Volcanic cinder, also known as scoria, is an extrusive igneous rock that forms when gas-rich magmas of basaltic or andesitic composition cool quickly. It is typically dark in color, ranging from ...black to red depending on its chemical composition. Sometimes fresh cinder samples show a variety of shiny metallic colors on its surface ranging from blue to gold to silver. The origin of these colors has remained unknown up to now. Cinder samples from an eruptive event occurred in October 2005 have been collected in the surroundings of the Sierra Negra volcano in the Galápagos Islands. The samples’ crystallographic structure, chemical composition, and surface morphology have been analyzed using X-Ray diffractometry (XRD), energy dispersive X-Ray spectroscopy (EDS) and a field gun emission scanning electron microscopy (SEM), respectively. Based on an extensive physical and chemical analysis, we were able to demonstrate that these colors are due to a light interference phenomenon. These results have a great potential to be used for a wide variety of purposes such as determining the temperature and composition of magma and evaluating volcanic samples for planetary studies.
After 138 years of apparent silence, the Cotopaxi volcano awoke on August 14th of 2015 with a sequence of eruption events and the emission of both fine-grained volcanic material and gases. Four ...samples of the very first eruption were collected at different sites within the fallout area. The analysis of such samples, by using X-Ray Diffraction (XRD) as well as Electron Diffraction Scattering (EDS) techniques, allow us to determine the geochemical and mineralogical composition. On the basis of these results, together with the characterization and classification of the morphology of the collected fine-grained material, the presence of juvenile magma at the proximity of the crater has been categorically excluded. Therefore major eruptions and the subsequent generation of far-reaching lahars can be discarded for the duration of this volcanic stage.
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•First report on the Mortiño berry extract mediated synthesis of Silver–Graphene nanocomposite.•Different instrumental techniques confirmed its morphology, structure, composition, and ...optical properties.•It showed enhanced photocatalytic activity for the degradation of methylene blue and methylene orange.•Environmentally benign, rapid and low-cost method is suggested.
Mortiño (Vaccinium floribundum Kunth) is a wild shrub native to South America, whose berries are widely consumed in Ecuador as fresh fruit, juice and jam. We reported a green synthesis of Silver–Graphene (Ag-G) nanocomposite through the reduction of Ag+ and graphene oxide using berry extract of Mortiño. Silver nanoparticles were anchored onto the graphene sheets by ultrasonication and solar light irradiation. The as-prepared Ag-G nanocomposite was characterized by Fourier transform infrared spectroscopy, UV–vis spectroscopy, Scanning transmission electron microscopy, Scanning electron microscopy with energy dispersive X-ray spectrometry, and X-ray diffraction techniques. The photocatalytic activities of the Ag-G nanocomposite were evaluated by the degradation of methylene blue (MB) and methylene orange (MO) in an aqueous medium under sunlight irradiation. The photocatalytic activity of Ag-G nanocomposite for the degradation of MB (k=0.0163283min−1)>MO (k=0.0140985min−1), due to the anchoring of Ag nanoparticles on the graphene sheets and thiazine ring of MB is more susceptible to photodegradation than the azo bond of MO. This ecofriendly and green reduction method avoids the use of toxic reagents, and it might be useful for biocompatible materials in the future engineering applications.
We have developed a fast, reliable and robust code to analyze size distributions and morphological properties of nanostructures. A segmentation algorithm, based on watershed transformation, has been ...implemented and tested. We have used consistent definitions to quantify the sphericity, roundness and roughness, which critically modify the physicochemical properties at the nanoscale. Finally, our approach has been applied to some example systems. We demonstrate that our code can be applied to guide the synthesis of nanoparticles, to distinguish dead from living bacteria and also to predict the reactivity of nanoparticles used for environmental remediation.
In this work we have analyzed the dynamic behavior of steel reinforcing bars under low cycle force-controlled fatigue measurements. We compare the results obtained for rebars produced by three steel ...companies of Ecuador, which fulfill the technical requirements of the national standards specified in ASTM A706. The measurements were carried out by using an universal testing machine model MTS 810. To determine the critical factors on the dynamic response of reinforcing bars, we have characterized the fractured section by macroscopic parameters and employing the Scanning Electron Microscopy (SEM). The results obtained point out that, although the three companies produce rebars with similar static behavior exist important differences on their dynamical properties.
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