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Sustainable energy production, inherently transient and non-uniformly distributed around the world, requires the rapid development of sustainable energy storage technologies. Recently, pure iron powder was proposed as a high-energy density carrier. While promising, challenges are faced, such as nanoparticle emissions, micro-explosions or cavitation. In this work, a screening of the impact of the most common impurities in iron sources on these mechanisms was conducted through purely thermodynamic simulations. Two idealized models were considered to obtain a range of plausible flame temperatures and emitted gases when considering a purely diffusive regime in standard conditions and stoichiometric air–fuel mixture. The flame temperature and iron evaporation are increasing with the specific energy. A strong evaporation of C, S, Mo, Cu and P is also expected. Most impurities are predicted to decrease cavitation, except for Mn and MnO. The regeneration process by hydrogen-based direct reduction in fluidized bed reactors is also discussed. MgO and CaO are the most promising additions in terms of reducing nanoparticles and porosities, as well as to improve the fluidization and reduction kinetics of the combusted products. The potential of Fe powder as sustainable fuel, already very promising, could be further improved by the addition of selectively chosen impurities. This article is part of the discussion meeting issue 'Sustainable metals: science and systems'. [ABSTRACT FROM AUTHOR]

Metallic alloy fuels from fast reactors will be reprocessed by a non‐aqueous electrochemical technique known as electrorefining. Electrorefining of spent metal fuel results in the accumulation of heat‐generating fission products, especially 137Cs in the eutectic salt. These fission products need to be removed from the salt so as to reduce the decay heat load and contamination. The melt crystallization technique is a simple separation process being pursued for the separation of fission products. This is a single‐step process that utilizes the difference in solubility of fission products in the solid and liquid phase. This process is also less energy intensive. Crystallization involves the purification of a substance from a liquid mixture by solidification of the desired component. Since separation is based on selective solidification, which involves phase change, it is essential to evaluate the transient solidification pattern, liquid fraction distribution, solute distribution, and separation time and efficiency. Numerical modeling of the separation of CsCl from a LiCl‐KCl eutectic mixture has been carried out using Ansys Fluent (19.2). The effect of crystallizer geometry and cooling rates on the separation of CsCl has been numerically simulated. [ABSTRACT FROM AUTHOR]

LaYO3 which has phase stability at high temperature is introduced as a promising candidate for reaction-preventing crucible materials with Uranium-Zirconium (U-Zr) melt containing rare-earth elements (RE). RE is composed of rare-earth elements such as Nd, Ce, Pr and La. The LaYO3 material was synthesized by a solid-state reaction method at elevated temperature according to a pseudo-phase diagram of LaYO3 and Y2O3. Green compacts blended with La2O3 and Y2O3 powder were made by the Cold Isostatic Pressing (CIP) method, with La2O3 and Y2O3 powders varying with molar ratios from 1.0 to 1:2. LaYO3 synthetics were fabricated at sintering temperatures ranging from 1450°C to 1600°C. LaYO3 pellets sintered at below 1550°C showed a highly dense orthorhombic phase with a perovskite structure, resulting in an enhancing reaction-resistant effect with RE.

Metal fuel is a promising candidate for the pyro-processed nuclear fuel, but the problem of loss of nuclear material due to the high reactivity of metal fuel and melting crucible in the metal fuel casting process must be solved for loss control and waste reduction. In this study, fabrication test was conducted to develop a new material NdYO3 as a new crucible material to improve the degree of anti-reactivity. The NdYO3 compact was manufactured by the CIP (Cold isostatic pressing) method with changing fraction of Nd2O3 and Y2O3 powders. Sintering process was performed at 1550°C for 10 hours. The systematic trends of XRD patterns shows that phase transformations form cubic structure to monoclinic structures occurred with the addition of Y2O3. The rate of pore were discussed with change of fraction of Nd2O3 and Y2O3.

Oxidation of metals in water has been explored to generate sustainable carbon free hydrogen and power. This paper studies the thermal ignition of micro aluminum powders in high-pressure deionized (DI) water for cogeneration of hydrogen, heat, and alumina. Thermal ignition (temperature runaway) is necessary to ensure achieving high reaction temperatures, past the saturation temperature, where alumina formation is thermodynamically favorable. Aluminum powders with nominal particle diameters of 1, 10 and 45 μm with spherical morphology and 2 μm with flake morphology were mixed with DI water to form slurries with equivalence ratio of 1.3 in a 100 mL batch reactor. The reactor was pressure maintained between 500 and 2000 psig using a back-pressure regulator, and heat was injected into the slurry through an electric band heater. It was found that 1 and 2 μm powders ignite in compressed water, but only the 2 μm slurries achieved temperatures above saturation temperature at pressures above 700 psig. On the other hand, 10 and 45 μm powders require saturated steam for ignition at pressures above 1000 and 1200 psig, respectively. Hydrogen volume data indicate that larger powders at higher pressures optimize reaction yield, which is likely due to delayed ignition which preserves the active aluminum content and the particle-water reaction interfaces. Scanning electron microscopy images illustrate that the byproduct particles crack upon ignition at the saturation temperature, which increases the specific surface area by an order of magnitude relative to the aluminum powders. Pore size distribution data indicates the formation of micro, meso and macropores upon the ignition. X-ray powder diffraction data indicate that reaction temperatures above 450 °C promote the formation of alumina (Al 2 O 3) instead of boehmite (ALOOH). • Hydrogen, heat and alumina are cogenerated from reaction of aluminum with water. • Pressure controls the onset of reaction. • Specific surface area of the powder has a significant impact on ignition. • Presence of steam is necessary for ignition of larger powders. • High specific surface area alumina powder is produced. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Explosives & Propellants is the property of Chinese Journal of Explosives & Propellants Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Explosives & Propellants is the property of Chinese Journal of Explosives & Propellants Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Iron powder, classified as a metal, serves as a versatile energy carrier and stands as a compelling alternative to traditional fossil fuels. Its appeal lies in its remarkable abundance and wide availability, attributes that position it favorably as a sustainable energy source. Notably, iron-based fuels are characterized by their environmentally benign nature, thus constituting a valuable contribution to the realization of a carbon–neutral future. Given the ongoing concerns surrounding climate change, largely attributed to the combustion of fossil fuels and the subsequent emission of carbon dioxide, iron, with its substantial reserves, emerges as a prospective candidate to address the escalating global energy demands. Owing to its exceptional energy density, iron-based fuel holds the capacity to serve multifarious purposes, encompassing the generation of heat, electricity, and the propulsion of energy facilities and vehicular fleets. The noteworthy energy density of iron renders it an indispensable resource across a spectrum of industries and tools, allowing it to function as a reservoir of considerable potential. Iron powder exhibits the capacity to react with air and water, culminating in the production of both heat and electricity through the conversion of its inherent energy. Within the combustion of each iron particle, this chemical carrier behaves akin to a microreactor emitting heat, with the combustion rate of these particles remaining impervious to the ignition time. Furthermore, the combustion by-products of iron powder can be recycled and seamlessly integrated into clean energy technologies, minimizing carbon emissions. This comprehensive review seeks to provide a thorough assessment of renewable iron-based energy carrier. It will encompass an exploration of our current understanding of these fuels, including their reactivity with atmospheric air and the ignition mechanisms responsible for unleashing the flames of this promising energy source. While iron fuel, in its classification as a metal fuel, holds immense promise for the future energy landscape, its true environmental impact and the overall efficiency of the energy cycle remain subjects of ongoing study. This paper also examined both the practical applications and fundamental aspects of combustion involving iron powders, aiming to establish a comprehensive foundation essential for evaluating prospective metal engine technologies. Anticipated outcomes project energy and power densities of envisioned metal-fueled zero-carbon heat engines to approximate those of existing fossil-fuel-based combustion engines. This compelling similarity positions such engines as an enticing technological prospect for an impending era characterized by low-carbon imperatives. [ABSTRACT FROM AUTHOR]

Metal fuel is a promising candidate for the pyro-processed nuclear fuel, but the problem of loss of nuclear material due to the high reactivity of metal fuel and melting crucible in the metal fuel casting process must be solved for loss control and waste reduction. In this study, fabrication test was conducted to develop a new material NdYO3 as a new crucible material to improve the degree of anti-reactivity. The NdYO3 compact was manufactured by the CIP (Cold isostatic pressing) method with changing fraction of Nd2O3 and Y2O3 powders. Sintering process was performed at 1550°C for 10 hours. The systematic trends of XRD patterns shows that phase transformations form cubic structure to monoclinic structures occurred with the addition of Y2O3. The rate of pore were discussed with change of fraction of Nd2O3 and Y2O3. [ABSTRACT FROM AUTHOR]

Three-dimensional carrier-phase direct numerical simulations (CP-DNS) of reacting iron particle dust clouds in a turbulent mixing layer are conducted. The simulation approach considers the Eulerian transport equations for the reacting gas phase and resolves all scales of turbulence, whereas the particle boundary layers are modelled employing the Lagrangian point-particle framework for the dispersed phase. The CP-DNS employs an existing sub-model for iron particle combustion that considers the oxidation of iron to FeO and that accounts for both diffusion- and kinetically-limited combustion. At first, the particle sub-model is validated against experimental results for single iron particle combustion considering various particle diameters and ambient oxygen concentrations. Subsequently, the CP-DNS approach is employed to predict iron particle cloud ignition and combustion in a turbulent mixing layer. The upper stream of the mixing layer is initialised with cold particles in air, while the lower stream consists of hot air flowing in the opposite direction. Simulation results show that turbulent mixing induces heating, ignition and combustion of the iron particles. Significant increases in gas temperature and oxygen consumption occur mainly in regions where clusters of iron particles are formed. Over the course of the oxidation, the particles are subjected to different rate-limiting processes. While initially particle oxidation is kinetically-limited it becomes diffusion-limited for higher particle temperatures and peak particle temperatures are observed near the fully-oxidised particle state. Comparing the present non-volatile iron dust flames to general trends in volatile-containing solid fuel flames, non-vanishing particles at late simulation times and a stronger limiting effect of the local oxygen concentration on particle conversion is found for the present iron dust flames in shear-driven turbulence. [ABSTRACT FROM AUTHOR]

In this work, we use a boundary layer resolved model to improve a Lagrangian point particle model to simulate the combustion of single iron particles. By resolving the full boundary layer, mass and heat transfer are accurately modeled, including Stefan flow. Therefore, the model is suitable to improve point particle models. This work focuses on the first stage of iron combustion, which lasts up to the maximum temperature. Temperature- and composition-dependent properties are used and phase transitions from solid to liquid and liquid to gas are taken into account. The Nusselt and Sherwood correlations are investigated in conditions typical for iron particle combustion. It is found that the $$1/2$$ 1 / 2 -film temperature is the best film rule to use to model heat- and mass transfer for iron particle combustion. The boundary layer resolved model is used to validate the point particle models. Then, the model is systematically elaborated by including a temperature-dependent particle density, slip velocity and Stefan flow. The individual and combined effect of these phenomena on the burn duration are investigated. Including all these effects decreases the time to maximum temperature by around $$25\% $$ 25 %. Furthermore, it is shown that if one neglects physical phenomena like slip and Stefan flow, but uses the $$1/3$$ 1 / 3 -film rule instead of the $$1/2$$ 1 / 2 -film rule, errors cancel and still reasonable agreement is obtained with experiments. [ABSTRACT FROM AUTHOR]

Al–Mg–Li ternary alloy particles can be a promising metal additive to replace aluminum in solid propellants to improve combustion efficiency by reducing agglomeration during combustion. In this paper, Al–Mg–Li ternary alloy was prepared and its basic physical and chemical characterization parameters were obtained by SEM-EDS, ICP-AES, and XRD analysis. The ignition and combustion characteristics of single Al–Mg–Li particles under different pressures were investigated by using a self-developed experimental setup. The ignition process and combustion flame structure of Al–Mg–Li particles were significantly affected by the increasing pressure, and the ignition delay and combustion time decreased. The ignition mode was clearly identified: surface ignition (0.1–0.2 MPa) and gas phase ignition (0.4–1.2 MPa). Al–Mg–Li particles showed white-pink flame during combustion, and the characteristic peaks of AlO, MgO, and Li were identified, confirming that the particles performed a gas-phase combustion at pressures above 0.4 MPa. The combustion temperature of Al–Mg–Li particles could exceed 3000 °C when the pressure surpassed 0.6 MPa. The composition of different regions in the condensed combustion products were analyzed. Reaction mechanism was proposed to reveal the addition of elemental Mg and Li could improve the ignition and combustion characteristics of Al, especially at higher ambient pressures.

The development of fast reactors with complex designs and operation status requires more accurate and effective simulation. The Monte-Carlo method can generate multi-group cross-sections in arbitrary geometry without approximation on resonances treatment and leads to good results in combination with diffusion codes. However, in previous studies, the coupling of Monte-Carlo generated multi-group cross-sections (MC-MGXS) and transport solvers has shown relatively large biases in fast reactor problems. In this paper, the main contribution to the biases is proved to be the neglect of the angle-dependence of the total cross-sections. The flux-moment homogenization technique (MHT) is proposed to take into account this dependence. In this method, the angular dependence is attributed to the transfer cross-sections, keeping an independent form for the total sections. For the MET-1000 benchmark, the multi-group transport simulation results with MC-MGXS generated with MHT are improved by 700 pcm and an additional 120 pcm with higher order scattering. The factors that cause the residual bias are discussed. The core power distribution bias is also significantly reduced when MHT is used. It proves that the MC-MGXS with MHT can be applicable with transport solvers in fast reactor analysis.

Nanosizing and alloying of aluminum (Al) promisingly improve ignition and combustion performance of Al-based propellants. To aim this, lased-induced ignition and combustion characteristics of micro/nano-Al and aluminum@nickel (Al@Ni) alloy powders at elevated pressures (0.1–3.0 MPa) were investigated and the pressure effect on these characteristics was correspondingly evaluated. Comparative results demonstrate that nanosizing and alloying significantly shorten ignition delay and total burn time at elevated pressures, with ignition delay reduction of 98.04% and 52.28% at 1.0 MPa for nano-Al and Al@Ni alloy compared to micro-Al counterpart. Nanosizing and alloying can decrease crucial pressure values (‘mid-pressure extinction domains’) influencing ignition delay, and promote the transfer from the surface to gaseous combustion mode. Maximum combustion temperatures of nano-Al are higher than micro-Al and Al@Ni alloy. During combustion, the combustion of Al@Ni alloy is further intensified due to the microexplosion, while possibly inhibited at higher pressures.

To meet the requirements of mitigating the climate change, a large scale deployment of nuclear energy is expected, which impulses higher efficiency in the utilization of uranium resources. As one of the promising solutions, the integral fast reactor featuring in a high internal breeding can reach a high burn-up, low reprocessing mass, and a long refueling period. In this paper, the relationship between the breeding characteristics and two main design parameters of the core, the rod diameter and the pitch-to-diameter ratio (P/D), was studied. The negative impact on internal breeding caused by the measures for reduction of sodium void reactivity was also analyzed. All calculations were carried out with the Monte Carlo code RMC and ENDF/B-Ⅶ.1 continous-energy ACE data libraries. In each case the breeding characteristics were shown by both breeding ratio of the fissile nuclides and the regeneration ratio of the TRU nuclides. The variation of keff, fissile nuclides, TRU nuclides along with burnup were also illustrated. The calculation results indicate that the internal breeding can be significantly enhanced by increasing the rod diameter and by decreasing the P/D. With the current U-Pu-10Zr fuel parameters, a satisfactory burnup reactivity curve can be realized with the rod diameter at 7.0 mm and the P/D at 1.14, taking into account a balance between neutronics and thermal-hydraulics. The positive sodium void reactivity effect makes one of the largest risks of sodium cooled fast reactor (SFR) under unprotected severe accidents. The sodium void reactivity effect can be reduced by setting an upper sodium plenum and reducing the core height-to-diameter ratio (H/D). However, both methods bring significant cost to the internal breeding, due to a higher leakage of neutrons under normal operation. In this paper it is found that to bring the whole-core sodium void reactivity down to zero, the H/D must be as low as 0.15 approximately under the existence of an upper sodium plenum at the height of 40 cm. Such a design results in a fast drop of the burnup reactivity, as well as a low breeding ratio, a low regeneration ratio, and the decreasing of the fissile mass. It can be concluded that in the integral fast reactor design a dilemma exists between the high internal breeding and the low sodium void reactivity effect. This paper suggests that the integral fast reactor should focus on the breeding characteristics and thus a high efficiency of the utilization of uranium resources, leaving the sodium void reactivity to be incorporated into the overall design of the reactor safety features.

Ternary alloy fuel will be used as driver fuel for future fast reactors. Reprocessing of this spent alloy fuels will be carried out by pyrochemical reprocessing which is based on molten salt electrorefining at high temperature. During electrorefining, fission products get accumulated in the electrolyte along with some actinides in the form of their chlorides. The presence of fission products in the salt will add to the radioactivity levels and hence have to be stripped off. Melt crystallization is pursued to remove fission products from contaminated salt and to reuse the purified salt for electrorefining. Numerical modeling and experimental studies on tracking the phases during solidification of molten sodium nitrate salt were carried out. The numerical predictions closely matched with the experimental results. A resistance measurement technique was developed to accurately track the solidification interface so as to validate the numerical predictions. [ABSTRACT FROM AUTHOR]

Aluminum nanoparticles present excellent combustion characteristics, but such advantage is weakened due to particle agglomeration. This work focuses on this crucial behavior of aluminum nanoparticles in propellant and explore its underlying evolution mechanism from an atomic view. Molecular dynamic simulation method is used to simulate the agglomeration behavior under typical temperature of aluminum-based propellant. A two-staged accumulation-aggregation behavior is observed under low temperature due to atom movement driven by surface diffusion and grain boundary diffusion. A third stage of agglomeration dominated by viscous flow mechanism is achieved when the particle temperature is above 1500 K. The transition from aggregation to agglomeration is initiated by the solid-liquid phase transformation of the oxide shell, which happens under temperature lower than the melting point of alumina due to the formation of aluminum suboxide with low melting point. Decreasing the oxide layer thickness and integrity as well as particle size could accelerate the agglomeration and thus weakening the size advantage of aluminum nanoparticles. • Staged agglomeration behavior of ANPs and critical transition point is determined. • Underlying mechanism of agglomeration based on atom diffusion modes is revealed. • The transition is triggered by bi-directional atom diffusion to form Al suboxide. • Influences of oxide layer properties and particle size are explored. [ABSTRACT FROM AUTHOR]

To further our understanding of iron particle combustion, especially in the liquid state, i n s i t u optical measurements are performed for the size evolution and temperature of laser-ignited iron particles in a narrow size range around 45–55 μ m. The particle size evolution is monitored by a high-speed shadowgraphy system, and the particle temperature is probed using a two-color pyrometer synchronized with the shadowgraphy system. Before a particle reaches the peak temperature, its diameter grows linearly with elapsed time. Near the peak temperature, three types of particle size behavior are detected, namely, smooth transition, micro-explosion, and rapid inflation. For particles with smooth transition, the size and temperature reach the maximum values at the same time, and thereafter the size remains constant, while the temperature drops until rapid solidification of the iron oxide droplet. The micro-explosion and rapid inflation clearly indicate towards a quick gas release inside the particle. The ambient oxygen concentration has a strong effect on the growth rate of the particle size before the peak temperature but no influence on the final particle size. The measured relative particle diameter at the peak temperature suggests that iron has been fully oxidized and the degree of oxidation could be higher than FeO. At the onset of solidification, gas release occurs again, resulting in a second inflation or burst of already inflated particles. This suggests that the oxygen dissolved in the liquid iron oxide is at least more than needed to form solid Fe 3 O 4 , and the solidification process is accompanied with gaseous oxygen release via the phase transition: L2 ⟶ Fe 3 O 4 (s) + O 2 (g) at 1855 K, where L2 represents liquid iron oxide with dissolved excess oxygen. [ABSTRACT FROM AUTHOR]

We present a numerical study of the combustion of single iron particles in an O 2 –N 2 atmosphere. By resolving the full boundary layer, mass and heat transfer are accurately modeled, including Stefan flow. Only the conversion of Fe to FeO is taken into account and evaporation is implemented to investigate the formation of nano-sized iron-oxides products. Temperature- and composition-dependent heat capacity and density are used and phase transitions from solid to liquid (and vice-versa) are accounted for by the apparent heat capacity method. The model is validated by comparing the time to maximum temperature (t max) and the maximum temperature (T max) of a 40 and 50 µm particle in an O 2 –N 2 atmosphere with experiments. The current model, which assumes infinitely fast internal transport, can well estimate the maximum particle temperature and the time to reach this maximum temperature, but it does not capture the particle size effect on the maximum temperature. Even though the particle temperature stays below its boiling temperature, a small but non-negligible amount of mass is lost due to evaporation of the particle. Evaporation of the particle and oxidization of the gaseous Fe-containing species in the boundary layer limit the maximum temperature of the particle when increasing the oxygen concentration. By means of a sectional model, the formation and growth of the iron oxide nano-particles is numerically investigated. It is shown that somewhat further downstream of the particle, the volume fraction of nano-particles attains a maximum. An average nano-particle diameter of 40 nm is found at t / t max = 1 in the wake of a 50 µm iron particle burning at 21% oxygen concentration. [ABSTRACT FROM AUTHOR]

Metal fuels have a high potential for applications in space propulsion owing to their superior energy density and distinct combustion characteristics. Therefore, research into the combustion properties of metal fuels in microgravity has become necessary. The principles, applications, benefits, and limitations of experimental methods for microgravity combustion of metal fuels were compared in this review. Drop towers, aircrafts, sounding rockets or microgravity balloons, acoustic or ultrasonic levitation, electrodynamic levitation, space stations, and numerical simulations are common methods used to provide microgravity for combustion research. Among them, the devices providing microgravity environment on the ground has become a good choice for simulating microgravity environment owing to its convenience, reliability and relatively low cost. Further, the physical and chemical properties of common metal fuels, such as aluminum, boron magnesium, and so on, were introduced, and the existing research achievements on the combustion of metal fuels in microgravity are succinctly summarized in this paper. The melting process, ignition temperature, combustion temperature, flame structure, and extinction of metal fuel combustion will be affected by microgravity. Moreover, the necessity and insufficiency of the research are also illustrated. Finally, the existing and potential applications of metal fuels in space propulsion and space weapons are introduced. Metal fuels’ superior energy density and combustion performance can benefit deep-space exploration, particularly Mars exploration, and bring new insights into the design of space weapons. This paper may throw some new light on the study of metal fuel combustion in microgravity.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Following the ignition and solid-to-liquid phase transition of a fine (on the order of 10–100µm in diameter) iron particle, the self-sustained combustion of a liquid-phase droplet of iron and its oxides takes place. The objective of the current work is to develop an interpretive and explanatory model for the liquid-phase combustion of a single fine iron particle. A zero-dimensional physicochemical model is developed assuming fast internal processes, such that the combustion rate is limited by the rate of external oxygen (O2) transport. The model considers a particle covered by a shell of liquid-phase FeO enclosing a core of liquid-phase Fe. Stefan flow and diffusion are considered for the gas-transport of O2, while the gas-transport of gas-phase Fe and FeO are calculated via diffusion only. The outward gas-phase Fe and FeO consume inward-transported O2 to stoichiometrically form hematite (Fe2O3), and the remaining oxygen that reaches the particle surface is entirely consumed to form liquid-phase FeO. The time history of simulated particle temperature shows consistent overprediction of the peak particle temperature when compared to experimental temperature measurements, indicating that the assumption of fast internal kinetics may be incorrect. The model is also unable to capture the apparent slow cooling rate observed in experiments. A further analysis is performed through a heuristic model with a calibrated reaction-rate law, where the internal diffusion of reactive Fe and O ions may become rate-limiting. The calibration of the pre-exponential factor in the Arrhenius term to match the experimental peak temperature yielded good agreement of time to peak temperature, as well as the slow cooling rate. The heuristic model considering internal diffusion predicts a plateau in peak temperature with increasing oxygen concentration. Possible uncertainties of the models, as well as future work, are discussed.

The effective usage of renewable energy sources requires ways of storage and delivery to balance energy demand and availability divergences. Carbon-free chemical energy carriers are proposed solutions, converting clean electricity into stable media for storage, long-distance energy trade and on-demand electricity generation. Among them, hydrogen (H2) is noteworthy, being the subject of significant investment and research. Metal fuels, such as iron (Fe), represent another promising solution for a clean energy supply, but establishing an interconnected ecosystem still requires considerable research and development. This work proposes a model to assess the supply chain characteristics of hydrogen and iron as clean, carbon-free energy carriers and then examines case studies of possible trade routes between the potential energy exporters Morocco, Saudi Arabia, and Australia and the energy importers Germany and Japan. The work comprises the assessment of economic (levelized cost of electricity - LCOE), energetic (thermodynamic efficiency) and environmental (CO2 emissions) aspects, which are quantified by the comprehensive model accounting for the most critical processes in the supply chain. The assessment is complemented by sensitivity and uncertainty analyses to identify the main cost drivers. Iron is shown to be lower-cost and more efficient to transport in longer routes and for long-term storage, but potentially more expensive and less efficient than H2 to produce and convert. Uncertainties related to the supply chain specifications and the sensitivity to the used variables indicate that the path to viable energy carriers fundamentally depends on efficient synthesis, conversion, storage, and transport. A break-even analysis demonstrated that clean energy carriers could be competitive with conventional energy carriers at low renewable energy prices, while carbon taxes might be needed to level the playing field. Thereby, green iron shows potential to become an important energy carrier for long-distance trade in a globalized clean energy market.

In order to clarify the relationship between elemental compilation, phase compilation and intrinsic characteristics of Al-based alloy fuels, the influence laws on physicochemical characteristics and combustion properties when Iowa bowling point metals, tow meriting point mete! and high meriting point mete! are used as al toying cements were summarized respectively, when the differences in ignition and Combusiion mechanisms of different aluminum-based alloy leis wet analyzed. Aluminum-tow boiling point metal afro(Al-MB), labium meriting point metal alloy(Al-MM) and aluminum-high meting point metal alloy(Al-MM) have particulate ignition and Combusiion mechanism, and thus possess the menace of physicochemical properties and Combusiion characteristics. Dicing the Combusiion process of labium-based alloy fuels, thee ate various principles font improving Combusiion efficiency such as interposition of Al-MB, exothermic alloying/oxidation channels in Al-MM, and expo-thermic erasable phase in AI-Mm . Research poetess of the research on he application of Al-based alloy leis in sod to-paeans was summarized in terms of energy enhancement and burning ate regulation. it is pointed out that the energy perform-lance of sod propellants can be improved through the increase of theoretical specific impulse, Combusiion efficiency, density and the decease of two-phase low kiosks. The effect of the Al-based alloy leis on the burning ate of sod propellants can be adjusted by the component of oxidize and bidet. The key point is to determine the relationship font preparation-structures-characteristics, solve he contradiction between he safety and activity, and improve the mechanism of Combusiion carnalities and energy td ease in reaction, which ate coca font the deign, application and performance control font Al-based alloy as leis font propellants. 75 References were attached. [ABSTRACT FROM AUTHOR]

Ignition temperatures of metal particles play an essential role in not only the fundamental theories of non-volatile dust flames but also the robust operation of practical metal fuel burners. The present paper introduces a novel approach to accurately measure the ignition temperature of an isolated particle. Micron-sized single particles are injected downwards into a quartz tube heated externally by a premixed flame near the bottom end. During free fall, a particle, if sufficiently small, closely follows the gas-phase temperature that increases gradually from top to bottom. By measuring the ignition position of the particles, the ignition temperature is determined from the gas-phase temperature profile that is quantified a priori. Applying the approach together with high-speed imagining and diffuse backlight-illumination techniques, the ignition temperature of approximately 30–60 μ m iron particles in O 2 /N 2 mixtures are comprehensively measured at oxygen mole fractions of 10%–50%. The experimental results reveal that the measured ignition temperatures is in the range of 1030–1130 K that are independent of the oxygen mole fraction and the particle size. In contrast, the particle size significantly influences the ignition probability. Smaller particles have lower probabilities to ignite. At the oxygen mole fraction of 10%, ignition is only observed for iron particles larger than approximately 45 μ m. For all other cases, ignition is detected for all particle diameters. Possible mechanisms underlying the experimental observations are discussed. Novelty and significance statement A novel approach to measure the ignition temperature of an isolated, micron-sized particle is developed. Compared to existing methods, the new approach provides a convenient way to determine the ignition temperature accurately and examine the size dependence of the ignition characteristics. For the first time, size-resolved ignition temperatures of isolated iron particles are reported. For a fixed particle diameter, the existence of an ignition probability is revealed. The quantitative experimental results have a high potential to be widely used to validate models of iron particle ignition. [ABSTRACT FROM AUTHOR]

Simultaneous, in-situ , optical diagnostics are performed to measure initial diameters and the temporal temperature evolution of iron microparticles burning in hot laminar oxidizing atmospheres with 10–30 vol% O 2. The pre-ignition particle diameter and temperature evolution during combustion are monitored using synchronized high-speed diffuse backlight-illumination and two-color pyrometry techniques, respectively. Average temperature histories are obtained for particles sorted into three size fractions centered at 40, 45, and 50 μ m with a span of 5 μ m. Increasing the oxygen level from 10 to 30 vol%, particles burn faster and reach a higher peak temperature that increases approximately from 2400 to 3200 K. From their temperature trajectories, the peak temperatures of individual particles are extracted and correlated with their initial diameters. It is observed that the maximum particle temperature decreases with the increasing particle diameter, attributed to the enlarged radiative and evaporative heat losses relative to the chemical heat release of the larger particles that burn in the diffusion-limited regime. In addition, the size dependence of the maximum particle temperature enhances considerably when the particle peak temperature increases from approximately 2400 K to around 2800 K, but its further variation is small as the particle peak temperature continues approaching the boiling point of the particles. This observation does not align with previous non-size-resolved measurements that have lower temporal resolutions and wider particle size distributions. Possible reasons for this inconsistency are discussed. A theoretical analysis is performed to quantitatively reveal the role of surface radiation and evaporation in the size dependence of the particle peak temperature. The results suggest that at relatively low particle temperatures the size dependence is determined mainly by radiation and that the effect of evaporation becomes more dominant at higher particle temperatures. Moreover, with increasing particle temperature, radiation strengthens the size dependence of the particle peak temperature. On the contrary, evaporation weakens the size dependence at higher temperatures because of the increasing sensitivity of vapor pressure (evaporative heat loss) to the temperature according to Clausius–Clapeyron relation. Novelty and significance statement This work presents, for the first time, the simultaneous, in-situ measurements of the initial sizes and time-resolved temperatures of micrometer-sized iron particles burning at elevated gas temperatures. Using current size-resolved measurements, particle-temperature evolutions for several particle diameters are statistically obtained with significantly increased precision. This high-fidelity experimental database over a wide range of operating conditions is a very valuable reference for the iron fuel community to validate and improve numerical models of iron particle combustion. Due to the novel design of the experiment, in this work negative correlations between the initial diameters and the maximum temperatures of isolated burning iron particles are observed and theoretically explained. This result does not align with previous non-size-resolved measurements that have lower temporal resolutions and wider particle size distributions. [ABSTRACT FROM AUTHOR]

• Ignition of Mg particles in CO 2 includes melting, evaporation, breaking and ignition phases. • Fractures occur preferentially at weak locations with low compressive strength limits. • Ignition of Mg particles occur almost simultaneously at the moment of Mg vapor injection. • Increasing pressure shortens ignition delay and accelerates gaseous combustion rate of Mg/CO 2. • Ignition and combustion of Mg particles in CO 2 are dominated by a liquid-gas reaction. Combustion studies of individual Mg particles under CO 2 atmosphere are essential for the development of Mg/CO 2 powder rocket engines for in-situ resource utilization (ISRU) technology on Mars. In this work, the ignition and combustion characteristics of individual micron-sized Mg particles prepared by gas-atomization method under CO 2 atmosphere were investigated in detail. It was found that the ignition delay of Mg particles was determined by two factors, i.e., ambient pressure and particle size, and the former had a greater influence on the ignition delay of the particles. As the pressure increased, the ignition delay time of the particles decreased significantly. For particle sizes between 30 μm and 35 μm, the ignition delay times of Mg particles at 0.9 MPa and at 1.6 MPa were only ∼2 % and ∼1 % of that at atmospheric pressure. The ignition delay time of Mg particles increased linearly with the increasing particle size at both atmospheric pressure (0.1 MPa) and high-pressure (1.6 MPa) CO 2. During melting and evaporation, the newly generated non-dense oxides grew unevenly along the surface of Mg particles, leading to inhomogeneity in the mechanical strength of the oxide layer. Fracture occurred preferentially at weak locations with low compressive strength limits, resulting in selectivity in the direction of the Mg vapor injection at the moment of shell breaking. Finally, it is proposed that the ignition and combustion of individual Mg particles should be dominated by a liquid-gas reaction and that pressure and particle size are crucial for the combustion performance of micron-sized Mg particles. Classical understanding of Mg/CO 2 combustion for in-situ resource utilization technology of Mars exploration relies on the gas-phase reaction, however, difficultly explaining the overall ignition and combustion evolution. A novel observation and recognition of traditional Mg/CO 2 combustion reaction through self-built real-time microscope with high-speed cinematography and highly-focused inductive laser ignition, indicating that the oxides of individual Mg particles in CO 2 atmosphere grow non-uniformly along the surface, which leads to the preferential shell breaking of Mg vapors at the weak points with lower mechanical strength and eventually causes the particles to be ignited. Highly temporally and spatially resolved visualized images, spectrum, temperature, and product SEM information firstly demonstrate that the ignition and combustion of individual Mg particles in CO 2 are dominated by a liquid-gas reaction, experiencing the surface and gas-phase combustion and confirming that high pressure significantly improves the ignition performance of Mg particles and promotes gas-phase combustion in CO 2. [ABSTRACT FROM AUTHOR]

Micrometric spherical particles of iron in two narrow size ranges of (38–45) µm and (45–53) µm were injected in a bench scale, transparent drop-tube furnace (DTF), electrically heated to 1400 K. Upon experiencing high heating rates (104–105 K/s) the iron particles ignited and burned. Their combustion behavior was monitored pyrometrically and cinematographically at three different oxygen mole fractions (21%, 50% and 100%) in nitrogen. The results revealed that iron particles ignited readily and exhibited a bright stage of combustion followed by a dimmer stage. There was evidence of formation of envelope micro-flames around iron particles (nanometric particle mantles) during the bright stage of combustion. As the burning iron particles fell by gravity in the DTF, contrails of these fine particles formed in their wakes. Peak temperatures of the envelope flames were in the range of 2500 K in air, climbing to 2800 K in either 50% or 100% O2. Total luminous combustion durations of particles, in the aforesaid size ranges, were in the range of 40–65 ms. Combustion products were bimodal in size distribution, consisting of micrometric black magnetite particles (Fe3O4), of sizes similar to the iron particle precursors, and reddish nanometric iron oxide particles consisting mostly of hematite (Fe2O3).

Combustion of micron-sized particles of iron, a promising renewable alternative to fossil fuels, was investigated in a drop tube reactor (DTR) under overall lean conditions. A bimodal particle size distribution was observed after combustion: black micron-sized particles consisting of a mixture of iron oxides, with oxidation degrees ranging from 60% to 90%, and reddish fine particles of Fe 2 O 3. The oxidation degree of the products showed no obvious variation with the reactor temperature. The coarse product particles were comparable in size with those of the raw iron particles, independent of temperature. The evaporation of iron represented a mass loss of 1%–2%. The primary nm-sized particles agglomerated to form aggregates of the order of 1 μ m. A simplified model for the combustion was used to analyze the results. It was based on the Particle Equilibrium Composition approach by van Gool et al. (Appl Energy Combust Sci 2023;13:100115) that assumes the oxidation from Fe to FeO to be limited by external diffusion and further oxidation by thermodynamic equilibrium. The model predicted larger oxidation degrees than observed experimentally. The difference was believed to be due mainly to stratification in the drop tube reactor, resulting in local fuel-rich conditions. The small impact of reactor temperature on the final oxidation stage indicated that diffusion limitations, rather than kinetic barriers, were rate controlling. • Lean combustion of μ m -sized iron particles in a drop tube reactor resulted a bimodal product distribution with coarse melted particles and aerosols. • The oxidation degree of the coarse particles was 60%–90%, independent of reactor temperature in the 700-1200 °C range. • The incomplete oxidation to Fe 2 O 3 was attributed to mixing limitations. • The lack of temperature effect on oxidation degree indicated diffusion control. • The evaporation of iron represented a mass loss of 1%–2%. • The primary nm-sized particles agglomerated to form aggregates of the order of 1 μ m. [ABSTRACT FROM AUTHOR]

Significant heat generation will be required for humans and equipment to the lunar night. In this work, we investigate the use of a sustainable in-situ thermite material as a fuel to provide the thermal energy required to keep components in working conditions. Magnesium is used as a reactive metal fuel, with lunar regolith simulant ball milled to sub-micron sizes as a solid oxidizer producing exothermic reactions. Enhanced combustion is achieved by controlling particle size and composition of the thermite mixture. Simulant particles ranging from hundreds of nanometers to tens of microns in diameter are tested, as well as the magnesium fuel compositions of 20% to 40% by weight. Small pellets of 3 mm in diameter and 3 mm in height are ignited by laser in both air and vacuum to quantify the combustion properties in different environments. High speed video, infrared camera and pyrometry techniques are taken to quantify the sample combustion properties. These pellets demonstrate the burning rates between 2.3 and 5.9 mm/s and temperatures ranging from 1100 to 1480 °C in vacuum and in air conditions, respectively. The samples composed of 20% magnesium and 80% regolith simulant release around 400 J/g, and sustain elevated temperatures for 15 s after combustion, making them suitable for in-situ lunar heating. Novel 2D temperature mapping allows greater understanding of the simulant thermite combustion. Based on the results, we discuss the design considerations that would need to be made in the creation of an in-situ metal fuel heating lunar system. • Micro/nanoparticle combustion of magnesium/JSC-1A lunar regolith simulant. • Effects of composition and particle size suggest tunable reaction properties. • Self sustained combustion in vacuum with an energy release of 400 J/g. • Reaction temperatures over 1400 °C and burning rates of 2.3 to 5.9 mm/s. • 2D temperature data for future modeling studies. [ABSTRACT FROM AUTHOR]

This paper proposes a 0D modelling strategy for the combustion of a single iron particle. The primary objective was to accurately represent the evolution of the particle temperature, including key parameters such as the peak temperature T max and associated characteristic burn time τ b , and oxidation dynamics in a wide range of conditions. An optimisation approach, rather than a purely mechanistic model, was chosen to further close the current gap between numerical simulations and experimental observations. The model considers oxidation processes, heat transfer, solid–liquid phase changes and dissociative evaporation. Intra-particle reaction rates are controlled by external O 2 diffusion combined with an optimised O 2 absorption reduction quantity γ , but at the end of the combustion process by a more adequate empirical kinetic rate. A first combustion stage involving the reaction 2 Fe + O 2 → 2 FeO is followed by two successive stages with the respective reactions 6 FeO + O 2 → 2 Fe 3 O 4 and 4 Fe 3 O 4 + O 2 → 6 Fe 2 O 3 . This oxidation strategy is based on the Fe-O phase diagram and experimental observations of oxidation beyond FeO. Mass and enthalpy balances for the particle gave its temperature evolution, which was compared with experimental data and state of the art modelling approaches. The numerical overestimation of T max in environments with elevated O 2 concentration was addressed via the optimised quantity γ , which was modelled as piecewise constant, changing once at a predetermined burn time based on experimental measurements of the burn time τ b. Correlations for the moment of reduction of the quantity γ and for its initial value were introduced, both related to the initial particle diameter and O 2 molar fraction in the gas. Further model refinement is required to enhance the accuracy of simulated cooling rates in high-temperature combustion environments, where experimental data are particularly scarce. In another scenario, characterised by reduced O 2 conditions and hitherto unexplored in the numerical modelling literature, an underestimation of T max was found even assuming the maximum possible oxidation rate. This observation has prompted the authors to question the suitability of the correlations used in existing models to calculate the convection coefficient, which seems to be slightly overestimated. The proposed simple and efficient modelling framework has demonstrated its potential ability to accurately reproduce key combustion characteristics of a burning iron particle in a wide range of conditions. And it will thus serve as a good starting point for the simulation of heterogeneous particle-laden reactive flows. • Iron particle combustion model with time-controlled oxygen absorption reduction. • Optimisation of simulated combustion characteristics using experimental data. • Proposition of correlation models for the estimation of oxygen absorption rate. • Favourable comparison of results with those of state of the art modelling approaches. • Tendency to underestimate peak particle temperature in reduced oxygen conditions. [ABSTRACT FROM AUTHOR]

The present experimental study focuses on the determination of the oxidation progress and internal structures during the combustion of single iron particles using combined in-situ optical measurements and ex-situ material examination of rapidly quenched particles. Narrowly sieved iron particles with a mean diameter of 49 µm are ignited and burn in the hot exhaust of a premixed CH 4 /O 2 /N 2 flat flame with remaining 20 vol% O 2 , provided by a laminar flow reactor with well-defined thermal and flow boundary conditions. During particle combustion, key parameters of oxidation progress are determined optically in a time-resolved manner, such as the time-resolved particle surface temperature and the reaction time relative to the instant of the particle peak temperature. Furthermore, individually burning particles are rapidly quenched at different combustion stages and then extracted from the exhaust gas using an isokinetic extraction probe. The bulk composition of the quenched particles with respect to α -Fe and its three oxides FeO, Fe 3 O 4 , and Fe 2 O 3 is determined using Wide-angle X-ray Scattering and 57Fe Mössbauer Spectroscopy. Combining the information obtained from in-situ and ex-situ measurements, it is shown that iron particles oxidize rapidly to FeO during the initial stage of combustion, followed by a much slower oxidation to Fe 3 O 4 as the particles cool down. The peak particle temperatures are measured during the fast initial oxidation. Finally, particles sampled from representative positions of the oxidation process are analyzed by Energy-Dispersive X-ray Spectroscopy and Focused Ion Beam Scanning Electron Microscopy, revealing different particle morphology and internal structures. For the first time, the clear presence of an oxide shell and iron-core structure in quenched particles suggests that liquid iron and liquid iron oxide are layered during liquid phase combustion, if the particle remains within the miscible gap. • Iron particle peak temperature is near the stoichiometric ratio of Fe and O. • Iron particles combust in a core shell structure initially. • Micron sized iron particle oxidation history plotted on Fe O phase diagram. • Particle sampling with well characterized sampling probe. [ABSTRACT FROM AUTHOR]

• Metal alloy microparticles directly derived from the waste stream of additive manufacturing. • Experiments were conducted on micro-sized AlSi10Mg particles via two unique approaches. • Reactivity was investigated in gaseous oxygen and using a solid oxidizer (CuO nanoparticles of 500 nm) in thermal analysis. • Combustion tests were performed in ambient conditions as well as at low pressure (100 Pa) Metal powders including aluminum, iron and metal alloys have been considered as a fuel for energy generation without releasing carbon dioxide and being recyclable. While additive manufacturing processes desire feedstock microparticles with a specific size range, a significant amount of metallic powders is left in its waste stream. In this work to investigate the potential applications of these alloy powders, they are mixed with solid metal oxide particles for combustion tests in ambient and low-pressure environments. The thermochemical properties and exothermic characteristics are measured on the mixtures of micro-sized AlSi10Mg particles with a median diameter of 13 µm and CuO nanoparticles of 500 nm. Experimental results indicate, compared to Al micron particles with a similar average diameter, the reaction between AlSi10Mg powder and oxygen shows a comparable onset temperature (around 1000⁰C), a similar activation energy (316.9 kJ/mol), but a much higher energy release (11.5 kJ/g vs. 4.2 kJ/g). When mixed with CuO nanoparticles, AlSi10Mg/CuO and Al/CuO mixtures exhibit a similar reaction kinetics which is characterized by the diffusion of gaseous oxygen produced from the thermal decomposition of CuO. In the ambient combustion tests, the AlSi10Mg/CuO powder shows a 20 % shorter ignition delay, 3 times faster burning rate, and up to 2 times higher impulse than these of the Al/CuO powder. When a low air pressure (about 100 Pa) is applied, the AlSi10Mg/CuO powder is successfully ignited and combusted, while the micron-Al/CuO powder cannot be ignited. We conclude the micro-sized Al-Si-Mg alloy particles recycled from the advanced manufacturing processes can be a good candidate for metal fuel. [ABSTRACT FROM AUTHOR]

The ignition temperature is closely linked to the reaction front speed in iron dust flames, a crucial target quantity when trying to predict the characteristics of such flames. To this end, the ignition of iron microparticles is analyzed in this paper by means of single particle simulations which are compared with recent ignition experiments by Ning et al. Different particle sizes and oxygen concentrations in the gas phase are investigated, since iron particles in a dust flame are polydisperse and experience vastly different oxygen atmospheres. Several modeling approaches have been proposed for the reaction kinetics governing the ignition process and in this work, two of the most widely used models are considered: one describing the kinetics as a surface reaction and the other assuming the diffusion of iron cations through the solid oxide layer as the rate-limiting mechanism. The onset of the particle oxidation can be characterized by the solid-phase oxidation time (SOT) during which inert heating and thermal runaway of the iron microparticles occur. Therefore, the SOT allows for the assessment of the predictive capabilities of the models regarding ignition. With this background, it is the objective of this work to gain insights into the rate-limiting mechanisms controlling the ignition and to assess, whether the state-of-the-art models require further calibration. Uncertainty assessment is performed for the SOT predictions reflecting experimental uncertainties for particle sizes. It is found that the current models mostly underpredict the SOT which is a strong indication that the limiting factors for all cases of iron oxidation are still not sufficiently well understood. The experimental measurements indicate that the SOT depends on the oxygen concentration of the surrounding gas. Possible rate-limiting mechanisms are discussed and new kinetics parameters are proposed from model calibration with the experimentally measured SOT. The ignition temperature of the calibrated model is compared with measured ignition temperatures from various experimental studies in the literature and reasonable agreement is found. • Kinetic-limited iron oxidation is influenced by O 2 concentration in ambience. • State-of-the-art 0D models underpredict solid oxidation times (SOT) from experiments. • First Order Surface Kinetics model qualitatively captures trend of the SOT. • Solid Oxide Layer Diffusion model requires extension to capture influence of O 2. • New kinetics parameters are proposed for First Order Surface Kinetics model. [ABSTRACT FROM AUTHOR]

• In situ resource utilization of carbon dioxide. • Detailed analysis of multilayer oxidation shell structures provided. • Moving micron-scale single-particle combustion was observed and measured. • Temperature data enhances burning time measurement and mode classification. An experimental system integrating micro-sized single particle generation, ignition, and observation was proposed and constructed for investigating the combustion characteristics of magnesium single particles in carbon dioxide. Defining the onset of combustion using the boiling point temperature allows for precise measurement of combustion time without artificial interference. Results revealed four modes of combustion for magnesium particles (Vapor-phase combustion, surface reaction, Micro explosion and flash-out mode) in carbon dioxide. Vapor-phase combustion is diffusion-controlled (with a D 0 1.76 scaling, where D 0 is the initial particle diameter). Additionally, the micro-explosion mode primarily occurs in particles with diameters exceeding 70 μm, and the combustion time is rather insensitive to the particle size (Typically 0.5 ∼ 2.2 ms in this study). The characteristic temperatures of the particles were determined using two-color pyrometry, indicating that the particle combustion temperature decreases with increasing particle size. Magnesium particles typically reach temperatures approximately 800 K higher than normal vapor-phase combustion temperatures before experiencing micro-explosions. Analysis of combustion products shows that the oxide shell formed by the combustion of magnesium particles has a three-layer structure. Both the outer and inner layers are mixed layers of magnesium oxide and solid carbon produced during combustion reactions, and the middle layer is the initial oxidation layer of the particles. [ABSTRACT FROM AUTHOR]

Combining laser ignition tests with quenched particle cross-sectional analyses, this study explores the formation of bubbles and microexplosions in burning boron agglomerates, and discusses the plausible mechanisms behind the microexplosion (expansion–rupture) phenomenon. High-resolution images reveal that these phenomena are caused by bubble nucleation and growth within the molten droplet. Based on the timescale, it is categorized into weak expansion and strong expansion phenomena. The expansion rate of droplets during the weak expansion process mostly ranges between 0.006 m/s and 0.4 m/s, while during the strong expansion process, it predominantly falls between 0.4 m/s and 1 m/s. An increase in ambient pressure results in the delayed occurrence and reduced frequency of the expansion–rupture phenomenon. When the ambient pressure exceeds 3 atm, the expansion phenomenon no longer occurs. In addition, a decrease in the initial diameter of the agglomerates lowers the overall occurrences of expansion–rupture. Analysis of the quenched particle cross-sections reveals that the size and density distributions of the pores within the boron agglomerates reduce gradually during the combustion process. In addition, the surface oxide layers of certain pores are removed during combustion. Estimates of the vaporization rates of (BO) n and B 2 O 3 support the speculation that the expansion of molten boron droplets is attributed to the evaporation of boron oxide layer. In this process, the molten boron acts as a heating surface to evaporate the boron oxide trapped inside the droplet, thus producing B 2 O 3 , B 2 O 2 , and BO, and leading to droplet growth and tearing of the liquid film. Analysis of bubble growth indicates that the merging of adjacent bubbles to reach the critical nucleation size is probable the starting point of the expansion process. These results can be helpful in promoting the combustion efficiency of boron within the combustion chamber. [ABSTRACT FROM AUTHOR]

With the increasing interest in small modular reactors or microreactors, developers are working to design and submit licensing approval requests of U–10Zr-fueled fast reactors. The developers and their proponents cite prior metal fuel experience (worldwide, but U.S. experience in particular for many developers) as the motivation and justification for their reactor concepts. The experience with metal fuel deployment in sodium-cooled fast reactors as well as the underlying irradiation testing database, provide a suitable basis for analytically justifying the use of metal fuel in new reactors. The evolution of metal fuel design and capability illustrates the importance of key fuel design parameters to consider in new applications of the prior experience: fuel smeared density, plenum-to-fuel volume ratio, the ratio of cladding radius to thickness, fuel composition, and cladding and duct materials. In-service operating and deployment conditions to be considered include fuel linear heat generation rate, fuel temperature, cladding temperature, peak burnup and peak fast fluence. Fuel designs and in-service conditions that are bounded by the database and experience are most easily addressed, but deviations from those previous parameters and conditions can be addressed by considering impacts on previously established behavior and applying other mitigating conservatisms, as appropriate. The authors recommend any new deployment proceed with fuel surveillance and monitoring to mitigate risk, application of conservative measures to address uncertainties, and a fuel qualification program that addresses a range of in-service operating conditions with production fuel. The work reported should be of interest to students and regulators unfamiliar with metal fuel in fast reactors. • Metal fuel deployment in SFRs can be technically supported by prior experience. • Evolution of metal fuel design illustrates the importance of fuel design parameters to consider. • Fuel designs bounded by the database and experience are most easily addressed. • Deviations from previous designs can be addressed by considering impacts and mitigations. • New deployment should include fuel surveillance and monitoring to mitigate risk. [ABSTRACT FROM AUTHOR]

In this study, the influence of temperature (40, 60 and 80 ∘C) and light exposure on the dissolution of ▪ particles in aqueous, oxalic acid (0.45 mol/l) is experimentally investigated. A novel experimental setup, consisting of a vessel with undistorted optical access, allows the recording of dissolving particles using a video system. During post-processing, particles are automatically identified and their size and morphology are determined. Binning particles into discrete time-steps during the reaction yields heavy-tailed distributions characterized by a single parameter estimated through a maximum-likelihood estimation of a doubly truncated power-law fit. For the first time, up to three consecutive phases could be identified during the dissolution process of iron oxide particles. The contribution of each phase to the overall dissolution process is determined by a complex interplay between particle fragmentation, different reaction mechanisms and solid product formation. The initial phase is characterized by the fragmentation of larger particles with a more complex morphology, resulting in greater surface area available for reaction. In the second phase, fragmentation is less apparent and the available particle surface area is reduced. The transition to the third phase relies primarily on the supply of short wavelength light, which leads to the formation of a solid product that can increase the tracked particle diameter. • Up to three consecutive phases during iron oxide particle dissolution. • First phase dominated by particle fragmentation leading to increasing surface area. • Second phase dominated by surface area reduction, less by particle fragmentation. • Third phase occurs only at low temperatures and short-wavelength light exposure. • The third phase is characterized by solid product formation. [ABSTRACT FROM AUTHOR]

Iron powder can be a sustainable alternative to fossil fuels in power supply due to its high energy density and abundance. Iron powder releases energy through exothermic oxidation (combustion), and stores back energy through its subsequent hydrogen-based reduction, establishing a circular loop for renewable energy supply. Hydrogen-based direct reduction is also gaining global momentum as possible future backbone technology for sustainable iron and steel production, with the aim to replace blast furnaces. Here, we investigate the microstructural formation mechanisms and reduction kinetics behind hydrogen-based direct reduction of combusted iron powder at moderate temperatures (400–500 °C) using thermogravimetry, ex-situ X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscatter diffraction, as well as in-situ high-energy X-ray diffraction. The influence of pre-oxidation treatment was studied by reducing both as-combusted iron powder (50 % magnetite and 50 % hematite) and the same powder after pre-oxidation (100 % hematite). A gas diffusion-limited reaction was obtained during the in-situ high-energy X-ray diffraction experiment, with successive hematite and magnetite reduction, and a strong increase in reduction kinetics with initial hematite content. Faster reduction kinetics were obtained during the thermogravimetry experiment, with simultaneous hematite and magnetite reduction. In this case, the reduction reaction was limited by a mix of phase boundary and nucleation and growth models, as analyzed by multi-step model fitting methods as well as by microstructural investigation. When not limited by gas diffusion, the pre-oxidation treatment showed almost no influence on the reduction time but a strong effect on the final microstructure of the reduced powder. [Display omitted] [ABSTRACT FROM AUTHOR]

• An SFR-based Small Modular Reactor (SMR), SALUS-100 is developed by KAERI. • The reactor features incorporate a long fuel-cycle core concept with a metallic alloy fuel. • The inherent safety and reliability features focuses on preventing severe accidents. • The key research and development activities for technology advancements are introduced. • The innovative design of SALUS-100 offers diverse applications in future SMR markets. The paper introduces the innovative development of an SFR-based Small Modular Reactor (SMR) known as SALUS-100, with a 100 MWe electrical output, developed by KAERI. This innovative design, derived from the previous TRU transmutation burner SFR concept, represents a significant step forward in establishing a new model for SMRs and offers diverse applications, including on– and off-grid electricity generation, district heating, and industrial heat supply. The reactor features of SALUS-100 incorporate an integrated pool-type primary system configuration and a long fuel-cycle core concept with a metallic alloy nuclear fuel. Its design concept prioritizes preventing severe accidents by capitalizing on the inherent safety and reliability features achieved through emphasizing passive design characteristics. The paper describes the engineering design and safety analyses of SALUS-100, highlighting advanced design concepts in reactor core, fuel, materials, and systems. Additionally, the key research and development endeavors, focusing on vital areas such as enhancing system design capability, validating designs, demonstrating safety, and innovating in metal fuel technology, are briefly discussed, emphasizing the potential of SALUS-100 in revolutionizing the SMR market and utilizing efficient nuclear energy in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitriding reaction and combustion of Al-Li alloy with tiny Li contents in N 2 was investigated. • Nitriding reaction temperature decreased from 853 °C for Al to 245 °C for Al-2.5Li alloy. • Intermediate nitriding products of Al-Li revealed key cracks and loose "island" structures. • Thermal nitriding reaction of Al-Li alloy was significantly faster than that of pure Al. • Metal Li can significantly improve the ignition and combustion performance of Al in N 2. • Combustion mechanism of Al-Li alloy and pure Al in N 2 were discussed and compared. For aluminum-based alloy particles, the addition of alloying element lithium (Li) with the properties of a high chemical activity and a low melting/boiling point can significantly improve the thermo-reactive properties of aluminum (Al) particles. To further reveal the combustion mechanism, this paper presents the nitriding reaction and combustion characteristics of Al-Li alloy in nitrogen (N 2) through thermogravimetric analysis and differential scanning calorimetry (TG-DSC) analysis at a low heating rate and laser-induced ignition experiments at a high heating rate, considering the influences of two kinds of Li contents (1.0 wt% @ Al-1.0Li and 2.5 wt% @ Al-2.5Li) on these characteristics and making a comparison to the counterpart Al. Al-Li alloy powders as-prepared by gas atomization method showed the texture of the Li-rich eutectic phase compounds on the surface by scanning electron microscope (SEM) characterization. The TG-DSC results demonstrated that the thermal nitriding reaction of Al-Li alloy in N 2 was significantly faster than that of pure Al. The nitriding reaction temperature decreased from 853 °C for pure Al to 245 °C for Al-2.5Li alloy with a reduction of 71 %. The final weight gain of Al-2.5Li alloy was almost three times higher than that of pure Al in N 2. The SEM photograph of intermediate nitriding products revealed that the cracks and loose "island" structures in the Li-rich zone on the Al-Li surface were the key to preventing the formation of a "passivation effect" into Al and promoting N 2 uptake during melting. In addition, Li also acts as a catalytic carrier and "oxygen absorber" to enhance the Al-N reaction. The combustion of single Al-Li alloy microparticles induced by laser showed two stages: preheating and rapid nitriding. Al-Li alloy particles were ignited more rapidly and showed typical gas-phase / surface combustion modes different from pure Al. According to these findings, the combustion mechanism was proposed to help guide the development of Al-based solid propellants containing Li and the synthesis of AlN/Al composites in nitrogen-rich environments. [ABSTRACT FROM AUTHOR]

To improve the ignition and combustion performance of aluminum, complementary metal is introduced into it to form binary alloy like Al−Mg, Al−Ti, Al−Zr and Al−Li. This paper mainly investigated the preparation, characterization, ignition, and combustion characteristics of Al−Mg alloy powder. Melt atomization technique was used to produce the spherical Al−Mg alloy powder containing 20 % mass content of Mg composition. The crystalline structure, morphology, element distribution, and thermal performance were characterized by XRD, TEM, SEM, EDS, and TG‐DSC. Results show that the Al−Mg alloy had intermetallic phases of Al12Mg17 and Al3Mg2, uniform element distribution, and no dense oxide shell at the surface. The laser‐induced ignition and combustion characteristics of Al−Mg alloy powder were investigated by microscopic high‐speed cinematography, photoelectric detection, and infrared thermal imaging methods. It is testified that Al−Mg alloy powder took intermetallic phase decomposition, then followed the two‐stage combustion mode, and demonstrated gaseous emission and multiple microexplosion behavior during combustion. The ignition delay and ignition temperature were measured at elevated laser ignition power density. It is found that the temperature rise rate had a significant effect on the ignition delay. [ABSTRACT FROM AUTHOR]

This study investigates the potential of LaYO 3 as a crucible material to prevent interactions between a U-10 wt% Zr melt containing highly reactive lanthanide elements and the substrate during casting. The stability of LaYO 3 phases at casting temperature was evaluated based on reaction phenomenon, chemical and physical properties. Sintered pellets were fabricated using both La 2 O 3 and Y 2 O 3 powders and structure of bodies were investigated using X-ray diffraction. The reaction behaviors of U Zr and U-Zr-RE melts with the LaYO 3 and Y 2 O 3 specimens were investigated using sessile drop method, and microstructures of the interfaces were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The thermodynamics of LaYO 3 were analyzed to demonstrate its reaction-preventing effect. Results indicate that LaYO 3 is more effective than Y 2 O 3 in reducing the interaction between the substrate and the melt, and it significantly decreases the partial reduction of the reaction-preventing layer. These findings suggest that LaYO 3 has the potential to be an effective crucible material for preventing interactions during casting. • A novel reaction-preventing material, LaYO 3 , has been developed for metal fuel casting applications. • LaYO 3 was fabricated using sintering, resulting in a perovskite structure that prevents reactions during casting. • The LaYO 3 enhanced the reaction-preventing effect more than the conventional material Y 2 O 3. • The interaction behavior of both LaYO 3 and Y 2 O 3 was investigated using sessile drop tests and thermodynamic analysis. [ABSTRACT FROM AUTHOR]