Geoscience Reference
In-Depth Information
affect energy consumption and a low temperature leads to “soft processing.” A sig-
nificant example is biological processes that produce magnetite oxides at room
temperature.
The solution process also has merit in that some unique inorganic materials can
be synthesized only by this process. There are many kinds of processes related to
soft solution processing, and the important ones are soft solution electrochemical
process,
gel processing, hydrothermal technique,
coprecipitation, emulsions, the polymerizable complex method, biomimetic, sol-
vothermal, self-assembly, wet chemical processing, templating, and so on.
Development of simple patterning methods with nanometer resolution, acceleration
of kinetics of synthesis, framing (deducing) the theoretical approaches to the growth
of materials from solutions, and the development of in situ observation techniques
are some examples of emerging research subjects. One of the most important tech-
nological issues of the soft solution processing is its integration with functional
device technology, because the possibility of fabrication of a variety of materials
and microstructures from solutions has been already been demonstrated. In these
processes, solutions are always used and therefore, many factors, such as pH, con-
centration, ligand type, temperature, and electrode potential, are controlled in order
to design advanced materials. Additionally, the technique using the solution flow
may be used to synthesize various single phase and multilayered thin films and this
is an important step in the application of soft solution processing in the technology
of the future integrated functional devices. From this point of view, fabrication of
ceramic thin films in the solution flow in the recycled system
[432]
, below 200
C, is
very important. In this connection, a flow cell for hydrothermal
liquid phase deposition, sol
electrochemical
synthesis and its applicability to fabricate single phase thin films, as well as multi-
layered structures in the system BaTiO
3
SrTiO
3
, has been demonstrated by
Yoshimura and coworkers
[31,37,295,296]
. The technique using the solution flow
under the hydrothermal
electrochemical conditions is an important step in the inte-
gration of the solution processing with the functional devices technology and may
find applications for various single and/or multilayered thin films.
During the twenty-first century, hydrothermal technology, on the whole, will not
just be limited to the crystal growth, or leaching of metals, but it is going to take on
a very broad shape, covering several interdisciplinary branches of science. Therefore,
it has to be viewed from a different perspective, as it offers several new advantages,
like homogeneous precipitation using metal chelates, decomposition of hazardous
and/or refractory chemical substances, monomerization of high polymers, like poly-
ethylene or tetraphthalate, and other environmental engineering and chemical engi-
neering issues dealing with recycling of rubbers and plastics instead of burning.
Further, the growing interest to enhance the hydrothermal reaction kinetics using
microwave, ultrasonic, mechanical, and electrochemical reactions will be distinct
[433]
. Also, duration of the experiments is being reduced at least by two orders of
magnitude which, in turn, makes the technique more economic. With an ever-
increasing demand for composite nanostructures, the hydrothermal technique offers a
unique method for the coating of various compounds on metals, polymers, and cera-
mics, as well as the fabrication of powders or bulk ceramic bodies.
