Resistance-temperature Characteristics Research Articles

Study on the influence of thermal properties of paraffin on flexible PTC materials

Abstract This paper experimentally studied paraffin’s influence on flexible PTC materials’ temperature resistance and flexibility. Their resistance-temperature characteristics are notably influenced by PA’s phase transition range thermal properties. Specifically, the Curie temperature is intricately linked and determined by the PA’s phase transition temperature. PA’s phase state and proportion in the composite directly impact PTC material flexibility significantly. Specifically, a lower PA phase transition temperature results in better flexibility of PTC materials at room temperature. Additionally, a lower PA content minimizes interference with the overall flexible mesh structure, further enhancing material flexibility. The PTC of this series of formulations showed good adaptive temperature control ability. The thermal control performance can be customized by adjusting the PA.

Carrier scattering and temperature characteristics of mobility and resistivity of Fe-doped GaN

Abstract The electron mobility and dark resistivity of Fe-doped semi-insulating GaN (GaN:Fe) are calculated over the temperature range from 10 K to 500 K by considering the impurities compensation mechanism and majority carrier scattering. The temperature characteristic curve of the mobility exhibits unimodality and the curve of resistivity decreases monotonically with rising temperature. The carrier scatterings induced by ionized impurities, acoustic deformation potential, piezoelectric, and polar optical phonons are analyzed. It is found that the mobility is determined by ionized impurity scattering, piezoelectric scattering, and polar optical phonon scattering in different temperature ranges, and the contribution of acoustic deformation potential scattering is negligible over the entire temperature range. Furthermore, the effects of concentrations of shallow donors and deep acceptors on the temperature characteristic curves of mobility and resistivity, the peak mobility and its corresponding temperature (peak temperature), and the mobility and resistivity at room temperature are discussed. Our simulation shows the calculation results agree very well with the reported experimental and theoretical results when the Fe-related level is selected as 0.58 eV below the conduction band edge. Understanding of thermal properties of dark resistivity and mobility can be useful for optimizing GaN:Fe-based electronic and photonic devices performance in different temperature regimes.

Evaluation of a vacuum insulated temperature calibration device to calibrate thermistor characteristics for skin cancer diagnosis

AbstractRecent methods using thermistors as an early detection of skin cancer require the higher resolution of 5 mK. Previously, the authors developed a vacuum insulated temperature device that calibrates the resistance temperature characteristics of thermistors, so that it improves the temperature resolution and accuracy of skin cancer diagnosis. In this study, the operational methods of the calibration system were compared for improving further accuracy using the temperature calibration device and the oil tank calibration device. The results of the comparison indicated that the temperature calibration device is probably as accurate as the oil tank calibration device.

The critical anti-icing power study of the stayed-cable cylindrical structure based on positive temperature coefficient (PTC) electrothermal film with low Curie temperature

The low temperature and high humidity regions are prone to freezing rain during winter, causing the formation of icicles on the surface of the stayed-cable cylindrical structure. When dislodged by gravity and wind, these icicles may fall and significantly impede the normal movement of vehicles, posing a danger to pedestrians. In this paper, a new organic positive temperature coefficient (PTC) electrothermal film with a Curie temperature of 1 °C is developed by mixing 107 methyl room temperature vulcanized silicone rubber, acetylene black and n-tetradecane through continuous stirring. Subsequently, a numerical simulation of the anti-icing model for the stayed-cable cylindrical structure is established based on the resistivity-temperature characteristics of the new organic PTC electrothermal film. The analysis include variations in the critical anti-icing power of the stayed-cable cylindrical structure with different diameters, horizontal angles, wind speeds and environmental temperatures are analyzed. Finally, the anti-icing experiments are conducted under natural conditions using the stayed-cable cylindrical structure covered with the PTC electrothermal film. The results of the numerical simulation are compared with the natural experimental results, showing a relative error within 3%. This indicates that the anti-icing model of the stayed-cable cylindrical structure is appropriate. The findings of this work provides a theoretical and experimental basis for the subsequent design of an anti-icing device on the basis of PTC electrothermal film.

Structural property, temperature-resistance characteristics and infrared detection performance of manganese cobalt nickel oxide films deposited by sputtering under different oxygen concentrations

Structural property, temperature-resistance characteristics and infrared detection performance of manganese cobalt nickel oxide films deposited by sputtering under different oxygen concentrations

Improved electrical resistivity-temperature characteristics of oriented hBN composites for inhibiting temperature-dependence DC surface breakdown

In this paper, oriented hBN composites with anisotropic thermal conductivity are employed to improve electrical resistivity-temperature characteristics, thus inhibiting the occurrence of DC surface flashover under the temperature gradient by directionally manipulating heat flow. The DC surface flashover performance, electrical resistivity, carrier mobility, and electric field distribution of composites depending on the hBN orientation are studied at different temperatures. When the angle between the hBN basal plane and the axis of the electrodes is 90°, the out-of-plane oriented hBN composite shows the best electrical resistivity-temperature characteristics than that of the polymer filled with ceramic particles of positive temperature coefficient, whose surface flashover voltage is 28% higher than that of the out-of-plane oriented hBN composite with the angle of 0° between the hBN basal plane and the axis of the electrodes under the high-voltage electrode heated at 160 °C. The least rise in carrier mobility and electric field intensity near the GND electrode is the main factor in inhibiting the occurrence of DC surface flashover of the oriented hBN composites at high temperatures. The work presented in this paper will notably influence future research directions and modification solutions for DC dielectric materials.

Temperature characteristics of indentation rolling resistance of belt conveyor

Temperature characteristics of indentation rolling resistance of belt conveyor

Experimental investigation of ns pulse laser processing parameters for machining of Ti-6Al-4V alloy

Traditional machining faces technical barriers in producing microfeatures when the workpiece poses high-strength and temperature-resistance characteristics. Laser is a possible machining approach that works effectively in the aforementioned conditions. The present study utilized a low-power fiber laser system machining of the Ti-6Al-4V alloy surface. The influence of laser processing parameters, for example average power, scanning speed, and pulse frequency, were analyzed on the laser-machined microgroove profiles using the full factorial design of the experiment. The results revealed that the fabricated microgroove profile characteristics, that is, depth, width, heat-affected zone (HAZ), surface roughness, etc. of laser-processed zone strongly depend on the laser processing parameters. Furthermore, the laser microgroove size, that is, depth and width, increases with the increment in laser power combined with low scan speed and low frequency. High laser power (50 W), low scan speed (0.1 mm/s), and low frequency (50 kHz) produce a microgroove with high depth (754.28 µm) and width (285.71 µm). It has been also observed that average power has the most significant impact on the machined surface profile, HAZ, and surface roughness. Moreover, it has also been observed that crack forms at the center of the machined surface is by decreasing scanning speed. Further, lower surface roughness is found at the highest pulse frequency. Hence, the present study recommends laser processing at lower power, high scanning speed, and high pulse frequency to generate a smooth and uniform machined surface.

Effect of gradient distribution of fillers on polymeric PTC thermistors prepared by solution mixing and subsiding method

The PTC materials are widely utilized in regulating components of heat and electricity by virtue of the special resistivity-temperature characteristics. The high room temperature resistivity and low PTC intensity restrict the application of polymeric PTC thermistors. A solution mixing and subsiding method was developed to fabricate the thermistors with different gradient distributions of TiC and CB fillers in PVDF matrix, owing to the low viscosity of dispersion and the difference in density of fillers and solution. The easily settleable TiC assembled at the interface of copper foil and PTC material could provide abundant conductive sites to significantly reduce the interface resistances. The difficultly settleable CB uniformly distributed over the matrix could effectively decrease the bulk resistance. Through adjusting the subsidence time and filler compositions, the optimal conductivity (ρ = 0.58 Ω cm) and PTC intensity (7.0) of polymeric PTC thermistor were obtained. Moreover, the switch temperature was markedly improved and the NTC effect was weakened.

Dynamics of an Electrically Driven Phase Transition in Ca2RuO4 Thin Films: Nonequilibrium High‐Speed Resistive Switching in the Absence of an Abrupt Thermal Transition

AbstractIn Mott‐type resistive switching phenomena, which are based on the metal–insulator transition in strongly correlated materials, the presence of an abrupt temperature‐driven transition in the material is considered essential for achieving high‐speed and large‐resistance‐ratio switching. However, this means that the freedom of material/device design in applications is significantly reduced for this type of switching by the strict requirement of transition abruptness. Here, high‐speed, abrupt resistive switching with a switching time of 140 ns is demonstrated in epitaxial films of Ca2RuO4/LaAlO3 (001), which is a material with a nonthermal metal–insulator transition driven by current, despite the complete absence of an abrupt thermal transition in the resistivity–temperature characteristics. Highly smooth negative‐differential‐resistance behavior, very high cycling stability, and an endurance over 106 cycles are also demonstrated in the current–voltage and current–time characteristics, which confirm the nonstochastic nature of the abrupt switching. These results suggest that strict control of the resistivity–temperature characteristics is not necessarily required in a material with a nonthermal‐type metal–insulator transition to obtain high‐speed resistive switching because of the independence of the dynamics from those of the thermal transition, and this phenomenon potentially has important advantages in resistive switching applications.

Optimization of large magnetoresistance of polycrystalline Bi film

The oriented growth and morphology of polycrystalline bismuth (Bi) films deposited on insulating substrates is investigated based on the molecular beam epitaxy method. The film thickness effect on the resistance-temperature characteristics and magnetoresistance properties is analyzed. The Bi film resistivity with thickness range [25, 65] nm is investigated using the four-probe method at 2–300 K. The magnetic field contributes to opening the energy gap of Bi thin films and a more obvious opening of the energy gap is observed in the thinner films. The Bi film has the weak antilocalization (WAL) effect and the thickness increase affects the WAL effect. The large magnetic field is beneficial to the observation of the WAL effect. The temperature-dependent resistivity of Bi thin films is described based on the Ziman-Faber theory. The competition between the metal surface state and the bulk state explains the semimetal-semiconductor transition and the magnetoresistance effect in the thickness range [25, 65] nm. In addition, the thickness effect on the magnetoresistance property is researched, which provides a new approach to specify the Bi thin film magnetoresistance.

Non-recoverable creep behavior and micro-structural analysis of recycled bitumen containing aged bitumen and TLA modified bitumen

TLA modified bitumen can effectively improve the rutting resistance of asphalt mixture, and the application of reclaimed asphalt pavement (RAP) in TLA modified bitumen needs to be further improved. In order to further improve the rutting resistance of bitumen, and to more comprehensively evaluate the high temperature resistance characteristics, a variety of recycled bitumen containing different contents of aged bitumen and TLA modified bitumen were prepared. Then, based on the penetration grades (PG) analysis and multiple stress creep recovery (MSCR) tests, the effects of temperature, time, aging, loading stress and aged bitumen content on the non-recoverable creep behavior of recycled bitumen were evaluated. Finally, the enhancement mechanism of the rutting resistance was analyzed from the aspects of morphology and modulus by atomic force microscopy (AFM). Results indicate that recycled bitumen with a higher content of aged bitumen can show better creep recovery characteristics under constant temperature changes, and is less susceptible to aging and high stress. Under the same traffic load conditions, the service environment of recycled bitumen can be increased by 6 ℃ for every 20% increase in the aged bitumen content. Aged bitumen can help TLA modified bitumen better accumulate heavy components, enhance the overall surface roughness and material stiffness, which can contribute to the better resistance to the rutting deformation.

Flexible Liquid Crystal Thermistor and Its Application in Temperature Sensor

Liquid crystals (LCs) are an excellent material for temperature sensors because of their thermistor properties of negative temperature coefficient (NTC). In this study, a flexible thermistor, made by the indium tin oxide (ITO)-polyethylene terephthalate (PET) flexible substrate and the nematic LC (NLC) NHG715600-100 with negative dielectric anisotropic was presented and its application in temperature sensor was explored. It offers low power consumption, high transparency, high sensitivity, and high accuracy achieved through temperature-resistance characteristics. Using ln <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}$ </tex-math></inline-formula> as the intrinsic variable for characterizing temperature, the sensor achieves a better non-linear fit to the temperature at low voltages and reaches a maximum sensitivity of −6.615%/K at 0.05 V and 500 Hz. The transmittance reaches 61.29%–92.15% in the visible range, and the rising and fall times respectively reduces by 75.19% and 73.38% compared to the rigid LC thermistor. In addition, it also continues to show remarkable stability, recovery, and durability in various tests. Compared with common thermistors, this device is smaller and lighter in weight, resulting in a wider range of applications in temperature sensing.

Dual-gated hBN/bilayer-graphene superlattices and the transitions between the insulating phases at the charge neutrality point

We report on transport properties in dual-gated hexagonal boron nitride (hBN)/bilayer-graphene (BLG) superlattices. Here, BLG is nontwisted, i.e., plain. This paper focuses on the charge neutrality point (CNP) for a plain BLG. Under a perpendicular magnetic field, transitions between two insulating phases at the CNP are detected by varying a displacement field with the study on the resistance-temperature characteristics and the magnetoresistance. This work opens avenues for exploring the global phase diagram of the hBN/BLG superlattices beyond the CNP.

Synergistic improved electrical resistivity-temperature characteristics and DC breakdown strength in insulating XLPE composites by incorporating positive temperature coefficient particles

Weakening the electrical resistivity-temperature dependence of cross-linked polyethene (XLPE) is an effective way to enhance the electric field uniformity of high-voltage direct current (HVDC) cables. Therefore, an attempt is made to suppress the negative temperature coefficient (NTC) of electrical resistivity by incorporating BaTiO3-based ceramic fillers with positive temperature coefficient (PTC) electrical resistivity into XLPE. Morphology characterization indicated that PTC particles were well dispersed in the XLPE matrix. The measurements of electrical resistivity and DC breakdown strength are carried out from 30 °C to 90 °C. The electrical resistivity and DC breakdown strength of the sample at high temperatures were significantly improved with the introduction of PTC particles, which is attributed to the deep traps near the Curie temperature region. The high doping content has a better suppression of the NTC effect. The activation energy (0.63 eV) and NTC strength (1.74) of the sample with the addition of 10 wt% of PTC are considerably reduced compared with XLPE. The content of PTC particles was positively correlated to the enhancement of electrical resistivity and DC breakdown strength. The optimum content for DC breakdown strength is about 5 wt%. The low electrical resistivity-temperature dependence of insulation performance shows a potential to obtain temperature-stable HVDC cable insulation.

Interfacial microstructure and resistance-temperature characteristics of Ti(C, N)-based cermet/LaCrO3–Y2O3 laminated composite

A laminated Ti(C, N)-based cermet/LaCrO3–Y2O3 composite which is used for making smart temperature measuring cutting tool was prepared by spark plasma sintering. In this work, the interfacial microstructure and resistance-temperature (R-T) characteristics of double-layer and triple-layer structures with different layer thicknesses of LaCrO3–Y2O3 were investigated, the mechanism of interfacial evolution and changes in R-T characteristics of double-layer composites prepared at different sintering temperatures were studied, and the temperature measuring performance of the smart tool was tested. The results indicated as the thermosensitive ceramic layer thickness was 1.5 mm, the laminated composites showed the best performance. For the double-layer structure, its starting measuring temperature was 457K, and the thermal constant B reached 14194K. Cutting tests showed the resistance of the smart tool fluctuated sharply with cutting time, and the resistance variation reached up to 2 × 108Ω within 1 s, which indicated that the smart cutting tool had a short response time and high temperature measuring sensitivity.

CaMn0.05Zr0.95O3–NiMn2O4 composite ceramics with tunable electrical properties for high temperature NTC thermistors

A series of novel high temperature negative temperature coefficient (NTC) composite ceramics based on (1-x)CaMn0.05Zr0.95O3-xNiMn2O4 (x = 0, 0.1, 0.2, 0.3) were fabricated by using the solid-state method. The Rietveld refinement method and backscattered electron (BSE) image confirmed the absence of any other phase. The conduction mechanism of the composite ceramics was determined by analyzing the complex impedance and resistance-temperature characteristics, which could be related to the formation of a continuous Mn3+-O-Mn4+ network. The effect of spinel content on the high temperature stability was analyzed using aging tests. The ρ400°C, ρ700°C and B400/700 values of the NTC thermistors were determined to be 4.9 × 106–1.2 × 104, 1.4 × 105–0.8 × 103 Ω cm and 12739-5712 K, respectively. This indicated that the electrical properties could be tuned by adjusting the weight ratio of CaMn0.05Zr0.95O3 and NiMn2O4. The findings obtained in this study reveal that the composite NTC thermistor exhibits a good application potential at high temperatures and under harsh environments.

Improved electrical resistivity-temperature characteristics of insulating epoxy composites filled with polydopamine-coated ceramic particles with positive temperature coefficient

Incorporating positive temperature coefficient (PTC) ceramic particles into polymer matrices provides a promising solution to suppress the distortion of DC electric field within polymeric insulation caused by the negative temperature coefficient (NTC) of electrical resistivity. However, along with the suppressed NTC effect comes the decrease of dielectric strength due to the agglomeration of PTC particles. Here, we addressed this issue in the epoxy resin system by coating polydopamine onto PTC particles to improve the compatibility with matrix, thus achieving a maintained DC breakdown strength. The improved evenness of PTC particles dispersion also provided sufficient interface to generate interface charge traps, which contributed to the increase of electrical resistivity at elevated temperature. Combined with temperature dependent charge carrier amount affected by PTC filler, NTC effect of epoxy composites was further mitigated and the maximum DC electric field was reduced by 49% within insulation assessed by the simulation of HVDC bushing. The method proposed in this paper is crucially important for the reliable and economic application of composite dielectrics under harsh conditions.

Fabrication and characterization of screen printed NiMn2O4 spinel based thermistors

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.

Carrier Scattering and Temperature Characteristics of Mobility and Resistivity of Fe-Doped Gan

Carrier Scattering and Temperature Characteristics of Mobility and Resistivity of Fe-Doped Gan