Tech Briefs Magazine - August 2021 - 26

Materials & Coatings
segregation-driven gel. Instead of de -
signing nanoparticles to remain at the
interface between the two solvents, their
chosen particles concentrate within one
of them. While these particles tend to
repel one another, the particles' affinity
toward one of the solvents is stronger
and keeps them together in the channel.
The resulting gel could be far easier to
create, as its two solvents are essentially
oil and water and its nanoparticles are silicon
dioxide - essentially tiny spheres of
common quartz. It also could have a variety
of industrial uses. The gel is thermoreversible,
which refers to an optical
property that the finished SeedGel possesses:
It can switch from transparent to
opaque and back again just by changing
its temperature. This property could be
harnessed in smart windows that sandwich
a thin layer of the gel between two
panes of glass or in sensors.
Because the team's gel-creation ap -
proach could be used with other solvent-and-nanoparticle
combinations, it
could become useful in filters for
water purification and possibly other
filtration processes, depending on
what type of nanoparticles are used.
The creation approach allows for the
size of the channels within the gel to
be tuned by changing the rate at which
the temperature changes during the
formation process.
For more information, contact Chad Bou tin
at charles.boutin@nist.gov; 301-975-4261.
New Spraying Method for Producing Ceramic Coatings
High-quality coated components can be integrated into complex systems in a sustainable way.
University of Bayreuth, Bayreuth, Germany
he production of ceramic coatings
has only been possible by
means of sintering techniques conducted
at more than 1,000 °C. A new spray -
ing method called Powder Aerosol
Deposition (PAD) enables their production
at normal room temperatures. It is
therefore highly attractive for industrial
applications.
With PAD, dense ceramic films can be
applied to very different types of materials
such as steel, glass, silicon, or even
plastic. To achieve this, a dry ceramic
powder is first converted into an aero sol
- i.e. a mixture of gas and solid particles
- with the aid of a carrier gas. The
aerosol is then transported into a vacuum
chamber and accelerated to several hundred
meters per second through a nozzle
and directed onto the material to be coated.
On impact, the tiny ceramic particles
fracture. The resulting fragments, only a
few nanometers in size, feature fresh,
active surfaces. They form tightly adhering,
dense coatings with a thickness of
between 1 and 100 micrometers.
Because of their dense microstructure,
the coatings already exhibit excellent
mechanical properties even directly
after deposition. They are extraordinarily
hard and have good chemical resis -
tance; however, some functional properties
of the coatings, especially electrical
conductivity, proved inadequate without
carrying out further steps.
Crystalline structures are of crucial
importance in this context. The strong
impact of the ceramic particles on the
materials causes structural defects in the
resulting fragments. This not only af fects
electrical conductivity but also oth er functional
properties. Using a thermal postT
Vacuum
pump
26
Cov
Programmable x-y stage
with substrate table
Aerosol jet
Deposition chamber
with separated
compartments
Carrier gas supply
with mass flow
controllers
Aerosol chamber
with powder on
vibrating table
MFC
MFC
Operation of the Powder Aerosol Deposition (PAD) method.
treatment, or tempering, these defects
can be almost completely eliminated.
The type of ceramic materials pro cessed
depends on the intended technological
applications; for example, dielectric ce -
ramics are suitable for capacitors, electrically
conductive functional ceramics are
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ToC
preferred for sensors, and yttrium-stabilized
zirconium oxide is used in high-temperature
fuel cells. Even lithium-ion batteries
can be produced in this way.
For more information, contact Christian
Wissler at christian.wissler@uni-bayreuth.
de; +49 (0)921 55 5356.
Tech Briefs, August 2021
Carrier gas 1
Carrier gas 2
Carrier gas 1

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Tech Briefs Magazine - August 2021

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