A Thermistor with Variable Rate of Negative Temperature Coefficient of Resistance Made from Egyptian Raw Materials
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https://doi.org/10.1007/s11664-020-08540-w 2020 The Minerals, Metals & Materials Society
A Thermistor with Variable Rate of Negative Temperature Coefficient of Resistance Made from Egyptian Raw Materials R.M. MAHANI
1,3
and D.A. ABDEL AZIZ2
1.—Microwave Physics and Dielectrics Department, National Research Centre, 33 EL Buhouth St., P.O. 12622, Dokki, Cairo, Egypt. 2.—Ceramics Department, National Research Centre, 33 EL Buhouth St., P.O. 12622, Dokki, Cairo, Egypt. 3.—e-mail: [email protected]
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 110C for 1 h, pressing under 30 kN, drying at 110C for 24 h, firing at 550C, and finally sintering at 1200C 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 (q) over a wide range of temperature ( 100C to + 200C) 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 ( 20C to 200C) and shows high thermistor constant values (3009–4638 K), while its second function (NTCR/A) works in a narrower temperature range ( 40C to 20C) 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. Key words: Resistivity, NTCR, thermistor constant, clay, ceramic
INTRODUCTION Most physical, chemical, mechanical, biological, and electronic systems are greatly affected by temperature. Therefore, measuring the temperature is of great importance for a wide variety of applications. There are many different temperature sensors on the market today, including resistance temperature detectors, thermocouples, semiconductors, infrared, and thermistors. The majority of these applications are based on their resistance– temperature characteristics, operating temperature ranges, and speed of response to temperature, as well as on the materials they are made of. Most available temperature sensors are made of high-
(Received May 14, 2020; accepted September 29, 2020)
purity conducting metals, such as platinum, copper, or nickel, while thermistors are made of low-cost materials, such as polymers, or ceramic materials like the oxides of manganese, nickel, or cobalt.1–4 Furthermore, thermistors have a main advantage over other types of temperature sensors, which is their speed of response to even small changes in temperature, their accuracy, and their repeatability, so they can measure temperature with a higher accuracy (0.1C or ± 0
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