Enriquecimiento de los yacimientos de mineral feldespático existentes en Silán (Viveiro, Lugo)

[Resumen] Dentro de un proceso global de aprovechamiento de las masas pegmatíticas de Silán para su aplicación en la fabricación de cerámica fina se ha realizado ya en otra ocasión el estudio de su purificación. En este trabajo se aborda el enriquecimiento en base a una separación feldespato-cuarzo por flotación. Para ello se estudia un prototipo de flotación monolaminar señalando sus características principales. Se describe dicho prototipo así como los ensayos realizados, haciendo una valoración parcial de los resultados obtenidosAbstract] In the course of a global processing,the purification of the pegmatites of Silán in order to their use in the fine ceramics industry was studied in an earlier work. The separation of quartz and feldspar by means of flotation is considered in the present paper. A monolaminar flotation prototype is described, and its main features are pointed out. The test made are described and the results obtained are cornmente

O caolín materia prima industrial: estudio dun caolín localizado na zona centro da provincia de Lugo

[Resumen] Se lnicia el trabajo con la recogida de una muestra de 100 Kgrs. en un afloramiento descubierto en dicha zona del que, por el momento, no se conoce su geología y posibles reservas. La muestra en bruto se identifica mi nera1ógicamente medi ante· los métodos instrumenta1es usua1es y a continuación se somete a un proceso de lavado y clasificación granul ométrica. Las fracciones obtenidas se caracterizan desde el punto de vista técnico para su posible aplicación en las industrias del papel y la cerámica. Por último y como consecuencia de los resultados obtenidos, se hacen ensayos de deslaminación y blanqueo para mejorar 1as propiedades reo1ógicas y ópticas pensando en una posible mejora de la calidad de dicho caolín, lo que traería consigo un superior valor afiadido e interés económico[Abstract] This work begins picking up a 100 Kgrs. sample from an outcrop di scovered in that area; geo1ogy and possible reserves are unknown at presente The bulk sample is mineralogically identified –by means of the current instrumental methods and subsequently washed and sized. The obtained fractions are characterized from technical point of view for their possible application in paper and ceramics industries. Finally and in view of obtained results, delamination and bl eaching tests for optica1 and reo1ogi ca1 properties modification, are made for improve the quality of the kaolin, getting with that a superior added value and economic interest.[Resume] O traballo iníciase coa recollida dunha mostra de 100 Kgrs. nun afloramento descuberto na devandita zona, do cal, polo momento, non se conoce a súa xeoloxía e posibles reservas. A mostra en bruto identifícase mineralóxicamente mediante os métodos instrumentáis usuais e seguidamente sométese a un proceso de lavado e clasificación granulométrica. As fraccións obtidas caracterízanse desde o punto de vista técnico pola súa posible aplicación nas industrias do papel e a cerámica. Pra rematar e como consecuencia dos resultados obtidos, fanse ensaios de des laminación e branqueo pra modificar as propiedades reolóxicas é ópticas pensando nunha posible mellara da súa calidade, o que levaría consigo un superior valor engadido e interés ecocómico

Analysis of magnetic and structural properties in La0.6Sr 0.4MnO3 ferromagnetic particles under the influence of mechanical ball milling effect

We have investigated the magnetic, structural and morphological properties of La0.6Sr0.4MnO3 (LSMO-40) manganite particles, synthesized by solid state reaction method. The resulting LSMO-40 powders were milled in air atmosphere during 3, 6 and 12 hours, by using a planetary ball milling. Samples obtained were characterized by X-ray diffraction, scanning electron microscopy – SEM and magnetization measurements as a function of temperature and magnetic field. A Rietveld analysis was carried on each XRD pattern, and was observed a reduction in crystallite average size (Dv) with increased ball milling time, tM. This is associated with a decrease in particle size. A characteristic rhombohedral crystal structure for the LSMO-40 phase was identified (space group R3C), independent of the milling time of the powders. However, from SEM microstructure was observed more homogeneity in the grain distribution by milling process. The results of magnetic characterization, showed that samples with higher tM (smaller grain size), presented the lowest value of the saturation magnetization, which is attributed to surface effects that induce magnetically disordered states with decreasing particle sizes. This magnetic anisotropy surface is evidenced also on the changes of coercive fields, HC, measured at low temperatures, which increased with increasing tM

Stability of Monitoring Weak Changes in Multiply Scattering Media with Ambient Noise Correlation: Laboratory Experiments

Previous studies have shown that small changes can be monitored in a scattering medium by observing phase shifts in the coda. Passive monitoring of weak changes through ambient noise correlation has already been applied to seismology, acoustics and engineering. Usually, this is done under the assumption that a properly reconstructed Green function as well as stable background noise sources are necessary. In order to further develop this monitoring technique, a laboratory experiment was performed in the 2.5MHz range in a gel with scattering inclusions, comparing an active (pulse-echo) form of monitoring to a passive (correlation) one. Present results show that temperature changes in the medium can be observed even if the Green function (GF) of the medium is not reconstructed. Moreover, this article establishes that the GF reconstruction in the correlations is not a necessary condition: the only condition to monitoring with correlation (passive experiment) is the relative stability of the background noise structure

La cianita de O Pino (Santiago): caracterización, purificación e aplicaciones.

Resumen] Se caracteriza e identifica un tipo de cianita de aluvión «canto rodado» localizado en el Ayuntamiento de O Pino próximo a Santiago. Se estudia la purificación de la cianita después de su calcinación a temperaturas del orden de los 1.400-1.450 oC para su estabilización mediante transformación en mullita. El método seguido fue una separación electromagnética de alta intensidad del todo-uno previo acondicionamiento de las fracciones granulométricas. Las impurezas que acompañan a la cianita, principalmente óxido de hierro, funden rodeando los granos y dando lugar a especies de baja susceptibilidad magnética. Se propone otro método de purificación basado en hacer la separación rnagnética antes de la calcinación con lo que se logran mejores resultados obteniéndose una cianita de alta pureza pero con una granulometría por debajo de 1 mm. Se estudian las variables que influyen principalmente en la transformación a mullita durante la calcinación. Por último se ensaya el empleo de esta cianita en la preparación de diversas composiciones de cerámica técnica y la fabricación de piezas de aplicación en los laboratorios de control de la industria siderúrgica que en la actualidad están ya comercializándose.[Abstract] One type of alluvial kyanite (rolling stones) located at the region around O Pino, near of Santiago in A Coruña province, is characterized and identified. Refining of kyanite after heating in at temperatures ranging 14001450 oC for to stabilize it by transformation into mullite is studied. The method employed was an high intensity magnetic separation after size c1assification. The impurities of this kyanite, mainly iron oxides, melt surrounding the grains which are of low magnetic susceptibility. An alternative way of purification is proposed. This second method is based on making magnetic separation before calcination, and it gives better results obtaining an high purity kyanite, but with grain size below 1mm. Variables with main influence over the conversion into mullite during heating are studied. Finally compositions made with this kyanite are tested. These pastes are employed in technical ceramics and in making pieces for use in tests of iron and steel industries and that actually are in the marke

Time-dependent screening of a positive charge distribution in metals: Excitons on an ultra-short time scale

Experiments determining the lifetime of excited electrons in crystalline copper reveal states which cannot be interpreted as Bloch states [S. Ogawa {\it et al.}, Phys. Rev. B {\bf 55}, 10869 (1997)]. In this article we propose a model which explains these states as transient excitonic states in metals. The physical background of transient excitons is the finite time a system needs to react to an external perturbation, in other words, the time which is needed to build up a polarization cloud. This process can be probed with modern ultra-short laser pulses. We calculate the time-dependent density-response function within the jellium model and for real Cu. From this knowledge it is possible within linear response theory to calculate the time needed to screen a positive charge distribution and -- on top of this -- to determine excitonic binding energies. Our results lead to the interpretation of the experimentally detected states as transient excitonic states.Comment: 24 pages, 9 figures, to appear in Phys. Rev. B, Nov. 15, 2000, issue 2

Lifetime of d-holes at Cu surfaces: Theory and experiment

We have investigated the hole dynamics at copper surfaces by high-resolution angle-resolved photoemission experiments and many-body quasiparticle GW calculations. Large deviations from a free-electron-like picture are observed both in the magnitude and the energy dependence of the lifetimes, with a clear indication that holes exhibit longer lifetimes than electrons with the same excitation energy. Our calculations show that the small overlap of d- and sp-states below the Fermi level is responsible for the observed enhancement. Although there is qualitative good agreement of our theoretical predictions and the measured lifetimes, there still exist some discrepancies pointing to the need of a better description of the actual band structure of the solid.Comment: 15 pages, 7 figures, 1 table, to appear in Phys. Rev.

Mercury removal in wastewater by iron oxide nanoparticles

Mercury is one of the persistent pollutants in wastewater; it is becoming a severe environmental and public health problem, this is why nowadays its removal is an obligation. Iron oxide nanoparticles are receiving much attention due to their properties, such as: great biocompatibility, ease of separation, high relation of surface-area to volume, surface modifiability, reusability, excellent magnetic properties and relative low cost. In this experiment, Fe3O4 and γ-Fe2O3 nanoparticles were synthesized using iron salts and NaOH as precipitation agents, and Aloe Vera as stabilizing agent; then these nanoparticles were characterized by three different measurements: first, using a Zetasizer Nano ZS for their size estimation, secondly UV-visible spectroscopy which showed the existence of resonance of plasmon at λmax∼360 nm, and lastly by Scanning Electron Microscopy (SEM) to determine nanoparticles form. The results of this characterization showed that the obtained Iron oxides nanoparticles have a narrow size distribution (∼100nm). Mercury removal of 70% approximately was confirmed by atomic absorption spectroscopy measurements