A method for preparing a piezoelectric composite material

Abstract

The present invention provides a method for preparing a piezoelectric composite material, comprising the steps of: 1) mixing zinc carbide powder, aluminate coupling agent and polycrystalline PVDF in a ball mill, and ball milling for 3-6 hours; 2) adding bismuth tungstate powder, continuing ball milling for 10-15 minutes, and then heating to 170-186°C for reaction; 3) after cooling, applying silver paste, 4) placing the piezoelectric composite material coated with the silver paste in a polarizing device for polarization, the polarization direction being the thickness direction, cooling to room temperature, and obtaining a piezoelectric composite material. The present invention provides a method for preparing a piezoelectric composite material, and the prepared piezoelectric composite material has excellent performance in terms of piezoelectric constant and strain constant, and has a low relative density.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic piezoelectric modification, and in particular relates to a method for preparing a piezoelectric composite material. Background Art

[0002] The piezoelectric phenomenon was discovered by the Curie brothers when they were studying quartz more than 100 years ago. So, what is the piezoelectric effect? ​​When you light a gas stove or water heater, a piezoelectric ceramic has quietly served you. The manufacturer hides a piece of piezoelectric ceramic in this type of piezoelectric ignition device. When the user presses the spring of the ignition device, the transmission device applies pressure to the piezoelectric ceramic, causing it to generate a very high voltage, which then leads the electrical energy to the gas outlet for discharge. As a result, the gas is ignited by the electric spark. This function of piezoelectric ceramics is called the piezoelectric effect.

[0003] The principle of the piezoelectric effect is that if pressure is applied to a piezoelectric material, it will generate a potential difference (called the positive piezoelectric effect), and vice versa, if voltage is applied, mechanical stress will be generated (called the inverse piezoelectric effect). If the pressure is a high-frequency vibration, then a high-frequency current will be generated. When a high-frequency electrical signal is applied to a piezoelectric ceramic, a high-frequency acoustic signal (mechanical vibration) will be generated, which is what we usually call an ultrasonic signal. In other words, piezoelectric ceramics have the function of conversion and reverse conversion between mechanical energy and electrical energy, and this corresponding relationship is indeed very interesting.

[0004] Piezoelectric materials can generate electric fields due to mechanical deformation, and can also generate mechanical deformation due to electric fields. This inherent electromechanical coupling effect makes piezoelectric materials widely used in engineering. For example, piezoelectric materials have been used to make smart structures. In addition to self-bearing capacity, such structures also have self-diagnosis, self-adaptation and self-repairing functions, and play an important role in the design of future aircraft.

[0005] Application: The application fields of piezoelectric materials can be roughly divided into two categories: vibration energy and ultrasonic vibration energy-electric energy transducer applications, including electroacoustic transducers, hydroacoustic transducers and ultrasonic transducers, as well as other sensor and driver applications.

[0006] A transducer is a device that converts mechanical vibration into an electrical signal or generates mechanical vibration under the drive of an electric field. Piezoelectric polymer electroacoustic devices utilize the transverse piezoelectric effect of polymers, while the transducer design utilizes the bending vibration of polymer piezoelectric bimorphs or piezoelectric unimorphs under the drive of an external electric field. The above principle can be used to produce electroacoustic devices such as microphones, stereo headphones and high-frequency speakers. The research on piezoelectric polymer electroacoustic devices mainly focuses on utilizing the characteristics of piezoelectric polymers to develop devices with special electroacoustic functions that are difficult to achieve using other current technologies, such as anti-noise telephones, broadband ultrasonic signal transmission systems, etc.

[0007] In terms of ultrasonic sensors, the initial research on piezoelectric polymer hydroacoustic transducers was aimed at military applications, such as large-area sensor arrays and surveillance systems for underwater detection, and then the application areas gradually expanded to geophysical detection, acoustic wave testing equipment, etc. Various prototype hydroacoustic devices developed to meet specific requirements use piezoelectric polymer materials of different types and shapes, such as thin sheets, thin plates, laminates, cylinders and coaxial lines, to give full play to the characteristics of piezoelectric polymers such as high elasticity, low density, easy preparation into components with large and small cross-sections, and acoustic impedance of the same order of magnitude as water. The last characteristic allows the hydrophone made of piezoelectric polymers to be placed in the measured sound field to sense the sound pressure in the sound field without disturbing the measured sound field due to its own existence. The high elasticity of the polymer can reduce the transient oscillation in the hydrophone device, thereby further enhancing the performance of the piezoelectric polymer hydrophone.

[0008] Piezoelectric polymer transducers have been most successfully applied in the field of biomedical sensors, especially in ultrasound imaging. The excellent flexibility and formability of PVDF film make it easy to apply to many sensor products.

[0009] Piezoelectric actuators use the inverse piezoelectric effect to convert electrical energy into mechanical energy or mechanical motion. Polymer actuators are mainly based on polymer bimorphs, including the use of lateral and longitudinal effects. The application research of actuators based on polymer bimorphs includes display device control, micro-displacement generation system, etc. In order to make these creative ideas have practical applications, a lot of research is needed. Electron beam irradiation of P (VDF-TrFE) copolymers enables the material to have the ability to produce large tensile strains, thus creating favorable conditions for the development of new polymer actuators. Driven by the potential prospects of national defense applications, the research on the preparation of all-polymer material underwater acoustic emission devices using irradiation-modified copolymers is being systematically carried out with the strong support of the US military. In addition, using the excellent properties of irradiation-modified copolymers, research and development of their applications in medical ultrasound, vibration reduction and noise reduction, etc., still requires a lot of exploration.

[0010] Sensors are mainly used in the following two aspects:

[0011] 1. Piezoelectric pressure sensor

[0012] Piezoelectric pressure sensors are made using the piezoelectric effect of piezoelectric materials. Since the amount of charge in piezoelectric materials is fixed, special attention should be paid to avoid leakage when connecting. The advantages of piezoelectric pressure sensors are self-generated signals, large output signals, high frequency response, small size, and sturdy structure. Its disadvantages are that it can only be used for kinetic energy measurement. It requires special cables and has a slow self-recovery when subjected to sudden vibration or excessive pressure.

[0013] 2. Piezoelectric accelerometer

[0014] Piezoelectric elements are generally composed of two piezoelectric chips. Electrodes are plated on both surfaces of the piezoelectric chip, and leads are drawn out. A mass block is placed on the piezoelectric chip. The mass block is generally made of relatively large metal tungsten or a high-density alloy. Then a hard spring or bolt or nut is used to preload the mass block, and the entire assembly is installed in a metal shell of the original base. In order to isolate any strain of the specimen from being transmitted to the piezoelectric element and avoid generating false signal output, the base is generally thickened or made of a material with greater rigidity. The weight of the shell and base accounts for almost half of the weight of the sensor.

[0015] During measurement, the sensor base and the specimen are rigidly fixed together. When the sensor is subjected to vibration force, since the rigidity of the base and the mass block is quite large, and the mass of the mass block is relatively small, it can be considered that the inertia of the mass block is very small. Therefore, the mass block undergoes the same movement as the base and is subjected to the inertial force in the opposite direction of the acceleration. In this way, the mass block has a strain force proportional to the acceleration acting on the piezoelectric chip. Since the piezoelectric chip has a piezoelectric effect, alternating charges (voltage) are generated on its two surfaces. When the acceleration frequency is much lower than the natural frequency of the sensor, the sensor outputs a voltage proportional to the force, that is, proportional to the acceleration of the specimen. The output power is drawn from the output end of the sensor and input into the preamplifier. The acceleration of the specimen can be tested with ordinary measuring instruments; if an appropriate integration circuit is added to the amplifier, the vibration velocity or displacement of the specimen can be tested.

[0016] There are three main purposes for installing proximity sensors on robots: first, to obtain necessary information before contacting the object and prepare for the next movement; second, to detect whether there are obstacles in the movement space of the robot's hands and feet. If obstacles are found, certain measures will be taken in time to avoid collision; third, to obtain general information about the surface shape of the object.

[0017] Ultrasonic waves are mechanical waves that can be heard by human ears, with a frequency of more than 20KHZ. The vibration frequency range of the sound that can be heard by human ears is only 20HZ-20000HZ. Ultrasonic waves can become sound waves and propagate in a directional manner because of their short wavelength and small diffraction. The purpose of using ultrasonic sensors in robots is to detect the existence of surrounding objects and measure the distance of objects. It is generally used to detect larger objects in the surrounding environment and cannot measure objects with a distance less than 30mm.

[0018] The ultrasonic sensor consists of four main parts: ultrasonic transmitter, ultrasonic receiver, timing circuit and control circuit. Its working principle is roughly as follows: First, the ultrasonic transmitter emits pulsed ultrasonic waves in the direction of the object to be measured. After the transmitter emits a series of ultrasonic waves, it automatically turns off and stops transmitting. At the same time, the ultrasonic receiver starts to detect the echo signal, and the timing circuit also starts timing. When the ultrasonic wave encounters an object, it is reflected back. When the ultrasonic receiver receives the echo signal, the timing circuit stops timing. At this time, the time recorded by the timing circuit is the propagation time from the start of ultrasonic emission to the receipt of the echo wave signal. Using the propagation time value, the distance between the object to be measured and the ultrasonic sensor can be converted. The conversion formula is very simple, that is, the product of half of the sound wave propagation time and the speed of sound wave propagation in the medium. The entire working process of the ultrasonic sensor is carried out sequentially under the control of the control circuit. In addition to the above uses, piezoelectric materials have other quite extensive applications. Such as frequency detectors, piezoelectric oscillators, transformers, filters, etc.

[0019] The inventors of this case found that among piezoelectric materials, the piezoelectric properties of inorganic piezoelectric materials are significantly better than those of polymer materials. However, inorganic materials have high hardness, high brittleness, and are difficult to process. Summary of the invention

[0020] According to the problems existing in the prior art, the present invention provides a method for preparing a piezoelectric composite material.

[0021] To achieve the above objectives, the specific plan is as follows:

[0022] A preparation method of a piezoelectric composite material comprises the following steps: 1) mixing zinc carbide powder, an aluminate coupling agent and polycrystalline PVDF in a ball mill and ball milling for 3-6 hours; 2) adding bismuth tungstate powder, continuing ball milling for 10-15 minutes, and then heating to 170-186°C for reaction; 3) coating silver paste after cooling; 4) placing the piezoelectric composite material coated with the silver paste in a polarization device for polarization in the thickness direction, and cooling to room temperature to obtain the piezoelectric composite material.

[0023] In the present invention, the temperature in the polarization device is further preferably 120-140° C., and the electric field is 20-40 kV / cm.

[0024] The present invention is further preferred, the weight parts of the zinc carbide powder, aluminate coupling agent, polycrystalline PVDF, bismuth tungstate powder and silver paste are respectively: 30-38 weight parts of zinc carbide powder, 1-5 weight parts of aluminate coupling agent, 45-60 weight parts of polycrystalline PVDF, 5-12 weight parts of bismuth tungstate powder, and 2-10 weight parts of silver paste.

[0025] The present invention is further preferred, the weight parts of the zinc carbide powder, aluminate coupling agent, polycrystalline PVDF, bismuth tungstate powder and silver paste are respectively: 30-38 weight parts of zinc carbide powder, 1-5 weight parts of aluminate coupling agent, 45-55 weight parts of polycrystalline PVDF, 5-12 weight parts of bismuth tungstate powder, and 6-10 weight parts of silver paste.

[0026] In the present invention, the weight ratio of the aluminate coupling agent to the bismuth tungstate powder is 1:2.

[0027] Further preferably, the mixing temperature in the ball mill is 88-96°C.

[0028] The difference between the present invention and the prior art is that the present invention achieves the following technical effects:

[0029] 1. The present invention provides a method for preparing a piezoelectric composite material. The prepared piezoelectric composite material has excellent performance in terms of piezoelectric constant and strain constant, and has a relatively low relative density.

[0030] 2. The piezoelectric composite material of the present invention has good mechanical properties, high flexibility, and is convenient for large-area molding and processing.

[0031] 3. The raw material polycrystalline PVDF in the piezoelectric composite material of the present invention has a β-crystal crystallinity of more than 70% in the processed composite material. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Part I:

[0034] Embodiment 1:

[0035] The following raw materials were weighed: 300 g zinc carbide powder; 20 g aluminate coupling agent; 550 g polycrystalline PVDF; 50 g bismuth tungstate powder; and 80 g silver paste.

[0036] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, an aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball-milled for 3-6 hours; 2) bismuth tungstate powder is added, and the ball milling is continued for 10-15 minutes, and then the mixture is heated to 170-186° C. for reaction; 3) after cooling, silver paste is coated; 4) the piezoelectric composite material coated with the silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140° C., the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the mixture is cooled to room temperature to obtain the piezoelectric composite material of Example 1.

[0037] Embodiment 2:

[0038] The following raw materials were weighed: 320 g zinc carbide powder; 40 g aluminate coupling agent; 460 g polycrystalline PVDF; 80 g bismuth tungstate powder; and 100 g silver paste.

[0039] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added, and ball milling is continued for 10-15 minutes, and then heated to 170-186° C. for reaction; 3) after cooling, silver paste is coated; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140° C., the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the piezoelectric composite material of Example 2 is obtained by cooling to room temperature.

[0040] Embodiment 3:

[0041] The following raw materials were weighed: 340 g zinc carbide powder; 30 g aluminate coupling agent; 470 g polycrystalline PVDF; 100 g bismuth tungstate powder; and 60 g silver paste.

[0042] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added, and ball milling is continued for 10-15 minutes, and then heated to 170-186° C. for reaction; 3) after cooling, silver paste is coated; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140° C., the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the piezoelectric composite material of Example 3 is obtained after cooling to room temperature.

[0043] Embodiment 4:

[0044] The following raw materials were weighed: 360 g zinc carbide powder; 10 g aluminate coupling agent; 500 g polycrystalline PVDF; 60 g bismuth tungstate powder; and 70 g silver paste.

[0045] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added, and ball milling is continued for 10-15 minutes, and then heated to 170-186° C. for reaction; 3) after cooling, silver paste is coated; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140° C., the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the piezoelectric composite material of Example 4 is obtained by cooling to room temperature.

[0046] Embodiment 5:

[0047] The following raw materials were weighed: 370 g zinc carbide powder; 50 g aluminate coupling agent; 450 g polycrystalline PVDF; 70 g bismuth tungstate powder; and 60 g silver paste.

[0048] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added, and ball milling is continued for 10-15 minutes, and then heated to 170-186° C. for reaction; 3) after cooling, silver paste is coated; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140° C., the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the piezoelectric composite material of Example 5 is obtained by cooling to room temperature.

[0049] The piezoelectric composite materials prepared in Examples 1-5 were tested for performance, and the results were as follows:

[0050]

[0051] The relative density of Examples 1-5 is low, the piezoelectric constant is higher than that of β-crystalline PVDF, the strain constant is close to that of polycrystalline PVDF, the tensile strength is high, and the obtained piezoelectric composite material has strong processability.

[0052] Part 2: Compared with Example 1, the raw materials of this part do not use silver paste.

[0053] Embodiment 6:

[0054] The following raw materials were weighed: 300 g zinc carbide powder; 20 g aluminate coupling agent; 630 g polycrystalline PVDF; and 50 g bismuth tungstate powder.

[0055] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, the mixture is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the mixture is cooled to room temperature to obtain the piezoelectric composite material of Example 6.

[0056] Embodiment 7:

[0057] The following raw materials were weighed: 320 g zinc carbide powder; 40 g aluminate coupling agent; 560 g polycrystalline PVDF; and 80 g bismuth tungstate powder.

[0058] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, the mixture is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the mixture is cooled to room temperature to obtain the piezoelectric composite material of Example 7.

[0059] Embodiment 8:

[0060] The following raw materials were weighed: 340 g zinc carbide powder; 30 g aluminate coupling agent; 530 g polycrystalline PVDF; and 100 g bismuth tungstate powder.

[0061] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, the mixture is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the mixture is cooled to room temperature to obtain the piezoelectric composite material of Example 8.

[0062] Embodiment 9:

[0063] The following raw materials were weighed: 360 g zinc carbide powder; 10 g aluminate coupling agent; 570 g polycrystalline PVDF; and 60 g bismuth tungstate powder.

[0064] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, the mixture is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the mixture is cooled to room temperature to obtain the piezoelectric composite material of Example 9.

[0065] Embodiment 10:

[0066] The following raw materials were weighed: 370 g zinc carbide powder; 50 g aluminate coupling agent; 510 g polycrystalline PVDF; and 70 g bismuth tungstate powder.

[0067] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, the mixture is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40 kV / cm, the polarization direction is the thickness direction, and the mixture is cooled to room temperature to obtain the piezoelectric composite material of Example 10.

[0068] The piezoelectric composite materials prepared in Examples 6-10 were tested for performance, and the results were as follows:

[0069]

[0070]

[0071] The relative density, piezoelectric constant and tensile strength of Examples 6-10 did not change significantly compared with Examples 1-5, but the strain constant was significantly reduced.

[0072] Part 3: Compared with Part 1, the difference is that no bismuth tungstate powder is added to the raw materials.

[0073] Embodiment 11:

[0074] The following raw materials were weighed: 300 g zinc carbide powder; 20 g aluminate coupling agent; 600 g polycrystalline PVDF; and 80 g silver paste.

[0075] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) heating to 170-186°C for 6-10 minutes; 3) after cooling, coating with silver paste; 4) placing the piezoelectric composite material coated with silver paste in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, cooling to room temperature, and obtaining the piezoelectric composite material of Example 11.

[0076] Embodiment 12:

[0077] The following raw materials were weighed: 320 g zinc carbide powder; 40 g aluminate coupling agent; 540 g polycrystalline PVDF; and 100 g silver paste.

[0078] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) heating to 170-186°C for 6-10 minutes; 3) after cooling, coating with silver paste; 4) placing the piezoelectric composite material coated with silver paste in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, cooling to room temperature, and obtaining the piezoelectric composite material of Example 12.

[0079] Embodiment 13:

[0080] The following raw materials were weighed: 340 g zinc carbide powder; 30 g aluminate coupling agent; 570 g polycrystalline PVDF; and 60 g silver paste.

[0081] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) heating to 170-186°C for 6-10 minutes; 3) after cooling, coating with silver paste; 4) placing the piezoelectric composite material coated with silver paste in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, cooling to room temperature, and obtaining the piezoelectric composite material of Example 13.

[0082] Embodiment 14:

[0083] The following raw materials were weighed: 360 g zinc carbide powder; 10 g aluminate coupling agent; 560 g polycrystalline PVDF; and 70 g silver paste.

[0084] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) heating to 170-186°C for 6-10 minutes; 3) after cooling, coating with silver paste; 4) placing the piezoelectric composite material coated with silver paste in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, cooling to room temperature, and obtaining the piezoelectric composite material of Example 14.

[0085] Embodiment 15:

[0086] The following raw materials were weighed: 370 g zinc carbide powder; 50 g aluminate coupling agent; 520 g polycrystalline PVDF; and 60 g silver paste.

[0087] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder, aluminate coupling agent and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) heating to 170-186°C for 6-10 minutes; 3) after cooling, coating with silver paste; 4) placing the piezoelectric composite material coated with silver paste in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, cooling to room temperature, and obtaining the piezoelectric composite material of Example 15.

[0088] The piezoelectric composite materials prepared in Examples 11-15 were tested for performance, and the results were as follows:

[0089]

[0090] The piezoelectric constant and strain constant of Examples 11-15 are significantly reduced, especially the strain constant, which changes significantly and the processability is reduced.

[0091] Part 4: Compared with Part 1, this part does not add the raw material aluminate coupling agent.

[0092] Embodiment 16:

[0093] The following raw materials were weighed: 300 g zinc carbide powder; 570 g polycrystalline PVDF; 50 g bismuth tungstate powder; and 80 g silver paste.

[0094] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder and polycrystalline PVDF are mixed in a ball mill and ball-milled for 3-6 hours; 2) bismuth tungstate powder is added and ball-milled for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, silver paste is applied; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, and cooled to room temperature to obtain the piezoelectric composite material of Example 16.

[0095] Embodiment 17:

[0096] The following raw materials were weighed: 320 g zinc carbide powder; 520 g polycrystalline PVDF; 80 g bismuth tungstate powder; and 100 g silver paste.

[0097] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, silver paste is applied; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, and cooled to room temperature to obtain the piezoelectric composite material of Example 17.

[0098] Embodiment 18:

[0099] The following raw materials were weighed: 340 g zinc carbide powder; 500 g polycrystalline PVDF; 100 g bismuth tungstate powder; and 60 g silver paste.

[0100] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder and polycrystalline PVDF are mixed in a ball mill and ball-milled for 3-6 hours; 2) bismuth tungstate powder is added and ball-milled for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, silver paste is applied; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, and cooled to room temperature to obtain the piezoelectric composite material of Example 18.

[0101] Embodiment 19:

[0102] The following raw materials were weighed: 360 g zinc carbide powder; 510 g polycrystalline PVDF; 60 g bismuth tungstate powder; and 70 g silver paste.

[0103] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, silver paste is applied; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, and cooled to room temperature to obtain the piezoelectric composite material of Example 19.

[0104] Embodiment 20:

[0105] The following raw materials were weighed: 370 g zinc carbide powder; 500 g polycrystalline PVDF; 70 g bismuth tungstate powder; and 60 g silver paste.

[0106] The preparation steps of the piezoelectric composite material are as follows: 1) zinc carbide powder and polycrystalline PVDF are mixed in a ball mill and ball milled for 3-6 hours; 2) bismuth tungstate powder is added and ball milling is continued for 10-15 minutes, and then heated to 170-186°C for reaction; 3) after cooling, silver paste is applied; 4) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, and cooled to room temperature to obtain the piezoelectric composite material of Example 20.

[0107] The piezoelectric composite materials prepared in Examples 16-20 were tested for performance, and the results were as follows:

[0108]

[0109] The tensile strength, piezoelectric constant and strain constant of Examples 16-20 are significantly reduced, especially the tensile strength and strain constant, which change significantly and have extremely low processability.

[0110] Part V:

[0111] Example 21: Referring to the raw materials of Example 1 in the first part, the preparation method is as follows: 1) zinc carbide powder, aluminate coupling agent, polycrystalline PVDF and bismuth tungstate powder are mixed in a ball mill and ball-milled for 3-6 hours; heated to 170-186°C for reaction; 2) silver paste is applied; 3) the piezoelectric composite material coated with silver paste is placed in a polarization device for polarization, the temperature in the polarization device is 120-140°C, the electric field is 20-40kv / cm, the polarization direction is the thickness direction, and cooled to room temperature to obtain the piezoelectric composite material of Example 21.

[0112] Example 22: Referring to the raw materials of Example 2 in the first part, the preparation method is as follows: 1) zinc carbide powder, aluminate coupling agent, polycrystalline PVDF and bismuth tungstate powder are mixed in a ball mill and ball milled for 3-6 hours; heated to 170-186°C, reacted, and cooled to room temperature to obtain the piezoelectric composite material of Example 22.

[0113] The piezoelectric composite material prepared in Example 21 was subjected to performance testing, and the results were as follows:

[0114]

[0115] It can be concluded from the above embodiments that the raw materials and preparation method of the present invention play a key role in the performance of the piezoelectric composite material.

[0116] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a piezoelectric composite material, comprising the following steps: 1) mixing zinc carbide powder, an aluminate coupling agent and polycrystalline PVDF in a ball mill and milling for 3-6 hours; 2) adding bismuth tungstate powder, continuing to ball mill for 10-15 minutes, and then heating to 170-186°C for reaction; 3) coating silver paste after cooling; 4) placing the piezoelectric composite material coated with the silver paste in a polarization device for polarization in the thickness direction, and cooling to room temperature to obtain a piezoelectric composite material.

2. The method for preparing a piezoelectric composite material according to claim 1, characterized in that: The temperature in the polarization device is 120-140° C., and the electric field is 20-40 kv / cm.

3. The method for preparing the piezoelectric composite material according to claim 2, characterized in that: The weight proportions of the zinc carbide powder, aluminate coupling agent, polycrystalline PVDF, bismuth tungstate powder and silver paste are respectively: 30-38 weight proportions of zinc carbide powder, 1-5 weight proportions of aluminate coupling agent, 45-60 weight proportions of polycrystalline PVDF, 5-12 weight proportions of bismuth tungstate powder and 2-10 weight proportions of silver paste.

4. The method for preparing a piezoelectric composite material according to claim 1, characterized in that: The weight proportions of the zinc carbide powder, aluminate coupling agent, polycrystalline PVDF, bismuth tungstate powder and silver paste are respectively: 30-38 weight proportions of zinc carbide powder, 1-5 weight proportions of aluminate coupling agent, 45-55 weight proportions of polycrystalline PVDF, 5-12 weight proportions of bismuth tungstate powder and 6-10 weight proportions of silver paste.

5. The method for preparing a piezoelectric composite material according to any one of claims 3 or 4, characterized in that: The weight ratio of the aluminate coupling agent to the bismuth tungstate powder is 1:

2.

6. The method for preparing the piezoelectric composite material according to claim 5, characterized in that: The mixing temperature in the ball mill is 88-96°C.

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