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Assembly--Gas-flow Overview and Terminology
Oxygen is an electrochemically active gas. Its reduction can act as the cathodic half-reaction in a corrosion
reaction. You probably want to remove oxygen from the solution whenever the real-world corrosion system that
you are modeling is oxygen-free.
Remove oxygen from the test solution by bubbling nitrogen, or another electrochemically inert gas, through the
solution. This process is often (imprecisely) called deaeration. It is more correctly called deoxygenation. At least
half an hour of vigorous bubbling with nitrogen is required to remove most of the oxygen from a test solution.
Bubbling gas through your test solution can cause noise while you are running your experiment. To avoid this
noise, you can stop gas purging during the data-acquisition phase of your experiment. Instead, flow the inert
gas over the top of the test solution, often referred to as "blanketing" the cell. In general, blanketing is used
after solution purging, where blanketing prevents acquiring new oxygen from the gas above the solution.
Many modern electrochemical test systems include automatic control of gas flow in their experimental
sequencing. This is true of Gamry Instruments' PV and PHE software. These sets of software generate a digital
signal that is intended to control a solenoid valve, which in turn routes gas flow to the cell. Gamry's
VistaShield™ Faraday cage, when equipped with a Purge and Stir option, provides a complete solution for
purge gas control.
Pre-saturation of the Purge Gas
Bubbling dry purge gas through your cell electrolyte can cause significant evaporation of the electrolyte's solvent
during the purge process. This can be a significant source of error in some experiments. This problem can often
be avoided by pre-saturation of the purge gas with the electrolyte prior to it entering the cell. This is commonly
done using a "gas washing bottle," which can be obtained at most laboratory supply companies.
The MultiPort does not include a gas washing bottle, because they are already available in many laboratories.
Gas Dispersion Tube
In the MultiPort, gas-flow control is via a gas dispersion tube that fits a 24/40 standard taper. At Gamry, we
often refer to the gas bubbler assembly as a three-way adapter, because it can be used to implement three
functions: purge, blanket and vent.
Figure 4
Gas Dispersion Tube
The vent function is critical. Regardless of whether gas is flowing through or over the test solution, you must
provide a way for it leave the cell. If you do not, the gas may not flow, or worse, the cell may burst apart
unexpectedly. Not providing a vent for the escape of purge gas is a very common and often dangerous
"mistake" made when setting up an electrochemical cell.
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