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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

CO2 upgrading into bioproducts using a two-step abiotic–biotic system

The valorization of CO2 to chemicals beyond C1-2 products is receiving significant interest; however, the direct electrosynthesis of Cn molecules (n > 4) remains a challenge. Here, we present a two-step abiotic-biotic system for upgrading CO2 into the biopolymer, poly(3-hydroxybutyrate). In the electrolysis system, CO2 is converted into C2 oxygenates using a Cu-Ag tandem electrocatalyst. The electrolysis process generates a liquid stream containing ~ 200 mM acetate in a bio-compatible electrolyte. This electrosynthesized acetate is then fed to a bioreactor, where the substrate is upgraded by Cupriavidus necator to biopolymer with a maximum rate of 32 ± 3.5 mg L-1 h-1. We further demonstrate the purification of the resulting biopolymer into a powder. The high productivity of the abiotic-biotic system demonstrates its feasibility for sustainable chemical manufacturing.

CO2 upgrading↗
NASA NTRS1993

An assessment of volatile release from recent volcanism in Elysium, Mars

The amount and rate of release of volatiles (H2O, CO2, etc.) from recent volcanism in Elysium, Mars, are estimated. Possible implications of these volatiles on the climate, weathering, and surface morphology are discussed. Total eruptic volcanics may amount to about 4 x 10 exp 5 cu km and would have released large quantities of volatiles into the Martian environment. Assuming that the lavas contained 1.0 wt pct water, about 7.6 x 10 exp 15 kg of the water, or about 1000 times the present atmospheric water inventory, would have been released. Release amounts of other volatiles are estimated to be 10 exp 15 kg of S, 10 exp 13 kg of Cl, and 10 exp 13 kg of F. The short-term effect of the SO2 gas would be to warm the climate due to its greenhouse properties. Conversion to sulfate aerosols might have resulted in a net surface cooling due to scattering of sunlight. As the sulfate aerosols settled from the atmosphere, the climate could have returned to its preeruption equilibrium.

Plescia, J. B.↗
DOE OSTI2020

Materials Data on CoCu2(BO3)2 by Materials Project

Cu2CoB2O6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Co2+ is bonded to six O2- atoms to form edge-sharing CoO6 octahedra. There are a spread of Co–O bond distances ranging from 2.09–2.30 Å. There are two inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded in a 6-coordinate geometry to five O2- atoms. There are a spread of Cu–O bond distances ranging from 1.92–2.61 Å. In the second Cu2+ site, Cu2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Cu–O bond distances ranging from 1.88–2.45 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.36 Å) and one longer (1.42 Å) B–O bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.34–1.44 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to one Co2+, two equivalent Cu2+, and one B3+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Co2+, one Cu2+, and one B3+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to one Co2+, two equivalent Cu2+, and one B3+ atom. In the fourth O2- site, O2- is bonded to two equivalent Co2+ and two Cu2+ atoms to form corner-sharing OCo2Cu2 tetrahedra. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Cu2+ and one B3+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one Cu2+ and two B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Switching CO 2 Electroreduction Selectivity Between C 1 and C 2 Hydrocarbons on Cu Gas-Diffusion Electrodes

We report that regulating the selectivity toward a target hydrocarbon product is still the focus of CO 2 electroreduction. Here, we discover that the original surface Cu species in Cu gas-diffusion electrodes plays a more important role than the surface roughness, local pH, and facet in governing the selectivity toward C 1 or C 2 hydrocarbons. The selectivity toward C 2 H 4 progressively increases, while CH 4 decreases steadily upon lowering the Cu oxidation species fraction. At a relatively low electrodeposition voltage of 1.5 V, the Cu gas-diffusion electrode with the highest Cu δ+ /Cu 0 ratio favors the pathways of hydrogenation to form CH 4 with maximum Faradaic efficiency of 65.4% and partial current density of 228 mA cm -2 at -0.83 V vs RHE. At 2.0 V, the Cu gas-diffusion electrode with the lowest Cu δ+ /Cu 0 ratio prefers C–C coupling to form C 2+ products with Faradaic efficiency topping 80.1% at -0.75 V vs RHE, where the Faradaic efficiency of C 2 H 4 accounts for 46.4% and the partial current density of C 2 H 4 achieves 279 mA cm -2 . This work demonstrates that the selectivity from CH 4 to C 2 H 4 is switchable by tuning surface Cu species composition of Cu gas-diffusion electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Co8Cu7(MoO4)12 by Materials Project

Co8Cu7(MoO4)12 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are eight inequivalent Mo6+ sites. In the first Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share corners with two CuO6 octahedra and corners with three CoO6 octahedra. The corner-sharing octahedra tilt angles range from 26–58°. There are a spread of Mo–O bond distances ranging from 1.79–1.85 Å. In the second Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share corners with two CuO6 octahedra and corners with three CoO6 octahedra. The corner-sharing octahedra tilt angles range from 26–60°. There is two shorter (1.79 Å) and two longer (1.85 Å) Mo–O bond length. In the third Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share a cornercorner with one CuO6 octahedra and corners with three CoO6 octahedra. The corner-sharing octahedra tilt angles range from 19–59°. There are a spread of Mo–O bond distances ranging from 1.75–1.86 Å. In the fourth Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share a cornercorner with one CuO6 octahedra and corners with three CoO6 octahedra. The corner-sharing octahedra tilt angles range from 45–60°. There are a spread of Mo–O bond distances ranging from 1.75–1.86 Å. In the fifth Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share a cornercorner with one CuO6 octahedra and corners with six CoO6 octahedra. The corner-sharing octahedra tilt angles range from 44–63°. There are a spread of Mo–O bond distances ranging from 1.73–1.86 Å. In the sixth Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share a cornercorner with one CuO6 octahedra and corners with six CoO6 octahedra. The corner-sharing octahedra tilt angles range from 16–63°. There are a spread of Mo–O bond distances ranging from 1.73–1.85 Å. In the seventh Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share corners with two CuO6 octahedra and corners with six CoO6 octahedra. The corner-sharing octahedra tilt angles range from 21–63°. There are a spread of Mo–O bond distances ranging from 1.77–1.85 Å. In the eighth Mo6+ site, Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share corners with two CuO6 octahedra and corners with six CoO6 octahedra. The corner-sharing octahedra tilt angles range from 21–63°. There are a spread of Mo–O bond distances ranging from 1.76–1.84 Å. There are four inequivalent Co2+ sites. In the first Co2+ site, Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one CoO6 octahedra, corners with six MoO4 tetrahedra, and edges with two equivalent CoO6 octahedra. The corner-sharing octahedral tilt angles are 56°. There are a spread of Co–O bond distances ranging from 2.07–2.21 Å. In the second Co2+ site, Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one CoO6 octahedra, corners with six MoO4 tetrahedra, and edges with two equivalent CoO6 octahedra. The corner-sharing octahedral tilt angles are 58°. There are a spread of Co–O bond distances ranging from 2.05–2.19 Å. In the third Co2+ site, Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one CoO6 octahedra, corners with six MoO4 tetrahedra, and edges with two equivalent CoO6 octahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Co–O bond distances ranging from 2.05–2.16 Å. In the fourth Co2+ site, Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one CoO6 octahedra, corners with six MoO4 tetrahedra, and edges with two equivalent CoO6 octahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Co–O bond distances ranging from 2.04–2.16 Å. There are seven inequivalent Cu+1.14+ sites. In the first Cu+1.14+ site, Cu+1.14+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 2.05–2.60 Å. In the second Cu+1.14+ site, Cu+1.14+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 2.05–2.60 Å. In the third Cu+1.14+ site, Cu+1.14+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 2.05–2.62 Å. In the fourth Cu+1.14+ site, Cu+1.14+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of Cu–O bond distances ranging from 2.04–2.62 Å. In the fifth Cu+1.14+ site, Cu+1.14+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with six MoO4 tetrahedra. There are a spread of Cu–O bond distances ranging from 2.07–2.24 Å. In the sixth Cu+1.14+ site, Cu+1.14+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with six MoO4 tetrahedra and faces with two equivalent CuO6 octahedra. There are a spread of Cu–O bond distances ranging from 2.11–2.26 Å. In the seventh Cu+1.14+ site, Cu+1.14+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with six MoO4 tetrahedra and faces with two equivalent CuO6 octahedra. There are a spread of Cu–O bond distances ranging from 2.10–2.28 Å. There are twenty-eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mo6+ and one Cu+1.14+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Mo6+ and one Cu+1.14+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+, one Co2+, and one Cu+1.14+ atom. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+, one Co2+, and one Cu+1.14+ atom. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+, one Co2+, and one Cu+1.14+ atom. In the eighth O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+, one Co2+, and one Cu+1.14+ atom. In the ninth O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+ and two equivalent Co2+ atoms. In the tenth O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+ and two equivalent Co2+ atoms. In the eleventh O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+ and two equivalent Co2+ atoms. In the twelfth O2- site, O2- is bonded in a trigonal planar geometry to one Mo6+ and two equivalent Co2+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted linear geometry to one Mo6+ and one Cu+1.14+ atom. In the fourteenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Mo6+ and one Cu+1.14+ atom. In the fifteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the sixteenth O2- site, O2- is bonded in a 1-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the eighteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the nineteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the twentieth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the twenty-first O2- site, O2- is bonded in a 2-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the twenty-second O2- site, O2- is bonded in a 2-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the twenty-third O2- site, O2- is bonded in a 2-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the twenty-fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Mo6+ and two Cu+1.14+ atoms. In the twenty-fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the twenty-sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the twenty-seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms. In the twenty-eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mo6+ and two Co2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Constructing a square-like copper cluster to boost C–C coupling for CO 2 electroreduction to ethylene

The CO 2 electroreduction reaction (CO 2 ER) to ethylene (C 2 H 4 ) offers the dual promise of lowering CO 2 emission while storing energy from renewable electricity, for which the development of highly efficient electrocatalysts is of great significance. Herein, by means of density functional theory (DFT) computations, we designed an electrocatalyst for CO 2 -to-C 2 H 4 conversion by anchoring a Cu 5 cluster supported on a MoS 2 monolayer with an S monovacancy (Cu 5 @MoS 2 ). Our results revealed that one Cu atom of the Cu 5 cluster was embedded into the framework of the defective MoS 2 monolayer, while the other four Cu atoms form a square-like island over the substrate surface. Interestingly, the C–C coupling between two *CO species can easily occur on the unique square-like active site with a low kinetic barrier of 0.56 eV to form the key *C 2 O 2 intermediate, which can then be hydrogenated to the C 2 H 4 product with a very low limiting potential (–0.32 eV). Significantly, alkaline conditions (pH = 13) are beneficial to further promote C 2 H 4 synthesis. Finally, our work may offer a new avenue to precisely modulate the structures of Cu clusters for converting CO 2 into high-value target products.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Electrochemical CO2 Reduction over Metal-/Nitrogen-Doped Graphene Single-Atom Catalysts Modeled Using the Grand-Canonical Density Functional Theory

Renewably driven, electrochemical conversion of carbon dioxide into value-added products is expected to be a critical tool in global decarbonization. However, theoretical studies based on the computational hydrogen electrode largely ignore the nonlinear effects of the applied potential on the calculated results, leading to inaccurate predictions of catalytic behavior or mechanistic pathways. Here, we use grand canonical density functional theory (GC-DFT) to model electrochemical CO2 reduction (CO2R) over metal- and nitrogen-doped graphene catalysts (MNCs) and explicitly include the effects of the applied potential. We used GC-DFT to compute the CO2 to CO reaction intermediate energies at -0.3, -0.7, and -1.2 VSHE catalyzed by MNCs each doped with 1 of the 10 3d block metals coordinated by four pyridinic nitrogen atoms. Our results predict that Sc-, Ti-, Co-, Cu-, and Zn-N4Cs effectively catalyze CO2R at moderate to large reducing potentials (-0.7 to -1.2 VSHE). ZnN4C is a particularly promising electrocatalyst for CO2R to CO both at low and moderate applied potentials based on our thermodynamic analysis. Our findings also explain the observed pH independence of CO production over FeN4C and predict that the rate-determining step of CO2R over FeN4C is not *CO2- formation but rather *CO desorption. Additionally, the GC-DFT-computed density of states analysis illustrates how the electronic states of MNCs and adsorbates change non-uniformly with applied potential, resulting in a significantly increased *CO2- stability relative to other intermediates and demonstrating that the formation of the adsorbed *CO2- anion is critical to CO2R activation. This work demonstrates how GC-DFT paves the way for physically realistic and accurate theoretical simulations of reacting electrochemical systems.

CO2 reduction↗
NASA NTRS1977

Production of dense plasmas in a hypocycloidal pinch apparatus

A high-power pinch apparatus consisting of disk electrodes was developed, and diagnostic measurements to study its mechanism of dense plasma production have been made. The collapse fronts of the current sheets are well organized, and dense plasma foci are produced on the axis with radial stability in excess of 5 microsec. A plasma density greater than 10 to the 18th power per cu cm is determined with Stark broadening and CO2 laser absorption. Essentially complete absorption of a high-energy CO2 laser beam has been observed. A plasma temperature of approximately 1 keV is measured with differential transmission of soft X-rays through thin foils. The advantages of this apparatus over the coaxial plasma focus are improvements in (1) plasma volume, (2) stability, (3) containment time, (4) access to additional heating by laser or electron beams, and (5) the possibility of scaling up to a multiple array for high-power operation.

Lee, J. H.↗
DOE OSTI2023

Organic Additive–derived Films on Cu Electrodes Promote Electrochemical CO 2 Reduction to C 2+ Products Under Strongly Acidic Conditions

Electrochemical CO 2 reduction (CO 2 R) at low pH is desired for high CO 2 utilization; the competing hydrogen evolution reaction (HER) remains a challenge. High alkali cation concentration at a high operating current density has recently been used to promote electrochemical CO 2 R at low pH. Herein we report an alternative approach to selective CO2R (>70 % Faradaic efficiency for C 2+ products, FE C2+ ) at low pH (pH 2; H 3 PO 4 /KH 2 PO 4 ) and low potassium concentration ([K + ]=0.1 M) using organic film-modified polycrystalline copper (Modified-Cu). Furthermore, such an electrode effectively mitigates HER due to attenuated proton transport. Modified-Cu still achieves high FE C2+ (45 % with Cu foil /55 % with Cu GDE) under 1.0 M H 3 PO 4 (pH≈1) at low [K + ] (0.1 M), even at low operating current, conditions where HER can otherwise dominate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Highly selective electrocatalytic CO 2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper

Direct electrochemical conversion of CO 2 to ethanol offers a promising strategy of lowering CO 2 emission while storing energy from renewable electricity. However, current electrocatalysts offer only limited selectivity toward ethanol. Here we report a copper catalyst synthesized by a unique Cu-Li amalgm method over a commercial carbon support that achieved Faradaic efficiency (FE) higher than 91% at -0.7 V (RHE) and the active potential as low as -0.4 V (RHE) during direct electrocatalytic CO 2 -to-ethanol conversion. The catalyst also demonstrated stability over an extended period of operation. A strong correlation between the catalytic selectivity and the initial Cu atoms dispersion was found and Operando X-ray absorption spectroscopy identified a dynamic and reversible transformation from atomically dispersed copper atoms to Cu n (n = 3 and 4) under the electrochemical reaction. Frist-principles calculations further elucidate the possible catalytic mechanism of CO 2 reduction over Cu n .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Atomic Layer Deposition of Cu Electrocatalysts on Gas Diffusion Electrodes for CO 2 Reduction

Electrochemical reduction of CO 2 using Cu catalysts enables the synthesis of C 2+ products including C 2 H 4 and C 2 H 5 OH. Here, in this study, Cu catalysts were fabricated using plasma-enhanced atomic layer deposition (PEALD), achieving conformal deposition of catalysts throughout 3-D gas diffusion electrode (GDE) substrates while maintaining tunable control of Cu nanoparticle size and areal loading. The electrochemical CO 2 reduction at the Cu surface yielded a total Faradaic efficiency (FE) > 75% for C 2+ products. Parasitic hydrogen evolution was minimized to a FE of ~10%, and a selectivity of 42.2% FE for C 2 H 4 was demonstrated. Compared to a line-of-sight physical vapor deposition method, PEALD Cu catalysts show significant suppression of C 1 products compared to C 2+ , which is associated with improved control of catalyst morphology and conformality within the porous GDE substrate. Finally, PEALD Cu catalysts demonstrated a stable performance for 15 h with minimal reduction in the C 2 H 4 production rate.

42 ENGINEERING↗
DOE OSTI2020

Materials Data on Sr3Co2Cu2S2O5 by Materials Project

Sr3Co2Cu2S2O5 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, faces with four equivalent SrO12 cuboctahedra, and faces with eight equivalent CoO5 square pyramids. There are four shorter (2.78 Å) and eight longer (2.96 Å) Sr–O bond lengths. In the second Sr2+ site, Sr2+ is bonded in a 4-coordinate geometry to four equivalent S2- and four equivalent O2- atoms. All Sr–S bond lengths are 3.26 Å. All Sr–O bond lengths are 2.48 Å. Co2+ is bonded to five O2- atoms to form CoO5 square pyramids that share corners with five equivalent CoO5 square pyramids and faces with four equivalent SrO12 cuboctahedra. There is one shorter (1.92 Å) and four longer (1.99 Å) Co–O bond length. Cu2+ is bonded to four equivalent S2- atoms to form a mixture of corner and edge-sharing CuS4 tetrahedra. All Cu–S bond lengths are 2.40 Å. S2- is bonded in a 8-coordinate geometry to four equivalent Sr2+ and four equivalent Cu2+ atoms. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to four Sr2+ and two equivalent Co2+ atoms. In the second O2- site, O2- is bonded to four equivalent Sr2+ and two equivalent Co2+ atoms to form a mixture of distorted corner and edge-sharing OSr4Co2 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CuC4(NO2)4 by Materials Project

CuO2(N2CO)2(CO2)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four carbon dioxide molecules, two copper(ii) hydroxide molecules, and four N2CO clusters. In each N2CO cluster, C4+ is bonded in a 1-coordinate geometry to two N+0.50- and one O2- atom. Both C–N bond lengths are 1.40 Å. The C–O bond length is 1.20 Å. There are two inequivalent N+0.50- sites. In the first N+0.50- site, N+0.50- is bonded in a 1-coordinate geometry to one C4+ and one N+0.50- atom. The N–N bond length is 1.32 Å. In the second N+0.50- site, N+0.50- is bonded in a 1-coordinate geometry to one C4+ and one N+0.50- atom. O2- is bonded in a single-bond geometry to one C4+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Deccan volcanism at the Cretaceous-Tertiary boundary

The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as the Deccan and KTB events appears to rest on an increasingly stronger basis.

Courtillot, V.↗