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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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Role of deformation twinning in fatigue of CrCoNi medium-entropy alloy at room temperature
Here cylindrical specimens of CrCoNi alloy with electropolished surfaces were subjected to constant total strain amplitude low cycle fatigue. The alloy exhibited an initial period of cyclic hardening followed by cyclic softening until failure occurred. At the end of hardening stage at the peak of cyclic stress, well-developed persistent slip markings (PSMs) consisting of extrusions and intrusions were associated with thin deformation twins. A sophisticated experimental workflow was designed to extract information from the surface and the bulk of tested material. A combination of SEM, EBSD, ECCI, FIB and HR-STEM was used to study the internal structure and the surface profiles around the deformation twins, which were produced during the initial period of cyclic loading. Furthermore, localized cyclic plastic strain and stress concentrations near deformation twins led not only to early, well-developed PSMs, but also to the activation of TWIP and TRIP plasticity even at low macroscopic stress amplitudes.
Effect of crystal structure of manganese dioxide on response for electrolyte of ahydrogen sensor operative at room temperature
Sensoring properties of a hydrogen sensor that used electrolytes made of different crystal type manganese dioxides were compared. An electrolyte made of a manganese dioxide, which has a high purity of ramsdellite-type crystal structure, provided the best characteristics for the hydrogen sensor. To explain the sensor property, network model of oxygen-pairs to store protons with a weak covalent bond and to conduct protons along the network in the ideal crystal structure of ramsdellite manganese dioxide was proposed. The inter-atomic distance of those oxygen-pairs in the high purity of ramsdellite manganese dioxide was estimated between 2.57 and 2.60 A using inelastic neutron scattering measurements. The property of the hydrogen sensor supported the unique proton conduction based on the network model.
Real-time monitoring of room-temperature ionic liquid purity through optical diode-based sensing
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Compact TDLAS based optical sensor for ppb-level ethane detection by use of a 3.34 μm room-temperature CW interband cascade laser
A mid-infrared ethane (C 2 H 6 ) sensor based on a wavelength modulation spectroscopy (WMS) technique was developed using a thermoelectrically cooled (TEC), continuous-wave (CW) interband cascade laser (ICL) emitting at 3.34 μm and a dense multi-pass gas cell (MPGC, 17 × 6.5 × 5.5 cm 3 ) with a 54.6 m optical path length. A compact optical sensor system with a physical size of 35.5 × 18 × 12.5 cm 3 was designed and constructed. An ICL was employed for targeting a strong C 2 H 6 line at 2996.88 cm -1 at <100 Torr gas pressure in the fundamental absorption band of C 2 H 6 . The sensor performance, including the minimum detection limit (MDL) and the stability were improved by reducing the effect of laser power drift by means of the 2f/1f-WMS technique. A MDL of ~1.2 parts per billion (ppbv) for 2f-WMS and ~1.0 ppbv for 2f/1f-WMS were achieved, respectively, with a measurement time of 4 s. The MDL was further improved from 299 pptv (@108 s for 2f-WMS) to 239 pptv (@208 s for 2f/1f-WMS), based on an Allan deviation analysis.The rise time (@0 → 100 ppbv) and fall time (@100 → 0 ppbv) were determined to be ~64 s and ~48 s,respectively, at a gas pressure of <100 Torr for the C 2 H 6 sensor operation.
A flexible and disposable poly(sodium 4-styrenesulfonate)/polyaniline coated glass microfiber paper for sensitive and selective detection of ammonia at room temperature
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STEM Study of Structure and Local Short-Range Orders in the Fe 5- x GeTe 2 Crystals with Ferromagnetism Near Room Temperature
Van der Waals (vdW) bonded materials have historically attracted intense attention, due to their promise for advanced electronic and optical functionalities. Recently, magnetically-active vdW materials have been recognized as an important class of materials for realizing new physics and functionalities. Of the magnetic vdW materials, ferromagnetic Fe 3 GeTe 2 has garnered significant attention for its high Curie temperature T C ~230 K. Recently, a Fe 5-x GeTe 2 compound with thicker Fe-Ge slabs and stronger magnetism has been successfully obtained. As viewed by bulk diffraction, the material has a relatively large unit cell and contains intrinsic disorder. The nature of the local structure is anticipated to impact the Curie temperature, which ranges from 270–310K depending on processing conditions. As such, an atomic-scale probe of the local structures and compositions is essential for understanding the intrinsic magnetism in this vdW material.
In Situ Grain Growth of Nanograined Magnetite under Ion Irradiation at Room Temperature and 500 ℃
Grain growth studies of nanograined metals under both thermal and ion irradiation conditions has been studied extensively. Oxides, on the other hand, have not been studied as extensively, especially under irradiation. Some studies have focused on nanograined oxide grain growth on ZnO under thermal conditions only and on SnO 2 and CeO 2 using 250 keV Ar 2+ and 3 MeV Au + ions at 300 K, respectively. There does not appear to be any studies on grain growth of nanosized oxides which are commonly found to form under light water reactor conditions. Oxides such as magnetite (Fe 3 O 4 ), hematite (α-Fe 2 O 3 ), maghemite (γ-Fe 2 O 3 ), and wustite (FeO) are examples of common oxides which have not been studied. Here, this study focused on the grain growth of nanograined Fe 3 O 4 under both thermal and ion irradiation conditions in situ inside a Transmission Electron Microscope (TEM) to better understand the kinetics of grain growth of oxides.
Pressure-Driven Polar Orthorhombic to Tetragonal Phase Transition in Hafnia at Room Temperature
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Ferroelectric Particles Generated through a Simple, Room-Temperature Treatment of CdSe Quantum Dots
II–VI quantum dots (QDs) are of keen scientific interest due to their size-dependent optoelectronic properties, which make them viable candidates for a plethora of fields including biomedics, solar power, LEDs, electronic displays, and agriculture. Efforts to improve the effectiveness of QDs for these applications continue through the utilization of ligand exchanges, cation exchanges, and doping. Building upon these efforts and following the literature precedent of Sb-doped CdSe thin films, this paper presents the treatment of colloidal CdSe QDs with SbCl 3 as a synthetic strategy for producing Sb-doped CdSe QDs. Finally, however, rather than self-limited exchange as predicted by the thin film work, a unique two-phase reaction is observed that yields ferroelectric particles.
d -Electron Heavy Fermion Behavior in a Near-Room-Temperature Polar Metallic Ferrimagnet: A Case of Mn 5 SiC
Polycrystalline Mn 5 SiC was synthesized by using a high-temperature solid-state method. Mn 5 SiC adopts a polar space group (Cmc2 1 ) with six crystallographic Mn sites confirmed by X-ray and neutron diffraction, transmission electron microscopy, and second harmonic generation experiments. The complex crystal structure features edge-sharing trigonal prisms and icosahedra, as well as face/edge-sharing pentagonal prisms. Magnetic measurements indicate ferrimagnetic ordering with a transition temperature of 284 K. The ferrimagnetic structure (magnetic space group Cm’c’2 1 ) was further identified by powder neutron diffraction, where collinear Mn spins align along the crystallographic c-axis. The refined magnetic moment for each crystallographic Mn site at 4 K is 1.8(2), −2.42(9), −1.72(8), 0.51(6), 0.50(4), and 1.7(2) μ B . Density functional theory calculations confirm both the metallic behavior and the ferrimagnetic structure observed experimentally and further provide insight into the observed Mn moment dependence across crystallographic sites. The resistivity and specific heat measurements and density functional theory calculations reveal a substantially large Kadowaki–Woods ratio of 5 × 10 –5 μΩ·cm/(mJ/mol) 2 and a many-body renormalization factor of 5.5, indicating the unusual heavy Fermion behavior in such an itinerant magnetic metal.
Compatibility of Fuel System Elastomers and Plastics with a Fast-Pyrolysis Oil (Bio-oil) at Room Temperature
Herein the compatibility of a fast-pyrolysis bio-oil with 17 elastomer and 21 plastic materials common to fuel storage, dispensing, and delivery systems was assessed by measuring volume and hardness. Diesel was used as the baseline for comparison. The elastomer and plastic specimens were exposed to the test fuels at 23 °C. The exposure times were 4 and 16 weeks for the elastomers and plastics, respectively. The elastomers (except for silicone and styrene butadiene) exhibited pronounced swelling in the bio-oil. This was especially true for the fluorocarbons and acrylonitrile rubbers. For the elastomers, a strong correlation between polarity and volume swell was observed. Compositional and structural analysis on one of the fluorocarbon materials showed that the bio-oil was less effective at extracting phthalate additives than the diesel. However, the crystallinity of a fluorocarbon was altered by the bio-oil. Unlike the elastomers, the plastic materials were less impacted by exposure to the bio-oil. This finding is attributed to their denser and more rigid molecular structures (compared to the elastomers). Notable swelling did occur in the nylons, but this swelling was attributed to water absorption rather than polarity. Comparison with previous studies showed that the observed swelling was lower for both the elastomers and the plastics. Solubility (and hence swell) increases with temperature, and because this study was conducted at 23 °C rather than 50 °C, the reduced temperature is responsible for the lower swell levels.