The present work shows the results of investigation on the effects of sintering temperatures of (Mg0.25Mn0.1Zn0.65)Fe2O4 ferrite on its sintered density, initial permeabilty, resistivity and microstructure. To achieve better sintered density and initial permeabilty, the sintering temperature should be ≥1200oC. However, the higher sintering temperature results in larger the grain size, which causes the reduction of the resistivities of Mg-Mn-Zn ferrites. Furthermore, the resistivities of samples are environmental temperature sensitive, and possibly possess the similar function of NTC thermistor over the testing range 25-225oC.
A study on the effect of heat treatment condition on the characteristics of MnO2 added-Fe2TiO5 ceramics for NTC thermistor has been carried out. The ceramics were produced by pressing an homogenous mixture of Fe2O3 (local/ yarosite), TiO2 and MnO2 (2.0 mole %) powders in appropriate proportions to produce Fe2TiO5 based ceramics and sintering the pressed powder at 1050 °C for 3 hours in oxygen gas. Some sintered pellets were heat treated by heating them at 300 °C for 5, 15 and 25 minutes in Ar + 7% H2 gas. The XRD analyses showed that the Fe2TiO5 ceramics with and without heat treatment time had orthorhombic structure. No peak from second phase was observed from the XRD profiles. From the electrical characteristics data, it was known that the heat treatment could change the electrical characteristics of the Fe2TiO5 based-thermistor. The thermistor constant (B) and room temperature resistivity (ρRT) decreased with the increasing of heat treatment time. All ceramics made had thermistor characteristics namely B = 3459-7596 K and ρRT = 1.056-6936.062 MΩcm. Thermistor constant of the ceramics was relatively big, indicated that ceramics made from local iron oxide in this work fit the market requirement for NTC thermistor.
The Effect of Sintering Atmosphere on Electrical Characteristics of Fe2TiO5Pellet Ceramics Sintered at 1200°C for NTC Thermistor