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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Compositional and Thermal Characterization of Potential Nano-Carbon Copper Composite

Covetic materials have been claimed to be new types of metal matrix nano-composite materials. These materials are formed from face-centered-cubic metals which are alleged to be super-saturated with up to ~ 10 wt pct of activated nano-carbon. The focus of this study was to characterize the chemical composition of copper covetic materials of varying nano-carbon concentrations, and characterize the thermal properties of these materials in order to determine if these materials exhibit enhanced material properties.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Platelet composite coatings for tin whisker mitigation

In this study, reliable methods for tin whisker mitigation are needed for applications that utilize tin-plated commercial components. Tin can grow whiskers that can lead to electrical shorting, possibly causing critical systems to fail catastrophically. The mechanisms of tin whisker growth are unclear and this makes prediction of the lifetimes of critical components uncertain. The development of robust methods for tin whisker mitigation is currently the best approach to eliminating the risk of shorting. Current mitigation methods are based on unfilled polymer coatings that are not impenetrable to tin whiskers. In this paper we report tin whisker mitigation results for several filled polymer coatings. The whisker-penetration resistance of the coatings was evaluated at elevated temperature and high humidity and under temperature cycling conditions. The composite coatings comprised Ni and MgF 2 -coated Al/Ni/Al platelets in epoxy resin or silicone rubber. In addition to improved whisker mitigation, these platelet composites have enhanced thermal conductivity and dielectric constant compared with unfilled polymers.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Material processing, microstructure, and composite properties of low carbon Engineered Cementitious Composites (ECC)

Traditional PVA fiber-reinforced Engineered Cementitious Composites (ECC) show high tensile ductility and superior durability with tight crack width, but the high cost and embodied carbon can hinder its wider application in infrastructures. The objective of this study is to develop a better understanding of the fresh and hardened properties of an ECC that employs a lower embodied-carbon binder, Limestone Calcined Clay Cement (LC3), and lower-cost PP fiber that is widely available. Specifically, the interrelations between material processing, microstructure, and composite properties were studied experimentally. The results showed that ECC with high tensile ductility up to 9% tensile strain and tight crack width with 50 μm at 2% tensile strain can be achieved. It was found that a matrix paste with higher viscosity generally enhanced fiber dispersion uniformity and robustness in tensile strain-hardening. The paste viscosity is increased when OPC is replaced by LC3 and can be tuned with superplasticizer content. Larger maximum flaw size leads to lower first crack strength, beneficial for microcrack initiation and multiple cracking. This study generates fundamental knowledge linking processing-microstructure-performance of PP-LC3-ECC. This class of low embodied carbon ECC with tight crack width is expected to contribute to reducing the carbon footprint of the built environment.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Improving microstructure of silicon/carbon nanofiber composites as a Li battery anode

We report the interfacial study of a silicon/carbon nanofiber (Si/CNF) nanocomposite material as a potentially high performance anode for rechargeable lithium ion batteries. The carbon nanofiber is hollow, with a graphitic interior and turbostratic exterior. Amorphous silicon layers were uniformly coated via chemical vapor deposition on both the exterior and interior surfaces of the CNF. The resulting Si/CNF composites were tested as anodes for Li ion batteries and exhibited capacities near 800 mAh g1 for 100 cycles. After cycling, we found that more Si had fallen off from the outer wall than from the innerwall of CNF. Theoretical calculations confirmed that this is due to a higher interfacial strength at the Si/Cedge interface at the inner wall than that of the Si/C-basal interface at the outer wall. Based upon the experimental analysis and theoretical calculation, we have proposed several interfacial engineering approaches to improve the performance of the electrodes by optimizing the microstructure of this nanocomposite.

Howe, Jane Y↗
DOE OSTI2024

Mild chemical recycling of carbon fiber-reinforced epoxy composites in aqueous buffers and development of hydrothermally recyclable vitrimer composites from recyclates

Carbon fiber-reinforced polymer (CFRP) composites have gained widespread adoption across diverse industries. However, their inherent stability, stemming from the crosslinked structure of the matrix resin, poses a significant challenge in managing the growing volume of CFRP waste. Consequently, there is a pressing need for an eco-friendly upcycling method that effectively recovers and reuses both the valuable carbon fibers and the polymer matrix from CFRP waste. This study presents a novel approach for upcycling CFRP waste under environmentally friendly conditions. Firstly, CFRP waste with an amine-cured epoxy matrix was completely decomposed in aqueous buffer solutions under mild conditions (≤ 220 °C, pH = 4.8). Further, decomposed matrix polymer (DMP) was employed to transform conventional epoxy resins into recyclable vitrimers. Lastly, new composites that can be hydrothermally recycled were fabricated using both DMP and recovered carbon fibers. As a result, this work proposes a novel strategy for achieving a circular economy within the CFRP industry.

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

Nanophotonic Atomic Force Microscope Transducers Enable Chemical Composition and Thermal Conductivity Measurements at the Nanoscale [Nanophotonic AFM Transducers Enable Chemical Composition and Thermal Conductivity Measurements at the Nanoscale]

The atomic force microscope (AFM) offers a rich observation window on the nanoscale, yet many dynamic phenomena are too fast and too weak for direct AFM detection. Integrated cavity-optomechanics is revolutionizing micromechanical sensing; however, it has not yet impacted AFM. Here, we make a groundbreaking advance by fabricating picogram-scale probes integrated with photonic resonators to realize functional AFM detection that achieve high temporal resolution (<10 ns) and picometer vertical displacement uncertainty simultaneously. The ability to capture fast events with high precision is leveraged to measure the thermal conductivity (η), for the first time, concurrently with chemical composition at the nanoscale in photothermal induced resonance experiments. The intrinsic η of metal–organic-framework individual microcrystals, not measurable by macroscale techniques, is obtained with a small measurement uncertainty (8%). The improved sensitivity (50×) increases the measurement throughput 2500-fold and enables chemical composition measurement of molecular monolayer-thin samples. In conclusion, our paradigm-shifting photonic readout for small probes breaks the common trade-off between AFM measurement precision and ability to capture transient events, thus transforming the ability to observe nanoscale dynamics in materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

How Microstructure and Pore Moisture Affect Strength Gain in Portlandite-Enriched Composites That Mineralize CO 2

Binders containing portlandite (Ca(OH) 2 ) can take up carbon dioxide (CO 2 ) from dilute flue gas streams (<15% CO 2 , v/v), thereby forming carbonate compounds with binding attributes. While the carbonation of portlandite particulates is straightforward, it remains unclear how CO 2 transport into monoliths is affected by microstructure and pore moisture content. Therefore, this study elucidates the influences of pore saturation and CO 2 diffusivity on the carbonation kinetics and strength evolution of portlanditeenriched composites (“mortars”). To assess the influences of microstructure, composites hydrated to different extents and conditioned to different pore saturation levels (S w ) were exposed to dilute CO 2 . First, reducing saturation increases the gas diffusivity and carbonation kinetics so long as saturation exceeds a critical value (S w,c ≈ 0.10) independent of microstructural attributes. Second, careful analysis reveals that both traditional cement hydration and carbonation offer similar levels of strengthening, the magnitude of which can be estimated from the extent of each reaction. As a result, portlandite-enriched binders offer cementation performance that is similar to traditional materials while offering an embodied CO 2 footprint that is more than 50 % smaller. Furthermore, these insights are foundational to create new “low-CO 2 ” cementation agents via in situ CO 2 mineralization (utilization) using dilute CO 2 waste streams.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Carbohydrate composition of mucus from scleractinian corals from the central Red Sea

Coral mucus is continuously released by most corals and acts as an important protective barrier and as a substrate for host-associated microbial communities due to its complex composition of carbohydrates, lipids, and proteins. On a reef scale, coral mucus functions as a particle trap, thereby retaining nutrients and energy in the ecosystem. Given the distinct environmental conditions in the Red Sea (high temperature, high salinity, high total alkalinity), we sought to investigate the carbohydrate composition of mucus from five corals from the central Red Sea. Our aim was to assess whether mucus from Red Sea corals is different from what is known from other corals and whether those differences could be aligned to putative beneficial functions with regard to the prevailing environment. Using gas chromatography/mass spectrometry, we detected nine sugars as the main prevalent carbohydrates. Although we detected significant differences between species with regard to the relative abundance of given carbohydrates, the identified sugars resembled those found in mucus from corals elsewhere, and we could corroborate high abundance of arabinose in acroporid corals. Taken together, our results suggest the presence of a common set of carbohydrates across a broad range of coral species from geographically diverse environments, highlighting the important role of mucus with regard to coral and reef ecosystem function.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Effect of microalgae cell composition and size on responsiveness to ultrasonic harvesting

Ultrasonic harvesting could reduce the energy consumption and costs associated with separating microalgae from growth media. The responsiveness of microalgae cells to an ultrasonic standing wave depends on the cell radius and acoustic contrast factor (ACF). The ACF can vary as cell composition (e.g. lipid, protein, carbohydrate content) varies depending on the algae strain, cultivation conditions, and growth stage. Here, two independent experimental methods were used to characterize the ACF of three algae ;strains—Nannochloropsis salina, Chlamydomonas reinhardtii, and Tetraselmis chuii—as a function of dynamic cellular composition over 9- to 14-day growth periods. For N. salina, lipid content increased from 25 ± 1% to 33 ± 1% ash-free dry weight (AFDW) and ACF decreased by 46% (from 0.041 ± 0.002 to 0.022 ± 0.002) between growth days 3 and 10. For C. reinhardtii, lipid content increased from 26 ± 1% to 40 ± 1% AFDW and ACF decreased by 33% (from 0.051 ± 0.013 to 0.034 ± 0.006) between growth days 3 and 9. For T. chuii, lipid content and ACF remained stable (~ 10% AFDW and ~ 0.3) over the growth period. ACF decreased as lipid content increased because lipids have a negative ACF in the growth media; however, cell size had a greater impact on cell responsiveness because the ratio of the acoustic radiation force to the drag force is proportional to cell radius squared.

09 BIOMASS FUELS↗
DOE OSTI2018

Interactive Influence of Biofiber Composition and Elastomer on Physico-Mechanical Properties of PLA Green Composites

The objective of this work was to improve the impact and thermal properties of polylactic acid (PLA)-based biocomposite by appropriate application of cellulosic fiber and a bioelastomer. Biocomposites formulations with fiber contents of up to 20% in combination with a bioelastomer were extrusion-compounded in a twin-screw extruder followed by molding in an injection molding system. Fibers used in the formulations included three types of cellulosic fiber; namely, raw fiber from oat hull biomass (RF), hydrolysis byproduct (ATF) which was the solid fraction obtained from an acid-catalyzed hydrolysis of RF, and delignified fibers (AD30, AD65, AD100) which were the products of delignification of ATF. Formulated biocomposites were characterized for thermal (glass transition and melting temperatures, and enthalpy of melting) and physico-mechanical (tensile and bending strengths, stiffness, impact energy, and water absorption) properties. Among all types of biofibers, RF resulted in poor properties in the biocomposites due to the high hemicellulose content in the structure. On the other hand, the ratio of lignin to cellulose (in the absence of hemicellulose) in the modified fibers did not significantly affect the physico-mechanical and thermal properties of the biocomposites. The elastomer applied in the formulations improved the impact energy, thermal properties, and elongation at break of the composites. However, it adversely affected the strength and water resistance of biocomposites, especially in the presence of hemicellulose. The results indicated that, depending on the application, a wide range of PLA green composites with different physico-mechanical properties can be achieved.

09 BIOMASS FUELS↗
DOE OSTI2019

Manufacturing of a Metal Matrix Composite Coating on a Polymer Matrix Composite Through Cold Gas Dynamic Spray Technique

In this work, the manufacturing through cold gas dynamic spray (cold spray or CS) of metallic composite coatings of Al-Al{sub 2}O{sub 3} on organic composite substrates with thermoplastic PLA matrix and hemp fibers was studied. Alumina powders, with a mean diameter of 50 μm, were used blended with aluminum powders in three different weight concentration percentages (0, 15, 20, and 45%) as feedstock material in order to highlight and discuss the variations of the coating surface properties depending on the alumina percentage. The coatings were produced by using a low-pressure cold spray equipment. A detailed experimental campaign, including microstructural observations and confocal microscopy, was carried out to study the structure of the coatings. Moreover, the tribological behavior of the coatings was studied through both scratch test and pin-on-disk test. The experiments showed that a small addition of alumina improves the compactness of the coating and its resistance to scratch and wear behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2014

On the Composition of Bimetallic Near-Surface Alloys in the Presence of Oxygen and Carbon Monoxide

Periodic, self-consistent density functional theory calculations (GGA-PW91) are used to examine surface segregation in close-packed bimetallic Pt-overlayer alloy surfaces (Pt*/M, M = Au, Ag, Cu, Pd, Ir, Rh, Os, Ru, and Re) in different environments. In particular, we find that the thermodynamically stable surface termination in these Pt*/M alloys can be inverted from Pt-terminated in vacuum to M-terminated under exposure to oxygen (for an M that is more oxophillic than Pt). Interestingly, in many of these alloys, Pt is not driven into the bulk, rather it remains in the first subsurface layer where it enhances oxygen binding through a ligand interaction with the surface metal atoms. On the other hand, exposure to CO provides a much milder driving force for the surface composition inversion. To quantify segregation under catalytically relevant conditions, we constructed approximate phase diagrams for the PtRu system as a function of O2 and CO chemical potential (temperature, pressure). The results show that the surface termination inverts with many orders of magnitude higher CO pressure than with O2.

Environmental Molecular Sciences Laboratory↗