| 1. |
- Schalk, Oliver, et al.
(författare)
-
Dissociation kinetics of excited ions : PEPICO measurements of Os-3(CO)(12) - The 7-35 eV single ionization binding energy region
- 2018
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:8
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os-3(CO)(12), in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behaviorwas observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 similar to 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 similar to 0.4 eV, corresponding to one electron being ejected from the Os3 center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.
|
|
| 2. |
- Gunneriusson, Lars, et al.
(författare)
-
Jarosite inclusion of fluoride and its potential significance to bioleaching of sulphide minerals
- 2009
-
Ingår i: Hydrometallurgy. - : Elsevier BV. - 0304-386X .- 1879-1158. ; 96:1-2, s. 108-116
-
Tidskriftsartikel (refereegranskat)abstract
- Incorporation of fluoride ions into the structure of jarosite, a common precipitate in bioleaching, was studied. Crystalline jarosite was synthesized in the presence of various concentrations of fluoride ions and characterized by spectroscopic- and chemical analysis.The results showed that substantial amounts of fluoride were sorbed to jarosite, increasing with pH and fluoride concentration. FTIR, XRD and Mössbauer analysis supported a structural incorporation of the fluoride. Due to the size similarity between fluoride and hydroxide ions, a probable mechanism is an exchange of hydroxide ions and fluoride ions within the jarosite, giving the composition KFe3(SO4)2(OH)6 - xFx(s). For the maximum concentration of fluoride used during synthesis, 200 mM, about 25% of the hydroxide ions were exchanged for fluoride ions. The mass of jarosite precipitated shown to be highly dependent on the fluoride concentration, with approximately half the yield using 200 mM potassium fluoride compared to in the absence of fluoride ions.To test the influence on toxicity of the incorporation of fluoride in jarosite, a bioleaching study was performed at 65 °C. A suspension of pyrite concentrate with 4% solid content (w/v) in the modified 9 K medium was bioleached under additions of potassium fluoride. The results indicated a higher tolerance for fluoride ions, as compared to earlier reported studies on fluoride toxicity during bioleaching.
|
|
| 3. |
- Korzhavyi, Pavel A., 1966-, et al.
(författare)
-
Constitutional and thermal point defects in B2 NiAl
- 2000
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:9, s. 6003-6018
-
Tidskriftsartikel (refereegranskat)abstract
- The formation energies of point defects and the interaction energies of various defect pairs in NiAl are calculated from first principles within an order N, locally self-consistent Green's-function method in conjunction with multipole electrostatic corrections to the atomic sphere approximation. The theory correctly reproduces the ground state for the off-stoichiometric NiAl alloys. The constitutional defects (antisite Ni atoms and Ni vacancies in Ni-rich and Al-rich NiAl, respectively) are shown to form ordered structures in the ground state, in which they tend to avoid each other at the shortest distance on their sublattice. The dominant thermal defects in Ni-rich and stoichiometric NiAl are calculated to be triple defects. In Al-rich alloys another type of thermal defect dominates, where two Ni vacancies are replaced by one antisite Al atom. As a result, the vacancy concentration decreases with temperature in this region. The effective defect formation enthalpies for different concentration regions of NiAl are also obtained.
|
|
| 4. |
- Wang, Zheng, et al.
(författare)
-
Zeolite coated ATR crystal probes
- 2006
-
Ingår i: Sensors and actuators. B, Chemical. - : Elsevier BV. - 0925-4005 .- 1873-3077. ; 115:2, s. 685-690
-
Tidskriftsartikel (refereegranskat)abstract
- Thin and well-defined MFI type molecular sieve films were grown on a range of ATR crystals by employing a seeding method. The type of ATR crystal does not influence film morphology. FTIR spectroscopy was used to evaluate the coated ATR crystals as sensor probes. These novel sensor probes could be used to detect low concentrations of organic molecules in a gas flow.
|
|
| 5. |
- Wang, Zeng, et al.
(författare)
-
Zeolite coated ATR crystals for new applications in FTIR-ATR spectroscopy
- 2004
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :24, s. 2888-2889
-
Tidskriftsartikel (refereegranskat)abstract
- Thin silicalite-1 films were grown on ATR crystals and used for detection of low amounts of organic molecules in a gas flow by FTIR spectroscopy.
|
|
| 6. |
- Sun, Xun, et al.
(författare)
-
Can experiment determine the stacking fault energy of metastable alloys?
- 2021
-
Ingår i: Materials & design. - : Elsevier Ltd. - 0264-1275 .- 1873-4197. ; 199
-
Tidskriftsartikel (refereegranskat)abstract
- Stacking fault energy (SFE) plays an important role in deformation mechanisms and mechanical properties of face-centered cubic (fcc) metals and alloys. In many concentrated fcc alloys, the SFEs determined from density functional theory (DFT) calculations and experimental methods are found having opposite signs. Here, we show that the negative SFE by DFT reflects the thermodynamic instability of the fcc phase relative to the hexagonal close-packed one; while the experimentally determined SFEs are restricted to be positive by the models behind the indirect measurements. We argue that the common models underlying the experimental measurements of SFE fail in metastable alloys. In various concentrated solid solutions, we demonstrate that the SFEs obtained by DFT calculations correlate well with the primary deformation mechanisms observed experimentally, showing a better resolution than the experimentally measured SFEs. Furthermore, we believe that the negative SFE is important for understanding the abnormal behaviors of partial dislocations in metastable alloys under deformation. The present work advances the fundamental understanding of SFE and its relation to plastic deformations, and sheds light on future alloy design by physical metallurgy.
|
|
| 7. |
- Al-Zoubi, Noura, et al.
(författare)
-
Elastic properties of 4d transition metal alloys : Values and trends
- 2019
-
Ingår i: Computational materials science. - : ELSEVIER SCIENCE BV. - 0927-0256 .- 1879-0801. ; 159, s. 273-280
-
Tidskriftsartikel (refereegranskat)abstract
- Using the Exact Muffin-Tin Orbitals method within the Perdew-Burke-Ernzerhof exchange-correlation approximation for solids and solid surfaces (PBEso1), we study the single crystal elastic constants of 4d transition metals (atomic number Z between 39 and 47) and their binary alloys in the body centered cubic (bcc) and face centered cubic (fcc) structures. Alloys between the first neighbors Z(Z + 1) and between the second neighbors Z(Z + 2) are considered. The lattice constants, bulk moduli and elastic constants are found in good agreement with the available experimental and theoretical data. It is shown that the correlation between the relative tetragonal shear elastic constant C-fcc'-2C(bcc)' and the structural energy difference between the fcc and bcc lattices Delta E is superior to the previously considered models. For a given crystal structure, the equiatomic Z(Z + 2) alloys turn out to have similar structural and elastic properties as the pure elements with atomic number (Z + 1). Furthermore, alloys with composition Z(1-x)(Z + 2)(x) possess similar properties as Z(1-2x)(Z + 1)(2x). The present theoretical data on the structural and the elastic properties of 4d transition metal alloys provides consistent input for coarse scale modeling of material properties.
|
|
| 8. |
- Bleskov, I. D., et al.
(författare)
-
Ab initio calculations of elastic properties of Ru1-xNixAl superalloys
- 2009
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:16
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio total energy calculations based on the exact muffin-tin orbitals method, combined with the coherent potential approximation, have been used to study the thermodynamical and elastic properties of substitutional refractory Ru1-xNixAl alloys. We have found that the elastic constants C' and C11 exhibit pronounced peculiarities near the concentration of about 40 at. % Ni, which we ascribe to electronic topological transitions. Our suggestion is supported by the Fermi surface calculations in the whole concentration range. Results of our calculations show that one can design Ru-Ni-Al alloys substituting Ru by Ni (up to 40 at. %) with almost invariable elastic constants and reduced density.
|
|
| 9. |
- Sundell, Gustav, 1985
(författare)
-
Atom Probe Tomography of Hydrogen and of Grain Boundaries in Corroded Zircaloy-2
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to their low thermal neutron capture cross-section, zirconium alloys are widely used in the nuclear industry for fuel cladding and structural components. The lifetime of the fuel assemblies in the reactors are largely dictated by the ability of the fuel cladding to withstand corrosion and mechanical damage. The waterside corrosion mechanism of zirconium alloys is closely related to another material degradation process, namely hydrogen pick-up. In order to study the hydrogenation of zirconium on the atomic level, atom probe tomography (APT) is utilized. This technique offers some unique virtues for nanometer scale materials analysis, such as equal sensitivity to all elements. However, as APT has rarely been used for hydrogen studies previously, methods for accurate quantitative analysis need to be developed.The vacuum chamber in which APT analysis is carried out typically contains small amounts of residual gases, e.g. hydrogen. Hydrogen gas can be adsorbed onto the APT specimen, and analyzed along with the specimen material. This will obscure the true hydrogen content that is found in subsequent data evaluation.A study of the experimental parameters that govern hydrogen adsorption has been carried out on a nickel-based alloy. Hydrogen adsorption can be reduced significantly by field evaporation either at low field strengths, using high laser pulse energies, or at very high field strengths using voltage pulsing. Supply of hydrogen to the tip apex is concluded to occur by direct gas phase adsorption, and it resides on the surface in a field-adsorbed state. It will then be desorbed through field evaporation, where the field strength in the tip vicinity will determine whether it is detected in atomic ion or molecular ion form.The metal-oxide interface in corroded Zircaloy-2 was also studied using APT. Segregation of the alloying elements Fe and Ni to deformation-induced sub-grain boundaries in the metal was observed. The chemistry of these grain boundaries is subsequently inherited by the oxide as the metal is consumed. This is concluded to be of importance for the corrosion and hydrogen-pickup kinetics, as oxide grain boundaries may act as transport paths for oxygen and hydrogen.
|
|
| 10. |
- Tiburski, Christopher, 1988
(författare)
-
Alloy Plasmonics - Fundamentals and Applications
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alloys have for a long time been important in the development of our society; from the Bronze Age, where man learned how to alloy copper with tin, to today, where many products are made of steel and aluminum alloys. Similarly, but maybe not as generally well known, alloys have lately been proposed as a new paradigm in nanophotonics, to tailor optical properties of nanomaterials that find applications within telecommunication, sensing, or biotechnology. Furthermore, alloys are explored in heterogeneous catalysis to develop solutions to increase activity and selectivity of chemical processes. Nanophotonics and catalysis, separately and in combination, are the focus of this thesis. Specifically, we have compiled a library of alloy complex dielectric functions for the late transition metals by utilizing time-dependent density-functional theory. The calculated dielectric functions were benchmarked by (i) nanofabricating series of alloy nanoparticle arrays with systematically varying composition, (ii) measuring their plasmonic properties, and (iii) comparing these properties with electrodynamic simulations of alloy nanoparticles, using the dielectric function library as the input. These dielectric functions allowed us further to screen the absorption efficiency of nanoparticles of multiple combination of size and composition to show the superior performance of alloys compared to their neat constituents. The second theme in this thesis is plasmon-enhanced catalysis. In this field, there is a continuous discussion regarding the reaction enhancing mechanisms when noble metal catalyst nanoparticles are irradiated with visible light during a catalytic reaction. Here we investigated the role of photothermal enhancement of reactions by tailoring the catalytic activity of nanofabricated particles without radiation by means of alloying Pd with Au, while keeping the optical absorption cross section constant, as confirmed by electrodynamics simulations using our dielectric function library as the input. Temperature is a crucial parameter during catalysis in general and photocatalysis in specifically. However, it is intrinsically difficult to measure the temperature of nanoparticles with traditional methods. Therefore, we presented a hydrogen nanothermometry method that allows measuring nanoparticle temperature directly and noninvasively via the temperature dependent phase transition during Pd-hydride formation. We showed that the Pd particle temperature during light-induced heating can be measured with a resolution of 1 °C.
|
|
