Study On Preparation And Properties Of PMN/EP Composites

The 0-3 type piezoelectric ceramic/polymer composite has both a piezoelectric ceramic and a polymer merits. This composite is the new type functional material. Epoxy resin has a great of virtues, such as large rigidity, good corrosion resistance, good flame retardancy and excellent insulating property. With combining piezoelectric ceramic and epoxy resin, the dielectric and damping properties of epoxy resin will be improved because of high dielectric and piezoelectric properties of piezoelectric ceramic. So epoxy resin will be expanded the application in the field of the intelligent material.The PMN/EP composites of epoxy resin (EP), Magnesium Niobate-Lead Titanate (PMN) piezoelectric ceramic of high piezoelectric property and conductive materials that include carbon (CB) and iron powder (Fe) are prepared by casting and pressing methods. With changing the material composition, the effects of composition on the structure, conductive property, dielectric property and damping property are studied in details. The piezoelectric effect on the damping property is also investgated.The content of curing agent and curing processes are determined by DSC. The experimental results of densities and structures show that the composites prepared by casting method are more uniform, better interface and denser than by pressing method.The results of the conductive property show that the resistivity of PMN/EP composites decreases rapidly with increasing the conductive material content. And the resistivity of PMN/EP composites also decreases with increasing the frequency. With the PMN content of 30%, the CB percolation value of composite is 6.0%. And the Fe percolation value of composite is more than 6.0%.The results of the dielectric property show that the dielectric property of composites is better than epoxy resin, based on the high dielectric property of PMN. With increasing the PMN content the dielectric constant of PMN/EP composites increases. With the PMN content of 40%, the dielectric constant increases from 18.64 to 36.39 and the dielectric loss increases from 0.016 to 0.091 with increasing the PMN particle size from 0.65μm to 150μm. And with the PMN content of 30%, the dielectric constant and the dielectric loss of PMN/EP composites show a non-linear increase with increasing the conductive material content. From the relation between dielectric constant and frequency, it is obtained that in the frequency range between 10²-10⁶Hz, the dielectric constant of 0-3 PMN/EP composites decreases with the frequency increasing. At the high frequency, PMN/EP composites dielectric constants are more stable. The more PMN content is, the larger PMN particle is or the conductive material content is near the percolation value, the more rapidly decrease of dielectric constant with the frequency increasing is. From the relation between dielectric constant and temperature, it is obtained that comparing with the PMN, in the temperature range between 25℃and 150℃,the PMN/EP composites show excellent dielectric temperature stability.The results of the damping property show that the damping property of PMN/EP is better than ZrO₂/EP, based on the piezoelectric effect of PMN. In the same load and frequency, the damping property has the nonlinear change with the PMN content increasing. The damping property is the best when PMN content is 30%. The damping property improves with PMN particle sizes decreasing. And in the PMN particle size range between 7μm and 35μm, the composites show good damping property. The maximal damping loss factor decreases with conductive material content increasing. In the content of 0.5% to 4.0%, the damping property is improved more by adding Fe than CB. The damping mechanism of composite is called "piezoelectric damping" mechanism. It includes three parts, that is, the polymer damping loss, the damping loss of the friction among the particles and polymer, the damping loss of piezoelectric effect.