Thermal-sensitive Materials Research Articles

A general thermo-elastoplastic constitutive theory for thermal-sensitive materials with temperature-dependent properties

A general thermo-elastoplastic constitutive theory for thermal-sensitive materials with temperature-dependent properties

Photonic enhanced flexible photothermoelectric generator using MXene coated fullerenes modified PEDOT:PSS films for solar energy harvesting

Photothermoelectric conversion technology from light and heat into electricity has been proved to be an effective method and associated with photothermal and thermoelectric (TE) effects. Wherein, there are great challenges in the structural design that the cold and hot side distribution in planar structure limits the selection of materials to obtain the high output voltage. Here, the half-vertical heterojunction structure of the photothermoelectric generator (PTEG) is adopted for enhanced performance to realize effective energy utilization. The PTEG is constituted by the MXene half-coated fullerenes-modified PEDOT:PSS to obtain wide spectral response. The output voltage of the prepared PTEG can be stabilized at 2.15 mV under the irradiation of a laser wavelength 808 nm with power of 25 mW. Under simulated sunlight irradiation, with the assistant of fullerenes, the output voltage was improved by 43.83 % from 146 to 210μ V. Furthermore, the voltage can be enhanced by TE voltage increasement via temperature gradient, and the 66.19 % increment of output voltage is evaluated from 210 to 349 μV. In addition, PTEG has also excellent electrothermal effect, which was applied into detecting whether the battery is fully charged via adhering to thermal sensitive materials. By means of half-vertical heterojunction structure to the PTEG, a new choice for the PTEG is provided to make better use of sunlight.

Laser-assisted direct coating of Graphene-Based films on plastic substrates with bactericidal properties

Bacterial growth on surfaces is a substantial problem in medical equipment, fresh food storage, and water supply industries. Antibacterial coatings offer a preferred method to prevent this dangerous hazard. However, to provide a complete solution, the developed coating must not only efficiently prevent bacterial growth and consist of cost-effective, stable, and bio-friendly materials but also offer a simple coating method. In this work, we use novel laser processing that offers significant advancements, including (1) fast, single-step, and waste-free synthesis, (2) allowing direct printing of graphene over any substrate, including thermal-sensitive materials (i.e., polymers), and (3) micron-resolution patterning of the coated materials. We use an intense laser beam to fabricate metal-oxide/graphene nanoparticle composite films directly on plastic surfaces. The metal-oxide nanoparticles (cobalt and copper) are tested for antibacterial activity. Due to the combined formation, the metal-oxide nanoparticles are highly dispersed and firmly adhered to the graphene matrix. Notably, the structure and properties of the laser product, such as the nanoparticle's size and the graphitization level, can be controlled by tuning laser parameters. The composite coatings demonstrate excellent antibacterial activity. Studying substrates coated with different metal compositions found that 4.5–5 % of metal contents have antibacterial activity (percentage inhibition) by 89 % (PBS). Additionally, leaching studies demonstrate that the fabricated substrates are stable in different pH solutions.

Design of a High Sensitivity Pirani Gauge Based on Vanadium Oxide Film for High Vacuum Measurement

We have designed a hot-plate-type micro-Pirani vacuum gauge with a simple structure and compatibility with conventional semiconductor fabrication processes. In the Pirani gauge, we used a vanadium oxide (VOx) membrane as the thermosensitive component, taking advantage of the high temperature coefficient of resistance (TCR) of VOx. The TCR value of VOx is -2%K-1∼-3%K-1, an order of magnitude higher than those of other thermal-sensitive materials, such as platinum and titanium (0.3%K-1∼0.4%K-1). On one hand, we used the high TCR of VOx to increase the Pirani sensitivity. On the other hand, we optimized the floating structure to decrease the thermal conductivity so that the detecting range of the Pirani gauge was extended on the low-pressure end. We carried out simulation experiments on the thermal zone of the Pirani gauge, the width of the cantilever beam, the material and thickness of the supporting layer, the thickness of the thermal layer (VOx), the depth of the cavity, and the shape and size. Finally, we decided on the basic size of the Pirani gauge. The prepared Pirani gauge has a thermal sensitive area of 130 × 130 μm2, with a cantilever width of 13 μm, cavity depth of 5 μm, supporting layer thickness of 300 nm, and VOx layer thickness of 110 nm. It has a dynamic range of 10-1~104 Pa and a sensitivity of 1.23 V/lgPa. The VOx Pirani was designed using a structure and fabrication process compatible with a VOx-based uncooled infrared microbolometer so that it can be integrated by wafer level. This work contains only our MEMS Pirani gauge device design, preparation process design, and readout circuit design, while the characterization and relevant experimental results will be reported in the future.

Tunable band gap and wave guiding in periodic grid structures with thermal sensitive materials

In this paper, a tunable lattice structure composed of thermal sensitive materials is proposed. A series of metal films are periodically attached to the structure as a local heat source to produce a periodic heat field in the lattice structure. Local change of Young's modulus triggered by periodic thermal fields can be applied to manipulate the band structure and waveguide of such lattice structure. Therefore, a thermal-effected model based on finite element method is employed to obtain the dispersion curves and the transmission spectrum of in-plane wave propagation. Results shows that band width and locations of band gaps can be effectively manipulated by controlling the periodic thermal fields. More than that, by injecting different heat fluxes at different locations, different defect states can be generated with the structure intact. Based on this, the waveguide can be turned on or off at different frequencies by changing the thermal fields. Finally, a kind of frequency divider is designed depending on the properties of waveguides. This work may pave theoretical foundation for intelligent control of band gaps and waveguides of lattice structures with thermal sensitive materials, and is a meaningful try for application in the area of acoustic device.

WEDM Machining Performance of Al Based Metal Matrix Composites Reinforced with Rice Husk Ash

With the enhancement in science and technology, necessity of complex shapes in manufacturing industries becomes essential for more versatile applications. These lead to demand for light weight and durable materials for applications in aerospace, defence, automotive, as well as sports and thermal management. Due to its high-tech structural, functional applications like defence, automobile, aerospace, thermal sensitive materials. Al-Matrix composites are considered as one of those classes of advanced engineering materials. In the present study, Al-RHA (Rice Husk Ash) composites are prepared by powder metallurgy route using 10% and 15% RHA by weight as reinforcement. Presence of abrasive particles leads to difficulty of conventional machining on Al-RHA composites hence non-conventional machining WEDM (Wire-Electric Discharge Machining) has been investigated. Suitable machining parameters for composites using wire EDM have been tried to get maximum material removal rate and speed. Optimizations of experimental parameters have been studied using Taguchi and Anova to standardize the process parameters for machining. Prime process parameters like servo-voltage, pulse-on time and pulse-off-time have been taken into consideration to study cutting quality of Al-RHA Metal matrix Composite using cutting speed as response parameters while effect of RHA weight fraction addition is also considered for evaluation to understand its influence on affecting the response.

SiGe/Si Multi-Quantum-Well Micro-Bolometer Array Design and Fabrication with Heterogeneous Integration.

The micro-bolometer is important in the field of infrared imaging, although improvements in its performance have been limited by traditional materials. SiGe/Si multi-quantum-well materials (SiGe/Si MQWs) are novelty thermal-sensitive materials with a significantly high TCR and a comparably low 1/f noise. The application of such high-performance monocrystalline films in a micro-bolometer has been limited by film integration technology. This paper reports a SiGe/Si MQWs micro-bolometer fabrication with heterogeneous integration. The integration with the SiGe/Si MQWs handle wafer and dummy read-out circuit wafer was achieved based on adhesive wafer bonding. The SiGe/Si MQWs infrared-absorption structure and thermal bridge were calculated and designed. The SiGe/Si MQWs wafer and a 320 × 240 micro-bolometer array of 40 µm pitch L-type pixels were fabricated. The test results for the average absorption efficiency were more than 90% at the wavelength of 8–14 µm. The test pixel was measured to have a thermal capacity of 1.043 × 10−9 J/K, a thermal conductivity of 1.645 × 10−7 W/K, and a thermal time constant of 7.25 ms. Furthermore, the total TCR value of the text pixel was measured as 2.91%/K with a bias voltage of 0.3 V. The SiGe/Si MQWs micro-bolometer can be widely applied in commercial fields, especially in early medical diagnosis and biological detection.

Tool Downscaling Effects on the Friction Stir Spot Welding Process and Properties of Current-Carrying Welded Aluminum–Copper Joints for E-Mobility Applications

According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools—i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum–copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process.

Innovative applications of freeze-drying to produce compound formula instant foods: A review

Due to the fast pace of life around the globe and the increasing demand for high-quality convenience foods by consumers, instant foods have attracted widespread attention. By adjusting the process and formula, the quality of compound formula foods can be optimized. Drying is a common way. However, conventional drying methods have some shortcomings. Freeze drying can overcome most of them. Foam mat freeze-drying can increase the drying area of materials, and the drying efficiency of it is also higher. For thermal-sensitive materials, it is a suitable drying method. Microwave freeze drying, infrared drying, and others are relatively new processing technologies that are suitable for the production of instant foods. This paper provides an overview of recent developments in processing technologies for the production of compound formula instant foods.

Effect of sintering temperature on structural and electrical properties of Mn0.55Fe1.25Cu2Ni2.2O4+δ NTC thick film

Mn0.55Fe1.25Cu2Ni2.2O4+δ glass-free thick films with negative temperature coefficient (NTC) character were fabricated on Al2O3 substrate by screen printing technology. The microstructural, electrical parameters, and cation distribution of materials varied with the slight change in sintering temperature (1000 °C, 1025 °C, 1050 °C) were investigated. All the thick film samples showed spinel structure of its main phase. CuAl2O4 phase was found when the sintering temperature was above 1025 °C, which is of practical importance for copper-containing thermal-sensitive materials bonding Al2O3 substrate. Both the room-temperature resistance R25 and material constant B value increased as temperature increased, R25 in the range of 17.3–125 kΩ, and B lying in the range of 2824–3074 K. Such feature was attributed to the redistribution of the multivalent state Mn, bivalence Fe and Cu cations with increasing sintering temperature. The optimal sintering temperature was 1000 °C due to its pure phase, best crystallinity, and lowest B value (2824 K), which was a good candidate for temperature monitoring and control in a relative widen temperature range.

Numerical Simulation and Experimental Verification of Ultra-High Frequency Induction Cladding with Metal Wire

This paper proposes a novel approach of ultra-high frequency induction cladding with metal wire, in which AISI type 316L stainless steel wire (SS316L) is coated on gray cast iron to improve the specific surface properties of gray cast iron. The corresponding numerical model coupled with electromagnetic field and temperature field has been developed to obtain the representative distribution of induction heat. The established numerical model has been validated experimentally, and the temperature distribution captured in experiment shows good agreement with the calculated results. Given the high heating efficiency and selective heating characteristics of ultra-high frequency induction cladding technology, this method can be applied to the micro-crack repair on the surface of the thermal-sensitive materials.

NTC thermo-sensitive ceramics with low B value and high resistance at low temperature in Li-doped Mn0.6Ni0.9Co1.5O4 system

In this paper, negative temperature coefficient (NTC) thermistors Mn0.6Ni0.9Co1.5−xLixO4 (x = 0, 0.05, 0.1, 0.2) used for low temperature were synthesized by the co-precipitation method. XRD indicates the formation of single-phase LiMn2O4 spinel. SEM shows that the incorporation of lithium reduces the sintering activity and increases the grain size 2 to 6.8 μm. XPS presents that the remarkable change of the contents of Mn3+/Mn4+ and Co2+/Co3+ confirms the conduction mechanism of the variable ion transition. The relationship between the electrical resistivity and the temperature shows that the doping of Li benefits the Mn0.6Ni0.9Co1.5O4 material to increase the resistance value and reduce the material constant B value. This is significant because of traditional thermal-sensitive materials with high resistance and high B, while low-B high resistance materials have been scarcely reported. The materials are expected to be used for deep sea thermal detector.

Effect of Thermally Induced Oxygen Vacancy of α-MnO2 Nanorods toward Oxygen Reduction Reaction.

MnO2 has been explored for various applications in environmental and energy aspects. However, the thermal sensitivity of the MnO2 crystal structure never been studied. As a potential cathode material for fuel cell, α-MnO2 has a higher specific activity than Pt/C based on per metals cost. In this work, the physical and electrochemical properties of α-MnO2 nanorods were explored for the first time under thermal treatment with different temperatures (300, 400, and 500 °C). Under thermal treatment, oxygen vacancies were induced. The high-angle annular dark-field (HAADF) images and electron energy loss spectroscopy (EELS) have been taken to explore oxygen vacancies of α-MnO2 materials. From EELS and X-ray photoelectron spectroscopy (XPS) analysis, the oxygen vacancies on the α-MnO2 nanorods were strengthened with the temperature increasing. The sample with 400 °C treatment exhibited the best performance toward ORR, excellent methanol tolerance and higher stability compared to commercial Pt/C in alkaline media due to its combination of preferable growth on (211) plane and moderate oxygen vacancies as well as coexistence of Mn (IV)/ Mn (III) species. It was also observed the α-MnO2 nanorods tended to become longer and thinner with increasing temperature. This work suggests that the α-MnO2 nanorods are thermal sensitive materials and their performance for ORR can be boosted under certain temperatures.

Metal transfer and thermal characteristics in drop-on-demand deposition using ultra-high frequency induction heating technology

In the paper a drop-on-demand deposition system using ultra-high frequency induction heating technology is proposed for the aim of depositing metal materials with high melting point onto the substrate at a low thermal input. The numerical model coupled with electromagnetic field, thermal field and flow field was established to investigate the metal transfer and thermal characteristics of the deposition process. Results indicate that the metal droplet can be deposited onto the substrate at a low thermal input. The effects of current frequency and current density on the deposition temperature and time duration of the deposition were also numerically studied. Analysis of the electromagnetic force and temperature of the pendent molten metal during deposition demonstrates that the current frequency as well as current density influences the time duration by determining the electromagnetic force and the heating rate. The numerical model was verified by experiments, and the experimental results show good agreement with the calculated results. With the advantage of depositing high melting point material while limiting the thermal input for the substrate, the drop-on-demand deposition method using ultra-high frequency induction heating technology is expected to be applied in metal droplet-based applications where the thermal-sensitive materials are used.

Thermoresponsive Memory Behavior in Metallosupramolecular Polymer-Based Ternary Memory Devices.

Thermal-sensitive materials, such as metallosupramolecular polymers, have been integrated into devices for a broad range of applications. However, the role of these materials is limited to temperature sensing and the lack of a memory function. Herein, we present novel [PolyCo-L1xL2y-PF6]-based organic resistive memories (ORMs) possessing both a thermal response and ternary memory behavior with three electrical resistance states [high (HRS), intermediate (IRS), and low (LRS)]. Furthermore, the thermal behavior can be memorized by the Al/[PolyCoL1xL2y-PF6]/indium-tin oxide devices. Heating and cooling the devices at a LRS results in a switch from the LRS to a HRS and further to a LRS, indicating that the thermal behavior can be efficiently memorized. Following the heating and cooling process, devices at a HRS retain their ternary memory behavior, while an unstable resistance variation behavior is observed at the IRS. We propose a possible mechanism for the thermoresponsive memory behavior, and this finding provides a guide for the design of future thermoresponsive ORMs.

Thermal sensitive flexible phase change materials with high thermal conductivity for thermal energy storage

Application of thermal energy storage technology in practical engineering has been inhibited due to the constant strong rigidity of phase change materials (PCMs) at any given temperature. To solve this problem, a novel kind of thermal sensitive flexible PCMs was developed by using difunctional olefin blockcopolymer (OBC) replacing conventional supporting materials. Due to phase separation morphology, OBC presents physical crosslinked network and elasticity which is essential for macroscopical elastic deformation of composite. The developed PCMs based on OBC not only exhibit the same high latent capacity and stable shape as shape-stabilized PCMs, but also present thermal sensitive flexibility with the melting point of paraffin Tparaffin,m as the stimulus. Below the melting point of OBC-TOBC,m, the transformation from rigid to flexibility is reversible. The above excellent flexibility of the developed PCMs contributes to reducing thermal contact resistance and improving poor installation for conventional PCMs in energy storage field, such as in energy-storage air-conditioning and compact electron device thermal control, especially in spacecraft thermal control system. Furthermore, thermal conductivity was improved to a breakthrough level (479% of original rate) by adding 3wt.% of the maximum size of expanded graphite, which is based on the guidance of the novel calculation model on account of thermal conductivity for thermal sensitive flexible PCMs.

Effect of different drying techniques on bioactive components, fatty acid composition, and volatile profile of robusta coffee beans

This study investigated the effect of different drying techniques, namely, room-temperature drying (RTD), solar drying (SD), heat-pump drying (HPD), hot-air drying (HAD), and freeze drying (FD), on bioactive components, fatty acid composition, and the volatile compound profile of robusta coffee beans. The data showed that FD was an effective method to preserve fat, organic acids, and monounsaturated fatty acids. In contrast, HAD was ideal for retaining polyunsaturated fatty acids and amino acids. Sixty-two volatile compounds were identified in the differently dried coffee beans, representing 90% of the volatile compounds. HPD of the coffee beans produced the largest number of volatiles, whereas FD resulted in the highest volatile content. A principal component analysis demonstrated a close relationship between the HPD, SD, and RTD methods whereas the FD and HAD methods were significantly different. Overall, the results provide a basis for potential application to other similar thermal sensitive materials.

The microstructures and electrical properties of Y-doped amorphous vanadium oxide thin films

One of promising approaches for further improving the sensitivity of microbolometer arrays with greatly-reduced pixel size is using the thermal-sensitive materials with higher performance. In this paper, Y-doped vanadium oxide (VOx) thin films prepared by a reactively sputtering process exhibit enhanced performance for the microbolometer application compared with frequently-applied VOx thin films. Both undoped and Y-doped VOx thin films are amorphous due to the relatively low deposition temperature. Y-doped VOx thin films exhibit smoother surface morphology than VOx due to the restrained expansion of particles during depositions. Y-doping increases the temperature coefficient of resistivity by over 20% for the doping level of 1.30at%. The change rate of resistivity, after aging for 72h, of thin films was reduced from about 15% for undoped VOx to 2% due to the introduction of Y. Moreover, Y-doped VOx thin films have a low 1/f noise level as VOx ones. Y-doping provides an attractive approach for preparing VOx thermal-sensitive materials with enhanced performance for microbolometers.

Laser-Assisted Waterjet Micro-Grooving of Silicon Wafers for Minimizing Heat Affected Zone

Laser-assisted waterjet micro-machining can significantly reduce the thermal damages to the workpiece as compared to the traditional laser machining process, and hence can overcome the problems associated with laser machining, such as the formation of heat-affected zone, which is a serious issue for thermal sensitive and functional materials. An experimental study on micro-grooving of monocrystalline silicon wafers is reported in this study to explore the effects of process parameters on the groove depth and width as well as the heat-affected zone (HAZ) width. Predictive models based on dimensionl analysis are then developed for estiamting the groove characteristics.

Preliminary Study of Ultrasonic Assisted Underwater Laser Micromachining of Silicon

The disturbances of vapor bubble to a laser beam in the underwater laser machinig process importantly limits the material removal rate and cut quality obtained. This issue is more essential for the laser micromachining process that a precise and small trench cut is highly needed. In this study, the ultrasound was used to energize and break up the bubble while the laser beam was performing a cut in water. Silicon was used as a work sample in this study as its significant usage in many micro-components. An ultrasonic transducer was located nearby the workpiece in an attempt to vibrate surrounding water. The results revealed that an increase in ultrasonic power increased the width and depth of cut channel. In addition, the workpiece surface obtained after the ablation was clean as similar to that performed by the ultrasonic cleaning. This combination of laser machining and ultrasonic cleaning processes can be another effective approach to cut thermal sensitive materials and also small components whose thermal damage and deposition of cut debris can be harmful to their functionality after laser ablation.