Search

Alkaline cleaning of Zn–Al–Mg coated hot-dip galvanized steel is a central process in the industrial galvanized steel production. This process removes carbonaceous contaminants from the surface and modifies the surface chemistry profoundly. We implement a combined analytical and surface science approach to characterize the dissolution mechanism and surface chemistry of Zn-Al-Mg coatings after treatment with industrial cleaners with pH 9.3 and 12.7, respectively. Our data indicate that weak alkaline cleaning can significantly increase the surface concentration of Zn-oxide, while strong alkaline cleaning dissolves the native oxide and generates a transient Zn/Mg-hydroxide on the surface. The observed dissolution mechanisms are largely consistent with the expectations from the Pourbaix diagrams, i.e. at pH 12.7 aluminium dissolution is expected while Mg is stable and forms a transient passive film. In contrast, mild alkaline cleaning at pH 9.3 is dominated by Mg and Zn dissolution, while the native Al passive film remains stable. Hence the cleaning provides an effective direct modification of the surface chemistry for subsequent process steps during the coating. Mild alkaline cleaning offers an increase of Zn at the surface, which has important implications for subsequent conversion and adhesive applications, that have been traditionally optimized for pure Zn coatings.

A composite anodic oxide film is formed by electrochemical treatment of an ultra-thin Hf film superimposed on Ta, due to the growth of Ta2O5 columns through HfO2. The oxidation dynamic is governed by an electrical version of the Rayleigh–Taylor effect, the current preferring the more conductive path via Ta during anodization of the superimposed Hf film. Memristive devices obtained by patterning Pt top electrodes are investigated and their electrical behavior is reported. The effect of electrolyte species incorporation on the memristive behavior is analyzed by anodization in different solutions. The influence of citrate-buffered (CB) and phosphate-buffered (PB) electrolytes is studied, and the presence of P in the composite anodic oxides is evidenced in the latter case leading to early device failure. Composite memristors grown in citrate electrolytes show both unipolar and bipolar switching, high stability, very good retention, and endurance. The coexistence of both switching mechanisms is related to the special composite oxide nanostructuring. Fonds zur Förderung der Wissenschaftlichen Forschung P32847-N Version of record

Activated carbons derived from viscose fibers were prepared using potassium hydroxide, carbon dioxide, or water vapor as activation agents. The produced activated carbon fibers were analyzed via scanning electron microscopy and energy dispersive X-ray spectroscopy, and their porosity (specific surface area, total pore volume, and pore size distribution) was calculated employing physisorption experiments. Activated carbon fibers with a specific surface area of more than 2500 m2 g−1 were obtained by each of the three methods. Afterwards, the suitability of these materials as electrodes for electrochemical double-layer capacitors (supercapacitors) was investigated using cyclic voltammetry, galvanostatic measurements, and electrochemical impedance spectroscopy. By combining CO2 and H2O activation, activated carbon fibers of high purity and excellent electrochemical performance could be obtained. A specific capacitance per electrode of up to 180 F g−1 was found. In addition, an energy density per double-layer capacitor of 42 W h kg−1 was achieved. These results demonstrate the outstanding electrochemical properties of viscose-based activated carbon fibers for use as electrode materials in energy storage devices such as supercapacitors. Version of record

For delayed crosslinking of waterborne epoxy varnishes, dicyandiamide (DICY) is often used as a latent curing agent. While, for amine-based curing agents such as diaminoethane (DAE), chemical interactions with metal oxides are well described, so far, no studies have been performed for DICY and waterborne epoxy varnishes. Hence, in this work X-ray photoelectron spectroscopy (XPS) was used to investigate reactions of DICY and varnishes with technical surfaces of Al, Zn, and Sn. To directly study the reaction of DICY with metal oxides, immersion tests in a boiling solution of DICY in pure water were performed. A clear indication of the formation of metal–organic complexes was deduced from the change in the N1s peak of DICY. To understand the interfacial interaction and consequently the interphase formation during coating of waterborne epoxy varnishes, advanced cryo ultra-low-angle microtomy (cryo-ULAM) was implemented. Interestingly, a comparable reaction mechanism and the formation of metal complexes were confirmed for varnishes. The coatings exhibited a pronounced enrichment of the DICY hardener at the metal oxide–polymer interface

For delayed crosslinking of waterborne epoxy varnishes, dicyandiamide (DICY) is often used as a latent curing agent. While, for amine-based curing agents such as diaminoethane (DAE), chemical interactions with metal oxides are well described, so far, no studies have been performed for DICY and waterborne epoxy varnishes. Hence, in this work X-ray photoelectron spectroscopy (XPS) was used to investigate reactions of DICY and varnishes with technical surfaces of Al, Zn, and Sn. To directly study the reaction of DICY with metal oxides, immersion tests in a boiling solution of DICY in pure water were performed. A clear indication of the formation of metal–organic complexes was deduced from the change in the N1s peak of DICY. To understand the interfacial interaction and consequently the interphase formation during coating of waterborne epoxy varnishes, advanced cryo ultra-low-angle microtomy (cryo-ULAM) was implemented. Interestingly, a comparable reaction mechanism and the formation of metal complexes were confirmed for varnishes. The coatings exhibited a pronounced enrichment of the DICY hardener at the metal oxide–polymer interface. Osterreichische Forschungsforderungsgesellschaft 865864 Version of record

The detection and quantification of carbon by conventional energy dispersive X-ray spectroscopy (EDXS) performed under standard conditions is not feasible due to occurring contaminations in common electron microscopes. In contrast, novel ultra high vacuum EDXS (UHV-EDXS) was used to acquire elemental mappings of carbon on dual phase (DP) steel, which exhibits a microstructure consisting of ferrite and martensite. These phases differ in hardness, local dislocation density and, most importantly, in their carbon content. Since the UHV conditions in combination with a customized windowless EDXS detector ensured a minimization of hydrocarbon contamination during the measurements and a maximization of the sensitivity for the detection of light elements, UHV-EDXS carbon mappings could successfully be obtained, which clearly reflect the ferrite and martensite microstructure of the investigated DP steels, as confirmed by electron back scatter diffraction (EBSD). Most importantly, it was possible to quantify the carbon content of individual grains with concentrations as low as 0.25 wt%. Furthermore, nano-hardness tests were performed on the very same grains which were characterized by UHV-EDXS and EBSD. It is shown that the hardness of the martensite grains is correlated to their carbon content, as directly determined by UHV-EDXS. With this new method an additional tool for advanced material characterization of multiphase materials on the level of individual grains is now available. Version of record

Bacterial adhesion and biofilm formation on surfaces are associated with persistent microbial contamination, biofouling, and the emergence of resistance, thus, calling for new strategies to impede bacterial surface colonization. Using ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns), laser-induced periodic surface structures (LIPSS) featuring different sub-micrometric periods ranging from ~210 to ~610 nm were processed on commercial poly(ethylene terephthalate) (PET) foils. Bacterial adhesion tests revealed that these nanorippled surfaces exhibit a repellence for E. coli that decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Although chemical and structural analyses indicated a moderate laser-induced surface oxidation, a significant influence on the bacterial adhesion was ruled out. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the role of extracellular appendages in the bacterial repellence observed here. Fonds zur Förderung der Wissenschaftlichen Forschung T1270-N Europaische Kommission (DE-588)1024466-9 H2020 No 862016 Version of record

In this study, the production of porous carbon fibers from viscose fibers was investigated. The effects of final carbonization temperature (6001000 C) and heating rate (6600 C h1), which determine the carbonization process, on carbon yield, and specific surface area were investigated using a central composite design. The statistical models found were then used to optimize both the yield and the porosity of the carbonized fibers, which are the most important factors for further use as precursors for activated carbon fibers. Despite the contrary effects, porous carbon fibers with a yield of 21.2% could be produced, which at the same time have a specific surface area of 175 m2 g1. The fibers produced were also characterized by SEM, FTIR and Raman spectroscopy, XRD and CHNS analysis. Version of record

Cold atmospheric pressure plasma from a plasma jet was used to improve the adhesion properties of polypropylene (PP). Differences in adhesion were at first observed for either air or N2 as process gas, tested on a PP-acrylic pressure sensitive adhesive (PSA) model system. For a deeper understanding changes in the surface chemistry and topography on PP after plasma jet treatment, using several different O2/N2 mixtures, were investigated in a comprehensive surface analytical study. Independent of the gas composition a majority of plasma induced polar groups exist as water soluble low molecular weight oxidized material (LMWOM), located within the first few nanometers. Consequently, the observed changes in the surface chemistry for various process gas compositions are mainly attributed to differences in the formed LMWOM. However, these chemical changes indicated also differences in the interaction mechanism of plasma reactive species with the polymer surface and therefore, in the resulting plasma-polymer etching process. Hence, significant changes in the topography have been observed for different process gas compositions, which could be reliably correlated with the obtained adhesion results. (VLID)5686993 Version of record

submitted by Juri Duchoslav Zusammenfassung in deutscher Sprache Universität Linz, Dissertation, 2017 OeBB