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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 OSTI2022

Microstructural and physicochemical origins of electroless copper deposition on graphite enhanced by acid pretreatment

We report Acid treatment is the most widely used surface modification method for enhancing the electroless metal deposition (EMD) on carbon reinforcement materials (CRMs) for metal matrix nanocomposites. However, specific microstructural and physicochemical origins of the enhanced EMD on carbon surfaces by acid treatments have been rarely studied. Here, we investigated the effects of the nitric acid treatment on graphite, a prototypical combination of acid treatment and CRM, on the fidelity of Cu EMD and their structural and chemical origins. Complementary materials characterizations and density functional theory calculations revealed the acid-induced formation of broken C–C/C=C graphitic bonds and resulting surface micropores on graphite; this enabled a uniform dispersion of catalytic Sn/Pd nanoparticles during pre-EMD sensitization/activation processes via spontaneous binding of Sn and Pd ions and, consequently, a much more uniform Cu layer EMD compared to the untreated graphite. We proposed a general mechanism illustrating how the acid-induced microstructural and chemical modifications of carbon surface affected the spatial uniformity of catalytic metal reduction during EMD and, finally, the quality of deposited metal layer. The results clearly reveal the origins of the enhanced EMD on carbon materials by acid treatments, providing guidelines for optimizing EMD on general CRMs for high-performance metal matrix nanocomposites.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structural characterization of sugarcane lignins extracted from different protic ionic liquid pretreatments

Previous studies based on protic ionic liquids have shown them to be effective for extracting lignins from biomass. Moreover, ILs synthesized with amine cations can promote the insertion of nitrogen into lignin, favoring its valorization for industrial applications. Here, lignins extracted from sugarcane bagasse by eight different PILs were analyzed. Several techniques of characterization were employed (2D HSQC NMR, 31P NMR, GPC, Py-GC/MS, TGA, FTIR, and elemental analysis), seeking a deeper understanding of lignin structure post-PILS treatment. In particular, lignin obtained with acetate and lactate anions with monoethanolamonium cations showed similar structural compositions. Lignins obtained from ethylenediamonium cation combined anions acetate and lactate exhibited relatively higher molecular weights compared to the other lignins studied. The elemental analysis of these lignins further revealed the presence of nitrogen in their structures, suggesting that amination occurred. In this work we used PILs not yet reported in the literature for this purpose, and consequently obtained lignins with specific structures. Overall, our results demonstrated that depending on the PILs used, lignins with distinct properties could be obtained which might be used for value-added applications. This work covered new advances in elucidation of lignin chemical structure and opened a new path for lignin valorization.

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

Study of the Hydrogen Pretreatment of Gallium and Platinum Promoted ZSM-5 for the Ethane Dehydroaromatization Reaction

Here, the performances of gallium and platinum promoted ZSM-5 catalysts, fresh and reduced, were studied for the dehydroaromatization of ethane to aromatics. Fresh and reduced 2% Ga/ZSM-5, 1.5% Ga–0.5% Pt/ZSM-5, and 0.5% Pt/ZSM-5 were tested in a fixed-bed reactor system at 615 °C for 2 h time on stream. It was observed that the hydrogen reduction of the fresh Pt-containing catalysts led to an increase in catalytic conversion. The addition of platinum to the gallium catalyst resulted in an increase in the reducibility of the Ga species on the surface of the zeolite. The GaPt catalysts exhibited an increase in ethane conversion and the stability of aromatic production selectivity over the Ga and Pt catalysts. The as-prepared fresh catalysts were characterized by ICP and BET methods. The fresh and reduced catalysts were further analyzed by XRD, H 2 -TPR, XPS, pyridine DRIFTS, TGA, and TEM.

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

Production of itaconic acid from alkali pretreated lignin by dynamic two stage bioconversion

Abstract Expanding the portfolio of products that can be made from lignin will be critical to enabling a viable bio-based economy. Here, we engineer Pseudomonas putida for high-yield production of the tricarboxylic acid cycle-derived building block chemical, itaconic acid, from model aromatic compounds and aromatics derived from lignin. We develop a nitrogen starvation-detecting biosensor for dynamic two-stage bioproduction in which itaconic acid is produced during a non-growth associated production phase. Through the use of two distinct itaconic acid production pathways, the tuning of TCA cycle gene expression, deletion of competing pathways, and dynamic regulation, we achieve an overall maximum yield of 56% (mol/mol) and titer of 1.3 g/L from p -coumarate, and 1.4 g/L titer from monomeric aromatic compounds produced from alkali-treated lignin. This work illustrates a proof-of-principle that using dynamic metabolic control to reroute carbon after it enters central metabolism enables production of valuable chemicals from lignin at high yields by relieving the burden of constitutively expressing toxic heterologous pathways.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Interfacial oxide and other species in trimethylaluminum-pretreated atomic layer deposition-Al 2 O 3 /GaN characterized by sputter-assisted ToF-SIMS

Deposition techniques, like atomic layer deposition (ALD), are used to form high-quality dielectrics for GaN-based metal–oxide–semiconductor (MOS) gate structures due to the lack of a reliable thermal oxide in GaN. Moreover, interfacial GaO x from pre-existing native oxides is thought to adversely impact channel carrier dynamics and induce undesired threshold voltage shifts in GaN-based MOS gate structures. Exposure of the GaN surface to the trimethylaluminum (TMA) precursor prior to standard alumina ALD decreases the native oxide layer on GaN, but the extent of chemical modification has not been well studied in the context of interface composition in a MOS gate structure. Herein, we compare annealed 55 nm Al 2 O 3 dielectric films on GaN grown using either a water-first ALD process or a process including sequential pulses of TMA immediately before the initiation of Al 2 O 3 ALD. Time-of-Flight Secondary Ion Mass Spectrometry measures differences in the interfacial GaO x content between each ALD film. Here, it also detects surface contaminant species like Si, F, S, and C. Furthermore, we report the formation of an AlN species at the Al 2 O 3 /GaN interface, which is more prominent for the film grown using the TMA pre-pulse step. In general, this work demonstrates that the TMA pre-pulse step is an effective strategy for cleaning substrate surfaces prior to ALD.

Atomic layer deposition↗