Table of Contents
Advertisement
AssemblyCounter Electrode
Figure 3
Reference Bridge Tube
Many experiments do not require a "true" reference electrode to be run. If a pseudo- or quasi-reference
electrode is sufficient, you do not need to use the reference bridge tube.
Counter Electrode
The standard counter electrode is a plate of high-density graphite. To fit the counter electrode to the cell, clamp
it over one of the end-plate holes (normally the red/orange side).
The graphite plate that is shipped with your ParaCell is spectroscopic grade. It is very pure and is therefore
unlikely to be a significant source of contamination in your initial experiment. However, it is somewhat porous
and can adsorb substances present in your test solution. Reuse of a graphite counter can contaminate your test
solution. The effect is small, and you are unlikely to see it unless the test solution changes drastically between
tests. Any effect can also be ameliorated by sanding the surface with a fine-grit sandpaper.
If this is a concern to you, consider a platinum counter electrode: platinum foil (or a Pt-coated metal sample)
can be substituted in the same way. If you have a a platinum wire or mesh, this can be introduced to the cell
body through one of the threaded holes. Mesh, in particular, may require this to be added before assembly of
the main cell. If you are not using a (counter) electrode on the end plate opposite the working electrode, then
make sure to block that hole with a non-conductive material such as a small square of glass.
Gas-flow Overview and Terminology
Gas dispersion may or may not be required for your experiment. Most of the cases in which you use it involve
the removal of atmospheric oxygen from the test solution.
Oxygen is an electrochemically active gas. Its reduction can act as the cathodic half reaction in a corrosion
reaction. You will probably want to remove oxygen from the solution whenever the real-world 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. Depending on how you
have the cell set up, it may be possible to flow gas over the top of the solution while doing your
11
Advertisement
Table of Contents
