PTC Characteristics of(TiC/ Polyethylene) Conductive Composites in Relation to their Particle-filled Structures

Titanium carbide (TiC)/polyethylene (PE) composites have been prepared with various volume fractions of TiC by a melt bleeding method. Two types of TiC powder with their different particle diameters, 1.48 µm (TiC-A) and ca. 100 µm (TiC-B), were utilized in the present study. The electric resistivities (ρ) of the samples decreased gradually with increasing TiC volume fraction (ϕA); in the case of smaller particle size, the value of ρ at room temperature jumped down in the relatively narrow range of ϕA = 0.39 to 0.42, reaching as low as 0.1 Ωcm. Temperature dependencies of ρ were also measured to examine the possible application of the composite to polymer PTC thermistors. The resistivity showed positive temperature dependence and changed abruptly in the tenth order of its magnitude during the melting transition of PE. The electric current cutoff characteristics of the samples indicated excellent features in the overcurrent response despite their low resistivity values, as compared with those of other PTC materials. In parallel, the mechanism of conductivity of the composite was discussed in terms of the percolation theory. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 1–9, 2005; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/eej.20115