Views: 0 Author: Site Editor Publish Time: 2023-02-10 Origin: Site
Piezoelectric ceramics are artificial polycrystalline piezoelectric materials. The crystal grains inside the material have many spontaneously polarized electric domains, which have a certain polarization direction, so that there is an electric field. When there is no external electric field, the electrical domains are randomly distributed in the crystal, their respective polarization effects are canceled out, and the internal polarization of the piezoelectric ceramic is zero. Therefore, the original piezoelectric ceramics are neutral and do not have piezoelectric properties.
When an external electric field is applied to the ceramic, the polarization direction of the electric domains is rotated and tends to be arranged according to the direction of the external electric field, so that the material is polarized. The stronger the external electric field, the more electric domains are more precisely turned to the direction of the external electric field. Let the intensity of the external electric field be large enough to saturate the polarization of the material, that is, when the polarization direction of the electric domain is neatly consistent with the direction of the external electric field, when the external electric field is removed, the polarization direction of the electric domain basically changes, that is, the remaining pole When the strength is very high, the material has piezoelectric properties.
Common ultrasonic piezoelectric ceramics:
(1) Barium titanate (BaTiO3) piezoelectric ceramics
It has high piezoelectric coefficient and dielectric constant, and its mechanical strength is not as good as quartz.
(2) Lead zirconate titanate Pb(Zr Ti)O3 series piezoelectric ceramics (PZT)
The piezoelectric coefficient is high, and the changes of various electromechanical parameters with temperature, time and other external conditions are small. Adding one or two trace elements to the base of lead zirconate titanate can obtain PZT materials with different properties.
(3) Pb(MgNb)O3-PbTiO3-PbZrO3 Piezoelectric Ceramics (PMN)
With a high piezoelectric coefficient, it can continue to work under pressure up to 700kg/cm2, and can be used as a force sensor at high temperature.
Piezoelectric material:
Piezoelectric semiconductor
Including zinc sulfide, cadmium sulfide, zinc oxide, cadmium sulfide
It has both piezoelectric and semiconductor properties
Organic polymer piezoelectric materials:
One is high molecular polymer
Advantages of polyvinylidene fluoride (PVF2), polyvinyl chloride (PVC), and polyvinyl fluoride: soft texture, high tensile strength, and impact resistance. The other type is the polymer compound doped with barium titanate (BaTiO3)
1. Ingredients: Carry out pre-processing of materials, remove impurities and moisture, and then weigh various raw materials piezoceramics disc according to the formula ratio. Note that a small amount of additives should be placed in the middle of the large ingredients.
2. Mixing and grinding: the purpose is to mix and grind various raw materials to prepare conditions for the solid-phase reaction of pre-calcination. Generally, dry grinding or wet grinding is adopted. Dry milling can be used for small batches, and stirring ball milling or jet milling can be used for large batches, with high efficiency.
3. Pre-firing: The purpose is to carry out solid-state reaction of various raw materials at high temperature to synthesize piezoelectric ceramics. This process is very important. It will directly affect the sintering conditions and the performance of the final product.
4. Secondary fine grinding: The purpose is to finely vibrate, mix and grind the pre-fired piezoelectric ceramic powder, so as to lay a solid foundation for the uniform performance of the porcelain.
5. Granulation: The purpose is to make the powder form high-density granules with good fluidity. The method can be carried out manually but the efficiency is low. The current efficient method is to use spray granulation. This process involves the addition of adhesives.
6. Forming: The purpose is to press the granulated material into a blank of the required prefabricated size.
7. Plastic discharge: the purpose is to remove the binder added during granulation from the blank.
8. Sintering into porcelain: The blank is sealed and sintered into porcelain at high temperature. This link is very important.
9. Shape processing: Grinding the burnt product to the required finished product size.
10. Electrode: Set the upper conductive electrode on the required ceramic surface. The general methods include silver layer burn-in, chemical deposition and vacuum coating.
11. High-voltage polarization: make the electric domains inside the ceramics aligned, so that the ceramics have piezoelectric properties.
Twelve. Aging test: After the performance of the ceramic is stable, check various indicators to see if the expected performance requirements have been met.
In comparison, underwater piezoelectric ceramics transducers have strong piezoelectricity, high dielectric constant, and can be processed into shapes, but have low mechanical quality factors, large electrical losses, and poor stability, so they are suitable for high-power transducers and broadband filters And other applications, but not ideal for high frequency, high stability applications. Piezoelectric single crystals such as quartz have weak piezoelectricity, low dielectric constant, and size limitations due to cut-type restrictions, but they have high stability and high mechanical quality factors. They are mostly used as oscillators for standard frequency control, high selectivity (multiple It is a high-frequency narrow bandpass) filter and a high-frequency, high-temperature ultrasonic transducer, etc.
