Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “additives”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

An additively manufactured AlCuMnZr alloy microstructure and tensile mechanical properties

In this study, selective laser melting (SLM) was used to fabricate an AlCuMnZr alloy. The microstructural features that resulted from additive manufacturing (AM) were significantly refined compared to the corresponding cast alloy features. A combination of fine equiaxed and columnar grains along with in-situ formation of θ' precipitates during AM leads to enhanced yield strength (up to 300°C) in the as-fabricated AM alloy. The refinement of brittle intermetallics and a bimodal grain size distribution leads to improved tensile elongation in the AM alloy. The results illustrate the microstructural advantages that can result from additive processing over conventionally processed microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

First measurement of the cross section for top quark pair production with additional charm jets using dileptonic final states in pp collisions at $\sqrt{s}$= 13 TeV

The first measurement of the inclusive cross section for top quark pairs ($t\bar{t}$) produced in association with two additional charm jets is presented. The analysis uses the dileptonic final states of $t\bar{t}$ events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 41.5 fb -1 recorded by the CMS experiment at the LHC. A new charm jet identification algorithm provides input to a neural network that is trained to distinguish among $t\bar{t}$ events with two additional charm ($t\bar{t}c\bar{c}$), bottom ($t\bar{t}b\bar{b}$), and light-flavour or gluon ($t\bar{t}LL$) jets. By means of a template fitting procedure, the inclusive $t\bar{t}c\bar{c}$, $t\bar{t}b\bar{b}$, and $t\bar{t}LL$ cross sections are simultaneously measured, together with their ratios to the inclusive $t\bar{t}$ + two jets cross section. This provides measurements of the $t\bar{t}c\bar{c}$ and $t\bar{t}b\bar{b}$ cross sections of 10.1 ± 1.2 (stat) ± 1.4 (syst) pb and 4.54 ± 0.35 (stat) ± 0.56 (syst) pb, respectively, in the full phase space. The results are compared and found to be consistent with predictions from two different matrix element generators with next-to-leading order accuracy in quantum chromodynamics, interfaced with a parton shower simulation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Insights on keto-hydroperoxide formation from O 2 addition to the beta-tetrahydrofuran radical

Cyclic ethers provide an interesting case study of low-temperature oxidation chemistry, especially in relevance to biofuels. A recent experimental study revealed new questions regarding the low-temperature oxidation mechanism of tetrahydrofuran (THF) concerning the formation of keto-hydroperoxides. In particular, keto-hydroperoxides originating from the THF-β radical were not captured accurately by current literature models, motivating this work to calculate the energetics of the first and second O 2 -addition pathways for THF radicals. Electronic structure calculations at the CCSD(T)/cc-pV∞Z//M06-2X/cc-pVTZ level of theory were used to generate potential energy surfaces for the α-C and β-C THF radicals and subsequent pathways to the formation of the keto-hydroperoxide isomers. These are the first theoretical calculations of the second O 2 -addition radical pathways for the THF-β radical. Results from the theorical work provided further insight into the low-temperature oxidation of THF. This included identifying the pathways most likely to form the keto-hydroperoxide isomers observed in prior experimental work; and detecting that the shortcomings in prior models are likely due to uncertainties in R + THF abstraction reaction rates. Here, these conclusions will motivate future work for accurate THF kinetic model development.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Bay capping via acetylene addition to polycyclic aromatic hydrocarbons: Mechanism and kinetics

The bay-capping mechanism on PAH armchair edges and the kinetics of acetylene addition to 6–6–5 and 5–6–5 bays have been explored by ab initio/RRKM-ME calculations. The bays on the edges were modeled by C 21 H 11 and C 20 H 9 radicals produced by H abstractions from 7H-benzo[c]cyclopenta[e]pyrene and dicyclopenta[cf]pyrene. The C 20 H 9 + C 2 H 2 reaction is shown to have a low entrance barrier and to rapidly form the capped product, indaceno[2,1,8,7-cdefg]pyrene, along with ethynyl substituted dicyclopenta[cf]pyrene at temperatures above 1400 K. The reactivity of C 21 H 11 is shown to be governed by the location of the unpaired electron; the π radical R1 formed by H abstraction from the CH 2 group in 7H-benzo[c]cyclopenta[e]pyrene reacts with C 2 H 2 very slowly owing to a high entrance barrier, with the bay-capping rate constant approaching 10 -16 cm 3 molecule -1 s -1 only at temperatures above 2000K. Further, this result reaffirms that the growth of π aryl radicals via acetylene addition is inefficient and reflects the generally low reactivity of such radicals where the spin density is highly delocalized over the entire polyaromatic system. Alternatively, the σ C 21 H 11 radical R2 produced by H abstraction from the five-membered ring at the bay rapidly reacts with C 2 H 2 forming the bay-capped product, with the rate constant on the order of 10 -12 cm 3 molecule -1 s -1 at T≥1500K. Rate constants for the capping reactions at the 6–6–5 and 5–6–5 bays are compared with those at the 6–0–6, 6–6–6, and 6–5–6 bays. The site-specific bay-capping rate constants have been utilized in kMC simulations of the PAH growth and the results showed measurable differences when the 6–6–5 and 5–6–5 bay-capping reactions are taken into account, including an increase of the growth rate and the formation of closed-shell PAH and a rise of the number of embedded five-membered rings accompanied with a slight decrease of their overall amount.

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

Utilizing a Dynamic Segmentation Convolutional Neural Network for Microstructure Analysis of Additively Manufactured Superalloy 718

Additive manufacturing (AM) is revolutionizing almost all industries through the production of intricate geometries previously prohibited by cost or machinability. Ni-based superalloys form a primary alloy class for high temperature applications in the petrochemical, aerospace, and nuclear industries because of their intrinsic resistance to creep and the ability to heat treat the superalloy for high strength. Despite these attractive properties, the extreme work hardening of Ni-based superalloys makes traditional manufacturing of complex shapes difficult and thus, these alloys are an attractive target for AM. Superalloy 718 was chosen as an example superalloy because of the wide variety of precipitates that can form within its composition space from the repetitive heating and cooling cycles of the AM process. The precipitates and other microstructure features, such as grain boundaries and dislocations, will dictate the mechanical properties and thus, there is an extensive challenge to characterize the size, number density, composition, and volume fraction of each microstructural feature from AM fabrication using analytical electron microscopy. This work focused on the application of a pixel-wise classification machine learning (ML) model called a dynamic segmentation convolutional neural network (DSCNN) to identify the microstructural features of an as-fabricated additively manufactured superalloy 718.

Taller, Stephen↗
DOE OSTI2023

ortho -Fluoro or ortho Effect? Oxidative Addition of Zerovalent Nickel into the C–CN Bond of Substituted Benzonitriles

Substitution effects on the oxidative addition of [Ni(dmpe)] to the C—CN bond of CF 3 and CH 3 substituted benzonitriles was studied by DFT and compared to their F analogs. C—CN oxidative addition products were stabilized slightly more by the first o-CF 3 group (-7.4 kcal/mol) compared to F groups (-6.6 kcal/mol per o-F), but due to steric crowding the second o-CF 3 group did not show considerably more stabilization (-0.8 kcal/mol). CH 3 groups led to destabilization.

02 PETROLEUM↗
DOE OSTI2026

Formation of 1 H -Phenalene (C 13 H 10 ) in the Taurus Molecular Cloud via Methylidyne Addition-Cyclization-Aromatization (MACA)

The formation of 1H-phenalene (C 13 H 10 ) in cold molecular clouds, such as the Taurus Molecular Cloud-1 (TMC-1), presents a significant challenge to traditional astrochemical models, which predominantly suggest high-temperature pathways for polycyclic aromatic hydrocarbon (PAH) formation. In this study, we explore computationally the Methylidyne Addition-Cyclization-Aromatization (MACA) mechanism as a viable, barrierless pathway for phenalene synthesis under low-temperature conditions. Through electronic structure calculations and Rice–Ramsperger–Kassel–Marcus (RRKM) statistical methods, we demonstrate that the reaction of 1-vinylnaphthalene (C 10 H 7 C 2 H 3 ) with the methylidyne radical (CH) leads to the formation of 1H-phenalene via a bimolecular reaction, a process that is exoergic and without entrance barrier. The MACA mechanism facilitates the growth of the aromatic carbon backbone via a [5 + 1] ring annulation, providing a new insight into PAH formation in cold molecular clouds. Notably, the MACA mechanism has previously been shown to form indene (C9H8), which was detected in TMC-1 as well, via a [4 + 1] annulation, demonstrating its potential to produce a variety of complex PAHs by addition of a five- and six-membered ring to a benzene moiety via [4 + 1] and [5 + 1] annulation, respectively. As a result, this work highlights the importance of barrierless, exoergic reactions involving MACA in the synthesis of complex aromatic molecules in space, expanding our physicochemical understanding of carbon-rich chemistry in cold molecular clouds.

Aromatic compounds↗
DOE OSTI2020

Improved CO 2 Capture Performance of Electrochemically Mediated Amine Regeneration Processes with Ionic Surfactant Additives

For the effective reduction of global CO 2 emissions, it is essential to develop and deploy efficient and cost-effective technologies for CO 2 capture, especially from large point sources. We recently developed an electrochemically mediated amine regeneration (EMAR) system to replace traditional thermal desorption for the capture of CO 2 from post-combustion flue gases. Despite EMAR effectiveness on a laboratory scale, concerns regarding the high gas-to-liquid ratio in the electrochemical cell and long-term instability of the electrodes need to be addressed before further scale-up of the process to a pilot plant and beyond can be entertained. Accordingly, we investigated the effect of using sodium dodecyl sulfate (SDS) as an anionic surfactant and dodecyltrimethylammonium bromide (DTAB) as a cationic surfactant on the process operation. It was found that it is advantageous to use an anionic surfactant for a system such as EMAR that contains hydrophilic electrodes and a positively charged electrochemically active species. The overall cell resistance was notably reduced when SDS anionic surfactant was used. The precipitation of copper particles observed in the anode outlet when no surfactant was used was effectively avoided when SDS was added to the electrolyte, resulting in electrode stability. In addition, smaller gas bubbles were produced in the presence of the SDS surfactant, which resulted in less blockage of the electrode by the gas with a resultant lower cell potential under constant current conditions, driving more efficient CO 2 desorption. This led to an ~25% reduction in the electrochemical energy requirement, the lowest ever achieved experimentally for the EMAR process. Altogether, the addition of a very low concentration of SDS resulted in the successful circumvention of the important problems faced by the EMAR system regarding further scale-up.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Poly(vinylferrocene) as an Ionomer and Sulfur-Confining Additive for Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries are promising owing to their high energy density, environmental benignity, and low cost. Most of the commonly used binders in Li-S battery cathodes are inert and have no significant effect on the challenges of sulfur as a cathode material, such as the polysulfide shuttle effect, low ionic/electronic conductivity, and a sluggish redox reaction. In this work, we demonstrate the use of poly(vinylferrocene) (PvFc) as a binder additive that can effectively increase the ionic conductivity of the cathode and act as a sulfide confining agent. Electrochemical tests performed with PvFc as part of the binder mixture used to cast the cathodes demonstrate an increase in rate capability and cycle life when compared to the baseline samples. Ionic conductivity measurements and X-ray photoelectron spectroscopy suggest that the π-cation molecular interaction between the cyclopentadienyl rings from ferrocene and Li + act like an ion couple with ferrocene acting as a static, covalently bound acceptor of Li + ions that enhances their mobility through the cathode. This coupled with the affinity between the ferrocenyl cations and the Li salt anions, which provides more distribution of counterions for Li + movement and improves accessibility to the cathode S reservoir, make PvFc a promising ionomer for Li-S batteries. In addition, the π-cation bonds between cyclopentadienyl and lithium polysulfides produce a sulfide confining effect that mitigates capacity fade through polysulfide dissolution. Furthermore, this work demonstrates an expansion in the utility of PvFc as a component in Li-ion batteries, which so far is mostly limited to use as an active material in organometallic batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Addition of Short Polymer Chains Mechanically Reinforces Glassy Poly(2-vinylpyridine)–Silica Nanoparticle Nanocomposites

The addition of hard fillers to a polymer matrix is a well-known process for achieving mechanical reinforcement. With a decrease in the size of the fillers, the contribution from polymer–particle nanometer-sized interfaces become significant, and these interfaces affect the mechanical performance of polymer nanocomposites (PNCs) beyond the limits established for conventional composites. However, the molecular mechanisms underlying the improvement in the mechanical performance of glassy PNCs remain unresolved, necessitating a deeper understanding of the structure–property relationships in these intrinsically heterogeneous systems. In this effort, by using Brillouin light scattering (BLS) and dynamic mechanical analysis (DMA), we demonstrated that adding shorter chains to a PNC prepared with high molecular weight polymers significantly improved the mechanical properties of the PNC in the glassy state. The strongest enhancement of mechanical properties occurred at an optimum concentration of short chains. This is in contrast to behavior of the glass transition temperature of PNCs which shows a monotonic decrease with an increase in the concentration of shorter chains. Using experimental data and coarse-grained molecular dynamics (MD) simulations, we have identified the molecular mechanism leading to the observed non-monotonic changes in mechanical reinforcement. Here, this mechanism includes changes in the nanoscale organization at the interface, combined with chain stretching amplified by the addition of the short chains. Overall, our approach paves a simple, cost-effective pathway to fabricating glassy PNCs with significantly improved mechanical properties that will fill various practical needs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Block Polyelectrolyte Additives That Modulate the Viscoelasticity and Enhance the Printability of Gelatin Inks at Physiological Temperatures

We demonstrate the utility of block polyelectrolyte (bPE) additives to enhance viscosity and resolve challenges with the three-dimensional (3D) printability of extrusion-based biopolymer inks. The addition of oppositely charged bPEs to solutions of photocurable gelatin methacryloyl (GelMA) results in complexation-driven self-assembly of the bPEs, leading to GelMA/bPE inks that are printable at physiological temperatures, representing stark improvements over GelMA inks that suffer from low viscosity at 37 °C, leading to low printability and poor structural stability. The hierarchical microstructure of the self-assemblies (either jammed micelles or 3D networks) formed by the oppositely charged bPEs, confirmed by small-angle X-ray scattering, is attributed to the enhancements in the shear strength and printability of the GelMA/bPE inks. Varying bPE concentration in the inks is shown to enable tunability of the rheological properties to meet the criteria of pre- and postextrusion flow characteristics for 3D printing, including prominent yielding behavior, strong shear thinning, and rapid recovery upon flow cessation. Moreover, the bPE self-assemblies also contribute to the robustness of the photo-cross-linked hydrogels; photo-cross-linked GelMA/bPE hydrogels are shown to exhibit higher shear strength than photo-cross-linked GelMA hydrogels. Last, the assessment of the printability of GelMA/bPE inks indicates excellent printing performance, including minimal swelling postextrusion, satisfactory retention of the filament shape upon deposition, and satisfactory shape fidelity of the various printed constructs. We envision this study to serve as a practical guide for the printing of bespoke extrusion inks where bPEs are used as scaffolds and viscosity enhancers that can be emulated in a range of photocurable precursors.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Additive-Induced Morphology Change of Polymer Film Enables Enhanced Charge Mobility and Faster Organic Electrochemical Transistor Switching

Conjugated polymers (CPs) play an important role in organic electrochemical transistors (OECTs) for bioelectronics and related applications, where they serve as channel materials. Currently, most successful polymers for CPs are re-engineered from traditional CPs by replacing hydrophobic alkyl side chains with hydrophilic ethylene glycol or ionic groups. Frustratingly, the enhanced ion transport often compromises the charge mobility of the original CP. In this work, we present an additive-mediated method to construct a modified poly(3-hexylthiophene) (P3HT) film to enable efficient ion migration. The additive is designed with a cleavable diazo group that releases nitrogen and 2-methoxyethanol, a volatile compound, to alter the P3HT film morphology. OECTs based on the film exhibit improved response times. Interestingly, the process also enhances the crystallinity of P3HT, leading to higher hole mobility compared with pristine P3HT. This study proposes an in situ strategy to achieve the functionality of the OMIEC via morphological regulation, offering a promising route to simultaneously enhance both ion accessibility and charge mobility.

Organic polymers↗
DOE OSTI2024

Defining Reactivity–Deconstructability Relationships for Copolymerizations Involving Cleavable Comonomer Additives

The incorporation of cleavable comonomers as additives into polymers can imbue traditional polymers with controlled deconstructability and expanded end-of-life options. The efficiency with which cleavable comonomer additives (CCAs) can enable deconstruction is sensitive to their local distribution within a copolymer backbone, which is dictated by their copolymerization behavior. While qualitative heuristics exist that describe deconstructability, comprehensive quantitative connections between CCA loadings, reactivity ratios, polymerization mechanisms, and deconstruction reactions on the deconstruction efficiency of copolymers containing CCAs have not been established. Here, in this work, we broadly define these relationships using stochastic simulations characterizing various polymerization mechanisms (e.g., controlled/living, free-radical, and reversible ring-opening polymerizations), reactivity ratio pairs (spanning 2 orders of magnitude between 0.01 and 100), CCA loadings (2.5% to 20%), and deconstruction reactions (e.g., comonomer sequence-dependent deconstruction behavior). We show general agreement between simulated and experimentally observed deconstruction fragment sizes from the literature, demonstrating the predictive power of the methods used herein. These results will guide the development of more efficient CCAs and inform the formulation of deconstructable materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Production of a Sustainable Aviation Fuel Additive from Waste Polystyrene

Sustainable aviation fuels (SAFs) are an important lever to achieving net zero CO 2 emissions in aviation. Fuel quality standards limit the blend volume of nonpetroleum-based jet fuel such as synthetic paraffinic kerosene (SPK) in Jet A to 50 vol %. One reason for this limit is the limited seal-swelling ability of SPK. Ethylbenzene (EB) as an additive can improve the swelling propensity of SPK. In this study, EB was produced through polystyrene pyrolysis, hydrogenation, and separation. The thermal pyrolysis of polystyrene produced a styrene-rich pyrolyzate. The pyrolyzate was hydrogenated by using Pd/C to produce an EB-rich mixture that yielded a crude EB of ∼90% purity on distillation. The O-ring swelling ability of crude EB of ∼90% purity was tested as a 12 and 16 vol % blend with SPK. Results reveal that EB addition enhanced seal swelling, but a more refined EB grade would be preferable. The results provide a pathway to address the twin issues of plastic pollution and SPK property improvement.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2025

Electrochemical Reduction Pathways from Goethite to Green Iron in Alkaline Solution with Silicate Additive

Energy-efficient and low-temperature iron electrolysis in alkaline solutions is a low-cost and sustainable ironmaking process with zero-carbon emissions when renewable electrical sources are involved. However, its implementation is hindered by electrochemically inert Fe 3 O 4 and parasitic H 2 gas formation during the electrochemical reduction process, resulting in the low energy efficiency of iron electrolysis. Here, we further explore the potential of electrochemical reduction of goethite (FeOOH) by employing a low concentration of silicate additive in an alkaline solution to mitigate Fe 3 O 4 accumulation and H 2 generation. Electrochemical measurements coupled with operando X-ray diffraction and X-ray absorption spectroscopy suggested FeOOH → Fe 3 O 4 → Fe(OH) 2 → Fe reduction pathways. Interestingly, a poorly crystalline or amorphous Fe(OH) 2 phase formed in the NaOH/silicate mixed electrolyte, possibly due to the inhibitive effect of silicate on water and ion transport, which eventually contributed to the improved reduction of Fe 3 O 4 , also supported by atomistic simulations. This work demonstrates the potential for silicate as a low-cost and effective electrolyte additive to improve room-temperature green iron formation via electrolysis.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Non-additive microbial community responses to environmental complexity

Environmental composition is a major, though poorly understood, determinant of microbiome dynamics. Here we ask whether general principles govern how microbial community growth yield and diversity scale with an increasing number of environmental molecules. By assembling hundreds of synthetic consortia in vitro, we find that growth yield can remain constant or increase in a non-additive manner with environmental complexity. Conversely, taxonomic diversity is often much lower than expected. To better understand these deviations, we formulate metrics for epistatic interactions between environments and use them to compare our results to communities simulated with experimentally-parametrized consumer resource models. We find that key metabolic and ecological factors, including species similarity, degree of specialization, and metabolic interactions, modulate the observed non-additivity and govern the response of communities to combinations of resource pools. Our results demonstrate that environmental complexity alone is not sufficient for maintaining community diversity, and provide practical guidance for designing and controlling microbial ecosystems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Controlling process instability for defect lean metal additive manufacturing

The process instabilities intrinsic to the localized laser-powder bed interaction cause the formation of various defects in laser powder bed fusion (LPBF) additive manufacturing process. Particularly, the stochastic formation of large spatters leads to unpredictable defects in the as-printed parts. Here we report the elimination of large spatters through controlling laser-powder bed interaction instabilities by using nanoparticles. The elimination of large spatters results in 3D printing of defect lean sample with good consistency and enhanced properties. We reveal that two mechanisms work synergistically to eliminate all types of large spatters: (1) nanoparticle-enabled control of molten pool fluctuation eliminates the liquid breakup induced large spatters; (2) nanoparticle-enabled control of the liquid droplet coalescence eliminates liquid droplet colliding induced large spatters. The nanoparticle-enabled simultaneous stabilization of molten pool fluctuation and prevention of liquid droplet coalescence discovered here provide a potential way to achieve defect lean metal additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Critical role of slags in pitting corrosion of additively manufactured stainless steel in simulated seawater

Abstract Pitting corrosion in seawater is one of the most difficult forms of corrosion to identify and control. A workhorse material for marine applications, 316L stainless steel (316L SS) is known to balance resistance to pitting with good mechanical properties. The advent of additive manufacturing (AM), particularly laser powder bed fusion (LPBF), has prompted numerous microstructural and mechanical investigations of LPBF 316L SS; however, the origins of pitting corrosion on as-built surfaces is unknown, despite their utmost importance for certification of LPBF 316L SS prior to fielding. Here, we show that Mn-rich silicate slags are responsible for pitting of the as-built LPBF material in sodium chloride due to their introduction of deleterious defects such as cracks or surface oxide heterogeneities. In addition, we explain how slags are formed in the liquid metal and deposited at the as-built surfaces using high-fidelity melt pool simulations. Our work uncovers how LPBF changes surface oxides due to rapid solidification and high-temperature oxidation, leading to fundamentally different pitting corrosion mechanisms.

36 MATERIALS SCIENCE↗