| 1. |
- Amirthalingam, M., et al.
(författare)
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Synchrotron diffraction analysis of retained austenite in welded transformation induced plasticity (TRIP) steels
- 2012
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Ingår i: Science and Technology of Welding and Joining. - 1362-1718. ; 17:2, s. 146-154
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Tidskriftsartikel (refereegranskat)abstract
- A quantitative analysis of the retained austenite (RA) fractions in gas tungsten arc welded silicon and aluminium containing transformation induced plasticity steels was carried out by synchrotron X-ray diffraction measurements. The variation in RA transverse to the weld line was measured to study the effect of weld thermal cycles on the stabilisation of austenite in the heat affected zone (HAZ) and the fusion zone (FZ). The results showed that the FZ of silicon based steels contained a higher amount of RA (similar to 7%) than aluminium based steels, which contained only similar to 4%. During the solidification of the weld pool, aluminium was found to partition to solidifying delta-ferrite and to stabilise the soft delta-ferrite grains at the fusion boundaries. Owing to this partitioning, the HAZ was enriched in carbon and the RA content was found to increase with distance from the fusion boundaries. In contrast, this partitioning behaviour was not present in silicon based transformation induced plasticity steels and a lesser amount of RA was found in the coarse grained HAZ than in the FZ.
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| 2. |
- Borthwick, Verity E., et al.
(författare)
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Quantification of mineral behavior in four dimensions : grain boundary and substructure dynamics in salt
- 2012
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Ingår i: Geochemistry Geophysics Geosystems. - 1525-2027. ; 13, s. Q05005-
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Tidskriftsartikel (refereegranskat)abstract
- Here we present the first four dimensional (time and three dimensional space resolved) experiment on a strongly deformed geological material. Results show that even complicated microstructures with large continuous and discontinuous changes in crystallographic orientation can be resolved quantitatively. The details that can be resolved are unprecedented and therefore the presented technique promises to become influential in a wide range of geoscientific investigations. Grain and subgrain scale processes are fundamental to mineral deformation and associated Earth Dynamics, and time resolved observation of these processes is vital for establishing an in-depth understanding of the latter. However, until recently, in situ experiments were restricted to observations of two dimensional surfaces. We compared experimental results from two dynamic, in situ annealing experiments on a single halite crystal; a 2D experiment conducted inside the scanning electron microscope and a 3D X-ray diffraction experiment. This allowed us to evaluate the possible effects of the free surface on grain and subgrain processes. The extent to which surface effects cause experimental artifacts in 2D studies has long been questioned. Our study shows that, although the nature of recovery processes are the same, the area swept by subgrain boundaries is up to 5 times larger in the volume than observed on the surface. We suggest this discrepancy is due to enhanced drag force on subgrain boundaries by thermal surface grooving. Our results show that while it is problematic to derive absolute mobilities from 2D experiments, derived relative mobilities between boundaries with different misorientation angles can be used.
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| 3. |
- Borthwick, Verity, 1983-, et al.
(författare)
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In-situ 3DXRD annealing of a geological material : Evaluating the validity of 2D
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Most in-situ heating experiments where substructure is investigated have been restricted to 2D. We compare a 2D experiment to a 3D X-ray diffraction experiment to evaluate the validity of the 2D method. Until now 3D X-ray diffraction has been limited to well-recovered substructures. We conducted a 3D in-situ annealing experiment on a halite crystal with a significant orientation gradient. This is the first experiment of its kind on a geological material and shows that even complicated microstructures can be resolved. Comparison of 2D and 3D showed that, although general results were similar, subgrain boundary movement occurred with higher frequency in 3D. We suggest this discrepancy is due to enhanced drag force on subgrain boundaries by surface thermal grooving. Thus, while results from 2D experiments largely reflect what is happening in the volume, analysis of boundary movement with regard to absolute mobilities needs to be considered with some care.
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| 4. |
- Borthwick, Verity, 1983-, et al.
(författare)
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Substructure dynamics in halite : Comparison of 2D in-situ annealing experiments with 3D X-ray diffraction annealing
- 2009
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Ingår i: Deformation Mechanisms, Rheology and Tectonics 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The understanding of substructural behaviour during post-deformational annealing is key to interpreting rheological adjustments during tectonic change, and the processes which cause them. The focus of this study is to use in-situ experimental techniques to increase understanding of substructure dynamics in geological materials. 2D in-situ annealing experiments have been conducted in the scanning electron microscope, using electron backscatter diffraction (EBSD) to collect information about the crystallographic orientation of the surface. A single crystal of halite, pre-deformed under uniaxial compression at temperatures of ~450 ºC with a strain rate of 6.9x10-6s-1, and to a final strain of 0.165, was examined. Different temperature time-paths were investigated with temperatures between 280-470 ºC and durations of heating between 30 min and 6 h. EBSD maps were taken before, during and after heating. Behaviour during annealing was found to be temperature dependent and could be divided into three main phases of development. Subgrain boundaries could be divided into five categories based on behaviour during annealing, morphology and orientation. Annealing behaviour could be directly related to preferential activation of one set of slip systems due to the chosen aspect ratio of the crystal. While the 2D experiments provided valuable information, it is impossible to rule out the potential influence surface effects may have on annealing behaviour. In order to verify the results of these experiments, a 3D X-ray diffraction experiment was conducted at the synchrotron in Grenoble, France. The experiment followed a similar heating procedure as that for the 2D experiments and was performed on the same sample. This newly developed technique allows non-destructive internal examination of the crystal. Data was collected before, during and after each heating stage. During heating crystallographic information was collected within a limited rotation threshold (12-30º) in order to illuminate one or two subgrains and allow us to follow their progress. Comparison of the shape and strength of intensity spots has allowed us to draw some early conclusions from the data without a full crystallographic analysis. Preliminary results suggest that similar processes may be occurring as those observed in the 2D experiments, including spots becoming more distinct as well as some spots rotating away from the bulk of the subgrain indicating some subdivision and potential polygonisation. We can thus suggest that some of the behaviour exhibited in the 3D experiment is similar to that from the 2D experiment. Full crystallographic analysis of large maps taken after heating will allow us to examine the behaviour of the substructure in more detail and potentially rule out surface effects from the 2D experiments.
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| 5. |
- Borthwick, Verity, et al.
(författare)
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The application of in-situ 3D X-ray Diffraction in annealing experiments : First interpretation of substructure development in deformed NaCl
- 2010
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Ingår i: Recrystallization and Grain Growth.
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Konferensbidrag (refereegranskat)abstract
- In-situ 3D X-ray diffraction (3DXRD) annealing experiments were conducted at the ID-11 beamline at the European Synchrotron Radiation Facility in Grenoble. This allowed us to non-destructively document and subsequently analyse the development of substructures during heating, without the influence of surface effects. A sample of deformed single crystal halite was heated to between 260-400 ºC. Before and after heating a volume of 500 by 500 by 300 mm was mapped using a planar beam, which was translated over the sample volume at intervals of 5-10 µm in the vertical dimension. In the following we present partially reconstructed orientation maps over one layer before and after heating for 240min at 260 ºC. Additional small syn-heating “maps” over a constrained sample rotation of 12-30º. The purpose of this was to illuminate a few reflections from 1 or 2 subgrains and follow their evolution during heating. Preliminary results show that significant changes occurred within the sample volume, for which, surface effects can be excluded. Results show a number of processes, including: i) change in subgrain boundary misorientation angle and ii) subgrain subdivision into areas of similar lattice orientation with new subgrain boundary formation. These results demonstrate that 3DXRD coupled with in-situ heating is a successful non-destructive technique for examining real-time post-deformational annealing in strongly deformed crystalline materials with complicated microstructures.
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| 6. |
- Geiker, Mette R., et al.
(författare)
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Concluding destructive investigation of a nine-year-old marine-exposed cracked concrete panel
- 2023
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- This study undertaken on a nine-year-old cracked concrete panel further investigates the impact of cracks on the corrosion performance of conventional steel reinforcement in marine-exposed concrete to explain observed monitoring data. The present data covers seven 1.80 m long (12.6 m) reinforcing bars embedded in good quality concrete (w/b = 0.40 and cover >75 mm). Each bar was crossed by two horizontal cracks (surface crack widths 0.20–0.30 mm). The investigation showed no corrosion on the surface of the reinforcing bars, in either cracked or uncracked areas. Two of the seven reinforcing bars were instrumented in the vicinity of the cracks. Extensive corrosion was found in the interior of all instrumented parts of these bars. This may explain the monitoring data despite the lack of corrosion on the exterior surface of the two instrumented rebars. However, with no other weaknesses, the remaining conventional rebars showed no impact from the cracks.
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| 7. |
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| 8. |
- Hansen, Bjarne R. S., et al.
(författare)
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Hydrogen Storage Capacity Loss in a LiBH4-Al Composite
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:15, s. 7423-7432
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Tidskriftsartikel (refereegranskat)abstract
- A detailed investigation of the decomposition reactions and decay in the hydrogen storage capacity during repeated hydrogen release and uptake cycles for the reactive composite LiBH4-Al (2:3) is presented. Furthermore, the influence of a titanium boride, TiB2, additive is investigated. The study combines information from multiple techniques: in situ synchrotron radiation powder X-ray diffraction, Sieverts measurements, simultaneous thermogravimetric analysis, differential scanning calorimetry and mass spectroscopy, solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), and Raman spectroscopy. The decomposition of LiBH4-Al results in the formation of LiAl, AlB2, and Li2B12H12 via several reactions and intermediate compounds. The TiB2 additive appears to have a limited effect on the decomposition pathway of the samples, but seems to facilitate formation of intermediate species at lower temperatures compared to the sample without additive. Solid solutions of LixAl1-xB2 or Al1-xB2 are observed during decomposition and from Rietveld refinement the composition of the solid solution is estimated to be Li0.22Al0.78B2. The intercalation of Li in the AlB2 structure is further investigated by B-11 and Al-27 MAS NMR spectra of the LiH-AlB2 and AlB2 samples (presented in Supporting Information). Hydrogen release and uptake for LiBH4-Al reveals a significant loss in the hydrogen storage capacity, that is, after four cycles a capacity of about 45% remains, and after 10 cycles, the capacity is degraded to approximately 15% of the theoretically available hydrogen content. This capacity loss may be due to the formation of Li2B12H12, as observed by B-11 MAS NMR and Raman spectroscopy. Formation of Li2B12H12 has previously been observed during the decomposition of LiBH4, but it has not been reported earlier in the LiBH4-Al (2:3) system.
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| 9. |
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| 10. |
- Liu, Haichun, et al.
(författare)
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Balancing power density based quantum yield characterization of upconverting nanoparticles for arbitrary excitation intensities.
- 2013
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 5:11, s. 4770-4775
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Tidskriftsartikel (refereegranskat)abstract
- Upconverting nanoparticles (UCNPs) have recently shown great potential as contrast agents in biological applications. In developing different UCNPs, the characterization of their quantum yield (QY) is a crucial issue, as the typically drastic decrease in QY for low excitation power densities can either impose a severe limitation or provide an opportunity in many applications. The power density dependence of the QY is governed by the competition between the energy transfer upconversion (ETU) rate and the linear decay rate in the depopulation of the intermediate state of the involved activator in the upconversion process. Here we show that the QYs of Yb(3+) sensitized two-photon upconversion emissions can be well characterized by the balancing power density, at which the ETU rate and the linear decay rate have equal contributions, and its corresponding QY. The results in this paper provide a method to fully describe the QY of upconverting nanoparticles for arbitrary excitation power densities, and is a fast and simple approach for assessing the applicability of UCNPs from the perspective of energy conversion.
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