Keywords: hydrophobic coating, radome coating, rain attenuation,
rain fade, signal loss, super hydrophobic, improved satellite reception,
Ku Band, Ka Band, Fluorothane.
Note: See Fluorothane for hydrophobic
and super-hydrophobic aircraft, marine and ground radome coatings. See FluoroPel
for fluoropolymers and FluoroSyl for flluorosilanes.
Chlorine Corrosion Test For Fluorothane ME and MS On Acrylic Painted
SMC Panels and Reflectors
Description: This chlorine corrosion test follows in part the International
Electrochemical Commission guidelines in IEC68-2-60 . Surfaces are exposed
to in excess of 75 micrograms of chlorine gas per cubic meter at 75% relative
humidity for 10 days. Chlorine concentration is validated by the the weight
increase of copper chloride on clean copper coupons.
Substrate: SMC panels and reflectors were painted with white acrylic
paint and dried. The panels were then spray painted with Fluorothane ME
or MS using gravity feed HVLP spray equipment. Dynamic pressure was 35 psi,
feed was 2, and fan out was set to full width (1/3 turn). HVLP gun was held
6 inches from substrate, moved at 6 inches per second, with 10% overlap.
Reflectors were coated with ME or MS using automated HVLP equipment with
similar parameters. The coated substrates were allowed to cure at least
48 hours. Reflectors were then sawed into sections for this and other testing.
Drop roll-off angles at 20 locations on the panel were less than 2 degrees,
corresponding to receding contact angles of 140 to 170 degrees.
After curing, one corner of each panel and section was cross-scored with
a razor blade through the coating and acrylic paint every half inch in a
4 inch square pattern. A two inch band along an opposite edge was also abraded
by placing a 2 inch diameter one pound weight on a paper towel and dragging
it across the panel adjacent the edge. Drop roll-off angles at 5 locations
on the abraded areas were still less than 2 degrees.
Corrosion Test: Coated substrates and 1.3 square decimeter copper
coupons were placed in a 0.1 cubic meter chamber containing one pound of
calcium hypochlorite and a vessel of water. The chamber was sealed for 10
days and maintained between 68° and 72°F.
After the exposure period, the coated substrates and copper coupon was removed
from the chamber and allowed to air out for one hour. Even after an hour,
the odor of chlorine was very strong from the panels and reflector sections.
The unpainted back side of the substrates was coated with a fine powder
of disintegrated SMC resin. The copper coupon indicated that the average
chlorine concentration was over 3 times the IEC severity 3 recommendations
of 60-75 micrograms per cubic meter.
Evaluation: The substrates appeared to have ambered slightly in the
chlorine atmosphere, but it was not obvious whether the white acrylic, the
Fluorothane ME and MS or all coatings were effected. Roll off angles taken
after airing out for 30 minutes at 20 evenly spaced locations were less
than 2 degrees.
The substrates were then challenged with 10 inches of rain per hour for
24 hours. Roll off angles for all locations except the abraded area were
less than 2 degrees. The abraded areas showed roll-off angles of 10 to 15
degrees, corresponding to contact angles of 120 to 130 degrees. The cross-cut
area showed no delamination or loss of contact angle.
Conclusion: Fluorothane ME and MS were functionally uncompromised
by the extremely corrosive chlorine atmosphere and can be expected to perform
well in many other corrosive environments. The results of abrasion were
no better or worse than those observed using fresh panels that have not
been challenged by adverse environmental conditions. Scored areas and unabraded
areas showed no evidence of erosion or water penetration.
Cytonix Corporation
8000 Virginia Manor Road
Beltsville, MD 20705
phone: (888) CYTONIX or (301) 470-6267
fax: (301) 470-6269 or email: emailbox@cytonix.com
