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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LaCeRh4 by Materials Project

CeLaRh4 is Cubic Laves-derived structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to twelve equivalent Rh atoms. All Ce–Rh bond lengths are 3.17 Å. La is bonded in a 12-coordinate geometry to twelve equivalent Rh atoms. All La–Rh bond lengths are 3.17 Å. Rh is bonded to three equivalent Ce, three equivalent La, and six equivalent Rh atoms to form a mixture of edge, corner, and face-sharing RhLa3Ce3Rh6 cuboctahedra. All Rh–Rh bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce3(GaRh)2 by Materials Project

Ce3Rh2Ga2 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are two inequivalent Ce sites. In the first Ce site, Ce is bonded in a 9-coordinate geometry to four equivalent Rh and five Ga atoms. There are two shorter (3.08 Å) and two longer (3.13 Å) Ce–Rh bond lengths. There are a spread of Ce–Ga bond distances ranging from 3.03–3.35 Å. In the second Ce site, Ce is bonded in a 7-coordinate geometry to four equivalent Rh and five Ga atoms. There are a spread of Ce–Rh bond distances ranging from 2.79–3.22 Å. There are a spread of Ce–Ga bond distances ranging from 3.14–3.32 Å. Rh is bonded in a 9-coordinate geometry to six Ce and three Ga atoms. There are a spread of Rh–Ga bond distances ranging from 2.57–2.69 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a 9-coordinate geometry to seven Ce and two equivalent Rh atoms. In the second Ga site, Ga is bonded in a 12-coordinate geometry to eight Ce and four equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La3(GaRh)2 by Materials Project

La3(RhGa)2 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are two inequivalent La sites. In the first La site, La is bonded in a 9-coordinate geometry to four equivalent Rh and five Ga atoms. There are two shorter (3.21 Å) and two longer (3.24 Å) La–Rh bond lengths. There are a spread of La–Ga bond distances ranging from 3.13–3.42 Å. In the second La site, La is bonded in a 7-coordinate geometry to four equivalent Rh and five Ga atoms. There are a spread of La–Rh bond distances ranging from 2.91–3.30 Å. There are a spread of La–Ga bond distances ranging from 3.25–3.46 Å. Rh is bonded in a 9-coordinate geometry to six La and three Ga atoms. There are a spread of Rh–Ga bond distances ranging from 2.59–2.70 Å. There are two inequivalent Ga sites. In the first Ga site, Ga is bonded in a 9-coordinate geometry to seven La and two equivalent Rh atoms. In the second Ga site, Ga is bonded to eight La and four equivalent Rh atoms to form a mixture of distorted face, edge, and corner-sharing GaLa8Rh4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3RhCl6O by Materials Project

K3RhOCl6 crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. there are three inequivalent K sites. In the first K site, K is bonded in a 9-coordinate geometry to nine Cl atoms. There are a spread of K–Cl bond distances ranging from 3.18–3.47 Å. In the second K site, K is bonded in a 8-coordinate geometry to one O and seven Cl atoms. The K–O bond length is 2.82 Å. There are a spread of K–Cl bond distances ranging from 3.02–3.43 Å. In the third K site, K is bonded in a 1-coordinate geometry to one O and eight Cl atoms. The K–O bond length is 2.85 Å. There are a spread of K–Cl bond distances ranging from 3.20–3.80 Å. Rh is bonded in an octahedral geometry to six Cl atoms. There are a spread of Rh–Cl bond distances ranging from 2.36–2.40 Å. O is bonded in a water-like geometry to two K atoms. There are six inequivalent Cl sites. In the first Cl site, Cl is bonded in a 1-coordinate geometry to three K and one Rh atom. In the second Cl site, Cl is bonded to four K and one Rh atom to form distorted ClK4Rh square pyramids that share corners with four equivalent ClK4Rh square pyramids, corners with three equivalent ClK4Rh trigonal bipyramids, edges with two equivalent ClK5Rh octahedra, an edgeedge with one ClK4Rh square pyramid, an edgeedge with one ClK4Rh trigonal bipyramid, a faceface with one ClK5Rh octahedra, a faceface with one ClK4Rh square pyramid, and a faceface with one ClK4Rh trigonal bipyramid. In the third Cl site, Cl is bonded to four K and one Rh atom to form distorted ClK4Rh square pyramids that share corners with two equivalent ClK5Rh octahedra, corners with four equivalent ClK4Rh square pyramids, a cornercorner with one ClK4Rh trigonal bipyramid, an edgeedge with one ClK5Rh octahedra, an edgeedge with one ClK4Rh square pyramid, edges with two equivalent ClK4Rh trigonal bipyramids, a faceface with one ClK5Rh octahedra, a faceface with one ClK4Rh square pyramid, and a faceface with one ClK4Rh trigonal bipyramid. The corner-sharing octahedra tilt angles range from 37–44°. In the fourth Cl site, Cl is bonded in a 1-coordinate geometry to four K and one Rh atom. In the fifth Cl site, Cl is bonded to five K and one Rh atom to form distorted ClK5Rh octahedra that share corners with four equivalent ClK5Rh octahedra, corners with two equivalent ClK4Rh square pyramids, corners with four equivalent ClK4Rh trigonal bipyramids, edges with three ClK4Rh square pyramids, an edgeedge with one ClK4Rh trigonal bipyramid, and faces with two ClK4Rh square pyramids. The corner-sharing octahedra tilt angles range from 46–49°. In the sixth Cl site, Cl is bonded to four K and one Rh atom to form distorted ClK4Rh trigonal bipyramids that share corners with four equivalent ClK5Rh octahedra, corners with four ClK4Rh square pyramids, corners with two equivalent ClK4Rh trigonal bipyramids, an edgeedge with one ClK5Rh octahedra, edges with three ClK4Rh square pyramids, edges with two equivalent ClK4Rh trigonal bipyramids, and faces with two ClK4Rh square pyramids. The corner-sharing octahedra tilt angles range from 1–55°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb5(Sn3Rh)6 by Materials Project

Tb5Rh6Sn18 crystallizes in the cubic F-43m space group. The structure is three-dimensional and consists of four tin powder molecules and one Tb5Rh6Sn17 framework. In the Tb5Rh6Sn17 framework, there are two inequivalent Tb sites. In the first Tb site, Tb is bonded in a 1-coordinate geometry to three equivalent Rh and ten Sn atoms. All Tb–Rh bond lengths are 3.05 Å. There are a spread of Tb–Sn bond distances ranging from 2.91–3.41 Å. In the second Tb site, Tb is bonded in a 12-coordinate geometry to six equivalent Rh and twelve equivalent Sn atoms. All Tb–Rh bond lengths are 3.56 Å. All Tb–Sn bond lengths are 3.47 Å. Rh is bonded in a 9-coordinate geometry to three Tb and six Sn atoms. There are four shorter (2.69 Å) and two longer (2.83 Å) Rh–Sn bond lengths. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a tetrahedral geometry to four equivalent Tb atoms. In the second Sn site, Sn is bonded in a hexagonal planar geometry to three equivalent Tb and three equivalent Rh atoms. In the third Sn site, Sn is bonded in a 2-coordinate geometry to three Tb and two equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy3(GeRh)2 by Materials Project

Dy3(RhGe)2 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are two inequivalent Dy sites. In the first Dy site, Dy is bonded in a 9-coordinate geometry to four equivalent Rh and five Ge atoms. There are two shorter (3.03 Å) and two longer (3.07 Å) Dy–Rh bond lengths. There are a spread of Dy–Ge bond distances ranging from 3.01–3.31 Å. In the second Dy site, Dy is bonded in a 7-coordinate geometry to four equivalent Rh and five Ge atoms. There are a spread of Dy–Rh bond distances ranging from 2.91–3.15 Å. There are a spread of Dy–Ge bond distances ranging from 3.00–3.36 Å. Rh is bonded in a 9-coordinate geometry to six Dy and three Ge atoms. There are a spread of Rh–Ge bond distances ranging from 2.54–2.62 Å. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to seven Dy and two equivalent Rh atoms. In the second Ge site, Ge is bonded in a 12-coordinate geometry to eight Dy and four equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoPdRuRh by Materials Project

MoRuRhPd is beta-derived structured and crystallizes in the trigonal P3m1 space group. The structure is three-dimensional. Mo is bonded to six equivalent Mo, three equivalent Ru, and three equivalent Rh atoms to form MoMo6Ru3Rh3 cuboctahedra that share corners with six equivalent MoMo6Ru3Rh3 cuboctahedra, corners with twelve equivalent PdPd6Ru3Rh3 cuboctahedra, edges with six equivalent MoMo6Ru3Rh3 cuboctahedra, edges with six equivalent RuMo3Pd3Ru6 cuboctahedra, edges with six equivalent RhMo3Pd3Rh6 cuboctahedra, faces with two equivalent PdPd6Ru3Rh3 cuboctahedra, faces with six equivalent MoMo6Ru3Rh3 cuboctahedra, faces with six equivalent RuMo3Pd3Ru6 cuboctahedra, and faces with six equivalent RhMo3Pd3Rh6 cuboctahedra. All Mo–Mo bond lengths are 2.78 Å. All Mo–Ru bond lengths are 2.67 Å. All Mo–Rh bond lengths are 2.69 Å. Ru is bonded to three equivalent Mo, six equivalent Ru, and three equivalent Pd atoms to form RuMo3Pd3Ru6 cuboctahedra that share corners with six equivalent RuMo3Pd3Ru6 cuboctahedra, corners with twelve equivalent RhMo3Pd3Rh6 cuboctahedra, edges with six equivalent MoMo6Ru3Rh3 cuboctahedra, edges with six equivalent RuMo3Pd3Ru6 cuboctahedra, edges with six equivalent PdPd6Ru3Rh3 cuboctahedra, faces with two equivalent RhMo3Pd3Rh6 cuboctahedra, faces with six equivalent MoMo6Ru3Rh3 cuboctahedra, faces with six equivalent RuMo3Pd3Ru6 cuboctahedra, and faces with six equivalent PdPd6Ru3Rh3 cuboctahedra. All Ru–Ru bond lengths are 2.78 Å. All Ru–Pd bond lengths are 2.79 Å. Rh is bonded to three equivalent Mo, six equivalent Rh, and three equivalent Pd atoms to form RhMo3Pd3Rh6 cuboctahedra that share corners with six equivalent RhMo3Pd3Rh6 cuboctahedra, corners with twelve equivalent RuMo3Pd3Ru6 cuboctahedra, edges with six equivalent MoMo6Ru3Rh3 cuboctahedra, edges with six equivalent RhMo3Pd3Rh6 cuboctahedra, edges with six equivalent PdPd6Ru3Rh3 cuboctahedra, faces with two equivalent RuMo3Pd3Ru6 cuboctahedra, faces with six equivalent MoMo6Ru3Rh3 cuboctahedra, faces with six equivalent RhMo3Pd3Rh6 cuboctahedra, and faces with six equivalent PdPd6Ru3Rh3 cuboctahedra. All Rh–Rh bond lengths are 2.78 Å. All Rh–Pd bond lengths are 2.83 Å. Pd is bonded to three equivalent Ru, three equivalent Rh, and six equivalent Pd atoms to form PdPd6Ru3Rh3 cuboctahedra that share corners with six equivalent PdPd6Ru3Rh3 cuboctahedra, corners with twelve equivalent MoMo6Ru3Rh3 cuboctahedra, edges with six equivalent RuMo3Pd3Ru6 cuboctahedra, edges with six equivalent RhMo3Pd3Rh6 cuboctahedra, edges with six equivalent PdPd6Ru3Rh3 cuboctahedra, faces with two equivalent MoMo6Ru3Rh3 cuboctahedra, faces with six equivalent RuMo3Pd3Ru6 cuboctahedra, faces with six equivalent RhMo3Pd3Rh6 cuboctahedra, and faces with six equivalent PdPd6Ru3Rh3 cuboctahedra. All Pd–Pd bond lengths are 2.78 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y3Si3Rh2 by Materials Project

Y3Rh2Si3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are two inequivalent Y sites. In the first Y site, Y is bonded in a 10-coordinate geometry to four equivalent Rh and six Si atoms. There are a spread of Y–Rh bond distances ranging from 3.08–3.16 Å. There are a spread of Y–Si bond distances ranging from 2.96–3.10 Å. In the second Y site, Y is bonded in a 9-coordinate geometry to four equivalent Rh and five Si atoms. All Y–Rh bond lengths are 3.22 Å. There are a spread of Y–Si bond distances ranging from 2.94–3.29 Å. Rh is bonded in a 10-coordinate geometry to six Y and four Si atoms. There are a spread of Rh–Si bond distances ranging from 2.44–2.66 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to five Y, three equivalent Rh, and one Si atom. The Si–Si bond length is 2.60 Å. In the second Si site, Si is bonded in a 9-coordinate geometry to seven Y and two equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Er5(Sn3Rh)6 by Materials Project

Er5Rh6Sn17Sn crystallizes in the cubic F-43m space group. The structure is three-dimensional and consists of four 7440-31-5 molecules and one Er5Rh6Sn17 framework. In the Er5Rh6Sn17 framework, there are two inequivalent Er sites. In the first Er site, Er is bonded in a 12-coordinate geometry to six equivalent Rh and twelve equivalent Sn atoms. All Er–Rh bond lengths are 3.56 Å. All Er–Sn bond lengths are 3.46 Å. In the second Er site, Er is bonded in a 4-coordinate geometry to three equivalent Rh and ten Sn atoms. All Er–Rh bond lengths are 3.03 Å. There are a spread of Er–Sn bond distances ranging from 2.91–3.40 Å. Rh is bonded in a 9-coordinate geometry to three Er and six Sn atoms. There are four shorter (2.69 Å) and two longer (2.80 Å) Rh–Sn bond lengths. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a tetrahedral geometry to four equivalent Er atoms. In the second Sn site, Sn is bonded in a distorted hexagonal planar geometry to three equivalent Er and three equivalent Rh atoms. In the third Sn site, Sn is bonded in a 2-coordinate geometry to three Er and two equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho5(Sn3Rh)6 by Materials Project

Ho5Rh6Sn17Sn crystallizes in the cubic F-43m space group. The structure is three-dimensional and consists of four 7440-31-5 molecules and one Ho5Rh6Sn17 framework. In the Ho5Rh6Sn17 framework, there are two inequivalent Ho sites. In the first Ho site, Ho is bonded in a 12-coordinate geometry to six equivalent Rh and twelve equivalent Sn atoms. All Ho–Rh bond lengths are 3.56 Å. All Ho–Sn bond lengths are 3.46 Å. In the second Ho site, Ho is bonded in a 4-coordinate geometry to three equivalent Rh and ten Sn atoms. All Ho–Rh bond lengths are 3.04 Å. There are a spread of Ho–Sn bond distances ranging from 2.91–3.40 Å. Rh is bonded in a 9-coordinate geometry to three Ho and six Sn atoms. There are four shorter (2.69 Å) and two longer (2.81 Å) Rh–Sn bond lengths. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a tetrahedral geometry to four equivalent Ho atoms. In the second Sn site, Sn is bonded in a hexagonal planar geometry to three equivalent Ho and three equivalent Rh atoms. In the third Sn site, Sn is bonded in a 2-coordinate geometry to three Ho and two equivalent Rh atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Modeling Volatility-Based Aerosol Phase State Predictions in the Amazon Rainforest

Organic aerosol (OA) is a complex matrix of various constituents—fresh (primary organic aerosols—POA) and aged via oxidation (secondary organic aerosols—SOA), generated from biogenic, anthropogenic, and biomass burning sources. The viscosity of OA can be critical in influencing new particle formation, reactive uptake processes that impact evaporation-growth kinetics, and the lifetime of particles in the atmosphere. We report this work utilizes a well-defined relationship between volatility and viscosity for pure compounds, which we incorporated within the Weather Research and Forecasting Model coupled to chemistry (WRF-Chem) to simulate the phase state and viscosity of bulk OA during the dry-to-wet transition season (September–October) in the Amazon rainforest during 2014. Our simulations indicate spatial and temporal heterogeneity in aerosol phase state often not captured by global-scale models. We show the strong role of water associated with organic aerosol ($w_s$) as the dominant factor that can be used to quantitatively estimate OA viscosity. Analysis of WRF-Chem simulations across the entire atmospheric column indicates a strong inverse log-linear relationship between $w_s$ and OA viscosity with a correlation coefficient approaching 1, in the background and biomass burning-influenced conditions. At high altitudes where relative humidity (RH) and temperatures are low, our simulations indicate that OA exists in a semisolid-/solid-like phase state, consistent with previous studies. OA hygroscopicity is strongly correlated (ca. –0.8) with OA viscosity at RH ca. 30–50%, but this RH range is found mostly at low OA concentrations and the middle troposphere (ca. 6–10 km altitudes) in our simulated domain. OA hygroscopicity is uncorrelated with viscosity at higher-RH (near surface) and lower-RH (upper troposphere) regimes. At the urban site near surface, where day–night differences in RH are significant, RH is found to drive the phase state. At the background forested site near surface, where day–night RH differences are small, biomass burning-influenced OA is semisolid and a significant OA associated with background conditions is liquid-like. Simulations indicate a long tail of OA viscosity frequency distributions extending in the semisolid/solid regimes over background biogenic-influenced conditions due to the role of low-volatility OA components such as monoterpene oxidation products.

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

Multiphase Processing of the Water-Soluble and Insoluble Phases of Biomass Burning Organic Aerosol

Biomass burning is one of the most significant sources of organic aerosol in the atmosphere. Biomass burning organic aerosol (BBOA) has been observed to undergo liquid– liquid phase separation (LLPS) to give core–shell morphology with the hydrophobic phase encapsulating the hydrophilic phase, potentially impacting the evolution of light-absorbing components, i.e., brown carbon (BrC), through multiphase processes. Here, we demonstrate how multiphase processing differs between the watersoluble (i.e., hydrophilic) and insoluble (i.e., hydrophobic) phases of BBOA in terms of reactive uptake of ozone in a coated-wall flow tube. Effects of relative humidity (RH) and ultraviolet (UV) irradiation were investigated. Experimental timeseries were used to inform simulations using multilayer kinetic modeling. Among non-irradiated thin films, the uptake coefficient was greatest for the water-soluble phase at 75% RH (3 × 10 –5 , corresponding to a diffusion coefficient of BrC, D BrC , of 3 × 10 –9 cm 2 s –1 ) and least for the same phase at 0% RH (1 × 10 –5 , corresponding to D BrC of 1 × 10 –10 cm 2 s –1 ). The uptake coefficient for the water-insoluble phase fell between these two (about 1.5 × 10 –5 ), regardless of RH, and the corresponding D BrC increased only slightly (8 × 10 –10 cm 2 s –1 at 0% RH to 9 × 10 –10 cm 2 s –1 at 75% RH). The uptake coefficients of both phases at 0% RH decreased significantly after UV irradiation, consistent with a transition from viscous liquid to solid and supported by qualitative microscopy observations. Modeling multiphase ozone oxidation of primary BrC components in the atmosphere demonstrated, first, that LLPS may extend the lifetime of water-soluble BBOA encapsulated by water-insoluble species by a factor of 1.5 at moderate to high RH and, also, that UV irradiation may extend the lifetime of both phases by more than a factor of 2.5.

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

Controlling Reaction Pathways of Ethylene Hydroformylation Using Isolated Bimetallic Rhodium–Cobalt Sites

Designing efficient ligand-free heterogeneous catalysts for ethylene hydroformylation to produce C 3 oxygenates is of importance for both fundamental research and practical applications, but it is often hindered by insufficient catalytic activity and selectivity. Here, this work designs isolated rhodium–cobalt (Rh–Co) sites confined within a ZSM-5 zeolite to enhance ethylene hydroformylation rates and selectivity while maintaining catalyst stability. By adjusting the Co/Al ratio in Co-ZSM-5, different sizes of Co are formed; subsequent Rh introduction produces isolated Rh 1 Co x clusters with different Rh–Co coordination numbers (CNs). In-situ characterizations and density functional theory calculations reveal that a Rh–Co CN of 3, corresponding to an isolated Rh 1 Co 3 site, provides optimal bindings to reaction intermediates and thus achieves the highest hydroformylation rates among supported Rh-based catalysts. This study demonstrates the role of coordination-tuning via a secondary metal in effectively controlling the reaction pathway over single Rh atom catalysts.

03 NATURAL GAS↗
DOE OSTI2023

The Role of Interactive Soil Moisture in Land Drying Under Anthropogenic Warming

Abstract Relative humidity (RH) is projected to increase over ocean but decrease over land under anthropogenic warming. The land RH decrease was previously attributed to ocean influences on land changes. Here, we show that interactive soil moisture (SM) is necessary and may be sufficient for anthropogenic warming to reduce the land RH. The land RH decrease is absent in simulations with realistic land‐ocean geometry but fixed SM, and present in simulations with interactive SM but no oceans or changes in precipitation minus evaporation. The land RH decrease is coupled to the SM decline and the latter could be understood as a natural response of interactive SM to anthropogenic warming. Specifically, prior to adjustments in SM and RH, evaporation would increase by ∼6% K −1 following the Clausius–Clapeyron relation, outpacing the radiatively constrained ∼2% K −1 precipitation increase. This prior imbalance depletes SM and consequently reduces RH through the coupling between SM and RH.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Integrated in situ spectroscopic studies on syngas production from partial oxidation of methane catalyzed by atomically dispersed rhodium cations on ceria

Catalytic reforming of methane to produce syngas is an important strategy for producing value-added chemicals. The conventional reforming catalyst relies on supported nickel nanoparticles. Here, in this work, we investigated singly dispersed Rh cations anchored on a CeO 2 catalyst (Rh 1 /CeO 2 ) for high activity and selectivity towards the production of syngas via partial oxidation of methane (POM) in the temperature range of 600–700 °C. The yields of H 2 and CO at 700 °C are 83% and 91%, respectively. The anchored Rh 1 atoms on CeO 2 of Rh 1 /CeO 2 are in the cationic state, and on an average each Rh 1 atom coordinates with 4–5 surface lattice oxygen atoms of CeO 2 . Compared to inert CeO 2 for POM, via the incorporation of single-atom sites, Rh 1 modifies the electronic state of oxygen atoms proximal to the Rh 1 atoms and thus triggers the catalytic activity of CeO 2 . The high activity of single-atom catalyst Rh 1 /CeO 2 suggests that the incorporation of single atoms of transition metals to the surface of a reducible oxide can modulate the electronic state of proximal anions of the oxide support toward forming an electronic state favorable for the selective formation of ideal products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

Nonlinear evolution of high frequency R-mode waves excited by water group ions near comets - Computer experiments

An ion beam resonates with R-mode waves at a high-frequency RH mode and a low-frequency RL mode. The nonlinear evolution of ion beam-generated RH waves is studied here by one-dimensional hybrid computer experiments. Both wave-particle and subsequent wave-wave interactions are examined. The competing process among coexisting RH and RL mode beam instabilities and repeated decay instabilities triggered by the beam-excited RH mode waves is clarified. It is found that the quenching of the RH instability is not caused by a thermal spreading of the ion beam, but by the nonlinear wave-wave coupling process. The growing RH waves become unstable against the decay instability. This instability involves a backward-traveling RH electromagnetic wave and a forward-traveling longitudinal sound wave. The inverse cascading process is found to occur faster than the growth of the RL mode. Wave spectra decaying from the RH waves weaken as time elapses and the RL mode waves become dominant at the end of the computer experiment.

Kojima, H.↗
NASA NTRS2019

Subsurface Cl-bearing salts as potential contributors to recurring slope lineae (RSL) on Mars

We report laboratory experimental results that support a brine-related hypothesis for the recurring slope lineae (RSL) on Mars in which the subsurface Cl-salts, i.e., hydrous chlorides and oxychlorine salts (HyCOS) are the potential source materials. Our experiments revealed that within the observed RSL temperature window TRSL (250–300 K), the deliquescence of HyCOS could occur in relative humidity ranges (RH≥22%–46%) much lower than those for hydrous (Mg, Fe)-sulfates (RH≥75%–96%). In addition, we demonstrated that the RH values kept by common HyCOS and hydrous sulfates in enclosures have a general trend as RH(sulfates) > RH(perchlorates) > RH(chlorides) (with same type of cation) in wide T range. It means that the required RH range for a Cl-bearing salt to deliquescence can be satisfied by a co-existing salt of different type, e.g., in the subsurface layers of mixed salts on Mars. Furthermore, we found a strong temperature dependence of the deliquescence rates for all tested HyCOS, e.g., a duration of 1–5 sols for all HyCOS at the high end (300 K) of TRSL, and of 20–70 sols for all tested HyCOS (except NaClO4·H2O) at the low end (250 K) of TRSL, which is consistent with the observed seasonal behavior of RSL on Mars. From a mass-balance point of view, the currently observed evidences on Mars do not support a fully-brine-wetted track model, thus we suggest a brine-triggered granular-flow model for the most RSL. Considering the recurrence of RSL in consecutive martian years, our experimental results support the rehydration of remnant HyCOS layers during a martian cold season through H2O vapor-to-salt direct interaction. We found that the evidences of HyCOS rehydration under Mars relevant P-T-RH conditions are detectable in a few minutes by in situ Raman spectroscopy. This rehydration would facilitate the recharge of H2O back into subsurface HyCOS, which could serve as the source material to trigger RSL in a subsequent warm season. The major limiting factor for this rehydration is the H2O supply, i.e., the H2O vapor density carried by current Mars atmospheric circulation and the diffusion rate of H2O vapor into the salt-rich subsurface in a cold season. In a worst-case scenario, these H2O supplies can support a maximum increase of hydration degrees of two for totally dehydrated HyCOS, whereas the full rehydration of subsurface HyCOS layers can be easily reached during a>30° obliquity period that has H2O vapor density 10× to 20× times the value of current obliquity. Overall, our results imply the existence of a large amount of Cl-bearing salts in the subsurface at RSL sites.

Alian Wang↗
NASA NTRS2023

Combined Experimental and Modeling Study of the Interactions of Acid Gas with Common Spacecraft Surfaces for Fire Safety Applications

A fire in a spacecraft poses detrimental consequences and risks mission success in addition to crew safety. This is compounded during long-duration missions when the crew has limited options to recover from a fire. A common spacecraft fire concern is the smoldering of wire insulation, typically made from Polyvinyl chloride (PVC) or Polytetrafluoroethylene (PTFE). This creates acid gases such as Hydrogen Chloride (HCl), Hydrogen Fluoride (HF) and Hydrogen Cyanide (HCN). These poisonous gases are hazardous to the crew. They also interact with common surfaces within the spacecraft more than dominant combustion products such as CO2 and H2O. This makes them more difficult to track for potential fire detection techniques, or for postfire clean-up. It is imperative to be able to understand and predict the fate of these poisonous species in a microgravity environment in order to design a safe vehicle. HCl interacts with a number of materials inside a spacecraft. Primary among these materials is aluminum, which is abundantly used due to its strong and light weight nature. Aluminum has a natural oxide layer that protects it from corrosion but is typically treated to enhance this oxide layer. Among these treatments is a chromate conversion coating (CCC), which provides a thin enough protective oxide layer to still conduct electricity, and a traditional anodized material that has a thicker oxide layer that does not conduct electricity. Nomex is another common material found inside a spacecraft. It is a flame-resistant woven polymer that is related to nylon. This commercially available material is used for cargo storage bags and as a fire barrier. Physics-based models were developed to predict the uptake of HCl by these materials. The ultimate objective of these models is to predict the fate of HCl within the spacecraft so that sensors can be placed in meaningful locations in future missions based on the model predictions. To support these modeling efforts, experiments were performed in a cast acrylic test cell that measured the difference between the inlet and outlet concentration of HCl after inserting a sample rod of the test material. Different uptake capacities were realized for each type of sample tested. A computational fluid dynamics model (CFD) model of the reactor was then constructed that used a one-step global reaction rate with calibratable reaction (or kinetic) constants. These constants were calibrated to match the HCl uptake on the CCC aluminum samples, and the same kinetic constants were then tested for the stock and anodized aluminum samples. Model predictions matched the experimental data for the stock aluminum, and to a much lesser extent, the anodized aluminum. The model was additionally validated at different flow rates, sample surface areas, and inlet concentrations, and showed good agreement for all stock and CCC samples. The model did not accurately predict the HCl uptake in the anodized samples compared to the other two types of aluminum. Adjusting the kinetic constants and transport properties did little to improve the prediction. X-Ray Photoelectron Spectroscopy (XPS) was used to determine that the oxide layer thickness of anodized aluminum is approximately 5,000 nm, compared to 250 nm for CCC and 50 nm for stock. XPS also revealed presence of chlorine further down in the aluminum oxide layer in anodized samples than CCC and stock samples after the samples were saturated with HCl, indicating that accounting for diffusion of HCl into the oxide layer is important for accurate prediction of HCl uptake onto anodized aluminum. Consequently, a multi-scale model was developed and tested. First, a single pore inside the anodized aluminum oxide layer was modeled and is referred to as the pore-scale model. In this model, HCl diffused through the pore and reacted with the aluminum oxide pore wall to create aluminum chloride. The sample was then saturated when the mass transfer resistance through the growing aluminum chloride layer became too large for the HCl to reach the aluminum oxide wall and continue the reaction. This pore-scale model was coupled to the reactor-scale model using a concentration-dependent diffusion coefficient, resulting in much more accurate predictions (approximately half the sum square error of the aforementioned reactor-scale model that produced good agreement for stock and CCC) for a variety of operating conditions. The amount of water vapor or relative humidity (RH) in the flow during a reactor experiment was determined to influence HCl uptake. Experiments were performed to understand the interaction of gaseous HCl with aluminum surfaces in the presence of water vapor. The results show that increasing levels of RH increased the capacity of aluminum to adsorb HCl but decreased the capacity of Nomex to uptake HCl. A series of tests were performed on individual aluminum samples after they had been saturated with a fixed concentration of HCl in dry air conditions with the goal of determining how their HCl uptake capacity changes after various treatments with water relative to the original saturation tests. HCl-saturated aluminum samples subjected to a second dry air flow at the same HCl concentration as the original test had an uptake of 23.5% of the original sample with no treatment in between. Saturated aluminum samples subjected to an air flow with a RH of 90% in between tests had an uptake of 35.6% of the original. Saturated aluminum samples submerged in distilled water for 12 hours in between tests had an uptake of 82.2% of the original sample. Previously saturated aluminum tested with HCl and a 50% RH air flow resulted in similar uptake characteristics in multiple repeated tests. The experiments show the profound effect water vapor has on HCl uptake onto aluminum surfaces. In the samples subjected to water vapor or liquid water, capillary condensation and capillary diffusion alters the transport of HCl significantly. A model was proposed that developed a relationship between RH and the coefficient of HCl diffusion in aluminum chloride. This produced an “S-shaped” curve with diffusion coefficient as a function of RH, with 45% RH represented as the point where the diffusion coefficient is halfway between no water saturation and 100% water saturation in the aluminum chloride product layer. No difference in uptake characteristics for the experiment or model were realized between 50% and 62% RH. The results from the large-scale microgravity experiment, Saffire, are discussed as they pertain to the fate of HCl throughout a spacecraft. HCl was released, both as a standalone event, and in concurrence with the burning of a structured cloth. These events only produced a small response in the far field HCl sensor, while a PMMA burn that did not produce HCl had a significantly greater response. A ground-based large-scale facility was constructed to flow acid gas at the scale and configuration realized in the Saffire experiments. A CFD model of this duct was constructed to test kinetic parameters developed in this work at a larger scale and different geometric configuration and to predict the results of the large-scale facility. The models developed in this work were used to interpret the results of the microgravity tests and lead the discussion on what further experiments and models are needed in order to predict the fate of acid gas in a spacecraft environment. To summarize, the major contributions of this work are as follows: the capacity to uptake HCl, with and without the presence of water vapor, was measured for a variety of real spacecraft surfaces. Several different models (single reactor-scale, multiscale, spacecraft-scale) were developed and with the aid of modeling, the rate of uptake for those surfaces was also predicted and validated. The kinetic parameters determined from the small-scale reactor experiments and models were used to predict large-scale and microgravity tests. Conclusions from this research will be used in the design of spacecraft vehicles and large-scale microgravity fire safety experiments. The models built by this work will aid designers in sensor placement and could be used to predict acid gas transport from fires in partial gravity, as would be seen in Lunar and Martian habitats.

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