Julian Martínez Fernández

Silicon carbide‐based fiber‐bonded ceramics, obtained from hot pressing of woven silicon carbide fibers, are a cost‐effective alternative to ceramic‐matrix composites due to their ease of fabrication, involving few processing steps, and competitive thermomechanical properties. In this work, we studied the high‐temperature strength and thermal shock resistance of Si‐Al‐C‐O and Si‐Ti‐C‐O fiber‐bonded SiC ceramics obtained from hot pressing of two types of ceramic fibers, by mechanical testing in four‐point bending. The bending strength of Si‐Al‐C‐O‐based fiber‐bonded ceramics at room temperature is ∼250–260 MPa and remains constant with temperature, while the bending strength of Si‐Ti‐C‐O increases slightly from the initial 220 to ∼250 MPa for the highest temperature. Both materials retain up to 90% of their room temperature strength after thermal shocks of 1400°C and show no reduction in elastic moduli. After thermal shock, failure mode is the same as in the case of as‐received materials.

To meet the increasingly strict emission limits imposed by regulations, internal combustion engines for transport applications require the urgent development of novel emission abatement systems. The introduction of biodiesel or other biofuels in the engine operation is considered to reduce greenhouse gas emissions. However, these alternative fuels can affect the performance of the post-combustion systems due to the variability they introduce in the exhaust particle distribution and their particular physical properties. Bioceramic materials made from vegetal waste are characterized by having an orthotropic hierarchical microstructure, which can be tailored in some way to optimize the filtration mechanisms as a function of the particle distribution of the combustion gases. Consequently, they can be good candidates to cope with the variability that new biofuel blends introduce in the engine operation. The objective of this work is to predict the filtration performance of a wall-flow particulate filter (DPF) made of biomorphic silicon carbide (bioSiC) with a systematic procedure that allows to eventually fit different fuel inputs. For this purpose; a well-validated DPF model available as commercial software has been chosen and adapted to the specific microstructural features of bioSiC. Fitting the specific filtration and permeability parameters of this biomaterial into the model; the filtration efficiency and pressure drop of the filter are predicted with sufficient accuracy during the loading test. The results obtained through this study show the potential of this novel DPF substrate; the material/microstructural design of which can be adapted through the selection of an optimum precursor.

Graphitized carbon materials from biomass resources were successfully synthesized with an iron catalyst, and their electrochemical performance as anode materials for lithium‐ion batteries (LIBs) was investigated. Peak pyrolysis temperatures between 850 and 2000 °C were covered to study the effect of crystallinity and microstructural parameters on the anodic behavior, with a focus on the first‐cycle Coulombic efficiency, reversible specific capacity, and rate performance. In terms of capacity, results at the highest temperatures are comparable to those of commercially used synthetic graphite derived from a petroleum coke precursor at higher temperatures, and up to twice as much as that of uncatalyzed biomass‐derived carbons. The opportunity to graphitize low‐cost biomass resources at moderate temperatures through this one‐step environmentally friendly process, and the positive effects on the specific capacity, make it interesting to develop more sustainable graphite‐based anodes for LIBs.

The microstructural characteristics and amplitude dependences of the Young’s modulus E and\ud internal friction (logarithmic decrement δ) of biocarbon matrices prepared by beech wood carbonization at\ud temperatures Tcarb = 850–1600°C in the presence of a nickelcontaining catalyst have been studied. Using\ud Xray diffraction and electron microscopy, it has been shown that the use of a nickel catalyst during carbon\ud ization results in a partial graphitization of biocarbons at Tcarb ≥ 1000°C: the graphite phase is formed as 50\ud to 100nm globules at Tcarb = 1000°C and as 0.5 to 3.0μm globules at Tcarb = 1600°C. It has been found that\ud the measured dependences E(Tcarb) and δ(Tcarb) contain three characteristic ranges of variations in the\ud Young’s modulus and logarithmic decrement with a change in the carbonization temperature: E increases and\ud δ decreases in the ranges Tcarb < 1000°C and Tcarb > 1300°C; in the range 1000 < Tcarb < 1300°C, E sharply\ud decreases and δ increases. The observed behavior of E(Tcarb) and δ(Tcarb) for biocarbons carbonized in the\ud presence of nickel correlates with the evolution of their microstructure. The largest values of E are obtained\ud for samples with Tcarb = 1000 and 1600°C. However, the samples with Tcarb = 1600°C exhibit a higher suscep\ud tibility to microplasticity due to the presence of a globular graphite phase that is significantly larger in size and\ud total volume.Peer reviewe