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Effect of Added Gadolinium Oxide on the Thermal Air Oxidation of Uranium Dioxide
To develop a more reliable and stable UO2-based nuclear fuel, the Pacific Northwest National Laboratory (PNNL) investigated modifying fuel with several soluble lanthanides and zirconium. This article provides the results of these studies investigating gadolinium doping at levels up to 10 mass%. The authors characterized and compared commercially- and PNNL-prepared gadolinium-doped UO2 to determine the oxygen-to-metal ratio, elemental distribution, chemical composition, physical appearance, lattice parameters, and grain structure using atomic force microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and X-ray diffractometry. After confirming PNNL-prepared UO2 and (Gd,U)O2 were similar to commercially prepared UO2 and (Gd,U)O2, we measured the thermal behavior of these gadolinium-doped UO2 materials to air oxidation using differential scanning calorimetry and thermogravimetric analysis. Addition of gadolinium stabilized the first oxidation product U4¬O9/U3O7 and slowed the subsequent oxidation to U3O8. Comparison of our measured two-step oxidation of UO2 to U3O8 at 325°C to common gas/solid kinetic reaction models found that each oxidation step is best described as a convolution of kinetic behaviors; the gadolinium insertion into the UO2 lattice enforces a significant alteration in mechanism and oxidation rate. Noticeable changes in mechanism become apparent between 1% and 3% gadolinium content.
Thermally drawn rechargeable battery fiber enables pervasive power
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Nanoparticle Superlattices with Negative Thermal Expansion (NTE) Coefficients
In this work, we report on the assembly of gold nanoparticles grafted with poly(ethylene glycol) (PEG–AuNPs) in aqueous solutions into the face-centered cubic superlattice by synchrotron X-ray scattering. At sufficiently high salt concentrations, the lattice constant decreases with increasing temperature, i.e., it exhibits a negative thermal expansion (NTE) coefficient that is 2–4 orders (in magnitude) larger than previously reported in NTE materials. The generality of the effect is demonstrated with different salts and different PEG chain lengths. Theoretical calculations show that PEG–AuNP becomes more insoluble (with the Flory–Huggins parameter χ > (1/2)) as temperature increases through water dehydration, with a decrease in the volume of the superlattice and an increase in the entropy of the system. Implications on the formation of nanoparticle superlattices and NTE properties are also discussed.
Thermal Emission Spectroscopy of Single, Isolated Carbon Nanoparticles: Effects of Particle Size, Material, Charge, Excitation Wavelength, and Thermal History
Findings are introduced for thermal emission from individually trapped carbon nanoparticles (NPs) in the temperature range from ~1000 to ~2100 K. We explore the effects on the magnitude and wavelength dependency of the emissivity, ε(λ), of the NP size and charge and of the type of carbon material, including graphite, graphene, diamond, carbon black, and carbon dots. Furthermore, it is found that heating the NPs, particularly to temperatures above ~1900 K, results in significant changes in the emission properties, which is attributed to changes in the distribution of surface and defect sites caused by annealing and sublimation.
Optimization of Thermal Pretreatment of Food Waste for Maximal Solubilization
Not provided.
Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity
Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd-based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure-phase PdSn nanocatalyst. Furthermore, PdSn shows an >96% selectivity toward hydrogenating C=O bonds of various α,β-unsaturated aldehydes, highest in reported Pd-based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn- to Pd 3 Sn 2 -structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.
Real-Time Defect Correction in Large-Scale Polymer Additive Manufacturing via Thermal Imaging and Laser Profilometer
Defects can result in a failed part and are costly in terms of time and material. This cost is even greater in the context of large-scale additive manufacturing where the objects can be very large. As a result, a great deal of research has focused on defect identification and mitigation. To address defects during object construction, researchers at Oak Ridge National Laboratory’s Manufacturing Demonstration Facility investigated an in-situ control system comprised of two sensors: a thermal camera and laser profilometer. This control system adjusted material flow and build speed to mitigate three types of defects: low layer times, underfill, and overfill. Several test objects were constructed. The control system was found to adjust build parameters to handle low layer times of approximately 15 seconds and height deviations from -100% underfill (the absence of a layer) to 50% overfill. Within two layers, height deviations could be returned to within 10% of the expected layer height. Further, preliminary results suggest the system can compensate for uneven build surfaces.
Thermal Stability and Mechanical Properties of Cold-Sprayed Nickel-Yttria Coating
The microstructural evolution under the extreme environments imposed during cold spray deposition of cermet coatings and the microstructural recovery during post-processing annealing treatments is rather complex and not well understood. Here, Ni-Yttria cermet coatings on an SS304 substrate were produced using cold spray technique, resulting in a bimodal grain structure. The grain growth, phase stability, hardness, and wear properties are observed in as-deposited and annealed (at 400 °C) Ni-Yttria and pure Ni coatings. A multimodal microstructural characterization using electron microscopy, and atom probe tomography shows the structural and compositional stability of yttria particles and Ni grains. A fragmentation of Y-rich particles and dispersion in Ni was observed, however, no forced mixing/dissolution of Y in Ni is detected. Nano-yttria dispersed within the Ni grains slowed the grain growth during annealing. After annealing, Yttria reinforced coating was 1.5 times harder and showed better thermal and mechanical stability compared to the Ni coating.
Optimized Microwave-Based Synthesis of Thermally Stable Inverse Catalytic Core-shell Motifs for CO2 Hydrogenation
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Tip-enhanced Raman imaging of photocatalytic reactions on thermally-reshaped gold and gold–palladium microplates
The plasmonic/photocatalytic properties of thermally-reshaped walled gold–palladium microplates (WAu@PdMPs) have been explored by TERS.
Trends in the thermal stability of two-dimensional covalent organic frameworks
Here, we study the thermal stability of ten 2D covalent organic frameworks using a combination of variable-temperature X-ray diffraction, thermogravimetric analysis, diffuse reflectance infrared spectroscopy, and density-functional theory.
Intrinsic volumetric negative thermal expansion in the “rigid” calcium squarate
A strong volumetric negative thermal expansion was found to exist in a rigid MOF without carboxylate like buffering units.
Rapid, interface-driven domain orientation in bottlebrush diblock copolymer films during thermal annealing
Thick (>20 μm) films of bottlebrush block copolymers self-assemble within minutes of thermal annealing between hard interfaces. Photonic properties are modified by thickness-dependent gradients of grain size and orientation between the surface and bulk.
Transparent thermal insulation ceramic aerogel materials for solar thermal conversion
Transparent ceramic aerogel materials toward emerging energy-efficient solar thermal window technologies.
Distinct anharmonic characteristics of phonon-driven lattice thermal conductivity and thermal expansion in bulk MoSe 2 and WSe 2
Machine-learning molecular dynamics simulations pave the way to completely treat the anharmonicity of phonons. Low-energy anharmonic modes in transition-metal dichalcogenides drive the thermal and transport properties.
Estimate of pre-thermal quench non-thermal electron density profile during Ar pellet shutdowns of low-density target plasmas in DIII-D
The radial density profile of pre-thermal quench (pre-TQ) early-time runaway electrons (REs) is estimated by combining electron cyclotron emission (ECE) and soft x-ray (SXR) data during rapid shutdown of low-density (n e ≲ 10 13 cm -3 ) DIII-D target plasmas with cryogenic argon pellet injection. This technique is limited in these experiments to the pre-TQ phase and quickly loses validity during the TQ. Two different cases are studied: a high (10 keV) temperature target and a lower (4 keV) temperature target. The results indicate that early-time, low-energy (~10 keV) REs form ahead of the argon pellet as it enters the plasma, affecting the pellet ablation rate; it is hypothesized that this may be caused by rapid cross-field transport of argon ions ahead of the pellet. Fokker-Planck modeling of the two shots suggests that the RE current is quite significant during the pre-TQ phase (up to 50% of the total current). Comparison between modeled pre-TQ RE current and post-TQ RE current inferred from avalanche theory suggests that RE current increases during the high temperature target TQ but decreases during the low temperature target TQ. Here, the uncertainties in this estimate are large; but, if true, this suggests that TQ loss of REs can be larger than previously estimated in DIII-D.