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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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10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Differentiating the bonding states in calcium carbonate polymorphs by low-loss electron-energy-loss spectroscopy

Calcium carbonate is one of the important building components in organisms, especially the two most common polymorphs, calcite and aragonite. Here, to understand the difference in bonding state, the two polymorphs are characterized by valence (low-loss) electron energy loss spectroscopy. It is found that the difference in Ca M 23 edge originating from 3p to 3d states is consistent with the change of Ca-O bonds in the two studied polymorphs. Surprisingly, the measured Ca M 23 edge is in qualitative agreement with the calculated partial density of states (PDOS) of Ca-d states in contrast to their L edges (from 2p to 3d states) which are strongly influenced by atomic multiplet effect (spin-orbit coupling). This is because the atomic multiplet effect is much reduced for the Ca 3p orbital, which permits the corresponding Ca M 23 edge to be compared with the PDOS results. Our findings show insights that PDOS can potentially be used to interpret the M 23 edge of lighter 3d transition metals such as scandium, titanium, vanadium and chromium when such interpretation may not be achieved for their L edges.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unraveling disadhesion mechanism of epoxy/CSH interface under aggressive conditions

Almost all FRP-reinforced concrete exposed to the marine environment are susceptible to durability deficiencies due to failure of the FRP/epoxy/concrete interface, especially the vulnerable epoxy/concrete interface, which is frequently attacked by water and ions. Herein, molecular dynamics simulations of epoxy/CSH interface under different environmental exposures are utilized to specifically elucidate the degradation principles of water and ions on the bonding properties and mechanical responses of the epoxy/concrete interface. The environmental sequences associated with the interfacial bonding degradation are arranged as Na{sub 2}SO{sub 4} + NaCl>NaCl>Na{sub 2}SO{sub 4} > Water>Dry. Remarkably, water molecules weaken the interaction between the epoxy and CSH by robbing interfacial H- and Ca-O bonds, thereby reducing the energy barrier to interfacial peel and shear failure. The weakening effects are exacerbated by the presence of aggressive ions, as Na{sup +} ions attracted to the CSH surface accumulate more water molecules in the interfacial region by forming hydrated ions clusters, which ultimately accelerates the epoxy/CSH interfacial degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Unveiling the Degradation Mechanism of High-Temperature Superconductor Bi 2 Sr 2 CaCu 2 O 8+δ in Water-Bearing Environments

We report the physical properties of copper oxide high-temperature superconductors have been studied extensively, such as its band structure, and doping effects of Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212). However, some chemical-related properties of these superconductors are rarely reported, such as their stability in air. Here, we report experiments combined with ab initio calculations that address the effects of water in contact with Bi-2212. The evolution of Bi-2212 flake with exposure to water for different time intervals were tested and characterized by optical microscopy (OM), atomic force microscopy (AFM), Raman spectroscopy, transmission electron microscopy (TEM) and electrical measurements. The thickness of Bi-2212 flakes is gradually decreased in water, and some thin flakes can be completely etched away after a few days. The stability of Bi-2212 in other solvents is also evaluated, including alcohol, acetone, HCl and KOH. The morphology of Bi-2212 flakes is relatively stable in organic solvents. However, the flakes are etched relatively quick in HCl and KOH, especially in acidic environment. Our results imply that hydrogen ion is primarily responsible for the deterioration of their properties. Both TEM and calculation results demonstrate that the atoms in Bi-O plane is relatively stable when compared to the inner atoms in Sr-O, Ca-O and Cu-O planes. This work contributes towards understanding the chemical stability of Bi-2212 superconducting device in environmental medium, which is important for both fundamental studies and practical applications of copper oxide high-temperature superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Structural Modifications of Single-Crystal Aragonite CaCO 3 Beginning at ~15 GPa: In Situ Vibrational Spectroscopy and X-Ray Diffraction Evidence

The structural chemistry of carbonates under mantle conditions facilitates our understanding of carbon recycling pathways in the earth’s interior. It also has impacts on the dynamics of mantle–slab interactions. Aragonite is a common calcium carbonate mineral in pelagic marine sediments. The structural chemistry of single-crystal aragonite during successive compression and the behavior of a structural H+ have been investigated by micro-vibrational spectroscopy and synchrotron X-ray diffraction techniques in diamond anvil cells. We describe a reduction of the b-axial compressibility beginning at ~15 GPa, and the related discontinuities in the first-order derivatives of the vibrational modes. The structural modifications of aragonite are manifested by mutations occurring in the pressure relations of the wavenumbers of the O-C-O bending modes, and of the bandwidth and band intensities of the measured internal and external modes. These anomalies are indicative of changes occurring in the force constant of the C-O bonds, and possibly a second-order phase transition. Besides, the [CaO 9 ] polyhedra begin to deform, possibly with some Ca-O bonds becoming elongated and the others shortening. An increase in the co-ordination number for the Ca 2+ sites could be expected under higher pressures. Additionally, the weakening of the OH modes may imply H + -loss from the aragonite lattice above 11.5 GPa.

58 GEOSCIENCES↗
DOE OSTI2020

Materials Data on CaO by Materials Project

CaO is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent O2- atoms to form a mixture of corner and edge-sharing CaO6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ca–O bond lengths are 2.42 Å. O2- is bonded to six equivalent Ca2+ atoms to form a mixture of corner and edge-sharing OCa6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaO by Materials Project

CaO crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ca2+ is bonded to five equivalent O2- atoms to form a mixture of edge and corner-sharing CaO5 trigonal bipyramids. There are three shorter (2.31 Å) and two longer (2.41 Å) Ca–O bond lengths. O2- is bonded to five equivalent Ca2+ atoms to form a mixture of edge and corner-sharing OCa5 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaO2 by Materials Project

CaO2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ca is bonded in a distorted q4 geometry to ten equivalent O atoms. There are eight shorter (2.45 Å) and two longer (2.74 Å) Ca–O bond lengths. O is bonded in a 6-coordinate geometry to five equivalent Ca and one O atom. The O–O bond length is 1.52 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaO2 by Materials Project

CaO2 is Calaverite structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one CaO2 sheet oriented in the (0, 0, 1) direction. Ca is bonded to six equivalent O atoms to form distorted edge-sharing CaO6 octahedra. All Ca–O bond lengths are 2.36 Å. O is bonded in a trigonal non-coplanar geometry to three equivalent Ca atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaO2 by Materials Project

CaO2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ca is bonded in a body-centered cubic geometry to eight equivalent O atoms. There are six shorter (2.42 Å) and two longer (2.45 Å) Ca–O bond lengths. O is bonded to four equivalent Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaO2 by Materials Project

CaO2 is Fluorite-like structured and crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are two inequivalent Ca sites. In the first Ca site, Ca is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.39–2.46 Å. In the second Ca site, Ca is bonded in a body-centered cubic geometry to eight O atoms. There are a spread of Ca–O bond distances ranging from 2.38–2.46 Å. There are four inequivalent O sites. In the first O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra. In the second O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra. In the third O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra. In the fourth O site, O is bonded to four Ca atoms to form a mixture of edge and corner-sharing OCa4 tetrahedra.

36 MATERIALS SCIENCE↗