Characterization of transition metal oxide ceramic material for continuous thermocouple and its use as NTC fire wire sensor

The ceramic powder prepared from the mixture of Mn3O4 and La2O3 have been characterized for NTC behavior and the same have been used as CT2C (continuous thermocouple) sensor in the form of a thin metal cable to detect over-heating. These materials have mega ohm resistance at room temperature and showed exponential drop in resistance with the rise in temperature over a temperature range of 100-400 °C. It has been observed that as the concentration of La2O3 increases from 0 to 10% the NTC behavior drops from (400-260 °C) ±10%. The material was pressed into pellets and sintered at 700 °C for 3 h resulting in good bonding strength. Electrical characterization of the material was done by measuring the resistance over a temperature range of 100-400 °C. The material showed reproducible NTC characteristics over the temperature range 400, 370, 340, 280, and 260 °C with decreasing thermistor constant values (B = 9588, 9210, 8500, 5170, 3330 K−1) and activation energy (ΔE = 826, 794, 733, 445, 287 meV), respectively. The decrease in activation energy of the ceramic powder with increase in La2O3 concentration makes it possible to fabricate thermal sensors which can be used in different temperature ranges. The microstructure was studied using SEM and evidence of a sintered body with grain size around 1 μm was observed in the material. XRD analysis indicated the single-phase tetragonal structure of the ceramic material. The process of using this ceramic material for fabrication of 10 ft continuous fire wire sensor has been explained.