Study On The Preparation Of Lead-free Piezoelectric Ceramics Based On 3D Printing Technology

Ultrasonic transducer is a key component of ultrasonic detection instrument and ultrasonic treatment instrument,determining the image quality of ultrasonic imaging and the distribution and intensity of ultrasonic energy.The ultrasonic transducer mainly consists of three parts:piezoelectric layer,matching layer and backing layer.The piezoelectric layer is an important part that determines the performance of the transducer.At present,lead-based piezoelectric ceramics are widely used because of their good piezoelectric properties.However,the preparation,application and discard of lead-based materials may cause the environmental pollution.Therefore,the research and application of lead-free piezoelectric ceramics have become research focus in recent years.In addition,the complex-structure piezoelectric ceramics can be better used for the special complex devices to achieve high properties.Nevertheless,it is difficult to prepare complex piezoelectric ceramics by traditional machining due to their hardness and brittleness performance.3D printing technology has such characteristics as fast molding speed,high precision and mold free forming,which can meet the needs of personalized,refined and complicated rapid manufacturing.In this subject,in order to improve the performance of complex structure piezoelectric ceramic devices for furtherly satisfying a extensive application requirements,the preparation of lead-free piezoelectric ceramics by stereolithography apparatus technology are studied in the following three aspects:1.The photocuring properties and viscosity of （1-x）NaNbO₃-xBaTiO₃ ceramic slurry were studied.In this paper,the research on the dimensional deviation of the curing depth of （1-x）NaNbO₃-xBaTiO₃ ceramic slurry under different light intensity and exposure time mainly are investigated in detail.The optimal illumination intensity and exposure time is 10% and 4s,respectively,which can not only ensure the curing depth but also ensure the minimum dimensional deviation.The impact of rotating speed and content of dispersant on viscosity of slurry is also studied,drawing a conclusion that the viscosity is the lowest when rotational speed is 6r/min,which could be applied to the subsequent 3D printing parameter setting.And the slurry viscosity is lowest when the content of dispersant is 1%-1.5%.2.BaTiO₃（BT） ceramics were prepared by stereolithography apparatus technology,and the impact of solid content of BT ceramic slurry（75-86wt%） on the density,microstructure,crystal structure and electrical properties of sintered ceramics is studied.The result shows that the density of the sintered ceramics is getting higher with the solid content increased.The ceramics all have perovskite structure,and the crystal structure does not change much,while the electrical properties get increased.When the solid content is 80wt%,the ceramic performance reaches the best,and piezoelectric constant d₃₃,dielectric constantε_r,dielectric loss tanδand electromechanical coupling coefficient k_t is 166p C/N,2100,0.02 and 41%,respectively.To evaluate the performance of 3D-printed ceramics,acoustics field of one-dimensional focused array is firstly simulated and then it is prepared into an ultrasonic transducer with a center frequency of 1.4MHz,a bandwidth（@-6d B）of 40%,and an insertion loss of 50d B.3.The influence of the preparation process of Bi_0.5Na_0.5TiO₃（BNT）template on the morphology of the template is studied.Bi_4.5Na_0.5Ti₄O₁₅ template is prepared by molten salt method,and BNT template was synthesized from precursor particles of Bi_4.5Na_0.5Ti₄O₁₅ template through topological chemical reaction The morphology of the BNT template is studied under different preparation conditions,such as different temperatures in the second step of molten salt method and whether Na₂CO₃ is excessive or not.The experiment shows that the optimal temperature in the second step of molten salt method is 980℃,and the morphology of Bi_0.5Na_0.5TiO₃ template prepared by adding 90mol%excessive Na₂CO₃ is rectangular,which is suitable for seed crystal.The average thickness of BNT template is about 2μm and the average size is 10-14μm.