A multi-analytical approach based on in-situ and ex-situ local probing techniques was employed to investigate localized corrosion mechanisms of some aluminum alloys in chloride containing solutions, focusing on the influence of intermetallic particles (IMPs) in the alloys. In the EN AW-3003 alloy, SEM-EDS analysis revealed constituent and dispersoid IMPs. There are two types of constituent IMPs, with size ranging from 0.5 to several μm, and composition typically Al6(Fe,Mn) or Al12(Mn,Fe)3Si, respectively,having a Mn/Fe ratio of about 1:1. Fine dispersoids of 0.5 μm or less in size normally have the composition Al12Mn3Si1-2. Scanning Kelvin probe force microscopy (SKPFM measurements showed that the constituent IMPs have a higher Volta potential compared to the matrix, and the Volta potential difference increased with particle size, probably related to the composition of the IMPs. The SKPFM results also showed a Volta potential minimum in the boundary region adjacent to some larger IMPs. The open-circuit potential and electrochemical impedance spectroscopy measurements indicated local electrochemical activities occurring on the surface, and active-like dissolution in the acidic solutions, but a passive-like behavior in the near-neutral solutions. Infrared reflection-absorption spectroscopy measurements after exposure and thermodynamic calculations suggested the formation of mixtures of aluminum oxyhydroxide and acetate on the surface in acetic acid solutions. The formation and fraction of dominant species of the corrosion products depend on the pH of the solution, and aluminum chloride compounds may form at very low pH. Moreover, an integrated in-situ atomic force microscopy (AFM) and scanningelectrochemical microscopy (SECM) set-up was used to investigate the localized activities on the surface. With a dual mode probe, acting as both AFM tip and SECM microelectrode, concurrent topography and electrochemical current images were obtained on the same area of the surface. Numerical simulations of the SECM suggested a micrometer lateral resolution under favorable conditions and the ability to resolve μmsized active sites with a separation distance of about 3 μm or larger. The simulations were verified by SECM mapping of the aluminum alloys in the chloride solutions. The AFM/SECM measurements revealed enhanced cathodic activity on some larger IMPs and local anodic dissolution around larger IMPs. In-situ AFM monitoring confirmed preferential dissolution in the boundary region adjacent to some of these IMPs. The results elucidate the micro-galvanic effect and size effect of the IMPs during the initiation of localized corrosion of the Al alloys. Furthermore, differences in corrosion properties between EN AW-3003 and a newly developed Al–Mn–Si–Zr alloy were studied with a similar approach. Compared to EN AW-3003, the new alloy had a smaller number of particles with a large Volta potential difference relative to the matrix. In slightly corrosive solutions extensive localized dissolution and deposition of corrosion products occurred on EN AW-3003, whereas only a small number of corroding sites and “tunnel-like” pits occurred on the Al–Mn–Si–Zr alloy. The lower corrosion activity and the smaller tunnel-like pits resulted in lower material loss of the Al–Mn–Si–Zr alloy, which is beneficial for applications using a thin material. / QC 20100702

Conventional phase-contrast imaging entails stepping an analyser grating across the detector to resolve the interference pattern caused by the x-rays after passing through a series of gratings in a so-called Talbot-Lau interferometer. However, the analyser grating in the interferometer poses a challenge, not only due to the machinery and alignment required but also due to each exposure delivering a dose to the subject. Another downside of the analyser grating is that whilst the phase-step length can be adjusted, the x-rays allowed through the grating depend on its slit-width ratio, which cannot be changed without changing the whole grating.This thesis evaluates if the analyser grating can be removed by instead using a deep silicon photon-counting detector which can determine the photon interaction position with an uncertainty of around one micrometre. It is concluded that such a high-resolution detector will not only be able to remove the need for an analyser grating and its associated challenges, but the results also imply a three-fold increase in the contrast-to-noise ratio when dose-matching the grating-based approach with the grating-less approach. Furthermore, the conventional absorption image, which is lost when using an analyser grating, will still be available using a high-resolution detector. Finally, the removal of the analyser grating shifts most of the system conditions to the source grating and the phase grating, making it possible to design a compact unit of the two gratings for integration into a CT scanner. / Konventionell faskontrast involverar att stega ett analysgitter över detektorn för att detektera interferensmönstret som skapas av röntgenstrålarna efter att de passerat genom en serie gitter i en så kallad Talbot-Lau interferometer. Analysgittret introducerar en utmaning, inte enbart på grund av maskineriet och kalibreringen som krävs, utan även då varje steg utsätter det röntgade föremålet för strålning. Ytterligare en begränsning är att även om längden på stegen kan justeras beror mängden röntgenstrålar som passerar genom analysgittret på gittrets slitsbredd, vilken inte går att ändra på utan att byta hela gittret.Den här uppsatsen utvärderar om analysgittret kan tas bort genom att istället använda en högupplöst fotonräknande djup kiseldetektor som har förmågan att uppskatta positionen av en fotoninteraktion inom en mikrometer. Slutsatsen är att en sådan detektor kommer att kunna ersätta analysgittret och resultaten tyder på en trefaldig ökning av contrast-to-noise ratio vid dosmatchning mellan metoden med analysgitter och metoden med en högupplöst detektor. Vidare behålls den konventionella absorptionsbilden då man använder en högupplöst detektor, någonting som annars går förlorat vid användandet av analysgittret. Slutligen skiftas de flesta villkoren på systemet till källgittret och fasgittret, vilket tyder på att en kompakt konstruktion av dessa två gitter skulle kunna integreras i en CT-skanner.