Abstract
PurposeThe purpose of this work was to characterize NiMn2O4 spinel-based thermistor powder, to use it in screen printing technology to fabricate temperature sensors, to study their performance for different sintering temperatures of thermistor layer, with and without insulative cover, as well as to investigate stability of the fabricated thermistors and their applicability in water quality monitoring.Design/methodology/approachAfter the characterization of starting NiMn2O4 spinel-based thermistor powder, it was converted to thick film paste which was screen printed on alumina substrate. Thermistor layers were sintered at four different sintering temperatures: 980°C, 1050°C, 1150°C and 1290°C. An interdigitated pattern of Ag-Pd conductive layer was used to reduce the resistance. Temperature-resistance characteristics were investigated in air and water, with and without insulative cover atop the thermistor layer. Stability of the fabricated thermistors after aging at 120°C for 300 h was also examined.FindingsThick film NiMn2O4 spinel thermistors, prepared by screen printing and sintering in the temperature range 980°C–1290°C, exhibited good negative temperature coefficient (NTC) characteristics in the temperature range −30°C to 145°C, including high temperature coefficient of resistance, good stability and applicability in water.Originality/valueThis study explores the range of sintering temperature that can be applied for NiMn2O4 thermistor thick films without compromising on the temperature sensing performance in air and water, as well as stability of the thermistors after aging at elevated temperatures.
Highlights
The accurate measurement and monitoring of temperature are crucial for controlling most biological, chemical and environmental processes and proper operation of many domestic, industrial, electronic and medical devices
The most popular are bulk negative temperature coefficient (NTC) thermistors manufactured as ceramic discs or chips using conventional pressing-sintering or tape casting–firing processing
This study presents the fabrication procedure of NiMn2O4 spinel-based thick film thermistors and the investigation of the influence of sintering temperature on the composition, microstructure, electrical properties and stability of the fabricated sensors
Summary
The accurate measurement and monitoring of temperature are crucial for controlling most biological, chemical and environmental processes and proper operation of many domestic, industrial, electronic and medical devices. The main groups of temperature sensors comprise thermometers, thermocouples, pyrometers and thermistors, each based on different measurement principles and fitted to various temperature ranges. Thermistors (thermally sensitive resistors) use thermoresistance effect for measurements in low and moderate temperature ranges (Kamat and Naik, 2002; Feteira, 2009). The best known materials for NTC thermistors are compounds with a spinel AB2O4 structure (A = Ni, Cu, Zn, B, Mn, Co, Fe, Cr). Low and elevated temperatures from À50°C to 150°C are their typical operating range, some spinel compositions are suitable for high temperature measurements. The most popular are bulk NTC thermistors manufactured as ceramic discs or chips using conventional pressing-sintering or tape casting–firing processing
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