Preparation And Properties Of PZT Aerogel Coating

Piezoelectric ceramics are widely used in underwater acoustic transducers.Lead zirconate titanate?PZT?ceramics are the most important members of the piezoelectric ceramic family because of their excellent piezoelectric properties,such as high Curie point and good stability.However,both the PZT polycrystalline piezoelectric ceramics and their composite materials have the characteristics of high bulk density,high acoustic impedance and brittleness.Consequently,the reflection loss at the interface is large and it is difficult to match the water load.Moreover,the lateral coupling is also too strong.In addition,the hydrostatic piezoelectric coefficient?d_h?and hydrostatic voltage coefficient?g_h?of the dense ceramic are relatively small,which makes the signal driving ability and sensitivity of the underwater acoustic transducer low,resulting in the performance of the dense piezoelectric ceramics in the underwater acoustic transducer unsatisfactory.In view of the above statement,there is an urgent need to develop novel piezoelectric materials with high piezoelectric constant,low density,high porosity,low acoustic impedance,high strength and good flexibility to meet the modern application requirements of high-performance underwater acoustic transducers.The piezoelectric aerogel and its composite coatings are suitable for underwater acoustic transducers to improve their comprehensive performance due to their low density,high porosity and easy matching with acoustic impedance of air,organisms and water.Therefore,the preparation and properties of PZT aerogels and their composite coatings were studied in this paper.The specific work is as follows:Lead acetate trihydrate,zirconium propoxide solution,tetrabutyl titanate were used as lead,zirconium and titanium sources in the precursor of PZT sol respectively.Using ethylene glycol monomethyl ether as solvent,based on the traditional sol-gel process,the PZT wet gel was successfully prepared by controlling the dosage of gel promoters and adding time?two step catalytic method?.PZT aerogels were prepared by supercritical drying of carbon dioxide.The morphology,composition,thermal stability,specific surface area and pore size distribution of the prepared aerogels were studied.It was found that the PZT aerogel was prepared with a specific surface area of 260.03 m²/g,a most probable aperture of 104.1 nm and heterozygotes PbCO₃.The effects of different annealing temperatures on the specific surface area,pore size distribution and composition of the prepared PZT aerogels were studied.The annealing temperature was 350-700?,the heating interval was kept at 50?,and the annealing time was 4h.The effects of composition,morphology,specific surface area and pore size distribution of annealed samples were analyzed.The study found that after annealing treatment at 550?for 4 h,the aerogel sample began to change from amorphous to perovskite phase,the specific surface area of the sample decreased to 29.34 m²/g,and the most probable aperture was 230 nm.The specific surface area and total adsorption pore volume of aerogel samples decrease with the increase of annealing temperature,and the most probable aperture increases with the increase of annealing temperature.The preparation cycle of PZT aerogel is generally a longer process and the operation is relatively tedious.Also the transition process from sol to gel is difficult to control.After a great deal of practical investigations,a novel method of simple and rapid preparation of PZT aerogel is developed by combining sol-gel method with solvent-thermal method or we can simply call it sol-solvent-heat method.In this method,acetyl acetone was used as a stabilizer to prepare highly stable sol but it was difficult to gel at room temperature and normal atmospheric pressure.Therefore,the prepared sol is heated and pressurized to gel in a short period of time unlike the conventional methods used in the past.The effects of reaction temperature and reaction time on the specific surface area and pore size of aerogels prepared by sol-solvent-thermal method were investigated.The surface morphology,composition,thermal stability,specific surface area and pore size distribution of aerogels were also studied.It was found that PZT aerogel prepared at 220?for 4 hours had a maximum specific surface area of 323.1 m²/g and the most probable aperture of 44.6 nm,and still contained heterozygotes PbCO₃.In order to remove the heterozygotes in the prepared PZT aerogel and not to cause the destruction of the pore structure of PZT aerogel in the crystallization process,the samples were annealed for 0.5 h in the range of 550-800?,with 50?as the temperature interval.The changes of morphology,composition,specific surface area and pore size of aerogel samples during crystallization were studied.The study found that after annealing treatment at 600?for 0.5 h,the aerogel samples began to transform to perovskite phase,and the specific surface area of the samples decreased to 55.1 m²/g,and with the increase of annealing temperature,the specific surface area of the samples began to decrease.After annealing treatment,impurities such as PbCO₃ are removed,but still contain impurities such as ZrO₂,PbO and PbO₂.Finally,PZT aerogel coating was prepared and the effects of doping SiO₂ aerogel powder,PZT ceramic powder and coating layers on the piezoelectric and dielectric properties of PZT aerogel coating were studied.It is found that adding PZT ceramic powder to PZTA/PVDF composite coating can improve the piezoelectric property of composite coating.Adding SiO₂ aerogel powder to the composite coating and increasing the number of layers of the composite coating can improve the remanent polarization of the composite coating.Adding SiO₂ aerogel powder to the composite coating can improve the dielectric constant and dielectric loss of the coating.Increasing the number of layers can reduce the dielectric constant and dielectric loss of the coating.