Browsing by Keyword "Coalescence"
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Item The ice–vapour interface during growth and sublimation(2021-12-22) Cascajo-Castresana, Maria; Morin, Sylvie; Bittner, Alexander M.; Tecnalia Research & Innovation; BiomaterialesWe employed environmental scanning electron microscopy (ESEM) in low-humidity atmosphere to study the ice growth, coalescence of crystallites, polycrystalline film morphology, and sublimation, in the temperature range of −10 to −20 ∘C. First, individual ice crystals grow in the shape of micron-sized hexagonal columns with stable basal faces. Their coalescence during further growth results in substantial surface defects and forms thick polycrystalline films, consisting of large grains separated by grain boundaries. The latter are composed of 1 to 3 µm wide pores, which are attributed to the coalescence of defective crystallite surfaces. Sublimation of isolated crystals and of films is defect-driven, and grain boundaries play a decisive role. A scallop-like concave structure forms, limited by sharp ridges, which are terminated by nanoscale asperities. The motivation for this work is also to evaluate ESEM's ability to provide a clean and reproducible environment for future study of nucleation and growth on atmospherically relevant nucleators such as materials of biological origin and inorganic materials. Hence, extensive information regarding potential ESEM beam damage and effect of impurities are discussed.Item Preparation of porous stainless steel hollow-fibers through multi-modal particle size sintering towards pore engineering(2017-09) Allioux, Francois Marie; David, Oana; Benavides, Miren Etxeberria; Kong, Lingxue; Tanaka, David Alfredo Pacheco; Dumée, Ludovic F.; TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOSThe sintering of metal powders is an efficient and versatile technique to fabricate porous metal elements such as filters, diffusers, and membranes. Neck formation between particles is, however, critical to tune the porosity and optimize mass transfer in order to minimize the densification process. In this work, macro-porous stainless steel (SS) hollow-fibers (HFs) were fabricated by the extrusion and sintering of a dope comprised, for the first time, of a bimodal mixture of SS powders. The SS particles of different sizes and shapes were mixed to increase the neck formation between the particles and control the densification process of the structure during sintering. The sintered HFs from particles of two different sizes were shown to be more mechanically stable at lower sintering temperature due to the increased neck area of the small particles sintered to the large ones. In addition, the sintered HFs made from particles of 10 and 44 µm showed a smaller average pore size (<1 µm) as compared to the micron-size pores of sintered HFs made from particles of 10 µm only and those of 10 and 20 µm. The novel HFs could be used in a range of applications, from filtration modules to electrochemical membrane reactors.