FY2010 - Oak Ridge National Laboratory

Seed Money Fund—
Environmental Sciences Division
decontamination power. The repetition rate of laser firing (10–20 Hz) was too slow to generate stable
seed for NTP production based on emissions spectroscopy and the current measured on charged particles.
Also, we had no laser that could fire faster than 20 Hz to confirm our initial hypothesis.
CWA simulant–contaminated samples of the composite C-17 material, 12 4 in. in size, were prepared
by adding a known amount of CWA simulant to the surface of the C-17 material. The surface strip of the
sample, which has both clean and contaminated sections, was entirely exposed to the plasma. Plasmatreated
surfaces were visually inspected for crack and color changes, because there is some concern that
exposure to nonthermal plasma will degrade the polymer matrix of the fiber-reinforced composite over
time. This could have led to cracking, color alteration, or changes in the mechanical properties of the
composite material. Thus, extended exposure to NTP (~10 min) served as an upper bound of damage that
could reasonably be expected from repetitive short duration (30 s) decontamination treatments. A digital
image of the samples was taken for detailed computerized image analysis.
A breakdown potential on the C-17 samples was evaluated using a commercial 200 W APNTP instrument
and found to occur at a scanning height of 1.5 cm from the material surface. Since the plasma did not
have a cooling apparatus, the temperature at this distance was 100°C as a result of radio frequency (RF)
heating on the head that also heated the plasma. Field operation should include a cooling component.
Subsequent reduction of the RF power to 150 W mitigated the thermal damage issue, and the temperature
at 1.5 cm was about the room temperature. Decontamination results indicate that the RF-discharge
APNTP was able to remove the simulant completely in 3 min at a rate of ~3.7 mg/min. The removal was
99.997% complete based on follow-on gas chromatography–mass spectroscopy analysis of grab samples,
and three-dimensional topographic imaging showed no sign of damage on the surface.
The aerosol electrometer readings on-line during the decontamination did not indicate an alarming level
of charged particle generation. The readings were comparable or slightly higher than those commonly
found in indoor air. However, the total mass of the particles (assuming the unit density of particles)
generated was calculated to be on the order of femtograms based on the measurement using the Scanning
Mobility Particle Sizer (SMPS ® ), which also showed that the nanoparticles peaked at about 10 nm during
the operation.
The RF-discharge nonthermal plasma is an effective alternative to surface decontamination. The
engineering scale requires additional studies. We were able to accomplish the proposed activities. The
project (funded at $27,000 in FY 2010) has yielded a return of 5.5 fold by wining a SERDP award of
$150,000, which would enable continued research and development of the RF-discharge and other types
of discharge technology to be used for a new APNTP technology for surface cleanup.
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