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Reactividad de Sólidos - Tribología y Protección de Superficies

BN nanosheets reinforced zirconia composites: An in-depth microstructural and mechanical study

Muñoz-Ferreiro, C; Reveron, H; Rojas, TC; Reyes, DF; Cottrino, S; Moreno, P; Prada-Rodrigo, J; Morales-Rodriguez, A; Chevalier, J; Gallardo-López, A; Poyacto, R
Journal of the European Ceramic Society, 44(10) (2024) 5846-5860

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This paper deals with the effect of hydroxylated boron nitride nanosheets (BNNS) incorporation on the microstructural and mechanical features of zirconia ceramics. Few-layered BNNS were synthesized via a simple hydroxide-assisted planetary ball milling exfoliation technique. 3 mol% yttria tetragonal zirconia polycrystal (3Y-TZP) with 2.5 vol% BNNS powders were prepared by an environmentally friendly process in water, and spark-plasma sintered at three temperatures to explore the in-situ reduction of the functionalized BNNS. An exhaustive study by (S)TEM techniques was performed to elucidate the influence of the sintering temperature on the matrix and the 3Y-TZP/BNNS interfaces, revealing that BNNS were homogeneously distributed throughout the matrix with an abrupt transition at 3Y-TZP/BNNS interfaces. BNNS effectively hindered slow crack growth, thus increasing the composite's crack growth resistance by about 30 %. A 1 MPa·m1/2 rising R-curve was also induced by crack bridging.

August, 2024 | DOI: 10.1016/j.jeurceramsoc.2024.02.002

Reactividad de Sólidos

On the athermal origin of flash sintering: Separating field-induced effects from Joule heating using a current ramp approach

Molina-Molina, S; Perejón, A; Pérez-Maqueda, LA; Sánchez-Jiménez, PE
Scripta Materialia, 247 (2024) 116086

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Joule heating is generally acknowledged as the main driving force behind Flash Sintering. However, this view is challenged by the presence of athermal phenomena and the similarities between the flash process and dielectric breakdown. This work offers new insights into flash as an electrical runaway. Using current ramps to perform flash experiments on zinc oxide, two distinct stages within the process were revealed by electrical, thermal and microstructural measurements: a field-dominated regime where the flash event is triggered and a subsequent current-dominated regime associated with power dissipation. The contribution of each regime to the whole flash process was found to be determined by the initial resistivity of the sample. Furthermore, impedance spectroscopy data confirmed field-induced enhancement of conductivity at the flash-onset without significant Joule heating.

July, 2024 | DOI: 10.1016/j.scriptamat.2024.116086

Reactividad de Sólidos

In situ study on enhanced plastic deformability of Lanthanum-doped Bismuth ferrite processed by flash sintering

Yang, B; Sánchez-Jiménez, PE; Niu, TJ; Sun, TY; Shang, ZX; Cho, J; Perejón, A; Shen, C; Pérez-Maqueda, LA; Tsakalakos, T; Wang, HY; Zhang, XH
Journal of the European Ceramic Society, 44 (2024) 3985-3994

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BiFeO3 is a promising multiferroic material for versatile device applications due to its co-existence of magnetic (i.e., antiferromagnetic) and ferroelectric ordering at room temperature. While its functional properties have been extensively investigated, the exploration of its mechanical behavior was limited mostly to the thin-film form of BiFeO3. In this work, we conducted in situ micropillar compression experiments to investigate the deformation behavior of La-doped BiFeO3 (La-BFO) samples processed by both conventional and flash sintering methods. The conventionally sintered La-BFO exhibited limited deformability at room temperature and 450 degrees C. In contrast, the deformability of the flash-sintered La-BFO specimens was substantially improved by nearly 100% at both testing temperatures. Detailed post-mortem studies suggest that preexisting dislocations and wide anti-phase boundaries introduced during flash sintering can toughen flash-sintered La-BFO by easing dislocation migration and ferroelastic domain switching. This study provides a fresh perspective to design an advanced multifunctional system with improved mechanical properties.

June, 2024 | DOI: 10.1016/j.jeurceramsoc.2023.12.099

Materiales Nanoestructurados y Microestructura

DC magnetron sputter deposition in pure helium gas: formation of porous films or gas/solid nanocomposite coatings

Ibrahim, S; Fernández, A; Brault, P; Sauldubois, A; Desgardin, P; Caillard, A; Hufschmidt, D; De Haro Jiménez, MC, Sauvage, T; Barthe, MF, Thomann, AL
Vacuum, 224 (2024) 113184

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Magnetron sputtering of two materials (Aluminum and Silicon) was performed in He gas and led to the formation of very different porous thin films: a fiberform nanostructure or a gas/solid nanocomposite. The composition of the thin films obtained was analyzed by means of ion beam techniques: Rutherford backscattering and proton elastic backscattering spectroscopies to measure the amount of Al(Si) deposited atoms and that of He atoms inserted inside the films. Microstructural and crystalline properties were analyzed by scanning electron microscopy and X-ray diffraction. Transmission electron microscopy coupled with electron energy loss spectroscopy were used to investigate the presence of empty or He filled pores or even bubbles. Correlating the Al(Si) film properties with the deposition conditions evaluated by SRIM (sputtering process at the target) and by a homemade collision code (species transport to the substrate) gave a better insight into the reason for the formation of such different films. The role of both He ions backscattered at the target and surface mobility during the growth is discussed. Comparison with low kinetic energy He + implantation experiments indicates that similar mechanisms, such as He insertion, diffusion inside the lattice, release or accumulation into pores and bubbles, are certainly taking place.

June, 2024 | DOI: 10.1016/j.vacuum.2024.113184

Química de Superficies y Catálisis

Biomass gasification, catalytic technologies and energy integration for production of circular methanol: New horizons for industry decarbonisation

Bobadilla, Luis F; Azancot, Lola; González-Castaño, Miriam; Ruíz-López, Estela; Pastor-Pérez, Laura; Durán-Olivencia, Francisco J.; Ye, Runping; Chong, Katie; Blanco-Sánchez, Paula H; Wu, Zenthao; Reina, TR; Odriozola, JA
Journal of Environmental Sciences, 140 (2024) 306-318

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The Intergovernmental Panel on Climate Change (IPCC) recognises the pivotal role of renewable energies in the future energy system and the achievement of the zero-emission target. The implementation of renewables should provide major opportunities and enable a more secure and decentralised energy supply system. Renewable fuels provide long-term solutions for the transport sector, particularly for applications where fuels with high energy density are required. In addition, it helps reducing the carbon footprint of these sectors in the long-term. Information on biomass characteristics feedstock is essential for scaling-up gasification from the laboratory to industrial-scale. This review deals with the transformation biogenic residues into a valuable bioenergy carrier like biomethanol as the liquid sunshine based on the combination of modified mature technologies such as gasification with other innovative solutions such as membranes and microchannel reactors. Tar abatement is a critical process in product gas upgrading since tars compromise downstream processes and equipment, for this, membrane technology for upgrading syngas quality is discussed in this paper. Microchannel reactor technology with the design of state-of-the-art multifunctional catalysts provides a path to develop decentralised biomethanol synthesis from biogenic residues. Finally, the development of a process chain for the production of (i) methanol as an intermediate energy carrier, (ii) electricity and (iii) heat for decentralised applications based on biomass feedstock flexible gasification, gas upgrading and methanol synthesis is analysed.

June, 2024 | DOI: 10.1016/j.jes.2023.09.020