Infrared spectra of calcium sulfite tetrahydrate crystals (metastable phase) obtained from the Ca (OH)
2-S0
2 reaction systems (0°C) by adding Cu (II) ion, Zn (II) ion, or Ni (II) ion (5.0×10
-3M) were measured.
The infrared spectra of calcium sulfite hemihydrate crystals (stable phase) indicated a relatively small peak of O-H stretching of the crystal water at 3,380 cm
-1, while spectra of the tetrahydrate crystals had a very large peak (3,000-3,900 cm
-1) in the 0-H stretching region.
The infrared spectra of the hemihydrate crystals indicated a peak of S-O (S=0) of the sulfite ions only at 930 cm
-1, while spectra of the tetrahydrate crystals showed the presence of two distinct groups of bands (930 and 980 cm
-1) in the S-O (S=O) stretching region. These results suggested the differences of bonding around S-atoms and 0-atoms in the tetrahydrate crystal and in the hemihydrate crystal.
The thermostability of the tetrahydrate crystals were examined by DTA, TG and DSC. The order of the magnitude of the function of metal ions to stabilize the tetrahydrate crystal was as follows; Cu (II) > Zn (II) >Ni (II).
It was revealed that the change of tetrahydrate to hemihydrate gave the heat absorption of about 17 kJ/mol almost irrespective of kinds of metal ion added to the reaction system.
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