| 1. |
- Zhang, J. G., et al.
(författare)
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Microstructure and mechanical properties of spray formed ultrahigh-carbon steels
- 2004
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 383:1, s. 45-49
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and mechanical properties of the spray formed 1.25C-3.0Si-1.5Cr ultrahigh-carbon steel (UHCS) were described. The 1.25C-3.0Si-1.5Cr UHCS was processed by spray forming to break up carbide networks. The fine pearlites with average interlamellar spacing of 0.20 mum was observed in the as-sprayed microstructure. The ultimate tensile strength and the pearlite spacing can be related by the Hall-Petch equation. The as-sprayed 1.25C-3.0Si-1.5Cr UHCS consisting of fine lamellar pearlites has been shown to exhibit superplastic behavior at elevated temperature. The dramatic change of microstructure from fine lamellar pearlites to equiaxed grains stabilized by spheroidized particles during superplastic deformation has been observed. The estimation on the basis of thermodynamics shows that the content of chromium of 1.54 wt.% is needed to inhibit graphite formation in the l.25C-3.OSi-1.5Cr UHCS.
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| 2. |
- Guo, J.-H., et al.
(författare)
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Molecular structure of alcohol-water mixtures
- 2003
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 91:15
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Tidskriftsartikel (refereegranskat)abstract
- We use x-ray emission spectroscopy to elucidate the molecular structure of liquid methanol, water, and methanol-water solutions. We find that molecules in the pure liquid methanol predominantly persist as hydrogen-bonded chains and rings with six and/or eight molecules of equal abundance. For water-methanol solutions we find evidence of incomplete mixing at the microscopic level. Our results provide a new explanation for a smaller entropy increase in the solution due to water molecules bridging methanol chains to form rings.
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| 3. |
- Guo, J. H., et al.
(författare)
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X-ray emission spectroscopy of hydrogen bonding and electronic structure of liquid water
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 89:13
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Tidskriftsartikel (refereegranskat)abstract
- We use x-ray emission spectroscopy to examine the influence of the intermolecular interaction on the local electronic structure of liquid water. By comparing x-ray emission spectra of the water molecule and liquid water, we find a strong involvement of the a(1)-symmetry valence-orbital in the hydrogen bonding. The local electronic structure of water molecules, where one hydrogen bond is broken at the hydrogen site, is separately determined. Our results provide an illustration of the important potential of x-ray emission spectroscopy for elucidating basic features of liquids.
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| 4. |
- Hellgren, N., et al.
(författare)
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Nitrogen bonding structure in carbon nitride thin films studied by soft x-ray spectroscopy
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:26, s. 4348-4350
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Tidskriftsartikel (refereegranskat)abstract
- Soft x-ray absorption (SXAS) and emission (SXES) spectroscopies were applied to study the nitrogen bonding structure in magnetron sputtered CNx thin films. By comparing with calculated spectra of N in different model systems, N in three main bonding environments can be identified: (i) C equivalent toN bonds, with a sharp SXAS peak at 399.5 eV, (ii) pyridine-like N (i.e., N bonded to two C atoms), with an x-ray absorption resonance at similar to 398.5 eV, and (iii) N substituted in graphite, possibly with one sp(3) carbon as a neighbor (SXAS energy similar to 401 eV). These bondings are present in all CNx films analyzed; however, as shown earlier, the relative intensities between the peaks may vary with the growth conditions. Differences in the coordination of the nearest or second nearest C neighbors only cause slight changes in the peak positions and spectrum shape.
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| 5. |
- Kashtanov, Stepan, et al.
(författare)
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Local structures of liquid water studied by x-ray emission spectroscopy
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:2
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Tidskriftsartikel (refereegranskat)abstract
- The O Kalpha x-ray emission spectra of water clusters with different sizes and conformations embedded in a continuum medium are simulated. The calculations have successfully explained the experimental spectra of water in both gas and liquid phases. It is shown that the x-ray emission spectra are very sensitive to the local hydrogen bonding structures. Strong electron sharing between different water molecules is observed and its possible connection to the covalency of hydrogen bonding is discussed. The experimentally observed strong excitation energy dependence of the spectra has been interpreted in terms of the polarization and angular dependence for the gas phase, and in terms of variations of local hydrogen bonding structures for the liquid phase.
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| 6. |
- Nyberg, M., et al.
(författare)
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Bond formation in titanium fulleride compounds studied through x-ray emission spectroscopy
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:11, s. art. no.-115117
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Tidskriftsartikel (refereegranskat)abstract
- The geometric and electronic structures of titanium fulleride complexes have been studied at the gradient corrected density-functional theory level by using various C60Tix (x=1,2) clusters. The cluster with the Ti atom binding on the six-ring site (eta (6)) Of the fullerene is shown to be lower in energy than those with Ti atom adsorbed on either five-ring (eta (5)) Or bridge(eta (2)) sites. The bond formation for titanium fulleride has further been examined by calculated nonresonant, resonant, and off-resonant . x-ray emission spectra of the clusters, and a comparison to the experimental counterpart. The examination shows that only the theoretical spectra of clusters with a six-ring adsorption site are in close agreement with the experimental x-ray emission spectra of titanium fulleride films. Our results indicate that off-resonant x-ray emission spectra provide an excellent basis for the probing of the bonding between metals and organic molecules.
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| 7. |
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| 8. |
- O'Shea, J. N., et al.
(författare)
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Hydrogen-bond induced surface core-level shift in isonicotinic acid
- 2001
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:10, s. 1917-1920
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular hydrogen-bonding in thick films of isonicotinic acid evaporated onto rutile TiO2(110) has been investigated with X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The rate of deposition is found to be a key factor in overcoming the kinetic barriers to extensive hydrogen-bond formation, which, when present, gives rise to large energy shifts between bulk and surface in both the N1s XPS and XAS. The origin of the surface core-level shift is attributed to the presence of non-hydrogen-bonded nitrogen atoms in the surface layer.
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| 9. |
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| 10. |
- O'Shea, J. N., et al.
(författare)
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Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids
- 2001
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 486:3, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic; picolinic and bi-isonicotinic acid) evaporated onto rutile TiO2(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. These molecules are shown to be strongly H-bonded in the condensed phase, and a surface core-level shift is observed due to the presence of non-H-bonded nitrogen atoms in the surface layer. Density functional theory calculations are used to relate the experimental data to the proposed bonding configurations based on the surface termination of the known equilibrium solid-state structure. A kinetic barrier, attributed to the high degree of molecular orientation required for the formation of extended H-bonding networks, has also been investigated.
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