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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A TEM study on the very early crystallization of C-S-H in the presence of polycarboxylate superplasticizers: Transformation from initial C-S-H globules to nanofoils

Polycarboxylate superplasticizers (PCEs) present common admixtures to adjust the rheology of concrete. Previous studies revealed that they can also influence the crystallization of cement hydrates, such as e.g. ettringite. In this study, we investigated the impact of methacrylate ester-based PCEs on the nucleation and crystal growth of C-S-H precipitated from aqueous solutions of Ca(NO{sub 3}){sub 2} and Na{sub 2}SiO{sub 3}. TEM imaging revealed that in the absence of PCEs following a non-classical nucleation mechanism C-S-H initially precipitates as metastable, globular nanoparticles (droplets, d ~ 20–60 nm) which within less than one hour convert to the characteristic nanofoils of early C-S-H. In the presence of PCEs, the initial globuli exhibit a core-shell morphology, presumably with PCE as shell. The shell was found to delay the conversion to nanofoils for several hours by stabilizing the metastable globules. The PCE polymer exhibiting higher anionicity delayed the conversion to nanofoils more than the PCE possessing fewer carboxylate groups.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of aluminum on the FeCr(Al) alloy oxidation resistance in steam environment at low temperature (400 °C) and high temperature (1200 °C)

The effect of aluminum in the FeCr(Al) alloys on the corrosion behavior was studied at two temperatures (400 °C and 1200 °C). For the Fe-21Cr alloy, Cr 2 O 3 layer was formed upon exposure to both temperatures. The addition of Al altered the corrosion mechanism of the alloy. At 1200 °C, a thin α-Al 2 O 3 is formed on the Fe-21Cr-5.5Al alloy. Whereas, at low temperature, a continuous Cr 2 O 3 is formed at the top with an internal Al 2 O 3 layer. These results show that FeCrAl alloys hold promise as Fuel Cladding Materials with Al playing a crucial role under operational as well as accident-like conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of Composition on the Voltage Fade Phenomenon in Lithium-, Manganese-Rich xLiMnO 3 •(1-x)LiNi a Mn b Co c O 2 : A Combinatorial Synthesis Approach

The effect of composition on the voltage fade phenomenon was probed using combinatorial synthesis methods. In compositions that have the general formula, (Li 2 MnO 3 ) a (LiNiO 2 ) b (LiMnO 2 ) c (LiCoO 2 ) d , where 0 ≤ a≤0.83, 0.15 ≤ b ≤ 0.42, 0 ≤ c ≤ 0.85, and 0 ≤ d ≤ 0.30 (a + b + c + d = 1), the dependence of features in the x-ray diffraction pattern and of voltage fade on composition were identified and mapped. The observed values of voltage fade indicated that it displayed some sensitivity to composition, but that the sensitivity was not large. The values of voltage fade were found to be amenable to statistical modeling. The model indicated that it may be possible to lower the value of voltage fade below 0.01% by adjusting the composition of the system; however, the composition is not expected to have the layered–layered structure.

combinatorial synthesis↗
DOE OSTI2014

Chlorine atom-initiated low-temperature oxidation of prenol and isoprenol: The effect of C=C double bonds on the peroxy radical chemistry in alcohol oxidation

The chlorine atom-initiated oxidation of two unsaturated primary C5 alcohols, prenol (3-methyl-2-buten-1-ol, (CH 3 ) 2 CCHCH 2 OH) and isoprenol (3-methyl-3-buten-1-ol, CH 2 C(CH 3 )CH 2 CH 2 OH), is studied at 550 K and low pressure (8 Torr). The time- and isomer-resolved formation of products is probed with multiplexed photoionization mass spectrometry (MPIMS) using tunable vacuum ultraviolet ionizing synchrotron radiation. The peroxy radical chemistry of the unsaturated alcohols appears much less rich than that of saturated C4 and C5 alcohols. The main products observed are the corresponding unsaturated aldehydes – prenal (3-methyl-2-butenal) from prenol oxidation and isoprenal (3-methyl-3-butenal) from isoprenol oxidation. No significant products arising from QOOH chemistry are observed. These results can be qualitatively explained by the formation of resonance stabilized allylic radicals via H-abstraction in the Cl + prenol and Cl + isoprenol initiation reactions. The loss of resonance stabilization upon O 2 addition causes the energies of the intermediate wells, saddle points, and products to increase relative to the energy of the initial radicals and O 2 . These energetic shifts make most product channels observed in the peroxy radical chemistry of saturated alcohols inaccessible for these unsaturated alcohols. The experimental findings are underpinned by quantum-chemical calculations for stationary points on the potential energy surfaces for the reactions of the initial radicals with O 2 . Under our conditions, the dominant channels in prenol and isoprenol oxidation are the chain-terminating HO 2 -forming channels arising from radicals, in which the unpaired electron and the –OH group are on the same carbon atom, with stable prenal and isoprenal co-products, respectively. These results suggest that the presence of C=C double bonds in alcohols will reduce low-temperature reactivity during autoignition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Crystal structure of haloxon, C 14 H 14 C l3 O 6 P

The crystal structure of haloxon has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional theory techniques. Haloxon crystallizes in space group P2 1 /n (#14) with a = 19.60382(6), b = 10.05473(3), c = 8.73591(2) Å, β = 92.6617(2)°, V = 1720.088(11) Å 3 , and Z = 4. The structure consists of discrete molecules. The mean planes of the fused ring systems are approximately 0–11 and 011. The rings form staggered stacks perpendicular to these planes. There are no traditional hydrogen bonds in the structure, but several C–H∙∙∙O and C–H∙∙∙Cl hydrogen bonds contribute to the crystal energy. The powder pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ (PDF®).

36 MATERIALS SCIENCE↗
DOE OSTI2026

TiO 2 Nanoparticles Enabling Photocatalytic Desulfurization for C–C Coupling Reaction Using Visible Light

We uncover a surface-mediated mechanism for visible-light-driven photocatalytic desulfurization of thiols on titanium dioxide (TiO 2 ) nanoparticles under LED illumination (>420 nm). Combined diffuse reflectance, infrared, and cryogenic electron paramagnetic resonance spectroscopy verify the formation of a surface thiol–Ti charge-transfer complex that introduces visible-light absorption into an otherwise UV-active reaction system. Selective photoexcitation of this surface complex drives interfacial charge transfer, directly activating the adsorbed thiol and inducing C–S bond scission without the band gap excitation of TiO 2 . The resulting carbon-centered radical intermediates are intercepted by styrene to form C–C coupling products. These results uncover a distinct surface-mediated photocatalytic mechanism in which charge-transfer complex formation governs both light absorption and chemical activation, providing a mechanistic framework for extending visible-light reactivity to wide-bandgap metal oxide photocatalysts.

addition of carbon radical to vinyl groups↗
DOE OSTI2014

Crossed Beam Reactions of the Phenyl (C 6 H 5 ; X 2 A 1 ) and Phenyl- d 5 Radical (C 6 D 5 ; X 2 A 1 ) with 1,2-Butadiene (H 2 CCCHCH 3 ; X 1 A')

We investigated the reactions on the phenyl (C 6 H 5 ; X 2 A 1 ) and phenyl- d 5 (C 6 D 5 ; X 2 A 1 ) radical with 1,2-butadiene (C 4 H 6 ; X 1 A') at a collision energy of about 52 ± 3 kJ mol –1 in a crossed molecular beam apparatus. The reaction of phenyl with 1,2-butadiene is initiated by adding the phenyl radical with its radical center to the π electron density at the C1/C3 carbon atom of 1,2-butadiene. Later, the initial collision complexes isomerize via phenyl group migration from the C1/C3 carbon atoms to the C2 carbon atom of the allene moiety of 1,2-butadiene. The resulting intermediate undergoes unimolecular decomposition through hydrogen atom emission from the methyl group of the 1,2-butadiene moiety via a rather loose exit transition state leading to 2-phenyl-1,3-butadiene in an overall exoergic reaction (Δ R G = -72 ± 10 kJ mol –1 ). This result reveals the strong collision-energy dependence of this system when the data are compared with those of the phenyl radical with 1,2-butadiene previously recorded at collision energies up to 160 kJ mol –1 , with the previous study exhibiting the thermodynamically less stable 1-phenyl-3-methylallene (Δ R G = -33 ± 10 kJ mol –1 ) and 1-phenyl-2-butyne (Δ R G = -24 ± 10 kJ mol –1 ) to be the dominant products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Dissociative recombination and mutual neutralization of heavier molecular ions: C{sub 10}H{sub 8}{sup +}, WF{sub 5}{sup +}, and C{sub n}F{sub m}{sup +}

Dissociative recombination (DR) rate coefficients for the naphthalene cation, C{sub 10}H{sub 8}{sup +}, and WF{sub 5}{sup +}, and mutual neutralization (MN) rate coefficients for these species and five C{sub n}F{sub m}{sup +} ions, were determined at 300 K using variable electron and neutral density attachment mass spectrometry (VENDAMS). DR proceeds at 9 ± 3 × 10{sup −7} cm{sup 3} s{sup −1} for C{sub 10}H{sub 8}{sup +} and at 6.1 ± 1.4 × 10{sup −7} cm{sup 3} s{sup −1} for WF{sub 5}{sup +}. Consistent with previous results, MN for the polyatomic cations with the halide anions Cl{sup −}, Br{sup −}, and I{sup −} exhibits an approximate μ{sup −1/2} reduced mass dependence of the reactant partners, demonstrating that ion collision velocities influence the rate coefficients. This work is an extension of VENDAMS to systems, where low reactant concentrations are necessary to avoid significant reaction of product ions with the neutral precursor, i.e., conditions not suitable for traditional flowing afterglow measurements, as well as to ions of masses > ∼ 100 Da, which are not amenable to the study of DR in magnetic storage rings. Our results expand the sparse literature on DR and MN of heavier ions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

ELECTRONIC TRANSITIONS OF JET-COOLED SiC{sub 2}, Si{sub 2}C{sub n} (n=1−3), Si{sub 3}C{sub n} (n = 1,2), AND SiC{sub 6}H{sub 4} BETWEEN 250 AND 710 nm

Electronic transitions of the title molecules were measured between 250 and 710 nm using a mass-resolved 1 + 1’ resonant two-photon ionization technique at a resolution of 0.1 nm. Calculations at the B3LYP/aug-cc-pVQZ level of theory support the analyses. Because of their spectral properties, SiC{sub 2}, linear Si{sub 2}C{sub 2}, Si{sub 3}C, and SiC{sub 6}H{sub 4} are interesting target species for astronomical searches in the visible spectral region. Of special relevance is the Si–C{sub 2}–Si chain, which features a prominent band at 516.4 nm of a strong transition (f = 0.25). This band and one from SiC{sub 6}H{sub 4} at 445.3 nm were also investigated at higher resolution (0.002 nm)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

LINE LISTS FOR THE A {sup 2}Π-X {sup 2}Σ{sup +} (RED) AND B {sup 2}Σ{sup +}-X {sup 2}Σ{sup +} (VIOLET) SYSTEMS OF CN, {sup 13}C{sup 14}N, AND {sup 12}C{sup 15}N, AND APPLICATION TO ASTRONOMICAL SPECTRA

New red and violet system line lists for the CN isotopologues {sup 13}C{sup 14}N and {sup 12}C{sup 15}N have been generated. These new transition data are combined with those previously derived for {sup 12}C{sup 14}N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Observation of an alternative χ c 0 ( 2 P ) candidate in e + e - → J / ψ D D ¯

IN this work, we perform a full amplitude analysis of the process e + e - → J / ψ D D ¯ , where D refers to either D 0 or D + . A new charmoniumlike state X * ( 3860 ) that decays to D D ¯ is determined with a significance of 6.5 σ . Its mass is ( 3862 - 32 + 26 - 13 + 40 ) MeV / c 2 , and its width is ( 201 - 67 + 154 - 82 + 88 ) MeV . The J P C = 0 + + hypothesis is favored over the 2 + + hypothesis at the level of 2.5 σ . The analysis is based on the 980 fb - 1 data sample collected by the Belle detector at the asymmetric-energy e + e - collider KEKB.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

SU-C-207-02: A Method to Estimate the Average Planar Dose From a C-Arm CBCT Acquisition

Purpose: The planar average dose in a C-arm Cone Beam CT (CBCT) acquisition had been estimated in the past by averaging the four peripheral dose measurements in a CTDI phantom and then using the standard 2/3rds peripheral and 1/3 central CTDIw method (hereafter referred to as Dw). The accuracy of this assumption has not been investigated and the purpose of this work is to test the presumed relationship. Methods: Dose measurements were made in the central plane of two consecutively placed 16cm CTDI phantoms using a 0.6cc ionization chamber at each of the 4 peripheral dose bores and in the central dose bore for a C-arm CBCT protocol. The same setup was scanned with a circular cut-out of radiosensitive gafchromic film positioned between the two phantoms to capture the planar dose distribution. Calibration curves for color pixel value after scanning were generated from film strips irradiated at different known dose levels. The planar average dose for red and green pixel values was calculated by summing the dose values in the irradiated circular film cut out. Dw was calculated using the ionization chamber measurements and film dose values at the location of each of the dose bores. Results: The planar average dose using both the red and green pixel color calibration curves were within 10% agreement of the planar average dose estimated using the Dw method of film dose values at the bore locations. Additionally, an average of the planar average doses calculated using the red and green calibration curves differed from the ionization chamber Dw estimate by only 5%. Conclusion: The method of calculating the planar average dose at the central plane of a C-arm CBCT non-360 rotation by calculating Dw from peripheral and central dose bore measurements is a reasonable approach to estimating the planar average dose. Research Grant, Siemens AG.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Study of the Involvement of {sup 8}Be and {sup 9}B Nuclei in the Dissociation of Relativistic {sup 10}C, {sup 10}B, and {sup 12}C Nuclei

The results obtained by estimating the contribution of 8Be and 9B nuclei to the coherent dissociation of {sup 10}C, {sup 10}B, and {sup 12}C relativistic nuclei in nuclear track emulsions (“white” stars) are presented. The selection of white stars accompanied by 9B leads to a distinct peak appearing in the distribution of the excitation energy of 2α2p ensembles and having a maximum at 4.1 ± 0.3 MeV. A 8Be nucleus manifests itself in the coherent-dissociation reaction {sup 10}B → {sup 2}He + H with a probability of (25 ± 5)%, (14 ± 3)% of it being due to 9B decays. The ratio of the branching fractions of the {sup 9}B + n and {sup 9}Be + p mirror channels is estimated at 6 ± 1. An analysis of the relativistic dissociation of {sup 12}C nuclei in a nuclear track emulsion revealed nine 3α events corresponding to the Hoyle state.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Photoluminescence spectra of thin films of ZnTPP–C{sub 60} and CuTPP–C{sub 60} molecular complexes

The results of studies of thin composite films of zinc and copper tetraphenylporphyrins with different fractions of fullerene C{sub 60} are reported. The photoluminescence spectra are recorded, and the composition and surface morphology are analyzed by means of scanning electron microscopy. The results show a difference in the structure of films with two types of metals (Zn, Cu) entering into the complex of the porphyrin macrocycle. An additional long-wavelength photoluminescence band at 1.4 eV is detected for the first time, which is evidence of the formation of ZnTPP–C{sub 60} molecular complexes from a gas-dynamic vapor flow upon condensation. In CuTPP thin films, the processes of self-assembly into nanowires 20 nm in diameter and up to 50 µm in length and the formation of nanoheterojunctions upon the addition of fullerene C{sub 60} are observed. Quantum-chemical calculations in the context of density-functional theory are carried out to interpret the experimental data.

36 MATERIALS SCIENCE↗
DOE OSTI2016

On the main photoelectric characteristics of three-junction InGaP/InGaAs/Ge solar cells in a broad temperature range (–197°C ≤ T ≤ +85°C)

This study is aimed at investigating the main photoelectric characteristics of three-cascade InGaP/InGaAs/Ge photoelectric converters in a broad temperature range (–197°C ≤ T ≤ +85°C). On account of analysis of photosensitivity spectra and optical current–voltage characteristics, such temperature dependences as the open-circuit voltage (V{sub oc}), filling factor of the current–voltage characteristic (FF), and the photoelectric conversion efficiency of solar radiation are determined. Investigations are performed at illumination intensities corresponding to operation under concentrated radiation. Decreased temperatures facilitate the selection of samples with the minimal “parasitic” potential barriers. The influence of excitationtransfer processes from a cascade into a cascade is estimated by means of secondary luminescent radiation. The highest photoelectric conversion efficiency of 52% is measured at a concentration multiplicity of 100 “suns” and a temperature of–160°C.

14 SOLAR ENERGY↗