Vivianite and Beraunite

Abstract

Wet chemical methods, such as the hydrothermal, template, and precipitation process provide effective-cost preparation techniques, especially if compared to “high-temperature” methods (Dominkó et al., J Power Sour. 153, 274–280, 2006; Yang et al., Electrochem. Commun. 3, 505–508, 2001; Zhang et al., Funct. Mater Lett. 3, 177–180, 2010; Palomares et al., J. Power Sour. 171, 879–885, 2007). Liquid-phase synthesis has the advantage to be carried out at low temperatures (low energy), to be flexible and controllable and to give materials with homogeneous nano-particle structures. An obvious disadvantage of the synthesis in liquid phase is that the so-obtained materials show low density. In this chapter a sol–gel route to prepare iron (II) phosphate is reported. Synthetic vivianite (Fe₃(PO4)₃×nH₂O) (Scaccia et al., Thermochim. Acta. 397, 135–141, 2003) was obtained by adding phosphate ions to a solution of Fe²⁺. It is well known that natural ferrous phosphate (vivianite) rapidly oxidizes on exposure to air, passing through deepening shades of blue to finally become brown beraunite (3Fe₂O₃•2P₂O₅•10H₂O). The vivianite obtained by the sol–gel route was dried in air at 100°C. The so-obtained material was characterized by TG/DTG/DTA, XRD, SEM and Mössbauer spectroscopy and its electrochemical behavior as a cathode in a non-aqueous lithium cell was evaluated (Prosini et al., J. Electrochem. Soc. 148, A1125–A1129, 2001) .