Aluminum sacrificial anodes are widely used in cathodic protection of steel structures in sea water. In the present work, samples of Al-5.3 at.% Zn-x at.% Mg (x = 5.5-8.5) alloys were microstructurally and electrochemically characterized to evaluate their performance as Al-sacrificial anodes for cathodic protection of structures exposed to marine environments. The experiments focussed on the influence of Mg content on electrochemical behavior and efficiency. Mg was used in different concentrations ranging from 5.5 to 8.5 at.%. Short-term electrochemical tests, DNV RP B401, as well as polarization curves and electrochemical impedance spectroscopy were performed to obtain electrochemical behavior and efficiency and to reveal any tendencies to passivation. It is shown that by increasing Mg content an improvement of electrochemical properties of Al-alloy such as current capacity and then electrochemical efficiency can be obtained.

La Cueva de la Orquídea es uno de los atractivos turísticos en Xalapa. Se ubica en un parque público con el mismo nombre en medio de la ciudad. Sin embargo, esta “cueva” en realidad es parte de un sistema de túneles de lava que se forman cuando lava poco viscosa (comúnmente basáltica) se enfría en el contacto con el subsuelo y la atmósfera, pero sigue fluyendo en su interior. La mayor parte del centro de Xalapa está construido por encima de estas lavas basálticas que subyacen el cono de escoria del Macuiltépetl. Se desconoce la ubicación de los túneles subterráneos de lava; solo en ocasiones se reportan hundimientos en la zona urbana, debido al colapso de algunas oquedades subterráneas, así como se descubren al excavar antes de iniciar una construcción. En este estudio, se emplean dos técnicas geofísicas no-invasivas dentro del área del Parque, así como en calles no pavimentadas en la cercanía del mismo. Los resultados del estudio de gravimetría y georadar no solamente hacen visibles las cámaras grandes (3 conectadas) previamente conocidas, sino revelan su continuidad hacia el Este, justo por debajo de las viviendas aledañas al parque. Se considera importante de seguir con los estudios para ubicar las oquedades más cercanos a la superficie y/o más voluminosas para identificar zonas potencialmente en peligro de colapsarse, adaptar planes de construcciones, entre otras medidas de mitigación.   Geophysical study of underground cavities near the Cueva de la Orquídea Park, Xalapa, Veracruz, Mexico Abstract: The Cueva de la Orquida (Orchid cave) is one of the tourist attractions in Xalapa. It is located in a public park with the same name in the middle of the city. However, this "cave" is actually part of a system of lava tunnels that are formed when low-viscosity lava (commonly basaltic) cools on contact with the underground and the atmosphere, but continues to flow inside. Most of the center of Xalapa is built on top of these basaltic lavas that underlie the Macuiltépetl cinder cone. The location of the underground lava tunnels is unknown; only occasionally collapses are reported in the urban area, due to the collapse of some underground cavities, as well as being discovered when digging before starting construction. In this study, two non-invasive geophysical techniques are used within the Park area, as well as on unpaved streets in the vicinity of the Park. The results of the gravimetry and georadar study not only make the previously known large cameras (3 connected) visible, but also reveal their continuity to the East, just below the houses surrounding the park. It is considered important to continue with the studies to locate the cavities closer to the surface and/or more voluminous to identify areas potentially in danger of collapsing, adapt construction plans, among other mitigation measures.

A partir de la interpretación de propiedades físicas medidas en el subsuelo por medio de diferentes técnicas geofísicas, podemos localizar y delimitar la distribución de los diferentes cuerpos de agua subterráneos, el espesor y distribución de los estratos, el tipo de roca, además de estructuras geológicas como diaclasas, fallas o pliegues. En este trabajo se presentan los resultados de los datos adquiridos durante la aplicación de estudios de tomografía de resistividad eléctrica y sísmica de refracción, así como del levantamiento geológico de la zona de estudio, realizados en el municipio de Jalcomulco, estado de Veracruz. Después de la interpretación y constricción de los diferentes métodos, se llegó a la conclusión de que existe la presencia de un volumen de agua libre de contaminación a los 16 metros de profundidad. Además, se identifican al menos tres estratos con características geofísicas distintas, correspondientes a la capa de suelo reciente, depósitos fluviales y de lahares. Esta información puede ser de utilidad para futuros proyectos de excavación de pozos.   Geophysical studies for the detection of groundwater in the municipality of Jalcomulco, Veracruz, Mexico Abstract From the interpretation of physical properties, measured in the subsoil by means of different geophysical techniques, we can locate and delimit the distribution of the different underground water bodies, the thickness and distribution of the strata, the type of rock, as well as structures geological features such as joints, faults or folds. This paper presents the results of the data acquired during the application of tomography studies of electrical resistivity and seismic refraction, as well as the geological survey of the study area, carried out in the municipality of Jalcomulco, state of Veracruz. After the interpretation and constraint of the different methods, it was concluded that there is the presence of a volume of water free of contamination at a depth of 16 meters. In addition, at least three strata with different geophysical characteristics are identified, corresponding to the recent soil layer, fluvial and lahar deposits. This information may be useful for future well drilling projects.

<p>Basaltic volcanism is strongly influenced by magmatic viscosity, which, in turn, is controlled by magma composition, crystallisation, oxygen fugacity and vesiculation. We developed an environmental cell to replicate the pressure and temperature during magma ascent from crustal storage to the surface, while capturing crystallisation using in-situ 4D X-ray computed microtomography. Crystallisation experiments were performed at Diamond Light Source, using monochromatic 53 keV X-rays, a pixel size of 3.2 μm, a sample to detector distance of 2000 mm, 1440 projections per 180 deg, an acquisition time of 0.04 s, and a rotation velocity of 3.125 deg.s-1. The redox conditions were controlled using an oxidised nickel disk for each experiment. Our starting materials were samples made of crystal-free glass cylinders (Ø 3 mm) from the 2001 Etna eruption with 0.9 and 0.8 wt. % water content. In the experiments, samples and crucibles were sealed initially by applying ~10 N loads. All samples were then heated up above glass transition (between 800 °C and 900 °C) in order to allow sample homogenisation while preventing volatiles exsolution. We then pressurised each sample by applying uniaxial loads (between 80 and 380 N), using high-degree alumina pistons, in order to generate enough internal pressure to maintain bubble-free samples when the desired high temperature was reached. Once at the initial high temperature, we began experiments via dropping the temperature to different target isothermal (from 1210 to 1130 °C or 1180 to 1110 °C) and isobaric conditions (8 and 10 MPa, respectively). For the whole duration of the experiments, we were able to observe directly and record pyroxene crystal nucleation and growth. Specifically, we were able to observe pyroxene nucleation on bubbles at small undercooling (∆T) and epitaxial growth of pyroxene at large ∆T. An increase of ∆T (up to 50 °C) can be associated with a decompression of a magma chamber or a decompression during magma ascent in the conduit. As ∆T = 30 - 50 °C can be reached in most of the basaltic volcanic systems on Earth, our results provide a feasible explanation of which mechanisms control nucleation and growth of pyroxene crystals in hydrous basaltic magmas. In addition, epitaxial growth promotes a faster increase of the crystal volume. As a larger crystal content translates into a higher viscosity, our results have important implications for magma rheology, and are extremely important to improve our understanding of magma ascent dynamics during volcanic eruptions, and our capacity to predict eruptions and mitigate volcanic hazards.</p>