High Temperature Operation Research Articles

Progress in Fast Modular Reactor Conceptual Design

The Fast Modular Reactor (FMR) is a 100-MW(thermal) gas-cooled fast reactor being developed by General Atomics Electromagnetic System with the goal of developing a FMR for flexible and dispatchable power to the U.S. electricity market in the mid-2030s. The conceptual design aims to develop and verify simplified design features. These include an inert helium gas coolant, pellet-loaded fuel rods, installations with air cooling as ultimate heat sink, and small and passive heat removal systems. The goal is to ensure the development of a safe, maintainable, cost-effective, and distributed nuclear energy-generating station. The baseline technologies selected to achieve this goal are a helium coolant that is an inert gas with no chemical reaction with structural components, not activated, single phase, enabling high-temperature operation and a high thermal efficiency Brayton cycle; conventional uranium dioxide (UO2) fuel, which is the most widely used and well-known fuel material, capable of high burnup (100 MWd/kg) and a long fuel life; and silicon carbide composite (SiGA®) cladding and internal structures that are chemically inert in the helium environment, exceptionally radiation tolerant, and being derisked by accident tolerant fuel technology development. The reactor was specifically designed with passive safety features, including high-temperature in-core materials and a reactor vessel cooling system consisting of cooling panels of naturally circulating water. The passive safety of the core was confirmed for the depressurized loss-of–forced cooling accident, which showed the peak cladding temperature at ~1600°C during the transient, which is below the current design limit of 1800°C. The conceptual design of the FMR has been conducted for the reactor system, vessel system, generator and turbomachine, instrumentation and control, residual heat removal system, plant service system, and containment, as well as pre-application licensing documents.

Efficient and bright broadband electroluminescence based on environment-friendly metal halide nanoclusters

Broadband electroluminescence based on environment-friendly emitters is promising for healthy lighting yet remains an unprecedented challenge to progress. The copper halide-based emitters are competitive candidates for broadband emission, but their high-performance electroluminescence shows inadequate broad emission bandwidth of less than 90 nm. Here, we demonstrate efficient ultra-broadband electroluminescence from a copper halide (CuI) nanocluster single emitter prepared by a one-step solution synthesis-deposition process, through dedicated design of ligands and subtle selection of solvents. The CuI nanocluster exhibits high rigidity in the excitation state as well as dual-emissive modes of phosphorescence and temperature-activated delayed fluorescence, enabling the uniform cluster-composed film to show excellent stability and high photoluminescent efficiency. In consequence, ultra-broadband light-emitting diodes (LEDs) present nearly identical performance in an inert or air atmosphere without encapsulation and outstanding high-temperature operation performance, reaching an emission full width at half maximum (FWHM) of ~120 nm, a peak external quantum efficiency of 13%, a record maximum luminance of ~50,000 cd m−2, and an operating half-lifetime of 137 h at 100 cd m−2. The results highlight the potential of copper halide nanoclusters for next-generation healthy lighting.

Chemiresistive Sensor for Enhanced CO2 Gas Monitoring.

Carbon dioxide (CO2) gas sensing and monitoring have gained prominence for applications such as smart food packaging, environmental monitoring of greenhouse gases, and medical diagnostic tests. Although CO2 sensors based on metal oxide semiconductors are readily available, they often suffer from limitations such as high operating temperatures (>250 °C), limited response at elevated humidity levels (>60% RH), bulkiness, and limited selectivity. In this study, we designed a chemiresistive sensor for CO2 detection to overcome these problems. The sensing material of this sensor consists of a CO2 switchable polymer based on N-3-(dimethylamino)propyl methacrylamide (DMAPMAm) and methoxyethyl methacrylate (MEMA) [P(D-co-M)], and diethylamine. The designed sensor has a detection range for CO2 between 103 and 106 ppm even at high humidity levels (>80% RH), and it is capable of differentiating ammonia at low concentrations (0.1-5 ppm) from CO2. The addition of diethylamine improved sensor performance such as selectivity, response/recovery time, and long-term stability. These data demonstrate the potential of using this sensor for the detection of food spoilage.

Enhanced thermal safety and rate capability of nickel-rich cathodes via optimal Nb-doping strategy

Nickel-rich layered oxides have garnered great attention as promising cathode materials in lithium-ion batteries for their high specific capacity, rate capability and comparatively lower cost. However, the long cycling with a high current scenario is still a critical challenge, resulting from the lattice cracks and high temperature which are induced by rapid Li-ions intercalation/extraction and local heat accumulation under component voltage. Besides the deterioration of electrochemical performance, these limitations further lead to the impairment of structure or even thermal runaway for nickel-rich layered oxides. Herein, considering the superiorities of niobium element with multilevel electron orbitals and suitable atomic radius, a strategy of nickel-rich material modified by niobium-doping is proposed. The incorporated niobium forms a strong niobium-oxygen bonding, which promotes structure stability, ions diffusivity, and electron conductivity of nickel-rich cathode (LiNi0.8Co0.1Mn0.1O2). Accordingly, the niobium-doping cathode deliver the specific capacities of 166.4 mAh g−1 and 151.02 mAh g−1 after 100 cycles at 1 C and 5 C (1C = 200 mAh g−1), especially with the capacity retention of 88.90 % and 89.06 %. Moreover, the niobium-doping cathode exhibit a more stable thermal safety with a reversibility around 76.75 % after 100 cycles at 1 C under 50 ℃, whereas is only 36.03 % for blank sample. Accompanied with exploring the stabilization for crystalline structure and superficial electronic structure, a generic approach to synthesize excellent Ni-rich cathode materials is identified, accelerating their endurance application in complicated scenes, particularly at high-temperature and high-rate operation conditions.

Enhancing room-temperature gas sensing performance of metal oxide semiconductor chemiresistors through 400 nm UV photoexcitation

One of the most significant drawbacks of metal oxide (MOS) based chemiresistive gas sensors is the requirement of high operating temperature (250–450 °C), which results in significant power consumption and shorter lifetime. To develop room temperature (21±2 °C) MOS chemiresistive gas sensors, the sensing performance of different MOS nanostructures (i.e., tin (IV) oxide (SnO2) nanoparticles (NPs), indium (III) oxide (In2O3) NPs, zinc oxide (ZnO) NPs, tungsten trioxide (WO3) NPs, copper oxide (CuO) nanotubes (NTs), and indium tin oxide (In90Sn10O3 (ITO)) NPs) were systematically investigated toward different toxic industrial chemicals (TICs) (i.e., nitrogen dioxide (NO2), ammonia (NH3), hydrogen sulfide (H2S), carbon monoxide (CO), sulfur dioxide (SO2) and volatile organic compounds (VOCs) (i.e., acetone (C3H6O), toluene (C6H5CH3), ethylbenzene (C6H5CH2CH3), and p-xylene (C6H4(CH3)2)) in the presence and absence of 400 nm UV light illumination.Sensing performance enhancement through photoexcitation is strongly dependent on the target analytes. Under 400 nm UV photoexcitation at 76.0 mW/cm2 intensity, room temperature (21±2 °C) NO2 sensing was readily achieved where SnO2 NPs exhibited the highest sensor response (S = 474.4 toward 10 ppmm (parts per million by mass)) with good recovery followed by ZnO NPs > In2O3 NPs > ITO NPs. Meanwhile, indirect bandgap n-type WO3 NPs showed limited NO2 sensing performance under illumination, whereas p-type CuO NTs showed relatively good sensing response. The most significant improvements in SnO2 compared to other MOS nanoparticles might be attributed to the highest number of photogeneration electrons, which rapidly reacted with adsorbed NO2− species to enhance the reaction kinetics. WO3 NPs showed a unique sensing response toward aromatic compounds (e.g., ethylbenzene and p-xylene) under UV illumination, where maximum sensitivity was achieved under 36 mW/cm2 irradiation. Changing light intensity from 0.0 to 36.4 mW/cm2, WO3 showed 15.4-fold and 6.3-fold enhancement in sensing response toward 25 ppmm ethylbenzene and 100 ppmm p-xylene, respectively. 400 nm optical excitation has a limited effect on the sensing performance toward CO, SO2, toluene, and acetone.

MICROSTRUCTURE CHARACTERISTICS OF Cr3C2-NiCr COATINGS DEPOSITED WITH THE HIGH-VELOCITY OXY-FUEL THERMAL-SPRAY TECHNIQUE

With the goals of protecting boiler tubes from hostile surroundings, increasing thermal efficiency, and minimizing time losses from damage, thermal-spray coating methods for high-temperature operations were created. Ceramic-metal composite materials (e.g., Cr3C2-NiCr) are well known for protecting components from erosion decay in a high-temperature environment. In this investigation, the high-velocity oxy-fuel (HVOF) thermal-spray technique was employed to successfully deposit several variations of feedstocks containing Cr3C2-NiCr and NiCr powders onto a medium-carbon steel substrate, with and without filtering through a 400-mesh screen. Utilizing X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the microstructure features of the deposited coatings were assessed. The experiment results demonstrate that the crystallite and grain sizes of the deposited coatings can be increased by reducing the powder size through a sifting process using a 400-mesh sieve. This procedure also resulted in a coating with a higher density and lower porosity. Furthermore, new compounds including Cr2O3 and MnCr2O4 were formed in the coating layers as indicated by the XRD spectra. These phenomena are in good agreement with the EDS mapping of Cr and O, which reveals highly similar distributions. Manganese was originally a part of the substrate composition. Manganese could diffuse rapidly across the Cr2O3 layer and form the MnCr2O4 compound, indicating the manganese diffusion from the substrate into the Cr3C2-NiCr coating. The formation of MnCr2O4 can be attributed to the prior emergence of the Cr2O3 compound.

Thermally stable high carrier mobility nanocomposite infrared photodetector

Quantum dots (QDs) show excellent optical properties, such as a high extinction coefficient, tunable colors, and superior photostability. However, the transport properties of QDs, such as carrier mobility, are quite limited, which hinder optoelectronic applications. On the other hand, carbon nanotubes (CNTs) generally have high carrier mobility and thermal stability with a weak optical response. These features inspire us to couple QDs with CNTs to achieve improved optoelectronics. We take infrared HgTe QDs and multi-walled CNTs as examples. With appropriate coupling between QD and CNT matrices, carrier mobility could reach 34.6–54.1 cm2/Vs in the nanocomposite, a 1000-fold increase compared with the reference. The nanocomposite benefits external quantum efficiency up to 12 500% and detectivity 1012 Jones on the 2500 nm infrared photodetectors. The CNT matrix also helps relaxing thermally generated carriers, improving the photodetector thermal stability. We also demonstrate that the device maintains high detectivity at a high operating temperature.

Production increase of high-grade crude zinc oxide pellets at Shisaka Smelting Co., Ltd.

Shisaka Smelting Co., Ltd. has recovered crude zinc oxide pellets from an electric arc furnace dust (EAF dust) by the Waelz kiln process since 1977. The EAF dust processing line consists of a reduction roasting process, a Waelz oxide washing process, and a drying/calcination process. In late years, about 90,000 tons of EAF dust is processed annually at Shisaka. The recovered zinc is sold to zinc smelters as crude zinc oxide pellets, and the amount of production of the pellets is about 40,000 tons per year. Two types of zinc oxide pellets are produced, and the product for electro-refinery requires high quality, especially in fluorine reduction. Most of fluorine are distributed to the clinker in a reduction roasting process, and others are distributed to the Waelz oxide. Conventionally, high-grade crude zinc oxide pellets were produced by washing the Waelz oxide and by volatilizing and separating fluorine under high temperature operation in a drying rotary kiln. However, formation of accretion in the kiln and damage of the shell and refractories of the kiln often occurred under the influence of high temperature operation, and stable consecutive operation of the kiln was difficult.To improve this situation, the fluorine input was reduced by compounding management of EAF dust in the reduction roasting process, and the material residence time in the drying rotary kiln was extended by reducing rotary speed. These improvements resulted in stable consecutive operation under low temperature conditions and increased production of high-grade crude zinc oxide pellets. To improve this situation, the fluorine input was reduced by compounding management of EAF dust in the reduction roasting process, and the material residence time in the drying rotary kiln was extended by reducing rotary speed. These improvements resulted in stable consecutive operation under low temperature conditions and increased production of high-grade crude zinc oxide pellets.

A high-temperature solar selective absorber based on one-dimensional multilayer nanostructures

Selective absorbers play a crucial role in harvesting solar energy and realizing effective solar-thermal energy conversion in concentrated solar power systems and thermophotovoltaic systems. This study focuses on obtaining a high-temperature solar selective absorber which can well balance its thermal performance as well as structural complexity. Based on this, a selective absorber with simple one-dimensional multilayer nanostructures is designed to adapt to the high-temperature operation environments. The obtained absorber exhibits a total solar absorptance of 0.9504 to the AM1.5 solar radiation. Taking into account the infrared radiation loss, the solar-thermal efficiency of the absorber is found to be 91.2% under 1000 suns at 1273 K, and the total emittance is 0.1504 at the corresponding temperature. The absorber shows high insensitivity to both incident polarization angles and wide-angle incidence. Analysis of impedance and electromagnetic field distribution indicates that the selective absorption performance of the absorber is attributed to its impedance matching properties, resulting from the coupling effect of surface plasmon polaritons and magnetic polaritons.

High Performance Proprioceptive Fiber Actuators Based on Ag Nanoparticles-Incorporated Hybrid Twisted and Coiled System.

Thermally driven fiber actuators are emerging as promising tools for a range of robotic applications, encompassing soft and wearable robots, muscle function restoration, assistive systems, and physical augmentation. Yet, to realize their full potential in practical applications, several challenges, such as a high operational temperature, incorporation of intrinsic self-sensing capabilities for closed-loop feedback control, and reliance on bulky, intricate actuation systems, must be addressed. Here, an Ag nanoparticles-based twisted and coiled fiber actuator that achieves a high contractile actuation of ≈36% is reported at a considerably low operational temperature of ≈83°C based on a synergistic effect of constituent fiber elements with low glass transition temperatures. The fiber actuator can monitor its contractile actuation in real-time based on the piezoresistive properties inherent to its Ag-based conductive region, demonstrating its proprioceptive sensing capability. By exploiting this capability, the proprioceptive fiber actuator adeptly maintains its intended contractile behavior, even when faced with unplanned external disturbances. To demonstrate the capabilities of the fiber actuator, this study integrates it into a closed-loop feedback-controlled bionic arm as an artificial muscle, offering fresh perspectives on the future development of intelligent wearable devices and soft robotic systems.

Polycrystalline hollow MOF derived Co3O4 semiconductor to achieve room-temperature ammonia detection in human exhaled breath

Functional gas-sensing devices, on their portable and non-invasive merits, have stimulated a new exploring in clinical detection of gaseous biomarkers for critical diseases such as hepatopathy and nephropathy. Metal oxide semiconductor (MOS) sensors owing to their high sensitivity and facile manufacture appears to be the most promising for integration into illness surveillance devices. However, the high operating temperature of MOS poses great challenge for their realistic application. Herein, MOF-derived Co3O4 sensor series are prepared by facile manipulation of the morphological structure and crystalline state of their maternal ZIF-67. It shows that polycrystalline hollow ZIF-67 (PH-ZIF-67) derived PH-Co3O4 exhibits the optimum response and selectivity to trace NH3 at room-temperature sensing. PH-Co3O4 has a low limit of detection and well moisture resistance, which further behaves a significant quantitative response to actual exhaled breath of patients with hepatic encephalopathy. Furthermore, the scientific link between performance enhancement and structural adjustment is revealed by XPS, EPR, etc. It is found that the construction of the polycrystalline structure increases the oxygen vacancies generated during calcination, and additionally, the hollow structure provides more chemisorbed oxygen on the extra inner surface, which coupled to enhance the number of reactive oxygen sites responsible for the response improvement.

Enhanced Acetone Sensing Properties Based on Au-Pd Decorated ZnO Nanorod Gas Sensor.

The mature processes of metal oxide semiconductors (MOS) have attracted considerable interest. However, the low sensitivity of metal oxide semiconductor gas sensors is still challenging, and constrains its practical applications. Bimetallic nanoparticles are of interest owing to their excellent catalytic properties. This excellent feature of bimetallic nanoparticles can solve the problems existing in MOS gas sensors, such as the low response, high operating temperature and slow response time. To enhance acetone sensing performance, we successfully synthesized Au-Pd/ZnO nanorods. In this work, we discovered that Au-Pd nanoparticles modified on ZnO nanorods can remarkably enhance sensor response. The Au-Pd/ZnO gas sensor has long-term stability and an excellent response/recovery process. This excellent sensing performance is attributed to the synergistic catalytic effect of bimetallic AuPd nanoparticles. Moreover, the electronic and chemical sensitization of noble metals also makes a great contribution. This work presents a simple method for preparing Au-Pd/ZnO nanorods and provides a new solution for the detection of acetone based on metal oxide semiconductor.

Above-77 K operation of charge sensitive infrared phototransistor with dynamically controlled optical gate

Charge sensitive infrared phototransistors (CSIPs) show great promise for sensitive mid-infrared photodetection, extending up to single-photon counting, owing to the built-in amplification mechanism. However, the operating temperature of previously reported CSIPs has been limited to below 30 K. In this work, we propose a technique that enhances the operating temperature to above liquid nitrogen temperature by dynamically controlling the electrostatic potential of the optical floating gate (FG). This control effectively suppresses the annihilation of photogenerated holes in the FG, mitigating the vertical recombination process of thermally excited electrons. We detected the photosignal up to ∼85 K under a photon flux of Φ∼3.6×108 s−1. An outstanding photoresponsivity (R=39.11 A/W) to external blinking light at the peak wavelength of λ=11μm is achieved at 77 K. Our work not only extends the practical application of CSIPs, meeting the high demand for high temperature operation, but also offers more flexibility in fabricating more general highly sensitive phototransistors.

Retraction Note: Optimal design of garments for high-temperature operations based on the finite difference method

Retraction Note: Optimal design of garments for high-temperature operations based on the finite difference method

Development of a steady state electrothermal cosimulation model of SiC power modules

Silicon carbide power modules are suitable for high temperature, high voltage and high frequency applications. High operating temperature and high power density bring enormous challenges in chip parallel connection and junction temperature predicting. In this work, a steady state electrothermal cosimulation model is established based on Matlab electrical model and ANSYS thermal analysis model. An experimental study is conducted using a customized single die SiC module. The experimental and numerical results exhibit great agreement, with deviation consistently below 4 %. Then, comprehensive research is conducted to investigate the electrothermal performance of several dies in parallel configuration. The findings unequivocally validate the efficacy of the proposed model in accurately capturing the intricate electrical and thermal characteristics. The proposed numerical model offers a reliable and accurate electrothermal modeling approach for SiC power modules.

What will it take to get to 250,000 ppm brine concentration via ultra-high pressure reverse osmosis? And is it worth it?

The possibility of ultra-high pressure reverse osmosis (UHPRO) to replace thermal brine concentration promises to reduce up to 50 % of both energy consumption and capital cost. However, commercially available reverse osmosis (RO) membranes lose up to 50 % of their water permeability when operated up to 200 bar. Higher temperature operations such as in Middle East seawater desalination and brine mining further exacerbate compaction due to softening of the polysulfone support membrane. Assuming that pressure and temperature-related compaction issues can be resolved through innovations in membrane materials and/or module designs, this study asks the questions, “What will it take to get to 250,000 ppm via ultra-high pressure reverse osmosis? And is it worth it?” Herein we comprehensively examine a three stage RO process beginning with seawater RO (SWRO) to high-pressure RO (HPRO) and ultra-high-pressure RO (UHPRO). We elucidate the influence of thermophysical properties, hydraulic pressure, permeate flux, water permeability, feed spacer design, concentration polarization (CP), salt rejection and stage design on recovery and specific energy consumption (SEC). Our analysis of high rejection (HR) and high flux (HF) RO membranes reveals that while HF RO membranes boast superior water permeability and lower trans-membrane (hydraulic) pressure (TMP), they require higher operating flux, which leads to severe CP and operating pressures of 300 to 400 bar to meet the targeted brine concentration of ~250 g/L TDS. In addition, membrane compaction drives up the TMP, SEC, and capital cost of UHPRO systems. To bring the applied pressure below 300 bar, compaction-resistant UHPRO membranes and mass-transfer enhancing feed spacers will be required. The findings herein show that it will take time, money and technological innovation to enable UHPRO at commercial scale, and it may or may not be worth it. Further, this work makes clear the technological refinements needed to enable UHPRO membrane brine concentration.

In Situ Construction of Interface with Photothermal and Mutual Catalytic Effect for Efficient Solar-Driven Reversible Hydrogen Storage of MgH2.

Hydrogen storage in MgH2 is an ideal solution for realizing the safe storage of hydrogen. High operating temperature, however, is required for hydrogen storage of MgH2 induced by high thermodynamic stability and kinetic barrier. Herein, flower-like microspheres uniformly constructed by N-doped TiO2 nanosheets coated with TiN nanoparticles are fabricated to integrate the light absorber and thermo-chemical catalysts at a nanometer scale for driving hydrogen storage of MgH2 using solar energy. N-doped TiO2 is in situ transformed into TiNxOy and Ti/TiH2 uniformly distributed inside of TiN matrix during cycling, in which TiN and Ti/TiHx pairs serve as light absorbers that exhibit strong localized surface plasmon resonance effect with full-spectrum light absorbance capability. On the other hand, it is theoretically and experimentally demonstrated that the intimate interface between TiH2 and MgH2 can not only thermodynamically and kinetically promote H2 desorption from MgH2 but also simultaneously weaken Ti─H bonds and hence in turn improve H2 desorption from the combination of weakened Ti─H and Ti─H bonds. The uniform integration of photothermal and catalytic effect leads to the direct action of localized heat generated from TiN on initiating the catalytic effect in realizing hydrogen storage of MgH2 with a capacity of 6.1wt.% under 27 sun.

Comparative Analysis of LiCo0.6Sr0.4O2 Cathode Electrochemical Performance in Oxide- and Proton-Conducting Intermediate-Temperature Solid Fuel Oxide Cells

Solid fuel oxide cells (SOFCs) are made up of three main parts: anode, electrolyte, and cathode. The main challenge in SOFCs is their high operating temperature, which can reach 1000 °C and lead to cell degradation issues. To address this, the utilization of lithium-based materials is suggested for the cathode component, facilitating intermediate-temperature SOFC operation within the temperature range of 500 to 800 °C. Previous studies have demonstrated the potential of producing high-quality lithium-based cathode ink using a triple-roll mill (TRM). By employing the fabrication parameters recommended in these studies, the lithium-based cathode (LCSO) was tested in different working environments, specifically the oxide-conducting SOFC and proton-conducting SOFC. The LCSO inks were screen-printed on SDC for oxide-conducting SOFC and BCZY for proton-conducting SOFC electrolyte before the analysis. Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) are used to characterize the electrochemical performance and morphology of the LCSO cathode. Based on the results, the LCSO cathode is found to respond well in oxide-conducting SOFC environment with an area-specific resistance (ASR) value of 0.75 ohms-cm2 compared to proton-conducting SOFC which shows an ASR value higher by 11.45 ohms-cm2.

Machine learning assisted design of BCC high entropy alloys for room temperature hydrogen storage

Body-centered cubic (BCC) alloy systems can theoretically store double amounts of hydrogen compared with commercial metal hydrides at room temperature, and BCC high entropy alloys (HEAs) have shown the potential to reach this theoretic limit. However, the high thermodynamic stability of the dihydrides formed during hydrogen storage results in high operating temperatures. Here, by employing multi-objective Bayesian optimization-aided density functional theory calculations, we discovered 8 new HEA candidates for hydrogen storage, including the VNbCrMoMn HEA that can store 2.83 wt% hydrogen at room temperature and atmospheric pressure, vastly exceeding the hydrogen capacities of 1.38 wt% and 1.91 wt% for commercial LaNi5H6 and TiFeH2. Such a high performance of VNbCrMoMn is ascribed to the optimized hydrogen absorption thermodynamics, which is achieved under the guidance of interpretable machine learning which revealed that the thermodynamics of the first and second stages of absorption are largely determined by the bulk modulus and the number of states in the d-band, respectively.

The Effect of Carbide Concentration at Grain Boundaries on Thermal Stresses in Castings for Heat Treatment Furnace Tooling

Austenitic Fe-Ni-Cr alloys are commonly used for the production of castings intended for high-temperature applications. One area where Fe-Ni-Cr castings are widely used is the equipment for heat treatment furnaces. Despite the good heat resistance properties of the materials used for the castings, they tend to develop cracks and deformations over time due to cyclic temperature changes experienced under high temperature operating conditions. In the case of carburizing furnace equipment, thermal stresses induced by the temperature gradient in each operating cycle on rapidly cooled elements have a significant influence on the progressive fatigue changes. In the carburized subsurface zone, also the different thermal expansion of the matrix and non-metallic precipitates plays a significant role in stress distribution. This article presents the results of analyses of thermal stresses in the surface and subsurface layer of carburized alloy during cooling, taking into account the simultaneous effect of both mentioned stress sources. The basis for the stress analyzes were the temperature distribution in the cross-section of the cooled element as a function cooling time, determined numerically using FEM. These distributions were taken as the thermal load of the element. The study presents the results of analyses on the influence of carbide concentration increase on stress distribution changes caused by the temperature gradient. The simultaneous consideration of both thermal stress sources, i.e. temperature gradient and different thermal expansions of phases, allowed for obtaining qualitatively closer results than analyzing the stress sources independently