Rare earth metal corrosion inhibitor

Rare earth metal salts have been found to be effective inhibitors for various forms of corrosion as illustrated in Table 12. lb. 

General uniform corrosion on pure magnesium has been drastically reduced by the use of inhibitors sueh as ehromate, dichromate, molybdate, nitrate, phosphates and vanadates that promote the formation of a protective layer, tend to retard corrosion (Ghali, 2006). Addition of substances that can form soluble complexes as tartrate, metaphosphate, etc. or insoluble salts as oxalate, carbonate, phosphate, fluoride, etc. is efficient at reducing corrosion. Adding soluble chromates, neutral fluorides or rare earth metal salts is effective in reducing magnesium-base metal corrosion (Schmutz et al, 2003). 

The chemistry of rare earth metals, compounds, and corrosion inhibitors... 

Abstract This chapter provides an overview of major corrosion testing and analysis techniques and their applications in corrosion inhibitor research, with a particular focus on electrochemical evaluation of corrosion protection by rare earth metal (REM) compounds. Attempts are made to discuss fundamental issues in inhibitor test design such as limitations in corrosion measurement techniques and challenges that may lead to the reporting of inaccurate corrosion rates and patterns. 

Key words corrosion inhibition, rare earth metal inhibitors, corrosion testing, electrochemical methods, surface analytical technique. 

M. Forsyth, K. Wilson, T. Behrsing, C. Forsyth, G. B. Deacon and A. Phanasgoankar, Effectiveness of rare-earth metal compounds as corrosion inhibitors for steel . Corrosion 58, 953 (2002). 

Development of new inorganic REM salt corrosion inhibitors has been slow and has not reached the same level of sophistication as that of organic inhibitors, although important contributions have appeared recently. In this chapter, an overview of inorganic corrosion inhibitors based on rare earth metal salts is presented. 

Forsyth M, Wilson K, Behrsing T, Forsyth C, Deacon GB, Phanasgoankar A (2002a) Effectiveness of Rare-Earth Metal Compoxmds as Corrosion Inhibitors for Steel . Corrosion 58, 11, 953-960. 

It can be seen from the large body of work in the literature dedicated to investigating rare earth metal compounds as corrosion inhibitors for a wide range of aluminium alloys that they show a great deal of promise as potential... 

One of the most common approaches involves the application of rare earth compounds as corrosion inhibitors. In the last decade, a significant and increasing number of researchers have focused on the search for new rare earth compounds able to provide corrosion protection equivalent to or better than chromates for a wide variety of metal substrates. The first reports of the effectiveness of rare earth metal salts, for example CeClj, as cathodic corrosion inhibitors appeared in the... 

Besides the measures described in the main part of this paper, significant improvement of the corrosion resistance of a material can be obtained by use of inhibitors. In this case, good results seem to be achieved with rare earths employed in low amounts as alloying metals or as protective dense oxide coatings. The use of coatings often means the research into the best compromise between mechanical properties and corrosion resistance of the material. 

Since pyromellitic acid sequesters heavy metals, it can also be used as an antiscaling agent(32) and as a corrosion inhibitor(33) but whether it has sufficient benefits for market applications has yet to be shewn. An unusual proposed use is to dissolve kidney stones(34). A related property is that pyromellitic acid will precipitate lanthanide ions frem solutions containing a number of divalent cations such as Mg, Ni, Mn, etc.(35). As a consequence, there may be possible applications for large scale purification of the rare earths. 

This section is devoted solely to rare earth caiboxylates, as they are potential (or actual) dual function corrosion inhibitors. The largest class of rare earth polymeric complexes is that which contains carboxylate ligands. These oxophihc metals are well suited to forming complexes with carboxylate ligands. Many examples of... 

Published literature also deals with the effect of the incorporation of REM salts in mixed aqueous media in order to inhibit the corrosion of different metallic materials. An example is the addition of Ce ions to flowing ethylene glycol-water solutions to inhibit the corrosion of aliuninum alloy 3003 used in refrigerating systems (Liu and Cheng, 2011). However, in recent years, the most innovative developments in this area of REM salt corrosion inhibitors have involved the study of the synergic effects of the mixtures of these rare earths with various organic and inorganic compounds. 

Abstract Rare earths have been studied extensively as corrosion inhibitors for a range of metals. However, there is little information about the viabihty of the rare earths as inhibitors from the perspective of price and availability. This chapter reveals that from a price perspective, Ce and La are competitive with V and cheaper than Mo, but more expensive than Ti and Zr compoimds. In terms of availabihty La, Ce, Nd and Pr are relatively plentiful, but production volumes fall far short of that required to replace chromium inhibitors. Nd and Pr are nearly ten times more expensive than either Ce or La. 

Key words rare earths, inhibitors, corrosion, conversion coatings, supply and demand, availability, metal finishing. 

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