I tested my suggested Ferrous carbonate path with some success (at least enough to produce a visble color change).
In 5 hours, after heating 3 times for 30 seconds in a microwave, and periodic shaking, a mix of water, Iron filings, NaHCO3, to which is added a
small amount of vinegar (the latter two acting as a CO2 source with the Sodium bicarbonate in excess) with a touch of sea salt. I employed a sealed
and deflated plastic 3.3 liter bottle to address the CO2 gas expansion issue on heating. Note, acidic pH, increase in the partial pressure of CO2,
warming, agitation of solution and the presence of chloride and acetic acid are all reported as accelerating the corrosion of steel.
Per my cited reference by Anderko above with respect to a surface reaction forming ferrous carbonate:
Fe + HCO3- ⇒ ≡FeCO3 + H+ + 2e-
Other anodic half reactions:
Fe + OH- ⇒ FeOH + e-
FeOH ⇒ FeOH+ + e-
FeOH+ ⇒ Fe++ + OH-
Net: Fe ⇒ Fe++ + 2e-
Cathodic reaction (my expanded rendition featuring the hydrogen atom radical):
H+ + e- ⇒ .H
.H + .H ⇒ H2
As: HCO3- = H+ + CO3(2-) , we have similarly:
HCO3- + e- ⇒ 1/2 H2 + CO3(2-)
In my opinion, it may be further possible that:
HCO3- + .H ⇒ 1/2 H2 + .CO3-
with the possible transient formation of the carbonate radical anion. Its self reaction is said to proceed as follows:
.CO3- + .CO3- ⇒ CO2 + CO4(2-) (p. 11 at https://www.google.com/url?sa=t&source=web&rct=j&... )
Also, a possible reaction between the hydrogen atom radical (and/or e-) and the acetate anion or undissociated HAc, may account for the reported
acceleration of steel corrosion in the presence of acetic acid (thesis idea?, see https://www.google.com/url?sa=t&source=web&rct=j&... ).
Visible result was a light green solution. See picture in attached document.
[Edited on 12-5-2017 by AJKOER]
[Edited on 12-5-2017 by AJKOER] |
