Quantification of the chemical reactivity of molten nitrate salts with heat treatable aluminum alloys

This work explores the conditions for safe heat treatment of aluminum alloys containing lithium and magnesium in molten sodium nitrate (NaNO3) bath furnaces, and conditions where industrial accidents may occur. Using calorimetry coupled to classical thermodynamics, the strength of classical thermodynamics when analyzing thermal curves was demonstrated through a series of small-scale thermal analyses of various aluminum alloys in contact with sodium nitrate. This system was selected to illustrate reactions that may lead to severe and violent heat effect phenomena. Using idealized binary alloys, severe oxidation of magnesium- and lithium-rich aluminum alloy samples were shown to occur near 500 °C, a temperature range dangerously close to the operating temperature of solution heat treatment furnaces in manufacturing processes of heat treatable aluminum alloy sheets used in the aerospace industry. Commercial aluminum alloys AW257, 2198, 2024, and 1050 were also assessed with the same tools. The temperature that needed to be reached for these commercial aluminum alloys to react with molten sodium nitrate was significantly higher than the normal operating temperature of a conventional solution heat treatment furnace

Subatomic movements of a domain wall in the Peierls potential

Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity. Domain walls are found to be weakly mobile within valleys of the atomic washboard but become unexpectedly flexible on Peierls ridges, where they can be kept in a bi-stable state by ac magnetic field. We describe the latter observation in terms of a single magnetic kink propagating along a domain wall

Genomic epidemiology of SARS-CoV-2 in a UK university identifies dynamics of transmission

AbstractUnderstanding SARS-CoV-2 transmission in higher education settings is important to limit spread between students, and into at-risk populations. In this study, we sequenced 482 SARS-CoV-2 isolates from the University of Cambridge from 5 October to 6 December 2020. We perform a detailed phylogenetic comparison with 972 isolates from the surrounding community, complemented with epidemiological and contact tracing data, to determine transmission dynamics. We observe limited viral introductions into the university; the majority of student cases were linked to a single genetic cluster, likely following social gatherings at a venue outside the university. We identify considerable onward transmission associated with student accommodation and courses; this was effectively contained using local infection control measures and following a national lockdown. Transmission clusters were largely segregated within the university or the community. Our study highlights key determinants of SARS-CoV-2 transmission and effective interventions in a higher education setting that will inform public health policy during pandemics.</jats:p

Fire and explosion hazards related to the industrial use of potassium and sodium methoxides

International audienceSodium and potassium methoxides are used as an intermediary for a variety of products in several industrial applications. For example, current production of so called '1G-biodiesel' relies on processing a catalytic reaction called 'transesterification'. This reaction transforms lipid resources from biomass materials into fatty acid methyl and ethyl esters. 1-G biodiesel processes imply the use of methanol, caustic potash (KOH), and caustic soda (NaOH) for which the hazards are well characterized. The more recent introduction of the direct catalysts CH3OK and CH3ONa may potentially introduce new process hazards. From an examination of existing MSDSs concerning these products, it appears that no consensus currently exists on their intrinsic hazardous properties. Recently, l'Institut National de l'Environnement Industriel et des Risques (France) and the Canadian Explosives Research Laboratory (Canada) have embarked upon a joint effort to better characterize the thermal hazards associated with these catalysts. This work employs the more conventional tests for water reactivity as an ignition source, fire and dust explosion hazards, using isothermal nano-calorimetry, isothermal basket tests, the Fire Propagation Apparatus and a standard 20 L sphere, respectively. It was found that these chemicals can become self-reactive close to room temperature under specific conditions and can generate explosible dusts

Thermal hazards related to the use of potassium and sodium methoxides in the biodiesel industry

International audienceThe introduction of sodium and potassium methoxides in processes leading to biodiesel production has triggered several questions about their stability under actual biofuel manufacturing conditions. In most biodiesel production facilities, basic homogenous catalysis is obtained through the introduction of caustic potash (KOH) or caustic soda (NaOH) in the reactor. In this process, the hydroxides are converted into their corresponding methoxide forms (CH3OK/Na), which then become the actual catalysts in the reactor. Supplying the actual catalyst directly, instead of the low cost hydroxides, may offer several advantages, but may also introduce new hazards that deserve further characterisation work. From a review of the available literature, it was found that very little was known about the thermal decomposition properties of these methoxides. Therefore, as a starting point, l'Institut National de l'Environnement Industriel et des Risques (France) and the Canadian Explosives Research Laboratory (Canada) have recently undertaken a joint effort to better characterise their thermal behaviour. This was achieved by means of a variety of calorimetric techniques including differential scanning calorimetry, accelerating rate calorimetry and 'large scale' thermogravimetry- differential thermal analysis. It was found that these chemicals can become self-reactive close to room temperature under specific physical conditions

What factors are important in smoking cessation amongst deprived communities? A qualitative study

Objective: There is limited evidence regarding effective smoking cessation interventions in deprived communities. This study explored what factors are considered most important in smoking cessation, from the perspective of a group of NHS Stop Smoking Service users from a deprived community. Design: A qualitative study. Setting: A deprived community in Brighton and Hove City, Southeast England. Methods: Fifteen adults who had used the local NHS Stop Smoking Service were recruited to the focus groups. Thematic analysis was used to identify key themes regarding factors that were considered most helpful during the smoking cessation attempt. Results: Factors deemed most important for a successful smoking cessation attempt were counsellors’ attitude and knowledge, flexibility of appointments, personalized one-to-one support including additional support between sessions, all provided in an accessible local community setting. Individuals were most likely to decide to quit smoking for health reasons, and support from family and friends was important during the quit attempt. Conclusion: This study shows that smokers from deprived communities require more intensive, flexible and personalized support from a stop smoking service which should ideally be located in their community setting. A more innovative, tailored and less prescriptive approach to providing stop smoking services may help to improve cessation rates among smokers in deprived communities

Managing co-operation: trust and power in Ghanaian associations

Through a rich empirical study of forms of collective action in Ghana, this paper examines how groups sustain co-operation in the absence of strong legal institutions and mechanisms (such as legal contracts or regulated loan finance) that are often taken for granted in most ‘western’ economies. It presents evidence from case studies of micro-saving groups, palm oil processing groups and transport associations, which indicate that co-operation is based on trust and power, both of which are based on culturally specific norms. Decisions to co-operate are shaped by a combination of conscious calculations, habitual actions and unquestioning compliance or obedience. The way that trust and power are articulated also varies according to local context, and attempts to facilitate and support co-operative activities have to build on the existing co-operative structures that are embedded in the local, culturally specific, social relations