Solidification

Résumé

La solidification est l'opération (plus ou moins réversible) au cours de laquelle un liquide passe à l'état solide. Cela peut se faire par refroidissement (cas le plus courant), par augmentation de la pression, par cristallisation, par catalyse ou bien par une combinaison de ces phénomènes. La congélation peut aussi permettre la solidification de certains fluides (l'eau par exemple). La solidification de l'eau se fait à une température de . Enjeux industriels Il y a de très nombreux enjeux et applications industrielles à la bonne compréhension et maîtrise des phénomènes de solidification : coulée continue de l'acier, croissance du Si pour l'électronique, moulage d'implants dentaires... La solidification se fait en général par précipitation ou cristallisation à partir de la formation de germes de phase solide au sein du liquide (germination, nucleation en Anglais) puis croissance de ces germes ; avec donc une redistribution des éléments chimiques (quand la matière n'est

Source officielle

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

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Publications associées (31)

Freezing-induced stiffness and strength anisotropy in freezing clayey soil: Theory, numerical modeling, and experimental validation

Edward Ando, Gioacchino Viggiani

This paper presents a combined experimental-modeling effort to interpret the coupled thermo-hydro-mechanical behaviors of the freezing soil, where an unconfined, fully saturated clay is frozen due to a temperature gradient. By leveraging the rich experimental data from the microCT images and the measurements taken during the freezing process, we examine not only how the growth of ice induces volumetric changes of the soil in the fully saturated specimen but also how the presence and propagation of the freezing fringe front may evolve the anisotropy of the effective media of the soil-ice mixture that cannot be otherwise captured phenomenologically in the isotropic saturation-dependent critical state models for plasticity. The resultant model is not only helpful for providing a qualitative description of how freezing affects the volumetric responses of the clayey material, but also provide a mean to generate more precise predictions for the heaving due to the freezing of the ground.

WILEY2022

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, , , , ,

The additive manufacturing (AM) of the gamma' precipitation strengthened Ni-base superalloys still remains a challenge due to their susceptibility to micro-cracking. Post-processing, such as HIPing, has been shown to heal the micro-cracks but it remains desirable to prevent the micro-cracking from even occurring. Numerous studies highlighting potential mechanisms for micro-cracking exist but few solutions have been demonstrated. The intent of this study was to identify the micro-crack mechanisms and demonstrate how process and alloy modifications can reduce the micro-cracking. The micro-crack surfaces exhibit a dendritic appearance that is indicative of solidification cracking. Additionally, Gleeble experiments, simulating the L-PBF induced Heat Affected Zone (HAZ), were conducted below the y' solvus temperature and reveal the existence of grain boundary liquation, indicative of liquation cracking. Two cracking mechanisms are thus coexisting during Laser Powder Bed Fusion (L-PBF) of CM247LC. Based on experimental evidence, reduction in the solidification interval of CM247LC was investigated as a candidate for micro-crack mitigation and a new alloy was developed. As Hf is found to have a significant influence on the freezing range of the alloy, a new CM247LC without Hf was produced and tested. The study also involved two separate and distinct processing conditions to highlight the importance of melt pool geometry on micro-crack density. Samples fabricated with the Hf-free CM247LC, CM247LC NHf, in combination with optimized processing conditions exhibit a reduction in crack density of 98 %. This study demonstrates the importance of both processing conditions and alloy chemistry on micro-cracking in L-PBF fabricated gamma' hardening Ni-base superalloys.

ELSEVIER2020

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Freezing effects of oil-in-water emulsions studied by sum-frequency scattering spectroscopy

Sylvie Roke, Nikolay Smolentsev

Temperature-dependent sum-frequency scattering spectroscopy is used to study the properties of hexadecane and dodecane oil droplets in water. The sum-frequency scattering spectra contain vibrational bands that correspond to the symmetric and antisymmetric CH stretching vibrations of the methylene (CH2) and methyl (CH3) groups of the alkane molecules. The relative amplitudes of the vibrational bands provide information on the surface structure and the shape of the oil droplets. We study the sum-frequency scattering spectra over a temperature range of -48 to 24 degrees C, including the freezing transitions of the water matrix and the oil droplets. Hexadecane oil droplets freeze at a higher temperature than the surrounding water, whereas dodecane oil droplets freeze at a lower temperature than the surrounding water. This allows us to independently study the freezing effect of oil and water on the surface structure of the oil droplets. In both cases, freezing leads to a change in the polarization dependencies that are valid in the case of the spherical-symmetric shapes that the oil droplets assume when both water and oil are liquid. We find that the freezing of water leads to a strong distortion of the liquid dodecane surface but has little effect on the surface of already solidified hexadecane. For completely frozen emulsions a further decrease in temperature is observed to lead to a further distortion of the surface of the solid oil particles, which might be caused by increasing hardness of the ice matrix encapsulating the particles. Published by AIP Publishing.

Amer Inst Physics2016

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