Quantitative APT analysis of Ti(C,N)

A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the 13C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified. \ua9 2011 Elsevier B.V

Cerebral gene expression in response to single or combined gestational exposure to methylmercury and selenium through the maternal diet

Controversy remains regarding the safety of consuming certain types of seafood, particularly during pregnancy. While seafood is rich in vital nutrients, it may also be an important source of environmental contaminants such as methylmercury (MeHg). Selenium (Se) is one essential element present in seafood, hypothesised to ameliorate MeHg toxicity. The aim of the present study was to ascertain the impact of Se on MeHg-induced cerebral gene expression in a mammalian model. Microarray analysis was performed on brain tissue from 15-day-old mice that had been exposed to MeHg throughout development via the maternal diet. The results from the microarray analysis were validated using qPCR. The exposure groups included: MeHg alone (2.6 mg kg−1), Se alone (1.3 mg kg−1), and MeHg + Se. MeHg was presented in a cysteinate form, and Se as Se–methionine, one of the elemental species occurring naturally in seafood. Eight genes responded to Se exposure alone, five were specific to MeHg, and 63 were regulated under the concurrent exposure of MeHg and Se. Significantly enriched functional classes relating to the immune system and cell adhesion were identified, highlighting potential ameliorating mechanisms of Se on MeHg toxicity. Key developmental genes, such as Wnt3 and Sparcl1, were also identified as putative ameliorative targets. This study, utilising environmentally realistic forms of toxicants, delivered through the natural route of exposure, in association with the power of transcriptomics, highlights significant novel information regarding putative pathways of selenium and MeHg interaction in the mammalian brain

Cards for circularity: Towards circular design in practice

The transition towards a Circular Economy (CE) in the built environment is crucial to achieve the Sustainable Development Goals (SDGs). Theoretical frameworks and methods for circular design have been developed. Yet, there is a lack of knowledge on circular design in practice and how circular design thinking can be supported. This study aims to provide insights on circular design in practice and how this can be supported through circular design methods. First, we reviewed existing circular design methods and developed a card-based circular design tool. Next, an interactive survey and design workshop using the tool was carried out with 12 design experts to gather knowledge on circular design in practice. Finally, we derive key learnings that can support the development of circular design methods and advancement of CE in practice. Overall, circular design remains highly conceptual and is challenging due to the interconnectedness of parameters and temporal aspects such as product life cycle. Designers need ways of educating and convincing stakeholders on the value and feasibility of circular design. Advancing the CE in practice requires circular design methods that help to contextualize the design process and reduce complexity, and examples are needed of how CE can be implemented in practice.</p

Atomic scale characterisation of electrodeposited nanocrystalline Ni-P alloys

Nanocrystalline Ni-P alloys produced by electrodeposition have been characterised by three-dimensional atom probe (3DAP) analysis. In the as-deposited materials, there are indications of some variation in P concentration between grains and segregation to grain boundaries. After heat treatment however, strong grain boundary segregation and the formation of Ni3P precipitates have been observed

Early Precipitation Stages of Sigma Phase in Alloy 28 Studied with Scanning Electron Microscopy and Atom Probe Tomography

This study deals with early stages of sigma phase growth in a high end austenitic stainless steel - Alloy 28 (EN 1.4563/UNS N08028). Its precipitation kinetics was followed by a series of heat treatments at 800 degrees C for holding times up to 30 000 s. The samples were studied with high resolution scanning electron microscopy and atom probe tomography. Detailed image analysis of the micrographs made it possible to quantify the growth rate of the precipitates. It was shown that diffusion limited growth along grain boundaries was about 15 times faster than growth perpendicular to a grain face. By combining the image data with quantitative chemical analysis of the phase boundaries, it was possible to estimate diffusion coefficients in the lattice and in the grain boundaries; grain boundary diffusion coefficients were about 250 times those of the lattice

Direct observation of hydrogen and deuterium in oxide grain boundaries in corroded Zirconium alloys

Atom probe tomography has been used to the study the distribution of hydrogen and deuterium in the oxide scale of two common zirconium alloys after autoclave testing in H2O and D2O, respectively. Comparison between hydrogen and deuterium in the mass spectra allows for separation of hydrogen as a corrosion product from adsorbed H2 gas from the vacuum chamber. Enrichment of hydrogen and deuterium, as OH+ and OD+, was observed in grain boundaries. The grain boundaries were identified through segregation of iron. This lends experimental support to existing theories for the mechanism of hydrogen pick-up in zirconium alloys