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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Assessing the vulnerability of solar inverters to EMPs: Port testing, PCI modeling, and protection strategies
Renewable energy sources are becoming an ever-larger contributor to the power grid. These renewable energy sources depend upon the power electronic devices, specifically inverters, being essential for connecting Photovoltaic (PV) generation to the grid. However, the Electromagnetic Pulses (EMPs) caused by the high-altitude nuclear explosions can generate fast broad-band pulses with nanosecond rise time, potentially causing damage or destruction to electronic components. To assess the vulnerability of PV inverters to high-altitude EMPs, the port testing and Pulsed Current Injection (PCI) modeling schemes are proposed based on the port impedance analysis. Wide-band frequency measurements are achieved by fusing impedance results from three vector network analyzers. Then, a PCI model is used to simulate the induced response to EMP, with two typical immunity levels of EC5 and EC8 tested. Here, the experiment successfully excites the induced voltage and current under EMP, where the voltage and current can reach 1500V/40A and 8000V/150Aunder EC5 andEC8, respectively. The port vulnerability analysis results demonstrate that only some ports can survive under EC5. To defend against the impact of EMP, three protection strategies are discussed.
Ultrathin polyorganosilica membranes synthesized by oxygen-plasma treatment of polysiloxanes for H 2 /CO 2 separation
Oxygen plasma treatment of polydimethylsiloxane (PDMS) induces an ultrathin polyorganosilica (POSi) layer (<10 nm) on top of a PDMS membrane, leading to excellent H 2 /gas separation properties and providing a rapid and scalable way to fabricate robust silica membranes compared with conventional high-temperature and time-consuming sol-gel methods. Here, we thoroughly investigate POSi membranes derived from poly (dimethylsiloxane-co-methylhydroxidesiloxane) (poly (DMS-co-MHOS)) containing -SiOH groups that can be more easily converted to silica networks than the -SiCH 3 in PDMS. Further, the effect of the polysiloxane structure and plasma treatment conditions (including plasma generating powers, oxygen flowrate, chamber pressure, and treatment time) on the silica chemistry, structure, and H 2 /CO 2 separation properties are systematically determined to derive structure/property relationships. An optimized membrane exhibits H 2 permeance of 880 GPU and H 2 /CO 2 selectivity of 67 at 150 °C, superior to state-of-the-art polymeric membranes. The membrane retains H 2 /CO 2 selectivity as high as 46 when challenged with simulated syngas containing 2.8 mol% water vapor at 150 °C, demonstrating the potential of these POSi membranes for practical applications.
Investigation of competitive sorption and plasticization of hyperaged CANAL ladder polymers for acid gas purification
Identifying membrane materials that have exceptional separation performance and stability to complex CO 2 -containing mixtures is a pressing topic in separation science. In this work, the membrane separation performance for a recently discovered class of contorted polymers synthesized via catalytic arene-norbornene annulation (CANAL) polymerization is presented. These CANAL polymers achieve high CO 2 /CH 4 selectivity of 68 after physical aging (up to ∼1 year), which significantly augments the size-sieving capabilities of the membranes. Binary CO 2 /CH 4 and ternary H 2 S/CO 2 /CH 4 testing result in a 41 % and 50 % enhancement in selectivities, respectively, for hyperaged (∼1 year) contorted CANAL polymers, highlighting their size-sieving capabilities. The remarkably high CO 2 /CH 4 mixed-gas and combined acid gas (CAG, (CO 2 +H 2 S)/CH 4 ) selectivities of 88 and 95, respectively, for CANAL-Me-S 5 F in particular surpass both the 2018 CO 2 /CH 4 mixed-gas and CAG upper bounds. Performance stability was also investigated for high concentrations of CO 2 , revealing a reduction in CO 2 /CH 4 mixed-gas selectivity without compromising CO 2 permeability, suggesting strong sorption of CO 2 but minimal plasticization effects for short testing periods. In addition, time-dependent plasticization shows negligible effects on CO 2 /CH 4 mixed-gas selectivity despite an increase in CO 2 permeability when exposed to high concentrations of plasticizing CO 2 over an extended period of 170 h. This study provides valuable insights into hyperaged CANAL polymers and their performance in practical industrial processes.
Self-equilibrated backstresses induce compensation between hardening and softening: Micromechanical and microstructural features
For crystal plasticity formulation neglecting the strain gradients at the dislocation scale, backstresses are necessary to satisfy the mesoscopic stress equilibrium and strain compatibility requirements. Backstresses in a material point and those between neighboring points are treated separately. Physically backstresses can dynamically induce either hardening or softening effects to adjust the dislocation hardening of slip systems, whereas the sum of the stresses resulting in backstresses in the representative volume element (RVE) is zero. Backstress hardening suppresses certain slip activities, while backstress softening triggers excess dislocations. A two-phase brass is studied. Backstresses make the hard phase deform smaller and the soft phase deform more than those without employing backstresses in a model. In the former, more homogeneous lattice strain and higher yield stress are obtained. Backstress has limited effects on the evolution of the critical resolved shear stress and crystallographic texture. Furthermore, it is a major cause of the banded structures featuring sharp crystallographic contrasts which are not parallel to the slip planes. Tests indicate that backstress induces a serrated behavior at the early stages of deformation and induces the geometrically necessary bands (GNBs), which are parallel to the macroscopic axes.
SA508 low alloy steel to 316L stainless steel dissimilar metal joint made by powder metallurgy hot isostatic pressing
Joining ferritic SA508 low alloy steel (LAS) and austenitic 316 L stainless steel (SS) via powder metallurgy hot isostatic pressing (PM-HIP) was evaluated as an alternative method to welding. This study investigated the mechanical and microstructural evolutions of the bimetallic interface under different joint designs and heat treatments. Here, the direct joining of dissimilar metal alloys by PM-HIP method resulted in two designs: 1) powder SA508 to solid bar 316 L (P508–B316L) and 2) powder 316 L solid bar SA508 (P316L-B508). In both cases, P508–B316L and P316L-demonstrated satisfactory tensile strength, however, high hardness and severe depreciation in toughness were located on the bimetallic interface. The mechanisms responsible for the detrimental mechanical properties were verified. Large oxides were observed in P508–B316L due to the prior powder boundary (PPB) oxides present in SA508 powder. The intense sensitization occurred from the formation of M 23 C 6 carbides, consequently from the slow cooling after PM-HIP in P316L-B508. Post-HIP heat treatments were explored to reduce the distance of carbide formation; however, the heat treatment could not eliminate the carbides. The experimental results were compared to the diffusion couple simulation as a function of carbide formation with distance. The analysis also showed the high hardness at the bimetallic interface was primarily contributed by solid solution strengthening. In conclusion, the direct joining of P316L-B508 and P508–B316L via PM-HIP was deemed to be unfeasible, and a transitional material is necessary to impede the diffusion of carbon.
Stoichiometric irreversibility of aged garnet electrolytes
Solid-state lithium batteries (SSLBs) have been regarded as one of the next-generation energy storage systems. With the adoption of solid-state electrolytes (SSEs) and lithium metal anodes, SSLBs enable higher energy density and more reliable safety than the state-of-the-art lithium-ion batteries. Among potential SSEs, the cation-doped Li 7 La 3 Zr 2 O 12 (LLZO) is promising for its high ionic conductivity (~10 –3 S cm –2 ) at room temperature and high stability with Li metal anode. However, the storage of doped LLZO in the ambient condition suffers the aging effect, including the structural transition (i.e. low-temperature cubic form) and the stoichiometric changes (i.e. Li 2 CO 3 ). These changes are detrimental to LLZO ionic conductivity and interfacial stability in SSLBs. To this end, in this study we are motivated to investigate the structural and stoichiometric reversibility of aged LLZO during thermal treatment. With the help of an in-situ synchrotron-based high-energy X-ray diffraction technique, our experiments revealed that the LLZO powders became a low-temperature cubic phase when exposed to the ambient condition for an extended period of time. A high temperature cubic form can be restored after a thermal treatment of the aged LLZO powder, regardless of the type of dopant. However, the restoration of the stoichiometry remained a challenge, and the degree of the restoration showed a clear dependence on the dopant chemistry.
Grain growth of nanocrystalline aluminum under tensile deformation: A combined in situ TEM and atomistic study
Nanocrystalline Al thin films have been strained in situ in a transmission electron microscope using two separate nanomechanical techniques involving a push-to-pull device and a microelectromechanical system (MEMS) device. Deformation-induced grain growth was observed to occur via stress-assisted grain boundary migration with extensive grain growth occurring in the necked region, indicating that the increase in local stress drives the boundary migration. Under applied tensile stresses close to the ultimate tensile strength of 450 MPa for a nanocrystalline Al specimen, measured boundary migration speeds are 0.2 – 0.7 nm s -1 for grains outside necked region and increases to 2.5 nm s -1 for grains within the necked region where the local estimated tensile stresses are elevated to around 630 MPa. By tracking grain boundary motion over time, molecular dynamics simulations showed qualitative agreement in terms of pronounced grain boundary migration with the experimental observations. The combined in situ observation and molecular dynamics simulation results underscore the important role of stress-driven grain growth in plastically deforming nanocrystalline metals, leading to intergranular fracture through predominant grain boundary sliding in regions with large localized deformation.
Temperature dependent plasticity in BCC micropillars
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Highly variable chemical short-range order in a high-entropy metallic glass
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Effect of Fermi surface topology change on the Kagome superconductor CeRu 2 under pressure
The cubic Laves phase compound CeRu 2 with a Kagome substructure of Ru has been investigated to understand myriad fascinating phenomena resulting from competition among its various physical and geometric features. Such phenomena include flat bands, van Hove singularities, Dirac cones, reentrant superconductivity, magnetism, the Fulde–Ferrell–Larkin–Ovchinnikov state, valence fluctuations, time-irreversible anisotropic s-state superconductivity, etc. Extensive studies have thus been carried out since 1958 when the highly unusual coexistence of superconductivity and ferromagnetism was proposed for the mixed compounds (Ce,Gd)Ru 2 . Activity has accelerated in recent years due to increasing interest in topological states in superconductors. However, there has been little investigation of the mutual influence of these fascinating states. Therefore, we systematically investigated the superconductivity and possible Fermi surface topological change in CeRu 2 via magnetic, resistivity, and structural measurements under pressure up to ~168 GPa. An unusual phase diagram that suggests an intriguing interplay between the compound’s superconducting order and Fermi surface topological order has been constructed. A resurgence in its superconducting transition temperature was observed above 28 GPa. Our experiments have identified a structural transition above 76 GPa and a few tantalizing phase transitions driven by high pressure. Our high-pressure results further suggest that superconductivity and Fermi surface topology in CeRu 2 are strongly intertwined.
Tunning the linkage of structure units to enable stable spinel-based cathode in the wide potential window
The low practical capacity (<140 mA h g –1 ) of spinel phase LiMn 2–x Ni x O 4 (0 < x < 1) excludes it from high energy density lithium ion batteries (LIBs) for powering electric vehicles. Extending the operating potential window from 3.0 to 4.8 V to 2.0–4.8 V can double the capacity, but result in fast capacity decay due to the drastic cubic-tetragonal phase transition below 3.0 V, induced by serious Jahn-Teller (J-T) distortion of structure units (Mn 3+ )O 6 octahedra. Herein, we propose a novel strategy to suppress J-T distortion by tuning the linkage of structure units MnO 6 octahedra. The original full-vertex-sharing LiO 4 tetrahedra around MnO 6 octahedra in spinel phase are partially replaced by edge-sharing LiO 6 octahedra, which relate Mn-O bonds along the dz 2 direction with those along the d xy plane, thus significantly mitigating J-T distortion and suppressing the phase transition when discharged to 2.0 V. Following this strategy, the prepared spinel-based cathode achieves a high reversible capacity of about 290 mA h g –1 and an energy density up to 957 W h kg –1 with improved cycling stability. Furthermore, this work finds a new opportunity for the traditional spinel cathode towards applications in high energy density LIBs in a low cost and sustainable manner.
Boosting photovoltaic performance of ternary organic solar cells by integrating a multi-functional guest acceptor
Constructing ternary structure is one of the most effective design strategies to break the efficiency ceiling of traditional binary organic solar cells (OSCs). Here, a new Y-series non-fullerene acceptor (Y-T) featuring 1,3-diethyl-2-thiobarbituric acid (DTBA) end groups is developed as a third component for the classical PM6:Y6 binary system. The champion power conversion efficiency of ternary OSCs is increased from 15.64% to 17.37% via incorporating 10 wt% Y-T, with the simultaneously enhanced open-circuit voltage (Voc) of 0.865 V, a short-circuit current density (Jsc) of 26.90 mA/cm 2 , and a fill factor (FF) of 74.97%. The positive contribution of Y-T in the ternary blend can be ascribed to the improved spectroscopic complementarity and enhanced exciton utilization ratio due to the additional energy transfer process. Moreover, Y-T guest acceptor plays a critical role in adjusting the active layer morphology and facilitating three-dimension phase separation, resulting in a balanced charge transport and enhanced FF of ternary OSCs. Overall, this work provides insight into the molecular design of non-fullerene acceptor and suggest guidelines to rationally select guest component for ternary OSCs.