Estudio Arqueometalúrgico de una escoria metalúrgica aparecida en el yacimiento de Begastri

Se trata de una escoria encontrada en la segunda campaña de la excavación, en el corte A-111-80, Estrato 11, recogida el 12 de diciembre de 1980, habiéndole sido asignado el número de inventario 149. Estaba envuelta en tierra como corresponde a un objeto que ha permanecido largo tiempo enterrado. Dado el nulo valor museable de la pieza, parece rentable arriesgarse a su destrucción en un estudio que determine el tipo de horno en el que fue generada, lo cual puede servir de orientación en la futura continuación de la excavación, en la actualidad apenas comenzada, ya que la aparición de un trozo aislado enterrado de escoria puede sugerir la posibilidad de que los hornos no estén muy lejos

Estudio Arqueometalúrgico de una escoria metalúrgica aparecida en el yacimiento de Begastri

Se trata de una escoria encontrada en la segunda campaña de la excavación, en el corte A-111-80, Estrato 11, recogida el 12 de diciembre de 1980, habiéndole sido asignado el número de inventario 149. Estaba envuelta en tierra como corresponde a un objeto que ha permanecido largo tiempo enterrado. Dado el nulo valor museable de la pieza, parece rentable arriesgarse a su destrucción en un estudio que determine el tipo de horno en el que fue generada, lo cual puede servir de orientación en la futura continuación de la excavación, en la actualidad apenas comenzada, ya que la aparición de un trozo aislado enterrado de escoria puede sugerir la posibilidad de que los hornos no estén muy lejos

Confident methods for the evaluation of the hydrogen content in nanoporous carbon microfibers

Abstract Nanoporous carbon microfibers were grown by chemical vapor deposition in the vapor-liquid solid mode using different fluid hydrocarbons as precursors in different proportions. The as-grown samples were further treated in argon and hydrogen atmospheres at different pressure conditions and annealed at several temperatures in order to deduce the best conditions for the incorporation and re-incorporation of hydrogen into the microfibers through the nanopores. Since there are some discrepancies in the results on the hydrogen content obtained under vacuum conditions, in this work, we have measured the hydrogen content in the microfibers using several analytical methods in ambient conditions: surface tension, mass density, and Raman measurements. A discussion on the validity of the results obtained through the correlation between them is the purpose of the present work.Peer Reviewe

Problemática actual de la biosoldadura como proceso utilizable para la fijación de prótesis quirúrgicas

Peer Reviewe

Problemática actual de la biosoldadura como proceso utilizable para la fijación de prótesis quirúrgicas

Peer Reviewe

Atomic force microscopy study of vapor-grown carbon fibers: evidence of nanofiber structure

Vapor-grown carbon fibers (VGCF) are a type of short carbon fibers, not yet commercially available, but with a potentially excellent cost/performance ratio owing to the simplicity of their production process. Scanning electron and atomic force microscopy studies have been performed. In each study, a similar structure was observed at the micrometer scale, the so-called 'tree-trunk' structure, consisting of concentric cylindrical layers. This atomic force microscopy study revealed the nanometer structure. The layers are composed of several nanofibers approximately 200 nm in width, each exhibiting a fine structure of nanofibers approximately 15 nm in width. This nanostructure is similar to the ex-PAN fibers and explains the acceptable level of mechanical properties obtained for VGCF.Peer Reviewe

Characterisation of carbon fibres grown from carbonaceous gases by measurements of their density and oxidation resistance

In the present work it has been demonstrated, by measurements of their density and air oxidation resistance, that different sorts of carbon fibres grown from a gaseous stage, vapour grown carbon fibres (VGCF), present a duplex structure. By means of these two experimental techniques, structural differences between both constituent phases of this kind of fibres have been determined. It has been proved that the catalytic phase or nucleus presents higher level of crystalline perfection than the pyrolytic or cortical phase. This is corroborated by the fact that thin VGCF show better mechanical properties than thick fibres. In the same way, it has been possible to determine the mean nucleus diameter of a batch of VGCF, and to establish a mathematical expression, of the rule of mixtures type, for their density.Peer Reviewe

Electrical resistivity as a tool for the characterisation of carbonaceous phases in vapour-grown carbon fibres

By making electrical resistivity measurements as a function of diameter, it has been possible to prove that the kind of carbon fibres grown from a gaseous stage (VGCF), possess a duplex structure. We have found that these fibres present a catalytic phase or core, which shows a higher level of crystalline perfection than the pyrolytic or cortical phase. This is clearly revealed by the high electrical conductivity observed for thin fibres, when compared to thick VGCF. Estimations of electrical resistivity have allowed us to establish that this physical property, for different sorts of VGCF, can be accurately expressed by the rule of mixtures. In the same way, we have noticed that fibres fabricated from acetylene-containing precursor atmospheres show better electrical properties than VGCF grown from standard reactant gases. We have also observed that over-hydrogenation of VGCF, which gives rise to an improvement in mechanical properties, involves a decrease in electrical conductivity. | By making electrical resistivity measurements as a function of diameter, it has been possible to prove that the kind of carbon fibres grown from a gaseous stage (VGCF), possess a duplex structure. We have found that these fibres present a catalytic phase or core, which shows a higher level of crystalline perfection than the pyrolytic or cortical phase. This is clearly revealed by the high electrical conductivity observed for thin fibres, when compared to thick VGCF. Estimations of electrical resistivity have allowed us to establish that this physical property, for different sorts of VGCF, can be accurately expressed by the rule of mixtures. In the same way, we have noticed that fibres fabricated from acetylene-containing precursor atmospheres show better electrical properties than VGCF grown from standard reactant gases. We have also observed that over-hydrogenation of VGCF, which gives rise to an improvement in mechanical properties, involves a decrease in electrical conductivity.Peer Reviewe

Uptake of hydrogen from some carbon fibres examined by Secondary Ion Mass Spectrometry

The use of carbonaceous materials for hydrogen storage is not as simple as it may seem. Hydrogen atoms have different bonding energies and are incorporated into different types of these materials. Therefore, it is particularly important to distinguish between the surfacial atoms and those that are embedded in the bulk of the sample. SIMS spectrograph with periodical interruptions of the ion beam enables us to appreciate that at room temperature and in high vacuum, some outgassing of the surfacial hydrogen takes place. © 2010 Elsevier B.V. All rights reserved.Peer Reviewe