CHARACTERIZATION OF (CuO-Fe2O3) CERAMICS WITH THREE DIFFERENT COMPOSITIONS SINTERED AT 1100 oC FOR NTC THERMISTOR

Abstract

CHARACTERIZATION OF (CuO-Fe₂O₃) CERAMICS WITH THREE DIFFERENT COMPOSITIONS SINTERED AT 1100 oC FOR NTC THERMISTOR. The formation of (CuO-Fe₂O₃) ceramics for NTC thermistors based on CuO-Fe₂O₃ phase diagram has been studied. The ceramics were produced by pressing an homogeneous mixture of powder of (50 mole % CuO and 50 mole % Fe₂O₃ as composition 1), (40 mole % CuO and 60 mole % Fe₂O₃ as composition 2) and (34 mole % CuO and 66 mole % Fe₂O₃ as composition 3) and sintering the pressed powder at 1100 oC for 2 hours in air with cooling rate of 10 ^oC/minutes. Electrical characterization was performed by measuring electrical resistivity of the ceramics at various temperatures (25 ^oC - 100 ^oC). Analyses of microstructure and crystal structure were carried out by using optical microscope and x-ray diffractometer (XRD), respectively. The x-ray diffraction (XRD) analyses showed that the ceramics of composition 1 and 3 were composed of tetragonal spinel and that of composition 2 was composed of cubic spinel. Hematite second phase was found in the ceramic of composition 3. According to the optical microscopy data, it was known that the ceramics having three different microstructures have been produced. Very large rounded grains were observed in the ceramic of composition 1, polygonal grains were observed in that of composition 2 and very small grains were seen in that of composition 3. According to the electrical data, it was known that the ceramics having thermistor constant (B) between 2000 K and 5000 K have been produced. It was known also that the room temperature resistivity (ρ_RT) and thermistor constant (B) increased with the increase of Fe₂O₃ content. The value of B and ρ_RT of the produced (CuO-Fe₂O₃) ceramics fits the market requirement.