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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Galvanic Transformation Dynamics in Heterostructured Nanoparticles

Corrosion is a significant problem for the stability of structural metals and potentially for functional nanomaterials in operating environments. When two metals with different electrochemical potentials form a junction, galvanic corrosion occurs, resulting in the sacrificial dissolution of the metal with a higher oxidation potential (lower electrode potential). In this report it is shown that bimetallic hetero-nanostructures composed of phase-segregated metals undergo galvanic corrosion in aqueous environments. Such selective etching of the sacrificial metal in heterojunction particles leads to the formation of unusual and kinetically stabilized half-spheroid particles. By using a fluid cell and in situ scanning transmission electron microscopy, a two-stage corrosion process can be observed where the Cu experiences a fractal breakdown before the Ag corrodes due to the lack of a protective oxide layer. However, when treated with a mild Ar plasma, the stability of these structures against corrosion is enhanced due to the conversion of the amorphous native oxide to a denser, thin layer of CuO on the Cu surface. Taken together, this work highlights the importance of considering the effects of galvanic corrosion on the stability of multicomponent nanoparticles, and it shows how mass transport in a nanoscale system is influenced by redox processes.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Soliton formation and topology manipulation of coupled spins via ultrafast re-magnetization

The major goal of the project was to explore the properties of magnetic order driven far out of equilibrium by optical excitations. These include fundamental questions related to the interplay of magnetic, structural and electronic degrees of freedom in materials that are optically excited. These problems break down in short term quenching of the magnetization as a results of the energy of the optical pulse studying how the energy of the optical pulse and the angular momentum of the magnetization flow between the different degrees of freedom. This is followed by the longer time re-emergence of the magnetism as the system cools. Within this goal we explored the formation of solitons, both with and without non-trivial topology, via rapid re-magnetization processes after optical-driven ultrafast demagnetization. Guided by theory, we predict that turbulence and modulational instabilities will drive the formation of solitons, including dispersive shock waves, magnon droplets, and skyrmions. In the case of topological defect formation, i.e. skyrmion generation, related processes have long been predicted based on general principles of symmetry-breaking phase transitions; the density of topological defects in a long-range-ordered phase can be controlled by varying the quench rate through the second-order phase transition, i.e. the Kibble-Zurek (KZ) mechanism. We, more broadly, had the goal to study a range of other emergent magnetic behaviors after optical excitation. While great attention has been given to ultrafast demagnetization, less is known of the subsequent spin dynamics and coupling to the lattice. What is increasingly appreciated is that ultrafast demagnetization leads to spin currents that can carry angular momentum from the rapidly demagnetized sample. These spin currents appear in many ways but fundamentally controls demagnetization, drives interactions between regions of the material, and control the spin resulting structure. They can be probed many ways including THz emission which, in turn, gives insight into the demagnetization processes. Simultaneously if there is magneto-elastic coupling ultrafast demagnetization can drive structural excitations that are not expected from thermal energy added to the lattice. We explored a range of complex phenomena that arise from photo-excitation of magnetic systems with the coupling of electronic, magnetic and structural degrees of freedom. We have made a number of fundamental discoveries that are reflected in our publications list with additional work still being prepared for publication. Highlights of this work include (i) ultra-efficient, nonlinear THz surface acoustics (ii) spin-current-mediated rapid magnon localization and coalescence, (iii) spin-wave soliton formation in ferromagnetic FePt nanoparticles, (iv) dynamic phonon coupling in elemental antiferromagnetic Cr, (v) THz emission from Co/Pt bilayers and FeRh/Pt bilayers, (vi) theoretical investigation of spin hydrodynamics, solitons and shock waves, and (vii) ultrafast perturbation of magnetic domains by optical pumping.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure

As circuitry approaches single nanometer length scales, it has become important to predict the stability of single nanometer-sized metals. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at single nanometer dimensions. Here, we report the formation of dislocations within individual 3.9 nm Au nanocrystals under nonhydrostatic pressure in a diamond anvil cell. We used a combination of x-ray diffraction, optical absorbance spectroscopy, and molecular dynamics simulation to characterize the defects that are formed, which were found to be surface-nucleated partial dislocations. These results indicate that dislocations are still active at single nanometer length scales and can lead to permanent plasticity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Reactive Species and Reaction Pathways for the Oxidative Cleavage of 4-Octene and Oleic Acid with H 2 O 2 over Tungsten Oxide Catalysts

The oxidative cleavage of carbon-carbon double bonds (C=C) in alkenes and fatty acids produces aldehydes and acids valued as chemical intermediates. Solid tungsten oxide catalysts are low cost, non-toxic, and selective for the oxidative cleavage of C=C bonds with hydrogen peroxide (H 2 O 2 ) and are, therefore, a promising option for continuous processes. Despite the relevance of these materials, the elementary steps involved and their sensitivity to the form of W sites present on surfaces have not been described. In this work, we combine in situ spectroscopy and rate measurements to identify significant steps in the reaction, the reactive species present on catalysts, and examine differences between the kinetics of this reaction on isolated W atoms grafted to alumina and on those exposed on crystalline WO 3 nanoparticles. Raman spectroscopy shows that W-peroxo complexes (W-(η 2 -O 2 ) formed from H 2 O 2 ) react in a kinetically relevant step to produce epoxides, which undergo hydrolysis at protic surface sites. Subsequently, the CH 3 CN solvent deprotonates diols to form alpha hydroxy ketones that react to form aldehydes and water following nucleophilic attack of H 2 O 2 . Turnover rates for oxidative cleavage, determined by in situ site titrations, on WO x -Al 2 O 3 are 75% greater than those on WO 3 at standard conditions. These differences reflect activation enthalpies (ΔH ‡ ) for oxidative cleavage of 4-octene that are much lower for the isolated WO x sites (36±3 and 60±6 kJ∙mol -1 for WO x -Al 2 O 3 and WO 3 , respectively) and correlate strongly with the difference between enthalpies of adsorption for epoxyoctane (ΔH ads,epox ), which resembles the transition state for epoxidation. The WO x -Al 2 O 3 catalysts mediate oxidative cleavage of oleic acid with H 2 O 2 following a mechanism comparable to that for 4-octene. The WO 3 materials, however, form only the epoxide and do not cleave the C-C bond or produce aldehydes and acids. These differences reflect the distinct site requirements for these reaction pathways and indicate that acid sites required for diol formation are strongly inhibited by oleic acids and epoxides on WO 3 whereas the Al 2 O 3 support provides sites competent for this reaction and increase the yield of the oxidative cleavage products.

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

Semiconductor nanocrystal photocatalysis for the production of solar fuels

Colloidal semiconducting nanocrystals (NCs) are powerful elements of a photocatalytic system useful for enabling a variety of chemical transformations owing to their strong light-absorbing properties and high degree of size-, shape-, and composition-tunability. Key to their utility is our understanding of the photoinduced charge transfer processes required for these photochemical transformations. This Perspective will focus on the implementation of semiconductor NCs for photochemical fuel formation. Three general system designs for photocatalytic proton reduction using semiconductor NCs will be reviewed: metal–semiconductor heterostructures, NC photosensitizers with molecular catalysts, and hydrogenase-based systems. Additionally, other relevant reactions toward solar fuel targets, such as CO 2 and N 2 reductions with NCs, will also be highlighted. Illustrating the versatile roles that NCs can play in light-driven chemical reactions, advances made toward NC-catalyzed organic transformations will be discussed. Finally, we will share a few concluding thoughts and perspectives on the future of the field, with a focus on goals toward improving and implementing NC-based technologies for solar fuel development.

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

The role of manganese in CoMnO x catalysts for selective long-chain hydrocarbon production via Fischer-Tropsch synthesis

Cobalt is an efficient catalyst for Fischer–Tropsch synthesis (FTS) of hydrocarbons from syngas (CO + H 2 ) with enhanced selectivity for long-chain hydrocarbons when promoted by Manganese. However, the molecular scale origin of the enhancement remains unclear. Here we present an experimental and theoretical study using model catalysts consisting of crystalline CoMnO x nanoparticles and thin films, where Co and Mn are mixed at the sub-nm scale. Employing TEM and in-situ X-ray spectroscopies (XRD, APXPS, and XAS), we determine the catalyst’s atomic structure, chemical state, reactive species, and their evolution under FTS conditions. We show the concentration of CH x , the key intermediates, increases rapidly on CoMnO x , while no increase occurs without Mn. DFT simulations reveal that basic O sites in CoMnO x bind hydrogen atoms resulting from H 2 dissociation on Co 0 sites, making them less available to react with CH x intermediates, thus hindering chain termination reactions, which promotes the formation of long-chain hydrocarbons.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding the Importance of Labile Fe(III) during Fe(II)-Catalyzed Transformation of Metastable Iron Oxyhydroxides

Transformation of metastable Fe(III) oxyhydroxides is a prominent process in natural environments and can be significantly accelerated by the coexisting aqueous Fe(II) (Fe(II) aq ). Recent evidence points to the solution mass transfer of labile Fe(III) (Fe(III) labile ) as the primary intermediate species of general importance. However, a mechanistic aspect that remains unclear is the dependence of phase outcomes on the identity of the metastable Fe(III) oxyhydroxide precursor. Here, we compared the coupled evolution of Fe(II) species, solid phases, and Fe(III) labile throughout the Fe(II)-catalyzed transformation of lepidocrocite (Lp) versus ferrihydrite (Fh) at equal Fe(III) mass loadings with 0.2–1.0 mM Fe(II) aq at pH = 7.0. Similar to Fh, the conversion of Lp to product phases occurs by a dissolution–reprecipitation mechanism mediated by Fe(III) labile that seeds the nucleation of products. Though for Fh we observed a transformation to goethite (Gt), accompanied by the transient emergence and decline of Lp, for initial Lp we observed magnetite (Mt) as the main product. Further, a linear correlation between the formation rate of Mt and the effective supersaturation in terms of Fe(III) labile concentration shows that Fe(II)-induced transformation of Lp into Mt is governed by the classical nucleation theory. When Lp is replaced by equimolar Gt, Mt formation is suppressed by opening a lower barrier pathway to Gt by heterogeneous nucleation and growth on the added Gt seeds. The collective findings add to the mechanistic understanding of factors governing phase selections that impact iron bioavailability, system redox potential, and the fate and transport of coupled elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

The effect of varying powder feedstock chemistry and printing atmosphere on the microstructure of additively manufactured nickel-based ODS alloys: Role on stabilization of cellular structures vs. oxide dispersion formation

Nickel-based alloys have a wide variety of structural applications due to their high corrosion resistance and mechanical strength which depend on solid solution strengthening, or the formation of oxides and/or intermetallic precipitation for their properties. In this study, the microstructure of six Ni–Cr–Y–Ti–Al powder batches designed for the production of oxide dispersion strengthened nickel were compared. These batches varied in chemistry and atomization technique used which included Gas Atomization Reactive Synthesis (GARS). The batches of powder were then consolidated via Additive Manufacturing (AM) Powder Bed Fusion using Laser Beam (PBF-LB) and characterized via transmission electron microscopy to elucidate the influence of powder feedstock (i.e. synthesis methodology and chemistry) on the PBF-LB microstructure. The study investigates (i) how the amount of yttrium and titanium additions in the powder feedstock and the addition of oxygen during the processing (through GARS) affect the microstructure of the powder itself and the AM printed microstructure, and (ii) how the control of oxygen addition in the printing atmosphere during the PBF-LB printing process itself is another important parameter for achieving the formation of the wanted oxide dispersion versus the stabilization of the cellular structure (often observed in AM processed alloys). Microstructural characterization of both powder particles and additively manufactured nickel alloys in this study provide important insights into the movement of yttrium within the material upon solidification, particularly along cell boundaries, and how yttrium behaves depending on alloy chemistry. When a threshold of yttrium content is reached within the system, yttrium consistently reacts to form an intermetallic along cell boundaries instead of forming oxide nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Continuous Encodable Reshaping of Gold Nanocrystals through Facet Modulation

Shape control of nanocrystals (NCs) is crucial for tuning their assembly behavior and functional properties, yet the precise manipulation of facet composition remains challenging. Here, we present a nanocrystal reshaping strategy to control and modulate the facets of gold (Au) NCs. Our one-pot approach, conducted at room temperature, requires only initial Au NCs, Au 3+ ions, and surfactants, distinguishing it from conventional reduction-mediated “etching-and-regrowth” methods. Detailed structural studies using electron microscopy, small-angle X-ray scattering (SAXS), and UV−vis spectroscopy reveal the surfactant-encoded pathway for NC transformation from shaped particles to spheres and then into various polyhedral shapes while preserving the individual particles' volume. The proposed reshaping mechanism involves the dissolution of surface Au atoms into Au + complexes in the presence of Au 3+ and surfactant, followed by surfactant-guided redeposition and formation of facets with different atomic planes. Using the ethanol oxidation reaction (EOR) as a probe, we observe a quasi-linear decrease in onset potential and an increase in activity with increasing {100} facet exposure. This work broadens synthetic strategies by offering precise NC reshaping and facet control.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Resolving protein-mineral interfacial interactions during in vitro mineralization by atom probe tomography

Organic macromolecules exert remarkable control over the nucleation and growth of inorganic crystallites during (bio)mineralization, as exemplified during enamel formation where the protein amelogenin regulates the formation of hydroxyapatite (HAP). However, it is poorly understood how fundamental processes at the organic-inorganic interface, such as protein adsorption and/or incorporation into minerals, regulates nucleation and crystal growth due to technical challenges in observing and characterizing mineral-bound organics at high-resolution. Here, atom probe tomography techniques were developed and applied to characterize amelogenin-mineralized HAP particles in vitro, revealing distinct organic-inorganic interfacial structures and processes at the nanoscale. Specifically, visualization of amelogenin across the mineralized particulate demonstrates protein can become entrapped during HAP crystal aggregation and fusion. Identification of protein signatures and structural interpretations were further supported by standards analyses, i.e., defined HAP surfaces with and without amelogenin adsorbed. These findings represent a significant advance in the characterization of interfacial structures and, more so, interpretation of fundamental organic-inorganic processes and mechanisms influencing crystal growth. Ultimately, this approach can be broadly applied to inform how potentially unique and diverse organic-inorganic interactions at different stages regulates the growth and evolution of various biominerals.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unraveling the Intermediate Reaction Complexes and Critical Role of Support-Derived Oxygen Atoms in CO Oxidation on Single-Atom Pt/CeO 2

CeO 2 -supported Pt single-atom catalysts have been extensively studied due to their relevance in automobile emission control and for the fundamental understanding of CeO 2 -based catalysts. Though CeO 2 -supported Pt nanoparticles are often more active than their single-atom counterparts, the former could easily redisperse to Pt single atom under oxidizing diesel conditions. Therefore, to maximize the reactivity of every Pt atom, it is important to fully understand the reaction mechanism of CeO 2 -supported Pt single atoms. Here, we report a CO oxidation study on a Pt/CeO 2 single-atom catalyst, where we can account for all of the neighbors using in situ and operando spectroscopy techniques and microcalorimetric measurements. Coupled with density functional theory calculations, we present a comprehensive picture of the dynamics of the surface species, the role of surface intermediates, and explain the observed reaction kinetics. We started with a catalyst containing exclusively single atoms and used in situ/operando spectroscopy to provide evidence for their stability during the reaction and to identify the Pt 1 complexes before and during the reaction and their binding to CO. The results reveal that in the precatalyst, Pt is present as Pt(O) 4 on the CeO 2 (111) step edge sites, but during CO oxidation, we find that two Pt 1 complexes coexist, representing two states of the same active site in the reaction cycle. The dominant state/complex remains Pt(O) 4 , which adsorbs CO very weakly as shown by CO microcalorimetry. The second, minority state/complex, Pt(CO)(O) 3 is generated through the reaction of Pt(O) 4 with CO, and CO is bound strongly to Pt 1 . Labile oxygen adatoms from the CeO 2 surface play a major role in the regeneration of Pt(O) 4 either directly from Pt(O) 3 or by reaction with the strongly adsorbed CO in Pt(CO)(O) 3 . We show that the formation of an oxygen vacancy and generation of a labile O* are not barrierless, which explains the long lifetime of Pt(CO)(O) 3 and its detectability despite being a minority complex. The results help to develop a comprehensive view of the dynamic evolution of Pt 1 complexes along the reaction cycle and provide mechanistic insights to guide the design of Pt-based single-atom catalysts.

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

Strong Coupling Between Plasmons and Molecular Excitons in Metal–Organic Frameworks

This Letter describes strong coupling of densely packed molecular emitters in metal–organic frameworks (MOFs) and plasmonic nanoparticle (NP) lattices. Porphyrin-derived ligands with small transition dipole moments in an ordered MOF film were grown on Ag NP arrays. Angle-resolved optical measurements of the MOF-NP lattice system showed the formation of a polariton that is lower in energy and does not cross the uncoupled MOF Q 1 band. Modeling predicted the upper polariton energy and a calculated Rabi splitting of 110 meV. The coupling strength was systematically controlled by detuning the plasmon energy by changing the refractive index of the solvents infiltrating the MOF pores. Through transient absorption spectroscopy, we found that the lower polariton decays quickly at shorter time scales (<500 ps) and slowly at longer times because of energy transfer from the upper polariton. Furthermore, this hybrid system demonstrates how MOFs can function as an accessible excitonic material for polariton chemistry.

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

Supramolecular Effects of Alkyl Sulfonates in Silver Nanocrystal Synthesis

While cationic surfactants such as hexadecyltrimethylammonium bromide (CTAB) are ubiquitous in the synthesis of noble metal nanocrystals, anionic surfactants are rarely used. This work explores the addition of sodium alkyl sulfonates with chain lengths ranging from one to eight carbons to a silver nanoplatelet reaction. Short-chain sulfonates comprised of one to four carbons show little effect on the nanocrystal synthesis, but alkyl sulfonates comprised of five or more carbons at concentrations above 1 mM have a pronounced effect on the absorbance of the nanocrystals, causing a blueshift in the wavelength of maximum absorbance (λ max ) from approximately 800 to 400 nm as the sulfonate concentration is increased to 7 mM. Higher concentrations of sulfonate result in a subsequent red-shift of the peak. Investigation into the possible formation mechanisms responsible for this synthetic control revealed the absence of sulfonate micelles under the reaction conditions. Instead, we hypothesize that sulfonate bilayers are nucleated around the silver nanocrystals at concentrations below the critical micelle concentration and interact with either the citrate ligands or the silver surface to influence nanocrystal morphology, and thus absorbance. Strikingly, the addition of long-chain alkyl sulfonates to already-synthesized nanocrystals results in similar changes to the nanocrystal absorbance that occur within seconds, providing further support for the proposal that these effects are related to the surface chemistry of the nanocrystals, which appear to be highly dynamic.

alkyls↗
DOE OSTI2020

The Role of Secondary Particle Structures in Surface Phase Transitions of Ni-Rich Cathodes

Nanometer-thick reconstruction layers on layered cathode surfaces have been widely observed on both pristine and cycled materials. However, the mechanisms of reconstruction and the role that these structures play in electrochemical performance are not fully understood. From a crystallographic perspective, such surface reconstruction layers result from cation site-mixing between Li and transition-metal ions, but it remains far from clear as to what the critical factors are that control such cation mixing for various cathode chemistries. In this paper, we report observations on surface transformations during cycling of a Ni-rich cathode-oxide that are governed by direct contact with the liquid electrolyte. Specifically, within a secondary particle, the three-dimensional hierarchical aggregate of primary particles leads to the formation of grain boundaries of different characteristics, including open grain boundaries that allow the permeation of liquid electrolyte, and closed grain boundaries that exclude liquid electrolyte penetration. Upon battery cycling, surfaces in direct contact with the liquid electrolyte showed a surface reconstruction layer while the surfaces that did not have contact with the electrolyte showed no such reconstructions. In addition, the critical role of oxygen in reconstruction of grain boundaries is demonstrated, and the unexpected oxygen depletion at twin boundaries result in severe phase transitions. The present work provides further insights into phase transitions at solid-solid and solid-liquid interfaces within secondary cathode particles and suggests strategies for mitigating surface/interfacial degradation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Semi-grand canonical Monte Carlo simulation of the acrolein induced surface segregation and aggregation of AgPd with machine learning surrogate models

The single atom alloy of AgPd has been found to be a promising catalyst for the selective hydrogenation of acrolein. It is also known that the formation of Pd islands on the surface will greatly reduce the selectivity of the reaction. As a result, the surface segregation and aggregation of Pd on the AgPd surface under reaction conditions of selective hydrogenation of acrolein are of great interest. In this work, we lay out a workflow that can predict the surface segregation and aggregation of Pd on a FCC(111) AgPd surface with and without the presence of acrolein. We use machine learning surrogate models to predict the AgPd bulk energy, AgPd slab energy, and acrolein adsorption energy on AgPd slabs. Then, we use the semi-grand canonical Monte Carlo simulation to predict the surface segregation and aggregation under different bulk Pd concentrations. Under vacuum conditions, our method predicts that only trace amount of Pd will exist on the surface at Pd bulk concentrations less than 20%. However, with the presence of acrolein, Pd will start to aggregate as dimers on the surface at Pd bulk concentrations as low as 6.5%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Self-Healing Nanocomposites for Reusable Composite Cryotanks

Composite cryotanks, or composite overwrapped pressure vessels (COPVs), offer advantages over currently used aluminum-lithium cryotanks, particularly with respect to weight savings. Future NASA missions are expected to use COPVs in spaceflight propellant tanks to store fuels, oxidizers, and other liquids for launch and space exploration vehicles. However, reliability, reparability, and reusability of the COPVs are still being addressed, especially in cryogenic temperature applications; this has limited the adoption of COPVs in reusable vehicle designs. The major problem with composites is the inherent brittleness of the epoxy matrix, which is prone to microcrack formation, either from exposure to cryogenic conditions or from impact from different sources. If not prevented, the microcracks increase gas permeation and leakage. Accordingly, materials innovations are needed to mitigate microcrack damage, and prevent damage in the first place, in composite cryotanks. The self-healing technology being developed is capable of healing the microcracks through the use of a novel engineered nanocomposite, where a uniquely designed nanoparticle additive is incorporated into the epoxy matrix. In particular, this results in an enhancement in the burst pressure after cryogenic cycling of the nanocomposite COPVs, relative to the control COPVs. Incorporating a novel, self-healing, epoxy-based resin into the manufacture of COPVs allows repeatable self-healing of microcracks to be performed through the simple application of a low-temperature heat source. This permits COPVs to be reparable and reusable with a high degree of reliability, as microcracks will be remediated. The unique phase-separated morphology that was imparted during COPV manufacture allows for multiple self-healing cycles. Unlike single-target approaches where one material property is often improved at the expense of another, robustness has been introduced to a COPV by a combination of a modified resin and nanoparticle additives. Unique nanoparticles were used that have been surface-functionalized to be compatible with the resin. Both organic and inorganic components toughen the matrix and result in a more impact-resistant COPV. In one resin system containing an inorganic nanomaterial additive, a significant improvement in burst performance was observed after the COPV was cryo-impact-damaged and then self-healed, with a greater than 10% improvement in burst pressure after the self-healing process was performed. Initial cross-sectional analysis via microscopy showed good resin infiltration of the carbon fibers and without voids. To further enhance the capability between the nanomaterial additives and the resin, a surface modification was successfully performed. A second specialty epoxy resin was prepared using a surface modified nanomaterial additive, and COPVs were fabricated. Steps were taken to improve the mechanical properties of the COPVs by using a low-viscosity resin system that contained a different curing agent. This lower viscosity improves the processing of the COPV, and preliminary results show that the burst pressure of these new vessels is 20 to 25% higher than that of the original. The self-healing concept demonstrated in this research and development effort represents a platform technology, and the self-healing property is neither restricted to the particular epoxy system used here, nor to the COPV application. Self-healing is a direct result of a unique phase separated morphology created via the resin and is aided by the nanoparticles. The self-healing function can be introduced to other customer-specific resin systems in coating, bulk, or composite applications provided that the unique phase separated morphology can be enabled in those systems.

Eberly, Daniel↗
DOE OSTI2020

A general mechanism for gel layer formation on borosilicate glass under aqueous corrosion

Mineral and glass dissolution is a scientific topic deeply investigated but incompletely understood and of a great interest for the geochemical and materials science communities. If the interfacial dissolution/reprecipitation mechanism seems to be applicable to most of silicate minerals, the debate remains open concerning glass. Here we studied two model glasses, a ternary borosilicate (CJ1) and the same glass doped with 4.1 mol% of Al2O3 (CJ2). The two glasses were altered at 90°C, pH 9, and in conditions far and close to saturation with respect to amorphous silica, to determine the initial and residual rates. Moreover, a specific experiment was conducted for a short duration with a solution highly enriched with 18O and 29Si isotopes to understand how passivating gels form. SEM, TEM and ToF-SIMS characterization, along with Monte Carlo simulations were used to understand the rate limiting reactions at play and infer the role of Al. We show that Al yields a slower matrix dissolution in dilute conditions. However, it slows down he formation and the maturation of the passivating gel and favors alteration by partial hydrolysis of Si and Al entities followed by in-situ reorganization/relaxation into a porous network. Unexpectedly, CJ1 experienced both interfacial dissolution/reprecipitation and partial hydrolysis followed by in situ reorganization of the silicate network during the course of a single experiment. This study offers a unified concept that can pave the way for the future development of a predictive kinetic model based on a detailed description of bond breaking and bond forming as a function of glass composition and alteration conditions.

Gin, Stephane↗