Chapter 19 Ionic Liquids in Surface Protection Joaquı´n Arias-Pardilla, Tulia Espinosa, and Marı´a Dolores Bermu´dez 19.1 Ionic Liquids in Surface Protection Room temperature ionic liquids (ILs) are salts that are liquid at or below 373 K. Although there exist millions of theoretical combinations of anions and cations, some of the most commonly studied species contain the following cation moieties (ammonium, phosphonium, imidazolium and pyridinium) (Fig. 19.1 and Table 19.1): A variety of anions have been described. Many of them contain boron, sulphur or phosphorus and fluorine in their formulations: [BF4] _ , [CH3BF3] _ , [CF3BF3] _ , [n-C3F7BF3] _ , [n-C4F9BF3] _ , [PF6] _ , [(C2F5)3PF3] _ , [CF3SO3] _ and [N(SO2CF3)2] _ (Table 19.2). Unfortunately, these fluorine-containing anions are susceptible to hydrolysis in the presence of water or moisture from the atmosphere in contact with ILs. The reactions are of the general type described for [BF4] _ and [PF6] _ [1, 2]: BF _ 4 þ 4H2O ! BðOHÞ_ 4 þ 4HF ð19:1Þ PF _ 6 þ 4H2O ! H2PO _ 4 þ 6HF ð19:2Þ The evolution of the toxic and highly corrosive HF must be avoided in ILs for corrosion protection or tribological uses. The present chapter on the application of ionic liquids (ILs) in surface protection will be divided into two sections: • Ionic liquids in corrosion protection and coatings • Ionic liquids in lubrication and tribology J. Arias-Pardilla (*) • T. Espinosa • M.D. Bermu´dez Grupo de Ciencia de Materiales e Ingenierı´a Metalu´rgica, Departamento de Ingenierı´a de Materiales y Fabricaci_on, Universidad Polite´cnica de Cartagena, Campus de la Muralla del Mar., Cartagena 30202, Spain e-mail: [email protected]
