Electrolytic cathodic reduction

Diana Hamann <dhamann2000 [at] yahoo__com__ar> writes

>I am a BS in Chemistry and work in conservation in a museum for
>History, which preserves a large collection. As part of my Master
>studies, I'm carrying out an indoor air corrosivity determination,
>following the method outlined in the ISO standard 11844-2 (2005)
>(Corrosion of metals and alloys--Classification of low corrosivity
>of indoor atmospheres--Part 2: Determination of corrosion attack in
>indoor atmospheres), by electrolytic cathodic reduction.
>
>...
>So my question is: Is there an optimal way to connect the probes as
>the working electrode, in a standard three-electrode cell? (since
>welding a connector can affect or disrupt the corrosion film).

I am doing regularly this type of environmental evaluation; See

    Impact of the environmental conditions on the conservation of
    metal artifacts: an evaluation using electrochemical techniques
    <URL:http://www.padfield.org/tim/cfys/mm/index.html>

I would be glad to discuss further details with you later. But
concerning your question about how to connect the working electrode
in a 3-electrode arrangement, you can do it simply using a crocodile
clamp (that shall of course be kept outside of the electrolyte!).

The important thing when measuring tarnishing thickness is to have a
well defined area in contact with the electrolyte. This can be
obtained by limiting the area of the surface exposed to the
solution, either by immersing a defined part of your sample, or by
applying a varnish to mask part of it. In this way the electrolytic
reduction of the tarnish layer can be expressed in charge per unity
of area (Coulombs/mm2). At that point, knowing the chemical nature
of the reduced product, you can apply the Faraday's law (Q=nFM) to
determine its mass and further use its density value to calculate
the equivalent thickness. Last, I would not weld a contact, since
the heat generated by the procedure could disturb the tarnish film.

Virginia Costa
Conservare - France


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                  Conservation DistList Instance 21:60
                    Distributed: Friday, May 9, 2008
                       Message Id: cdl-21-60-001
                                  ***