Page 612 - Book Hosokawa Nanoparticle Technology Handbook

APPLICATIONS 39 INSTANTANEOUS NANOFOAMING METHOD FOR FABRICATION OF CLOSED-POROSITY SILICA PARTICLE
nanofoaming in the present case. Fig. 39.2 shows
TEM images of the foamed silicas which were
instantaneously heated at various temperatures
ranging from 500 to 950 C. At 500 C, the shape of
each cell was not completely spherical. The foaming
behavior was enhanced with the temperature for the
instantaneous heat treatment. Both the average size
of the balloons and total pore volume are seen to
increase with the temperature.
In addition to the nanoscopic size of the balloon,
the high fraction of the closed pores is to be stressed
as an important structural feature of the foamed silica.
Fig. 39.3 shows nitrogen adsorption isotherms at 77 K
of the foamed silicas obtained by instantaneous heat-
ing at various temperatures from 500 to 950 C. On the
whole, the adsorbed amount of nitrogen for a unit
weight of the foamed silica increased with the tem-
perature for instantaneous heating. This tendency cor-
responds to the enhancement in the extent of the
foaming behavior. The amount of the cell which was
Figure 39.1 directly linked to the outer surface of the foamed sil-
Typical TEM image of nanofoamed silica. ica particles increased with the extent of the foaming.

(b) (c)
100 nm

(a) 200 nm 500 nm

(f)
(d) 100 nm
(e)

100 nm
200 nm

Figure 39.2
TEM images of nanofoamed silica. The foaming was carried out at various temperatures of instantaneous heat treatment as
given below: (a) 500 C, (b) 600 C, (c) 700 C, (d) 800 C, (e) 900 C, (f) 950 C.

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