I brought up a simple voltaic couple between a sacrificial magnesium anode
+ 2.47 volts
against a Pd cathode - 0.82 volts (on the electromotive series 3.29 volts
total) based the fact that the pipeline
protection industry has been using a magnesium plate buried in the ground,
wired to the iron
or steel (+ 0.44 volts) pipelines for cathodic protection for over a
century. Apparently the anions keep the
surface of the magnesium clean enough to do the job.
Electromotive Series of Metals
Metal on Formed Potential
Lithium Li +2.96
Rubidium Rb +2.93
Potassium K +2.92
Strontium Sr +2.92
Barium Ba +2.90
Calcium Ca +2.87
Sodium Na +2.71
Magnesium Mg +2.40
Alumunium Al +1.70
Berylium Be +1.69
Manganese Mn +1.10
Zinc Zn +0.76
Chromium Cr +0.56
Iron (ferrous) FE +0.44
Cadmium Cd +0.40
Indium In +0.34
Thallium Tl +0.33
Cobalt Co +0.28
Nickel Ni +0.23
Tin Sn +0.14
Lead Pb +0.12
Iron (ferric) Fe +0.04
Hydrogen H 0.00
Antimony Sb -0.10
Bismuth Bi -0.30
Arsenic As -0.30
Copper (cupric) Cu -0.34
Copper (cuprous) Te -0.56
Tellurium Te -0.56
Silver Ag -0.80
Mercury Hg -0.80
Palladium Pd -0.82
Platinum Pt -0.86
Gold (auric) Au -1.36
Gold (aurous) Au -1.50
I wrote:
>
> Ed. Wouldn't the Cl- ions arriving at the anode dissolve the MgO which is
> acid soluble?
>
> Frederick
>
> Ed Storms wrote:
> >
> > Nice idea, Horace, but you fail to consider one important aspect of
using
> Mg as
> > the anode. Oxygen that forms at the anode will react to form MgO, which
> is an
> > insulator and is insoluble. As a result, cell resistance will increase
> to
> > unacceptable values. This same kind of reaction occurs when Zr or Ti
are
> used
> > as the anode as well. A very low applied current would be the only
> condition
> > permitting use of Mg. The current would have to be small enough so that
> the
> > formation rate of MgO would have to be less than its rate of dissolution
> from
> > the surface.
> >
> > Regards,
> > Ed
>
>
