Gelcasting Was Prepared 1-3 Of Pmn-pzt / Epoxy Piezoelectric Composite

1-3 piezoelectric composites have many advantages, such as excellent piezoelectric properties, low dielectric constant, high hydrostatic piezoelectric constant and sound impedance approximates to water or organism, so it is the ideal material which is widely used in medical ultrasonic imaging and hydrophone. At present, there are lots of methods preparing 1-3 piezoelectric composite, which include mainly cut-filling and arranging-casting, but these methods with some problems that are long time, high energy consummation and high cost. Piezoelectric composites are more difficult to fabricate caused piezoelectric ceramic has high hard, high toughness and hard to be arranged. To solve these problems, this paper uses gelcasting technology to fabricate 1-3 piezoelectric composite for the first time, and at the same time using gelcasting and rapid protyping technologies to produce the piezoelectric ceramic phase of PMN-PZT with complex shape and 1-3 piezoelectric composite fitted for hydro-acoustic hydrophone devices. These technologies are successfully used to overcome the problem of hard to control distributing orderliness of the piezoelectric ceramic phase by conventional technology.The preparation of ceramic slurry with high solid phase and low viscosity is an indispensable and key condition to carry out gelcasting. In this paper, PMN-PZT slurry with 60 vol% solid loading and below 1 Pa·s viscosity was prepared by using superultronic, adding dispersant, adjusting dispersant content and pH value, which can reach the requirement of gelcasting. The optimized condition for the preparation of PMN-PZT slurry was obtained that the amount of dispersant (PMAA-NH4) was about 0.6 wt%, pH was 10, superultronic power and time were about 150W and 6 periods respectively. The PMN-PZT slurry in the optimized conditions was a plastic fluid, which showed the character of shear thinning. The green body with homogeneous microscopic structure and best properties was produced by PMN-PZT slurry with 55vol% solid loading. The disperse properties of slurry were investigated by sedimentation test,ζpotential, viscosity, particle size analysis and scanning electron microscopy (SEM). The results indicated that superultronic and dispersant adding could reduce the concentration of ceramic powder, make slurry stability, rheological properties and dispersibility better.To avoid toxicity of acrylamide in gelcasting process at present, the nontoxicity N-hydroxymothl acrylamide (NMAM) was choosen as monomer, and its polymerization mechanism was studied. The results showed that the gelling could be formed both by monomer free radical polymerization and its self-crosslinking reaction because the molecular structure of N-hydroxymothl acrylamide has not only unsaturation vinyl but also hydroxyl methyl. FTIR analysis results indicated that ceramic powder added only increased slurry viscosity and didn't destroy the structure of the gellatin.The effects of temperature, initiator, catalyst, monomer and pH value on idle time were discussed. It was proved that idle time was shorten by increasing temperature, the amount of initiator and catalyst and the concentration monomer solution, but idle time will be long by the rise of pH value. When adjusting the concentration of monomer to 10-15 wt%, the amount of initiator to 0.4-0.5vol%, the amount of catalyst to 0.4vol%, pH about 10-11, idle time was about 20 minutes, which can get better forming effect. The solidification in situ of slurry could be performed successfully by controlling the addition of catalyst (TEMED) at room temperature, which can avoid some abuses, such as easy to generate green bodies'defects caused by increasing temperature and too complex processing technology. The results of scanning electron microscopy (SEM) and electrical properties test indicated that the gelcasting samples had more homogeneous microscopic structure, higher density, more excellent piezoelectric and dielectric properties in comparison with those of die pressed ones.Base on the composite theory, the relationship between PMN-PZT volume fraction and 1-3 composites dielectric and piezoelectric properties was investigated. The results show that the volume fraction of piezoelectric ceramic phase had great effects on properties of 1-3 composites, and the experimental results were consistent with that of theory. With increasing the ceramic volume fraction, the permittivity dielectric constantεr, the dielectric loss tgδand piezoelectric constant d33 and d31 all rose. The piezoelectric strain constant dh increased when PMN-PZT volume fraction was below 40vol%, and decreased when PMN-PZT volume fraction was above 40vol%. Because of different rule between piezoelectric constant and dielectric constant, its piezoelectric voltage constant gh and optimized hydrophone figure of merit q rose firstly and then decreased. The maxium hydrophone figure of merit q could reach 1900 at 10vol% of PMN-PZT volume fraction. The electromechanical coupling coefficient kt fluctuated between 0.45 and 0.75. The mechanical quality factor Qm increased firstly and then decreased, it exist a maximal value.In this paper, PMN-PZT piezoelectric ceramic with homogeneous microscopic structure, low defects, complex shape and good piezoelectric properties could be prepared successfully by gelcasting of N-hydroxymothl acrylamide system. The optimized hydrophone figure of merit of 1-3 composites could be through volume fraction of piezoelectric ceramic, which can meet the requirement about hydro-acoustic hydrophone devices. This preparation technique has no toxicity, no harm and no pollution, simplified process flow, easy in operation, good quality products, which is a novel method for preparating piezoelectric composites.