Final Report - Strategic Environmental Research and Development ...

of the coated sample, which is tightened down with the help of a plastic coated C-shaped
stainless steel sheet and four screws. All tubing and tubing accessories are made of stainless steel.
The setup also has an environmental chamber made of polycarbonate, which is attachable on top
of the sample holder. This chamber is sealed against the sample holder using an o-ring. The
relative humidity of the air flowing through the chamber can be controlled by the solution in
washing bottles and is measured by a sensor in a downstream mini-chamber. Unless otherwise
noted, water saturated air is pumped through the chamber using an aquarium pump and two
washing bottles during all BT experiments.
The environmental chamber has a quartz window in the upper face to allow viewing and
recording of the blister growth with a CCD camera attached to a face-down stereoscopic
microscope (SZX12 OLYMPUS). The syringe pump is controlled by a program written in
DasyLab software. The BT can be set up to run in Constant Infusion (CI) rate mode or Constant
Pressure (CP) mode. The infusion/withdrawal rates, target pressure and other variables can be
adjusted in the program. Unless otherwise mentioned, all the CI experiments used an infusion
rate of 0.050 mL/h, with DI water as the pressurizing fluid.
Stereoscopic
Microscope
r
Pressure control
Program and frame
grabber
Environmental
Chamber
Coating
Substrate with throughhole
(AA 2024-T3)
Pressure transducer
Sample holder
Fluid
Syringe pump
5.4.3.2 The Galvanic Blister Test
Figure 4.1. Schematic of the Blister Test.
The Galvanic Blister Test (GBT) is a CPBT where the pressure is achieved by a column of 5
wt% NaCl inside a SS316 tube that is galvanically coupled to the sample. The sample holder is
placed upside down to avoid gas accumulation at the surface, which would disrupt the
electrochemical reactions taking place in the system. A chloridized silver wire is used as
reference electrode. The electrolyte is circulated through the system using a fixed-flow peristaltic
metering pump (Fisher Scientific) at a rate of 37 L/hr to avoid gas bubble accumulation.
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