Low acoustic impedance bt piezoelectric ceramic and preparation method of material thereof

Abstract

This invention relates to the field of piezoelectric ceramics technology, specifically to a method for preparing low acoustic impedance BT piezoelectric ceramics and their materials. The method includes: Step S1, molding a raw material mixture containing BT powder and a sacrificial pore-forming agent to obtain a green body; Step S2, preheating and holding the green body to remove volatiles; Step S3, degreasing the preheated green body under an oxygen-rich atmosphere to form a uniform fine-pore structure within the green body; Step S4, sintering the degreased green body to obtain the low acoustic impedance BT piezoelectric ceramic material. In this application, by burning off the sacrificial pore-forming agent under an oxygen-rich atmosphere, uniform fine pores are formed inside the piezoelectric ceramic, thus solving the problem that traditional pore-forming techniques in the prior art cannot form a uniform and regular fine-pore structure in the ceramic green body.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramics technology, and in particular to a low acoustic impedance BT piezoelectric ceramic and a method for preparing the same material. Background Technology

[0002] Lead-free piezoelectric ceramics possess excellent piezoelectric, dielectric, and chemical stability, and are widely used in ultrasonic sensing, underwater acoustic transducers, and biomedical detection devices. However, dense piezoelectric ceramics generally suffer from excessively high acoustic impedance, resulting in poor impedance matching with water and soft human tissue, severely impacting signal transmission efficiency and detection accuracy.

[0003] To overcome this deficiency, existing technologies generally employ the doping of pore-forming agents to prepare porous piezoelectric ceramics. By constructing a porous structure within the ceramic, the overall density of the material is reduced, thereby lowering the acoustic impedance and improving the signal transmission performance of the device. Currently, in the conventional manufacturing process of porous piezoelectric ceramics, the pore-forming agent degreasing step is completed using ordinary air atmosphere. The pore-forming agent and organic additives in the green body are removed by firing in natural air environment. This process is simple and low-cost, and is currently the mainstream process for the mass production of porous piezoelectric ceramics.

[0004] Existing conventional air atmosphere degreasing processes have limited oxygen content, which cannot guarantee the complete and sufficient burning-off of sacrificial pore-forming agents. This easily leads to residual carbon inside the ceramic body, causing uneven pore size and disordered pore distribution within the ceramic, making it impossible to form a regular and uniform fine pore structure. It also results in limited reduction of acoustic impedance and poor performance consistency, making it difficult to stably achieve low acoustic impedance characteristics and failing to meet the requirements for high-precision and high-stability ultrasonic transducers. Summary of the Invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a method for preparing low acoustic impedance BT piezoelectric ceramics and their materials, so as to solve the problem that the traditional pore-forming technology in the prior art cannot form a uniform and regular fine pore structure in the ceramic body.

[0006] In a first aspect, the present invention discloses a method for preparing a low acoustic impedance BT piezoelectric ceramic material, comprising the following steps: Step S1: The raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to molding treatment to obtain a green body; Step S2: Preheat and heat-keep the billet to remove volatiles from the billet. Step S3: Degreasing the preheated billet under an oxygen-enriched atmosphere to form a uniform fine pore structure in the billet. Step S4: Sinter the degreased green body to obtain a low acoustic impedance BT piezoelectric ceramic material.

[0007] Optionally, in step S1, the raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to molding treatment to obtain a green body. Specifically, the raw material mixture is ground and dispersed by a grinding device, and the raw material mixture after grinding and dispersion is subjected to de-agglomerate treatment to obtain a slurry. An auxiliary system is then added to the slurry for slurry conditioning treatment, and the slurry after slurry conditioning treatment is subjected to molding treatment to obtain a green body.

[0008] Optionally, the grinding equipment is a ball mill, the sacrificial pore-forming agent is nano-carbon black, and the raw material mixture also includes a dispersant and an organic carrier; the auxiliary system includes a 10% PVA solution, oleic acid, and tributyl phosphate.

[0009] Optionally, the grinding and dispersion specifically involves: grinding and dispersing the raw material mixture in a ball mill for 3-5 hours; the agglomerate removal treatment specifically involves: subjecting the raw material mixture to ultrasonic vibration for 20-35 minutes to remove agglomerates, so that the nano-carbon black is uniformly dispersed in the slurry and a slurry is obtained; the molding treatment specifically involves: drying and granulating the slurry to obtain a molding material, and then pressing the molding material to obtain a green body.

[0010] Optionally, in step S2, the preheating and heat preservation of the billet specifically involves: after the billet is placed to room temperature, it is preheated and heat-preserved to remove volatiles from the billet; the conditions for the preheating and heat preservation are: heating rate ≤ 1℃ / min, heating to 250℃-350℃, and heat preservation for 1h-2h.

[0011] Optionally, in step S3, the degreasing treatment conditions are: heating rate of 0.5℃ / min-1℃ / min, heating to 500℃-700℃, holding in an oxygen-rich atmosphere for 4h-5h, and burning off organic matter and sacrificial pore-forming agent in the green body.

[0012] Optionally, in step S4, the sintering conditions are: heating to 1340-1440℃ and holding for 2-4 hours.

[0013] Secondly, the present invention also discloses a low acoustic impedance BT piezoelectric ceramic, comprising a low acoustic impedance BT piezoelectric ceramic material prepared by the preparation method of any one of the above-mentioned low acoustic impedance BT piezoelectric ceramic materials, wherein uniform fine pores are formed in the low acoustic impedance BT piezoelectric ceramic material.

[0014] Optionally, the low acoustic impedance BT piezoelectric ceramic further includes two electrode layers, which are respectively disposed on opposite sides of the low acoustic impedance BT piezoelectric ceramic material. The electrode layers are dense conductive electrode structures formed by high-temperature sintering.

[0015] Optionally, the low acoustic impedance BT piezoelectric ceramic has an internally oriented domain structure with a uniform orientation, which provides stable positive and negative piezoelectric effects.

[0016] Compared with existing technologies, the beneficial effects of the preparation method of low acoustic impedance BT piezoelectric ceramics and their materials provided in this invention are as follows: The preparation method of low acoustic impedance BT piezoelectric ceramic materials sequentially includes four steps: raw material mixture forming treatment, green body preheating treatment, oxygen-enriched atmosphere degreasing treatment, and green body sintering treatment. The forming treatment can prepare BT powder and sacrificial pore-forming agent into a structurally integrated green body, providing a uniform raw material distribution basis for the subsequent construction of pore structures. The preheating treatment can gradually remove volatiles inside the green body, avoiding structural defects in the green body during subsequent high-temperature treatment and ensuring the structural integrity of the green body. The oxygen-enriched atmosphere degreasing treatment can fully burn off the sacrificial pore-forming agent inside the green body, forming a uniformly distributed fine pore structure inside the green body while reducing impurity residues inside the green body. The sintering treatment can solidify the internal structure and fine pore morphology of the green body, improving the structural stability and mechanical properties of the low acoustic impedance BT piezoelectric ceramic material matrix.

[0017] The aforementioned method for preparing low acoustic impedance BT piezoelectric ceramic materials involves multiple coordinated processes. By utilizing sacrificial pore-forming agents to create pores, the overall density of the low acoustic impedance BT piezoelectric ceramic material is adjusted, enabling stable control of its acoustic impedance parameters and achieving low acoustic impedance structural performance. Furthermore, the entire process is logically integrated, and the supporting equipment is highly versatile, ensuring consistent performance of the low acoustic impedance BT piezoelectric ceramic materials produced in batches and making it suitable for large-scale production of conventional piezoelectric ceramics. Attached Figure Description

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic flowchart of the preparation method of low acoustic impedance BT piezoelectric ceramic material provided in the embodiments of the present invention; Figure 2 This is a microscopic schematic diagram of the structure of the low acoustic impedance BT piezoelectric ceramic material provided in an embodiment of the present invention. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] This invention provides a method for preparing a low acoustic impedance BT piezoelectric ceramic material, such as... Figure 1 As shown, the preparation method includes the following steps: Step S1: The raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to molding treatment to obtain a green body; Step S2: Preheat and heat-insulate the billet to remove volatiles from inside the billet; Step S3: Degrease the preheated billet under an oxygen-enriched atmosphere to form a uniform fine pore structure inside the billet. Step S4: Sinter the degreased green body to obtain a low acoustic impedance BT piezoelectric ceramic material.

[0021] In this embodiment, the preparation method of low acoustic impedance BT piezoelectric ceramic material sequentially includes four steps: raw material mixture forming treatment, preheating treatment of the green body, oxygen-enriched atmosphere degreasing treatment, and green body sintering treatment. The forming treatment can prepare a green body with BT powder and sacrificial pore-forming agent into a structurally integrated green body, providing a uniform raw material distribution basis for the subsequent construction of the pore structure. The preheating treatment can gradually remove volatiles inside the green body, avoiding structural defects in the green body during subsequent high-temperature processing and ensuring the structural integrity of the green body. The oxygen-enriched atmosphere degreasing treatment can fully burn off the sacrificial pore-forming agent inside the green body, forming a uniformly distributed fine pore structure inside the green body while reducing residual impurities. The sintering treatment can solidify the internal structure and pore morphology of the green body, improving the structural stability and mechanical properties of the low acoustic impedance BT piezoelectric ceramic material matrix. The entire preparation method of low acoustic impedance BT piezoelectric ceramic material, through the coordination of multiple steps and the use of sacrificial pore-forming agent to create pores, adjusts the overall density of the low acoustic impedance BT piezoelectric ceramic material, stably controls the acoustic impedance parameters of the low acoustic impedance BT piezoelectric ceramic material, and achieves low acoustic impedance structural performance. Meanwhile, the entire process has reasonable steps and the supporting equipment is highly versatile, which can ensure the performance consistency of the low acoustic impedance BT piezoelectric ceramic materials prepared in batches and is suitable for the large-scale production conditions of conventional piezoelectric ceramics.

[0022] In step S1, the raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to a molding process, which enables the sacrificial pore-forming agent to be uniformly distributed inside the green body. The green body obtained after the molding process has good structural integrity, which can provide a stable structural foundation for subsequent debinding and sintering processes. The uniformly distributed sacrificial pore-forming agent inside the green body can provide a distribution prerequisite for the formation of a uniform fine pore structure in subsequent processes.

[0023] Further, in step S1, the raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to molding treatment to obtain a green body. Specifically, the raw material mixture is ground and dispersed by grinding equipment. After grinding and dispersing, the raw material mixture is subjected to de-agglomerate treatment to obtain a slurry. Then, an auxiliary system is added to the slurry for slurry conditioning treatment. The slurry after slurry conditioning treatment is subjected to molding treatment to obtain a green body.

[0024] In this embodiment, the raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to grinding and dispersion treatment, agglomerate removal treatment, auxiliary system slurry preparation treatment and molding treatment in sequence. The various processes cooperate with each other and are connected in sequence to complete the preparation of a ceramic green body with a uniform structure.

[0025] Specifically, grinding and dispersing treatment refines the particle size of the raw material mixture, achieving preliminary uniform mixing of BT powder and sacrificial pore-forming agent. This reduces particle agglomeration, providing a foundation for uniform component distribution in the subsequent slurry system. Agglomerate removal treatment eliminates large agglomerated particles within the slurry, preventing localized enrichment or component deficiencies and ensuring uniform dispersion of BT powder and sacrificial pore-forming agent within the slurry system. This avoids uneven internal component distribution in the green body obtained after subsequent molding. Auxiliary system slurry conditioning treatment adjusts the rheological properties of the slurry, improving its flowability and molding stability. This adapts the slurry to the requirements of subsequent molding processes, enhancing the surface smoothness and structural integrity of the green body obtained after molding. Molding treatment solidifies the uniformly dispersed slurry into a uniformly shaped, integral green body with consistent component distribution, fixing the distribution position of the sacrificial pore-forming agent within the green body.

[0026] The above preparation steps can achieve uniform distribution of the sacrificial pore-forming agent inside the green body, avoid the problem of local dense pores and local non-pores in the subsequent degreasing process, provide a stable green body foundation for the subsequent degreasing process to build a fine pore structure with uniform pore size and regular distribution, and ensure that the final low acoustic impedance BT piezoelectric ceramic material has a consistent pore structure.

[0027] Furthermore, the grinding equipment is a ball mill, the sacrificial pore-forming agent is nano-carbon black, and the raw material mixture also includes a dispersant and an organic carrier; the auxiliary system includes a 10% PVA solution, oleic acid, and tributyl phosphate.

[0028] Specifically, nano-carbon black, acting as a sacrificial pore-forming agent, has a small particle size. These nano-carbon black particles can be uniformly incorporated into the raw material system, facilitating the formation of a small, regularly arranged pore structure within the low acoustic impedance BT piezoelectric ceramic material in subsequent processes. Ball mills can thoroughly grind and disperse the raw material mixture. The stable operation of ball mills reduces the particle size of the raw materials, promoting thorough mixing of BT powder and nano-carbon black.

[0029] On the other hand, dispersants can reduce the surface forces of raw material particles, reduce particle adsorption and agglomeration, and assist in the uniform mixing of various components of the raw materials. Organic carriers can support solid particles, maintain the stable morphology of the slurry, and ensure the overall stability of material transportation and processing. A ball milling time of 3-5 hours can fully disperse the raw material particles and achieve thorough mixing of BT powder and nano-carbon black.

[0030] Specifically, the 10% PVA solution, acting as a binder, can uniformly coat the surface of BT powder and nano-carbon black particles. The 10% PVA solution enhances the interfacial bonding force between solid particles, ensuring a stable particle bond during drying, granulation, and molding processes. Furthermore, the 10% PVA solution improves the overall integrity of the molded material, preventing structural defects such as looseness, powder shedding, and delamination, effectively maintaining the integrity of the molded material's structure.

[0031] Oleic acid, as a surface modifier, can reduce the surface tension of the slurry system. Oleic acid can improve the wetting effect of solid particles in the liquid phase and reduce adsorption and aggregation between particles. Oleic acid can enhance the compatibility of various raw material components in the slurry, promote further uniform dispersion of nano-carbon black and BT powder, and reduce localized enrichment of components in the slurry.

[0032] Tributyl phosphate has dispersing and defoaming properties, inhibiting the formation and residue of fine bubbles within the slurry. It can alleviate secondary agglomeration of ultrafine particles, further improving the uniformity and stability of the slurry system. Tributyl phosphate can reduce bubble defects within the green body, preventing problems such as porosity and uneven structural voids after subsequent degreasing and sintering processes.

[0033] In this embodiment, the synergistic effect of 10% PVA solution, oleic acid, and tributyl phosphate optimizes the slurry's flowability, dispersion uniformity, and molding stability. This slurry preparation system ensures uniform particle size and consistent performance in the molding material, resulting in a more uniform distribution of nano-carbon black within the pressed green body. This provides a stable foundation for the subsequent degreasing process, which forms a fine pore structure with uniform pore size and regular distribution. Ultimately, this ensures that the final low acoustic impedance BT piezoelectric ceramic material possesses uniform and stable acoustic impedance performance.

[0034] It should be noted that the amount of 10% PVA solution added is 0.22 times the mass of BT powder, the amount of oleic acid added is 0.01 times the mass of BT powder, and the amount of tributyl phosphate added is 0.003 times the mass of BT powder. The pressure during compression molding is 16.0 MPa-18.0 MPa.

[0035] In this embodiment, the sacrificial pore-forming agent, in addition to nano-carbon black, can also be one or more of starch powder, polyethylene powder, polymethyl methacrylate microspheres, or lignin powder, used in combination. The organic carrier can be isopropanol or anhydrous ethanol.

[0036] In an optional embodiment of the present invention, the ball mill drum speed is set to 700rpm-750rpm. The raw material mixture is first ball-milled in the ball mill, then a dispersant is added, and then ball milling continues in the ball mill. The overall ball milling time is 3h-5h.

[0037] It should be noted that in this embodiment, the particle size of the nano-carbon black is less than 100 nm. The dispersant can be one or more of ammonium polyacrylate or polyethylene glycol. The dispersant accounts for 1%-2.5% of the total mass of BT powder and nano-carbon black.

[0038] Further, the grinding and dispersion process specifically involves: grinding and dispersing the raw material mixture in a ball mill for 3-5 hours; the agglomerate removal process specifically involves subjecting the raw material mixture to ultrasonic vibration for 20-35 minutes to remove agglomerates, thereby ensuring uniform dispersion of the nano-carbon black in the slurry and obtaining the slurry; the molding process specifically involves drying and granulating the slurry to obtain a molding material, which is then pressed into a green body. Ball milling and dispersion treatment for 3-5 hours can gradually refine the particle size of BT powder and nano carbon black, promote the full contact and mixing of dispersant, organic carrier and various solid raw materials, reduce the agglomeration and accumulation of raw material particles, and provide the basic conditions for the subsequent ultrasonic oscillation treatment to achieve uniform dispersion of each component in the slurry.

[0039] Ultrasonic oscillation treatment can break up agglomerated particles within the slurry, improving the dispersion of its components and reducing localized aggregation of raw materials. Drying and granulation removes excess media from the slurry, regularizing particle morphology and giving the material a physical state suitable for compression molding. Ultrasonic oscillation treatment for 20-35 minutes further breaks down fine agglomerates within the slurry, improving the uniformity of nano-carbon black distribution. After uniform dispersion of the raw material components, the distribution differences of pore-forming components within the green body are reduced, resulting in more uniform pore size and arrangement during subsequent molding.

[0040] Compression molding can compact and shape the molding material, making the overall structure of the resulting blank compact and stabilizing the distribution of nano-carbon black inside the blank, thus providing a qualified blank substrate for subsequent heat treatment processes.

[0041] In step S2, the preheating and heat preservation treatment of the formed blank can gradually remove volatile substances inside the blank, avoid the problem of cracking, bubbling and structural deformation caused by rapid volatilization of volatile substances, stabilize the initial structural state of the blank, and improve the structural performance of the blank to withstand subsequent high-temperature degreasing treatment.

[0042] Further, in step S2, the preheating and heat preservation of the billet are specifically as follows: after the billet is placed to room temperature, it is preheated and heat-preserved; the conditions for preheating and heat preservation are: heating rate ≤1℃ / min, heating to 250℃-350℃, preferably 300℃, and heat preservation for 1h-2h after the billet is heated to fully remove the volatiles inside the billet.

[0043] In this embodiment, the formed blank is placed at room temperature before preheating. At the same time, process parameters with limited heating rate and holding time are used to stably and thoroughly remove various volatiles inside the blank, ensuring the integrity of the blank structure and providing a qualified blank substrate for the subsequent degreasing process.

[0044] Specifically, the billet is first cooled to room temperature before preheating, which can eliminate the forming stress inside the billet after pressing and forming, avoid structural deformation of the billet due to sudden temperature changes, and maintain the regular shape of the billet after forming.

[0045] By employing a low heating rate of no more than 1℃ / min, a uniform temperature rise can be achieved across the entire billet. This low-speed heating method reduces the temperature difference between the inside and outside of the billet, preventing the instantaneous large-scale vaporization of volatiles inside the billet and effectively avoiding structural defects such as blistering, cracking, and delamination, thus maintaining the structural integrity of the billet.

[0046] Heating to 250℃-350℃, preferably 300℃, and holding for 1-2 hours provides sufficient time for the volatilization and decomposition of organic additives such as PVA, oleic acid, and tributyl phosphate, as well as residual liquid media, inside the green body. The holding process gradually and thoroughly removes volatiles from the green body, reducing the accumulation of organic residues and preventing rapid decomposition and gas generation during subsequent degreasing and sintering processes, which could lead to structural damage.

[0047] In step S3, the preheated green body is degreased under an oxygen-rich atmosphere. This provides a sufficient oxygen environment for the oxidative decomposition of the sacrificial pore-forming agent, promoting its complete decomposition and burn-off, and reducing the formation of carbonaceous residues within the green body. In this configuration, the uniform burn-off of the sacrificial pore-forming agent within the green body creates a uniformly distributed, regularly sized fine pore structure. This fine pore structure alters the density of the ceramic matrix, providing the foundation for low acoustic impedance BT piezoelectric ceramic materials.

[0048] In this embodiment, the preheating process can stabilize the internal structure of the green body, solidify the basic morphology of the green body, and remove volatile impurities inside the green body to the greatest extent, ensuring that the nano carbon black can burn off stably and uniformly during the subsequent degreasing process, providing a good structural foundation for the green body to form a uniform and regular fine porous structure.

[0049] Further, in step S3, the degreasing conditions are as follows: the temperature is increased to 500℃-700℃, preferably 550℃, at a heating rate of 0.5℃ / min-1℃ / min. After the green body is heated, it is kept in an oxygen-rich atmosphere for 4h-5h, preferably 4h, to fully burn off the organic matter and sacrificial pore-forming agent inside the green body, thereby completing the degreasing and demolding of the green body.

[0050] After preheating, the green body is heated to 500℃-700℃ at a heating rate of 0.5℃ / min-1℃ / min and held at that temperature for 4 hours under an oxygen-rich atmosphere. This process can complete the oxidation and burn-off of organic matter and nano-carbon black sacrificial pore-forming agent inside the green body in steps, stably complete the degreasing and demolding process of the green body, and prepare a porous green body with qualified structure for subsequent sintering treatment.

[0051] Using a low heating rate of 0.5℃ / min to 1℃ / min ensures that the internal temperature of the billet rises synchronously and uniformly. This heating rate reduces the temperature difference between the inside and outside of the billet, avoids a rapid and violent oxidation reaction between residual organic matter inside the billet and nano-carbon black, prevents rapid gas generation inside the billet from causing defects such as blistering, cracking, and structural detachment, and effectively maintains the structural integrity of the billet during the heating process.

[0052] The degreasing temperature range of 500℃-600℃ can match the oxidation and decomposition temperature of organic additives and nano-carbon black inside the green body. This temperature range can ensure the gradual oxidation and decomposition of various organic impurities, while providing suitable temperature conditions for the complete combustion and burn-off of nano-carbon black. It avoids the problems of residual pore-forming agent due to excessively low temperature and premature sintering and shrinkage of the green body due to excessively high temperature, which can block the pores.

[0053] The oxygen-enriched atmosphere provides a continuous supply of oxygen for the oxidation reaction. This atmosphere ensures the complete and thorough oxidation and burn-off of organic matter and nano-carbon black within the green body, significantly reducing the probability of residual carbon and organic matter, and preventing the formation of irregular defects and pores due to residual impurities. In this embodiment, the oxygen volume fraction in the oxygen-enriched gas is not less than 26%.

[0054] A constant temperature holding treatment for 4-5 hours can prolong the oxidation reaction time. The holding process allows oxygen to fully penetrate into the microporous structure inside the green body, ensuring that organic matter and sacrificial pore-forming agents on the surface and inside of the green body burn off simultaneously. This results in a uniformly distributed, regular-sized fine pore structure inside the green body, achieving a stable degreasing and demolding effect.

[0055] Specifically, in this embodiment, the complete process conditions for degreasing are as follows: first, heat the green body to 30°C and hold it at 30°C for 120 minutes; then continue heating the green body to 70°C and hold it for a long time; after holding, raise the green body to 330°C and 430°C in sequence and hold it in sections; after completing the preheating and holding, raise the temperature to about 550°C at a heating rate of 0.5°C / min-1°C / min and hold it in an oxygen-rich atmosphere with an oxygen volume fraction of not less than 26% for 4 hours; finally, raise the temperature to 700°C and hold it for 60 minutes to complete the overall degreasing process.

[0056] In step S4, the degreased green body is sintered, which promotes ceramic grain growth and interface bonding, improves the structural compactness and mechanical strength of the low acoustic impedance BT piezoelectric ceramic material matrix, solidifies the fine porous structure formed by the degreasing process, and avoids the problems of pore collapse or pore deformation during high temperature treatment. Finally, a low acoustic impedance BT piezoelectric ceramic material with stable structure and controllable parameters is prepared.

[0057] Further, in step S4, the degreased green body is heated to 1340℃-1440℃ for sintering and held at that temperature for 2h-4h to obtain a low acoustic impedance BT piezoelectric ceramic material. The preferred heating temperature for the degreased green body is 1390℃.

[0058] After degreasing, the green body is heated to 1340℃-1440℃ for sintering and held for 2h-4h. This process can achieve stable growth of grains and interfacial bonding of low acoustic impedance BT piezoelectric ceramic materials, solidify the porous structure formed by the degreasing process, and prepare low acoustic impedance BT piezoelectric ceramic materials with stable structure and uniform performance.

[0059] Preferably, a sintering temperature of 1390℃ is suitable for the grain sintering and growth characteristics of BT ceramics. This temperature provides sufficient thermal energy for grain boundary fusion and grain growth of BT powder particles, promotes tight bonding of particles within the green body, improves the structural strength and overall density of the low acoustic impedance BT piezoelectric ceramic material matrix, and ensures that the low acoustic impedance BT piezoelectric ceramic material has a stable mechanical structural foundation. On the other hand, this sintering temperature setting is reasonable, avoiding the problems of insufficient grain growth and loose grain boundary bonding caused by excessively low temperatures, while avoiding abnormal grain growth and pore collapse deformation caused by excessively high temperatures. It can maintain the fine pore structure morphology formed after degreasing treatment and ensure the integrity of the porous structure.

[0060] A constant temperature holding time of 2-4 hours ensures uniform heating of the entire green body. The holding process allows for full and uniform grain growth within the green body, reducing grain size differences in different regions, improving the consistency of the microstructure of the finished low acoustic impedance BT piezoelectric ceramic material, and reducing device performance fluctuations.

[0061] The heat preservation sintering process can completely eliminate trace residual impurities and microstructural defects inside the green body, and can stabilize the crystal structure and piezoelectric properties of low acoustic impedance BT piezoelectric ceramic materials. The above-mentioned setup can fix the pore distribution state inside the low acoustic impedance BT piezoelectric ceramic material, stabilize the overall density of the low acoustic impedance BT piezoelectric ceramic material, and enable the low acoustic impedance BT piezoelectric ceramic material to have stable low acoustic impedance characteristics.

[0062] In this embodiment, the low acoustic impedance BT piezoelectric ceramic material after sintering can be cooled rapidly or in stages to control the grain growth state of the pore walls and the stability of the microstructure.

[0063] Table 1 Comparison of performance parameters between dense BT ceramic and the low acoustic impedance BT piezoelectric ceramic of this invention. Sample type, size, C(pF), tanδ(%), D33(pC / N), Fs(kHz), R1(Ω), Fp(kHz), QmKp Dense BT data φ14×1mm 1503.558.21161228.9711.67241.54417.980.373 Low acoustic impedance (BT) comparison data: φ14×1mm 938.06 11.08 111 146.88 54.47 152.58 300.95 0.306 As shown in Table 1, under the test conditions where the sample size is uniformly Φ14×1mm, compared with the dense BT ceramic sample, the low acoustic impedance BT piezoelectric ceramic material prepared by the process of this invention, due to the introduction of a uniform fine porous structure inside, exhibits the following changes: the sample capacitance C decreases from 1503.55pF to 938.06pF, the dielectric loss tanδ increases from 8.21% to 11.08%, the piezoelectric constant D33 decreases from 161pC / N to 111pC / N, the resonant frequency Fs and anti-resonant frequency Fp decrease simultaneously, the equivalent series resistance R1 increases from 11.67Ω to 54.47Ω, and the mechanical quality factor Qm and electromechanical coupling coefficient Kp show a slight decrease. These parameter changes confirm that the porous structure inside the preform can effectively change the matrix density and microstructure of the low acoustic impedance BT piezoelectric ceramic material, achieving a reduction in acoustic impedance while retaining piezoelectric response capability, thus meeting the impedance matching requirements of low acoustic impedance BT piezoelectric ceramics for underwater acoustic and ultrasonic devices.

[0064] Among them, the low acoustic impedance BT ceramic with a φ14×1mm specification exhibits lower frequency constant and dielectric constant, indicating that its uniform microporous structure can reduce the acoustic impedance-related parameters of the material. Compared with the dense BT ceramic of the same specification, the frequency constant of the low acoustic impedance BT ceramic can be reduced to about 64.15%, and the dielectric constant can be reduced to about 62.39%, which is beneficial to reducing the overall acoustic impedance of the material. The capacitance of the φ14×1mm low acoustic impedance BT ceramic is about 938pF, the resonant frequency is about 146.88kHz, and the anti-resonant frequency is about 154.95kHz.

[0065] The technical solution of this application will be further described below with reference to specific embodiments. Example A method for preparing a low acoustic impedance BT piezoelectric ceramic material comprises the following steps: S1. Measure BT powder, nano carbon black and dispersant according to the ratio, place them in a ball mill container, add organic carrier and ball mill for dispersion; after ball milling, ultrasonic oscillation is performed to remove agglomerates and form a uniform slurry.

[0066] S2, add a molding auxiliary system to the slurry obtained in step S1 to adjust the slurry, then dry and granulate to obtain molding material, and press to obtain a green body.

[0067] S3. After placing the green body obtained in step S2 at room temperature, preheat it to 300℃ at a heating rate of no more than 1℃ / min, keep it at that temperature for 1-2 hours, and then remove the volatiles.

[0068] S4. Continue to heat the preheated green body to 500℃-600℃ at a heating rate of 0.5℃ / min-1℃ / min. Then, place it in an oxygen-rich atmosphere and keep it at that temperature for 4 hours to allow the organic matter and nano-carbon black to burn off completely, complete the degreasing and demolding, and form a uniform fine porous structure inside the green body.

[0069] S5, the degreased and demolded green body is heated to 1390℃ for sintering and held for 2-4 hours to obtain a low acoustic impedance BT ceramic skeleton. After sintering, rapid cooling or segmented cooling is used to control the growth of pore wall grains.

[0070] S6, electrode preparation and sintering are carried out on the sintered ceramic body.

[0071] S7. The sintered ceramic body is polarized according to the conventional BT ceramic process to obtain a low acoustic impedance BT piezoelectric ceramic material.

[0072] S8, the polarized material is aged at natural room temperature for 24 hours.

[0073] This embodiment fully discloses the complete preparation process of low acoustic impedance BT piezoelectric ceramic material. The process uses nano-carbon black as a sacrificial pore-forming agent, and sequentially achieves uniform powder dispersion through ball milling and ultrasonication, slurry preparation and compaction with additives, segmented low-temperature preheating, degreasing and pore-forming in an oxygen-enriched atmosphere, high-temperature sintering and shaping, electrode sintering, polarization, and room temperature aging. The uniform porous structure is constructed inside the ceramic by the high-temperature oxidation and sintering loss of nano-carbon black, and finally, a BT piezoelectric ceramic material with low acoustic impedance is obtained. The aforementioned formula and process parameters are fully implemented, and it is verified that the preparation route can stably prepare the target product.

[0074] This invention also provides a low acoustic impedance BT piezoelectric ceramic, such as... Figure 2 As shown, the low acoustic impedance BT piezoelectric ceramic is prepared by the preparation method of the low acoustic impedance BT piezoelectric ceramic material in the aforementioned embodiment. The low acoustic impedance BT piezoelectric ceramic contains the low acoustic impedance BT piezoelectric ceramic material, and uniform fine pores are formed inside the low acoustic impedance BT piezoelectric ceramic material.

[0075] This low acoustic impedance BT piezoelectric ceramic has the same structure and beneficial effects as the low acoustic impedance BT piezoelectric ceramic material preparation method in the foregoing embodiments. The structure and beneficial effects of the low acoustic impedance BT piezoelectric ceramic material preparation method have been described in detail in the foregoing embodiments and will not be repeated here.

[0076] Furthermore, the low acoustic impedance BT piezoelectric ceramic also includes two electrode layers, which are respectively disposed on opposite sides of the low acoustic impedance BT piezoelectric ceramic material. The electrode layers are dense conductive electrode structures formed by high-temperature sintering.

[0077] Electrode layers are disposed on opposite sides of the low acoustic impedance (HA) BT piezoelectric ceramic material. These electrode layers employ a dense, conductive electrode structure formed by high-temperature sintering. This provides stable conductivity and polarization conditions for the HA BT piezoelectric ceramic without compromising its porous structure and low HA performance. The two electrode layers are positioned on opposite sides of the HA BT piezoelectric ceramic material. This structural arrangement creates a uniform electric field region at both ends of the HA BT piezoelectric ceramic substrate, ensuring uniform polarization throughout the HA BT piezoelectric ceramic and maintaining consistent piezoelectric effects across all regions, thus reducing performance deviations during device operation.

[0078] Specifically, the electrode layer is prepared using a high-temperature sintering process, which allows for a tight interfacial bond between the electrode layer and the low acoustic impedance BT piezoelectric ceramic substrate. This reduces the contact resistance between the electrode layer and the substrate, ensuring the stability of electrical signal transmission. The high-temperature sintered electrode layer has a dense conductive electrode structure, which avoids defects such as pores and breaks in the electrode layer. This ensures the overall conductivity continuity of the electrode layer, improves its conductivity uniformity, and prevents localized conductivity anomalies from affecting the working state of the low acoustic impedance BT piezoelectric ceramic.

[0079] The dense electrode layer structure can prevent external moisture and impurities from penetrating the internal porous structure of the low acoustic impedance BT piezoelectric ceramic material. It can protect the internal fine pore structure and crystal structure of the low acoustic impedance BT piezoelectric ceramic material, reduce the impact of environmental factors on the acoustic and piezoelectric properties of the low acoustic impedance BT piezoelectric ceramic, and improve the working stability and service life of the low acoustic impedance BT piezoelectric ceramic device.

[0080] It should be noted that the specific preparation process of the electrode layer is as follows: double-sided silver electrodes are screen-printed on both sides of the low acoustic impedance BT piezoelectric ceramic material, dried at 120℃ for 15 minutes, and then heated to 810℃ and held for 20 minutes to complete the high-temperature sintering and forming of the electrode layer.

[0081] Furthermore, the low acoustic impedance BT piezoelectric ceramic has an internally oriented domain structure. The uniform orientation of the domain structure enables the low acoustic impedance BT piezoelectric ceramic to have stable positive and negative piezoelectric effects.

[0082] The low acoustic impedance (HAI) BT piezoelectric ceramics exhibit a directionally aligned domain structure with uniform domain orientation, enabling stable piezoelectric response. This directional domain structure regulates the internal polarization state, reducing performance losses caused by disordered domain distribution. The uniformly oriented domain structure ensures consistent charge distribution changes during deformation, guaranteeing stable direct piezoelectric output. Furthermore, the uniformly oriented domain structure allows for controllable deformation when receiving electrical signals, ensuring a consistent inverse piezoelectric effect. This regular and uniform domain structure reduces performance fluctuations during operation, ensuring consistently stable electromechanical conversion performance under operating conditions.

[0083] In this embodiment, the low acoustic impedance BT piezoelectric ceramic needs to be polarized to give it an internally oriented domain structure. The polarization process is as follows: polarization is performed at a polarization field strength of 0.6-0.8 kV / mm and a polarization temperature of 120-150℃. The polarization process is carried out under pressure for 20 minutes, and then cooled to 50℃ under the same pressure to complete the polarization process.

[0084] In this embodiment, the low acoustic impedance BT piezoelectric ceramic after polarization is aged for 24 hours under natural room temperature conditions before its electrical properties, impedance, and microstructure are tested.

[0085] like Figure 2 As shown, this low acoustic impedance BT piezoelectric ceramic sample is composed of irregularly packed ceramic particles. The particles undergo a certain degree of sintering bonding, forming distinct grain boundaries and sintering necks. Pores in the sample are mainly distributed in the interparticle region, with pore shapes mostly being irregular polygons or slits, and pore sizes mostly in the micrometer range. Overall, the sample exhibits a high degree of sintering, a relatively dense structure, and porous characteristics.

[0086] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features; all such modifications and substitutions fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a low acoustic impedance BT piezoelectric ceramic material, characterized in that, The method includes the following steps: Step S1: The raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to molding treatment to obtain a green body; Step S2: Preheat and heat-keep the billet to remove volatiles from the billet. Step S3: Degreasing the preheated billet under an oxygen-enriched atmosphere to form a uniform fine pore structure in the billet. Step S4: Sinter the degreased green body to obtain a low acoustic impedance BT piezoelectric ceramic material.

2. The method for preparing the low acoustic impedance BT piezoelectric ceramic material according to claim 1, characterized in that, In step S1, the raw material mixture containing BT powder and sacrificial pore-forming agent is subjected to molding treatment to obtain a green body. Specifically, the raw material mixture is ground and dispersed by grinding equipment. After grinding and dispersing, the raw material mixture is subjected to de-agglomerate treatment to obtain a slurry. Then, an auxiliary system is added to the slurry for slurry conditioning treatment. The slurry after slurry conditioning treatment is subjected to molding treatment to obtain a green body.

3. The method for preparing low acoustic impedance BT piezoelectric ceramic material according to claim 2, characterized in that, The grinding equipment is a ball mill, the sacrificial pore-forming agent is nano-carbon black, and the raw material mixture also includes a dispersant and an organic carrier; the auxiliary system includes a 10% PVA solution, oleic acid, and tributyl phosphate.

4. The method for preparing the low acoustic impedance BT piezoelectric ceramic material according to claim 3, characterized in that, The grinding and dispersion process specifically involves grinding and dispersing the raw material mixture in a ball mill for 3-5 hours. The agglomerate removal process specifically involves subjecting the raw material mixture to ultrasonic oscillation for 20-35 minutes to remove agglomerates, thereby ensuring uniform dispersion of the nano-carbon black in the slurry and obtaining the slurry. The molding process specifically involves drying and granulating the slurry to obtain a molding material, and then pressing the molding material to obtain a green body.

5. The method for preparing the low acoustic impedance BT piezoelectric ceramic material according to claim 1, characterized in that, In step S2, the preheating and heat preservation of the billet are specifically as follows: after the billet is placed to room temperature, it is preheated and heat-preserved to remove volatiles from the billet; the conditions for preheating and heat preservation are: heating rate ≤ 1℃ / min, heating to 250℃-350℃, and heat preservation for 1h-2h.

6. The method for preparing the low acoustic impedance BT piezoelectric ceramic material according to claim 1, characterized in that, In step S3, the degreasing treatment conditions are as follows: heating rate 0.5℃ / min-1℃ / min, heating to 500℃-700℃, holding at the temperature in an oxygen-rich atmosphere for 4h-5h, and burning off organic matter and sacrificial pore-forming agent in the green body.

7. The method for preparing the low acoustic impedance BT piezoelectric ceramic material according to claim 1, characterized in that, In step S4, the sintering conditions are: heating to 1340-1440℃ and holding for 2-4 hours.

8. A low acoustic impedance BT piezoelectric ceramic, characterized in that, The low acoustic impedance BT piezoelectric ceramic material prepared by the preparation method of the low acoustic impedance BT piezoelectric ceramic material according to any one of claims 1-7, wherein the low acoustic impedance BT piezoelectric ceramic material has uniform fine pores formed inside.

9. The low acoustic impedance BT piezoelectric ceramic according to claim 8, characterized in that, The low acoustic impedance BT piezoelectric ceramic also includes two electrode layers, which are respectively disposed on opposite sides of the low acoustic impedance BT piezoelectric ceramic material. The electrode layers are dense conductive electrode structures formed by high-temperature sintering.

10. The low acoustic impedance BT piezoelectric ceramic according to claim 8, characterized in that, The low acoustic impedance BT piezoelectric ceramic has an internally oriented domain structure with a uniform orientation, which provides stable positive and negative piezoelectric effects.

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