High Temperature Applications Research Articles

High-temperature oxidation behaviors of Co-free Cr30Fe30Ni30Al5Ti5 dual-phase multi-component alloys with multi-scale nanoprecipitates

In the context of the growing research interest in multi-component alloys (MAs) and their exceptional performance under extreme environments, the high-temperature oxidation resistance and applications of MAs have attracted significant attention in the field of metallic materials. While the cost-effective and mechanical properties of Co-free MAs are of great importance, their oxidation resistance remains insufficiently understood. In this work, we designed multiple heterogeneous structures within a cast dual-phase Cr30Fe30Ni30Al5Ti5 MA by tailoring the Al and Ti ratio, which consists of body-centered-cubic (BCC) grains reinforced by multi-scale nanoprecipitates (i.e., L21, B2, and η phase) and an L12-strengthened face-centered cubic (FCC) skeleton. Isothermal oxidation experiments at 800 °C, 1000 °C, and 1200 °C with varying exposure durations were conducted. The oxidation kinetics at 800 °C and 1000 °C followed a parabolic law, while both low weight increment and oxidation rate confirm remarkable oxidation resistance. At 800 °C, the oxides mainly consist of Cr2O3 and Al2O3, while are dominated by (TiO2 + Cr2O3) and the mixed oxides of Al2O3, TiO2, and Ti2O above 1000 °C. Importantly, the inability to form a continuous Al2O3 oxide scale at higher temperatures led to a deterioration in oxidation resistance. These findings offer valuable insights into underlying mechanisms contributing to oxidation resistance for Co-free MAs.

Exploring Rare-Earth compound ErMn2Si2 for thermoelectric and photoelectrochemical applications using Density functional theory

The physical and magnetic properties of the ErMn2Si2 compound are investigated with PDE and RPBE functions using the generalized gradient approximations (GGA) approach within the ferromagnetic phase. The obtained structural optimization results carried out using general gradient approximation (GGA) applying Perdew-Burke-Ernzerhof (PBE), which were consistent with the previously experimental findings. The result shows that the ferromagnetic phase of ErMn2Si2 exhibits the highest thermodynamic stability. Furthermore, the electronic band structure analysis within the ferromagnetic phase indicates the metallic behaviour of the compound in both spin channels. A hybridization between Er-f and Mn-d states is observed in the valence band along with the Si-p state in the conduction band. Total magnetic moments confirm the ferromagnetic characteristics of the ternary inter-metallic ErMn2Si2 compound. In this study, analysis of the Seebeck coefficient was discussed in detail. The electrical and thermal conductivities of the compound were investigated in a broad range of temperatures (0 to 600 K). Additionally, we present the quasi-harmonic model-calculated thermodynamic characteristics as a function of pressure (0–60 GPa) and temperature (0–1200 K). Evaluating the optical characteristics, ErMn2Si2 shows strong dielectricmaterial characteristics in the visible regions of the electromagnetic spectrum. Further, the figure of merit (ZT) was probed. The enhanced ZT values of ErMn2Si2 compounds at elevated temperatures make it a potential candidate for high-temperature applications especially for thermoelectric devices. These results may be useful for further investigations of the rear-earth substituted ErMn2Si2-based compounds for various applications.

Preparation method and industrialization of Ta-based ultra high temperature ceramic Tujia jar tea baking jar materials

The production materials of traditional Tujia jar tea often face problems such as poor high-temperature performance and poor durability. To improve the temperature resistance and durability of tea baking utensils, this study proposes a new type of TaC ultra-high temperature ceramic. TaC ceramics with excellent performance were prepared through powder metallurgy technology, including high-energy ball milling to ensure uniform mixing, followed by compression molding and high-temperature sintering. The test results demonstrated excellent mechanical properties, with a maximum depth of 948.67 nm and a contact depth of 954.45 nm, proving outstanding compressive and wear resistance. The hardness reached 21.4±0.5 Gpa, and the elastic modulus was 397.2±8.7 Gpa, both of which indicate its stability under high loads. In addition, the fracture toughness was 2.8±0.2 Mpa*m1/2. At a high temperature environment of 1000 °C, the oxidation rate constant of TaC ceramics was only 0.183 mg2 *cm−4 *h, which demonstrates its excellent high-temperature stability. The development of this TaC ceramic not only strengthened the traditional production process of Tujia teapots and tea roasting teapots, thereby improving the product’s service life, but also holds potential for other industrial applications that demand ultra-high temperature stability. These contributions provide new directions for the high-temperature application of ceramic materials and bring tangible economic and technological value to related industries.

Optical Basicity for Understanding the Lewis Basicity of Chloride Molten Salt Mixtures.

Currently, there is a lack of reliable measurement techniques for understanding the basicity of molten chloride salts. Optical basicity, an ultraviolet-visible (UV-vis) spectroscopic method for measuring Lewis basicity, is explored for its applicability to molten chloride salts. Shifts in probe ion (Pb2+ and Bi3+) electronic transitions are observed that show that cations in chloride salts follow the same basicity series as in oxide melts, and an increase in basicity is observed with increasing temperature. Pb2+ and Bi3+ are validated as effective probe ions in alkali, alkaline earth, and aluminum-sodium chloride molten salts. However, the utility of Bi3+ is limited by the volatility of BiCl3 at high temperatures, posing a challenge for use in high-temperature molten salt applications. Since optical basicity measures the extent of electron donation, it may be a useful metric for electrochemical corrosion.

Investigation of High-Speed Rubbing Behavior of GH4169 Superalloy with SiC/SiC Composites

The silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC), ceramic matrix composite (CMC) and nickel-based superalloy GH4169 can be utilized in high-temperature applications due to their high-temperature performance. The SiC/SiC composites are commonly used in turbine outer rings, where they encounter friction and wear against the turbine blades. This high-speed rubbing occurs frequently in aircraft engines and steam turbines. To investigate the tribological behavior of these materials, rubbing experiments were conducted between the SiC/SiC and the GH4169 superalloy. The experiments involved varying the blade tip speeds ranging from 100 m/s to 350 m/s and incursion rates from 5 μm/s to 50 μm/s at room temperature. Additionally, experiments were conducted at high temperatures to compare the tribological behavior under ambient conditions. The results indicated that the GH4169 superalloy exhibited abrasive furrow wear during rubbing at both room temperature and high temperature. Furthermore, at elevated temperatures, some of the GH4169 superalloy adhered to the surface of the SiC/SiC. The analysis of the experiments conducted at ambient temperatures revealed that the friction coefficient increased with higher blade tip velocities (100~350 m/s). However, the coefficient was lower at high temperatures compared to room temperature. Furthermore, significant temperature increases were observed during rubbing at room temperature, whereas minimal temperature changes were detected on the rubbing surface at high temperatures.

A Processible and Ultrahigh-temperature Organic Photothermal Material through Spontaneous and Quantitative [2+2] Cycloaddition-Cycloreversion.

Energy conversion, particularly light to heat conversion, has garnered significant attention owing to its prospect in renewable energy exploitation and utilization. Most previous efforts have focused on developing organic photothermal materials for low-temperature applications, whereas the importance of simplifying the preparation methods of photothermal materials and enhancing their maximum photothermal temperature have been less taken. Herein, we prepare an organic near-infrared (NIR) photothermal material namely ATT by a spontaneous [2+2] cycloaddition-cycloreversion reaction. In addition to the solution-based method, ATT could also be readily preapred by ball milling in a high yield of 90% in just 15 min. ATT powder exhibits a broad absorption extending beyond 2000 nm, excellent processability, and thermal stability. Remarkably, ATT powder can reach an unprecedently temperature as high as 450 °C while maintaining excellent photostability upon photoirradiation. Leveraging its extraordinary photothermal and processable properties, ATT was used in the high-temperature applications, such as photo-ignition, photo-controlled metal processing and high-temperature shape memory, all of which offer spatiotemporal control capabilities. This work provides a new approach to prepare organic photothermal materials with high temperatures, and pave the way for their applications in extreme environments.

Corrosion behaviour of SiC particulate reinforced AZ31 magnesium matrix composite in 3.5 % NaCl with and without heat treatment

Magnesium is a lightweight structural material widely utilised in automotive applications. To enhance its mechanical properties, ceramic particulate reinforcement can be incorporated, particularly for wear resistance and high-temperature applications. However, the addition of ceramic particles to magnesium can compromise its corrosion resistance due to microgalvanic cell formation at the interfaces between the Mg matrix and the second phase. This reduces the chemical protection provided by the passive film. In this study, the corrosion properties of AZ31 and AZ31-5SiC samples were investigated, with a focus on the effect of heat treatment. Detailed microstructural and electrochemical analyses revealed that the AZ31 cast sample forms an effective passive film, resulting in improved corrosion resistance. However, the addition of SiC particles to AZ31 increased the corrosion rate, with corrosion mechanisms evolving over time. To mitigate these effects, a heat treatment process was employed to dissolve β-Mg17Al12 eutectic and Al8Mn5 intermetallic phases. The heat-treated AZ31 with SiC exhibited an improvement in corrosion resistance. These findings highlight the potential for heat treatment to enhance their corrosion resistance, thereby broadening their application prospects.

High temperature stability of regrown and alloyed Ohmic contacts to AlGaN/GaN heterostructure up to 500 °C

This Letter reports the stability of regrown and alloyed Ohmic contacts to AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) for high temperature applications up to 500 °C. Transfer length method (TLM) measurements from 25 to 500 °C in air show that the regrown contacts appear to be stable up to 500 °C during short term (approximately 1 h) testing, while alloyed contacts appear to decrease in contact resistance from 300 to 500 °C though increases in the error bounds due to increase sheet resistance make it difficult to conclude definitely. Additionally, longer term testing shows both technologies remain stable at least up to 48 h at 500 °C, after which the large increase in sheet resistance makes the measurement uncertainty too large to conclude definitively. Advanced microscopy images indicate both the regrown and alloyed contact regions remain structurally intact after prolonged high temperature exposure with no visible degradation in crystallinity or metal composition.

Manufacturing of High Purity Cr2AlC MAX Phase Material and Its Characterization

AbstractPresent study discusses about a technique for producing high-purity Cr2AlC MAX phase materials and gaining insight into their thermal behavior for high-temperature applications. The research conducted involved synthesizing a pure layered ternary carbide Cr2AlC MAX phase material by mixing powders of Chromium, Aluminum, and Carbon and then subjecting them to two-step pressureless sintering process in argon atmosphere. First step involves the annealing of ball-milled mixture at 750 °C for 2 h followed by the second step in which the annealed mixture is subjected to heat-treatment at 1350 °C for 2 h. Analysis using XRD and Raman techniques revealed that the synthesized product consists of Cr2AlC phase, without any impurities. SEM studies confirmed that the Cr2AlC had a layered topography, while EPMA analysis indicated that the atomic percentage of Cr, Al, and C was consistent with the XRD phase analysis. XPS investigations confirmed the presence of Cr-C bonds representing Mn+1Xn of the MAX phase material. TG-DSC results showed an approximately 2% increase in weight. The Cr2AlC phase exhibited an endothermic pattern below 725 °C, an exothermic pattern above it, and did not decompose up to 1400 °C in vacuum environment. High-temperature XRD analysis at various temperatures also confirmed no formation of Al2O3 or CrO impurity compounds.

Precycling Strategy in Suitable Voltage to Improve the Stability of Interfacial Film and Suppress the Decline of LiNi0.6Mn0.2Co0.2O2 Cathode at Elevated Temperatures.

Layered ternary oxide LiNixMnyCo1-x-yO2 is a promising cathode candidate for high-energy lithium-ion batteries (LIBs). However, the capacity of LIBs is significantly restricted by several factors, including the repeated dissolution-regeneration of the interfacial film at high temperatures, the dissolution of transition metals, and the increase of impedance. Herein, a new precycling strategy in suitable voltage scope at room temperature is proposed to construct a uniform, thermally stable, and insoluble cathode-electrolyte interface (CEI), which helps to maintain stable cycling performances at high temperatures. Specifically, after 5 precycles in the range of 3.85-4.3 V at room temperature, a CEI layer containing numerous inorganic components and oligomers is formed on the surface of LiNi0.6Mn0.2Co0.2O2. Subsequently, the harmful side reactions are effectively suppressed, endowing the cell with an excellent capacity retention of 84.67% after 50 cycles at 0.5C and 55 °C, much higher than that of 65.61% under the conventional film-forming process conditions. This work emphasizes the crucial role of the precycling strategy in regulating the characteristics of CEI layer on the surface of cathode electrode, opening up a new avenue for the high-temperature application of positive electrodes of LIBs.

The influence of thermo-electromechanical coupling on the performance of lead-free BNT-PDMS piezoelectric composites

In recent times, there have been notable advancements in haptic technology, particularly in screens found on mobile phones, laptops, light-emitting diode (LED) screens, and control panels. However, it is essential to note that the progress in high-temperature haptic applications is still in the developmental phase. Due to their complex phase and domain structures, lead-free piezoelectric materials such as Bi0.5Na0.5TiO3 (BNT)-based haptic technology behave differently at high temperatures than in ambient conditions. Therefore, it is essential to investigate the aspects of thermal management and thermal stability, as temperature plays a vital role in the phase and domain transition of BNT material. A two-dimensional thermo-electromechanical model has been proposed in this study to analyze the thermal stability of the BNT-PDMS composite by analyzing the impact of temperature on effective electromechanical properties and mechanical and electric field parameters. However, the thermo-electromechanical modelling of the BNT-PDMS composite examines the macroscopic effects of the applied thermal field on mechanical and electric field parameters, as phase change and microdomain dynamics are not considered in this model. This study analyzes the impact of thermo-electromechanical coupling on the performance of the BNT-PDMS composite compared to conventional electromechanical coupling. The results predicted a significant improvement in piezoelectric response compared to electromechanical coupling due to the increased thermoelectric effect in the absence of phase change and microdomain switching for temperature boundary conditions below depolarization temperature ( Td∼200∘ C for pure BNT material).

High-throughput discovery of metal oxides with high thermoelectric performance via interpretable feature engineering on small data

In this work, we have proposed a data-driven screening framework combining the interpretable machine learning with high-throughput calculations to identify a series of metal oxides that exhibit both high-temperature tolerance and high power factors. Aiming at the problem of weak generalization ability of small data with power factors at high temperatures, we employ symbolic regression for feature creation which enhances the robustness of the model while preserving the physical meaning of features. 33 candidate metal oxides are finally targeted for high-temperature thermoelectric applications from a pool of 48,694 compounds in the Materials Project database. The Boltzmann transport theory is utilized to perform electrical transport properties calculations at 1,000 K. The relaxation time is approximated by employing constant electron-phonon coupling based on the deformation potential theory. Considering band degeneracy, the electron group velocity is obtained using the momentum matrix element method, yielding 28 materials with power factors greater than 50 μWcm−1K−2. The high-throughput framework we proposed is instrumental in the selection of metal oxides for high-temperature thermoelectric applications. Furthermore, our data-driven analysis and transport calculation suggest that metal oxides rich in elements such as cerium (Ce), tin (Sn), and lead (Pb) tend to exhibit high power factors at high temperatures.

Development of Ag@Si composite sinter joining with ultra-high resistance to thermal shock test for SiC power device: Experiment validation and numerical simulation

Owing to its cost-effectiveness and low coefficient of thermal expansion (CTE), micron Si is incorporated into sintered Ag matrix to develop an Ag@Si composite sintering strategy. The Si integration helps reduce cost and alleviate CTE-mismatch of Ag-sintered die attachments. An innovative Ag@Si composite sintering structure is achieved by low-temperature and pressure-less sintering process, where a possibly slight diffusion of native SiO2 on the Si surface toward Ag is indicated by TEM observation, enabling the integration of Ag and Si into one continuous network. Owing to the robust well-bonded composite sintering, the Ag@Si joining strategy provides mechanical/microstructural reliability far beyond the pure Ag sinter joining, demonstrating significant prospects in high-temperature interconnection applications. During the harsh thermal cycling (−50–250 °C), the mitigating effect of the Si addition on CTE mismatch is manifested through the substantial suppression of microstructure deterioration in Ag@Si joint that occurs in pure-Ag-sintered joint, while the shear strength retention rate is doubled. Detailed investigation into the mechanism for elevated performance was conducted by material property and Missies stress analysis. The incorporation of Si helps modify the CTE, elastic properties, and stress distribution of Ag@Si-sintered material, synergistically contributing to the satisfactory joining reliability.

Numerical analysis-based performance assessment of the small-scale organic Rankine cycle turbine design for residential applications

The organic Rankine cycle (ORC) is one of the most common ways to use energy resources to utilise waste heat. Integrating ORC with other systems, such as cooling or heating applications, is also helpful for residential uses. In the ORC system, the turbines are the most critical component determining the system's efficiency. This study conducted a computational fluid dynamics study on a regenerative flow turbine that can be used in small-scale organic Rankine cycle systems. For the higher temperature applications, the analyses were performed using n-pentane working fluid for 1500 and 3000 rpm turbine speeds, inlet temperature between 475–550 K, outlet pressure between 0.9–1.2 MPa, and mass flow rates between 0.5–1.0 kg/s. As a result of the analysis, the isentropic efficiency varies between 4.97 % and 12.52 %. It was concluded that the output power obtained from the turbine varies between 0.53 kW and 2.96 kW. The analyses were also performed for lower temperature (363 and 393 K), pressure (0.05 MPa and 0.3 MPa) and mass flows (0.1 to 0.25 kg/s) applications. In this case, the isentropic efficiency of the turbine varies between 6.23 % and 14.52 %, whereas the power generation varies between 0.068 and 0.521 kW.

A New Strategy for the Design of Triple-Phase Eutectic High-Entropy Alloys Based on Infinite Solid Solution and Pseudo-Ternary Method.

Eutectic high-entropy alloys (EHEAs) have combined both high-entropy alloys and eutectic alloy contributions, with excellent castability and high-temperature application potential. Yet, multielement/triple-phase eutectic high-entropy alloy (TEHEA) designs remain puzzling. This work proposed a new strategy based on an infinite solid solution and pseudo-ternary model to reveal the puzzle of TEHEAs. The designed triple-phase eutectic high-entropy alloys (TEHEAs) with more than seven elements were identified as face-centered cubic (FCC), ordered body-centered cubic (B2), and Laves phase structures. In this work, the alloy C showcases outstanding comprehensive mechanical properties, offering a novel avenue for the design of high-performance EHEAs.

A synergistic approach to optimizing the performance of a concentrating solar segmented variable area leg thermoelectric generator using numerical methods and neural networks

AbstractThis study presents an optimized design for segmented variable area leg thermoelectric modules using finite element methods and Bayesian regularized neural networks. We explored the impact of geometry and thermal parameters on module performance using ANSYS software, identifying optimal parameters for power output and efficiency. Key findings revealed the higher influence of geometric parameters and confirmed the advantages of segmented thermoelectric generators for high-temperature applications like concentrated solar systems. With this optimization, power output and efficiency of the module increased by 875% and 165%, respectively, under 25 Suns. To refine the optimization process, a Bayesian regularized neural network was utilized, proving effective in predicting module performance with a low mean squared error and high coefficient of determination. This research provides important insights into high-performance thermoelectric modules for sustainable energy applications, demonstrating the significant role of advanced computational methods in energy solutions.

Development of thermal barrier coating on single crystal superalloy CMSX-4 by two-source evaporation EB-PVD and hot corrosion performance of the coating in a simulated aero-engine environment

Superalloys are crucial in high-temperature applications, particularly in the gas turbine industries. With the development of high-temperature superalloy materials, efforts are still being made to improve the turbine entry temperature (TET), which will ultimately raise the efficiency of gas turbines. In this research, a second-generation single-crystal superalloy CMSX-4 based on nickel was prepared. The surface was coated by thermal barrier coating (TBC) with a bond coat of NiCoCrAlY with vacuum plasma spray (VPS) and a top coat with Yttria Stabilized Zirconia (YSZ) by Electron Beam Physical Vapor Deposition (EB-PVD) with a minimal current of 2.3 A with two sources compared to the conventional high-current that has been currently employed. These CMSX-4 specimens, both the as-cast and TBC coated, were used to test the effects of cyclic oxidation and hot corrosion at 1000 °C, simulating an aircraft engine. Also, a hot corrosion test using salt compositions (Wt%) of 60Na2SO4 - 40NaCl was performed simulating an aviation engine environmental condition. A FE-SEM/EDS analysis was used to examine the surface and cross-section microstructures of oxidized, hot-corroded as-cast, and hot-corroded TBC-coated CMSX-4 and its corrosion products. Using the XRD technique, the phases that were found in the oxidized and hot-corroded samples were identified. The outcome demonstrated that the EB-PVD TBC-coating on CMSX-4 with beam switching technique and a lower electron beam current has adequate protection without any damage to the coatings at 1000 °C.

Structural origins of dielectric anomalies in the filled tetragonal tungsten bronze Sr2NaNb5O15

The tetragonal tungsten bronze, Sr2NaNb5O15, shows promise for application in high-temperature high-efficiency capacitors vital for the sustainable energy revolution. Previously, the structural complexity of this and related materials has obscured the mechanisms underpinning two large anomalies in relative permittivity (εr) which give rise to their exceptionally broad dielectric response. Here, we comprehensively investigate the structural evolution from −173 to 627 °C, combining electron, X-ray and neutron diffraction, electron microscopy, and first principles electronic structure calculations to unambiguously identify the structural origins of both anomalies. The peak in εr at 305 °C is associated with a polar-nonpolar phase transition, wherein cations displace along the c axis. Guided by DFT, we identify a further transition upon cooling, associated with the second peak at −14 °C, linked to the softening of an in-plane polar distortion with a correlation length limited by ferroelastic nano-domains arising from rigid-unit-like tilting of NbO6 octahedra at high temperature, imparting relaxor-like behaviour. Thus, the two dielectric anomalies in Sr2NaNb5O15 are associated with two distinct crystallographic phase transitions and their interplay with a microstructure that arises from a third, non-polar structural distortion. Chemical control of these will enable development of tuneable materials with dielectric properties suitable for high-temperature energy storage applications.

Fracture toughness evolution and failure mechanisms of two-dimensional SiCf/SiC composites at temperatures up to 1500 °C in air

Silicon carbide fiber reinforced silicon carbide composites (SiCf/SiC) are of the few most promising materials for high-temperature structural applications. In this study, two-dimensional (2D) plain-woven SiCf/SiC composites were prepared by chemical vapor infiltration process and subjected to single-sided notched beam three-point bending tests from room temperature (RT) to 1500 °C in air. The temperature-dependent bending load–deflection curves and fracture toughness were obtained. The results show that the SiCf/SiC composites exhibit linear deformation characteristics initially, followed by nonlinear deformation behavior which become more pronounced with increasing temperature. The fracture toughness decreases in the range of RT to 1000 °C due to the evolution of components properties, and increases at 1200 °C due to the interface property degradation and fiber pull-out. Above 1200 °C, it decreases with increasing temperature owing to the serious high-temperature oxidation. Further, the failure mechanisms of the 2D plain-woven SiCf/SiC composites at different temperatures was analyzed through macro and micro analysis. The evolution of components properties affected by high temperature and oxidation as well as fiber pull-out play a leading role in fracture toughness of composites. The findings of this study provide important support for the mechanical behavior and failure mechanisms of SiCf/SiC composites at ultra-high temperatures in air.

Dielectric Properties of Materials Used for Microwave-Based NOx Gas Dosimeters.

Nitrogen oxides (NOx), primarily generated from combustion processes, pose significant health and environmental risks. To improve the coordination of measures against excessive NOx emissions, it is necessary to effectively monitor ambient NOx concentrations, which requires the development of precise and cost-efficient detection methods. This study focuses on developing a microwave- or radio frequency (RF)-based gas dosimeter for NOx detection and addresses the optimization of the dosimeter design by examining the dielectric properties of LTCC-based (Low-Temperature Co-fired Ceramics) sensor substrates and barium-based NOx storage materials. The measurements taken utilizing the Microwave Cavity Perturbation (MCP) method revealed that these materials exhibit more pronounced changes in dielectric losses when storing NOx at elevated temperatures. Consequently, operating such a dosimeter at high temperatures (above 300 °C) is recommended to maximize the sensor signal. To evaluate their high-temperature applicability, LTCC substrates were analyzed by measuring their dielectric losses at temperatures up to 600 °C. In terms of NOx storage materials, coating barium on high-surface-area alumina resolved issues related to limited NOx adsorption in pure barium carbonate powders. Additionally, the adsorption of both NO and NO2 was enabled by the application of a platinum catalyst. The change in dielectric losses, which provides the main signal for an RF-based gas dosimeter, only depends on the stored amount of NOx and not on the specific type of nitrogen oxide. Although the change in dielectric losses increases with the temperature, the maximum storage capacity of the material decreases significantly. In addition, at temperatures above 350 °C, NOx is mostly weakly bound, so it will desorb in the absence of NOx. Therefore, in the future development of a reliable RF-based NOx dosimeter, the trade-off between the sensor signal strength and adsorption behavior must be addressed.