True active surface area as a key indicator of corrosion behavior in additively manufactured 316L stainless steel
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316L stainless steel↗
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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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Reference Surface Activities for Crewed Mars Mission Systems and Utilization
This presentation was made at the “COSPAR Planetary Protection Knowledge Gaps for Human Missions to Mars” virtual workshop. As the workshop title implies, the presentation is intended to explain basic features of current human Mars surface mission scenarios being analyzed by NASA. The specific scenario details described is documented in HEOMD-415 “Reference Surface Activities for Crewed Mars Mission Systems and Utilization.” Other workshop presentations will expand on details related to scientific investigations that could have planetary protection impacts.
Mars↗
Stabilization of Catalytically Active Surface Defects on Ga-doped La–Sr–Mn Perovskites for Improved Solar Thermochemical Generation of Hydrogen
Solar thermochemical hydrogen (STCH) production from water splitting typically requires performing redox cycles at temperatures above 1200 °C to reduce and re-oxidize the bulk of a reversible material. Bulk processes such as oxygen vacancy formation and oxygen diffusion energies dictate the viability of a material for STCH. The surface plays an important role in the formation and destruction of vacancies and interacts with gas phase water and surface adsorbed species. These surface processes can lead to surface reconfigurations and even the formation of surface phases with stoichiometry and oxygen content very different from the bulk composition. Understanding in-situ the surface chemical state and its evolution under water splitting is important to design nonstoichiometric oxides capable of longer-lasting STCH generation at lower temperatures. In this work, we describe the water splitting active defect sites in LSM ((La 0.65 Sr 0.35 ) 0.95 MnO 3–δ ) and Ga-doped LSM ((La 0.6 Sr 0.4 ) 0.95 (Mn 0.8 Ga 0.2 )O 3–δ ) perovskites during Operando thermochemical water splitting conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments at 800 °C under steam. We show that sub-stoichiometric La +3 in the oxygen-vacancy rich surface at operating conditions can be used to correlate surface water splitting activity and the creation of surface hydroxide intermediates. The addition of Ga in LSM is shown to drastically stabilize the surface chemical composition by preventing Sr segregation and stabilizing catalytically active surface defects that promote the binding of adsorbed hydroxides. Here, we use Operando AP-XPS quantification of metastable surface hydroxide intermediates (La(OH) 3 ) to determine the amount of catalytically active surface sites in LSM (2.9%) and in LSMG (7.8–8.1%, depending on the bulk oxidation state).
08 HYDROGEN↗
Identification of highly active surface iron sites on Ni(OOH) for the oxygen evolution reaction by atomic layer deposition
Atomic layer deposition (ALD) has become a versatile tool in catalysis, allowing for precise synthesis of catalysts useful for gaining fundamental understanding of complex systems. In this work, ALD was used to perform surface-directed modification of Ni(OH) 2 /Ni(OOH) electrocatalysts for the oxygen evolution reaction (OER) to elucidate the different roles of iron as a surface dopant and as iron distributed throughout the NiOOH structure. Electrochemical and material characterization of FeO x ALD-modified Ni(OH) 2 indicates that iron is deposited on the surface of Ni(OH) 2 sheets without modifying its bulk properties. Sub-monolayer amounts of iron were deposited on the surface of Ni(OH) 2 using low cycle numbers of ALD. This surface iron results in high OER activity, characteristic of Ni-Fe(OOH) catalysts. Ni(OH) 2 /Ni(OOH) catalysts modified to incorporate iron throughout the structure were prepared by depositing large cycle numbers of FeO x ALD, which results in the deposition of a Fe 2 O 3 overlayer. Corrosion of this Fe 2 O 3 overlayer during electrochemical cycling in alkaline electrolyte leads to the incorporation of iron throughout the structure of Ni(OH) 2 /Ni(OOH) while leaving some Fe at the surface. Incorporation of iron throughout the Ni(OH) 2 /Ni(OOH) structure was found to increase OER geometric activity for thick, high surface area Ni(OH) 2 /Ni(OOH) catalysts. Lastly, NiFeO x electrocatalysts synthesized fully by ALD were investigated for the OER; these catalysts demonstrated high OER activity and potential for photocatalysis applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Revisiting heat treatment and surface activation of GaAs photocathodes: In situ studies using scanning tunneling microscopy and photoelectron spectroscopy
The lifetime of GaAs photocathodes in polarized electron guns is limited due to the delicate activation layer. An atomically clean and smooth GaAs surface is needed to deposit a robust activation layer, such as Cs 2 Te, with longer lifetime compared to traditional (Cs,O) activation. A previous experiment with Cs 2 Te activation on GaAs used heat cleaning temperatures around 400°C to avoid an increase in surface roughness [Bae et al., Appl. Phys. Lett. 112, 154101 (2018)]. Furthermore, high-temperature heat cleaning around 580°C, which results in a relatively contamination-free surface, could be one possible way to improve quantum efficiency. However, one should be cautious about surface roughness degradation during high-temperature heat cleaning. In this paper, we report results of surface roughness measurements on native, heat cleaned, and (Cs,O) activated GaAs photocathodes under vacuum. The results, measured by ultrahigh vacuum scanning tunneling microscopy, show that the surface roughness improves as the heat cleaning temperature is increased, by at least a factor of three for 580°C heat cleaning, compared to the native sample. Activation with (Cs,O) is shown to increase surface roughness by a factor of four compared to a 580°C heat cleaned sample. This confirms that high-temperature heat cleaning can be useful for depositing good quality robust activation layers on GaAs. Additionally, we also report chemical analysis for each step of preparation for p-doped GaAs photocathodes using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and ultraviolet photoelectron spectroscopy. Our results indicate that the (Cs,O) activation layer forms a sandwich structure consists of Cs and oxygen. We found no formation of any specific compound such as Cs 2 O or Cs 11 O 3 .
43 PARTICLE ACCELERATORS↗
Trace Fe activates perovskite nickelate OER catalysts in alkaline media via redox-active surface Ni species formed during electrocatalysis
The accurate description of activity trends among perovskite-oxide oxygen-evolution-reaction (OER) catalysts using electronic-structure descriptors requires that the bulk structure of the catalyst is comparable to that of the surface. Few studies have addressed the dynamic nature of the catalyst's structure during the OER and the consequential implications for understanding activity. Here, we use a combination of electrochemical and materials-characterization techniques to study the surface reconstruction and the associated formation of a new redox-active phase on LaNiO 3 particles, LaNiO 3 epitaxial films, and an analogous Ruddlesden-Popper phase, La 2 NiO 4 . Small, but characteristic, redox features corresponding to Ni redox in nominally amorphous NiO x H y are observed during cyclic voltammetry of these initially fully crystalline materials. The size of these redox features grows with prolonged cycling and contributes to an increased surface area as determined from electrochemical impedance spectroscopy (EIS). Here we find the OER activity is strongly dependent on soluble Fe species in the electrolyte, common impurities in alkaline media. These observations are consistent with the reconstruction of the crystalline surface to form NiO x H y species and subsequent activation by adsorption of Fe forming the well-known and extremely active NiFeO x H y OER catalyst.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Lunar surface activities
Possible excursions for typical 35-hour lunar surface exploration, experimental and recording instruments, sample collection, and photography
PHOTOGRAPHIC RECORDING↗
An application of active surface heating for augmenting lift and reducing drag of an airfoil
Application of active control to separated flow on the RC(6)-08 airfoil at high angle of attack by localized surface heating is numerically simulated by integrating the compressible 2-D nonlinear Navier-Stokes equation solver. Active control is simulated by local modification of the temperature boundary condition over a narrow strip of the upper surface of the airfoil. Both mean and perturbed profiles are favorably altered when excited with the same natural frequency of the shear layer by moderate surface heating for both laminar and turbulent separation. The shear layer is found to be very sensitive to localized surface heating in the vicinity of the separation point. The excitation field at the surface sufficiently altered both the local as well as the global circulation to cause a significant increase in lift and reduction in drag.
Maestrello, Lucio↗
Reference Surface Activities for Crewed Mars Mission Systems and Utilization
This paper describes the current reference being used by NASA for the surface exploration portion of a human Mars mission architecture, documented in HEOMD-415. (It is important to note that no decisions have been made by NASA regarding human Mars mission objectives, durations, or architectures, and this document is intended to aid in analysis of options.) The HEOMD-415 report details constraints and considerations in planning daily activity timelines for crewed exploration on Mars. This work was done for the purpose of estimating how much time during each martian sol might be available for exploration activities, (also referred to as utilization activities in this document), after accounting for time needed for crew and equipment care. The report describes activities, on a sol-by-sol basis, for a surface exploration mission with a total duration of 30 sols on the surface. At the conclusion of this description, the total amount of time used in the activities is presented, summarized into relevant mission planning categories. In addition, the amount of time used specifically for extravehicular activities (EVAs) is gathered in a tabular form, showing the amount of time by sol and by crewmember that resulted from this analysis. As future analyses related to this surface mission are conducted, these summary results will be updated and revisions of the document will be released.
Mars↗
Perovskite Catalysts for Pure-Water-Fed Anion-Exchange-Membrane Electrolyzer Anodes: Co-design of Electrically Conductive Nanoparticle Cores and Active Surfaces
Anion-exchange-membrane water electrolyzers (AEMWEs) are a possible low-capital-expense, efficient, and scalable hydrogen-production technology with inexpensive hardware, earth-abundant catalysts, and pure water. However, pure-water-fed AEMWEs remain at an early stage of development and suffer from inferior performance compared with proton-exchange-membrane water electrolyzers (PEMWEs). One challenge is to develop effective non-platinum-group-metal (non-PGM) anode catalysts and electrodes in pure-water-fed AEMWEs. We show how LaNiO3-based perovskite oxides can be tuned by cosubstitution on both A- and B-sites to simultaneously maintain high metallic electrical conductivity along with a degree of surface reconstruction to expose a stable Co-based active catalyst. The optimized perovskite, Sr0.1La0.9Co0.5Ni0.5O3, yielded pure-water AEMWEs operating at 1.97 V at 2.0 A cm-2 at 70 °C with a pure-water feed, thus illustrating the utility of the catalyst design principles.
Zhai, Tingting↗
Friction induced surface activity of some simple organic chlorides and hydrocarbons with iron.
Sliding friction studies were conducted on an iron surface with exposure of that surface to various hydrocarbons and organic chlorides. The hydrocarbons included ethane, ethylene, ethyl chloride, methyl chloride and vinyl chloride. Auger cylindrical-mirror analysis was used to follow interactions of the hydrocarbon and organic chlorides with the iron surface. Results with vinyl chloride indicate friction-induced surface reactivity, adsorption to surface oxides, friction sensitivity to concentration and polymerization. Variation in the loads employed influence adsorption and, accordingly, friction. Unlike results with ethyl and vinyl chloride, friction-induced surface reactivity was not observed with ethane and ethylene.
Buckley, D. H.↗
Observation and Characterization of Vibrationally Active Surface Species Accessed with Nonthermal Nitrogen Plasmas
Polycrystalline Ni, Pd, Cu, Ag, and Au foils exposed to nonthermal plasma (NTP)-activated N 2 are found to exhibit a vibrational feature near 2200 cm –1 in polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) observations that are not present in the same materials exposed to N 2 under nonplasma conditions. The feature is similar to that reported elsewhere and is typically assigned to chemisorbed N 2 . We employ a combination of temperature-dependent experiments, sequential dosing, X-ray photoelectron spectroscopy, isotopic labeling, and density functional theory calculations to characterize the feature. Results are most consistent with a triatomic species, likely NCO, with the C and O likely originating from ppm-level impurities in the ultrahigh-purity (UHP) Ar and/or N 2 gas cylinders. Here, this work highlights the potential for nonthermal plasmas to access adsorbates inaccessible thermally as well as the potential contributions of ppm-level impurities to corrupt the interpretation of plasma catalytic chemistry.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Friction-induced surface activity of some hydrocarbons with clean and oxide-covered iron
Sliding friction studies were conducted on a clean and oxide-covered iron surface with exposure of that surface to various hydrocarbons. The hydrocarbons included ethane, ethylene ethyl chloride, methyl chloride, and vinyl chloride. Auger cylindrical mirror analysis was used to follow interactions of the hydrocarbon with the iron surface. Results with vinyl chloride indicate friction induced surface reactivity, adsorption to surface oxides, friction sensitivity to concentration and polymerization. Variation in the loads employed influence adsorption and accordingly friction. In contrast with ethyl and vinyl chloride, friction induced surface reactivity was not observed with ethane and ethylene.
Buckley, D. H.↗
Mapping of surface activity on the W UMa-type system VW Cephei
After multifilter photometry of the W UMa-type contact binary VW Cep (P = 6.67 hr; G5V + K0V) in 1986/87 revealed large asymmetries in the light curves believed to be caused by large, cool starspot regions on the surface of the larger stars, in Apr. 1987 it was observed with IUE to study the chromospheres and transition regions of the components. During one complete orbital cycle, three SWP and four LWP low dispersion spectra were obtained, including and then excluding the suspected active region. Phase dependent TR line emission strengths were found, most notably C IV, which is 50 percent stronger when the spot region is most visible. The results could be important because VW Cep represents an extreme case for studying stellar dynamo theory and observations can play a crucial role in the unterstanding of magnetic fields and activity cycles in rapidly rotating solar-like stars.
Bradstreet, David H.↗
Surface activation of air oxidation of hydrazine on kaolinite. 2. Consideration of oxidizing/reducing entities in relationship to other compositional, structural, and energetic factors
The rates (previously reported) for the air oxidation of hydrazine on kaolinite and substituent oxides of kaolinite showed a complex dependence on the relative amounts of several structural oxidizing/reducing entities within the reaction-promoting solids. The rates indicated an important role of the clay but no dominant role of any one of the oxidizing/reducing entities. In this paper we review (a) the reaction-promoting activity of these centers as studied in other systems, (b) various spectroscopic results showing interaction between these entities in clays, and (c) reported spectroscopic studies of the complexation between hydrazine and aluminosilicate surfaces as a whole, in an effort to propose a mechanism for the reaction. Whereas some uncertainties remain, the present synthesis concludes that a mechanism operating through single electron/hole transfers and hydrogen atom transfers by discrete centers is adequate to explain the observed rate behaviors including the observed second order dependence of the oxidation rate on catalyst amount. The effects of these operations on the catalyst can result in no alteration of, or complete or partial electronic relaxation of its contingent of trapped separated charge pairs. The degree to which surface complexation as a whole, intercalation, or luminescent processes may also be associated with the reaction cannot be adequately assessed with the information in hand.
NASA Program Exobiology↗
Surface-active antibiotic production as a multifunctional adaptation for postfire microorganisms
Abstract Wildfires affect soils in multiple ways, leading to numerous challenges for colonizing microorganisms. Although it is thought that fire-adapted microorganisms lie at the forefront of postfire ecosystem recovery, the specific strategies that these organisms use to thrive in burned soils remain largely unknown. Through bioactivity screening of bacterial isolates from burned soils, we discovered that several Paraburkholderia spp. isolates produced a set of unusual rhamnolipid surfactants with a natural methyl ester modification. These rhamnolipid methyl esters (RLMEs) exhibited enhanced antimicrobial activity against other postfire microbial isolates, including pyrophilous Pyronema fungi and Amycolatopsis bacteria, compared to the typical rhamnolipids made by organisms such as Pseudomonas spp. RLMEs also showed enhanced surfactant properties and facilitated bacterial motility on agar surfaces. In vitro assays further demonstrated that RLMEs improved aqueous solubilization of polycyclic aromatic hydrocarbons, which are potential carbon sources found in char. Identification of the rhamnolipid biosynthesis genes in the postfire isolate, Paraburkholderia kirstenboschensis str. F3, led to the discovery of rhlM, whose gene product is responsible for the unique methylation of rhamnolipid substrates. RhlM is the first characterized bacterial representative of a large class of integral membrane methyltransferases that are widespread in bacteria. These results indicate multiple roles for RLMEs in the postfire lifestyle of Paraburkholderia isolates, including enhanced dispersal, solubilization of potential nutrients, and inhibition of competitors. Our findings shed new light on the chemical adaptations that bacteria employ to navigate, grow, and outcompete other soil community members in postfire environments.
59 BASIC BIOLOGICAL SCIENCES↗
Kaolinite-catalyzed air oxidation of hydrazine: Consideration of several compositional, structural and energetic factors in surface activation
Clay minerals have been shown to have numerous, curious, energetic properties by virtue of ultra-violet light release which can be triggered by gentle environmental changes such as wetting and dewetting by a variety of liquids, unique among them water and hydrazine. Since both water and hydrazine play multiple key roles in the air-oxidation of hydrazine on kaolinite surfaces, this reaction would seem to have prime potential for studying interrelationships of energy storage, release and chemical reactivity of clay surfaces, capacities basic to either the Bernal or Cairns-Smith roles of minerals in the origin of life. Establishment of the capacity for stored electronic energy to significantly alter surface chemistry is important, regardless of the reaction chosen to demonstrate it. Hydrazine air oxidation is overawingly complex, given the possibilities for step-wise control and monitoring of parameters. In the light of recently extended characterization of the kaolinite and model sheet catalysts we used to study hydrazine oxidation and gamma-irradiated silica, previous studies of hydrazine air-oxidation on aluminosilicate surfaces have been reevaluated. Our former conclusion remains intact that, whereas trace structural and surface contaminants do play some role in the catalysis of oxidation, they are not the only, nor even the dominant, catalytic centers. Initial intermediates in the oxidation can now be proposed which are consistent with production via O(-)-centers as well as ferric iron centers. The greater than square dependence of the initial reaction rate on the weight of the clay is discussed in the light of these various mechanistic possibilities.
Coyne, L. M.↗
Surface activation of Concorde by Be-7
Activation analysis of two airframe components from the Concorde aircraft has identified the presence of Be-7, a nuclide found by other investigators that was deposited on the forward edge of the Long Duration Exposure Facility (LDEF) structure. The results of the Concorde analysis indicate that this phenomenon is very much a surface effect, and that the areal densities of the Be-7 are comparable to those found for LDEF. The collection of Be-7 by the aircraft must be greater than in the case of LDEF (since duration for which Concorde is accumulating the nuclide is shorter) and is of the order of 1.2 to 41 nuclei/sq cm(-)s(exp -1) depending upon assumptions made regarding the altitude at which collection becomes appreciable, and the efficiency of the process which removes the radionuclide.
Truscott, P. R.↗