The first is the separation of nucleation and growth process,which is promoting nucleation and controlling growth,to ensure that the nucleation rate is greater than the growth rate, that is, ensuring that the PZT materials piezo ceramic powder precursor is formed under a large degree of supercooling or high supersaturation. Second, the prevention of PZT powder agglomeration is including how to inhibit agglomeration during powder preparation. 1. Selecting reasonable reaction conditions (such as pH, reaction concentration and temperature; 2. Powder synthesis,drying process and special treatment, including low surface tension during powder synthesis, so that powder compacts with less agglomeration can be obtained; special drying processes are used in the drying process, mainly freeze-drying, supercritical drying and far-infrared drying, etc. The basic principle is to eliminate the gas-liquid interface with a large surface tension, or to make the particles fixed and not close to each other. For example, lyophilization is the use of low temperature and negative pressure to sublime the raw liquid medium frozen into a solid phase under negative pressure due to The solid phase particles are frozen in the raw liquid medium, and there is no gas-liquid interface with a large surface tension in the capillary between the particles, thereby avoiding the serious agglomeration problem caused by the liquid bridge.
Choosing the best calcination conditions or special processes, such as the use of microwave heating without heat transfer, high energy efficiency and other characteristics to replace the traditional high-temperature electric furnace,A single component PZT hot body was obtained at 600°C. The methods of piezoelectric element transducer for eliminating agglomeration after group formation are: deposition or sedimentation, grinding and ultrasonic treatment and dispersant, and the like. For example, Wang Xicheng uses metal alkoxides and nitrates as raw materials to strictly control the conditions of coprecipitation, washing and dispersion. By using freeze-drying technology and reasonable calcination process, the components are homogeneous and have no hard agglomerates. Single perovskite phase, high sintering activity of micron-sized PZT 52 fine powder. Formed by cold isostatic pressing (CIP) technology, densification sintering can be achieved at 800°C, and its relative density reaches 98%.
The influence on the quality of PZT piezoelectric disc element products mainly includes two aspects: First, the lead volatilization during the sintering process of PZT piezoelectric ceramics causes the components to deviate from the accurate stoichiometry to reduce the performance of the products; on the other hand, it refers to the Zr/Ti in the components. Fluctuation affects the stability of PZT product performance.Lead volatilization is generally considered to be due to the higher sintering temperature of PZT ceramics, lead oxide has a relatively high saturated vapor pressure in the high temperature environment of lead volatilization, the higher is the saturated vapor pressure. The more easily lead is volatilized, and as Zr/Ti increases, the sintering temperature of PZT piezoelectric ceramics increases, the saturated vapor pressure of lead oxide gradually increases, and the lead loss becomes more serious, so PZT with high Zr/Ti piezoelectric ceramics are more difficult to sinter, it is too low oxygen partial pressure during sintering can cause lead to volatilize. The PZT material prepared by the traditional solid phase method has low sintering activity .the sintering temperature is generally around 1200°C, which is easy to cause a large amount of lead to volatilize, and the product performance is not high. Therefore, the PZT product is prepared by the solid phase method is difficult to meet the performance requirements. At present, the main measures taken by material researchers at home and abroad for lead volatilization are as follows: First, excessive lead is added to the powder synthesis. in the initial stage of sintering is due to the formation of liquid phase, which can increase the contact area of the reactants, accelerating the diffusion rate of zirconium, titanium and dopants improve the uniformity of the product; the forming liquid phase can also accelerate the dissolution and precipitation.The diffusion movement facilitates the arrangement and close packing of the particles.which accelerates the densification of the product.However, when the amount of lead added is too much, excessive lead will deposit on the grain boundary on the one hand, which will reduce the performance of the product. On the other hand, it will easily cause the local concentration of titanium in the piezos discs crystal component to be too high, which is due to the solubility of TiO2 in liquid phase lead oxide. It is larger than the solubility of ZrO2, thus causing the local titanium content of the PZT product after sintering to be high, especially at the grain boundary, thereby affecting the uniformity of the microstructure and reducing the performance of the product. The addition of excess lead also affects the mechanical properties of PZT piezoelectric ceramic components: when the product has excessive lead excess, the fracture mode is transgranular fracture; the lead deficiency is the grain boundary fracture.
Second, in the sintering process of the product, according to the volatilization mechanism of lead, a reasonable sintering system and special measures are adopted. It is widely used to add a sintering atmosphere sheet and to sinter by using a double-layer bismuth technique, and to control the sintering atmosphere to be an oxidizing atmosphere. This will reduce lead volatilization and prevent the product from blackening. In a reducing atmosphere, Ti4+ is easily made to be black by the original Ti3+.
The third is to add an appropriate amount of dopants. Doping on the one hand reduces lead volatilization and on the other hand improves the performance of PZT articles.The fourth is to further study the synthesis of high-activity PZT powder, so that PZT piezoelectric ceramics can achieve densification and sintering at a temperature lower than the volatilization temperature range of lead. In addition, the mechanism of lead volatilization remains to be further studied.
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