Zinc

Résumé

Le zinc (prononciation /zɛ̃g/ en France, /zɛ̃k/ au Canada, /zɛ̃/ en Suisse) est l'élément chimique de numéro atomique 30 et de symbole Zn. Le corps simple zinc est un métal. Généralités sur l'élément zinc, histoire et lexicographie Le zinc est par certains aspects semblable au magnésium dans la mesure où son état d'oxydation courant est +2, donnant un cation de taille comparable à celle de Mg. C'est le le plus abondant dans l'écorce terrestre. Il possède cinq isotopes naturels stables. Le zinc est un élément du groupe 12 et de la période 4. Stricto sensu, c'est un métal pauvre, qui ne répond pas à la définition des éléments de transition par l'IUPAC ; en pratique cependant, il est très souvent assimilé aux métaux de transition dans les manuels et de très nombreux ouvrages. Il fait partie du « groupe du zinc », ou groupe B, qui comprend, par numéro atomique croissant, Zn, Cd et Hg, éléments caractérisés par deux électrons sur la sous-couche s au-delà d'une sous-couche d

Source officielle

https://fr.wikipedia.org/wiki/Zinc

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This work was focused on the phytoextraction of zinc, copper, zinc oxide and copper oxide by Lolium perenne cultivated in hydroponic conditions, with gibberellic acid (GA) and ethylenediamine-N,N’-disuccinic acid (EDDS) amendments tested separately and in combination. GA is a plant hormone which permits a better uptake of trace elements by increasing the biomass of shoots and the transpiration. EDDS is a chelator permitting to the metal to complex and cross physiological barriers. These two amendments were tested separately and in combination because a good synergy effect should be observed. The duration of treatment was first 11 days and then 28 days. The enzyme activity of catalase and ascorbate peroxidase was measured. The results showed a higher uptake for zinc with the GA treatment, where the final quantity after 21 days was 24 μg instead of 14 μg for the control, and the translocation index was 0.3 instead of 0.1 for the control. For copper the best results were obtained with EDDS, which gave a quantity of 4.5 μg after 28 days instead of 3.5 μg for the control and the translocation index was 0.275 instead of 0.12 for the control. For the metal oxides the results were less significant, especially for enzyme activities. Finally a hydric stress was observed after 28 days, cumulated with metal stress.

2013

Chargement

Interfacial Energy Anisotropy and Growth Morphologies in Aluminium-Zinc Alloys

Jonathan Friedli

This thesis presents an investigation aimed at the understanding of the effect of interfacial energy anisotropy on growth morphologies in Al-Zn alloys. Most low alloyed metals form dendritic structures that grow along directions that correspond to low index crystal axes, e.g., 〈100〉 directions in fcc aluminum. However, recent findings [Gon06, Gon08] have shown that an increase in the zinc content of Al-Zn continuously changes the dendrite growth direction from 〈100〉 to 〈110〉 in the (100) plane. At intermediate compositions, 〈320〉 dendrites and textured seaweeds were even observed. The reason for this dendrite orientation transition (DOT) is that this system exhibits a large solubility of the element zinc, which forms hexagonal crystals, in the primary fcc aluminum phase, thus modifying its weak solid-liquid interfacial energy anisotropy γsl. Due to the complexity of the phenomenology, there is still no satisfactory theory that predicts all the observed microstructures. The goal of this work was to measure the anisotropy of γsl, to gain further insight in the dendrite growth morphologies and mechanisms in Al-Zn via X-ray tomography and investigate the relationship between dendrite growth directions and the anisotropy of γsl via phase-field modeling. The values of the anisotropy in Al-82 wt.% Zn, obtained by equilibrium shape measurement, suggests a DOT in a regime with very low anisotropy, favoring the formation of seaweed structures. The enhanced experimental procedures and observation methods allowed an unprecedented characterization of such complex morphologies. Observations showed that seaweeds are far from random structures. They grow in a (100) symmetry plane by an alternating growth direction mechanism and are therefore less hierarchically ordered than common dendrites. Phase-field simulations of equiaxed growth of a dilute alloy showed that the DOT is not a continuous transition of growth directions, but rather a competition between the 〈100〉 and the 〈110〉 character of dentrites. However, crystallographic orientation measurements showed that the macroscopic texture evolves as evidenced by Gonzales and Rappaz. This showed that the preferred growth direction is not the same as the final texture of a sample, which is uncommon. Simulations of directional growth showed that seaweeds, which do not appear in equiaxed growth, are in fact produced by the interplay of low or degenerate crystalline anisotropy and the misorientation of the crystal with respect to the thermal gradient.

EPFL2011

Chargement

Phytoextraction is a non-invasive remediation method using plants. Phytotech Foundation and AGB in Berne are performing phytoextraction on an old landfill of a former hot dip galvanization plant, using sunflowers and tobaccos as extractors. Every year since 2007, total and soluble zinc concentrations in soil as well as zinc concentrations in shoot of the plants have been measured. To study the role of roots in phytoextraction, 14 root samples were harvested in autumn 2010 and their zinc concentration was measured. The results show that sunflowers were more efficient in fast transfer of zinc from root to shoot. They were also compared with the 4-year measurements and a mass balance was performed. This has shown that phytoextraction was so efficient that even the decrease in soluble zinc did not explain itself the concentrations in the plant. The roots may mobilize total zinc, which might re-load the soluble zinc pool in soil. In parallel, a pot experiment was performed at laboratory scale with young tobacco plants growing on polluted soils, monitoring root, stem, leaves, leachates and soil zinc concentrations. A mass balance was also performed, which confirmed the previous statement, even at young stage and for detailed values. Finally thanks to both experiments, it was suggested that there should be a potential concentration for each part of plants. Once this concentration reached, transfer of zinc could occur from the root to the stem, and then from the stem to the leaves where it is accumulated.

2011

Chargement

Interfacial Energy Anisotropy and Growth Morphologies in Aluminium-Zinc Alloys

Jonathan Friedli

EPFL2011