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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Quantitation of buried contamination by use of solvents

An investigation was made to determine (1) sporicidal properties of amine solvents that solubilize silicon resins, (2) recovery properties of a silicon potting compound (RTV 41) used in spacecraft, and (3) viability of spores during chemical curing of the potting compound. Results show that: (1) spores do remain viable during RTV 41 silicon potting chemical curing, and (2) spore recovery from cured silicon potting compound RTV 41 is very high when silicon rubber is dissolved in butylamine and series dilution with benzene prior to plate curing.

Pappas, S. P.↗
NASA NTRS1997

Advanced Modeling Techniques to Study Anthropogenic Influences on Atmospheric Chemical Budgets

This research work is a collaborative effort between research groups at MCNC and the University of North Carolina at Chapel Hill. The overall objective of this research is to improve the level of understanding of the processes that determine the budgets of chemically and radiatively active compounds in the atmosphere through development and application of advanced methods for calculating the chemical change in atmospheric models. The research performed during the second year of this project focused on four major aspects: (1) The continued development and refinement of multiscale modeling techniques to address the issue of the disparate scales of the physico-chemical processes that govern the fate of atmospheric pollutants; (2) Development and application of analysis methods utilizing process and mass balance techniques to increase the interpretive powers of atmospheric models and to aid in complementary analysis of model predictions and observations; (3) Development of meteorological and emission inputs for initial application of the chemistry/transport model over the north Atlantic region; and, (4) The continued development and implementation of a totally new adaptive chemistry representation that changes the details of what is represented as the underlying conditions change.

Mathur, Rohit↗
DOE OSTI2023

Health monitoring device

Example aspects of a volatile organic compound detection device, a wearable health monitoring device, and a method of monitoring a user's health are disclosed. The volatile organic compound detection device can comprise a collector comprising a collector material configured to collect volatile organic compounds given off from a user's skin; a separator comprising a gas chromatography column configured to separate mixtures of the volatile organic compounds into their constituent chemicals; and an identifier comprising a detector and a processor, the detector configured to transduce the constituent chemicals into a signal, the processor configured to process the signal to identify specific volatile organic compounds indicative of a health condition.

42 ENGINEERING↗
DOE OSTI2025

Impacts of Precipitation Events on Concentrations of Oxygenated Gas- and Particle-Phase Compounds Observed in the Amazon

Removal of gases and particles by precipitation (wet deposition) is a critical process that significantly influences the transport and chemical transformation of atmospheric compounds. However, there are few studies that directly measure or constrain the rates of this process under real-world conditions. This work quantifies the net change in ambient concentrations during precipitation events (removal rates) of gas- and particle-phase organic compounds at a surface site near Manaus, Brazil, during the GoAmazon2014/5 campaign. Removal rates of identified and unknown compounds that have been previously classified into source-based clusters are measured during rain events and categorized based on estimated properties of compounds and clusters. Highly oxygenated gases, such as isoprene oxidation products, are removed during precipitation events with a median removal rate of 0.09 h –1 and the fastest analyte is removed at a rate of 0.22 h –1 . Removal rates of particle-phase compounds are observed at roughly this median rate, while less soluble gases, such as terpenes, exhibit low removal rates. These results are roughly in agreement with prior theoretical estimates of wet deposition rates for comparable compounds, providing an empirical point of comparison while noting that our metric reflects the net influence of precipitation events rather than wet deposition alone.

atmospheric chemistry↗
NASA NTRS2021

Volatile chemical product emissions enhance ozone and modulate urban chemistry

Decades of air quality improvements have substantially reduced the motor vehicle emissions of volatile organic compounds (VOCs). Today, volatile chemical products (VCPs) are responsible for half of the petrochemical VOCs emitted in major urban areas. We show that VCP emissions are ubiquitous in US and European cities and scale with population density. We report significant VCP emissions for New York City (NYC), including a monoterpene flux of 14.7 to 24.4 kg ⋅ d−1 ⋅ km−2 from fragranced VCPs and other anthropogenic sources, which is comparable to that of a summertime forest. Photochemical modeling of an extreme heat event, with ozone well in excess of US standards, illustrates the significant impact of VCPs on air quality. In the most populated regions of NYC, ozone was sensitive to anthropogenic VOCs (AVOCs), even in the presence of biogenic sources. Within this VOC-sensitive regime, AVOCs contributed upwards of ∼20 ppb to maximum 8-h average ozone. VCPs accounted for more than 50% of this total AVOC contribution. Emissions from fragranced VCPs, including personal care and cleaning products, account for at least 50% of the ozone attributed to VCPs. We show that model simulations of ozone depend foremost on the magnitude of VCP emissions and that the addition of oxygenated VCP chemistry impacts simulations of key atmospheric oxidation products. NYC is a case study for developed megacities, and the impacts of VCPs on local ozone are likely similar for other major urban regions across North America or Europe.

Matthew M. Coggon↗
DOE OSTI2020

Exotic bonding interactions and coexistence of chemically distinct periodic lattice distortions in the charge density wave compound TaTe2

The superstructure of TaTe 2 is examined by total high-energy x-ray scattering and large-scale structure modeling over a broad temperature range. At room temperature, it features double zigzag chains of Ta atoms exhibiting metallic bonding. The chains are sandwiched between planes of weakly interacting Te atoms. Below 170 K, the chains appear broken to “butterflylike” clusters and single zigzag chains of covalently bonded Te atoms emerge while Ta-Te interactions remain largely ionic. This is a rare example of a charge density wave compound stabilized by bonding that is a mix of covalent, ionic, and metallic character giving rise to chemically distinct periodic lattice distortions. We argue that the formation of periodic lattice distortions in the Te sublattice in addition to those in the Ta sublattice favors charge delocalization, which may explain the unusually diminished resistivity and increased magnetic susceptibility exhibited by the low-temperature charge density wave phase of TaTe 2 . The effect may be common for 5d transition metal chalcogenides containing Te because of the extended electronic orbitals of the constituent atoms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1999

Prebiotic Nitrogen Fixation by FeS Reduction of Nitrite Under Acidic Conditions

Theories for the origin of life require the availability of reduced nitrogen for the formation of such species as amino acid and nucleic acids. In a strongly reducing atmosphere, compounds essential to the chemical evolution of life, such as amino acids, can form by reactions between HCN, NH3, and carbonyl compounds produced in spark discharges. However, under non-reducing atmospheres, electric discharges produced NO rather than HCN or NH3. This raises the questions of; how ammonia can be formed under a neutral atmosphere, and what conditions are needed such formation to occur? On possibility is the conversion of NO into nitric and nitrous acids (through HNO) and rained into the oceans. The reduction of nitrite by aqueous Fe(II) (6 Fe(+2) + 7 H(+) + NO2(-) yields 6 Fe(III) + 2 H2O + NH3) such as was present on the early Earth could then have produced ammonia. However, this reaction does not proceed at pHs less than 7.3. An alternative is reduction by other forms of Fe(II), such as FeS. We will present results that show that FeS can reduce nitrite to ammonia at pHs as low as pH 5 under a variety of conditions.

Summers, David P.↗
NASA NTRS2011

Search for Chemical Biomarkers on Mars Using the Sample Analysis at Mars Instrument Suite on the Mars Science Laboratory

One key goal for the future exploration of Mars is the search for chemical biomarkers including complex organic compounds important in life on Earth. The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) will provide the most sensitive measurements of the organic composition of rocks and regolith samples ever carried out in situ on Mars. SAM consists of a gas chromatograph (GC), quadrupole mass spectrometer (QMS), and tunable laser spectrometer to measure volatiles in the atmosphere and released from rock powders heated up to 1000 C. The measurement of organics in solid samples will be accomplished by three experiments: (1) pyrolysis QMS to identify alkane fragments and simple aromatic compounds; pyrolysis GCMS to separate and identify complex mixtures of larger hydrocarbons; and (3) chemical derivatization and GCMS extract less volatile compounds including amino and carboxylic acids that are not detectable by the other two experiments.

Glavin, D. P.↗
DOE OSTI2022

Compositional stability of peat in ecosystem-scale warming mesocosms

Peatlands historically have acted as a C sink because C-fixation rates exceeded the rate of heterotrophic decomposition. Under future warmer conditions predicted for higher latitudes, however, that balance may shift towards higher rates of heterotrophic respiration leading to the release of previously stored C as CO 2 and CH 4 . The Spruce and Peatlands Response Under Changing Environments (SPRUCE) experiment is designed to test the response of peatlands to climate forcing using a series of warmed enclosures in combination with peat below-ground heating from 0 to +9°C above ambient conditions. This experimental design allowed a test of chemical changes occurring within peatland soils following five years of warming. We analyzed samples in the uppermost 2m of peat using Fourier Transform Infrared Spectroscopy (FT-IR) to quantify the relative abundance of carbohydrate and aromatic compounds in the peat. The peat soils were subjected to deep peat heating (DPH) beginning in June of 2014 followed by whole ecosystem warming (WEW) in August of 2015. We found that the relative amounts of labile and recalcitrant chemical compound groups across the full peat depth interval did not significantly change after five years of exposure to warming. This appears the case even though previous studies have shown that net C losses and loss of bulk peat mass to be instability over that time period. Results suggest that the current store of carbon in peatlands are largely compositionally stable leading to no changes the in the ratio of chemical moieties on the initial four-year timescale of this experiment.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1995

Application of Ni-63 photo and corona discharge ionization for the analysis of chemical warfare agents and toxic wastes

Over the past decade, advances in instrumental design and refinements in the understanding of ion molecule reactions at atmospheric pressure enabled the application of Ion Mobility Spectrometry (IMS) as a simple inexpensive and sensitive analytical method for the detection of organic trace compounds. Positive and negative gas-phase ions for ion mobility spectrometry have been produced by a variety of methods, including photo-ionization, laser multi photon ionization, surface ionization, corona discharge ionization. The most common ion source used in ion mobility spectrometry is a radioactive Ni-63 foil which is favored due to simplicity, stability, convenience, and high selectivity. If reactant ions like (H2O(n)H)(+) or (H2O(n)O2)(-) dominate in the reaction region, nearly all kinds of compounds with a given proton or electron affinity; are ionized. However, the radioactivity of the Ni-63 foil is one disadvantage of this ion source that stimulates the development and application of other ionization techniques. In this paper, we report analyses of old chemical warfare agents and toxic wastes using Bruker RAID ion mobility spectrometers. Due to the modular construction of the measuring cell, the spectrometers can be equipped with different ion sources. The combined use of Ni-63, photo- and corona discharge ionization allows the identification of different classes of chemical compounds and yields in most cases comparable results.

Stach, J.↗
DOE OSTI2020

Applications of plasma-enhanced metalorganic chemical vapor deposition

The use of plasma enhancement for growth of III-V compound semiconductor materials by metalorganic chemical vapor deposition (MOCVD) is examined, to improve control of microstructure, develop understanding of the underlying growth mechanisms, and expand the range of materials combinations for photovoltaic and solid-state lighting applications. Whereas plasma is commonly used with group-IV materials, such as silicon, few studies have examined the impact of plasma-enhanced MOCVD (PE-MOCVD) for III-V materials growth. PE-MOCVD provides improved decomposition of metalorganic precursors, which is driven by hydrogen plasma to augment hydride reactions and thermal pyrolysis, but plasma generation requires low reactor pressure. We have demonstrated elemental Al films grown by PE-MOCVD, which show distinct crystallographic texturing, and assume epitaxial microstructure upon post-growth annealing. We also demonstrate PE-MOCVD of GaAs at temperatures as low as 300 °C. With increasing radio-frequency power, the GaAs growth rate shows a transition from power limited to mass-transport limited. PE-MOCVD grown Ga 0.5 In 0.5 P shows no detectable spontaneous atomic ordering, which offers a mechanism to form order/disorder unicompositional heterostructures, without temperature change or impurity incorporation. In its current implementation, PE-MOCVD grown films have shown microstructural degradation, that we attribute to direct plasma exposure during growth. Improvements in the system design and growth sequences are at the focus of on-going efforts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

The role of cometary particle coalescence in chemical evolution

Important prebiotic organic compounds might have been transported to earth in dust or produced in vapor clouds resulting from atmospheric explosions or impacts of comets. These compounds coalesced in the upper atmosphere with particles ejected from craters formed by impacts of large objects. Coalescence during exposure to UV radiation concentrated organic monomers and enhanced formation of oligomers. Continuing coalescence added material to the growing particles and shielded prebiotic compounds from prolonged UV radiation. These particles settled into the lower atmosphere where they were scavenged by rain. Aqueous chemistry and evaporation of raindrops containing monomers in high temperature regions near the earth's surface also promoted continued formation of oligomers. Finally, these oligomers were deposited in the oceans where continued prebiotic evolution led to the most primitive cell. Results of present studies suggest that prebiotic chemical evolution may be an inevitable consequence of impacting comets during the late accretion of planets anywhere in the universe if oceans remained on those planetary surfaces.

Oberbeck, V. R.↗
DOE OSTI2020

Chespa: Streamlining Expansive Chemical Space Evaluation of Molecular Sets

Thousands of chemical properties can be calculated for small molecules, which can be used to place the molecules within the context of a broader “chemical space.” These definitions vary based on compounds of interest and the goals for the given chemical space definition. Here, we introduce a customizable (i.e., modular) Python module, chespa, built to easily assess different chemical space definitions through cluster-ing of compounds in these spaces and visualize trends of these clusters. To demonstrate this, chespa currently streamlines prediction of vari-ous molecule descriptors (predicted chemical properties, molecular substructures, AI-based chemical space, and chemical class ontology) in order to test 6 different chemical space definitions. Furthermore, we investigated how these varying definitions trend with mass spectrometry (MS)-based observability, i.e., the ability of a molecule to be observed with MS (e.g., as a function of the molecule ionizability), using an example data set from the U.S. EPA's Non-Targeted Analysis Collaborative Trial (ENTACT), where blinded samples had been analyzed previously, providing 1,398 data points. Improved understanding of observability would offer many advantages in small molecule identifica-tion, such as (i) a priori selection of experimental conditions based on suspected sample composition, (ii) the ability to reduce the number of candidate structures during compound identification by removing those less likely to ionize, and, in turn, (iii) a reduced false discovery rate and increased confidence in identifications. Factors controlling observability are not fully understood, making prediction of this property non-trivial and a prime candidate for chemical space analysis. Chespa is available at github.com/pnnl/chespa.

Nunez, Jamie↗
DOE OSTI2022

Emergent Chemical Behavior in Mixed Food and Lignocellulosic Green Waste Hydrothermal Liquefaction

Hydrothermal liquefaction (HTL) is a promising strategy for the conversion of energy-dense waste streams to fuels. Mixed-feed HTL aggregates multiple feed streams to achieve greater scales that capitalize on local resources, hence lowering costs. The potential for new pathways and products upon feedstock blending becomes a compounding level of complexity when unlocking emergent chemistries. Here, food and green waste streams were evaluated under HTL conditions (300 °C, 1 h) to understand the effect of feed molecular composition on product distributions and mechanisms. Thousands of emergent chemical compounds were detected via Fourier transform ion cyclotron resonance mass spectrometry, ultimately leading to the emergence of two dominant outcomes. First, the presence of small amounts of food waste into green waste results in substantial decarboxylation and subsequent polymerization to biocrude than chars. Second, in the other limit, small amounts of green waste promote the capping of oxygenates into the biodiesel range, such as with the emergence of fatty acid methyl esters.

09 BIOMASS FUELS↗
DOE OSTI2022

Computational Workflow for Accelerated Molecular Design Using Quantum Chemical Simulations and Deep Learning Models

Efficient methods for searching the chemical space of molecular compounds are needed to automate and accelerate the design of new functional molecules such as pharmaceuticals. Given the high cost in both resources and time for experimental efforts, computational approaches play a key role in guiding the selection of promising molecules for further investigation. Here, we construct a workflow to accelerate design by combining approximate quantum chemical methods [i.e. density-functional tight-binding (DFTB)], a graph convolutional neural network (GCNN) surrogate model for chemical property prediction, and a masked language model (MLM) for molecule generation. Property data from the DFTB calculations are used to train the surrogate model; the surrogate model is used to score candidates generated by the MLM. The surrogate reduces computation time by orders of magnitude compared to the DFTB calculations, enabling an increased search of chemical space. Furthermore, the MLM generates a diverse set of chemical modifications based on pre-training from a large compound library. We utilize the workflow to search for near-infrared photoactive molecules by minimizing the predicted HOMO-LUMO gap as the target property. Our results show that the workflow can generate optimized molecules outside of the original training set, which suggests that iterations of the workflow could be useful for searching vast chemical spaces in a wide range of design problems.

Blanchard, Andrew↗