Nanoindentation and tribological tests – Suitable tools for modelling the nanostructure of sheet nacre

1. Introduction Nacre (the pearly internal layer of seashells) is a natural nanocomposite currently studied for the design of new organic/inorganic hybrid materials by mimicking biomineralization processes. It is a bioceramic formed at ambient temperature and pressure [1] which displays an exceptional high strength, stiffness and toughness [2] to weight ratio, as well as a natural biocompatibility with human bones [3]

“Microbiota, symbiosis and individuality summer school” meeting report

How does microbiota research impact our understanding of biological individuality? We summarize the interdisciplinary summer school on “Microbiota, symbiosis and individuality: conceptual and philosophical issues” (July 2019), which was supported by a European Research Council starting grant project “Immunity, DEvelopment, and the Microbiota” (IDEM). The summer school centered around interdisciplinary group work on four facets of microbiota research: holobionts, individuality, causation, and human health. The conceptual discussion of cutting-edge empirical research provided new insights into microbiota and highlights the value of incorporating into meetings experts from other disciplines, such as philosophy and history of science

Characterization of SiC/C(B)/SiC microcomposites by transmission electron microscopy

International audienceUniform or composition graded C(B) interphases in SiC/SiC model microcomposites were characterized by transmission electron microscopy after tensile tests and thermal ageing in air. A specific method was developed to prepare thin longitudinal sections of the tested specimens. Deflection of matrix cracks occurs within the uniform C(B) interphase as long as its anisotropy remains high enough (i.e. when the boron content is not too high). It takes place close to the most anisotropic layer (i.e. that containing 8 at. % of boron) in composition graded interphases. In both cases, crack deflection path does not reach the fiber, a feature which is consistent with the good mechanical properties. After ageing in air under tensile loading beyond the proportional limit (600 °C; σ = 800 MPa), the composition graded interphase (made of five sublayers in which the boron content increases from 0 at. % near the fiber to 33 at. % near the matrix) was observed to act as a glass forming protection, the pyrocarbon sublayer (at the fibre surface) remaining unoxidized

Deposition process of laminar pyrocarbon from propane

The deposition mechanisms of smooth laminar (SL) and rough laminar (RL) pyrocarbons from propane are found to be very different, as evidenced by (i) gas phase analysis, (ii) nucleation experiments and (iii) analysis of the deposit composition and nanostructure. SL pyrocarbon results mainly from aliphatic species ; its nucleation needs surface reactive sites where chemisorption and hydrogen abstraction occur ; its growth leads to extended but highly distorted graphene layers which can enclose internal nanoporosity. RL pyrocarbon results mainly from polycyclic aromatic hydrocarbons (PAH) ; its nucleation, which does not depend on the substrate, occurs widely by physisorption of PAH ; the corresponding graphene layers are not very extended but parallel to each other and parallel to the anisotropy plane