Study On Fabrication And Properties Of NKN-LT-LS/Epoxy Resin 1-3 Composite

Piezoelectric composites have been used widely in many fields, such as sensor, breaker, transducer, etc. 1-3 piezoelectric composites combine the excellent properties of piezoelectric ceramic and polymer. Compared with pure ceramic or piezoelectric polymer, 1-3 piezoelectric composites have more advantages, such as higher piezoelectric constant, higher mechanical-electrical coupling coefficient, lower dielectric constant, mechanical quality factor and smaller acoustic impedance. They are suitable for transducer of high sensitivity, wide band, narrow pulse, which are ideal materials for ultrasonic, nondestructive test and hydrophone.For the environmental harmony and the application of the 1-3 type piezoelectric composites to medical ultrasonic transducer, NKN-LT-LS fibers were fabricated based on viscous polymer processing technique (VPP) and 1-3 type piezoelectric composites were prepared by arrangement–pouring method. A systematic study was made in this article on the effect of different volume fractions and aspect ratios of piezoelectric fibers on the composite properties. The experimental data of 1-3 composites were consistent with the theoretical models, which were useful for their application and development. The major works and conclusions as follows:1. The NKN-LT-LS lead-free piezoelectric fibers were fabricated by VPP. Effects of different organic contents and sintering conditions on fiber structures and properties were analyzed. Based on the results obtained, the compositions of pud were optimized as the solid content of 0.8571 (PVB vs DBP vs NKN-LT-LS = 4:1:30 wt%), and the best sintering condition was set at 1100℃for 4h. The bulk densityρv, apparent porosityΡαand hygroscopic coefficient Wαof NKN-LT-LS fibers were 4.39g/cm3, 0.00154 and 0.00676, respectively.2. By arranging NKN-LT-LS fibers and casting epoxy resin E-51, 1-3 piezoelectric composite with different ceramic volume fraction were fabricated. The micro-structure was determined by a scanning electron microscope. As a result, the structure of epoxy resin was tight and almost had no pores when the curing agent was maleic acid anhydride. The electric field,temperature and time during poling dramatically influenced the properties of 1-3 composites. The optimal poling conditions were determined as dwell time of 25 min, temperature of 80℃, and electric field of 2.5 kV/mm.3. Piezoelectric fibers influence piezoelectric composite effectively. It can be concluded that as the NKN-LT-LS volume fraction increases, the relative dielectric constant and acoustic impedance increase linearly. The piezoelectric stain constant increases evidently, while the piezoelectric voltage constant decreases. The thickness electromechanical coupling coefficient is higher than NKN-LT-LS ceramics.4. There is an obvious effect of aspect ratio t/d on the electrical properties of 1-3 composites. With the increase of aspect ratio, the resonant frequency and anti-resonant frequency move to the lower frequency. The relative dielectric constant and relative loss decrease, while the piezoelectric stain constant and piezoelectric voltage increase.