Hydrogen permeation is a phenomenon that introduces defects due to hydrogen penetration and hydrogen accumulation in the bulk of the material alloy. It is encountered during electrochemical processes that involve hydrogen evolution, such as electroplating, corrosion or cathodic protection. Hydrogen tends to accumulate in areas of high stress and can reach critical concentration causing cracks to occur which in turn compromises the mechanical integrity of the structure. The test is described in ASTM G148.
The electrochemical cell used for this type of experiment is the so-called Devanathan-Stachurski permeation cell. The cell is comprised of two individual electrolytic cells, filled with electrolyte solution, separated with a membrane made from the material to be investigated. Two potentiostats need to be connected to the sample (the membrane), so floating potentiostats need to be used.
‘Floating’ potentiostats are isolated from earth-ground. This allows them to be used to study grounded electrodes or solutions (such as autoclaves or rebar). Multiple earth-ground points can generate ground loops, which can cause oscillations and result in untrustworthy, unpredictable data. The PARSTAT4000+, VersaSTAT3F, PARSTAT MC and ModuLab are all capable of operating in ‘Floating’ or ‘Isolated’ mode.
We have recommended the use of our VersaStats for this application. On the generator side (production of hydrogen -cathodic compartment-), it is not required to have a highly sensitive instrument. On the detector side (anodic compartment), small amounts of hydrogen penetrating through the membrane need to be detected. The corresponding current will be quite low. A very sensitive potentiostat is required for this compartment. While our instrumentation natively provides both the accuracy and resolution to measure low current extremely well; the VersaSTAT-LC (Princeton Applied Research) and ModuLab Femto Ammeter (Solartron Analytical) hardware options expand to industry-leading capability.