Investigating the Corrosion Behaviour of Ni-based alloys in Industrially Relevant Environments

Typical engineering materials may experience high corrosion rates when exposed to aggressive service conditions. Such conditions include high concentrations of aggressive anions and oxidants, high solution acidity, and/or high temperatures. Alloys with high corrosion resistance may be selected to avoid material failure caused by corrosion, for example, Ni-Cr-Mo alloys. These alloys exhibit excellent corrosion resistance due to the formation of a passive oxide film, primarily containing Cr and Mo. However, film breakdown can result in localized corrosion, e.g., crevice corrosion. Localized corrosion processes can penetrate deep into the bulk alloy, threatening its integrity. While the oxide film and localized corrosion processes have been extensively studied, many mechanistic features remain unresolved. Here, the corrosion behaviour of commercially available Ni-Cr-Mo alloys has been studied using electrochemical, spectroscopic, and microscopy techniques. Electrochemical measurements (Chapter 3) showed that increases in Cr content improve passive film properties, while increases in Mo content improve film stability in acidic solutions. Atomic emission spectroelectrochemistry (AESEC) measurements (Chapters 4 and 5) revealed a dynamic role for Mo deposition during film breakdown. Transpassive dissolution occurring in neutral solutions led to the deposition of Mo-rich species, while repassivation resulted in their release to solution. Surface activation followed by repassivation in acidic solution was found to cause a similar process. The mechanism of crevice corrosion (Chapter 6) was investigated using a galvanostatic technique combined with weight loss measurements. Internal cathodic reactions were found to be an important feature, intensifying damage by as much as 76 %, depending on the Mo content of the alloy. The effect of fluoride (Chapter 7) on the corrosion behaviour of Ni- and Fe-based alloys was investigated. Film stability was found to decrease in the presence of trace quantities, especially as the applied potential was increased. The findings reported throughout this thesis suggest a delicate balance between Cr and Mo is required for optimal corrosion performance, however, an optimal alloy composition has yet to be determined. The results presented in this thesis provide new mechanistic information necessary for understanding the corrosion of these industrially important alloys

Investigating the structure of the oxide on Ni-Cr-Mo alloys while presenting a method for analysis of complex oxides using QUASES

X-ray photoelectron spectroscopy (XPS) is a technique that is widely used to studythin oxide films because of its extremely high surface sensitivity. Utilizing theQUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy) software pack-age developed by Sven Tougaard (University of Southern Denmark), a user canobtain additional information that is not extracted in conventional XPS analysis, spe-cifically the composition as a function of depth. Presented here is the QUASES analy-sis of four Ni-Cr-Mo alloys performed while testing various inelastic mean free path(IMFP) determination methods in the context of providing a framework for the analy-sis of complex oxides in QUASES. Ni-Cr-Mo alloys are often used to replace conven-tional materials under aggressive conditions, because of their exceptional corrosionresistance. Their corrosion resistance is conferred by the formation of an inert sur-face oxide film that protects the underlying metal. Using the QUASES software, thethickness of the air-formed oxide on four Ni-Cr-Mo alloys was found to lie within therange of 2.5–3.6 nm. They were found to be composed of an inner Cr2O3layer andan outer Cr (OH)3layer, with a transition zone where the two coexisted. OxidizedMo species, MoO2and MoO3, were found in trace amounts at the boundarybetween the Cr2O3-only and mixed Cr2O3/Cr (OH)3regions of the oxide. We alsodetermined that using 20% reduced IMFP values gave results similar to thoseobtained using electron effective attenuation length (EAL) values. Auger depth pro-files showed comparable trends to the QUASES models

The value of best-practice guidelines for OSCEs in postgraduate program in an Australian remote area setting

Introduction: Nurses in remote areas of Australia are the primary healthcare professionals, who need to be able to deliver comprehensive and culturally sensitive care to clients, many of whom are Indigenous Australians. Adequate and specific preparation for practice is crucial to the quality of care delivered by remote area nurses (RANs). Objective structured clinical examinations (OSCE) provide an excellent opportunity for student practice in a simulated environment that is safe, authentic, fair and valid when well constructed. Seven integrated best practice guidelines (BPGs), previously developed by project team members to inform OSCEs within educational programs, provided guidance in restructuring the OSCE. This paper provides a detailed analysis of the value of BPGs used in the development, teaching and learning, and evaluation of OSCEs in a rural and remote postgraduate course for RANs. Method: A pre-site visit to the Centre for Remote Health, Alice Springs, Northern Territory, was conducted with modification of the course and previous OSCE according to BPGs. Following delivery of the course and OSCE, evaluations occurred via a mixed method approach. Student surveys (n=15) and focus groups (n=13) and staff interviews (n=5) provided an in-depth analysis of their perceptions of the revised OSCE. Descriptive statistics were used to describe the student sample. The narrative data were transcribed verbatim and analysed using content analysis. Triangulation was achieved with the convergence of the separate data sources focusing on themes and patterns within and between students and tutors.Results: All 15 students and five tutors provided feedback. The majority of student participants had limited experience in working in remote area nursing prior to participation and therefore the opportunities that availed themselves were critical in adequately equipping them with the requisite knowledge, skills and abilities. Three themes emerged from the data: (1) value of common and significant events in OSCE; (2) power of deliberate actions; and (3) learning cultural sensitivity.Discussion: OSCEs in this setting proved to be a good way for students to learn the skills required by RANs. Overwhelmingly, the modifications using the BPGs were highly valued by students and staff. Three themes emerged and were clearly linked to specific BPGs, indicating the positive impact the BPGs had on the OSCEs and student learning. The authentic content for the scenarios was seen as relevant and motivational for student learning. The practice element of the OSCEs enhanced the learning experience and feedback supported learning. Conclusions: OSCEs developed, taught and assessed using BPGs were highly valued. The BPGs provided an integrated approach with real-life scenarios with a strong cultural perspective – all important features to the RANs’ future success in providing individualised care to clients in remote areas of Australia. Further use of BPGs is recommended

Metabolomics As an Emerging Tool in the Search for Astrobiologically Relevant Biomarkers

It is now routinely possible to sequence and recover microbial genomes from environmental samples. To the degree it is feasible to assign transcriptional and translational functions to these genomes, it should be possible, in principle, to largely understand the complete molecular inputs and outputs of a microbial community. However, gene-based tools alone are presently insufficient to describe the full suite of chemical reactions and small molecules that compose a living cell. Metabolomic tools have developed quickly and now enable rapid detection and identification of small molecules within biological and environmental samples. The convergence of these technologies will soon facilitate the detection of novel enzymatic activities, novel organisms, and potentially extraterrestrial life-forms on solar system bodies. This review explores the methodological problems and scientific opportunities facing researchers who hope to apply metabolomic methods in astrobiology-related fields, and how present challenges might be overcome

A systems biology approach sheds new light on Escherichia coli acid resistance

In order to develop an infection, diarrhogenic Escherichia coli has to pass through the stomach, where the pH can be as low as 1. Mechanisms that enable E. coli to survive in low pH are thus potentially relevant for pathogenicity. Four acid response systems involved in reducing the concentration of intracellular protons have been identified so far. However, it is still unclear to what extent the regulation of other important cellular functions may be required for survival in acid conditions. Here, we have combined molecular and phenotypic analysis of wild-type and mutant strains with computational network inference to identify molecular pathways underlying E. coli response to mild and strong acid conditions. The interpretative model we have developed led to the hypothesis that a complex transcriptional programme, dependent on the two-component system regulator OmpR and involving a switch between aerobic and anaerobic metabolism, may be key for survival. Experimental validation has shown that the OmpR is responsible for controlling a sizeable component of the transcriptional programme to acid exposure. Moreover, we found that a ΔompR strain was unable to mount any transcriptional response to acid exposure and had one of the strongest acid sensitive phenotype observed

Metabolomics as an emerging tool in the search for astrobiologically relevant biomarkers

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Seyler, L., Kujawinski, E. B., Azua-Bustos, A., Lee, M. D., Marlow, J., Perl, S. M., & Cleaves, H. J. Metabolomics as an emerging tool in the search for astrobiologically relevant biomarkers. Astrobiology, (2020), doi:10.1089/ast.2019.2135.It is now routinely possible to sequence and recover microbial genomes from environmental samples. To the degree it is feasible to assign transcriptional and translational functions to these genomes, it should be possible, in principle, to largely understand the complete molecular inputs and outputs of a microbial community. However, gene-based tools alone are presently insufficient to describe the full suite of chemical reactions and small molecules that compose a living cell. Metabolomic tools have developed quickly and now enable rapid detection and identification of small molecules within biological and environmental samples. The convergence of these technologies will soon facilitate the detection of novel enzymatic activities, novel organisms, and potentially extraterrestrial life-forms on solar system bodies. This review explores the methodological problems and scientific opportunities facing researchers who hope to apply metabolomic methods in astrobiology-related fields, and how present challenges might be overcome.This study was partially supported by the ELSI Origins Network (EON), which is supported by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This work was partially supported by a JSPS KAKENHI Grant-in-Aid for Scientific Research on Innovative Areas “Hadean Bioscience,” grant number JP26106003, and also partially supported by Project “icyMARS,” funded by the European Research Council, ERC Starting Grant No. 307496. A.A-B thanks the contribution from the Project “MarsFirstWater,” funded by the European Research Council, ERC Consolidator Grant No. 818602 and the HFSP Project UVEnergy RGY0066/2018

Mechanical design and development of TES bolometer detector arrays for the Advanced ACTPol experiment

The next generation Advanced ACTPol (AdvACT) experiment is currently underway and will consist of four Transition Edge Sensor (TES) bolometer arrays, with three operating together, totaling ~5800 detectors on the sky. Building on experience gained with the ACTPol detector arrays, AdvACT will utilize various new technologies, including 150mm detector wafers equipped with multichroic pixels, allowing for a more densely packed focal plane. Each set of detectors includes a feedhorn array of stacked silicon wafers which form a spline profile leading to each pixel. This is then followed by a waveguide interface plate, detector wafer, back short cavity plate, and backshort cap. Each array is housed in a custom designed structure manufactured from high purity copper and then gold plated. In addition to the detector array assembly, the array package also encloses cryogenic readout electronics. We present the full mechanical design of the AdvACT high frequency (HF) detector array package along with a detailed look at the detector array stack assemblies. This experiment will also make use of extensive hardware and software previously developed for ACT, which will be modified to incorporate the new AdvACT instruments. Therefore, we discuss the integration of all AdvACT arrays with pre-existing ACTPol infrastructure.Comment: 9 pages, 5 figures, SPIE Astronomical Telescopes and Instrumentation conference proceeding