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 materialsâ size dependent mechanical characterization over the past decade, particles as free standing structures, however, have widely been omitted . 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 SiO2
[2-5] particles for the a size range of 200 nm to 4 Âµm. Mechanical compression of the individual particles was performed by a custom-made scanning electron microscope (SEM) supported manipulation device . 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 . For fully densified and de-hydroxylated vitreous silica particles a clear brittle-to-ductile transition is found in the size range of 500 â 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 . By ex situ Raman spectroscopy the observed plasticity is found to be accommodated by structural densification . In the TiO2
system the influence of crystallinity was studied: Single-phase nanocrystalline (nc) anatase or rutile particles were obtained by annealing . 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.
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