Characterization of NTC thick film thermistor paste Cu0.2Ni0.5Zn1.0Mn1.3O4

A powder of Cu0.2Ni0.5Zn1.0 Mn1.3O4 composition for custom thermistor was prepared by using the respective mixture of metal oxides and solid state reaction at 1000 °C/4h in air. The obtained thermistor powder was milled in the planetary ball mill and agate mill for a prolonged time to achieve submicron powder. The prepared thermistor powder was further characterized by using XRD and SEM techniques. After that, the thermistor powder was pressed into small disc-shaped samples and sintered at 1150 °C/2h. The sintered samples were also characterized by using XRD and SEM. The main electrical properties such as nominal resistance R and thermistor exponential factor B were measured in the climatic test chamber. After that, the thick film paste was prepared using the same powder, an organic vehicle and a glass frit. The paste was printed on alumina substrate, dried at 150 °C /30 min and sintered in air at 850 °C /10 min in a hybrid conveyor furnace. Planar electrodes were printed on the sintered NTC thermistor layer using PdAg thick film paste. The electric properties of the sintered thick film thermistor were also measured in the climatic test chamber. The obtained results were used for development of novel self-heating thermistor applications

Segmented thermistors printed using NTC nanometric paste on alumina and Sr-ferrite substrates

Poster presented at 12th Annual Conference of the Materials Research Society of Serbia - YUCOMAT 2010, Herceg Novi, Montenegro, 6–10. septembar 2010

Three-Axis’ Heat Loss Anemometer Comprising Thick-Film Segmented Thermistors

NTC thick-film segmented thermistors were used as anemometer sensing devices. They were screen printed of thick-film thermistor paste based on modified NiMn2O4 fine powder, organic vehicle, and glass frit. Their electrical properties, such as resistance vs. temperature R(T) and thermistor exponential factor B were obtained using measurements in the climatic test chamber. A uniaxial anemometer was formed using a thick-film segmented thermistor, which was placed in the hole drilled in rectangular piece of thermally insulating material. The uniaxial anemometer was used for the optimization of operating point of segmented thermistors as self-heating/wind sensing devices. The dc supply voltage was correlated with the air temperature sub-ranges (RCV). The power save mode such as 30s self-heating/5 min pause was used to measure the thermistor response on stable wind blow. The three-axis' anemometer was formed using five sensor devices placed in five holes drilled in the cubical piece of thermally insulating material: three thermistor sensors measure wind speed on the x, y, z - axes, the fourth sensor Pt 1000 measures the air temperature T, while the fifth sensor (capacitive type) measures humidity H. The obtained sensitivity and inaccuracy were compared with respective ones of other anemometers

Nanocrystalline SnO2-Zn2SnO4 composite thick films applied as humidity sensors

Starting ZnO and SnO2 nanopowders (<100 nm) were mixed in a suitable ratio and calcined at 1050 °C for 2 hours to obtain nanocrystalline SnO2-Zn2SnO4 composite powder. Structural characterization performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) showed that a nanocrystalline composite SnO2-Zn2SnO4 powder was obtained. Thick film paste was made by adding organic vehicles to the powder. Screen printing of four and five layers of thick film paste was performed on two interdigitated test electrode configurations. They were calcined at 500 and 600 °C for 30 minutes. Impedance response was analyzed at several working temperatures (20-60 °C) in the relative humidity range 30-90% and frequency 42 Hz to 1 MHz. Increase in relative humidity lead to a decrease in impedance, especially at lower frequencies. The sensor time delay between absorption and desorption processes was low and the response and recovery times fast showing that the nanocystalline SnO2-Zn2SnO4 composite has potential for application in humidity sensing

Humidity sensing potential of Fe2TiO5—pseudobrookite

Bulk samples of pseudobrookite with an orthorhombic crystal structure were prepared by sintering a mixture of starting hematite and anatase nano powders in the weight ratio 60:40 at three different sintering temperatures (950, 1050 and 1150 °C) resulting in different microstructures determined by SEM analysis. Humidity sensing properties of pseudobrookite were investigated by measuring changes in electrical properties at operating temperatures of 20, 40 and 60 °C in the frequency range 100 Hz–100 kHz in the relative humidity range 30–90% in a climatic chamber. At 100 Hz, and 20 °C the impedance of pseudobrookite sintered at 1150 °C reduced over 5 times in the humidity range 40–90%, and 7 times at 60 °C for pseudobrookite sintered at 950 °C. Detailed analysis of dielectric properties showed that the dielectric constant increased noticeably with increase in humidity at low frequencies. Electrical conductivity change with frequency followed the Jonscher power law, and increased with increase in relative humidity. The determined frequency constant reduced with increase in sample temperature and increase in relative humidity. The conduction mechanism can be explained using the correlated barrier hopping model. Analysis of complex impedance using an equivalent circuit showed the dominant influence of grain boundaries. Low hysteresis (3.6 and 2.99%) was obtained in the 40–90% humidity range at room temperature (25 °C) for pseudobrookite sintered at 950 and 1150 °C. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.This is the peer-reviewed version of the article: Nikolic, M.V., Lukovic, M.D., Vasiljevic, Z.Z., Labus, N.J., Aleksic, O.S., 2018. Humidity sensing potential of Fe2TiO5—pseudobrookite. Journal of Materials Science: Materials in Electronics 29, 9227–9238. [https://doi.org/10.1007/s10854-018-8951-1

Humidity sensing potential of iron manganite (FeMNO3)

Though different metal oxide systems have been investigated and applied in humidity sensing as resistive or capacitive ceramic humidity sensors new materials remain the subject of much research. Iron manganite (FeMnO3) has a bixybyite type structure with the cubic space group. Iron manganite powder was obtained by solid state synthesis (milling in a planetary ball mill, calcination at 1000°C for 2 hours, milling) of starting hematite (Fe2O3) and manganese carbonate (MnCO3) powders mixed in a suitable ratio. Bulk samples were obtained by sintering green samples of pressed powder 8 mm in diameter at 1000oC for 4 hours. Thick film paste was obtained by mixing the powder with organic vehicles. Four layers were screen printed on test interdigitated electrodes on alumina substrate and fired at 900oC for 6 h. XRD analysis of bulk and thick film samples confirmed the formation of iron manganite with a perovskite structure. Scanning electron microscopy (SEM) analysis of freshly cleaved bulk samples showed a network of interconnected grains and pores. A similar structure was observed for the thick film sample surface. Change of complex impedance was monitored in a humidity chamber in the relative humidity range 30-90% at the working temperature of 25°C and frequency range 42 Hz to 1 MHz. In bulk samples at 100 Hz the impedance decreased from 32 (RH 30%) to 3 MΩ (RH 90%), while in thick film samples on test interdigitated electrodes it decreased from 8.24 (RH 30%) to 0.87 MΩ ((RH 90%). The thick film sensor response and recovery was several seconds and a low hysteresis value of 2.78% was obtained showing that iron manganite can successfully be applied for humidity sensing applications

Nanocomposite Zn2SnO4/SnO2 Thick Films as a Humidity Sensing Material

Nanocomposite Zn2SnO4/SnO2 powder was obtained by solid state synthesis from homogenized starting nanopowders of ZnO and SnO2, mixed in the 1:1 molar ratio, structurally and morphologically characterized using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Thick film paste was made by adding organic vehicles to the obtained powder. Three to five layers (layer thickness approx. 12 µm) were screen printed on alumina substrate with small test PdAg electrodes and fired at 600oC for 30 minutes. SEM analysis confirmed formation of a porous structure suitable for humidity sensing. Impedance response was studied at the working temperatures of 25 and 50oC in a humidity chamber where the relative humidity (RH) was 30-90% and measured frequency 42 Hz – 1 MHz. With increase in film thickness the overall sensor impedance increased. It reduced at 100 Hz from 36 to 0.25 MΩ (60 µm), from 23.4 to 0.25 MΩ (48 µm) and from 6.8 to 0.02 MΩ (36 µm) at 25 oC, while at 50 oC and also 100 Hz it reduced from 14 MΩ to 0.72 MΩ (48 µm) for RH 30 and 90%, respectively. The response (8 s) and recovery (10 s) was fast, showing that this nanocomposite has potential for application in humidity sensing.© 20XX IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This is the peer-reviewed version of the article: Nikolić Maria Vesna, Dojčinović Milena, Vasiljević Zorka Ž., Luković Miloljub D., Labus Nebojša, "Nanocomposite Zn2SnO4/SnO2 Thick Films as a Humidity Sensing Material" IEEE Sensors Journal, 20, no. 14 (2020):7509-7516, [https://doi.org/10.1109/JSEN.2020.2983135]Published version: [https://hdl.handle.net/21.15107/rcub_dais_8942

Application of thick film segmented thermistors for measurement and analysis of ground top layer temperature profile

A new sensor for measuring ground top layer temperature profile was formed as a row of 40 thermistor segments connected in series, with which the change of temperature in the soil is mesaured and placed on 550 mm depth. The temperature sensor is multiple protected of humidity, calibrated on room temperature and placed vertically in the hole drilled on the lawn. The main electrical properties of the new sensor based on NTC thick film segmented thermistors are given in brief. The ground top layer temperature profile measurements were done in 40 points at 7am and 2 pm each day from the beginning of November 2017 to the end of February 2018.At the same time and in the same period of time the air temperature were measured and recorded. The results of measurements of ground top layer temperatureT(t,z) were given in daily and monthly diagrams as a function of time t and ground deepness d on z-axis. The correlation between ground top layer temperature profile and air temperature was analyzed: changes of ground temperature gradient and effect of precipitations on ground temperature profile. The results obtained enable study of temperature regime of ground top layer.Novi senzor temperaturnog profila gornjeg sloja zemlje, formiran je kao niz od 40 termistorskih segmenata redno vezanih, kojim se meri promena temperature, u zemlji do dubine d=550 mm. Temperaturni senzor je višestruko zaštićen od vlage, kalibrisan na sobnoj temperaturi i postavljen u vertikalno izbušenu rupu na travnjaku. Osnovne električne karakteristike novog senzora na bazi NTC debeloslojnih segmentiranih termistora date su ukratko. Merenje temperaturnog profila gornjeg sloja zemlje u 40 tačaka vršeno je u 7 i u 14 časova od početka novembra 2017. do kraja februara 2018. godine. U tom periodu u istim terminima merena je i temperatura vazduha. Rezultati merenja temperature gornjeg sloja zemlje T(t,z) prikazani su dijagramima sa dnevnim i mesečnim pregledom kao funkcija vremena t i dubine zemlje d po z-osi. Analizirana je korelacija između temperature gornjeg sloja zemlje i vazduha: promena gradijenta temperature tla i uticaj padavina na temperaturni profil. Dobijeni rezultati omogućavaju dalje proučavanje temperaturnog režima gornjeg sloja zemlje

Nanocrystalline SnO2-Zn2SnO4 composite thick films applied as humidity sensors

Starting ZnO and SnO2 nanopowders (<100 nm) were mixed in a suitable ratio and calcined at 1050 °C for 2 hours to obtain nanocrystalline SnO2-Zn2SnO4 composite powder. Structural characterization performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) showed that a nanocrystalline composite SnO2-Zn2SnO4 powder was obtained. Thick film paste was made by adding organic vehicles to the powder. Screen printing of four and five layers of thick film paste was performed on two interdigitated test electrode configurations. They were calcined at 500 and 600 °C for 30 minutes. Impedance response was analyzed at several working temperatures (20-60 °C) in the relative humidity range 30-90% and frequency 42 Hz to 1 MHz. Increase in relative humidity lead to a decrease in impedance, especially at lower frequencies. The sensor time delay between absorption and desorption processes was low and the response and recovery times fast showing that the nanocystalline SnO2-Zn2SnO4 composite has potential for application in humidity sensing

Characterization of NTC thick film thermistor paste Cu0.2 Ni0.5 Zn1.0 Mn1.3O4

A powder of Cu0.2Ni0.5Zn1.0 Mn1.3O4 composition for custom thermistor was prepared by using a certain mixture of metal oxides and solid state reaction at 1000 °C/4h in air. The obtained thermistor powder was milled in the planetary ball mill and agate mill for a prolonged time to achieve submicron powder. The prepared thermistor powder was further characterized by using XRD and SEM techniques. After that, the thermistor powder was pressed into small disc-shaped samples and sintered at 1150 °C/2h. The sintered samples were also characterized by using XRD and SEM. The main electrical properties such as nominal resistance R and thermistor exponential factor B were measured in the climatic test chamber. After that, the thick film paste was prepared using the same powder, an organic vehicle and a glass frit. The paste was printed on alumina substrate, dried at 150 °C / 30 min and sintered in air at 850 °C / 10 min in the hybrid conveyor furnace. The planar electrodes were printed on the sintered NTC thermistor layer using the PdAg thick film paste. The electric properties of sintered thick film thermistor were also measured in the climatic test chamber. The obtained results were used for development of novel self-heating thermistor applications