| 1. |
- Chen, Zhe, et al.
(author)
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Nano-scale characterization of white layer in broached Inconel 718
- 2017
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In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - Amsterdam : Elsevier BV. - 0921-5093 .- 1873-4936. ; 684, s. 373-384
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Journal article (peer-reviewed)abstract
- The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718.TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ′ and γ′′ clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.
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| 2. |
- Sauer, Christopher, 1993
(author)
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Green Aromatics: Catalytic Valorisation of bio-derived 2,5-dimethylfuran over Zeolites and Zeotypes
- 2022
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Doctoral thesis (other academic/artistic)abstract
- This thesis discusses the use of biomass as a potentially green feedstock for the chemical industry in the urgent shift away from fossil resources. I elaborate on reasons why we cannot afford to burn virgin biomass for energy production, among them a variety of ecosystem services that forests and other lands provide. In addition, the utilisation of biomass should be focused on products that sequester and lock away carbon for more extended periods, e.g. timber, materials and chemicals. In particular, biomass can be used as an alternative "carbon neutral" feedstock for the chemical industry, where we can preserve the already existing chemical complexity in the bio-based molecules. One example is the upgrading of furans to benzene, toluene and xylene (BTX) aromatics with the help of zeolite catalysis. These aromatics are important commodity chemicals, where the shift to a bio-based resource could make use of already existing knowledge, catalyst and production infrastructure. However, research is necessary to understand these new feedstock molecules and their interaction with the catalysts and to enable the design of applicable catalysts. In order to study the interaction of the furans, in particular 2,5-dimethylfuran (2,5-dmf), I describe and discuss the development of an analytical methodology that utilises infrared spectroscopy and mass spectrometry for the on-line identification and quantification of product molecules during catalytic reactions. This on-line analysis method is then applied to the catalytic conversion of 2,5-dmf to aromatics over a range of zeolite and zeotype catalysts. In-depth studies with ammonia as a probe molecule of the catalytic active acid sites, as well as temperature programmed experiments with ammonia and 2,5-dmf give insights into product distribution, selectivity changes and deactivation of the catalyst. For example, olefins and aromatics are initially preferred products, while with increasing time on stream, the isomerisation of 2,5-dmf becomes dominant. The incorporation of Ga into the zeotype framework, resulting in a Ga-Silicate, shows how targeted catalyst design can increase overall aromatics production. This catalyst is also suitable for selective isomerisation of 2,5-dmf to 2,4-dimethylfuran, which has a rare substitution pattern. Finally, itwas found that the most valuable of BTX, p -xylene, can be produced more selectively when 2,5-dmf is pre-adsorbed onto zeolite ZSM-5 and then released during a temperature programmed product desorption.
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| 3. |
- He, Wenxiao, 1985
(author)
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Biomimetic Formation of Calcium Phosphate Based Nanomaterials
- 2014
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Doctoral thesis (other academic/artistic)abstract
- The intercellular material in bone is a nanocomposite of aligned “hard” inorganics—calcium phosphate (CaP) platelets embedded in the long-range ordered “soft” organic collagen matrix. This elaborate structural arrangement redeems the weaknesses of the individual components (being soft protein or brittle mineral) and gives bone its excellent mechanical properties for the protection and support of our bodies. The structural order and hierarchy in the soft matrix is organized via self-assembly of collagen molecules and is reinforced by intermolecular crosslinking. The subsequent growth of “hard” crystallites inside the “soft” matrix compartments, likely through the deposition of a transient amorphous calcium phosphate (ACP) phase, results in the interpenetrated composite structure.The aim of this thesis was to prepare synthetic mimetics of “hard” material (CaP) with well-defined nanostructures, soft organic matrices with long-range order and interpenetrated composites composing of the two. The work was inspired by the material deposition process in natural bone. Lyotropic liquid crystal (LC) phases self-assembled by block copolymers were used to mimic the structural order of the collagen matrix. Both the inorganic morphogenesis of CaP in LCs and the controlled crystallization of ACP were investigated. To explore ordered organic matrices, crosslinking of the LCs and the self-assembly of an amphiphilic peptide with designed sequence were performed. In addition, controlled mineralization within crosslinked LCs was examined for the formation of nanocomposites.ACP nanospheres, CaP nanowires and nanosheets were prepared from LCs via templated growth. The ACP nanospheres were capable of transforming into bone-like apatite by controlled aging in water and the prepared nanoparticles were shown to affect osteoblast gene expression. Dicalcium phosphate crystals (brushite and monetite) with structural hierarchy and distinct features were also grown in LCs through epitaxial overgrowth or a self-organization regime. Polymerized LCs were successfully prepared from a modified block copolymer (diacrylate derivative of Pluronic® F127), which served as a resilient matrix for the deposition of ACP nanospheres. A subsequent in situ crystallization of ACP into bone-like apatite resulted in mechanically stable composites retaining nanostructures that resembled that of natural bone. An amphiphilic peptide was designed using mainly natural amino acids and it was shown to self-assemble into distinct structures at different concentrations. Based upon the results presented in this thesis, nanomaterials with assorted structures can be further designed for bio-related applications.
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| 4. |
- Tam, Eric, 1980
(author)
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Tailoring of Transition Metal Silicides as Protective Thin Films on Austenitic Stainless Steel
- 2011
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Doctoral thesis (other academic/artistic)abstract
- The objective of this study is to make use of transition metal silicides in a novel way as protective thin films on engineering metals. It can then be possible to take advantage of the potentially good corrosion resistance of metal silicides while compensating for their brittle nature by the ductile bulk material. Transition metal silicide thin films based on the systems of Ti-Si, Cr-Si, Fe-Si, Ni-Si were fabricated by means of ion-beam co-sputter deposition on 304 stainless steel substrates, with or without subsequent annealing treatment. Thin film characterisation was done by means of X-ray photoelectron and X-ray diffraction analysis. For the films in crystalline form after annealing, the silicides were well-characterised by means of both techniques. The co-sputtered films showed short-range ordered structures, but the possible silicide phases could be depicted from the core-level XPS spectra of the transition metal peaks defined by the crystalline forms. Except for the Cr-Si system, the phase formation sequence during annealing processes was possible to predict by means of Pretorius’ effective heat of formation (EHF) model provided that the initial thin film compositions were determined. The corrosion properties of the as-deposited silicide films and the uncoated stainless steel specimens were assessed by means of polarisation measurements in dilute hydrochloric (HCl) and sulphuric (H2SO4) acid solutions. All silicide-coated specimens showed lower current densities along the measured potentials than the uncoated steel, suggesting their lower reactivity. Among the silicide films, the Ti-Si and Ni-Si based films showed the best corrosion properties and Si content above 60 at.% for all films facilitated high integrity Si-oxide layer development, whereby corrosion properties improved. Further studies conducted on the Ni-Si system showed that composition is a more important design factor than structure. When considering their tribological properties, Rockwell-C adhesion tests and reciprocating sliding wear tests proved the silicide films to be well-adhering on the substrates and to show lower specific wear rate (10e-13 m3/Nm) than that (10e-12 m3/Nm) of the uncoated steel. It is supposed that transition metal silicides can act as protective thin films on stainless steel as well as any other engineering materials as far as good adhesion is guaranteed.
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| 5. |
- Kosaraju, Sravya, 1983
(author)
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A review of the importance of recycling lithium-ion batteries for lithium, in view of impending electric vehicle industry
- 2012
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Reports (other academic/artistic)abstract
- Automobile electrification is one the technological developments, that will commence an earth friendly transport system, by mitigating emissions and hopefully lead to a less fossil fuel dependent society. With commercial success attained by models like Nissan’s leaf and Chevy’s Volt, the consumer market looks promising to assimilate vehicle electrification. At present these technologies include HEVs (hybrid electric vehicles), PHEVs (plug-in hybrid electric vehicles), EVs (complete electric vehicles).A closer look at these technologies will lead us to one of the crucial components of electric vehicles, the “batteries”. This component decides one of the key performance factors which is the energy storage and usage, which means it is the basis for public acceptability.The lithium-ion battery chemistries are chosen to fulfill this requirement. Although lithium constitutes of a small fraction of the complete battery weight, still its contin-ued availability in future is debated among many resource analysts.
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| 6. |
- Öhman, Sebastian, 1991-, et al.
(author)
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Selective kinetic growth and role of local coordination in forming Al2TiO5-based coatings at lower temperatures
- 2021
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In: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; 2:17, s. 5737-5751
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Journal article (peer-reviewed)abstract
- Negative thermal expansion is an elusive property found among certain materials, whose potential applications have remained limited due to the many challenges faced in their synthesis. Herein, we report the successful formation of aluminium titanate-based coatings (Al2TiO5), a material renowned for its low-to-negative thermal expansion, by the co-deposition of aluminium-isopropoxide and titanium-isopropoxide in a hot-wall chemical vapour deposition instrument. While coatings grown at 450 °C were amorphous as-deposited, a short-range order into the Al2TiO5-phase was found and analysed by using Raman spectroscopy. Upon subsequent annealing at 700 °C for 3 hours, crystalline coatings were achieved without forming any binary phases. The selective synthesis of the Al2TiO5 phase is ascribed to the precursors’ inherent chemical similarities, resulting in a kinetic targeting of this phase and a short-range homogeneity, entailing its preferred crystallisation. The role of local coordination is expressed by demonstrating the formation of intergrowth phases ascribed to lower coordinating interstices in the compound. Both the formation and crystallisation temperatures reported herein, as well as the timescales needed for the synthesises, are considerably lower than any conventional adopted solid-state techniques used so far to attain the Al2TiO5 phase.
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| 7. |
- Lee, Kyuho, et al.
(author)
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Benchmarking van der Waals density functionals with experimental data: potential-energy curves for H2 molecules on Cu(111), (100) and (110) surfaces
- 2012
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In: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:42
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Journal article (peer-reviewed)abstract
- Detailed physisorption data from experiment for the H2 molecule on low-index Cu surfaces challenge theory. Recently, density functional theory (DFT) has been developed to account for nonlocal correlation effects, including van der Waals (dispersion) forces. We show that the functional vdW-DF2 gives a potential-energy curve, potential-well energy levels and difference in lateral corrugation promisingly close to the results obtained by resonant elastic backscattering–diffraction experiments. The backscattering barrier is sensitive to the choice of exchange functional approximation. Further, the DFT-D3 and TS-vdW corrections to traditional DFT formulations are also benchmarked, and deviations are analyzed.
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| 8. |
- Grolig, Jan Gustav, 1986
(author)
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Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Solid oxide fuel cells (SOFCs) are attracting increasing interest as devices with potentialuses in decentralized and clean electricity and heat production. Several challengeswith respect to materials have to be overcome to achieve efficiencies and life-spansthat are sufficient for long-term applications.An important element of an SOFC stack is the interconnect component, which connectstwo adjacent fuel cell elements. Interconnects, which are commonly composedof ferritic stainless steels, have to be corrosion-resistant, mechanically stable and costoptimized.This work aimed to investigate economic solutions for interconnect materials and tounderstand the underlying mechanisms of degradation and electrical conduction ofthese materials. Mainly two substrates, a commercially available steel (AISI 441) anda ferritic stainless steel that was optimized for an SOFC application (Sandvik SanergyHT) were combined with different barrier coatings and exposed to a cathode-sideatmosphere. A method was developed that allows for the electrical characterizationof promising material systems and model alloys, thereby facilitating a fundamentalunderstanding of the dominant electrical conduction processes linked to the oxidescales that grow on interconnects. The AISI 441 steel coated with reactive elementsand cobalt showed good corrosion and chromium evaporation profiles, while AISI 441coated with cerium and cobalt also had promising electrical properties. The SanergyHT steel was examined with coatings of copper and iron and copper and manganese,respectively. The corrosion and chromium evaporation profiles of Sanergy HT wereimproved by coating with copper and iron. The copper and iron-coated Sanergy HTshowed lower area specific resistance values than cobalt-coated Sanergy HT. Chromia,which is the main constituent of oxide scales, was synthesized using differentmethods. The electrical properties of chromia were found to be sensitive to not onlyimpurities, but also heat treatment. Finally the electrical properties of cobalt- andcobalt cerium-coated Sanergy HT steels were investigated. It was revealed that theaddition of cerium improved the conductivity of the interconnect by both slowingdown chromia growth and preventing the outward diffusion of iron into the spinel.
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| 9. |
- Han, Joonsoo, 1990
(author)
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NH3-SCR chemistry for NOx abatement: Influence of zeolite support on N2O formation & phosphorus species addition.
- 2021
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Licentiate thesis (other academic/artistic)abstract
- Different lattice arrangements of Si, Al, and O atoms result in a variety of pore dimensions and zeolite channel network systems, giving rise to different physicochemical environments inside the catalyst cage. The objective of the thesis work was to understand the influence of zeolite topology on NH3-assisted SCR chemistry over CHA, MFI, and BEA frameworks, on the formation of N2O and the addition of phosphorus species to attain fundamental insight into NOx emission control. A variety of characterization techniques and mechanistic experimental protocols were used to examine Cu2+ ions coordinated with 1Al and 2Al in frameworks, denoted as Z2Cu and ZCuOH, respectively. Catalytic activity tests were performed to investigate the influence of ammonium nitrate (AN)-forming N2O and phosphorus species on DeNOx performance over the Cu-impregnated CHA, MFI, and BEA. In Paper I, ammonium nitrate (AN) formation and decomposition were thoroughly investigated to see the effect of zeolite topology, copper species, and water vapor on the N2O formation in NH3 SCR of NOx at low temperatures. Three different Cu/zeolites (CHA, MFI, and BEA) were used, and these were compared with H/zeolites as the reference. H2 temperature programmed reduction and in-situ IR spectroscopy suggest that the CHA framework structure is more favorable than MFI and BEA to form AN inside the catalyst cage. AN formation was enhanced in the presence of Cu ions over the Cu/zeolites. Catalyst activity tests demonstrated that Cu/CHA has a potential for uncontrolled N2O emission in transient conditions despite it shows lower N2O formation over standard and fast SCR reaction due to a highly stabilized AN inside the catalyst cage at low temperatures. This indicates pros and cons of AN stability over CHA in NH3-SCR systems. The critical effect of water vapor on AN formation and decomposition was found. The water vapor causes the cleavage of Cu dimers into Cu2+-OH groups, which are responsible for NO oxidation forming NO+ and surface nitrates. Thus, it results in the formation of fewer surface nitrates, leading to less AN and less N2O formation in wet conditions. In Paper II, phosphorus poisoning of different zeolite topologies was investigated. Fresh Cu/zeolites (CHA, MFI, and BEA) were used as the reference, and these were compared with P-poisoned Cu/zeolites. X-ray powder diffraction (XRD) revealed that the MFI framework was vulnerable to phosphorus species attack, resulting in the deformation of the framework structure. A variety of phosphorus species, such as PO-3, PO3- 4, and P2O5 populations, were observed over Cu/zeolites with Xray photoelectron spectroscopy. Transient response methodologies suggest that ZCuOH sites were significantly poisoned by PO-3 and PO3- 4 over Cu/CHA. Accordingly, a promoted or deteriorated redox feature of Cu ions (i.e., Z2Cu and ZCuOH) was suggested. A significant drop in catalytic activity was demonstrated over Cu/MFI in catalytic activity tests. It is suggested that MFI framework deformation, such as pore-blockage, local expansion, and cracking, impedes the mobility of Cu+(NH3)2 complexes at low temperatures under standard SCR conditions. Consequently, we hypothesize that MFI framework degradation hinders the formation of NH3-solvated Cu dimer complexes, which are responsible for O2 activation.
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| 10. |
- Rzepka, Przemyslaw, et al.
(author)
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CO2-Induced Displacement of Na+ and K+ in Zeolite INaKI-A
- 2018
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:30, s. 17211-17220
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Journal article (peer-reviewed)abstract
- Adsorption technologies offer opportunities to remove CO2 from gas mixtures, and zeolite A has good properties that include a high capacity for the adsorption of CO2 . It has been argued that its abilities to separate CO2 from N-2 in flue gas and CO2 from CH4 in raw biogas can be further enhanced by replacing Na+ with K+ in the controlling pore window apertures. In this study, several compositions of I Na12-xKxI-A were prepared and studied with respect to the adsorption of CO2 N-2, and CH4, and the detailed structural changes were induced by the adsorption of CO2. The adsorption of CO2 gradually decreased on an increasing content of K+, whereas the adsorption of N-2 and CH4 was completely nulled already at relatively small contents of K. Of the studied samples, INa9K3I-A exhibited the highest CO2 over N-2/CH4 selectivities, with a(CO2/N-2 ) > 21 000 and a(CO2/CH4) > 8000. For samples with and without adsorbed CO2 analyses of powder X-ray diffraction (PXRD) data revealed that K+ preferred to substitute Na+ at the eight-ring sites. The Na(+ )ions at the six-ring sites were gradually replaced by K+ on an increasing content, and these sites split into two positions on both sides of the six-ring mirror plane. It was observed that both the eight-ring and six-ring sites tailored the maximum adsorption capacity for CO2 and possibly also the diffusion of CO2 into the alpha-cavities of INa12-xKxI-A. The adsorption of CH4 and N-2 on the other hand appeared to be controlled by the K+ ions blocking the eight-ring windows. The in situ PXRD study revealed that the positions of the extra-framework cations were displaced into the a-cavities of INa12(_)x,KxI-A on the adsorption of CO2 . For samples with a low content of K+, the repositioning of the cations was consistent with a mutual attraction with the adsorbed CO(2 )molecules.
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