Optimizing the homogenization technique for graphene nanoplatelet/yttria tetragonal zirconia composites: Influence on the microstructure and the electrical conductivity

3 mol% yttria tetragonal zirconia polycrystalline (3YTZP) ceramic composite powders with 10 vol% nominal content of graphene nanoplatelets (GNPs) were prepared using four different homogenization routines: dispersion of the powder mixture by ultrasonication in isopropyl alcohol, homogenization in a high-energy planetary ball mill in wet or dry conditions after ultrasonication, and milling of the powders in a high-energy planetary ball mill in dry conditions. A significant effect of the homogenization routine on the powders particle size distribution was revealed by laser granulometry and Raman spectroscopy. Highly densified composites were obtained after spark plasma sintering (SPS) and remarkable differences on the GNP size, shape and distribution throughout the ceramic matrix and also in the electrical conductivity were observed in the four different composites. The composite with the best performance in terms of electrical conductivity was the one prepared after planetary ball milling of the powders in dry conditions as a consequence of the reduced dimensions of the GNPs and their excellent distribution throughout the ceramic matrix.Financial support from project MAT2015-67889-P (Spanish Ministerio de Economía y Competitividad), cofunded by European FEDER funding, is acknowledged

Spark Plasma Sintered Zirconia Ceramic Composites with Graphene-Based Nanostructures

The addition of graphene-based nanostructures (GBNs) can improve the inherent fragility of ceramics and provide them with improved electrical and thermal conductivities. However, both the starting material (ceramic matrix and GBNs) and the processing/sintering approach are crucial for the final composite microstructure and properties. This work focuses on the influence of the content and dimensions of the GBN filler (10 and 20 vol%; 3 and ~150 layers), the powder-processing conditions (dry versus wet), and the homogenization method (ultrasound sonication versus high-energy planetary ball milling) on GBN/tetragonal zirconia (3YTZP) composites. The microstructure and electrical properties of the spark plasma sintered (SPS) composites were quantified and analyzed. The highest microstructural homogeneity with an isotropic microstructure was achieved by composites prepared with thicker GBNs milled in dry conditions. A high content (20 vol%) of few-layered graphene as a filler maximizes the electrical conductivity of the composites, although it hinders their densification.This research was funded by the Ministerio de Economía y Competitividad, and European FEDER fundings, with grant number MAT2015-67889-P. Acknowledgments: The authors would like to acknowledge the CITIUS (Centros de Investigación, Tecnología e Innovación de la Universidad de Sevilla) for the microanalysis, X-ray diffraction and SEM facilities.Peer reviewe

Electrical Performance of Orthotropic and Isotropic 3YTZP Composites with Graphene Fillers

3 mol% yttria tetragonal zirconia polycrystal (3YTZP) composites with orthotropic or isotropic microstructures were obtained incorporating few layer graphene (FLG) or exfoliated graphene nanoplatelets (e-GNP) as fillers. Electrical conductivity was studied in a wide range of contents in two configurations: perpendicular (σꓕ) and parallel (σ//) to the pressing axis during spark plasma sintering (SPS). Isotropic e-GNP composites presented excellent electrical conductivity for high e-GNP contents (σꓕ ∼ 3200 S/m and σ// ∼ 1900 S/m for 20 vol% e-GNP), consequence of their misoriented distribution throughout the matrix. Optimum electrical performance was achieved in the highly anisotropic FLG composites, with high electrical conductivity for low contents (σꓕ ∼ 680 S/m for 5 vol%), percolation threshold below 2.5 vol% FLG and outstanding electrical conductivity for high contents (σꓕ ∼ 4000 S/m for 20 vol%), result of the high aspect ratio and low thickness of FLG.Ministerio de Ciencia e Innovación GC2018–101377-B-100, MCIN/AEI/ 10.13039/501100011033European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER) P20_01024Ministerio de Economía y Competitividad BES-2016- 078711Universidad de Sevilla USE-18740-

EL TIPO DE PLATAFORMA DE CONTACTO INFLUYE EN EL REGISTRO DE LA ALTURA DE SALTO VERTICAL ESTIMADA A PARTIR DEL TIEMPO DE VUELO

<p> </p><p class="titulo1" align="center"><strong>RESUMEN</strong></p> <p class="resumenyabstract" align="justify">Registrar el tiempo de vuelo (Tv) en una plataforma de contacto es una metodología muy utilizada para estimar la altura del salto vertical. Los objetivos del trabajo son: a-analizar si el tipo de plataforma de contacto influye en el Tv, y b-comprobar la validez y fiabilidad de una nueva plataforma de contacto de tipo optoeléctrico. 89 estudiantes realizaron 3 saltos verticales máximos registrados simultáneamente en una Plataforma de Fuerzas (PF) y dos plataformas de contacto: ErgoJump Plus (EJ) y SportJump System Pro (SJ), en los sentidos longitudinal y transversal respecto a PF. EJ subestimó el Tv en 50.8 ms, mientras que SJ lo subestimó en 10.6 ms. La altura del salto no influyó en estas diferencias, aunque fueron mayores para EJ cuando se saltó en sentido transversal. La relación PF-EJ (r=0.6597) fue menos alta que PF-SJ (r=0.9992). El coeficiente de variación fue mayor en EJ (6.61±4.81%*) que en SJ (1.21±0.81%) y PF (1.19±0.78%). El tipo de plataforma de contacto (optoeléctrica vs. mecánica) influye sustancialmente en el Tv y la altura del salto vertical, por lo que estos dispositivos deberían ser validados antes de ser utilizados en estudios científicos. El nuevo sistema SJ que incorpora tecnología láser, ha resultado válido y fiable para medir saltos verticales.<br /> <strong>Palabras Clave:</strong> <strong></strong>biomecánica, instrumentación, salto vertical, plataforma de contacto.</p> <p class="tabulado" align="justify"> </p> <p class="titulo1" align="center"><strong>ABSTRACT</strong></p> <p class="resumenyabstract" align="justify">Measuring flight time (Ft) on a contact mat is a common methodology to estimate vertical jump height. The aims of this study were: a-to analyze the influence of the contact mat technology on Ft, and b-to verify the validity and reliability of a new optoelectronic contact mat. Eighty-nine physical students performed 3 maximal jumps which were simultaneously registered by one force plate (FP) and two contact mats: ErgoJump Plus (EJ) and SportJump System Pro (SJ). They which were performed in a randomized order in the directions longitudinal and transversal with respect to PF. EJ underestimated Ft in 50.8 ms, while SJ underestimated it in 10.6 ms. Jump height did not affect these differences, although they increased when the jump direction was transversal in EJ. Correlation PF-EJ (r=0.6597) was lower than PF-SJ one (r=0.9992). Coefficient of variation of EJ (6.61±4.81%*) was higher than SJ (1.21±0.81%) and PF (1.19±0.78%) ones. The contact mat technology (optoelectronics vs. mechanics) had a great influence on both Ft and vertical jump height; therefore these instruments should be validated before using them in scientific studies. The new system SJ that use laser technology, was valid and reliable to measure vertical jumps.<br /> <strong>Key Words: </strong>biomechanics, instrumentation, vertical jump, contact mat.</p&gt