Iron oxide particles in a perfluorosulfonate membrane

Particles of (α-Fe₂O₃ and α-FeOOH have been observed directly in ultrathin (～ 500 Å) sections of Nafion® perfluorosulfonate membranes by transmission electron microscopy, α-Fe₂O₃ is obtained by heating a membrane, previously exchanged with 0.2 M FeCl₃, in an autoclave with water at 150°C. The individual particles are roughly spherical, ～ 100 Å in diameter, but they are grouped together in clusters ranging from a few hundred angströms up to about 1000 Å in size, which are uniformly distributed across the membrane thickness. α-FeOOH is obtained by boiling the membrane in water and exchanging first in 0.2 M FeCl₃ and then in 0.2 M KOH. Well-separated acicular or blade-shaped crystallites up to 1000 Å long and about 100 Å across are observed; they become more numerous towards the membrane surfaces. Amorphous ferric hydroxide, obtained by treating an unboiled membrane in the same way, could not be observed directly.