Hygroscopique

Résumé

Une substance hygroscopique est une substance qui a tendance à retenir l'humidité de l'air, par absorption ou par adsorption. Quelques exemples de substances hygroscopiques : ; Minéraux

Halite : le chlorure de sodium (sel de cuisine) ;
Sylvine.

; Autres

l'acide hyaluronique ;
le pentoxyde de phosphore ;
le balsa ;
l'acide sulfurique concentré ;
l'acétate de calcium ;
la glycérine ;
l'éthanol, le méthanol ;
le biogazole ;
le liquide de frein (DOT, sauf DOT 5) ;
le miel ;
le carboxyméthylcellulose sodique ;
l'oxyde de magnésium (magnésie) ;
la soude ;
le sorbitol ;
le chlorure de calcium, souvent utilisé pour cette propriété dans les absorbeurs d'humidité commerciaux encore appelés dispositifs dessiccateurs ou desséchants ;
le lactose ;
l’anhydride borique (oxyde de bore).
le propylène glycol, utilisé dans les liquides à vapoter de la cigarette électronique notamment.

Déliquescente Une substance déliquescente est une substance qui a l

Source officielle

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

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Séances de cours associées (5)

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, , , ,

Droplet formation provides a direct microphysical link between aerosols and clouds (liquid or mixed-phase), and its adequate description poses a major challenge for any atmospheric model. Observations are critical for evaluating and constraining the process. To this end, aerosol size distributions, cloud condensation nuclei (CCN), hygroscopicity, and lidar-derived vertical velocities were observed in alpine mixed-phase clouds during the Role of Aerosols and Clouds Enhanced by Topography on Snow (RACLETS) field campaign in the Davos, Switzerland, region during February and March 2019. Data from the mountain-top site of Weissfluhjoch (WFJ) and the valley site of Davos Wolfgang are studied. These observations are coupled with a state-of-the-art droplet activation parameterization to investigate the aerosol–cloud droplet link in mixed-phase clouds. The mean CCN-derived hygroscopicity parameter, κ, at WFJ ranges between 0.2–0.3, consistent with expectations for continental aerosols. κ tends to decrease with size, possibly from an enrichment in organic material associated with the vertical transport of fresh ultrafine particle emissions (likely from biomass burning) from the valley floor in Davos. The parameterization provides a droplet number that agrees with observations to within ∼ 25 %. We also find that the susceptibility of droplet formation to aerosol concentration and vertical velocity variations can be appropriately described as a function of the standard deviation of the distribution of updraft velocities, σw, as the droplet number never exceeds a characteristic limit, termed the “limiting droplet number”, of ∼ 150–550 cm−3, which depends solely on σw. We also show that high aerosol levels in the valley, most likely from anthropogenic activities, increase the cloud droplet number, reduce cloud supersaturation (

2021

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Influence of the moisture content on the shear strength of welded wood-to-wood connections

Benjamin Hahn, Georg Lorenz Rossmair, Bernhard Stamm, Yves Weinand

Friction welding of wood is an innovative process, able to join pieces of wood without additional adhesives. Because of its hygroscopic properties, the wood matrix absorbs humidity at the surface from the surrounding atmosphere. Its moisture content is strongly dependent on ambient conditions and seasonal changes. Former research showed that after samples passed a certain moisture content threshold, the creation of welded wood-towood connections becomes difficult and shear strength is significantly reduced. Tests carried out on spruce samples with different moisture content should help to spot the limits of the materials moisture content, regarding the feasibility of establishing a welded wood-to-wood connection, but also to calculate which conditions lead to the most solid welded joints. If specific moisture content is needed to gain a satisfactory weld, this will have an impact on the storage conditions of the pieces to be welded.

Berne University of Applied Sciences, Architecture, Wood and Civil Engineering2011

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Revising the hygroscopicity of inorganic sea salt particles

Athanasios Nenes

Sea spray is one of the largest natural aerosol sources and plays an important role in the Earth's radiative budget. These particles are inherently hygroscopic, that is, they take-up moisture from the air, which affects the extent to which they interact with solar radiation. We demonstrate that the hygroscopic growth of inorganic sea salt is 8-15% lower than pure sodium chloride, most likely due to the presence of hydrates. We observe an increase in hygroscopic growth with decreasing particle size (for particle diameters <150 nm) that is independent of the particle generation method. We vary the hygroscopic growth of the inorganic sea salt within a general circulation model and show that a reduced hygroscopicity leads to a reduction in aerosol-radiation interactions, manifested by a latitudinal-dependent reduction of the aerosol optical depth by up to 15%, while cloud-related parameters are unaffected. We propose that a value of κs=1.1 (at RH=90%) is used to represent the hygroscopicity of inorganic sea salt particles in numerical models. © The Author(s) 2017.

Nature Publishing Group2017

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