Toxic heavy metal | EPFL Graph Search

A toxic heavy metal is any relatively dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts. The term has particular application to cadmium, mercury and lead, all of which appear in the World Health Organization's list of 10 chemicals of major public concern. Other examples include manganese, chromium, cobalt, nickel, copper, zinc, silver, antimony and thallium. Heavy metals are found naturally in the earth. They become concentrated as a result of human caused activities and can enter plant and animal (including human) tissues via inhalation, diet, and manual handling. Then, they can bind to and interfere with the functioning of vital cellular components. The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of chelating agents. Some elements other

Periodic cellular aluminum structures for space applications

Florian Thibaut Gallien

Mass is one of the crucial parameters for hardware that has to be placed in Earth orbit. Due to its harsh environment, a material with highest specific properties is desired to achieve space missions. The rise and development of new technologies, such as additive manufacturing (AM), opened new opportunities in part-design complexity, periodic cellular structures (PCS) being one of them. The present thesis investigates the potential implementation of PCS in space applications, particularly for structures and micro-meteoroids and orbital debris (MMOD) impact shields. This was achieved in three steps: Four different types of AlSi12 PCS manufactured by selective laser melting (SLM) were tested under quasi-static compression to measure the mechanical properties dependency versus topology and to characterize the failure mode. Properties ranging from 3 to 4 GPa for the compressive modulus, 5 to 12 MPa for the yield stress, 12 to 20 MPa for the plateau stress, and 2 to 8 MJ/cm3 for the absorbed energy were obtained. An unexpected failure mode was observed when compared to classical cellular metals, namely a brittle failure occurring by global shearing. A predictive failure criterion was established based on topology considerations and correlated to most of the reported results in the literature. A preliminary test campaign on tensile specimens was performed to compute numerical models that were fed into a finite element analysis. Good agreement with experimental data was shown, and the importance of microplasticity effects in this class of material was highlighted. An alternative process was developed to produce AlSi1 PCS by investment casting. The process is based on replication of a polymer preform used to build a NaCl mold. It was observed that the quality of the final cast part depends mainly on the grain size of the salt, with an optimum identified for distributions between 125 and 180 um. Optimization of the process allowed to reduce the drying time by a factor 6. Main process parameters include a drying temperature of 80C and infiltration at 660C under 300 mbar. From this process, PCSs having an energy absorption capacity of 15 MJ/m3 with an efficiency of 80% were produced. Hypervelocity impact tests were conducted on cast PCS and stochastic structures. The objective being to hit the structures with a 2mm-diameter aluminum sphere at velocities close to 7 km/s. Influence of the sample topology, the orientation, and the bumper material was assessed. Stochastic structures successfully stopped the projectile in all configurations. The beneficial effect of the bumper was measured reducing the crater depth from 20 mm to 14 mm. This type of structure exhibited a comparable areal density (0.8 g/cm2) to simple Whipple shield design. PCS poorly performed in mitigating the impact as the debris passed through all the structures, independently of the test configuration due to the open-channels present. PCS are good candidates to be used in space hardware, but their design and the manufacturing process need to be carefully chosen depending on the specific application. AM PCS are suitable for structural application with a high compressive modulus and yield stress. Cast PCS would perfectly fit in shock absorbers. A more random design would be preferable for MMOD shielding applications.

EPFL2018

Etude du cycle biogéochimique du cuivre et du cadmium dans deux écosystèmes forestiers

Catherine Keller

The biogeochemical cycle of copper and cadmium has been studied in two forested ecosystems for two years. These two sites are: a) a Norway spruce forest (Picea abies) on an acid brown soil (FAQ: Dystric cambisol) and b) a mixed coniferous forest (Picea abies, Pinus cembra, Larix decidua and Abies alba) on a podzol. Both of them are located on low heavy metal polluted sites: the Swiss Plateau (850 m a.s.l.) for the first one and the oriental edge of the Mont-Blanc Massif (1650 m a.s.l.) for the second one. The Cu and Cd stocks in the vegetation and in the soil are evaluated. Heavy metal fluxes through the ecosystems are determined by analysis of concentrations and quantities of rain, throughfalls, stemflows, lysimetric soil solution and litterfall. In addition, the forms of Cu and Cd immobilization in soils are studied by means of sequential extraction, whereas immobilization forms in solution are studied by means of ion exchange chromatography and selective electrode. The results obtained allowed us to draw conclusions concerning the general pollution level in the experimental sites and the annual and/or detailed behaviour of Cu and Cd in the ecosystems. The conclusions are the following: As expected, the sites are not polluted since concentrations and fluxes are low. The chemical composition of solutions is modified during transition through the ecosystem, especially the copper concentrations. The acid brown soil humic layer is more efficient than the podzol humic layer in modifying this composition. There is no significant seasonal variation of concentrations and fluxes. However, the metal diffusion through the ecosystem is almost immediate. The soil plays an essential role in the immobilization of the heavy metals. The organic and organo-mineral layers are particularly active in this process. Exportations out of the ecosystems are limited. They are relatively more important for the podzol than for the acid brown soil and higher for Cd than for Cu. Transfer and stocking forms, and the ways of input to the soil depend on the metal considered: Copper input to the soil is mainly due to litterfall. In the soil, the metal has a preference to be associated with organic matter. In solution, it forms complexes with dissolved organic matter (mainly fulvic acid of MW < 1000 dalton). So, it is strongly retained within the soil and it cannot be easily drained out of the soil profile. At the opposite, cadmium is mostly transported by liquid means (throughfalls). In solution, it is present as free cadmium ions. In the soil, it is less strongly fixed than Cu since Cd is mostly associated with Fe and Mn oxides. For both of the metals, the free ion concentration in solution depends on pH and the saturation rate of organic matter. The latter has a heterogenous and polyfunctional character which explains a similar complexing capacity for all the samples studied. The differences observed in copper and cadmium behaviour can explain the variable diffusion of a polluting Cu and Cd flux through a given ecosystem and to the aquifer. The soil intervenes as a discriminating factor when the two experimental sites are compared.

EPFL1991

Development of a Heavy Metal Sensing Boat for Automatic Analysis in Natural Waters Utilizing Anodic Stripping Voltammetry

Bhawna Nagar, Qiuyue Yang

Determination of the levels of heavy metal ions would support assessment of sources and pathways of water pollution. However, traditional spatial assessment by manual sampling and off-site detection in the laboratory is expensive and time-consuming and requires trained personnel. Aiming to fill the gap between on-site automatic approaches and laboratory techniques, we developed an autonomous sensing boat for on site heavy metal detection using square-wave anodic stripping voltammetry. A fluidic sensing system was developed to integrate into the boat as the critical sensing component and could detect

AMER CHEMICAL SOC2021