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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Controlling the hydrogenolysis of silica-supported tungsten pentamethyl leads to a class of highly electron deficient partially alkylated metal hydrides

The well-defined single-site silica-supported tungsten complex [( Si–O–)W(Me) 5 ], 1 , is an excellent precatalyst for alkane metathesis. The unique structure of 1 allows the synthesis of unprecedented tungsten hydrido methyl surface complexes via a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, 1 is quickly transformed at -78 °C into a partially alkylated tungsten hydride, 4 , as characterized by 1 H solid-state NMR and IR spectroscopies. Species 4 , upon warming to 150 °C, displays the highest catalytic activity for propane metathesis yet reported. DFT calculations using model systems support the formation of [( Si–O–)WH 3 (Me) 2 ], as the predominant species at -78 °C following several elementary steps of hydrogen addition (by σ-bond metathesis or α-hydrogen transfer). Rearrangement of 4 occuring between -78 °C and room temperature leads to the formation of an unique methylidene tungsten hydride [( Si–O–)WH 3 ( CH 2 )], as determined by solid-state 1 H and 13 C NMR spectroscopies and supported by DFT. Thus for the first time, a coordination sphere that incorporates both carbene and hydride functionalities has been observed.

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

Advances and challenges for experiment and theory for multi-electron multi-proton transfer at electrified solid–liquid interfaces

Multi-electron, multi-proton transfer is important in a wide spectrum of processes spanning biological, chemical and physical systems. These reactions have attracted significant interest due to both fundamental curiosity and potential applications in energy technology. In this Perspective Review, we shed light on modern aspects of electrode processes in the 21st century, in particular on the recent advances and challenges in multistep electron/proton transfers at solid–liquid interfaces. Ongoing developments of analytical techniques and operando spectrometry at electrode/electrolyte interfaces and reliable computational approaches to simulate complicated interfacial electrochemical reactions enable us to obtain microscopic insights about these complex processes, such as the role of quantum effects in electrochemical reactions. Our motivation in this Perspective Review is to provide a comprehensive survey and discussion of state-of-the-art developments in experiments, materials, and theories for modern electrode process science, as well as to present an outlook for the future directions in this field.

Sakaushi, Ken↗
DOE OSTI2022

Probing growth of metal–organic frameworks with X-ray scattering and vibrational spectroscopy

Nucleation and crystallization arising from liquid to solid phase are involved in a multitude of processes in fields ranging from materials science to biology. Controlling the thermodynamics and kinetics of growth is advantageous to help tune the formation of complex morphologies. In this report, we harness wide-angle X-ray scattering and vibrational spectroscopy to elucidate the mechanism for crystallization and growth of the metal–organic framework Co-MOF-74 within microscopic volumes enclosed in a capillary and an attenuated total reflection microchip reactor. The experiments reveal molecular and structural details of the growth processes, while the results of plane wave density functional calculations allow identification of lattice and linker modes in the formed crystals. Synthesis of the metal–organic framework with microscopic volumes leads to monodisperse and micron-sized crystals, in contrast to those typically observed under bulk reaction conditions. Reduction in the volume of reagents within the microchip reactor was found to accelerate the reaction rate. The coupling of spectroscopy with scattering to probe reactions in microscopic volumes promises to be a useful tool in the synthetic chemist's kit to understand chemical bonding and has potential in designing complex materials.

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

Achieving the hydrogen shot: Interrogating ionomer interfaces

The aim of this study is to enable the hydrogen economy and decarbonize various sectors in our environment that requires less expensive and more durable water electrolyzers, which can meet the Hydrogen-Shot target. The key is to improve the ionomer interfaces in low-temperature water electrolyzers as rapidly as possible, but to do so, it requires a systematic and holistic campaign combining both experiments and theory. In this perspective, we discuss the issues of electrolyzers and needs for translational science. We then present the approach that the Energy EarthShot Research Center: Center for Ionomer-based Water Electrolysis is taking in hopes of inspiring the community with this approach that can be leveraged to multiple problems and technologies.Graphical abstractHighlightsOne way to achieve the Hydrogen-Shot goal of low-cost, clean hydrogen, is advancing research and development on the interfaces of water electrolyzers for both performance and lifetime. The Center for Ionomer-based Water Electrolysis is exploring new techniques and strategies to not only interrogate interfacial phenomena in water electrolyzers to increase efficiency and durability, but also a new paradigm related to synergistic, cojoined experimental and theoretical research.DiscussionCatalyst\ionomer interfaces are complex and not fully understood, but through investigating different interfaces and utilizing digital and physical twins, we can elucidate key mechanisms and understanding.Understanding the dynamic double layer in electrochemical systems that use solid electrolytes is crucial to identifying and mitigating the controlling phenomena to enable increased performance and durability at the technology level.Studying the time and length scales of interfacial changes can be a powerful tool to understand reaction mechanisms and changes in the electrolyzer performance and durability.

Fornaciari, Julie C↗
DOE OSTI2020

Machine Learning in Environmental Chemistry: Application to Surface Complexation Modeling

Environmental chemistry – or biogeochemistry – is the scientific discipline typically invoked when examining and quantifying groundwater or surface water contamination, and nutrient cycling in the environment. Over the last three decades, there have been significant advances in mechanistic model development to describe and predict these complex biogeochemical processes. In particular, surface complexation models (SCMs) have been developed to describe the rock/soil surface reactions of metals and radionuclides, and their partitioning between various mobile species in the aqueous phase or immobile species sorbed on solid surfaces. Often represented by a simplified linear isotherm constant – Kd – in reactive transport models, these reactions play a critical role in many environmental science applications; particularly in contamination risk assessments and nuclear waste disposal performance assessments. In the past several decades, efforts by various institutions across the world have focused on developing SCMs based on datasets from laboratory measurements, including the identification of key parameters such as equilibrium constants.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

A Solid Polarized Target Development Facility at Jefferson Lab

Solid polarized targets are a crucial tool used in scattering experiments to investigate different properties of the nucleon. The equipment used to produce, measure, and maintain conditions for the polarized material is complex in comparison to nonpolarized targets. This, in combination with the frequency of polarized experiments run at Jefferson Lab, limits the opportunity to refine and build upon experience gained from previously constructed targets. To address this, the Jefferson Lab Target Group has begun the construction of a permanent facility dedicated to creating and testing material for Dynamic Nuclear Polarization. The design elements and manufacture of the test cryostat along with the incorporation of other DNP associated equipment will be presented.

Brock, James [Thomas Jefferson National Accelerato↗
DOE OSTI2020

Analysis of Exposure during Transportation of Waste to the Nevada National Security Site (NNSS) - 20445

Safety is a priority for the U.S. Department of Energy (DOE) Environmental Management (EM) Nevada Program. This commitment to safety is integrated into requirements and work procedures at DOE sites across the U.S. that generate low-level radioactive waste, mixed low-level radioactive waste, and classified waste that is transported to the Nevada National Security Site (NNSS) for permanent disposal. Generators of this waste are responsible for ensuring it is packaged and transported in a safe and compliant manner. These generators and their contracted commercial carriers must comply with U.S. Department of Transportation (DOT) regulations; the Nevada National Security Site Waste Acceptance Criteria (NNSSWAC); and other applicable federal, state, and local regulations and requirements. This includes packaging and shipping the waste to meet DOT regulatory radiation dose limits to ensure public safety during transportation. NNSS waste generators have a solid safety record for complying with these stringent regulations as demonstrated by the fact that no shipments exceeding DOT dose rate limits were received at the NNSS Area 5 Radioactive Waste Management Complex (RWMC) during FY 2014 through FY 2018. A 2005 study conducted by the Desert Research Institute validated shipments to the NNSS comply with DOT radiation dose limits. In response to recent Nevada stakeholder requests for an updated study, an analysis was conducted to verify and provide evidence that the public continues to be safe from exposure to radioactive waste shipment to the NNSS. Radiation exposure from radioactive waste shipments in transit to the NNSS was evaluated. Three studies were performed: 1. Confirm compliance of waste shipments to the DOT radiation limits using dose rate surveys taken at the generator site and at the disposal site. 2. Estimate the dose to the public from waste shipments using the dosimetry results for disposal site personnel by comparing time of exposure for various individuals/scenarios. 3. Estimate the truck driver dose using the receipt dose rate surveys and time of exposure, and from dosimetry results. Study 1 confirmed compliance with the DOT dose rate limits for a sample of waste shipments (123 of 1,038) received during fiscal year (FY) 2017. Study 2 showed that the average annual radiation equivalent dose for disposal site personnel during FY 2017 was approximately 6.7% [0.415 mSv (41.5 millirem)] of the annual average dose that a person living in the U.S. receives from all sources [6.2 mSv (620 mrem)]. Maximum dose to a member of the public, a person resting/sleeping in an adjacent truck at a rest area to a waste shipment, was 0.0166 mSv (1.66 mrem), which is less than the dose received from a person taking a round trip from the east coast to the west coast of the continental U.S. on an airplane [0.07 mSv (7 mrem) per round trip]. Study 3 showed that the truck driver who made the most shipments of radioactive waste to the NNSS, who drove the most hours (estimated time of exposure 2,520 hours), during FY 2017 had a total dose of 0.15 mSv (15 mrem), which was obtained from their personal dosimeter. The annual dose recorded for disposal site personnel, the dose estimates for the public, and the truck driver dose were all a small percentage of the average radiation dose a person receives from all sources (e.g., background and medical radiation). At these levels, risk should only be described qualitatively. Radiation exposure from radioactive waste shipments to the NNSS were shown to be compliant with the DOT dose rate limits, safe, and very low (i.e., within background levels). (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Defect Thermodynamics and Transport Properties of Proton Conducting Perovskite Electrode and Electrolyte Materials Evaluated Based on Density Functional Theory Modeling

Both electron-rich and electron-poor perovskite oxides have been used in solid oxide cell applications as electrode and electrolyte materials. The rich oxygen defect chemistry and its coupling to temperature, hydrogen-steam or oxygen-steam gas pressure, or to the applied potentials creates enormous complexities for modeling performance and degradation of the materials. Herein, density functional theory-based thermodynamic modeling was carried out to describe the defect chemistry and transport properties of the proton-conducting electrolyte BaZr1-xYxO3-δ (x≤0.1) and of the triple-conducting perovskite (La,Ba)(Fe,M)O3-δ (M=Y and Zr). The defect thermodynamics of intrinsic point defects and the hydrogen-related defect reactions were solved in integrated defect models and further used to predict the Brouwer diagram and the transport properties of the functional perovskites. For the electron-poor electrolytes BaZr0.9Y0.1O3-δ, the developed model has been used to describe the experimental transport properties in the SOC operating conditions. Specifically, the roles played by the acceptor-bound holes and the intrinsic and hydrogen point defects upon the conductivities of holes, protons, and oxygen vacancies under the hydrogen-rich and oxygen-rich conditions at various humidity levels were demonstrated. A defect modeling tool was also developed for the triple-conducting perovskite (La,Ba)(Fe,M)O3-δ (M=Y and Zr) to examine magnetic effects and hydride defects in defect equilibria.

defect thermodynamics↗
DOE OSTI2011

Structure, morphology and ionic conductivity of solid polymer electrolyte

Graphical abstract: Two-dimensional atomic force image of pure polyethylene oxide presents a crystallized network of regular spherulites developing spirals and branches of well distributed surface contours. Highlights: {yields} The incorporation of ceria significantly modifies the morphology of polyethylene oxide (PEO)-KI complex. {yields} The ionic conductivity increases by about two orders of magnitude by the addition of ceria nanoparticles. {yields} Ionic conductivity as a function of ceria concentration reveals two maxima. {yields} Grain boundary effect of nanofiller, strong Lewis acid-base interaction between PEO and nanosized ceria, change of conformation of PEO molecule and epitaxial effect of ceria nanoparticles control the ionic conductivity of composite polymer electrolyte. -- Abstract: Polyethylene oxide (PEO) complexed with potassium iodide (KI) is synthesized to investigate the ionic conductivity of alkaline based polymer electrolytes. The structural and morphological characterizations of the nanocomposite polymer electrolytes are performed by X-ray diffractometry (XRD), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. The ionic conductivity increases with the increase of KI concentration up to about 20 wt.%. The effect of nanosized ceria (CeO{sub 2} {approx} 10 nm) fillers on ionic conductivity in PEO-KI polymer electrolyte is also carried out, keeping PEO to KI wt.% ratio 80:20 and 85:15. The result reveals that the addition of ceria nanoparticles enhances the conductivity by two orders of magnitude. The presence of ceria at the highest concentration induces the same molecular environment within PEO chain as that of undoped PEO. Temperature dependence of ionic conductivity follows Arrhenius mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Nondestructively Visualizing and Understanding the Mechano-Electro-chemical Origins of “Soft Short” and “Creeping” in All-Solid-State Batteries

All-solid-state Li-metal batteries (ASLMBs) represent a significant breakthrough in the quest to overcome limitations associated with traditional Li-ion batteries, particularly in energy density and safety aspects. However, widespread implementation is stymied due to a lack of profound understanding of the complex mechano-electro-chemical behavior of Li metal in the ASLMBs. Herein, operando neutron imaging and X-ray computed tomography (XCT) are leveraged to nondestructively visualize Li behaviors within ASLMBs. This approach offers real-time observations of Li evolutions, both pre- and post- occurrence of a “soft short”. The coordination of 2D neutron radiography and 3D neutron tomography enables charting of the terrain of Li metal deformation operando. Concurrently, XCT offers a 3D insight into the internal structure of the battery following a “soft short”. Despite the manifestation of a “soft short”, the persistence of Faradaic processes is observed. To study the elusive “soft short”, phase field modeling is coupled with electrochemistry and solid mechanics theory. The research unravels how external pressure curbs dendrite growth, potentially leading to dendrite fractures and thus uncovering the origins of both “soft” and “hard” shorts in ASLMBs. Furthermore, by harnessing finite element modeling, it dive deeper into the mechanical deformation and the fluidity of Li metal.

25 ENERGY STORAGE↗
DOE OSTI2013

Systems approaches to integrated solid waste management in developing countries

Highlights: ► Five drivers led developed countries to current solid waste management paradigm. ► Many unique factors challenge developing country solid waste management. ► Limited transferability of developed country approaches to developing countries. ► High uncertainties and decision stakes call for post-normal approaches. ► Systems thinking needed for multi-scale, self-organizing eco-social waste systems. - Abstract: Solid waste management (SWM) has become an issue of increasing global concern as urban populations continue to rise and consumption patterns change. The health and environmental implications associated with SWM are mounting in urgency, particularly in the context of developing countries. While systems analyses largely targeting well-defined, engineered systems have been used to help SWM agencies in industrialized countries since the 1960s, collection and removal dominate the SWM sector in developing countries. This review contrasts the history and current paradigms of SWM practices and policies in industrialized countries with the current challenges and complexities faced in developing country SWM. In industrialized countries, public health, environment, resource scarcity, climate change, and public awareness and participation have acted as SWM drivers towards the current paradigm of integrated SWM. However, urbanization, inequality, and economic growth; cultural and socio-economic aspects; policy, governance, and institutional issues; and international influences have complicated SWM in developing countries. This has limited the applicability of approaches that were successful along the SWM development trajectories of industrialized countries. This review demonstrates the importance of founding new SWM approaches for developing country contexts in post-normal science and complex, adaptive systems thinking.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Electrochemical Investigation of Low-Valent Multiply M≡M Bonded Group VI Dimers: A Standard Chemical Reduction Leads to an Unexpected Product

The synthesis and investigation of multimetallic complexes bearing metal–metal bonds have been significantly advanced over the last 30 years with exciting applications across many fields. While the outlook for synthetically innovative metal–metal species is promising, the reactivity of the classic M 2 X 6 alkyl dimers (where M = W, Mo; X = CH 2 CMe 3 , CH 2 SiMe 3 ) is still not fully understood. In particular, the redox characteristics of these complexes have not been explored by cyclic voltammetry (CV). In this work, W 2 (CH 2 CMe 3 ) 6 and Mo 2 (CH 2 CMe 3 ) 6 (1 and 2, respectively) were characterized using CV to show differing electrochemical behavior between the two species. Stoichiometric reactions, guided by the results of the CV experiments, led to the isolation of an alkylidyne-bridged dimer bearing a rare structural motif, W 2 (μ-CCMe 3 ) 2 (CH 2 CMe 3 ) 4 (3). Single-crystal X-ray diffraction (SCXRD) and 1 H and 13 C nuclear magnetic resonance spectroscopy (NMR) were used to establish the connectivity of the structure in the solid and solution phases. Density functional theory (DFT) calculations on 1–3 and the previously reported W 2 (CSiMe 3 ) 2 (CH 2 SiMe 3 ) 4 (4) were used to rationalize the reactivity of 1 to form 3 and the structural differences between 3 and 4. Complexes 3 and 4 constitute a case in which the stereoelectronic properties of the silyl neopentyl ligand can affect differences in structure and bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Photoluminescence in solid solutions and thin films of tungstates CaWO{sub 4}-CdWO{sub 4}

In this study, we present two types of studies on the luminescence properties under UV and X-ray excitations of solid solutions Ca{sub 1-x}Cd{sub x}WO{sub 4} and of thin layers of CaWO{sub 4} and CdWO{sub 4}. These tungstate based solid solutions are susceptible to be integrated into new radiation sensors, in order to be used in different fields of applications such as reactor measurements, safeguards, homeland security, nuclear nondestructive assays, LINAC emission radiation measurement. However these complex materials were rarely investigated in the literature. One first objective of our studies was to establish correlations between luminescence efficiency, chemical substitution and the degree of crystallization resulting from elaboration conditions. A second objective will be to determine the efficiency of luminescence properties of thin layers of these materials. In the present work, we focus our attention on the role of chemical substitution on photon emissions under UV and X-ray irradiations. The luminescence spectra of Ca{sub 1-x}Cd{sub x}WO{sub 4} polycrystalline materials have been investigated at room temperature as a function of composition (0≤x≤1). In addition, we present a preliminary study of the luminescence of CaWO{sub 4} and CdWO{sub 4} thin layers: oscillations observed in the case of X-ray excitations in the luminescence spectra are discussed. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

TaRh 2 B 2 and NbRh 2 B 2 : Superconductors with a chiral noncentrosymmetric crystal structure

It is a fundamental truth in solid compounds that the physical properties follow the symmetry of the crystal structure. Nowhere is the effect of symmetry more pronounced than in the electronic and magnetic properties of materials—even the projection of the bulk crystal symmetry onto different crystal faces is known to have a substantial impact on the surface electronic states. The effect of bulk crystal symmetry on the properties of superconductors is widely appreciated, although its study presents substantial challenges. The effect of a lack of a center of symmetry in a crystal structure, for example, has long been understood to necessitate that the wave function of the collective electron state that gives rise to superconductivity has to be more complex than usual. However, few nonhypothetical materials, if any, have actually been proven to display exotic superconducting properties as a result. We introduce two new superconductors that in addition to having noncentrosymmetric crystal structures also have chiral crystal structures. Because the wave function of electrons in solids is particularly sensitive to the host material’s symmetry, crystal structure chirality is expected to have a substantial effect on their superconducting wave functions. Our two experimentally obtained chiral noncentrosymmetric superconducting materials have transition temperatures to superconductivity that are easily experimentally accessible, and our basic property characterization suggests that their superconducting properties may be unusual. We propose that their study may allow for a more in-depth understanding of how chirality influences the properties of superconductors and devices that incorporate them.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Accelerating Optical Absorption Spectra and Exciton Energy Computation via Interpolative Separable Density Fitting

© Springer International Publishing AG, part of Springer Nature 2018. We present an efficient way to solve the Bethe–Salpeter equation (BSE), a method for the computation of optical absorption spectra in molecules and solids that includes electron–hole interactions. Standard approaches to construct and diagonalize the Bethe–Salpeter Hamiltonian require at least (Formula Presented) operations, where Neis the number of electrons in the system, limiting its application to smaller systems. Our approach is based on the interpolative separable density fitting (ISDF) technique to construct low rank approximations to the bare exchange and screened direct operators associated with the BSE Hamiltonian. This approach reduces the complexity of the Hamiltonian construction to (Formula Presented) with a much smaller pre-constant, and allows for a faster solution of the BSE. Here, we implement the ISDF method for BSE calculations within the Tamm–Dancoff approximation (TDA) in the BerkeleyGW software package. We show that this novel approach accurately reproduces exciton energies and optical absorption spectra in molecules and solids with a significantly reduced computational cost.

Hu, W↗
DOE OSTI2016

Volatility Studies of Lanthanide Hexafluoroacetylacetone Chelates

Nuclear forensics has become very important to the field of nuclear security, where there is considerable interest in developing rapid separations of radionuclides and isotopes. Although prevention and detection form the foundation of nuclear security science, in the unfortunate event of detonation of a nuclear device, the fallout debris can be analyzed for signature isotopes that may provide evidence on the origin and type of nuclear materials. This is of considerable political importance to many governing bodies and this information is desired in a timely manner. One method of analysis is the rapid gas phase separation of rare earth metals from other components of the debris via isothermal thermochromatography. Lanthanides cover a portion of the fission product curve with varying yields dependent on a number of variables (e.g. neutron energy, fissile parent, etc), motivating the chromatographic separation of these elements. In previous work, 1,1,1,5,5,5 - hexafluoroacetylacetone (hfac) has been shown to produce volatile complexes with lanthanides. Thermochromatography is a gas phase separation method that utilizes temperature gradients on a column to vary adsorption location or constant column temperatures to vary retention time. The adsorption time of a compound on a column, i.e. retention time, is dependent on the thermodynamics, most notably the adsorption enthalpy. Studies of heavy metals have generated empirical correlations between adsorption enthalpy on a quartz column and sublimation enthalpy of the solid material. Thermogravimetric analysis (TGA) is useful in the characterization of the thermodynamics of materials, especially the sublimation enthalpy. Many methods analyze weight loss curves as a function of a constant heating rate. Another method introduced by Ashcroft analyzes weight loss curves over isothermal heating regions. Work presented here focuses on the determination of the sublimation enthalpies of thirteen lanthanide hfac complexes via the latter method. Additionally, there is investigation into the degradation of the compound via constant heating TGA up to higher temperatures. This provides information on the onset and end-set temperatures of degradation stages, as well as the peak temperature at which total sublimation occurs. (authors)

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

Are continuum predictions of clustering chaotic?

Gas-solid multiphase flows are prone to develop an instability known as clustering. Two-fluid models, which treat the particulate phase as a continuum, are known to reproduce the qualitative features of this instability, producing highly-dynamic, spatiotemporal patterns. However, it is unknown whether such simulations are truly aperiodic or a type of complex periodic behavior. By showing that the system possesses a sensitive dependence on initial conditions and a positive largest Lyapunov exponent, λ 1 ≈1/τ, we provide a tentative answer: continuum predictions of clustering are chaotic. We further demonstrate that the chaotic behavior is dimensionally dependent, a conclusion which unifies previous results and strongly suggests that the chaotic behavior is not a direct consequence of the fundamental kinematic instability, but requires a secondary (inherently multidimensional) instability. Granular matter is a collection of discrete, interacting solid particles which, like classic (molecular) matter, can be generally classified into one of three states:1 (i) under static conditions granular heaps or piles can sustain gravity-induced stress and behave like a solid; (ii) dense granular flows characterized by enduring and multi-particle contacts behave similarly to a fluid; and (iii) rapid granular flows characterized by instantaneous contacts described as a granular gas. However, it is worth noting that all three granular states are only superficially similar to their molecular counterparts due to the dissipative nature of particle-particle contacts (inelasticity, friction, etc.). In industrial operations, rapid (collision-dominated) granular flows are often encountered in devices in which the particles are fluidized by a gas; such gas-solid flows are the focus of this work. Rapid gas-solid flows are prone to an instability termed clustering in which particles tend to form spatially inhomogeneous patterns of high and low concentrations. Continuum or two-fluid models (TFM) have long been known to be able to predict the qualitative nature of the clustering instability and more recent quantitative assessments have also shown promising results. However, it is yet unknown whether or not such predictions are chaotic. We take a first step in answering this question by simulating fluidization in an unbounded domain and calculating a positive largest Lyapunov exponent (LLE), thereby indicating that continuum predictions of clustering are in fact chaotic. Further, we show that chaotic behavior may be reduced to periodic behavior by constraining the dimensionality of the system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Reactions between atomic chlorine and pyridine in solid para-hydrogen: Infrared spectrum of the 1-chloropyridinyl (C{sub 5}H{sub 5}N-Cl) radical

With infrared absorption spectra we investigated the reaction between Cl atom and pyridine (C{sub 5}H{sub 5}N) in a para-hydrogen (p-H{sub 2}) matrix. Pyridine and Cl{sub 2} were co-deposited with p-H{sub 2} at 3.2 K; a planar C{sub 5}H{sub 5}N-Cl{sub 2} complex was identified from the observed infrared spectrum of the Cl{sub 2}/C{sub 5}H{sub 5}N/p-H{sub 2} matrix. Upon irradiation at 365 nm to generate Cl atom in situ and annealing at 5.1 K for 3 min to induce secondary reaction, the 1-chloropyridinyl radical (C{sub 5}H{sub 5}N-Cl) was identified as the major product of the reaction Cl + C{sub 5}H{sub 5}N in solid p-H{sub 2}; absorption lines at 3075.9, 1449.7, 1200.6, 1148.8, 1069.3, 1017.4, 742.9, and 688.7 cm{sup -1} were observed. The assignments are based on comparison of observed vibrational wavenumbers and relative IR intensities with those predicted using the B3PW91/6-311++G(2d, 2p) method. The observation of the preferential addition of Cl to the N-site of pyridine to form C{sub 5}H{sub 5}N-Cl radical but not 2-, 3-, or 4-chloropyridine (ClC{sub 5}H{sub 5}N) radicals is consistent with the reported theoretical prediction that formation of the former proceeds via a barrierless path.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗