Kinetics of 1-butyl and 2-butyl radical reactions with molecular oxygen: Experiment and theory
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Eskola, Arkke J.↗
SEARCH · Engineering Papers
Results for “Reaction Time”
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X-ray multiphoton-induced Coulomb explosion images complex single molecules
Following structural dynamics in real time is a fundamental goal towards a better understanding of chemical reactions. Recording snapshots of individual molecules with ultrashort exposure times is a key ingredient towards this goal, as atoms move on femtosecond (10 -15 s) timescales. For condensed-phase samples, ultrafast, atomically resolved structure determination has been demonstrated using X-ray and electron diffraction. Pioneering experiments have also started addressing gaseous samples. However, they face the problem of low target densities, low scattering cross sections and random spatial orientation of the molecules. Therefore, obtaining images of entire, isolated molecules capturing all constituents, including hydrogen atoms, remains challenging. Here we demonstrate that intense femtosecond pulses from an X-ray free-electron laser trigger rapid and complete Coulomb explosions of 2-iodopyridine and 2-iodopyrazine molecules. We obtain intriguingly clear momentum images depicting ten or eleven atoms, including all the hydrogens, and thus overcome a so-far impregnable barrier for complete Coulomb explosion imaging—its limitation on molecules consisting of three to five atoms. In combination with state-of-the-art multi-coincidence techniques and elaborate theoretical modelling, this allows tracing ultrafast hydrogen emission and obtaining information on the result of intramolecular electron rearrangement. Our work represents an important step towards imaging femtosecond chemistry via Coulomb explosion.
74 ATOMIC AND MOLECULAR PHYSICS↗
Time-dependent nonlinear cosmic ray shocks confirming abstract
Numerical studies of time dependent cosmic ray shock structures in planar geometry are interesting because analytical time-independent solutions are available which include the non-linear reactions on the plasma flow. A feature of these time asymptotic solutions is that for higher Mach numbers (M approximately 5) and for a low cosmic ray upstream pressure the solution is not uniquely determined by the usual conservation laws of mass, momentum and energy. These numerical solutions clearly indicate that much work needs to be done before we understand shock acceleration as a time dependent process. The slowness of the process is possibly due to the fact that there is a diffusive flux into the downstream region in addition to the usual advective losses. Analytic investigations of thie phenomenon are required.
Dorfi, E. A.↗
Changes of solar luminosity and radius following secular perturbations in the convective envelope
The effect on solar models of several types of slow, spherically symmetric perturbations, acting at various depths within the convective envelope, are calculated. Results are presented on perturbations of the efficiency of convective energy transport (alpha perturbations) and on changes in the nongas component of pressure (beta perturbations). The effects of magnetic fields concentrated near the interface between the radiative core and the convective envelope are explored. It is found that the response and relaxation diagnostics depend both on the type of perturbation and on the depth at which the perturbation is applied. In addition to the general depth dependence, model behavior is sensitive to the presence of major ionization zones near the perturbed layer. The time dependence of the solar model behavior is characterized by an initial hydrostatic reaction followed by a thermal readjustment on a time scale of about 100 years, and finally relaxation to a new thermal equilibrium on a Kelvin time scale.
Endal, A. S.↗
Operando MAS NMR Reaction Studies at High Temperatures and Pressures
Operando MAS-NMR studies provide unique insights into the details of chemical reactions; comprehensive information about temperature- and time-dependent changes in chemical species is accompanied by similarly rich information about changes in phase and chemical environment. Here we describe a new MAS-NMR rotor (the WHiMS rotor) capable of achieving internal pressures up to 400 bar at 20 °C or 225 bar at 250 °C, a range which includes many reactions of interest. The MAS-NMR spectroscopy enabled by these rotors is ideal for studying the behavior of mixed-phase systems, such as reactions involving solid catalysts and volatile liquids, with the potential to add gases at high pressure. The versatile operation of the new rotors is demonstrated by collecting operando 1H and 13C spectra during the hydrogenolysis of benzyl phenyl ether, catalyzed by Ni/-Al2O3 at ca. 250 ºC, both with and without H2 (g) supplied to the rotor. The 2-propanol solvent, which exists in the supercritical phase under these reaction conditions, serves as an internal source of H2. The NMR spectra provide detailed kinetic profiles for the formation of the primary products toluene and phenol, as well as secondary hydrogenation and etherification products.
Walter, Eric D.↗
In situ {sup 1}H-TD-NMR: Quantification and microstructure development during the early hydration of alite and OPC
An in situ framework for {sup 1}H time-domain nuclear magnetic resonance analysis was developed and applied on alite and OPC hydration. Highly time-resolved quantitative data on the evolution of proton reservoirs during hydration was collected for up to 40 h. Reservoirs could be clearly assigned to mobile (mix water), intermediate (C-S-H) and rigid fractions (CH, ettringite). Comparison of determined fraction quantities with data from in situ XRD measurements and heat flow calorimetry show very good agreement. During alite hydration at 23 °C, a bulk water content of 4 H{sub 2}O in C{sub 1.7}SH{sub x} was confirmed. T2 relaxation times of the mobile fraction shifted towards shorter times from the start of the main reaction until the maximum of the heat flow. Microstructure evolution is nearly finished at that point in time. T2 relaxation times are severely shortened for iron-containing OPC, but are still evaluable.
36 MATERIALS SCIENCE↗
Additional chain-branching pathways in the low-temperature oxidation of branched alkanes
Chain-branching reactions represent a general motif in chemistry, encountered in atmospheric chemistry, combustion, polymerization, and photochemistry; the nature and amount of radicals generated by chain-branching are decisive for the reaction progress, its energy signature, and the time towards its completion. In this study, experimental evidence for two new types of chain-branching reactions is presented, based upon detection of highly oxidized multifunctional molecules (HOM) formed during the gas-phase low-temperature oxidation of a branched alkane under conditions relevant to combustion. The oxidation of 2,5-dimethylhexane (DMH) in a jet-stirred reactor (JSR) was studied using synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS). Specifically, species with four and five oxygen atoms were probed, having molecular formulas of C 8 H 14 O 4 (e.g., diketo-hydroperoxide/keto-hydroperoxy cyclic ether) and C 8 H 16 O 5 (e.g., keto-dihydroperoxide/dihydroperoxy cyclic ether), respectively. The formation of C 8 H 16 O 5 species involves alternative isomerization of OOQOOH radicals via intramolecular H-atom migration, followed by third O 2 addition, intramolecular isomerization, and OH release; C 8 H 14 O 4 species are proposed to result from subsequent reactions of C 8 H 16 O 5 species. The mechanistic pathways involving these species are related to those proposed as a source of low-volatility highly oxygenated species in Earth's troposphere. At the higher temperatures relevant to auto-ignition, they can result in a net increase of hydroxyl radical production, so these are additional radical chain-branching pathways for ignition. Furthermore, the results presented herein extend the conceptual basis of reaction mechanisms used to predict the reaction behavior of ignition, and have implications on atmospheric gas-phase chemistry and the oxidative stability of organic substances.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ultrafast Structural Dynamics in Combustion Relevant Model Systems
The research project explored the time resolved structural dynamics of important model reaction system using an array of novel methods that were developed specifically for this purpose. They include time resolved electron diffraction, time resolved relativistic electron diffraction, and time resolved Rydberg fingerprint spectroscopy. Toward the end of the funding period, we also developed time-resolved x-ray diffraction, which uses ultrafast x-ray pulses at LCLS. Those experiments are just now blossoming, as the funding period expired. In the following, the time resolved Rydberg Fingerprint Spectroscopy is discussed in some detail, as it has been a very productive method. The binding energy of an electron in a Rydberg state, that is, the energy difference between the Rydberg level and the ground state of the molecular ion, has been found to be a uniquely powerful tool to characterize the molecular structure. To rationalize the structure sensitivity we invoke a picture from electron diffraction: when it passes the molecular ion core, the Rydberg electron experiences a phase shift compared to an electron in a hydrogen atom. This phase shift requires an adjustment of the binding energy of the electron, which is measurable. As in electron diffraction, the phase shift depends on the molecular, geometrical structure, so that a measurement of the electron binding energy can be interpreted as a measurement of the molecule’s structure.
99 GENERAL AND MISCELLANEOUS↗
Catalytic Photodegradation of p-aminobenzoic Acid on TiO 2 Nanowires with High Surface Area.
Pharmaceutical personal care products (PPCP’s) production and consumption have increased exponentially in recent years due to medicine and technology advances related to the development of dangerous skin diseases such as cancer. These PPCP’s usually are found in wastewaters and their removal represents a very important environmental issue. With the aim of studying the possible degradation of these compounds, we have synthesized TiO 2 nanowires (rutile phase) that have been fully characterized by BET measurements, XRD and SEM and used in the photodegradation reaction of p-aminobenzoic acid (PABA). Furthermore, we studied the photocatalytic degradation of PABA under different experimental conditions (i.e. catalyst loading). The photocatalytic reaction was monitored as a function of time by UV-Vis spectroscopy. The highest degradation rate occurred with 1.0 g L-1 of catalyst while the reaction does not proceed without radiation or in absence of the catalyst. Our present work demonstrates that p-aminobenzoic acid could be successfully degraded in a relatively short time period with high degradation percentages.
36 MATERIALS SCIENCE↗
Randomized Control Trial: Evaluating Aluminum-Based Antiperspirant Use, Axilla Skin Toxicity, and Reported Quality of Life in Women Receiving External Beam Radiotherapy for Treatment of Stage 0, I, and II Breast Cancer
Purpose: Standard skin care instructions regarding the use of antiperspirants during radiotherapy to the breast varies across North America. Women have articulated that when instructed to not use antiperspirant, the potential for body odor is distressing. Historical practices and individual opinions have often guided practice in this field. The present study had 2 purposes. To evaluate whether the use of aluminum-based antiperspirant while receiving external beam radiotherapy for stage 0, I, or II breast cancer will increase axilla skin toxicity and to evaluate whether the use of antiperspirant during external beam radiotherapy improves quality of life. Methods: A total of 198 participants were randomized to either the experimental group (antiperspirant) or control group (standard care-wash only). The skin reactions in both groups were measured weekly and 2 weeks after treatment using the National Cancer Institute Common Toxicity Criteria Adverse Events, version 3, toxicity grading criteria. Both groups completed the Functional Assessment for Chronic Illness Therapy's questionnaire for the breast population quality of life assessment tool, with additional questions evaluating the effect of underarm antiperspirant use on quality of life before treatment, immediately after treatment, and 2 weeks after treatment during the study. Results: The skin reaction data were analyzed using the generalized estimating equation. No statistically significant difference was seen in the skin reaction between the 2 groups over time. The quality of life data also revealed no statistically significant difference between the 2 groups over time. Conclusions: Data analysis indicates that using antiperspirant routinely during external beam radiotherapy for Stage 0, I, or II breast cancer does not affect the intensity of the skin reaction or the self-reported quality of life. This evidence supports that in this particular population, there is no purpose to restrict these women from using antiperspirants during their treatment, and the decision to use an antiperspirant or not in this setting should be left to the discretion of the patient.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
First Measurement of the {sup 19}F(α, p){sup 22}Ne Reaction at Energies of Astrophysical Relevance
The observational {sup 19}F abundance in stellar environments systematically exceeds the predicted one, thus representing one of the unsolved challenges for stellar modeling. It is therefore clear that further investigation is needed in this field. In this work, we focus our attention on the measurement of the {sup 19}F(α,p){sup 22}Ne reaction in the astrophysical energy range, between 0.2 and 0.8 MeV (far below the Coulomb barrier, 3.8 MeV), as it represents the main destruction channel in He-rich environments. The lowest energy at which this reaction has been studied with direct measurements is ∼0.66 MeV, covering only the upper tail of the Gamow window, causing the reaction-rate evaluation to be based on extrapolation. To investigate lower energies, the {sup 19}F(α,p){sup 22}Ne reaction has been studied by means of the Trojan horse method, applied to the quasi-free {sup 6}Li({sup 19}F,p{sup 22}Ne){sup 2}H reaction at E {sub beam} = 6 MeV. The indirect cross section of the {sup 19}F(α,p){sup 22}Ne reaction at energies ≲1 MeV was extracted, fully covering the astrophysical region of interest and overlapping existing direct data for normalization. Several resonances have been detected for the first time inside the Gamow window. The reaction rate has been calculated, showing an increase up to a factor of 4 with respect to the literature at astrophysical temperatures. This might lead to potential major astrophysical implications.
79 ASTRONOMY AND ASTROPHYSICS↗
Repurposing Drilling Control Diagnostics for Subsurface Edge Detection and Boundary Advisement During Planetary Drilling
Informed decision-making during lunar drilling and sampling missions will require data monitoring tools and specialized ground data systems. Accurate and updated situational awareness, with ongoing data monitoring, is critical for timely responses by to incoming science data. Traverse plans and scheduled activities may need to be flexibly changed in order to react to unexpected data or situations. Unlike (for example) Mars missions, the relative lightspeed closeness of the Moon allows for near-real-time ground processing of incoming mission and instrument data. An Apollo-class lunar regolith drill will in a sense “travel” a meter or two vertically at a given subsurface characterization site. As the drill penetrates into lunar regolith, it is likely to encounter a range of material densities, orientations, fracture toughness, and (perhaps) ice percentages. Lunar drill telemetry can provide science teams with a valuable first look into the subsurface structure, the regolith bulk properties, and constituents at each drilled site. Real-time AI-based recognition and reaction to downhole situations has been developed for automated deeper drilling on Mars and beyond. We can leverage the same knowledge bases and pattern-matching as areal-time interpreter of the subsurface, a situational awareness tool during drilling operations. We recently (Sept. 2019) demonstrated this AI drilling monitoring and analysis capability, in control of in-situ drilling and sampling operations, mounted on a KREX-2 rover in Chile’s Atacama Desert. Terrestrial automated drilling log analyses in oil exploration have used similar machine learning techniques in classifying and identifying features in drilling logs –but these typically are designed assuming a drilling fluid influencing downhole measurements and data (permeability, resistivity). Drilling models and existing AI software designed to detect and respond to drilling faults and hard materials can be repurposed, for near-real-time (ground-based) interpretation of drilling telemetry –a potentially valuable advisory tool for strata boundaries and changes in drilling parameters. On the Moon, this approach could be used to study the structure and to some extent the composition of lunar regolith vs. borehole depth, based on recognizable variations in fracture hardness, drilling energy and penetration rates while actively drilling. Since the early 2000s, a series of increasingly-capable real-time drilling telemetry interpretation and characterization software tools have been developed. These subsurface models and software tools have monitored the real-time drilling data received, and automatically identified changes in drill behavior (e.g., encountering a harder target layer, bit inclusions, drill choking due to infall downhole, and others) correlating these with subsurface structures and features. We discuss the mappings between drill borehole parameters, faults or events detected, and modeled changes in rock layer boundaries, in examples drawn from field testing at analog sites in an Arctic impact crater, Rio Tinto, and Chile’s Atacama Desert. These demonstrate how subsurface structural boundaries led to fault detections and responses by the software.
drilling advisor↗
Assessing the potential of ToF-SIMS as a complementary approach to investigate cement-based materials — Applications related to alkali–silica reaction
In this study, the potential of time-of-flight secondary ion mass spectrometry (ToF-SIMS) for the application in cement-based materials is assessed in combination and comparison with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). Mortar, concrete and samples from model systems providing products formed by the alkali–silica reaction (ASR) were studied. ToF-SIMS provides qualitative data on alkalis in cases where EDX reaches its limits in regard to detectable concentration, lateral resolution and atomic number of the elements. Due to its high in-depth resolution of a few atomic monolayers, thin layers of reaction products can be detected on the surfaces and chemically analyzed with ToF-SIMS. Additionally, it delivers information on the molecular conformation within the ASR product, its hydrogen content and its isotope ratios, information not provided by EDX. Provided the samples are carefully prepared, ToF-SIMS opens up new possibilities in the analysis of cement-based materials.
36 MATERIALS SCIENCE↗
Glacial cycles influence marine methane hydrate formation
Methane hydrates in fine-grained continental slope sediments often occupy isolated depth intervals surrounded by hydrate-free sediments. As they are not connected to deep gas sources, these hydrate deposits have been interpreted as sourced by in situ microbial methane. We investigate here the hypothesis that these isolated hydrate accumulations form preferentially in sediments deposited during Pleistocene glacial lowstands that contain relatively large amounts of labile particulate organic carbon, leading to enhanced microbial methanogenesis. To test this hypothesis, we apply an advection-diffusion-reaction model with a time-dependent organic carbon deposition controlled by glacioeustatic sea level variations. In the model, hydrate forms in sediments with greater organic carbon content deposited during the penultimate glacial cycle (~120-240 ka). As a result, the model predictions match hydrate-bearing intervals detected in three sites drilled on the northern Gulf of Mexico continental slope, supporting the hypothesis of hydrate formation driven by enhanced organic carbon burial during glacial lowstands.
58 GEOSCIENCES↗
Perovskite-Type Solid Solution Nano-Electrocatalysts Enable Simultaneously Enhanced Activity and Stability for Oxygen Evolution
A trade-off between catalytic activity and structural stability generally exists in oxygen evolution electrocatalysis, especially in acidic environment. This dilemma limits the development of higher-performance electrocatalysts that are required by next-generation electrochemical technologies. In this work it is demonstrated that the inverse catalytic activity–structural stability relation can be broken by alloying catalytically inert strontium zirconate with the other catalytically active perovskite, strontium iridate. This strategy results in an alloyed perovskite electrocatalyst with simultaneously improved iridium mass activity and structural stability, by about five times, for the oxygen evolution reaction under acidic conditions. The experimental and theoretical results suggest that the alloying strategy generates multiple positive effects, mainly including the reduction of catalyst size, the decrease of catalyst covalency, and the weakening of surface oxygen-binding ability. The synergistic optimization of bulk and surface properties, as a result, enhances the intrinsic activity and availability of surface iridium sites, whilst significantly inhibiting the surface cation corrosion during electrocatalysis.
36 MATERIALS SCIENCE↗
A Low-Cost Fabrication Technique for the Growth of Single-Domain GdBCO Bulk Superconductor from Raw Metal Oxides
A single-domain GdBCO bulk superconductor is usually fabricated using a mixture of pre-reacted precursor powders (including GdBa{sub 2}Cu{sub 3}O{sub 7−δ} and Gd{sub 2}BaCuO{sub 5}) by the top-seeded melt texture growth (TSMTG) process. However, the synthesis of pure-phase precursor powder by the solid-state sintering reaction can not only consume time for weeks but also prolong the fabrication process and can lead to a low-efficiency and high-cost process. In this paper, we reported the successful growth of single-domain GdBCO bulk superconductors by the top-seeded metallic oxide melt growth (TS-MOMG) process in which the raw materials of Gd{sub 2}O{sub 3}, BaO, and CuO, the three different metallic oxides, are just involved to fabricate the single-domain GdBCO bulk superconductors. After detailed investigations in the morphology, levitation force, trapped magnetic field, and critical temperature of the grown samples with different ratios, it was found that the simplified precursor-phase source can be used to fabricate the single-domain GdBCO bulk superconductors more efficiently, which can combine the crystal growth procedure and greatly economize the preparation cost and the time to the most extent.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Photocatalytic activity of anatase titanium dioxide nanostructures prepared by reactive magnetron sputtering technique
In this work, nanostructured titanium dioxide (TiO{sub 2}) photocatalysts with high optical and structural homogeneity were successfully synthesized by dc reactive magnetron sputtering technique. The TiO{sub 2} thin films were produced with high structural homogeneity without any heat treatment. Analysis of the X-ray diffraction patterns and UV–visible spectroscopy gave an indication that the structure of prepared films is anatase with energy band gap of 3.23 eV. The Fourier-transform infrared spectroscopy has confirmed the formation of Ti–O bond. The average size of TiO{sub 2} particles in the deposited films was ranging in 5–7 nm. These nanostructures are very applicable as photocatalysts as their photocatalytic activity was determined from the degradation rate with UV irradiation time as the first order reaction rate constant was determined to be 2.4 × 10{sup −3} min{sup −1}.
36 MATERIALS SCIENCE↗
Comparison of HMF hydrodeoxygenation over different metal catalysts in a continuous flow reactor
The three-phase hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) and hydrogenation of 2,5-dimethylfuran (DMF) were studied over six carbon-supported metal catalysts (Pt, Pd, Ir, Ru, Ni, and Co) using a tubular flow reactor with 1-propanol solvent, at 180 °C and 33 bar. By varying the space time in the reactor, the reaction of HMF is shown to be sequential, with HMF reacting first to furfuryl ethers and other partially hydrogenated products, which then form 2,5-dimethylfuran (DMF). Ring-opened products and 2,5-dimethyltetrahydrofuran (DMTHF) were produced only from reaction of DMF. Rate constants for the pseudo-first-order sequential reactions were obtained for each of the metals. The selectivities for the reaction of DMF varied with the metal catalyst, with Pd forming primarily DMTHF, Ir forming a mixture of DMTHF and open-ring products, and the other metals forming primarily open-ring products. Catalyst stabilities followed the order Pt ~ Ir > Pd > Ni > Co > Ru. Since the stability order correlated with carbon balances in the product (>93% for Pt; <75% for Ru), deactivation appears to be caused by deposition of humins on the catalyst.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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