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In this work, a newly developed UHV-based high precision low background setup for hydrogen thermal desorption analysis (TDA) of metallic samples is presented. Using an infrared heating with a low thermal capacity enables a precise control of the temperature and rapid cool down of the measurement chamber. This novel TDA-set up is superior in sensitivity to almost every standard hydrogen analyzer available commercially due to the special design of the measurement chamber, resulting in a very low hydrogen background. No effects of background drift characteristic as for carrier gas based TDA instruments were observed, ensuring linearity and reproducibility of the analysis. This setup will prove to be valuable for detailed investigations of hydrogen trapping sites in steels and other alloys. With a determined limit of detection of 5.9×10−3 µg g−1 hydrogen the developed instrument is able to determine extremely low hydrogen amounts even at very low hydrogen desorption rates. This work clearly demonstrates the great potential of ultra-high vacuum thermal desorption mass spectroscopy instrumentation.

Rust Resistance The rusting of iron and steel can be prevented through the addition of 11% or more chromium. The addition of molybdenum can enhance the corrosion resistance, with a complex interplay between the Cr and Mo atoms. However, if chemical variations exist, corrosion can still occur in localized regions or if the surface layer is mechanically abraded. Duarte et al. (p. 372 ) studied the corrosive failure of an iron-based glassy alloy. A combination of atom probe tomography, electron microscopy, and x-ray diffraction was used to build up a near atomistic picture of local variations in the metal as it was heated and allowed to crystallize, and the impact these processes have on the corrosion resistance.

As we could recently show, scanning Kelvin probe force microscopy (SKPFM) is a very promising and powerful tool for the in situ investigation of filiform corrosion. Here we present how the underlying processes, namely the galvanic coupling of active head and intermetallic particles, can be visualised by performing SKPFM experiments under gas change conditions, i.e. by switching the atmosphere between nitrogen and air. It will be shown that, the different activity of the active particles can be detected by SKPFM at the buried coating/alloy interface and that these differences in activity play a role in determining the course of the FFC.

The grain boundary oxidation mechanism in hot rolled chromium – manganese steels during heat exposure at 700 °C was mathematically modeled. Given a fixed exposure time, the migration of the atomic species (iron, oxygen, chromium and manganese) has been calculated with the parabolic rate equation for diffusion. After each small time step, the data was transferred into the database ChemApp (GTT-Technologies, Germany) to calculate the oxide composition for each point in thermodynamic equilibrium. The concentration for each phase was illustrated in a phase map, similar to a cross section polish of the respective specimen. Total element concentration is shown as density plot to give a better comparison with experimental pictures from EDX or AES measurements. The obtained results are in good agreement with experimental data for alloyed steel samples with an element concentration below the critical concentration of protective oxide scale formation.

We discuss how kinetic effects can be utilized to prepare polar ZnO(0001)−Zn surfaces as very well defined and single-crystalline surfaces by hydroxide stabilization of the polar face via a wet chemical etching process in 3N NaOH. An in situ AFM imaging study of the etching process is presented. In addition, measurement and analyses of grazing incidence X-ray diffraction experiments, reflectivity, and crystal truncation rods (CTRs) of the resulting ZnO(0001) surface structures in both dry and humid atmospheres are discussed. Analysis of the CTRs shows that these surfaces are topographically extremely flat, Zn-terminated, but covered with a defect-containing hydroxide/oxygen adlayer, which is adsorbed at hcp-hollow sites. This result is fully consistent with a stabilization of the polar surface by means of an adlayer of disordered hydroxides, which is adsorbed at hcp positions. Moreover, these studies indicate that the water structure at the solid/liquid interface is ordered within the first few layers, bu...

Gold nanoparticles with diameters ranging from 3.2 to 9.7 nm were prepared on an ultrathin anodic aluminum film by means of molecular beam deposition. Coverages ranging from 17.9% to 48.5% and the subsequent anodic anodization behavior were studied. Further oxide growth does not completely cover the gold nanoparticles but takes place preferentially under the particles with a surprisingly low kinetic hindrance. The gold nanoparticles are electrically isolated from the substrate as demonstrated by the absence of electrocatalytic reactions on the gold surface. A strong surface charge phenomenon is observed, which increases with increasing gold coverage that yields an increase of the capacity up to the minimum potential required for further oxide formation.

Two different approaches under ambient conditions were developed for the preparation of clean, non-reconstructed, single crystalline ZnO(0001)-Zn surfaces. The surface preparation by a wet chemical etching procedure was compared with the same treatment in combination with a subsequent heat treatment in humidified oxygen atmosphere. Depending on the preparation technique, atomically flat terraces with a width of 100 nm to several micrometers were observed using an atomic force microscope (AFM). The obtained surface structures were further characterized by means of angle resolved X-ray photoelectron spectroscopy (AR-XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) measurements. Based on these results it is shown that the obtained surfaces are, in contrast to surfaces prepared under UHV conditions, stabilised by the adsorption of a monolayer of hydroxides. The important role of H(2)O during the heat treatment is pointed out by comparing the results of the same heat treatment in the absence of water. H(2)O turned out to play an important role in the reorganization process of the surface at elevated temperatures, thereby yielding extremely large atomically flat terraces. The terminating edges of these terraces were found to include 120 degrees and 60 degrees angles, thus perfectly reflecting the hexagonal surface structure.

In order to understand the initial oxidation of Fe–Cr alloys a single crystal of Fe–15Cr (100) was oxidized at 440°C under controlled oxygen partial pressure in a UHV system and the surface morphology was observed using in situ STM (basic pressure 1×10−10 mbar); in addition, polycrystalline Fe&15Cr was oxidized at 400°C in an IR-furnace in atmospheric air and the morphology was observed using ex situ SEM. The chemistry of the surface oxide layers was studied by XPS.Preparation of the single crystal in the UHV system did not lead to segregation of Cr to the surface during heating. In situ STM investigation showed that oxidation of Fe–Cr commenced by nucleation of Cr oxide on the surface, due to selective oxidation of Cr. When the Cr at the surface and at the interface was completely consumed by nucleation of Cr oxide, Fe oxidized and covered the initial Cr oxide nuclei, resulting in an Fe oxide layer on the surface. Ex situ experiments showed that initial oxidation of the mechanically prepared poly...

Pigmented tooth enamel occurs in several vertebrate clades, ranging from mammals to fish. Although an iron compound is associated with this orange to red colored pigmentation, its chemical and structural organization within the enamel is unknown. To determine the nature of the iron compound, we investigated heavily pigmented teeth of the northern short-tailed shrew Blarina brevicauda using combined characterization techniques such as scanning and transmission electron microscopy and synchrotron X-ray diffraction. We found that the pigmentation of the enamel with an iron content of around 8wt% results from a close to amorphous magnetite phase deposited around the nm-sized enamel crystals. Furthermore, the influence of the pigmentation on the enamel hardness was determined by nanoindentation measurements. Finally, the biomechanical function and biological context are discussed in light of the obtained results.

Dealloying is widely utilized but is a dangerous corrosion process as well. Here we report an atomistic picture of the initial stages of electrochemical dealloying of the model system Cu(3)Au (111). We illuminate the structural and chemical changes during the early stages of dissolution up to the critical potential, using a unique combination of advanced surface-analytical tools. Scanning tunneling microscopy images indicate an interlayer exchange of topmost surface atoms during initial dealloying, while scanning Auger-electron microscopy data clearly reveal that the surface is fully covered by a continuous Au-rich layer at an early stage. Initiating below this first layer a transformation from stacking-reversed toward substrate-oriented Au surface structures is observed close to the critical potential. We further use the observed structural transitions as a reference process to evaluate the mechanistic changes induced by a thiol-based model-inhibition layer applied to suppress surface diffusion. The initial ultrathin Au layer is stabilized with the intermediate island morphology completely suppressed, along an anodic shift of the breakdown potential. Thiol-modification induces a peculiar surface microstructure in the form of microcracks exhibiting a nanoporous core. On the basis of the presented atomic-scale observations, an interlayer exchange mechanism next to pure surface diffusion becomes obvious which may be controlling the layer thickness and its later change in orientation.

A combined approach of pH-dependent in-situ AFM topography and ex-situ LEED studies of the stability and dissolution of single-crystalline ZnO(0001)-Zn surfaces in aqueous media is presented. Hydroxide-stabilized and single-crystalline ZnO(0001)-Zn surfaces turned out to be stable within a wide pH range between 11 and 4 around the point of zero charge of pH PZC = 8.7 +/- 0.2. Hydroxide stabilization turned out to be a very effective stabilization mechanism for polar oxide surfaces in electrolyte solutions. The dissolution of the oxide surface started at an acidic pH level of 5.5 and occurred selectively at the pre-existing step edges, which consist of nonpolar surfaces. In comparison, the oxide dissolution along the ZnO(0001) direction proved to be effectively inhibited above a pH value of 3.8. On the basis of these microscopic observations, the mechanistic understanding of the acidic dissolution process of ZnO could be supported. Moreover, both the in-situ AFM and the ex-situ LEED studies showed that the stabilization mechanism of the ZnO(0001) surfaces changes in acidic electrolytes. At pH values below 3.8, the hydroxide-stabilized surface is destabilized by dissolution of the well-ordered radical3. radical3. R30 hydroxide ad-layer as proven by LEED. Restabilization occurs and leads to the formation of triangular nanoterraces with a specific edge termination. However, below pH 4 the surface structure of the crystal itself is ill-defined on the macroscopic scale because preferable etching along crystal defects as dislocations into the bulk oxide results in very deep hexagonal etching pits.

In different production steps steels are exposed to high temperature either in reducing condition (for e.g. N2-H2during recrystallization annealing) or in oxidizing environments (e.g. during hot rolling and cooling after hot rolling). These processes are accompanied by external and internal oxidation, which can affect further processing steps. For example, during cooling after hot rolling of high strength steels especially grain boundary oxidation can lead to significant problems during pickling and cold rolling. In this paper a fundamental investigation of grain boundary oxidation during annealing under model atmospheres simulating the oxygen partial pressure beneath the scale will be addressed, based on model alloys which are relevant to industrial steel grades. The focus will be on questions such as how the different alloying elements and the various annealing conditions influence the internal selective oxidation. In order to develop a fundamental understanding, binary and ternary model alloys (for instance, Fe-Mn, Fe-Cr etc.) are considered. Significant focus will be given to the oxidation kinetics i.e., monitoring of the mass gain during isothermal oxidation using a thermo-gravimetric balance (TG). The partial pressure of oxygen during the experiments is kept just below the equilibrium pressure for FeO/Fe. As the mass changes during internal oxidation are very low, errors from buoyancy effects in a standard set-up are in the same range as the mass change to be investigated. Hence, a novel under-pressure TG set-up was developed and applied here. In this under-pressure TG the same gas composition of water vapor and hydrogen are used, but the inert carrier gas N2is omitted, significantly decreasing buoyancy effects. Thus the mass gain measurement is carried out with so far unequaled accuracy. Furthermore, the role of elemental segregation to the grain boundaries on grain boundary oxidation was investigated. The results will be discussed also on the basis of earlier simulation work [1]. [1] M. Auinger, S. Borodin, S. Swaminathan and M. Rohwerder, Materials Science Forum 696 (2011) 76-81

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