Phase transformations in doped ice: concentration effect in frozen ferrous solutions

Mossbauer studies of frozen dilute ferrous solutions have shown a disappearance and reappearance of Mossbauer resonance at -90 degrees C, with no apparent change m quadrupole splitting. Upon subsequent warming to somewhat higher temperatures, the resonance signal again disappears and returns with a larger quadrupole splitting, as previously found for more concentrated solutions and associated with an ice-phase transformation. Stannic ions do not exert any significant effects on the Mossbauer spectra of either dilute or concentrated ferrous solutions, in contrast to europic ions which have a pronounced influence. This difference may arise from partially chlorinated, as opposed to fully aquated, complexes in solution. The possible crystallization of FeCl2 center dot 6H(2)O from the frozen solution at -45 degrees C is inferred from the coexistence of two sets of resonance lines whose relative intensities change with time.