Anodic behaviour

Birss V I and Smith C K 1987 The anodic behaviour of silver in chloride solutions-l. The formation and reduction of thin silver chloride films Electrochim. Acta 32 259-68... 

Nagayama, M. and Okamoto, G., The Anodic Behaviour of Passive Iron in Chromic Acid-Chromate Solutions , Corros. Sci., 2, 203 (1962)... 

Myers, J. R., Crow, W. B., Beck, F. H. and Saxer, R. K., Observation on the Anodic Behaviour of Nickel and Chromium Surface Topography and Temperature Effect , Corrosion, 22, 32 (1966)... 

Piggott, A. R., Leckie, H. and Shreir, L. L., Anodic Polarisation of Titanium in HCOOH— 1 Anodic Behaviour of Titanium in Relation to Anodising Conditions , Corros. Sci., S, 165... 

Fig. 3.36 Effect of nickel on the anodic behaviour of iron alloys in 1 N H2SO4 at 25°C. Curve 1 Fe curve 2 Fe-lONi Curve 4 Ni (after Beauchamp )...

In an aqueous electrolyte, the anodic behaviour of lead vanes greatly depending on the conditions prevailing. Extensive reviews of the anodic behaviour of lead have been produced Under certain conditions, the passive film may be converted to lead dioxide which has an electronic resistivity of 1 - 4 x 10" Ohm cm. Two polymorphs of PbO, exist, a and... 

Many investigators have studied the anodic behaviour of nickel. A complete discussion of the reactions occurring during anodic dissolution and passivation of the metal is outside the scope of this chapter, which is confined to a brief summary of the main features of practical significance. 

The influence of temperature on the anodic behaviour of nickel has been studied, and in acidic and neutral solutions the active-passive transition is not observed at temperatures greater than about 100°C (Fig. 4.21). 

Fig. 4.21 Effect of temperature on the anodic behaviour of nickel in 0 025 m H2SO4 -I-0-025 M K2SO4 (pH 1 -3) de-aerated with H2. The curves were determined potentiokinetically at a scan rate of 2 V/h and proceeding from negative to positive (after Cowan and Staehle )...

As with most other metals, the anodic behaviour of nickel is influenced by the composition of the solution in which measurements are made, particularly if the solution is acidic. Acidic solutions containing d ions or certain sulphur compounds in particular have a pronounced influence both in increasing the rate of anodic dissolution in the active range and in preventing passivation, and in stimulating localised corrosion . Thiourea and some of its derivatives have a complex effect, acting either as anodic stimulators or inhibitors, depending on their concentration . 

As indicated when discussing anodic behaviour the mechanism of film formation is complex, involving adsorption of OH ions to form a prepassive layer followed by either dissolution or film formation as alternative processes. 

During recent years a considerable amount of information has been published on the anodic behaviour of nickel alloys. The data include studies both of binary alloy systems in which nickel forms the major alloying component and of more complex commercially produced nickel alloys. The data are sufficiently numerous to permit a rational and fairly complete interpretation of many of the corrosion-resistant properties of nickel alloys on the basis of their anodic behaviour. 

Fig. 4.22 Effect of chromium content on the anodic behaviour of Ni-Cr alloys in 0-5 M H2SO4 (de-aerated with H2) at 25°C the potential was increased incrementally by 0-025 V every 3 min (after Hodge and Wilde...

Table 4.24 Influence of alloying on anodic behaviour of nickel...

Fig. 4.24 Anodic behaviour of Alloy 600 in 0-5 M H2SO4 (de-aerated willi Nj) ai 24°C...

Eig. 4.25 Anodic behaviour of Alloy F and Alloy G in boiling 10% H SO de-aeraled with Hj (the potential was increased incrementally every 3 min , after Leonard see also... 

Fig. 4.26 Anodic behaviour of Ni-Cu alloys in 0-5 m H2SO4 (de-aerated with N2) at 25°C the curve was determined potentiokinetically at 0-4 V/h for the 78-3 and 49-9% Ni alloys and at 3 V/h for the 30-4% Ni alloy proceeding from more positive to more negative (after...

An interesting illustration of the effect that quite small alloying additions may sometimes have on anodic behaviour is seen in Fig. 4.27 from a comparison of the Ni-30Cu alloy Alloy 400 with its age-hardening variant Alloy K500, which contains 2-7% A1 and 0-6% Ti. The presence of these elements in the latter alloy is responsible for a well-defined passive region, whereas the former alloy shows only a slight tendency to passivate in acidic... 

Fig. 4,27 Anodic behaviour of Ni-Cu alloys in 10% H2SO4 at ambient temperature. 1, Ni 2, Alloy 400 3, Alloy K500 solution treated 4, Alloy K500 aged (after Flint and...

Another indication of the influence of precipitated phases on anodic behaviour may be seen in the curve for Alloy C in Fig. 4.28, where the small peak in the middle of the passive range is probably attributable to anodic dissolution of an intermetallic phase (n) and MjC carbide . ... 

The influence of minor alloying elements and the effect of formation of other phases on the anodic behaviour of nickel alloys are thus not negligible and should not be ignored. 

Fig. 4.28 Anodic behaviour of Alloys B, C and N in boiling 10% H2SO4 de-aerated with H2 the potential was increased incrementally (after Leonard )...

Fig. 4.29 Anodic behaviour of Ni-Si alloys in 25% FI2SO4 (de-aerated with Nj) at ambient temperature (after Barker and Evans )...

Fig. 4.30 Suggested anodic behaviour of electrodeposited Sn-35Ni alloy 1, observed curve 2a, H2 evolution 2b, H2 oxidation 3, true anodic curve (after Clarke and Elbourne " )...

Fig. 4.31 Anodic behaviour of Ni-Ti alloys in HCl + 3 -5% NaCKpFl 1), de-aerated with argon, at 22-2°C the potential was increased by 0-02 V every minute (after Sedriks, el al )...

Fig. 4.32 Anodic behaviour of Ni-Al alloys in 0-5 m H2SO4, de-aerated with H2, at 22°C the potential was increased by 0-01 or 0-02 V every 3 min in the active range and by 0-04 V in the passive range (after Crow, era/. )...

Fig. 4.33 Anodic behaviour of Ni-Mn alloys in 0-5 m H2SO4 saturated with H2 at 20°C...

As with the chemical behaviour of the noble metals in aqueous solutions, their anodic behaviour closely follows the predictions of the Pourbaix diagrams if due allowance is made for the formation of complexes. 

The anodic behaviour of platinum and certain of its alloys is of considerable technical importance, since they can be employed under a wide range of conditions without appreciable corrosion, and often in circumstances where no other metal can be used. Their use industrially has recently been extended by applying them as thin coatings to a substrate of a passive metal such as tantalum or, more commonly nowadays, titanium, to reduce the cost. Platinised titanium anodes are discussed in detail in Section 11.3. 

The anodic behaviour of Pb varies depending upon the electrolyte composition and the electrode potential and has been the subject of a number of reviews . In NO,", CHjCOO and BF4" solutions, lead will form highly soluble lead salts whilst in Cl" and 804 solutions, insoluble lead salts are formed when Pb is anodically polarised. 

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