Rubber-ceramic composites applicable in flexible antennas.

Glass ceramics from the CaO–P₂O₅–SiO₂ system were synthesized. They were characterized by XRD, SEM and EDX methods. It was found that they contain two crystalline [Whitlockite, Ca₃ (PO₄)₂ and Hydroxylapatite, Ca₅ (PO₄)₃ (OH)] and one residual amorphous phase. The ceramics are composed of porous aggregates of fine particles with predominant macro- and mesopores in it. The ceramics were used as a functional filler in natural rubber based composites, as the filling is in the range of 5–50 phr. The influence of the chemical nature and structure of the ceramics and the degree of filling on the vulcanization characteristics, physicomechanical parameters, dielectric and dynamic properties, the coefficient of thermal conductivity and the volume resistivity, including external pressure or bending on the specimens were investigated. An influence of the filler and the degree of filling on all studied properties was found. All tested composites have dielectric parameters (ε′, real part of complex permittivity; ε′′, imaginary part of complex permittivity; σ, conductivity; tanδ_ɛ, tangent from dielectric loss angle) suitable for use as substrates and insulating layers of flexible antennas. Particularly impressive are composites containing 30 and 50 phr fillers, which have the lowest tangent from dielectric loss angle values. [ABSTRACT FROM AUTHOR]