Size Effects of Brittle Particles in Aerosol Deposition—Molecular Dynamics Simulation

Abstract

Up to now, the role of particle sizes on the impact behavior of ceramic particles in aerosol deposition not yet fully understood. Hence, with the aim to supply a more general understanding, modeling series of low strain rate compression and high-speed impact were performed by molecular dynamics on single-crystalline particles in sizes of 10-300 nm that are tuned to match mechanical properties of TiO2-anatase. The modeling results reveal that particles with original diameter of 25-75 nm exhibit three different impact behaviors that could be distinguished as (i) rebounding, (ii) bonding and (iii) fragmentation, depending on their initial impact velocity. In contrast, particles larger than 75 nm do not exhibit the bonding behavior. Detailed stress and strain field distributions reveal that combination of “localized inelastic deformation” along the slip systems and “shear localization” cause bonding of the small and large particles to the substrate. The analyses of associated temperature rise by the inelastic deformation revealed that heat diffusion at these small scales depend on size. Whereas small particles could reach a rather homogeneous temperature distribution, the evolved heat in the larger ones keeps rather localized to areas of highest deformation and may support deformation and the formation of dense layers in aerosol deposition.

Room temperature deposition of freestanding BaTiO3 films: temperature-induced irreversible structural and chemical relaxation

“…In fact, the stress calibration data provided by Sakshita et al [86] applies a maximum stress of 60 MPa to BaTiO 3 corresponding to a shift to 519 cm -1 , well exceeded by the as-processed film., i.e., 522 cm -1 . This is a strong indication that the as-processed film is deformed by the impact loading during the AD-process resulting in a lattice distortion [20,56,71,90]. During thermal treatment, as can be seen in Fig.…”

Features of ceramic nanoparticle deformation in aerosol deposition explored by molecular dynamics simulation

“…The test was used to adjust the ε parameter for finally reaching a compressive strength of 11.11 GPa in compression test simulation, comparable to the experimental data that are available from literature for TiO 2 -anatase nanoparticles within a diameter range of 30-40 nm [2,43]. Details of compression test simulation and its results can be found in our previous study [41].…”

“…3. In addition, extended MD simulations showed that the velocity regime for rebounding is not size dependent [41]. For the present material description of TiO 2 -anatase, the maximum rebounding velocity, here defined as threshold velocity, v threshold , is determined to 400 m/s for a range of particle diameters from 25 to 300 nm [41].…”

“…Based on these studies, various bonding mechanisms have been proposed for AD [26][27][31][32][33][34][35][36][37][38][39][40]. The main proposed mechanisms are (1) room temperature impact consolidation (RTIC) [26][27][35][36][37][38][39][40], (2) fragmentation and packing [31], (3) interlocking along with creation of highly activated surfaces [32,33], and (4) 'shear localization' [41]. It is not clear whether and to what extent these explanations, especially the latter, can be applied to intrinsically brittle ceramics particles.…”

Aerosol Deposition of Ti3SiC2-MAX-Phase Coatings

“…By experiments and modelling, most established descriptions associate bonding and layer formation in Aerosol Deposition with (dynamic) particle fragmentation into nanocrystalline microstructures (Ref 19,20,28). Another approach was followed by Daneshian et al by using molecular dynamic (MD) simulations (Ref 40,41). For nanoparticle impact, their computations distinguish regimes of (i) rebound (ii) deformation and bonding and (iii) particle fracture, whereas only deformation associated effects are defined to contribute to layer formation.…”