Surface analysis of advanced corrosion protection coatings on steel by XPS and AES

Steel is one of the most important materials and finds its applications almost everywhere around us. Nevertheless, despite its excellent properties, steel is prone to a degradation process corrosion. Although corrosion cannot be stopped completely, its negative effects can be minimized by means of zinc coatings. Diverse zinc coatings were invented several decades ago, however, due to numerous open issues regarding to their structure and properties as well as continuously increasing demands for better corrosion protection, they are still under intensive research and development. In this context, two kinds of advanced coating systems are considered: binary Zn-Cr and ternary Zn-Mg-Al alloyed coatings. Both coatings were investigated by surface sensitive methods, namely X-ray photoelectron spectroscopy and Auger electron spectroscopy. While Zn-Cr coatings were analyzed with respect to their elemental and chemical composition, the study of Zn-Mg-Al coatings focused also on the initial stages of corrosion induced by short exposures to NaCl rich environments. Within the experimental part of the here presented work, several issues and problems appeared and had to be solved, e.g. the evaluation routine for XPS data or different degradation processes connected to standard measurements or to Ar+ ion sputtering. Nevertheless, on the basis of the gained knowledge and understanding of the methods as well as of the material systems, the assigned scientific and analytical tasks could be successfully fulfilled and are reported in numerous scientific publications constituting the present thesis which is written in a cumulative form.submitted by Juri DuchoslavZusammenfassung in deutscher SpracheUniversität Linz, Dissertation, 2017OeBB(VLID)214792

Threshold Switching in Forming-Free Anodic Memristors Grown on Hf–Nb Combinatorial Thin-Film Alloys

The development of novel materials with coexisting volatile threshold and non-volatile memristive switching is crucial for neuromorphic applications. Hence, the aim of this work was to investigate the memristive properties of oxides in a Hf–Nb thin-film combinatorial system deposited by sputtering on Si substrates. The active layer was grown anodically on each Hf–Nb alloy from the library, whereas Pt electrodes were deposited as the top electrodes. The devices grown on Hf-45 at.% Nb alloys showed improved memristive performances reaching resistive state ratios up to a few orders of magnitude and achieving multi-level switching behavior while consuming low power in comparison with memristors grown on pure metals. The coexistence of threshold and resistive switching is dependent upon the current compliance regime applied during memristive studies. Such behaviors were explained by the structure of the mixed oxides investigated by TEM and XPS. The mixed oxides, with HfO2 crystallites embedded in quasi amorphous and stoichiometrically non-uniform Nb oxide regions, were found to be favorable for the formation of conductive filaments as a necessary step toward memristive behavior. Finally, metal–insulator–metal structures grown on the respective alloys can be considered as relevant candidates for the future fabrication of anodic high-density in-memory computing systems for neuromorphic applications

Comparative Behavior of Viscose-Based Supercapacitor Electrodes Activated by KOH, H2O, and CO2

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

Habitat Utilization and Behaviour of Adult Parnassius Mnemosyne (Lepidoptera: Papilionidae) in the Litovelske Pomoravi, Czech Republic

Volume: 24Start Page: 39End Page: 5

XPS investigation on the reactivity of surface imine groups with TFAA

The chemical reaction of imine groups with vapors of trifluoroacetic anhydride (TFAA) was investigated in detail with Xray photoelectron spectroscopy (XPS) for the potential application in chemical derivatization (CD) studies of plasma treated surfaces. Imine groups were at first prepared by converting surface amine groups of a polymer precursor using a common vapor phase derivatization reaction with fluorine tagged aldehydes and ketones. The originally low yield for the imine forming reaction of approx. 50%, performed under standard conditions was dramatically enhanced up to 100% by an own developed procedure using a catalyst. This step allowed to obtain a consistent quantification and interpretation of the complex surface reaction products from different types of imine groups derivatized by TFAA.(VLID)356299

The Interaction of Waterborne Epoxy/Dicyandiamide Varnishes with Metal Oxides

International audienceFor 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 interfac

Spatial Period of Laser-Induced Surface Nanoripples on PET Determines <i>Escherichia coli</i> Repellence

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

l‑Ascorbic Acid Treatment of Electrochemical Graphene Nanosheets: Reduction Optimization and Application for De-Icing, Water Uptake Prevention, and Corrosion Resistance

The aeronautical industry demands facile lightweight and low-cost solutions to address climate crisis challenges. Graphene can be a valid candidate to tackle these functionalities, although its upscalability remains difficult to achieve. Consequently, graphene-related materials (GRM) are gathering massive attention as top-down graphite exfoliation processes at the industrial scale are feasible and often employed. In this work, environmentally friendly produced partially oxidized graphene nanosheets (POGNs) reduced by green solvents such as l-Ascorbic Acid to rGNs are proposed to deliver functional coatings based on a glass fiber composite or coated Al2024 T3 for strategic R&D questions in the aeronautical industry, i.e., low energy production, de-icing, and water uptake. In detail, energy efficiency in rGNs production is assessed via response-surface modeling of the powder conductivity, hence proposing an optimized reduction window. De-Icing functionality is verified by measuring the stable electrothermal property of an rGNs based composite over 24 h, and water uptake is elucidated by evaluating electrochemical and corrosion properties. Moreover, a mathematical model is proposed to depict the relation between the layers’ sheet resistance and applied rGNs mass per area, which extends the system to other graphene-related materials, conductive two-dimensional materials, and various substrates. To conclude, the proposed system based on rGNs and epoxy paves the way for future multifunctional coatings, able to enhance the resistance of surfaces, such as airplane wings, in a flight harsh environment