Piezeoelectric ceramic-polymer composites

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.degree. 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.

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.degree. 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%.

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%.