Novel use of a micro-optode in overcoming the negative influence of the amperometric micro-probe on localized corrosion measurements

The local concentration of dissolved oxygen over a metal-coated steel sample of cut-edge geometry was recorded by using either an amperometric probe or an optode (fibre-optic oxygen micro-sensor). Hydroxide ions, being the product of the current determining reaction on the amperometric micro-probe, were found to change the chemical composition of corrosion products. Application of an O2 selective micro-optode for local measurements allows avoiding the indicated problem and is reported here for the first time when applied to localized corrosion measurements. The concentration of dissolved oxygen was mapped 100 μm above the cut-edge steel coated with Al–Zn–Mg alloy. This was performed quasi-simultaneously with rastering local current density and pH over the same sample area.