Low temperature sensing capability of polyaniline and Mn 3O 4 composite as NTC material

Abstract

The paper deals with the synthesis of composite of polyaniline with Mn 3O 4 via oxidative polymerization of monomer by ammonium persulphate in presence of finely graded (45 μM) Mn 3O 4. The characterization of composite was done by FT-IR, XRD, TGA, conductivity and TCR. The composite possesses the resistance in the range of kilo-ohms at ambient temperature, which starts decreasing with the increase in temperature and becomes minimum at 170 °C and remains constant up to 200 °C, thus behaves like semiconductor with respect to temperature resistance characteristics. The factor responsible for decrease in the resistance values during the temperature range of ambient to 170 °C is hopping of electrons between Mn 2+/Mn 3+ and its enhanced mobility due to polyaniline chain. After 200 °C the resistance values of composite again increases slowly, because of waning interaction of Mn 3O 4 and PANI. Above 300 °C the resistance values increases significantly due to complete decomposition of polyaniline which has been confirmed by thermal analysis. The blend of polyaniline/Mn 3O 4 was also prepared in the same ratio, the TG of which shows that the blend is just the physical mixture of the two constituents while in case of composite proper interaction is proved, supported by FT-IR, TG and XRD analysis. Thermal analysis shows that the decomposition of polyaniline and its composite is slow in nitrogen atmosphere as compared to air. The thermistor constant B and temperature become linearly dependent. The study shows the potential of composite to act as negative temperature coefficient (NTC) material for thermistor applications and continuous thermocouple.