A Thermistor with Variable Rate of Negative Temperature Coefficient of Resistance Made from Egyptian Raw Materials

Abstract

A dual-function negative temperature coefficient thermistor (NTCR/AB) has been successfully fabricated from the available and inexpensive Egyptian raw materials (clay and nepheline tailings). The disc-shaped thermistor was fabricated by grinding and mixing its raw material in a porcelain ball mill for 1 h, drying at 110°C for 1 h, pressing under 30 kN, drying at 110°C for 24 h, firing at 550°C, and finally sintering at 1200°C for 1 h. The crystalline phases developed in the ceramic thermistor were characterized by x-ray diffraction. The thermistor performance has been examined by measuring its electrical resistivity (ρ) over a wide range of temperature (− 100°C to + 200°C) at a constant frequency (0.1 Hz), using a broadband dielectric spectrometer. The fabricated ceramic thermistor showed a decrease in resistivity with increasing temperature at two different rates, displaying the NTCR/AB. One of its functions (NTCR/B) works in a wide temperature range (− 20°C to 200°C) and shows high thermistor constant values (3009–4638 K), while its second function (NTCR/A) works in a narrower temperature range (− 40°C to − 20°C) and shows exceptionally high thermistor constant values (40,122 K). NTCR/B can be used for many electronic devices applications, while NTCR/A is promising for thermal switching devices.