Figure 6

SEM microphotographs of reacted metals and alloys. A) Fe⁰ reacted in N₂(aq) solution depicting coexisting magnetite and Fe-(oxy)hydroxides; B) Detail of magnetite single crystals formed on Fe⁰; C) clusters of needle-like Fe-(oxy)hydroxide crystals formed on Fe⁰; D) pseudomorphoses of magnetite after Fe⁰ in the H₂/N₂ solution; E) magnetite crystals formed on Ni₅₀Fe₅₀ in the KNO₃ solution; F) Ni⁰ skeletal crystal revealing no change after reaction.