Cadmium Substitution - garteur

GARTEUR LIMITED
the salt spray was adjusted to pH 3 with acetic acid whilst at NLR the pH of the test
solution used was kept at pH 5.
C.2.1.3
Exposure to 100% humidity
Coated test panels were exposed to 100% humidity according to ASTM D2247 [C4]. The
temperature of the saturated air in the cabinet was maintained at 38+1 o C throughout the
2000 hours exposure period. The test panels were inspected on a regular basis for signs
of white rust and the onset of red rust.
C.2.2
Outdoor exposure trials
Outdoor exposure trials on coated panels were carried out at four sites as follows:-
• DERA Fraser, Portsmouth, England
• British Aerospace, Warton, Preston England
• Fokker, Schiphol, The Netherlands
• NLR, NE Polder, The Netherlands
At each site specimens were placed on racks inclined at an angle of 45 o to the horizontal
and facing due south. The sky ward faces of the panels were inspected at least once a
month for signs of corrosion and general degradation.
Two of the sites, DERA Fraser and NLR NE Polder, are close to open sea whilst the
British Aerospace site is some distance from sea. The Fokker site is in land adjacent to
Schiphol Airport.
C.2.3
C.2.3.1
Electrochemical measurements
Polarisation sweeps
Anodic and cathodic polarisation sweeps were carried out on small test electrodes cut
from the coated panels. Details of the manufacture of the test electrodes used at DERA
are given in reference [C5] together with the design of the test cell and the scan rate etc.
employed. Research at NLR used a modified flat cell and further details of the test
procedure are described in reference [C6].
C.2.3.2
Potential-time measurements
The open-circuit potential of each coating system was determined by immersing small
test electrodes prepared from coated test panels in quiescent sodium chloride solution.
The change in open circuit corrosion potential was monitored over a period of several
hours using a reference electrode. The laboratories carrying out these measurements
looked at the effects of sodium chloride concentration and pH on the potential. More
detailed information is included in references [C6,C7 and C8].
C.2.3.3
Scratch-Model electrochemical measurements
The Scratch-Model approach was developed at DERA to model the situation that may
arise in a coating scratch, where a small area of the steel becomes exposed to the
environment. Precise details of the specimen construction have been published in the
literature [C9]. The experimental arrangement employed in the present work is illustrated
in figure C1. Briefly a steel strip (1mm x 20mm) was positioned on a glass slide. On
either side of this was positioned coated, steel coupons (20mmx20mm). The assembly
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GARTEUR SM/AG17 TP128