Browsing by Keyword "Scanning electron microscopy"
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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 Study of the failure of one machining tool(2010-03) Irisarri, A. M.; Silveira, E.; Tecnalia Research & Innovation; Caracterización y Validación. MaterialesThis paper presents the study of the failure of one tool that was broken in two pieces inducing a serious damage in the component that was being machined. The main difficulty for this analysis came up against the need of keeping the broken tool in the as-received condition due to legal requirements. Due to this situation it was not possible obtaining tensile test specimens to determine the strength and ductility of the material or metallographic samples which could reveal its microstructure. Consequently, the study was restricted to observing the fracture surfaces in the scanning electron microscope and identifying by X-ray energy dispersive spectrometry, the nature of the substances which could have played a role in the failure process. This analysis allowed identifying the failure origin was sited on a notch induced on the periphery of the tool in a zone where a section change and a marked stress concentration existed. This notch was covered by a dark substance whose composition was near the same than that of the blueing coating, indicating that it was already opened when this surface treatment was applied. These results, leaded to a conclusion blaming the machining operation previous to the blueing coating for the failure.