Accession Number : ADA215988


Title :   Carbon Black - Polyethylene Composites for PTC (Positive Temperature Coefficient) Thermistor Applications


Descriptive Note : Master's thesis,


Corporate Author : PENNSYLVANIA STATE UNIV UNIVERSITY PARK


Personal Author(s) : Rohlfing, Lori L


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a215988.pdf


Report Date : Dec 1987


Pagination or Media Count : 110


Abstract : A new class of composite Positive Temperature Coefficient (PT C) thermistors are commercially available. These composite thermistors exhibit a PTC measuring 6-8 orders of magnitude and have several advantages over conventional Barium Titanate 3 thermistors, including lower room temperature resistivity, better thermal shock resistance, and high temperature stability. In this study, composite PTC thermistors are produced from a carbon black/ polyethylene composition that exhibited a PTC of resistance measuring 6-8 orders of magnitude at 125 C. The composites are irradiated (gamma source) to induce polymer crosslinking. Crosslinking imparts mechanical integrity and prevents the onset of an NTC effect above the transition temperature. Crosslinking stabilizes the high temperature resistivity to 200 C. The electrical properties of these crosslinked composites are examined as functions of temperature, frequency, and thermal cycling. To eliminate the crosslinking procedure, an insulating mullite phase was incorporated into the diphasic mixture to form a triphasic composite. Addition of the third filler yielded two effects. First, the filler provided sufficient mechanical stabilization of the composite structure to maintain high post-PTC resistance without an NTC effect. Second, the addition of an insulating filler resulted in a shift of the room temperature resistivity caused by a shift in the percolation curve. (KT)


Descriptors :   *THERMISTORS , *TEMPERATURE COEFFICIENTS , *COMPOSITE MATERIALS , MECHANICAL PROPERTIES , POLYMERS , HIGH TEMPERATURE , INSULATION , RESISTANCE , GRAPHS , COMPOSITE STRUCTURES , THERMAL STABILITY , ELECTRICAL PROPERTIES , CYCLES , ROOM TEMPERATURE , CROSSLINKING(CHEMISTRY) , TRANSITION TEMPERATURE , HEATING , SHOCK RESISTANCE , GAMMA RAYS , CARBON BLACK , THERMAL RESISTANCE , FILLERS , POLYETHYLENE , LOW TEMPERATURE , PERCOLATION , STABILIZATION , SOURCES


Subject Categories : Electrical and Electronic Equipment
      Laminates and Composite Materials


Distribution Statement : APPROVED FOR PUBLIC RELEASE