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Garcia-Moreno O.,Research Center en Nanomateriales y Nanotecnologia | Fernandez A.,Fundacion ITMA | Torrecillas R.,Research Center en Nanomateriales y Nanotecnologia
Ceramics International | Year: 2011

Lithium aluminosilicate powder precursors of compositions Li 2O:Al2O3:SiO2 as 1:1:2; and 1:1:3.11 were synthesized and sintered by the Spark Plasma Sintering technique. The sintering conditions were adjusted to obtain dense ceramic materials in an attempt to avoid the presence of a glassy phase. XRD and SEM images were employed for composition and microstructure characterization. The coefficient of thermal expansion of the sintered samples was studied down to cryogenic conditions. Rietveld quantification was performed with the use of an external standard. Pure β-eucryptite of different compositions in dense ceramic bodies was obtained with a negative expansion coefficient. © 2011 Elsevier Ltd and Techna Group S.r.l. Source


Bonache V.,ITM University | Salvador M.D.,ITM University | Rocha V.G.,Fundacion ITMA | Borrell A.,University of Oviedo
Ceramics International | Year: 2011

The aim of this present work is to study the effect of VC and/or Cr 3C2 in densification, microstructural control and mechanical behaviour of WC-12Co ultrafine and nanocrystalline mixtures, consolidated by spark plasma sintering at 1100 °C, applying a pressure of 80 MPa in combination with a heating rate of 100 °C min-1. Nanocrystalline and ultrafine mixtures with an average size of 30 nm and 100-250 nm, respectively, with the addition of 1 and 0.5 wt.% of VC/Cr 3C2 grain growth inhibitors, respectively, were investigated. The density, microstructure, hardness and fracture toughness of the consolidated samples were measured and observed. The addition of VC inhibitor allows an excellent grain growth control keeping microstructures with an average grain size of 154 nm. The hardness values and fracture toughness obtained were about 2000 HV30 and above 10 MPa m1/2, respectively. © 2010 Elsevier Ltd and Techna Group S.r.l. Source


Garcia-Moreno O.,Research Center en Nanomateriales y Nanotecnologia | Fernandez A.,Fundacion ITMA | Khainakov S.,Research Center en Nanomateriales y Nanotecnologia | Torrecillas R.,Research Center en Nanomateriales y Nanotecnologia
Scripta Materialia | Year: 2010

Five lithium aluminosilicate compositions of the LAS system have been synthesized and sintered. The coefficient of thermal expansion of the sintered samples has been studied down to cryogenic conditions. The data presented here under cryogenic conditions will be of value in the future design of new composite materials with very low thermal expansion values. The variation in thermal expansion properties with composition and sintering temperature was studied and is discussed in relation to composition and crystal structure. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


Bonache V.,ITM University | Salvador M.D.,ITM University | Fernandez A.,Fundacion ITMA | Borrell A.,Research Center en Nanomateriales y Nanotecnologia
International Journal of Refractory Metals and Hard Materials | Year: 2011

The aim of present work is to study the effect of VC and/or Cr 3C2 in densification, microstructural development and mechanical behavior of nanocrystalline WC-12wt.%Co powders when they are sintered by spark plasma sintering (SPS) and hot isostatic pressing (HIP). The results were compared to those corresponding to conventional sintering in vacuum. The density, microstructure, X-ray diffraction, hardness and fracture toughness of the sintered materials were evaluated. Materials prepared by SPS exhibits full densification at lower temperature (1100 °C) and a shorter stay time (5 min), allowing the grain growth control. However, the effect of the inhibitors during SPS process is considerably lower than in conventional sintering. Materials prepared by HIP at 1100 °C and 30 min present full densification and a better control of microstructure in the presence of VC. The added amount of VC allows obtaining homogeneous microstructures with an average grain size of 120 nm. The hardness and fracture toughness values obtained were about 2100 HV30 and close to 10 MPa m1/2, respectively. © 2010 Elsevier Ltd. All rights reserved. Source


Borrell A.,Nanomaterials and Nanotechnology Research Center | Fernandez A.,Fundacion ITMA | Torrecillas R.,Nanomaterials and Nanotechnology Research Center
International Journal of Materials Research | Year: 2010

Graphitic materials obtained at low temperatures are interesting for a wide range of industrial applications including bipolar plates. In this work, graphite based nanocomposites have been obtained starting from carbon nanofibers and a mixture of carbon nanofibers with 20 vol.% of alumina nanopowders. High density carbon components were obtained by using Spark Plasma Sintering at temperatures as low as 1500-1800°C for this kind of materials. The effect of spark plasma sintering parameters on the final density, and the mechanical and electrical properties of resulting nanocomposites have been investigated. Pure carbon nanofibers with around 90% of theoretical density and fracture strength of 60 MPa have been obtained at temperatures as low as 1500°C applying a pressure of 80 MPa during sintering. It has been proved that attrition milling is a suitable method for preparing homogeneous mixtures of carbon nanofibers and alumina powders. © Carl Hanser Verlag GmbH & Co. KG. Source

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