Photoluminescence-Based Techniques for the Detection of Micro- and Nanoplastics

The growing numbers related to plastic pollution are impressive, with ca. 70 % of produced plastic (>350 tonnes/year) being indiscriminately wasted in the environment. The most dangerous forms of plastic pollution for biota and human health are micro- and nano-plastics (MNPs), which are ubiquitous and more bioavailable. Their elimination is extremely difficult, but the first challenge is their detection since existing protocols are unsatisfactory for microplastics and mostly absent for nanoplastics. After a discussion of the state of the art for MNPs detection, we specifically revise the techniques based on photoluminescence that represent very promising solutions for this problem. In this context, Nile Red staining is the most used strategy and we show here its pros and limitations, but we also discuss other more recent approaches, such as the use of fluorogenic probes based on perylene-bisimide and on fluorogenic hyaluronan nanogels, with the added values of biocompatibility and water solubility

Mechanism-based modeling of solute strengthening:Application to thermal creep in Zr alloy

In this work, a crystallographic thermal creep model is proposed for Zr alloys that accounts for the hardening contribution of solutes via their time-dependent pinning effect on dislocations. The core-diffusion model proposed by Soare and Curtin (2008a) is coupled with a recently proposed constitutive modeling framework (Wang et al., 2017, 2016) accounting for the heterogeneous distribution of internal stresses within grains. The Coble creep mechanism is also included. This model is, in turn, embedded in the effective medium crystallographic VPSC framework and used to predict creep strain evolution of polycrystals under different temperature and stress conditions. The simulation results reproduce the experimental creep data for Zircaloy-4 and the transition between the low (n∼1), intermediate (n∼4) and high (n∼9) power law creep regimes. This is achieved through the dependence on local aging time of the solute-dislocation binding energy. The anomalies in strain rate sensitivity (SRS) are discussed in terms of core-diffusion effects on dislocation junction strength. The mechanism-based model captures the primary and secondary creep regimes results reported by Kombaiah and Murty (2015a, 2015b) for a comprehensive set of testing conditions covering the 500–600 °C interval, stresses spanning 14–156 MPa, and steady state creep rates varying between 1.5·10−9s−1 to 2·10−3s−1. There are two major advantages to this model with respect to more empirical ones used as constitutive laws for describing thermal creep of cladding: 1) specific dependences on the nature of solutes and their concentrations are explicitly accounted for; 2) accident conditions in reactors, such as RIA and LOCA, usually take place in short times, and deformation takes place in the primary, not the steady-state creep stage. As a consequence, a model that accounts for the evolution with time of microstructure is more reliable for this kind of simulation

A Physics-Based Crystallographic Modeling Framework for Describing the Thermal Creep Behavior of Fe-Cr Alloys

In this work, a physics-based thermal creep model is developed based on the understanding of the microstructure in Fe-Cr alloys. This model is associated with a transition state theory-based framework that considers the distribution of internal stresses at sub-material point level. The thermally activated dislocation glide and climb mechanisms are coupled in the obstacle-bypass processes for both dislocation and precipitate-type barriers. A kinetic law is proposed to track the dislocation densities evolution in the subgrain interior and in the cell wall. The predicted results show that this model, embedded in the visco-plastic self-consistent framework, captures well the creep behaviors for primary and steady-state stages under various loading conditions. The roles of the mechanisms involved are also discussed

Mechanism-based modeling of thermal and irradiation creep behavior:An application to ferritic/martensitic HT9 steel

In this work, the creep behavior of HT9 steel in both thermal and irradiation environments is predicted using an integrated modeling framework. Multiple physical mechanisms such as diffusional creep and dislocation climb are incorporated into crystal plasticity calculations using the Visco-Plastic Self-Consistent (VPSC) approach. Climb velocities are informed by mean field rate theory laws in place of empirical power law formulations. More interestingly, the climb velocities explicitly consider the contribution of irradiation-induced point defects, i.e., stress induced preferential absorption (SIPA) effect. The developed expressions are shown to apply under conventional thermal creep and to the more complex irradiation conditions as well. This physically-informed, mechanism-based model is used to simulate the creep strain evolution of HT9 pressurized tubes under various loading conditions. It is demonstrated that the experimental behavior of this material reported in the literature is well described by this theoretical framework. The role of each relevant mechanism is discussed

Continuous modeling of the structure of symmetric tilt boundaries

International audienceIn polycrystals, the discontinuity of lattice rotation occurring across symmetric tilt boundaries is accommodated by the periodic arrangement of atoms in structural units. A crossover between this atomistic description and a continuous representation of tilt boundaries is carried out by designing periodic arrays of appropriately chosen smooth disclination dipoles. A comprehensive description of the boundary structure in terms of elastic strain, curvature and energy fields is then derived from a continuous theory of dislocation and disclination density fields, by allowing the initial distributions to relax in their own stress/couple stress fields. The resulting fields are obtained at nanoscale from finite element approximations of the theory. They compare remarkably well with predictions from molecular statics and experimental data. Beyond this description of grain boundaries as continua, the theory naturally provides a basis for coarse-grained spatio-temporal continuous descriptions of polycrystals

Disclination mediated plasticity in shear-coupled boundary migration

International audienceThe shear-coupled boundary migration of symmetric tilt boundaries is investigated within the framework of an elasto-plastic theory of disclination and dislocation fields. The tilt boundaries are built from periodic partial wedge-disclination dipole arrays, on the basis of their atomistic topography. Non-locality of the elastic response of the adjacent crystals stems from the defected structure of their boundary. Upon applying a shear strain to the bicrystal, couple stresses are generated, which set the disclination dipole array into motion normal to the boundary. In the process, edge dislocation densities with partial Burgers vector lying along the boundary are nucleated, whose glide parallel to the boundary and annihilation produces plastic shear. The misorientation dependence of the shear coupling factor predicted by the model is in full agreement with data from atomistic simulations and experiments. It is found to depend on the polarity and the magnitude of the wedge disclination dipoles composing the grain boundary