A solid-state reaction preparation method for zinc manganate ceramics and its doping modification method
Zinc manganate ceramics were successfully prepared through a two-step sintering method and doping modification, which solved the problems of difficult synthesis and high dielectric loss of ZnMn2O4 ceramics. This enabled the controllable regulation of the varistor and dielectric properties of zinc manganate ceramics, thus broadening their application range.
Patent Information
- Application Number
- CN202410132831.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-31
- Publication Date
- 2025-11-14
- Estimated Expiration
- 2044-01-31
AI Technical Summary
The synthesis of ZnMn2O4 ceramics is difficult, and high-temperature sintered materials age faster under prolonged overvoltage, resulting in high dielectric loss, making them unsuitable for long-term use as voltage regulators.
Zinc manganate ceramics were prepared by a two-step sintering method. Zinc oxide, manganese oxide and modified materials were mixed by ball milling, and then pressed and sintered with a binder at high temperature to obtain modified zinc manganate ceramics. The varistor and dielectric properties were controlled by using doped ions to form local stress fields and electric fields.
Single-phase zinc manganate ceramics were successfully prepared, reducing dielectric loss, broadening the application range, enabling controllable regulation of the nonlinear conductivity coefficient of zinc manganate ceramics, and improving the aging problem caused by heat generation.
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Abstract
Description
Technical Field
[0001] This invention relates to a solid-state reaction preparation method for zinc manganate ceramics and a doping modification method thereof, belonging to the technical field of zinc manganate ceramic preparation and doping modification. Background Technology
[0002] To protect circuit components from overvoltage, varistor fuses are typically connected in parallel with the protected components. 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. Varistors are usually made of zinc oxide semiconductor ceramic, but zinc oxide ceramic typically has high dielectric loss, leading to a significant increase in device temperature and accelerated aging under prolonged overvoltage. With in-depth research into the current-voltage characteristics of the Zn-Mn-O ternary oxide system, researchers have discovered that ZnMn2O4 exhibits excellent electroresistive switching effects, making it suitable for use as a varistor. Currently, most widely used varistor devices are made of ceramic materials; however, due to the influence of sintering temperature and reaction time on the high-temperature sintering of ceramic materials, research on the solid-state reaction synthesis of ZnMn2O4 ceramics is rarely reported. Therefore, it is essential to provide a solid-state reaction preparation method for zinc manganese oxide ceramics. Summary of the Invention
[0003] To address the difficulties in synthesizing existing ZnMn2O4 ceramics, this invention provides a solid-state reaction preparation method for zinc manganate ceramics and a doping modification method thereof.
[0004] The technical solution of the present invention:
[0005] One objective of this invention is to provide a solid-state reaction preparation method for zinc manganate ceramics, the method comprising the following steps:
[0006] (1) Zinc oxide, manganese oxide and modified materials are used as raw materials for the first step of sintering to obtain pre-sintered powder;
[0007] (2) Using pre-fired powder and binder as raw materials, the modified zinc manganate ceramic is obtained by pressing and molding and then sintering for the second time.
[0008] Further, the operation process of step (1) is as follows: zinc oxide, manganese oxide and modified raw materials are dispersed in ethanol solvent and mixed evenly by ball milling process; then the mixed powder is dried and sintered at high temperature to obtain pre-calcined powder.
[0009] Furthermore, the mass ratio of zinc oxide to manganese oxide in step (1) is 0.6:1.
[0010] Furthermore, the amount of ethanol solvent used in step (1) is 5-5.2 times the total mass of zinc oxide, manganese oxide and modified materials.
[0011] To further specify, the ball milling process conditions in step (1) are: room temperature, rotation speed of 300 rad / min, and time of 12 h.
[0012] Furthermore, the powder drying conditions in step (1) are: temperature of 60-80℃ and time of 4-6h.
[0013] Furthermore, the sintering conditions in step (1) are as follows: the temperature is increased to 800℃ at a rate of 10℃ / min and held for 2 hours.
[0014] Further specified, the modified material in step (1) consists of Al2O3 and Li2O in a molar ratio of 1:1.
[0015] Further specifying, the molar ratio of the modified material to zinc oxide in step (1) is (0-2):100.
[0016] Furthermore, the molar ratio of the modified material to zinc oxide in step (1) is (0.5-2):100.
[0017] Furthermore, the molar ratio of the modified material to zinc oxide in step (1) is 1:100.
[0018] Furthermore, the molar ratio of the modified material to zinc oxide in step (1) is 1.5:100.
[0019] Further specifying, the operation process of step (2) is as follows: after the pre-fired powder and the binder are mixed evenly, they are pressed into pre-made blocks, and then sintered into ceramics at high temperature and annealed to obtain the finished product.
[0020] Further specifying, the adhesive in step (2) is a PVA aqueous solution with a volume fraction of 5 wt%.
[0021] Furthermore, the molecular weight of PVA is specified as 10,000.
[0022] Furthermore, the mass ratio of pre-fired powder to PVA is 1:0.5.
[0023] Furthermore, the mixing process of pre-fired powder and binder in step (2) is as follows: the binder is added to the pre-fired powder and pre-mixed using a mixer at a speed of 40-45 rad / min for 10 min; then the binder and pre-fired powder are fully mixed using a high-speed flying knife mixer at a speed of 12-16 rad / min and a speed of 1400-1450 rad / min for 1-1.5 h; after obtaining a uniformly mixed powder, it is dried at 60°C for 8-10 h.
[0024] Furthermore, the compression molding conditions in step (2) are: room temperature, pressure 12-22 MPa, and time 10-15 min.
[0025] Furthermore, the sintering conditions in step (2) are as follows: heat up to 1300℃ at a rate of 2℃ / min, hold for 4-6 hours, and then cool down to room temperature at a rate of 5℃ / min.
[0026] A second objective of this invention is to provide a zinc manganate ceramic prepared as described above, which exhibits a pressure-sensitive effect.
[0027] Beneficial effects:
[0028] This invention successfully prepared ZnMn2O4 ceramics using a two-step sintering method via solid-state reaction. Addressing the issue of high loss in ZnMn2O4 ceramics, which limits their long-term use as voltage regulators, this invention modifies zinc manganese oxide ceramics through doping. The localized stress and electric fields created by the dopant ions induce controllable changes in the varistor and dielectric properties of the zinc manganese oxide ceramics, enabling effective regulation of the nonlinear conductivity coefficient. Furthermore, the threshold electric field is adjustable, broadening the application range of zinc manganese oxide ceramics. In addition, at a certain doping concentration, the doped ceramics exhibit low dielectric loss, mitigating aging caused by heat generation. Attached Figure Description
[0029] Figure 1 Comparison diagrams of crystal phase analysis of the ceramics prepared in Examples 1-5;
[0030] Figure 2 IV characteristic curves of the ceramics prepared in Examples 1-5;
[0031] Figure 3 The relative permittivity-frequency spectrum of the ceramics prepared in Examples 1-5;
[0032] Figure 4 The dielectric loss tangent-frequency spectrum of the ceramics prepared in Examples 1-5;
[0033] Figure 5 Comparison diagrams of crystal phase analysis of ceramics prepared in Example 1 and Comparative Examples 1-2. Detailed Implementation
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] Example 1:
[0039] (1) Disperse 3.4g of zinc oxide and 5.9g of manganese oxide in 48.4mL of ethanol solvent, and ball mill them at 300rad / min for 12h at room temperature to mix them evenly; then dry them at 80℃ for 6h, and dry the mixed powder. Using a muffle furnace temperature control program, raise the temperature from room temperature to 800℃ at a rate of 10℃ / min, and sinter for 2h to obtain pre-calcined powder.
[0040] (2) 3.8g of binder was added to 7.6g of pre-fired powder and pre-mixed using a mixer at a speed of 40 rad / min for 10 min. Then, the binder and pre-fired powder were thoroughly mixed using a high-speed fly knife mixer at a speed of 12 rad / min and a fly knife speed of 1400 rad / min for 1 h. The resulting powder was dried at 60℃ for 8-10 h. The binder was a 5 wt% PVA aqueous solution with a molecular weight of 10000. The powder was then pressed at 12 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 1300℃ for 6 h at a heating rate of 2℃ / min. After the heating was completed, the powder was cooled to room temperature at a rate of 5℃ / min to obtain zinc manganate ceramic. The surface of the sintered ceramic is coated with silver paste and annealed at 600℃ for 40 min with a heating rate of 10℃ / min to obtain zinc manganate ceramic capacitors.
[0041] The crystal structure of the obtained zinc manganate ceramic was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown. By Figure 1As can be seen from PCPDF card #24-1133, the diffraction peaks of the ceramic are the same as the standard diffraction peaks of tetragonal spinel zinc manganate. Apart from the standard peak position, no other diffraction peaks were observed, indicating that zinc manganate ceramics have been successfully prepared and no other phases have been generated.
[0042] The room temperature voltammetric characteristic curve of the zinc manganate ceramic is as follows: Figure 2 As shown. By Figure 2 It can be seen that the IV curve of the ceramic exhibits nonlinear characteristics, with a nonlinear coefficient of 1.39 and a threshold electric field of 16.3 kV / cm, which is consistent with the conductivity characteristics of varistor ceramics.
[0043] The room temperature dielectric constant-frequency spectrum of the zinc manganate ceramic is as follows: Figure 3 As shown. By Figure 3 It can be seen that in 50-10 7 Within the Hz frequency range, the dielectric constant of this zinc manganate ceramic gradually decreases with increasing frequency, and the dielectric constant at the power frequency is 328.
[0044] The room temperature dielectric loss-frequency of this zinc manganate ceramic is as follows: Figure 4 As shown, by Figure 3 It can be seen that the dielectric loss of ceramics gradually decreases with increasing frequency. At low frequencies, the dielectric loss of ceramics is relatively high, and the dielectric loss factor at power frequency is 2.76.
[0045] Example 2
[0046] (1) 16.943 g zinc oxide, 29.676 g manganese oxide, 0.0314 g Al2O3 and 0.0078 g Li2O were dispersed in 242.6 mL of ethanol solvent and ball-milled at 300 rad / min for 12 h at room temperature to mix evenly; the mixture was then dried at 80 °C for 6 h. The pre-calcined powder was obtained by heating from room temperature to 800 °C at a rate of 10 °C / min using a muffle furnace temperature control program and sintering for 2 h.
[0047] (2) 21g of binder was added to 42g of pre-fired powder and pre-mixed using a mixer at a speed of 45 rad / min for 10 min. Then, the binder and pre-fired powder were thoroughly mixed using a high-speed fly knife mixer at a speed of 16 rad / min and a fly knife speed of 1400 rad / min for 1.5 h. The resulting powder was dried at 60℃ for 8-10 h. The binder was a 5 wt% PVA aqueous solution with a molecular weight of 10000. The powder was then pressed at 12 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 1300℃ for 4 h at a heating rate of 2℃ / min. After the heating was completed, the powder was cooled to room temperature at a rate of 5℃ / min to obtain zinc manganate-doped 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 manganate-doped ceramic capacitors.
[0048] The crystal structure of the obtained zinc manganate-doped ceramic was characterized by X-ray diffraction analysis, and the results are as follows: Figure 1 As shown. By Figure 1 As can be seen from PCPDF card #24-1133, the diffraction peaks of the doped ceramic are the same as the standard diffraction peaks of tetragonal spinel zinc manganate, indicating that the dopant ions have entered the zinc manganate lattice. No other diffraction peaks were observed besides the standard peaks, indicating that the doped ceramic is a single phase.
[0049] The room temperature IV properties of the zinc manganate-doped ceramic are as follows: Figure 2 As shown, by Figure 2 It can be seen that the nonlinear coefficient is 1.37 and the threshold electric field is 20.6 kV / cm.
[0050] The dielectric-frequency spectrum and dielectric loss-frequency spectrum of the doped ceramic at room temperature are as follows: Figure 3 and 4 As shown. By Figure 3 and Figure 4 It can be seen that in 50-10 7 Within the Hz frequency range, the dielectric constant and dielectric loss of doped ceramics change little with increasing frequency. The dielectric constant at power frequency is 39 and the dielectric loss at power frequency is 0.44. Compared with undoped ceramics, zinc manganate doped ceramics show significant improvement in dielectric properties.
[0051] Example 3
[0052] The difference between this embodiment and embodiment 2 is that (1) the amount of Al2O3 and Li2O used is 0.0534g and 0.0157g respectively (Al2O3 and Li2O account for 1 mol% of zinc oxide). The remaining process steps and parameter settings are the same as in embodiment 2.
[0053] The crystal structure of the zinc manganate-doped ceramic obtained in this embodiment 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, apart from the standard peak position of the tetragonal spinel type zinc manganate, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase. The dopant ions can enter the zinc manganate lattice and do not precipitate in the form of other phases.
[0054] The room temperature IV properties of the doped ceramic are as follows Figure 2 As shown, its nonlinear coefficient is 1.46 and its threshold electric field is 13.92 kV / cm.
[0055] The dielectric-frequency spectrum and dielectric loss-frequency spectrum of the doped ceramic at room temperature are as follows: Figure 3 and 4 As shown. By Figure 3 and Figure 4 It can be seen that in 50-10 7 Within the Hz frequency range, the dielectric constant and dielectric loss of doped ceramics change little with increasing frequency. The dielectric constant of the doped ceramics at power frequency is 54, and the dielectric loss at power frequency is 0.65. Compared with undoped ceramics, the dielectric properties of zinc manganate doped ceramics are significantly improved.
[0056] Example 4
[0057] The difference between this embodiment and embodiment 2 is that (1) the amount of Al2O3 and Li2O used is 0.0802g and 0.0236g respectively (Al2O3 and Li2O account for 1.5mol% of zinc oxide). The remaining process steps and parameter settings are the same as in embodiment 2.
[0058] The crystal structure of the obtained doped zinc manganate 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, apart from the standard peak position of tetragonal spinel zinc manganate, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase. At this doping level, the dopant ions can enter the zinc manganate lattice and do not precipitate in the form of other phases.
[0059] The room temperature IV properties of the doped ceramic are as follows Figure 2 As shown, its nonlinear coefficient is 1.54 and its threshold electric field is 7.6 kV / cm.
[0060] The dielectric-frequency spectrum and dielectric loss-frequency spectrum of the doped ceramic at room temperature are as follows: Figure 3 and 4 As shown. By Figure 3 and Figure 4 It can be seen that in 50-10 7Within the Hz frequency range, the dielectric constant and dielectric loss of the doped ceramic gradually decrease with increasing frequency, and are similar to the dielectric spectrum of the undoped ceramic. The dielectric constant of this ceramic at the power frequency is 205 and the dielectric loss is 2.05. At this doping level, the dielectric properties of the doped ceramic are close to those of the undoped ceramic.
[0061] Example 5
[0062] The difference between this embodiment and embodiment 2 is that (1) the amount of Al2O3 and Li2O used is 0.1067g and 0.0315g respectively (Al2O3 and Li2O account for 2mol% of zinc oxide). The remaining process steps and parameter settings are the same as in embodiment 2.
[0063] The crystal structure of the obtained doped zinc manganate 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, apart from the standard peak position of the tetragonal spinel type zinc manganate, no other diffraction peaks were observed, indicating that the doped ceramic is a single phase and the dopant ions can enter the zinc manganate lattice.
[0064] The room temperature IV properties of the doped ceramic are as follows Figure 2 As shown, its nonlinear coefficient is 1.30 and its threshold electric field is 6.38 kV / cm.
[0065] The dielectric-frequency spectrum and dielectric loss-frequency spectrum of the doped ceramic at room temperature are as follows: Figure 3 and 4 As shown. By Figure 3 and Figure 4 It can be seen that in 50-10 7 Within the Hz frequency range, the dielectric constant and dielectric loss of doped ceramics gradually decrease with increasing frequency, similar to the dielectric spectrum of undoped ceramics. The dielectric constant of doped ceramics at power frequency is 357, and the dielectric loss is 2.53. At this doping level, the dielectric properties of doped ceramics are close to those of undoped ceramics.
[0066] Comparative Example 1
[0067] Comparative Example 1 uses a direct sintering method to prepare zinc manganate ceramics. The specific operation process is as follows:
[0068] (1) Disperse 7.1g zinc oxide and 5.9g manganese oxide (the mass ratio of zinc oxide to manganese oxide is 1.2:1) in 67.6mL ethanol solvent, and mix them evenly by ball milling at 300rad / min for 12h at room temperature; and dry the mixed powder at 80℃ for 6h.
[0069] (2) Add 6.2g of binder to the above powder and premix using a mixer at a speed of 40 rad / min for 10 min. Then, use a high-speed fly knife mixer to fully mix the binder and powder at a speed of 12 rad / min and a fly knife speed of 1400 rad / min for 1 h. After obtaining the powder, dry it at 60℃ for 8-10 h. The binder is a 5 wt% PVA aqueous solution with a molecular weight of 10000. Then, press it at room temperature under a pressure of 12 MPa for 10 min to obtain a preform. Place the ceramic preform into a muffle furnace and raise the temperature from room temperature to 1300℃ at a rate of 2℃ / min using the muffle furnace temperature control program. Hold the temperature for 6 h and lower it to room temperature at a rate of 5℃ / min to obtain the ceramic.
[0070] X-ray diffraction analysis was performed on the ceramics prepared in this comparative example. Figure 5 It can be seen that, in addition to the diffraction peaks of zinc manganate, there are also diffraction peaks of the raw materials MnO and ZnO. The prepared ceramic is not a single-phase structure, but a mixed phase of multiple oxides. Also, because some raw materials did not form a solid solution, the diffraction peak positions of the prepared ceramic are significantly shifted compared with the zinc manganate standard card (JCPDS: 24-1133).
[0071] Comparative Example 2
[0072] This comparative example uses a two-step sintering method to prepare doped zinc manganate ceramics. The specific operation process is as follows:
[0073] (1) 16.943 g zinc oxide, 29.676 g manganese oxide, 0.0314 g Al2O3 and 0.0014 g Li2O (molar ratio of aluminum oxide to lithium oxide is 1:0.3) were dispersed in 242.6 mL of ethanol solvent and ball-milled at 300 rad / min for 12 h at room temperature to mix evenly; and then dried at 80 °C for 6 h. The mixed powder was then dried. The temperature was controlled by a muffle furnace and increased from room temperature to 800 °C at a rate of 10 °C / min, and sintered for 2 h to obtain pre-calcined powder.
[0074] (2) 21g of binder was added to 42g of pre-fired powder and pre-mixed using a mixer at a speed of 45 rad / min for 10 min. Then, the binder and pre-fired powder were thoroughly mixed using a high-speed fly knife mixer at a speed of 16 rad / min and a fly knife speed of 1400 rad / min for 1.5 h. The resulting powder was dried at 60℃ for 8-10 h. The binder was a 5 wt% PVA aqueous solution with a molecular weight of 10000. The powder was then pressed at 12 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 1300℃ for 4 h at a heating rate of 2℃ / min. After the heating was completed, the powder was cooled to room temperature at a rate of 5℃ / min to obtain zinc manganate-doped ceramic.
[0075] X-ray diffraction analysis was performed on the doped ceramics prepared in this comparative example. Figure 5 It can be seen that, in addition to the diffraction peaks of zinc manganate, there are also diffraction peaks of the raw materials MnO and ZnO, indicating that the prepared ceramic is a mixed phase of multiple oxides. The molar ratio of the modified raw materials affects the position of the dopant ions in the crystal lattice and the degree of solid solution, resulting in a significant shift in the diffraction peak positions of the prepared doped ceramic compared with the zinc manganate standard card (JCPDS: 24-1133).
[0076] 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 solid-state reaction preparation method for zinc manganate ceramics, characterized in that, include: (1) Using zinc oxide, manganese oxide and modified materials as raw materials, the first step of sintering is carried out to obtain pre-sintered powder; The modified material consists of Al2O3 and Li2O in a molar ratio of 1:1; (2) Using pre-fired powder and binder as raw materials, the modified zinc manganate ceramic is obtained by pressing and molding and then sintering for the second time.
2. The preparation method according to claim 1, characterized in that, The mass ratio of zinc oxide to manganese oxide is 0.6:
1.
3. The preparation method according to claim 1, characterized in that, The first sintering conditions are: heating to 800℃ at a rate of 10℃ / min and holding at that temperature for 2 hours.
4. The preparation method according to claim 1, characterized in that, The adhesive is a 5 vt% aqueous solution of PVA with a molecular weight of 10,000.
5. The preparation method according to claim 4, characterized in that, The mass ratio of pre-calcined powder to PVA is 1:0.
5.
6. The preparation method according to claim 1, characterized in that, The compression molding conditions are: room temperature, pressure 12-22 MPa, and time 10-15 min.
7. The preparation method according to claim 1, characterized in that, The second sintering conditions are as follows: heat to 1300℃ at a rate of 2℃ / min, hold at that temperature for 4-6 hours, and then cool to room temperature at a rate of 5℃ / min.
8. The preparation method according to claim 1, characterized in that, The molar ratio of the modified material to zinc oxide is (0.5-2):
100.
9. A zinc manganate ceramic obtained by the preparation method according to claim 1, characterized in that, This ceramic exhibits a pressure-sensitive effect.