Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “TiO2”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Influence of crystalline order and defects on the absolute work functions and electron affinities of TiO2- and SrO-terminated n-SrTiO3(001)

We establish how the detailed structure and composition of the terminal layer of n-SrTiO3 (001) determine key surface electronic properties. We have measured and calculated from first principles the absolute work functions and electron affinities of bulk SrNb0.01Ti0.99O3(001) with both TiO2 and nominally SrO terminal planes. The match between theory and experiment is excellent at 4.6(1) eV for the TiO2 termination if an ideal, bulk-truncated surface structure is assumed. In contrast, the ideal SrO-termination leads to a calculated work function that is ~1.3 eV lower than the experimental value of 3.6(1) eV. We show that this discrepancy is associated with defects on the SrO surface that serve as electron scavengers. These defects deplete the concentration of itinerant electrons in the subsurface region and increase the negative charge density on the surface, thus increasing the work function. Several different surface defect configurations were modeled; the ones that yield the best agreement with experiment involve Sr vacancies in the terminal layer along with OH–/H– pairs or O22– occupying anion sites adjacent to the Sr vacancies.

Chambers, Scott A.↗
NASA NTRS1982

Chemical modification of TiO2 surfaces with methylsilanes and characterization by infrared absorption spectroscopy

Infrared absorption spectra of methylsilanes bonded to a TiO2 powder were obtained. The reacting silanes include Me sub (4-n)SiX sub n (n=1-4; X=Cl, OMe) and hexamethyldisilazane (HMDS). Reactions were performed on hydroxylated-but-anhydrous TiO2 surfaces in the gas phase. IR spectra confirm the presence of a bonded silane layer. Terminal surface OH groups are found to react more readily than bridging OH groups. By-products of the modification adsorp tenaciously to the surface. The various silanes show only small differences in their ability to sequester surface OH groups. Following hydrolysis in moist air, Si-OH groups are observed only for the tetrafunctional silanes.

Finklea, H. O.↗
NASA NTRS1991

A reevaluation of spectral ratios for lunar mare TiO2 mapping

The empirical relation established by Charette et al. (1974) between the 400/560-nm spectral ratio of mature mare soils and weight percent TiO2 has been used extensively to map titanium content in the lunar maria. Relative reflectance spectra of mare regions show that a reference wavelength further into the near-IR, e.g., above 700 nm, could be used in place of the 560-nm band to provide greater contrast (a greater range of ratio values) and hence a more sensitive indicator of titanium content. An analysis of 400/730-nm ratio values derived from both laboratory and telescopic relative reflectance spectra suggests that this ratio provides greater sensitivity to TiO2 content than the 400/560-nm ratio. The increased range of ratio values is manifested in higher contrast 400/730-nm ratio images compared to 400/560-nm ratio images. This potential improvement in sensivity encourages a reevaluation of the original Charette et al. (1974) relation using the 400/730-nm ratio.

Johnson, Jeffrey R.↗
NASA NTRS2012

Fischer-Tropsch Cobalt Catalyst Improvements with the Presence of TiO2, La2O3, and ZrO2 on an Alumina Support

The objective of this study was to evaluate the effect of titanium oxide, lanthanum oxide, and zirconium oxide on alumina supported cobalt catalysts. The hypothesis was that the presence of lanthanum oxide, titanium oxide, and zirconium oxide would reduce the interaction between cobalt and the alumina support. This was of interest because an optimized weakened interaction could lead to the most advantageous cobalt dispersion, particle size, and reducibility. The presence of these oxides on the support were investigated using a wide range of characterization techniques such as SEM, nitrogen adsorption, x-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed reduction after reduction (TPR-AR), and hydrogen chemisorptions/pulse reoxidation. Results indicated that both La2O3 and TiO2 doped supports facilitated the reduction of cobalt oxide species in reference to pure alumina supported cobalt catalysts, however further investigation is needed to determine the effect of ZrO2 on the reduction profile. Results showed an increased corrected cluster size for all three doped supported catalysts in comparison to their reference catalysts. The increase in reduction and an increase in the cluster size led to the conclusion that the support-metal interaction weakened by the addition of TiO2 and La2O3. It is also likely that the interaction decreased upon presence of ZrO2 on the alumina, but further research is necessary. Preliminary results have indicated that the alumina-supported catalysts with titanium oxide and lanthanum oxide present are of interest because of the weakened cobalt support interaction. These catalysts showed an increased extent of reduction, therefore more metallic cobalt is present on the support. However, whether or not there is more cobalt available to participate in the Fischer-Tropsch synthesis reaction (cobalt surface atoms) depends also on the cluster size. On one hand, increasing cluster size alone tends to decrease the active site density; on the other hand, by increasing the size of the cobalt clusters, there is less likelihood of forming oxidized cobalt complexes (cobalt aluminate) during Fischer-Tropsch synthesis. Thus, from the standpoint of stability, improving the extent of reduction while increasing the particle size slightly may be beneficial for maintaining the sites, even if there is a slight decrease in overall initial active site density.

Klettlinger, Jennifer Lindsey Suder↗
NASA NTRS2016

Visible-Light-Responsive Photocatalysis: Ag-Doped TiO2 Catalyst Development and Reactor Design Testing

In recent years, the alteration of titanium dioxide to become visible-light-responsive (VLR) has been a major focus in the field of photocatalysis. Currently, bare titanium dioxide requires ultraviolet light for activation due to its band gap energy of 3.2 eV. Hg-vapor fluorescent light sources are used in photocatalytic oxidation (PCO) reactors to provide adequate levels of ultraviolet light for catalyst activation; these mercury-containing lamps, however, hinder the use of this PCO technology in a spaceflight environment due to concerns over crew Hg exposure. VLR-TiO2 would allow for use of ambient visible solar radiation or highly efficient visible wavelength LEDs, both of which would make PCO approaches more efficient, flexible, economical, and safe. Over the past three years, Kennedy Space Center has developed a VLR Ag-doped TiO2 catalyst with a band gap of 2.72 eV and promising photocatalytic activity. Catalyst immobilization techniques, including incorporation of the catalyst into a sorbent material, were examined. Extensive modeling of a reactor test bed mimicking air duct work with throughput similar to that seen on the International Space Station was completed to determine optimal reactor design. A bench-scale reactor with the novel catalyst and high-efficiency blue LEDs was challenged with several common volatile organic compounds (VOCs) found in ISS cabin air to evaluate the system's ability to perform high-throughput trace contaminant removal. The ultimate goal for this testing was to determine if the unit would be useful in pre-heat exchanger operations to lessen condensed VOCs in recovered water thus lowering the burden of VOC removal for water purification systems.

Photocatalysis↗
NASA NTRS2019

Microstructural Characterization of TiO2-II in the Chicxulub Peak Ring

The peak ring of the approximately 180 kilometer-diameter Chicxulub impact crater on the Yucatan Peninsula, Mexico, was recently drilled during IODP-ICDP (International Ocean Discovery Program-International Continental Scientific Drilling Program) Expedition 364, producing core M0077A. The new core provides insights into the anatomy, composition, tectonic deformation, shock metamorphism, and post-impact overprint of crater-filling impactites and crystalline basement rocks. The basement rocks were shocked to approximately 12.5-17.5 gigapascals, uplifted, and hydrothermally altered. This study presents a combined Raman spectroscopic and electron backscatter diffraction (EBSD) study of TiO2-II, a high-pressure polymorph of TiO2 with an alpha-PbO2 structure (orthorhombic; space group Pbcn; density 4.34 grams per cubic centimeter, in shocked granitoid rock of the Chicxulub peak ring.

Schmieder, Martin↗
DOE OSTI2020

Aqueous Phase Aldol Condensation of Formaldehyde and Acetone on Anatase TiO2(101) Surface: A Theoretical Investigation

A mechanistic understanding of catalytic reactions at solid-liquid interface is limited both experimentally and theoretically but attracts much interest. Using density functional theory calculations (DFT) and ab initio molecular dynamics (AIMD) simulations, we investigated the effect of liquid water on a-H abstraction, C-C coupling, and dehydration steps of aldol condensation of formaldehyde and acetone on an anatase TiO2(101) surface. The existence of the aqueous phase lowered the Gibbs energy of activation of dehydration step pronouncedly from 187 to 74 kJ/mol through proton transfer mechanism, making the hydrogenation pathway more favorable in the aqueous phase. In contrast, a mixed route prevails in the vapor phase. This work provides insights into the effect of the bulk water through a proton transfer mechanism on the dehydrogenation, C-C coupling, and dehydration

anatase TiO2, formaldehyde and acetone, aldol cond↗
DOE OSTI2024

Nanoporous Tio2 Water Training Data

Data and input files used to train a Deep Potential (DP) model for the nanoporous TiO2-water interface. The DeepMD-kit code was used to train the DP. Information about data format, and how to use DeepMD-kit can be found at https://docs.deepmodeling.com/projects/deepmd/en/master/

08 HYDROGEN↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form a mixture of corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles are 49°. There is four shorter (1.96 Å) and two longer (2.00 Å) Ti–O bond length. O2- is bonded in a distorted trigonal planar geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is zeta iron carbide-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 51–52°. There are a spread of Ti–O bond distances ranging from 1.88–2.13 Å. O2- is bonded in a distorted trigonal planar geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is trigonal omega-like structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form edge-sharing TiO6 octahedra. All Ti–O bond lengths are 1.99 Å. O2- is bonded in a 3-coordinate geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is beta Vanadium nitride-like structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form a mixture of distorted corner and edge-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles are 23°. There are a spread of Ti–O bond distances ranging from 1.93–2.00 Å. O2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is beta Vanadium nitride-like structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Ti4+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge and corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles are 25°. There is four shorter (1.95 Å) and two longer (2.01 Å) Ti–O bond length. O2- is bonded in a distorted T-shaped geometry to three equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is Baddeleyite structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ti4+ is bonded to seven O2- atoms to form a mixture of distorted edge and corner-sharing TiO7 pentagonal bipyramids. There are a spread of Ti–O bond distances ranging from 1.88–2.26 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three equivalent Ti4+ atoms. In the second O2- site, O2- is bonded to four equivalent Ti4+ atoms to form a mixture of distorted edge and corner-sharing OTi4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 is quartz (alpha) structured and crystallizes in the trigonal P3_121 space group. The structure is three-dimensional. Ti4+ is bonded to four equivalent O2- atoms to form corner-sharing TiO4 tetrahedra. All Ti–O bond lengths are 1.83 Å. O2- is bonded in a bent 150 degrees geometry to two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiO2 by Materials Project

TiO2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.78–2.34 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form a mixture of distorted edge and corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles are 28°. There are a spread of Ti–O bond distances ranging from 1.86–2.16 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three Ti4+ atoms. In the second O2- site, O2- is bonded in a distorted T-shaped geometry to three Ti4+ atoms. In the third O2- site, O2- is bonded in a linear geometry to two Ti4+ atoms. In the fourth O2- site, O2- is bonded to four Ti4+ atoms to form a mixture of distorted edge and corner-sharing OTi4 trigonal pyramids.

36 MATERIALS SCIENCE↗