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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Synthesis and Characterization of a Triphos Ligand Derivative and the Corresponding Pd II Complexes: Triphos Ligand Derivative and Corresponding Pd II Complexes

The synthesis of the new bis(2-(diphenylphosphino)ethyl)methylhydroxyphosphine tridentate phosphine ligand, LCH2OH/Ph, is reported. The ligand reacts with [Pd(Cl)2(PhCN)2 to form [Pd(LCH2OH/Ph)Cl]Cl. Exchange of the chloride ions for triflate (OTf–) using AgOTf yielded pure [Pd(LCH2OH/Ph)OTf]OTf. In addition to spectral characterization the free ligand, LCH2OH/Ph, and Pd(II) complex, [Pd(LCH2OH/Ph)OTf]OTf, are structurally characterized. This research was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences, and Geosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated by Battelle for DOE.

Miller, Deanna L.↗
DOE OSTI2013

Structural and Spectroscopic Characterization of 17- and 18-Electron Piano-Stool Complexes of Chromium. Thermochemical Analyses of Weak Cr–H Bonds

The 17-electron radical CpCr(CO)2(IMe)• (IMe = 1,3-dimethylimidazol-2-ylidene) was synthesized by the reaction of IMe with [CpCr(CO)3]2, and characterized by single crystal X-ray diffraction and by EPR, IR and variable temperature 1H NMR spectroscopy. The metal-centered radical is monomeric under all conditions and exhibits Curie paramagnetic behavior in solution. An electrochemically reversible reduction to 18-electron CpCr(CO)2(IMe)- takes place at E½ = -1.89(1) V vs Cp2Fe+•/0 in MeCN, and was accomplished chemically with KC8 in THF. The salts K+(18-crown-6)[CpCr(CO)2(IMe)]- • ½THF and K+[CpCr(CO)2(IMe)]- • ¾THF were crystallographically characterized. Monomeric ion pairs are found in the former, whereas the latter has a polymeric structure due to a network of K∙∙∙O(CO) interactions. Protonation of K+(18-crown-6)[CpCr(CO)2(IMe)]- • ½THF gives the hydride CpCr(CO)2(IMe)H, which could not be isolated, but was characterized in solution; a pKa of 27.2(4) was determined in MeCN. A thermochemical analysis provides the Cr-H bond dissociation free energy (BDFE) for CpCr(CO)2(IMe)H in MeCN solution as 47.3(6) kcal mol-1. This value is exceptionally low for a transition metal hydride, and implies that the reaction 2 [Cr-H] → 2 [Cr•] + H2 is exergonic (ΔG = -9.0(8) kcal mol-1). This analysis explains the experimental observation that generated solutions of the hydride produce CpCr(CO)2(IMe)• (typically on the timescale of days). By contrast, CpCr(CO)2(PCy3)H has a higher Cr-H BDFE (52.9(4) kcal mol-1), is more stable with respect to H2 loss, and is isolable. We thank the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences for support. M.L.H. carried out the crystallographic studies and was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The EPR studies were performed at the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at PNNL. Pacific Northwest National Laboratory is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Comparison of the One-electron Oxidations of CO-Bridged vs Unbridged Bimetallic Complexes: Electron-transfer Chemistry of Os2Cp2(CO)4 and Os2Cp*2(μ-CO)2(CO)2 (Cp = η5-C5H5, Cp* = η5-C5Me5)

The one-electron oxidations of two dimers of half-sandwich osmium carbonyl complexes have been examined by electrochemistry, spectro-electrochemistry, and computational methods. The all-terminal carbonyl complex Os2Cp2(CO)4 (1, Cp = η5-C5H5) undergoes a reversible one-electron anodic reaction at E1/2 = 0.41 V vs ferrocene in CH2Cl2/0.05 M [NBu4][B(C6F5)4], giving a rare example of a metal-metal bonded radical cation unsupported by bridging ligands. The IR spectrum of 1+ is consistent with an approximately 1:1 mixture of anti and gauche structures for the 33 e- radical cation in which it has retained all-terminal bonding of the CO ligands. DFT calculations, including orbital-occupancy-perturbed Mayer bond-order analyses, show that the HOMOs of anti-1 and gauche-1 are metal-ligand delocalized. Removal of an electron from 1 has very little effect on the Os-Os bond order, accounting for the resistance of 1+ to heterolytic cleavage. The Os-Os bond distance is calculated to decrease by 0.10 Å and 0.06 Å as a consequence of one-electron oxidation of anti-1 and gauche-1, respectively. The CO-bridged complex Os2Cp*2(μ-CO)2(CO)2 (Cp* = η5-C5Me5), trans-2, undergoes a more facile oxidation, E1/2 = - 0.11 V, giving a persistent radical cation shown by solution IR analysis to preserve its bridged-carbonyl structure. However, ESR analysis of frozen solutions of 2+ is interpreted in terms of the presence of two isomers, most likely anti-2+ and trans-2+, at low temperature. Calculations show that the HOMO of trans-2 is highly delocalized over the metal-ligand framework, with the bridging carbonyls accounting for about half of the orbital makeup. The Os-Os bond order again changes very little with removal of an electron, and the Os-Os bond length actually undergoes minor shortening. Calculations suggest that the second isomer of 2+ has both the trans CO-bridged and the anti all-terminal CO structures. DRL and WEG acknowledge the support of the National Science Foundation under grant CHE-0808909. K-WH acknowledges financial support from KAUST. RMB thanks the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences for support. Pacific Northwest National Laboratory is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy. We thank Dr. S. I. Gorelsky for the discussion on the OOP analysis.

bonding↗
DOE OSTI2014

Marine Sciences Laboratory Radionuclide Air Emissions Report for Calendar Year 2013

The U.S. Department of Energy Office of Science (DOE-SC) Pacific Northwest Site Office (PNSO) has oversight and stewardship duties associated with the Pacific Northwest National Laboratory (PNNL) Marine Sciences Laboratory (MSL) located on Battelle Land – Sequim (Sequim). This report is prepared to document compliance with the Code of Federal Regulations (CFR), Title 40, Protection of the Environment, Part 61, National Emission Standards for Hazardous Air Pollutants (NESHAP), Subpart H, “National Emission Standards for Emissions of Radionuclides Other than Radon from Department of Energy Facilities” and Washington Administrative Code (WAC) Chapter 246-247, “Radiation Protection–Air Emissions.” The EDE to the Sequim MEI due to routine operations in 2013 was 5E-05 mrem (5E-07 mSv). No non-routine emissions occurred in 2013. The MSL is in compliance with the federal and state 10 mrem/yr standard.

air emissions↗
DOE OSTI2015

Marine Sciences Laboratory Radionuclide Air Emissions Report for Calendar Year 2014

The U.S. Department of Energy Office of Science (DOE-SC) Pacific Northwest Site Office (PNSO) has oversight and stewardship duties associated with the Pacific Northwest National Laboratory (PNNL) Marine Sciences Laboratory (MSL) located on Battelle Land – Sequim.This report is prepared to document compliance with the Code of Federal Regulations (CFR), Title 40, Protection of the Environment, Part 61, National Emission Standards for Hazardous Air Pollutants (NESHAP), Subpart H, ''National Emission Standards for Emissions of Radionuclides Other than Radon from Department of Energy Facilities” and Washington Administrative Code (WAC) Chapter 246-247, “Radiation Protection–Air Emissions.'' The EDE to the MSL MEI due to routine operations in 2014 was 9E-05 mrem (9E-07 mSv). No non-routine emissions occurred in 2014. The MSL is in compliance with the federal and state 10 mrem/yr standard.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Tribute to Bruce C. Garrett

This special issue of The Journal of Physical Chemistry B honors the many and wide-ranging contributions of Bruce C. Garrett to theoretical chemistry. Bruce’s contributions have spanned the scope of theoretical chemistry from undergraduate trajectory studies with Don Bunker at UC Irvine, to graduate work on semiclassical reactive dynamics at UC Berkeley with Professor William H. Miller, through postdoctoral studies mainly on chemical reaction theory at the University of Minnesota with one of us, and then on to a long independent career studying a wide array of complex problems, mainly in kinetics and liquid-phase chemistry at Battelle Columbus, at Chemical Dynamics Corporation, and at Pacific Northwest National Laboratory (PNNL). Let's start by recalling some of his research. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

Dang, Liem X.↗
DOE OSTI2020

Experimental and DFT Calculated IR Spectra of Guests in Zeolites: Acyclic Olefins and Host-Guest Interactions

We performed experimental and periodic density functional theory (DFT) IR spectroscopy to investigate the adsorption of acyclic olefins over both acidic and non-acidic zeolites. Two conjugated polyenes, 2,4-dimethyl-1,3-pentadiene (I) and 2,6-dimethyl-2,4,6-octatriene (II) were studied to probe organic intermediates that can form during methanol conversion, and that can lead to deactivating species known collectively as “coke.” We computed vibrational spectra using zeolite-adsorbed and gas-phase models for both neutral and protonated forms of I and II, and compared these DFT results to diffuse reflectance IR Fourier transform (DRIFT) spectra of zeolite-guest systems. Our experimental and computational results are precise enough to pinpoint that the gauche s-cis conformation of species I predominates during adsorption over de-aluminated zeolite beta. Computed zeolite-adsorbed spectra of the protonated species I and II best represent the DRIFT spectra obtained after the adsorption of the olefins on HMOR at 20 ?, with computed bands at 1543 and 1562 cm–1 for molecules I+ and II+, respectively, attributed to the allylic stretching mode, ?(C=C–C+). These computed band frequencies are within 6 cm–1 of experimental data and confirm that the interaction between neutral acyclic olefins and acidic zeolites leads to protonation of the olefin. Comparison of computed spectra of the protonated species in the gas phase to those in the zeolite indicates that the electrostatic interaction between alkenyl and alkadienyl cations and negative zeolite framework does not significantly impact the position of the allylic stretching bands. These results highlight that computed spectroscopy and thermodynamics coupled with experimental spectra can be used for elucidating complex mixtures in zeolites, and certain spectral features of adsorbed olefins can be accurately modeled by gas-phase calculations. ACKNOWLEDGMENTS BM and SMA were supported by the National Science Foundation under Award # CBET-1512442. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for support (or partial support) of this research (#589978-ND5, EDH and FCJ). MDB was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Division of Materials Science and Engineering. CJM was supported by the DOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated by Battelle for the U.S. DOE. Computing resources were generously provided through PNNL’s institutional computing (PIC).

Manookian, Babgen↗
DOE OSTI2015

Nanocrystalline Anatase Titania Supported Vanadia Catalysts: Facet-dependent Structure of Vanadia

Titania supported vanadia, a classic heterogeneous catalyst for redox reactions, typically has nonhomogeneous vanadia species on various titania facets, making it challenging not only to determine and quantify each species but also to decouple their catalytic contributions. We prepared truncated tetragonal bipyramidal (TiO2-TTB) and rod-like (TiO2-Rod) anatase titania with only {101} and {001} facets at ratios of about 80:20 and 93:7, respectively, and used them as supports of sub-monolayer vanadia. The structure and redox properties of supported vanadia were determined by XRD, TEM, XPS, EPR, Raman, FTIR and TPR, etc. It was found that vanadia preferentially occupy TiO2 {001} facets and form isolated O=V4+(O-Ti)2 species, and with further increase in vanadia surface coverage, isolated O=V5+(O-Ti)3 and oligomerized O=V5+(O-M)3 (M = Ti or V) species form on TiO2 {101} facets. The discovery on support facet-dependent structure of vanadia on anatase titania is expected to enable the elucidation of structure-function correlations on high surface area TiO2 supported vanadia catalysts. This work was supported by U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. The research was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE Office of Biological and Environmental Research, and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for DOE by Battelle.

catalyst characterization↗
DOE OSTI2018

Kinetic Coupling of Water Splitting and Photoreforming on SrTiO 3 -Based Photocatalysts

Coupling the anodic half-reactions of overall water splitting and oxygenate photoreforming (i.e., proton reduction and oxygenate oxidations) on Al-doped SrTiO3 decorated with a co-catalyst enables efficient photocatalytic H2 generation along with oxygenate conversion without accumulating undesired intermediates such as formaldehyde. The net H2-evolution rates result from the interplay between water oxidation, oxygenate oxidation, and the back-reaction of H2 and O2 to water. When the latter pathway is quantitatively suppressed (e.g., on RhCrOx co-catalyst or in excess of oxygenated hydrocarbons), the initial H2-evolution rates are independent of the oxygenate nature and concentration. This is a consequence of the reduction equivalents for H2-evolution provided by water oxidation compensating changes in the rates of oxygenate conversion. Thus, under conditions of suppressed back-reaction, water and oxygenate oxidations have equal quantum efficiencies. The selectivities to water and oxygenate oxidation depend on oxygenate nature and concentration. Transformations mediated by indirect hole transfer dominate as a result of the water oxidation at the anode and the associated intermediates generated in O2-evolution catalysis (e.g. ·OH, ·O and ·OOH). On the undecorated semiconductor, the O2 produced during overall water splitting is reductively activated to participate in glycerol oxidation without consuming evolved H2. Acknowledgements The authors would like to thank ESRF in Grenoble, France, for providing beam time at the ID26 station for XAFS experiments. K.E.S. gratefully acknowledges financial support by the Fond der Chemischen Industrie (FCI). J.A.L. and O.Y.G. acknowledge support for his contribution by the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory, a multi-program national laboratory operated by Battelle for the U.S. Department of Energy. The authors thank Xaver Hecht for BET measurements, Martin Neukamm for SEM and AAS measurements and Dr. Udishnu Sanyal for TEM imaging. Christine Schwarz is acknowledged for technical assistance in NMR experiments.

Sanwald, Kai E.↗
DOE OSTI2015

Toward Molecular Catalysts by Computer

Rational design of molecular catalysts requires a systematic approach to designing ligands with specific functionality and precisely tailored electronic and steric properties. It then becomes possible to devise computer protocols to predict accurately the required properties and ultimately to design catalysts by computer. In this account we first review how thermodynamic properties such as oxidation-reduction potentials (E0), acidities (pKa), and hydride donor abilities (ΔGH-) form the basis for a systematic design of molecular catalysts for reactions that are critical for a secure energy future (hydrogen evolution and oxidation, oxygen and nitrogen reduction, and carbon dioxide reduction). We highlight how density functional theory allows us to determine and predict these properties within “chemical” accuracy (~ 0.06 eV for redox potentials, ~ 1 pKa unit for pKa values, and ~ 1.5 kcal/mol for hydricities). These quantities determine free energy maps and profiles associated with catalytic cycles, i.e. the relative energies of intermediates, and help us distinguish between desirable and high-energy pathways and mechanisms. Good catalysts have flat profiles that avoid high activation barriers due to low and high energy intermediates. We illustrate how the criterion of a flat energy profile lends itself to the prediction of design points by computer for optimum catalysts. This research was carried out in the Center for Molecular Electro-catalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory (PNNL) is operated for the DOE by Battelle.

acidity↗
DOE OSTI2019

Genesis and Stability of Hydronium Ions in Zeolite Channels

Zeolite-catalyzed reactions are profoundly altered by the presence of water changing the nature of the Brønsted acid site. High resolution solid-state NMR spectroscopy shows how water interacts with zeolite Brønsted acid sites converting them to hydrated hydronium ions over a wide range in temperature and thermodynamic activity of water. A signal at 9 ppm was observed at loadings of 2–9 water molecules per Brønsted acid site, and assigned to hydrated hydronium ions on the basis of chemical shift calculations and the observation of the signal after addition of HClO4. The intensity of 1H-29Si cross-polarization signal first increased and then decreased with increasing water chemical potential. This shows that the hydrogen bonds between water molecules and tetrahedrally coordinated aluminum in zeolite lattices weaken with the formation of hydronium ion-water clusters and increase the mobility of protons. Above 140 °C, however, fast proton exchange between bridging hydroxyl groups and water occur even in the presence of only one water molecule per acid site, suggesting that water acts at higher temperatures as a competitor for zeolite protons rather than as constituent of catalytically active hydronium ions. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Portions of the work were performed at the William R. Wiley Environmental Molecular Science Laboratory, a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory, a multiprogram national laboratory operated for DOE by Battelle Memorial Institute. Addi-tional 1H MAS NMR spectra we acquired using a Bruker 600 MHz NMR spectrometer acquired with support from the US Department of Energy, Office of Science, office of Basic Energy Sciences (Pro-ject Number 66628).

Zeolite, Brønsted acid, water, hydronium ion, NMR ↗
DOE OSTI2018

Ni3P as a high-performance catalytic phase for the hydrodeoxygenation of phenolic compounds

The catalytic performance of an unsupported Ni2P in the aqueous phase hydrodeoxygenation (HDO) of phenol was investigated. It was found that the unsupported Ni2P was water-sensitive, being transformed stepwise, first to an amorphous phase and then to Ni5P2 and Ni12P5, and finally to Ni3P in the presence of water at elevated temperatures. Nonetheless, the generated Ni3P phase exhibited extraordinary hydrogenation activity at low temperatures and high HDO activity at high temperatures. The unsupported Ni3P was more active for the hydrogenation of the aromatic ring in the phenol molecule than Pd/SiO2 (1.0 wt%). The unsupported Ni3P was catalytically active and stable in phenol HDO in both the aqueous phase and the organic phase. In addition to phenol, catechol and o-cresol were investigated in the HDO catalyzed by the unsupported Ni3P in both aqueous solution and decalin solution. The HDO reactivity decreased in the order of phenol > catechol > o-cresol in the aqueous phase, and in the order of phenol > o-cresol in the organic phase (catechol is insoluble in decalin). In the oil phase HDOs of phenol and o-cresol, the unsupported Ni3P exhibited superior hydrogenation activity to that of the unsupported Ni2P at low temperatures. J. A. L. and D. M. C. acknowledge support from the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated for the DOE by the Battelle Memorial Institute.

Yu, Zhiquan↗
DOE OSTI2021

Scaling up of High-Performance Single Crystalline Ni-rich Cathode Materials (CRADA 509)

This is a collaborative effort between Battelle Memorial Institute as manager and operator of Pacific Northwest National Laboratory (PNNL) and Albemarle Corporation (“Participant”) to develop and scale up an innovative and low-cost synthesis approach for preparing high-performance single crystalline Ni-rich cathode materials, i.e., LiNi0.8Mn0.1Co0.1O2 (NMC811) and LiNi0.9Mn0.05Co0.05O2 (NMC90) for next-generation LIBs. At the end of this project, the team will (1) develop a cost-effective synthesis approach for preparing single crystalline MNC811 (>200 mAh/g) and NMC90 (>210 mAh/g) by using advanced lithium salts, (2) address the performance issues of single crystals prepared from large-scale synthesis, and (3) demonstrate the processing/scaling up capabilities of up to 1 kg/batch of high-performance NMC811 and NMC90 single crystals.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Development of Efficient Process for Manufacturing of Thermoplastic Composites with Tailored Properties (CRADA 511)

This is a collaborative effort between Battelle Memorial Institute as manager and operator of Pacific Northwest National Laboratory (PNNL) and ESI North America Inc. (“ESI” or “Participant”) to apply computation and data analytics to the challenge of light weighting with a focus on the battery enclosures of electric vehicles (EVs). EVs use heavy batteries to increase range and power. A complex-shaped battery enclosure is required to meet a host of challenging performance requirements. The ability to virtually develop composite parts such as battery enclosure with tailored properties to meet required performance will be highly valuable to the automotive industry. However, efficient simulation of composite-manufacturing processes remains a challenging issue since simulation involves multiscale models in space and time, highly non-linear and anisotropic behavior, strongly coupled multi-physics, and complex geometries. This work will advance the state of the art by reducing the computational burden of composite optimization by using simulation data from a limited number of configurations off-line and then developing a reduced order model (ROM) using data analytics and machine learning (ML). Develop a data driven approach to link features of the material and manufacturing processes to the mechanical properties of thermoplastic composite parts.

42 ENGINEERING↗
DOE OSTI2013

Density functional simulations as a tool to probe molecular interactions in wet supercritical CO2

Recent advances in mixed Gaussian and plane wave algorithms have made possible the effective use of density functional theory (DFT) in ab initio molecular dynamics (AIMD) simulations for large and chemically complex models of condensed phase materials. In this chapter, we are reviewing recent progress on the modeling and characterization of co-sequestration processes and reactivity in wet supercritical CO2 (sc-CO2). We examine the molecular transformations of mineral and metal components of a sequestration system in contact with water-bearing scCO2 media and aim to establish a reliable correspondence between experimental observations and theory models with predictive ability and transferability of results in large scale geomechanical simulators. This work is funded by the Department of Energy, Office of Fossil Energy. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at Pacific Northwest National Laboratory. The Pacific Norhtwest National Laboratory (PNNL) is operated by Battelle for DOE under contract DE-AC06-76RL01830.

Glezakou, Vassiliki Alexandra↗
DOE OSTI2025

Mitigate Stress Corrosion Cracking (SCC) in High-strength Al Castings (CRADA 508)

Development of high strength, corrosion resistant, aluminum alloys is important to a number of industries, including automotive, aerospace, power, etc. Understanding how processing methods such as casting, chemistry, additives and recycle content affect an alloy’s microstructure and performance in real world environments is crucial to their implementation. One major concern is how the repeated exposure to saline solutions can be detrimental to the structural integrity of aluminum alloy components. This study was undertaken as a collaboration between Eck Industries and PNNL to investigate the stress corrosion cracking (SCC) and corrosion behavior of aluminum alloys. This work examines the SCC response of three different materials set. First is cast A206 Al alloy produced by three different casting techniques (i.e., permanent mold, and sand casting with and without chill) and with or without nano forming additives as potential grain refiners. The second materials set comprises Al alloy tubes extruded by PNNL’s ShAPE process and produced using raw material with three different ratios of twitch and pre-consumer Al 6061 scrap. Finally, the third materials set comprises two Al-Si-Mg-Fe alloys with controlled Si% and Fe% to mimic recycle grade Al alloys. The corrosion behavior of these materials was characterized using SCC testing and scanning electrochemical cell microscopy (SECCM) technique; mechanical behavior was characterized using tensile testing, and microstructure was characterized using optical and electron microscopy techniques. Of the A206 Al alloys, the samples with nano forming additives performed poorly compared to those without. The best SCC performance (i.e. least degradation in mechanical properties) was demonstrated by A206 alloy sand cast with chill while the permanent mold sample showed the worst SCC performance. The SECCM was performed on A206 alloy sand cast with chill to understand the effect of microstructure and determine the location-dependent corrosion properties on grain boundaries (GB) and inside grains (IG) on the sample. The corrosion potential and current measured on GB and IG at various points on the sample established that the GB locations are more cathodic and corrosive than the IG locations. Further work needs to be conducted to investigate the mechanisms behind the observed dependence of SCC on casting technique and nano forming additives. Among the ShAPE extruded tubes, SECCM data suggests the decreasing order of tendency to corrode as follows: 100% twitch > 75% twitch > 50% twitch. Finally, both variants of the Al-Si-Mg-Fe alloys showed a large volume fraction of Fe- and Si-containing intermetallics and additional work is needed to discern differences in their respective corrosion responses. In summary, correlating local electrochemical behavior (e.g. via SECCM) with micro/nanostructure, in conjunction with bulk mechanical behavior, can help identify the right fabrication method and alloy chemistry to minimize SCC issues in Al alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Thermodynamics and Kinetics of Na+/K+-Formate Ion Pairs Association in Polarizable Water: A Molecular Dynamics Study

To elevate our understanding of ion specific activity in biological systems, the potential of mean force approach was utilized to study solvent effects on interactions between two alkali cations (Na+ and K+) with a formate anion in water. A very complex free energy landscape was observed, much more so than alkali-halide ion pairs. Furthermore, stronger binding between the Na+-formate pair was found in comparison to the K+-formate pair in water, a finding that agrees with experimental and theoretical studies of these systems. The kinetics of ion-pair interconversions were studied using transition rate theory, along with a variety of theoretical approaches such as the Kramers and Grote Hynes theories. These rate results were used to predict solvent effects on dynamical features of contact ion-pair association, in which faster dynamics were found for K+-formate pairs than for Na+-formate pairs. This work was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for DOE by Battelle.

Nguyen, Phuong T↗