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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Elucidating the Effect of Ion Exchange Protocol on the Copper Exchange Efficacy, Copper Siting, and SCR activity in Cu-SSZ-13

The influence of the copper ion exchange protocol on SCR activity of SSZ-13 is quantified. Using the same parent SSZ-13 zeolite, four exchange protocols are used to assess how exchange protocol impacts metal uptake and SCR activity. Large differences in the SCR activity, nearly 30 percentage points at 160 °C at constant copper content, are observed for different exchange protocols implying that different exchange protocols lead to different copper species. Hydrogen temperature programmed reduction on selected samples and infrared spectroscopy of CO binding corroborates this conclusion as the reactivity at 160 °C correlates with the intensity of the IR band at 2162 cm -1 . DFT-based calculations show that such an IR assignment is consistent with CO adsorbed on a Cu(I) cation within an eight-membered ring. This work shows that SCR activity can be influenced by the ion exchange process even when different protocols lead to the same metal loading. Perhaps most interesting, a protocol used to generate Cu-MOR for methane to methanol studies led to the most active catalyst both on a unit mass or unit mole copper basis. This points to a yet not recognized means to tailor catalyst activity as the open literature is silent on this issue.

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

Thermal Properties of the Very Low Thermal Conductivity Ternary Chalcogenide Cu 4 Bi 4 M 9 (M = S, Se)

Temperature-dependent thermal properties of phase-pure polycrystalline ternary chalcogenides Cu 4 Bi 4 S 9 and Cu 4 Bi 4 Se 9 are reported. The structure and bonding in these materials result in very low thermal conductivity values (<0.8 W m -1 K -1 at room temperature) for both materials. The lattice contribution, Debye temperatures, and Sommerfeld coefficient are obtained from low-temperature heat capacity data that also indicate very small electronic contributions to the heat capacity for these materials. This study aids in the identification of new nontoxic, earth-abundant resistive ternary chalcogenide materials with low thermal conductivity for potential thermal barrier coating and rewriteable storage applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Deriving Stable Peak Models to Fit Complex XPS Data From Cu Contaminated Pt Electrocatalysts

X-ray Photoelectron Spectroscopy spectra peak models, designed to partition photoemission signals emanating from different elements or chemical states within an atom, are fitted to data limited to an energy interval over which inelastically scattered photoemission signal can be estimated. While the choice of background approximation and line shapes of components to the peak model requires careful consideration, the energy interval used to define the data to which the peak model is optimized has a significant impact on the final peak model. The relationship between the background intensity and data intensity at the start and end of the energy interval dictates the line shapes used in the peak model. In this work, we devise a method to peak fit a complex overlapping Cu 3p and Pt 4f XPS peak structure to perform the elemental quantification. We first use an Al 2s peak to illustrate how background curves approach data at the limits of the energy interval over which the background is defined, influencing the analysis of XPS spectra. Next, we demonstrate the nature of interactions between specific line shapes (Voigt and pseudo-Voigt profiles) suitable for photoemission peaks and a specific background curve (Shirley) and a peak model is presented that includes components to the peak model that accommodates background intensity during fitting of the peak model to data. The peak model allowed for quantification of the contributions of Pt 4f peaks emanating from the substrate that exhibits strong asymmetry in the presence of the inhomogeneously distributed Cu species, mostly of Lorentzian character.

XPS↗
DOE OSTI2024

Cu Based Dilute Alloys for Tuning the C 2+ Selectivity of Electrochemical CO 2 Reduction

Electrochemical CO 2 reduction is a promising technology for replacing fossil fuel feedstocks in the chemical industry but further improvements in catalyst selectivity need to be made. So far, only copper-based catalysts have shown efficient conversion of CO 2 into the desired multi-carbon (C 2+ ) products. This work explores Cu-based dilute alloys to systematically tune the energy landscape of CO 2 electrolysis toward C 2+ products. Selection of the dilute alloy components is guided by grand canonical density functional theory simulations using the calculated binding energies of the reaction intermediates CO*, CHO*, and OCCO* dimer as descriptors for the selectivity toward C 2+ products. Here, a physical vapor deposition catalyst testing platform is employed to isolate the effect of alloy composition on the C 2+ /C 1 product branching ratio without interference from catalyst morphology or catalyst integration. Six dilute alloy catalysts are prepared and tested with respect to their C 2+ /C 1 product ratio using different electrolyzer environments including selected tests in a 100-cm 2 electrolyzer. Consistent with theory, CuAl, CuB, CuGa and especially CuSc show increased selectivity toward C 2+ products by making CO dimerization energetically more favorable on the dominant Cu facets, demonstrating the power of using the dilute alloy approach to tune the selectivity of CO 2 electrolysis.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Counterintuitive Trend of Intrusion Pressure with Temperature in the Hydrophobic Cu 2 (tebpz) MOF

Liquid porosimetry experiments reveal a peculiar trend of the intrusion pressure of water in hydrophobic Cu 2 (3,3',5,5'-tetraethyl-4,4'-bipyrazolate) MOF. At lower temperature (T) range, the intrusion pressure (P i ) increases with T. For higher T values, P i first reaches a maximum and then decreases. This is at odds with the Young–Laplace law, which for systems showing a continuous decrease of contact angle with T predicts a corresponding reduction of the intrusion pressure. Though the Young–Laplace law is not expected to provide quantitative predictions at the subnanoscale of Cu 2 (tebpz) pores, the physical intuition suggests that to a reduction of their hydrophobicity corresponds a reduction of the P i . Molecular dynamics simulations and sychrothron experiments allowed to clarify the mechanism of the peculiar trend of P i with T. At increasing temperatures the vapor density within the MOF’ pores grows significantly, bringing the corresponding partial pressure to ≈5 MPa. This pressure, which is consistent with the shift of P i observed in liquid porosimetry, represents a threshold to be overcame before intrusion takes place. Beyond some value of temperature, the phenomenon of reduction of hydrophobicity (and water surface tension) dominated over the opposite effect of increase of vapor pressure and P i inverts its trend with T.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

How Atomic Bonding Plays the Hardness Behavior in the Al–Co–Cr–Cu–Fe–Ni High Entropy Family

A systematic study on a face-centered cubic-based compositionally complex alloy system Al–Co–Cr–Cu–Fe–Ni in its single-phase state is carried out, where a mother senary compound Al 8 Co 17 Cr 17 Cu 8 Fe 17 Ni 33 and five of its suballoys, obtained by removing one element at a time, are investigated and exhaustively analyzed determining the contribution of each alloying element in the solid solution. The senary and the quinaries are compared using experimental techniques including X-ray absorption spectroscopy, X-ray diffraction, transmission electron microscopy, and first principles hybrid Monte Carlo/molecular dynamics simulations. Chemical short-range order and bond length distances have been determined both at the experimental and computational level. Electronic structure and local atomic distortions up to 5.2 Å have been correlated to the microhardness values. A linear regression model connecting hardness with local lattice distortions is presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Nonradiative Recombination Dominates Voltage Losses in Cu(In,Ga)Se 2 Solar Cells Fabricated using Different Methods

Voltage losses reduce the photovoltaic conversion efficiency of thin‐film solar cells and are a primary efficiency limitation in Cu(In,Ga)Se 2 . Herein, voltage loss analysis of Cu(In,Ga)Se 2 solar cells fabricated at three institutions with variation in process, bandgap, absorber structure, postdeposition treatment (PDT), and efficiency is presented. Nonradiative voltage losses due to Shockley–Read–Hall charge carrier recombination dominate and constitute >75% of the total compared to <25% from radiative voltage losses. The radiative voltage loss results from nonideal absorption and carriers in band tails that stem from local composition‐driven potential fluctuations. It is shown that significant bulk lifetime improvements are achieved for all alkali PDT processed absorbers, chiefly associated with reductions in nonradiative recombination. Primary voltage loss contributions (radiative and nonradiative) change little across fabrication processes, but variation in submechanisms (bulk lifetime, net acceptor concentration, and interface recombination) differentiate nonradiative loss pathways in this series of solar cells.

14 SOLAR ENERGY↗
DOE OSTI2020

The synergistic role of Mn and Zr/Ti in producing θ'/L12 co-precipitates in Al-Cu alloys

Microstructural stability is a critical factor to consider when designing new alloys for high-temperature applications. An Al-Cu alloy with Mn and Zr additions has recently been developed to withstand extended exposures of up to 350 °C. The addition of Mn in combination with Zr and their segregation to precipitate interfaces play a significant role in stabilizing the metastable θ ' precipitates responsible for the alloy&#x27;s hardness; however, adding Zr and Mn separately only improves the stability to 200 °C and 300 °C, respectively. To this end, the effect of the synergistic additions on interfacial structure and chemistry was studied in detail using atom probe tomography (APT) and scanning transmission electron microscopy (STEM) for Al-Cu-Mn-Zr/Ti-containing alloys subjected to long-term annealing (up to 2,100 h) in the critical temperature range, 300 °C and 350 °C, to investigate the role of Zr/Ti in increasing the θ '-precipitate stability. The APT and STEM results reveal that Mn additions stabilize θ ' long enough for the slower diffusing Zr atoms to segregate to coherent θ ' interfaces that eventually create a θ '/ L1 2 -Al 3 (Zr x ,Ti 1-x ) co-precipitate structure. The co-precipitate is highly stable, as shown by density functional theory calculations, and is a key factor that governs microstructural stability beyond 300 °C. This study reveals how solute additions with different stabilization mechanisms can work in concert to stabilize a desired microstructure, and the results provide insights that can be applied to other high-temperature alloy systems.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Crystallographic orientation-dependent strain hardening in a precipitation-strengthened Al-Cu alloy

While the strengthening of Al-Cu alloys due to precipitation has been extensively studied, the effect of crystallographic orientation of the matrix and precipitates, as well as precipitate morphology, on the strain hardening behavior is not well understood. In this paper, we investigate this effect with in situ neutron diffraction during deformation of an Al-Cu alloy (206) after multiple aging treatments. Precipitate-dislocation interactions were found to change from precipitate shearing for microstructures predominantly containing GPI and θ" precipitates to Orowan looping for microstructures with primarily θ' and θ precipitates. Notably, significant anisotropy in strain hardening behavior was observed when θ' precipitates were present, which was attributed to crystallographic orientation dependent load transfer from the Al matrix to the θ' precipitates. The anisotropic load transfer is hypothesized to be caused by the extent of rotation of high aspect-ratio θ' precipitates, owing to dislocations looping around them during plastic deformation of the matrix. Predictions from an analytical model describing the anisotropic magnitude of load transfer from precipitate rotation agree well with experimental results, successfully validating the precipitate rotation hypothesis and explaining the anisotropic strain hardening behavior. This model allows for the prediction of stresses separately in the precipitate and matrix phases as a function of crystallographic orientation, only given the bulk mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Additively manufactured novel Al-Cu-Sc-Zr alloy: Microstructure and mechanical properties

An in-depth understanding of microstructure and resultant properties is paramount in the design of a novel alloy system, especially for additive manufacturing (AM). The present investigation aims to characterize a prototypical AM Al alloy with great potential for structural applications. An Al-1.5Cu-0.8Sc-0.4Zr alloy designed using integrated computational material engineering was printed using the laser powder bed fusion AM process. This novel alloy shows promising combination of strength and ductility in as-built and peak-aged conditions. This improvement in the tensile properties is attributed to the presence of both coherent L1 2 Al 3 Sc/Al 3 (Sc,Zr) precipitates and Cu-rich regions. The microstructures were studied via extensive microscopy at different length scales using X-ray microscopy, scanning electron microscopy, and transmission electron microscopy. Fractography revealed that the columnar grain boundaries in as-built condition allow easy slip transfer as compared to the equiaxed grains, with the apex of the melt pool acting as the crack nucleation site. Furthermore, the peak aged condition resulted in improved strength while marginally sacrificing ductility due to precipitates decorating dislocations, grain boundaries and melt pool boundaries thus acting as obstacles to slip transfer.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Creep deformation and cavitation in an additively manufactured Al-8.6Cu-0.4Mn-0.9Zr (wt%) alloy

Creep deformation and cavitation were investigated at 300 ºC in both tension and compression for an additively manufactured Al-8.6Cu-0.5Mn-0.9Zr (wt%) alloy in the as-fabricated state and after various aging treatments (aging at 300 °C/200 h or 350 °C/24 h and overaging at 400 °C/200 h). Creep mechanisms at 300 °C were determined by relating the measured creep response to corresponding microstructural and X-ray computed tomography observations. In compression, alloys in the as-fabricated and two aging conditions exhibited similarly high creep resistance. Overaging (400 °C/200 h) led to substantial coarsening of intragranular θ-Al2Cu precipitates and an expected drop in their Orowan strengthening contribution. In tension, minimum strain rates comparable to those in compression were obtained at any given stress; however, upon accumulation of some plastic strain in the matrix, creep cavities started to form, leading to accelerated tertiary stage creep deformation and rupture. Cavitation occurred exclusively along melt pool boundaries due to locally enhanced diffusion enabled by (i) large grain-boundary area in adjacent fine-grained zones and (ii) localization of creep strain in nearby heat-affected zones. Although cavity growth was initially diffusion-controlled, its rate was determined by matrix creep rate, consistent with constrained cavity growth mechanisms. This study reveals how microstructural complexities induced by the additive manufacturing process affect the creep and cavitation behavior of Al-Cu-Mn-Zr alloys. The underlying creep and cavitation mechanisms uncovered in this study point to pathways that improve the high-temperature properties of additively manufactured alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Assessing factors that determine adatom migration and clustering on a thin film oxide; Pt 1 and Rh 1 on the “29” Cu x O/Cu(1 1 1) surface

The dynamical nature of single-site catalysts under non-equilibrium conditions poses significant challenges in the full characterization of their active sites. The “29” oxide is a thin Cu x O film grown on Cu(111) which provides a well-defined surface on which to study the structure and chemistry of atomically dispersed precious metals. A combination of experimental and first-principles approaches is used to investigate the factors that influence the mobility of metal adatoms and their clustering tendencies. Our work elucidates how a homogenous coordination environment of neutral single-atoms can be obtained when its tendency to break oxide bonds within its vicinity is low. Herein we demonstrate that this in turn affects the chemical atomically dispersed species on thin-film oxides, as defects on the oxide would in fact allow such species to be more accessible to CO. We thus highlight the importance of understanding the relationship between defects and atomically dispersed active sites upon designing single-site catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electrochemically-assisted removal of cadmium ions by redox active Cu-based metal-organic framework

An electrochemically-assisted wastewater treatment using Faradaic materials offers a promising technique for the selective removal of hazardous substances. Here, we demonstrate the reversible capture and release of cadmium ions in aqueous solutions, using a redox-active metal-organic framework (MOF) electrode. As-synthesized copper-based MOF (Cu-MOF-74; copper 2,5-dihydroxyterephthalate) is a highly attractive candidate for Faradaic electrosorption due to its large surface area, water stability, and redox-active metal nodes. Our work demonstrates the reversible capture and release of Cd 2+ ions assisted by the electrochemical redox reaction of Cu 2+ /Cu + within the MOF structure. Combined material characterization and electrosorption tests were carried out to determine the operational conditions for maximizing adsorption capacity, energy efficiency, and material stability, thus leading to excellent electrosorption (>100 mg g -1 ) and regeneration efficiency (>90%). This study demonstrates the feasibility of leveraging MOFs containing redox-active metal nodes for the selective separation of toxic cations, and paves the way for promising future applications of these 3-D porous structures for wastewater treatment and environmental remediation.

42 ENGINEERING↗
DOE OSTI2021

Cu- and Zn-doped alkali activated mortar – Properties and durability in (bio)chemically aggressive wastewater environments

Metakaolin-based alkali activated mortars (AAM) - with and without CuSO{sub 4}·5H{sub 2}O and ZnO addition (mass ratio M{sup n+}/solid binder 0.08% to 1.7%) - were casted and exposed within an extensive long-term field campaign over the period of 20 months to a sewer basin, strongly affected by biogenic acid corrosion. (Un-)exposed AAM were tested regarding their physicochemical and microstructural properties, bioreceptivity and overall durability. Metal addition led to a retarding effect during alkali-activation reaction, as well as to an increase in open porosity of up to 3.0% and corresponding lower compressive strength of up to 10.9%. Reduced microbial colonization and diversity were observed on AAM with Cu, while Zn addition led to increased biodiversity. We propose that the observed higher durability of Cu-doped AAM is due to antibacterial effects and associated reduction of biogenic acid production, superseding overall negative effects of metal-dosage on physical material properties. Observed lower durability of Zn-doped AAM was related to combined negative physicochemical and microbial effects.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Influence of artificial aging on corrosion of abraded Al-Zn-Mg-Cu alloys

Surface abrasion has been shown to create altered surface layers (ASLs) that are hundreds of nm thick on all types of Al alloys. Such ASLs have lower corrosion resistance than the underlying substrate of Al-Zn-Mg-Cu alloys. Here, we demonstrate how heat treatments affect the ASL microstructure on abraded Al-Zn-Mg-Cu alloys using transmission electron microscopy and atom probe tomography, and also how the corrosion properties change using electrochemical polarization. Additionally, high temperature treatments on the abraded bulk samples enhance η phase precipitation in the ASL, leading to a decreased Zn content in the ASL solid solution, which ennobles the ASL breakdown potential.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Data on Cu- and Ni-Si-Mn-rich solute clustering in a neutron irradiated austenitic stainless steel

The data presented in this article is supplementary to the research article “Phase instabilities in austenitic steels during particle bombardment at high and low dose rates” (Levine et al.). Needle-shaped samples were prepared with focused ion beam milling from a 304L stainless steel that was irradiated with fast neutrons (E 0.1 MeV) in the BOR-60 reactor at 318 °C to 47.5 dpa. Atom probe tomography (APT) experiments in voltage mode were then conducted on a Cameca LEAP 5000X HR. Atom position, range, and mass spectrum files after reconstruction with Cameca’s IVAS software are included. Cu- and Ni-Si-Mn-rich solute nanoclusters were identified and analyzed using the Open Source Characterization of APT Reconstructions (OSCAR) program. Python code for OSCAR, information on the program’s underlying algorithm, and sample output files are provided. A proximity histogram of a Ni-Si-Mn-rich cluster and a 1D density/solute concentration profile of a Cu-rich cluster are given to demonstrate OSCAR’s analytical functionalities. The provided APT dataset is valuable for benchmarking phase instabilities in neutron-irradiated austenitic stainless steels that occur at high doses. The OSCAR program can be reused to process other APT data sets where solute nanoclustering is of interest.

42 ENGINEERING↗
DOE OSTI2022

Residual elastic strain evolution due to thermal cycling of a ceramic-metal composite (WC-Cu) via high energy X-ray diffraction and analytical modeling

Residual stress, when superimposed with in-service loading, can significantly reduce the lifetime and performance of a component. Ceramic-metal composites are susceptible to residual stresses due to the thermal expansion mismatch of the ceramic and metallic phases. The WC-Cu composite explored in the present study provides a promising combination of thermal conductivity and strength properties, while exhibiting counterintuitive improvements in strength and ductility after thermal cycling. Further, this work quantifies the evolution of the residual elastic strains as a result of processing and cyclic thermal loading in a co-continuous WC-Cu composite through experimental high energy X-ray diffraction and kinetics-based modeling. Both analyses indicate that processing-induced residual tensile stress in the copper phase is relieved upon subsequent thermal cycling, with kinetics modeling revealing the cyclic-dependent nature of the active power-law creep mechanisms. The results indicate that, through stress relaxation, this material system maintains structural stability during thermal cycling. The illustrated kinetics of relaxation can inform general material processors and designers of ceramic-metal composites to minimize detrimental residual stress and improve performance of these material systems.

36 MATERIALS SCIENCE↗