Preparation method and application of glass-coated copper powder and internal electrode paste thereof

Abstract

The application discloses a kind of glass-coated copper powder and preparation method and application of inner electrode paste thereof, belong to electronic functional material and component manufacturing field.First, copper powder is dispersed in solvent I, silane coupling agent is added and ultrasonic treatment is carried out, to obtain copper powder suspension;While tetraethyl orthosilicate, boric acid ester is mixed in solvent II, acetic acid and water are stirred to form sol;Then, in inert atmosphere, copper powder suspension is added dropwise to sol to carry out reaction, separation, washing, drying to obtain gel layer coated copper powder;Finally, gel layer coated copper powder is placed in mixed atmosphere and heat treated, and glass-coated copper powder is obtained after heat treatment.The glass-coated copper powder and organic carrier are mixed to prepare inner electrode paste, which is applied to the field of piezoelectric ceramic actuator preparation.The multilayer piezoelectric ceramic chip prepared has excellent conductivity, good interface bonding, thin and dense electrode layer, small damping to piezoelectric vibration, and high device efficiency.

Description

Technical Field

[0001] This invention relates to the field of electronic functional materials and component manufacturing, specifically to a method for preparing glass-coated copper powder and its internal electrode paste, and its application. Background Technology

[0002] Multilayer piezoelectric actuators (MLAs) are widely used in precision positioning, valves, and ultrasonic motors due to their large displacement, fast response, and high thrust. The core of their manufacturing lies in the alternating lamination and co-firing of piezoelectric ceramic layers and internal electrode layers. However, currently, almost all commercially available internal electrodes use silver-palladium (Ag-Pd) alloys, which suffer from drawbacks such as high cost and the risk of silver migration. Palladium is a major component of the cost of MLAs; however, its price is expensive and highly volatile. Furthermore, under DC or high-temperature and high-humidity environments, Ag… + Electrochemical migration can easily occur, leading to short-circuit failure and reduced reliability. Due to these drawbacks, the industry currently uses pure copper as the internal electrode as a solution.

[0003] However, the oxidation problem of copper (significant oxidation begins at >200℃) is fundamentally contradictory to the oxidizing sintering atmosphere of piezoelectric ceramics (usually air, to control the stoichiometry of the ceramic). Existing technologies attempt to add a large amount of glass binder to copper powder and use a physical mixing method to mechanically mix copper powder with low-melting-point glass powder and various oxide additives. However, this method suffers from uneven distribution of the glass phase and easy agglomeration. In the early stage of sintering, it cannot provide timely and comprehensive anti-oxidation protection for each copper powder particle. Moreover, excessive glass phase can reduce the conductivity of the electrode, leading to increased resistivity and poor density of the electrode layer. Furthermore, too much glass phase can affect the vibration transmission of the piezoelectric layer and reduce actuator performance. According to relevant experiments, the conductivity of electrodes prepared using this method is reduced by 5-10% compared to the theoretical optimal value. In addition, alloying methods are used to prepare copper alloy powders (such as Cu-Ni, Cu-Zn) to improve oxidation resistance. However, this usually sacrifices some conductivity and increases costs. Research data shows that electrodes prepared with Cu-Ni alloy powder have 8-15% lower conductivity compared to pure copper powder. Besides the two methods mentioned above, there is also the complex atmosphere protection method, which involves sintering in a strongly reducing atmosphere or vacuum. This method has extremely high equipment requirements and consumes a lot of energy, making it unsuitable for large-scale production. For example, in one production case, using this method, the energy cost increased by 10-20% compared to conventional methods for producing 1KKPCS of product.

[0004] Based on the above-mentioned shortcomings, it is essential to propose a new method for preparing and applying glass-coated copper powder and its internal electrode slurry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing glass-coated copper powder and its internal electrode slurry, as well as its application. A composite powder with a glass layer uniformly coated on the surface of copper powder is prepared using a liquid-phase chemical method. This glass-coated copper composite powder is used as the sole inorganic functional phase in the slurry and co-fired with a piezoelectric ceramic green body to form a high-performance piezoelectric ceramic chip, without the need for any additional glass powder or other inorganic binders.

[0006] The first aspect of this invention is to provide a method for preparing glass-coated copper powder, comprising the following steps: (1) Disperse copper powder in solvent I, add silane coupling agent and sonicate to obtain copper powder suspension; (2) Mix tetraethyl orthosilicate and borate ester in solvent II, add acetic acid and water, and stir to form a sol; (3) Under an inert atmosphere, copper powder suspension is added dropwise to sol to react. After the reaction is completed, the copper powder is separated, washed and dried to obtain a gel layer coated with copper powder. (4) The copper powder coated with the gel layer is placed in a mixed atmosphere for heat treatment. After the heat treatment is completed, glass-coated copper powder is obtained.

[0007] It should be noted that this invention, by selecting a precursor with affinity for copper surfaces and introducing a trace amount of coupling agent, optimizes the chemical environment of the copper powder surface, creatively enabling selective heterogeneous nucleation and growth of the glass precursor on the copper powder surface. The purpose of adding the silane coupling agent KH-550 in this invention is to utilize the ethoxy group after hydrolysis to co-condense with the glass precursor (such as TEOS hydrolysis products), while the amino terminus can bind to the trace oxide layer on the copper powder surface or through physical adsorption, thereby establishing a molecular bridge between the copper powder and the glass precursor, strongly promoting heterogeneous nucleation and dense coating.

[0008] In some embodiments, the average particle size of the copper powder is 0.5-1 μm; solvent I is selected from at least one of ethanol, isopropanol, and methanol; the mass amount of silane coupling agent is 0.5-2% of the mass of the copper powder, and the silane coupling agent is KH-550.

[0009] In some embodiments, the molar ratio of tetraethyl orthosilicate to borate ester is 4.5-5.5:3.8-4.2, and the borate ester is triethyl borate or trimethyl borate; the mass amount of acetic acid is 1-5% of the mass of tetraethyl orthosilicate; the mass amount of water is 40-55% of the sum of the masses of tetraethyl orthosilicate and borate ester; solvent II is selected from at least one of anhydrous ethanol and isopropanol, and the mass amount of solvent II is 5-8 times the sum of the masses of tetraethyl orthosilicate and borate ester; the mass ratio of sol to copper powder is 1:4-7.

[0010] In some embodiments, in step (1), the ultrasonic treatment time is 25-40 min; in step (2), the stirring is carried out at 35-45℃ for 1.5-2.5 h of stirring and hydrolysis; in step (3), the reaction is carried out at 45-55℃ for 4-8 h of stirring, and the drying is carried out in a vacuum chamber at 75-85℃ for 10-14 h; in step (4), the mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5, and the heat treatment is carried out at a rate of 4-6℃ / min to 530-580℃ and held for 50-70 min.

[0011] In step (3), the reaction time is 4-8 hours. If the time is too short, the coating will be incomplete; if it is too long, the gel particles in the solution may grow independently (homogeneous nucleation) instead of being deposited on the surface of the copper powder (heterogeneous nucleation), resulting in uneven coating and powder agglomeration.

[0012] The second aspect of the present invention is to provide a method for preparing glass-coated copper powder to obtain glass-coated copper powder.

[0013] A third aspect of the present invention is to provide an internal electrode paste, comprising, by mass percentage, the following raw materials: 80-90% glass-coated copper powder and 10-20% organic carrier.

[0014] In some embodiments, the organic carrier is a mixture of ethyl cellulose, terpineol, phosphate ester dispersant, and castor oil derivative leveling agent in a mass ratio of 8-11:86-90:0.8-1.2:0.8-1.2; wherein the phosphate ester dispersant is selected from one of tributyl phosphate, dodecyl phosphate, and oleyl alcohol polyoxyethylene ether phosphate, and the castor oil derivative leveling agent is selected from one of hydrogenated castor oil, castor oil ester, and castor oil polyoxyethylene ether.

[0015] A fourth aspect of the present invention is to provide an application of an internal electrode paste, which is used in the field of piezoelectric ceramic actuator fabrication.

[0016] In some implementations, the following steps are included: S1: Roll the internal electrode slurry to obtain a uniform slurry; S2: A uniform paste is screen-printed onto a piezoelectric ceramic, stacked, statically pressed, and then cut to obtain a green chip. S3: Place the green chip in air to remove the adhesive, heat it to 340-360℃ at a rate of 0.8-1.2℃ / min and hold it for 50-70min, then heat it to 540-560℃ at a rate of 0.3-0.7℃ / min and hold it for 1.8-2.2h. S4: Place the green chip after S3 adhesive removal in a nitrogen atmosphere, heat it to 955-965℃ at a rate of 2.5-3.5℃ / min, hold it at that temperature for 1.8-2.2h, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

[0017] It should be noted that this invention, through sintering kinetics design, achieves co-firing with piezoelectric ceramics under standard or weakly modified atmospheres. During sintering, the coating glass layer is a dynamic binder phase. During the low-temperature protection period, the organic carrier decomposes, and at this time, the coating glass has not yet softened. Its dense structure effectively isolates oxygen, protecting the copper core. During the rheological bonding period, the coating glass reaches its softening point and begins to flow viscously. On the one hand, the flowing glass layer seals all pores on the surface of the copper powder, providing extremely strong anti-oxidation protection; on the other hand, the flowing glass binds adjacent copper particles together and forms a tight physical bond with the upper and lower ceramic green bodies. Finally... During the diffusion absorption and copper recrystallization period, the flowing glass reacts with lead oxides and other materials in the piezoelectric ceramic (usually PZT) at the interface, gradually diffusing and dissolving into the ceramic grain boundaries. Ultimately, an extremely thin transition layer is formed at the electrode / ceramic interface, rather than an independent insulating layer. As the glass layer is absorbed and thinned, the copper particles, which are tightly wrapped and in a reducing microenvironment, are activated on the surface, undergoing surface diffusion and volume diffusion. This leads to the formation of a sintering neck and recrystallization, ultimately forming a continuous, low-resistance metallic conductive network composed of pure copper grains. The glass components absorbed by the ceramic help fill the internal pores of the ceramic, improving the overall density.

[0018] In some embodiments, in S1, the material is rolled to a fineness of <5μm; the piezoelectric ceramic is PZT.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The chemical glass coating method used in this invention achieves uniform mixing and deposition at the molecular / atomic scale. The resulting glass layer is continuous, dense, and has a controllable thickness, providing comprehensive antioxidant protection for each copper powder. Furthermore, the glass layer generated by the in-situ chemical reaction has a strong bond with the copper core, making it less prone to peeling off during subsequent slurry processing and sintering. In addition, the process is highly controllable. By adjusting the precursor formula and process parameters, the composition, softening point, and coefficient of thermal expansion of the coated glass can be precisely controlled to adapt to different downstream application requirements. The liquid phase process equipment is relatively simple and easy to achieve mass production.

[0020] 2. This invention applies an electrode paste containing chemically coated copper powder to the fabrication of piezoelectric ceramic actuators, producing a multilayer piezoelectric ceramic chip. After sintering, the inner electrode layer is dense and tightly bonded to the ceramic without delamination. The resulting multilayer piezoelectric actuator has a piezoelectric constant d. 33 Maximum displacement, fatigue resistance cycles (>10) 9The overall performance of this electrode (cycles) reaches over 98% of that of silver-palladium (70 / 30) electrodes with the same structure, while reducing material costs by approximately 70%. Furthermore, high-temperature and high-humidity bias voltage testing showed no silver migration, eliminating dependence on precious metals such as palladium and silver, significantly reducing material costs. The internal electrode is free from oxidation, exhibiting superior long-term stability compared to silver-palladium electrodes. The electrode is constructed of pure copper, providing excellent conductivity, good interface bonding, and a thin, dense electrode layer with low damping for piezoelectric vibrations, resulting in high device efficiency. In addition, it can be sintered in a weakly reducing or optimized air atmosphere, requiring relatively low modification requirements to existing production lines and facilitating industrialization. Attached Figure Description

[0021] Figure 1 This is an electron microscope image of the glass-coated copper powder prepared according to the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below through embodiments.

[0023] Example 1 A glass-coated copper powder is prepared by the following steps, and the prepared glass-coated copper powder is as follows: Figure 1 As shown: (1) Copper powder with a particle size of 0.8 μm was dispersed in ethanol, and silane coupling agent KH-550 was added and ultrasonically treated for 35 min to obtain a copper powder suspension; wherein, the mass of silane coupling agent was 1.2% of the mass of copper powder; (2) Tetraethyl orthosilicate and triethyl borate in a molar ratio of 5:4 are mixed in anhydrous ethanol, acetic acid and water are added, and the mixture is stirred and hydrolyzed at 40°C for 2 hours to form a sol; wherein the mass of acetic acid is 3% of the mass of tetraethyl orthosilicate, the mass of water is 48% of the sum of the masses of tetraethyl orthosilicate and triethyl borate, and the mass of anhydrous ethanol is 6 times the sum of the masses of tetraethyl orthosilicate and triethyl borate; (3) Under an inert atmosphere, copper powder suspension was added dropwise to the sol and stirred at 50°C for 6 hours. After the reaction was completed, the mixture was centrifuged and washed multiple times with ethanol. Then, it was dried in a vacuum oven at 80°C for 12 hours to obtain a gel layer coated with copper powder. The mass ratio of sol to copper powder was 1:5.5. (4) The copper powder coated with gel layer is placed in a mixed atmosphere and heated to 550°C at a rate of 5°C / min and held for 60 min. After cooling with the furnace, the glass-coated copper powder is obtained; wherein, the mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5.

[0024] An internal electrode slurry comprising the above-mentioned glass-coated copper powder comprises, by mass percentage, the following raw materials: 85% glass-coated copper powder and 15% organic carrier; wherein the organic carrier is composed of ethyl cellulose, terpineol, tributyl phosphate and hydrogenated castor oil in a mass ratio of 10:88:1:1.

[0025] The application of the above-mentioned internal electrode paste in the field of piezoelectric ceramic actuator fabrication includes the following steps: S1: Roll the internal electrode slurry to a fineness of <5μm to obtain a uniform slurry; S2: A uniform paste is screen-printed onto piezoelectric ceramic PZT, stacked, statically pressed, and then cut to obtain a green chip. S3: Place the green chip in the air to remove the adhesive, heat it to 350°C at a rate of 1°C / min and hold it for 60 min, then heat it to 550°C at a rate of 0.5°C / min and hold it for 2 h. S4: Place the green chip with the adhesive removed in S3 under a nitrogen atmosphere, heat it to 960℃ at 3℃ / min, hold it for 2 hours, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

[0026] Example 2 A glass-coated copper powder is prepared by the following steps: (1) Copper powder with a particle size of 1 μm was dispersed in isopropanol, and silane coupling agent KH-550 was added and ultrasonically treated for 40 min to obtain a copper powder suspension; wherein, the mass of silane coupling agent was 2% of the mass of copper powder; (2) Tetraethyl orthosilicate and trimethyl borate in a molar ratio of 5.5:4.2 are mixed in isopropanol, acetic acid and water are added, and the mixture is stirred and hydrolyzed at 45°C for 1.5 h to form a sol; wherein the mass of acetic acid is 5% of the mass of tetraethyl orthosilicate, the mass of water is 55% of the sum of the masses of tetraethyl orthosilicate and trimethyl borate, and the mass of isopropanol is 8 times the sum of the masses of tetraethyl orthosilicate and trimethyl borate; (3) Under an inert atmosphere, copper powder suspension was added dropwise to the sol and stirred at 55°C for 4 hours. After the reaction was completed, the mixture was centrifuged and washed multiple times with ethanol. Then, it was dried in a vacuum oven at 85°C for 14 hours to obtain a gel layer coated with copper powder. The mass ratio of sol to copper powder was 1:7. (4) The copper powder coated with gel layer is placed in a mixed atmosphere and heated to 580°C at a rate of 6°C / min and held for 50 min. After cooling with the furnace, the glass-coated copper powder is obtained; wherein, the mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5.

[0027] An internal electrode slurry comprising the above-mentioned glass-coated copper powder comprises, by mass percentage, the following raw materials: 90% glass-coated copper powder and 20% organic carrier; wherein the organic carrier is composed of ethyl cellulose, terpineol, dodecyl phosphate and ricinoleate in a mass ratio of 11:90:1.2:0.8.

[0028] The application of the above-mentioned internal electrode paste in the field of piezoelectric ceramic actuator fabrication includes the following steps: S1: Roll the internal electrode slurry to a fineness of <5μm to obtain a uniform slurry; S2: A uniform paste is screen-printed onto piezoelectric ceramic PZT, stacked, statically pressed, and then cut to obtain a green chip. S3: Place the green chip in the air to remove the adhesive, heat it to 360°C at a rate of 1.2°C / min and hold it for 50 min, then heat it to 560°C at a rate of 0.7°C / min and hold it for 1.8 h. S4: Place the green chip after S3 adhesive removal in a nitrogen atmosphere, heat it to 965℃ at 3.5℃ / min, hold it at that temperature for 1.8h, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

[0029] Example 3 A glass-coated copper powder is prepared by the following steps: (1) Copper powder with a particle size of 0.5 μm was dispersed in methanol, and silane coupling agent KH-550 was added and ultrasonically treated for 25 min to obtain a copper powder suspension; wherein, the mass amount of silane coupling agent was 0.5% of the mass of copper powder; (2) Tetraethyl orthosilicate and triethyl borate in a molar ratio of 4.5:3.8 are mixed in anhydrous ethanol, acetic acid and water are added, and the mixture is stirred and hydrolyzed at 35°C for 2.5 h to form a sol; wherein the mass of acetic acid is 1% of the mass of tetraethyl orthosilicate, the mass of water is 40% of the sum of the masses of tetraethyl orthosilicate and triethyl borate, and the mass of anhydrous ethanol is 5 times the sum of the masses of tetraethyl orthosilicate and triethyl borate; (3) Under an inert atmosphere, copper powder suspension was added dropwise to the sol and stirred at 45°C for 8 hours. After the reaction was completed, the mixture was centrifuged and washed multiple times with ethanol. Then, it was dried in a vacuum oven at 75°C for 14 hours to obtain a gel layer coated with copper powder. The mass ratio of sol to copper powder was 1:4. (4) The copper powder coated with gel layer is placed in a mixed atmosphere and heated to 530°C at a rate of 4°C / min and held for 70 min. After cooling with the furnace, the glass-coated copper powder is obtained. The mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5.

[0030] An internal electrode slurry comprising the above-mentioned glass-coated copper powder comprises, by mass percentage, the following raw materials: 80% glass-coated copper powder and 20% organic carrier; wherein the organic carrier is composed of ethyl cellulose, terpineol, oleyl alcohol polyoxyethylene ether phosphate and castor oil polyoxyethylene ether in a mass ratio of 8:86:0.8:0.8.

[0031] The application of the above-mentioned internal electrode paste in the field of piezoelectric ceramic actuator fabrication includes the following steps: S1: Roll the internal electrode slurry to a fineness of <5μm to obtain a uniform slurry; S2: A uniform paste is screen-printed onto piezoelectric ceramic PZT, stacked, statically pressed, and then cut to obtain a green chip. S3: Place the green chip in the air to remove the adhesive, heat it to 340℃ at a rate of 0.8℃ / min and hold it for 70min, then heat it to 540℃ at a rate of 0.3℃ / min and hold it for 2.2h. S4: Place the green chip after S3 adhesive removal in a nitrogen atmosphere, heat it to 955℃ at 2.5℃ / min, hold it at that temperature for 2.2h, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

[0032] Example 4 A glass-coated copper powder is prepared by the following steps: (1) Copper powder with a particle size of 0.6 μm was dispersed in ethanol, and silane coupling agent KH-550 was added and ultrasonically treated for 30 min to obtain a copper powder suspension; wherein, the mass of silane coupling agent was 0.8% of the mass of copper powder; (2) Tetraethyl orthosilicate and triethyl borate in a molar ratio of 4:4.2 are mixed in isopropanol, acetic acid and water are added, and the mixture is stirred and hydrolyzed at 35°C for 1.5 h to form a sol; wherein the mass of acetic acid is 2% of the mass of tetraethyl orthosilicate, the mass of water is 45% of the sum of the masses of tetraethyl orthosilicate and trimethyl borate, and the mass of isopropanol is 6 times the sum of the masses of tetraethyl orthosilicate and trimethyl borate; (3) Under an inert atmosphere, copper powder suspension was added dropwise to the sol and stirred at 55°C for 8 hours. After the reaction was completed, the mixture was centrifuged and washed multiple times with ethanol. Then, it was dried in a vacuum oven at 85°C for 11 hours to obtain a gel layer coated with copper powder. The mass ratio of sol to copper powder was 1:5. (4) The copper powder coated with gel layer is placed in a mixed atmosphere and heated to 540°C at a rate of 4°C / min and held for 55 min. After cooling with the furnace, the glass-coated copper powder is obtained. The mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5.

[0033] An internal electrode slurry comprising the above-mentioned glass-coated copper powder comprises, by mass percentage, the following raw materials: 82% glass-coated copper powder and 18% organic carrier; wherein the organic carrier is composed of ethyl cellulose, terpineol, tributyl phosphate and hydrogenated castor oil in a mass ratio of 9:87:0.9:1.1.

[0034] The application of the above-mentioned internal electrode paste in the field of piezoelectric ceramic actuator fabrication includes the following steps: S1: Roll the internal electrode slurry to a fineness of <5μm to obtain a uniform slurry; S2: A uniform paste is screen-printed onto piezoelectric ceramic PZT, stacked, statically pressed, and then cut to obtain a green chip. S3: Place the green chip in the air to remove the adhesive, heat it to 355℃ at a rate of 0.9℃ / min and hold it at that temperature for 55min, then heat it to 545℃ at a rate of 0.4℃ / min and hold it at that temperature for 2h. S4: Place the green chip with the adhesive removed in S3 under a nitrogen atmosphere, heat it to 960℃ at 3℃ / min, hold it at that temperature for 2.2h, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

[0035] Example 5 A glass-coated copper powder is prepared by the following steps: (1) Copper powder with a particle size of 0.9 μm was dispersed in isopropanol, and silane coupling agent KH-550 was added and ultrasonically treated for 35 min to obtain a copper powder suspension; wherein, the mass of silane coupling agent was 1.8% of the mass of copper powder; (2) Tetraethyl orthosilicate and triethyl borate in a molar ratio of 5:4 are mixed in isopropanol, acetic acid and water are added, and the mixture is stirred and hydrolyzed at 45°C for 2.5 h to form a sol; wherein the mass of acetic acid is 5% of the mass of tetraethyl orthosilicate, the mass of water is 55% of the sum of the masses of tetraethyl orthosilicate and triethyl borate, and the mass of isopropanol is 7 times the sum of the masses of tetraethyl orthosilicate and triethyl borate; (3) Under an inert atmosphere, copper powder suspension was added dropwise to the sol and stirred at 50°C for 7 hours. After the reaction was completed, the mixture was centrifuged and washed multiple times with ethanol. Then, it was dried in a vacuum oven at 85°C for 13 hours to obtain a gel layer coated with copper powder. The mass ratio of sol to copper powder was 1:6. (4) The copper powder coated with gel layer is placed in a mixed atmosphere and heated to 570°C at a rate of 5°C / min and held for 65 min. After cooling with the furnace, the glass-coated copper powder is obtained. The mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5.

[0036] An internal electrode slurry comprising the above-mentioned glass-coated copper powder comprises, by mass percentage, the following raw materials: 88% glass-coated copper powder and 12% organic carrier; wherein the organic carrier is composed of ethyl cellulose, terpineol, tributyl phosphate and hydrogenated castor oil in a mass ratio of 11:88:1.1:0.9.

[0037] The application of the above-mentioned internal electrode paste in the field of piezoelectric ceramic actuator fabrication includes the following steps: S1: Roll the internal electrode slurry to a fineness of <5μm to obtain a uniform slurry; S2: A uniform paste is screen-printed onto piezoelectric ceramic PZT, stacked, statically pressed, and then cut to obtain a green chip. S3: Place the green chip in the air to remove the adhesive, heat it to 355℃ at a rate of 1.2℃ / min and hold it for 65min, then heat it to 555℃ at a rate of 0.6℃ / min and hold it for 2h. S4: Place the green chip with the adhesive removed in S3 under a nitrogen atmosphere, heat it to 960℃ at 3℃ / min, hold it at that temperature for 2.2h, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

[0038] Comparative Example 1 The process is basically the same as in Example 1, except that: instead of using a chemical method to coat the copper powder, the same mass of copper powder as in Example 1 is physically mixed with low-melting-point glass powder to form a slurry.

[0039] Comparative Example 2 It is basically the same as Example 1, except that the glass-coated copper powder in Example 1 is replaced with the same ordinary copper powder.

[0040] Comparative Example 3 The process is basically the same as in Example 1, except that the internal electrode paste in Example 1 is replaced with a silver-palladium (Ag / Pd=70 / 30) alloy paste to prepare a multilayer piezoelectric ceramic chip.

[0041] The performance of the multilayer piezoelectric ceramic chips prepared in Examples 1-5 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1.

[0042] Internal electrode sheet resistance Rs: The terminal electrode is coated on the exposed internal electrode end on the side of the chip. The resistance is measured using a four-probe tester and converted into sheet resistance (mΩ / □) according to the electrode layer geometry to characterize its conductivity (unit: mΩ / □). piezoelectric constant d 33 : Using quasi-static d 33 The measuring instrument measures the piezoelectric constant (unit: pC / N) of the chip under a low electric field (e.g., 1 kV / cm). Maximum displacement: The chip is placed under the electric field driven by a high-voltage amplifier (usually close to the maximum operating electric field), and the maximum displacement of its free end is measured using a laser displacement sensor (unit: μm). Fatigue resistance characteristics: The chip is continuously driven under an alternating electric field (such as a square wave, frequency 100Hz, field strength 80% of the maximum working electric field), and the number of cycles it takes for its displacement amplitude to decay to 90% of the initial value is recorded.

[0043] Table 1

[0044] As can be seen from Table 1, Examples 1-5 of this invention are all based on the solution of this invention, and their performance is excellent and similar. Combined with the comparative examples, it can be seen that the physical mixing of glass powder in Comparative Example 1 leads to uneven distribution of the glass phase. As an insulator, the glass powder, randomly distributed during physical mixing, easily forms insulating barriers between conductive copper particles, blocking the conductive path and significantly increasing the resistivity. The agglomerated glass phase still exists as isolated islands in the electrode after sintering, which dampens piezoelectric vibrations (leading to d...). 33 On the one hand, it reduces displacement, and on the other hand, it becomes a mechanical weakness, easily inducing microcracks under fatigue and thermal stress. Comparative Example 2 uses ordinary copper powder, which is severely oxidized during the debinding stage at 300-600℃, generating insulating copper oxide, leading to electrode failure. Comparative Example 3 uses Ag-Pd alloy, and the Ag-Pd electrode is comparable to the embodiments of the present invention in terms of room temperature electrical, electromechanical performance and basic fatigue characteristics. This shows that the present invention, through innovative design of material structure, enables the preparation of multilayer piezoelectric ceramic chips to achieve more than 98% of the comprehensive performance of silver palladium (70 / 30) electrode products with the same structure, while reducing material costs by about 70%.

[0045] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing glass-coated copper powder, characterized in that, Includes the following steps: (1) Disperse copper powder in solvent I, add silane coupling agent and sonicate to obtain copper powder suspension; (2) Mix tetraethyl orthosilicate and borate ester in solvent II, add acetic acid and water, and stir to form a sol; (3) Under an inert atmosphere, the copper powder suspension is added dropwise to the sol to react. After the reaction is completed, the copper powder is separated, washed, and dried to obtain a gel layer coated with copper powder. (4) The copper powder coated with the gel layer is placed in a mixed atmosphere for heat treatment. The glass-coated copper powder is obtained after the heat treatment is completed.

2. The method for preparing glass-coated copper powder according to claim 1, characterized in that, The copper powder has an average particle size of 0.5-1 μm; the solvent I is selected from at least one of ethanol, isopropanol, and methanol; the mass amount of the silane coupling agent is 0.5-2% of the mass of the copper powder, and the silane coupling agent is KH-550.

3. The method for preparing glass-coated copper powder according to claim 1, characterized in that, The molar ratio of the tetraethyl orthosilicate to the borate ester is 4.5-5.5:3.8-4.2, and the borate ester is triethyl borate or trimethyl borate; the mass amount of the acetic acid is 1-5% of the mass of the tetraethyl orthosilicate; the mass amount of the water is 40-55% of the sum of the masses of the tetraethyl orthosilicate and the borate ester. Solvent II is selected from at least one of anhydrous ethanol and isopropanol, and the mass of solvent II is 5-8 times the sum of the mass of tetraethyl orthosilicate and borate ester; the mass ratio of the sol to the copper powder is 1:4-7.

4. The method for preparing glass-coated copper powder according to claim 1, characterized in that, In step (1), the ultrasonic treatment time is 25-40 min; in step (2), the stirring is carried out at 35-45℃ for 1.5-2.5 h; in step (3), the reaction is carried out at 45-55℃ for 4-8 h, and the drying is carried out in a vacuum chamber at 75-85℃ for 10-14 h; in step (4), the mixed atmosphere is composed of nitrogen and argon in a volume ratio of 95:5, and the heat treatment is carried out at a rate of 4-6℃ / min to 530-580℃ and held for 50-70 min.

5. Glass-coated copper powder prepared by the method of any one of claims 1-4.

6. An internal electrode paste, characterized in that, The product comprises, by weight percentage, the following raw materials: 80-90% of the glass-coated copper powder as described in claim 5 and 10-20% of the organic carrier.

7. The internal electrode paste according to claim 6, characterized in that, The organic carrier is composed of ethyl cellulose, terpineol, phosphate ester dispersant, and castor oil derivative leveling agent in a mass ratio of 8-11:86-90:0.8-1.2:0.8-1.2; wherein the phosphate ester dispersant is selected from one of tributyl phosphate, dodecyl phosphate, and oleyl alcohol polyoxyethylene ether phosphate, and the castor oil derivative leveling agent is selected from one of hydrogenated castor oil, castor oil ester, and castor oil polyoxyethylene ether.

8. An application of the internal electrode paste according to claim 7, characterized in that, The internal electrode slurry is used in the field of piezoelectric ceramic actuator fabrication.

9. The application of the internal electrode paste according to claim 8, characterized in that, Includes the following steps: S1: The internal electrode slurry is rolled to obtain a uniform slurry; S2: The uniform paste is screen-printed onto the piezoelectric ceramic, stacked, statically pressed, and then cut to obtain a green chip; S3: Place the green chip in air to remove the adhesive, heat it to 340-360℃ at a rate of 0.8-1.2℃ / min and hold it for 50-70min, then heat it to 540-560℃ at a rate of 0.3-0.7℃ / min and hold it for 1.8-2.2h. S4: Place the green chip after S3 adhesive removal in a nitrogen atmosphere, heat it to 955-965℃ at a rate of 2.5-3.5℃ / min, hold it at that temperature for 1.8-2.2h, and then cool it down to obtain a multilayer piezoelectric ceramic chip.

10. The application of the internal electrode paste according to claim 9, characterized in that, In S1, the material is rolled to a fineness of <5μm; the piezoelectric ceramic is PZT.

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