Sulfate

Résumé

Un sulfate est un sel de l'acide sulfurique HSO. On appelle ion sulfate l'anion SO. Les sulfates font partie des polluants de l'air et en particulier lors des phénomènes de smog. Sulfates inorganiques Les sulfates de potassium, d'ammonium et de magnésium sont utilisés dans les engrais. Ceux de zinc, de manganèse, de cuivre et de fer sont utilisés en micro-fertilisation, pour corriger les carences en ces éléments. Le sulfate de cuivre ou vitriol bleu est aussi un fongicide et un bactéricide puissant utilisé en agriculture. Il entre dans la composition de la bouillie bordelaise. Le sulfate ferreux a pour formule FeSO4.7H2O. Ce composé se présente sous la forme de cristaux vert pâle ; c'est un sous-produit du fer de décapage. Il est utilisé comme mordant en teinture, comme reconstituant en médecine, et pour la fabrication des encres et des pigments noir, rouge, bleu, vert ou bien violet. Le sulfate de zinc est aussi utilisé contre la prolifération des mousses et lichens.

Source officielle

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

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Atomistic Simulation of Cementitious Systems: An Insight Into Adsorption of Ions and Small Molecules Onto Portlandite and C-S-H Surfaces

Masood Valavi

AbstractCalcium-Silicate-Hydrate (C-S-H) has been studied extensively over the last few decades to gain understanding toward the underlying mechanism of different stages during cement hydration. The variable stoichiometry and nanocrystallinity of C-S-H makes it difficult to characterize experimentally. The second most abundant hydration product of cement is portlandite which has a simpler crystalline structure in comparison to C-S-H and has been used as a training/building system for future simulation of C-S-H bulk and surfaces. In this PhD project we are interested in a better fundamental understanding of the interaction of sulfate and secondary ions (Aluminium, Magnesium,...) with cementitious materials (e.g. portlandite and C-S-H). It has been shown that sulfate considerably affects the morphology of growing portlandite and C-S-H which will affect the physical properties of cement and concrete. A better fundamental understanding of this adsorption or incorporation into bulk structures will improve our understanding of the growth of C-S-H in the presence of such ions. In this project, utilizing molecular dynamics and metadynamics, we will systematically investigate the interaction of ions found in cement pore solutions with portlandite and C-S-H. For this purpose, we will use the Brick model recently developed in our group by Mohamedet al. (1) to create model structures for the C-S-H. We also have started to develop a new force field (ERICA FF1) which constitute different atom types needed for these simulations which are not included in previous cement force fields (Cement FF1 (2) and Cement FF2 (3)â .

EPFL2022

Chargement

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Supplementary materials that are utilized to replace ordinary Portland cement (OPC) decrease the workability of the cementitious mixtures and superplasticizers are usually added to cement to control their fluidity. In general, current superplasticizers are solely optimized for single component systems such as OPC. Here, we report the performance of a series of a modified poly(carboxylate ether)-based superplasticizers (PCEs) in a ternary OPC-calcined clay-limestone blend. We have utilized: i) a co-monomer with high ionic character, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) to be incorporated into the acrylic acid backbone of PCEs and ii) low density of polyethylene glycol (PEG) grafted chains < 0.01 mol/mol. The optimized polymer does not intercalate into the layered structure of calcined clay and preserves its steric size in the presence of high concentration of sulfate ions.

Elsevier2017

Chargement

Biogenic secondary organic aerosol (BSOA) contributes significantly to summertime organic particulate matter. In this study, a simulation of BSOA for summer 2012 over China is performed using the Community Multiscale Air Quality model with an explicit representation of BSOA formation via reactive uptake of isoprene-derived intermediates, species-specific parameters for monoterpene-derived BSOA production, and a multigenerational oxidation scheme. Simulated BSOA tracks the measurements well (normalized mean bias of 1% and r(2) of 0.59). Elevated BSOA occurs in the Sichuan Basin and southeastern China (except the coastal areas) where concentrations are mostly within the range of 5-7.5 mu g/m(3). Nitrate oxidation dominates fresh BSOA originating from monoterpenes. Simulated monoterpene-formed BSOA increases by a factor of 3-11 with multigenerational oxidation. Isoprene-formed BSOA shows high concentrations in southwestern China, formed primarily by two methyltetrols (2-MT) and organosulfates (62%-83%). High concentrations in this region are driven by the abundance of IEPOX and high particle surface area of sulfate-laden aerosols. NOx emissions influence the formation pathways of isoprene-formed BSOA, as a high ratio of two-methylglyceric acid (2-MG)/2-MT is found in the North China Plain and part of the Yangtze River Delta Region. The simulated isoprene-formed BSOA is more strongly correlated with sulfate than with particle water mass concentration or particle acidity, in part because sulfate increases the surface area increasing uptake for heterogeneous reactions. Decreases in isoprene-formed BSOA were simulated with a pH increase of 2, implying that particle acidity mediates the BSOA formation. Plain Language Summary Emissions from plants contribute to particulate matter formation when they interact with emissions due to human activities. With intense anthropogenic emissions in China, how biogenic aerosols are formed as well as how the formation processes are impacted by anthropogenic emissions are not clear yet. This study applied an advanced modeling approach to simulate formation of biogenic aerosols over continental China in summer. We modeled high levels of biogenic aerosols in the Sichuan Basin and southeastern China, not only because of more forests in these areas than elsewhere but also due to particulate matter of anthropogenic origin. Based on the simulation, there is a clear evidence that anthropogenic emissions impact the chemical formation and composition of biogenic aerosols and particle acidity. Therefore, a decrease (increase) in biogenic aerosols and particle acidity would be a cobenefit (side effect) of anthropogenic emission controls.

2018

Chargement

2018