Cadmium Substitution - garteur

GARTEUR LIMITED
ANNEX G
Resistance to aircraft chemicals
G.1 Introduction
During an aircraft's operational life it comes into contact with a large number of
chemicals and fluids. These include aviation fuel, engine oils and hydraulic fluids as well
as cleaners and paint strippers used in the maintenance and repair of protective
treatments. The aim of the work described below was to establish whether any of the
cadmium replacements being investigated were likely to degrade on prolonged contact
with some of the commonly used aircraft chemicals.
G.2 Test procedures
Studies of the resistance of replacement coatings to aircraft fluids were carried out by
British Aerospace and Shorts. Details of the fluids examined by each of the organisations
are given in table G1.
G.2.1
British Aerospace
All specimens were subjected to immersion in the above fluids for a period of 7 days.
Following immersion the panels except for the water and Propanol were wiped clean with
a clean cloth moistened with Petroleum spirit and left to dry. The remaining panels were
wiped with a dry clean cloth. On completion of above the panels were visually assessed
using x10 magnification before carrying out microscopic evaluation using an optical
microscope.
G.2.2
Shorts
G.3 Results
Coated panels 100 x 150mm were immersed in the various fluids identified in table G1.
The panels were inspected daily for signs of corrosion attack, coating removal and colour
changes.
Tables G2 and G3 summarise the results obtained from the B.Ae and Shorts studies.
Several of the coatings investigated, including electrodeposited cadmium, were found to
be susceptible to corrosion attack when in contact with the aircraft cleaner Turco 5948.
For ED Zn/Ni (passivated and non-passivated) the cleaner starts to remove the coating
within 24 hours whilst for ED Cadmium (passivated and non-passivated) some attack is
apparent after 500h immersion.
Data presented in table G3 further indicate that Skydrol has a detrimental on both
electrodeposited cadmium and zinc-cobalt-iron coatings. In each case a significant
weight loss was recorded.
G.4 Conclusions
Most of the replacement coatings examined failed to show any significant degradation on
exposure to a range of chemicals used on aircraft. Exceptions were ED zinc-nickel
coatings in contact with Turco 5948 and ED zinc-cobalt coatings immersed in Skydrol
hydraulic fluid. Cadmium plating was also found to be degraded by these fluids.
G.5 Tables
GARTEUR SM/AG17 TP128 Page 89