Particles quasi-spherical

Altliough tire majority of studies on model colloids involve (quasi-) spherical particles, tliere is a growing interest in the properties of non-spherical colloids. These tend to be eitlier rod-like or plate-like. 

High-resolution transmission electron microscopy (HREM) is the technique best suited for the structural characterization of nanometer-sized graphitic particles. In-situ processing of fullerene-related structures may be performed, and it has been shown that carbonaceous materials transform themselves into quasi-spherical onion-like graphitic particles under the effect of intense electron irradiation[l 1],... 

Fig. 2. HREM image of a quasi-spherical onion-like graphitic particles generated by electron irradiation (dark lines represent graphitic shells, and distance between layers is 0.34 nm).

The progressive ordering from the surface to the center has been experimentally observed in the case of the electron irradiation-induced formation of the quasi-spherical onion-like particles[25]. In this case, the large inner hollow space is unstable under electron bombardment, and a compact particle (innermost shell C( ) is the final result of the graphitization of the carbon volume (see Fig. 3e-h). 

Fig. 3. Schematic illustration of the growth process of a graphitic particle (a)-(d) polyhedral particle formed on the electric arc (d)-(h) transformation of a polyhedral particle into a quasi-spherical onion-like particle under the effect of high-energy electron irradiation in (f) the particle collapses and eliminates the inner empty space[25j. In both schemes, the formation of graphite layers begins at the surface and progresses towards the center.

We hope that macroscopic samples of quasi-spherical onion-like particles will soon become available, and then we will be able to characterize these systems in detail. Probably a new generation of carbon materi-aks can be generated by the three-dimensional packing of quasi-spherical multi-shell fullerenes. 

Fig. 9.23 SEM images of monodisperse silver powders obtained by reduction of AgNOj in ethylene glycol in the presence of PVP (a) quasi-spherical particles obtained by spontaneous nucleation (dm = 0.64 pun, cr = 0.13 p.m) (b) rodlike particles obtained by heterogeneous nucleation using H2PtCl6 as nucleating agent (particle dimensions 3 xm long and 0.3 xm thick). (From Ref. 13.)...

In synthetic materials, the surface organization also depends on the internal structure of particles. Carbon black is good example. Figure 5.11 shows the models of carbon black primary particles. The most recent model developed by Hess, Ban and Heidenreich is commonly accepted as being characteristic of carbon black particles. The particle is composed of small elements which are interconnected to form quasi-spherical parti-... 

PbS/polyacrylonitrile nanocomposite which consists of quasi-spherical PbS particles of 8nm in diameter, homogeneously dispersed and well separated in the polymer matrix. The polyacrylonitrile was chosen, being a good heat-insulator and an aging-resistive material. To provide an homogeneous system, in which the reactants are well mixed at the molecular lever, and to ensure the presence of solvated electrons, absolute ethanol was used as solvent [2] ... 

The first carbon onions were synthesized in arc discharge experiments by lijima. It was demonstrated that the condensation of carbon vapor results in the formation of not only single-shell fullerene molecules but also of multishell fullerenes (i.e., carbon onions). It was proposed that quasi-spherical spiral-like particles could be intermediates for the formation of carbon onions via condensation of carbon vapor. - The close value of the diameter of the innermost shells of these carbon onions to the diameter of the Cgo fullerene molecule suggested the idea that another possible candidate for growth centers for carbon onions can be fullerenes themselves. ... 

BiFeOs (BFO) Hydrothermal (HTMW) Adapted microwave oven The microwave reaction was carried out at 200 C for 5,15,20, 30, 40,50, 60,70, and 80 min All samples are mostly composed of particles with a quasi-spherical morphology... 

DIELECTRIC PROPERTY OF THE ER SUSPENSIONS OF SPHERICAL OR QUASI-SPHERICAL PARTICLES... 

Ferroelectric order in single ferroelectric domain BaTiOs nanoparticles has been examined recently by Polking et al These particles were also prepared through solvothermal methods, using a two-phase approach. The reaction conditions were altered to prepare nanocubes and quasi-spherical nanoparticles. Abberation corrected transmission electron microscopy has probed the ferroelectric structural distortions in these nanoparticles. In conjuction with off-axis electron holography, which maps the electric fields created by atomic displacement, this has resulted in direet imaging of the ferroeleetrie polarisation. 

---