Page 63 - Nanotechnology an introduction

where m and d are, respectively, the mass and diameter of the object), one may refer to a powder (or an ultrafine powder or a nanopowder if the
smallness of the objects needs to be explicitly stated, or indeed “nanoscale granular material”). If the objects attract each other weakly, one may
refer to an agglomerate; typically the external surface area of an agglomerate is similar to the sum of the surface areas of the individual objects
comprising it. If the objects are strongly bonded to one another one may refer to an aggregate (typically the external surface area of an aggregate is
significantly smaller than the sum of the surface areas of the individual objects prior to aggregation). In terms of interaction energies (Figure 4.4),
the particles in an agglomerate are separated by a distance , and those in an aggregate by a distance .
If a material comprises two or more distinct phases, if one or more dimensions of the zones of the phases are in the nanoscale one may refer to a
nanostructured material. Certain alloys would fall into this category but not, presumably, solid solutions.
If nano-objects are dispersed into a continuous medium (matrix), one may describe the result as a nanodispersion. Depending on the states of the
objects and the matrix, different terms are used to describe them (see Table 6.1).
Table 6.1 The ontology of nanodispersions
State of the nano-objects
Matrix
Solid Liquid Gaseous
Solid Nanocomposite a – Nanofoam b
Liquid Nanosuspension c Nanoemulsion Nanofoam b
Gaseous Aerosol Aerosol –
a
Other materials falling into this category are nano-alloys, metal–matrix composites, etc.
b These materials may be described with the adjective “nanoporous” (or, in French, using the noun “nanoporeux”).
Nanofluids are included here (Section 6.5.4).
c
The remainder of this chapter firstly covers the fabrication of the various kinds of nano-objects mentioned above, except for carbon-based
materials, which are dealt with in a separate chapter (9) because of their unique importance and versatility. Secondly, the fabrication of composites
is described.