27 Search Results

Tristructural isotropic (TRISO)-coated fuel particles are designed for use in high-temperature gas-cooled nuclear reactors, featuring a structural SiC layer that may be exposed to oxygen-rich environments over 1000 °C. Surrogate TRISO particles were tested in 0.2–20 kPa O₂ atmospheres to observe the differences in oxidation behavior. Oxide growth mechanisms remained consistent from 1200–1600 °C for each P_{O$$_2$$}, with activation energies of 228 ± 7 kJ/mol for 20 kPa O₂ and 188 ± 8 kJ/mol for 0.2 kPa O₂. At 1600 °C, kinetic analysis revealed a change in oxide growth mechanisms between 0.2 and 6 kPa O2. In 0.2 kPa O₂,more » oxidation produced raised oxide nodules on pockets with nanocrystalline SiC. Oxidation mechanisms were determined using Atom probe tomography. Active SiC oxidation occurred in C-rich grain boundaries with low P_{O$$_2$$}, leading to SiO₂ buildup in porous nodules. Here, this phenomenon was not observed at any temperature in 20 kPa O₂ environments.« less

Current extraction technologies for rare earth elements at ambient conditions are reagent and energy intensive, giving rise to significant quantities of secondary waste streams. Exploration of the removal of common cations from aqueous streams has been undertaken with carbon materials and have shown promising results. However, those promising materials have not been explored extensively for rare earth element capture from aqueous process streams. In this study, a carbon electrode was investigated for the adsorption and immobilization of REE elements from aqueous solutions. Cyclic voltammetry studies of the carbon electrode displayed a pseudocapacitive behavior where it was verified that cation adsorptionmore » is accompanied by an electron transfer process. Preliminary tests showed that a current density of 89.1 mA. g^-1, allowed for the pseudocapacitive adsorption (PSA) of Nd³⁺ cation without the formation of rare earth hydroxides. Hence, the selective PSA of Nd³⁺ was verified in an electrolyte solution with equimolar concentrations of Nd³⁺, Mg²⁺, Li⁺, Na⁺ and K⁺, achieving separation factors of 8.6, 1.1, and 10.9 for Nd³⁺/Li⁺, Nd³⁺/Na⁺, and Nd³⁺/Mg²⁺, respectively. Analysis of the potential-time curves for the various cations suggests that storage of ions in the electrode involved pore-spacings rather than interlayer spacings and was corroborated by XRD analysis. Specific capacitance as high as >640 F.g^-1 for Nd³⁺ was also observed for the carbon electrode, with Faradaic efficiencies (FE) of > 20% for Nd³⁺ and Mg²⁺, and > 9% for Na⁺. Furthermore, adsorption capacity of >125 mg g^-1 after 4hrs of electrosorption was observed for Nd³⁺. In the presence of the Nd³⁺ electrolyte, the electrode achieved increasing storage of Nd³⁺ with >94% retention of Nd³⁺ with a FE > 20% over 6 cycles between loading and releases in 1 M KCl solution. In conclusion, these preliminary results provide information and some guidance on the selective recovery of rare earth elements, such as Nd, in aqueous streams in the presence of competitive cations employing the use of carbon-based materials.« less

Carbon capture has been an important topic of the twenty-first century because of the elevating carbon dioxide (CO2) levels in the atmosphere. CO2 in the atmosphere is above 420 parts per million (ppm) as of 2022, 70 ppm higher than 50 years ago. Carbon capture research and development has mostly been centered around higher concentration flue gas streams. For example, flue gas streams from steel and cement industries have been largely ignored due to lower associated CO2 concentrations and higher capture and processing costs. Capture technologies such as solvent-based, adsorption-based, cryogenic distillation, and pressure-swing adsorption are under research, but manymore » suffer from higher costs and life cycle impacts. Membrane-based capture processes are considered cost-effective and environmentally friendly alternatives. Over the past three decades, our research group at Idaho National Laboratory has led the development of several polyphosphazene polymer chemistries and has demonstrated their selectivity for CO2 over nitrogen (N2). Poly[bis((2-methoxyethoxy)ethoxy)phosphazene] (MEEP) has shown the highest selectivity. A comprehensive life cycle assessment (LCA) was performed to determine the life cycle feasibility of the MEEP polymer material compared to other CO2-selective membranes and separation processes. The MEEP-based membrane processes emit at least 42% less equivalent CO2 than Pebax-based membrane processes. Similarly, MEEP-based membrane processes produce 34–72% less CO2 than conventional separation processes. In all studied categories, MEEP-based membranes report lower emissions than Pebax-based membranes and conventional separation processes.« less

The rise in population, urbanization, and industrial developments have led to a substantial increase in waste generation and energy demand, posing significant challenges for waste management as well as energy conservation and production. Bioenergy conversions have been merged as advanced, sustainable, and integrated solutions for these issues, encompassing energy generation and waste upcycling of different types of organic waste. Municipal solid waste (MSW) and agricultural residues (AR) are two main resources for bioenergy conversions. Bioenergy production involves feedstock deconstruction and the conversion of platform chemicals to energy products. This review provides a detailed overview of waste sources, biofuel, and bioelectricitymore » production from fermentation and microbial fuel cell (MFC) technology, and their economic and environmental perspectives. Fermentation plays a critical role in liquid biofuel production, while MFCs demonstrate promising potential for simultaneous production of electricity and hydrogen. Fermentation and MFCs hold a significant potential to be integrated into a single pipeline, enabling the conversion of organic matter, including a variety of waste material and effluent, into diverse forms of bioenergy via microbial cultures under mild conditions. Furthermore, MFCs are deemed a promising technology for pollutant remediation, reducing COD levels while producing bioenergy. Importantly, the consolidated fermentation–MFC system is projected to produce approximately 7.17 trillion L of bioethanol and 6.12 × 10⁴ MW/m² of bioelectricity from MSW and AR annually, contributing over USD 465 billion to the global energy market. Such an integrated system has the potential to initiate a circular economy, foster waste reduction, and improve waste management practices. This advancement could play a crucial role in promoting sustainability across the environmental and energy sectors.« less

Activated carbon (AC)-based materials have shown promising performance in carbon capture, offering low cost and sustainable sourcing from abundant natural resources. Despite ACs growing as a new class of materials, theoretical guidelines for evaluating their viability in carbon capture are a crucial research gap. We address this gap by developing a hierarchical guideline, based on fundamental gas–solid interaction strength, that underpins the success and scalability of AC-based materials. The most critical performance indicator is the CO₂ adsorption energy, where an optimal range (–0.41 eV) ensures efficiency between adsorption and desorption. Additionally, we consider thermal stability and defect sensitivity to ensuremore » consistent performance under varying conditions. Further, selectivity and capacity play significant roles due to external variables such as partial pressure of CO₂ and other ambient air gases (N₂, H₂O, O₂), bridging the gap between theory and reality. We provide actionable examples by narrowing our options to methylamine- and pyridine-grafted graphene.« less

Abstract Surrogate tristructural‐isotropic (TRISO)‐coated fuel particles were oxidized in 0.2 kPa O ₂ at 1200–1600°C to examine the behavior of the SiC layer and understand the mechanisms. The thickness and microstructure of the resultant SiO ₂ layers were analyzed using scanning electron microscopy, focused ion beam, and transmission electron microscopy. The majority of the surface comprised smooth, amorphous SiO ₂ with a constant thickness indicative of passive oxidation. The apparent activation energy for oxide growth was 188 ± 8 kJ/mol and consistent across all temperatures in 0.2 kPa O ₂ . The relationship between activation energy and oxidation mechanism is discussed. Raised nodules of porous,more » crystalline SiO ₂ were dispersed across the surface, suggesting that active oxidation and redeposition occurred in those locations. These nodules were correlated with clusters of nanocrystalline SiC grains, which may facilitate active oxidation. These findings suggest that microstructural inhomogeneities such as irregular grain size influence the oxidation response of the SiC layer of TRISO particles and may influence their accident tolerance.« less

Exploring the reduction of recalcitrance in lignocellulosic feedstocks using fungal-induced degradation and associated impacts in molecular structure.

In this work, the electrochemistry of liquid Ga electrodes in aqueous media was examined in the presence of praseodymium acetate (PrOAc) as an alternate path for low temperature reduction of rare earth elements (REE). This study investigated the aqueous electrochemistry of Ga with and without REEs (Pr). Cyclic voltammetry experiments showed that in the presence of PrOAc, an order of magnitude increase in cathodic current was observed for the Ga electrode, compared to that in the absence of Pr. Decrease in the reduction current with the increase of scan rate, with and without Pr, suggests catalytic reactions following electron transfer,more » which was attributed to the Ga₂O disproportionation reaction. Chronoamperometric experiments performed in Pr containing solutions formed a precipitate. Over 50% of the Pr ions from the aqueous electrolyte were immobilized in the precipitate; a solid Ga-rich phase. Formation of this precipitate was only possible when Ga oxidation was induced. This condition was achieved by circulation of liquid Ga from the pool via external pump and returned dropwise to the liquid Ga pool. When the collected precipitate was leached in dilute HCl, Pr was released with H₂ evolved as a byproduct, and Ga returned to its initial liquid metallic state. These preliminary results show encouraging new routes that could be applied for the recovery of diluted REE leachates, such as those obtained from magnets, coal fly ash, and ores.« less

Given a growing interest in uranium salts for pyrochemical processing of used fuel and uranium-fueled molten salt reactors, the synthesis of uranium trichloride in alkali-metal chloride media was investigated in a series of four experiments. Specifically, uranium metal powder and uranium hydride powder were prepared and separately blended with ammonium chloride and lithium chloride – potassium chloride eutectic in two runs, while the same powders were separately blended with ammonium chloride and sodium chloride in two additional runs. Each of the lithium chloride – potassium chloride containing blends was slowly heated to 923 K, while those containing sodium chloride weremore » heated to 1123 K. During each heat up, the ammonium chloride sublimed into gaseous ammonia and hydrogen chloride, leading to the chlorination of uranium metal or uranium hydride and the formation of molten salt solutions of the respective chlorides. Experimental conditions were incorporated in the runs to promote formation of uranium trichloride over uranium tetrachloride in the respective media. Molten samples of each run product were taken and characterized via chemical analyses, diffractometry, and microscopy. The final products from each run were dark dense ingots of the respective salt systems with uranium concentrations ranging from 44 to 51 wt%. Finally, chemical analyses and diffractometry identified the predominant presence of uranium trichloride in these systems; however, a possible minor presence of uranium tetrachloride could not be conclusively dismissed.« less

The electrodeposition of Al was investigated in an ionic liquid (IL), with 1-ethyl-3-methylimidazolium tetrachloroaluminate ([EMIm]AlCl4) as the electrolyte with AlCl3 precursor. The [EMIm]AlCl4 electrolyte exhibited a wide and stable electrochemical window from 3.2 to 2.3 V on a glassy carbon electrode when temperature was increased from 30 °C to 110 °C. The addition of AlCl3 into [EMIm]AlCl4 generated significant well-developed nucleation growth loops, and new coupled reduction and oxidation peaks in cyclic voltammograms corresponding to the Al deposition and dissolution, respectively. A calculation model was proposed predicting compositions of anions in AlCl3/[EMIm]AlCl4 system, and [Al2Cl7]− was found to be themore » active species for Al deposition. In AlCl3/[EMIm]AlCl4 (1:5), the reduction rate constants were 1.18 × 10−5 cm s−1 and 3.37 × 10−4 cm s−1 at 30 °C and 110 °C, respectively. Scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and X-ray diffraction (XRD) microscope results showed that the metallic Al film had been successfully deposited on glassy carbon electrodes through constant-potential cathodic reductions. The [EMIm]AlCl4 was a promising electrolyte directly used for Al deposition.« less