Platinum corrosion potentials

An interesting field of application is the protection of tantalum against hydrogen embrittlement by electrical connection to platinum metals. The reduction in hydrogen overvoltage and the shift of the free corrosion potential to more positive values apparently leads to a reduced coverage by adsorbed hydrogen and thereby lower absorption [43] (see Sections 2.1 and 2.3.4). 

This system seems to be the only alloy to date whose hydrous oxide growth behavior under potential cycling conditions has been investigated.189 190 Burke and O Sullivan189 demonstrated that with an alloy containing 10% by weight of rhodium in platinum both components corroded on cycling between certain limits (0-1.5 V) in 1.0 mol dm-3 NaOH. However, while the platinum corrosion product was found to be soluble under these conditions the rhodium one was not—in fact the hydrous film developed on the surface in this case was apparently derived almost totally from the minor component in the alloy. 

The corrosion rate and corrosion potential are estimated using electrochemical kinetic parameters such as exchange current density for hydrogen evolution reaction on titanium and platinum, reversible potentials, and cathodic and anodic slopes. 

Table 6.2 The Corrosion Current and the Corrosion Potential of Titanium Before and After Coupling With Platinum...

If a piece of platinum wire is coupled to zinc which is corroding in an air-free, acidic solution, vigorous hydrogen evolution begins on the platinum surface and the rate of zinc dissolution also increases. In terms of polarization curves (Fig. 14.10), the corrosion rate is /corr(Zn), which is obtained as the point of intersection of the Zn dissolution and hydrogen evolution Tafel plots. The corrosion potential is represented by Fcorr-... 

Platinum catalyst Potential static holding conditions and potential step conditions effect on platinum dissolution and carbon corrosion Shao et al., 2008... 

In electrochemical noise (EN) measurements fluctuations in potential or current are measured as a function of time. The measurements can be done (see Chapter 7) either without or with an externally applied signal. In the first case one monitors the open circuit corrosion potential of the test metal versus a suitable reference electrode or versus a second electrode of the seune material exposed under identical conditions. The advantage of this technique for use in MIC research is that there is no external signal to disturb the biological community on the metal surface. Alternatively, one can measure fluctuations in potential (E) at an applied current (I), or the reverse, fluctuations in I at an applied E. It has also been suggested that one could couple the metal of interest to a platinum electrode and measure the noise... 

RG. 7—Spontaneous passivation of an active-passive metal, such as titanium, by galvanically coupling to a noble metal such as platinum. The noble metal has a high rale constant for the proton-hydrogen reaction thus, the corrosion potential of the system Is near to the reversible potential for this reaction [7]. 

Scanning reference electrodes make it possible to measure the potential as a function of the location. The utilization of glass capillaries in combination with reference electrodes, such as the calomel electrode, make it possible to measure corrosion potentials, while pseudo-reference electrodes such as platinum wires are used to measure the potential difference between two points in solution. Included in this latter category are closely spaced reference electrodes which give a direct measure of the current density from the potential gradient and distance between them, as shown in Fig. 7-25 a. Such electrodes are used for the scanning reference electrode technique (SRET). 

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