Abstract: A reactive ReaxFF force field is developed for studying the influence of intrinsic point defects on the chemistry with TiO2 condensed phases. The force field parameters are optimized to ab initio data for the equations of state, relative phase stabilities for titanium and titanium dioxide, potential energy differences for (TiO2)n-clusters (n = 116). Also data for intrinsic point defects in anatase were added. These data contain formation energies for interstitial titanium and oxygen vacancies, diffusion barriers of the oxygen vacancies and molecular oxygen adsorption on a reduced anatase (101) surface. Employing the resulting force field, we study the influence of concentration of oxygen vacancies and expansion or compression of an anatase surface on the diffusion of the oxygen vacancies. Also the barrier for oxygen diffusion in the subsurface region is evaluated using this force field. This diffusion barrier of 27.7 kcal/mol indicates that the lateral redistribution of oxygen vacancies on the surface and in the subsurface will be dominated by their diffusion in the subsurface, since both this barrier as well as the barriers for diffusion from the surface to the subsurface and vice versa (17.07 kcal/mol and 21.91 kcal/mol, respectively, as calculated with DFT), are significantly lower than for diffusion on the surface (61.12 kcal/mol as calculated with DFT).

Abstract: The application of fixed operational protocols and settings for membrane bioreactors (MBR) often leads to suboptimal filtration conditions due to the dynamic nature of mixed liquor characteristics. With regard to process optimization and energy savings, the potential benefits of a dynamic control system, enabling to adapt fouling control actions (ACS outputs) in an automated way to the actual mixed liquor fouling propensity, are thus obvious. In this paper, the pilot-scale validation of such an advanced control system (ACS) is elaborated. A specific on-line fouling measurement method, the MBR-VFM (VITO Fouling Measurement), was used for the evaluation of the mixed liquors reversible fouling propensity, which was used as a primary ACS input parameter. A first series of tests with a gradual increase in complexity of the selected input and output parameters indicated the functionality of the ACS and demonstrated a substantial reduction of aeration, however sometimes at the expense of a higher fouling rate. The ACS was further fine-tuned and subsequently tested for a longer period under more dynamic operating conditions. A significant correlation was found between the reversible fouling potential measured by the MBR-VFM and the on-line permeability, indicating that the MBR-VFM is a suitable ACS input. Furthermore, an average 22% reduction in aeration flow to the membranes could be achieved without any obvious negative effect on filtration performance. This indicates that this approach is promising to optimize energy consumption in MBRs.

Abstract: In this study, a new fouling sensor was validated under different conditions of hydraulic (HRT) and sludge retention time (SRT). The MBR-VFM (membrane bioreactor-VITO Fouling Measurement) allows the simultaneous determination of the physically reversible and irreversible fouling potential of a mixed liquor during a single crossflow filtration test. In accordance with the on-line filtration behavior, the measured reversible and irreversible fouling propensities differed significantly between MBRs operated at different combinations of HRT-SRT. Moreover, a significant negative correlation was found between the on-line permeability and the reversible and irreversible fouling propensity measured by the MBR-VFM. This corresponded to observations made on membrane recovery after physical or chemical cleaning actions. Higher reversible and irreversible fouling were observed at lower HRT, presumably as a consequence of increased concentrations of foulants present. The effect of SRT was much smaller and restricted to the reversible fouling component. Possible explanations for the increased fouling at prolonged SRT are the higher sludge and colloid concentration and the smaller floc size. It can be concluded that the MBR-VFM is a useful tool to monitor fluctuations in a mixed liquors (ir)reversible fouling potential and can contribute to a deeper understanding of the occurring fouling phenomena.

Abstract: Intragranular amorphization shear lamellae are found in deformed olivine aggregates. The detailed trans-mission electron microscopy analysis of intragranular lamella arrested in the core of a grain provides novel information on the amorphization mechanism. The deformation field is complex and heteroge-neous, corresponding to a shear crack type instability involving mode I, II and III loading components. The formation and propagation of the amorphous lamella is accompanied by the formation of crystal defects ahead of the tip. These defects are geometrically necessary [001] dislocations, characteristics of high-stress deformation in olivine, and rotational nanodomains which are tentatively interpreted as disclinations. We show that these defects play an important role in dictating the path followed by the amorphous lamella. Stress-induced amorphization in olivine would thus result from a direct crystal-to -amorphous transformation associated with a shear instability and not from a mechanical destabilization due to the accumulation of high number of defects from an intense preliminary deformation. The pref-erential alignment of some lamellae along (010) is a proof of the lower ultimate mechanical strength of these planes.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Abstract: In this paper we review the work related to amorphization under mechanical stress. Beyond pressure, we highlight the role of deviatoric or shear stresses. We show that the most recent works make amorphization appear as a deformation mechanism in its own right, in particular under extreme conditions (shocks, deformations under high stresses, high strain-rates).

Abstract: The fundamental plasticity mechanisms in thin freestanding Zr65Ni35 metallic glass films are investigated in order to unravel the origin of an outstanding strength/ductility balance. The deformation process is homogenous until fracture with no evidence of catastrophic shear banding. The creep/relaxation behaviour of the films was characterized by on-chip tensile testing, revealing an activation volume in the range 100–200 Å3. Advanced high-resolution transmission electron microscopy imaging and spectroscopy exhibit a very fine glassy nanostructure with well-defined dense Ni-rich clusters embedded in Zr-rich clusters of lower atomic density and a ~2–3 nm characteristic length scale. Nanobeam electron diffraction analysis reveals that the accumulation of plastic deformation at roomtemperature
correlates with monotonously increasing disruption of the local atomic order. These results provide experimental evidences of the dynamics of shear transformation zones activation in metallic glasses. The impact of the nanoscale structural heterogeneities on the mechanical properties including the rate dependent behaviour is discussed, shedding new light on the governing plasticity mechanisms in metallic glasses with initially heterogeneous atomic arrangement.

Abstract: Although it is well known that FeMnC TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability of the twins, but also the strength of these twins and their interactions with the gliding dislocations present in the matrix. This experimental evidence is discussed and compared to recent results in order to relate the defects analysis to the macroscopic behaviour of this category of material.

Abstract: The microstructure of a Fe-Mn-Si-Al twinning-induced plasticity (TWIP) steel exhibiting remarkable work hardening rate under uniaxial tensile deformation was investigated using transmission electron microscopy to uncover the mechanism(s) controlling the nucleation and growth of the mechanically induced twins. The results show that the stair-rod cross-slip deviation mechanism is necessary for the formation of the twins, while large extrinsic stacking faults homogenously distributed within the grains could act as preferential sources for the activation of the deviation process. The influence of such features on the thickness and strength of the twins and the resulting mechanical behaviour is discussed and compared to similar works recently performed on Fe-Mn-C TWIP steels.

Abstract: The determination of the mechanical properties of serpentinites is essential towards the understanding of the mechanics of faulting and subduction. Here, we present the first in situ tensile tests on antigorite in a transmission electron microscope. A push-to-pull deformation device is used to perform quantitative tensile tests, during which force and displacement are measured, while the microstructure is imaged with the microscope. The experiments have been performed at room temperature on beams prepared by focused ion beam. The specimens are not single crystals despite their small sizes. Orientation mapping indicated that some grains were well-oriented for plastic slip. However, no dislocation activity has been observed even though engineering tensile stress went up to 700 MPa. We show also that antigorite does not exhibit an pure elastic-brittle behaviour since, despite the presence of defects, the specimens underwent plastic deformation and did not fail within the elastic regime. Instead, we observe that strain localizes at grain boundaries. All observations concur to show that under our experimental conditions, grain boundary sliding is the dominant deformation mechanism. This study sheds a new light on the mechanical properties of antigorite and calls for further studies on the structure and properties of grain boundaries in antigorite and more generally in phyllosilicates.