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Results for “surface functionalization”

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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Probabilistic #D data fusion for multiresolution surface generation

In this paper we present an algorithm for adaptive resolution integration of 3D data collected from multiple distributed sensors. The input to the algorithm is a set of 3D surface points and associated sensor models. Using a probabilistic rule, a surface probability function is generated that represents the probability that a particular volume of space contains the surface. The surface probability function is represented using an octree data structure; regions of space with samples of large conariance are stored at a coarser level than regions of space containing samples with smaller covariance. The algorithm outputs an adaptive resolution surface generated by connecting points that lie on the ridge of surface probability with triangles scaled to match the local discretization of space given by the algorithm, we present results from 3D data generated by scanning lidar and structure from motion.

3D data fusion multiresolution surface generation ↗
DOE OSTI2021

Strategies for Post-Synthetic Functionalization of Mesoporous Carbon Nanomaterial Surfaces

Most widely used carbon-based materials feature a bulk framework tolerant of extreme pH and temperature conditions while maintaining physical robustness, electrical conductivity, and biological relevance due to its inherent nontoxicity. At the nanoscale, the study of porous carbons has been of interest because of the enhanced accessible surface area relative to nonporous analogues. The evolution of synthetic techniques has developed structural allotropes with tunable internal pore diameter averages spanning from sub-nanometer to micron-plus sizes. Within the mesopore range, surface chemical phenomena abide by a kinetic-limited ruleset (ignoring the effects of bulk diffusion, as they do not pertain to this size regime). Further, mesopores provide sufficient volume and surface area for hosting guest species, including metal nanoparticles (MNP), polymers, small organics, and enzymes. These two unique features of mesoporous carbon (MC) drive interest in surface modifications to create new physicochemical functionality to these systems and their hosted species. As a result, the evolution of surface modification techniques has been scattered to disparate niches across the literature. This review compiles the array of elegant methods by which these carbon systems are topically engineered.

functionalization↗
NASA NTRS1974

A note on the annual cycles of surface heat balance and temperature over a continent

A surface heating function, defined as the ratio of the time derivative of the mean annual temperature curve to the surface heat balance, is computed from the annual temperature range and heat balance data for the North American continent. An annual cycle of the surface heat balance is then reconstructed from the surface heating function and the annual temperature curve, and an annual cycle of evaporative plus turbulent heat loss is recomputed from the annual cycles of radiation balance and surface heat balance for the continent. The implications of these results for long range weather forecasting are discussed.

Spar, J.↗
NASA NTRS1987

High-surface-area, dual-function oxygen electrocatalysts for space power applications

The processes of hydration/dehydration and carbonation/decarbonation are investigated as an approach to provide higher surface area mixed metal oxides that are more active electrochemically. These materials are candidates for use as electrocatalysts and electrocatalyst supports for alkaline electrolyzers and fuel cells. For the case of the perovskite, LaCoO3 , higher surface areas were achieved with no change in structure and a more active oxygen electrocatalyst.

Ham, David O.↗
DOE OSTI2022

Data–driven and constrained optimization of semi–local exchange and nonlocal correlation functionals for materials and surface chemistry

Reliable predictions of surface chemical reaction energetics require an accurate description of both chemisorption and physisorption. Herein, we present an empirical approach to simultaneously optimize semi-local exchange and nonlocal correlation of a density functional approximation to improve these energetics. A combination of reference data for solid bulk, surface, and gas-phase chemistry and physical exchange-correlation model constraints leads to the VCML-rVV10 exchange-correlation functional. Owing to the variety of training data, the applicability of VCML-rVV10 extends beyond surface chemistry simulations. It provides optimized gas phase reaction energetics and an accurate description of bulk lattice constants and elastic properties.

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

Adsorption Properties of Au−Ni Surface Alloys with a Nonstoichiometric Moiré Structure: A Density Functional Theory Study

Due to the large lattice mismatch between gold and nickel, gold–nickel surface alloys can form unique nonstoichiometric overlayer structures characterized by a moiré pattern and subsurface defects. For this work, we performed density functional theory (DFT) calculations to study the adsorption of molecular oxygen, atomic hydrogen, and atomic carbon on a gold–nickel(111) surface alloy with 0.46 monolayer gold randomly distributed in the surface layer. We observed six distinct adsorption structures for molecular oxygen characterized by intramolecular stretching frequencies of <700, 729, 795, 857, 929, and 1004 cm –1 , which describe well the experimentally observed high-resolution electron energy-loss spectra. Surface atomic hydrogen adsorption is associated with adsorbate–surface modes in the ∼1000 cm –1 range, while subsurface hydrogen can have features as low as ∼400 cm –1 . We observed a unique adsorption structure for atomic carbon inside the surface dislocation loop defect, which explains the experimentally observed low carbon-surface mode at ∼340 cm –1 . Our study sheds light on the unique adsorption properties of the gold–nickel surface alloys and helps with rationalizing vibrational frequency experimental studies for this system.

adsorption↗
DOE OSTI2021

Spot the difference: hydrogen adsorption and dissociation on unsupported platinum and platinum-coated transition metal carbides

Hydrogenation reactions are involved in several processes in heterogeneous catalysis. Platinum is the best-known catalyst; however, there are limitations to its practical use. Therefore, it is necessary to explore alternative materials and transition metal carbides (TMCs) have emerged as potential candidates. We explore the possibility of using cheap TMCs as supports for a Pt monolayer, aiming to reduce the amount of the noble metal in the catalyst without a significant loss of its activity towards H 2 dissociation. Hence, analyzing H 2 dissociation from a fundamental point of view is a necessary step towards a further practical catalyst. By means of periodic DFT calculations, we analyze H 2 adsorption and dissociation on Pt/β-Mo 2 C and Pt/α-WC surfaces, as a function of hydrogen surface coverage ( Θ H ), resembling a more realistic model of a catalyst. H 2 dissociation rates were analyzed as a function of the reaction temperature. Overall, the results show that Pt/C-WC and Pt/Mo-Mo 2 C have a Pt-like behavior for H 2 dissociation at Θ H > 1/2 ML. At a particular temperature of 298 K, Pt/C-WC and Pt/Mo-Mo2C have low energy barriers for H 2 * → 2H* (0.13 and 0.11 eV, respectively), close to the value of Pt (0.06 eV). For the highest coverage, i.e. Θ H = 1, Pt/C-WC has a lower activation energy and a higher reaction rate than Pt. Finally, the H 2 dissociation rate is higher in Pt/Mo-Mo 2 C than in Pt when increasing the temperature above 298 K. Our results put Pt/C-WC and Pt/Mo-Mo 2 C under the spotlight as potential catalysts for H 2 dissociation, with a similar performance to Pt, paving the way for further experimental and/or theoretical studies, addressing the capability of Pt/TMC as practical catalysts in hydrogenation reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Uncertainty Quantification and Error Propagation in the Enthalpy and Entropy of Surface Reactions Arising from a Single DFT Functional

Accounting for parametric uncertainty in models is essential for quantifying the models’ predictive ability. Recently, approaches have been introduced to estimate parametric uncertainty in kinetic models while accounting for correlations among energy parameters. However, correlations have been estimated indirectly and correlations in entropies have not been accounted for. For surface-catalyzed microkinetic models of >C2 (more than two carbon-containing) molecules, which consist of thousands of reaction steps and intermediate surface species, first-principles density functional theory (DFT) is costly, and thus, estimation of thermochemistry and reaction barriers requires surrogate methods of DFT, such as group additivity and Brønsted–Evans–Polanyi relationships, respectively. For such parametrization, model uncertainty is unclear. This work develops a framework to overcome these gaps using group additivity and a single DFT functional. We estimate correlations in parameters of kinetic models and quantify uncertainty for thermochemistry, reaction barriers, reaction paths, and ultimately reaction rates, accounting also for the contribution of entropic uncertainty. Furthermore, the approach is illustrated on propane combustion and ethane oxidative dehydrogenation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2001

Response Surface Modeling Using Multivariate Orthogonal Functions

A nonlinear modeling technique was used to characterize response surfaces for non-dimensional longitudinal aerodynamic force and moment coefficients, based on wind tunnel data from a commercial jet transport model. Data were collected using two experimental procedures - one based on modem design of experiments (MDOE), and one using a classical one factor at a time (OFAT) approach. The nonlinear modeling technique used multivariate orthogonal functions generated from the independent variable data as modeling functions in a least squares context to characterize the response surfaces. Model terms were selected automatically using a prediction error metric. Prediction error bounds computed from the modeling data alone were found to be- a good measure of actual prediction error for prediction points within the inference space. Root-mean-square model fit error and prediction error were less than 4 percent of the mean response value in all cases. Efficacy and prediction performance of the response surface models identified from both MDOE and OFAT experiments were investigated.

Morelli, Eugene A.↗
NASA NTRS2010

Highly porous and mechanically strong ceramic oxide aerogels

Structurally stable and mechanically strong ceramic oxide aerogels are provided. The aerogels are cross-linked via organic polymer chains that are attached to and extend from surface-bound functional groups provided or present over the internal surfaces of a mesoporous ceramic oxide particle network via appropriate chemical reactions. The functional groups can be hydroxyl groups, which are native to ceramic oxides, or they can be non-hydroxyl functional groups that can be decorated over the internal surfaces of the ceramic oxide network. Methods of preparing such mechanically strong ceramic oxide aerogels also are provided.

Leventis, Nicholas↗
NASA NTRS2012

Highly porous and mechanically strong ceramic oxide aerogels

Structurally stable and mechanically strong ceramic oxide aerogels are provided. The aerogels are cross-linked via organic polymer chains that are attached to and extend from surface-bound functional groups provided or present over the internal surfaces of a mesoporous ceramic oxide particle network via appropriate chemical reactions. The functional groups can be hydroxyl groups, which are native to ceramic oxides, or they can be non-hydroxyl functional groups that can be decorated over the internal surfaces of the ceramic oxide network. Methods of preparing such mechanically strong ceramic oxide aerogels also are provided.

Leventis, Nicholas↗
DOE OSTI2021

A universal and facile approach for building multifunctional conjugated polymers for human-integrated electronics

Polymer semiconductors have shown distinct promise for the development of human- integrated electronics, owing to their solution processability and mechanical softness. However, numerous functional properties required for this application domain face synthetic challenges to be imparted onto conjugated polymers and thus combined with efficient charge- transport property. Here, we develop a “click-to-polymer” (CLIP) synthesis strategy for conjugated polymers, which uses a click reaction for the facile and versatile attachment of diverse types of functional units to a pre-synthesized conjugated-polymer precursor. With four types of functional groups, we show that functionalized polymers from this CLIP method can still retain good charge-carrier mobility. Here, we take two realized polymers to showcase the photo-patternable property and biochemical sensing function, both of which advance the state of the art of realizing these two types of functions on conjugated polymers. We expect the expanded use of this synthesis approach can largely enrich the functional properties from conjugated polymers.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Possible temperature variation effects on the interpretation of spatially resolved reflectance observations of asteroid surfaces

In virtue of the extent to which the visible and near-IR spectral reflectance of minerals that may be encountered on asteroid surfaces is a function of temperature, surface temperature distributions must be taken into account in the mineralogical evaluation of spectral reflectance data obtained from a spatially resolved asteroid surface. Possible errors of this type are presently illustrated for the case of a silicate mineral assemblage measured at the various temperatures that may be encountered over an asteroid surface, in order to allow optimal mineralogical data extraction.

Roush, Ted L.↗
DOE OSTI2021

“Flower-like” Li 4 Ti 5 O 12 -multiwalled carbon nanotube composite structures with performance as highrate anode-materials for li-ion battery applications and methods of synthesis thereof

A method of fabricating nanocomposite anode material embodying a lithium titanate (LTO)-multi-walled carbon nanotube (MWNT) composite intended for use in a lithium-ion battery includes providing multi-walled carbon nanotube (MWNTs), including nanotube surfaces, onto which functional oxygenated carboxylic acid moieties are arranged, generating 3D flower-like, lithium titanate (LTO) microspheres, including thin nanosheets and anchoring the acid-functionalized MWNTs onto surfaces of the 3D LTO microspheres by π-π interaction strategy to realize the nanocomposite anode material.

25 ENERGY STORAGE↗
DOE OSTI2024

“Flower-like” LI 4 TI 5 O 12 -multiwalled carbon nanotube composite structures with performance as highrate anode-materials for Li-ion battery applications and methods of synthesis thereof

A method of fabricating nanocomposite anode material embodying a lithium titanate (LTO)-multi-walled carbon nanotube (MWNT) composite intended for use in a lithium-ion battery includes providing multi-walled carbon nanotube (MWNTs), including nanotube surfaces, onto which functional oxygenated carboxylic acid moieties are arranged, generating 3D flower-like, lithium titanate (LTO) microspheres, including thin nanosheets and anchoring the acid-functionalized MWNTs onto surfaces of the 3D LTO microspheres by π-π interaction strategy to realize the nanocomposite anode material.

Wong, Stanislaus S.↗