Publicaciones: Nanocomposites Multifuncionales

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12

Jan 2018

Microstructural development and mechanical performance of mullite-alumina and hibonite-alumina ceramics with controlled addition of a glass phase

Posted by / in Publicaciones Materiales Multifuncionales 2018, Publicaciones: Nanocomposites Multifuncionales, Publications 2018, Últimas Publicaciones CINN / No comments yet

Robust mechanical properties of refractory ceramics are critical to their performance in industrial applications. To investigate the effects of glass on the sinterability and mechanical properties of refractory ceramics, a controlled amount of glassy phase (10 wt%) was added to mullite (Al6Si2O13)-alumina (Al2O3) and hibonite (CaAl12O19)-alumina composites. Two liquid compositions within the Al2O3-SiO2-CaO system were chosen to produce a glass at 1600 °C that exists in equilibrium with a mullite-alumina composite and a hibonite-alumina composite. We performed a comparative study of the mechanical properties (hardness, flexural strength, and creep resistance) of mullite-alumina and hibonite-alumina composites with and without glassy phases. The observed microstructures clearly affected the mechanical properties. The strong interface created between the three phases in each subsystem and the reduced amount of residual porosity in the composites with an added glassy phase may explain the increase in strength, hardness, and creep resistance of the composites. However, better mechanical properties and finer grain sizes of mullite make the mullite-alumina (-glass) system a better candidate for refractory applications that require improved mechanical properties.

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11

Jan 2018

Intermolecular C−C Coupling between 1-Methyl-1,2,3-Triazole and 2,2′-Bipyridine or 1,10-Phenanthroline in MoII Complexes

Posted by / in Publicaciones 2017, Publicaciones Destacadas, Publicaciones Materiales Multifuncionales y Nanocomposites 2017, Publicaciones: Nanocomposites Multifuncionales, Últimas Publicaciones CINN / No comments yet

Unsupported 1-methyl-1,2,3-triazole has been coordinated to {Mo(η3-methallyl)(CO)2(N-N)} (N-N=2,2′-bipyridine, bipy; or 1,10-phenanthroline, phen) fragments, yielding cationic complexes that can be regarded as metalated triazolium salts. Their reactivity towards a strong base led to the deprotonation of the C5−H group of the triazole moiety, followed by an intermolecular nucleophilic attack to the ortho CH group of a bipy or phen ligand affording cyclic, bimetallic dearomatized C−C coupling products. The reaction of the neutral bipy derivative with an acid led to the formation of dihydropyridyl units by protonation of a CH group of the dearomatized rings, the dimeric nature of complexes being mantained upon protonation.

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08

Jan 2018

Phase relations in the Cabeza de Araya cordierite monzogranite, Iberian Massif: Implications for the formation of cordierite in a crystal mush

Posted by / in Publicaciones 2017, Publicaciones Materiales Multifuncionales y Nanocomposites 2017, Publicaciones: Nanocomposites Multifuncionales, Últimas Publicaciones CINN / No comments yet

Experimental investigations and thermodynamic calculations of the phase relations of a cordierite-rich monzogranite from the Cabeza de Araya batholith (Cáceres, Spain) have been performed to understand the formation of cordierite. The experiments failed to crystallize cordierite in the pressure range 200-600MPa, in the temperature range 700-975ºC and for different water activities (melt water contents between 2 and 6 wt.%). In contrast, clinopyroxene and orthopyroxene (absent in the natural mineral rock assemblage), together with biotite, were observed as ferromagnesian assemblage in a wide range of experimental conditions. Thermodynamic calculations, using the software PERPLE_X, describe the formation of cordierite only at 200 and 400MPa and very low water contents, and the amount of cordierite formed in the models is always below 3.5 vol.%. The results indicate that cordierite is not in equilibrium with the bulk rock compositions. The most probable explanation was that cordierite nucleated and crystallized from a melt that is not in equilibrium with part of the mineral assemblage present in the magma. This “non-reactive” mineral assemblage was mainly composed of plagioclase. The silicate melts from which cordierite crystallized was more Al-rich and K-rich than the silicate melt composition in equilibrium with the bulk composition. One possible process for the high Al content of the silicate melt is related to assimilation and partial melting of Al-rich metasediments. An exo-perictetic reaction is assumed to account for both textural and geochemical observations. On the other hand, hybridization processes typical for calc-alkaline series can also explain the high proportions of “non-reactive” minerals observed in relatively high temperature magmas. This study clearly demonstrates that silicate melts in a crystal mush can depart significantly from the composition of melt that should be in equilibrium with the bulk solid assemblage.

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