Jornadas sobre la enseñanza de la Geología en las Escuelas Universitarias de Ingeniería Técnica Minera

En el Simposio sobre la Enseñanza de Geología, celebrado en Barcelona en Septiembre del 84, entraron en contacto algunos profesores de Linares y Manresa, planteándose realizar unos encuentros entre los que practican la docencia geológica en las Escuelas de Minas. Estos encuentros fueron factibles y dieron sus frutos. Hoy en día se han realizado seis reuniones: una en linares, una en Madrid, una en Belmez y tres en Almadén, estando pendiente una pr6xima en Madrid. Esto supone una experiencia didáctica única a nivel nacional, que se ha traducido en un mejor conocimiento de la realidad actual de la enseñanza geológica en nuestros centros

El uso de los hornos pachamanca y guayra para la fundición en los Andes

El presente estudio ofrece una reseña sobre la tradición metalúrgica andina, discrimina al horno de pachamanca del horno guayra, así como de otros hornos, y trata sobre su uso para la fundición en los Andes. Se apoya en las descripciones aportadas por los cronistas españoles coloniales, arqueólogos, etc. Haciendo referencia a evidencias arqueológicas pertenecientes a los períodos prehispánicos y colonial que se presentan en los distritos mineros de Morococha (Huancavelica, Perú), Porco (Bolivia) y en algunos sitios del Noroeste de Argentina, etc. Cabe acotar que la temática abordada aporta al conocimiento de los hornos de fundición andinos y constituye una parte apenas divulgada del patrimonio minero

Molinos mineros de tradición andina

El presente trabajo contiene aportes para la clasificación tipológica de los molinos mineros utilizados en los Andes precolombinos. Se apoya en las descripciones que nos han legado los arqueólogos, ingenieros de minas, cronistas españoles, etc., con referencias a evidencias arqueológicas y etnográficas presentes en Cobres, Incahuasi, Rosario de Coyahuaima, Capillitas, Andalgalá y Tacuil (Argentina); Zapar (Chile); Porco y Potosí (Bolivia); así como en Santiago de Tulpo (Perú), etc. Es necesario destacar que la temática abordada contribuye al conocimiento de los molinos mineros y constituye un aspecto apenas divulgado del patrimonio minero andino. ABSTRACT This paper contains contributions on the typological classification of the Pre-Columbian Andean mining mills. It is based on the descriptions of archaeologists, mining engineers, Spanish chroniclers, etc., with references to archaeological and ethnographic evidences present in Cobres, Incahuasi, Rosario de Coyahuaima, Capillitas, Andalgalá and Tacuil (Argentina); Zapar (Chile); Porco and Potosi (Bolivia); as well as in Santiago de Tulpo (Peru), etc. It is necessary to emphasize that the topics treated contribute to the knowledge of the mining mills and constitutes a non well known aspect of the Andean mining heritage

Importance of tetrahedral coordination for high-valent transition metal oxides: YCrO4_4 as a model system

We have investigated the electronic structure of the high oxidation state material YCrO$_4$ within the framework of the Zaanen-Sawatzky-Allen phase diagram. While Cr$^{4+}$-based compounds like SrCrO$_3$/CaCrO$_3$ and CrO$_2$ can be classified as small-gap or metallic negative-charge-transfer systems, we find using photoelectron spectroscopy that YCrO$_4$ is a robust insulator despite the fact that its Cr ions have an even higher formal valence state of 5+. We reveal using band structure calculations that the tetrahedral coordination of the Cr$^{5+}$ ions in YCrO$_4$ plays a decisive role, namely to diminish the bonding of the Cr $3d$ states with the top of the O $2p$ valence band. This finding not only explains why the charge-transfer energy remains effectively positive and the material stable, but also opens up a new route to create doped carriers with symmetries different from those of other transition-metal ions.Comment: 6 pages, 6 figure

Large magnetocaloric effect and magnetic properties of polymorphic RCrO4 (R=rare earth) oxides

Trabajo presentado al: "International Symposium on the Reactivity of Solids" celebrado en San Petersburgo (Rusia) del 9 al 13 de junio de 2014.-- et al.RCrO4 oxides, where R=rare earth, crystallize at ambient conditions with the tetragonal zircon-type structure, S.G. I41/amd. Recently, we have succeeded to synthesize the scheelite polymorphs (S.G. I41/a) for most of the R elements, by treating the zircon phases at 40 kbar and 813 K. These scheelite high pressure forms are quencheable after releasing the pressure, and TGA and X-ray diffraction data reveal a reversible transition from scheelite polymorph to zircon at 700 K. The coexistence of two paramagnetic ions in these phases, namely Cr5+ and R3+, constitutes a very interesting scenario to study 3d-4f magnetic interactions. In this sense, most of the zircon-type RCrO4 oxides behave as ferromagnetic, while the scheelite polymorphs are antiferromagnetic. The change in the sign of the magnetic interaction can be explained by considering the changes in both distances and bond angles of Cr-O-R pathway through which the superexchange interactions take place. Neutron diffraction studies have been used to determine the nuclear and magnetic structures for these zircon and scheelite RCrO4 polymorphs. The analysis of the data reveals the onset of new reflections below the estimated Néel temperature from the previous magnetic susceptiblity data corresponding to the scheelite phases. The magnetic structure for these scheelite RCrO4 oxides can be described with a propagation vector κ = [0 0 0], where the moments of R3+ and Cr5+ are aligned along the c-axis or confined in the ab-plane of the tetragonal structure depending on the nature of the R element. This behavior has been confirmed from heat capacity measurements where the onsets of λ-anomalies at the ordering temperatures are almost coincident with those determined from magnetic susceptibility and neutron diffraction analysis. A detailed analysis of the zircon and scheelite structural types is included in this work to explain the different magnetic behavior showed by these two polymorphic phases allowing establishing relationships structure-magnetic properties. Very recently it has been reported that the zircon RCrO4 (R= Ho and Dy) phases show large values of the magnetocaloric parameters that make of these oxides potential refrigerant materials to be used for the liquefaction of hydrogen. It is noting that the field induced magnetization in the case of the scheelite polymorphs yields magnetic moments larger than in the case of the homologous zircon phases and hence the magnetocaloric effect is expected to be larger for the scheelite polymorphs in comparison with the zircon ones. In this work a preliminary study has been done in order to determine the magnetocaloric parameters of the two polymorphic phases of TbCrO4 and HoCrO4. In this sense the isothermal entropy change, ΔST, as a function of temperature has been calculated for magnetic field variations from the measurements of magnetization versus field at different temperatures. Both magnetocaloric parameters, ΔST and the adiabatic temperature change, ΔTad, have also been evaluated from the entropy functions at different fields obtained from the heat capacity data.Peer Reviewe

The vibrational spectrum of Nd<SUB>2</SUB>BaCuO<SUB>5</SUB>

Compounds of general composition Ln2BaCuO5 (Ln=lanthanide) adopt different structural types. Two series of structures have been reported for LnzBaCuO5 compounds. For lanthanide ions smaller than Nd(III) (Y and Sm-Lu) the so-called "green phases" (orthorhombic, space group Pbnm) are stabilized. They are one of the main impurities generated during the synthesis of the LnBa2Cu3OT_x-type high-T¢ superconducting oxides. A different structural type (tetragonal, space group P4/mbm) becomes stabilized for Ln = La or Nd, although in the case of the lanthanum-containing material the totally stoichiometric composition does not seem to be attainable.Facultad de Ciencias Exacta

Effect of Gd polarization on the large magnetocaloric effect of GdCrO4 in a broad temperature range

The ferromagnetic zircon-type phase of GdCrO4 presents high values for the magnetocaloric (MC) parameters. This compound has large isothermal entropy changes ¿ST under the magnetic field action in a wide temperature range, from 5 to 35 K, reaching a maximum |¿ST|=29.0±0.1J/kgK at 22 K, for a field increment ¿B=9 T. It orders ferromagnetically at TC=21.3K via the Cr-Cr exchange interaction and shows a second transition at 4.8 K due to the ordering of the Gd sublattice. The large MC effect is enhanced by the polarization of the Gd3+ ions by the Cr5+ ones via a weaker Gd-Cr interaction. This effect is an interesting feature to be considered in the search for new compounds with a high MC effect in the range of liquid hydrogen or natural gas, regarding the liquefaction of gases by magnetization-demagnetization cycles. This paper contains experimental measurements of magnetization, heat capacity, and direct determinations of the MC effect. The magnetic contribution to the heat capacity Cm has been obtained after subtracting the lattice component. Approximate values for the exchange constants J1 (Cr-Cr) and J3 (Gd-Cr) have been deduced from Cm

Application of the Wigner-Ville distribution for the detection of rotor asymmetries and eccentricity through high-order harmonics

The diagnosis of induction machines through the use of methods based on the study of the startup current has become an issue of special interest. These techniques may provide, in certain situations (unbalanced supply voltages, load torque oscillations, variable load, etc.) and for certain faults (broken bars, eccentricity, stator short circuit, etc.) substantial advantages in comparison with the classical method, based on the Fourier spectrum of the steady-state current. Nevertheless, in the case of rotor asymmetries, these transient-based techniques have been mainly focused on the tracing of the lower sideband harmonic (LSH). In this paper, a wideband diagnosis method is proposed, in which the Wigner-Ville distribution is applied to the detection of eccentricity and other high-order components also introduced by the rotor asymmetry. It is shown that the proposed wide band analysis might help to reach a more reliable diagnosis conclusion in cases in which the tracing of commonly used harmonics may be difficult (inter-bar currents, load torque oscillations, non stationary regimes, etc.). An evaluation of the method is carried out through simulations and laboratory tests. The results show the potential of the tool for the detection and quantification of these components as a basis to diagnose such faults. © 2012 Elsevier B.V

El penitente: una profesión trágica de la minería del carbón

Hubo una época en que la forma más habitual para evitar las explosiones de grisú y asfixias provocadas por este fluido gaseoso en las explotaciones de carbón era mediante el trabajo del penitente. En aquellos tiempos los tajos no eran muy grandes, se laboreaba en ellos de forma manual, y el gas generado no aparecía, por lo general, en gran cantidad. El penitente era una persona de experiencia que entraba en las minas antes de que los mineros llegasen a su trabajo, para explosionar los gases que allí existieran. Estaba cubierto con una especie de pasamontañas, guantes y capa, prendas realizados con tejidos gruesos o cuero, que eran humedecidas para protegerse del fuego. Iba arrastrándose sobre su vientre, mientras que con una larga pértiga, que portaba delante de él, llevaba una candela encendida en el extremo de la misma, para favorecer la explosión del grisú acumulado en el techo de las labores. Este personaje desaparecerá paulatinamente tras el invento de la lámpara de seguridad de Davy (1815). Aunque hay bastantes datos dispersos sobre esta profesión, en nuestro trabajo pretendemos abordar los siguientes aspectos: 1.-Cuándo y cómo aparece este personaje y hasta que época permanece en la minería. 2.- En que ámbitos geográficos se presenta y cuáles son sus diferentes denominaciones. 3.-Cuánto duraba su trabajo y cuál era su salario, en el caso de que lo tuviese. 4.-Cuál era su modus operandi. 5.-Cuáles y cómo son sus representaciones, indicando si es posible el nombre de los artistas que las hicieron. 6.-Cuál ha sido su presencia en la literatura. In a certain time, the most common way to avoid explosions and suffocation due to the presence of methane (fire damp) in coal mines was the labour of the fireman, also called penitent. As the coal beds were no so large, manual extraction were employed, and fire damp did not appeared in high amounts, but it was dangerous. The fireman was an experienced man who entered the mines before miners, in order to ascertain if gas exists and provoke the explosion of firedamp. He was covered by a mask, gloves and a cap, all of them made by thick textiles or leather, which were humidified to protect from fire. The fireman creep over his belly, and with the aid of a pole with a candle at its edge, to produce the explosion of fire damp. The work of fireman progressively disappeared after the discovery of the Davy´s lamp. Although there are some data about the existence of firemans, this paper deals with the following topics: 1.-When and how the fireman appeared and for how long was employed in coal mines. 2.- In which regions the fireman was employed, and which were the different names. 3.-Which was his workday and which was his salary. 4.- Which was his modus operandi. 5.-Which and how were the artistic representations, indicating, if possible, the name of the artists. 6.-Which was his presence in literatur