Ultrasonic atomization for uniform dispensing and coating of nanoparticles
Ultrasonic atomization for
uniform dispensing and
coating of nanoparticles
by Joseph Riemer, PhD, Sono-Tek Corporation, Milton, New York, USA
Ultrasonic atomization nozzle operat-
median droplet size.
Ultrasonic atomization is a
ing principle
proven spray-coating technol-
Ultrasonic nozzles operate by converting a
Unique advantages for
ogy of unmatched functional
high frequency electrical signal, fed into two
nanotechnology
and economic performance,
electrodes sandwiched between two piezo-
When conventional mixing devices and
especially for applications
electric transducers,
pumps are used for dispensing nanopar-
where expensive chemical
resulting in mechanical expansion and
ticles, the particles tend to agglomerate
contraction of the transducers. This causes
solutions and suspensions
and separate from the liquid suspension.
vibrations to be sent down the nozzle’s
are accurately and uniformly
Technology such as Sono-Tek’s SonicSyringe
titanium horn, ultrasonically vibrating at
deposited on substrates.
imparts ultrasonic energy while dispensing
the nozzle’s atomizing tip. Liquid emerging
the suspension to the spray coating nozzle,
The technology’s unique
onto the atomizing surface is broken into a
which breaks down and eliminates agglomer-
advantage is based on two
spray by the ultrasonic energy concentrated
ates that have formed during earlier han-
features—its ability to gener-
there. This ultrasonic nozzle design provides
dling. The SonicSyringe keeps the nanopar-
ate very small droplets of an easily controllable atomized spray that
ticles continuously suspended in a uniform
an extremely narrow range cannot clog because of the large liquid feed
and homogenous mixture, thus guarantee-
diameter size, and its ability
orifice and the self-cleaning ultrasonic vibra-
ing a steady state dispensing process.
to apply these droplets gently
tion.
When conventional coating technolo-
on the substrate with mini- gies (e.g. pressure spray coating, spinning
mum ‘bounce back’ from the
Droplet size
disc coating and web printing technologies)
target surface. These features
In an ultrasonically produced spray, droplet
are used to coat nanoparticles on substrates,
enable superior transfer
size is governed by the frequency at which
their uniformity control is limited, and the
coefficients when compared
the nozzle vibrates, and by the surface ten-
amount of nanomaterial that must be used
with conventional coating
sion and density of the liquid being atom-
is excessive and costly. Ultrasonic spray
ized. Frequency is the predominant factor.
technologies, providing high-
nozzles, however, are capable of uniformly
The higher the frequency, the smaller the
quality functional coatings
at significantly lower cost of
goods sold (COGs).
This paper describes ultra-
sonic atomization principle
and its unique advantages for
nanotechnology.
Keywords: Ultrasonic
Atomization, Liquid Dopant,
Flux Application
Adopted from a presentation at the
National Nano Engineering Conference,
Figure 1. Ultrasonic atomization nozzle.
Boston MA , November 12, 2008
22 – Global Solar Technology – November/December 2008 www.globalsolartechnology.com
issue_2.1.indd 22 2/22/09 9:40:01 PM
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