57Fe Mössbauer Spectroscopy In The Investigation of The Precipitation of Iron Oxides

Abstract

Iron oxide is a general term often used to describe chemical compounds of iron such as hydroxides, oxyhydroxides, and oxides. These compounds are widespread in nature, in soils, sediments, water systems (rivers, lakes, oceans), and in the atmosphere, as well as in living organisms. Iron oxides played an important role in the history of man. They were used by early man as pigments in cave drawings and later on to produce iron metal. It is impossible to imagine the life of modern man without this metal. The precipitation of iron oxides in nature by weathering of magmatic rocks has a long geological history. Iron oxides also precipitate at the location of acid mine deposits or by rusting of iron (steel), thus creating ecological problems. On the other hand, precipitated iron oxides produced by man find important applications as pigments, fillers, catalysts, sensors, particles for drug delivery, and so on. In order to understand the formation of iron oxides in nature, and to make use of the precipitation processes of these compounds in industry, over the past decades researchers and engineers extensively investigated the precipitation of iron oxides. These investigations were used to study the kinetics and mechanisms of the phase transformations as well as the correlations between the iron oxide synthesis conditions and their chemical, microstructural, and physical properties. The list of iron oxides is given in Table 23.1. 57Fe M€ossbauer spectroscopy is a very important method in the investigation of iron oxide precipitation. The precipitation of iron oxides is of a complex nature and therefore other methods must also be used, for example, X-ray diffraction, infrared, Raman, and visible spectroscopies as well as electron microscopy. In this chapter, we shall focus on the precipitation of iron oxides mainly from aqueous iron salt solutions.