Geoscience Reference
In-Depth Information
Singlestep
Multistep
Vapor, ion, atom
Firing (sintering)
(pyrolysis)
Vacuum,
gas
processing
Firing
Green body
Materials
(shaped solids)
Solid-state
reactions
Shape forming
Soft solution processing
Interfacial reactions:
Hydrothermal, electro
deposition, etc.,
biomimetic, self-assembly,
templating
Substances
(powders)
Sol-gel
Soft chemistry
Solution
Synthesis
Resources (solids)
Figure 10.3 Schematic diagram of advanced materials processing showing single-step
versus multistep process [18] .
during the crystallization of the fine particles. This marked the beginning of the
study of precursor preparation for different systems, the surface interactions with
the capping agents or surfactants, and polymerized complexes. The surfaces of the
particles could be altered to hydrophobic or hydrophilic depending upon the appli-
cations [19,20] . Today, this approach is playing a key role in nanotechnology to
prepare highly dispersed, oriented, and self-assembled particles. Such an approach
leads to the processing of highly controlled and also self-assembled particles of
even complex and multicomponent materials. Using such an approach, a wide
range of advanced materials like the PZT family of ceramics, ferrites, phosphates,
sulfides, oxides, and HAps and composites have been prepared as fine particles for
technological applications with preferred morphology such as whiskers, rods, nee-
dles, plates, and spheres, depending upon the applications. This precursor-based
chemical approach to hydrothermal synthesis has made tremendous progress in
recent years and also drastically reduced the temperature and the pressure condi-
tions of processing of materials. The addition of surface modifiers also helps to
inhibit the crystal growth that facilitates the smaller particle size with a narrow
particle-size distribution. Figure 10.4 shows the Transmission Electron Microscopy
(TEM) images of nanoparticles synthesized under supercritical hydrothermal condi-
tions [19] . As is clearly seen from Figure 10.4 , those nanoparticles without modi-
fier are aggregated and they do not disperse in the aqueous solvents. Also the
particle size is larger compared to the modified particles. When the pH of the
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