Steel open circuit potential

Legault, Mori and Leckie have used open-circuit potential vs. time measurements and cathodic reduction of rust patinas for the rapid laboratory evaluation of the performance of low-alloy weathering steels. The steel specimens are first exposed for 48 h to the vapour of an 0-(X)l mol dm sodium bisulphite solution maintained at 54°C (humid SOj-containing atmosphere) to stimulate corrosion under atmospheric conditions. They are then subjected to two types of test (tt) open-circuit potential-time tests for periods up to 3 000 s in either distilled water or 0 -1 mol dm Na2S04 and... 

In order to evaluate the tests determinations were carried out on the steels that had been exposed to the atmosphere for 1,2, 3, 4 and 6-month periods. It was established that the initial open-circuit potential and the decrease in potential (more negative) with time varied with the nature of the steel and the time of exposure to the atmosphere, and the maximum negative potential was taken as a measure of corrosion resistance the more negative the... 

Fig. 19.16 Schematic E — I diagrams of local cell action on stainless steel in CUSO4 + H2SO4 solution showing the effect of metallic copper on corrosion rate. C and A are the open-circuit potentials of the local cathodic and anodic areas and / is the corrosion current. The electrode potentials of a platinised-platinum electrode and metallic copper immersed in the same solution as the stainless steel are indicated by arrows, (a) represents the corrosion of stainless steel in CUSO4 -I- H2 SO4, (b) the rate when copper is introduced into the acid, but is not in contact with the steel, and (c) the rate when copper is in contact with the stainless steel...

Figure 9 shows the first and second cycle of a cyclic voltammogram of a 0.2 molal (mol kg"1) solution of lithium bis[2,2 biphenyldiolato(2-)-0,0 ]borate in PC at a stainless steel electrode. The sweep covers the potential range from open circuit potential ER versus a lithium reference electrode up to 4500 mV versus Li and back to ER. The first cycle shows... 

A prepassivated platinum electrode and an electrode of the metal of interest have been used to follow the development of a biofilm to determine its effects on the corrosion behavior of structural materials. The time dependence of the open circuit potential of several stainless steels... 

Figure 1. Open circuit potential vs. time in sterile medium and in medium with bacteria (a) platinum, (b) 304L stainless steel. (Reprinted from Ref 1 with permission from NACE International.)...

The corrosion of stainless steel in 0.1 mol-1 NaCl solutions at open circuit potential was studied in detail by Bruesch et al. [106] using XPS in combination with a controlled sample transfer system [38]. It was verified by XPS analysis that the passivating film contains chromium oxide. The position and the height of the Cr concentration maximum depends critically on the bulk chromium content of the steel. Significant variations in the electrode passivation properties were observed at a Cr concentration of 12%, while the film behaviour was found to be rather independent of the other components like Mo, Ni, Cu. From the fact that the film structures and... 

Twelve different Bonderite 40 coated steel (B40) panels were examined to provide a statistically valid value for the open circuit potential. Their average rest potential was -0.578 V (vs. SCE) with an average deviation of 20 mv. After recording the open circuit potential, polarization curves were obtained (Figure 1). 

Figure 2. Changes in open circuit potential (OPC) and rust rating (RR) with temperature for post-thermally treated Bonderite 40 coated steel (B40) panels and Barex 210/N-vinylpyrrolidone (B210/NVP) photocured coatings on B40 panels.

High nitrile photocured coatings on B40 coated steel panels exhibit corrosion resistance when their open circuit potentials are either more noble or less noble than the B40 coated steel panel (Figure 3). At first, we assumed that enhanced nobility should give rise to enhanced corrosion resistance, i.e. the galvanic series. 

Corrosion of Iron Alloys. Other recent work Q) presents experimentally measured values of the open circuit potentials of iron alloys in water at ambient and supercritical conditions. For iron and its alloys (1080 carbon steel, 304 stainless steel and 316 stainless steel), the open circuit potentials varied from -0.112 to +0.055 volt in water at its critical point, and varied from -0.138 to -0.060 volt in water at ambient conditions. These values were... 

Thermodynamic predictions were consistent with experimentally measured corrosion rates and open circuit potentials. The results indicate enhanced corrosion of stainless alloys containing chromium may be expected in supercritical water. These corrosion rates appear comparable to those for mild steel or iron. 

Electrochemical potentlostat measurements have been performed for the corrosion of iron, carbon steel, and stainless steel alloys in supercritical water. The open circuit potential, the exchange or corrosion current density, and the transfer coefficients were determined for pressures and temperatures from ambient to supercritical water conditions. Corrosion current densities increased exponentially with temperature up to the critical point and then decreased with temperature above the critical point. A semi-empirical model is proposed for describing this phenomenon. Although the current density of iron exceeded that of 304 stainless steel by a factor of three at ambient conditions, the two were comparable at supercritical water conditions. The transfer coefficients did not vary with temperature and pressure while the open circuit potential relative to a silver-silver chloride electrode exhibited complicated behavior. 

Multiwall carbon nanotube (MWCNT)-reinforced hydroxyapatite composite coatings (80% HAp/20% MWCNT) were deposited on austenitic stainless steel AISI 316L by laser surface alloying (LSA) with a 2.5-kW CW Nd YAG laser (Kwok, 2007). EIS of unprotected AISI 316L and HAp/MWCNT-coated steel obtained at open circuit potential are shown in Figure 7.60 after immersion in 0.9% NaCl solution for 2 h. The Bode plot shows that the total impedance Z has noticeably increased for the steel substrate coated with HAp/MWCNT. While the thin passive oxide film on the stainless steel surface was rendered less protective... 

Figure 7.60 Electrochemical impedance spectra (Bode plots) of unprotected surgical AISI 316L stainless steel and HAp/MWCNT-coated AISI 316L steel obtained at open circuit potential after corrosion in 0.9% NaCI solution for 2 h. ((Modified after Kwok (2007).)...

Obviously, the oxide layer thickness should be of great importance for the possibility to observe any fronts experimentally. It is known from XPS studies of stainless steel that the properties of the protective oxide layer change with time while being immersed in an electrolyte [1]. In the fol-f lowing we kept the sample for 90 min at open circuit potential after it was immersed. Then the potential was rapidly scanned to a pre-defined value at which the experiment should been conducted and held constant. 

Figure 16.5 Open-circuit potential (OCP) of the steel/epoxy-hole electrode vs. time in aerated 0.1 M UCIO4 solution, r and d indicate the times at which the steel electrode is connected and disconnected, respectively, from the PMT/Pt electrode. (Reprinted with permission from Electrochimica Acta, Corrosion protection by ultrathin films of conducting polymers by U. Rammelt, P.T. Nguyen and W. Plieth, 48, 9, 1257-1262. Copyright (2003) Elsevier Ltd)...

Open circuit potential As defined by the McGraw-Hill Dictionary of Scientific and Technical Terms, open circuit potential (OCP) is the steady-state or equilibrium potential of an electrode in absence of external current flow to or from the electrode. OCP measures the corrosion potential of a corroding metal with regard to a reference electrode. For instance, increased susceptibility of stainless steels to pitting and crevice corrosion in seawater has been attributed to increase in OCP, which could partly be due to biofllm formation. Monitoring of OCP spectra can be used to rank the corrosion vulnerability of metals in comparison with each other. 

F.K. Sahrani, M. Aziz, Z. Ibrahim, A. Yahya. Open circuit potential study of stainless steel in environment containing marine sulphate-reducing bacteria. Sains Malaysiana, Vol. 37, No. 4, pp. 359-364, 2008. 

Figure 11.41 Open-circuit potential of a mild steel electrode connected to a polythiophene electrode (d) disconnected and (r) reconnected.

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