Knowledge of mechanical properties and particle breakage behavior is of fundamental importance for many particle related processes and the application of particles. Although many (in situ) studies have been dedicated to materials’ size dependent mechanical characterization over the past decade, particles as free standing structures, however, have widely been omitted [1]. Important questions include the size dependent deformation behavior of particles and small structures confined in one- or two dimensions and the corresponding structureÂpropertyÂcorrelations at these small scales. Within this account, structural and mechanical characterÂization under compression will be discussed for sol-gel derived micron sized spherical SiO
2 and TiO
2 [2-5] particles for the a size range of 200 nm to 4 µm. Mechanical compression of the individual particles was performed by a custom-made scanning electron microscope (SEM) supported manipulation device [1]. The internal structural of the sol-gel particles was tuned in a wide range by thermal annealing. For the amorphous silica particles the degree of internal cross-linking and hydroxylation was changed systematically towards vitreous silica. The changes of the internal structure are directly reflected by the mechanical properties [2]. For fully densified and de-hydroxylated vitreous silica particles a clear brittle-to-ductile transition is found in the size range of 500 – 800 nm, i.e. with increasing particle size the plasticity of the particles decrease and the stable crack propagation and brittle fracture becomes the predominant failure mode [3]. By ex situ Raman spectroscopy the observed plasticity is found to be accommodated by structural densification [4]. In the TiO
2 system the influence of crystallinity was studied: Single-phase nanocrystalline (nc) anatase or rutile particles were obtained by annealing [5]. For the amorphous and the nc particles a significant plastic deformation behavior accompanied by crack initiation occurring at high deformations were observed. The crack propagation is found to follow presumably grain boundaries. The corresponding fracture stresses are Weibull distributed.
References:
[1] S. Romeis, J. Paul, M. Ziener, W. Peukert, A novel apparatus for in situ compression of submicron structures and particles in a high resolution SEM, Rev Sci Instrum 83 (2012).
[2] S. Romeis, J. Paul, M. Hanisch, V.R.R. Marthala, M. Hartmann, R.N. Klupp Taylor, J. Schmidt et al., Correlation of enhanced strength and internal structure for heat-treated submicron Stöber silica particles, Part Part Syst Char 31 (2014) 664–674.
[3] J. Paul, S. Romeis, M. MaÄković, V. Marthala, P. Herre, T. Przybilla, M. Hartmann et al., In situ cracking of silica beads in the SEM and TEM - effect of particle size on structure-property correlations, Powder Technol. 270 (2015) 337–347.
[4] S. Romeis, J. Paul, P. Herre, D. de Ligny, J. Schmidt, W. Peukert, Local densification of a single micron sized silica sphere by uniaxial compression, Scripta Mater. (2015) 84–87.
[5] P. Herre, S. Romeis, M. MaÄković, T. Przybilla, J. Paul, J. Schwenger, B. Torun et al., Deformation behavior of nanocrystalline titania particles accessed by complementary in situ electron microscopy techniques, J. Am. Ceram. Soc. 330 (2017) 556.
