Piezeoelectric ceramic-polymer composites
First Claim
1. A piezoelectric composite comprising a mixture of piezoelectric ceramic particles in a polymeric material, which polymeric material is continuous in three dimensions, wherein(a) the weight-average diameter D of the piezoelectric ceramic particles ranges from 30 microns to 200 microns,(b) at least 50 weight percent of the piezoelectric ceramic particles have an average diameter that is in the range from 0.5 D to 1.5 D,(c) the dielectric constant of the piezoelectric ceramic particles at one kHz is less than about 700,(d) the dielectric constant of the polymeric material at one kHz is above 2.8,(e) the dielectric loss of the polymeric material at one kHz is less than 0.02, and(f) the volume fraction of the piezoelectric ceramic in the composite is from 40% to 74%.
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Abstract
Methods and compositions are described for the preparation of piezoelectric ceramic-polymer composites having improved properties for application in piezoelectric devices. These composites consist of piezoelectric particles embedded in a polymer matrix. The improvements of this invention result from discoveries of the effects of particle size, particle size dispersity, volumetric loading levels, ceramic dielectric constant, and polymer dielectric constant on performance. Various improved devices based on these compositions are also described.
57 Citations
27 Claims
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1. A piezoelectric composite comprising a mixture of piezoelectric ceramic particles in a polymeric material, which polymeric material is continuous in three dimensions, wherein
(a) the weight-average diameter D of the piezoelectric ceramic particles ranges from 30 microns to 200 microns, (b) at least 50 weight percent of the piezoelectric ceramic particles have an average diameter that is in the range from 0.5 D to 1.5 D, (c) the dielectric constant of the piezoelectric ceramic particles at one kHz is less than about 700, (d) the dielectric constant of the polymeric material at one kHz is above 2.8, (e) the dielectric loss of the polymeric material at one kHz is less than 0.02, and (f) the volume fraction of the piezoelectric ceramic in the composite is from 40% to 74%.
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17. A process of making a composite comprising forming a mixture of piezoelectric ceramic particles in a polymeric material, which polymeric material is continuous in three dimensions, wherein
(a) the weight-average diameter D of the piezoelectric ceramic particles ranges from 30 microns to 200 microns, (b) at least 50 weight percent of the piezoelectric ceramic particles have an average diameter that is in the range from 0.5 D to 1.5 D, (c) the dielectric constant of the piezoelectric ceramic particles at one kHz is less than about 500, (d) the dielectric constant of the polymeric material at one kHz is above 2.8, (e) the dielectric loss of the polymeric material at one kHz is less than 0.025, and (f) the volume fraction of the piezoelectric ceramic in the composite is from 40% to 74%, wherein said piezoelectric ceramic particles are in the form of a free-flowing sintered powder obtained by heating a free-flowing mixture of ceramic-forming metal oxide powders at a temperature of at least about 400° - C. for a sufficient time that would sinter a compacted disk of said free-flowing mixture of ceramic-forming metal oxide powders, and wherein said mixture of piezoelectric ceramic powder and polymeric material is melt processed at a pressure of at least 5,000 psi to produce a shaped form.
- View Dependent Claims (18)
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19. A process for the preparation of a shaped, piezoelectric composite article comprising
(I) dispersing a free-flowing powder of piezoelectric ceramic particles into a solution of a solvent and a polymeric material, (II) forming a composite by steps comprising at least one of (i) and (ii): -
(i) adding a non-solvent for the polymeric material to the solvent and separating formed solids from the mixture of said solvent and non-solvent; and (ii) evaporating the solvent from the solution to form a composite, and (III) pressing the composite into a shaped form at a temperature of above 200°
C. and at a pressure of at least about 10,000 psi, wherein(a) the weight-average diameter D of the piezoelectric ceramic particles is from 30 microns to 200 microns, (b) at least about 50 weight percent of the piezoelectric ceramic particles have an average diameter that is in the range from 0.5 D to 1.5 D, (c) the dielectric constant of the piezoelectric ceramic at one kHz is less than 500, (d) the dielectric constant of the polymeric material at one kHz is above 2.8, (e) the dielectric loss of the polymeric material at one kHz is less than 0.025, and (f) the volume fraction of the piezoelectric ceramic in the composite is from 40% to 74%. - View Dependent Claims (20)
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21. A process of poling a composite article having edges, which composite article comprises a mixture of ceramic particles in a polymeric material, which process comprises placing the composite article in an electrical path between a corona discharge and ground so that the edges of said composite are shielded from the corona discharge by an insulating material positioned on the edge of the composite article, wherein a side of said composite article opposite to the corona discharge is contacted with a metallic conductor, the composite article is positioned in a heated bath containing a fluid, the field applied to the composite article from the corona discharge is above about 120 kV/cm, and the temperature of the bath is at least about 30°
- C. below the highest melting temperature of the polymeric material.
- View Dependent Claims (22)
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26. A process for forming a composite comprising forming a mixture of piezoelectric ceramic particles in a monomer or prepolymer, followed by reaction of said monomer or prepolymer to produce a polymeric matrix material that is continuous in three dimensions, wherein
(a) the weight-average diameter D of the piezoelectric ceramic particles ranges from 30 microns to 200 microns, (b) at least 50 weight percent of the piezoelectric ceramic particles have an average diameter that is in the range from 0.5 D to 1.5 D, (c) the dielectric constant of the piezoelectric ceramic particles at one kHz is less than about 700, (d) the dielectric constant of the polymeric material at one kHz is above 2.8, (e) the dielectric loss of the polymeric material at one kHz is less than 0.02, and (f) the volume fraction of the piezoelectric ceramic in the composite is from 40% to 74%.
Specification