microstructure without any pores.

[0048] The current-voltage characteristics of the zinc oxide-doped ceramic were tested, and its nonlinear coefficient was 21.08, and the voltage gradient was 18.56 V / mm.

[0049] Impedance analysis was performed on the doped zinc oxide ceramics, and the test results were fitted. The results are as follows: Figure 4 As shown in (b), there are two regions with a significant difference in conductivity in the zinc oxide doped ceramic. The varistor properties of the zinc oxide doped ceramic are caused by the Schottky barrier formed between the ZnO grains and the embedded AlN grains. (Comparison) Figure 4 As shown in (a), the conductivity difference between the two models gradually increases with the increase of AlN content.

[0050] Example 5:

[0051] The difference between this embodiment and embodiment 1 is that in step (1), AlN accounts for 1.5 mol% of zinc oxide, and the remaining process steps and parameter settings are the same as in embodiment 1.

[0052] The crystal structure of the obtained doped zinc oxide ceramic was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the diffraction peaks of the doped zinc oxide ceramic are the same as the standard diffraction peaks of hexagonal wurtzite zinc oxide. Apart from the standard peak positions, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase.

[0053] The scanning electron microscope image of the doped zinc oxide ceramic surface obtained in this embodiment is as follows: Figure 3 As shown in Figure (g), the ceramic forms a dense microstructure without pores, and the grain size gradually decreases with increasing doping content.

[0054] The current-voltage characteristics of the zinc oxide-doped ceramic obtained in this embodiment were tested, and its nonlinear coefficient was 21.28 and its voltage gradient was 20.82 V / mm.

[0055] Impedance analysis was performed on the doped zinc oxide ceramic obtained in this embodiment, and the test results were fitted. The results are as follows: Figure 4 As shown in (c), there are two regions with a significant difference in conductivity in the doped zinc oxide ceramic. The varistor properties of the doped ceramic are caused by the Schottky barrier formed between the ZnO grains and the embedded AlN grains. Furthermore, the conductivity difference between the two models gradually increases with the increase of AlN content.

[0056] Example 6:

[0057] The difference between this embodiment and embodiment 1 is that in step (1), AlN accounts for 2 mol% of zinc oxide, and the remaining process steps and parameter settings are the same as in embodiment 1.

[0058] The crystal structure of the obtained doped zinc oxide ceramic was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the diffraction peaks of the doped zinc oxide ceramic are the same as the standard diffraction peaks of hexagonal wurtzite zinc oxide. Apart from the standard peak positions, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase.

[0059] The scanning electron microscope image of the doped zinc oxide ceramic surface obtained in this embodiment is as follows: Figure 3 As shown in Figure (h), the doped zinc oxide ceramics form a dense microstructure without pores, and the grain size gradually decreases with increasing doping content.

[0060] The current-voltage characteristics of the zinc oxide doped ceramic obtained in this embodiment were tested, and its nonlinear coefficient was 23.28 and the voltage gradient was 19.62 V / mm.

[0061] Impedance analysis was performed on the doped zinc oxide ceramic obtained in this embodiment, and the test results were fitted. The results are as follows: Figure 4 As shown in (d), there are two regions with a significant difference in conductivity in the doped zinc oxide ceramic. The varistor properties of the doped ceramic are caused by the Schottky barrier formed between the ZnO grains and the embedded AlN grains. Furthermore, the conductivity difference between the two models gradually increases with the increase of AlN content.

[0062] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing zinc oxide ceramics with adjustable nonlinear coefficients, characterized in that, include: (1) Zinc oxide and modified raw materials are added to ethanol, mixed evenly by ball milling, dried into mixed powder, and then subjected to high-temperature sintering to obtain pre-sintered powder; the modified raw material is AlN powder; The molar ratio of the modified raw material to zinc oxide in (1) is (0.5-2):100; The high-temperature sintering temperature in (1) is 200-800 ℃, the holding time is 2h, and the heating rate is 10 ℃ / min; (2) The pre-fired powder and binder are mixed, pressed into prefabricated blocks, and then sintered at high temperature again to obtain zinc oxide ceramic; The high-temperature sintering process in (2) is as follows: heat up to 1100℃ at a rate of 10℃ / min and hold for 1 hour, then heat up to 1250-1450℃ and hold for 3 hours.

2. The preparation method according to claim 1, characterized in that, (1) The drying temperature is 60-80 ℃ and the holding time is 4-6 h.

3. The preparation method according to claim 1, characterized in that, (2) The adhesive is a PVA aqueous solution with a volume fraction of 5 vt% and a molecular weight of 10000.

4. The preparation method according to claim 3, characterized in that, The mass ratio of pre-calcined powder to PVA is 1:0.

5.

5. The preparation method according to claim 1, characterized in that, (2) The pressing temperature is room temperature, the pressure is 10-12 MPa, and the holding time is 10 min.

6. A zinc oxide ceramic obtained by the preparation method according to any one of claims 1 to 5.

7. An application of the zinc oxide ceramic according to claim 6, characterized in that, Used in the manufacture of energy storage devices, lightning protection devices, and grounding devices.

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