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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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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

High-Spin and Reactive Fe 13 Cluster with Exposed Metal Sites

We report atomically defined large metal clusters have applications in new reaction development and preparation of materials with tailored properties. Expanding the synthetic toolbox for reactive high nuclearity metal complexes, we report a new class of Fe clusters, Tp* 4 W 4 Fe 13 S 12 , displaying a Fe 13 core with M-M bonds that has precedent only in main group and late metal chemistry. M 13 clusters with closed shell electron configurations can show significant stability and have been classified as superatoms. In contrast, Tp* 4 W 4 Fe 13 S 12 displays a large spin ground state of S=13. This compound performs small molecule activations involving the transfer of up to 12 electrons resulting in significant cluster rearrangements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Binding, Release and Functionalization of Intact Pnictogen Tetrahedra Coordinated to Dicopper Complexes

The bridging MeCN ligand in the dicopper(I) complexes [(DPFN)Cu 2 (μ,η 1 : η 1 -MeCN)][X] 2 (X=weakly coordinating anion, NTf 2 (1 a), FAl[OC 6 F 10 (C 6 F 5 )] 3 (1 b), Al[OC(CF 3 ) 3 ] 4 (1 c)) was replaced by white phosphorus (P 4 ) or yellow arsenic (As 4 ) to yield [(DPFN)Cu 2 (μ,η 2 : η 2 -E 4 )][X] 2 (E=P (2 a-c), As (3 a-c)). The molecular structures in the solid state reveal novel coordination modes for E 4 tetrahedra bonded to coinage metal ions. Experimental data and quantum chemical computations provide information concerning perturbations to the bonding in coordinated E 4 tetrahedra. Reactions with N-heterocyclic carbenes (NHCs) led to replacement of the E 4 tetrahedra with release of P 4 or As 4 and formation of [(DPFN)Cu 2 (μ,η 1 : η 1 - Me NHC)][X] 2 (4 a,b) or to an opening of one E-E bond leading to an unusual E 4 butterfly structural motif in [(DPFN)Cu 2 (μ,η 1 : η 1 -E 4 Dipp NHC)][X] 2 (E=P (5 a,b), E=As (6)). With a cyclic alkyl amino carbene ( Et CAAC), cleavage of two As-As bonds was observed to give two isomers of [(DPFN)Cu 2 (μ,η 2 : η 2 -As 4 Et CAAC)][X] 2 (7 a,b) with an unusual As 4 -triangle+1 unit.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Uncovering Multiple Metal-Metal Bonding in a Tetranuclear Fluoride Rhenium Cluster or the Curious Case of {[Ni(H 2 O) 6 ](NH 4 ) 4 }[Re 4 F 18 ]·4H 2 O

The compound {[Ni(H 2 O) 6 ](NH 4 ) 4 }[Re 4 F 18 ]·4H 2 O (1) has been isolated and characterized by single-crystal X-ray diffraction, Raman spectroscopy and computational methods. The compound 1 crystallizes in the triclinic space group P 1 (a = 6.6620(9) Å, b = 9.7121(13) Å, c = 11.2007(15) Å, α = 67.644(2)°, β = 83.827(2)°, γ = 84.366(2)°). In 1, the [Re 4 F 18 ] 6– anion is composed of four Re(III) atoms bridged by two µ-bridging fluorine atoms and two di-µ-bridging fluorine atoms. Furthermore, in [Re 4 F 18 ] 6– , the shortest Re–Re distance (i.e., 2.3631(6) Å) is characteristic of the presence of a Re=Re double bond; the Re–F distances range from 1.854(6) to 2.008(5) Å. Theoretical calculations confirm the presence of a weak Re=Re double bond; the Mayer–Mulliken bond order of the doubly bridged Re atoms is 1.8097 and the natural localized molecular orbital bond order is 1.8751. The Raman spectrum of 1 has been measured and shows a series of bands in the region 167–1449 cm –1 that have been attributed to Re–F and Ni–O stretches, Re 4 F 18 ring breathing and NH 4 + bending and libration modes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Dynamical Bond Formation in KNi 2 Se 2

Emphanisis, or the appearance out of nothing, has been used to describe the phenomena of spontaneous atom off-centering and dipole formation at elevated temperatures in lead chalcogenides. Here, we provide spectroscopic evidence of spontaneous formation of metal-metal bonds above T~50 K in the layered metal KNi 2 Se 2 . These bonds form zig-zag chains that lower the local symmetry from tetragonal to monoclinic. Energy-resolved pair distribution function measurements exclude a pure phonon origin of our observations, and instead imply the existence of extra, slowly fluctuating, Ni-Ni bonds above T=50 K. Density functional theory calculations support this lower symmetry configuration as an instability of tetragonal KNi 2 Se 2 . We thus demonstrate that the phenomena of emphansis is not limited to local electric dipole formation, but can also be driven by the formation of metal-metal bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Energy absorption of architectured PrintCast interpenetrating composites in tension

Additively manufactured (AM) metal-metal composites consisting of PrintCasted 316 L austenitic stainless-steel lattice structures infiltrated with A356 casting alloy, have recently been developed for use in high energy absorption systems with potential applications ranging from static load bearing to dynamic blast containment structures. This system has a unique mechanical behavior as the volume fraction of lattice increases showing a transition from localized to de-localized failure and dramatic increase in energy absorption capability. In this work, PrintCast A356/316 L composite tensile specimens were produced with lattice volume fractions ranging from 20 % to 50 % to capture the range of this behavior. Finite element simulations support neutron diffraction measurements of stress state. Results illustrate that in tension, the reinforcement material is in tension while the matrix support material is in compression, information offering significant insight into the transition to de-localized failure. Moreover, the simulation results provide further insight into how interfacial bonding (or lack of bonding) affects the energy absorption capabilities of the PrintCast composites.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Oxide layer delamination: An energy dissipation mechanism during high-velocity microparticle impacts

The break-up of microparticle surface oxides is needed to generate a clean metal-metal contact for metallurgical bonding during impact events such as seen in cold-spray. However, the mechanism by which this occurs is not clear. Here, using a laser-induced particle impact tester, we conduct site-specific experiment of single Cu microparticle impacts on a polished Cu substrate and characterize the impact sites. We observe that oxide layers on the particles begin to delaminate at velocities high enough to cause jetting of the substrate around the periphery of the impact site. We show that the energy cost of such delamination is ~30% of the energy needed to slow and stop particle as it bonds to the substrate, with the remainder being associated with the jetting process and bonding itself. At higher velocities, the oxide barrier is broken up to permit metallurgical bonding. Closer to the particle south-pole where hoop strain is low, oxide layers break up with few gaps and thus no metallurgical bonding is observed. Away from the south-pole where larger strains develop, oxide breakup permits intermittent bonding by the extrusion of bare metal into the gaps between oxide islands. These observations provide new insights towards understanding impact-induced metallurgical bonding during cold-spray process.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Plasma treatment on both adhesive tape and adherends for significantly enhanced CFRTP-related adhesive joints

Unlike existing literature that primarily concentrates on either the plasma treatment of adherends alone or solely on adhesive surfaces, this work leverages plasma modification of both adhesive in tape form and adherend surfaces to largely enhance the interfacial bonding between a thermoset-based adhesive tape and carbon-fiber-reinforced thermoplastic polymer (CFRTP) for structural bonding applications. Here, by conducting single lap shear tests on adhesively-bonded AA6061-CFRPPA (carbon-fiber-reinforced polyphthalamide) dissimilar joints, it is shown that the plasma treatment of adherends alone can increase the lap shear strength (LSS) of the joints by approximately 200% compared to non-treated counterparts. An additional plasma treatment of adhesive tape surfaces leads to even higher LSS improvement, reaching up to 315%, due to the formation of a denser crosslinked network of covalent bonds and a reduced area fraction of interfacial voids at the CFRPPA/adhesive interface. The highest plasma-enhanced LSS of the metal-CFRTP dissimilar joints rivals that of metal-metal joints, which is typically stronger than the joints associated with fiber-reinforced polymers. This study is important for achieving strong CFRTP-related structural components bonded using adhesive tape, providing better compatibility with plasma treatment and other joining methods like riveting compared to adhesive paste or liquid.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mode I tensile fracture behavior of adhesively-bonded metal–metal, metal–CFRP, and CFRP–CFRP bi-material combinations analyzed by size effect method

Understanding the adhesive and interfacial fracture is important for developing and achieving better adhesive jointing in bi-materials, the location which becomes less vulnerable in engineered structure components. Still, to characterize the fracturing behavior of various adhesively-bonded materials, it was shown in this work that the Mode I fracture energies estimated from conventional methods (e.g., work-of-fracture, (modified) compliance calibration method, (modified) beam theory, etc.) can be strongly affected by adherent thickness, adhesive bond length, and material type. Consequently, this hindered the proper understanding of fracturing in adhesive jointing of bi-materials since the estimated fracture energies can exhibit unreasonable difference among various material combinations, thus leading to the confusion in the literature due to the unfair comparison on these non-objective results estimated by leveraging conventional methods on the specimens with different geometries. This work compared size effect method with conventional methods on the calculation of the Mode I fracture energies of metal-metal, metal-CFRP, and CFRP-CFRP material combinations via Double Cantilever Beam (DCB) tests. The results showed that the estimated fracture energies of various material combinations are not dependent on the specimen geometries. This aspect allowed the fair comparison particularly on the interfacial fracturing between metal/adhesive and CFRP/adhesive, and the difference was further explained and correlated with the damage morphology on the material surface after failure identified through three-dimensional profilometer.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Photochemical behavior of the quadruply metal-metal bonded [Tc 2 Cl 8 ] 2– anion in acetonitrile

Here, the photochemical behavior of [Tc 2 Cl 8 ] 2– was investigated in acetonitrile. The speciation of Tc before and after irradiation at 254 nm was performed by UV-visible spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Upon irradiation at 254 nm, [Tc 2 Cl 8 ] 2– was unstable, the scission of the Tc ≡ Tc unit occurred and the complex [TcCl 4 (CH 3 CN) 2 ] was identified. The disappearance rate of [M 2 Cl 8 ] 2– (M = Tc, Re) under irradiation has been measured and was ~7.5 time faster for Tc than for Re.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Electronic origins of the giant volume collapse in the pyrite mineral MnS 2

The pyrite mineral MnS 2 was recently shown to undergo a giant pressure-induced volume collapse at 12 GPa, via a disordered intermediate phase. The high pressure arsenopyrite phase is stabilised by metal-metal bonding, a mechanism now shown to be ubiquitous for Mn 2+ chalcogenides. Here we report a spectroscopic investigation of this transition up to pressures of 22 GPa. Using XANES we show that the transition does not involve a change in oxidation state, consistent with the arsenopyrite crystal structure proposed at high pressure. Notably, the XANES spectrum is almost identical in the pressure-induced disordered phase, and after crystallisation induced by laser-heating. The former is therefore a `valence bond glass', and is likely disordered due to kinetic hindrance of the phase transition. We also detect electronic changes in the compressed pyrite phase, and this is con rmed by Raman scattering which shows that the disulphide vibrations in the pyrite phase saturate before the volume collapse. Together with detailed DFT calculations, these results indicate that electronic changes precede valence bond formation between the Mn 2+ cations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of nanocrystallised multilayered metallic materials produced by the SMAT followed by constrained compression

Highlights: • Nanocrystallised multilayered metallic material was produced by novel technique. • Bonding between nanocrystallised plates was achieved by constrained compression. • The metal-metal bonding occurred between fragmented oxide layers. • A high degree of structural inhomogeneity was observed near bonded regions. - Abstract: Nanocrystallised multilayered metallic material was obtained via duplex technique combining the surface mechanical attrition treatment (SMAT) with a novel constrained compression (CC) process. At the initial stage the 1 mm thick sheets of 316L austenitic stainless steel were processed by the SMAT in order to form a nanocrystalline structure. At the final stage disc-shaped plates excised from SMATed sheets, were assembled in a package and compressed in order to produce metallurgical bonding between individual plates. The characterization of such a multilayered structure was studied both experimentally and numerically. The microscopic examination revealed that the bonding occurred in the central portions of the package where the oxide scale covering each plate was fragmented by high shear strains. The numerical analysis confirmed that the strains at the interior interfaces are significantly higher than at the external ones. A high degree of structural inhomogeneity was observed via TEM studies in the regions where the successful bonding was achieved. Regions characterised by fine band structure with the presence of α′-martensite phase as well as coarse cellular structure within a single γ-austenite phase were identified.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Solvothermal synthesis and solid-state characterization of metal-metal bonded tetracarboxylatoditechnetium(II,III) polymers

Investigations of solvothermal reactions with pertechnetate, [TcO 4 ] - , have produced four new low-valent Tc extended metal atom chain (EMAC) complexes with multiple metal-metal bonds. The thermal reaction of potassium pertechnetate with glacial acetic acid, under in-situ hydrogen production from the decomposition of sodium borohydride, yields purple elongated crystals determined to be tetraacetato ditechnetium (II,III) acetate (1), [Tc 2 (O 2 CCH 3 ) 4 (μ-O 2 CCH 3 ] n . Compound 1 was characterized by single crystal X-ray diffraction and its magnetic properties recorded between 10 and 300 K. Single crystal X-ray diffraction analysis of 1 indicates the Tc 2 +5 tetraacetato unit is linked by the carboxylate oxygens of the bridging acetate, similar to known chloride and bromide linkage polymers of composition [Tc 2 (μ-O 2 CCH 3 ) 4 Cl] n , and [Tc 2 (μ-O 2 CCH 3 ) 4 Br] n . Here, using the same synthetic method three similar compounds have been synthesized from propionic, benzoic and pivalic acid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Controlling the corrosion resistance of multi-principal element alloys

Multi-principal element alloys (MPEAs) offer the possibility of many degrees of freedom in the choice of alloying elements to produce either single phase solid solutions or more complex multiphase microstructures. Large ranges of material properties have been observed for MPEAs and mastery of the selection of elements and their compositions can enable novel combinations of properties not possible in traditional alloys. From the aqueous corrosion perspective, optimization of phase stability, control of heterogeneities, passive film identity and its protectiveness, as well as substrate properties such as metal-metal bond strength and activation energy associated with dissolution, can all be controlling factors governed by alloy composition and structure. These factors can mediate the electrochemical reactions controlling spontaneous corrosion. The quest for superior properties based on well-informed element choice is suggested as a path forward guiding MPEA formulations for corrosion performance. However, gaps in fundamental knowledge exist regarding (a) the specific functions of each element, (b) the behavior of elements in unusual combinations, and (c) the formation of complex protective oxides. These issues currently hold back progress in optimization of corrosion properties.

Scully, John R.↗
DOE OSTI2016

Lithium Assisted “Dissolution–Alloying” Synthesis of Nanoalloys from Individual Bulk Metals

We report new fundamental chemistry involved in the synthesis of bimetallic nanoalloys via dissolving the pure bulk transition metals in molten lithium. It is revealed at the atomic level that when two pure bulk transition metals such as Pd and Pt are placed in molten lithium (similar to 200 degrees C), they undergo a dissolution process in which the metal-metal bonds in pure bulk transition metals are completely ruptured, which results in the existence of individual Pd and Pt atoms surrounded by lithium atoms, as is evident by synchrotron X-ray adsorption techniques. Then, upon the conversion of metal lithium to LiOH in humid air, the Pd and Pt atoms undergo an alloying process to aggregate into nanoalloys. This method was further expanded to include PdZn, which is notoriously difficult to prepare via traditional nanoalloy synthesis methods due to the easily oxidizable Zn component. The constantly reducing environment of metallic Li allowed for preparation of PdZn nanoalloys with minimal Zn oxidation via dissolution-alloying of individual bulk transition metals in molten lithium. Additionally, this lithium assisted "dissolution-alloying" method bypasses many complications intrinsic to conventional ion reduction-based nanoalloy synthesis including the necessity of ligated metal ions, the use of proper reducing agents and dispersing surfactants, and the presence of segregated phases due to different reduction potentials of the constituent metal ions.

alloying↗
DOE OSTI2016

Octafluorodirhenate(III) Revisited: Solid-State Preparation, Characterization, and Multiconfigurational Quantum Chemical Calculations

A simple method for the high-yield preparation of (NH 4 ) 2 [Re 2 F 8 ]· 2H 2 O has been developed that involves the reaction of (n-Bu 4 N)2[Re 2 Cl 8 ] with molten ammonium bifluoride (NH 4 HF 2 ). Using this method, the new salt [NH 4 ] 2 [Re 2 F 8 ]·2H 2 O was prepared in ~90% yield. The product was characterized in solution by ultraviolet-visible light (UV-vis) and 19 F nuclear magnetic resonance (19F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re 2 F 8 ] 2- anion. The metal-metal bonding in the Re 2 6+ unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re 2 Cl 8 ] 2- and [Re 2 Br 8 ] 2- analogues.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Molecular and electronic structure of Re 2 Br 4 (PMe 3 ) 4

The dinuclear rhenium(II) complex Re 2 Br 4 (PMe 3 ) 4 was prepared from the reduction of [Re 2 Br 8 ] 2– with ( n -Bu 4 N)BH 4 in the presence of PMe 3 in propanol. The complex was characterized by single-crystal X-ray diffraction (SCXRD) and UV–visible spectroscopy. It crystallizes in the monoclinic C2/c space group and is isostructural with its molybdenum and technetium analogues. The Re–Re distance (2.2521(3) Å) is slightly longer than the one in Re 2 Cl 4 (PMe 3 ) 4 (2.247(1) Å). The molecular and electronic structure of Re 2 X 4 (PMe 3 ) 4 (X = Cl, Br) were studied by multiconfigurational quantum chemical methods. The computed ground-state geometry is in excellent agreement with the experimental structure determined by SCXRD. The calculated total bond order (2.75) is consistent with the presence of an electron-rich triple bond and is similar to the one found for Re 2 Cl 4 (PMe 3 ) 4 . The electronic absorption spectrum of Re 2 Br 4 (PMe 3 ) 4 was recorded in benzene and shows a series of low-intensity bands in the range 10 000–26 000 cm –1 . The absorption bands were assigned based on calculations of the excitation energies with the multireference wave functions followed by second-order perturbation theory using the CASSCF/CASPT2 method. As a result, calculations predict that the lowest energy band corresponds to the δ* → σ* transition, while the next higher energy bands were attributed to the δ* → π*, δ → σ*, and δ → π* transitions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Observation of Vacancies, Faults, and Superstructures in Ln 5 Mo 2 O 12 (Ln = La, Y, and Lu) Compounds with Direct Mo–Mo Bonding

Among oxide compounds with direct metal–metal bonding, the Y 5 Mo 2 O 12 (A 5 B 2 O 12 ) structural family of compounds has a particularly intriguing low-dimensional structure due to the presence of bioctahedral B 2 O 10 dimers arranged in one-dimensional edge-sharing chains along the direction of the metal–metal bonds. Furthermore, these compounds can have a local magnetic moment due to the noninteger oxidation state (+4.5) of the transition metal, in contrast to the conspicuous lack of a local moment that is commonly observed when oxide compounds with direct metal–metal bonding have integer oxidation states resulting from the lifting of orbital degeneracy typically induced by the metal–metal bonding. Although a monoclinic C2/m structure has been previously proposed for Ln 5 Mo 2 O 12 (Ln = La–Lu and Y) members of this family based on prior single crystal diffraction data, it is found that this structural model misses many important structural features. On the basis of synchrotron powder diffraction data, it is shown in this paper that the C2/m monoclinic unit cell represents a superstructure relative to a previously unrecognized orthorhombic Immm subcell and that the superstructure derives from the ordering of interchangeable Mo 2 O 10 and LaO 6 building blocks. The superstructure for this reason is typically highly faulted, as evidenced by the increased breadth of superstructure diffraction peaks associated with a coherence length of 1–2 nm in the c* direction. Finally, it is shown that oxygen vacancies can occur when Ln = La, producing an oxygen deficient stoichiometry of La 5 Mo 2 O 11.55 and an approximately 10-fold reduction in the number of unpaired electrons due to the reduction of the average Mo valence from +4.5 to +4.05, a result confirmed by magnetic susceptibility measurements. Finally, this represents the first observation of oxygen vacancies in this family of compounds and provides an important means of continuously tuning the magnetic interactions within the one-dimensional octahedral chains of this system.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis, and Crystal and Electronic Structures, of the Titanium-Rich Bismuthides AE 3 Ti 8 Bi 10 ( AE = Sr, Ba, Eu)

Three isotypic compounds with the chemical formula AE 3 Ti 8 Bi 10 (AE = Sr, Ba, Eu) have been obtained via both high-temperature solid state and flux growth reactions. Their crystal structure, representing a new type (space group P6 3 /mmc, Pearson symbol hP 42 ), features an open framework composed of interlinked TiBi 5 square pyramids and TiBi 6 octahedra. The Ti–Bi substructure is penetrated by infinite columns of face-sharing AE 6 polyhedra centered by Bi atoms. First-principle calculations and physical property measurements indicate metallic behavior and absence of localized magnetic moments on the Ti atoms. Analysis of the chemical bonding reveals strong Ti–Bi and Ti–Ti bonds. Finally, the latter demonstrate classic two-center, as well as multicenter interactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗