Indagine spettrometrica ultrarossa sul sistema $CaSO_{4} \cdot 2H_{2}O-CaSO_{4}$

Bertoluzza, Alessandro ; Righetti, Benito ; Saporetti, Pierluigi

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 53 (1972) no. 1-2, pp. 149-163

Résumé

Infrared spectra of the materials composing the $CaSO_{4} \cdot 2H_{2}O-CaSO_{4}$ system have been examined. $CaSO_{4} \cdot 2H_{2}O$ films laid down from a n-hexane suspension on KBr disks were heated to controlled temperatures in the atmosphere, under vacuum ($5 \cdot 10^{-2}$mmHg) and at the vapour pressure of 21 mmHg. Infrared spectra indicate that a direct transformation of $CaSO_{4} \cdot 2H_{2}O$ into anhydrous $CaSO_{4}$ occurs in a definite temperature interval, which depends on each case. Infrared spectra, recorded from $CaSO_{4} \cdot 2H_{2}O$ film heated under the vapour pressure of 140 mmHg, show, on the contrary, that $CaSO_{4} \cdot 2H_{2}O$ turns into anhydrous sulphate $CaSO_{4}$ through the formation of the intermediate $CaSO_{4} \cdot 0,5 H_{2}O$ hemihydrate compound. By a comparative study with u.r. spectra of materials obtained from thermal dehydration of $CaSO_{4} \cdot 2H_{2}O$ at different temperatures between room temperature and 6oo°C, we may assign to the anhydrous calcium sulphate, the final product of film dehydration, the soluble anhydride or $CaSO_{4} \gamma$ structure.