Passivation of metals

It is possible to deactivate a metal ioa by adding a compouad such as disahcyhdeae alkyl diamiae, which readily forms a chelate with most metal atoms to reader them iaeffective. Metal deactivator has beea showa to reduce oxidatioa deposits dramatically ia the JFTOT test and ia single tube heat exchanger rigs. The role of metal deactivator ia improving fuel stabiUty is complex, siace quantities beyond those needed to chelate metal atoms act as passivators of metal surfaces and as antioxidants (13). 

Passivity of Metals and Semiconductors. (M. Froment, ed.) Elsevier, Amsterdam, 1983. 

Marcus, P. and Oudar, J., Proc. Conf. Passivity of Metals and Semiconductors , Bombannes, France, June 1983, (Ed. Froment, M.), Elsevier 119 (1983)... 

Szklarska-Smialowska, Z., Passivity of Metals, p. 443, The Electrochemical Society, Princeton (1978)... 

When boiler cleaning takes place, it often is followed by the circulation of a hot alkaline phosphate solution to provide adequate passivation of metal surfaces. (A typical formulation may also include sodium gluconate, antifoam, and dispersants.)... 

The values of AX for pc Ni and Fe are reported in Table 27 in brackets. Polycrystalline surfaces of these metals are still used both in surface science and in electrochemical studies. The relevance of Eam0 to the potential of initial passivation of metals has been pointed out.862... 

Oxide and salt layers on metal electrodes are of great practical value. Electrodes with thick phase layers are used in batteries, and varions types of thin layers will pro-dnce passivation of metals. 

Passivation of an electrode with respect to a certain electrochemical reaction is the term used for the strong hindrance experienced under certain conditions by a reaction which under other conditions (in the electrode s active state) will occur without hindrance at this electrode. Passivation of metals imphes the hindrance frequently observed with respect to anodic metal dissolution. 

It was learned that pitting-type metal and semiconductor corrosion is attended by the generation of noise seen in the form of dynamic irregularities in the changes of the anodic potential and current density. Thus, electrochemical noise studies were applied to the corrosion and passivation of metals and to their activation by external chemical (activating additives in the electrolyte) or electrochemical (anodic or cathodic polarization) agents. 

Iron and Stainless Steel. The purpose of XPS investigations on typical corrosion systems like iron or stainless steel, is the determination of the composition of the passive surface layer, if possible, as a function of depth. As a consequence of the technical and economic relevance of corrosion reactions, XPS investigations on corrosion systems are numerous. With respect to the application of XPS, there is no difference between corrosion systems and any other electrochemical surface reaction like oxide formation on noble metals. Therefore, in this paragraph only a few recent typical results of such studies, using XPS, will be mentioned. For a detailed collection of XPS corrosion studies the reader is referred to references [43,104], A review of aqueous corrosion studies, using XPS, was given by McIntyre for the elements O, Cr, Mn, Fe, Co, Ni, Cu and Mo [105], The book edited by M. Froment [111] gives an impression of the research achieved on passivity of metals up to 1983. 

V. P. Parkhutik, in Extended Abstracts, 5th International Symposium on the Passivity of Metals, ISE, Bombannes, 1983, p. 253. 

Pourbaix diagrams illustrate graphically the dominant solution or precipitate species of a component or components as a function of pH and oxidation potential (Jj. They are particularly useful for defining the conditions for selective precipitation or solution in hydrometallurgical extraction (2j and for passivation of metals. However, they are tedious to produce manually, especially when a number of components are present. 

Le31[ V. Lehmann, in Proceedings of the 8th International ECS Symposium on Passivity of Metals and Semiconductors, 2000, p. 410. 

It is weD known that metallic iron corrodes violently in dilute nitric acid solutions, but metallic iron is passivated in concentrated nitric add solutions as shown in Fig. 11-14(a). This passivation of metallic iron results from a strong oxidizing action of concentrated nitric add that changes the iron electrode irom the active state to the passive state. 

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