The properties of particle ensembles are defined by a complex multidimensional parameter space, namely particle size, shape, surface, structure, composition and their distributions. Macroscopic product properties are a direct result of these disperse particle properties. Therefore, the comprehensive multidimensional characterization of particle ensembles is a key task in any product design. However, the determination of complex property distributions is major challenge. We provide a broad overview of the current tools for multidimensional particle characterization. First, the mathematical handling of multidimensional (nD) property distribution is outlined as a necessary framework for the correct handling of nD particle size distributions (PSDs). Then, well-established techniques as well as recent developments with the potential to extract nD property distributions are reviewed. Exsitu imaging techniques like electron tomography or Raman spectroscopy with AFM co-localization, for instance, provide a resolution on the level of single particles but are limited in terms of sample statistics. A particular focus lies therefore on methods in the gas and the liquid phase, which provide multidimensional particle properties either directly or by a combination of one-dimensional techniques.
The central concern in the fabrication of carbon nanotube (CNT) reinforced metal composites is the well balance between uniform dispersion and structural integrity of CNTs. Rapid and uniform self-assembly of CNTs and spherical Aluminum (Al) particles into a core-shell structure is realized by a smart mechanical powder processing. The factors influencing the dispersion uniformity and structural integrity of CNTs during the processing are studied, including the size of Al particles, mixing speed and mixing time. It is revealed that a size of 35 μm is preferred for the Al particles to tear apart the CNT clusters and obtain a uniform dispersion of CNTs on Al surface. Different composite states, CNTs are singly dispersed, thickly wrapped, or embedded in the Al particles, can be obtained by changing the mixing speed. Well coordination between the CNT dispersion homogeneity and structural integrity could be achieved under suitable processing condition. Therefore, it can be adopted as an efficient and intelligent technology to achieve the desired performance in CNT/Al composites.
Recently, various types of functionalized metal oxide nanoparticles have been used for many applications because of their unique chemical and physical properties. To synthesize metal oxide nanoparticles, liquid-phase synthesis techniques have been developed. The production process of metal oxide nanoparticles in aqueous media is extremely complex because the formation, crystal structure, crystallinity, chemical composition, and morphology of the particles are considerably dependent on the preparation conditions (e.g., anion and cation concentrations and species, additives, solution pH, and reaction temperature and time). Accordingly, clarifying these effects is fundamental to accurately understand the formation mechanism of metal oxide nanoparticles to further develop new functionalized nanoparticles. In this review, the influence of anions (Cl–, SO42–, and NO3–) and cations (Ni2+, Cu2+, and Cr3+) on the formation and structure of iron oxide nanoparticles in aqueous media is described.
The synthesis of noble metals and their alloy nanoparticles by laser-induced nucleation is described. Femtosecond laser pulses with an energy on the order of mJ were tightly focused to create an intensity of 1014 W/cm2 or more in an aqueous solution of noble metal ions. The intense laser field generated solvated electrons and hydrogen radicals that have a highly reducing ability, resulting in nucleation through the reduction of the noble metal ions and particle growth through ripening. This laser-induced nucleation method can be performed without any reducing agents. Excess irradiation of chloroauric acid solution led to the formation of a stable colloidal solution of gold nanoparticles without any surfactants. Additionally, the irradiation of a mixed solution of different noble metal ions formed solid–solution alloy nanoparticles, even though these metals were immiscible in the bulk. Moreover, the laser-induced nucleation made it possible to form quinary solid-solution alloy nanoparticles of noble metals. The mechanism of superior catalytic activity found for alloy nanoparticles by using Rh–Pd–Pt solid–solution nanoparticles is discussed in terms of elemental distributions inside the particles.
The grain sizes can significantly influence the granular mechano-morphology, and consequently, the macro-scale mechanical response. From a purely geometric viewpoint, changing grain size will affect the volumetric number density of grain-pair interactions as well as the neighborhood geometry. In addition, changing grain size can influence initial stiffness and damage behavior of grain-pair interactions. The granular micromechanics approach (GMA), which provides a paradigm for bridging the grain-scale to continuum models, has the capability of describing the grain size influence in terms of both geometric effects and grain-pair deformation/dissipation effects. Here the GMA based Cauchy-type continuum model is enhanced using simple power laws to simulate the effect of grain size upon the volumetric number density of grain-pair interactions, and the parameters governing grain-pair deformation and dissipation mechanisms. The enhanced model is applied to predict the macroscopic response of cohesive granular solids under conventional triaxial tests. The results show that decreasing grain-sizes can trigger brittle-to-ductile transition in failure. Grain size is found to affect the compression/dilatation behavior as well as the post-peak softening/hardening of granular materials. The macro-scale failure/yield stress is also found to have an inverse relationship with grain-sizes in consonance with what has been reported in the literature.