Publications

Deciphering Earthʼs impact history before ∼2 Ga relies heavily on the lunar record and terrestrial spherule layers, which are distal ejecta from large impacts. This study focuses on the Paraburdoo and Reivilo spherule layers in Western Australia and South Africa respectively, that were probably formed by one impact around 2.57 Ga. Both layers contain an aggregate thickness of ∼2 cm of spherules, known as microkrystites. These spherules are up to ∼0.6 mm in diameter and crystallized during flight, but were diagenetically replaced by K-feldspar and phlogopite with remarkable textural retention. Unlike any other Archaean layer, except for the 3.2 Ga S3 layer in the Barberton greenstone belt, the Paraburdoo and Reivilo spherules contain Ni-rich spinel crystals and high concentrations of meteoritic material (up to 357 ng g−1 Ir for bulk samples of several gram). These exceptional characteristics shed new light on the distribution of the meteoritic component carrier phases (metallic alloys dispersed in the pristine glass) and the processes involved in impact spherule formation and secondary alteration.

No abstract is provided for this article.

The sequence of phase transformations during Sr2FeMoO6-x crystallization by the citrate-gel method was studied for powders synthesized with initial reagent solutions with pH values of 4, 6 and 9. Scanning electron microscopy revealed that the as-produced and annealed powders had the largest Sr2FeMoO6-x agglomerates with diameters in the range of 0.7-1.2 µm. The average grain size of the powders in the dispersion grows from 250 to 550 nm with increasing pH value. The X-ray diffraction analysis of the powders annealed at different temperatures between 770 and 1270 K showed that the composition of the initially formed Sr2FeMoO6-x changes and the molybdenum content increases with further heating. This leads to a change in the Sr2FeMoO6-x crystal lattice parameters and a contraction of the cell volume. An optimized synthesis procedure based on an initial solution of pH 4 allowed a single-phase Sr2FeMoO6-x compound to be obtained with a grain size in the range of 50-120 nm and a superstructural ordering of iron and molybdenum cations of 88%.

No abstract is provided for this article.

Aluminium brazing sheet is a sandwich material made out of two aluminium alloys (AA4XXX/AA3XXX) and is widely used in automotive heat exchangers. Re-solidification of an AA4XXX cladding as well as the related particle formation and distribution in a modified AA3XXX core material before and after brazing has been investigated with a new microstructural analysis approach. Optical microscope (OM), scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDX) and thermo-dynamical calculations (JmatPro software) have been used. The particles size, distribution and chemical composition have been analyzed. The equilibrium phases, their weight percentages and the temperature ranges through which various phases are stable have been calculated. The results were used to identify the particles in the clad and the core material. Analysis of the structure before brazing showed that besides silicon (which is the most dominant particle), β-AlFeSi and α-Al(Fe-Mn)Si are the other existing primary particles in the clad material. α-Al(Fe-Mn)Si and Al2Cu were found to be the primary dominant particles that exist in the core structure. Accumulation of copper on the surface of the re-solidified clad material, the reduction of the copper content of the particles and the increase of silicon concentration in the diffusion zone were found to be the major changes that occurred due to brazing process. Low concentrations of some transition elements (Cu, Cr) in the phase that is expected to be α-Al(Fe,Mn)Si particle were detected.

Lithium carbonate and lithium oxalate were incorporated as leachable corrosion inhibitors in model organic coatings for the protection of AA2024-T3. The coated samples were artificially damaged with a scribe. It was found that the lithium-salts are able to leach from the organic coating and form a protective layer in the scribe on AA2024-T3 under neutral salt spray conditions. The present paper shows the first observation and analysis of these corrosion protective layers, generated from lithium-salt loaded organic coatings. The scribed areas were examined by scanning and transmission electron microscopy before and after neutral salt spray exposure (ASTM-B117). The protective layers typically consist of three different layered regions, including a relatively dense layer near the alloy substrate, a porous middle layer and a flake-shaped outer layer, with lithium uniformly distributed throughout all three layers. Scanning electron microscopy and white light interferometry surface roughness measurements demonstrate that the formation of the layer occurs rapidly and, therefore provides an effective inhibition mechanism. Based on the observation of this work, a mechanism is proposed for the formation of these protective layers.

Abstract Transient electrolyte films govern atmospheric corrosion but remain difficult to monitor outdoors. Here, a novel field approach integrates imaging, environmental logging, AI and real-time corrosion sensing to capture data on surface wetting, weather and electrochemical response. Across multiple wetting events, incorporating image-derived electrolyte coverage improved prediction performance over a weather-only model. The approach enables linking electrolyte geometry with corrosion sensor signals, validating mechanistic models and comparing laboratory and field wetting.

No abstract is provided for this article.

The microhardness and fretting wear resistance of anodic oxide layers, produced on commercially pure aluminium by potentiostatic anodizing in sulphuric acid under conditions of controlled convection and heat transfer in a reactor with a wall-jet configuration, were evaluated as a function of the electrolyte temperatures in a wide range from 5 °C up to 55 °C. Additionally, information on the microstructure of the anodic films was acquired by FE-SEM analyses whereas image analysis of high-resolution surface images yielded quantitative information on the evolution of the surface porosity as a function of the electrolyte temperature. Hence measured mechanical properties were directly related to the corresponding microstructure. The microhardness of the anodic films progressively decreased with increasing electrolyte temperatures whereas the wear resistance remained constant for the lower considered temperatures from 5 °C to 25 °C, followed by a decreasing wear resistance with increasing electrolyte temperature from 25 °C onwards. Both mechanical properties displayed an important decrease when the electrolyte temperature was raised from 45 °C to 55 °C. FE-SEM analyses indicated the formation of porous oxides with initially equal pore diameters at the metal-oxide interface, though pore widening due to chemical dissolution of the oxide by the electrolyte led to films with cone-shaped pores. This phenomenon became more pronounced with increasing electrolyte temperature and towards the surface of the anodic layer. The deterioration of the microhardness with increasing electrolyte temperatures could mainly be attributed to the increase of the porosity in the outer region of the oxides since the rate of microhardness reduction is almost synchronous with the rate of porosity increase. In contrast, the variation of the wear resistance with increasing anodizing temperature indicates that the degradation of the wear resistance does not only depend on the oxide porosity and is also affected by other characteristics of the oxide.

Four different accelerated corrosion tests on steel are simulated with a Dynamic Electrolyte Film Corrosion model. Based on the time dependent temperature and humidity, combined with the presence of hygroscopic salts, a time dependent electrolyte thickness is calculated. At every timestep, the modeled film thickness dictates the corrosion current. Focussing on the thickness predictions, an elementary corrosion model is adopted to enable the corrosion depth estimations. The trends of the simulated corrosion depths are compared with experimental data obtained with an electrical resistance corrosion sensing system, demonstrating the importance of the electrolyte thickness and composition for a thorough understanding and modeling of atmospheric corrosion on steel.

No abstract is provided for this article.