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Benavente R.,Polytechnic University of Valencia | Salvador M.D.,Polytechnic University of Valencia | Penaranda-Foix F.L.,Polytechnic University of Valencia | Garcia-Moreno O.,Research Center en Nanomateriales y Nanotecnologia PA | Borrell A.,Polytechnic University of Valencia
Ceramics International | Year: 2015

Low-temperature sinterable microwave LiAlSiO4-based solid-state material was investigated with regard to microwave dielectric properties as functions of the sintering temperature. β-eucryptite materials and alumina-reinforced β-eucryptite composites were sintered by microwave technology at 1100°C and 1200°C. The combination of fast heating and the dramatic reduction in cycle time, along with the non-conventional heating source, opens the way to produce materials with desired multifunctional properties.The microstructure and crystalline composition of the materials were characterised, and the mechanical, thermal and microwave dielectric behaviours were analysed. X-ray diffraction showed good chemical stability in materials without between-phase reactions during the microwave sintering process. The excellent mechanical (~8GPa of hardness and ~100GPa of Young's modulus), thermal (-0.23·10-6 K-1) and microwave dielectric properties (ε r =4.10; Q=1494) were obtained from the LAS/Al2O3 composites sintered at a very low temperature (1100°C). The results achieved show the possibility of designing ceramic nanocomposites at low sintering temperatures using microwave technology with near-zero thermal expansion coefficients, high mechanical and chemical stability and low dielectric properties. © 2015 Elsevier Ltd and Techna Group S.r.l.


Borrell A.,ITM University | Salvador M.D.,ITM University | Rocha V.G.,ITMA Materials Technology | Fernandez A.,ITMA Materials Technology | And 3 more authors.
Journal of Alloys and Compounds | Year: 2013

Alumina-aluminium titanate (A-AT) composites and laminates have been recently investigated because they can provide improved flaw tolerance and toughness associated to a microcracking mechanism. A-AT composites have been produced by slip casting and reaction sintering of submicron sized alumina and titania powders. This work deals with the preparation of thick self-sustained A-AT films from mixtures of submicron sized alumina and nanosized titania powders and further sintering by conventional and non-conventional (spark plasma sintering, SPS) methods. Suspensions were prepared in water to high solid loadings, up to 50 vol.%. Self-sustained films were obtained by aqueous electrophoretic deposition (EPD) using graphite substrates under constant current density conditions. The evolution of mass per unit area with current density and deposition time was recorded. The films were characterized in the green state and after sintering at different temperatures (1300-1400) °C. Fully dense A-AT reaction sintered materials were obtained at low temperature by SPS. © 2013 Elsevier B.V. All rights reserved.


Benavente R.,Polytechnic University of Valencia | Salvador M.D.,Polytechnic University of Valencia | Penaranda-Foix F.L.,Polytechnic University of Valencia | Garcia-Moreno O.,Research Center en Nanomateriales y Nanotecnologia PA | Borrell A.,Polytechnic University of Valencia
Ceramics International | Year: 2015

Low-temperature sinterable microwave LiAlSiO4-based solid-state material was investigated with regard to microwave dielectric properties as functions of the sintering temperature. β-eucryptite materials and alumina-reinforced β-eucryptite composites were sintered by microwave technology at 1100°C and 1200°C. The combination of fast heating and the dramatic reduction in cycle time, along with the non-conventional heating source, opens the way to produce materials with desired multifunctional properties. The microstructure and crystalline composition of the materials were characterised, and the mechanical, thermal and microwave dielectric behaviours were analysed. X-ray diffraction showed good chemical stability in materials without between-phase reactions during the microwave sintering process. The excellent mechanical (∼8 GPa of hardness and ∼100 GPa of Young's modulus), thermal (-0.23·10-6 K-1) and microwave dielectric properties (ε r=4.10; Q=1494) were obtained from the LAS/Al2O3 composites sintered at a very low temperature (1100°C). The results achieved show the possibility of designing ceramic nanocomposites at low sintering temperatures using microwave technology with near-zero thermal expansion coefficients, high mechanical and chemical stability and low dielectric properties. © 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.


Borrell A.,Polytechnic University of Valencia | Salvador M.D.,Polytechnic University of Valencia | Rocha V.G.,ITMA Materials Technology | Fernandez A.,ITMA Materials Technology | And 4 more authors.
Composites Part B: Engineering | Year: 2014

Zirconium titanate (ZrTiO4), have many attractive properties such as high resistivity, high dielectric constant, high permittivity at microwave frequencies and excellent temperature stability for microwave properties. Zirconium titanate dense materials are proposed for many structural applications, but fully reacted and completely dense pieces are difficult to obtain by conventional routes. In this work, fully dense zirconium titanate materials (∼98%) were obtained at lower temperatures (1300-1400 C) and short processing time by non-conventional technique; spark plasma-reaction sintering (SPRS). Homogeneous and stable starting powders mixture with the adequate composition was prepared from the raw materials: m-ZrO2 (∼0.3 μm) and anatase-TiO2 (∼40 nm). Dense materials were mechanically and microstructural characterised. The fracture strength was measured by biaxial testing, giving values of about 200 MPa. © 2013 Published by Elsevier Ltd. All rights reserved.


Borrell A.,ITM University | Salvador M.D.,ITM University | Rocha V.G.,ITMA Materials Technology | Fernandez A.,ITMA Materials Technology | And 3 more authors.
Composites Part B: Engineering | Year: 2013

Full dense alumina + 40 vol.% aluminium titanate composites were obtained by colloidal filtration and fast reaction-sintering of alumina/titania green bodies by spark plasma sintering at low temperatures (1250-1400 °C). The composites obtained had near-to-theoretical density (>99%) with a bimodal grain size distribution. Phase development analysis demonstrated that aluminium titanate has already formed at 1300 °C. The mechanical properties such as Vickers hardness, flexural strength and fracture toughness of bulk composites are significantly higher than those reported elsewhere, e.g. the composite sintered at 1350 °C show values of about 24 GPa, 424 MPa and 5.4 MPa m 1/2, respectively. The improved mechanical properties of these composites are attributed to the enhanced densification and the finer and more uniform nanostructure achieved by non-conventional fast sintering of slip-cast dense green compacts. © 2012 Elsevier Ltd. All rights reserved.

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